Thin waveguide wavelength selective projector

Abstract

A device for providing a 1D line image is disclosed. The device includes a wavelength-tunable light source for providing image light having an angular distribution encoded in a spectrum. The device also includes an outcoupler thin slab waveguide in the form of a diffraction grating for outcoupling the image light at an angle that depends on the wavelength. The image can be formed by scanning a collimated light beam propagating in the slab waveguide when a tunable monochromatic light source is used, or by simultaneously forming a 1D singular distribution of brightness when a spectrally tunable light source is used. The device can be used in a near-eye display for forming a 2D image in the angular domain.

Description

[0001] Related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 002,817, filed on March 31, 2020, entitled “Single-or Few-Mode Waveguide Display,” and U.S. Provisional Patent Application No. 63 / 012,625, filed on April 20, 2020, entitled “Single-or Few-Mode Waveguide Display.” Technical Field

[0003] The present disclosure relates to optical devices, particularly display systems and modules. Background Art

[0004] Head-mounted displays (HMDs), helmet-mounted displays (HMDs), near-eye displays (NEDs), and the like are increasingly being used to display virtual reality (VR), augmented reality (AR), and mixed reality (MR) content. These displays are finding applications in a variety of fields, including entertainment, education, training, and biomedical science, to name a few. The displayed VR / AR / MR content can be three-dimensional (3D) to enhance the experience and match virtual objects with real objects observed by the user.

[0005] To provide better optical performance, display systems and modules may include a large number of components, such as lenses, waveguides, display panels, etc. Because the display of an HMD or NED is typically worn on the user's head, a large, bulky, unbalanced, and / or heavy display device would be cumbersome and may be uncomfortable for the user to wear. Compact, lightweight, and efficient head-mounted display devices and modules are needed. Summary of the Invention

[0006] According to a first aspect of the present disclosure, there is provided an apparatus for providing a line of an image in an angular domain, the apparatus comprising: a wavelength-tunable light source for providing image light comprising a spectral component at a first wavelength; and a low-mode waveguide comprising: an inner coupler for coupling the image light into the low-mode waveguide; and a slab waveguide portion for propagating the image light coupled by the inner coupler; wherein the slab waveguide portion comprises an outer coupler configured to outcouple the spectral component of the image light at an angle to a plane of the slab waveguide portion, wherein the angle depends on the first wavelength. The slab waveguide portion may comprise a single-mode slab waveguide. The slab waveguide portion may comprise a core and a top cladding supported by the core. The inner coupler may comprise a diffraction grating formed in the core of the slab waveguide portion.

[0007] The slab waveguide portion may include a first core and a first cladding supported by the first core. The first core and the first cladding may be configured for single-mode propagation of the image light. The outcoupler may include a first diffraction grating formed in the first core. The first diffraction grating may be configured to outcouple a spectral component of the redirected image light at a first angle depending on a first wavelength. The first angle may be within a first angular range corresponding to a tunable range of the wavelength tunable light source. The slab waveguide portion may further include a second core supported by the first cladding and a second cladding supported by the second core. The second core and the second cladding may be configured for single-mode propagation of the image light. The outcoupler may further include a second diffraction grating formed in the second core. The second diffraction grating may be configured to outcouple a spectral component of the redirected image light at a second angle different from the first angle. The second angle may be within a second angular range corresponding to the tunable range of the wavelength tunable light source. The second range may be different from the first range.

[0008] A multimode interference (MMI) coupler can be arranged in an optical path between an inner coupler and the first and second cores of the slab waveguide portion for coupling image light into at least one of the first and second cores of the slab waveguide portion. In such a device, the device may also include a 1×2 optical switch in the optical path between the inner coupler and the MMI coupler and a vertical mode converter downstream of the 1×2 optical switch. The input port of the 1×2 optical switch can be coupled to the inner coupler, and the first output port and the second output port of the 1×2 optical switch can be coupled to the first input port and the second input port of the vertical mode converter, respectively. The vertical mode converter can be configured to couple light at its first input port to the first core of the slab waveguide portion and to couple light at its second input port to the second core of the planar waveguide portion.

[0009] The device may further include a focusing grating supported by the slab waveguide portion. The focusing grating may include an array of grating stripes having a first refractive index, and a substrate between individual stripes of the grating stripe array, the substrate having a second refractive index. At least one of the first refractive index or the second refractive index may be tunable to provide a gradient of at least one of the first refractive index or the second refractive index for focusing or defocusing image light coupled out of the slab waveguide portion by the outcoupler. The substrate may include or contain a liquid crystal. A spatially selective heater may be coupled to the focusing grating and configured to generate a temperature gradient across the focusing grating to provide a gradient of at least one of the first refractive index or the second refractive index.

[0010] The slab waveguide portion may include a photonic crystal slab supporting a cladding layer and having a group refractive index of at least 10. The outcoupler may include a diffraction grating supported by the cladding layer for outcoupling image light propagating in the photonic crystal slab layer.

[0011] The slab waveguide portion may include a few-mode slab waveguide supporting no more than ten lateral propagation modes. The few-mode slab waveguide may include a core. The outcoupler may include a diffraction grating formed in or on the core. The diffraction grating may be configured to outcouple spectral components of the redirected image light at an angle depending on the first wavelength. The angle may be within an angular range corresponding to the tunable range of the wavelength tunable light source. The angular range may be different for different lateral propagation modes of the few-mode slab waveguide.

[0012] An MMI coupler can be provided in the optical path between the inner coupler and the few-mode slab waveguide portion for coupling the image light into at least one propagation mode of the few-mode slab waveguide. The device may also include a 1×N optical switch in the optical path between the inner coupler and the MMI coupler and a vertical mode converter downstream of the 1×N optical switch. The input port of the 1×N optical switch can be coupled to the inner coupler, and the N output ports of the 1×N optical switch can each be coupled to a specific one of the N input ports of the vertical mode converter, where N is an integer. The vertical mode converter can be configured to couple the light received at its input port to the corresponding propagation mode of the few-mode slab waveguide portion.

[0013] The outcoupler may include a diffraction grating configured to outcouple spectral components of the image light at an angle exceeding 90 degrees relative to the propagation direction of the image light in the slab waveguide portion. In such a device, the device may also include a corrugated reflector supported by the slab waveguide portion, configured to reflect the image light diffracted by the diffraction grating through the slab waveguide portion and out of the low-mode waveguide. The corrugated reflector may include a polarization-selective reflector configured to reflect light of a first polarization and transmit light of a second polarization orthogonal to the first polarization. In such a device, the device may further include a quarter-wave plate (QWP) supported by the slab waveguide portion on a side of the slab waveguide portion opposite to the polarization-selective reflector and configured to receive image light reflected by the polarization-selective reflector, the image light having a first polarization; and a diffraction structure supported by the quarter-wave plate and configured to reflect light propagating through the QWP back to propagate through the QWP a second time, converting the polarization of the image light to a second polarization, passing through the slab waveguide portion, and passing through the polarization-selective reflector.

