HK1197457A - Ned polarization system for wavelength pass-through - Google Patents

Description

NED polarization system for passing wavelengths

Background

A see-through near-eye display (NED) unit may be used to blend the virtual image with the real objects in the physical environment for display. Such NED cells include a light engine for generating an image, and partially transmissive, partially reflective optical elements. The optical element is transmissive in order to allow light from the outside world to reach the observer's eye, and is also partially reflective in order to allow light from the light engine to reach the observer's eye. The optical element may include a Diffractive Optical Element (DOE) or hologram within the planar waveguide to diffract an image from the microdisplay into the user's eye.

In practice, the NED cell may comprise a stack of a plurality of waveguides, each waveguide being assigned a wavelength component. In particular, by controlling aspects of the DOE within the waveguide, the waveguide can be matched or optimized to couple with a particular wavelength component with maximum efficiency. Different DOEs are optimized for different colors of the visible spectrum to allow the NED cell to provide a full color experience.

In a stack of multiple waveguides, wavelength components that match the distal waveguides in the stack (i.e., those waveguides furthest from the light engine) pass through the more adjacent waveguides in the stack. The wavelength components for the distal waveguide are typically coupled in the more proximal waveguide rather than directly through the more proximal waveguide. This results in a loss of brightness, resulting in color non-uniformity from the NED cells to the viewer, and degradation of the quality of the reproduced virtual image.

Disclosure of Invention

Embodiments of the present technology relate to a system and method for selectively changing the polarization state of different wavelength bands as they pass through waveguides in a NED cell. The DOEs on or in the waveguides are polarization sensitive. By changing the polarization of a wavelength band to a state to which the DOE on the waveguide is less sensitive, the wavelength band can pass through the DOE to the greatest extent or completely without attenuation. The polarization of the wavelength band is controlled to be in a state such that light is coupled into its intended waveguide by the DOE before entering the waveguide.

In one example, the present technology relates to a method for presenting an image, the method comprising: (a) projecting light from a light source into an optical element, said light comprising at least a first wavelength band and a second wavelength band, and the optical element comprising at least a first waveguide and a second waveguide, each having at least one grating; (b) controlling the polarization of the first wavelength band incident on the first waveguide to be different from the polarization of the other wavelength bands incident on the first waveguide, so that the first wavelength band can be coupled in the first waveguide to a greater extent than the other wavelength bands; and (c) controlling the polarization of the second wavelength band incident on the second waveguide to be different from the polarization of the wavelength bands other than the second wavelength band incident on the second waveguide, so that the second wavelength band can be coupled into the second waveguide to a greater extent than the wavelength bands other than the second wavelength band.

In another example, the present technology relates to a method for presenting an image, the method comprising: (a) projecting light from a light source into an optical element, the light comprising 2 to n wavelength bands, and the optical element comprising 2 to m waveguides, an ith wavelength band being matched to a jth waveguide, wherein i is 1 to n, and j is 1 to m; and (b) passing one or more of the 2 to n wavelength bands through a plurality of polarization state generators, each polarization state generator associated with one of the 2 to m waveguides, the plurality of polarization state generators controlling polarization of the one or more wavelength bands passing therethrough to facilitate coupling of the ith wavelength band in the jth waveguide while preventing coupling of the remaining wavelength bands into a state passing through the jth waveguide.

In another example, the present technology relates to an optical element for transmitting light from a light source to an eye box (eye box), the optical element including: a first waveguide comprising at least a first grating for receiving light from a light source and coupling a first portion of said light into the first waveguide; a second waveguide comprising at least a second grating for receiving light from the light source and coupling a second portion of said light into the second waveguide; a first polarization state generator between the light source and the first waveguide, the first polarization state generator modifying a polarization of a first portion of the light to be coupled in the first waveguide; and a second polarization state generator between the first diffraction grating and the second diffraction grating, the second polarization state generator modifying a polarization of a second portion of the light to be coupled in the second waveguide.

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

Drawings

FIG. 1 illustrates example components of one embodiment of a system for presenting a virtual environment to one or more users.

Fig. 2 is a perspective view of one embodiment of a head mounted NED unit.

Fig. 3 is a side view of a portion of one embodiment of a head mounted NED unit.

Fig. 4 is an edge view of an optical element in a NED cell, the optical element including a waveguide having a diffraction grating.

Fig. 5 is a partially enlarged view of the structure of a surface relief (surface relief) diffraction grating.

Fig. 6 is a side view of a portion of one embodiment of a head-mounted NED unit including an optical element with multiple waveguides.

Fig. 7 shows the plane of incidence of light incident on the diffraction grating.

Fig. 8 is an end view of a first embodiment of imaging optics in a NED cell that includes multiple waveguides and a polarization state generator for changing the polarization of a wavelength band as they enter the waveguides.

