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Bioinspired Zoom Compound Eyes Enable Variable-Focus Imaging
Abstract
Natural compound eyes provide the inspiration for developing artificial optical devices that feature large field of view (FOV). However, the imaging ability of artificial compound eyes is generally based on the large number of ommatidia. The lack of tunable imaging mechanism significantly limits the practical applications of artificial compound eyes, for instance, distinguishing targets at different distances. Herein, we reported zoom compound eyes that enable variable-focus imaging by integrating a deformable polydimethylsiloxane (PDMS) microlens array (MLA) with a microfluidic chamber. The thin and soft PDMS MLA was fabricated by soft lithography using a hard template prepared by a combined technology of femtosecond laser processing and wet etching. As compared with other mechanical machining strategies, our combined technology features high flexibility, efficiency and uniformity, as well as designable processing capability, since the size, distribution and arrangement of the ommatidia can be well controlled during femtosecond laser processing. By tuning the volume of water injected into the chamber, the PDMS MLA can deform from a planar structure to a hemispherical shape, evolving into a tunable compound eye of variable FOV up to 180°. More importantly, the tunable chamber can functionalize as a main zoom lens for tunable imaging, which endows the compound eye with additional capability of distinguishing targets at different distances. Its focal length can be turned from 3.03 mm to infinity with an angular resolution of 3.86×10⁻⁴ rad. This zoom compound eye combines the advantages of monocular eyes and compound eyes together, holding great promise for developing advanced micro-optical devices that enable large FOV and variable-focus imaging.
... In nature, the compound eyes of arthropods are distinguished from mammalian eyes, which endows exceptional merits such as a large field of view (FOV) compared to planar microlens array(MLA), near-infinite depth of field, high sensitivity, and fast motion detection [1][2][3][4][5][6][7][8][9][10][11]. With the rapid development of optical microelectromechanical systems (MEMS) and standard complementary metal oxide semiconductor (CMOS) fabrication technologies [12][13][14][15], the fabrication techniques of compound eyes have experienced changes from waveguide self-writing initially to advanced femtosecond laser method through thermal reflow and self-assembly [4,[16][17][18][19][20][21][22][23][24][25][26]. ...
... In nature, the compound eyes of arthropods are distinguished from mammalian eyes, which endows exceptional merits such as a large field of view (FOV) compared to planar microlens array(MLA), near-infinite depth of field, high sensitivity, and fast motion detection [1][2][3][4][5][6][7][8][9][10][11]. With the rapid development of optical microelectromechanical systems (MEMS) and standard complementary metal oxide semiconductor (CMOS) fabrication technologies [12][13][14][15], the fabrication techniques of compound eyes have experienced changes from waveguide self-writing initially to advanced femtosecond laser method through thermal reflow and self-assembly [4,[16][17][18][19][20][21][22][23][24][25][26]. In recent years, there are also some innovative approaches springing up such as inkjet printing, inductively coupled plasma etching, etc [3][4][5]27,28]. ...
... With the rapid development of optical microelectromechanical systems (MEMS) and standard complementary metal oxide semiconductor (CMOS) fabrication technologies [12][13][14][15], the fabrication techniques of compound eyes have experienced changes from waveguide self-writing initially to advanced femtosecond laser method through thermal reflow and self-assembly [4,[16][17][18][19][20][21][22][23][24][25][26]. In recent years, there are also some innovative approaches springing up such as inkjet printing, inductively coupled plasma etching, etc [3][4][5]27,28]. A well-functioning compound eye has a wide range of applications including automatic spatial navigation, medical endoscope, digital camera which can realize automatic scanning and data acquisition system [29][30][31][32][33]. ...
The compound eyes of natural insects endowed with the merits of a wide field of view (FOV), high sensitivity, and detection of moving targets, have aroused extensive concern. In this work, a large-scale artificial compound eye is fabricated by a high-efficiency and low-cost strategy that involves the combination of the thermal reflow method and pressure deformation. About 30,000 ommatidia are evenly distributed on the surface of a hemisphere with an ultralow surface roughness and a large numerical aperture (NA) of 0.66. Moreover, the FOV of the artificial compound eye investigated is about 120°. The collaboration of the compound eye and CMOS sensor makes the ommatidia capturing multiple images of human organs enabled. This micro-based imaging system has considerable potential in integrated pinhole cameras, medical endoscopes, and drone navigation.
... After the introduction of versatile shape-programming strategies and the driven mechanisms of the 4DM/NRs, determining a method to predict and apply 4DM/NRs has grasped our attention [104][105][106][107][108][109][110][111][112][113][114][115][116][117][118][119][120]. To enhance the control over shape transformations while minimizing response time, researchers have been exploring nanofabrication approaches with sophisticated designs. ...
... However, the shape-mutation-induced functional changing brings the fifth-dimensional 5D ability of optical functions into the 4DM/NRs. The 4DM/NRs possess 5D biomimetic functions of sensory function [109,110], chameleon-like coloration [111][112][113][114], dynamic optical devices [115][116][117][118][119] with variable focus, information encoding/transmission [120], wettability tailoring [121], and even electronic skin [122]. The typical 5D optical devices can be represented by color-shifted photonic crystals [18] or smart biomimetic compound eyes [118]. ...
Miniaturized four-dimensional (4D) micro/nanorobots denote a forerunning technique associated with interdisciplinary applications, such as in embeddable labs-on-chip, metamaterials, tissue engineering, cell manipulation, and tiny robotics. With emerging smart interactive materials, static micro/nanoscale architectures have upgraded to the fourth dimension, evincing time-dependent shape/property mutation. Molecular-level 4D robotics promises complex sensing, self-adaption, transformation, and responsiveness to stimuli for highly valued functionalities. To precisely control 4D behaviors, current laser-induced photochemical additive manufacturing, such as digital light projection, stereolithography, and two-photon polymerization, is pursuing high-freeform shape-reconfigurable capacities and high-resolution spatiotemporal programming strategies, which challenge multi-field sciences while offering new opportunities. Herein, this review summarizes the recent development of micro/nano 4D laser photochemical manufacturing, incorporating active materials and shape-programming strategies to provide an envisioning of these miniaturized 4D micro/nanorobots. A comparison with other chemical/physical fabricated micro/nanorobots further explains the advantages and potential usage of laser-synthesized micro/nanorobots.
... The specific structure not only possesses excellent optical performance, but also imparts superhydrophobic and easy-to-clean capability of the compound eye for normal visual capability in high humidity and dusty environments [1]. Inspired by natural compound eyes, researchers have actively developed their fabrication processes in the past decade, such as thermal reflow [2][3][4], laser ablation wet or dry etching [5][6][7], laser direct writing [8][9][10], imprinting [11,12], soft lithography [13], inkjet printing [14,15], electrodynamic deformation [16,17], and so on [18]. These methods can effectively control the geometric profile and/or packing density of MLA. ...
... σ(r, θ) is the energy density, r is the radius of focusing spot and θ is the polar angle. Due to the circular symmetry of focusing spot, Eq. (4) is converted as: The gray value g(r) of focusing spot photo is linear relation to the energy density, so the total energy can be expressed as: (6) k is the scaling factor of gray value to energy density. The ratio of total energy of the focusing spots of full-packing npMLA and close-packing smMLA is: ...
The high-quality imaging and easy cleaning property of microlens array (MLA) are two very important factors for its outdoor work. Herein, a superhydrophobic and easy-to-clean full-packing nanopatterned MLA with high-quality imaging is prepared by thermal reflow together with sputter deposition. Scanning electronic microscopy (SEM) images demonstrate that the sputter deposition method can improve 84% packing density of MLA prepared by thermal reflow to 100% and add nanopattern on the surface of microlens. The prepared full-packing nanopatterned MLA (npMLA) possess clear imaging with a significant increase of signal-to-noise ratio and higher transparency compared with the MLA prepared by thermal reflow. Besides for excellent optical properties, the full-packing surface displays a superhydrophobic property with a contact angle of 151.3°. Further, the full-packing contaminated by chalk dust become easier to be cleaned by nitrogen blowing and deionized water. As a result, the prepared full-packing is considered to be potential for various applications in the outdoor.
... (a) Schematic of the principle of electrowetting method (EWOD) [22] ; (b) SEM image of a concave microlens array prepared using the EWOD under the application of a certain external voltage [27] ; (c) schematic illustration of microelectrodes printed by a stabilized conical jet printing mode and droplet microlenses printed by a droplet mode of electronic jet printing [28] ; (d) normalized light intensity distribution of the focused spot of the lens in MLAs induced by the EWOD mechanism at different voltages [28] ; (e) schematic representation of the processes of wetting, merging, growth, and dewetting of sulfur droplets on a gold electrode [29] 中国光学十大进展·特邀综述 第 61 卷第 10 期/2024 年 5 月/激光与光电子学进展 Fig. 2 Forcedeformed microlens array. (a) Schematic of the fabrication process of a zoom compound eye [35] ; (b) schematic of the fabrication process of a negativepressure artificial compound eye [36] ; (c) PDMS microsphere imaging switch [31] ; (d) imaging of PDMS microbeads as an elliptical lens [31] 中国光学十大进展·特邀综述 第 61 卷第 10 期/2024 年 5 月/激光与光电子学进展 Fig. 4 Schematic and working mechanism of electrical control of electroreconfigurable adaptive PVC gelbased microlens [45] . Fig. 5 Thermally tuned microlens arrays. ...
... To ameliorate the issue, two promising strategies based on advanced micro-nano fabrication and soft electronics have been explored. One approach involved precisely shaping optical structures with a microlens array on curved surfaces through photopolymerization (7,8), laser writing (9,10), laser-assisted etching (11,12), microfluid-assisted molding (13,14), or 3D printing (15,16). These optical structures were further assembled on planar imagers with the aid of complex waveguide units and costly lens systems. ...
Garnering inspiration from biological compound eyes, artificial vision systems boasting a vivid range of diverse visual functional traits have come to the fore recently. However, most of these artificial systems rely on transformable electronics, which suffer from the complexity and constrained geometry of global deformation, as well as potential mismatches between optical and detector units. Here, we present a unique pinhole compound eye that combines a three-dimensionally printed honeycomb optical structure with a hemispherical, all-solid-state, high-density perovskite nanowire photodetector array. The lens-free pinhole structure can be designed and fabricated with an arbitrary layout to match the underlying image sensor. Optical simulations and imaging results matched well with each other and substantiated the key characteristics and capabilities of our system, which include an ultrawide field of view, accurate target positioning, and motion tracking function. We further demonstrate the potential of our unique compound eye for advanced robotic vision by successfully completing a moving target tracking mission.