[0014] According to a second aspect of the present disclosure, there is provided a low-mode waveguide comprising: a slab waveguide portion for propagating light therein, the slab waveguide portion including an outcoupler configured to outcouple light at an angle to a plane of the slab waveguide portion; and a liquid crystal (LC) cell evanescently coupled to the slab waveguide portion; wherein, in operation, the LC cell defines an effective refractive index for light propagating in the slab waveguide portion, wherein the effective refractive index varies in a propagation direction of the light in the low-mode slab waveguide, whereby a direction of light outcoupled from the slab waveguide portion by the outcoupler varies along the propagation direction of the light in the low-mode slab waveguide. The LC cell may form an acute angle with the slab waveguide portion.

[0015] According to a third aspect of the present disclosure, there is provided a low-mode waveguide comprising: a slab waveguide portion for propagating light therein, the slab waveguide portion comprising a core layer and an outcoupler configured to outcouple light at an angle to a plane of the slab waveguide portion, wherein the core layer has a refractive index that varies according to an applied electric field; and electrodes above and below the core layer for applying an electric field to the core layer such that the electric field varies spatially along a propagation direction of the light in the core of the slab waveguide portion, whereby, in operation, an effective refractive index of light propagating in the slab waveguide portion varies along the propagation direction of the light in the low-mode slab waveguide, whereby a direction of light outcoupled from the slab waveguide portion varies along the propagation direction of the light in the low-mode slab waveguide. The electrodes may be arranged at an acute angle to each other. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Examples will now be described with reference to the accompanying drawings, in which:

[0017] Figure 1A is a 3D view of a device for redirecting light in two dimensions, the device including a low-mode waveguide;

[0018] Figure 1B yes Figure 1A A side cross-sectional view of a low-mode waveguide;

[0019] Figure 1C It is shown by Figure 1A A schematic diagram of an image drawn by a device;

[0020] Figure 2 yes Figure 1A and 1B A system-level block diagram of an example of a device;

[0021] Figure 3 yes Figure 2 A schematic front view of an example near-eye display of a device;

[0022] Figure 4A yes Figure 3A schematic front view of an example of a photonic integrated circuit (PIC) for a near-eye display;

[0023] Figure 4B and 4C Wear Figure 4A Side and top views of a person with a near-eye display device;

[0024] Figure 5 is a schematic side view of a wavelength tunable light source including an intracavity spectrally selective element;

[0025] Figure 6A is a schematic side view of a spectrally tunable light source including an external dynamic spectrum selection element;

[0026] Figure 6B is the output spectrum of the light source superimposed with the transmission spectrum of the spectrum selection element, used to illustrate Figure 6A The operating principle of the tunable spectrum light source;

[0027] Figure 6C yes Figure 6A The output spectrum of the light source;

[0028] Figure 7 is a side cross-sectional view of a free-space grating coupler for coupling light into a waveguide;

[0029] Figure 8 is a side cross-sectional view of an adiabatic waveguide coupler for coupling light into a waveguide;

[0030] Figure 9 is a schematic diagram of a phased array 1D imager disclosed herein;

[0031] Figure 10A yes Figure 9 Schematic top view of the PIC implementation of the phased array 1D imager;

[0032] Figure 10B yes Figure 10A Schematic top view of the PIC implementation of a Mach-Zehnder interferometer (MZI) array (MZIA) of a PIC 1D imager.

[0033] Figure 10C yes Figure 10B Schematic top view of a single MZI;

[0034] Figure 10D yes Figure 10A Schematic top view of the phase shifter array (PSA) of the PIC 1D imager;

[0035] Figure 10E yes Figure 10A Schematic top view of the implementation of the waveguide fan of the PIC 1D imager;

[0036] Figure 11 is a schematic top view of a hybrid 1D imager comprising a 1D lens etched in a waveguide;

[0037] Figure 12 is a schematic diagram of a free space optics (FSO) implementation of a 1D scanner including a microelectromechanical system (MEMS) tiltable reflector;

[0038] Figure 13A is a top schematic diagram of a field of view (FOV) expander based on liquid crystal (LC) cladding waveguide;

[0039] Figure 13B yes Figure 13A Side cross-sectional view of the FOV extender;

[0040] Figure 14 is a schematic top view of a hologram-based beam expander according to the present disclosure;

[0041] Figure 15 is a schematic top view of a PIC implementation of a phased array 1D imager with a beam expander;

[0042] Figure 16 is a side cross-sectional view of the output waveguide used to illustrate the angular dispersion calculation;

[0043] Figure 17 is a side cross-sectional view of a dual-core waveguide used to widen the angular dispersion range of an outcoupler;

[0044] Figure 18 Top view of the few-mode waveguide (FMW) used to broaden the angular dispersion range of the outcoupler.

[0045] Figure 19 This is a side cross-sectional view of a high-dispersion outcoupler based on a slow-light waveguide;

[0046] Figure 20A is a side cross-sectional view of a high-dispersion outcoupler based on a waveguide grating and a corrugated reflector;

[0047] Figure 20B is a side cross-sectional view of a high-dispersion outcoupler based on a waveguide grating and a polarization-selective corrugated reflector;

[0048] Figure 21A and 21B is a schematic side view of a low-mode slab waveguide with a refractive index gradient for variably focusing or defocusing image light coupled out of the waveguide;

[0049] Figure 22 is a side cross-sectional view of an example of a variable focus outcoupler based on a tilted liquid crystal (LC) cell;

[0050] Figure 23 is a side cross-sectional view of an example of a zoom outcoupler based on a wedge-shaped Pockels cell;

[0051] Figure 24 is a side cross-sectional view of an example of a zoom outcoupler based on a Pockels cell with buried electrodes;

[0052] Figure 25 is a side cross-sectional view of an example of a zoom outcoupler based on the thermo-optic effect;

[0053] Figure 26 is a flow chart of a method for providing an image in an angular domain;

[0054] Figure 27 It is a 1D scan / drawing at a set wavelength. Figure 26 Flowcharts of variations of the method;

[0055] Figure 28 is used to simultaneously generate the frames of the image to be displayed Figure 26 Flowcharts of variations of the method;

[0056] Figure 29 is an illustration of an augmented reality (AR) display of the present disclosure having the form factor of a pair of glasses; and

[0057] Figure 30 is an isometric view of a virtual reality (VR) display of the present disclosure. DETAILED DESCRIPTION

[0058] Although the present teachings have been described in conjunction with various embodiments and examples, the present teachings are not intended to be limited to these embodiments. On the contrary, the present teachings include various alternatives and equivalents, as will be understood by those skilled in the art. All statements of the principles, aspects, and embodiments of the present disclosure, as well as specific examples thereof, are listed herein and are intended to include structural and functional equivalents thereof. In addition, these equivalents are intended to include currently known equivalents and equivalents developed in the future, i.e., any element developed that performs the same function, regardless of structure.

