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(a) Conventional polarization holography setup. (b) Interferometric holography setup with a non-polarizing beam splitter (NPBS), mirrors (M), and quarter-waveplates (QWP). (c) Schematic illustration of the incoming and outgoing beams in the NPBS. (d) A picture of the actual optics setup of the interferometric scheme.
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![Fig. 2. Total number of steering angle comparison: binary [13]...](profile/Michael-Escuti/publication/273312103/figure/fig2/AS:614311546343449@1523474694644/Total-number-of-steering-angle-comparison-binary-13-dotted-ternary-14-dashed_Q320.jpg)
We present a wide-angle, nonmechanical laser beam steerer based on polymer polarization gratings with an optimal design approach for maximizing field-of-regard (FOR). The steering design offers exponential scaling of the number of steering angles, called suprabinary steering. The design approach can be easily adapted for any 1-D or 2-D (e.g, symmet...
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In this paper, the implementation of optical elements in the form of Pancharatnam-Berry optics is considered. With respect to 3D bulk and diffractive optics, acting on the dynamic phase of light, Pancharatnam-Berry optical elements transfer a phase which is geometric in nature by locally manipulating the polarization state of the incident beam. The...
Citations
... Notably, LC polarization gratings (LCPGs), whose optical anisotropy is spatially and periodically modulated on the device, show unique optical properties such as circular polarization separation and 100% diffraction efficiency [1][2][3][4]. Based on these optical properties, numerous applications such as polarized imaging [5][6][7][8][9], headup/mounted displays [10][11][12][13], aerial imaging [14], and beam steering [15][16][17][18] have been reported. ...
A lot of research on liquid crystal polarization gratings (LCPGs) that can separate circularly polarized light with 100% diffraction efficiency has been conducted in the visible and near-infrared wavelength regions. In this paper, we tried to design and fabricate the LCPGs that are available for use in the mid- and far-infrared (MIR and FIR) wavelength regions. The materials for making LCPGs were selected in view of low absorption characteristics measured by the use of a Fourier-transform infrared (FT-IR) spectrometer. LCPGs designed for 3.88 µm and 9.5–10.6 µm were fabricated, and we evaluated their diffraction properties experimentally. The MIR and FIR LCPGs should open new application fields of LC technologies including polarimetry, spectroscopy, and beam steering.
... At their core, optical gratings consist of a periodic structure that modulates the refractive index of a material on a scale that is comparable to the wavelength of the light being diffracted. This modulation produces diffraction patterns that can be used for spectral analysis [7,8], beam steering [9], optical sensing [10], and many other functions [11]. Meta-gratings achieve control over light by precisely arranging and designing micro-and nanostructures on a planar surface. ...
In this paper, unlike many researches that focus on beam splitters based on gratings with symmetrical structures, an asymmetric grating with double-groove structure is proposed. Based on the double-groove grating, multi-port beam splitters including dual-port, three-port, and four-port, under normal incidence working at terahertz frequency are designed for both transverse-electric and transverse-magnetic polarizations. Rigorous couple-wave analysis and simulated annealing algorithm are employed to get the optimal parameters of the grating and accelerate the computing process. For the purpose of understanding the phenomenon of the beam incident, the finite element method is also applied to get the simulation result. It is proven that the proposed beam splitters all present great efficiency and uniformity on the energy distribution. High manufacturing tolerance of the beam splitters is also analyzed, which allows for greater flexibility in the fabrication process. Compared with beam splitters based on single-groove grating, multi-port beam splitters based on double grooves show great performance and universality.
Graphical abstract
... However, the aperture is important in optical devices [4] which defines the capability to collect light and is crucial in terms of various performance parameters such as the imaging quality, the angular resolution, the transmitting power, etc. al. The pressing need for optical systems with significantly reduced weight, size and driving power requirements promotes the development of next-generation optics [3,[5][6][7]. In such background, the development and application of the planar optical technologies, such as the diffractive optics and metamaterial optics, are being intensively investigated [8][9][10][11]. ...
