WO2017066859A1

WO2017066859A1 - Compact dual-function optics for lcos displays

Info

Publication number: WO2017066859A1
Application number: PCT/CA2015/000544
Authority: WO
Inventors: Michael David Thorpe
Original assignee: Raytheon Canada Limited
Priority date: 2015-10-20
Filing date: 2015-10-20
Publication date: 2017-04-27

Abstract

An optical device and method for illuminating an LCOS display and relaying a real image of the display to where it can be overlaid with a scene image. One example of an optical device includes a Dyson lens assembly and a polarizing beamsplitter. The Dyson lens assembly has 1:1 magnification and is configured to receive and double-pass first input light having a first polarization and to provide a first telecentric output beam having the first polarization, and to receive and double-pass second input light having a second, orthogonal polarization and to provide a second telecentric output beam having the second polarization. The polarizing beamsplitter has a polarizing beam-splitting coating, is arranged adjacent the Dyson lens assembly, and is configured to transmit the first input light to the Dyson lens assembly and to reflect the second telecentric output beam received from the Dyson lens assembly to a display image plane.

Description

COMPACT DUAL-FUNCTION OPTICS FOR LCOS DISPLAYS

BACKGROUND

Liquid crystal on Silicon (LCOS) is a type of miniaturized reflective active-matrix liquid- crystal display, also termed a microdisplay, that is formed with an active liquid crystal layer on a silicon substrate or backplane. LCOS displays are widely used in a variety of applications, including a variety of near-eye applications such as electronic viewfinders for digital cameras and head-mounted displays, for example.

LCOS displays also have some advantages for use as information display overlays in portable visual systems, such as goggles and sighting systems, because their high optical efficiency allows a high display brightness with relatively low optical power input and the display technology itself is inexpensive. In certain applications, for an LCOS display to be integrated into a portable visual optical devices it is necessary to both illuminate LCOS the display and create a real image of the display that can be overlaid with the scene image. Conventionally this is achieved using an illumination lens which injects light into the display and a very high resolution relay lens which relays the display to create the real image of the display. The combined optical system is bulky and relatively expensive and not ideal for a portable system. SUMMARY OF INVENTION

Aspects and embodiments are directed to a compact dual-function illumination and relay optics package for LCOS displays. As discussed in more detail below, certain embodiments are directed to the use of the different polarization states to select either a relay light path or an illumination light path through a common Dyson lens, thereby providing both the illumination function and the relay function in a compact package. Embodiments of the design disclosed herein allows significant simplification of the optics compared to conventional systems, providing an advantageous solution for suing LCOS displays to display and overlay information in portable optical devices. According to one embodiment an optical device comprises a Dyson lens assembly having 1:1 magnification and configured to receive and double-pass first input light having a first polarization and to provide a first telecentric output beam having the first polarization, and to receive and double-pass second input light having a second polarization and to provide a second telecentric output beam having the second polarization, the first and second polarizations being orthogonal to one another, and a polarizing beamsplitter having a polarizing beam-splitting coating and being arranged adjacent the Dyson lens assembly and configured to transmit the first input light to the Dyson lens assembly and to reflect the second telecentric output beam received from the Dyson lens assembly to a display image plane.

In one example the Dyson lens assembly includes a first lens element that receives the first input light and the second input light and outputs the first telecentric output beam and the second telecentric output beam, a second lens element, and a third lens element, the second lens element being positioned between the first and third lens elements. In one example the third lens element has a first surface disposed adjacent the second lens element and an opposing second surface, and wherein the Dyson lens assembly further includes a reflective coating disposed on the second surface of the third lens element. In another example the second and third lens elements share a cemented interface.

In one example the first input light is H-polarized input light, and the second input light is V-polarized input light.

According to another embodiment an optical system comprises an illumination light source configured to provide illumination light having a first polarization, a liquid crystal on silicon (LCOS) display configured to provide display light having a second polarization in response to being illuminated by the illumination light, a Dyson lens assembly having 1:1 magnification and configured to receive and relay the illumination light to illuminate the LCOS display with a telecentric illumination beam having the first polarization, and to receive and relay the display light from the LCOS display to output a telecentric display image, and a polarizing beamsplitter configured to transmit the illumination light from the illumination light source to the Dyson lens assembly, to receive the telecentric display image from the Dyson lens assembly and to reflect the telecentric display image to a display image plane that is spatially offset with respect to the LCOS display and the illumination light source.

