Design of a large field-of-view see-through near to eye display with two geometrical waveguides

Augmented reality display with high eyebox uniformity over the full field of view based on a random mask grating

Ensuring uniform illuminance in waveguide-based augmented reality (AR) display devices is crucial for providing an immersive and comfortable visual experience. However, there is a lack of a straightforward and efficient design method available to achieve illuminance uniformity over the full field of view. To address this issue, we propose a novel design that utilizes random mask gratings (RMGs) as the folding grating and the out-coupling grating. Unlike traditional approaches that modify the grating structure, we control the diffraction efficiency distribution by adjusting the filling factor of the mask while keeping the grating structure unchanged in one RMG. The grating structures are designed and optimized based on rigorous coupled wave analysis and particle swarm optimization. The feasibility of our method is verified by the simulation results in Lighttools. In the FOV range of 20°×15°, the eyebox uniformities of all fields are greater than 0.78, which can provide a good visual experience for users.

Compact pupil-expansion AR-HUD based on surface-relief grating

Augmented reality head-up display (AR-HUD) using diffractive waveguide is a challenging research field. It can drastically reduce the system volume compared with AR-HUD based on freeform mirror. However, one of the remaining challenges that affects the performance of the diffractive waveguide is to expand the eye-box while maintaining the illuminance uniformity. In this paper, a one-dimensional pupil expansion diffractive optical waveguide system for AR-HUD is presented. The optimization of grating parameters is based on scalar diffraction theory and rigorous coupled wave analysis (RCWA). Then, the illuminance uniformity is optimized through non-sequential ray tracing. We simulate and construct a waveguide-based AR-HUD. The presented AR-HUD realized an exit pupil size of 80 mm × 15 mm and a field of view of 10° × 5° at the wavelength of 532 nm.

Hybrid waveguide based augmented reality display system with extra large field of view and 2D exit pupil expansion

For a waveguide display device, the field of view (FOV) is a key parameter for evaluating its optical performance. To address this issue, we propose a hybrid waveguide system, which is composed of two projectors, two in-couplers, two half-mirror arrays and an out-coupler. We use two projectors to generate the left and right parts of the output image separately, which can increase the upper limit of the FOV significantly. Unlike conventional waveguide-based system, we use half-mirror arrays instead of folding gratings to realize 2D exit pupil expansion. By doing so, the total internal reflection condition can always be met during the pupil expansion process. To solve the difficulty in designing collimating optical system with large FOV, we propose a method of tilting the projection system. The hybrid waveguide system can realize a FOV of 88°(H) × 53°(V).

Design and fabrication method of holographic waveguide near-eye display with 2D eye box expansion

Augmented reality near-eye display (AR-NED) technology has attracted enormous interests for its widespread potential applications. In this paper, two-dimensional (2D) holographic waveguide integrated simulation design and analysis, holographic optical elements (HOEs) exposure fabrication, prototype performance evaluation and imaging analysis are completed. In the system design, a 2D holographic waveguide AR-NED integrated with a miniature projection optical system is presented to achieve a larger 2D eye box expansion (EBE). A design method for controlling the luminance uniformity of 2D-EPE holographic waveguide by dividing the two thicknesses of HOEs is proposed, which is easy to fabricate. The optical principle and design method of the HOE-based 2D-EBE holographic waveguide are described in detail. In the system fabrication, laser exposure fabrication method of eliminating stray light for HOEs is proposed, and a prototype system is fabricated and demonstrated. The properties of the fabricated HOEs and the prototype are analyzed in detail. The experimental results verified that the 2D-EBE holographic waveguide has a diagonal field of view (FOV) of 45°, an ultra-thin thickness of 1 mm, and an eye box of 16 mm × 13 mm at an eye relief (ERF) of 18 mm, the MTF values of different FOVs at different 2D-EPE positions can be better than 0.2 at 20 lp/mm, and the whole luminance uniformity is 58%.