The liquid crystal (LC) geometrical phase optics, which is realized by the high-resolution control of the optical axis orientation in transparent micrometer-thin polymer films, is emerging as a next generation of planar optics. It features pronounced optical properties and stimuli-responsive behaviors, which could introduce appealing and new possibilities for photonic purposes. The development of fabrication techniques producing elements with large aperture sizes and arbitrarily varying molecular orientation is of significance in terms of practical utility. Here, we propose the pulsed polarization patterning technique to create large-aperture and defect-free LC geometrical phase elements. We investigated the capability of the azo photo-alignment material responding to nanosecond laser pulses and the corresponding anchoring behaviors to LCs. The threshold was reduced to one fourth of that under the continuous wave recording. The patterning resolution was found to be enhanced to around 0.71 µm, due to the ultra-fast interaction nature of the photo-alignment material with the polarized light field. We proposed the flying exposure mode to deliver high frequency modulated polarized laser pulses (8 kHz), with the precision stage moving in a uniform velocity for light-field stitching and the servo auto-focusing in the sample normal, enabling the stable and reliable polarization patterning for large aperture sizes. We further report on representative fabrication of LC polarization gratings with an aperture of 4 inch and 99.2% average diffraction efficiency.
... Traditional mechanical beam steering method suffers from the drawbacks of large volume, high power consumption, limited pointing accuracy, etc. Over the past years, scholars from various countries have been exploring non-mechanical beam steering (NMBS) technology and have made much progress, such as acousto-optic deflectors [5,6], electro-wetting electrodes [7], liquid crystal optical phased arrays (LCOPAs) [8,9], and liquid crystal polarization gratings (LCPGs) [10,11]. Currently, achieving fast, large field-of-view and high-precision beam steering remains the core technical challenge faced by NMBS technology. ...
This paper proposes an extended prism coupling analysis method to accurately analyze the coupling structure of liquid crystal (LC) cladding waveguide beam steerer. We analyze the effects of LC anisotropy on the coupling of transverse electric (TE) and transverse magnetic (TM) modes and derive the expression of the optical field distribution that perfectly matches the given coupling structure. Based on this method, we present the optimal coupling structure for Gaussian beam. Taking into account the practical manufacturing process, we propose a simplified coupling structure and perform a detailed analysis of its performance based on numerical simulations. Experimental results show a coupling efficiency of 91% and a coupling angle full width at half maximum (FWHM) of about ±0.02°, demonstrating the effectiveness of the proposed method in predicting the coupling performance of anisotropic cladding waveguides.
... An illustration of the beam-steering concept and configuration is shown in Fig. 1. In this work, we demonstrate optical beam-steering of an LC laser both in the horizontal and vertical directions, but in principle, additional discrete positions can be obtained by adding extra tuneable phase shifters and PGs, in accordance with the work of Jihwan Kim et al [16,19,27]. The steering of the beam takes place with minimal impact on the intensity of the laser beam because there is no change to the helical structure of the chiral nematic LC. ...
... Besides the primary beam, which is diffracted to different spatial locations, other minor spots are observed, which are significantly lower in intensity compared with the main beam. These additional spots, which also have been observed by other researchers [19,27], can be divided into three categories: zero-order, sub-order, and opposite-order spots. The zero-order spots are non-diffracted spots (with zero diffraction angle) that appear at the zero position in the x and y-coordinates defined in this work. ...
... The primary beam has a relative intensity of 0.91 while that of the zero-order spot at (0, +1) is 0.02 which is the highest of all the spots excluding the primary beam. This result is similar to that found in another study that employed a ray-tracing tool to simulate twodimensional beam-steering achieved by a 1550 nm laser and corresponding PGs [27]. The main spot had a relative power of 87% of the total power and any of the highest intensity single side spots were still lower than 1.5% of the total power (these side spots were claimed to be caused mainly by the zero-order leakage of the PGs). ...