[0059] As used herein, the terms "first," "second," etc., are not intended to imply a sequential order, but rather to distinguish one element from another, unless explicitly stated. Similarly, the sequential ordering of method steps does not imply a sequential order of their execution, unless explicitly stated. Figure 1A 、 Figure 1B 、 Figure 2 、 Figure 3 、 Figure 4A 、 Figure 5 、 Figure 6A 、 Figure 7-Figure 9 、 Figures 10A-10E 、 Figure 11、 Figure 12 、 Figure 13A 、 Figure 13B and Figure 14-Figure 25 In the drawings, like reference numerals denote like elements.

[0060] Near-eye displays (NEDs) can use pupil-replicating waveguides to extend the projected image above the display's eyebox—that is, over the area where the user's eyes are likely to be located during normal operation, such as when the user is wearing the display. Pupil-replicating waveguides are typically parallel plates of transparent material that spread image light in a zigzag pattern through total internal reflection (TIR) ​​from the top and bottom surfaces of the waveguide. Such waveguides can be prone to diffraction effects that cause dispersion as a function of field angle, are generally unsuitable for curved substrates, and exhibit ghost images for objects at close range in the real world.

[0061] According to the present disclosure, single-mode (SM) or few-mode (FM) waveguides (collectively referred to herein as "low-mode" waveguides) can be used to deliver light to the eyebox and form an image. The advantage of low-mode waveguides is that the frequency at which light interacts with the grating is several orders of magnitude higher than with conventional multimode lightguides. Therefore, for each individual interaction, the diffraction efficiency of the grating can be made small enough to reduce or eliminate perspective artifacts such as rainbows and improve display clarity. In addition, single-mode waveguides enable more precise control of light distribution across the eyebox, which results in better uniformity and efficiency.

[0062] The challenge with using single-mode waveguides is that they only have the ability to transmit 1D information, such as horizontal resolution but not vertical resolution, or vice versa. This limitation can be overcome by encoding other components of a 2D image in non-spatial properties of light, such as wavelength. The wavelength range used for each color channel can be made small enough so as not to significantly reduce the color gamut.

[0063] Now refer to Figure 1A , the device 100 provides an image in the angular domain. The image can be defined by a light field having a two-dimensional (2D) angular distribution of brightness I(α, β). The angles α, β are the ray angles of the image light that define the ray angles in 3D space, such as Figure 1A More generally, the device 100 can be used to redirect light in two dimensions or along two non-parallel planes or surfaces, such as for 2D beam rastering, long-range sensing, depth sensing, LIDAR applications, etc. Here, the term "redirection" includes rastering of a collimated beam, as well as providing a temporal distribution of light in one or two dimensions or planes.

[0064] The device 100 includes a light source 102, a 1D redirector 104 coupled to the light source 102, and a low-mode waveguide 106 coupled to the 1D redirector 104 via a coupler 103. The low-mode waveguide 106 includes a slab waveguide portion 107. Here, the term "slab waveguide" refers to a waveguide that restricts light propagation in only one dimension, i.e., the vertical direction or Z direction perpendicular to the waveguide plane, allowing light to propagate freely in the waveguide plane, e.g., Figure 1A In the example of FIG. 1 , light source 102 provides light 108 having an adjustable spectrum that is a function of a desired distribution of brightness I(α, β). For example, the adjustable spectrum can have multiple spectral components; in some examples, one spectral component can be provided at an adjustable wavelength.

[0065] The 1D redirector 104 receives light 108 from the light source 102 and redirects (e.g., angularly disperses) the light 108 in the XY plane (i.e., the plane of the low-mode waveguide 106) according to a desired distribution of brightness I(α, β). In display applications, the 1D redirector 104 functions as a 1D imager that provides a line of 2D images. The slab waveguide portion 107 is a single-mode waveguide or a few-mode waveguide that is configured to propagate the light 108 in the XY plane, but confines and guides the light to propagate along the Z axis. The slab waveguide portion 107 includes an outcoupler 110 that outcouples the image light 108 into the plane of the low-mode waveguide 106 (the XY plane) at an angle that is based on the wavelengths of the spectral components of the light 108. In some examples, a single tunable spectral component can be outcoupled by outcoupler 110 at an angle corresponding to its wavelength in a plane angled relative to the plane of low-mode waveguide 106 (i.e., the XY plane); and in some examples, multiple spectral components can be outcoupled simultaneously or instantaneously at an angular distribution corresponding to the wavelength distribution of the spectral components. The distribution of outcoupling angles is defined by the tunable spectrum of light 108. The angular distribution of luminance in the X and Y directions can be controlled to provide an image in an angular domain having a desired distribution of luminance I(α, β) for direct observation by an observer.

[0066] Figure 1B An example of a low-mode waveguide 106 is shown in a side cross-sectional view. The low-mode waveguide 106 includes a substrate 112 supporting a thin waveguide layer 114 in which light 108 propagates. Depending on the refractive index contrast and thickness of the waveguide layer 114, only one mode or a few modes (e.g., up to 10 modes) can propagate in the thin waveguide layer 114. Therefore, the term "low-mode" waveguide is defined herein to mean a waveguide that supports up to 10 different lateral propagation modes. Light 108 propagates in the plane of the waveguide 106 (i.e., the XY plane), but is confined or guided in the Z direction.

[0067] The wavelength selective outcoupler 110 outcouples the image 108 at different angles depending on the wavelength. For example, a first spectral component 121 at a wavelength λ1 is outcoupled to the low mode waveguide 106 at a right angle, while a second spectral component 122 at a wavelength λ2 is outcoupled to the low mode waveguide 106 at an acute angle. The spectral composition of the light 108 provided by the light source 102 and the angular dispersion of the wavelength selective outcoupler 110 are selected so as to provide a desired angular distribution of the brightness I(α, β(λ)). As a non-limiting example, refer to Figure 1C , the entire image 116 in the angular domain can be formed. The image 116 is represented by the angular distribution of the brightness I(α, β(λ)).

[0068] refer to Figure 2 , device 200 is Figure 1A and 1B An example implementation of device 100 is provided. Figure 2 The display device 200 comprises in series optically coupled: a spectrally tunable single mode light source 202, an inner coupler 203, a 1D imager 204, the following optional modules: a 1D FOV expander 224, a 1D lateral beam expander 226 and an angular dispersion enhancer 228; and an outer coupler 210. Other elements may also include a zoom adjuster 230, a stray light filter 232 and a distributed temperature sensor 234. The optional elements are shown as dashed rounded rectangles. All or some of the elements may be part of the low mode waveguide 206, for example, may be formed in or on the low mode waveguide 206. It should be noted that the low mode waveguide 206 may include portions having linear waveguides, i.e. straight or curved ridge waveguides that guide light in two dimensions, and slab waveguide portions that guide light in only one dimension, i.e., Figure 2 direction in the Z direction while allowing free propagation in the XY plane. Figure 2 The coupling order of the elements shown may be changed.

