RU2814092C2 - Optical device, in particular, for high-performance compact helmed-head display system with small input aperture - Google Patents

Abstract

FIELD: optics.

SUBSTANCE: invention relates to light guide optical devices with a substrate. The optical device includes a light-transmitting substrate, entrance and exit apertures, an exit pupil, an intermediate element located outside the substrate for introducing light waves into the substrate through the entrance aperture, a first reflective surface between two main surfaces of the light-transmitting substrate for reflecting the introduced light waves, a second flat reflective surface parallel to the first planar reflective surface located between the main surfaces of the light transmitting substrate for extracting light waves from the substrate, and an optical element for deflecting light waves extracted from the substrate through the exit aperture into the exit pupil.

EFFECT: input aperture is substantially smaller than the output aperture, all incoming light waves pass into the input aperture, all light waves output from the substrate by the second flat reflective surface are introduced into the substrate by reflection from the first reflective surface, the active area of the first reflective surface is similar to the active area of the second reflective surface, and each of the introduced light waves completely covers the aperture of the exit pupil.

15 cl, 75 dwg

Description

Field of technology

The present invention relates to light guide optical devices with a substrate and, in particular, to devices having reflective surfaces on a light transmitting substrate and an array of partially reflective surfaces attached to the substrate.

The invention may benefit many imaging devices, such as head-mounted displays and heads-up displays, as well as cell phones, compact displays, and 3-D displays.

State of the art

One important application for compact optical elements is their use in a head-mounted display (HMD), where the optical module simultaneously functions as an imaging lens and an image fusion device in which a two-dimensional display is displayed at infinity and reflected at the eye of the observer. The display can be formed directly either by a spatial light modulator (SLM), for example, a cathode ray tube (CRT), a liquid crystal display (LCD), an array of organic light-emitting diodes (OLED - from the English organic light-emitting diode), or a scanning source or similar devices, or indirectly through an image transfer lens or fiber optic bundle. The display comprises a matrix of elements (pixels) imaged at infinity by a collimating lens and transmitted to the viewer's eye via a reflective or partially reflective surface, acting as a combiner for applications that do not provide or provide "see-through" vision, respectively. Typically, a well-known spatial optical module is used for these purposes. As the desired field of view (FOV) of the system increases, the size and weight of such a known optical module increases, becoming bulky and therefore impractical even for a device with moderate performance characteristics. This is a major disadvantage of displays of all types, but especially head-mounted displays, where the system must be as light and compact as possible.

The quest for compactness has led to the development of several different complex optical solutions that, on the one hand, are still not compact enough for most practical applications and, on the other hand, have major disadvantages in terms of manufacturability, cost and performance.

The principles set forth in WO 2017/141239, WO 2017/141240, WO 2017/141242 and PCT/IL2018/051105 are incorporated herein by reference in their entirety.

Disclosure of the Invention

The present invention is directed to the creation of compact substrates for head-mounted displays (HMDs) and other applications. The invention is characterized by a relatively wide field of view (FOV) in combination with a relatively large exit pupil (EMB - eye-motion box). The resulting optical system provides a high-quality wide-angle image that also accommodates large eye movements. The main advantage of the optical system proposed in the invention is its compactness in comparison with existing designs, as well as the ease of its integration even into optical systems with highly specialized designs.

The overall objective of the present invention is, therefore, to mitigate the shortcomings of existing compact optical display devices, and to provide optical components and systems having improved performance characteristics to meet specific requirements.

According to the present invention, there is therefore provided an optical system, which is an optical device including: a first light transmitting substrate having at least two parallel main surfaces and two opposite edges (ribs); entrance aperture; an exit aperture located adjacent one of the main surfaces of the substrate; exit pupil, characterized by aperture; a first intermediate element having at least two surfaces located outside the substrate for introducing incoming light waves having a field of view into the substrate through the entrance aperture; a first flat reflective surface, the active area of which is located between two main surfaces of the light-transmitting substrate, for reflecting light waves arriving from the first intermediate element, to provide total internal reflection from the main surfaces of the substrate; a second planar reflective surface parallel to the first planar reflective surface having an active area and located between two main surfaces of the light transmitting substrate for removing light waves from the substrate, and a deflection optical element having at least two surfaces located outside the substrate for deflecting light waves , output from the substrate through the exit aperture into the exit pupil, and the entrance aperture is significantly smaller than the exit aperture, all incoming light waves pass inside the entrance aperture, all light waves output from the substrate by the second flat reflective surface are introduced into the substrate by reflection from the first reflective surface, the active area of the first reflective surface is similar (close in size) to the active area of the second reflective surface, and each of the introduced light waves completely covers the exit pupil aperture.

Brief description of drawings

The invention is described in relation to certain preferred embodiments with reference to the accompanying drawings, which illustrate the invention and make it more understandable.

With regard to specific references to the drawings, it should be emphasized that the details shown are provided by way of example and illustration only in considering the preferred embodiments of the present invention and demonstrating what appears to be the most appropriate and well understood description of the principles and essential features of the invention. Therefore, no attempt has been made to describe the design features of the invention in more detail than is necessary to understand its basic provisions.

The description, together with the drawings, is intended to provide guidance to those skilled in the art in practicing the several forms of the invention.

On the drawings:

in fig. 1 is a side view of a known particular embodiment of a light-transmitting substrate;

in fig. 2 is a side view of another known particular embodiment of a light transmitting substrate;

in fig. 3A and 3B illustrate the required reflectance and transmission characteristics of selectively reflective surfaces used in a particular embodiment of a known light-transmitting substrate for two ranges of incidence angles;

in fig. Figure 4 shows the dependence of the reflection coefficient on the angle of incidence for a particular version of the dielectric coating;

in fig. 5 is a schematic cross-sectional view of a known light-transmitting substrate in which both the input and output elements are diffractive optical elements;

in fig. 6A, 6B, and 6B are cross-sectional views of a known transparent substrate having lead-in and lead-out surfaces and a partially reflective deflector;

in fig. 7 schematically shows the active parts of the output surface corresponding to the visual angle and exit pupil (EMP) of the system;

in fig. 8A, 8B, 8B and 8D schematically show the active parts of the input surface corresponding to the viewing angle and EMB of the system;

in fig. 9A, 9B, 9B and 9D are schematic cross-sectional views of embodiments with a light guide substrate having one output element, an intermediate prism and an input aperture much smaller than the output aperture, in accordance with the present invention;

in fig. Figure 10 shows a graph of the dependence of the reflection coefficient of incident light waves on the interface plane on the angle of incidence for three different wavelengths;

in fig. 11 shows a graph of the dependence of the angle of incidence on the interface plane of two different light waves and the critical angle of the interface plane on the wavelength;

in fig. 12A, 12B and 12B are graphs of the reflectance of incident light waves onto the interface plane as a function of the angle of incidence for three different wavelengths, and the angles of incidence of two specific light waves;

in fig. 13A, 13B, 13B and 13D are schematic cross-sectional views of other embodiments with light guide substrates having a single output element, an intermediate prism, and an input aperture whose size is substantially smaller than the size of the output aperture;

in fig. 14A, 14B, 14B and 14D are schematic cross-sectional views of still further embodiments with light guide substrates having a single output element, an intermediate prism, and an input aperture whose size is substantially smaller than the size of the output aperture;

in fig. Figure 15 shows a graph of the dependence of the reflection coefficient of incident light waves on the input surface on the angle of incidence for three different wavelengths;

in fig. 16 shows a graph of the dependence of the angle of incidence of two different light waves on the input surface on the wavelength, and the critical angle of the input surface;

in fig. 17A, 17B and 17B are graphs of the reflection coefficient of incident light waves on the input surface versus the angle of incidence for three different wavelengths, and the angles of incidence of two specific light waves;

in fig. 18A, 18B, 18B and 18D are schematic cross-sectional views of light guide substrate embodiments having one output element, two intermediate prisms, and an input aperture whose size is substantially smaller than the size of the output aperture;

in fig. 19A, 19B, 19B and 19D schematically show other cross-sectional views of embodiments with a light guide substrate having one output element, two intermediate prisms and an input aperture whose size is significantly smaller than the size of the output aperture;