Fig. 9 is an end view of a second embodiment of imaging optics in a NED cell that includes multiple waveguides and a polarization state generator for changing the polarization of a wavelength band as they enter the waveguides.

Fig. 10 is a flowchart of the operation of the imaging optics of the first embodiment shown in fig. 8.

Fig. 11 is a flow chart of the operation of the imaging optics of the second embodiment shown in fig. 9.

Fig. 12 is an end view of a third embodiment of imaging optics in a NED cell that includes multiple waveguides and a polarization state generator for changing the polarization of the wavelength bands as they enter the waveguides.

Fig. 13 is an end view of a fourth embodiment of imaging optics in a NED cell, the imaging optics including a plurality of waveguides and a polarization state generator for changing the polarization of wavelength bands as they enter the waveguides.

Fig. 14 is an edge view showing a wavelength band without controlled polarization traveling through a pair of waveguides.

Fig. 15 is an edge view illustrating a wavelength band with controlled polarization traveling through a pair of waveguides in accordance with various embodiments of the invention.

Fig. 16 is a graph showing coupling efficiencies of the wavelength bands of fig. 14 and 15.

Detailed Description

Embodiments of the present technology will now be described with reference to fig. 1-16, which generally relate to imaging optics for selectively changing the polarization state of different wavelength bands as they pass through waveguides in a NED cell. The DOE on the waveguide is sensitive to light polarization. Thus, by selectively controlling the polarization of the wavelength band entering a DOE on a waveguide, a wavelength band that matches that waveguide can pass through the DOE with high efficiency coupling, while a wavelength band that DOEs not match can pass through the DOE and waveguide largely or entirely unaffected. Although one example of the use of DOEs is described herein, it should be understood that in each optical element, the waveguide may include a DOE, hologram, surface relief grating, or other type of periodic structure. These structures may be referred to herein as "gratings".

In the embodiments described below, the NED unit may be a head mounted display unit used in a mixed reality system. However, it should be understood that embodiments of the NED cell and imaging optics contained therein may be used in various other optical applications, for example, in optical couplers or other light modulator devices. The accompanying drawings are provided for understanding the present technology and are not drawn to scale.

Fig. 1 shows the NED unit 2 as one example of a head mounted display used in the mixed reality system 10. The NED unit may be worn as glasses including lenses that are transparent to an extent such that a user may view real world objects 27 in the user's field of view (FOV) through the display elements. The NED unit 2 also provides the ability to project virtual images 21 into the FOV of the user so that these virtual images may also appear to be alongside real objects. Although not critical to the present technology, the mixed reality system may automatically track where the user is looking so that the system can determine where to insert the virtual image in the FOV of the user. Once the system knows where to project the virtual image, the display element is used to project the image.

Fig. 1 shows a plurality of users 18a, 18b and 18c each wearing a head mounted NED unit 2. In one embodiment, the head mounted NED unit 2 is in the shape of eyeglasses that are worn on the head of the user so that the user can see through the display to have a realistic and intuitive view of the space in front of the user. More details of the head mounted NED unit 2 are provided below.

NED element 2 may provide signals to and receive signals from processing element 4 and central computing device 12. NED unit 2, processing unit 4, and central computing device 12 may cooperate to determine the FOV of each user 18, what virtual images should be provided within the FOV, and how the virtual images should be presented. The central computing device 12 also includes a capture device 20 for capturing image data from portions of the scene within its FOV. The central computing device 12 may also be connected to an audiovisual device 16 and speakers 25, which audiovisual device 16 and speakers 25 may provide game or application visuals and sounds. For example, details regarding the processing unit 4, the central computing device 12, the capture device 20, the audiovisual device 16, and the speakers 25 are provided in U.S. patent publication No. 2012/0105473 entitled "Low-Latency Fusing of virtual and real content," published, for example, on 3.5.2012, which is incorporated herein by reference in its entirety.

Fig. 2 and 3 show perspective and side views of the head mounted NED unit 2. Fig. 3 does not show the right side of the head mounted NED unit 2, which includes a part of the apparatus with the temple 102 and the nose piece 104. A part of the frame of the head mounted NED unit 2 will enclose the display (which comprises one or more lenses). The display includes light-guiding optical element 115, see-through lens 116, and see-through lens 118. In one embodiment, light guide optical element 115 is behind and aligned with see-through lens 116, and see-through lens 118 is behind and aligned with light guide optical element 115. See-through lenses 116 and 118 are standard lenses used in eyeglasses and may be manufactured to conform to any prescription (including no prescription). Light guide optics 115 direct the artificial light to the eye. More details of the light-guiding optical element 115 will be provided below.

Mounted to or within the temple 102 is an image source, which (in embodiments) includes a light engine, such as a microdisplay 120 for projecting virtual images and a lens 122 for directing images from the microdisplay 120 to the light-guiding optical element 115. In one embodiment, the lens 122 is a collimating lens. Microdisplay 120 projects an image through lens 122.