[0069] In operation, the spectrally tunable single-mode light source 202 provides image light 208 having an adjustable spectrum that is a function of the desired angular distribution of brightness I(α, β(λ)) as described above. Coupler 203 couples image light 208 into 1D imager 204. 1D imager 204 receives image light 208 from light source 202 and redirects or angularly disperses image light 208, scans a collimated beam of image light 208, etc. 1D FOV expander 224 can be configured to switch image light 208 between multiple connected FOV portions to enhance or widen the spread of light. 1D lateral beam expander 226 increases the width of the collimated portion of the image light in the XY plane, i.e., widens the beam of image light 208 in the plane of the low-mode waveguide 206, thereby increasing the lateral size of the eyebox of display device 200. Here, the term "eyebox" refers to the geometric area of ​​an image of acceptable quality that can be viewed by a user of display device 200. Angular dispersion enhancer 228 increases the spectral dispersion of image light 208 to achieve a desired second ID angular distribution of brightness I(β) when outcoupled by wavelength-selective outcoupler 210. Zoom adjuster 230 can adjust the convergence or divergence of the outcoupled image light to change the perceived depth of focus. Stray light filter 232 can remove or reduce the portion of image light that is not coupled to the user's eyes but is outcoupled to the outside world. Distributed temperature sensor 234 can obtain the temperature distribution across low-mode waveguide 206 to provide correction and operate thermally driven optical elements and components. More details will be given below.

[0070] refer to Figure 3 , the display device 300 is the device 100 of FIG. 1 or Figure 2 Implementation of device 200. Figure 3 The display device 300 is a near-eye display device having the form factor of a pair of glasses 311, with a mode waveguide 306 occupying the lens area of ​​the glasses. Figure 3 The display device 300 includes a light source 302, a coupler 303, a 1D imager 304, a 1D FOV expander 324, a 1D lateral beam expander 326, an angular dispersion enhancer 328, an outcoupler 310, and a zoom adjuster 330 optically coupled in series. All components can be implemented in a low-mode waveguide 306. The light source 302 can be provided separately, as shown.

[0071] refer to Figure 4A , the display device 400 is the device 100 of FIG. 1 , Figure 2 Device 200 or Figure 3 Implementation of the display device 300. Figure 4ADisplay device 400 is a near-eye display device having the form factor of a pair of glasses 411, having active components / features implemented in a PIC portion 436 of a waveguide 406. PIC portion 436 can be driven by an integrated circuit (IC) driver unit 407. Display device 400 includes a light source 402 having an adjustable emission spectrum, coupled to PIC portion 436 via an optical fiber 403. PIC portion 436 can include, for example, a 1D imager and / or a 1D FOV expander. Light beams 408A, 408B, and 408C (collectively, 408) formed in LC portion 436 are expanded by intra-waveguide optical elements 426A, 426B, and 426C, respectively, which have optical power (i.e., focusing / defocusing power) for collimating / redirecting light beams 408A, 408B, and 408C to a highly dispersive output grating 410. The function of the high dispersion output grating 410 is to provide outcoupling of the image light 408 at different vertical angles to provide a vertical FOV, such as Figure 4B shown. Figure 4C The horizontal FOV shown is provided by the PIC portion of the image light 408 within the plane of the extended waveguide 406.

[0072] Now we will consider Figure 1, Figure 2 、 Figure 3 and Figure 4A Various implementations of the different modules depicted in .

[0073] First reference Figure 5 The tunable laser source 502 can be used as a wavelength-tunable light source for the display device of the present disclosure. The tunable laser source 502 includes an optical cavity formed by a pair of mirrors 501, a gain medium 504, and a wavelength-selective intracavity element 506. The wavelength-selective intracavity element 506 has a tunable transmission peak within the gain band of the gain medium 504. The transmission peak of the wavelength-selective element 506 can be scanned in conjunction with the 1D angle of the scanned collimated light beam 508 to provide the 2D FOV required by the display device, such as the horizontal FOV provided by the beam scanning and the vertical FOV provided by the output wavelength scanning of the tunable laser source 502.

[0074] Go to Figure 6A , the tunable spectrum light source 602 can be used as a wavelength tunable light source for the display device of the present disclosure. The tunable spectrum light source 600 includes a broadband light source 604 coupled to a dynamic spectrum filter 606 having a selectable arbitrary spectrum shape. The emission spectrum 630 of the broadband source 604 is Figure 6B , where it overlaps with either the example broadband spectral shape 632 of the dynamic spectral filter 606 or the example narrowband (single wavelength) spectral shape 633 of the dynamic spectral filter 606 .

[0075] The dynamic spectral filter 606 can be configured to independently adjust the transmission of a single or multiple adjacent narrow spectral bands or channels. For example, the dynamic spectral filter 606 can adjust the shape of the broadband spectral shape 632 according to the desired angular distribution of brightness at the output of the display device. In some examples, the narrowband spectral shape 633 can be scanned in wavelength, which causes the output beam to be angularly scanned according to the dispersion function of the outcoupler of the display device.

[0076] The output spectrum obtained is Figure 6C For example, the broadband spectral shape 632 generates a broadband emission spectrum 634 , and the narrowband spectral shape 633 correspondingly generates a narrowband emission spectrum 635 , the emission wavelength being tunable by the dynamic spectral filter 606 .

[0077] refer to Figure 7 The free space grating coupler 703 can be used to couple light from a spectrally tunable light source 702A (such as Figure 5 Adjustable laser source 502 or Figure 6A The free-space grating coupler 703 includes a plurality of grating lines 705 that receive image light 708 and couple the image light 708 into the core 707 of the waveguide 706. The grating lines 704 extend parallel to each other and can be straight or curved, for example, having a direction perpendicular to the grating line 704. Figure 7 The concentric arc shape provides focusing of the image light 708 so that its mode size matches the size of the optical mode 709 that can propagate in the core 707 of the waveguide 706.

[0078] Go to Figure 8 The waveguide coupler 803 can be used to couple light from a spectrally tunable, waveguide-based, or fiber-coupled light source into a waveguide or PIC of a display of the present disclosure. The waveguide coupler 803 includes a tapered portion 836 in which the tapered core 813 of the source fiber 802 is positioned proximate to and parallel to the tapered waveguide core 805 of the waveguide 806 having the waveguide core 807. The tapered portion 836 can be sufficiently long to ensure adiabatic transition of light energy from the source fiber 802 to the waveguide core 807 of the waveguide 806.