in fig. 20A, 20B, 20B and 20D schematically show yet another cross-sectional views of light guide substrate embodiments having one output element, two intermediate prisms, and an input aperture whose size is substantially smaller than the size of the output aperture;

in fig. 21 is a schematic cross-sectional view of an embodiment with two adjacent substrates with different angles of inclination of the input surfaces;

in fig. 22A, 22B, 22B and 22D are schematic cross-sectional views of a single light wave introduced into a light guide substrate embodiment having two adjacent substrates;

in fig. 23A, 23B, 23B and 23D are schematic cross-sectional views of another light wave introduced inside a light guide substrate embodiment having two adjacent substrates;

in fig. 24A, 24B, 24B and 24D are schematic cross-sectional views of another light wave introduced inside a light guide substrate embodiment having two adjacent substrates;

in fig. 25 is a schematic cross-sectional view of three different light waves introduced into a light guide substrate embodiment having two adjacent substrates, an intermediate prism, and an input aperture substantially smaller than the output aperture;

in fig. 26A and 26B are schematic cross-sectional views of embodiments with a light guide substrate in which unwanted light waves reach the exit pupil of the system;

in fig. 27 is a schematic cross-sectional view of an embodiment with a light guide substrate having an array of absorption surfaces to eliminate total internal reflection from an external surface;

in fig. 28A, 28B, 28B, 28D, 28D and 28E are views illustrating a method for manufacturing a plate with an array of absorbent surfaces;

in fig. 29A and 29B are schematic cross-sectional views of embodiments with a light guide substrate in which unwanted stray rays are absorbed within the thin plate;

in fig. 30 is an image illustrating a method for expanding an output aperture along two axes using a dual-substrate design; And

in fig. 31A and 31B are schematic cross-sectional views of other light guide substrate embodiments using reflective lenses as a collimating element for polarized and non-polarized source displays.

Detailed Description of the Invention

In fig. 1 shows a cross-sectional view of a known light-transmitting substrate in which the first reflective surface 16 is illuminated by a collimated light beam 12 emanating from a display source 4 and collimated by a lens 6 located between the source 4 and the device substrate 20. The reflective surface 16 reflects incident light from the source 4 such that the light wave is channeled within the flat substrate 20 due to total internal reflection. After several reflections from the main surfaces 26, 27 of the substrate 20, the channeled light waves reach a partially reflective element 22, which outputs the light from the substrate to the observer's eye 24 having a pupil 25. In this case, the entrance aperture 17 of the substrate 20 is defined as the aperture through which the input light waves enter the substrate, and the substrate output aperture 18 is defined as the aperture through which the channeled light waves exit the substrate. In the case of the substrate shown in FIG. 1, both the input and output apertures coincide with the bottom surface 26. However, other designs can be envisioned in which the input and image light waves from the display source 4 are located on opposite sides of the substrate, or on one of the edges of the substrate. As shown in the drawing, the active areas of the input and output apertures, which respectively represent approximately the projections of the input element 16 and the output element 22 onto the main surface 26, are similar to each other.

Head-mounted display (HMD) systems require that the entire exit pupil area (EPA) be illuminated by all light waves emerging from the display source to ensure that the viewer's eye simultaneously perceives the entire field of view (FOV) of the projected image. As a result, the system's output aperture must be expanded accordingly. On the other hand, it is necessary for the optical module to be lightweight and compact. Since the transverse extent of the collimating lens 6 is determined by the transverse dimensions of the input aperture of the substrate, it is desirable that the input aperture has the smallest possible size. In systems like the one shown in FIG. 1, where the transverse dimensions of the inlet aperture and outlet aperture are the same, these requirements turn out to be internally contradictory. Most systems based on such an optical design suffer from small EMB and small achievable FOV, and also have a large and bulky imaging module.

An embodiment that at least partially solves this problem is illustrated in FIG. 2, where the element that outputs light waves from the substrate is an array of partially reflective surfaces 22a and 22b, etc. The output aperture in such a design can be expanded by increasing the number of partially reflective surfaces built into the substrate 20. In this way, it is possible to design and create an optical module having a small input aperture and at the same time a large output aperture. It can be seen from the drawing that the rays channeled by the substrate arrive at the reflective surfaces from two different directions 28, 30. In this particular embodiment, the channeled rays arrive at the partially reflective surface 22a from one of these directions 28 after an even number of reflections from the main surfaces of the substrates 26 and 27, while the angle of incidence between the channeled beam and the normal to the reflecting surface is β _ref .

The channeled rays arrive at the partially reflective surface 22b from the second direction 30 after an odd number of reflections from the substrate surfaces 26 and 27, and the angle of incidence between the channeled ray and the normal to the reflective surface is β _ref.

As further shown in FIG. 2, for each reflective surface, each ray first falls on the surface from direction 30, after which some of the rays fall again on that surface from direction 28. In order to prevent unwanted reflections and ghost images, the reflectance of rays incident on the surface from the second direction 28 should be negligible.

A solution to this requirement, using the angular sensitivity of thin film coatings, was previously proposed in the Publications mentioned above. The required selection between two directions of incidence can be achieved if one angle is significantly smaller than the other. It is possible to create a coating with very low reflectance at high incidence angles and high reflectivity at low incidence angles. This property can be used to prevent unwanted reflections and ghost images by eliminating reflection in one of two directions.

In fig. 3A and 3B illustrate the desired reflection characteristics of partially reflective surfaces 34. While ray 32 (FIG. 3A) off-axis at angle β _ref is partially reflected and exited from substrate 20, ray 36 (FIG. 3B) incident at an angle to the axis, equal to the reflective surfaces 34, is transmitted through the reflective surfaces 34 without noticeable reflections.

In fig. Figure 4 shows a curve of reflectance versus angle of incidence for a typical partially reflective surface of this particular system, for S-polarized light with a wavelength of λ=550 nm. For a color display, similar reflectance curves must be obtained for all other wavelengths in the relevant visible spectrum, which for most commonly used display sources is between 430 nm and 660 nm. There are two important regions in the graph: from 65° to 85°, where the reflection is very small, and from 10° to 40°, where the reflection increases monotonically with increasing angles of incidence. As can be seen in FIG. 3 and 4, the desired reflectance variation pattern of the partially reflective surfaces 22 of the embodiment shown in FIG. 2, is not common. Moreover, to maintain low reflection in the high-angle region, the reflectance in the low-angle region cannot be higher than 20%-30%. Further, to achieve uniform luminance across the entire field of view (FOV), it is necessary that the reflectance of partially reflective surfaces gradually increases towards the edge of the substrate and, as a result, the maximum achievable efficiency is comparatively small and cannot typically exceed 10%.

Another method of introducing light waves into and out of a light guide optical element is based on the use of diffractive elements. As shown in FIG. 5, light beams 34 and 36 are introduced into the transparent substrate 20 by a diffractive element 48, and after several total internal reflections from the outer surfaces of the substrate, the light beams are output from the substrate by a second diffraction element 50. As shown in the drawing, beam 34 is output at least twice. at two different points 52 and 54 on the element 50. Accordingly, to achieve uniformity of the output light waves, the diffraction efficiency of the element 50 must gradually increase along the ξ, axis. As a result, the overall efficiency of the optical system is even lower than that of the system shown in FIG. 2, and usually does not exceed several percent. In other words, in those shown in FIGS. 2 and 5 embodiments, a significant increase in the output aperture compared to the input aperture is achieved at the cost of a significant reduction in the efficiency of the optical module in terms of brightness, as well as complicating the substrate manufacturing process.

