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Image quality. (a) Resolution test board (1951 USAF) and (b) synthetic vision of virtual message and real-world scene.
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It is difficult to design and fabricate a head-up display (HUD) with a large asymmetric field of view (FOV) while maintaining a good image quality. In this paper, we design and develop such a holographic HUD system. To improve luminance and enhance the environmental adaptability of the HUD, we use a liquid crystal display with high brightness as we...
Citations
... In aircraft applications, HUDs improve the interface between pilots and control systems, enhancing decision-making at high speeds. Recent research delves into HUD technology advancements, including broader field of view and enhanced performance HUDs are now applied in automobiles, virtual reality, and commercial aircraft cockpits [2]. Refractive HUDs employ a specialized transparent element to bend light, projecting information onto a combiner glass that appears integrated into the user's field of view [3]. ...
... The efficacy of refractive-type HUDs hinges on factors such as brightness, resolution, and source size. High brightness is crucial for dynamic adjustment based on ambient light conditions [2]. In this condition ambient contrast ratio should obey the relation given in Eq. 1. ...
... 'T' is the transmittance of augmented reality display. The contrast ratio between ambient and displayed luminance is essential for optimal visibility [2]. Cathode-ray Tube (CRT), P-53 source commonly used in refractive HUDs, possesses a minimum brightness of 10,000 cd/m 2 and a contrast ratio of 1.2:1 [1][2][3]. ...
The optimization of weight and volume of each component of aircraft, including mechanical, electronics and optical systems is crucial aspect. The cockpit of aircraft is loaded with different opto-mechanical, opto-electronics payloads such as head-up display (HUD), Head-Down Display (HDD) Multi-Function Display (MFD) etc. to assist the pilot. HUD is a critical payload of an aircraft which is designed using augmented reality and is being used since 4 decades. This HUDs realised with bulky optical systems having monochromatic cathode ray tubes (CRTs) of 543 nm wave length P-1, P-43, P-53 phosphors with a contrast ratio of 1.2:1 display source. CRT needs high power and specialized electronics to trace the synthetic display on CRT screen to the pilot. All this results in a lot of challenges w.r.t. weight, volume, and electromagnetic interference (EMI)/electromagnetic compatibility (EMC) management. Upgrading the display source by replacing of CRT with a compact Digital Micro-Mirror Device (DMD) is a potential solution for these challenges. However, maintaining the existing opto-mechanical parameter of the system is a challenging task. This paper proposed a design solution for optical components for compact and lightweight HUD. A non-imaging optics is designed for LED source with 543 nm wavelength to give uniform distribution of light, and imaging optics is designed for DMD of resolution of 750 × 750 pixels, pixel size 10 um with aspect ratio 1:1, of 543 nm wavelength projects an image of same size of CRT screen, with Modulation Transform Function (MTF) 0.6 at 5ln/mm, distortion around 5%. A prototype has been developed based on an optimized opto-mechanical design to fulfil the engineering requirements of the HUD.
... Another technical route is to directly project the image into the human eye through free space. This method can yields a large field angle and receive the image while ensuring uniformity and high efficiency [6]. The free space combiner is an off-axis system, including a free space catadioptric optical element [7], metasurface [8][9][10], holographic lenses (HLs) [11]. ...
Holographic optical elements (HOEs) play an important role in augmented reality (AR) systems. However, the fabrication of full-color HOEs is difficult and the diffraction efficiency is low. In this paper, we use the time-scheduled iterative exposure method to fabricate full-color HOEs with high diffraction efficiency. Through this method, a full-color HOE with an average diffraction efficiency of 73.4% was implemented in a single photopolymer, the highest rate yet reported. In addition, the AR system is simulated by the geometric optics method combining k-vector circle and ray tracing and structured by combining laser micro-drop and high diffraction efficiency HOEs. A good color blending effect was achieved in a full-color AR system by using the reconstruction wavelength consistent with the recording light. It can present clear holographic images in a full-color AR display system.
... 26 In a typical lens-HOE-based AR display system, the virtual image is first delivered by the relay optics onto the focal plane of the lens-HOE, which will collimate the relayed image and direct it into the eye [ Fig. 1(e)]. 27,28 The image source can be a microdisplay or a spatial light modulator (SLM) combined with a laser light source for 2D and 3D image generation, respectively. By employing a lens-array-HOE, 3D AR display can also be realized utilizing integral imaging techniques. ...
... Lots of research have been conducted to develop the AR-HUD system with wide FOV as well as multiple configurations with various pupils. Peng presented a HUD system based on an optical waveguide [23]. Due to the limited installation space, an off-axis optical system configuration is widely adopted to design HUDs with compact structures. ...
