Optical system for light guide-based display

Abstract

An optical system includes a prism (36) having a planar input surface (38, 44a, 44b, 54) for injecting a laser beam, the prism being integrated with a light guide (10, 220). A fast scanning mirror (32) is disposed in facing relationship with the scanner interface surface (12) of the prism. A laser beam introduced via the input surface passes through the prism and scanner interface surface to impinge on the fast scan mirror to generate a scanned reflected beam that scans a diagonal field of view to pass through the prism to enter the light guide. One side of the light guide entrance aperture has an optical cutoff edge (24a) that modifies the edge of the scanned reflected beam for both a first beam direction (102) at a first end of the angular field of view and for a second beam direction (104) at a second end of the angular field of view.

Description

[0001] Technical Field and Background Art of the Present Invention

[0002] The present invention relates to optical systems, and in particular, to light-guide-based displays that inject scanned laser beams.

[0003] It is known to use a transparent light guide to transmit an image to the front of a viewer by internal reflection within the light guide and to couple out the image towards the viewer's eyes for viewing in combination with the scene of the real world. A particularly compact option for injecting an image into the light guide is to use a laser beam modulated synchronously with a scanning motion to generate the image. In principle, the beam of a scanning laser image generator can be directly injected into the light guide. However, it is difficult to achieve compactness, ergonomic design, and efficiency with such an arrangement. Summary of the Invention

[0004] The present invention is an optical system that injects a scanned laser beam into a light guide.

[0005] In accordance with the teachings of an embodiment of the present invention, there is provided an optical system that includes: (a) a light guide formed of a transparent material and having a pair of parallel surfaces for supporting the propagation of light within the light guide by internal reflection at the pair of surfaces; (b) a prism optically integrated with the light guide, the prism having: a planar input surface for injecting a laser beam, and a planar scanner interface surface; and (c) a fast steering mirror in a facing relationship with the scanner interface surface, the fast steering mirror performing a scanning motion about at least one axis, wherein the prism and the fast steering mirror are arranged such that the laser beam introduced via the input surface passes through the prism and exits from the scanner interface surface, thereby irradiating the fast steering mirror to generate a scanned reflected beam that scans a diagonal field of view, the scanned reflected beam re-entering the scanner interface surface and passing through the prism to enter the light guide at the light guide entrance aperture, and wherein at least one side of the light guide entrance aperture has an optical cutoff edge that trims the edges of the scanned reflected beam for both a first beam direction at a first end of the angular field of view and a second beam direction at a second end of the angular field of view.

[0006] In accordance with another feature of an embodiment of the present invention, the prism further includes a mirror for reflecting the laser beam introduced via the input surface towards the scanner interface surface.

[0007] In accordance with another feature of an embodiment of the present invention, the mirror is coplanar with one of the parallel surfaces of the light guide.

[0008] In accordance with another feature of an embodiment of the present invention, the prism further includes a redirecting mirror deployed to redirect the laser beam introduced via the input surface towards the mirror.

[0009] According to another feature of an embodiment of the present invention, the mirror surface is not parallel to the parallel surface of the light guide, and wherein the mirror surface meets one of the parallel surfaces at the optical cut-off edge.

[0010] According to another feature of an embodiment of the present invention, the optical cut-off edge is deployed to trim the edge of the laser beam before the laser beam impinges on the fast steering mirror.

[0011] According to another feature of an embodiment of the present invention, the fast steering mirror is configured to perform a scanning motion about two perpendicular axes.

[0012] According to another feature of an embodiment of the present invention, the light guide has a second pair of mutually parallel surfaces perpendicular to the pair of mutually parallel surfaces, thereby forming a light guide having a rectangular cross-sectional shape, and the light guide having a rectangular cross-sectional shape supports the propagation of the scanned reflected beam by four-fold internal reflection. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention is described herein by way of example only with reference to the accompanying drawings, in which:

[0014] Figure 1 is a schematic side view of a fast steering mirror that injects a scanned beam into a light guide, showing the geometric considerations for positioning the mirror relative to the light guide;

[0015] Figure 2 is a schematic side view of an optical system that injects a scanned laser beam into a light guide according to a first embodiment of the present invention;

[0016] Figure 3 is a schematic side view of an optical system that injects a scanned laser beam into a light guide according to a second embodiment of the present invention;

[0017] Figure 4 is a schematic side view of an optical system that injects a scanned laser beam into a light guide according to a third embodiment of the present invention;

[0018] Figure 5 is a schematic side view of an optical system that injects a scanned laser beam into a light guide according to a fourth embodiment of the present invention;

[0019] Figure 6 is a schematic overview of a display implemented using an optical system according to one of the above embodiments; and

[0020] Figure 7A and Figure 7B is a schematic isometric view showing the scanning of a laser beam in two dimensions using a fast steering mirror for introduction into a light guide having a rectangular cross-section, wherein Figure 7A shows the scanning motion in the X-Y plane (about the Z-axis), andFigure 7B Shows a scanning motion in the Y-Z plane (about the X axis). Detailed implementation

[0021] The present invention is an optical system that injects a scanned laser beam into an optical waveguide.