In fig. 6A and 6B show embodiments that overcome the disadvantages described above. Instead of using a single element (22 in FIG. 2, or 50 in FIG. 5) that is designed to simultaneously output light waves from the substrate 20 and to direct the light waves into the user's eye 24, these functions are divided between two different elements, namely, one element embedded inside the substrate leads light waves out of the substrate, while a second conventional partially reflective element located outside the substrate deflects light waves into the eye of the observer. As shown in FIG. 6A, two beams 63 (dashed lines) of a plane light wave emitted by a display source and a collimating lens (not shown) enter a light transmitting substrate 64 having two parallel main substrate surfaces 70 and 72 through an entrance aperture 86 at an angle of incidence. relative to the main surfaces 70 and 72 of the substrate. The rays fall on a reflective surface 65 inclined at an angle α _surl to the main surfaces of the substrate. The reflective surface 65 reflects incident light rays such that the light rays are channeled within the planar substrate 64 due to total internal reflection from the main surfaces. To distinguish the “order of propagation” of light waves channeled in the substrate, a subscript (i) is introduced, which determines the order of the i wave. Zero-order input light waves incident on the substrate will be designated by the index (0). After each reflection from the reflective input surface, the order of the channeled beam increases by one from . from the axis between the first order channeled beam and the normal to the main surfaces 70, 72 is

After several reflections from the surfaces of the substrate, the channeled light rays reach a second flat reflective surface 67, which leads the light rays out of the substrate. Assuming that surface 67 is inclined at the same angle to the main surfaces as the first surface 65, i.e., surfaces 65 and 67 are parallel and α _sur2 =α _sur1 , the angle α _out between the output rays and the normal to the plane of the surface is

As a result, the extracted light rays are inclined relative to the substrate at the same angle as the incident light rays. Up to this point, the injected light waves propagate similarly to the light waves shown in FIG. 1. In FIG. 6A showing two beams 68 (dash-dotted lines) having the same angles incidences similar to that of beam 63 and incident on the right side of reflective surface 65 illustrate a different propagation pattern. After two reflections from the surface 65, the light waves are introduced into the substrate 64 using total internal reflection and the angle of inclination of the channeled rays within the substrate is now

After several reflections from the main surfaces of the substrate, the channeled light rays reach the second reflective surface 67. The light rays 68 are reflected twice from the output surface 67 and exit the substrate at the same angle α _out relative to the axis as the other two rays 63, which were reflected only once. from surfaces 65 and 67, which is equal to the input angle of incidence of these four rays on the main planes of the substrate. Although all four rays enter and exit the substrate at the same angle relative to the axis, there is a significant difference between them: two light rays 68 incident on the right side of the reflective surface 65, closer to the right edge 66 of the substrate 64, are reflected twice from the surfaces 65 and 67, and are discharged from the substrate on the left side of the surface 67, which is closer to the opposite left edge 69 of the substrate. On the other hand, two light beams 63 incident on the left side of the reflective surface 65 are located closer to the center of the substrate 64, are reflected once from the surfaces 65 and 67, and exit the substrate from the right side of the surface 67 located closer to the middle of the substrate.

As also shown in FIG. 6A and 6B, the image tilt angle α _out can be adjusted by adding a partially reflective surface 79 inclined at an angle α _γed to the substrate surface 72. As shown in the drawings, the image is reflected and rotated so that it again passes through the substrate generally perpendicular to the major surfaces of the substrate and reaches the observer's eye 24 through the substrate exit aperture 89. To minimize distortion and chromatic aberration, it is desirable to embed the surface 79 in the deflecting prism 80 and supplement the substrate 64 with a second prism 82 made of the same material as the substrate, but not necessarily the same as the material of the prism 80. To obtain a minimum system thickness, possible, as shown in Fig. 6B, replace one reflective surface 79 with an array of parallel partially reflective surfaces 79a, 79b, etc., where the number of partially reflective surfaces can be determined according to system requirements. Another way to change the direction of light waves output into the observer's eye is to use a flat meta-surface, the structure of which is determined by a characteristic size less than the wavelength.

In the embodiments shown here, it is assumed that only first- and second-order angular waves propagate within the substrate. There are, however, systems that have a relatively small angle α _sur of inclination of the input and output surfaces, in which even third and fourth orders can be used.

As shown in FIG. 6B, the input beam 71 is incident on the substrate 64 at an angle to the axis After three reflections from the surface 65 at points 75a, 75b, 75c, this beam is introduced into the substrate and propagates inside at an angle third order. After several reflections from the main planes of the substrate 64, the beam 71 is incident on the surface 67. After three reflections from the surface at points 77a, 77b and 77c, the beam exits the substrate 64 at an angle to the axis. Next, the light beam 71 is reflected by the surface 79a generally perpendicular to the main surface of the substrate into the eye 24 of the observer. Typically, for systems that have a small number of orders entering the substrate, the lower order will be introduced into and out of the substrate on parts of the reflective surfaces located closer to the edges of the substrate, the higher order will be introduced and introduced on parts of the reflective substrates closer to the center of the substrate, in while the middle order will be input and output through the central parts of the input and output surfaces.

There are two conflicting requirements regarding the terminal surface 67 portion. On the one hand, images the first three orders must be reflected from this plane, while on the other hand, the image zero-order from the substrate 64 should pass through it without significant reflections, after reflection from the surface 79. In addition, for systems providing see-through vision, the transparency of the optical system for a light beam 83 incident almost normally from the external scene should be as high as possible. This can be achieved by using an air gap in the surface 67. To construct a rigid system, it is preferable, however, to apply an optical adhesive to the surface 67 to bond the substrate 67 to the prism 82, using an optical adhesive with a refractive index significantly lower than that of the substrates. There are, however, situations where an optical adhesive with a refractive index that provides the required total internal reflection for the entire input FOV is required, a very small value - on the order of 1.31-1.35. Optical adhesive with the required refractive index is available on the market, but the adhesive strength provided is insufficient and its resistance to external influences is also insufficient for military and special applications. An alternative solution is to deposit a thin film of dielectric material on the surface 67 using spin coating. The refractive index of the applied coating material is significantly lower than that of the substrate and must be of a suitable value that provides the required total internal reflection from the surface 67 for the entire FOV. The substrate 64 can now be bonded to the prism 82 with an optical adhesive having the desired adhesive strength and environmental resistance, and its specific refractive index can be of any reasonable value.

In any of the proposed methods of minimizing the Fresnel reflection of passing light waves from the terminal surface 67, it is desirable to apply an anti-reflective coating to this surface (AR). In this case, the overall efficiency of transmission of light waves through the substrate can be very high, namely, the reflectance of the surface 67 extracting light waves from the substrate is 100% due to the total internal reflection from this surface, while the transmission of light waves by this surface , reflected from the surface 79, as well as light rays from the external scene are also close to 100% thanks to the AR coating. Likewise, it is desirable to adhere the prism 80 to the bottom surface 72 of the substrate 64 to form an interface plane 81 using an optical adhesive with a refractive index substantially lower than that of the substrate, while a suitable AR coating is applied to the interface plane. Again, total internal reflection from surface 72 can be achieved by coating that surface with a suitable material by spin coating the coating and using a conventional optical adhesive to adhere prism 80 to surface 72. As a result, the brightness of the light waves output by surface 67 from the substrate is similar to that of input light waves before they are introduced into the substrate by the surface 65, and the only factor reducing their brightness is partial reflection from the surface 79. As a result, the brightness transmission efficiency in the embodiment shown in FIG. 6A-6B may be an order of magnitude higher than the efficiency of the designs shown in FIGS. 2 and 5.

As shown above in relation to FIG. 6A, in systems that provide see-through vision, such as head-mounted displays in augmented reality applications in which the viewer can see an external scene through a substrate, the partially reflective surfaces 79 must be at least partially transparent to transmit external light rays 63 and 68 through the substrate and into the eye of the 24 observer. Because the surfaces 79 are only partially reflective, only a portion of the input light waves 63 and 68 are reflected by the surfaces 79 and reach the observer's eye, while another portion of the light waves 84 pass through the surfaces 79, are output from the prism 80, and do not reach the observer's eye. Likewise, since the surfaces 79 are only partially transmissive, only a portion of the external light rays 83 pass through the surfaces 79 and reach the observer's eye, while the other portion of the light rays 85 are reflected from the surfaces 79, exited from the prism 80, and also do not reach the observer's eye. . Naturally, the efficiency of the projected image can be increased by the external scene and vice versa, namely, as the reflectance of the partially reflective surfaces 79 increases, the brightness of the output beams 63 and 68 increases. As a consequence, however, the transmittance of the surfaces 79 decreases and, consequently, the brightness of the external image 83 decreases accordingly.