There are different image generation techniques that can be used to implement microdisplay 120. For example, microdisplay 120 can be implemented using a transmissive projection technology in which the light source is modulated by an optically active material and there is a white background light. These techniques are typically implemented using LCD type displays with strong background light and high optical power density. Microdisplay 120 can also be implemented using a reflective technology, where external light is reflected and modulated by an optically active material. Illumination is forward-emitted by either a white light source or an RGB light source depending on the technology. Digital Light Processing (DLP), Liquid Crystal On Silicon (LCOS) and Qualcomm IncDisplay techniques are examples of reflection techniques that are efficient because most of the energy is emitted from the modulated structure, and which may be used in the system of the present invention. Further, microdisplay 120 can be implemented using light-emitting technology, where light is generated by the display. For example, Picop of Microvision, Inc^TMThe display engine emits a laser signal that is either steered by a micromirror onto a small screen acting as a transmissive element or transmitted directly into the eye (e.g., a laser).

Light-guiding optical element (also simply referred to as optical element) 115 may transmit light from microdisplay 120 to 130. The eyebox 130 is a two-dimensional area disposed in front of the eye 132 of the user wearing the head-mounted NED unit 2 through which light passes after exiting the optical element 115. The optical element 115 also allows light to be transmitted from the front of the head mounted NED unit 2 through the light-guiding optical element 115 to the eyebox 130, as depicted by arrow 142. This allows the user to have a realistic, intuitive view of the space in front of the head mounted NED unit 2, in addition to receiving the virtual image from the microdisplay 120.

Fig. 3 shows half a head mounted NED unit 2. The entire head mounted display device may include another optical element 115, another microdisplay 120, and another lens 122. In the case of a head mounted NED unit 2 with two optical elements 115, each eye may have its own microdisplay 120, which may display the same image in both eyes, or different images in both eyes. In another embodiment, there may be one optical element 115 that reflects light from a single microdisplay 120 into both eyes.

Further details of the light guiding optical element 115 will now be explained with reference to fig. 4-13. Generally, the optical element 115 includes two or more waveguides that are stacked on top of each other to form an optical system (optical train). One such waveguide 140 is shown in fig. 4A. The waveguide 140 may be formed from a thin planar sheet of glass, but in other embodiments it may be formed from plastic or other materials. Waveguide 140 may include two or more diffraction gratings, including an input diffraction grating 144 to couple light into waveguide 140 and an exit diffraction grating 148 to diffract light out of waveguide 140. The gratings 144, 148 are shown as transmission gratings fixed on or in the lower surface 150a of the substrate 150. In other embodiments, reflective gratings affixed to opposite sides of the substrate 150 may be used.

FIG. 4 shows a wavelength band λ coupled in or out of a waveguide 140₁Total internal reflection of (a). As used herein, a wavelength band may include, for example, one or more wavelengths in the visible spectrum. The illustration of fig. 4 is a simplified view of a single wavelength band in a system where no second or higher diffraction orders are present. Although not shown in fig. 4, the optical element 115 may also include a polarization state generator in front of and sandwiched between the waveguides as described below.

Wavelength band λ from microdisplay 120₁Is collimated by lens 122 and input to diffraction grating 144 at an incident angle θ₁Coupled in the substrate 150. The input diffraction grating 144 redirects the wavelength band through a diffraction angle θ₂. Providing a refractive index n₂Angle of incidence theta₁And diffraction angle theta₂Making the wavelength band lambda₁All internal reflections in the substrate 150 are experienced. Wavelength band lambda₁Reflects off the respective surfaces of the substrate 150 until the wavelength band reaches the exit diffraction grating 148, in which case the wavelength band λ₁Is diffracted from the substrate 150 toward the eye rim 130. For example, additional details of waveguides such as waveguide 140 are disclosed in U.S. patent No. 4711512 entitled "Compact Head-Up Display," issued 12/8 1987, which is hereby incorporated by reference in its entirety.

Fig. 5 is a partial enlarged view showing one example of a grating 154 having surface irregularities forming part of a transmission diffraction grating such as the diffraction grating 144 and/or 148 (fig. 5 shows the diffraction grating 144 diffracting light into the substrate 150). The grating 154 may have a slanted profile with a period p, but in other embodiments the grating may have other profiles such as square and sawtooth. As illustrated, in other embodiments, the gratings 144, 148 may be reflective.

The waveguide can be optimized or matched for a particular wavelength band. This relationship can be determined according to the raster formula:

mλ＝p(n₁sinθ₁+n₂sinθ₂) (1)

wherein:

m ═ diffraction order;

λ ═ a wavelength band matched to the waveguide/diffraction grating;

p is the grating period;

n₁the refractive index of the incident medium;

n₂the refractive index of the waveguide 140;

θ₁-angle of incidence;

θ₂diffraction angle.