... And the modulation efficiency is still low. Alternatively, the varifocal lenses enable versatile and fast axial scanning without mechanically movement of the sections or the objective [21][22][23]. They have recently been used in imaging fields such as high-speed three-dimensional confocal microscopy [24], two-photon microscopy [25], and laser micro-machining fields [10,26,27]. ...
Fast and efficient separation of target samples is crucial for the application of laser-assisted microdissection in the molecular biology research field. Herein, we developed a laser axial scanning microdissection (LASM) system with an 8.6 times extended depth of focus by using an electrically tunable lens. We showed that the ablation quality of silicon wafers at different depths became homogenous after using our system. More importantly, for those uneven biological tissue sections within a height difference of no more than 19.2 µm, we have demonstrated that the targets with a size of microns at arbitrary positions can be dissected efficiently without additional focusing and dissection operations. Besides, dissection experiments on various biological samples with different embedding methods, which were widely adopted in biological experiments, also have shown the feasibility of our system.
... Compound eyes represent an exquisitely sophisticated imaging system in nature, prevalent among insects and crustaceans in the natural world. They are composed of thousands of tiny ommatidia, mainly hexagonal and circular in shape, each of which acts as an independent photoreceptor unit ( Figure 1a) [1]. The basic structure of an individual ommatidium includes the corneal lens, crystalline cone, and rhabdom bundle [2][3][4][5], as illustrated in Figure 1b [6]. ...
Over millions of years of evolution, arthropods have intricately developed and fine-tuned their highly sophisticated compound eye visual systems, serving as a valuable source of inspiration for human emulation and tracking. Femtosecond laser processing technology has attracted attention for its excellent precision, programmable design capabilities, and advanced three-dimensional processing characteristics, especially in the production of artificial bionic compound eye structures, showing unparalleled advantages. This comprehensive review initiates with a succinct introduction to the operational principles of biological compound eyes, providing essential context for the design of biomimetic counterparts. It subsequently offers a concise overview of crucial manufacturing methods for biomimetic compound eye structures. In addition, the application of femtosecond laser technology in the production of biomimetic compound eyes is also briefly introduced. The review concludes by highlighting the current challenges and presenting a forward-looking perspective on the future of this evolving field.
... The Ge composite microstructures also have good hydrophobicity properties. Overall, the anti-reflective properties of Ge microstructures are expected to play an important role in future photonics, wireless communications, and optical semiconductor devices [33,34]. ...
A femtosecond laser raster-type in situ repetitive direct writing technique was used for the fabrication of anti-reflective microhole structures in Germanium (Ge) in the visible near-infrared range (300–1800 nm). This technique builds a layer of microstructured arrays on the surface of Ge, enabling Ge to exhibit excellent anti-reflective properties. The large-area micro-nanostructures of Ge were fabricated using femtosecond laser raster-type in situ repetitive direct writing. Ge microstructures are characterized by their structural regularity, high processing efficiency, high reproducibility, and excellent anti-reflective properties. Experimental test results showed that the average reflectance of the Ge microporous structure surface in the range of 300–1800 nm was 2.25% (the average reflectance of flat Ge was 41.5%), and the lowest reflectance was ~1.6%. This microstructure fabrication drastically reduced the optical loss of Ge, thus enhancing the photothermal utilization of Ge. The many nanoburrs and voids in the Ge microporous structure provided excellent hydrophobicity, with a hydrophobicity angle of up to 133 ± 2° (the hydrophobicity angle of flat Ge was 70 ± 2°). The high hydrophobicity angle allows for strong and effective self-cleaning performance. The femtosecond laser raster-type in situ repeatable direct writing technology has many desirable properties, including simplicity, high accuracy, flexibility, and repeatability, that make it one of the preferred choices for advanced manufacturing. The Ge micro-nanostructured arrays with excellent optical anti-reflective properties and hydrophobicity have become an attractive alternative to the current photo-thermal absorbers. It is expected to be used in many applications such as solar panels, photovoltaic sensors, and other optoelectronic devices.
... Recently, the femtosecond laser direct writing technology has become a promising method because of its effective ability to realize various 3D complex microstructures and high precision [21,22,40,[70][71][72]. For example, the femtosecond laser direct writing technology is used to obtain microlenses with sizes as small as micrometers [21], as shown in Fig. 8Q. ...
Natural compound eyes (NCEs) are the most abundant and successful eye designs in the animal kingdom. An NCE consists of a number of ommatidia, which are distributed along a curved surface to receive light. This curved feature is critical to the functions of NCE, and it ensures that different ommatidia point to slightly different directions and thus enables panoramic vision, depth perception, and efficient motion tracking while minimizing aberration. Consequently, biomimetic curved artificial compound eyes (BCACEs) have garnered substantial research attention in replicating the anatomical configuration of their natural counterparts by distributing ommatidia across a curved surface. The reported BCACEs could be briefly categorized into 2 groups: fixed focal lengths and tunable focal lengths. The former could be further subcategorized into simplified BCACEs, BCACEs with photodetector arrays within curved surfaces, and BCACEs with light guides. The latter encompasses other tuning techniques such as fluidic pressure modulation, thermal effects, and pH adjustments. This work starts with a simple classification of NCEs and then provides a comprehensive review of main parameters, operational mechanisms, recent advancements, fabrication methodologies, and potential applications of BCACEs. Finally, discussions are provided on future research and development. Compared with other available review articles on artificial compound eyes, our work is distinctive since we focus especially on the “curved” ones, which are difficult to fabricate but closely resemble the architecture and functions of NCEs, and could potentially revolutionize the imaging systems in surveillance, machine vision, and unmanned vehicles.
... Brittle and hard materials, such as beryllium, fused quartz, diamond, and other difficult-to-process materials, are widely used in the fields of aerospace, new energy, and other cutting-edge equipment manufacturing [1][2][3][4]. Traditional machining methods often lead to damage when working with these materials. Laser processing, which utilizes high thermal energy to cut, melt, and modify material surfaces, offers a non-contact alternative [5,6]. ...
In this paper, we present a novel approach for calculating the heat distribution within a processed workpiece subjected to laser irradiation while accounting for the influence of bottom water vapor. A comprehensive mathematical model is introduced and numerical techniques using difference approximation are employed. Initially, the three-dimensional heat equation, originally defined in the rectangular coordinate system, is transformed into a corresponding model within the cylindrical coordinate system, incorporating a nonlinear boundary condition to account for coupling effects. Subsequently, leveraging the axial symmetry of the heat distribution, the three-dimensional model is simplified into a two-dimensional one. This simplified model is solved using the alternating direction implicit scheme coupled with the Crank-Nicolson method. Moreover, we develop a high-precision numerical treatment for the nonlinear boundary condition within the cylindrical coordinate system. To validate our methodology, simulation experiments are conducted on three distinct samples. Our comparative results demonstrate the feasibility and efficiency of the proposed approach in the context of water-jet guided laser processing.
... Compound eyes have a wide field of view, low aberration, and high time resolution. The visual range of an insect's compound eye can reach 180 degrees, and insect [1][2][3] imaging is distortion-free. It also has a very high sensitivity to moving objects and can quickly identify and locate moving objects, with a response speed that is more than five times that of humans. ...
Compound eye cameras are a vital component of bionics. Compound eye lenses are currently used in light field cameras, monitoring imaging, medical endoscopes, and other fields. However, the resolution of the compound eye lens is still low at the moment, which has an impact on the application scene. Photolithography and negative pressure molding were used to create a double-glued multi-focal bionic compound eye camera in this study. The compound eye camera has 83 microlenses, with ommatidium diameters ranging from 400 μm to 660 μm, and a 92.3 degree field-of-view angle. The double-gluing structure significantly improves the optical performance of the compound eye lens, and the spatial resolution of the ommatidium is 57.00 lp mm−1. Additionally, the measurement of speed is investigated. This double-glue compound eye camera has numerous potential applications in the military, machine vision, and other fields.
... Moreover, these reported compound eyes lose the objects when the distance changes because of the fixed focal length of the microlens array. Recently, Cao et al. proposed bioinspired zoom compound eye fabrication with variable-focus imaging [14]. However, the reported zoom compound eyes need fluid flushing to change the curvature of the base to recognize objects at different distances. ...
Natural compound eyes inspire the development of artificial optical devices that feature a large field of view and fast motion detection. However, the imaging of artificial compound eyes dramatically depends on many microlenses. The single focal length of the microlens array significantly limits the actual applications of artificial optical devices, like distinguishing objects at different distances. In this study, a curved artificial compound eye for a microlens array with different focal lengths was fabricated by inkjet printing and air-assisted deformation. By adjusting the space of the microlens array, secondary microlenses were created between intervals of the primary microlens. The diameter/height of the primary and secondary microlens arrays are 75/25 µm and 30/9 µm, respectively. The planar-distributed microlens array was transformed into a curved configuration using air-assisted deformation. Compared with adjusting the curved base to distinguish objects at different distances, the reported technique features simplicity and is easy to operate. The applied air pressure can be used to tune the field of view of the artificial compound eye. The microlens arrays with different focal lengths could distinguish the objects at different distances without additional components. When the external objects move a small distance, they can be detected by the microlens arrays due to their different focal lengths. It could effectively improve the motion perception of the optical system. Moreover, the focusing and imaging performances of the fabricated artificial compound eye were further tested. The compound eye combines the advantages of monocular eyes and compound eyes, holding great potential for developing advanced optical devices with a large field of view and automatic variable-focus imaging.
... With new principles to manipulate lens shapes, tunable lenses, based on electro-wetting [14][15][16], dielectro-wetting [17,18] or shape-changeable liquid [19][20][21][22][23][24][25], are capable of varying the focus with high speed, while it is difficult to control the curvature of the surface of the liquid lenses in a precision manner [26]. Micro-electromechanical systems (MEMs) such as curvature-variable mirror membranes [27,28] and metasurface lenses [29][30][31] adjust the focus by means of their deformation, while the limited refocusing response time based on these techniques is relatively slow, usually around 10 ms. Tunable acoustic gradient index (TAG) lens [32][33][34], driven by acoustic waves generated by cylindrical piezoelectric ceramics, can oscillate the focus rapidly with response time less than 1 µs. ...