[0079] refer to Figure 9 , the phased array 1D imager 904 is the 1D redirector / imager 104 of FIG. 1 , Figure 2 1D imager 204 or Figure 3 Example of a 1D imager 304. Figure 9The phased array 1D imager 904 includes a 1×N power divider 920, N phase shifters 922 coupled to the power divider 920, and an array of N linear waveguide emitters 924 coupled to the phase shifters 922. Throughout this specification, the term "linear waveguide" refers to a waveguide that confines light propagation in two dimensions, such as an optical fiber. A linear waveguide can be straight, curved, etc.; in other words, the term "linear" does not imply a straight waveguide section. An example of a linear waveguide is a ridge waveguide. All elements of the phased array 1D imager 904 can be implemented in a low-mode waveguide 906 including a slab waveguide section 907. For example, the number N can vary between 4 and 16,000.

[0080] In operation, an internal coupler, such as a free-space grating coupler 703, receives image light 908 ( Figure 9 (not shown) and couples the image light 908 into a power divider 920. The power divider 920 divides the image light 908 among the N linear waveguides 921 of the low-mode waveguide 906, each of which carries a portion of the image light 908. Each image light portion is phase-shifted or delayed by a corresponding phase shifter 922 based on a control signal provided by a controller 926. The image light portion is emitted by an array of N linear waveguide emitters 924, with a desired beam angle The corresponding phase distribution forms an output beam 919 having a phase wavefront 921. The output beam 919 propagates in the slab waveguide portion 907. In some examples, the phase distribution in 922 can be controlled to suppress all diffraction orders except one, so that all energy is concentrated into a single steered beam.

[0081] Go to Figure 10A , the PIC phased array 1D imager 1004 is Figure 9 10 includes a Mach-Zehnder interferometer array (MZIA) 1020 operating as a divider 920, a PIC phase shifter array (PSA) 1022 coupled to the MZIA 1020, and a waveguide concentrator 1024 coupled to the PIC phase shifter array 1022. The end of the output linear waveguide 1030 of the waveguide concentrator 1024 serves as a plane ( Figure 10A antenna 924 ( Figure 9 ) operation while maintaining the constraint in the direction perpendicular to the slab waveguide ( Figure 10A in the Z direction).

[0082] The MZIA 1020 may include a binary tree of passive Y-splitters and / or active Mach-Zehnder interferometers (MZIs) 1021, such as Figure 10B Each MZI may include Figure 10C The evanescent coupler 1026 shown has one input 1023 and two outputs 1033, 1034, or two inputs (one of which is idle) and two outputs, which are two waveguide sections coupled at two locations by the evanescent coupler. The function of the MZIA 1020 is to split the image light into N parts. In the example using a passive Y splitter, the PSA 1022 can be used to scan the collimated beam. In the implementation using an active MZI, if necessary, the MZI ( Figure 10C ) can be used to control the optical power distribution at the output to unequal optical powers, for example to provide apodization of the scanned collimated light beam, or even to create a fully desired 1D angular profile.

[0083] refer to Figure 10D The phase shifter array 1022 may include a plurality of phase shifters 1027 that provide a controllable amount of phase shift or delay to light propagating therein. The phase shifters 1027 may be, for example, thermo-optical phase shifters based on the thermo-optic effect, electro-optical phase shifters based on the Pockels effect and / or the Kerr effect, and / or electro-absorption phase shifters based on the electro-absorption effect in semiconductors, and accordingly may include heaters and / or electrodes on the waveguide as needed.

[0084] Go to Figure 10E The waveguide concentrator 1024 comprises a waveguide array that fans in or out to achieve the desired output spacing. Typically, the output spacing needs to be small enough to achieve a large field of view (FOV). The FOV is approximately equal to the ratio of the emission wavelength to the spacing of the output linear waveguides 1030.

[0085] refer to Figure 11 , the hybrid 1D imager 1104 is the 1D redirector 104 of FIG. 1 , Figure 2 1D imager 204 or Figure 3 An example implementation of the 1D imager 304 is provided. Figure 11The hybrid 1D imager 1104 includes an MZIA 1120, a waveguide concentrator 1124 coupled to the MZIA 1120, and a FOV collimator 4136 coupled to the waveguide concentrator 1124 implemented in the low-mode waveguide 1106. The MZIA 1120 functions as a 1×N splitter or switch, where N is the number of output MZIA waveguides 1129. The MZIA 1120 may include, for example, a binary tree of Mach-Zehnder switches for switching image light 1108 between the N linear output waveguides. The waveguide concentrator 1124 positions its output linear waveguides 1130 closer together than the output MZIA waveguides 1129. The ends of the output linear waveguides 1130 of the waveguide concentrator 1124 are positioned at the focal plane of the FOV collimator 1136, which is located within the slab waveguide portion 1107 of the few-mode waveguide 1106. The FOV collimator 1136 is a collimating element positioned one focal length away from the end of the output linear waveguides 1130 of the waveguide concentrator 1124. The function of the FOV collimator 1136 is to convert the position or Y-offset of the end of the output linear waveguides 1130 of the waveguide concentrator 1124 into the beam angle of the corresponding output light beam 1119 propagating in the slab waveguide portion 1107. In other words, the FOV collimator 1136 operates as an offset-angle optical element that converts the offset or Y-position of a selected one of the output waveguides 1130 carrying a portion of the image light 1108 into the angle of the output light beam 1119 originating from the image light portion propagating in the selected output waveguide.

[0086] The FOV collimator 1136 may be a single element, such as a lens or a mirror, or may include multiple lenses 1138, 1140, such as Figure 11 As shown. Lenses 1138, 1140 can be formed in the low-mode waveguide 1106 by etching and can have a folded configuration, such as a pancake lens configuration. The output beam 1119 can be reshaped, focused, collimated, etc. in the plane of the waveguide (XY plane) while remaining guided by the slab waveguide portion 1107, i.e., while remaining confined in the Z direction. The lens surface can include multiple tapers 1141 with sub-wavelength periodicity to facilitate adiabatic transitions between etched and unetched portions of the waveguide and in doing so prevent out-of-plane light scattering.