The illumination light can be H-polarized illumination light, and the display light can be V-polarized display light, for example.

In one example the Dyson lens assembly includes a first lens element, a second lens element, and a third lens element, the second lens element being positioned between the first and third lens elements, and the third lens element including a reflective coating thereon, the reflective coating configured to reflect the illumination light and the display light. In one example the second and third lens elements share a cemented interface.

In another example the polarizing beamsplitter includes a polarizing beam splitting coating that transmits the illumination light and reflects the display image.

The optical system can further include an objective configured to provide an image of a scene at a scene image plane that is conjugate to the display image plane, an optical coupler configured to receive and combine the image of the scene and the V-polarized display image to produce combined light, and an eyepiece configured to receive and collimate the combined light to produce a combined image including the display image overlaid with a portion of the image of scene. In one example the optical coupler includes a dichroic beamsplitter. The optical system can further include a field lens positioned between the objective and the scene image plane.

Another embodiment is directed to a method of producing a real image of a display at a display image plane that is spatially offset from the display. According to one example the method comprises producing illumination light having a first polarization, transmitting the illumination light along a double-pass path through a Dyson lens assembly to illuminate the display with a telecentric beam of the illumination light, emitting from the display display light having a second polarization in response to the display being illuminated by the telecentric beam of the illumination light, the second polarization being orthogonal to the first polarization, relaying the display light along the double-pass path through the Dyson lens assembly to provide telecentric output light, and reflecting the telecentric output light to the display image plane to provide the real image of the display at the display image plane. In one example producing the illumination light includes producing H-polarized illumination light, emitting from the display the display light includes emitting V-polarized display light, and providing the telecentric output light includes providing telecentric V- polarized output light. The method can further comprise transmitting the H-polarized illumination light through a polarizing beamsplitter to provide the H-polarized illumination light to the Dyson lens assembly, and wherein reflecting the telecentric V-polarized output light includes reflecting the telecentric V-polarized output light with the polarizing beamsplitter.

According to another embodiment an optical device comprises a Dyson lens assembly having 1:1 magnification and configured to receive and double-pass H-polarized input light and to provide a telecentric H-polarized output beam, and to receive and double-pass V- polarized input light and to provide a telecentric V-polarized output beam, and a polarizing beamsplitter having a polarizing beam-splitting coating and being arranged adjacent the Dyson lens assembly and configured to transmit the H-polarized input light to the Dyson lens assembly and to reflect the telecentric V-polarized output beam received from the Dyson lens assembly to a display image plane.

Still other aspects, embodiments, and advantages of these exemplary aspects and embodiments are discussed in detail below. Embodiments disclosed herein may be combined with other embodiments in any manner consistent with at least one of the principles disclosed herein, and references to "an embodiment," "some embodiments," "an alternate embodiment," "various embodiments," "one embodiment" or the like are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or characteristic described may be included in at least one embodiment. The appearances of such terms herein are not necessarily all referring to the same embodiment. BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of at least one embodiment are discussed below with reference to the accompanying figures, which are not intended to be drawn to scale. The figures are included to provide illustration and a further understanding of the various aspects and embodiments, and are incorporated in and constitute a part of this specification, but are not intended as a definition of the limits of the invention. In the figures, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every figure. In the figures:

FIG. 1A is a ray trace of one example of an optical device according to aspects of the present invention, showing the illumination light path;

FIG. IB is a ray trace of the optical device of FIG. 1, showing the relay light path; and FIG. 2 is a ray trace of one example of a visual optical system including a display overlay according to aspects of the present invention. DETAILED DESCRIPTION

There are a variety of optical systems and applications in which it is desirable to provide a particular type of overlay of information on the viewed image of a scene. This information can be created using an LCOS display, and overlaid with the scene image using an optical path coupler, such as a dichroic or polarizing beamsplitter, for example. In certain applications, particularly some using portable visual optical devices, for the LCOS display to be appropriately imbedded into or overlaid with the scene image, it is necessary both to illuminate the LCOS display and to create a real image of the display within the system which is at a conjugate plane to the real world scene image. Aspects and embodiments are directed to providing a compact optics package that can be used with an LCOS display to achieve both these functions of illuminating the display and relaying the real image of the display to where it can be overlaid with the scene image.