In this paper, we demonstrate dynamic optical beam-steering of a band-edge chiral nematic liquid crystal (LC) laser that does not involve any change in the configuration of the helical structure. This beam-steering is achieved by exploiting the circular polarisation of the LC laser in combination with tuneable nematic LC phase shifters and fixed polarisation gratings. Experimental results are presented, showing the optical steering of the LC laser emission to four separate discrete spatial positions and, using simulations based on Jones calculus, we explain the appearance and relative intensities of other minor spots that appear around the primary beam. Compared with other approaches of beam-steering an LC laser, this method does not result in an alteration of the laser wavelength, does not change the internal cavity structure of the laser, and has a minimal impact on the intensity of the laser emission. In addition, the whole system (except for the solid-state pump source) is comprised of thin films that are either liquid crystalline or polymers, which provides a tangible route towards a more compact and integrated optically steerable LC laser.
... In the process of research on LCPGs [15], a large-angle non-mechanical beam deflection system based on polymer LCPGs is designed to achieve coarse deflection control at 1064 nm with a transmission rate of 66%-70%. In [16], a super binary coarse deflection design method based on polymer LCPGs is proposed, demonstrating that the transmission rate can be improved by optimizing the substrate and electrode materials. In [17], a polarized laser beam steering system based on multi-stage rotating PGs is proposed, and the beam steering performance of two and four rotating grating schemes is analyzed theoretically, concluding that the grating can provide a faster rotation than the prism. ...
... (2) Choose the smaller set of solutions in Eq. (16) and Eq. (17) as the amount of angular change to be rotated between LCPG 1 and LCPG 2. ...
In this paper, the relationship between miss distance, target position, and rotation angle of dual liquid crystal polarization gratings (LCPGs) is proposed for the first time, a target tracking system based on the rotating dual LCPGs is established, and a closed-loop target tracking process based on the formula is described. We establish the optical structure of the dual LCPGs, and the simulation compares the difference between the altitude and azimuth angles of the target position from the formula and the ZEMAX simulation. In the simulation validation, we also compare and analyze the proposed formula with the formula for vertical incidence to illustrate the necessity to introduce miss distance. We assemble a target coarse tracking device and perform the tracking experiment using the proposed formula to test the coarse tracking accuracy of the system. The coarse tracking accuracy and the angle information we obtained from simulation and experiment meet our proposed technical specification of no more than 0.45mrad, showing that the proposed formula provides a good basis for stable target coarse tracking and is instructive for engineering applications.
... Polarization gratings (PGs) [1][2][3][4][5][6][7][8][9][10][11][12][13][14] have attractive features such as theoretical diffraction efficiency of up to 100%, incident polarized light selectivity, orthogonality of the polarization states of ±1st-order diffracted light, and offering nonbulky setup. Therefore, PGs are applied to a wide range of applications, including polarization imaging [15,16], beam steering [17][18][19], and aerial displays [20][21][22]. PGs are formed by periodically distributing an anisotropic medium and realize polarization diffraction based on the geometric-phase (Pancharatnam-Berry phase) [23][24][25] generated by the relationship between the incident polarized light and the anisotropic medium. ...
A theoretical framework for determining biaxial anisotropy suitable for reducing the incident angle dependence of a polarization grating is proposed. The principal refractive indices are uniquely given by quantifying the biaxial anisotropy through the $Nz$ N z coefficient. The numerical analysis based on the finite-difference time-domain method reveals that the incident angle dependences of the diffraction efficiency and the polarization ellipticity of the diffracted light are significantly reduced when $Nz = {0.5}$ N z = 0.5 . This result is expected to contribute to the design of polarization diffractive optical elements and the development of anisotropic materials and structures.
... Both mechanical and non-mechanical beam controls have been developed [3][4][5][6][7]. Non-mechanical beam steering promises substantial benefits, and can be fulfilled by several approaches, including electrowetting [8,9], microlens arrays [10], polarization gratings [11,12], and optical phased arrays (OPA) [1,2]. Among them, OPA can offer quasi-continuous deflection angles with high efficiency, but the steering range is relatively narrow, depending on the electrode width. ...
... However, the polymeric PB lens can be tailored to operate at nearly any wavelength, from visible to SWIR. To extend the operation wavelength to mid-wave IR, a thicker cell gap is required to satisfy the half-wavelength phase condition [11]. In the following, we will simulate the performance of BAE at 905 nm and 1550 nm. ...
