Optical device for producing polarized light

Abstract

A near-eye display system is provided, comprising a light source configured to emit unpolarized light constituting a collimated image; a lightguide optical element configured to expand the optical aperture of a collimated image injected therein; and an optical device for receiving the collimated image prior to expansion by the lightguide optical element, and for increasing its polarity. The optical device comprises a substantially transparent substrate and a plurality of optical polarization elements, defining a polarization dependent optical multipath through the substrate between input and output interfaces thereof. The multipath comprises a rotating optical path configured to transmit and to cause a net rotation of the polarization of a first polarized component of input light, and a non-rotating optical path configured to transmit a second polarized component of the input light, having a polarization opposite that of the first polarized component, without causing a net rotation of its polarization.

Description

OPTICAL DEVICE FOR PRODUCING POLARIZED LIGHTFIELD OF THE INVENTION

[0001] The presently disclosed subject matter relates to optical devices, and in particular to optical devices for outputting highly polarized light.BACKGROUND

[0002] Many near-eye display systems include a transparent light-guide optical element (LOE), or “waveguide,” placed before the eye of the user, which conveys an image within the LOE by internal reflection and then couples out the image by a suitable output coupling mechanism towards the eye of the user. The output coupling mechanism may be based on embedded partial reflectors or “facets” or may employ a diffractive pattern.

[0003] Such a system may comprise, inter alia, a micro-LED (light emitting diode) display, for example comprising an array of independently controlled self-emissive LEDs and collimating optics. While micro-LED displays typically produce unpolarized light, polarized light, for example s-polarized light, is often required for efficient operation of waveguides.SUMMARY

[0004] According to an aspect of the presently disclosed subject matter, there is provided an optical device comprising:a substantially transparent substrate comprising an input interface and an output interface; a plurality of optical polarization elements disposed within the substrate, the optical polarization elements and the substrate defining a polarization-dependent optical multipath through the substrate between the input interface and the output interface for input light entering the substrate at the input interface within a predetermined range of input angles;wherein the multipath comprises:a rotating optical path (i.e., one or more) configured to transmit a first component of the input light having a first polarization, and to cause a net rotation of the polarization of the first component traversing it from the input interface to the output interface; anda non-rotating optical path (i.e., one or more) configured to transmit a second component of the input light having a second polarization opposite the first polarization, and does not cause a net rotation of the polarization of the second component traversing it from the input interface to the output interface.

[0005] According to some examples, all components of the input light are output via a single output interface, i.e., the different optical paths are substantially unsegregated at the output interface. Accordingly, the optical device may be configured to output light with an increased polarization relative to the input light, and which at least partially maintains the mixture of components present in the input light.

[0006] The multipath may be configured to transmit, from the input interface to the output interface, a majority of each of the first and second components of the input light.

[0007] At least one of the optical polarization elements may be a polarizing beam splitter, and at least one of the optical polarization elements is an optical retarder.

[0008] The optical device may comprise a half-wave plate constituting at least one of the optical retarders.

[0009] The optical device may comprise a quarter-wave plate constituting at least one of the optical retarders.

[0010] The polarizing beam splitter may be configured to transmit light having the first polarization, and to reflect light having the second polarization.

[0011] The optical device may further comprise one or more reflective surfaces disposed within the substrate.

[0012] The substrate may comprise internal surfaces facing each other, at least portions of the facing surfaces being attached by an adhesive, the adhesive constituting at least one of the reflective surfaces. The adhesive may have a refractive index which is substantially lower than that of the material of the substrate.

[0013] The optical device may comprise a mirror constituting at least one of the reflective surfaces.

[0014] The substrate may comprise internal surfaces facing each other, at least portions of the facing surfaces being attached by an adhesive having a refractive index which is substantially the same as that of the material of the substrate.

[0015] The substrate may comprise two parallel external surfaces configured to facilitate guiding light through the substrate by internal reflection.

[0016] The rotating optical path may pass through the polarizing beam splitter and a primary optical retarder being a half-wave plate, and the non-rotating optical path may reflect off of the polarizing beam splitter.

[0017] The optical device may further comprise a polarization rotation unit, the polarization rotation unit comprising the polarizing beam splitter and a reflective surface disposed in opposition to (i.e., facing) the polarizing beam splitter, the polarization rotation unit further comprising the primary optical retarder spanning between the polarizing beam splitter and the reflective surface and being disposed at an end of the phase shift unit closer to the output interface.

[0018] The optical device may comprise a plurality of polarization rotation units arranged in a stepped arrangement.

[0019] The primary optical retarder may be disposed at the output interface, wherein the non-rotating optical path further makes two passes through one or more auxiliary optical retarders being quarter-wave plates.

[0020] The rotating optical path may pass through the polarizing beam splitter, and further passes two times through one or more primary optical retarders, each primary optical retarder being a quarter-wave plate; and the non-rotating optical path may reflect off the polarizing beam splitter.

[0021] The rotating optical path may further comprise a reflective surface configured to reflect the light after the first pass through one of the primary optical retarders, and before the second pass through one of the primary optical retarders.

[0022] The first polarization may be transverse -magnetic polarization, also referred to as p-polarization.

[0023] The first polarization may be electric-magnetic polarization, also referred to as s-polarization.

[0024] The output interface may comprise a plurality of mutually parallel, partially reflecting surfaces.

[0025] The partially reflecting surfaces may be embedded in the substrate.

[0026] The substrate may define a major axis spanning between the input and output interfaces, wherein the partially reflecting surfaces are disposed at an oblique angle to the major axis.

[0027] According to another aspect of the presently disclosed subject matter, there is provided a neareye display system comprising:a light source configured to emit unpolarized light constituting a collimated image; a lightguide optical element configured to expand the optical aperture of a collimated image injected therein; andan optical device as described above, and being configured to receive the collimated image prior to being expanded by the lightguide optical element, and increase its polarity.

[0028] The lightguide optical element may be configured to expand the optical aperture of the collimated image injected therein in two substantially perpendicular directions.

[0029] The lightguide optical element may comprise a plurality of partially reflecting internal surfaces configured to propagate the light of the collimated image therethrough.

[0030] The lightguide optical element may comprise a diffractive optical element, such as a diffraction grating, configured to reflect each light beam of the collimated image as a plurality of beams.

[0031] The optical device may be configured to (inter alia, it may be disposed within the near-eye display system so as to) receive the collimated image emitted by the light source and inject it into the lightguide optical element after increasing its polarity.

[0032] The lightguide optical element may comprise the optical element, the optical element being configured to (inter alia, it may be disposed within the near-eye display system so as to) receive the collimated image injected into the lightguide optical element and increase its polarity.BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0034] Fig. 1 is a schematic illustration of an example of an optical device according to the presently disclosed subject matter;

[0035] Fig. 2A is a schematic illustration of another example of an optical device according to the presently disclosed subject matter;

[0036] Fig. 2B is a schematic illustration of a non-rotating optical path of a multipath defined by elements of the optical device illustrated in Fig. 2A;

[0037] Figs. 2C and 2D are schematic illustrations of rotating optical paths of the multipath defined by elements of the optical device illustrated in Fig. 2A;

[0038] Fig. 3A is a schematic illustration of another example of an optical device according to the presently disclosed subject matter, showing a rotating optical path of a multipath defined by elements thereof;

[0039] Fig. 3B is a schematic illustration of the optical device illustrated in Fig. 3A, showing a nonrotating optical path of the multipath;

[0040] Figs. 4 through 17E are schematic illustrations of additional examples of optical devices according to the presently disclosed subject matter;

[0041] Fig. 18 is a schematic illustration of an example of an output interface of an optical device according to the presently disclosed subject matter;

[0042] Fig. 19 is a schematic illustration of an optical output element an output interface of an optical device according to the presently disclosed subject matter;

[0043] Figs. 20A through 21B illustrate examples of a near-eye display system according to the presently disclosed subject matter.DETAILED DESCRIPTION

[0044] The present disclosure is directed toward an optical device configured to facilitate passage therethrough of unpolarized light — i.e., light having a random, time-varying polarization, which may be modeled as an incoherent sum of two oppositely polarized beams — to a device such as a projector, a heads-up display, etc. The optical device comprises a plurality of polarization elements — i.e., optical elements which affect the polarization of light impinging thereon (e.g., by rotating it) for example a retarder such as a halfwave plate and / or a quarter-wave plate, and / or whose interaction with light depends on its polarization (e.g., by transmitting or reflecting light depending on its polarization) such as a polarizing beam splitter — within a substantially transparent substrate. Each of the polarization elements may be provided in any suitable configuration. For example, the polarizing beam splitter may be provided as a cube, plate, etc. The optical device may further comprise one or more reflective elements providing reflective surfaces, including, but not limited to, mirrors, adhesives such as low-refractive index adhesive, external surfaces, etc. In general, disclosures herein of specific types of reflective elements are provided by way of non-limiting example only and are not to be construed as limiting; in practice, when a specific type of reflective element is described, it may often be replaced with a different type of reflective element without departing from the scope of the presently disclosed subject matter, mutatis mutandis. The polarization elements define, alone or together with other features / elements of the optical device, an optical multipath within the substrate, i.e., a plurality of paths between input and output interfaces of the substrate, wherein the specific path traversed by light depends, inter alia, on its polarization. Moreover, at least some of the polarization elements are configured to change the polarization of light passing therethrough.