[0022] With reference to the accompanying drawings and the attached description, the principles and operations of the optical system according to the present invention can be better understood.

[0023] Now referring to the accompanying drawings, Figure 1 shows various geometric considerations for an optical system that realizes injecting a scanned laser beam into an optical waveguide, while Figures 2 to 7B shows aspects of an optical system that injects a scanned laser beam into an optical waveguide and a display that employs such a system. Generally, the optical system includes an optical waveguide 10 formed of a transparent material and having a pair of surfaces 20, 22 that are parallel to each other for supporting the propagation of light within the optical waveguide by means of total internal reflection at the pair of surfaces. A prism 36 optically integrated with the optical waveguide 10 has a planar input surface 38 for injecting a laser beam 34 and a planar scanner interface surface 12. A fast steering mirror 32 deployed in a facing relationship with the scanner interface surface 12 performs a scanning motion about at least one axis 14.

[0024] The prism 36 and the fast steering mirror 32 are arranged such that the laser beam 34 introduced via the input surface 38 passes through the prism 36 and exits from the scanner interface surface 12, thereby irradiating the fast steering mirror 32, and thus generating scanned reflected beams 102, 104 that scan a diagonal field of view 28. The scanned reflected beams re-enter the scanner interface surface 12 and pass through the prism 36, and thus enter the optical waveguide 10 at the optical waveguide entrance aperture 24a to the optical waveguide entrance aperture 24b.

[0025] According to certain particularly preferred implementations of the present invention, one side of the optical waveguide entrance aperture has an optical cutoff edge 24a that trims the edges of the scanned reflected beams for both a first beam direction 102 at a first end of the angular field of view and a second beam direction 104 at a second end of the angular field of view.

[0026] The optical systems described herein provide significant advantages, particularly with respect to near-eye displays, where the optical systems described herein facilitate compact and ergonomic implementations. In certain particularly preferred cases, there is no hardware protrusion in front of the optical waveguide. Additional considerations addressed by some of the optical systems disclosed herein include injecting the beam into the optical waveguide via a surface that is substantially perpendicular to the beam direction to minimize dispersion in a non-monochromatic beam.

[0027] It is also preferred that the laser beam scanning geometry is configured such that the angle between the incident beam and the normal of the scanning mirror is minimized. To achieve this, it is preferred to position the scanner as far as possible from the entrance of the light guide without degrading the beam quality or causing vignetting of the scanning beam.

[0028] Figure 1 A schematic cross-section of the light guide is shown where the scanning mirror 32 is placed at the maximum distance without compromising performance.

[0029] As a non-limiting specific example, the light guide 10 has a thickness of 1.25 mm between parallel surfaces 20 and 22 that guide light by total internal reflection (TIR). The light guide has an entrance aperture defined between the edge 24a and the virtual image (indicated as 24b) of that point reflected in the surface 22. For clarity, the entrance prism is not shown, but it is assumed that the beam enters the light guide within the refractive material of the coupling prism. In subsequent figures, the limiting envelope of the prism 36 is shown. It is assumed that the laser beam has a width 26 of 1 mm, and it is assumed that the field of view (FOV) corresponding to an angle 28 across which the beam scans between directions 102 and 104 is 20 degrees (within the coupling prism). The upper beam of the field is shown as two parallel solid arrows, while the lowest beam is shown as a parallel dashed arrow 102. The lower face 22 of the light guide is extended until point 30 such that the lowest beam (dashed arrow 102) aiming at the aiming virtual point 24b of the field (where the virtual continuation of the beam is shown as a dotted arrow) is reflected onto 24a and thus enters the light guide.

[0030] Figure 1 The arrangement shows the maximum distance of the scanning mirror from the entrance of the light guide, which can be achieved without loss of light due to vignetting for a given field of view, mirror size, and light guide thickness. In this case, the uppermost ray (solid arrow) 104 of the beam corresponding to the upper end of the field aims at 24a, while the lowermost ray (dashed arrow) 102 of the beam corresponding to the lower end of the field aims at 24b.

