Patent Description:
A PBS works by reflecting light of one polarization type in a reflected direction, typically <NUM> degrees, and transmitting light of the orthogonal polarization in a transmitted direction with no change in angle. The catadioptric system utilizing a PBS requires polarized light incident on the system, which reduces throughput efficiency for the entire optical path. For example, by polarizing an optical system, light utilization efficiency is reduced to ~<NUM>% in addition to other optical losses. Accordingly, it is desirable to provide a PBS-based optical system that provides adequate display characteristics while utilizing light with greater efficiency than conventional approaches. <CIT> relates to a near-eye display apparatus.

<CIT> discloses a head up display comprising a catadioptric collimating system.

An optical system according to the claimed invention is defined in claim <NUM>.

In some embodiments of the optical system, the light path of the first light beam and the light path of the second light beam are parallel when exiting the collimating optics.

In some embodiments of the optical system, the light path of the first light beam and the light path of the second light beam are collinear when exiting the collimating optics.

The optical system according to the claimed invention further includes a field lens disposed on the polarization beam splitter configured to receive the image light from the light source.

In some embodiments of the optical system, the corrector lens, the field lens, the first mirror, the second mirror, and the polarization beam splitter are configured to fit into a package with a volume less than two cubic centimeters.

In some embodiments of the optical system, the optical system further includes the light source.

In some embodiments of the optical system, the light source includes at least one of a light emitting diode display, a micro light emitting diode display, an organic light emitting diode display, an active-matrix liquid crystal display, or a liquid crystal on silicon display or a digital micromirror device display.

In some embodiments of the optical system, the optical system is configured as a collimating system for display on a substrate waveguide.

In some embodiments of the optical system, the substrate waveguide is to be configured as a head up display.

In some embodiments of the optical system, the light source includes at least one of a source beam splitter, a mirror, or a prism.

In some embodiments of the optical system, the optical system further comprises a color-sensitive beam splitter.

In some embodiments of the optical system, field lens comprises a diffractive surface.

In some embodiments of the optical system, one of the one or more polarization selective reflective surfaces comprises a quarter wave retarder film.

In some embodiments of the optical system, at least one of the first waveplate or the second waveplate includes a quarter wave retarder film.

In some embodiments of the optical system, the light path of the first light beam and the light path of the second light beam are within <NUM> of each other when exiting the collimating optics.

A method for providing light information to a user according to the claimed invention is defined in claim <NUM>.

A collimating catadioptric optical system is disclosed. The optical system includes a polarizing beam splitter, two waveplates, and two mirrors. The optical system is configured to receive incoming unpolarized light and split the unpolarized light into a linear polarized first light beam and a linear polarized second light beam. The first light beam transmits through a first waveplate to a first mirror, which reflects the first light beam back through the first waveplate, resulting in a (s)-polarized light. The second light beam transmits through a second waveplate to a second mirror, which reflects the second light beam back through the second waveplate, resulting in a (p)-polarized light. The (s)-polarized light and the (p)-polarized light are directed via the polarizing beam splitter into a parallel and collimated pair of light beams. Specifically, the polarization sensitive coating on the polarizing beam splitter selectively reflects (s)-polarized light, and transmits (p)-polarized light. In this matter, the light from the (p)-polarized light is not lost but reflected back into the system. The system may further include one or more lenses and other componentry for directing, collimating, and/or modifying the light. Catadioptric collimator systems are used in a variety of optical systems. <CIT> issued to Brown discloses a catadioptric collimator for head up displays (HUD).

<FIG> is a block diagram illustrating an optical system <NUM>, in accordance with one or more examples of this disclosure. In examples, the optical system <NUM> may be configured as a collimating system configured with collimating optics <NUM> that an image for display on a substrate waveguide, such as an HUD. The term HUD as used herein refers to a fixed HUD, a near eye display, a head worn display, a helmet mounted display or any type of display using a combiner for overlaying images from a light source over a real-world scene. The HUD system may be configured for use in smaller cockpit environments and in worn display applications and yet provides an appropriate field of view and eye box for avionic applications in some examples. The HUD system may be configured for use with worn components, such as, glasses, goggles, hats, helmets, etc. or be a HUD system with a fixed combiner in some examples. The substrate waveguide may be configured as a reflective combiner or holographic combiner. The collimating optics <NUM> are integrated or spaced apart from the substrate waveguide and/or other components of the optical system <NUM>. In some examples, the combiner may be configured as a waveguide combiner designed to combine light from two or more inputs into a single output.