[0045] Accordingly, the optical device is configured to transmit components of the unpolarized input light which are polarized in one direction, e.g., p-polarized components of the light, along one or more rotating optical paths and to cause a net rotation of its polarization, i.e., switching its polarization, and to transmit components of the unpolarized input light which are polarized in the opposite direction, e.g., s-polarized components of the light, along one or more non-rotating optical paths without causing a net rotation of its polarization, i.e., the polarizations of these components of the light at the output interface are the same as that at the input interface. As a result, the optical device may be configured to output polarized light from unpolarized input light, for example without filtering out components of the unpolarized light which have a polarization opposite that of the output light, for example without segregating components present in the unpolarized input light.

[0046] In the appended drawings, polarization elements and reflective elements are illustrated having an exaggerated thickness, in order to facilitate visually distinguishing among the various elements. Moreover, similar elements appearing in different figures are illustrated in the accompanying drawings with similar patterns.

[0047] As illustrated in Fig. 1, there is provided an optical device, which is generally indicated at 10, comprising a substantially transparent substrate 12 configured to allow transmission therethrough of light. One having skill in the art will recognize that the substrate may be “substantially” transparent based on theintended use thereof, i.e., a substrate with a relatively high transmittance may be considered “substantially transparent” for some uses and not for others. According to some examples, the substrate 12 has a transmittance exceeding about 90%. According to further examples, the substrate 12 has a transmittance exceeding about 95%.

[0048] The substrate 12 comprises an input interface 14 at an upstream end of the optical device 10 via which the optical device is configured to receive a input light, and an output interface 16 at a downstream end of the optical device via which the optical device is configured to produce an output light. Parallel upper and lower external surfaces 18a, 18b of the substrate 12 are configured to facilitate guiding light through the substrate by internal reflection. The optical device 10 further comprises a polarizing beam splitter 20 disposed parallel to the external surfaces 18 and being configured, e.g., to transmit p-polarized light and to reflect s-polarized light, and a half-wave plate 22 spanning between the polarizing beam splitter (e.g., at a downstream end thereof) and the lower external surface.

[0049] In addition, the optical device 10 may comprise a mirror 24 in opposition to the input interface 14, disposed at an oblique angle such that it couples input light into the substrate 12. In addition, a low refractive index (low-RI) adhesive 26 may be provided. The low-RI adhesive 26 is characterized by a refractive index which is substantially lower than that of the material of the substrate 12. It will be appreciated that while some examples of the optical device described herein include a low-RI adhesive, this is by way of non-limiting example only and is not to be construed as limiting. In practice, other adhesives which provide a reflective surface, such as those having refractive indices the same as or higher than that of the substrate 12, may be used in place of the low-RI described, without departing from the scope of the presently disclosed subject matter, mutatis mutandis.

[0050] One having skill in the art will recognize that the refractive index of the low-RI adhesive 26 is considered to be “substantially” lower than that of the material of the substrate 12 in that it provides a surface for total internal reflection, e.g., within a tolerable level of optical loss depending on the requirements of the user, for light impinging thereof within a range of angles, for example based on the expected angle which light impinges thereon, e.g., based on a predetermined range of input angles of input light to the optical device 10 at the input interface 14.

[0051] In order to provide the low-RI adhesive 26, two facing internal surfaces 30a, 30b of the substrate 12 may be formed by any suitable method (e.g., the substrate may be formed from at least two pieces, for example the lower-left portion shown in Fig. 1 — which is bound by the polarizing beam splitter 20, the halfwave plate 22, and the low-RI adhesive 26 — may constitute one piece of the substrate, with the remainer of the substrate constituting the other piece). The low-RI adhesive 26 facilitates attaching the facing internalsurfaces 30a, 30b (e.g., the two pieces of the substrate), as well as providing an internal surface having suitable reflective qualities.

[0052] The polarization elements and the reflective elements define a multipath spanning between the input interface 14 and the output interface 16, and cooperate to selectively change the polarization of the of the light passing therethrough, as will be described below.

[0053] The polarization elements define a polarization rotation unit 28 of the optical device 10 between an exit surface 20out (i.e., the downward-facing surface) of the polarizing beam splitter 20, the lower external surface 18b (which constitutes a reflective surface for light impinging on it, e.g., above the critical angle), and the half-wave plate 22.

[0054] In use, unpolarized input light Cm(unpolarized light is indicated in the accompanying drawings by a double line) enters the optical device 10 via the input interface 14. It reflects off the mirror 24, thereby propagating within the substrate 12. (In the presently description and appended claims, the term “input light” may be used to refer to the light upstream of all polarization elements, i.e., light whose polarization state has not been affected.)

[0055] The unpolarized input light impinges on the polarizing beam splitter 20, reflecting s-polarized component of the input light (s-polarized light is indicated in the accompanying drawings by a dashed line), and transmitting the p-polarized component of the input light (p-polarized light is indicated in the accompanying drawings by a dotted line) into the polarization rotation unit 28.

[0056] The reflected s-polarized component propagates through the substrate 12 toward the output interface 16. The transmitted p-polarized component passes through half-wave plate 22, thereby exiting the polarization rotation unit 28 and undergoing a rotation which converts it to s-polarized light. Depending on the length of the substrate 12, light propagating therethrough may be additionally internally reflected by the external surfaces 18.

[0057] The polarizing elements and reflective surfaces define a rotating optical path of the multipath, along which the p-polarized component of the input light Cinis transmitted. The rotating optical path reflects off the mirror 24 and the upper external surface 18a (i.e., the path follows the trajectory of a reflected beam; similarly, descriptions herein the present disclosure and the appended claims of an optical path which refer to the behavior of light are to be understood as describing the path in terms of the trajectory of light as described), passes through the polarizing beam splitter 20 thereby isolating the p-polarized component of the light, continues through the half-wave plate 22 which converts it to s-polarized light, and continues toward the output interface 16. It may further reflect off the external surfaces 18 of the substrate 12. Accordingly, the polarizing components along the rotating optical path cause a net rotation of the p-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0058] The polarizing elements and reflective surfaces further define a non-rotating optical path of the multipath, along which the s-polarized component of the input light Cinis transmitted. The non-rotating optical path reflects off the mirror 24, the upper external surface 18a, and the polarizing beam splitter 20 thereby isolating the s-polarized component of the light, and continues toward the output interface 16. It may further reflect off the external surfaces 18 of the substrate 12. Accordingly, the polarizing components along the non-rotating optical path cause no net rotation of the s-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0059] Accordingly, the light which exits via the output interface 16 is more polarized than the input light Cin, e.g., the output light may be fully polarized, or partially polarized with an increased degree of s-polarization. Full polarization may not be reached, e.g., some of the p-polarized light entering the polarization rotation unit 28 may reflect off the lower external surface 18b and transmitted out of the polarization rotation unit via the polarizing beam splitter 20, and thus not be rotated by the half-wave plate 22. The degree of polarization may be increased in any suitable way, e.g., by decreasing the distance between the upper external surface 18a and the polarizing beam splitter 20, reduces the amount of light which leaves the polarization rotation unit 28 and continues toward the output interface 16 without being transmitted through the half-wave plate 22.

[0060] As illustrated in Fig. 2A, an optical device 10 may be provided which is similar to that which is described above with reference to and as illustrated in Fig. 1, modified to include a plurality of polarization rotation units 28 formed in a stepped arrangement. According to some examples, a first polarization rotation unit 28a is disposed near the input interface 14. The first polarization unit 28a may extend only partially toward the lower external surface 18b. A reflective surface, for example low-RI adhesive 26a, is provided at a lower side of the first polarization rotation unit 28a, in opposition to the polarizing beam splitter 20a. A halfwave plate 22a is provided, spanning between the polarizing beam splitter 20a and the reflective surface, e.g., at respective downstream ends thereof.

