CN117250751A

CN117250751A - Maximum field angle exit pupil matching method of single-chip two-dimensional pupil expansion geometric waveguide

Info

Publication number: CN117250751A
Application number: CN202310853911.8A
Authority: CN
Inventors: 阮宁烨; 铁贵鹏; 石峰; 乔硕; 翟德德; 彭星
Original assignee: National University of Defense Technology
Current assignee: National University of Defense Technology
Priority date: 2023-07-12
Filing date: 2023-07-12
Publication date: 2023-12-19

Abstract

The application belongs to the technical field of waveguides, and relates to a maximum field angle exit pupil matching method of a monolithic two-dimensional pupil expansion geometric waveguide, which comprises the following steps: acquiring performance indexes of the monolithic two-dimensional pupil-expanding geometric waveguide, and constructing an optical waveguide structure; according to the optical waveguide structure, carrying out numerical calculation on an optical propagation path, and calculating an incident angle of light on the surface of the coupling-in prism, an included angle between the light inside the waveguide sheet and the surface of the coupling-in prism, an angle of view of the refracted light, an included angle between the projection of the light in a plane and a vertical axis and an included angle between the light and the plane, so as to obtain a propagation path of the incident light in the monolithic two-dimensional pupil-expanding geometric waveguide; and designing an offset angle for the coupling-in prism according to the propagation path, and carrying out exit pupil matching through numerical simulation to ensure that the exit pupil range covers the eye movement range and obtain the maximum field angle. By adopting the method and the device, the large exit pupil distance can be realized, and the exit pupil matching precision is ensured.

Description

Maximum field angle exit pupil matching method of single-chip two-dimensional pupil expansion geometric waveguide

Technical Field

The application relates to the technical field of waveguides, in particular to a maximum field angle exit pupil matching method of a monolithic two-dimensional mydriasis geometric waveguide.

Background

Augmented Reality (AR) technology is capable of superimposing a virtual screen generated by a computer with a real scene in real time, and of intuitively and efficiently displaying information. Therefore, since the first proposal in 1968, the augmented reality technology attracts a lot of attention, and is honored by a few institutions as a new generation of smart reality technology following a smart phone or a computer. In recent years, AR technology has rapidly developed and has been widely used in various fields of medical equipment, education, entertainment, and the like. Optical near-eye displays (NED) are key hardware for AR technology to achieve virtual-reality fusion. NED can complete the amplification, projection and display of the virtual image in front of human eyes under the condition of not blocking the real-world vision, and the fusion of the virtual image and the real-world scene is realized. To achieve better display effects, NED technology is evolving toward lighter, thinner, larger Field of view (FOV), wider Eye-movement range (Eye-box), and higher display quality. In recent years many companies have released their products such as microsoft HoloLens, lumus, magicLeap, waveoptics, lingxiAR. Related studies have proposed many ways to implement NED, such as prisms, freeform surfaces, birdbath, retinal projection, optical waveguides, super-structured lens displays, and the like. However, no fully satisfactory solution is currently available that can achieve both a large exit pupil range (Exit pupil diameter, EPD), a thin thickness and a large field angle.

Conventional optical display schemes, represented by freeform surfaces, prisms, are capable of achieving a large FOV, but typically have a thickness in excess of 10 mm. Cheng Dewen et al propose two compact, lightweight, freeform prism near-to-eye display methods with FOV up to 38 ° and 50 ° and excellent display picture quality, but prism thickness up to about 9.5 mm and 12 mm. The retinal projection display can achieve a large FOV and can overcome the effects of convergence conflicts, but requires the wearer to precisely aim the pupil at the convergence point of the Maxwell's observation, and thus it is intolerant of relative movement of the human eye when worn, with a very small eye movement range. The method of super-surface display proposed by Zhaoyi Li et al can realize a large FOV display using a light and thin super-surface, however, the color difference problem of super-surface display and the fabrication of super-structured lenses are limited to millimeter level, which limits the development thereof.

The waveguide is a technical scheme capable of realizing large FOV and compactness and thinness simultaneously. The light propagates along the waveguide in total reflection (TIR) inside the waveguide, so the waveguide is able to direct the light entering it to a specific direction. Optical waveguides can be divided into geometric waveguides [18-19] and diffractive waveguides according to the principles of input and output couplers. The diffraction waveguides are largely classified into surface relief grating waveguides Surface Relief Grating, SRG and volume hologram grating waveguides Volume Holographic Grating, VHG. The diffraction optical waveguide realizes the regulation and control of the light beam by utilizing the diffraction effect of the light, but has obvious color distortion and serious light leakage phenomenon due to the limitation of the diffraction principle. Geometric waveguides are the principle of geometric optics: when a light beam propagates inside a geometrical light guide and encounters a partial mirror array (PRMA), a beam of light is widened into multiple beams and exits in the same propagation direction, enabling an exit pupil expansion, the exiting light thus being able to cover a larger area. The geometric waveguide has no dispersion problem and can realize excellent imaging quality due to the pupil expansion principle and the relatively mature manufacturing technology, and is one of the schemes of the consumer-grade AR glasses.

Most of the existing geometrical optical waveguide research is focused on one-dimensional geometrical optical waveguides. The one-dimensional waveguide can only achieve exit pupil expansion in one direction, and only this direction can achieve expansion of the field angle and exit pupil. The other direction can only achieve a large field angle and exit pupil by means of the projection system, and therefore the projection system needs to be large in volume and thus has poor imaging quality, while the geometry of the geometric waveguide needs to be designed to be wide. The design and fabrication of a one-dimensional geometric waveguide is simpler than a two-dimensional waveguide, but has a smaller field angle, exit pupil distance, and eye movement range.

In 2005 Yaakov Amitai first proposed a two-dimensional mydriatic geometrical optical waveguide. In 2018, gu Luo et al proposed a design method for two-dimensional pupil-expanding geometric waveguide head-up display with stray light suppression. The designed head-up display uses two vertically arranged one-dimensional waveguides to complete pupil expansion in two directions and optimize stray light and illuminance uniformity. However, the design of vertical and horizontal mydriasis separation makes it necessary to design a long exit pupil distance for the projected optical path of the waveguide, which limits the range of view angles, and the two-dimensional geometric waveguide separating the mydriasis has a complicated structure and a large thickness. Lumus ltd 2020 proposes a single layer two-dimensional mydriatic geometrical optical waveguide near-eye display system in which the horizontal mydriatic region and the vertical mydriatic region are integrated in the same waveguide slice. In 2022, cheng Dewen et al designed a two-dimensional pupil-expanding geometric optical waveguide with a large field of view and a single layer, and completed the fabrication and testing of the prototype, achieving a field angle of 45.2 ° h×34.6 ° V, an eye movement range of 12.0mm×10.0mm, and an exit pupil distance of 18.0 mm. The research shows that the monolithic two-dimensional waveguide near-to-eye display device has the advantages of large field angle, thin shape and large exit pupil range, and can realize high-picture quality display.