[0087] refer to Figure 12, a free space optical (FSO) 1D scanner 1204 includes a microelectromechanical system (MEMS) beam scanner 1244 having a tiltable reflector 1245 and a cylindrical lens 1246. In operation, a multi-wavelength light source, such as a wavelength-scanned laser source 1202, emits a light beam 1208 at an adjustable (e.g., linearly scanned) emission wavelength. The light beam 1208 is focused by the cylindrical lens 1203 onto the MEMS tiltable reflector 1245. The cylindrical lens 1246 serves as a coupler that receives the image light 1208 scanned by the MEMS beam scanner 1244 and couples the image light 1208 to the low-mode slab waveguide 1207. For example, the cylindrical lens 1203 can be refractive or diffractive. Other types of couplers, such as mirrors, can be used. The MEMS tiltable reflector 1245 reflects the light beam 1208 at a variable angle, as indicated by the double-headed arrow. The cylindrical lens 1246 has focusing capability in the XZ plane, while propagating the light beam 1208 substantially unfocused in the XY plane. The cylindrical lens 1246 focuses the light beam 1208 onto the edge of the low-mode slab waveguide 1207 or onto a grating coupler formed in the low-mode slab waveguide 1207. The light beam 1208 is coupled into the low-mode slab waveguide 1207 and propagates freely in the low-mode slab waveguide 1207 in the XY plane, confined in the Z direction perpendicular to the plane of the low-mode slab waveguide 1207. For effective coupling, the cylindrical lens 1246 needs to be precisely parallel to the low-mode slab waveguide 1207.

[0088] Go to Figure 13A and 13B , Liquid Crystal (LC) 1D FOV Expander 1324 is Figure 2 1D FOV Extender 224 and Figure 3 Example of a 1D FOV expander 324 . Figure 13A and 13B The LC 1D FOV extender 1324 includes a slab waveguide 1306 having a core 1307 for guiding image light 1308 in the core 1307 while allowing the image light 1308 to propagate freely in the XY plane, as shown. The top cladding 1337 includes adjustable cladding portions 1339, 1340 that are evanescently coupled to the core 1307 of the slab waveguide 1306 and are shaped to deviate the light propagating in the core 1307 of the slab waveguide 1306 by a controllable amount. Figure 13A In the example shown, the adjustable cladding portions 1339, 1340 have a sawtooth shape in the XY plane, such as a triangular array, as shown in FIG. Figure 13A The array extends transversely with respect to the optical path of the image light in the core 1307 of the slab waveguide 1306. At least some of the triangular tunable cladding portions have a Figure 13AThe horizontal arrows in FIG. 13 show the side surfaces 1339A, 1340A extending at an acute angle to the optical path. A bottom layer 1338 ( Figure 13B ) to avoid direct contact between the tunable cladding portions 1339, 1340 and the waveguide core 1307. The bottom layer 1338 may be thin enough to ensure evanescent coupling of light propagating in the core 1307 with the tunable cladding portions 1339, 1340.

[0089] The tunable cladding sections 1339 and 1340 of the top cladding layer 1337 include a liquid crystal (LC) material, which changes its refractive index for light of a specific polarization when an electric field is applied to the tunable cladding sections 1339 and 1140. When the refractive index of the LC tunable cladding sections 1339 and 1140 of the top cladding layer 1337 changes, the effective refractive index of the slab waveguide 1306 also changes, causing the image light 1308 to deviate from its original propagation direction due to Fresnel refraction at the inclined surfaces of the LC tunable cladding sections 1339 and 1140. The magnitude of this deviation depends on the angle of the inclined surfaces and the vertical separation (in the Y direction) between the LC tunable cladding sections 1339 and 1340. The energy distribution along directions 1349 and 1350 depends on the switching state of the LC tunable cladding sections 1339 and 1340, which can be operated in a binary on / off mode. When the LC tunable cladding sections 1339 and 1340 are not continuously tunable, each array of LC tunable cladding sections 1339 and 1340 can shift the 1D FOV by a discrete amount. Thus, a cascade of m LC elements will produce 2 m By energizing different triangular LC tunable cladding sections 1339, 1340, the image light 1308 can be deflected at different angles. For example, energizing the larger triangular shape 1339 deflects the image light 1308 from propagating at an angle as shown at 1349, while energizing the shallower triangular shape 1340 deflects the image light 1308 from propagating at a steeper angle as shown at 1350. More arrays of LC sections with different deflection angles can achieve more precise angular control. When the different triangular shapes of the LC tunable cladding sections 1339, 1340 are energized in coordination with the operation of a 1D imager or scanner, the image light is switched between multiple connected FOV sections, enabling the effective controllable light expansion and associated horizontal FOV to be extended or enhanced.

[0090] refer to Figure 14Holographic beam expander 1426 includes a hologram 1456 within a low-mode slab waveguide 1406 that enables image light to propagate two-dimensionally in the plane of slab waveguide 1406, i.e., in the XY plane. Hologram 1456 is configured to receive image light 1408 comprising at least one collimated beam portion (e.g., a first (1451; dashed line) and a second (1452; dashed line) collimated beam portion propagating at an angle relative to each other) and reflect each collimated beam portion at a plurality of locations along the optical path of the collimated beam portion within hologram 1456. For example, first collimated beam portion 1451 is reflected at a first angle at a plurality of locations 1451A, 1451B, and 1451C, generating a first output beam (1461; dotted line); and second collimated beam portion 1452 is reflected at a second angle at a plurality of locations 1452A, 1452B, and 1452C, generating a second output beam (1462; dashed line). Any other light beam is reflected at a beam angle between the first angle and the second angle, propagating in a plurality of directions between the directions of the first output beam 1461 and the second output beam 1462. To this end, the hologram 1456 may include a plurality of fringes configured to ensure reflection in a desired direction depending on the angle of the impinging light beam. Figure 14 It can be seen that this reflection geometry results in an expansion of the light beams 1451 , 1452 .

[0091] Go to Figure 15 , the wide beam PIC phased array 1D imager 1504 is similar to Figure 10A PIC phased array 1D imager 1004, but in MZIA 1520 and PSA 1522 ( Figure 15 ) includes more linear waveguides. Output waveguide array coupler or beam expander 1524 is similar to concentrator 1024, but includes more output linear waveguides 1530, for example, 10,000; 20,000; 30,000, or more waveguides spanning a lateral distance of 5 mm; 10 mm; or 15 mm, as appropriate. The output beam can be as wide as the width of the array of linear waveguides 1530, thus eliminating the need for any subsequent beam expansion and collimation to expand the output beam across the eyebox of the near-eye display, simplifying the overall design.

[0092] Now refer to Figure 16 , the slab waveguide 1606 supports a diffraction grating 1661 for diffracting a portion of the image light 1608 propagating in the XY plane of the slab waveguide 1606. The K vector of the diffraction grating 1661 is aligned with the x component of the K vector of the image light 1608. The diffraction angle θ of the image light 1608 follows the following equation:

[0093]

[0094] Where n is the refractive index, T is the grating period, and λ is the wavelength of light in the propagation medium. Therefore,

[0095]

[0096] where n gr is the group refractive index. In a regular waveguide with small dispersion, n gr =n, therefore,

[0097]

[0098] From equation (3), we can see that at normal incidence and T = / λn,

[0099]

[0100] For n=2, the wavelength range is 510nm to 530nm. According to the present disclosure, the angular range can be increased to a certain extent by increasing the diffraction angle θ. For example, by reducing the grating pitch to 180nm, a diffraction angle dθ range of 14.4 degrees can be achieved.