[0061] Additional polarization rotation units 28b, 28c, 28d are provided, each similar to the first polarization rotation unit 28a. According to some examples, the lower external surface 18b constitutes the reflective surface of the last polarization rotation unit 28d. Each subsequent polarization rotation unit 28 is disposed downstream of the previous one and below it (e.g., farther from the input interface 14 in two orthogonal directions), such that a lower-downstream comer of each is adjacent an upper-upstream comer of the subsequent one.

[0062] The area 34 below the polarization rotation units 28 may be free of the substrate, for example being made of a material having a refractive index much lower than that of the substrate 12, being free of material, etc.

[0063] In addition to the stepped arrangement of the polarization rotation units 28, the optical device as illustrated in Fig. 2A does not comprise a mirror adjacent the input interface 14. Accordingly, the optical device 10 is configured to output highly polarized light from unpolarized input light which enters the substrate according to any suitable method, including, but not limited to, mirrors, prisms, refractive gratings, etc., for example as is known in the art. It will be appreciated that the optical device described above with reference to and as illustrated in Fig. 1 may be similarly modified, i.e., it may be provided without the mirror, thereby requiring that light enter at a suitable oblique angle. Moreover, any of the examples of optical devices 10 described herein may be modified such that input light enters its substrate according to any suitable method, mutatis mutandis.

[0064] As illustrated in Fig. 2B, the polarizing elements and reflective surfaces of the optical device 10 define a non-rotating optical path of the multipath, along which the s-polarized component of the input light Cmis transmitted. The non-rotating optical path reflects off the low-RI adhesive 26 (or other reflective surface provided) and the upper external surface 18a, then reflects off the polarizing beam splitter 20a of the first of the polarization rotation units 28a thereby isolating the s-polarized component of the light, and continues toward the output interface 16. The non-rotating optical path may further reflect off the upper and / or lower external surfaces 18, and / or polarizing beam splitters 20 of other polarization rotation units 28, depending on the geometry of the optical device 10, the angle of the transmitted light, etc. Accordingly, the polarizing components along the non-rotating optical path cause no net rotation of the s-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0065] The polarizing elements and reflective surfaces of the optical device 10 further define a several rotating optical paths of the multipath along which the p-polarized component of the input light Cmis transmitted, two of which are illustrated in Figs. 2C and 2D.

[0066] As illustrated in Fig. 2C, a rotating optical path reflects off the first low-RI adhesive 26 (or other reflective surface provided) and the upper external surface 18a, then passes through the polarizing beam splitter 20a and the half-wave plate 22a (optionally reflecting off the reflective surface in between) of the first of the polarization rotation units 28a, thereby isolating the p-polarized component of the light (via the polarizing beam splitter) and converting it to s-polarized light (via the half-wave plate), and continues toward the output interface 16. The non-rotating optical path may further reflect off the upper and / or lower external surfaces 18, and / or polarizing beam splitters 20 of other polarization rotation units 28, depending on the geometry of the optical device 10, the angle of the transmitted light, etc. Accordingly, the polarizing components along the rotating optical path cause a net rotation of the p-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0067] As illustrated in Fig. 2D, another rotating optical path reflects off the first low-RI adhesive 26 (or other reflective surface provided) and the upper external surface 18a, then passes through the polarizing beam splitter of the first of the polarization rotation units 28a thereby isolating the p-polarized component of the light. However, owing to the location and / or angle of the input light Cin, the rotating optical path reflects off the reflective surface of the polarization rotation unit 28a and leaves via the polarizing beam splitter 20a, remaining as p-polarized light. It reflects off the upper external surface 18a and passes through the polarizing beam splitter 20 of a subsequent polarization rotation unit 28, and passes through its half-wave plate 22 (optionally reflecting off the reflective surface in between), converting it to s-polarized light, and continues toward the output interface 16. The non-rotating optical path may further reflect off the upper and / or lower external surfaces 18, and / or polarizing beam splitters 20 of other polarization rotation units 28, depending on the geometry of the optical device 10, the angle of the transmitted light, etc. Accordingly, the polarizing components along the rotating optical path cause a net rotation of the p-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0068] Accordingly, the light which exits via the output interface 16 is more polarized than the input light Cin, e.g., the output light may be fully polarized, or partially polarized with an increased degree of s-polarization, for example as described above with reference to Fig. 1, mutatis mutandis.

[0069] As illustrated in Figs. 3A and 3B, an optical device 10 may be provided comprising a polarizing beam splitter 20 and a half-wave plate 22 disposed at the output interface 16 such that all light exiting of the substrate first passes through the polarizing beam splitter and then through the half-wave plate, e.g., spanning between the upper and lower external surfaces 18.

[0070] A low-RI adhesive 26 may be provided in opposition to the input interface 14 and spanning horizontally partway toward the output interface. A quarter-wave plate 32 is provided, spanning vertically between the downstream end of the low-RI adhesive 26 and the lower external surface 18b. A mirror 25 is further provided, spanning vertically between the upstream end of the low-RI adhesive 26 and the lower external surface 18b.

[0071] In use, input unpolarized light Cmenters the optical device 10 via the input interface 14, at an input angle within a predetermined range such that the light traversing through the substrate 12 interacts as necessary with elements of the optical device, for example as described above.

[0072] The polarizing elements and reflective surfaces define a rotating optical path of the multipath, shown in Fig. 3A, along which the p-polarized component of the input light Cinis transmitted. The rotating optical path reflects off the low-RI adhesive 26 and the upper external surface 18a, and continues toward the polarizing beam splitter 20. The rotating optical path passes through the polarizing beam splitter 20 (the reflection of the s-polarized component of the input light is shown for reference), thereby isolating thep-polarized component of the light, and continues through the half-wave plate 22 which converts it to s-polarized light, which exits via the output interface 16. Accordingly, the polarizing components along the rotating optical path cause a net rotation of the p-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0073] The polarizing elements and reflective surfaces further define a non-rotating optical path of the multipath, shown in Fig. 3B, along which the s-polarized component of the input light Cmis transmitted. The non-rotating optical path reflects off the low-RI adhesive 26 and the upper external surface 18a, and continues toward the polarizing beam splitter 20. The non-rotating optical path reflects off the polarizing beam splitter 20 (the transmission of the p-polarized component of the input light is shown for reference), thereby isolating the s-polarized component of the light. It then continues toward the quarter-wave plate 32, undergoing a conversion to circularly polarized light when passing therethrough (circularly polarized light is indicated in the accompanying drawings by a dash-dot-dot [ ] line), and reflects off the mirror 25, through the quarterwave plate 32, undergoing a conversion to p-polarized light. The non-rotating optical path passes through the polarizing beam splitter 20 and continues through the half-wave plate 22 which converts it to s-polarized light, which exits via the output interface 16. Accordingly, the polarizing components along the non-rotating optical path cause no net rotation of the s-polarized component of the input light traversing it from the input interface 14 to the output interface 16, i.e., the s-polarized component of the input light is rotated as it traverses the non-rotating path, but when traversing along the entire path from the input interface to the output interface, the net rotation is zero.

[0074] Accordingly, the light which exits via the output interface 16 is more polarized than the input light Cin, e.g., the output light may be fully polarized, or partially polarized with an increased degree of s-polarization.

[0075] As illustrated in Fig. 4, an optical device 10 may be provided which is similar to that which is described above with reference to and as illustrated in Figs. 3A and 3B, but modified as follows: the horizontal low-RI adhesive 26 is replaced by an auxiliary polarizing beam splitter 20', the quarter-wave plate 32 is disposed adjacent the mirror (i.e., spanning vertically between the downstream end of the auxiliary polarizing beam splitter 20' and the lower external surface 18b), and an auxiliary half-wave plate 22' is provided spanning vertically between the upstream end of the auxiliary polarizing beam splitter 20' and the upper external surface 18a.

[0076] In use, input unpolarized light Cmenters the optical device 10 via the input interface 14, at an input angle within a predetermined range such that the light traversing through the substrate 12 interacts as necessary with elements of the optical device, for example as described above.