However, it is difficult for the conventional two-dimensional optical waveguide design method to fully exhibit the display performance of the waveguide. The proposed conventional design uses a reverse design method, i.e. the shape that the waveguide should have is back-deduced from the index requirements. The method can rapidly design the waveguide meeting the index requirement, but in general, the waveguide with the same structure can realize more excellent performance by coupling in the methods of angular offset of the prism and the like. After the design is completed by using the traditional design method, a compromise needs to be made between the wearing comfort and the size performance, and the situation that the designed waveguide size is not suitable for being worn by a user is difficult to avoid. Meanwhile, the existing design method lacks accurate calculation of propagation tracks of four edge view fields, and the exit pupil matching precision is difficult to guarantee.

Disclosure of Invention

Based on the above, it is necessary to provide a method for matching the exit pupil of the maximum field angle of the monolithic two-dimensional expanded-pupil geometric waveguide, which can realize a large exit pupil distance and ensure the exit pupil matching precision.

The maximum field angle exit pupil matching method of the monolithic two-dimensional mydriasis geometric waveguide comprises the following steps:

acquiring performance indexes of the monolithic two-dimensional pupil-expanding geometric waveguide, and constructing an optical waveguide structure;

According to the optical waveguide structure, carrying out numerical calculation on the optical propagation path to obtain the propagation path of the incident light in the monolithic two-dimensional pupil-expanding geometric waveguide;

and designing an offset angle for the coupling-in prism according to the propagation path, and carrying out exit pupil matching through numerical simulation to ensure that the exit pupil range covers the eye movement range and obtain the maximum field angle.

According to the maximum field angle exit pupil matching method of the monolithic two-dimensional pupil expanding geometric waveguide, the structural characteristics of the two-dimensional waveguide are analyzed, in order to enable light rays of all view fields to cover an eye movement range, the propagation path of light rays of any view field is accurately calculated, and an exit pupil matching method is provided according to the exit pupil characteristics of four edge view fields; the maximum view angle which can be realized by the two-dimensional waveguide is found by combining the limit of the vertical view angle and the limit of the matching of the exit pupil, and the view angle of the waveguide can be maximized as much as possible.

Drawings

FIG. 1 is an application scenario diagram of a maximum field angle exit pupil matching method for a monolithic two-dimensional mydriatic geometry waveguide in one embodiment;

FIG. 2 is a flow diagram of a method of maximum field angle exit pupil matching for a monolithic two-dimensional mydriatic geometric waveguide in one embodiment;

FIG. 3 is a schematic diagram of a two-dimensional mydriatic geometric optical waveguide in one embodiment;

FIG. 4 is a top schematic view of a two-dimensional mydriatic geometric optical waveguide in one embodiment;

FIG. 5 is a schematic side view of a two-dimensional mydriatic geometry optical waveguide in one embodiment;

FIG. 6 is a schematic view of propagation of edge field light inside a waveguide in one embodiment, wherein (a) is a top view of propagation trajectories of four field light rays of different angles inside the waveguide, (b) is a schematic view of propagation trajectories of one edge field light ray, (c) is a schematic view of angular relationship of four edge field light rays of different angles on a surface of a waveguide coupling prism, and (d) is a schematic view of coverage areas of four edge field light rays of different angles on an eye movement range plane;

FIG. 7 is a diagram of any one of the fields of view (Ω) _h ,Ω _v ) Wherein (a) is any one of the fields of view (Ω) _h ,Ω _v ) (b) is a schematic view of the light incident on the coupling-in prism, wherein any one of the fields of view is (omega) _h ,Ω _v ) A schematic diagram of the light rays exiting the waveguide;

FIG. 8 is a schematic diagram of an exit pupil matching process in one embodiment;

fig. 9 is a schematic diagram of a process of exit pupil matching to obtain a maximum field angle in one embodiment, where (a) is fov=20° h×20° V, (b) is fov=40° h×20° V, (c) is fov=45° h×20 ° V, (d) is fov=50° h×20 ° V, (e) is fov=30° h×30 ° V, (f) is fov=30 ° h×40 ° V, (g) is fov=30 ° h×50 ° V, (H) is fov=45 ° h×45 ° V;

FIG. 10 is a graph of light propagation within a waveguide in one embodiment;

FIG. 11 is a schematic diagram of a stray light generation process in one embodiment;

FIG. 12 is a schematic diagram of stray light emission in one embodiment;

FIG. 13 is a graph of maximum vertical field angle in one embodiment;

FIG. 14 is a schematic diagram of a projection system including a sphere in one embodiment, wherein (a) is a projected light path of the design, (b) is a point plot of the projection system, (c) is a grid distortion of the projection system, and (d) is an MTF curve of the projection system;

FIG. 15 is a graph of maximum field angle exit pupil match results for a waveguide in one embodiment;

FIG. 16 is a schematic diagram of a simulation of an integrated near-eye display system in Lighttools simulation software in one embodiment;

FIG. 17 is a graph of the results of the simulation of the exit pupil range of four fringe fields in the exit pupil plane in one embodiment, where (a) is the result of the exit pupil simulation of fringe field 1, (b) is the result of the exit pupil simulation of fringe field 2, (c) is the result of the exit pupil simulation of fringe field 3, and (d) is the result of the exit pupil simulation of fringe field 4;

FIG. 18 is a schematic diagram of stray light simulating the observation of the human eye and inspecting the waveguide in one embodiment.

Reference numerals:

1. a micro display chip;

2. a projection system;

31. A waveguide coupling into the prism; 32. a waveguide horizontal pupil expansion region; 321. a partial mirror of the waveguide horizontal pupil expansion region; 33. a waveguide vertical pupil expansion region; 331. a partial mirror of the waveguide vertical pupil expansion region;

4. an eye movement range;

5. a human eye;

61. a central field of view ray; 62. orthofield light; 63. negative field light; 64. stray light.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application will be further described in detail with reference to the accompanying drawings and examples.