[0031] Figure 2 Shows a device structure based on Figure 1 The geometry shows the injection beam 34. The envelope shows the limiting volume of the prism 36 for this configuration. The beam 34 enters the prism 36 perpendicular to the surface 38, thereby minimizing dispersion. The input surface 38 is located outside the edge 30 such that the reflection of the scanning beam (dashed arrow 102) is not disturbed.

[0032] Figure 2The arrangement provides a highly compact and efficient optical system for implementing a display. However, this requires the scanning mirror and associated actuators (not shown) to be located outside the thickness of the light guide on one side, and the laser illumination arrangement to be located outside the thickness of the light guide on the other side. This may not be the optimal structure for a near-eye display, where it is generally preferred to have no components outside the light guide. Referring to Figures 3 to 5 Many alternative configurations illustrated employ a prism 36 that includes at least one mirror surface (reflective coating) 46 for reflecting a laser beam introduced via an input surface towards a scanner interface surface 12.

[0033] In Figure 3 and Figure 4 example, the mirror surface 46 is parallel to and generally coplanar with one of the parallel surfaces 22 of the light guide 10. In Figure 3 this case, the structure is optically equivalent to Figure 2 the structure, but here the incident beam 40a enters the prism 42a through an input surface 44a (perpendicular to the beam) adjacent to 24a so as not to interfere with the coupling of the scanned laser beam into the light guide. The beam 40a is reflected from the mirror surface 46 due to a reflective coating (dielectric or metal) that slightly extends beyond point 30 here. If the beam impinges on the surface 22 at an incident angle less than the critical angle, a reflective coating is required and thus total internal reflection is not provided. The reflected beam impinges on the fast scanning mirror 32 at an angle as close to perpendicular as possible while outside the angular FOV of the reflected scanned laser beam.

[0034] Figure 3 The configuration of Figure 2 may be advantageous relative to the configuration of Figure 4 since both the scanning mirror and the laser optics are located on one side of the light guide, thereby enabling an implementation where nothing protrudes outward from the outside of the light guide, suitable for an ergonomic implementation such as a glasses frame form factor. However, the angled laser beam injection direction may impose design limitations that are not ideal for all applications. Figure 4 Another variant implementation is shown that employs an additional redirecting mirror 48 that is deployed to redirect a laser beam 40b introduced via an input surface 44b towards the mirror surface 46. The redirecting mirror 48 is positioned so as not to compromise the reflective properties of the light guide surface 20 beyond the edge 24a, and optionally may abut the light guide surface 20 at the edge 24a to define an optical cutoff edge. Depending on the angles selected for the injection of the laser beam and for the redirecting mirror 48, the redirecting mirror may rely on TIR or may also require a dielectric or metal mirror coating. The remainder of the optical path and the operation of the optical system are the same as those in Figure 3

[0035] Figure 5Another variant implementation is shown, in which a single mirror 56 is not parallel to the light guide surface and redirects the injected laser beam 50 from the same side of the light guide as the side where the fast scanning mirror is located towards the scanner interface surface 12 and does not cross the path of the reflected scanning laser beam. The laser beam 50 is injected perpendicular to the input surface 54 before being reflected towards the fast scanning mirror 32 at the mirror 56. The mirror 56 can advantageously intersect the light guide surface 20 at the optical cut-off edge 24a. Thus, in Figure 4 and Figure 5 both cases, the optical cut-off edge 24a can be deployed to trim the edges of the laser beam 40b, laser beam 50 before the laser beam 40b, laser beam 50 impinges on the fast scanning mirror 32. The geometry is preferably designed such that the direction of beam injection is at an incident angle less than the critical angle with respect to the light guide surface 22, such that any light of the injected beam that is "trimmed" (i.e., falls to the left of the edge 24a) by the edge 24a will escape from the light guide at the surface 22.

[0036] Figure 6 A schematic overview of an optical system of the present invention incorporated into a display is provided. The display is arbitrarily shown using an Figure 5 embodiment, but the display is equally applicable to all of the above embodiments. The light guide 10 is here shown as extending to convey an image to in front of the viewer's eyes by internal reflection, where the image light is coupled out towards the viewer's eyes by a coupling-out arrangement 206, which can be a set of internal partial reflectors (as shown here) or diffractive optical elements, all of which are known in the art.

[0037] The input beam for injection into the scanning arrangement using collimating optics 210 to form a collimated beam is typically generated by a laser source 208. The fast scanning mirror 32 is thus operated by an associated component of a scanning driver 204 schematically shown here, which typically includes a piezoelectric actuator and corresponding driver circuitry. The modulation of the laser intensity is changed in synchronization with the scanning movement by a suitable controller 202 according to the image data, all of which are known in the art.