[0101] The angular dispersion range can be increased, for example, by using multiple layers of output waveguides. Figure 17 Dual-core slab waveguide 1706 extends in the XY plane. Dual-core slab waveguide 1706 includes a first core 1707 and a second core 1757, which extend parallel to each other in the XY plane of substrate 1736 and are surrounded by a first cladding 1705 and a second cladding 1755, respectively. First core 1707 and first cladding 1705 are configured for single-mode propagation of a first beam of image light (solid arrow 1708). Similarly, second core 1757 and second cladding 1755 are configured for single-mode propagation of a second beam of image light (dashed arrow 1758).

[0102] First core 1707 and second core 1757 have first and second diffraction gratings 1710 and 1760 formed in or on first core 1707 and second core 1757, respectively. First diffraction grating 1710 is configured to outcouple a spectral component of the redirected image light at a first angle dependent on a first wavelength. The first angle is within a first angular range corresponding to the tunable range of the wavelength tunable light source being used. Similarly, second diffraction grating 1760 is configured to outcouple a spectral component of the redirected image light at a second angle different from the first angle. The second angle is within a second angular range corresponding to the tunable range of the wavelength tunable light source.

[0103] For the same wavelength of image light, represented by first beam 1708 and second beam 1758, different angles and angular ranges of diffraction from the different cores 1707, 1757 of dual-core waveguide 1706 can be achieved by varying the thickness or refractive index of cores 1707 and 1757, the refractive index of claddings 1705 and 1755, or the spacing of diffraction gratings 1710 and 1760. To simplify manufacturing, a single grating can be etched into the first core 1707 layer, and the second core 1757 layer or any subsequent layers can simply reproduce this grating by directional material deposition. In the latter case, the FOV can be adjusted by varying the thickness of the layer, and therefore the effective refractive index.

[0104] The different diffraction angles can be used to expand the corresponding "vertical" 1D FOV by tiling a smaller range of angles from the separated layers. Here, the term "vertical" refers to the distinction from the 1D FOV by redirecting the image light in the plane of the low-mode waveguide (i.e., the XY plane, called "horizontal"). It should be noted that the terms "horizontal" and "vertical" in this article only refer to the differentiators used to distinguish between the in-plane 1D FOV and the wavelength-dispersive 1D FOV, and do not mean the actual orientation of the device when used. For example, a Mach-Zehnder interferometer and a directional coupler can be used to achieve switching between the first core 1707 and the second core 1757. More details on possible switching configurations are provided further below.

[0105] Go to Figure 18 Angular dispersion module 1828 provides enhanced wavelength dispersion of the image light to achieve the desired vertical 1DFOV. Angular dispersion module 1828 includes a serially coupled MZIA 1820, such as an asymmetric directional coupler, coupled to a vertical mode converter 1821; a multimode interference (MMI) coupler 1851 that receives light from vertical mode converter 1821; and a few-mode slab waveguide section 1856 that receives light from MMI coupler 1851. The number of transverse propagation modes of the image light that can propagate in the core of few-mode slab waveguide section 1856 can be, for example, 2, 3, 4, 5, or 6, or more generally, no more than 10 modes. A diffraction grating 1807 disposed in or on the core of few-mode slab waveguide section 1856 operates as an outcoupler, outcoupling the image light at an angle that depends on the wavelength. Diffraction grating 1807 is configured to outcouple each spectral component of the redirected image light at an angle that depends on the wavelength of the spectral component. The outcoupling angle is within a range of outcoupling angles corresponding to the tunable range of the wavelength tunable light source used. The outcoupling angle range is different for different lateral propagation modes of the few-mode slab waveguide portion 1856 because each propagation mode has a different effective refractive index.

[0106] Initially, only the fundamental mode of the image light is coupled into the MZIA 1820 by the inner coupler 1803. The MZIA 1820 acts as a 1×N optical switch, switching the image light between its output waveguides. At the end of each MZIA 1820 output waveguide, the image light is converted into a different vertical mode by the vertical mode converter 1821. The image light from all waveguides is combined into a few-mode slab waveguide section 1956 using the MMI coupler 1851. In this way, the in-plane image encoder layout (i.e., the one described above with reference to FIG) is realized. Figure 9-15 The disclosed horizontal 1D imager circuit system) can be shared between different propagation modes of image light in FMW 1856.

[0107] Different vertical modes have different effective refractive indices and, therefore, will be diffracted at different angles at the diffraction grating 1807 for the same wavelength. The entire vertical 1D FOV can be expanded in a time-sequential manner using the diffraction range of the separate modes, i.e., switching to a particular core providing a corresponding portion of the vertical 1D FOV, then switching to another core providing a different portion of the vertical 1D FOV, and so on, until all vertical 1D FOVs are covered. The MMI coupler 1851 can be optimized for the desired coupling of vertical modes using physical design software by defining an optimization function (also called a merit function) to have an operand representing the optical insertion loss of the MMI coupler for each vertical mode with predefined vertical coordinates, and having the physical design software run the optimization.

[0108] Figure 18 The coupling configuration, i.e., MZIA 182 coupled to vertical mode converter 1821 coupled to MMI 1851, can be used to couple the image light received by inner coupler 1803 to a different vertical mode of any waveguide component that supports several vertical modes. This configuration can be used, for example, to couple the image light to Figure 17 In the case of the dual-core slab waveguide 1706, only one Mach-Zehnder interferometer operating as a 1×2 optical switch can be used instead of the MZIA 1820. The multi-core slab waveguide may include multiple cores, and Figure 18 The coupling configuration can be used to couple image light into any core of a multi-core slab waveguide.

[0109] refer to Figure 19, the angular dispersion enhancer 1928 is based on a slow light slab waveguide 1906 extending in the XY plane and supporting a cladding 1905 having a diffraction grating structure 1910 for outcoupling the image light from the slow light waveguide 1906. The slow light waveguide 1906 may comprise a uniform 2D photonic crystal, a multilayer structure, or a combination of both, for increasing the group velocity refractive index by a factor of 20, for example, or at least by a factor of 10. Then, from equations (2)-(4), it can be seen that for a slowing factor of 20, the FOV can be increased tenfold, for example, from 4.4 degrees to 44 degrees. In some examples, the slow light waveguide 2006 may comprise an array of linear photonic crystal waveguides.