Unlike the embodiments shown in FIGS. 1-5, the surface 79 that reflects the output light from the substrate to the observer's eye while transmitting external rays is a conventional partially reflective mirror and does not have any special or complex characteristics like the surfaces 22 and 50 of the embodiments shown in FIGS. 2 and 5, respectively. This makes it possible to dynamically control the reflectance (and hence transmittance) of the partially reflective surfaces 79 according to ambient lighting conditions and the image being projected into the viewer's eye. One way to control the reflectance of surfaces 79 is to use an electrically switchable active-passive mirror, which is a solid-state thin-film device made of a special liquid crystal material that can be quickly switched between states of total reflection, partial reflection and full transmission. Another way to create a switchable element 79 is to form it as a dynamic metasurface. The desired state of the switchable mirror can be set either manually by the user or automatically using a photometer that controls the reflectance of the mirror according to the external brightness. This property can be useful in environments where the projected image is appropriately aligned with the external scene, but the brightness of the external scene is relatively high and therefore must be greatly suppressed to avoid blinding the viewer or interfering with the projected image. On the other hand, the efficiency of the projected image must be high enough to achieve reasonable contrast. Therefore, the dynamic surface 79 can be switched to a primary reflection state when the reflectance of the switched mirror is significantly higher than its transmittance. As a consequence, the light rays 63 and 68 extracted from the substrate are preferentially reflected from the surface 79 into the eye of the observer, and the overall efficiency of the optical system can exceed 90%, while a bright external scene will be clearly visible. As a result, the potential luminance efficiency of the embodiment shown in FIG. 6A-6B can exceed the efficiency of the designs shown in FIGS by more than an order of magnitude. 2 and 5.

As shown in FIGS. 6A-6B, the aperture of the input surface 65 is equal to the aperture of the output surface 67. As a result, the active area of the input aperture 86 is equal to the active area of the output aperture 89. As a result, although the potential luminance efficiency of the embodiment shown in FIG. 6A-6B can be very high, there is still a disadvantage of equal input and output apertures. Therefore, it is necessary to find a way to reduce the input aperture for a given value of the output aperture, or, otherwise, to increase the output aperture for a given value of the input aperture. To solve this problem, the fact that light waves output from the substrate does not necessarily have to illuminate the entire active area of the input surface is used.

In fig. 7 shows the rays that must strike the exit aperture surface 89 to illuminate the exit pupil (EMP) 100, including the two outermost and central image light waves that are output from the substrate and deflected into the observer's eye 24. As shown, light waves 107B, 107M and 107L having angles from the zero order axis, being the minimum, central and maximum angles of the FOV, respectively, illuminate only portions 67R, 67M and 67L of the reflective output surface 67, respectively, and are reflected by the surface 89 in the EMB 100. Thus, a method can be formulated in which the input the substrate aperture will be substantially reduced so that the injected waves illuminate only the desired corresponding portion of the surface 67 and therefore the original brightness will be maintained.

In fig. 8A-8D show the return path of three light waves from the EMB to the input aperture 86 of the substrate 64. As shown, the light wave 107L (dash-dotted lines in Fig. 8A) incident on the right side of the surface 65 is channeled by the substrate at an angle on-axis after three reflections from the surface 65, is output from the substrate after three reflections from the surface 67, and the third reflection, which outputs the light wave from the substrate, occurs on the left side of the surface 67. The light wave 107M (dashed line in Fig. 8B) is incident on the central part of the surface 65, channeled by a substrate with an angle after two reflections from the surface 65 and is output from the substrate after two reflections from the surface 67, the second reflection, which outputs the light wave from the substrate, occurring in the central part of the surface 67. Light wave 107B. (dashed lines in Fig. 8B) falls on the left side of the surface 65, is channeled in the substrate with an angle off-axis after one reflection from surface 65 and exits the substrate after one reflection from the right side of surface 67. As shown in FIG. 8D, the lateral surface area of the input aperture 86 covering the incoming light waves over the full EOV is equal to this area of the output aperture 89 and, therefore, in this embodiment, the problem of reducing the input aperture 86 has not been solved.

It should be noted, however, that although the incoming waves cover a significant entrance aperture, they are incident on the entrance aperture in an orientation opposite to that of a conventional optical system. In other words, when light waves are traced back from the input aperture 86, instead of diverging, they converge, moving closer to each other. As a result, an intermediate prism can be added to the optical system, which will allow the traced light waves to be converged into a pupil of a significantly smaller size compared to the entrance aperture 86.

In fig. 9A-9D show the embodiment shown in FIG. 8A-8D, in which an intermediate prism 108 is attached to the substrate at the entrance aperture 86. A surface 110 of the prism 108 may be optically coupled to the top surface 70 of the substrate 64 to form an interface plane 111. To reduce chromatic dispersion, the optical material of the prism 108 must be similar to the material of the deflecting prism 80. In addition, the surface 112 of the prism 108 onto which the light waves are incident must be oriented so that the incoming waves 107R, 107M and 107L are incident on the surface 112 under the same angles at which they are projected from the substrate 64 through the top surface 70 into the observer's eye 24. Moreover, surface 112 must be located in a plane where the back-tracing light waves have a minimum aperture. As shown in FIG. 9D, incoming light waves impinging on surface 112 inside a new input aperture 86', the size of which is significantly smaller, more than half the size of the original input aperture, as well as the output aperture 89.

The section plane 111 places conflicting demands on the intermediate prism 108 and the substrate 64. On the one hand, the images the first three orders must be reflected from this plane, while the image ' of zero order entering the substrate 64 through the intermediate prism 111 should generally pass through it without significant reflections. Likewise, the interface plane 81 between the substrate 64 and the deflection prism 80 must be transparent to output light waves having an entrance angle after the last reflection from the surface 67, and, at the same time, should well reflect the introduced light waves having entrance angles In addition, for systems providing through vision, the transparency of the optical system under normal (perpendicular) light incidence through the section plane 81 should be as high as possible. The preferred method of solving this problem is to apply to these section planes an optical adhesive whose refractive index is significantly less than the refractive index of the substrate or, in another case, to apply a thin film having the desired refractive index to the section plane 81 using spin coating technology. In addition, to minimize Fresnel reflections of transmitted light waves from the interface planes 81 and 111, it is preferable to apply a suitable anti-reflection (AR) coating to these planes. In this case, the overall transmission efficiency of light waves interacting with these planes can be very high. In other words, the reflectance of plane 111 when light waves are introduced into the substrate is 100% due to total internal reflection from this surface, while the transmittance of this surface to incident light waves is also close to 100% due to the presence of the AR coating. Likewise, the reflectance of light waves introduced into the substrate 64 from the surface 81 is 100% due to total internal reflection from that surface, while the transmittance of that surface for light waves output from the substrate 64 into the deflection prism 80, as well as for incoming light waves from the external scene are also close to 100% due to the presence of AR coating.

For most imaging systems for this purpose, both requirements must be met across the entire visible spectrum. It is therefore natural that the Abbe number (dispersion coefficient) of the optical adhesive (or otherwise the spin-applied thin film) adjacent to the interfaces and the optical substrate material should be close to prevent unwanted chromatic effects in the image. To achieve the effect of total internal reflection, the refractive indices of the substrate and the adhesive (or thin film) must be significantly different. As a result, it can be very difficult to meet this requirement and usually the Abbe numbers of the adhesive (or thin film) and the optical material are significantly different. Chromatic dispersion due to differences between Abbe numbers can, however, be compensated for by the choice of optical material for the input and deflection prisms 108 and 80, the Abbe number of which is different from the Abbe number of the substrate 64. When properly selected, the difference between the Abbe numbers can cause chromatic dispersion, having the same size and opposite direction. As a result, the two induced chromatic dispersions will cancel each other out.