In examples, the optical system <NUM> includes a light source <NUM> configured to emit image light <NUM> (e.g., light from the light source intended to form an observable image to a user) to the collimating optics <NUM>. The light source <NUM> can be any device for providing an image including but not limited to a digital micromirror device (DMD) display, a CRT display, a light emitting diode (LED) display, a micro LED display, an organic light emitting diode (OLED) display, an active-matrix liquid crystal display (AMLCD), a liquid crystal on silicon (LCOS) display, etc. In some examples, the light source <NUM> is a micro display and provides linearly polarized light.

In some examples, the collimating optics <NUM> are configured as a catadioptric collimator system and include a polarizing beam splitter <NUM>, a first mirror <NUM>, and a second mirror <NUM>. The first mirror <NUM> and/or second mirror may be configured as a having a curved surface. In some examples, the polarizing beam splitter <NUM> is configured as a rectangular prism form. The polarizing beam splitter <NUM> includes a front face <NUM>, a first waveplate face <NUM>, a second waveplate face <NUM>, an end face <NUM>, and one or more polarization selective reflective surfaces <NUM> in some examples. The polarization selective reflective surface may be configured as a dielectric coating, a wire-grid polarizer surface, or any other surface configured to selectively reflect polarized light. The first mirror is disposes on first waveplate face <NUM> and the second mirror is disposed on face <NUM>. The polarizing beam splitter <NUM> provides an internal folded optical path (e.g., the polarizing beam splitter <NUM> operating as a fold mirror).

In some examples, the collimating optics include a first waveplate <NUM> disposed adjacent to or upon the first waveplate face <NUM> and a second waveplate <NUM> disposed adjacent to or upon the second waveplate face <NUM>. The first waveplate <NUM> and second waveplate may be configured as any polarizing material capable of altering the polarization state of a light wave traveling through it. For example, the first waveplate <NUM> and/or second waveplate <NUM> may be configured as a half-wave plate, a half-wave retarder film, quarter-wave plate, or a quarter wave retarder film. For instance, the first waveplate <NUM> and/or second waveplate <NUM> may be configured as a quarter-wave plate that converts linearly polarized light into circular polarized light. The first waveplate <NUM> and/or second waveplate <NUM> may be constructed of any material including but not limited to quartz, mica, or plastic.

Image light <NUM> transmits through the face <NUM> of the polarizing beam splitter <NUM> from the light source <NUM> is partially reflected off of the one or more polarization selective reflective surfaces <NUM> within the polarizing beam splitter <NUM>, producing a first light beam <NUM> that is linear polarized. The first light beam <NUM> transmits through the first waveplate <NUM>, altering the linearly polarized light of the first light beam <NUM> to circularly polarized light. The first light beam <NUM> then reflects off of the first mirror, reversing the handedness of the circular polarized first light beam <NUM>, and the first light beam <NUM> passes back through the first waveplate <NUM>, becoming (p)-polarized light <NUM>. The (p)-polarized light <NUM> then transmits through the one or more polarization selective reflective surfaces <NUM> and through the end face <NUM>.

The splitting of the image light <NUM> by the polarizing beam splitter also produces a second light beam <NUM> that is linear polarized. The second light beam <NUM> transmits through the one or more polarization selective reflective surfaces <NUM> and transmits through the second waveplate <NUM>, altering the linearly polarized light of the first light beam <NUM> to circularly polarized light. The second light beam <NUM> then reflects off of the second mirror <NUM>, reversing the handedness of the circular polarized second light beam <NUM>, and the second light beam <NUM> passes back through the second waveplate <NUM> becoming (s)-polarized light <NUM>. The (s)-polarized light <NUM> then reflects off of the one or more polarization reflective surfaces <NUM> and transmits through the end face <NUM>.