Referring to FIGS. 1A and IB there is illustrated an example of an optical device that can be used as a sub-system in an overall visual optical system that is configured to view or image a scene, as discussed further below. The device 100 includes a single high resolution Dyson-type lens assembly 110 operating at 1:1 magnification. In the illustrated example, the Dyson lens assembly 110 includes three powered lens elements, namely, a first lens element 112, a second lens element 114, and a third lens element 116, all in compact contact with one another. In one example the second lens element 114 and the third lens element 116 share a cemented interface. The third lens element 116 includes a reflective coating 120 on its rear surface, as indicated. The effective system aperture stop controlling the light cone through the device is at 120.

A polarizing beamsplitter 130 is disposed on the illumination side of the Dyson lens assembly 110. The polarizing beamsplitter 130 includes a polarizing beam splitting coating 135 that acts to transmit light of one polarization and reflect light of an orthogonal polarization. As discussed in more detail below, aspects and embodiments make use of the different polarization state for light going from a source 140 into the display 150 for illumination (shown in FIG. 1A) and out of the display (shown in FIG. IB) for injection into the device to allow both illumination light 145 and display relay light 155 to substantially share the same optics, but to have different conjugate planes, namely, the light source plane for one polarization and a relay image plane for the other polarization. Thus, aspects and embodiments provide a single lens assembly 110 which both illuminates the LCOS display 150 and relays or projects the display to a fixed display image plane 160. This simplification of the dual-function optics relative to conventional systems, which as discussed above require both an illumination lens assembly and a separate very high resolution relay lens assembly, allows the implementation of an LCOS display with a real image plane with optics having lower volume, mass, or cost.

Referring to FIG. 1A, for illumination operation of the device 100, light 145 enters the system as a quasi-collimated source 140 with output at some limited numerical aperture. This light or source 140 can be generated from any of a variety of light emitters such as, for example, an area LED with an attached collimating taper, or a laser or vecsel array with a collimating lens. The illumination light is polarized, either intrinsically (e.g., as is the case from a laser light source) or by way of a polarizer (not shown). In one example the illumination light is H-polarized (horizontally polarized), as indicated by polarization identifier 170. In this case, as shown in FIG. 1, the polarizing beam splitting coating 135 of the polarizing beamsplitter 130 is configured to transmit H-polarized light and reflect V-polarized (vertically polarized) light. According to certain embodiments, the source or illumination light 145 is advantageously H-polarized, and the relayed display light 155 is V-polarized, to achieve more efficient operation of the polarizing beamsplitter 130 and arrangement of optics in device 100; however, those skilled in the art will appreciate that the device 100 can be modified to instead accommodate V-polarized illumination light 145 and H-polarized relayed display light 155.

Still referring to FIG. 1A, the illumination light 145 is transmitted through the coating 135 and reimaged at the plane of the LCOS display 150 to illuminate the display. The illumination light 145 travels through the Dyson lens assembly 110, is reflected by the reflective coating 120 on the back surface of the third lens element 116, and returns through the Dyson lens assembly to arrive as a collimated beam at the display 150. The Dyson lens assembly is thus configured to double-pass the illumination light 145. The Dyson lens assembly 110 is configured to provide telecentric illumination for display 150; that is, the angle of the central ray for any field point is zero degrees.