It should be noted that all directional indicators (such as up, down, left, right, front, and rear … …) in the embodiments of the present application are merely used to explain the relative positional relationship, movement, etc. between the components in a specific posture (as shown in the drawings), and if the specific posture is changed, the directional indicator is correspondingly changed.

In addition, descriptions such as those related to "first," "second," and the like, are provided for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated in this application. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature. In the description of the present application, "plurality of sets" means at least two sets, e.g., two sets, three sets, etc., unless specifically defined otherwise.

In the present application, unless explicitly specified and limited otherwise, the terms "coupled," "secured," and the like are to be construed broadly, and for example, "secured" may be either permanently attached or removably attached, or integrally formed; the device can be mechanically connected, electrically connected, physically connected or wirelessly connected; either directly or indirectly, through intermediaries, or both, may be in communication with each other or in interaction with each other, unless expressly defined otherwise. The specific meaning of the terms in this application will be understood by those of ordinary skill in the art as the case may be.

The method provided by the application can be applied to an application environment shown in fig. 1. The terminal 102 communicates with the server 104 through a network, where the terminal 102 may include, but is not limited to, various personal computers, notebook computers, smartphones, tablet computers, and portable wearable devices, and the server 104 may be various portal sites, servers corresponding to a background of a working system, and the like.

The application provides a maximum field angle exit pupil matching method of a monolithic two-dimensional mydriasis geometric waveguide, as shown in fig. 2, in an embodiment, the method is applied to a terminal in fig. 1 for illustration, and includes:

Step 202, obtaining performance indexes of the monolithic two-dimensional pupil expansion geometric waveguide, and constructing an optical waveguide structure.

Specifically: the optical waveguide structure includes: coupling into the prism and the waveguide sheet; the waveguide sheet includes: the horizontal pupil expansion area and the vertical pupil expansion area are respectively realized by partial mirror arrays (PRMA) facing different directions; the coupling-in prism is connected with the waveguide sheet (specifically, may be a glued connection manner) so as to couple the incident light of the projection optical device into the horizontal pupil expansion area and the vertical pupil expansion area of the waveguide sheet, thereby realizing the horizontal pupil expansion and the vertical pupil expansion.

The projection optical device includes: the micro display chip and the collimation light path are arranged at intervals.

The optical waveguide structure and the projection optical device form a two-dimensional pupil-expanding geometrical optical waveguide near-eye display system.

As shown in fig. 3, light rays emanate from the microdisplay, are amplified by the projection optics, collimated, and coupled into the waveguide by the coupling-in prism of the geometric optical waveguide. After entering the interior of the waveguide, the light propagates inside the waveguide by total reflection at the upper and lower surfaces due to the total reflection (TIR) condition being satisfied. The light firstly reaches the horizontal pupil expansion area in the waveguide, and when the light encounters the semi-transparent and semi-reflective film array arranged in the x direction of the horizontal plane, the light is split into reflected light and transmitted light, and the light is widened in the x direction, namely the expansion of the exit pupil in the x direction is completed. At the same time, the reflected light rays of the horizontal pupil expansion region are redirected and propagate into the vertical pupil expansion region. In the same way, the light passing through the semi-transparent and semi-reflective film array in the vertical pupil expansion area completes the expansion of the exit pupil in the y direction, is reflected out of the waveguide, propagates to the Eye movement range (Eye-box) in parallel, and finally enters the human Eye for imaging.

As shown in fig. 4, the light emitted by the center-most pixel of the micro display chip is emitted perpendicular to the projection light path, and is called the central view field light (indicated by the solid line in fig. 4), and the light emitted by the edge pixel of the micro display chip forms the largest included angle with the central view field light, and is called the edge view field light (indicated by the broken line in fig. 4). In the initial configuration, as shown in fig. 5, the coupling-in prism is parallel to the waveguide side, so that the central field of view ray propagates along the X-axis and the edge ray is symmetrical along the X-axis. With the exit pupil expansion in both directions, the exit pupil range of the near-eye display system is expanded from the smaller, inconveniently viewable exit pupil size of the original projection system to a larger, more distant, exit pupil range EPD suitable for human eye viewing _x ×EPD _y Known as Eye-movement range (Eye-box). The user can observe the display image by observing the display image within the eye movement range of the near-eye display system.

And 204, carrying out numerical calculation on the optical propagation path according to the optical waveguide structure to obtain the propagation path of the incident light in the monolithic two-dimensional pupil-expanding geometric waveguide.

Specifically:

fig. 6 (a) shows a top view of the propagation trajectory of four different angles of field rays inside the waveguide. It is noted that only the reflection of light from the horizontal mydriatic portion is shown, since only this portion of light is the "effective light" that ultimately covers the eye's range of motion, while the other portion of light is not observed by the human eye and therefore does not affect the imaging effect, and is therefore not shown in the figure. Fig. 6 (b) shows a schematic view of a single field of view (edge field of view 3) propagating inside the waveguide, being reflected out of the waveguide and finally reaching the eye movement plane, the area covered by the light in the eye movement plane being called the exit pupil area of the field of view, where the human eye can observe the light of this field of view. In the exit pupil plane of the waveguide, the exit pupil area of each field of view has different positions, shapes and sizes, and the overlapping part of the exit pupil areas of all fields of view is the effective imaging area, in which the human eye can observe a complete image. The process of exit pupil matching is a process of adjusting the light exit pupil areas of all fields of view, and finally, the imaging effective area meets the index requirement of the exit pupil range, as shown in fig. 6 (d).

The exit pupil matching process is an important step in the two-dimensional geometric waveguide design process, and a reasonable waveguide structure needs to be designed according to the propagation path of light rays. In the design process, three performance parameters of the view angle, the exit pupil distance and the exit pupil range of the waveguide are mutually restricted, one parameter becomes larger, and the other parameters become smaller. In general, the maximum field angle of the waveguide can be achieved by minimizing the additional exit pupil area on the premise that the exit pupils are matched to meet the exit pupil distance and eye movement range index.