[0077] The polarizing elements and reflective surfaces define a rotating optical path of the multipath along which the p-polarized component of the input light Cinis transmitted. The rotating optical path passes through the auxiliary polarizing beam splitter 20' and continues toward the polarizing beam splitter 20. It passes through the polarizing beam splitter 20 and the half-wave plate 22 as described above with reference to and as illustrated in Fig. 3A. Accordingly, the polarizing components along the rotating optical path cause a net rotation of the p-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0078] Some of the p-polarized light which passes through the auxiliary polarizing beam splitter 20' is reflected off the lower external surface 18b and returns through the auxiliary polarizing beam splitter. While some of this p-polarized light is reflected back downwardly through the auxiliary polarizing beam splitter 20', some of it passes through the auxiliary half-wave plate 22' and is converted to s-polarized light which continues downstream toward the polarizing beam splitter 20, and is reflected off the polarizing beam splitter 20 and returns upstream.

[0079] A portion of the upstream-reflected s-polarized light traverses between the auxiliary polarizing beam splitter 20' and the lower external surface 18b. It passes through the quarter-wave plate 32 and undergoes a conversion to circularly polarized light, and is immediately reflected by the mirror 25 to pass through the quarter-wave plate a second time, undergoing a conversion to p-polarized light, which continues toward the polarizing beam splitter 20. It passes through the polarizing beam splitter 20 and the half-wave plate 22 as described above.

[0080] Another portion of the upstream-reflected s-polarized light passes through the auxiliary halfwave plate 22' and is converted to p-polarized light. Some of this p-polarized light reaches the quarter-wave plate 32 and the mirror 25 which cooperate to convert it to s-polarized light, which continues downstream toward the polarizing beam splitter 20. This light is reflected off the polarizing beam splitter 20 and returns upstream as described above, i.e., a portion traverses between the auxiliary polarizing beam splitter 20' and the lower external surface 18b, and a portion passes through the auxiliary half-wave plate 22'.

[0081] Accordingly, a portion of the p-polarized component of the input light Cinwill always reach the polarizing beam splitter 20 as s-polarized light and will be reflected back upstream. Thus, this example of the optical device 10 may be configured to output most, but not all, of the unpolarized input light as highly polarized light, with some of the input light being lost by the design of the optical device. This loss may be mitigated by design choices, e.g., selecting a suitable distance between the auxiliary polarizing beam splitter 20' and the upper external surface 18a; or by adding addition elements, e.g., an additional mirror and quarterwave plate similar to those provided and spanning vertically between the downstream end of the auxiliary polarizing beam splitter and the lower external surface, etc.

[0082] The polarizing elements and reflective surfaces further define a non-rotating optical path of the multipath along which the s-polarized component of the input light Cmis transmitted. The non-rotating optical path reflects off auxiliary polarizing beam splitter 20' and the upper external surface 18a, and passes through the auxiliary half-wave plate 22' which converts it to p-polarized light which continues toward the polarizing beam splitter 20. It passes through the polarizing beam splitter 20 and the half-wave plate 22 as described above with reference to and as illustrated in Fig. 3A. Accordingly, the polarizing components along the nonrotating optical path cause no net rotation of the s-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0083] As illustrated in Figs. 5 and 6, an optical device 10 may be provided comprising a polarizing beam splitter 20 spanning horizontally through the substrate 12, and a half-wave plate 22 disposed therebelow, for example adjacent thereto. One or more reflective surfaces may be provided adjacent the polarizing beam splitter 20 and facing the input interface 14, configured such that light which enters the substrate 12 via the input interface 14 within a predetermined range of angles interacts as necessary with elements of the optical device 10 as it traverses therethrough, for example as described above. As illustrated in Fig. 5, the one or more reflective surfaces may comprise a substantially horizontal low-RI adhesive 26 may be provided, thereby dictating that input light Cmenter the substrate 12 at an oblique angle, for example as described above with reference to and as illustrated in Figs. 2A through 2D. As illustrated in Fig. 6, the one or more reflective surfaces may comprise a mirror 24 disposed at an angle, thereby facilitating providing the input light Cinat a substantially vertical angle, for example as described above with reference to and as illustrated in Fig. 1.

[0084] The polarizing elements and reflective surfaces of the optical device 10 define a rotating optical path of the multipath, along which the p-polarized component of the input light Cinis transmitted. The rotating optical path reflects off the reflective surfaces and the upper external surface 18a, and passes through the polarizing beam splitter 20 thereby isolating the p-polarized component of the light. It subsequently passes through the half-wave plate 22 converting it to s-polarized light, after which it continues toward the output interface 16. Accordingly, the polarizing components along the rotating optical path cause a net rotation of the p-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0085] The polarizing elements and reflective surfaces of the optical device 10 further define a nonrotating optical path of the multipath, along which the s-polarized component of the input light Cmis transmitted. The non-rotating optical path reflects off the reflective surfaces and the upper external surface 18a, and subsequently between the polarizing beam splitter 20 (thereby isolating the s-polarized component of the light) and the upper external surface, toward the output interface 16. Accordingly, the polarizingcomponents along the non-rotating optical path cause no net rotation of the s-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0086] As illustrated in Fig. 7, the optical device 10 as described above with reference to and as illustrated in Fig. 5 may be modified by provided a primary polarizing beam splitter 20a and a primary halfwave plate 22a as described above, optionally spaced from one another vertically. The optical device may further comprise a secondary polarizing beam splitter 20b and secondary half-wave plate 22b disposed therebelow, for example spaced therefrom.

[0087] According to some examples, the lengths of the primary and secondary polarizing beam splitters 20a, 20b are approximately the same. According to some examples, the upstream and / or downstream end of the primary polarizing beam splitter 20a is at approximately the same horizontal location of the respective end of the secondary polarizing beam splitter 20b.

[0088] The primary and secondary half-wave plates 22a, 22b may each be shorter than the primary and secondary polarizing beam splitters 20a, 20b. According to some examples, the upstream end of the secondary half-wave plate 22b is not farther upstream than the downstream end of the primary half-wave plate 22a.

[0089] The non-rotating optical path of the multipath is similar to that of the optical device described above with reference to and as illustrated in Fig. 5.

[0090] The rotating optical path of the multipath is similar to that of the optical device described above with reference to and as illustrated in Fig. 5. However, p-polarized light passing through an upstream portion of the primary polarizing beam splitter 20a and the primary half-wave plate 22a, thereby being converted to s-polarized light, is reflected off the top surface of the second polarizing beam splitter 20b (and subsequently may further reflect off the bottom surface of the first polarizing beam splitter, depending on the angle of the light and the geometry of the optical device 10 and its constituent elements) and continues toward the output interface 16. P-polarized light passing through a downstream portion of the primary polarizing beam splitter 20a continues directly toward the second polarizing beam splitter 20b, passing therethrough and the secondary half-wave plate 22b, thereby being converted to s-polarized light, which is reflected off the bottom external surface 18b toward the output interface 16. Accordingly, the polarizing components along the rotating optical path cause a net rotation of the p-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0091] As illustrated in Fig. 8, the optical device 10 as described above with reference to and as illustrated in Fig. 5 may be modified by replacing the half-wave plate 22 thereof with a quarter-wave plate 32 adjacent the lower external surface 18b. The non-rotating optical path of the multipath is similar to that of the optical device described above with reference to and as illustrated in Fig. 5.

[0092] The rotating optical path of the multipath is similar to that of the optical device described above with reference to and as illustrated in Fig. 5. However, after passing through the polarizing beam splitter 20 thereby isolating the p-polarized component of the light, it passes through the quarter-wave plate 32, undergoing a conversion to circularly polarized light, reflects off the lower external surface 18b and passes again through the quarter-wave plate, undergoing a conversion to s-polarized light. The rotating optical path then continues toward the output interface 16. Accordingly, the polarizing components along the rotating optical path cause a net rotation of the p-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0093] As illustrated in Fig. 9, the optical device 10 as described above with reference to and as illustrated in Fig. 1 may be modified by providing additional polarization and reflective elements as described with reference to Fig. 1, mirrored along a horizontal axis of the substrate 12. Accordingly, the optical device 10 comprises a first low-RI adhesive 26a (replacing the mirror of Fig. 1), a first polarizing beam splitter 20a, and a first half-wave plate 22a constituting a first polarization rotation units 28a; and a second low-RI adhesive 26b, a second polarizing beam splitter 20b, and a second half-wave plate 22b constituting a second polarization rotation unit 28b.

