EP-4740056-A1 - COMPACT DISPLAY SYSTEM HAVING A WIDE OUTPUT APERTURE

Abstract

There is provided an optical device having a first light-transmitting substrate having at least two parallel major surfaces and edges, defining a main propagation direction axis parallel to the major surfaces, a first reference plane parallel to the main propagation direction axis, and an orthogonal axis normal to the main propagation direction axis and parallel to the first reference plane, an input aperture, an output aperture, an eye-motion box, a first flat reflecting surface, located between the two major surfaces of the light- transmitting substrate, for coupling light waves into the substrate, to effect total internal reflection from the major surfaces of the substrate, a second flat reflecting surface parallel to the first flat reflecting surface, being located between the two major surfaces of the light- transmitting substrate, for coupling light waves out of the substrate, and a first redirecting mechanism having at least one pair of first and second mutually perpendicular flat reflecting surfaces for redirecting light waves coupled-out from the substrate through the output aperture, into the eye-motion-box, wherein light waves coupled out from the substrate are reflected at least once from the first and second flat reflecting surfaces before reaching the eye-motion-box.

Inventors

• AMITAI, YAAKOV
• AMITAI, Nadav

Assignees

• Oorym Optics Ltd.

Dates

Publication Date

20260513

Application Date

20240704

Claims (20)

1. 1. An optical device, comprising: a first light-transmitting substrate having at least two parallel major surfaces and edges, defining a main propagation direction axis parallel to the major surfaces, a first reference plane parallel to the main propagation direction axis, and an orthogonal axis normal to the main propagation direction axis and parallel to the first reference plane; an input aperture; an output aperture; an eye-motion box; a first flat reflecting surface, located between the two major surfaces of the light-transmitting substrate, for coupling light waves into the substrate, to effect total internal reflection from the major surfaces of the substrate; a second flat reflecting surface parallel to the first flat reflecting surface, being located between the two major surfaces of the light- transmitting substrate, for coupling light waves out of the substrate, and a first redirecting mechanism having at least one pair of first and second mutually perpendicular flat reflecting surfaces for redirecting light waves coupled- out from the substrate through the output aperture, into the eye-motion-box, wherein light waves coupled out from the substrate are reflected at least once from the first and second flat reflecting surfaces before reaching the eye-motion- box.
2. 2. The optical device according to claim 1, wherein the first and second flat reflecting surfaces are each inclined at an angle of substantially 45 degrees to the first reference plane.
3. 3. The optical device according to claim 2, wherein the first and second flat reflecting surfaces are substantially parallel to the main propagation direction axis.
4. 4. The optical device according to claim 3, wherein the propagation direction of the light waves coupled inside the first redirecting mechanism is defined by three original orthogonal components, a first component parallel to the main propagation direction axis, a second component normal to the first reference plane and a third component parallel to the orthogonal axis, wherein after the reflections from the first and second reflecting surfaces, absolute values of the three components are substantially preserved, the first component retains its original direction and the directions of the second and the third components are reversed.
5. 5. The optical device according to claim 1, wherein the first redirecting mechanism has at least one main flat surface optically cemented to one of the major surfaces of the substrate.
6. 6. The optical device according to claim 1, wherein the first redirecting mechanism comprises at least two transparent elements and is cemented by an optical adhesive defining interface surfaces, wherein the first and the second mutually perpendicular flat reflecting surfaces are located at the interface surfaces.
7. 7. The optical device according to claim 6, wherein the refractive index of the two transparent elements is substantially higher than that of the optical adhesive.
8. 8. The optical device according to claim 6, wherein the first and second reflecting surfaces are coated with a thin transparent material having a refractive index substantially lower than that of the two transparent elements.
9. 9. The optical device according to claim 8, wherein the first and second reflecting surfaces are coated with different transparent materials, respectively.
10. 10. The optical device according to claim 6, wherein the first and second reflecting surfaces are coated with an anti-reflection coating.
11. 11. The optical device according to claim 1, wherein the first redirecting mechanism comprises an array of pairs each having first and second mutually perpendicular reflecting surfaces, the first and second reflecting surfaces of all the pairs being respectively parallel.
12. 12. The optical device according to claim 11, wherein for at least part of the pairs, active areas of the first reflecting surface are bigger than the active area of the second reflecting surface.
13. 13. The optical device according to claim 12, wherein for at least part of the pairs, active areas of the second reflecting surface are bigger than the active area of the first reflecting surface.
14. 14. The optical device according to claim 1, further comprising a second redirecting mechanism having at least two surfaces positioned outside of the substrate, for redirecting light waves reflected from the first redirecting mechanism through the output aperture into the eye-motion-box.
15. 15. The optical device according to claim 1, further comprising a second reference plane rotated at a first pre-defined angle with respect to the orthogonal axis in relation to the first reference plane, wherein the first and second reflecting surfaces are each inclined at an angle of about 45 degrees to the second reference plane.
16. 16. The optical device according to claim 15, wherein the light waves are reflected from the first redirecting mechanism through the output aperture directly into the eye-motion-box.
17. 17. The optical device according to claim 15, wherein the propagation direction of the light waves coupled inside the first redirecting mechanism is defined by three original orthogonal components, a first component parallel to the main propagation direction axis, a second component normal to the second reference surface, and a third component parallel to the orthogonal axis, wherein after the reflections from the first and second reflecting surfaces, the absolute value of the third component is substantially preserved, its direction is reversed, and the direction of the vector sum of the first and second components is rotated at a second pre-defined angle.
18. 18. The optical device according to claim 1, wherein the reflecting surfaces are polarizing beamsplitters.
19. 19. The optical device according to claim 1, wherein the reflecting surfaces are reflective for a small part of the photopic region, and substantially transparent for other parts.
20. 20. The optical device according to claim 19, wherein the reflecting surfaces are color-sensitive holograms.