By varying the grating period p and the refractive index n, e.g. of the substrate 150₂Etc., the particular waveguide 140, including the diffraction gratings 144, 148, may be matched to a particular wavelength band. That is, a specific wavelength band may be coupled in the matched waveguide 140 with higher coupling efficiency than other wavelength bands. In addition, the profile parameters of the grating 154 (FIG. 5) may be optimized using Rigorous Coupled Wave Theory (RCWT) to improve waveguide performance such as angular bandwidth, diffraction efficiency, and polarization (as described below).

Figure 4 shows a single waveguide 140 being used for a particular wavelength band via diffraction gratings 144, 148. In embodiments of the present technique, the optical element 115 may include two or more waveguides 140 as described with reference to FIG. 4, stacked together to form an optical system. Each such waveguide 140 in the optical element 115 may be matched to a different wavelength band. In one example shown in FIG. 6, there are four such waveguides 140 stacked on top of each other₁-140₄. While it may not be practical to provide more than four layers, it is contemplated that the optical element may include more than four layers. Each layer of waveguides may be optimized for different light wavelengths including, for example, violet light having a wavelength of about 400nm, indigo light having a wavelength of about 445nm, blue light having a wavelength of about 475nm, green light having a wavelength of about 510nm, yellow light having a wavelength of about 570nm, orange light having a wavelength of about 590nm, and/or red light having a wavelength of about 650 nm.

Waveguide 140₁-140₄May be provided in any order and may allow the waveguide 140 to be₁-140₄Are matched to wavelengths other than those previously described. In an example, a single waveguide 140 may be matched to wavelength bands that include different color wavelengths of the visible spectrum.

In a stack of stacked waveguides, an emission wavelength band matched to a distal waveguide in the stack passes through all of the waveguides in the stackThere are more adjacent waveguides. For example, in the embodiment of FIG. 6, the remote-most waveguide 140 from microdisplay 120₁Matched wavelength band lambda₁Through a relatively adjacent waveguide 140₂-140₄. As described in the background section, one problem with conventional stacking of stacked waveguides is that the wavelength bands intended to be coupled in the distal waveguide are also partially coupled in the more proximal waveguide, thereby degrading the color of the image reaching the eyebox 130.

Polarization sensitivity of the wavelength bands through which the diffraction gratings in waveguide 140 pass is their property. Thus, a wavelength band at a first polarization may be coupled with one or more waveguide layers through which it passes, while the same wavelength band at a second polarization different from the first polarization may pass through the one or more waveguide layers without coupling. According to aspects of the present technique, the polarization of light in a wavelength band is controlled to couple into its matching waveguide while passing through other unmatched waveguides. Thus, in the example of fig. 6, at the wavelength band λ₁Is matched to couple at waveguide 140₁In the case of (3), its polarization is controlled so that it is coupled in the waveguide 140₁Through waveguide 140 before passing₂-140₄。

Referring now to FIG. 7, the polarization of light incident on the diffraction gratings 144, 148 may be determined by their electric and magnetic fields relative to the plane of incidence P_iIs defined by the orientation of (c). Plane P_iCan be defined by the propagation vector PV of the illumination source and the grating normal vector GN. Vector PV is the projection of the k-vector of light onto the waveguides 144, 148. The grating vector GV is the vector in the plane of the gratings 144, 148 that defines the orientation of the grating lines. As used herein, the term "state E" refers to a polarization state in which the electric field component of the wavelength band along the grating vector GV is zero. As used herein, the term "state M" refers to a polarization state in which the magnetic field component along the grating vector GV is zero.

In the example described below, the polarization of the wavelength band incident on the diffraction grating in each waveguide 140 is controlled to change between the state E and the state M. In embodiments, a wavelength band incident on a diffraction grating that is polarized in state M passes through the diffraction grating, while a wavelength band incident on the diffraction grating that is polarized in state E is coupled into a waveguide that includes the diffraction grating.

While the following examples describe the current technology in terms of controlling the conditions of state E and state M of polarized light, it should be understood that other polarization states may be used such that in a first polarization state, a wavelength band passes through the waveguide, and in a second polarization state, the wavelength band is coupled to the waveguide. Other examples of first and second polarization states are left and right polarizations of the wavelength passing through the waveguide 140. Further, although polarized light is described below as being in one of two states, it is contemplated that polarized light may have more than two states. In such embodiments, at least one state is coupled in the waveguide and at least one other state is passed through the waveguide without coupling.