This paper proposes a novel dynamic focusing module driven by galvanometers to position the laser focus with high speed and high precision. Thanks to the extremely high repeatability and the fast response time of galvanometers, the repeatability of the laser focus positioning is far less than the Rayleigh length of the beam and its response time is around 600 µs. An important feature of the proposed module lies in that it can be further integrated to an XY galvo scanner to realize a 3-axis laser scanning system. Due to the same galvanometers of the dynamic focus module and the XY scanner, the laser focus could be positioned in a simultaneous, rapid and precise manner in all three axes. Various simulation and experimental results demonstrate the feasibility and performance of the proposed dynamic focus module and the processing capability of the 3-axis scanning system with the proposed module.
... Liu et al. [13] proposed an ultra-smooth sapphire concave microlens fabricated by dry-etching-assisted femtosecond laser processing. Interest in MLAs is prompted by the superb performance of the insect compound eye due to its advantage in a wide field of view and high sensitivity for detecting fast-moving targets [14][15][16][17]. Some researchers have reported the fabrication method of multifocus MLAs. ...
We propose a high-precision method for the fabrication of variable focus convex microlens arrays on K9 glass substrate by combining femtosecond laser direct writing and hot embossing lithography. A sapphire master mold with a blind cylindrical hole array was prepared first by femtosecond laser ablation. The profile control of microlenses dependent on the temperature and the diameter of the blind hole in the sapphire mold was investigated. The curvature radius of the microlens decreased with temperature and increased with diameter. Uniform convex microlens arrays were fabricated with good imaging performance. Further, variable focus convex microlens arrays were fabricated by changing the diameter of the blind hole in sapphire, which produced the image at variable z planes. This method provides a highly precise fabrication of convex microlens arrays and is well suited for batch production of micro-optical elements.
... There are many animals and plants using unique micro-/nano-structures to improve their environmental adaptability (Han et al., 2016;Han et al., 2020a;Cao et al., 2020). For example, micro-/nano-structures on a lotus leaf and taro surface exhibit superhydrophobic properties (Zhang et al., 2012b;Wang et al., 2021b;Lv et al., 2021). ...
Due to unique optical and electrical properties, micro-/nano-structures have become an essential part of optoelectronic devices. Here, we summarize the recent developments in micro-/nano-structures fabricated by laser technologies for optoelectronic devices. The fabrication of micro-/nano-structures by various laser technologies is reviewed. Micro-/nano-structures in optoelectronic devices for performance improvement are reviewed. In addition, typical optoelectronic devices with micro-nano structures are also summarized. Finally, the challenges and prospects are discussed.
... What's more, the lack of adjustability limits the manufacturing yield and applications of the photonic devices [29][30][31][32][33]. Fortunately, attention has been paid to the research of adjustable artificial compound eyes. The focal lengths of the artificial compound eyes can be adjusted through temperature adjustment [34], pH adjustment [35] or hydraulic adjustment [36,37]. Although these works are very innovative, there are still many issues to be solved. ...
In this paper, a continuous zoom compound eye imaging system based on liquid lenses is proposed. The main imaging part of the system consists of a liquid compound eye, two liquid lenses and a planar image sensor. By adjusting the liquid injection volumes of the liquid compound eye and liquid lenses, the system can realize continuous zoom imaging without any mechanical movement of imaging components. According to the results of experiments, the paraxial magnification of the target can range from ∼0.019× to ∼0.037× at a fixed working distance. Moreover, the system can realize continuous focusing at a fixed paraxial magnification when the working distance ranges from ∼200mm to ∼300mm. Compared with the traditional artificial compound eye imaging systems, the proposed system increases the adjustability and matches the variable image surfaces of the liquid compound eye to a planar image sensor. The aspherical effects of the liquid compound eye and liquid lenses are also considered in the design of the system. The system is expected to be used for imaging in various scenes, such as continuous zoom panoramic imaging, 3D scanning measurement and so on.
... 17 Compared with single-aperture systems, small size, curvilinear layout, and a large number of ommatidium-like units synergistically compensate the limited FOV in each miniaturized vision unit. 18 Some artificial compound eyes have been studied in previous works [19][20][21][22][23][24][25][26][27][28][29] with small dimension. However, none of them would be feasible for near-field object detection, such as for this tactile sensing sensor. ...
Artificial tactile sensing for robots is a counterpart to the human sense of touch, serving as a feedback interface for sensing and interacting with the environment. A vision-based tactile sensor has emerged as a novel and advantageous branch of artificial tactile sensors. Compared with conventional tactile sensors, vision-based tactile sensors possess stronger potential thanks to acquiring multimodal contact information in much higher spatial resolution, although they typically suffer from bulky size and fabrication challenges. In this article, we report a thin vision-based tactile sensor that draws inspiration from natural compound eye structures and demonstrate its capability of sensing three-dimensional (3D) force. The sensor is composed of an array of vision units, an elastic touching interface, and a supporting structure with illumination. Experiments validated the sensor's advantages, including competitive spatial resolution of deformation as high as 1016 dpi on a 5 × 8 mm2 sensing area, superior accuracy of 3D force measurement at levels of 0.018 N for tangential force and 0.213 N (0.108 N at the center region) for normal force, and real-time processing at 30 Hz, while achieving a thin size of 5 mm. We further demonstrate the sensor capability in sensing 3D force and slip occurrence in real grasping experiments. This device paves the way for robotic applications that require rich tactile information with miniaturized sensor structure.
... This method modulates light selectively with a liquid crystal lens of variable focal length. In 2020, Cao, J.J. et al. [30] realized the bioinspired, zoom eye-enabled, variable-focus imaging with a deformable polydimethylsiloxane lens array. Similar to the lens of human eyes, it images the target with different distances clearly. ...
The properties of the human eye retina, including space-variant resolution and gaze characters, provide many advantages for numerous applications that simultaneously require a large field of view, high resolution, and real-time performance. Therefore, retina-like mechanisms and sensors have received considerable attention in recent years. This paper provides a review of state-of-the-art retina-like imaging techniques and applications. First, we introduce the principle and implementing methods, including software and hardware, and describe the comparisons between them. Then, we present typical applications combined with retina-like imaging, including three-dimensional acquisition and reconstruction, target tracking, deep learning, and ghost imaging. Finally, the challenges and outlook are discussed to further study for practical use. The results are beneficial for better understanding retina-like imaging.
... The contemporary femtosecond laser treatment of silicon surfaces is focused primarily on removing material using an energy higher than that required for silicon ablation threshold to ablate the material in the processing area. Ablation technology can be used to alter surface reflectivity [11,12] and wettability [13,14] as well as manufacture micro-lens arrays [15,16]. Moreover, owing to the heat accumulation effect, femtosecond lasers with high repetition rates can directly pattern silicon oxide patterns on a silicon substrate, which has potential applications in maskless lithography [17] and microfluidics [18]. ...
The ability to create controllable patterns of micro- and nanostructures on the surface of bulk silicon has widespread application potential. In particular, the direct writing of silicon oxide patterns on silicon via femtosecond laser-induced silicon amorphization has attracted considerable attention owing to its simplicity and high efficiency. However, the direct writing of nanoscale resolution is challenging due to the optical diffraction effect. In this study, we propose a highly efficient, one-step method for preparing silicon oxide nanopatterns on silicon. The proposed method combines femtosecond laser-induced silicon amorphization with a subwavelength-scale beam waist of photonic nanojets. We demonstrate the direct writing of arbitrary nanopatterns via contactless scanning, achieving patterns with a minimum feature size of 310 nm and a height of 120 nm. The proposed method shows potential for the fabrication of multifunctional surfaces, silicon-based chips, and silicon photonics.
This paper surveys adaptive cameras, i.e. any camera device able to change its geometric settings. We consider their classification in four categories: lensless, dioptric, catadioptric and polydioptric cameras. In each category, we report and describe all the existing adaptive cameras. Then, the known applications of these devices are summarized. Finally, we discuss open research lines for new adaptations of cameras, and their promising uses.
Limited by the planar imaging structure, the commercial camera needs to introduce additional optical elements to compensate for the curved focal plane to match the planar image sensor. This results in a complex and bulky structure. In contrast, biological eyes possess a simple and compact structure due to their curved imaging structure that can directly match with the curved focal plane. Inspired by the structures and functions of biological eyes, curved vision systems not only improve the image quality, but also offer a variety of advanced functions. Here, we review the recent advances in bioinspired vision systems with curved imaging structures. Specifically, we focus on their applications in implementing different functions of biological eyes, as well as the emerging curved neuromorphic imaging systems that incorporate bioinspired optical and neuromorphic processing technologies. In addition, the challenges and opportunities of bioinspired curved imaging systems are also discussed.
As an outstanding visual system for insects and crustaceans to cope with the challenges of survival, compound eye has many unique advantages, such as wide field of view, rapid response, infinite depth of field, low aberration and fast motion capture. However, the complex composition of their optical systems also presents significant challenges for manufacturing. With the continuous development of advanced materials, complex 3D manufacturing technologies and flexible electronic detectors, various ingenious and sophisticated compound eye imaging systems have been developed. This paper provides a comprehensive review on the microfabrication technologies, photoelectric detection and functional applications of miniature artificial compound eyes. Firstly, a brief introduction to the types and structural composition of compound eyes in the natural world is provided. Secondly, the 3D forming manufacturing techniques for miniature compound eyes are discussed. Subsequently, some photodetection technologies for miniature curved compound eye imaging are introduced. Lastly, with reference to the existing prototypes of functional applications for miniature compound eyes, the future development of compound eyes is prospected.
A multi-curvature compound eye with negative-meniscus substrate is developed to address the problem of the imaging defocus and spherical aberration in plano-convex spherical compound eye. In compound eye design, a negative meniscus substrate is designed to reduce spherical aberrations and the curvature radius of ommatidia at different levels adjusts to accommodate changes in focal length. The designed compound eye includes 37 ommatidia, offering a theoretical field of view spanning 80°, and its entire diameter is. Furthermore, optical evaluation of the imaging of compound eyes was conducted using spot diagrams and Modulation Transfer Function curves. A micro compound eye imaging system was used to detect the imaging of the fabricated compound eyes. The imaging quality of the compound eye was assessed using the root mean square value in the HSV color model. Compared with the plano-convex spherical compound eye, the maximum light intensity of the designed compound eye is increased by 15%. It is expected that the work in this paper will further promote the application of micro compound eye in the fields of integration, imaging and detection.