[0094] The polarizing elements and reflective surfaces define rotating optical paths of the multipath, along which the p-polarized component of the input light Cinis transmitted. Each of the rotating optical paths reflects off the first and / or second low-RI adhesive 26a, 26b, passes through one of the polarizing beam splitters 20a, 20b thereby isolating the p-polarized component of the light, continues through a respective half-wave plate 22a, 22b which converts it to s-polarized light, and continues toward the output interface 16, optionally reflecting off a respective one of the external surfaces 18. Accordingly, the polarizing components along the rotating optical path cause a net rotation of the p-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0095] The polarizing elements and reflective surfaces further define a non-rotating optical path of the multipath, along which the s-polarized component of the input light Cinis transmitted. The non-rotating optical path reflects off the low-RI adhesive 26a, 26b (or other reflective surface provided), internally reflects between the polarizing beam splitters 20a, 20b, and continues toward the output interface 16.

[0096] As illustrated in Fig. 10, the optical device 10 as described above with reference to and as illustrated in Fig. 5 may be modified by providing additional polarization and reflective elements as described with reference to Fig. 1, mirrored along a horizontal axis of the substrate 12. Accordingly, the optical device 10 comprises first and second low-RI adhesives 26a, 26b, first and second polarizing beam splitters 20a, 20b, and first and second first half-wave plates 22a, 22b.

[0097] The polarizing elements and reflective surfaces of the optical device 10 define rotating optical paths of the multipath, along which the p-polarized component of the input light Cinis transmitted. Each of the rotating optical paths reflects off the first and / or second low-RI adhesive 26a, 26b, passes through one of the polarizing beam splitters 20a, 20b thereby isolating the p-polarized component of the light, continues through a respective half-wave plate 22a, 22b converting it to s-polarized light, after which it continues toward the output interface 16, optionally reflecting off a respective one of the external surfaces 18. Accordingly, the polarizing components along the rotating optical path cause a net rotation of the p-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0098] The polarizing elements and reflective surfaces further define a non-rotating optical path of the multipath, along which the s-polarized component of the input light Cinis transmitted. The non-rotating optical path reflects off the low-RI adhesive 26a, 26b (or other reflective surface provided), internally reflects between the polarizing beam splitters 20a, 20b, and continues toward the output interface 16.

[0099] As illustrated in Fig. 11, the optical device 10 may comprise a polarizing beam splitter 20 spanning horizontally across the substrate 12, and a half-wave plate 22 therebelow. The input interface 14 may be configured to facilitate receipt of input light Cmabove the polarizing beam splitter 20 via a top and / or side surface of the substrate 12.

[0100] The polarizing elements and reflective surfaces define a rotating optical path of the multipath, along which the p-polarized component of the input light Cinis transmitted. The rotating optical path passes through the polarizing beam splitter 20 thereby isolating the p-polarized component of the light, continues through the half-wave plate 22 which converts it to s-polarized light, and continues toward a bottom portion of the output interface 16b. It may further reflect off the lower external surfaces 18b of the substrate 12. Accordingly, the polarizing components along the rotating optical path cause a net rotation of the p-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0101] The polarizing elements and reflective surfaces further define a non-rotating optical path of the multipath, along which the s-polarized component of the input light Cinis transmitted. The non-rotating optical path reflects off the polarizing beam splitter 20 thereby isolating the s-polarized component of the light, and continues toward an upper portion of the output interface 16a. It may further reflect off the upper external surface 18a and the polarizing beam splitter 20. Accordingly, the polarizing components along the non-rotating optical path cause no net rotation of the s-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0102] As illustrated in Fig. 12, the optical device 10 may comprise a horizontally disposed polarizing beam splitter 20 and a half-wave plate 22 thereabove. The input interface 14 may be configured to facilitatereceipt of input light Cinbelow the polarizing beam splitter 20, e.g., via a bottom and / or side surface of the substrate 12.

[0103] The polarizing elements and reflective surfaces define a rotating optical path of the multipath, along which the p-polarized component of the input light Cinis transmitted. The rotating optical path passes through the polarizing beam splitter 20 thereby isolating the p-polarized component of the light, continues through the half-wave plate 22 which converts it to s-polarized light, and continues toward the output interface 16. It may further reflect off the upper external surfaces 18a of the substrate 12. Accordingly, the polarizing components along the rotating optical path cause a net rotation of the p-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0104] The polarizing elements and reflective surfaces further define a non-rotating optical path of the multipath, along which the s-polarized component of the input light Cinis transmitted. The non-rotating optical path reflects off the polarizing beam splitter 20 thereby isolating the s-polarized component of the light, and continues toward the output interface 16. It may further reflect off the upper and / or lower external surfaces 18a, 18b and the polarizing beam splitter 20. Accordingly, the polarizing components along the nonrotating optical path cause no net rotation of the s-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0105] As illustrated in Fig. 13, an optical device 10 may be provided comprising a main a low-RI transition interface 36 dividing the substrate into upper and lower sections 12a, 12b. The transition interface 36 is configured to internally reflect light impinging upon it above the critical angle, and to transmit light impinging it at substantially an orthogonal angle. According to some examples, the transition interface 36 comprises a low-RI adhesive, for example as described above.

[0106] The upper section 12a comprises a polarization rotation unit 28 adjacent the input interface 14, comprising a low-RI adhesive 26a, a polarizing beam splitter 20a, and a half-wave plate 22a, with the transition interface 36 constituting a bottom reflective surface thereof.

[0107] The upper section further comprises an iteration arrangement 38 adjacent the output interface 16, configured to transmit p-polarized light to the output interface 16, and recycle s-polarized light through the lower section 12b to undergo rotation to s-polarized light. The iteration arrangement 38 comprises first and second half-wave plates 22b, 22c, and a polarizing beam splitter 20b spanning diagonally between ends halfwave plates 22b, 22c, such that s-polarized light from the first half-wave plate 22b is reflected downwardly off the polarizing beam splitter at an angle at which it is transmitted through the transition interface 36 to the lower section 12b, for example substantially orthogonal.

[0108] The lower section 12b comprises an coupling-in mirror 24a configured to reflect light entering the lower section from the iteration arrangement 38, such that it propagates through the lower section byinternal reflection, and a coupling-out mirror 24b configured to reflect light upwardly from the lower section 12b at an angle at which it is transmitted through the transition interface 36 to the upper section 12a, for example substantially orthogonal. The lower section further comprises, between the coupling-in mirror 24a and the coupling-out mirror 24b, a half-wave plate 22d spanning the entire height thereof. Accordingly, polarized light which propagates through the lower section 12b from the coupling-in mirror 24a to the coupling-out mirror 24b undergoes a rotation of polarity, thereby switching polarity.

[0109] The upper section 12a further comprises a return mirror 24c, configured to reflect light off the coupling-out mirror 24b such that it propagates through the upper section 12a toward the output interface 16. According to some examples, the return mirror 24c is disposed within the polarization rotation unit 28.

[0110] The polarizing elements and reflective surfaces define a rotating optical path of the multipath, along which the p-polarized component of the input light Cinis transmitted. The rotating optical path reflects off the low-RI adhesive 26a and the upper external surface 18a, passes through the polarizing beam splitter 20a thereby isolating the p-polarized component of the light, continues through the half-wave plate 22a which converts it to s-polarized light, and continues toward the output interface 16. It passes through the first halfwave plate 22b of the iteration arrangement 38 thereby being converted to p-polarized light, passes through the polarizing beam splitter 20b and through the second half-wave plate 22c thereby being converted back to s-polarized light, and exits through the output interface 16. Accordingly, the polarizing components along the rotating optical path cause a net rotation of the p-polarized component of the input light traversing it from the input interface 14 to the output interface 16. s[oni] The polarizing elements and reflective surfaces further define a non-rotating optical path of the multipath, along which the s-polarized component of the input light Cinis transmitted. The non-rotating optical path reflects off low-RI adhesive 26a, the upper external surface 18a, and the polarizing beam splitter 20a thereby isolating the s-polarized component of the light, and continues toward the output interface 16. Upon encountering the iteration arrangement 38, it proceeds therethrough to the output interface 16 as described above with reference to the rotating optical path. Accordingly, the polarizing components along the non-rotating optical path cause no net rotation of the s-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0112] As described above with reference to Fig. 1, some of the p-polarized light entering the polarization rotation unit 28 may be reflected out of it via the polarizing beam splitter 20, without passing through half-wave plate 22a. Accordingly, some of the light reaching the iteration arrangement 38 is p-polarized. This portion of the light follows an iterative optical path, which passes through the first halfwave plate of the iteration arrangement 38 thereby being converted to s-polarized light, and is reflected downwardly toward the transition interface 36 at an angle at which it is transmitted therethrough to the lowersection 12b. It is reflected by the coupling-in mirror 24a toward the coupling-out mirror 24b, passing through the half-wave plate 22d and being converted to p-polarized light. It is then reflected by the coupling-out mirror 24b through the transition interface 36 to the upper section 12a, and reflects off the return mirror 24c toward the output interface 16, passing through the polarization rotation unit 28. Some of the light passes through the half-wave plate 22a of the polarization rotation unit 28, being converted to s-polarized light, which continues toward the output interface 16. Upon encountering the iteration arrangement 38, it proceeds therethrough to the output interface 16 as described above with reference to the rotating optical path. Light which reflects off the return mirror 24c and does not pass through the half-wave plate 22a of the polarization rotation unit 28 reaches the iteration arrangement 38 as p-polarized light, and is iterated through the lower section 12b by the iteration arrangement, repeating the process. Each iteration reduces the amount of p-polarized light remaining in the optical guide 10.

