Exit Pupil Size Research Articles

Exit pupil uniformity improvement of holographic waveguide displays based on a genetic algorithm

Waveguide displays based on a volume holographic grating (VHG) have the benefit of expanding the exit pupil. Exit pupil size and exit pupil uniformity are two important indicators of waveguide displays. Most current optimizations for exit pupil uniformity are based on the central viewing angle. However, this does not ensure satisfied exit pupil uniformity for other viewing angles. In this paper, a method based on a genetic algorithm to optimize the exit pupil uniformity under the whole horizontal field of view (HFOV) is proposed. First, the ray-tracing-based mathematical model to analyze the uniformity of the whole HFOV at all wavelengths is established. Based on the mathematical model, the objective function can be defined, which can optimize the refractive index modulation distribution on several regions of the out-coupling VHG. The simulation results show that for a holographic waveguide display with the exit pupil size of 16mm×12mm, the average exit pupil uniformity can reach 86.87% at a diagonal field of view (DFOV) of 30°, a 9.16% improvement over the previous method. The genetic-algorithm-based method proposed in the paper can effectively improve the exit pupil uniformity.

Angular uniformity improvement of diffractive waveguide display based on region geometry optimization.

Augmented reality (AR) near-eye displays have significantly progressed due to advances in nanostructure fabrication. However, for diffractive waveguide AR displays requiring exit pupil expansion, the angular uniformity of each exit pupil position still needs to improve. In this paper, an angular uniformity improvement method based on region geometry optimization is proposed. This optimization method essentially introduces the interaction number of the light with the grating as one of the variables to manipulate the energy distribution. This distribution is obtained by the rigorous coupled wave analysis (RCWA) method and ray tracing process and is further optimized by a multi-objective genetic algorithm. A model is built, and the feasibility of the proposed method is verified. The diffractive waveguide system has a 10m m×10m m exit pupil size at the eye relief of 25mm and a field of view (FOV) of 21∘×12∘. After the optimization, the overall optical efficiency of the central field and the angular uniformity at the center exit pupil position increased from 0.9% and 66% to 3.1% and 80%, respectively.

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.

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%.

Freeform OST-HMD system with large exit pupil diameter and vision correction capability

Compactness and light weight, large exit pupil diameter and distance, small distortion for virtual image, and see-through light paths are pivotal factors to achieve a better, wearable experience of optical see-through head-mounted displays (OST-HMDs). In addition, light efficiency of the virtual image light path is an important factor for heat dissipation in HMD devices. This paper presents a new type of OST-HMD optical system that includes three wedge-shaped freeform prisms and two symmetric lenses. Based on a 0.71 in. microdisplay, an OST-HMD prototype with a diagonal field of view (FOV) of 45.3°, an F-number (F/#) of 1.8, an exit pupil size of 12 mm × 8 mm , and an eye relief of 18 mm is demonstrated. The maximum value of distortion of the final system is 0.6% and 0.4% for virtual image and see-through light path, respectively. The overall dimension of the optical system per eye is no larger than 30 mm ( width ) × 40 mm ( height ) × 14 mm (thickness), and the weight of the optical module including lenses, holder, and microdisplay is 12.8 g. The light efficiency of the virtual image light path is up to 50% higher than those of other OST-HMD optical solutions.

An Overview on the Use of a Low Magnification Telescope in Low Vision

A Galilean telescope in its simplest form is a two element system consisting of a positive lens as an objective and a nega­tive lens as an eyepiece. The system is restricted to lower magnifications and smaller fields of view in comparison with a Keplerian telescope. The image through the system, however, is always erect permitting its use for distance viewing for partially sighted patients. Other optical factors besides magnifica­tion and field of view that need to be con­sidered include exit pupil size, focus adjustability, vertex distance, and image quality in terms of color and brightness. Such non optical factors as weight, port­ability, ease of use, appearance and cost are also influencing variables'. In this overview on the clinical use of low power telescopes in the examination room, only a few properties will be exa­mined. The use of a low power full-field telescope in subjective and objective refractions will be discussed. Magnifica­tion through a telescope will also be elaborated upon.