Microlens array (MLA) has been widely applied in augmented reality and optical imaging. When used in a humid environment or medical endoscopy, MLA needs to be both superhydrophobic and multifocal. However, it is not easy to achieve both superhydrophobic and multifocal function by integrating superhydrophobic and multifocal structures on the same surface by means of a simple, efficient, and precise method. In this paper, the superhydrophobic multifocal MLA with superhydrophobic properties and multifocal functions is successfully designed for preparation based on a method of 3D lithography and soft lithography. The 3D lithography can further help the preparation of a multifocal MLA with varying apertures and a multistep superhydrophobic structure with a round dome. The superhydrophobic multifocal MLA with periods 50 and 120 μm has perfect superhydrophobic property. The water droplet can slide and bounce off the surface at a roll angle of less than 12.9° with both multifocal and integrated imaging function, as well as up to 397 μm depth-of-field (DOF) detection range; this greatly exceeds the conventional MLA. The perfect superhydrophobic and optical property can be achieved in an extremely humid environment. The superhydrophobic multifocal MLA proposed in this paper has a promising prospect for actual practices.
In extreme environments, fog formation on a microlens array (MLA) surface results in a device failure. One reliable solution for fog removal is to heat the surface using a microheater. However, due to the surface interference, the combination of these two microdevices remains elusive. In this study, we introduce lift-off and electroless plating into femtosecond laser processing to fabricate a microheater integrated MLA (μH-MLA) on the same substrate with high light transmittance, durability, and fog removal efficiency. Laser-induced micro-nano grooves enable the microheater to be tightly coupled with the MLA and have high heating performance, thus maintaining a stable performance for over 24 h during continuous operation as well as under long time ultrasonic vibration and mechanical friction. With a rapid response time (τ0.5) of 17 s and a high working temperature of 188 °C, the μH-MLA removed fog that covers the entire face within 14 s. Finally, we prove the use of this fabrication method in large areas and curved surface environments. This study provides a flexible, stable, and economical method to integrate micro-optical and microelectrical devices.
We present a microlens arrays (MLAs) based artificial compound eye for tuning a focal length. The flexible MLAs-patterned poly (dimetylsiloxane) (PDMS) film was deformed from planar to curved shape with the increase of the fluid injection, acting as a focus-tunable lens. With a designed optical system, we compared focused beam intensity depending on the radius of curvature of the fabricated lens.
The compound eyes of insects in nature provide many innovative perspectives for the development of bionic imaging devices. The construction of thousands of ommatidia favors compound eye imaging, and the close arrangement between each small eye generates a significant amount of optical crosstalk. This work reports an optical waveguide integrated with isolation‐layer microlens array (WIMLA) with high‐contrast, high‐resolution imaging inspired by the compound eyes of insects. This WIMLA is mainly fabricated by self‐written optical waveguide formed under ultraviolet exposure and the introduction of a black photoresist under the action of capillary force to achieve the effect of double isolation. The experimental results demonstrate that image contrast increases by 59.8% with double‐layer isolation and the full width at half‐maximum reduces by 27.7% in comparison with those of the MLA without any isolation layer. As a result, a more focused optical path can be confined inside the microlens for transmission. Panoramic stitching is accomplished by traversing all potential matching subimages with the edge detection and breadth‐first search algorithms. The combination of the prepared WIMLA with commercial cameras to capture faces will open up new possibilities for mobile navigation, face recognition, and medical monitoring.
Random microlens arrays (rMLAs) have been widely applied as a beam-shaping component within an optical system. Silica glass is undoubtedly the best choice for rMLAs because of its wide range of spectra with high transmission and high damage threshold. Yet, machining silica glass with user-defined shapes is still challenging. In this work, novel design and fabrication methods of random silica-glass microlens arrays (rSMLAs) are proposed and a detailed investigation of this technology is presented. Based on the molding technology, the fabricated rSMLAs with tunable divergent angles demonstrate superior physical properties with 1.81 nm roughness, 1074.33 HV hardness, and excellent thermal stability at 1250 °C for 3 h. Meanwhile, their characterized optical performance shows a high transmission of over 90% in the ultraviolet spectrum. The fabricated two types of rSMLAs exhibit excellent effects of beam homogenization with surprising energy utilization (more than 90%) and light spot uniformity (more than 80%). This innovative process paves a new route for fabricating rMLAs on solid silica glass and breaking down the barrier of rMLAs to broader applications.
Microactuators can autonomously convert external energy into specific mechanical motions. With the feature sizes varying from the micrometer to millimeter scale, microactuators offer many operation and control possibilities for miniaturized devices. In recent years, advanced microfluidic techniques have revolutionized the fabrication, actuation, and functionalization of microactuators. Microfluidics can not only facilitate fabrication with continuously changing materials but also deliver various signals to stimulate the microactuators as desired, and consequently improve microfluidic chips with multiple functions. Herein, this cross‐field that systematically correlates microactuator properties and microfluidic functions is comprehensively reviewed. The fabrication strategies are classified into two types according to the flow state of the microfluids: stop‐flow and continuous‐flow prototyping. The working mechanism of microactuators in microfluidic chips is discussed in detail. Finally, the applications of microactuator‐enriched functional chips, which include tunable imaging devices, micromanipulation tools, micromotors, and microsensors, are summarized. The existing challenges and future perspectives are also discussed. It is believed that with the rapid progress of this cutting‐edge field, intelligent microsystems may realize high‐throughput manipulation, characterization, and analysis of tiny objects and find broad applications in various fields, such as tissue engineering, micro/nanorobotics, and analytical devices.
Three-dimensional (3D) micro/nano structures are significant in many applications because of their novel multi-functions and potential in high integration. As is known, the traditional methods for the processing of 3D micro/nano structures exhibit disadvantages in mass production and machining precision. Alternatively, ultrafast laser machining, as a rapid and high-power-density processing method, exhibits advantages in 3D micro/nano structuring due to its characteristics of extremely high peak power and ultra-short pulse. With the development of ultrafast laser processing for fine and complex structures, it is attracting significant interest and showing great potential in the manufacture of 3D micro/nano structures. In this review, we introduce the optimization mechanism of ultrafast laser machining in detail, such as the optimization of the repetition rate and pulse energy of the laser. Furthermore, the specific applications of 3D micro/nano structures by laser processing in the optical, electrochemical and biomedical fields are elaborated, and a valuable summary and perspective of 3D micro/nano manufacturing in these fields are provided.
The compact and lightweight infrared (IR) optics devices are highly demanded in booming applications. However, fabrication of IR optics devices with high efficiency is still technically challenging, especially artificial compound eyes (ACE) with low aberration imaging and large field of view. In this work, a method of femtosecond laser wet etching combining with the “two‐step” precision glass molding based on chalcogenide glass is proposed to fabricate glass IR ACE. The as‐prepared consists of 6000 ommatidia (diameter of 88 µm and the sag height of 11 µm) arranged in a hexagonal manner with perfect parabolic morphology and high uniformity. The chalcogenide glass IR ACE exhibits excellent optical performance both in IR active imaging and IR passive imaging with high transmittance (60–70%) ranging from 2.5 to 15 µm. The ommatidia have a high resolution up to 20.16 lp mm⁻¹, and imaging with large field of view up to 60° and low aberration can be achieved. Furthermore, the proposed technology shows advantages to fabricate glass IR ACE with low cost and high efficiency, and glass IR ACE shows great potential in IR imaging, robot vision, IR 3D motion tracking, and so on.
The artificial compound eye (ACE) with zoom imaging requires complex power sources. Meanwhile, its curved substrate makes it difficult for the ACE to realize the zoom imaging on flat surfaces. To realize a wide field of view and a zoom function on both curved and flat surfaces simultaneously, a novel ACE is proposed, which is a bionic design inspired by an ancient creature, trilobite. Compared with a dragonfly, photosensitive units of a trilobite's compound eye are composed of ommatidia with different focal lengths. By learning from this concept, an artificial hyper compound eye (AHCE) was fabricated. Its basic components are five microlenses with different curvatures, and they are capable of being treated as five ommatidia with different focal lengths. Five ommatidia form a photosensitive unit to realize a zoom function. AHCE is capable of variable-focus imaging on curved surfaces. With the information share function, we found that the AHCE not only images on curved surfaces but also has a zoom-imaging function on flat surfaces. The results confirm that the AHCE demonstrates an advanced imaging capability, a variable-focus imaging function on both curved and flat surfaces, which may open new opportunities in developing advanced micro-optical devices.
Curved artificial compound eyes (ACEs) attract enormous research interest owing to their potential applications in medical devices, surveillance imaging, target tracking, and so on. However, fog, dust, or other liquids are likely to condense on the device surface under a humid, low‐temperature environment or outdoors, thus affecting the optical performance. In this work, a multi‐functional ACE (MF‐ACE) is fabricated by a combination of i) femtosecond laser wet etching, ii) soft lithography, and iii) polydimethylsiloxane (PDMS) swelling methods. The fabricated device is close‐packed with over 3000 microlenses (≈108 µm diameter and ≈15 µm height) on a spherical macrolens (6.56 cm diameter and 0.87 cm height). The trapped silicone oil in the cross‐linked PDMS endows the as‐fabricated ACE with excellent water repellence and anti‐fogging, anti‐fouling, and self‐cleaning abilities. In addition, the ACE shows high optical performance and the ommatidia have a spatial resolution of 50.8 lp mm⁻¹. The imaging and focusing experiments demonstrate its high optical properties and uniformity. It is anticipated that this research may provide useful guidelines for the fabrication of anti‐fogging and anti‐fouling optical devices, and such device enables potential applications in autonomous vehicles, medical, or vision systems under harsh environmental conditions.
Background
Nowadays, tunable antireflective characteristics have attracted considerable attention due to growing demands in next-generation optical energy-related fields.
Method
Bioinspired by the distinctive structural geometry on small yellow leafhopper wings, this study reports reversibly switchable antireflective characteristics enabled by ambient-temperature shape memory polymer-based soccer ball-shaped structure arrays with multilayer porous structures underneath.
Significant finds
The resulting structures behave a broadband omnidirectional antireflection performance, where the average reflectance in the visible spectrum can even be reduced by 22% for an incident angle of 75º. Interestingly, the structures can be instantaneously deformed or recovered through applying external stimuli in ambient environments. The antireflective property switches associated with the shape memory transitions deliver vast opportunities in developing smart optical devices. Moreover, the structure-shape effect and reversibility on the antireflective properties are systematically assessed in the research.
A retina-like scanning method based on liquid crystal optical phased array (LCOPA) is proposed to improve field of view and efficiency. The functions of human retina, lens and fovea gaze control are achieved with optimized designed scanning strategy. Beam splitting method and angular magnification system are used to meet the requirements of the efficient scanning and large FOV. The models are verified by several experiments and the results show that the scanning performance well with the flexible retina-like strategy, especially for eccentric fovea. The scanning FOV is magnified 2.2 times and the average scanning error is less than 5%.