[0113] It will be appreciated that while the optical device 10 is described as having a single polarization rotation unit 28 which is similar, in construction and operation, to that described above with reference to Fig. 1, it may comprise a plurality of polarization rotation units 28, e.g., formed in a stepped arrangement, for example as described above with reference to and as illustrated in Figs. 2A through 2D, mutatis mutandis.

[0114] As illustrated in Fig. 14, an optical device 10 may be provided which is similar to that which is described above with reference to and as illustrated in Fig. 13, modified to shorten the low-RI transition interface 36, replacing its ends with transparent interfaces 40. The transparent interfaces 40 are configured to allow light to pass freely therethrough. According to some examples, each of the transparent interfaces 40 comprises an index-matching adhesive. In addition, the iteration arrangement 38 spans the upper and lower sections 12a, 12b, with the polarizing beam splitter 20b and second half-wave plate 22c thereof spanning vertically substantially the height of the substrate 12. Moreover, the optical device 10 does not contain the mirrors 24a, 24b, 24c described above with reference to and illustrated in Fig. 13.

[0115] The polarizing elements and reflective surfaces define rotating and non-rotating optical paths of the multipath which are similar, mutatis mutandis, to those described above with reference to Fig. 13.

[0116] The iterative optical path is similar, mutatis mutandis, to that described above with reference to Fig. 13, with the s-polarized light being reflected directly into the bottom section 12b off the polarizing beam splitter 20b of the iteration arrangement 38, and reflecting back into the upper portion 12a (after passing through the half-wave plate 22d and being converted to p-polarized light) by internal reflection.

[0117] As illustrated in Fig. 15, an optical device 10 may be provided which is similar to that which is described above with reference to and as illustrated in Fig. 13, modified to remove the polarization rotation unit 28 (i.e., the polarizing beam splitter 20a and a half-wave plate 22a are removed; the low-RI adhesive 26a remains) and first half-wave plate 22b of the iteration arrangement 38. (In order to highlight the similaritieswith the example of Fig. 13, nomenclature and reference numbers have been retained for like elements; accordingly, the comprising a low-RI adhesive 26a of Fig. 15 includes a second half-wave plate 22c, even though it does not include a first half-wave plate, nor any element indicated by reference number 22b.)

[0118] The polarizing elements and reflective surfaces define a rotating optical path of the multipath, along which the p-polarized component of the input light Cinis transmitted. The rotating optical path reflects off the low-RI adhesive 26a and the upper external surface 18a, and continues toward the output interface 16. It passes through the polarizing beam splitter 20b and through the second half-wave plate 20c thereby being converted to s-polarized light, and exits through the output interface 16. Accordingly, the polarizing components along the rotating optical path cause a net rotation of the p-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0119] The polarizing elements and reflective surfaces further define a non-rotating optical path of the multipath, along which the s-polarized component of the input light Cinis transmitted. The non-rotating optical path reflects off the low-RI adhesive 26a and the upper external surface 18a, and continues toward the output interface 16. Upon encountering the iteration arrangement 38, it is reflected downwardly toward the transition interface 36 at an angle at which it is transmitted therethrough to the lower section 12b. It is reflected by the coupling-in mirror 24a toward the coupling-out mirror 24b, passing through the half-wave plate 22d and being converted to p-polarized light. It is then reflected by the coupling-out mirror 24b through the transition interface 36 to the upper section 12a, and reflects off the return mirror 24c toward the output interface 16. Upon encountering the iteration arrangement 38, it proceeds therethrough to the output interface 16 as described above with reference to the rotating optical path. According to some examples, almost 100% of the s-polarized component of the input light Cinexits through the optical device 10 after a single iteration. Accordingly, the polarizing components along the non-rotating optical path cause no net rotation of the s-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0120] As illustrated in Fig. 16, an optical device 10 may be provided comprising a main a first low-RI adhesive 26a adjacent the input interface 14, extending horizontally partway to the output interface. A transparent interface 40, for example comprising an index-matching adhesive, spans between the first low-RI index adhesive 26a and the output interface 16. A second low-RI adhesive 26b is provided below the first low-RI adhesive 26a and vertically spaced therefrom. The second low-RI adhesive is horizontally spaced from the side surfaces (including the output interface 16) by additional transparent interfaces 40.

[0121] The optical device 10 further comprises a polarizing beam splitter 20 and half-wave plate 22 at the output interface 16, and a quarter-wave plate 32 at the opposite end of the substrate 12. According to some examples, a mirror (not illustrated) may be provided between the quarter-wave plate 32 and the sidewall of the substrate.

[0122] The polarizing elements and reflective surfaces define a rotating optical path of the multipath, along which the p-polarized component of the input light Cinis transmitted. The rotating optical path internally reflects between the first low-RI adhesive 26a and the upper external surface 18a, and continues toward the output interface 16. It passes through the beam splitter 20 and half-wave plate 22 thereby being converted to s-polarized light, and exits through the output interface 16. Accordingly, the polarizing components along the rotating optical path cause a net rotation of the p-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0123] The polarizing elements and reflective surfaces further define a non-rotating optical path of the multipath, along which the s-polarized component of the input light Cinis transmitted. The non-rotating optical path internally reflects between the first low-RI adhesive 26a and the upper external surface 18a, and continues toward the output interface 16. It is reflected off the polarizing beam splitter 20, and passes through the transparent interface 40 to continue below the second low-IR adhesive 26b, internally reflecting between the second low-IR adhesive and the lower external surface 18. Upon reaching the quarter-wave plate 32, it passes therethrough undergoing a conversion to circularly polarized light, and is immediately reflected off the mirror to pass through the quarter-wave plate a second time, undergoing a conversion to p-polarized light. It continues between the first and second low-IR adhesives 26a, 26b toward the output interface 16. It passes through the polarizing beam splitter 20 and the second half-wave plate 22 thereby being converted to s-polarized light, and exits through the output interface 16. Accordingly, the polarizing components along the non-rotating optical path cause no net rotation of the s-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0124] As illustrated in Fig. 17A, an optical device 10 may be provided comprising a polarizing beam splitter 20 disposed at an angle (p relative to a main horizontal axis spanning between the input and output interfaces 14, 16 which is not less than 45°, in order to ensure that no light is reflected toward the input surface. According to some examples, the angle (p is greater than 45°, e.g., 49°. A half-wave plate 22 is provided downstream in the transmission path (i.e., relative to the input light Cin) of the polarizing beam splitter 20, spanning the vertical height thereof. A mirror 24 is provided facing the polarizing beam splitter 20 and disposed substantially parallel thereto, for example to preserve angular resolution. The mirror 24 is suitable spaced from the polarizing beam splitter 20, for example to ensure that light reflected off the polarizing beam splitter does not subsequently reflect off the mirror to the polarizing beam splitter.

[0125] In addition, masks 50a, 50b may be provided, e.g., to avoid ghost reflections from side faces of the polarizing beam splitter 20. Masks 50a may define therebetween a pupil of the optical device 10. According to some examples, the distance between each pair of masks may be inversely related to the angle of propagation of light through the optical device 10. The angle of propagation may be determined in anysuitable manner such as is known in the art, for example, but not limited to, based on the refractive index of elements of the optical device (e.g., wherein the angle of propagation is inversely related to with the higher refractive index), the angle of the polarizing beam splitter 20, etc.