A novel beam steering angle expander is demonstrated by cascading two polymeric liquid crystal polarization lenses with different diopters. The lens module performs as a planar telescope, which has features such as a light weight, low cost, and high precision. The magnifier offers wide-angle, continuous steering when integrated with an active fine-angle beam steering device. The potential application for LiDAR is emphasized.
... A sub-system consisting of a single LCPG and a wave plate can only produce three beam steering angles, Therefore, to achieve multi-angle and large-angle beam scanning, multiple sub-systems must be combined to construct a cascaded system [8]. Two cascade technologies are used in this beam steering system: the binary [9] cascade and the ternary cascade [10]. Both technologies use multiple sub-systems stacking, but differ in the geometric progressions of the cascaded LCPGs angles. ...
... Moreover, oblique incidence changes the polarization state of the beam incident on the subsequent LCPGs, and a change in the polarization state will further reduce the system's diffraction efficiency. The LCPG diffraction efficiency is approximately 100% only when the beam is at normal incidence and is circularly polarized [13], In addition, the LCPG's working voltage is the same at all steering angles in non-mechanical beam steering systems [9,10]. However, oblique beam incidence causes the working voltage of the system to differ depending on the steering angle. ...
The non-mechanical beam steering system is composed of multiple liquid crystal polarization gratings (LCPGs) cascaded by binary or ternary technologies. However, cascading multiple LCPGs cause the beam from one LCPG to obliquely enter the subsequent LCPGs, changing their diffraction efficiency and working voltage at different steering angles. This paper uses the elastic continuum theory of liquid crystals to simulate the tilt angle of liquid crystal molecules under different voltages. The transmission process of the beam in the system at oblique incidence is described with an extended Jones matrix, and the highest diffraction efficiency and working voltage of each LCPG at different steering angles are calculated using vector diffraction theory. It is convenient to calibrate the LCPGs’ working voltage and analyze the system’s diffraction characteristics. In addition, we used an improved binary cascade technology to design a LCPG non-mechanical beam steering system with a steering angle of ±10° and an angular resolution of 0.67°. Compared with binary cascade, this technology can effectively reduce the number of cascaded devices and increase the system throughput under the same maximum beam steering angle and angular resolution.
... In the output coupler case shown in Fig. 11(b) and 11(d), however, the unintended diffractions, i.e. green rays in Fig. 11(b) and magenta rays in Fig. 11(d), are toward the eye with ±9.14˚ from the normal direction, creating the ghost image next to the intended one. Figure 12 shows the diffraction efficiency of the HOEs in the output coupler HOE stack which is calculated by the coupled wave theory (CWT) [21]. In the calculation, the following parameters are used; the refractive index of waveguide = 1.504, relative permeability of the HOE = 1, thickness of the HOE = 16um, mean refractive index of the HOE = 1.504, refractive index modulation of the HOE = ± 0.015, and the wavelength of the input image = 532nm. ...
... (a) HOE for the RHCP 60°incident beam, (b) HOE for the LHCP 45°incident beam experiment, the leakage was measured to be 0.10% and 0.27% in RHCP and LHCP respectively when the beam is normally incident on the PG. The measured value is not large, but it has also been reported that the leakage increases with the tilted incident beam [21]. Therefore the PG high order diffraction is a factor that needs to be considered in the analysis of the ghost images. ...
Waveguide-type near-eye displays have useful properties such as compact form factor, lightweight and see-through capability. Conventional systems, however, support only a single image plane fixed at a certain distance, which may induce eye fatigue due to the vergence-accommodation conflict. In this paper, we propose a waveguide-type near-eye display with two image planes using a polarization grating. Two images with orthogonal polarizations propagate within the waveguide with different total internal reflection angles and form virtual images at different distances. The use of the polarization grating and two pairs of holographic optical elements enables dual image plane formation by a single waveguide with high transparency for the real scene. Optical experiments confirm the principle of the proposed optical system.