A bionic artificial compound eye manufactured on a concave mold with precision engraving method for imaging, which allows for the rapid fabrication of large-scale compound eyes at a low cost. Thousands of concave structures are accurately machined and positioned omnidirectionally in concentric rings with a minimum diameter of 100 μm on a hemisphere. The PDMS ommatidia can be obtained once replicated, which can greatly improve preparation efficiency, and the peel-off process can also be optimized by alcohol ultrasonic without edge damage. The optical performance and field of view of the artificial compound eye are also investigated, and the experimental results are around 120°. Furthermore, the combination of the prepared compound eye and the commercial CMOS camera successfully captures images of different shapes.
Nature has developed unique strategies to refine and optimise structural performance. Using surfaces designed at multiple length scales, from micro to nano levels, combined with complex chemistries, different natural organisms can exhibit similar wetting but different adhesion to liquids under specific environments. These biological surfaces have inspired researchers to develop new approaches to control surface wetting and liquid behaviour via surface adhesion. Here we review natural strategies to control the interaction of liquids with solid surfaces and the efforts to implement these strategies in synthetic materials designed to work in either atmospheric or underwater environment. Particular attention is paid to droplet behaviour on the special-adhesion surfaces in nature and artificial smart surfaces. We highlight recent progress, identify the common threads, and discuss the fundamental differences in a way that can help formulate rational approaches towards surface engineering, and identify current challenges as well as future directions for the field.
Compound eyes are ubiquitous natural biosensors that possess high temporal resolution and large fields of view (FOVs). While for solid materials based artificial imaging systems, flexible zooming ability while keeping the constant FOV is still challenging, as well as the low-cost fabrication. Herein, liquid compound eyes with natural structures are presented that synthesize optofluidics and bionics in a non-trivial manner, which enables the deformation-free zooming and flexible cell fluorescence sensing. Experimental results indicate that the innovatively manufactured bionic template possesses low roughness and uniform lens configuration with more than two thousands units, which endows the eyes with high-quality and low aberration imaging ability. Besides, digital controlled miscible liquids switching enables the focus of ommatidia simultaneously be adjusted from 150 μm to 5 mm with 100° view angle, and without bending the microlens curvature, to avoid FOV changing and image aberration. Due to large FOV and tunable ability, large-area cell fluorescence signal arrays and dynamic cell motion are imaged using this liquid compound eyes. This work presents novel strategy for compound lens manufacture at low-cost, and proposes deformation-free and continuous focus-tuning strategy, offering potentials for numerous applications, including biomedical sensing and adaptive imaging with large FOV.
The natural compound eyes provide great inspiration for design of advanced imaging devices. Artificial compound eyes (ACEs) with close‐packed microlens arrays (MLAs) have attracted enormous research interests due to their remarkable advantages in modern micro‐optical systems, such as miniaturization, high integration, tunable focal length, large field of view, and moving objects tracking. Over a decade of intense research, numerous approaches have been successfully developed to fabricate MLAs with high surface morphology and excellent optical performance. This paper gives a review of progress and continuous effort in the development and practical applications of ACEs. At first, two representative visual systems: single‐lens eye and compound eye are briefly introduced. Then, the main characteristic parameters of the microlens and MLAs are presented. After that, various fabrication technologies with different mechanisms that are successfully applied in planar and curved MLAs are summarized. The advantages and limitations of each processing method are discussed. Subsequently, some important practical applications of MLAs, particularly on imaging, beaming homogenizing, sensing, light extraction technique, micro‐total analysis systems (µ‐TAS), and microfabrication are also given. Finally, the current challenges and further prospects of this field are highlighted.
This work developed a method of femtosecond laser (fs-laser) parallel processing assisted by wet etching to fabricate 3D micro-optical components. A 2D fs-laser spot array with designed spatial distribution was generated by a spatial light modulator. A single-pulse exposure of the entire array was used for parallel processing. By subsequent wet etching, a close-packed hexagonal arrangement, 3D concave microlens array on a curved surface with a radius of approximately 120 μm was fabricated, each unit lens of which has designable spatial distribution. Characterization of imaging was carried out by a microscope and showed a unique imaging property in multi-planes. This method provides a parallel and efficient technique to fabricate 3D micro-optical devices for applications in optofluidics, optical communication, and integrated optics.
For single non-uniform surface compound eyes cannot achieve zoom imaging, resulting in poor imaging and other issues, a new type of aspherical artificial compound eye structure with variable focal length is proposed in this paper. The structure divides the surface compound eye into three fan-shaped areas, and different focal lengths of the micro-lens in different area make the artificial compound eye zoom in a certain range. The focal length and size of the micro-lens are determined by the area and the location of the micro-lens. The optimization of aspherical array of the micro-lens is calculated and the spherical aberration in each area is reduced to one percent of the initial value. Through simulation analysis, the designed artificial compound eye structure can realize the focal length adjustment, and effectively reduce the problem of the poor imaging quality of the curved compound eye edge. As a result, the aspherical artificial compound eye sample with the number of eyes of n=61 and the diameter of the base of 8.66mm was prepared using the molding method. The mutual relationship between the eyes of the child was calibrated and a mathematical model for the simultaneous identification of multiple sub eyes was established. An artificial compound eye positioning experimental system with the error value less than 10% was set up through a number of micro-lens capture target point settlement coordinates.
Detecting hydrogen changes with the naked eye A simple, low-cost sensor, designed for remotely detecting dangerous hydrogen levels, is extremely desired in hydrogen-related applications. Chongjun Jin at China’s Sun Yet-sen University, Jianfang Wang at the Chinese University of Hong Kong and co-workers have built a new type of optical hydrogen sensor by sputtering palladium on an elastic slab. As hydrogen was loaded, the palladium film would wrinkle deeply, namely, switching from the mirror-like surface to a coarse one. This phenomenon was not found in the palladium film on inelastic substrate. This hydrogen-induced surface deformation endows the sensor with a dramatically high reflectance change throughout the visible band and thus enables a distinct eye-readable change in color from dark to bright. These results offer great potential for developing inexpensive and sensitive eye-readable hydrogen sensors.
Muscles and joints make highly coordinated motion, which can be partly mimicked to drive robots or facilitate activities. However, most cases primarily employ actuators enabling simple deformations. Therefore, a mature artificial motor system requires many actuators assembled with jointed structures to accomplish complex motions, posing limitations and challenges to the fabrication, integration, and applicability of the system. Here, a holistic artificial muscle with integrated light‐addressable nodes, using one‐step laser printing from a bilayer structure of poly(methyl methacrylate) and graphene oxide compounded with gold nanorods (AuNRs), is reported. Utilizing the synergistic effect of the AuNRs with high plasmonic property and wavelength‐selectivity as well as graphene with good flexibility and thermal conductivity, the artificial muscle can implement full‐function motility without further integration, which is reconfigurable through wavelength‐sensitive light activation. A biomimetic robot and artificial hand are demonstrated, showcasing functionalized control, which is desirable for various applications, from soft robotics to human assists.
The focal lengths of the sub-eyes in a single-layer uniform curved compound eye are all the same, resulting in poor imaging quality for the compound eye. A non-uniform curved compound eye can effectively solve the problem of poor edge-imaging quality, however, it suffers from a large spherical aberration, and is unable to achieve zoom imaging. To solve these problems, a new type of aspherical artificial compound eye structure with variable focal length is proposed in this paper. The structure divides the surface compound eye into three fan-shaped areas with different focal lengths of the microlens in different areas, which allow the artificial compound eye to zoom in a certain range. The focal length and size of the microlens is determined by the area and the location of the microlens. The aspherical optimization of the microlens is calculated, and spherical aberration in each area is reduced to one percent of the initial value. Through simulation analysis, the designed artificial compound eye structure realizes focal length adjustment and effectively reduces the problem of the poor imaging quality of the curved compound eye edge. As a result, an aspherical artificial compound eye sample—where the number of sub-eyes is n = 61, and the diameter of the base is Φ = 8.66 mm—was prepared by using a molding method. Additionally, the mutual relationship between the eyes of the child was calibrated, and hence, a mathematical model for the simultaneous identification of multiple sub-eyes was established. This study set up an experimental artificial compound eye positioning system, and through a number of microlens capture target point settlement coordinates, achieved an error value of less than 10%.
By incorporating photosensitive molecules into a rubbery matrix, researchers have created a lens that can be dynamically re-shaped using visible light. Most tunable lenses rely on special lithographic patterns to manipulate light, but natural systems such as the human eye use variable refractive index changes for adjustable focus. Emiliano Descrovi at the Polytechnic University of Turin in Italy and colleagues have developed an optical element flexible enough to deliver refractive index gradients through laser beam writing. The team found that azopolymers — compounds that switch orientation and expand under light stimulus — could introduce predictable, parabolic refractive index changes of up to 0.4% inside a polydimethylsiloxane substrate after pinpoint irradiation. Imaging experiments demonstrated the possibility of resolving objects by manipulating laser exposure times to progressively increase the new lens’ focal length.
Microfluidic-based integrated molecular diagnostic systems, which are automated, sensitive, specific, user-friendly, robust, rapid, easy-to-use, and portable, can revolutionize future medicine. Current research and development largely relies on polydimethylsiloxane (PDMS) to fabricate microfluidic devices. Since the transition from the proof-of-principle phase to clinical studies requires a vast number of integrated microfluidic devices, there is a need for a high-volume manufacturing method of silicone-based microfluidics. Here we present the first roll-to-roll (R2R) thermal imprinting method to fabricate integrated PDMS–paper microfluidics for molecular diagnostics, which allows production of tens of thousands of replicates in an hour. In order to validate the replicated molecular diagnostic platforms, on-chip amplification of viral ribonucleic acid (RNA) with loop-mediated isothermal amplification (LAMP) was demonstrated. These low-cost, rapid and accurate molecular diagnostic platforms will generate a wide range of applications in preventive personalized medicine, global healthcare, agriculture, food, environment, water monitoring, and global biosecurity.