Design, analysis and optimization of a waveguide-type near-eye display using a pin-mirror array and a concaved reflector

Waveguides have become one of the most promising optical combiners for see-through near-eye displays due to the thickness, weight, and transmittance. In this study, we propose a waveguide-type near-eye display using a pin-mirror array and a concaved reflector with a compact outlook, optimized image uniformity and stray light. Issues have been discussed in detail, which include field of view (FOV), eye-box, resolution, depth of field (DOF), display uniformity and stray light artifacts. It can be shown that the DOF can be extended (when compared with traditional waveguide-type near-eye displays) to alleviate the vergence-accommodation conflict (VAC) problem, and the uniformity & stray light can be improved with an optimal structure. Moreover, reflective surfaces have been introduced as the input and output coupling with a compact outlook, an easy-processing structure and the achromatic performance. A prototype based on the proposed method have been successfully developed, and virtual images with an extended DOF can be shown along with the real-world.

Uniformity improvement of two-dimensional surface relief grating waveguide display using particle swarm optimization

Augmented reality head-mounted displays (AR-HMDs) based on diffractive waveguides have been a challenging and rewarding research topic focusing on near-eye displays. The size of the exit pupil and uniformity of the image illuminance are two important factors that affect the display performance of the diffractive waveguide. In this paper, a novel method for optimizing high uniformity of two-dimensional (2D) diffractive waveguide is proposed. A straight-line 2D surface relief grating (SRG) waveguide with divided grating regions is designed. An illuminance uniformity evaluation model of the energy propagation process is established, and non-sequential ray tracing is utilized to optimize the diffraction efficiency of multi-regions grating to achieve illuminance uniformity distribution. Then, the uniformity distribution of the diffraction efficiency in different fields of view (FOVs) is realized by combining the particle swarm optimization (PSO) algorithm and rigorous couple wave analysis (RCWA) to optimize the grating structural parameters, which further ensures the uniformity of the exit pupil illuminance and angular illuminance. The waveguide with exit pupil expansion (EPE) has exit pupil size of 16 mm × 14 mm at an eye relief (ERF) of 20 mm, exit pupil illuminance uniformity of 91%, and angular uniformity illuminance of 64%.

Design method of a wide-angle AR display with a single-layer two-dimensional pupil expansion geometrical waveguide

Waveguide near-eye displays (NEDs) consist of a planar waveguide combiner and a coupling-in projection system. A two-dimensional geometrical waveguide (TDGW) can achieve an ultra-thin, large exit pupil diameter (XPD), wide-angle NED. The design method of a single-layer TDGW is presented and discussed in detail in this paper. A high-precision processing technology that can effectively guarantee the parallelism accuracy is also presented. A miniature coupling-in projection optics is designed with a catadioptric structure and integrated with the waveguide accordingly. Finally, a TDGW with a thickness of 1.75 mm is designed and analyzed. The results show that the stray light over the normal light is less than 0.5%, and the illuminance uniformity is well optimized. The field of view is up to 55°, and the XPD exceeds 12mm×10mm at an eye relief (ERF) of 18 mm. A proof-of-concept prototype was fabricated and demonstrated.

Off-axis reflective imaging system design with a conicoid-based freeform surface

In this paper, we propose an off-axis reflective system design method based on a non-rotational symmetric conicoid-based freeform (CBF) surface description. The base description avoids complicated calculation of decenter and tilt when using the conventional conic expression, thus simplify the system modeling and optimization process, and it can reduce the number of coefficients that needed to represent mild freeform surfaces. A design method that includes the automatic initial system searching, preliminary optimization with rotationally symmetric surface deviation and fine-tuning with non-symmetric surface deviation is proposed. Two three-mirror systems have been designed to demonstrate the feasibility and conveniences of the proposed method.

Projection optical engine design based on tri-color LEDs and digital light processing technology

Digital light processing (DLP) is currently a cutting-edge technology for desktop projection optical engines. Due to the passive luminescence characteristics, the DLP projection engine needs a few specific illumination optical components for light collimation, homogenization, and color combination, together with a projection lens matching the DLP chip and magnifying the image. In this paper, we propose a design approach that first splits the DLP projection optical engine into individual components for separate design, and then integrates them into a whole system for further verification. For the first step, the collimating lens group is designed for light collection, and the dichroic mirrors are used to fold the light path based on tri-color LED light sources. For the second step, a fly-eye lens and the corresponding relay lens group are designed to achieve uniform illumination on the DMD chip. The third step is to optimize the projection lens group for high-resolution projection display. Based on the design and simulation, the optical efficiency is 63.4% and the uniformity reaches 94.9% on the projection screen. The modulation transfer function (MTF) of the projection lens is higher than 0.4 at 66 lines for the distance of 500∼1500mm, and the distortion is lower than 1%. Simulation results show that the total luminous flux is estimated to reach 224.15 lm when the powers of tri-color LEDs are 21 W, 15.5 W, and 25 W, respectively. A projector prototype is built and tested for further verification, which provides a luminous flux of 220.43 lm and uniformity of 90.22%, respectively. The proposed design, demonstrated by both simulation and experiment, exhibits high feasibility and application potential in state-of-the-art commercial projector design.