Exit Pupil Expansion Based on Polarization Volume Grating

In this paper, we demonstrate a waveguide display structure which can realize a large field of view on a two-dimensional plane and a larger exit pupil size at the same time. This waveguide structure has three polarization volume gratings as its coupling elements. We use Zemax to simulate the effect of monochromatic and full-color two-dimensional exit pupil expansion and actually prepared a monochromatic waveguide with a two-dimensional exit pupil expansion structure. For the red, green, and blue light beams, it can achieve a large diffraction angle and can achieve diffraction efficiency of more than 70%. The waveguide structure shown can have an angle of view of 35° in the horizontal direction and 20° in the vertical direction, and an exit pupil of 18 mm long and 17 mm wide was achieved at the same time. As measured, the overall optical efficiency was measured as high as 118.3 cd/m2 per lumen with a transparency of 72% for ambient light.

Foveated near-eye display using computational holography

Holographic display is the only technology that can offer true 3D with all the required depth cues. Holographic head-worn displays (HWD) can provide continuous depth planes with the correct stereoscopic disparity for a comfortable 3D experience. Existing HWD approaches have small field-of-view (FOV) and small exit pupil size, which are limited by the spatial light modulator (SLM). Conventional holographic HWDs are limited to about 20° × 11° FOV using a 4 K SLM panel and have fixed FOV. We present a new optical architecture that can overcome those limitations and substantially extend the FOV supported by the SLM. Our architecture, which does not contain any moving parts, automatically follows the gaze of the viewer’s pupil. Moreover, it mimics human vision by providing varying resolution across the FOV resulting in better utilization of the available space-bandwidth product of the SLM. We propose a system that can provide 28° × 28° instantaneous FOV within an extended FOV (the field of view that is covered by steering the instantaneous FOV in space) of 60° × 40° using a 4 K SLM, effectively providing a total enhancement of > 3 × in instantaneous FOV area, > 10 × in extended FOV area and the space-bandwidth product. We demonstrated 20° × 20° instantaneous FOV and 40° × 20° extended FOV in the experiments.

Characteristic and optimization of the effective perspective images\u2019 segmentation and mosaicking (EPISM) based holographic stereogram: an optical transfer function approach

Based on our proposed method for holographic stereogram printing using effective perspective images’ segmentation and mosaicking (EPISM), we analyze the reconstructed wavefront errors, and establish the exit pupil function model of proposed printing system. To evaluate the imaging quality, the optical transfer function (OTF) of the holographic stereogram is modelled from the aspect of frequency response. The characteristic of the OTF with respect to the exit pupil size and the aberration are investigated in detail. We also consider the flipping effect in spatial domain. The optimization of hogel sizes, i.e., the sampling interval of original perspective images and the printing interval of synthetic effective perspective images, are given for the optimized reconstruction. Numerical simulations and optical experiments are implemented, and the results demonstrate the validity of our analysis, and the optimized parameters of hogel sizes can improve the imaging quality of full parallax holographic stereogram effectively.

Projection-type integral imaging system using a three-dimensional screen composed of a lens array and a retroreflector film.

We propose an improved projection-type integral imaging system using a three-dimensional (3D) screen consisting of a lens array and a retroreflector film in this paper. The projection-type integral imaging system suffers from the disadvantage of low-visibility images because of the inherently small exit pupil size of the projector. In order to resolve this problem, we adopt a 3D screen to avoid the demerits of a diffuser screen, such as off-screen image blur and loss of parallax. To determine the appropriate configuration of the 3D screen in the system, a simulation based on a ray transfer matrix analysis method was performed. The results show that the 3D screen should be located near the central depth plane of the integral imaging system, which leads to the conclusion that only the real mode is available for the proposed system. Experiments to verify this configuration and the feasibility of the proposed system were conducted using a system constructed with a real mode integral imaging system including a convex mirror array, which can fundamentally eliminate the pseudoscopic problem.

79-1:Invited Paper:Optical Measurements of Different Near-Eye Display Types

Different near-eye display technologies set special requirements for the optical measuring methods and measurement systems. Display device properties with the most influence are display field-of-view, size of exit pupil, and whether the display is monocular or binocular. Experimental measurements are reported for three different near-eye display types.

Review and analysis of avionic helmet-mounted displays

With the development of new concepts and principles over the past century, helmet-mounted displays (HMDs) have been widely applied. This paper presents a review of avionic HMDs and shows some areas of active and intensive research. This review is focused on the optical design aspects and is divided into three sections to explore new optical design methods, which include an off-axis design, design with freeform optical surface, and design with holographic optical waveguide technology. Building on the fundamentals of optical design and engineering, the principles section primarily expounds on the five optical system parameters, which include weight, field of view, modulation transfer function, exit pupil size, and eye relief. We summarized the previous design works using new components to achieve compact and lightweight HMDs. Moreover, the paper presents a partial summary of the more notable experimental, prototype, fielded, and future HMD fixed-wing and rotary-wing programs.