Referring now to FIG. IB there is illustrated the light path for the relayed light 155 from the display 150. The LCOS display 150 controls reflected light at each pixel. Each pixel that is ON emits V-polarized light (responsive to being illuminated by H-polarized light, as discussed above), and pixels that are OFF emit no light. The p-polarization of the relayed display light 155 is indicated by polarization indicator 175 and is orthogonal to the s- polarization. Because of the telecentric illumination of the display 150 discussed above with reference to FIG. 1A, the reflected or relayed display light 155 transits the same, but reverse, path through the Dyson lens assembly 110 as does the illumination light 145. The Dyson lens assembly 110 is thus configured to double-pass the display light 155. However, when the relayed display light 155 reaches the polarizing beam splitting coating 135 of the polarizing beamsplitter 130, this V-polarized light is reflected, as shown in FG. IB, creating an image of the display 150 at the display image plane 160. This image 165 can then be injected into another system to be overlaid with a scene image, for example, as discussed above. Thus, the device 100 reimages the display 150 to the display image plane 160, which may be more conveniently located for coupling into a scene path than may be the display itself, using polarized light. The telecentric configuration of the Dyson lens assembly 110 and the presence of the polarizing beam-splitting coating 135 allow the device 100 to perform both illumination and imaging or display relay functions in a compact optical package.

The particular shapes (e.g., surface curvatures) and materials of the lens elements making up the Dyson lens assembly 110 may be selected based at least in part on the wavelengths of the illumination light 145 and the relayed display light 155. For example, for wavelengths in the visible range, the lens elements 112, 114, and 116 may be made of optical glass.

As discussed above, in certain applications and systems is it useful to overlay information, which can be produced by the display 150, on an image of a viewed scene. FIG. 2 illustrates an example of a visual optical system 200 that incorporates an example of the device 100 or in which the device 100 may be used. Referring to FIG. 2, an objective 210 directs electromagnetic radiation 215 from a viewed scene 220 to a field lens 230. The objective 220 images the scene 220, via the field lens 230, onto a conjugate image plane 240 which is conjugate to the display image plane 160. As discussed above, the device 100 produces a real image of the display 150 at the display image plane 160. A beamsplitter 250 is used to couple the image of the display 150 into the optical path of the electromagnetic radiation 215 from the scene 220. In one example the beamsplitter 250 is a dichroic beamsplitter; however, in other examples the beamsplitter 250 can be a polarizing beamsplitter. The beamsplitter 250 includes a beam-splitting coating 255. In one embodiment, a portion of the scene light 215 imaged at the conjugate plane 240 is transmitted through the beam splitting coating 255 where it is collimated by an eyepiece 260 for viewing by the eye 270. Similarly some of the light projected to the display image plane 160 by the device 100 is reflected at the beam splitting coating 255 and collimated by the eyepiece 260. The combined light 265 is transmitted to the eye 270, as shown. Thus, the eye 270 perceives the display information (from the image of the display 150) to be superimposed on a portion of the scene 220. In the example illustrated in FIG. 2, the objective 210 includes a pair of lens elements; however, any reflective or refractive objective can be used, including any number of lenses, mirrors, or combination thereof. Similarly, in the illustrated example the eyepiece 260 includes a pair of lens elements; however, any reflective or refractive eyepiece can be used, including any number of lenses, mirrors, or combination thereof. In addition, although the overlay of the display image 165 and the image of the scene 220 is achieved in the example of FIG. 2 using a dichroic or polarizing beamsplitter 250, other optical couplers can be used in other embodiments. For example, in certain applications it may be advantageous to use one or more wavelengths of light for the relayed display light 155 forming the display image 165 that are different from the wavelengths of the electromagnetic radiation 215 as this can allow the use of a dichroic beamsplitter with very high transmission efficiency for the scene light and very high coupling efficiency for the display light.

Having described above several aspects of at least one embodiment, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure and are intended to be within the scope of the invention. It is to be appreciated that embodiments of the methods and apparatuses discussed herein are not limited in application to the details of construction and the arrangement of components set forth above or illustrated in the accompanying drawings. The methods and apparatuses are capable of implementation in other embodiments and of being practiced or of being carried out in various ways. Examples of specific implementations are provided herein for illustrative purposes only and are not intended to be limiting. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use herein of "including," "comprising," "having," "containing," "involving," and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. References to "or" may be construed as inclusive so that any terms described using "or" may indicate any of a single, more than one, and all of the described terms. Any references to front and back, left and right, top and bottom, upper and lower, and vertical and horizontal are intended for convenience of description, not to limit the present systems and methods or their components to any one positional or spatial orientation. Accordingly, the foregoing description and drawings are by way of example only, and the scope of the invention should be determined from proper construction of the appended claims, and their equivalents.