High-performance reflection-type augmented reality 3D display using a reflective polarizer

We propose a high-performance reflection-type augmented reality (AR) 3D display by using a reflective polarizer (RP). The RP functions as a reflective imaging device as well as an image combiner that combines the real scenes and the 3D images reconstructed by the integral imaging display unit. Benefiting from the flawless imaging of the RP, the proposed reflection-type AR system can achieve high-definition 3D display. A prototype based on the proposed reflection-type AR structure is developed, and it presents good 3D display effects and reflection-type AR performances. The developed prototype is very compact, as thin as 3.4 mm, which makes it be a potential candidate in stomatology and vehicle AR display.

Design of achromatic augmented reality visors based on composite metasurfaces

A compact near-eye visor (NEV) system that can guide light from a display to the eye could transform augmented reality (AR) technology. Unfortunately, existing implementations of such an NEV either suffer from small field of view or chromatic aberrations. See-through quality and bulkiness further make the overall performance of the visors unsuitable for a seamless user experience. Metasurfaces are an emerging class of nanophotonic elements that can dramatically reduce the size of optical elements while enhancing functionality. In this paper, we present a design of composite metasurfaces for an ultracompact NEV. We simulate the performance of a proof-of-principle visor corrected for chromatic aberrations while providing a large display field of view (>77^∘ both horizontally and vertically) and good see-through quality [>70% transmission and less than a wavelength root mean-square (RMS) wavefront error over the whole visible wavelength range] as needed for an immersive AR experience.

Full-color see-through near-eye holographic display with 80° field of view and an expanded eye-box

A full-color see-through near-eye holographic display is proposed with 80° field of view (FOV) and an expanded eye-box. The system is based on a holographic optical element (HOE) to achieve a large FOV while the image light is focused at the entrance to human pupil and the image of entire field enters human eye. As we know, one of the major limitations of the large FOV holographic display system is the small eye-box that needs to be expanded. We design a double layer diffraction structure for HOE to realize eye-box expansion. The HOE consists of two non-uniform volume holographic gratings and a transparent substrate. Two fabricated holographic gratings are attached to front and back surfaces of the substrate to multiplex image light and achieve eye-box expansion. Simultaneously, the HOE is also manufactured for RGB colors to realize full-color display. The experiment results show that our proposed display system develops 80° round FOV and an enlarged eye-box of 7.5 mm (H) ×5 mm (V) at the same time. The dynamic display ability is also tested in the experiments. The proposed system provides a new solution for the practical application of augmented reality display.

Extended-viewing-angle waveguide near-eye display with a polarization-dependent steering combiner

A waveguide-based near-eye display (WNED) with an extended viewing angle using a polarization-dependent steering combiner (PDSC) is proposed. The novel eyepiece-combiner is composed of polarization gratings and polarization optics attached to the outcoupler part of the waveguide, which can control the output beam path depending on the polarization state. The viewing angle limited by the grating properties can be extended up to twice. Also, an ultrathinness of about 1.4 mm is suitable for the WNED. The demonstrated prototype system achieves a horizontal field of view of 33.2°, which is 2 times wider than the conventional structure (without the PDSC). The proposed configuration can resolve the viewing angle issue for the WNED.

Design of foveated contact lens display for augmented reality

We present a design of a contact lens display, which features an array of collimated light-emitting diodes and a contact lens, for the augmented reality. By building the infrastructure directly on top of the eye, eye is allowed to move or rotate freely without the need of exit pupil expansion nor eye tracking. The resolution of light-emitting diodes is foveated to match with the density of cones on the retina. In this manner, the total number of pixels as well as the latency of image processing can be significantly reduced. Based on the simulation, the device performance is quantitatively analyzed. For the real image, modulation transfer functions is 0.669757 at 30 cycle/degree, contrast ratio is 5, and distortion is 10%. For the virtual image, the field of view is 82°, best angular resolution is 0.38', modulation transfer function is above 0.999999 at 30 cycle/degree, contrast ratio is 4988, and distortion is 6%.