Investigation of viewing zone parameters for full color transmission type holographic screens

Viewing zone shape and size perform a key role in creating viewing comfort for the viewer. The horizontal and vertical sizes of viewing zones, formed by a full color transmission type holographic screen with a stereoscopic image projection are investigated. The screens have been recorded as holograms of a narrow stripe shaped object with different width; to extend the vertical size of the viewing zone the holograms were exposed two times with the hologram shifting between exposures. The viewing zone parameters were measured as a function of the stripe width of the object and of the exit pupil size of projection optics for several holographic screens having the size of the 30 <TEX>$\times$</TEX> 40 <TEX>$\textrm{cm}^2$</TEX>.

Double-pass measurements of the retinal-image quality with unequal entrance and exit pupil sizes and the reversibility of the eye's optical system.

We have used a modified double-pass apparatus with unequal entrance and exit pupil sizes to measure the optical transfer function in the human eye and have applied the technique to three different problems. First, we confirm that in the eye the double-pass spread function is the cross correlation of the input spread function with the output spread function [J. Opt. Soc. Am. A 12, 195 (1995)]. Consequently, when entrance and exit pupil sizes are equal, phase information is lost from the double-pass images. Second, we show that in double-pass measurements the eye behaves like a reversible optical system. That is, when entrance and exit pupils are equal, the double-pass image results from two passes through an optical system having a transfer function that is the same in both directions. To test for reversibility in the living eye we have used a double-pass apparatus with different exit and entrance pupil sizes (one of them small enough to consider the eye diffraction limited), so that the ingoing and the outgoing transfer functions are different. The measured image quality was unchanged when the pupils were interchanged, i.e., when the first-pass entrance pupil size becomes the second-pass exit pupil size, and vice versa. Third, the technique provides a means for inferring the complete optical transfer function of the eye, including the phase transfer function, and the shape of the point-spread function.

General analysis of two-mirror relay systems

The general two-mirror system used at finite conjugates is examined here. Relations for first-order geometric properties and third-order aberrations are given in terms of five design parameters: object distance, image distance, exit pupil size, and the two mirror magnifications. The conditions for aplanatic solutions are derived for conic mirrors. The curvatures of the astigmatic image surfaces are given, and the condition for anastigmatic solutions is derived. The relations are applied to infinite conjugate systems and spherical mirror systems as special cases.

Human Factors Considerations in the Design and Evaluation of a Helmet Mounted Display Using a Light Emitting Diode Matrix

The human factors considerations in the design and evaluation of a helmet mounted display (HMD) using a light emitting diode (LED) matrix are discussed. Specific issues including: helmet weight, bulk, image brightness/contrast, exit pupil size, reduction in visual field, and restriction of head movement were addressed and tradeoffs evaluated. The HMD was evaluated in flight as a device to provide energy maneuverability data to pilots. Preliminary findings are discussed.

Vision in Optical Instruments

IN his Thomas Young Oration of the Physical Society on December 6, Prof. Charles Fabry discussed “Vision in Optical Instruments”. Classical theory gives the resolving power of an optical instrument as determined by diffraction phenomena, but the result so obtained takes no account of the properties of the eye. Consequently, it does not indicate exactly what will actually be perceived with an instrument. What can actually be seen with such an instrument depends considerably on the brightness of the object examined, and on the degree of contrast between its parts and between the object and the background. In order to examine these questions, it is necessary to commence with the properties of the eye, and in particular, its ability to distinguish objects, not under the ideal conditions reached in the laboratory, but under conditions similar to those met with during observations. The effect of brightness is particularly large: for the greatest brightness the limit of resolution is about 1′, whilst it is 250 times as large (about 4 °) for barely perceptible brightness. Contrast also has a very large effect. With these data, it becomes possible to determine what the eye will really see in a given instrument, assumed to be of perfect geometrical construction. The optimum size of exit-pupil can be calculated, and is found to be 0-7 mm. for the highest illumination, in agreement with experience. For an instrument with geometrical imperfections, an efficiency can be defined characterising the qualities of this instrument as compared with those of a perfect instrument. Stray light (fog) is another cause of inferiority in instruments, and the effect of this factor was discussed by Prof. Fabry.