To accomplish exit pupil matching, first a numerical calculation should be performed on the optical propagation path. Use (omega) _h ,Ω _v ) Representing the horizontal and vertical fields of view in air of the coupled-in waveguide light rays, as shown in fig. 6 (c). Consider 4 edge field rays (+/- Ω) _{h max} ,±Ω _{v max} ) Coverage in the exit pupil plane: the edge fields of view 1, 2, 3, 4 are represented by red, orange, green, blue, respectively. When the exit pupil ranges of the light rays of the 4 edge fields of view can cover the whole eye movement range in the exit pupil plane, the exit pupil ranges of the light rays of all fields of view can completely cover the eye movement range, and at this time, a user can observe a complete display image in the eye movement range. In order to make the central field light rays exit perpendicularly to the waveguide surface, the tilt of the prism is coupled in The bevel angle is usually designed to be 2 theta _v The central field of view is perpendicular to the incoupling prism surface. Fig. 6 (c) shows a schematic view of the incidence of 4 edge fields of view on the coupling-in prism, wherein white light rays represent central field of view rays, white dashed lines represent auxiliary lines perpendicular to the coupling-in prism surface, and red line segments represent incident and refracted rays of the edge field of view 1.

According to the optical waveguide structure, the optical propagation path is numerically calculated, and fig. 7 (a) shows that any one of the fields of view is (Ω _h ,Ω _v ) Calculating the incident angle of the light ray on the surface of the coupling-in prism:

in phi, phi _in For the angle of incidence of light on the coupling-in prism surface, Ω _h Is the horizontal field of view of light in air;

through refraction, the included angle between the light inside the waveguide sheet and the surface of the coupling-in prism is as follows:

in the method, in the process of the invention,is the included angle between the light inside the waveguide sheet and the surface of the coupling-in prism;

according to the geometric relationship, the angle of view of the refracted light ray meets the following conditions:

in the method, in the process of the invention,for the vertical field of view of the light in the waveguide, +.>Is the horizontal field of view of light in the waveguide;

after entering the waveguide for propagation, for ease of computation, the propagation of light can be described by 2 parameters: angle alpha between projection of light ray in XOY plane and Y axis _v And the angle beta between the light and the XOY plane, which describes the propagation direction of the light in the top view and the angle between the light and the waveguide surface, respectively. For the waveguide sheet when the coupling-in prism has no offset angle, namely the coupling-in prism is parallel to the side surface of the waveguide, the following conditions are satisfied:

wherein alpha is _v Is the included angle alpha between the projection of the light ray in the vertical pupil expansion area on the bottom plane of the waveguide and the side edge of the vertical pupil expansion area _h The angle between the projection of the light ray in the horizontal pupil expansion area on the bottom plane of the waveguide and the side edge of the horizontal pupil expansion area is beta, and the angle between the light ray and the bottom plane of the waveguide is beta.

According to the formula, the propagation direction and the coverage range of the light rays of any one view field after entering the waveguide can be calculated, the propagation direction of the light rays of any one view field before exiting the waveguide can be calculated, and the propagation direction of the light rays after exiting the waveguide can be continuously calculated.

In the vertical pupil-expanding region section, the light is reflected by the vertical partial mirror, and a refractive exit waveguide occurs, as shown in fig. 7 (b). A perpendicular line AO of the bottom surface of the waveguide is drawn from the highest point (point A) of the light as a starting point, and the bottom surface of the waveguide is intersected at a point O. And the point O is set as the origin of the local coordinate system, the coordinates are (0, 0), and the point A coordinates are (0, d). Line segment AB is perpendicular to the normal vector of the normal partial mirror plane, i.e. the normal partial mirror The vector for light AC when reflection occurs is shown>Indicating that the reflected ray vector is +.>

In the method, in the process of the invention,for the light vector when reflection occurs, +.>Normal vector for the vertical partial mirror;

calculating the reflected ray vector:

in the method, in the process of the invention,is the reflected ray vector;

calculating an included angle between the reflected light and the top surface of the waveguide and an included angle between the projection of the light on the top surface and the vertical axis of the local coordinate system:

in the method, in the process of the invention,for the angle alpha between the reflected light and the top surface of the waveguide _out Is the angle between the projection of the light ray on the top surface and the vertical axis of the local coordinate system.

In general, the principle of the waveguide in the design process is that the central view field is emitted perpendicularly to the surface of the waveguide, and the waveguide does not have optical power, and the view angle of the light rays emitted from the waveguide is the same as that of the incident light rays. I.e. there is the following relationship:

using the formulas (10) to (16), the incident light ray (. OMEGA.) of any field of view can be calculated _h ,Ω _v ) Traces when coupled out within the waveguide. Therefore, forward ray tracing numerical simulation of the two-dimensional geometric optical waveguide can be carried out, the propagation path and the effective exit pupil range of each view field ray are calculated, and numerical simulation of the exit pupil matching of the two-dimensional optical waveguide is completed through optimal design. In the two-dimensional waveguide, a specific propagation path of the edge ray is shown in fig. 8 (a). The four edge rays propagate to the exit pupil plane whose exit pupil range can be calculated by numerical simulation, the numerical simulation results being shown in fig. 8 (b) as color filled parallelograms. In fig. 8 (b), it is shown that when the coupling-in prism is parallel to the waveguide side, the incident fringe field light is distributed horizontally symmetrically in the horizontal pupil expansion region, and the effective imaging region of the exit pupil plane cannot completely cover the eye movement range of the center square. Because the green and blue fields cannot propagate to the furthest end of the waveguide at this point, resulting in less coverage in the exit pupil plane. Thus, in FIG. 8 (b), the coupling-in prism is given a bias angle θ that rotates in the clockwise direction _p Note that the counter-clockwise bias is positive. At the moment, the green and blue marginal view field light rays can reach the far end of the waveguide, and the reflected light ray exit pupil range can also cover the eye movement range, namely, the two-dimensional waveguide exit pupil matching of the parameter meets the system requirement.

And 206, designing an offset angle for the coupling-in prism according to the propagation path, and performing exit pupil matching through numerical simulation to enable an exit pupil range to cover an eye movement range so as to obtain a maximum field angle.

Specifically:

in order to ensure that the central field of view light is perpendicular to the waveguide exit, an offset angle is designed for the coupling-in prism, when the coupling-in prism introduces an offset angle, the partial mirror tilt angle of the horizontal pupil expansion region should satisfy:

in θ _h Tilt angle θ of partial mirror, which is horizontal pupil expansion area _p Is the offset angle of the coupling-in prism.