Another issue to consider concerns the maximum achievable FOV of the image projected into the viewer's eye. In most head-mounted display (HMD) designs with a light guide substrate, both reflective and diffractive, light waves are coupled from the guide substrate substantially normal to the major surfaces of the substrate. As a result, due to the influence of Snell refraction from the substrate, the external field of view (FOV) of the image is:

where the FOV inside the substrate is , and the refractive index of the substrate is v _s . In addition, the orders of light waves introduced into the substrate must be strictly separated, namely

In addition, to ensure the transmission of all zero order through the separation planes 81 and 111 and the reflection of all first order from these planes, the following constraint must be satisfied

where α _cr is the critical angle for the interface planes. So the inner FOV is limited by the condition

where usually to confirm the division between two orders of magnitude is the difference between the angles should be maintained at about one degree.

The limitation established by expression (4) applies to systems in which the refractive indices of the substrate and the input and output elements are the same. To alleviate these limitations, the fact that optical light waves enter the substrate 64 from the intermediate prism 108 at very sharp angles can be used. As shown in FIG. 9A-9G, the intermediate prism 108 and the deflecting prism 80 are made of the same optical material, the refractive index of which has the following optical property

where v _p is the refractive index of the 108 and 80 prisms. In addition, the Abbe numbers A _p , A _{s of} the prisms and the substrate, respectively, are chosen to compensate for the chromatic dispersion induced by the difference between the Abbe numbers of the substrate and the optical adhesive (or thin film), as explained above.

As a result of the differences between the optical materials of the substrates 64 and the intermediate and deflecting prisms 108 and 80, and the very acute angles that the incident rays 107R, 107M and 107L form with the interface planes 111 and 81, light waves experience significant refraction when passing through the interfaces. Since the prisms 108 and 80 have the same optical parameters, the refraction at the surfaces 111 and 81 for each passing light wave is of the same magnitude and opposite directions, respectively, and therefore they will cancel each other out. The angle of deflection between two different light rays inside the prisms as a function of the deflection inside the substrates can be calculated using the following approximate expression

where α _s and α _p are the angles of deviation from the axis inside the substrate and prisms, respectively. Similarly, the angle of deflection between the rays in the air will be

Therefore, the ratio between the angle of deflection in air and inside the substrate 64 will be

or

In other words, by changing the optical material of the prisms 108 and 80, it is possible to increase the FOV of the system in air at once.

An implementation of the embodiment shown in FIG. 9A-9D, is illustrated here by an optical system having the following design parameters:

where the light waves are not polarized, the optical material of the substrate 64 is Ohara S-LAH88 with a refractive index v _d =1.917 and Abbe number A _d =31.6, the optical material of prisms 81 and 111 is Schott N-BK7 with a refractive index v _d =1.516 and Abbe number A _d =65.5, optical glue adjacent to surfaces 81 and 111 in FIG. 9A-9D is NOA 148, having a refractive index v _d =1.48 and an Abbe number A _d =48. As shown in the drawings, the FOV is 40° in air, 26° inside prisms 111 and 81, and 13° inside substrate 64. Thus, the field of view in air is more than triple that of the substrate, even though that the refractive index of the substrate is less than 2. The maximum angle in the third order exceeds 90° and, therefore, this direction of propagation is “forbidden”. As shown in FIG. 9A-9B, the third order is realized only for light waves in the lower FOV region. Light waves in the upper FOV region are introduced into the substrate after one reflection from the input surface 65 and, therefore, propagate only in the first order of propagation, which does not lead to the noted contradiction.

In fig. Figure 10 shows curves of the reflection coefficient AR of the coating deposited on interface surfaces 81 and 111 versus the angle of incidence. As a result of chromatic dispersion due to differences between the Abbe numbers of the substrate 64 and prisms 81 and 111, a strong dependence of the critical angle on wavelength is observed. In this case, the condition

must presumably be satisfied over the entire relevant visible spectrum to satisfy the condition expressed by equation (5). In other words, the field of view inside the substrate must be reduced to 12° and therefore the FOV in air will be reduced to 36°.

The high dispersion of the light waves entering the substrate 64 through the intermediate prism 111 causes each incoming white light wave to be spatially separated into components of different wavelengths. For example, the extreme light wave 107R with an off-axis angle of 20° for the entire visible spectrum is divided into propagation directions of 36.2°, 36.6° and 36.8° for zero-order light waves having wavelengths of 450 nm, 550 nm and 650 nm, respectively. The exact values of the parameters given in expression (13) for three different wavelengths are

where the subscripts sb, sg and sr denote the parameters of the light waves within the substrate 64 having wavelengths of 450 nm, 550 nm and 650 nm, respectively, and the subscripts surb, surg and surr denote the parameters of the incoming light waves incident on the input surface 65, having the same wavelengths, respectively.

In fig. 11 directions presented propagation, as well as the critical angle α _cr , in the form of a function of wavelength for the entire visible spectrum under consideration. It is shown that for the full spectrum, the requirements given in equations (5)-(6) are satisfied without complying with the restrictions of equation (14), and fields of view of at least 13° in the substrate and 40° in air are maintained.

In fig. 12A-12B show reflectance curves of the AR coating applied to interfaces 81 and 111 for wavelengths of 450 nm, 550 nm and 650 nm, respectively, in which two vertical lines on the graph indicate propagation directions for each corresponding wave. As shown in the graphs, for all wavelengths the reflectance for the angle is 100% as a result of total internal reflection from the interface plane, while the transmission for the angle negligible, which is what was required.

In fig. 9A-9D show an embodiment with a wide field of view of 40° along the direction of propagation of light waves within the substrate 64, even when using only one output element 67. The directions of arrival of the input light waves are, however, at very sharp angles. In many applications, it is required that incoming light waves strike the substrate substantially normally to the major surfaces 70 and 72 of the substrate. In fig. 13A-13B show a structure in which the leftmost 107L, center 107M, and rightmost 107R light waves, respectively, are incident on the substrate at right angles to the bottom surface 72. As shown in the drawing, the light waves enter the substrate and pass through the input surface 65 . Since the angles of incidence of the input light waves are quite small, and the surface 65 is coated with an anti-reflection coating, the reflection of light waves from this surface will be negligible. Light waves exiting the substrate 64 enter the intermediate prism 114 through its lower surface 116 attached to the upper surface 70 of the substrate, are reflected from the reflective surface 118, and reenter the substrate 64 through its upper surface 70 at the entrance angle. .

Light waves now fall on the input surface 65 at angles of incidence which are greater than the critical angle, and are introduced into the substrate in a similar manner, as shown above with reference to FIG. 9A-9G. As shown in FIG. 13D, light waves throughout the entire FOV are incident on the surface 72 within the new entrance aperture 86', which is significantly smaller, at least three times smaller, than the original entrance aperture 86, as well as the exit aperture 89. In this case, the entrance aperture 86' is not located nearby intermediate prism 114, but is located rather near the lower main surface 72 of the substrate. In general, the optical system should be designed such that the input aperture is located in a convenient location for the outer surface of the collimating module.

In the embodiment shown in FIG. 13A-13D, light waves are incident on the substrate at surface 72, and the light waves exit the substrate into the viewer's eye through the opposite surface 70, since the viewer's eye and the display source are located on opposite sides of the substrate. This arrangement is preferred for top-down viewing, however, there are other applications, such as eyeglasses, that require the viewer's eye and the display source to be on the same side of the substrate.

In fig. 14A-14B show a design in which the leftmost 107L, center 107M, and rightmost 107R light waves, respectively, are incident on the substrate substantially normally to the top surface 70, on the same side as the observer's eye. The figure shows the added lens 6 illustrating the ability to collimate light waves coming from the display source 4. The light waves are shown to enter the substrate and pass through the input surface 65 without significant reflections. Light waves exit the substrate 64, enter the intermediate prism 120 through its top surface 124 attached to the bottom surface 72 of the substrate, reflect from the reflective surface 122, and reenter the substrate through the bottom surface 72. The light waves again strike the input surface 65 at an angle incidences less than the critical angle pass through the surface 65 and are completely reflected from the top surface 70 of the substrate. Light waves again fall on the input surface 65, now at an angle exceeding the critical angle, and are introduced into the substrate in the same way as described above in relation to FIG. 13A-13B. As shown in FIG. 14D, light waves throughout the entire field of view are incident on a surface 70 within a new entrance aperture 86' located adjacent to the outer surface of a collimating lens 6 having a significantly smaller size than the original entrance aperture 86.