Example embodiments will now be described with reference to fig. 8-9, which illustrate an optical element 115 including two waveguides 140. Fig. 12, described below, shows an example of an embodiment in which optical element 115 may include n waveguides, where n may be a different number of waveguides. A first embodiment will now be described with reference to the flowcharts of fig. 8 and 10. FIG. 8 shows a pair of waveguides 140₁And 140₂. In step 300, a discrete light wavelength band λ is emitted from microdisplay 120₁And λ₂And collimated by lens 122. The waveguides are arranged so that light from microdisplay 120 enters waveguide 140 first₂And then into the waveguide 140₁。

Waveguide 140₁And 140₂Two different wavelength bands λ that may be respectively emitted from microdisplay 120₁And λ₂And (6) matching. As one example, the waveguide 140 may be made₁Can be tuned to red light to enable the waveguide 140₂Tuning to blue-green light. It is understood that in other embodiments, the waveguide 140₁And 140₂May be matched to other wavelength bands of one or more wavelengths of visible light.

In this embodiment, the light emitted from microdisplay 120 can be unpolarized or polarized in state E. Upon entering the first waveguide 140₂Previously, wavelength band λ₁And λ₂Both passed through a Polarization State Generator (PSG) 160. The PSG160 (as well as the PSGs described below) may be a known polarization state generator, such as a wave plate or polarization retarder that, by way of example, can shift the phase of a particular band of wavelengths between two orthogonal polarization states while leaving other wavelengths of light unaffected.

The PSG160 may be formed as a thin sheet of birefringent material that may be fixed in the optical element 115 in the waveguide 140₂In front of the diffraction grating 144 of the substrate 150. In the case where the diffraction grating is reflective, the PSG160 is incorporated into the waveguide 140₂In the substrate 150 in the waveguide 140₂In front of the diffraction grating 144. The PSG160 (as well as the PSGs described below) may be the same size as the waveguide 140, although it may be smaller or larger in embodiments. When smaller, the PSG160 may be located at least above the input diffraction grating 144. The PSG160 may be formed, for example, of a polymer film retarder, a birefringent crystal retarder, a liquid crystal retarder, or a combination of these. In other embodiments, the PSG160 may be formed of other materials. PSG160 (and PSGs described below) may be manufactured, for example, by Meadowlark optics ltd, fradlike county, usa.

The PSG160 may be configured in step 304 to direct the wavelength band λ₁Changes from state E to state M. The PSG160 may enable a wavelength band λ₁Is not affected. The PSG160 may also use a wavelength band λ₂Is not affected by the polarization, intensity and direction of the light, thereby allowing a wavelength band lambda₂Pass directly with little or no change.

As previously described, in embodiments, the discrete wavelengths from microdisplay 120 may be unpolarized. In such an embodiment, the PSG160 may convert the wavelength band λ₁Modulation into the solution as described previouslyAnd a second PSG (not shown) may be to convert the wavelength band λ₂Modulation is to state E.

As previously described, light polarized in state E can be coupled into waveguide 140, while light polarized in state M may not (or to a lesser extent) be coupled into waveguide 140. Thus, after the state change by the PSG160, in step 308, the wavelength band λ polarized in the state E₂Is coupled to the waveguide 140₂In the waveguide 140₂In the wavelength band lambda₂Is captured and driven from the waveguide 140₂To the eye box 130.

Wavelength band lambda when polarized in state M₁May pass largely or entirely through the waveguide 140₁Without coupling or attenuation. In order to allow the wavelength band lambda to be adjusted₁Is coupled to the waveguide 140₁In the wavelength band lambda₁At the exit of waveguide 140₁Then and after entering the waveguide 140₂Previously, through the second PSG 162.

PSG162 may be formed of the same material as PSG160, but configured to convert the wavelength band λ in step 310₁Is modulated from state M to state E. The PSG162 may be formed in the optical element 115 sandwiched between the waveguides 140₁And 140₂In between. Alternatively, the PSG162 may be formed in the waveguide 140₂Behind its diffraction grating 144, or formed in the waveguide 140₁In front of its diffraction grating 144 in the substrate 150.

After the phase change by the PSG162, in step 314, the wavelength band λ₁Can be coupled to the waveguide 140₁In the waveguide 140 as described above₁In the wavelength band lambda₁Is captured and driven from the waveguide 140₁To the eye box 130. In this manner, different wavelengths of light may be transmitted out of microdisplay 120 using waveguide 140 while maintaining the color quality of the wavelengths transmitted through optical element 115.

Another implementation is now described with reference to the flowcharts of FIGS. 9 and 11For example. In step 320, discrete wavelengths of light are emitted from microdisplay 120 and collimated by lens 122. The collimated light then initially enters the waveguide 140₂. As previously described, for two different wavelength bands λ corresponding to discrete wavelengths emitted from microdisplay 120₁And λ₂To optimize the waveguide 140₂And 140₁. In this embodiment, all wavelengths of light emitted from microdisplay 120 may be unpolarized or polarized in state M. Upon entering the first waveguide 140₂Previously, wavelength band λ₁And λ₂All pass through PSG 166.

PSG166 may be formed of the same material and size as PSG160, but configured to wavelength band λ in step 324₂Changes from state M to state E. PSG166 can convert wavelength band λ₂Is not affected. PSG166 may also use the wavelength band λ₁Is not affected by the polarization, intensity and direction of the light, thereby allowing a wavelength band lambda₁Directly through without change.