The combination of elements in the collimating optics <NUM> collimates light at an exit pupil associated with the end face <NUM>. The collimating optics <NUM> embodied as a catadioptric system advantageously assists in making the design of the system substantially smaller in volume than conventional designs in one example. For example, the collimating optics in some examples has a volume of less than <NUM> cubic centimeters. However, the collimating optics <NUM> may be of any size or size range. For example, the collimating optics may have a volume ranging from <NUM> cubic centimeters to <NUM> cubic centimeters. In another example, the collimating optics may have a volume greater than <NUM> cubic centimeters. In another example, the collimating optics may have a volume smaller than <NUM> cubic centimeters. In another example, the collimating optics may have a volume smaller than <NUM> cubic centimeters. In another example, the collimating optics may have a volume smaller than <NUM> cubic centimeters.

Importantly, the use (e.g., recycling) of (p)-polarized light <NUM> in the collimating optics <NUM> greatly increases the efficiency that image light <NUM> from the light source <NUM> reaches the end face <NUM> and/or a user (e.g., in the form of (s)-polarized light <NUM> and (p)-polarized light <NUM>) as nearly twice the available light reaches the end face <NUM> as would have in conventional collimating optics that utilize only (s)-polarized light <NUM>. For example, a user may receive <NUM>% more light energy from the optical system <NUM> than from a system that does not include a second mirror <NUM>, using identical light sources <NUM>. In another example, a user may receive <NUM>% more light energy from the optical system <NUM> than from a system that does not include a second mirror <NUM>, using identical light sources. Correspondingly, removal of the second mirror from the system <NUM> may reduce light energy transmitted by the system by over <NUM> percent. No noticeable change in image quality is detected, as the light path of the first light beam <NUM> and the second light beam <NUM> are substantially equivalent.

<FIG> is a block diagram illustrating an optical system <NUM>, in accordance with one or more embodiments of the claimed invention. The optical system <NUM> is configured with one or more components as the optical system <NUM>. For example, the optical system <NUM> may be configured with all of the components of optical system <NUM>. According to the claimed invention, the collimating optics <NUM> further includes a field lens <NUM> disposed on face <NUM> configured to receive light from the light source <NUM>, and a corrector lens <NUM> configured to receive (s)-polarized light <NUM> and (p)-polarized light <NUM> from the polarizing beam splitter <NUM>.

In some embodiments, the field lens <NUM> includes a diffractive surface and/or is configured as a plano-convex aspherical lens. For example, the diffractive surface may be configured as an aspheric surface processed by diamond grinding, etching, lithography, molding or other process to form diffractive grooves. The diffractive surface provides color correction and higher order aberration control for the collimating optics <NUM> in some embodiments. The field lens <NUM> is manufactured from optical glass or plastic material in some embodiments. In some embodiments, a retarder plate or retarder film can be provided before or after the field lens <NUM> to effect a polarization change. In some embodiments, the corrector lens <NUM> is manufactured from optical glass or plastic material.

In some embodiments, the first mirror <NUM> includes a curved reflective surface <NUM>. For example, the first mirror <NUM> may be configured with a curved reflective surface <NUM> having a dichroic surface, a silvered reflecting surface, a metallic reflecting surface, or any other reflecting surface. The first mirror <NUM> may be curved to assist the collimation of light through the collimating optics <NUM>. In some embodiments, the first mirror <NUM> provides an aspheric medium for the curved reflective surface <NUM> and is manufactured from optical glass or plastic material in some embodiments.

In some embodiments, the second mirror <NUM> includes a second reflective surface <NUM>. For example, the second mirror <NUM> may be configured with a second reflective surface <NUM> having a dichroic surface, a silvered reflecting surface, a metallic reflecting surface, or any other reflecting surface. The second mirror <NUM> may be curved to assist the collimation of light through the collimating optics <NUM>. In some embodiments, the second mirror <NUM> provides an aspheric medium for the second reflective surface <NUM> and is manufactured from optical glass or plastic material in some embodiments. The combination of the field lens <NUM>, the first mirror <NUM>, the second mirror <NUM>. the polarizing beam splitter <NUM> and the corrector lens <NUM> serve to collimate light in some embodiments.

The elements of the collimating optics <NUM> can be cemented together around polarizing beam splitter <NUM> to form a small, compact package. Mounting the field lens <NUM>, the first mirror <NUM> and/or the second mirror <NUM> directly to the polarizing beam splitter <NUM> or film provided on the polarizing beam splitter <NUM> provides mechanical alignment in very tight tolerances. Advantageously, the corrector lens <NUM> can have dimensions identical to dimensions associated with the face <NUM> of the polarizing beam splitter <NUM> such that easy alignment is obtained. Similarly, the field lens <NUM>, the first mirror <NUM> and/or the second mirror <NUM> can match the sizes of the respective faces <NUM>, <NUM> and <NUM>.