Unlike other construction schemes discussed previously, in the embodiment shown in FIG. 14A-14D, light waves are incident on the input surface 65 three times. For the first time, the requirement that light waves pass through the surface 65 without noticeable reflections can be easily fulfilled by coating the surface 65 with an AR coating. For the other two incidences, however, there are two conflicting requirements imposed by the surface 65. On the one hand, the light waves incident on this surface for the third time have angles falls must be reflected from this surface. On the other hand, light waves hit this surface for the second time, having angles falls should pass through it quite well without significant reflections. A preferred method of accomplishing this task, as described above with respect to the interface planes 81 and 111, is to spin-coat the input surface 65 with an optical adhesive or thin film having a refractive index that is significantly lower than the refractive index of the substrate. In addition, to minimize Fresnel reflections of light waves incident on the surface 65 a second time, it is necessary to apply a suitable AN coating to the sodium surface.

In fig. 15 shows curves depending on the angle of incidence of the reflectance AR of the coating deposited on the input surface 65 for a substrate having the following parameters: light waves are unpolarized, the optical material of the substrate 64 is Ohara S-LAH98 with a refractive index v _d =1.954 and Abbe number A _d =32.32, the optical adhesive adjacent to the surface 65 is NOA 1315 with a refractive index v _d =1.315 and an Abbe number A _d =56. As a result of chromatic dispersion due to differences in the Abbe numbers of the substrate 64 and the optical adhesive, the critical angle is highly dependent on wavelength.

In fig. 16 directions presented propagation, as well as the critical angle α _сγ , in the form of a dependence on wavelength for the entire visible spectrum under consideration. It is shown that for the full spectrum there is a difference between the angular spectrum of the second and third incidences, and the spectra are located respectively below and above the critical angle curve, as required.

In fig. 17A-17B show reflectance curves of the AR coating applied to the input surface 65 for wavelengths of 450 nm, 550 nm and 650 nm, respectively, in which two vertical lines on the graph indicate propagation directions And for each corresponding wave. As shown in the graphs, for all wavelengths the reflectance for third incidence with angle of incidence is 100% as a result of total internal reflection from the interface plane, while the transmittance for the second incidence with the angle of incidence negligible, which is what the axis required.

While in FIG. 13A-13D and 14A-14D show embodiments in which the input light waves are incident on the substrate substantially normal to the major surfaces; there are designs that require the input light waves to be oriented at an acute angle to the substrate. FIGS. 18A-18D show a modified version of the embodiment shown in FIGS. 13A-13G. Light waves illuminating the substrate at a predetermined angle enter the substrate through the surface 128 of the first intermediate prism 126 attached to the bottom surface 72 of the substrate 64 and pass through the input surface 65 without significant reflections. The light waves then exit the substrate 64, enter the second intermediate prism 132 through the bottom surface 136 attached to the top surface 70 of the substrate, are reflected by the reflective surface 134, and return to the substrate 64 through its top surface 70. The light waves are reflected by the input surface 65 and are channeled internally. substrates in the usual manner, as shown above with reference to FIG. 13A-13G.

In fig. 19A-19D show a modified version of the embodiment shown in FIG. 14A-14G. Light waves illuminating the substrate 64 at a predetermined angle enter the substrate through the surface 140 of the first intermediate prism 138 attached to the upper surface 70 of the substrate and pass through the input surface 65 without significant reflections. Light waves exiting the substrate 64 enter the second intermediate prism 144 through its upper surface 148 attached to the lower surface 72 of the substrate, are reflected from the reflective surface 146, and reenter the substrate 64 through its lower surface 72. Next, the light waves again fall onto the input surface 65 at angles Incidents less than the critical angle pass through surface 65 and are completely reflected from the top surface 70 of the substrate. Light waves again fall on the input surface 65, now at angles incidences exceeding the critical angle and are channeled inside the substrate in the same way as described above with reference to FIG. 14A-14B.

In fig. 14A-14D and 19A-19D show embodiments that may be used in eyewear construction. There are, however, cases, particularly in consumer products applications, where aesthetic considerations require that the folding prism attached to the front surface of the substrate 72 be kept to a minimum size. In fig. 20A-20D show modified versions of the embodiments shown in FIGS. 14A-14D and 19A-19D, in which light waves illuminating the substrate 64 at a predetermined angle enter the substrate through the surface 228 of the first intermediate prism 226 attached to the top surface 70 and pass through the input surface 65 without significant reflections. Light waves exiting the substrate 64 enter the second intermediate prism 220 through the upper surface 224 attached to the lower surface 72 of the substrate, are reflected from the reflective surface 222, and reenter the substrate 64 through its lower surface 72. Here, however, the angle of inclination reflective surface 222 relative to main surface 72 is significantly less than the angle of inclination of surfaces 122 and 146 in the designs shown in FIGS. 14A-14G and 19A-19G, respectively. As a result, light waves again fall on the input surface 65 at angles , where ε is an angle determined by design considerations, but usually greater than 5°. Now even the maximum angle the incidence is significantly less than the critical angle and, therefore, a simpler AR can be applied to the surface 65. Light waves continue to pass through the surface 65, re-entering the first intermediate prism 226 through its lower surface 230 attached to the upper surface 70 of the substrate. The waves are then completely reflected from the outer surface 228 and reenter the substrate 64 through its lower surface 72. The angle of the surface 228 is selected to compensate for the missing angle ε. As a result, light waves with an angle greater than the critical one, now having angles fall, fall again onto the input surface 65 and are inserted into the substrate in the same way as was described in relation to FIG. 14A-14B and 19A-19G.

In all of the embodiments described above, a large field of view of 40° along the propagation direction within the substrate was achieved using a single lead surface 67. In designs with side image input, such as glasses, the FOV diagonal can be 47° or 50°, depending on the format of the display source (9:1 6 or 3:4, respectively). For top-down designs, such as head-mounted displays, the diagonal FOV can be extended to more than 80° for a 9:16 source format. Assuming that to achieve maximum brightness efficiency, it is preferable to use a single output surface, for angular orientation This surface poses two contradictory requirements. On the one hand, as a result of the limitations imposed by equation (7), it is preferable to increase the angle to increase the total FOV that can be introduced into the substrate. On the other hand, the extension of the substrate exit aperture 89 is proportional to where d is the thickness of the substrate, namely, the exit aperture, and thus the exit pupil, will be increased by contraction . It is also possible to increase the output aperture by increasing the thickness of the substrate, but the input aperture will increase accordingly. In addition, the substrate is usually required to be as thin as possible.

In fig. 21 is a modified version of the embodiment shown in FIG. 14A-14G. Instead of using a single substrate 64, a system 150 is provided comprising two adjacent substrates 64a and 64b. The upper surface 70b of the substrate 64b is optically bonded to the lower surface 72a of the substrate 64a to form an interface 152. Corner the input and output surfaces 65b and 67b are set to the desired FOV in accordance with equation (7), while the angle input and output surfaces 65b and 67b are set to the lower value

As a result, the entire field of view can be introduced inside the lower substrate 64b. To meet the requirements of equation (7), however, only a portion of the FOV may be introduced into the top substrate 64a. In other words, the fields of view inside the two substrates are determined by the expressions

Bottom part is introduced only into the lower substrate 64b, and in order to avoid crosstalk with the upper part of the FOV, it is not introduced into the upper substrate 64a. Since light waves from the bottom of the FOV illuminate the viewer's eye from the left side of the output aperture, they must be output from the left output surface 67b, that is, they must be transmitted to the eye only through the bottom substrate 64b.

