TWM643184U - Projector - Google Patents

Abstract

A projector has: a scanning illumination subsystem; reflective converging optics that focus a scanned beam to form a true image at a non-planar focal surface with a convex field curvature; a transmissive beam expansion configuration that conforms to the non-planar focal surface; and refractive optics that collimate light from the transmissive beam expansion configuration to emerge from an output optical aperture as a collimated image. The refractive optic has a concave field curvature that at least partially cancels out the convex field curvature of the reflective converging optic.

Description

projector

The present invention relates to displays, and in particular to image projectors for head-mounted displays and augmented reality systems.

One sub-category of image projectors suitable for use in head-mounted displays employs one or more laser beams, typically scanned in a scanning pattern using fast scanning mirrors that simultaneously vary the beam intensity synchronously to generate an image. The image is focused to the image plane and then collimated by collimating optics to generate an output image at the projector output optical aperture. To fill the output aperture with an image, a beam expander (or numerical aperture expander) such as a microlens array is deployed at the image plane.

When coupling a laser projector into a waveguide, the following conditions are preferably met:

1. The plane of the scanning mirror should be imaged onto the output optical aperture corresponding to the entrance of the waveguide for delivering the image to the front of the user's eye.

2. A microlens array or diffuser (here Microlens Array, MLA) should be introduced at the focal plane to expand the beam to fill the exit aperture (entrance of the waveguide).

Keeping the laser beam in focus while preserving the temporary focal plane and full coverage of the MLA is important to maintain high-quality images across projected images. Therefore, it is important to overlap with the field curvature of the optics before and after MLA. Various features of a laser scanning image projector are disclosed in PCT Publication WO 2021/053661 Al, commonly assigned with the present creation.

Polarization Beam Splitters (PBS) combined with reflective lenses are known in the art, which result in a convex field curvature. In addition, scanning the focused laser beam also generates convex field curvature. However, combining PBS with a converging laser beam tends to have a large physical size, which is shown in near-eye It is unfavorable in the application of the device.

This creation is an image projector for head-mounted displays and augmented reality systems.

In accordance with the teachings of embodiments of the present invention there is provided a projector for projecting a collimated image via a projector output optical aperture, the projector comprising: a scanning illumination subsystem comprising: a light source generating at least one beam of light, a scanning arrangement arranged to deflect the at least one beam of light in an angular sweep motion in at least one dimension, and a modulator associated with the light source and scanning arrangement and arranged to modulate the brightness of the at least one beam of light synchronously with the angular sweep movement; reflective converging optics comprising at least one reflective converging lens Concentrating optics are arranged to focus the at least one scanned beam to form a real image, reflective converging optics have a convex field curvature to form a real image at a non-planar focal surface; a transmissive beam expansion arrangement is deployed to substantially conform to the non-planar focal surface; and refractive optics are arranged to collimate light from the transmissive beam expansion arrangement to emerge from the projector output optical aperture as a collimated image, wherein the scanning illumination subsystem , reflective converging optics, transmissive beam expansion configuration and refractive optics are sequentially deployed in the light path of the projector.

According to another feature of the creation, the light source comprises a collimating lens and a laser for generating a collimated beam incident on the scanning device.

According to another feature of the invention, the scanning device is a two-dimensional scanning device for generating an angular scanning motion about two axes.

According to another feature of the invention, there is also provided a beam splitter surface arranged to define an optical path from the scanning device to the focal surface in which at least one beam is transmitted at least once by the beam splitter surface and reflected at least once by the beam splitter surface.

According to another feature of the invention, the beam splitter surface is a polarizing beam splitter, and wherein the quarter wave plate is associated with reflective converging optics.

According to another feature of the invention, the beam splitter surface is a non-polarizing partially reflective beam splitter.

According to another feature of the invention, the beam splitter surface is comprised within the transparent prism, and wherein reflective converging optics are associated with the surface of the transparent prism.

According to another feature of the invention, the transmissive beam expansion arrangement is realized as a microlens array.

According to another feature of the invention, the reflective converging optics and the refractive optics are configured such that the convex field curvature of the reflective converging optics substantially coincides with the concave field curvature of the refractive optics.

According to another feature of the invention, the reflective converging optics and the refractive optics are configured such that the scanning device images the output optical aperture of the projector.

10:Laser

12: Collimating lens

14: scanning mirror

16: Polarizing Beam Splitter (PBS)

18: reflective converging lens

20: Transmissive beam expansion configuration / focal surface / microlens array or diffuser (MLA)

200: Projector

202,202T: coupling prism

202R: Reflective coupling prism

203L: Lateral aperture

203V: vertical aperture

204: waveguide

206: Partial reflector (facet)

206L, 206V: facet group

208: eye center

210: Coupling area

22: Refractive optical device

220A: image light

220B: Guide direction

24: output optical aperture

32: Scan controller

34: Controller

The present creation is described herein, by way of example only, with reference to the drawings in which: FIGS. 1A and 1B are schematic side views of a waveguide-based near-eye display showing two geometries for coupling image illumination into the waveguide; FIG. Schematic representation of the 1C display image projector.