<FIG> is a block diagram illustrating an optical system <NUM>, in accordance with one or more embodiments of this disclosure. The optical system <NUM> is configured with one or more components as the optical system <NUM>, <NUM>. For example, the optical system <NUM> may be configured with all of the components of optical system <NUM>. In some embodiments, the optical system <NUM>, includes the light source <NUM> and a light source beam splitter <NUM> configured with or without a source sensitive reflective coating <NUM>. For example, the light source <NUM> configured as a DMD micro display, wherein an image (e.g., image light <NUM>) transmitted from the DMD micro display is reflected by the source reflective coating <NUM> to the collimating optics <NUM>. The collimating optics <NUM> include the field lens <NUM>, the polarizing beam splitter <NUM>, the first waveplate <NUM>, the first mirror <NUM>, the second waveplate <NUM>, the second mirror <NUM> and the correcting lens <NUM>. In some embodiments, the optical system <NUM> may include a light source retarder disposed between the light source <NUM> and the light source beam splitter <NUM>. For instance, the light source retarder may be used with LCOS displays.

As in optical system <NUM>, <NUM>, optical system <NUM> creates (s)-polarized light <NUM> and (p)-polarized light <NUM>. For example, after the image light <NUM> is split into a first light beam <NUM> and a second light beam <NUM> and, the light waves are transformed into (p)-polarized light <NUM> and (s)-polarized light <NUM> via sequential transmittance through their respective waveplates (e.g., the first waveplate <NUM> and second waveplate <NUM>), with both the (p)-polarized light <NUM> and the (s)-polarized light <NUM> exiting as a collimated and parallel light sources via the correcting lens <NUM>.

<FIG> illustrates a perspective view of an optical system <NUM>, in accordance with one or more embodiments of this disclosure. The optical system <NUM> is configured with one or more components as the optical system <NUM>, <NUM>, <NUM>. For example, the optical system <NUM> may be configured with all of the components of optical system <NUM>. In embodiments, the optical system includes a light source <NUM> projecting image light (e.g., the green light in <FIG>). The image light passes through the field lens <NUM> through the polarizing beam splitter <NUM>, which splits the image light into a first light beam <NUM> and a second light beam <NUM>. The first light beam <NUM> is transmitted through the first waveplate <NUM> toward the first mirror <NUM>, which is reflected back through the first waveplate, converting the first light beam from linearly polarized light to (p)-polarized light. The (p)-polarized light <NUM> is then transmits through the one or more polarization selective reflective surfaces <NUM>, out of the polarizing beam splitter <NUM> and through the correcting lens <NUM>. The second light beam <NUM> is directed to and transmits through the second waveplate <NUM> to the second mirror <NUM>, which is reflected, and the second light beam is again transmitted through the second waveplate, converting the second light beam from linearly polarized light to (s)-polarized light <NUM>. The (s)-polarized light <NUM> is then reflected back to the one or the one or more polarization selective reflective surfaces <NUM>, where the (p)-polarized light <NUM> is reflected out of the polarizing beam splitter <NUM> and through the correcting lens <NUM>. The (p)-polarized light <NUM> and (s)-polarized light <NUM> exiting the correcting lens are collimated.

The optical systems <NUM>, <NUM>, <NUM>, <NUM> may be configured to be of any size of shape. For example, the optical systems <NUM>, <NUM>, <NUM>, <NUM>, may fit into a package with a volume less than <NUM> cubic centimeter. For instance, an optical system <NUM>, <NUM>, <NUM>, <NUM> containing the corrector lens <NUM>, the field lens <NUM>, the first mirror <NUM>, the second mirror <NUM>, and the polarization beam splitter <NUM> may fit into a package with a volume less than two cubic centimeters.