PSG166 may convert the wavelength band λ when the light from microdisplay 120 is unpolarized₂Modulated to the state E as described above, the second PSG (not shown) may transmit the wavelength band λ₁Adjusted to the state M.

Wavelength band λ polarized in state E after state change by PSG166₂Is coupled to the waveguide 140₂In the waveguide 140, as described above₂In the wavelength band lambda₂Is captured and driven from the waveguide 140₂And transmitted back to eye box 130.

Wavelength band lambda when polarized in state M₁May pass largely or entirely through the waveguide 140₁Without coupling or attenuation. In order to allow the wavelength band lambda to be adjusted₁Is coupled to the waveguide 140₁In (b), let the wavelength band lambda₁At the exit of waveguide 140₁Then and into the waveguide 140₂Previously passed through the second PSG 168. The PSG168 may be the same as the PSG162 in fig. 8, and in step 334, the wavelength band λ may also be determined₁Modulated from state M to state E. Thereafter, in step 338 the wavelength band λ₁Can be coupled to the waveguide 140₁In the waveguide 140, as described above₁In the wavelength band lambda₁Is captured and driven from the waveguide 140₁And transmitted back to eye box 130.

By using a system of PSGs in front of and sandwiched between waveguides, various numbers of wavelength bands can be polarized through unmatched waveguides and coupled in full or nearly full intensity in the waveguides to which they are matched, as described above. The system of PSG may have the polarization of the wavelength band near the unmatched waveguide already in the state M condition so that the wavelength band will pass through the unmatched waveguide unaffected. Alternatively, the polarization of the wavelength band near the unmatched waveguide may be in state E condition such that it passes through the PSG to modulate it to state M where it may pass through the unmatched waveguide unaffected. Thereafter, the wavelength band may be maintained in the state M condition until the wavelength band reaches its matched waveguide, at which time the wavelength band is passed through the PSG to modulate the wavelength band into the state E, so that the wavelength band may be coupled in the waveguide matched with the wavelength band.

One example including n wavelength bands and waveguides is now shown and described with reference to fig. 13. Although the example of fig. 13 shows n equal to four or more wavelength bands and waveguides, other examples may include three wavelength bands and waveguides.

Discrete wavelength band lambda₁，λ₂，λ₃，…λ_nEmitted from microdisplay 120 and collimated by lens 122. In one example, all light wavelengths from microdisplay 120 are polarized into state M. In this case, the present embodiment may include the PSG170 as described above₁The PSG170₁Is configured to convert lambda₁Is modulated to state E while the remaining wavelength bands are polarized in state M. In other embodiments, the band of wavelengths emitted from microdisplay 120 may have other polarizations, or no polarization. In these other areasIn an embodiment, one or more PSGs may be disposed on the waveguide 140₁Thereby passing through one or more PSGs and into waveguide 140₁After being input into the diffraction grating 144, the wavelength band λ₁Polarization in state E, wavelength band lambda₂To lambda_nPolarized in state M.

Thus, a wavelength band λ polarized in state E₁Can be coupled to the waveguide 140₁In the waveguide 140 as described above₁In the wavelength band lambda₁Is captured and driven from the waveguide 140₁And transmitted back to eye box 130. When polarized in state M, the remaining wavelength band λ₂To lambda_nTo a large extent or completely through the waveguide 140₁Without coupling or attenuation.

Then, the remaining wavelength band λ₂To lambda_nVia the second PSG170₂The second PSG170₂Wavelength band lambda₂Modulating to state E while leaving the remaining wavelength band λ₃To lambda_nSubstantially or completely unaffected.

Thereafter, the wavelength band λ polarized in state E₂Can be coupled to the waveguide 140₂In the waveguide 140, as described above₂In the wavelength band lambda₂Is captured and driven from the waveguide 140₂And transmitted back to eye box 130. When polarized in state M, the remaining wavelength band λ₃To lambda_nTo a large extent or completely through the waveguide 140₂Without coupling or attenuation.

This process is repeated for each of the remaining waveguides. Each wavelength band may be polarized through the unmatched waveguide until it reaches the waveguide to which it is matched, at which point it may be polarized to couple in the waveguide to which it is matched. Last wavelength band lambda_nThrough all of the waveguides 140₁To 140_n-1Up to the wavelength band lambda_nTo the waveguide 140_n. In passing through the waveguide 140_nPreviously, let the wavelength band λ_nBy PSG170_nAnd subjecting it toPolarized to be subsequently coupled into waveguide 140_nIs in the state (1).

It will be appreciated that other configurations of PSGs may be provided such that a wavelength band matched to a certain waveguide is polarized to couple with that waveguide, while all other wavelength bands are polarized to pass through that waveguide. In this manner, the previously described waveguides and PSGs can be used to transmit light of different wavelengths through the optical element 115 while maintaining the color quality of all wavelengths transmitted through the optical element 115.