Design of lensless retinal scanning display with diffractive optical element

We propose a design of a retinal-scanning-based near-eye display for augmented reality. Our solution is highlighted by a laser scanning projector, a diffractive optical element, and a moist eye with gradient refractive indices. The working principles related to each component are comprehensively studied. Its key performance is summarized as follows. The field of view is 122°, angular resolution is 8.09', diffraction efficiency is 57.6%, transmittance is 80.6%, uniformity is 0.91, luminance is 323 cd/m², modulation transfer functions are above 0.99999 at 3.71 cycle/degree, contrast ratio is 4878, and distortion is less than 24%.

Methods of optimizing and evaluating geometrical lightguides with microstructure mirrors for augmented reality displays

Waveguide or lightguide technology has been widely used in the state-of-the-art, see-through, near-eye displays to reduce system weight and form factor. Although a few of the current products use a geometrical lightguide as an optical combiner, its design and performance assessment methods have been barely discussed. In this paper, by taking into account the factors affecting retinal image quality, we presented novel methods for quantifying and evaluating the optical performances and artifacts of geometrical lightguides based on microstructure mirror arrays, and proposed new merit functions and a novel process for systematic optimization of such lightguides. A lightguide design example implementing the evaluation and optimization methods are demonstrated, and the resulted lightguide is then further utilized as a combiner for the design of a lightweight, glasses-like, see-through, near-eye display.

On-axis near-eye display system based on directional scattering holographic waveguide and curved goggle

The contradiction between the field of view (FOV), luminance uniformity (LU) and weight has always restricted the development of augmented reality display systems. An on-axis near-eye display (NED) system based on directional scattering holographic waveguide (DSHW) and curved goggle is proposed in order to realize a large FOV with high LU, light weight, and conformal design capability. The DSHW which consists of a linear volume holographic grating and holographic diffuser is used to deliver the virtual image and construct a transparent directional emission display screen with high LU. The curved goggle is used to project the image on the display screen into human eye and form a large FOV, with a suitable exit pupil diameter (EPD) and eye relief distance (ERF) and while keeping the external scene visible. Our proposed NED achieved an FOV of 44° horizontal (H) × 12° vertical (V) easily, which is almost consistent with the theoretical design. The EPD is 6 mm, ERF is 18.6 mm, and LU is about 88.09% at full viewing angle. The system is lightweight and flexible, which can be further applied in the next-generation, integrated protection-display helmet system through conformal optical design.

Flat metaform near-eye visor

A near-eye visor is one of the most vital components in a head-mounted display. Currently, freeform optics and waveguides are used to design near-eye visors, but these structures are complex and their field of view is limited when the visor is placed near the eye. In this paper, we propose a flat, freeform near-eye visor that uses a subwavelength patterned metasurface reflector. The visor design imparts a spatial phase profile on a projected display pattern and can be implemented using a micron-scale-thick metasurface. As the resulting metaform visor relies on diffraction, it can preserve a large field of view (77.3° both horizontally and vertically) when placed only 2.5 cm away from the eye. We simulate the metasurface visor to estimate the modulation transfer function, and find that the projected image quality is sufficiently high for human vision. While the design of the metasurface is initially performed via ray optics, using full-wave finite-difference time-domain simulation we validate a scaled version of our visor design.

Alternate optical designs for head-mounted displays with a wide field of view

The most widely applied design form for mixed reality head-mounted display (HMD) systems is generally a prism with one surface in total internal reflection (TIR). This, however, limits the angle of the incident rays, and thus decreases the design freedom and affects the performance. To obtain better performance of the HMD optics, in this paper two seldom used design forms of HMD systems are presented and compared to the standard TIR HMD optics. One of them is a catadioptric HMD system, consisting of one lens and two mirrors; the other is a prism HMD with a different folding geometry. The designs are compared for a field of view of 40°×30°; however, they are also investigated for an increased field of view of 50°×30°. The evaluation indicates good performance of our systems. In particular, the prism with an alternate folding geometry has advantages in both performance and size.