[0126] The polarizing elements and reflective surfaces define a rotating optical path of the multipath, along which the p-polarized component of the input light Cinis transmitted. The rotating optical path passes through the polarizing beam splitter 20 and then through the half-wave plate 22 thereby being converted to s-polarized light, and exits through the output interface 16. Accordingly, the polarizing components along the rotating optical path cause a net rotation of the p-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0127] The polarizing elements and reflective surfaces further define a non-rotating optical path of the multipath, along which the s-polarized component of the input light Cinis transmitted. The non-rotating optical path reflects off the polarizing beam splitter 20 toward the mirror 24. It further reflects off the mirror 24 toward the output interface 16 for exiting therethrough. Accordingly, the polarizing components along the non-rotating optical path cause no net rotation of the s-polarized component of the input light traversing it from the input interface 14 to the output interface 16.

[0128] As a result, the optical device 10 may be configured to output highly polarized light, e.g., two separate beams of the same polarization, from unpolarized input light, in particular which is provided as collimated light parallel to the main horizontal axis of the optical device. Moreover, if the input light is evenly distributed, the optical device 10 may be configured to provide highly polarized output light which is similarly distributed.

[0129] As illustrated in Fig. 17B, an optical device 10 may be provided according to a modification of that described above with reference to and as illustrated in Fig. 17A, in which the half-wave plate 22 is disposed downstream in the reflection path (i.e., relative to the input light Cin) of the polarizing beam splitter 20, either between the polarizing beam splitter and the mirror 24 or downstream of the mirror (not illustrated). Accordingly, the optical device 10 is configured to output s-polarized light, for example as described above, mutatis mutandis.

[0130] As illustrated in Fig. 17C, an optical device 10 may be provided which is substantially symmetrical, in which each half is provided as described above with reference to and as illustrated in Fig.17A. This may facilitate providing a compact optical device having a thickness along the optical propagation axis (i.e., in the horizontal direction of the figure as illustrated) which is proportionally less compared to the width of the input light.

[0131] According to some examples, masks 50 may be provided in or near the input interface 14, i.e., upstream of the polarizing beam splitter 20, thereby defining a pupil of the optical device 10 therebetween.

[0132] As illustrated in Fig. 17D, an optical device 10 may be provided which is similar to that described above with reference to and as illustrated in Fig. 17C, wherein each half is provided as described above with reference to and as illustrated in Fig. 17B, mutatis mutandis. Similarly, as illustrated in Fig. 17E, an optical device may be provided which is similar to that described with reference to and as illustrated in Fig. 17D, in which the half-wave plates 22 are disposed downstream of the mirror, mutatis mutandis.

[0133] It will be appreciated that while the output interfaces 16 are depicted in Figs. 1 through 17E as physical boundaries of the substrates 12 of the optical devices, this is for illustrative purposes only. According to some examples, such as is illustrated in Fig. 18, the output interface 16 may comprise a plurality of mutually parallel, partially reflecting surfaces 42 embedded in the material of the substrate. The reflecting surfaces may be disposed, e.g., at an oblique angle to a major axis X which spans between the input and output interfaces 14, 16.

[0134] As illustrated in Fig. 19, the output interface 16 may be configured to facilitate coupling out light exiting therethrough into an optical output element 44. According to some examples, the optical output element 44 comprises a mirror 46 configured to reflect light from the optical device into the optical output element. According to some examples, the optical output element 44 comprises a plurality of mutually parallel, partially reflecting surfaces 42 embedded therein.

[0135] As illustrated in Figs. 20A through 2 IB, an optical device 10 according to the presently disclosed subject matter may constitute part of a near-eye display system 100.

[0136] As illustrated in Figs. 20A and 20B, the near-eye display system 100 may comprise a compact image projector assembly 114 integrated so as to inject an image into a lightguide optical element (LOE) within which the image light is trapped by internal reflection at a pair of mutually parallel major external surfaces. The LOE typically includes an arrangement for expanding the optical aperture of the injected image in one or two dimensions, and for coupling out the image illumination toward the eye of an observer. According to some examples, these functions are based on internal partially reflecting surfaces or on diffractive optical elements.

[0137] In one non-limiting set of implementations, the light injected into the LOE impinges on a set of partially reflecting surfaces that are parallel to each other and inclined obliquely to a direction of propagation of the image light. Each successive surface deflects a proportion of the image light into a deflected direction that remains guided by internal reflection within the substrate. These surfaces are located in a first region 116. This partial reflection at successive surfaces progressively redirects the direction of guided propagation while expanding the optical aperture in a first dimension. The redirected image illumination then passes into a second region 118, which may be implemented as an adjacent distinct substrate or as a continuation of a single substrate, in which a coupling-out arrangement, either a further set of partially reflective surfaces or adiffractive optical element, progressively couples out a proportion of the image illumination toward an eye located within an eye-motion box, thereby achieving a second dimension of optical aperture expansion.

[0138] The overall device may be implemented separately for each eye, and is preferably supported relative to the head of a user with each LOE facing a corresponding eye. A support arrangement 120 may be implemented as an eyeglass frame with sides for supporting the device relative to the user’s ears. Other forms of support arrangement may also be used, including head bands, visors, or devices suspended from helmets.

[0139] Reference is made to an X-axis which extends in the general extensional direction of the first region of the LOE, and to a Y-axis which extends perpendicular thereto. In Fig. 20A the X-axis is horizontal and the Y-axis is vertical. In Fig. 20B the X-axis is vertical and the Y-axis is horizontal. In approximate terms, the first region 116 may be considered to achieve aperture expansion in the X-direction while the second region 118 achieves aperture expansion in the Y-direction. For simplicity of presentation, the invention will be illustrated in subsequent drawings using schematic partial side views of a lightguide and will omit most of the internal features of the lightguide. The invention may also be applied to LOEs that perform a single dimension of aperture expansion, omitting the internal redirection arrangement.

[0140] The image projector 114 employed with the devices of the present invention is preferably configured to generate a collimated image, i.e., in which the light of each image pixel is a parallel beam, collimated to infinity, with an angular direction corresponding to the pixel position. The image illumination thus spans a range of angles corresponding to an angular field of view in two dimensions.

[0141] Image projector 114 includes at least one light source which emits polarized light, for example comprising one or more active arrays of light-generating pixels, such as a micro-LED array. Collimating optics are provided to generate an output projected image which is collimated to infinity. Some or all of the above components are typically arranged on surfaces of one or more polarizing beam-splitter (PBS) cube or other prism arrangement, all as is known in the art.

[0142] The image injected into the lightguides is preferably a collimated image, in which light of each image pixel is a parallel beam, collimated to infinity, with an angular direction corresponding to pixel position so that the image illumination spans an angular field of view in two dimensions. The near-eye display system 100 may include additional components such as a controller 122 for operating the image projector 114, powered by an onboard battery or another suitable power source.

[0143] Fig. 21 A is a schematic illustration of the LOE of the near-eye display system 100 corresponding to the side-injection arrangement of Fig. 20B. Light Ctnwhich is emitted from projector 114 (not illustrated in Fig. 21A) enters an optical device 10, which is configured to increase the polarity of the light, for example as described above with reference to an as illustrated in any one or more of Figs. 1 through 17E. The light which is output by the optical device enters the LOE, and is deflected by reflection at one or more internalreflector 113, thereby facilitating injection of the image into the LOW, so as to be guided by internal reflection between major surfaces, and is progressively redirected, for example by impinging on internal partially reflective surfaces 126 in the first region 116, which progressively redirect the guided image light from a first guided propagation direction to a second guided propagation direction. The redirected image light passes through an interface 125 and into the second region 118, where an out-coupling arrangement, for example reflective out-coupling surfaces 128 or a diffractive out-coupler, directs the image light toward the viewer’s eye 150 located within an eye-motion box corresponding to an acceptable range of eye positions and designated by rectangle 152. In certain cases, an optical element may be deployed at interface 125, for example, to modify a polarization of light passing from the first region to the second region.

[0144] According to a modification, for example as illustrated in Fig. 21B, the near-eye display system 100 may be provided, mutatis mutandis, such that the optical device 10 is provided as part of the LOE, downstream of internal reflector 113. Accordingly, light Cmwhich is emitted from projector 114 is deflected by reflection at one or more internal reflector 113 into the optical device 10, which increases its polarity for example as described above with reference to an as illustrated in any one or more of Figs. 1 through 17E.

[0145] It will be appreciated that the examples of optical devices described above with reference to and illustrated in the accompanying drawings are provided to illustrate one or more inventive concepts of the presently disclosed subject matter, and are not to be construed as limiting. For example, one having skill in the art will recognize that relative positions, sizes, aspect ratios, etc., of the polarization elements and reflective elements may be selected to optimize the rotation of the p -polarized component of the input light at a desired location, e.g., the center, of a given field of view; to optimize polarizing switching efficiency; to optimize maximal mixing of the light; to optimize illumination filling of the output interface; to enhance the efficiency and / or uniformity of polarization conversion within the optical device, etc.