In some embodiments, the system <NUM>, <NUM>, <NUM>, <NUM> may include a color-selective beam splitter. For example, the polarizing beam splitter <NUM> may be configured as a color-selective beam splitter. In another example, the light source beam splitter <NUM> may be configured as a color-selective beam splitter. In another example, the system <NUM>, <NUM>, <NUM>, <NUM> may comprise a beam splitter in addition to the light source beam splitter <NUM> and/or the polarizing beam splitter <NUM> configured as a color sensitive beam splitter. It should be noted that a color sensitive polarizing beam splitter or fold mirror does not require optical paths into and out of the color sensitive polarizing beam splitter or fold mirror to be orthogonal. Rather, the angle of incidence needs to be different for the beam splitting path as compared to the recombining path. Therefore, the above description should not be interpreted as a limitation of the present disclosure, but merely as an illustration.

<FIG> is a flow diagram illustrating a method <NUM> for providing light information to a user, in accordance with one or more embodiments of this disclosure. According to the claimed invention, the method <NUM> includes a step <NUM> of transmitting image light <NUM> from a light source <NUM> to a polarizing beam splitter <NUM>. The light source <NUM> may be configured as any light source including but not limited to a DMD micro display. In accordance with the claimed invention, beam of the image light also passes through a field lens <NUM>.

The method <NUM> includes a step <NUM> of splitting the image light <NUM> into a first light beam <NUM> and a second light beam <NUM>, wherein the first light beam <NUM> and a second light beam <NUM> are linearly polarized. Image light <NUM> is split by the polarization selection reflection surface <NUM> of the polarizing beam splitter <NUM> into an (s)-polarized first light beam <NUM> and a (p)-polarized second light beam <NUM>.

The method <NUM> includes a step <NUM> of transmitting the first light beam <NUM> through a first waveplate <NUM>, wherein the first light beam <NUM> becomes circularly polarized. For example, when the electric field vector of the input, or incident, linear polarized first tight beam <NUM> is oriented at a <NUM>° angle to the slow and fast axes of the first waveplate <NUM> (e.g., a quarter waveplate), the output light of the first light beam <NUM> becomes circularly polarized.

The method <NUM> includes a step <NUM> of reflecting the first light beam <NUM> off of a first mirror <NUM>, wherein the first light beam <NUM> is converted to circularly polarized light of a different handedness. For example, the first mirror <NUM> may convert left-hand circular polarized light of the first light beam <NUM> to right-hand circular polarized light. In another example, the first mirror <NUM> may convert right-hand circular polarized light of the first light beam <NUM> to left-hand circular polarized light.

The method <NUM> includes a step <NUM> of transmitting the second light beam <NUM> through a second waveplate <NUM>, wherein the second light beam <NUM> becomes circularly polarized. For example, When the electric field vector of the input, or incident, linear polarized second tight beam <NUM> is oriented at a <NUM>° angle to the slow and fast axes of the second waveplate <NUM> (e.g., a quarter waveplate), the output light of the second beam <NUM> becomes circularly polarized.

The method <NUM> includes a step <NUM> of reflecting the second light beam <NUM> off of a second mirror <NUM>, wherein the second light beam <NUM> is converted to circular polarized light of a different handedness. For example, the second mirror <NUM> may convert left-hand circular polarized light of the second light beam <NUM> to right-hand circular polarized light. In another example, the second mirror <NUM> may convert right-hand circular polarized light of the second light beam <NUM> to left-hand circular polarized light.

The method <NUM> includes a <NUM> step of transmitting the first light beam <NUM> back through the first waveplate <NUM> and through a polarization selection reflection surface <NUM>, wherein the light from the first light beam <NUM> transmitting though the polarized selection reflection surface <NUM> is configured as (p)-polarized light. Therefore, the sequential transmitting and retransmitting of the first light beam <NUM> through the first waveplate <NUM> (e.g., a quarter-waveplate) and reflection off of the first mirror <NUM> converts the first light beam <NUM> to linear polarized light, albeit a linear polarized light having an opposite state as compared to the initial polarization state as the first light beam <NUM> formed from the initial split by the polarizing beam splitter <NUM>.