Flexible smart surfaces with tunable wettability are promising for emerging wearable uses. However, currently, wearable superhydrophobic surfaces with dynamic wetting behaviors are rarely reported. Here, a skin‐like superhydrophobic elastomer surface with switchable lotus leaf and rose petal states is reported. Direct laser writing technique is employed for one‐step, programmable, large‐scale fabrication of monolithic and hierarchical micro‐nanostructures on elastomer, leading to strong water repellence. The surface topography can be finely regulated in a rapid and reversible manner by simple stretching, providing the feasibility of controlling the surface wettability by simple body motions. The ability to switch wetting states enables the surface to capture and release multiple droplets in parallel. Furthermore, the active surface can be applied to the joints of fingers and operate as a droplet manipulator under finger motions without requiring energy supply or external appliance. In this work, dynamic tuning of wetting properties is integrated into the design of skin‐like wearable surfaces, revealing great potential in versatile applications such as wearable droplet manipulator, portable actuator, adaptive adhesion control, liquid repellent skin, and smart clothing.
The lossy nature of plasmonic wave due to absorption is shown to become an advantage for scaling-up a large area surface nanotexturing of transparent dielectrics and semiconductors by a self-organized sub-wavelength energy deposition leading to an ablation pattern - ripples - using this plasmonic nano-printing. Irreversible nanoscale modifications are delivered by surface plasmon polariton (SPP) using: (i) fast scan and (ii) cylindrical focusing of femtosecond laser pulses for a high patterning throughput. The mechanism of ripple formation on ZnS dielectric is experimentally proven to occur via surface wave at the substrate - plasma interface. The line focusing increase the ordering quality of ripples and facilitates fabrication over wafer-sized areas within a practical time span. Nanoprinting using SPP is expected to open new applications in photo-catalysis, tribology, and solar light harvesting via localized energy deposition rather scattering used in photonic and sensing applications based on re-scattering of SPP modes into far-field modes
We report an electrically controlled optofluidic zoom system which can achieve a large continuous zoom change and high-resolution image. The zoom system consists of an optofluidic zoom objective and a switchable light path which are controlled by two liquid optical shutters. The proposed zoom system can achieve a large tunable focal length range from 36mm to 92mm. And in this tuning range, the zoom system can correct aberrations dynamically, thus the image resolution is high. Due to large zoom range, the proposed imaging system incorporates both camera configuration and telescope configuration into one system. In addition, the whole system is electrically controlled by three electrowetting liquid lenses and two liquid optical shutters, therefore, the proposed system is very compact and free of mechanical moving parts. The proposed zoom system has potential to take place of conventional zoom systems.
Small fly eyes should not see fine image details. Because flies exhibit saccadic visual behaviors and their compound eyes have relatively few ommatidia (sampling points), their photoreceptors would be expected to generate blurry and coarse retinal images of the world. Here we demonstrate that Drosophila see the world far better than predicted from the classic theories. By using electrophysiological, optical and behavioral assays, we found that R1-R6 photoreceptors’ encoding capacity in time is maximized to fast high-contrast bursts, which resemble their light input during saccadic behaviors. Whilst over space, R1-R6s resolve moving objects at saccadic speeds beyond the predicted motion-blur-limit. Our results show how refractory phototransduction and rapid photomechanical photoreceptor contractions jointly sharpen retinal images of moving objects in space-time, enabling hyperacute vision, and explain how such microsaccadic information sampling exceeds the compound eyes’ optical limits. These discoveries elucidate how acuity depends upon photoreceptor function and eye movements.
Multi scale hierarchical structures underpin mechanical, optical, and wettability behavior in nature. Here we present a novel approach which can be used to mimic the natural hierarchical patterns in a quick and easy maskless fabrication. By using two-beam interference lithography with angle-multiplexed exposures and scanning, we have successfully printed large-area complex structures having a cascading resolution and 3D surface profiles. By precisely controlling the exposure dose we have demonstrated a capability to create different 3D textured surfaces having comparable aspect ratio with period spanning from 4 μm to 300 nm (more than one order of magnitude) and the height spanning from 0.9 μm to 40 nm, respectively. Up to three levels of biomimetic hierarchical structures were obtained that show several natural phenomena: superhydrophobicity, iridescence, directionality of reflectivity, and polarization at different colors.
We demonstrate a tunable imaging system based on the functionality of the mammalian eye using soft-matter micro-optical components. Inspired by the structure of the eye, as well as by the means through which nature tunes its optical behavior, we show that the technologies of microsystems engineering and micro-optics may be used to realize a technical imaging system whose biomimetic functionality is entirely distinct from that of conventional optics. The engineered eyeball integrates a deformable elastomeric refractive structure whose shape is mechanically controlled through application of strain using liquid crystal elastomer (LCE) actuators; two forms of tunable iris, one based on optofluidics and the other on LCEs with embedded heaters; a fixed lens arrangement; and a commercial imaging sensor chip. The complete microsystem, optimized to yield optical characteristics close to those of the human eye, represents the first fully functional, soft-matter-based tunable single-aperture eye-like imager.
We present the design, fabrication and characterization of hydraulically-tunable hyperchromatic lenses for two-dimensional (2D) spectrally-resolved spectral imaging. These hyperchromatic lenses, consisting of a positive diffractive lens and a tunable concave lens, are designed to have a large longitudinal chromatic dispersion and thus axially separate the images of different wavelengths from each other. 2D objects of different wavelengths can consequently be imaged using the tunability of the lens system. Two hyperchromatic lens concepts are demonstrated and their spectral characteristics as well as their functionality in spectral imaging applications are shown.
The natural compound eye is a striking imaging device with a wealth of fascinating optical features such as a wide field of view (FOV), low aberration, and high sensitivity. Dragonflies in particular possess large, sophisticated compound eyes that exhibit high resolving power and information-processing capacity. Here, a large-scale artificial compound eye inspired by the unique designs of natural counterparts is presented. The artificial compound eye is created by a high-efficiency strategy that combines single-pulse femtosecond laser wet etching with thermal embossing. These eyes have a macrobase diameter of 5 mm and ≈30 000 close-packed ommatidia with an average diameter of 24.5 μm. Moreover, the optical properties of the artificial compound eyes are investigated; the results confirm that the eye demonstrates advanced imaging quality, an exceptionally wide FOV of up to 140°, and low aberration.
The shape of liquid interfaces can be precisely controlled using electrowetting, an actuation mechanism which has been widely used for tunable optofluidic micro-optical components such as lenses or irises. We have expanded the considerable flexibility inherent in electrowetting actuation to realize a variable optofluidic slit, a tunable and reconfigurable two-dimensional aperture with no mechanically moving parts. This optofluidic slit is formed by precisely controlled movement of the liquid interfaces of two highly opaque ink droplets. The 1.5 mm long slit aperture, with controllably variable discrete widths down to 45 µm, may be scanned across a length of 1.5 mm with switching times between adjacent slit positions of less than 120 ms. In addition, for a fixed slit aperture position, the width may be tuned to a minimum of 3 µm with high uniformity and linearity over the entire slit length. This compact, purely fluidic device offers an electrically controlled aperture tuning range not achievable with extant mechanical alternatives of a similar size.
Free-volume of polymers governs transport of penetrants through polymeric films. Control over free-volume is thus important for the development of better membranes for a wide variety of applications such as gas separations, pharmaceutical purifications and energy storage. To date, methodologies used to create materials with different amounts of free-volume are based primarily on chemical synthesis of new polymers. Here we report a simple methodology for generating free-volume based on the self-assembly of polyethylene-b-polydimethylsiloxane-b-polyethylene triblock copolymers. We have used this method to fabricate a series of membranes with identical compositions but with different amounts of free-volume. We use the term artificial free-volume to refer to the additional free-volume created by self-assembly. The effect of artificial free-volume on selective transport through the membranes was tested using butanol/water and ethanol/water mixtures due to their importance in biofuel production. We found that the introduction of artificial free-volume improves both alcohol permeability and selectivity.
We have developed a self-contained, liquid tunable microlens based on polyacrylate membranes integrated with compact on-chip thermo-pneumatic actuation fabricated using full-wafer processing. Silicone oil is used as the optical liquid, which is pushed or pulled into the lens cavity via an extended microfluidic channel structure without any pumps, valves or other mechanical means. The heat load generated by the thermal actuator is physically isolated from the lens chamber. The back focal length may be tuned from infinity to 4 mm with a maximum power consumption of 300 mW. The principal application is fine tuning of the back focal length, for which tuning time constants as small as 100 ms are suitable.
The unique characteristics of ultrafast lasers, such as picosecond and femtosecond lasers, have opened up new avenues in materials processing that employ ultrashort pulse widths and extremely high peak intensities. Thus, ultrafast lasers are currently used widely for both fundamental research and practical applications. This review describes the characteristics of ultrafast laser processing and the recent advancements and applications of both surface and volume processing. Surface processing includes micromachining, micro-and nanostructuring, and nanoablation, while volume processing includes two-photon polymerization and three-dimensional (3D) processing within transparent materials. Commercial and industrial applications of ultrafast laser processing are also introduced, and a summary of the technology with future outlooks are also given.
A subregional slicing method (SSM) is proposed to increase the nanofabrication efficiency of a nanostereolithography (NSL) process based on two-photon polymerization (TPP). The NSL process can be used to fabricate three-dimensional (3D) microstructures via the accumulation of layers of uniform thickness; hence, the precision of the final 3D microstructure depends on the layer thickness. The use of a uniform layer thickness means that, to fabricate a precise microstructure, a large number of thin slices is inevitably required, leading to long processing times. In the SSM proposed here, however, the 3D microstructure is divided into several subregions on the basis of the geometric slope, and then each of these subregions is uniformly sliced with a layer thickness determined by the geometric slope characteristics of each subregion. Subregions with gentle slopes are sliced with thin layer thicknesses, whereas subregions with steep slopes are sliced with thick layer thicknesses. Here, we describe the procedure of the SSM based on TPP, and discuss the fabrication efficiency of the method through the fabrication of a 3D microstructure.
We report on the fabrication of a microlens on a fused silica chip with excellent optical performance by femtosecond laser microfabrication. We show, both in theory and experimentally, that the fabricated microlens offers a high resolution approaching the optical diffraction limit. Moreover, two-photon excitation of fluorescence with the fabricated microlens is demonstrated. The lateral and axial resolutions of fluorescence are measured to be ∼ 1.7 and 12.3 μm, respectively.
An alternative and novel approach for fabricating microlens arrays based on the confinement of surface wrinkles was presented. A selective ultraviolet/ozone (UVO) oxidation of a crosslinked polydimethylsiloxane (PDMS) film was performed to convert specific regions of the PDMS surface into silicate thin films. The chemical modification created the necessary elastic-moduli differences on the PDMS surface to control and define the wrinkle formation. The buckling process for microlens formation occurred as a result of the swelling of the moduli-mismatch oxidized PDMS regions. The high degree of lateral confinement played a significant role in the wrinkle formation and led to the development of the dimple pattern and microlens structure. Results show that spontaneous formation of wrinkle patterns provides a simple and rapid means to pattern large surfaces with a variety of surface-relief structures that include 2D wrinkles.