[0146] It will be further appreciated that according to any of the examples of the optical device 10 described herein, pairs of elements which are illustrated as being parallel to each other and separated by the substrate may, depending on how the optical device is configured to operate, be disposed adjacent each other with substantially no separation therebetween. Similarly, pairs of elements which are illustrated as being adjacent each other with substantially no separation therebetween may, depending on how the optical device is configured to operate, be separated from one another, e.g., by material of the substrate. Accordingly, while the half-wave plate 22 of the example of the optical device 10 described above with reference to and as illustrated in Figs. 3A and 3B is illustrated as being adjacent the output interface 16, this is for illustration only, and in practice they may be spaced from each other. Similarly, while the polarizing beam splitter 20 and the half-wave plate 22 of the example of the optical device 10 described above with reference to and asillustrated in Figs. 3A and 3B are illustrated as being spaced from each other, this is for illustration only, and in practice they may be adjacent each other with substantially no space therebetween.

[0147] Herein the present disclosure, different elements indicated by a single reference number and distinguished by their trailing letters may be collectively indicated using the single reference number without a trailing letter, e.g., reference number 18 may be used to collectively indicate upper and lower surfaces 18a, 18b, for example depending on the context. Similarly, unless otherwise indicated or clear from context, herein the present disclosure, two or more figures which are labeled using the same number and are distinguished only by their trailing letters illustrate the same example of an optical device 10, and differ only in the optical paths illustrated.

[0148] Herein the present disclosure and appended claims, terms relating to direction, including, but not limited to, “upper,” “lower,” “above,” “below,” “top,” “lower,” “vertical,” “horizontal,” etc., and similar / related terms are used with reference to the orientation shown in the accompanying drawings for the purposes of clarity of disclosure and to provide a reference based on which the scope of the claims can be determined. Accordingly, terms relating to direction are not to be construed as limiting, unless indicated otherwise or clear from context.

[0149] Herein the present disclosure and appended claims, the terms “upstream” and “downstream” are used with reference to the transmission path of light through the optical device. Accordingly, while the upstream and downstream ends of the examples of optical devices described above with reference to and as illustrated in the accompanying drawings are at physically located at opposite ends of a generally elongate substrate, this is by way of non-limiting example only, and is not to be construed as limiting. In practice, an optical device may be provided in which the upstream and downstream ends are, e.g., physically adjacent one another without departing from the scope of the presently disclosed subject matter, mutatis mutandis.

[0150] It will be recognized that examples, embodiments, modifications, options, etc., described herein are to be construed as inclusive and non-limiting, i.e., two or more examples, etc., described separately herein are not to be construed as being mutually exclusive of one another or in any other way limiting, unless such is explicitly stated and / or is otherwise clear. Those skilled in the art to which this invention pertains will readily appreciate that numerous changes, variations, and modifications can be made without departing from the scope of the presently disclosed subject matter, mutatis mutandis.

Claims

CLAIMS1. A near-eye display system comprising:a light source configured to emit unpolarized light constituting a collimated image;a lightguide optical element configured to expand the optical aperture of a collimated image injected therein; andan optical device configured to receive the collimated image prior to being expanded by the lightguide optical element, and increase its polarity;the optical device comprising:a substantially transparent substrate comprising an input interface and an output interface; a plurality of optical polarization elements disposed within the substrate, the optical polarization elements and the substrate defining a polarization-dependent optical multipath through the substrate between the input interface and the output interface for input light entering the substrate at the input interface within a predetermined range of input angles; wherein the multipath comprises:a rotating optical path configured to transmit a first component of the input light having a first polarization, and to cause a net rotation of the polarization of the first component traversing it from the input interface to the output interface; and a non-rotating optical path configured to transmit a second component of the input light having a second polarization opposite the first polarization, and does not cause a net rotation of the polarization of the second component traversing it from the input interface to the output interface.

2. The near-eye display system according to claim 1 , wherein the multipath is configured to transmit, from the input interface to the output interface, a majority of each of the first and second components of the input light.

3. The near-eye display system according to any one of the preceding claims, wherein at least one of the optical polarization elements is a polarizing beam splitter, and at least one of the optical polarization elements is an optical retarder.

4. The near-eye display system according to claim 3, the optical element comprising a half-wave plate constituting at least one of the optical retarders.

5. The near-eye display system according to any one of claims 3 and 4, the optical element comprising a quarter-wave plate constituting at least one of the optical retarders.

6. The near-eye display system according to any one of claims 3 through 5, wherein the polarizing beam splitter is configured to transmit light having the first polarization, and to reflect light having the second polarization.

7. The near-eye display system according to any one of the preceding claims, the optical element further comprising one or more reflective surfaces disposed within the substrate.

8. The near-eye display system according to claim 7, the substrate comprising internal surfaces facing each other, at least portions of the facing surfaces being attached by an adhesive, the adhesive constituting at least one of the reflective surfaces.

9. The near-eye display system according to claim, the adhesive having a refractive index which is substantially lower than that of the material of the substrate.

10. The near-eye display system according to any of claims 7 through 9, the optical element comprising a mirror constituting at least one of the reflective surfaces.

11. The near-eye display system according any one of the preceding claims, the substrate comprising internal surfaces facing each other, at least portions of the facing surfaces being attached by an adhesive having a refractive index which is substantially the same as that of the material of the substrate.

12. The near-eye display system according to any one of the preceding claims, the substrate comprising two parallel external surfaces configured to facilitate guiding light through the substrate by internal reflection.

13. The near-eye display system according to claim 3, wherein:the rotating optical path passes through the polarizing beam splitter and a primary optical retarder being a half-wave plate; andthe non-rotating optical path reflects off of the polarizing beam splitter.

14. The near-eye display system according to claim 13, the optical element further comprising a polarization rotation unit, the polarization rotation unit comprising the polarizing beam splitter and a reflective surface disposed in opposition to the polarizing beam splitter, the polarization rotation unit further comprising the primary optical retarder spanning between the polarizing beam splitter and the reflective surface and being disposed at an end of the phase shift unit closer to the output interface.

15. The near-eye display system according to claim 14, the optical element comprising a plurality of polarization rotation units arranged in a stepped arrangement.

16. The near-eye display system according to claim 13, the primary optical retarder being disposed at the output interface, wherein the non-rotating optical path further makes two passes through one or more auxiliary optical retarders being quarter-wave plates.

17. The near-eye display system according to claim 3, wherein:the rotating optical path passes through the polarizing beam splitter, and further passes two times through one or more primary optical retarders, each primary optical retarder being a quarterwave plate; andthe non-rotating optical path reflects off the polarizing beam splitter.

18. The near-eye display system according to claim 17, the rotating optical path further comprising a reflective surface configured to reflect the light after the first pass through one of the primary optical retarders, and before the second pass through one of the primary optical retarders.

19. The near-eye display system according to any one of the preceding claims, wherein the first polarization is transverse-magnetic polarization.

20. The optical device according to any one of claims 1 through 18, wherein the first polarization is electric-magnetic polarization.

21. The near-eye display system according to any one of the preceding claims, wherein the output interface comprises a plurality of mutually parallel, partially reflecting surfaces.

22. The near-eye display system according to claim 21, wherein the partially reflecting surfaces are embedded in the substrate.

23. The near-eye display system according to any one of claims 21 and 22, the substrate defining a major axis spanning between the input and output interfaces, wherein the partially reflecting surfaces are disposed at an oblique angle to the major axis.

24. The near-eye display system according to any one of the preceding claims, wherein the lightguide optical element is configured to expand the optical aperture of the collimated image injected therein in two substantially perpendicular directions.

25. The near-eye display system according to any one of the preceding claims, the lightguide optical element comprising a plurality of partially reflecting internal surfaces configured to propagate the light of the collimated image therethrough.

26. The near-eye display system according to any one of the preceding claims, the lightguide optical element comprising a diffractive optical element configured to reflect each light beam of the collimated image as a plurality of beams.

27. The near-eye display system according to any one of the preceding claims, wherein the optical device is configured to receive the collimated image emitted by the light source and inject it into the lightguide optical element after increasing its polarity.

28. The near-eye display system according to any one of claims 1 through 26, the lightguide optical element comprising the optical element, the optical element being configured to receive the collimated image injected into the lightguide optical element and increase its polarity.

Images