The method <NUM> includes a step <NUM> transmitting the second light beam <NUM> back through the second waveplate <NUM> and reflecting the second light beam <NUM> off of the polarization selection reflection surface <NUM>, wherein the light from the second light beam <NUM> reflected off of the polarization selection reflection surface <NUM> is configured as (s)-polarized light. Therefore, the sequential transmitting and retransmitting of the second light beam <NUM> through the second waveplate <NUM> (e.g., a quarter-waveplate) and reflection off of the second mirror <NUM> converts the second light beam <NUM> to linear polarized light, albeit a linear polarized light having an opposite state as compared to the initial polarization state as the second light beam <NUM> formed by the original split by the polarizing beam splitter <NUM>.

The method <NUM> includes a step <NUM> of directing the first light beam and second light beam to a corrector lens, wherein the first light beam and the second light beam are combined to form a user image (e.g., an image that is observed by a user). For example, the (p)-polarized light <NUM> may be reflected from the first mirror <NUM> through the one or more polarization selective reflective surfaces <NUM>, and through the corrector lens. At the same time, the (s)-polarized light <NUM> may be reflected from the second mirror <NUM> to the one or more polarization selective reflective surfaces <NUM>, wherein the one or more polarization selective reflective surfaces <NUM> reflects the (s)-polarized light <NUM>, directing the (s)-polarized light <NUM> through the corrector lens <NUM>. Because the light paths of the (p)-polarized light <NUM> and (s)-polarized light <NUM> are substantially equal (e.g., the length of the light paths from the initial splitting of the light by the polarizing beam splitter <NUM> to the end face <NUM>), the light from the (p)-polarized light <NUM> and (s)-polarized light <NUM> form a readily observable user image. For example, the substantially equal light paths may be within <NUM> of each other. In another example, the substantially equal light paths may be within <NUM> of each other. In another example, the substantially equal light paths may be within <NUM> of each other. In another example, the substantially equal light paths may be within <NUM> of each other. In another example, the substantially equal light paths may be within <NUM> of each other. As the (p)-polarized light and the (s)-polarized light reaches the end face <NUM>, light beams (e.g., light paths) from the (p)-polarized light and the (s)-polarized light are parallel and/or collimated. For example, as the (p)-polarized light and the (s)-polarized light reaches the end face <NUM>, light beams (e.g., light paths) from the (p)-polarized light and the (s)-polarized light may be collinear.

It should be understood that one or more components of the collimating optics <NUM> or one or more light paths for (e.g., (s)-polarization and (p)-polarization light paths) within the collimating optics <NUM> may be altered or otherwise modified. For example, the polarizing beam splitter <NUM> may be rotated (e.g., rotated -<NUM>° from the orientation shown in <FIG>) and the first waveplate <NUM> and first mirror <NUM> moved to the opposite side of the polarizing beam splitter. With this arrangement, the image light <NUM> will again be split and converted into (s)-polarized and (p)-polarized light paths, however, the light will leave the collimating optics <NUM> via what was originally the first waveplate face <NUM>. Any arrangement of components or arrangements of coatings of components (e.g., the one or more polarization selective reflective surfaces <NUM>) is possible.

Claim 1:
An optical system (<NUM>) comprising:
collimating optics (<NUM>), comprising:
a polarization beam splitter (<NUM>) comprising one or more polarization selection reflection surfaces configured to split image light from a light source into a first light beam and a second light beam;
a field lens (<NUM>) disposed on the polarization beam splitter (<NUM>) configured to receive the image light from the light source;
a first waveplate (<NUM>) configured to receive the first light beam;
a first mirror (<NUM>) configured to receive the first light beam from the first waveplate and reflect the first light beam back through the first waveplate, wherein the first light beam transmits through or reflects from one of the one or more polarization selection reflection surfaces, wherein the first light beam that transmits through or reflects from the one of the one or more polarization selection reflection surfaces is configured as (s)-polarized light;
a second waveplate (<NUM>) configured to receive the second light beam;
a second mirror (<NUM>) configured to receive the second light beam from the second waveplate and reflect the second light beam back through the second waveplate, wherein the second light beam transmits through or reflects from the one of the one or more polarization selection reflection surfaces, wherein the second light beam that transmits through or reflects from the one or more polarization selection reflection surfaces is configured as (p)-polarized light; and
a corrector lens (<NUM>) configured to receive the first light beam reflected from the first mirror and the second light beam reflected from the second mirror, wherein a length of a light path of the first light beam and a length of a light path of the second light beam are substantially equal, wherein the first light beam and the second light beam are configured to combine to form a user image.