So the full FOV can be stored for the entire exit pupil. In addition, the output aperture increases by the amount

Conversely, for a given output aperture, the thickness of the double substrate may be less in relation

Where represent the thicknesses of the substrates 64a and 64b, respectively, ad is the thickness of one substrate, for example, in the embodiment shown in FIG. 14A-14B. Therefore, an advantage of the embodiment in FIG. 21 consists of a wider field of view defined by a larger angle , as well as a larger output aperture, determined by a smaller angle . Since each of the two substrates 64a and 64b operate independently, each individual substrate may have different parameters other than the deflection angle. The two substrates may have, among other things, different thickness, refractive index and Abbe number, according to the requirements of the optical system. Moreover, the relative position of the input surfaces 65a and 65b, as well as the output surfaces 67a and 67b, can be freely adjusted to obtain a minimum input aperture 86' (see FIG. 25) and at the same time a maximum output aperture 89 (see FIG. 25) systems.

As shown in FIG. 22A, 22B and 22B, respectively, three beams from the leftmost light wave 153 (153a, 153b, 153c) are introduced into the lower substrate 64b after three reflections from the surface 65b, one beam 153d (Fig. 22B) is introduced after two reflections, and two other beams, 153e, 153f (Fig. 22B) are introduced after one reflection from the surface 65b. As shown in FIG. 22D, all rays are output from the substrate 64b by the output element 67b and deflected to illuminate the entire exit pupil 100.

In fig. 23A, 23B and 23B, respectively, show two beams from the central light wave 154 (154a, 154b) introduced into the lower substrate 64b after one reflection from the surface 65b, and output by the surface 67b, two beams (154c, 154d) introduced into the upper substrate 64a after three reflections from the surface 65a and are output by the surface 67a, and two other beams 154e, 154f (Fig. 23B) are introduced into the upper substrate 64a after two reflections from the surface 65a and are output by the surface 67a. As shown in FIG. 23D, all three beams are deflected by a deflection prism 80 to illuminate the entire exit pupil 100.

In fig. 24A shows two beams from the rightmost light wave 155 (155a, 155b) introduced into the top substrate 64a after two reflections from surface 65a, and three other beams, 155c, 155d, 155e, introduced after one reflection from surface 65a. As shown in FIG. 24B, all three beams are output from the substrate 64a by the output member 67a and are deflected to illuminate the full exit pupil 100. As shown in FIG. 25, full FOV light waves incident on the surface 70 within the entrance aperture 86', which is substantially smaller than the exit aperture 89, illuminate the entire exit pupil.

Another issue that needs to be considered is the ghosting that can be observed in the image as a result of unwanted reflections of stray rays from the external surfaces of the system. As shown in FIG. 26A, the input beam 160 is introduced into the substrate 64 after one reflection from the surface 65, and then exits the substrate after one reflection from the surface 67. The light beam is then partially reflected by the surfaces 79i and 79j as output beams 160a and 160b into the eye of the observer in the "proper" " direction. Part of the beam 160, however, passes through the surface 79j, is completely reflected from the lower surface 162 of the prism 80, is then partially reflected from the surface 79k, passes through the substrate 64, is completely reflected from the upper surface 70 of the substrate 64, passes through the substrate 64 again, then which is partially reflected from the surface 79 t in the form of an output beam of 160 s into the eye of the observer in the “wrong” direction. In other words, the scattered beam 160 s will appear as a ghost image in the projected image. In fig. 26A shows such a ghost image generated by the light waves of the input image. Other ghost images may, however, arise as a result of light waves from the external scene. As shown in FIG. 26B, the outer beam 163 passes through the partially reflective surface 79n, passes through the prism 80 and the substrate 64 and reaches the eye of the observer, having the original direction as the beam 163a. Part of the beam 163, however, is partially reflected from the surface 79n, fully reflected from the bottom surface 162 of the prism 80, partially reflected from the surface 79o, passes through the substrate 64, fully reflected from the top surface 70 of the substrate 64, passes through the substrate 64 again and is then partially reflected from the surface 79p as an output beam 163b into the observer's eye in the "wrong" direction. Thus, the scattered beam 163b will also be present as a ghost image in the projected image.

As shown in FIG. 26A and 26B, the main cause of ghost images is unwanted reflections from the surface 162. This phenomenon is typical not only of the embodiments presented herein, but also of other light guide substrate designs. Unlike these other designs, total internal reflection from surface 162 is not necessary for light wave propagation within the substrate and can therefore be eliminated entirely. A possible way to eliminate unwanted reflections from surface 162 is to apply an absorbent layer to the substrate. This simple method can be used for systems that do not provide see-through vision, where the outer surface 162 can be completely opaque. For systems providing see-through vision, since light rays from the external scene must pass through the surface 162 to enter the viewer's eye 24, the surface 162 does not need to be opaque.

In fig. 27 illustrates a more efficient method of removing total internal reflection from surface 162 while maintaining high transparency of the surface to light rays from the external scene. As shown in the drawing, the upper surface 166 of a thin flat transparent plate 167 is optically bonded to the lower surface 162 of a deflecting prism 80. Enclosed within the plate 167 is a lattice of parallel absorbing surfaces 168 ₁ , 168 ₂ ... oriented normal to the surface 166 to ensure that these surfaces absorb all of light rays incident on surface 162, the following ratio must be observed:

where T is the thickness of the plate 167, D is the distance between two adjacent surfaces _168i and 168i ₊₁ , and is the minimum angle of deviation from the normal of light waves incident on the plate 167. As shown in the drawing, beam 171 is absorbed by surface 168 _i after total reflection from the bottom surface 169 of plate 167, while beam 172 is absorbed when directly incident on surface 168 _j . Because the substrate 64 is thin and the absorbing surfaces are normal to the major surfaces of the substrate and therefore to the viewer's line of sight, the plate 167 remains highly transparent to light rays from the external scene.

In fig. 28A-28E illustrate a method for manufacturing the plate 167. A large number of transparent thin plates 174 _i having a thickness D are manufactured (FIG. 27). Since the main surfaces of these plates must be absorbent, there is no need to polish them and their parallelism is not critical. A thin absorbent layer 175 is applied to one of the main surfaces of each plate (Fig. 28B). This absorbent layer may be, but is not limited to, black paint, a thin silicon coating, a metal coating, or a coating of any absorbent material that can be applied in a thin layer. The plates 176 are then bonded using optical adhesive to form a stack (FIG. 28B). A number of segments are then cut from the plate stack 176 (Fig. 28D) in the direction normal to the main surfaces of the plates 174 _i , after which cutting, grinding and polishing are performed to obtain plates having thickness T' (Fig. 28D). One of the main surfaces of the plate is glued with optical glue to surface 162 (Fig. 28E). In many cases, the plate 167 is required to be very thin, on the order of 0.1 mm. In this case, it may be difficult to machine the plate 167' to the desired thickness T. Therefore, the plate having a thickness T'>T is bonded to the prism 80 and the bottom surface 169' of the bonded plate 167'' will be ground and polished to obtain the desired thickness. thickness T of the resulting plate 167.

In fig. 29A and 29B show embodiments similar to those shown in FIGS. 26A-26B, where the plate 167 is attached with optical adhesive to the bottom surface 162 of the prism 80. As shown in the drawing, instead of being completely reflected from the surface 162 and continuing to propagate through the system, the scattered light rays 160c and 163b are absorbed in the plate 167 and therefore , ghost images arising from the projected image as well as the external scene are completely eliminated. This method of attenuating spurious images resulting from unwanted total internal reflection can also be applied to other optical modules in which stray light rays are spuriously reflected from a surface that should be transparent to normally incident light. The plate 167 can thus be attached with optical adhesive to such a surface to suppress unwanted reflections while maintaining the desired transmittance of the surface.