This creation is a compact image projector for head-mounted displays and augmented reality systems.

The principles and operation of an image projector according to the present invention may be better understood with reference to the drawings and accompanying description.

Referring now to the drawings, FIGS. 1A-1C illustrate non-limiting examples of contexts in which the present invention may be used. A near-eye display optical engine is shown in FIG. 1A that includes an image projector 200 that projects image light with an angular field into a waveguide 204 through a transmissive coupling prism 202T and through a vertical aperture 203V. Light propagates in the waveguide and is reflected by total internal reflection. A partial reflector (or "facet") 206 embedded in the waveguide in the outcoupling region 210 reflects the image from the waveguide towards the observer with eye center 208 (dashed arrow). Figure IB shows an alternative form of coupling into a waveguide by using a reflective coupling prism 202R with a mirror on its rear surface.

The waveguide configuration can realize one-dimensional or two-dimensional (Two Dimensional, 2D) optical aperture expansion. Figure 1C schematically shows a front view of a 2D aperture expanding waveguide. Here, the image projector 200 The image is injected through coupling prism 202 into waveguide 204 through lateral aperture 203L (203V is also present but not visible from this orientation). When the image light 220A passes through total internal reflection (Total Internal Reflection, TIR) between the waveguide surfaces, the image light propagates laterally in the waveguide. Two sets of facets are used here: facet set 206L expands the aperture laterally by gradually reflecting the guided image into a different guide direction 220B, and facet set 206V expands the aperture vertically by gradually outcoupling the image from the outcoupling region 210 on the waveguide to the viewer's eye. The above examples provide non-limiting examples of contexts in which the inventive image projector may be used, but it should be understood that it may also be advantageously used in a wide variety of other optical arrangements, including light guides employing diffractive optical elements, or combinations of reflective and diffractive elements, as is known in the art.

Figure 2 shows an implementation of a projector 200 for providing a collimated image at an output optical aperture 24, which in use is aligned with a lateral aperture 203L and a vertical aperture 203V of a waveguide, according to an embodiment of the invention.

In general, the projector 200 includes a scanning illumination subsystem comprising: a light source, typically comprising a laser, that generates at least one light beam; a scanning device arranged to deflect the at least one light beam in an angular scanning motion in at least one dimension; and a controller 34 associated with the light source and the scanning device, the controller being arranged to modulate the brightness of the at least one light beam synchronously with the angular scanning motion. The projector also includes reflective converging optics comprising at least one reflective converging lens 18 . Reflective converging optics are deployed to focus the scanned beams to form a true image, the reflective converging optics having a convex field curvature to form a true image at a non-planar focal surface. The transmissive beam expansion arrangement 20, preferably realized as a microlens array, is deployed to substantially conform to a non-planar focal surface. Refractive optics 22 comprising at least one refractive lens are arranged to collimate light from the transmissive beam expansion arrangement to emerge from the output optical aperture as a collimated image, the refractive optics having a concave field curvature.

The light source preferably comprises a collimating lens 12 and a laser 10 for generating a substantially collimated beam incident on the scanning device. The scanning device itself is preferably a fast scanning mirror 14 mounted on a suitable scanning mechanism and driven by a scanning controller 32, all of which are known in the art. Most preferably, the scanning device is a two-dimensional scanning device for generating angular scanning motion about two axes. This can be achieved by using a single mirror tilted about two axes, or by employing two single-axis mirrors. Alternatively, in some In an implementation, the illumination system may provide a vector containing multiple beams (not shown) covering multiple rows of primitives such that a one-dimensional (single-axis) scanning motion may be used to construct the field of view.

A particularly preferred implementation of the projector employs polarizing beam splitter 16 surfaces arranged to define an optical path from scanning mirror 14 to focal surface 20 in which at least one beam is transmitted at least once by the beam splitter surface and reflected at least once by the beam splitter surface. In certain embodiments, the beam splitter surface is advantageously realized as a polarizing beam splitter (PBS), in which case a quarter wave plate is associated with the reflective converging lens 18 . The preferred configuration of the PBS 16 shown in Figure 2 employs only a single reflection, and therefore residual light leakage before and after reflection does not continue through the system. This minimizes image quality degradation. Alternatively, a non-polarizing configuration can be achieved using a non-polarizing partially reflective beam splitter such as a partially silvered reflector. In either case, the beam splitter surface may advantageously be comprised within a transparent prism with reflective converging optics associated with the surface of the transparent prism.

The transmissive beam expanding arrangement 20 is advantageously realized as a microlens array, but other numerical aperture expanding elements such as directional diffusers may also be used. Alternatively, the MLA can be embedded in the refractive material and thus integrated into the first element of the refractive optics 22 .