Description

COMPACT DISPLAY SYSTEM HAVING A WIDE OUTPUT APERTURE FIELD OF THE INVENTION The present invention relates to substrate-based light wave guided optical devices, and particularly to devices which include reflecting surfaces carried by a light- transmissive substrate. The invention can be implemented to advantage in a large number of imaging applications, such as, head-mounted and head-up displays, as well as cellular phones, compact displays, and 3-D displays. BACKGROUND OF THE INVENTION One of the important applications for compact optical elements is in head- mounted displays (HMDs), wherein an optical module serves both as an imaging lens and a combiner, in which a two-dimensional display is imaged to infinity and reflected into the eye of an observer. The display can be obtained directly from either a spatial light modulator (SLM), such as a cathode ray tube (CRT), a liquid crystal display (LCD), an organic light emitting diode (OLED) array, a scanning source and similar devices, indirectly, by means of a relay lens, or an optical fiber bundle. The display comprises an array of elements (pixels) imaged to infinity by a collimating lens and transmitted into the eye of the observer by means of a reflecting or partially reflecting surface acting as a combiner for non-see-through and see-through applications, respectively. Typically, a conventional, free-space optical module is used for these purposes. As the desired field-of-view (FOV) of the system increases, such a conventional optical module becomes larger, heavier and bulkier, and therefore, even for a moderate-performance device, is impractical. Hence, this is a major drawback for all kinds of displays but especially in HMDs, wherein the system should be as light and compact as possible. The necessity for compactness has led to several different complex optical solutions, all of which, on the one hand, are still not sufficiently compact for most practical applications, and on the other hand, suffer major drawbacks in terms of manufacturability, price and performance. The teachings of the field of the present invention included in International Patent Publication Numbers WO2017/141239, WO20 17/141240, WO2017/141242, WO2019/077601, W02020/157747, WO2022/029764, and W02022/054047 are herein incorporated by reference. SUMMARY OF THE INVENTION The present invention facilitates the provision of compact substrates for, amongst other applications, HMDs. The invention allows relatively wide FOVs together with relatively large eye-motion box (EMB) values. The resulting optical system offers a large, high-quality image, which also accommodates large movements of the eye. The optical system, according to the present invention, is particularly advantageous because it is substantially more compact than state-of- the-art implementations, and yet it can be readily incorporated even into optical systems having various specialized configurations. A broad object of the present invention is, therefore, to alleviate the drawbacks of state-of-the-art compact optical display devices and to provide other optical components and systems having improved performance according to specific requirements. In accordance with the present invention there is therefore provided an optical device, including a first light-transmitting substrate having at least two parallel major surfaces and edges, defining a main propagation direction axis parallel to the major surfaces, a first reference plane parallel to the main propagation direction axis, and an orthogonal axis normal to the main propagation direction axis and parallel to the first reference plane, an input aperture, an output aperture, an eye- motion box, a first flat reflecting surface, located between the two major surfaces of the light-transmitting substrate, for coupling light waves into the substrate, to effect total internal reflection from the major surfaces of the substrate, a second flat reflecting surface parallel to the first flat reflecting surface, being located between the two major surfaces of the light-transmitting substrate, for coupling light waves out of the substrate, and a first redirecting mechanism having at least one pair of a first and second mutually perpendicular flat reflecting surfaces for redirecting light waves coupled-out from the substrate through the output aperture, into the eye- motion-box, wherein light waves coupled out from the substrate are reflected at least once from the first and second flat reflecting surfaces before reaching the eye- motion-box. BRIEF DESCRIPTION OF THE DRAWINGS The invention is described in connection with certain preferred embodiments, with reference to the following illustrative figures so that it may be more fully understood. With specific reference to the figures in detail, it is stressed that the particulars shown are by way of example and for the purpose of illustrative discussion of the preferred embodiments of the present invention only and are presented to pro