This work reveals a cost-efficient and flexible approach to various microlens arrays on polymers, which is essential to micro-optics elements. An 800-nm femtosecond laser is employed to control the hydrofluoric (HF) acid etching process on silica glasses, and concave microstructures with smooth curved surfaces are produced by this method. Then, the micro-structured glass templates can serve as molds for replicating microlenses on polymers. In this paper, a high-ordered microlens array with over 16,000 hexagonal-shaped lenses is fabricated on poly (dimethyl siloxane) [PDMS], and its perfect light-gathering ability and imaging performance are demonstrated. The flexibility of this method is demonstrated by successful preparation of several concave molds with different patterns which are difficult to be obtained by other methods. This technique provides a new route to small-scaled, smooth and curved surfaces which is widely used in micro-optics, biochemical analysis and superhydrophobic interface.
In this research, a unique freeform microlens array was designed and fabricated for a compact compound-eye camera to achieve a large field of view. This microlens array has a field of view of 48 ° × 48 ° , with a thickness of only 1.6 mm. The freeform microlens array resides on a flat substrate, and thus can be directly mounted to a commercial 2D image sensor. Freeform surfaces were used to design the microlens profiles, thus allowing the microlenses to steer and focus incident rays simultaneously. The profiles of the freeform microlenses were represented using extended polynomials, the coefficients of which were optimized using ZEMAX. To reduce crosstalk among neighboring channels, a micro aperture array was machined using high-speed micromilling. The molded microlens array was assembled with the micro aperture array, an adjustable fixture, and a board-level image sensor to form a compact compound-eye camera system. The imaging tests using the compound-eye camera showed that the unique freeform microlens array was capable of forming proper images, as suggested by design. The measured field of view of ± 23.5 ° also matches the initial design and is considerably larger compared with most similar camera designs using conventional microlens arrays. To achieve low manufacturing cost without sacrificing image quality, the freeform microlens array was fabricated using a combination of ultraprecision diamond broaching and a microinjection molding process.
Closed-packed high numerical aperture (NA) microlens arrays (MLA) are highly desirable for high resolution imaging and high signal-to-noise-ratio detection in micro-optical and integrated optical applications. However, realization of such devices remains technically challenging. Here, we report high quality fabrication of curved surfaces and MLAs by taking the full advantage of surface self-smoothing effect by creating highly reproducible voxels and by adopting an equal-arc scanning strategy. MLA of approximately 100% fill ratio and NA of 0.46, much greater than those ever reported, 0.13, is demonstrated, whose excellent optical performance was approved by the sharp focusing and high resolution imaging. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3464979]
Imaging systems that exploit arrays of photodetectors in curvilinear layouts are attractive due to their ability to match the strongly nonplanar image surfaces (i.e., Petzval surfaces) that form with simple lenses, thereby creating new design options. Recent work has yielded significant progress in the realization of such "eyeball" cameras, including examples of fully functional silicon devices capable of collecting realistic images. Although these systems provide advantages compared to those with conventional, planar designs, their fixed detector curvature renders them incompatible with changes in the Petzval surface that accompany variable zoom achieved with simple lenses. This paper describes a class of digital imaging device that overcomes this limitation, through the use of photodetector arrays on thin elastomeric membranes, capable of reversible deformation into hemispherical shapes with radii of curvature that can be adjusted dynamically, via hydraulics. Combining this type of detector with a similarly tunable, fluidic plano-convex lens yields a hemispherical camera with variable zoom and excellent imaging characteristics. Systematic experimental and theoretical studies of the mechanics and optics reveal all underlying principles of operation. This type of technology could be useful for night-vision surveillance, endoscopic imaging, and other areas that require compact cameras with simple zoom optics and wide-angle fields of view.
We demonstrate a tunable focus liquid crystal (LC) lens by sandwiching a homogeneous LC layer between a planar electrode and a curved electrode. The curved electrode which is made of conductive polymer has parabolic shape with a large apex distance. Such design dramatically reduces the phase loss which leads to a short focal length (~15 cm). By using a thin top glass substrate on the curved electrode side, the operating voltage of the lens cell is reduced to ~23 V(rms). This LC lens has advantages in wide focal length tunability, low operating voltage, and good mechanical stability.
An elastomer-based tunable liquid-filled microlens array integrated on top of a microfluidic network is fabricated using soft lithographic techniques. The simultaneous control of the focal length of all the microlenses composing the elastomeric array is accomplished by pneumatically regulating the pressure of the microfluidic network. A focal length tuning range of hundreds of microns to several millimeters is achieved. Such an array can be used potentially in dynamic imaging systems and adaptive optics.
The number of light quanta available to photoreceptors of lens and different types of compound eyes are calculated by photometry. Results depend on the optical environment: For point like light sources (stars) receptors in compound eyes generally receive considerably less numbers of light quanta compared with the human eye. This is due to the small size of ommatidial facets. For extended optical surroundings, the numbers of quanta reaching the receptors in typical insect compound eyes of the apposition type are comparable to those in the human eye. The optical superposition eye of nocturnal insects like Ephestia is an exceptional case, with an improvement in the numbers of quanta reaching the receptors by a factor 100 to 1000 compared to the eyes of bee or man.
Observing systems in nature has inspired humans to create technological tools that allow us to better understand and imitate biology. Biomimetics, in particular, owes much of its current development to advances in materials science and creative optical system designs. New investigational tools, such as those for microscopic imaging and chemical analyses, have added to our understanding of biological optics. Biologically inspired optical science has become the emerging topic among researchers and scientists. This is in part due to the availability of polymers with customizable optical properties and the ability to rapidly fabricate complex designs using soft lithography and three-dimensional microscale processing techniques.
Water collection via heterogeneous condensation and fog harvesting has important implications in everyday life and in several industrial applications. Recently, the unique combination of surface morphology and wettability exhibited by natural and biological species is receiving increasing attention from the scientific community. Surface morphology of such species exhibit unique micro- and nano-structure arrangements, which play a paramount role in water vapor condensation and fog harvesting. In this work, we focus on the design and replication of the bioinspired surface Gladiolus dalenii (G. dalenii) using inexpensive, facile and scalable soft lithography fabrication technique. The extent of micro- and nano-structure surface replication is evaluated using scanning electron microscopy and 3D laser optical microscopy. In addition, we compare the performance of G. dalenii leaf and its bioinspired replica during droplet condensation at the microscale using environmental scanning electron microscopy and optical microscopy and also its fog harvesting behavior. Droplet nucleation and growth is investigated in detail and correlated with the unique surface micro- and nano-structures arranged in a hierarchical manner on such surfaces when compared to smooth control sample. In addition, the different water collection performance on fixated and on replicated G. dalenii, as well as on the smooth control sample is compared and demonstrated by the surface energy analysis proposed. To conclude, by taking advantage of the unique G. dalenii surface morphology, this work successfully demonstrates the excellent condensation heat transfer and fog harvesting behavior of bioinspired functional surfaces fabricated using soft lithography when compared to the flat configuration. In addition, we also demonstrate the near-accurate replication of the micro-surface structures and of the governing mechanisms behind condensation and fog harvesting.
Most animals that have compound eyes determine object distances by using monocular cues, especially motion parallax. In artificial compound eye imaging systems inspired by natural compound eyes, object depths are typically estimated by measuring optic flow; however, this requires mechanical movement of the compound eyes or additional acquisition time. In this paper, we propose a method for estimating object depths in a monocular compound eye imaging system based on the computational compound eye (COMPU-EYE) framework. In the COMPU-EYE system, acceptance angles are considerably larger than interommatidial angles, causing overlap between the ommatidial receptive fields. In the proposed depth estimation technique, the disparities between these receptive fields are used to determine object distances. We demonstrate that the proposed depth estimation technique can estimate the distances of multiple objects.
Development of tunable microlenses by taking advantage of the physical adaptability of fluids is one of the challenges of optofluidic techniques, since it offers many applications in biochips, consumer electronics, and medical engineering. Current optofluidic tuning methods using electrowetting or pneumatic pressure typically suffer from high complexity involving external electromechanical actuating devices and limited tuning performance. In this paper, a novel and simple tuning method is proposed that changes the liquid refractive index in an optofluidic channel while leaving the shape of the microlens unchanged. To create an optofluidic microlens with high robustness and optical performance, built-in microlenses are fabricated inside 3D glass microfluidic channels by optimized single-operation wet etching assisted by a femtosecond laser. Tuning of focusing properties is demonstrated by filling the channel with media having different indices. Continuous tuning over a wide range (more than threefold tunability for both focal length and focal spot size) is also achieved by pumping sucrose solutions with different concentrations into the microchip channels. Reversible tuning is experimentally verified, indicating intriguing properties of the all-glass optofluidic microchip. Both the proposed tuning method and the all-glass architecture with built-in microlens offer great potential toward numerous applications, including microfluidic adaptive imaging and biomedical sensing.
The small field-of-view (FOV) limits the range of vision in various detecting/imaging devices from biological microscopes to commercial cameras and military radar. To date, imaging with FOV over 90° has been realized with fish-eye lenses, catadioptric lens, and rotating cameras. However, these devices suffer from inherent imaging distortion and require multiple bulky elements. Inspired by compound eyes found in nature, here a small-size (84 μm), distortion-free, wide-FOV imaging system is presented via an advanced 3D artificial eye architecture. The 3D artificial eye structure is accomplished by exploiting an effective optical strategy — high-speed voxel-modulation laser scanning (HVLS). The eye features a hexagonal shape, high fill factor (FF) (100%), large numerical aperture (NA) (0.4), ultralow surface roughness (2.5 nm) and aspherical profile, which provides high uniformity optics (error < ±6%) and constant resolution (FWHM = 1.7 ± 0.1 μm) in all directions. Quantitative measurement shows the eye reduces imaging distortion by two/three times under 30°/45° incidence, compared with a single lens. The distortion-free FOV can be controlled from 30° to 90°.
The surface structure of the compound eyes of 6 Drosophila species and 12 eye mutants of D. melanogaster were compared by scanning electron microscopy.
D. melanogaster, D. simulans, D. hydei, D. funebris and D. virilis displayed hexagonal facets and differed only slightly in the distribution of bristles. D. lebanonensis displayed tetragonal facets.