What is claimed is:

Claims

1. An optical device comprising:

a Dyson lens assembly having 1:1 magnification and configured to receive and double- pass first input light having a first polarization and to provide a first telecentric output beam having the first polarization, and to receive and double-pass second input light having a second polarization and to provide a second telecentric output beam having the second polarization, the first and second polarizations being orthogonal to one another; and

a polarizing beamsplitter having a polarizing beam-splitting coating and being arranged adjacent the Dyson lens assembly and configured to transmit the first input light to the Dyson lens assembly and to reflect the second telecentric output beam received from the Dyson lens assembly to a display image plane.

2. The optical device of claim 1 wherein the Dyson lens assembly includes a first lens element that receives the first input light and the second input light and outputs the first telecentric output beam and the second telecentric output beam, a second lens element, and a third lens element, the second lens element being positioned between the first and third lens elements.

3. The optical device of claim 2 wherein the third lens element has a first surface disposed adjacent the second lens element and an opposing second surface, and wherein the Dyson lens assembly further includes a reflective coating disposed on the second surface of the third lens element.

4. The optical device of claim 2 or 3 wherein the second and third lens elements share a cemented interface.

5. The optical device of any one of claims 1-4 wherein the first input light is H-polarized input light, and the second input light is V-polarized input light.

6. An optical system comprising:

an illumination light source configured to provide illumination light having a first polarization;

a liquid crystal on silicon (LCOS) display configured to provide display light having a second polarization in response to being illuminated by the illumination light;

a Dyson lens assembly having 1:1 magnification and configured to receive and relay the illumination light to illuminate the LCOS display with a telecentric illumination beam having the first polarization, and to receive and relay the display light from the LCOS display to output a telecentric display image; and

a polarizing beamsplitter configured to transmit the illumination light from the illumination light source to the Dyson lens assembly, to receive the telecentric display image from the Dyson lens assembly and to reflect the telecentric display image to a display image plane that is spatially offset with respect to the LCOS display and the illumination light source.

7. The optical system of claim 6 wherein the illumination light is H-polarized illumination light, and the display light is V-polarized display light.

8. The optical system of claim 6 or 7 wherein the Dyson lens assembly includes a first lens element, a second lens element, and a third lens element, the second lens element being positioned between the first and third lens elements, and the third lens element including a reflective coating thereon, the reflective coating configured to reflect the illumination light and the display light.

9. The optical system of claim 8 wherein the second and third lens elements share a cemented interface.

10. The optical system of any one of claims 6-9 wherein the polarizing beamsplitter includes a polarizing beam splitting coating that transmits the illumination light and reflects the display image.

11. The optical system of any one of claims 6-10 further comprising:

an objective configured to provide an image of a scene at a scene image plane that is conjugate to the display image plane;

an optical coupler configured to receive and combine the image of the scene and the V-polarized display image to produce combined light; and

an eyepiece configured to receive and collimate the combined light to produce a combined image including the display image overlaid with a portion of the image of scene.

12. The optical system of claim 11 wherein the optical coupler includes a dichroic beamsplitter.

13. The optical system of claims 11 or 12 further comprising a field lens positioned between the objective and the scene image plane.

14. A method of producing a real image of a display at a display image plane that is spatially offset from the display, the method comprising:

producing illumination light having a first polarization;

transmitting the illumination light along a double-pass path through a Dyson lens assembly to illuminate the display with a telecentric beam of the illumination light;

emitting from the display display light having a second polarization in response to the display being illuminated by the telecentric beam of the illumination light, the second polarization being orthogonal to the first polarization;

relaying the display light along the double-pass path through the Dyson lens assembly to provide telecentric output light; and reflecting the telecentric output light to the display image plane to provide the real image of the display at the display image plane.

15. The method of claim 14 wherein producing the illumination light includes producing H- polarized illumination light, emitting from the display the display light includes emitting V- polarized display light, and providing the telecentric output light includes providing telecentric V-polarized output light.

16. The method of claim 15 further comprising transmitting the H-polarized illumination light through a polarizing beamsplitter to provide the H-polarized illumination light to the Dyson lens assembly, and wherein reflecting the telecentric V-polarized output light includes reflecting the telecentric V-polarized output light with the polarizing beamsplitter.