The operation of the image projector (described by way of example in the non-limiting context of a PBS implementation) is as follows. Light from laser 10 is collimated by collimator lens 12 and impinges on scan mirror 14 . The scanned beam (shown as a plurality of arrows) passes through the PBS 16 onto a reflective converging lens 18 . The lens includes a wave plate that rotates the polarization of the beam and also focuses the beam. The converging beam is reflected by the PBS 16 and focused on a (non-planar) image "plane" comprising the MLA 20 . As each beam passes through the MLA 20, it acquires an increased divergence such that after passing through the refractive optics 22, each beam (corresponding to a picture element of the image) fills the output optical aperture 24 with a collimated beam at a corresponding angle. Refractive optics 22 have a concave field curvature that at least partially offsets the convex field curvature of the reflective converging optics, resulting in enhanced image quality compared to total reflection or total refraction implementations. Furthermore, it has been found to be particularly advantageous to employ reflective optics in the beam path prior to the beam expansion configuration, since the narrow expansion of the beam enables the use of highly compact reflective converging optics with a much smaller weight and volume than would be required to use reflective optics for collimation in large numerical aperture optics after the beam expansion configuration.

By partially canceling the opposing field curvatures of the two optics even though they do not match exactly configuration, also achieves enhanced image quality. If there is a mismatch, the MLA is preferably curved to fit the back field curvature of the refractive optic 22 .

In some particularly preferred implementations, the reflective converging optics and the refractive optics are configured such that the convex field curvature of the reflective converging optics substantially coincides with the concave field curvature of the refractive optics to more precisely cancel each other out. The field curvature of the reflective converging optics can be modified by changing the divergence of the beam after the collimating lens 12 (so that it is not perfectly collimated) and correspondingly modifying the power of the reflective converging lens 18 and/or by changing the distance of the scanning mirror 14 from the reflective lens. Additionally or alternatively, the back field curvature of the refractive optics 22 can be modified by changing the design of the refractive elements.

Furthermore, the reflective converging optics and refractive optics are preferably configured such that the scanning mirror 14 is imaged at the output optical aperture 24 to ensure that the scanned illumination is efficiently coupled into the waveguide.

It will be appreciated that the above description is intended as an example only, and that many other implementations are possible within the scope of the invention as defined by the appended claims.

10:Laser

12: Collimating lens

14: scanning mirror

16: Polarizing Beam Splitter (PBS)

18: reflective converging lens

20: Transmissive beam expansion configuration / focal surface / microlens array or diffuser (MLA)

200: Projector

22: Refractive optical device

24: output optical aperture

32: Scan controller

34: Controller

Claims (10)

A projector for projecting a collimated image via a projector output optical aperture, the projector comprising: a scanning illumination subsystem comprising: a light source generating at least one light beam, a scanning device arranged to deflect the at least one light beam in an angular sweep motion in at least one dimension, and a modulator associated with the light source and the scanning device and arranged to modulate the brightness of the at least one light beam synchronously with the angular sweep motion; reflective converging optics, the reflective converging optics optics comprising at least one reflective converging lens arranged to focus at least one scanned light beam to form a real image, the reflective converging optic having a convex field curvature to form the real image at a non-planar focal surface; a transmissive beam expansion arrangement arranged to substantially conform to the non-planar focal surface; and refractive optics comprising at least one refractive lens arranged to collimate light from the transmissive beam expanding arrangement, Appearing as a collimated image from an output optical aperture of the projector, the refractive optic has a concave field curvature, wherein the scanning illumination subsystem, the reflective convergence optics, the transmissive beam expansion arrangement, and the refractive optic are sequentially disposed in an optical path of the projector. The projector of claim 1, wherein the light source includes a collimating lens and a laser for generating a collimated beam incident on the scanning device. The projector of claim 1, wherein the scanning device is a two-dimensional scanning device for generating angular scanning motion about two axes. The projector of claim 1 , further comprising a beam splitter surface arranged to define an optical path from the scanning device to the focal surface, upon exiting from the scanning device Placed in the optical path of the focal surface, at least one beam is transmitted at least once by the beam splitter surface and reflected at least once by the beam splitter surface. The projector of claim 4, wherein said beam splitter surface is a polarizing beam splitter, and wherein a quarter wave plate is associated with said reflective converging optics. The projector of claim 4, wherein the beam splitter surface is a non-polarizing partially reflective beam splitter. The projector of claim 4, wherein the beam splitter surface is included within a transparent prism, and wherein the reflective converging optics are associated with a surface of the transparent prism. The projector of claim 1, wherein the transmissive beam expansion arrangement is implemented as a microlens array. The projector of claim 1, wherein the reflective converging optics and the refractive optics are configured such that the convex field curvature of the reflective converging optics substantially coincides with the concave field curvature of the refractive optics. The projector of claim 1, wherein the reflective converging optics and the refractive optics are configured to image the scanning device at the projector output optical aperture.

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