The freeform imaging system is playing a significant role in developing an optical system for the automotive heads-up display (HUD), which is a typical application of augmented reality (AR) technology. There exists a strong necessity to develop automated design algorithms for automotive HUDs due to its high complexity of multi-configuration caused by movable eyeballs as well as various drivers’ heights, correcting additional aberrations introduced by the windshield, variable structure constraints originated from automobile types, which, however, is lacking in current research community. In this paper, we propose an automated design method for the automotive AR-HUD optical systems with two freeform surfaces as well as an arbitrary type of windshield. With optical specifications of sagittal and tangential focal lengths, and required structure constraints, our given design method can generate initial structures with different optical structures with high image quality automatically for adjusting the mechanical constructions of different types of cars. And then the final system can be realized by our proposed iterative optimization algorithms with superior performances due to the extraordinary starting point. We first present the design of a common two-mirror HUD system with longitudinal and lateral structures with high optical performances. Moreover, several typical double mirror off-axis layouts for HUDs were analyzed from the aspects of imaging performances and volumes. The most suitable layout scheme for a future two-mirror HUD is selected. The optical performance of all the proposed AR-HUD designs for an eye-box of 130 mm × 50 mm and a field of view of 13° × 5° is superior, demonstrating the feasibility and superiority of the proposed design framework. The flexibility of the proposed work for generating different optical configurations can largely reduce the efforts for the HUD design of different automotive types.
... Holographic optical elements (HOEs) that offer high diffraction efficiency, high transmittance, and thinness, have been widely used in augmented reality (AR) near-eye displays (NEDs) and head-up displays (HUDs) [1][2][3]. The wavelength selectivity of a HOE enables the system to achieve high diffraction efficiency while maintaining high transmittance to ambient light. ...
We propose a multiplane augmented reality (AR) head-up display (HUD) with a real–virtual dual mode based on holographic optical elements (HOEs). The picture generation unit (PGU) is only a single free-focus projector, and the optical combiner includes a HOE lens (HOEL) for long-distance virtual image display and a HOE diffuser (HOED) for in-plane real image display. A HOED with directional scattering characteristics in the real image mode can significantly increase the size of the eyebox (EB) without increasing the size of the HOE, and a HOEL with a flexible design for the optical focal length in the virtual image mode can be used to achieve a different depth of the AR display. The proposed AR HUD system, which has a compact structure and offers high light transmittance, high energy usage, a multiplane display, and a large EB, is expected to be widely used in the future.
... Meanwhile, most natural light from the real-world passes through the HLs, since it deviates from the Bragg condition. By the virtue of such a selective functionality and thin structure, various applications of the HLs have been studied such as NEDs [4,5], head-up displays [6], and light field displays [7][8][9]. Particularly, the emerging interest for compact NEDs has created the increased need to adopt the HLs as image combiners of them. ...
... Alternatively, pupil replication techniques by using the multiplexing of the HLs [15,16] and an eye-box enlargement method by exploiting an additional diffusive holographic optical element (HOE) [17] were proposed. They successfully mitigated the active components for pupil-steering, but the former suffered from the discontinuity in permitted viewpoints during a transition of the eye, and the latter suffered from a contrast degradation due to the coarse diffusing properties of the diffusive HOE. ( Meanwhile, diverging signal waves (DSWs) allow the HLs to have an affordable sized eye-box to enable practical NEDs [6,18]. In contrast to the CSW-based HLs, unfortunately, light rays emitted from most pixels of an image source deviate from the Bragg condition of the HLs as depicted in Fig. 1(b). ...
... Since aberrations arising from the inherent off-Bragg diffraction tend to degrade the quality of virtual images, design parameters required in a recording and playback geometry should be carefully analyzed to overcome these artifacts. By optimizing the multiple lenses-based projection system, Peng et al. experimentally demonstrated a large eye-box system over tens of millimeters for the application of head-up displays [6]. However, the system was too bulky and complicated to be used in the NEDs, and the overall design process mainly focused on optimizing the relay lens system, not on characterizing the image quality of the HL itself. ...