The advantages of reducing the transverse size of the input aperture described above become even more obvious if the aperture of the input light waves is required to be expanded in two planes. In fig. 30 schematically illustrates a biaxial beam expansion method using a double substrate design. For simplicity, intermediate prisms and deflecting elements are omitted in the drawing. The input image 256 is introduced through the input aperture 274 into the first substrate 264a, the same structure as one of the above embodiments, through the first reflective surface 265a, and then propagates along the η axis. The output element 267a outputs light from the substrate 264a through the output aperture 276, after which the light is introduced into the second main substrate 264b by the input element 265b through the input aperture, which coincides with the output aperture 276 of the first substrate 264a. The light waves then propagate along the ξ-axis and are output by the output element 267b through the exit aperture 278. As shown in the drawing, the original image 256 expands along two axes, with the overall expansion being determined by the ratio between the transverse dimensions of the apertures 274 and 278. It can be seen that each light wave (represented in the drawing by a single arrow) illuminates only part of the exit aperture 278, but all light waves are output into the exit pupil 100 in the desired directions.

In all embodiments discussed above, the display source was assumed to be non-polarized. There are, however, microdisplays, such as LCDs or silicon LCDs, whose light is linearly polarized, and this can be used to create a more compact collimating system. In fig. 31A shows that p-polarized input waves 107L, 107M, and 107R from the display light source 4 are coupled into a light guide 279, typically made of a light transmitting material, through its surface 280. The light waves pass through a polarizing beam splitter 282 and are output from the light guide. 279 through the surface 283. The light waves then pass through the quarter-wave slow phase plate 285, are collimated by the lens 286 on its reflective surface 289, return back to the slow wave plate 285 passing through it, and re-enter the light guide 279 through the surface 283. Now s-polarized the waves are reflected from the polarization beam splitter 282 and exit the light guide through the bottom surface 290. The light waves are then introduced into the substrate 64 through the intermediate prisms 226 and 220 in the same manner as previously shown in connection with FIG. 20A-20G. The reflective surface 289 may be implemented using a metal or dielectric coating.

Use of the reflective collimating lens 286 shown in FIG. 31A has some significant advantages, for example, achieving high performance due to the use of a small number of optical components due to additional compact collimating modules, etc. It is therefore advantageous to use this embodiment also for non-polarized light sources, for example based on Micro LED and Micro OLED. In this case, the main disadvantage is that only a single-polarization source-display component can be used and therefore the achievable brightness is reduced by more than half. In fig. 31B illustrates another method of using two orthogonal polarization components of an unpolarized source-display without losing image brightness. As shown in the drawing, the input light wave components 107L, 107M and 107R from the s-polarized display light source 4 are introduced into the light guide 279 through its right surface 280. After being reflected from the beam polarization splitter 282, the light waves are output from the substrate through the light guide surface 291. 279. Next, the light waves pass through the second quarter-wave slowing plate 293, are collimated by the second lens 296 on its reflective surface 297, return, passing again through the slowing plate 293 and again enter the light guide 279 through the surface 291. Next, p-polarized light waves pass through polarization beam splitter 282 exits the light guide through the bottom surface 290 and is introduced into the substrate 64 through intermediate prisms 226 and 220, as shown above. The p-polarized light source component is introduced into the substrate as shown in FIG. 31A. The two collimating lenses must be identical and must be mounted on the surfaces of the light guide 279 with very high precision to prevent ghosting.

It will be apparent to those skilled in the art that the invention is not limited to the above detailed description of the illustrated embodiments, and that the present invention may be practiced in other particular forms without departing from its spirit and essential features. The present embodiments are, therefore, to be considered in all respects in an illustrative and not a limiting sense, the scope of the invention being determined by the appended claims and not the foregoing description, and all variations falling within the spirit and scope of the claims are therefore deemed to be covered by this formula.

In particular, it should be noted that features given with reference to one or more embodiments are described by way of illustration and not by way of limitation of those embodiments. Thus, it is intended that, unless otherwise indicated or unless specific combinations are clearly prohibited, optional features described herein with reference to only certain embodiments are also applicable to all other embodiments.

Claims (23)

1. An optical device including: a first light-transmitting substrate having at least two parallel main surfaces and two opposite edges; entrance aperture; an output aperture located near one of the main surfaces of the substrate; exit pupil, characterized by aperture; a first intermediate element having at least two surfaces located outside the substrate for introducing incoming light waves having a field of view into the substrate through the entrance aperture; a first planar reflective surface, the active area of which is located between two main surfaces of the light transmitting substrate, for reflecting light waves arriving from the first intermediate element to provide total internal reflection from the main surfaces of the substrate; a second planar reflective surface parallel to the first planar reflective surface having an active area and disposed between two major surfaces of the light transmitting substrate for conducting light waves from the substrate, and a deflection optical element having at least two surfaces located outside the substrate for deflecting light waves output from the substrate through the exit aperture into the exit pupil, wherein the input aperture is substantially smaller than the output aperture, ensuring that all incoming light waves pass into the input aperture, all light waves output from the substrate by the second flat reflective surface are introduced into the substrate by reflection from the first reflective surface, the active area of the first reflective surface is similar active area of the second reflective surface, and each of the introduced light waves completely covers the aperture of the exit pupil. 2. The optical device according to claim 1, wherein the light waves introduced into and output from the substrate are characterized by brightness, and the brightness of the light waves output from the substrate by the second flat reflective surface is generally similar in magnitude to the brightness of the light waves introduced into the substrate . 3. The optical device of claim 1, wherein the first and second planar reflective surfaces couple light waves into and out of the substrate, respectively, using total internal reflection. 4. The optical device of claim 1, wherein the light waves introduced into the substrate experience an equal number of reflections from the first and second planar reflective surfaces. 5. The optical device of claim 1, wherein light waves passing through the input aperture and introduced into the substrate are incident on only a portion of the first and second planar reflective surfaces. 6. The optical device of claim 5, wherein light waves passing through the entrance aperture and the exit pupil aperture are incident on only a portion of the first reflective surface closer to one of the ribs of the substrate and are output from the substrate only by a portion of the second reflective surface located closer to the other edge of the substrate. 7. The optical device of claim 5, wherein light waves passing through the entrance aperture and the exit pupil aperture are incident on only a portion of the first reflective surface closer to the center of the substrate and are output from the substrate only by a portion of the second reflective surface located closer to the center of the substrate. 8. The optical device of claim 5, wherein light waves passing through the entrance aperture and the exit pupil aperture are incident on only the central portion of the first reflective surface and are output from the substrate only by the central portion of the second reflective surface. 9. The optical device of claim 1, further comprising a second intermediate element, the light waves passing through the first and second intermediate elements before being introduced into the substrate by the first reflective surface. 10. The optical device of claim 1, wherein the input light waves pass through the first planar reflective surface at least twice before being reflected by the input surface into the substrate. 11. The optical device according to claim 1, wherein the first intermediate element and the deflection optical element are made of the same optical material, the refractive index and Abbe number of which are significantly different from those of the substrate, which causes a first chromatic dispersion of light waves introduced into the substrate. 12. The optical device of claim 11, wherein the first intermediate element and the deflecting optical element are optically bonded by a first optical adhesive to the major surfaces of the substrate, the Abbe number of said first adhesive being substantially different from the Abbe number of the substrate, causing a second chromatic dispersion of light waves in the substrate , with the first and second chromatic dispersions generally canceling each other. 13. The optical device according to claim 1, further comprising a second light-transmitting substrate having at least two main surfaces, two opposite edges and third and fourth flat reflective surfaces parallel to each other, each of which has an angle of inclination, and the two substrates are optically connected , and the angle of inclination of the third and fourth flat reflective surfaces to the main surfaces of the second substrate is less than the angle of inclination of the first and second flat reflective surfaces to the main surfaces of the first substrate. 14. The optical device according to claim 1, further comprising a second light-transmitting substrate having at least two main surfaces, two opposite edges, and third and fourth flat reflective surfaces, entrance and exit apertures having transverse dimensions, and light waves output from the first substrate are introduced into the second substrate, and the transverse dimensions of the input aperture are significantly smaller than the transverse dimensions of the output aperture along two different axes. 15. The optical device according to claim 1, further comprising a flat plate optically connected to the surface of the deflecting optical element, and inside this plate is built a lattice of flat absorbing surfaces located generally normal to the surface of the deflecting optical element, the flat plate is generally transparent to normally incident light waves, and the light waves exiting the substrate and incident on the flat plate are absorbed by the absorbing surfaces.

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