US-20260126658-A1 - Laser-Illuminated Displays with Enhanced Uniformity and/or Eye Safety

US20260126658A1US 20260126658 A1US20260126658 A1US 20260126658A1US-20260126658-A1

Abstract

A display for displaying an image to a viewer includes an image generator having an illumination subsystem generating illumination of at least a first color, the image generator employing the illumination to generate an image. Projection optics projects illumination from the image for display to the viewer. The illumination subsystem includes a first laser generating a first laser beam of the first color with a first polarization and a second laser generating a second laser beam of the first color with a second polarization. The first and second polarizations are orthogonal at at least one location within the projection optics, thereby projecting a quasi-unpolarized image.

Inventors

Yochay Danziger
Daniel Michaels

Assignees

LUMUS LTD.

Dates

Publication Date: 20260507
Application Date: 20251230

Claims (13)

1 .- 16 . (canceled)
17 . A display for displaying an image to a viewer, the display comprising: a. an image projector comprising: (i) a first laser illumination source configured to emit a first laser beam of a first color; (ii) a second laser illumination source configured to emit a second laser beam of the first color, the first and second laser beams being spatially separated; (iii) a scanning arrangement comprising at least one scanning mirror and at least one actuator deployed for displacing the scanning mirror, the scanning arrangement being configured to deflect light incident on the scanning arrangement to generate a two-dimensional scanning pattern; (iv) beam optics arranged to deliver the first laser beam and the second laser beam onto the scanning arrangement with differing directions of incidence; and (v) a display controller configured to vary an intensity of the first laser illumination source and an intensity of the second laser illumination source synchronously with operation of the scanning arrangement to generate the image; and b. a lightguide having a pair of mutually parallel major surfaces for supporting propagation of light by internal reflection at the major surfaces, the image projector being coupled to the lightguide so as to introduce the image to propagate within the lightguide, the lightguide further comprising a coupling out arrangement for coupling the collimated image out of the lightguide for viewing by the viewer, wherein, during generation of the image, the first laser beam and the second laser beam are deflected by the scanning arrangement to follow distinct scanning paths, and wherein the display controller modulates the intensities of the first laser beam and the second laser beam such that the distinct scanning paths generate substantially non-overlapping pixels of the image, and wherein the first laser beam and the second laser beam differ in at least one of wavelength and polarization.
18 . The display of claim 17 , wherein the scanning arrangement has a first scanning axis and a second scanning axis, and wherein the first and second laser beams exit from the scanning arrangement in directions that are staggered with respect to both the first scanning axis and the second scanning axis.
19 . The display of claim 17 , wherein the beam optics are at least part of a focusing arrangement configured such that the first and second laser beams propagating along the scanning paths are focused at an image plane, the image projector further comprising collimating optics deployed to collimate light from the image plane to form a collimated image.
20 . The display of claim 19 , wherein the collimating optics includes at least one reflective lens arrangement deployed at a surface of a polarizing beam splitter prism.
21 . The display of claim 19 , wherein the first and second light beams have wavelengths that differ by less than 5% and are incident on the scanning arrangement with parallel polarization, the display further comprising a window of birefringent material deployed in a light path between the collimating optics and the lightguide to differentially rotate polarization of the first and second beams to be substantially orthogonal on entering the lightguide.
22 . The display of claim 21 , wherein the collimating optics includes at least one reflective lens arrangement deployed at a surface of a polarizing beam splitter prism.
23 . The display of claim 17 , wherein the first and second light beams have substantially orthogonal polarizations on entering the lightguide.
24 . The display of claim 17 , wherein the image projector further comprises: a. a third laser illumination source configured to emit a third laser beam of a second color; b. a fourth laser illumination source configured to emit a fourth laser beam of the second color; c. a fifth laser illumination source configured to emit a fifth laser beam of a third color; and d. a sixth laser illumination source configured to emit a sixth laser beam of the third color, wherein the beam optics are arranged to deliver the third, fourth, fifth and sixth laser beams onto the scanning arrangement with differing directions of incidence, and wherein the display controller is configured to vary an intensity of the third, fourth, fifth and sixth laser illumination sources synchronously with operation of the scanning arrangement to generate the image, and wherein, during generation of the image, the first, second, third, fourth, fifth and sixth laser beams are all deflected by the scanning arrangement to follow distinct scanning paths.
25 . The display of claim 24 , wherein the scanning arrangement has a fast scanning axis and a slow scanning axis, and wherein the first, second, third, fourth, fifth and sixth laser beams exit from the scanning arrangement in directions that are mutually staggered with respect to both the fast scanning axis and the slow scanning axis.
26 . The display of claim 24 , wherein the beam optics are at least part of a focusing arrangement configured such that the first and second laser beams propagating along the scanning paths are focused at an image plane, the display further comprising collimating optics deployed to collimate light from the image plane to form a collimated image.
27 . The display of claim 26 , wherein the first color is green and the second color is blue, and wherein the focusing arrangement and/or an additional optical element is configured to defocus the third and fourth laser beams such that point spread functions of the spots at the image plane generated by the third and fourth laser beams are at least twice as wide as point spread functions of the spot at the image plane generated by the first and second laser beams.
28 . The display of claim 27 , further comprising a diffuser or a microlens array deployed at the focal plane.