We analyze an image quality of a holographic lens (HL) in order to implement compact near-eye displays using a flat-panel-type micro-display panel. The proposed method utilizes a non-converging signal wave in a fabrication process of the HL, so that it provides affordable eye-box size with minimizing the aberration due to rays in the off-Bragg condition. For analyzing and optimizing the HL based on the non-converging signal wave, we introduce a comprehensive analysis model for an assessment of the image quality in the HL. The analysis model, inspired from the conventional lens design strategy for near-eye displays, evaluates the focal spot quality for incident rays forming each pixel with considering the on- and off-Bragg diffraction. The theoretical analysis is validated by simulation results using a volume hologram model in Zemax OpticStudio. As experimental verifications, we realize a prototype system using photopolymer-based HLs in a green color with the high transmittance of 89.3%. The image quality of the HLs is analyzed, which coincides well with the proposed analysis and assessment metric. By building a compact experimental setup employing the HL and a micro-organic light emitting diode display, we present see-through images with 8.0 mm of eye-box with reduced aberrations.
... A perfect holographic display is capable of faithfully reproducing the corresponding depth cues from a physical object, an approach closer-suited to the human psycho-visual system than traditional displays [4,5,6]. Although the system-level challenges are considerable [7], significant advances have been made in this field the past few years, with a number of real-world systems delivering impressive results in both near-eye [8,9,10,11,12] and far-field display applications [13,14,15,16,17]. ...
... Efficient signal transmission through OFC requires some indispensable optical components like, Coupler, Multiplexer, Demultiplexer, etc. Conventional couplers, multiplexers, and demultiplexers are bulky, costly and require cumbersome processing for their fabrication. Concept of holographic optics can be utilized advantageously for fabrication of various optical elements for different purposes [1][2][3][4][5]38] such as wavelength multiplexerdemultiplexer [6][7][8][9][10], couplers [11][12][13][14][15][16][32][33][34], branching elements and avionics [17][18][19], Optical interconnects [20], Optical switches [21][22][23][24] etc. Holographically fabricated optical elements are low-cost, lightweight, and compact having thin-film geometry. HOEs work on the phenomenon of diffraction hence they are also known as diffractive optical elements. ...
The diffraction efficiency of a recorded Holographic optical element changes with change in wavelength of reconstruction wave even for on-Bragg angle reconstruction. Diffraction efficiency also falls with change in angle of reconstruction with respect to Bragg angle for reconstruction wave of a given wavelength. Therefore, to achieve appreciable diffraction efficiency operation of Holographic Optical Elements at different operating wavelengths, processing parameters namely film-thickness (d), depth of refractive index modulation (Δn), and fringe spacing (ᴧ) must be optimized accordingly. In present work thickness (d) of the film of the recording medium, depth of refractive index modulation (Δn), and fringe spacing (ᴧ) have been optimized for holographic optical elements to be recorded in dichromated gelatin medium to achieve maximum efficiency operation for three different optical transmission windows 800 -900 nm, 1250 – 1350 nm and 1500 – 1600 nm operating at wavelengths 850 nm, 1310 nm, and 1550 nm respectively. A pair of such designed holographic optical elements can advantageously be used for coupling laser light from one fiber end to another fiber end. It is further shown that a single coupler consisting of properly designed holographic optical elements may be used for optical transmission windows 1250 – 1350 nm and 1500 – 1600 nm operating at wavelengths 1310 nm, and 1550 nm respectively.
... Transparent displays are favored as next-generation display devices with the characteristics of rendering images on the panel, and the observers can see the scenery from both sides at the same time [1] . It is widely used in various scenes, such as smart windows, head-up displays, near-eye displays, and advertising [2][3][4][5][6] . Transparent displays have been developed in various ways. ...
... Alternatively, our proposed method does not involve any temporal multiplexing manners for enlarging the eye-box of the HOEL-based DPT displays. Previously reported DPT displays have induced optical aberrations which degrade the image quality [7,13,[15][16][17]. Particularly, such aberrations become severe, as the beam width for each pixel broadens for enlarging the eye-box. ...
We propose a projection-type see-through near-to-eye display by combining two holographic optical elements (HOEs), a holographic lens with the on-axis projection configuration and a holographic diffuser. The proposed method provides an enlarged eye-box by virtue of diffusing properties of an HOE diffuser (HOED) without any temporal multiplexing methods. In this paper, a thorough analysis on imaging characteristics of an HOE lens (HOEL) according to the projection configuration is provided, so that we optimize the recording geometry of the HOEL with the passively enlarged eye-box. The theoretical analysis is validated by simulation results using a volume hologram model in OpticStudio. As experimental verifications, we realize a prototype of the proposed method using the photopolymer-based HOEs in a single color. The fabricated HOEL and HOED show high transmittance of 84.9% and 62.2%, respectively. By using the fabricated HOED with a diffusing angle over 20 ° and an angular selectivity of 8.7 °, the prototype successfully provides see-through images with the eye-box larger than 5 mm in width.