In the exit pupil matching process, the dimension L of the waveguide and the width w of the horizontal pupil expansion area _h Thickness d of waveguide, width w of coupling-in prism _p Position and angle of coupling-in prism, angle θ of perpendicular partial mirror _v Many parameters have an effect on the final result. And as the angle of view increases, the effective imaging area of the waveguide is so sharply reduced that the eye movement range index requirements are eventually not met, as shown in fig. 9. The basic parameters of the two-dimensional waveguide for exit pupil matching in fig. 9 are: refractive index n=1.65, exit pupil distance erf=18, eye movement range epd=12×12, width of coupling prism w _p =4. Tilt angle θ of partial mirror for vertical pupil expansion region _v As can be seen from the figure, the maximum vertical field angle without stray light is 30.22 °. θ in FIG. 9 _p Representing the offset angle of the coupling-in prism; EYE _{bias y} The distance bias of the eye movement range in the Y-axis direction is represented, the Y-axis positive direction is taken as positive, and the eye movement range is positioned at the center of the vertical pupil expansion area when no bias exists; prism _{bias y} And the distance offset of the coupling-in prism in the Y-axis direction is represented, the Y-axis positive direction is taken as positive, and the coupling-in prism is positioned at the center of the horizontal pupil expansion area when the coupling-in prism is not biased.

As can be seen from fig. 9, the increase in the horizontal field angle mainly affects the length of the effective imaging area, and the increase in the vertical field angle mainly affects the width of the effective imaging area. Through analysis, increasing the length L of the waveguide, angularly offsetting the coupling-in prism can effectively expand the width of the effective imaging area, while increasing the width of the vertical pupil expansion area can significantly increase the width of the effective imaging area. Therefore, in the process of carrying out exit pupil matching to find the maximum field angle of the waveguide on the premise of meeting the indexes of the exit pupil distance and the eye movement range, the waveguide parameters need to be changed for many times, and iterative attempts are carried out, so that the maximum field angle which can be realized by the waveguide is finally found.

According to the maximum field angle exit pupil matching method of the monolithic two-dimensional pupil expanding geometric waveguide, the structural characteristics of the two-dimensional waveguide are analyzed, in order to enable light rays of all view fields to cover an eye movement range, the propagation path of light rays of any view field is accurately calculated, and an exit pupil matching method is provided according to the exit pupil characteristics of four edge view fields; performing exit pupil matching to change the overlapping part of the exit pupil areas of the four edge view fields as an effective area, wherein the view angle, the exit pupil distance and the exit pupil range of the system are limiting conditions so that the system can work normally; the field angle is increased to change the area of the active area until the active area just covers the eye movement range, and the current field angle is taken as the maximum field angle of the waveguide. The maximum view angle which can be realized by the two-dimensional waveguide is found by combining the limit of the vertical view angle and the limit of the matching of the exit pupil, and the view angle of the waveguide can be maximized as much as possible. Meanwhile, the design of the projection light path of the two-dimensional geometric light guide is completed, the system integration is completed, a two-dimensional pupil expansion geometric light guide is designed by using a maximum view angle analysis method, simulation verification is carried out by using optical software Lighttools, and the two-dimensional pupil expansion geometric light guide has an eye movement range of 12.0mm multiplied by 12.0mm, an exit pupil distance of 18.0mm, a view angle of 50.00 DEG H multiplied by 29.92 DEG V and a thickness of 1.7 mm. Simulation results show that the feasibility of the proposed exit pupil matching is that the designed system has good illumination uniformity, and excellent performance can be realized by human eye observation.

It should be understood that, although the steps in the flowchart of fig. 2 are shown in sequence as indicated by the arrows, the steps are not necessarily performed in sequence as indicated by the arrows. The steps are not strictly limited to the order of execution unless explicitly recited herein, and the steps may be executed in other orders. Moreover, at least some of the steps in fig. 2 may include multiple sub-steps or stages that are not necessarily performed at the same time, but may be performed at different times, nor do the order in which the sub-steps or stages are performed necessarily performed in sequence, but may be performed alternately or alternately with at least a portion of the sub-steps or stages of other steps or other steps.

In a specific embodiment, the vertical field of view is analyzed according to the optical waveguide structure, so that the eye movement range condition satisfies the performance index, the total reflection condition satisfies the imaging condition, and the stray light suppression condition satisfies the imaging quality requirement, and the maximum vertical field of view angle is obtained.

Specifically:

the three most critical performance parameters of the near-to-eye display system are: angle of field, eye movement range, and exit pupil distance. The design of the projection light path determines the size of the field angle; the design of the waveguide determines the size of the eye movement range and the exit pupil distance. Generally, the eye movement range and exit pupil distance are first determined during the design of a near-eye display system: if the designed waveguide has a large eye movement range, the display image can still be clearly observed when the user generates tiny displacement relative to the near-eye display device, so the size of the eye movement range is usually set to be 8-14mm; the exit pupil distance of a near-eye display system is typically designed to be 16-20mm so that the user can use the near-eye display device as if wearing glasses. In order to fully realize excellent display performance, on the basis that the eye movement range and the exit pupil distance are already determined, the maximum value of the view angle of the waveguide is analyzed and found, and the method becomes the most critical step in the waveguide design process. In the Y direction, the maximum value of the vertical field angle is defined by: the eye movement range condition, the total reflection condition, and the stray light suppressing condition are limited in common.

The waveguide sheet is made of a material having a refractive index n, and generally a larger refractive index enables a larger angle of view. The length of the waveguide sheet is L, and the widths (along Y direction) of the horizontal pupil expansion region and the vertical pupil expansion region are w respectively _h And w _v . The thickness of the waveguide is d and the shape of the waveguide should be small and thin like glasses. The inclination angles of a semi-transparent semi-reflective film array (PRMA) and the bottom edge of the waveguide in the horizontal pupil expansion area and the vertical pupil expansion area are respectively theta _h And theta _v These two angles determine the direction of the incident light, affect the size of the angle of view, and have a relationship with the amount of stray light from the waveguide, and therefore require an important analysis. The width of the coupling-in prism is w _p Generally depends on the exit pupil size of the projection optics and affects the size of the system and illumination uniformity. The distance parameters of the partial mirror of the horizontal pupil expansion area are: t is t ₀ ,t ₁ ,t ₂ ,…,t _i-1 Where i is the total number of prisms in the horizontal pupil expansion region, determining the illumination continuity and uniformity across the range of eye movements.