After coupling in the distal waveguide and subsequently exiting the distal waveguide, the wavelength band passes through each of the more adjacent waveguides en route to the eyebox 130. As previously described with reference to fig. 4, each waveguide 140 includes an exit diffraction grating (148) that couples light already in the waveguide out of the waveguide. The exit grating 148 may allow the incoming wavelength band to return from the more distal waveguide to a large extent or to pass directly entirely without coupling. However, it may happen that light from the more distal waveguide is at least partially coupled in the more proximal waveguide on its way to the eyebox 130.

Thus, in other embodiments, in addition to providing a PSG on input diffraction grating 144 to control light from microdisplay 120 to couple into a corresponding waveguide, a PSG may be provided on exit diffraction grating 148. The exit grating PSG prevents light from the distal waveguide from coupling into the more proximal waveguide as it travels to the eyebox 130. One such example is shown in fig. 13. In this example, as described previously, the wavelength band λ₁To lambda_nCoupled in the waveguide with which it is matched, but through the unmatched waveguide. After a wavelength band exits the waveguide to which it is matched, its polarization may again be PSG180₁To 180_nOne switches from state E to state M so that the wavelength band passes through the nearer waveguide without coupling. In this example, the last PSG in front of the eye-box (i.e., PSG 180)₁₎The wavelength band lambda can be targeted in various ways as desired₁To lambda_nPolarized for presentation to the user's eye 132 through the eyebox 130.

In some of the embodiments described above, it has been described that wavelengths polarized in state E are coupled into a waveguide matched thereto, while wavelengths polarized in state M pass through a mismatched waveguide without attenuation. However, wavelengths polarized in state E and wavelengths polarized in state M may both be partially coupled into the respective waveguides upon which they are incident, rather than being fully coupled/passed through. However, by using the PSG described earlier, the coupling efficiency for wavelengths polarized in state E can be increased relative to the coupling efficiency for wavelengths polarized in state M.

An example is set forth in fig. 14 through 16. FIGS. 14 and 15 respectively show the input to a pair of waveguides 140₁And 140₂Edge view of the wavelength band λ above. Wavelength band lambda and waveguide 140₂Matched but first passed through waveguide 140₁. Fig. 14 and 15 are identical to each other, but in fig. 15, the PSG160 is used to control the polarization of the wavelength band, whereas in fig. 14, the PSG is not used.

In fig. 14, the wavelength band of the incoming light is at the incident angle θ₁Incident on the unmatched waveguide 140₁On the diffraction grating 144. Without control, the wavelength band may have a state E polarization such that a portion of λ_1cIs coupled to the waveguide 140₁In (1). Second part lambda_1mDiffracted in a second order diffraction (there may be additional grating orders diffraction not shown). The remaining part λ_1tThrough waveguide 140₁Is transmitted into the waveguide 140 matched therewith₂. Since a substantial part of the wavelength band lambda is coupled in the waveguide 140₁Inner, less part of lambda_2cIs left to couple at waveguide 140₂In (1).

In contrast, in FIG. 15, the same wavelength band λ is entering the waveguide 140₁Its polarization was previously set to state M (e.g., by a PSG not shown in the figure). As shown, a relatively small fraction λ of the wavelength band_1cCoupled to waveguide 140₁In (1). Thereby passing through the waveguide 140₁Part of the transmission lambda_ltIs relatively large. In the waveguide 140₁And 140₂In between, the polarization of the wavelength band is changed from state M to state E by the PSG 160. Thus, there is a substantial portion of wavelength λ polarized in state E_2cCoupled to a waveguide 140 to which it is mated₂In (1).

Fig. 16 is a graph of the relationship between coupling efficiency and angle of incident coupling. Coupling efficiency is defined herein as the ratio of the intensity of a wavelength band emitted from a light source to the intensity of a wavelength coupled into the waveguide to which it is matched (expressed as a number between 0 and 1). Red light (650nm) is used in this example as the light guide 140 shown in FIGS. 14 and 15₂Matching wavelength bands. The graph also shows a second green wavelength band (540 nm). The green wavelength band is not shown in fig. 14 and 15, but it is associated with the first waveguide 140₁Is matched and coupled to the first waveguide 140₁In (1). First waveguide 140₁Diffraction grating 144 of₁Having a grating period of 450nm, and a second waveguide 140₂Diffraction grating 144 of₂The grating period of (2) is 550 nm.

As can be seen from the graph of fig. 16, the curve 184 for the green wavelength band shows a maximum coupling efficiency of over 90% due to the fact that the green wavelength is coupled in the waveguide to which it is matched and does not have to travel through any other waveguide. As shown, the curve 186 of the red wavelength band of fig. 15 coupled to its waveguide using controlled polarization in accordance with the techniques of the present invention shows a coupling efficiency of approximately 88%. The curve 188 of the red wavelength band of fig. 14 without controlled polarization shows a lower coupling efficiency of less than 70%. Thus, as shown, the PSG of the present technology can prevent coupling light into a mismatched waveguide and facilitate coupling light into a matched waveguide.

Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims. The scope of the invention is defined by the claims appended hereto.

Claims (10)

1. A method for presenting an image, comprising:

(a) projecting light from a light source (120) into an optical element (115), the light comprising at least a first wavelength band and a second wavelength band, and the optical element comprising at least a first waveguide and a second waveguide (140)₁，140₂) The first and second waveguides each having at least one grating (144, 148);

(b) controlling the incidence to the first waveguide (140)₁) Of said first wavelength band is polarized such that it is incident on said first waveGuide (140)₁) Is different in polarization of the wavelength bands other than the first wavelength band, thereby coupling the first wavelength band to the first waveguide (140) to a greater extent than the wavelength bands other than the first wavelength band₁) Performing the following steps; and

(c) controlling the incidence to the second waveguide (140)₂) Is different from the polarization of the other wavelength bands than the second wavelength band incident on the second waveguide (1402), thereby coupling the second wavelength band to the second waveguide (140) to a greater extent than the other wavelength bands than the second wavelength band₂) In (1).

2. The method of claim 1, wherein the step of controlling the polarization of the first wavelength band to be different from the polarization of the wavelength bands other than the first wavelength band comprises the step of modifying the polarization of the first wavelength band incident on the first waveguide while maintaining the polarization of the wavelength bands other than the first wavelength band incident on the first waveguide.

3. The method of claim 1, wherein the step of controlling the polarization of the first wavelength band to be different from the polarization of the wavelength bands other than the first wavelength band comprises the step of modifying the polarization of the first wavelength band incident on the first waveguide from a first state to a second state in which the first wavelength band is coupled in the first waveguide to a greater extent than in the first state.

4. The method of claim 1, wherein the step of controlling the polarization of the first wavelength band to be different from the polarization of the wavelength bands other than the first wavelength band comprises the step of modifying the polarization of the wavelength bands other than the first wavelength band incident on the first waveguide from a first state to a second state.

5. The method of claim 4, wherein the step of controlling the polarization of the second wavelength band to be different from the polarization of wavelength bands other than the second wavelength band comprises the step of modifying the second wavelength band incident on the second waveguide from the second state to the first state.

6. A method for presenting an image, comprising:

(a) projecting light from a light source (120) into an optical element (115), the light comprising 2 to n wavelength bands, and the optical element comprising 2 to m waveguides (140), an ith wavelength band being matched to a jth waveguide (140), wherein i is 1 to n, and j is 1 to m; and is

(b) Passing one or more of the 2 to n wavelength bands through a plurality of polarization state generators (160, 162, 164, 166), each polarization state generator associated with one of the 2 to m waveguides (140), the plurality of polarization state generators (160, 162, 164, 166) controlling polarization of the one or more wavelength bands passing therethrough to facilitate coupling of the ith wavelength band in the jth waveguide (140) while preventing coupling of states of remaining wavelength bands passing through the jth waveguide (140).

7. The method of claim 6, wherein after passing through a first polarization state generator disposed between the light source and the first waveguide, the first wavelength band is in polarization state 1, where the electric vector is perpendicular to the grating vector, and wavelength bands 2 through n are in polarization state 2, where the electric vector is perpendicular to the electric vector of the first wavelength band.

8. The method of claim 6, wherein the nth wavelength band passes through the m-1 th waveguide when its polarization is set to a state that prevents coupling of the nth wavelength band into the m-1 th waveguide, and the nth wavelength band passes through the m-th waveguide when its polarization is set to a state that allows coupling of the nth wavelength band into the m-th waveguide.

9. An optical element (115) for transmitting light from a light source (120) to an eye-box (130), comprising:

a first waveguide (140)₂) The first waveguide comprises at least a first grating (144, 148) for receiving light from the light source (120) and coupling a first portion of the light to the first waveguide (140)₂) Performing the following steps;

a second waveguide (140)₁) The second waveguide comprising at least a second grating (144, 148) for receiving light from the light source (120) and coupling a second portion of the light to the second waveguide (140)₁) Performing the following steps;

between the light source (120) and a first waveguide (140)₂) A first polarization state generator (160, 166) between, the first polarization state generator (160, 166) modifying the polarization of the first portion of the light to be coupled to the first waveguide (140)₂) Performing the following steps; and

a second polarization state generator (162, 168) between the first and second diffraction gratings (144, 148, 144, 148), the second polarization state generator (162, 169) modifying a polarization of a second portion of the light to be coupled at a second waveguide (140)₁) In (1).

10. The optical element of claim 9, wherein the first and second waveguides and the polarization state generator are planar elements formed in a near-eye display for generating a mixed reality environment.