Description

FIELD AND BACKGROUND OF THE INVENTION The present invention relates to displays for displaying an image to a viewer and, in particular, it concerns displays that are illuminated by laser light sources. Certain displays, such as near eye displays and head-up displays, need to be of high brightness to be suitably visible when used in the bright conditions, such as daytime outdoor use. This is particularly true for augmented reality displays, where visual elements are displayed overlying bright outdoor scenery. Laser-based illumination systems can achieve this average high brightness, when used for illuminating a spatial light modulator (SLM), or when used alone by scanning a very bright spot across the projected field. The scanning is performed by two perpendicular actuators moving a single mirror or two separate mirrors. For color displays, the bright spot is generated by three separate lasers (red, green and blue). While use of lasers offers benefits of brightness and energy efficiency, it may also raise issues of image non-uniformity and, in some cases, questions of eye-safety. SUMMARY OF THE INVENTION The present invention is a display. According to the teachings of an embodiment of the present invention there is provided, a display for displaying an image to a viewer, the display comprising: (a) an image generator having an illumination subsystem generating illumination of at least a first color, the image generator employing the illumination to generate an image; (b) projection optics for projecting illumination from the image for display to the viewer, wherein the illumination subsystem comprises a first laser generating a first laser beam of the first color with a first polarization and a second laser generating a second laser beam of the first color with a second polarization, the first and second polarizations being orthogonal at at least one location within the projection optics. According to a further feature of an embodiment of the present invention, the first and second lasers are two of a set of at least three lasers of the illumination subsystem, the at least three lasers having polarizations that are mutually orthogonal at at least one location within the projection optics. According to a further feature of an embodiment of the present invention, the first laser beam and the second laser beam are deployed to generate side-by-side beams with mutually-orthogonal polarizations. According to a further feature of an embodiment of the present invention, the projection optics comprises collimating optics for generating a collimated image and a light-guide optical element having a pair of parallel major external surfaces for guiding the collimated image within the light-guide optical element by internal reflection, the light-guide optical element having a coupling-out configuration for redirecting at least part of the collimated image towards the viewer. According to a further feature of an embodiment of the present invention, the first laser beam and the second laser beam are combined into a single beam by a polarization beam combiner of the illumination subsystem to form a single beam containing two orthogonal polarizations. According to a further feature of an embodiment of the present invention, the projection optics comprises collimating optics for generating a collimated image and a light-guide optical element having a pair of parallel major external surfaces for guiding the collimated image within the light-guide optical element by internal reflection, the light-guide optical element having a coupling-out configuration for redirecting at least part of the collimated image towards the viewer. According to a further feature of an embodiment of the present invention, the first laser beam and the second laser beam have respectively a first wavelength and a second wavelength, the first and second wavelengths differing by less than 5%, and wherein the projection optics comprises a length of birefringent material configured to differentially rotate the first and second polarizations from a parallel state to a substantially orthogonal state. According to a further feature of an embodiment of the present invention, the image generator comprises a polarization-modifying spatial light modulator illuminated by the first and second laser beams. According to a further feature of an embodiment of the present invention, the image generator further comprises a scanning optical arrangement comprising at least one scanning mirror, the scanning arrangement being deployed for generating a scanning motion of the first and second laser beams in at least one direction so as to sequentially illuminate different regions of the spatial light modulator. According to a further feature of an embodiment of the present invention, the projection optics comprises collimating optics for generating a collimated image and a light-guide optical element for conveying the collimated image to the viewer, wherein the birefringent mate