The eye movement range condition satisfies performance criteria, including:

the distance between the partial mirrors of the vertical pupil expansion region satisfies:

wherein H is the distance between partial reflectors of the vertical pupil expansion region, a larger H can ensure better transmission observation effect, d is the thickness of the waveguide sheet, and theta _v The inclination angle of the semi-transparent and semi-reflective film array and the bottom edge of the waveguide sheet is the vertical pupil expansion area;

the display field angle in the vertical direction of the system is expressed as:

FOV _v ＝2Ω _{v max}

the size of the eye movement range is expressed as:

EPD _x ×EPD _y

the eye movement range in the vertical direction satisfies:

(EPD _y ) _max ＝m·H-2ERF·tan(Ω _{v max} ) (2)

in the formula, EPD _y For the dimension of the eye movement range in the vertical direction, m is the number of partial mirrors of the vertical pupil expansion region, ERF is the exit pupil distance, Ω _{v max} Half of the angle of view is displayed in the vertical direction in the air, and omega is satisfied _v ∈[-Ω _{v max} ,Ω _{v max} ]And defining the angle of the central field of view ray to be positive in the anticlockwise direction;

according to the formulas (1) and (2), when the thickness d of the waveguide increases, the Y-direction exit pupil range EPD _y And correspondingly increases; while at a vertical field angle FOV _v Or the exit pupil distance ERF increases, EPD _y Will decrease. Therefore, the key parameters of the waveguide are mutually restricted, and a trade-off (trade-off) is required in the design process. Typically, the eye movement range EPD _y Is selected and determined at design time, so that the vertical field angle FOV is designed at system design time _v It is necessary to be able to meet the requirements of the eye movement range.

According to equation (2), the vertical field angle satisfies:

the total reflection condition satisfies the imaging condition, including:

as shown in fig. 10, when the vertical direction field of view in air is at Ω _v When an angled light ray is coupled into the optical waveguide, refraction occurs at the surface of the waveguide, and according to the law of refraction, the refraction angle of the light ray inside the waveguide sheet satisfies:

ω _v ＝arcsin(sin(Ω _v )/n) (4)

Wherein omega is _v Is the included angle between the incident light ray in the straight direction and the central view field in the waveguide, omega _v The angle of the view field in the vertical direction in the air, n is the refractive index of the waveguide plate;

when propagating inside the waveguide, the light rays not reflected by the partial mirror must satisfy the total reflection condition to normally propagate. According to the geometric relationship, the field of view omega in the vertical direction _v (Ω _v ∈[-Ω _{v max} ,Ω _vmax ]) The incidence angle of the angle light ray when the total reflection occurs in the waveguide is 2 theta _v +ω _v Wherein (omega) _v ∈[-ω _{v max} ,ω _{v max} ]). The light rays meet the condition of total reflection when propagating inside the waveguide sheet, namely, the incident angle is larger than the critical angle of total reflection:

2θ _v +ω _v >θ _TIR ＝arcsin(1/n) (5)

in θ _TIR Is the critical angle at which light is totally reflected within the waveguide;

when omega _v Take-omega _{v max} When the incident angle reaches the minimum value, 2 theta _v -ω _{v max} Which should be greater than the critical angle for total reflection. Therefore, according to the total reflection condition, the vertical field angle satisfies:

Ω _{v max} <arcsin(n·sin(2θ _v -arcsin(1/n))) (6)

wang et al propose in operation that stray light from one-dimensional geometric waveguides can be divided into 3 types: i.e. stray light caused by coupling-in structures, stray light caused by abnormal reflection of the front and rear surfaces of the partial mirror. In this design, there are 2 of 3 types of stray light that may be generated by the two-dimensional waveguide vertical pupil expansion region: stray light caused by unnecessary reflection of light incident at a large angle on the front and rear surfaces of the partial mirror. The stray light propagates in the waveguide in a total reflection mode after being generated, and when the stray light meets the next partial reflector, the stray light is reflected and coupled out by the partial reflector to become the stray light which can be observed to influence the imaging quality; or reflected after being incident at a large angle and converted into normal light. In analyzing waveguide stray light, only stray light that is successfully coupled out needs to be considered.

The stray light suppression condition satisfies imaging quality requirements, including:

through geometric analysis, as shown in fig. 11, the stray light outgoing angle is inversely proportional to the half field angle, and the stray light outgoing angle satisfies:

ε＝π-6θ _v -ω _v (7)

wherein epsilon is the incident angle of stray light in the waveguide sheet when the stray light is refracted and emitted from the waveguide sheet, and the sign thereof represents the propagation of the stray light in the normal light propagation direction of the waveguide, omega _v Represents the included angle between the incident light ray in the vertical direction and the central view field in the waveguide, and the range is omega _v ∈[-ω _{v max} ,ω _{v max} ]The included angle of the light rays in the anticlockwise direction of the central view field is positive, and the included angle of the light rays in the anticlockwise direction of the central view field is negative;

according to the formula (7), the structure of the waveguide can be specially designed through calculation so as to guide stray light out of the eye movement range, and the stray light is directly prevented from being observed by human eyes in the eye movement range. When omega _v Take the maximum value omega _{v max} When the emergent angle E of the stray light reaches the minimum value E _min The stray light emitted at this time is closest to the eye movement range. It is noted that stray light will typically only occur at the second partial mirror. As shown in fig. 12, when stray light just reaches the boundary of the eye movement range, the angle between the stray light and the eye movement range is called a critical angle, and if δ is expressed, the critical angle is satisfied when the stray light reaches the boundary of the eye movement range:

In the formula, EYE _{bias y} The offset distance of the eye movement range in the vertical direction is positive by the positive direction of the Y axis, and the center of the eye movement range is opposite to the center of the vertical waveguide area when the Y axis is not offset. If the minimum emergence angle E of emergent stray light _min The stray light is larger than the critical value pi/2-delta of the emergence angle, and all stray light generated by the vertical waveguide is coupled out of the eye movement range, so that the suppression of the stray light is completed;

the vertical field angle satisfies:

in this step, from the above derivation, we can calculate the maximum vertical field angle under the eye movement range condition, the total reflection condition, and the stray light suppression condition. As shown in fig. 13, the horizontal axis is the partial mirror tilt angle θ of the vertical pupil expansion region _v The ordinate is the field of view omega of the incident light in air _v The line segments in the figure are the three limiting conditions and the field of view omega respectively _v And the limit of more than 0 is adopted, the safety area in the figure is an optional stray light-free imaging area, and the uppermost point of the safety area is the maximum field angle of the vertical pupil expansion area. For example: when the refractive index of the waveguide material n=1.65, the eye movement range EPD _x ×EPD _y 12×12mm, exit pupil distance erf=18 mm, thickness h=1.7 mm, number of partial mirrors m=7, EYE movement range offset EYE _{bias y} When=2 mm, as shown in the figure, it can be derived that when θ _v When=24.5°, the maximum view angle of the vertical view angle isThe field is omega _{v max} =19.54, i.e. FOV _{v max} =39.08°, i.e. the maximum vertical field angle under this configuration can reach 39.08 °.

In a waveguide near-eye display system, a projection optical system is required to magnify and project the image of the microdisplay into the coupling-in prism of the waveguide. Because the optical waveguide does not have optical power, the view angle of the waveguide near-to-eye display system is the view angle of the projection light path under the condition that the maximum view angle limit of the waveguide is met. Therefore, in order to exert the full performance of the waveguide display as much as possible, the angle of view of the projected light path should be close to the maximum angle of view achievable by the waveguide.

Through the analysis of the maximum angle of view that can be achieved by the previous waveguide, we choose the vertical partial mirror tilt angle θ _v The maximum vertical field angle without stray light is 30.22 °, i.e. FOV is selected _v =30°. We use the familiar 1920 x 1080 resolution microdisplay to choose the horizontal field angle FOV _h =50°. Through exit pupil matching, the configuration parameters of the two-dimensional waveguide we designed are listed in table 1.

TABLE 1

In this study, a 0.39 "silicon inorganic light emitting diode (Si-OLED) microdisplay was selected as the image source with a pixel size of approximately 4.6 μm. The display size of the Si-OLED microdisplay was 8.75mm by 4.97mm with a resolution of 1920 by 1080. From the waveguide designed during the exit pupil matching process, we have designed a projection system comprising a sphere, as shown in fig. 14 (a), the length (L _p ) 15.3mm. The FOV and exit pupil dimensions of the projection system were 56.5 ° (50.00 ° h× 29.92 ° V) and 4mm, respectively, with an exit pupil distance of 0.5mm. The effective focal lengths EFL and F-numbers of the projection system are 9.33mm and 2.31, respectively. Fig. 14 (b) shows a dot column diagram of the projection system of the design. Fig. 14 (c) shows the grid distortion of the projection system, with a maximum distortion of the system of less than 1%. FIG. 14 (d) is a graph of the modulation transfer function of the system, with the full field MTF of the system maintained at 56lpmmAbove 0.5.

The two-dimensional optical waveguide, the projection optical path and the micro display chip are integrated to obtain a compact near-eye display system similar to glasses, and the designed two-dimensional waveguide near-eye display system is proved to be free from the defects of larger size and heavier weight of the traditional near-eye display system. The integrated near-eye display system was simulated in Lighttools simulation software to verify the design approach presented herein, as shown in fig. 16. Fig. 16 shows an integrated two-dimensional waveguide near-to-eye display system, where light is emitted from a rectangular micro-display, collimated by a projection light path, incident into a prism, enters the interior of an optical waveguide, and exits the waveguide after pupil expansion.

We performed exit pupil matching of the waveguide to analyze the maximum field angle achievable by the waveguide, and figure 15 shows the results of the designed two-dimensional waveguide exit pupil matching, with the effective imaging area of the four fringe fields of view in the exit pupil plane fully covering the eye movement range, with a maximum field angle of the waveguide of 50.00 ° H x 30.00 ° V. To verify the full field exit pupil match of the designed two-dimensional geometric waveguide, a receiver was added in the exit pupil plane and four light sources were placed at the four corners of the microdisplay to simulate the fringe field of view created by the light rays from the pixels passing through the projection light path. The exit pupil ranges of the four fringe fields of view in the exit pupil plane are shown in FIG. 17, and the result is substantially identical to the image (FIG. 15) calculated as an exit pupil match. In this case, the exit pupil ranges of 3 out of the 4 marginal field rays just meet the index requirement of the eye movement range, and the field angle at this time of the waveguide is the maximum field angle that can meet the performance index, that is, the performance of the waveguide is fully exerted.

At a distance of 18mm from the exit pupil of the waveguide surface, an ideal lens with a caliber of 4mm is placed, and a receiver is placed at the focal plane of the ideal lens. The ideal lens has a focal length of 16mm, similar to the human eye, for simulating the human eye's observation and examining the stray light of the waveguide. As shown in fig. 18, 9 light source points are disposed on the surface of the micro-display, and the light emitted from each light source point is imaged on the receiver after passing through the ideal lens. As a result, as shown in fig. 18, each light source point is imaged as a point in the receiving plane, which proves that the pixels on the micro-display in the near-eye display system can be clearly observed by human eyes, that is, the near-eye display system can realize the projection function.

There is no stray light in the vertical pupil expansion region in the system, since the vertical field angle of the system does not exceed the analyzed vertical maximum field angle. The waveguide still has a small amount of crosstalk stray light as shown in fig. 17 (a), (b) and fig. 18. The reason for this is that the angle offset of the coupling prism is introduced during the design process, so that the angle of the light on one side when entering the vertical pupil expansion region is too large, the light is reflected by the vertical partial reflector, and returns to the horizontal pupil expansion region again, and the two pupil expansion regions act together to form crosstalk stray light. The crosstalk stray light can be partially suppressed by adding a triangular prism to the horizontal pupil expansion region, as shown in fig. 18, where only the crosstalk stray light exists near the edge field of view, but it is difficult to completely eliminate. Avoiding too large an offset angle of the incoupling prism is also a way to suppress crosstalk stray light, but this limits the angle of view of the waveguide.