[0038] For color images, a dichroic combiner can be used to combine laser beams of the three primary colors (e.g., RGB) into a single beam and then independently modulate it in synchronization with the scanning movement to generate a color image. Alternatively, scanning can be performed on the "vector" of side-by-side laser beams from closely spaced sources of different colors. In the latter case, the side-by-side beams are arranged to converge towards the scanning mirror at slightly different angles and thus instantaneously illuminate different pixels of the image. When modulating the beams in synchronization with the scanning pattern, corresponding offsets are used.

[0039] So far, all the illustrations have only shown one dimension of the scanning pattern. To generate a two-dimensional image, as is known in the art, the fast steering mirror 32 can be driven in a scanning pattern about two perpendicular axes. Alternatively, multiple illumination sources can be used for the dimension into the page of the above-mentioned drawings, where each illumination source provides a row of pixels in the generated image.

[0040] The arrangements shown so far can be used to inject an image directly into the flat-type optical waveguide 10, but can also be used with a rectangular cross-section optical waveguide such as the rectangular cross-section optical waveguide described in PCT Publication WO 2018 / 065975 A1. Figure 7A and Figure 7B Schematically shows the geometry of such an option for injecting an image into a rectangular cross-section optical waveguide 220, which has a second pair of mutually parallel surfaces 20z, 22z perpendicular to the first pair of mutually parallel surfaces 20, 22, thereby forming an optical waveguide having a rectangular cross-section shape, and the optical waveguide having a rectangular cross-section shape supports the propagation of the scanned reflected light beam through four internal reflections.

[0041] Such an implementation can be described as a combination of two dimensions, where each dimension is equivalent to one of the embodiments in the above-mentioned embodiments. Figure 7A Shows a scanning motion in the XY plane (about the Z axis) equivalent to the scanning motion described in Figure 1 , where all the reference numerals are similar to those in Figure 1 . The scanning mirror is shown as circular here, but a rectangular shape can also be used. Figure 7B Shows a scanning motion in the YZ plane (about the X axis), which is also equivalent to the geometry of Figure 1 , where the equivalent reference numerals include the suffix "z".

[0042] Since it is difficult to clearly show the prism structure in an isometric view, the details of the prism structure and the beam injection geometry are omitted here, but the prism can be implemented according to the principles described and shown above, where the top view and the side view can each be implemented according to any of the options in Figures 2 to 5 .

[0043] It should be understood that the above description is only intended to be exemplary, and it should be understood that many other embodiments are possible within the scope of the invention as defined in the appended claims.

Claims

1. An optical system, comprising: (a) An optical waveguide formed of a transparent material and having a pair of surfaces parallel to each other for supporting the propagation of light through total internal reflection at the pair of surfaces within the optical waveguide; (b) A prism optically integrated with the optical waveguide, the prism having: a planar input surface for injecting a laser beam, and a planar scanner interface surface; And (c) A fast steering mirror in a facing relationship with the scanner interface surface, the fast steering mirror performing a scanning motion about at least one axis, wherein the prism and the fast steering mirror are arranged such that the laser beam introduced via the input surface passes through the prism and exits from the scanner interface surface to irradiate on the fast steering mirror to generate a scanning reflected beam for scanning a diagonal field of view, the scanning reflected beam re-enters the scanner interface surface and passes through the prism to enter the optical waveguide at the optical waveguide entrance aperture, and wherein at least one side of the optical waveguide entrance aperture has an optical cut-off edge that trims the edge of the scanning reflected beam for both a first beam direction at a first end of the angular field of view and a second beam direction at a second end of the angular field of view.

2. The optical system according to claim 1, wherein, The prism further includes a mirror for reflecting the laser beam introduced via the input surface towards the scanner interface surface.

3. The optical system according to claim 2, wherein, The mirror is coplanar with one of the parallel surfaces of the optical waveguide.

4. The optical system according to claim 3, wherein, The prism further includes a redirecting mirror deployed to redirect the laser beam introduced via the input surface towards the mirror.

5. The optical system according to claim 2, wherein, The mirror is not parallel to the parallel surface of the optical waveguide, and wherein the mirror abuts one of the parallel surfaces at the optical cut-off edge.

6. The optical system according to claim 1, wherein, The optical cut-off edge is deployed to trim the edge of the laser beam before the laser beam irradiates on the fast steering mirror.

7. The optical system according to claim 1, wherein, The fast steering mirror is configured to perform a scanning motion about two perpendicular axes.

8. The optical system according to claim 7, wherein, The optical waveguide has a second pair of parallel surfaces perpendicular to the pair of parallel surfaces, thereby forming an optical waveguide having a rectangular cross-sectional shape, and the optical waveguide having a rectangular cross-sectional shape supports the propagation of the scanning reflected beam through quadruple total internal reflection.

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