No obvious differences in surface structure of the eyes of colour mutants of D. melanogaster were found. Mutants with structural modifications of the eyes revealed irregular patterns of bristles, variations in bristle number and variations in facet shape, size and organization. The mutant spapol does not display clear-cut delineated facets.
Thermal ageing studies over relative high temperature range (from 250 °C to 85 °C) have been conducted on polydimethylsiloxane (PDMS) rubber with the aim of investigating ageing behavior. Tensile elongation, compression set and creep measurements are introduced to monitor the ageing process. Time temperature superposition is performed and the linear trends are found in the Arrhenius plots for all the approaches, revealing an identical process dominates the degradation process. Activation energies are found to be depended on the methods used, which are 88.5 kJ/mol for tensile tests, 67.7 kJ/mol for compression set measurements and 75.3 kJ/mol for creep measurements. The phenomenon that activation energy obtained from tensile elongation is always higher than other approaches is rationalized by the sensitive modification of thermal degradation on the rubbery network. Moreover, correlations between the results from different approaches have been examined. The linear relationships have been found between tensile elongation and creep or compression set measurements for the three methods are all influenced by the network structure.
We present a method to develop single-wall carbon nanotube (SWCNT)/polymer composites into arbitrary three-dimensional micro/nano structures. Our approach, based on two-photon polymerization lithography, allows one to fabricate three-dimensional SWCNT/polymer composites with a minimum spatial resolution of a few hundreds nm. A near-infrared femtosecond pulsed laser beam was focused onto a SWCNT-dispersed photo resin, and the laser light solidified a nanometric volume of the resin. The focus spot was three-dimensionally scanned, resulting in the fabrication of arbitrary shapes of SWCNT/polymer composites. SWCNTs were uniformly distributed throughout the whole structures, even in a few hundreds nm thick nanowires. Furthermore, we also found an intriguing phenomenon that SWCNTs were self-aligned in polymer nanostructures, promising improvements in mechanical and electrical properties. Our method has great potential to open up a wide range of applications such as micro- and nanoelectromechanical systems, micro/nano actuators, sensors, and photonics devices based on CNTs.
Insects have evolved numerous adaptations to survive a variety of environmental conditions. Given that the primary interface between insects and the environment is mediated through their skin or cuticle, many of these adaptations are found in extraordinary cuticle diversity both in morphology and structure. Not all of these adaptions manifest themselves in changes in the chemical composition of the cuticle but rather as elaborations of the surface structures of the cuticle. Typically the examination of these micro- and nanoscale structures has been performed using scanning electron microscopy (SEM). Typically, in order to decrease surface charging and increase resolution, an obscuring conductive layer is applied to the sample surface, but this layer limits the ability to identify nanoscale surface structures. In this paper we use a new technology, helium ion microscopy (HIM) to examine surface structures on the cuticle of wild type and mutant Drosophila. Helium ion microscopy permits high resolution imaging of biological samples without the need for coating. We compare HIM to traditional SEM and demonstrate certain advantages of this type of microscopy, with our focus being high resolution characterization of nanostructures on the cuticle of Drosophila melanogaster and potentially other biological specimens.
We propose a method for three-dimensional microfabrication with photopolymerization stimulated by two-photon absorption with a pulsed infrared laser. An experimental system for the microfabrication has been developed with a Ti:sapphire laser whose oscillating wavelength and pulse width are 790 nm and 200 fs, respectively. The usefulness of the proposed method has been verified by fabrication of several kinds of microstructure by use of a resin consisting of photoinitiators, urethane acrylate monomers, and urethane acrylate oligomers.
Experimental studies on the fabrication of sub-30-nm nanofibers using two-photon initiated photopolymerization (TPP) have been carried out. To generate nanofibers at the interior region of microstructures, a photopolymerization method involving a long laser-exposure technique (LET) is proposed. A multitude of nanofibers with a notably high resolution (about 22 nm) in TPP were produced using the LET. Furthermore, it is also demonstrated that thin interconnecting networks were created regularly in a weakly polymerized region existing around the boundary of a densely polymerized voxel, allowing for the creation of various embossing patterns. By controlling the distance between adjacent voxels or lines, a selective generation of nanofibers in a local area is possible, which leads to the fabrication of high-functional filters and mixers. Embossing patterns and microchannels including nanofibers inside were fabricated by the LET so as to demonstrate the practical feasibility of this approach. These sub-30-nm nanofibers may find meaningful applications such as biofilters, mixers, and photon emitters in diverse research fields.
1.
Descending, movement-sensitive visual interneurons in the ventral nerve cord of the dragonfly,Anax junius, fall into two categories, based upon their responses to a variety of stimulus patterns. One group (object-movement detectors) is sensitive only to movement of small patterns; the other (self-movement detectors) responds maximally to movement of very large patterns or to rotation of the animal in the lighted laboratory.
2.
Object-movement-detector responses to repeated identical stimuli habituate very rapidly. The habituation is region specific; pattern movement elsewhere in the receptive field elicits a renewed response (Fig. 3). The habituation is very long lasting and is not subject to dishabituation by mechanical or visual stimulation. Self-movement detectors, in contrast, show little or no habituation (Fig. 3).
3.
Increasing the extent of the stimulus pattern in the direction of motion decreases responses of object-movement detectors slightly and greatly increases self-movement-detector responses (Fig. 4).
4.
Increasing the length of the advancing edges perpendicular to the line of motion dramatically reduces object-movement-detector responses (Fig. 5). Such increases enhance self-movement-detector responses only slightly, unless they result in the pattern occupying especially sensitive regions of the receptive field (Fig. 7).
5.
Over a wide velocity range, self-movement-detector responses are not dependent on pattern wavelength (Fig. 8).
6.
These results indicate that the parameter upon which the object/world discrimination is based is different for the two groups of interneurons. The critical parameter for the self-movement detectors is the extent of the pattern in the direction of motion, whereas for the object-movement detectors, the critical parameter is the extent of the pattern perpendicular to the direction of motion.
We have examined the retina of the tsetse fly Glossina morsitans and G. palpalis using anatomical, optical, biochemical and electrophysiological techniques. The eye is basically very similar to those of other higher Diptera such as Musca and Calliphora. The ommatidial organization has an open rhabdom arrangement typical of a neural superposition eye. The central rhabdomeres R7 and R8 are smaller in diameter than peripheral rhabdomeres (R1-6) except at the dorsal margin of the eye, where they are greatly enlarged. The number of secondary pigment cells is unusually large with 16–18 surrounding each ommatidium. The facet lenses are also unusually thick with a weakly curved outer surface and a strongly convex inner surface. It is shown how this gives rise to the characteristic striped reflections from the tsetse eye by total internal reflection, and possible functions for this are considered. As in most other dipterans, the visual pigment chromophore is 3-hydroxy retinal and an ultraviolet sensitizing pigment, 3-hydroxy retinol is present also. Photoreceptor cells R1-6 have a similar spectral sensitivity to those in Musca, although the position of the green peak (500 nm) is some 10 nm longer. Two spectral classes of R7 correspond to the so-called 7y and 7p cells in Musca, with predominantly ultraviolet sensitivity, and the spectral sensitivity of the R8 cells encountered resembles that of so-called 8y cells (λ max 520 nm). Due to a dietary deficiency, the eyes of flies raised on porcine blood contain no traces of C40 carotenoids. This is correlated with the observation that the spectral sensitivity of both 7y and 8y cells are systematically higher in the blue (400–500 nm) than their counterparts in Musca or Calliphora.
Pax 6 genes from various animal phyla are capable of inducing ectopic eye development, indicating that Pax 6 is a master control gene for eye morphogenesis. It is proposed that the various eye-types found in metazoa are derived from a common prototype, monophyletically, by a mechanism called intercalary evolution.
In this research paper, in a major departure from conventional 2D micromachining processes, design and fabrication of a 3D compound eye system consisting of a 3D microprism array, an aperture array, and a microlens array were investigated. Specifically, the 3D microprism array on a curved surface was designed to steer the incident light from all three dimensions to a 2D plane for image formation. For each microprism, there is a corresponding microlens to focus the refracted light on the image plane. An aperture array was also implemented between the microprism array and the microlens array to eliminate cross-talk among the neighboring channels. In this system, 601 individual micro-assemblies consisting of microprisms and microlenses were constructed in a 20 mm diameter area. In this configuration, the maximum light deviation angle was determined to be 18.43 degrees. This research demonstrated an innovative and integrated approach to fabricating true 3D micro and meso scale optical structures. This work also validated the feasibility of using ultraprecision machining process for 3D microoptical device fabrication. The technology demonstrated in this research has high potentials in optical sensing, vision research and many other optical and photonic applications.
A spherical artificial compound eye which is comprised of an imaging microlens array and a pinhole array in the focal plane serving as receptor matrix is fabricated. The arrays are patterned on separate spherical bulk lenses by means of a special modified laser lithography system which is capable of generating structures with low shape deviation on curved surfaces. Design considerations of the imaging system are presented as well as the characterization of the comprising elements on curved surfaces, with special attention on the homogeneity over the array. The assembled system is the first spherical compound eye able to capture images. It is evaluated by analyzing resolution and cross-talk between the single channels.
Over the last twenty years classical views of how compound eyes work optically have undergone a series of overhauls. Exner's central concept of an optically inhomogeneous lens cylinder has survived, and such devices are now made commercially. He was wrong, however, about some crustacean eyes. They produce images by a mirror mechanism that was not discovered until 1975, and which now shows promise as an optical system capable of development.
The highly complex eyes of vertebrates, insects and molluscs have long been considered to be of independent evolutionary origin. Recently, however, Pax-6, a highly conserved transcription factor, has been identified as a key regulator of eye development in both mammals and flies. Homologues of Pax-6 have also been identified in species from other phyla, including molluscs. The wide variety of eyes in the animal kingdom may, therefore, have evolved from a single ancestral photosensitive origin.
The Drosophila Pax-6 gene eyeless (ey) plays a key role in eye development. Here we show tht Drosophila contains a second Pax-6 gene, twin of eyeless (toy), due to a duplication during insect evolution. Toy is more similar to vertebrate Pax-6 proteins than Ey with regard to overall sequence conservation, DNA-binding function, and early expression in the embryo, toy and ey share a similar expression pattern in the developing visual system, and targeted expression of Toy, like Ey, induces the formation of ectopic eyes. Genetic and biochemical evidence indicates, however, that Toy functions upstream of ey by directly regulating the eye-specific enhancer of ey. Toy is therefore required for initiation of ey expression in the embryo and acts through Ey to activate the eye developmental program.