In this application, a single-layer, large exit pupil range, two-dimensional mydriatic geometric waveguide with a maximum field angle is designed. Basic design principles, analysis and calculation methods of two-dimensional geometric waveguides are proposed. The analysis method of the maximum field angle realized by the two-dimensional waveguide is provided, a compact projection system with the waveguide limit field angle is designed according to the waveguide field angle limit, and finally the waveguide near-to-eye display system is integrated and verified. Finally, the designed single-layer two-dimensional geometric waveguide has a thickness of 1.7mm, an angle of view of 50.00 DEG H× 29.92 DEG V, an exit pupil size of 12mm×12mm at an exit pupil distance of 18mm, and suppresses all vertical pupil-expanding stray light and most of crosstalk stray light. Simulation results prove the correctness of the maximum field angle exit pupil matching design method, and show that the brightness uniformity of different fields of the designed waveguide is in an acceptable degree, most of stray light is separated from normal light, and only crosstalk stray light near the edge field can be observed by simulated human eyes. For a waveguide with a given size, the proposed design method for analyzing the maximum field angle of the two-dimensional waveguide can fully exert the display performance of the waveguide. Generally, the size and exit pupil of the consumer-grade AR waveguide should meet the observation habit of the user and have excellent optical performance, and the design method provided by the application provides a possible answer for the consumer-grade AR device to meet the requirements of ergonomics and optical performance.

The technical features of the above embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.

The above examples only represent a few embodiments of the present application, which are described in more detail and are not to be construed as limiting the scope of the present application. It should be noted that it would be apparent to those skilled in the art that various modifications and improvements could be made without departing from the spirit of the present application, which would be within the scope of the present application. Accordingly, the scope of protection of the present application is to be determined by the claims appended hereto.

Claims

1. The maximum field angle exit pupil matching method of the monolithic two-dimensional mydriasis geometric waveguide is characterized by comprising the following steps of:

2. The method for maximum field angle exit pupil matching of a monolithic two-dimensional mydriasis geometric waveguide according to claim 1, wherein performing numerical calculation on an optical propagation path according to the optical waveguide structure to obtain a propagation path of an incident light ray in the monolithic two-dimensional mydriasis geometric waveguide comprises:

and according to the optical waveguide structure, carrying out numerical calculation on the optical propagation path, and calculating the incident angle of the light on the surface of the coupling-in prism, the included angle between the light inside the waveguide sheet and the surface of the coupling-in prism, the angle of the light field after refraction, the included angle between the projection of the light in the plane and the vertical axis and the included angle between the light and the plane, so as to obtain the propagation path of the incident light in the monolithic two-dimensional pupil-expanding geometric waveguide.

3. The method for matching the maximum field angle exit pupil of a monolithic two-dimensional mydriasis geometric waveguide according to claim 2, wherein performing numerical calculation on an optical propagation path according to the optical waveguide structure, calculating an incident angle of a light ray on a coupling prism surface, an included angle of the light ray inside a waveguide sheet and the coupling prism surface, an included angle of a refracted light ray field angle, a projection of the light ray in a plane and an included angle of a vertical axis, and an included angle of the light ray and the plane, to obtain the propagation path of the incident light ray in the monolithic two-dimensional mydriasis geometric waveguide, including:

According to the optical waveguide structure, numerical calculation is carried out on the optical propagation path, and the incidence angle of light on the surface of the coupling-in prism is calculated:

the included angle between the light inside the waveguide sheet and the surface of the coupling-in prism is as follows:

the angle of view of the refracted light ray satisfies:

the included angle between the projection of the light ray in the plane and the vertical axis and the included angle between the light ray and the plane are as follows:

4. The method for maximum field angle exit pupil matching of a monolithic two-dimensional mydriasis geometric waveguide according to claim 3, wherein performing numerical calculation on an optical propagation path according to the optical waveguide structure to obtain a propagation path of an incident light ray in the monolithic two-dimensional mydriasis geometric waveguide, further comprising:

And according to the optical waveguide structure, carrying out numerical calculation on the optical propagation path, and calculating the light vector when reflection occurs, the normal vector of the vertical partial reflector, the reflected light vector, the included angle between the reflected light and the top surface of the waveguide and the included angle between the projection of the light on the top surface and the vertical axis of the local coordinate system, so as to obtain the propagation path of the incident light in the monolithic two-dimensional pupil expansion geometric waveguide.

5. The method for matching the maximum field angle exit pupil of a monolithic two-dimensional mydriasis geometric waveguide according to claim 4, wherein calculating the propagation path of an incident ray in the monolithic two-dimensional mydriasis geometric waveguide by performing numerical calculation on the optical propagation path according to the optical waveguide structure, and calculating the ray vector at the time of reflection, the normal phase vector of a vertical partial reflector, the ray vector after reflection, the included angle between the reflected ray and the top surface of the waveguide, and the included angle between the projection of the ray on the top surface and the vertical axis of a local coordinate system, comprises:

according to the optical waveguide structure, numerical calculation is performed on the optical propagation path, and the light ray vector when reflection occurs and the normal phase vector of the vertical partial reflector are calculated:

in the method, in the process of the invention,for the light vector when reflection occurs, +. >Normal vector for the vertical partial mirror;

calculating the reflected ray vector:

in the method, in the process of the invention,is the reflected ray vector;

6. The method of maximum field angle exit pupil matching of a monolithic two-dimensional mydriatic geometric waveguide as defined in any one of claims 1 to 5, wherein designing an offset angle for the coupling-in prism based on the propagation path comprises:

7. The method for matching the maximum angle of view exit pupil of a monolithic two-dimensional mydriatic geometric waveguide according to any one of claims 1 to 5, wherein the exit pupil matching is performed by numerical simulation so that the exit pupil range covers the eye movement range, and the maximum angle of view is obtained, comprising:

performing exit pupil matching to change the overlapping part of the exit pupil areas of the four edge view fields into an effective area;

the field angle is increased to change the area of the active area until the active area just covers the eye movement range, and the current field angle is taken as the maximum field angle of the waveguide.

8. The maximum field angle exit pupil matching method of a monolithic two-dimensional mydriasis geometric waveguide according to any one of claims 1 to 5, characterized in that the optical waveguide structure includes: coupling into the prism and the waveguide sheet; the waveguide sheet includes: a horizontal mydriatic region and a vertical mydriatic region;

the coupling-in prism is connected with the waveguide sheet so as to couple incident light rays of the projection optical device into a horizontal pupil expansion area and a vertical pupil expansion area of the waveguide sheet to realize horizontal pupil expansion and vertical pupil expansion.