[0110] refer to Figure 20A Angular dispersion enhancer 2028A includes a low-mode waveguide 2006 having a slab waveguide portion 2056 disposed in the XY plane, and a corrugated reflector 2070A supported by slab waveguide portion 2056. Image light 2008, carrying image information encoded in its spectrum, propagates in slab waveguide portion 2056. A diffraction grating 2010 (e.g., a Bragg grating) in slab waveguide portion 2056 outcouples different spectral components of the image light 2008 at different angles exceeding 90 degrees relative to the propagation direction of the image light 2008 in slab waveguide portion 2056. For example, a first spectral component 2081 is outcoupled at a first angle θ1, while a second spectral component 2081 is outcoupled at a larger second angle θ2. The corrugated reflector 2070A reflects the first spectral component 2081 and the second spectral component 2082 of the image light 2008 diffracted by the diffraction grating 2010 through the slab waveguide portion 2056 and to the outside of the low-mode waveguide 2056 .

[0111] The angular dispersion of the outcoupled image light 2008 is maximized when the image light 2008 is outcoupled almost directly backward, i.e., when the angle θ is close to 180 degrees. For example, assuming a regular waveguide grating with a refractive index of 2, a wavelength shift from 510 nm to 530 nm causes a 4.4° shift if the average diffraction angle θ is zero, but causes a 14° shift if the average diffraction angle θ is ~65°. In this configuration, the diffraction grating 2010 outcouples the image light 2008 backward to maximize angular dispersion and, therefore, increase the FOV of the display. The corrugated reflector 2070A can include a plurality of prisms 2072 having a reflective coating 2074 supported by the slab waveguide portion 2056. The reflective coating redirects the image light 2008 in a direction perpendicular to the slab waveguide portion 2056 to ensure that the central field angle is perpendicular to the slab waveguide portion 2056, i.e., parallel to the Z axis. As non-limiting examples, the reflective layer 2074 can be made of any one or a combination of the following: (1) a low refractive index material for total internal reflection (TIR), (2) a thin metal layer forming a semi-reflective mirror, or (3) a narrow spectrum multilayer mirror coating or a reflective polarizer such as a wire grid polarizer or a dual brightness enhancement film (DBEF).

[0112] Go to Figure 20B , Angular Dispersion Enhancer 2028B is Figure 20A Example of polarization selectivity of angular dispersion enhancer 2028A. Figure 20B In the angular dispersion enhancer 2028B, the corrugated reflector includes a polarization-selective reflector 2070B configured to reflect light of a first polarization and transmit light of a second polarization orthogonal to the first polarization. The angular dispersion enhancer 2028B also includes a quarter-wave plate (QWP) 2076 supported by the slab waveguide portion 2056 on a side of the slab waveguide portion 2056 opposite the polarization-selective reflector 2070B. The QWP 2076 is configured to receive image light components 2081, 2082 reflected by the polarization-selective reflector 2070B. The image light components 2081, 2082 are in a first polarization state.

[0113] A diffractive structure 2078 (e.g., a reflective surface relief diffraction grating) is supported by the QWP 2076 and is configured to reflect image light components 2081, 2082 that have propagated through the QWP 2076 back through the QWP 2076 a second time, converting the polarization of the image light components 2081, 2082 from a first polarization to a second polarization. Components 2081, 2082 then propagate through the slab waveguide portion 2056 and pass through the polarization-selective reflector 2070B, which transmits them because they are in the second polarization state. The purpose of the diffractive structure 2078 is to further increase the angular dispersion of the image light 2008.

[0114] refer to Figure 21A and 21B , which illustrates the principle of zoom adjustment (i.e., adjustment of convergence / divergence) of outcoupled image light. Figure 21A The low-mode slab waveguide portion 2156A in FIG. 2 includes a grating outcoupler with a uniform refractive index. The image light component 2108 is outcoupled vertically, ie, perpendicular to the plane of the slab waveguide portion 2156A, as a parallel beam focused at infinity. Figure 21B The slab waveguide portion 2156B in the embodiment includes a grating outcoupler with a controllable non-uniform refractive index so that the image light component 2108 is coupled out of the plane of the slab waveguide portion 2156B vertically, that is, vertically to the plane of the slab waveguide portion 2156B, as shown in the figure, and converges as a focused beam at a focal length equal to the inverse of the optical power (focusing power) of the grating outcoupler. Assuming that the desired size of the eye box 2112 is 16 mm, a refractive index increment of 0.008 is required to focus the image light component 2108 from the slab waveguide portion 2156B into a focal spot 2185 two meters away from the eye box 2112. To achieve this focusing function, the effective refractive index n of the grating outcoupler is eff It needs to change linearly from 0.004 to -0.004 when passing through the eye box 2112. This principle can be used in any dispersion enhancer considered in this paper. For dispersion enhancers with resonant structures, any change in the physical refractive index of the material in the stack will produce a larger n eff Therefore, due to the change of refractive index along the outer coupler, focusing or defocusing is facilitated. Figures 22 to 25 Consider an illustrative example of a zoom adjuster based on this principle.

[0115] First reference Figure 22 Zoom adjuster 2230 includes a low-mode slab waveguide portion 2256 for propagating light (e.g., image light 2208). Slab waveguide portion 2256 includes an outcoupler 2210 (e.g., a Brag grating) configured to outcouple image light 2208 at an angle relative to the XY plane of slab waveguide portion 2256. A liquid crystal (LC) cell 2288 is evanescently coupled to slab waveguide portion 2256. The thickness of an upper cladding layer 2287 of slab waveguide portion 2256 is selected such that a tail of a guided mode 2290 of image light 2208 traveling in the core of mode slab waveguide portion 2256 overlaps with LC cell 2288, passes through upper cladding layer 2287 supporting LC cell 2288, and reaches LC layer 2289 of LC cell 2288. LC layer 2289 is disposed between a pair of electrodes 2283. The guided mode 2290 overlaps the LC layer 2289 of the LC cell 2288 .

[0116] The LC cell 2288 defines the effective refractive index of the guided mode 2290 of the image light 2208 propagating in the slab waveguide portion 2256. The effective refractive index n effThe propagation direction of the image light 2208 in the low-mode slab waveguide 2256 (ie, Figure 22 The effective refractive index n changes along the X direction. eff The direction of the out-coupled image light 2208 portion is varied along the X-axis, which causes the out-coupled image light 2208 to be focused or defocused, as described above with reference to FIG. Figure 21A and 21B As mentioned above, you can choose the upper cladding 2287 ( Figure 22 ) so that the change in the refractive index of the LC layer 2289 will result in an effective refractive index n of the propagating waveguide mode 2290 eff This will cause the outcoupled image light 2208 to be focused or defocused. The absolute value of the change, and thus the focal length, can be controlled by the voltage applied to the LC cell 2288. The thickness profile of the upper cladding layer 2287 can be linear, i.e., the LC cell 2288 can form an acute angle with the slab waveguide portion 2256, thereby changing the effective refractive index n of the waveguide mode 2290. eff .

[0117] The refractive index of LC layer 2289 is varied by applying a voltage to LC cell 2288. As described above, this causes the propagation direction of outcoupled image light 2208 to vary along the propagation direction of image light 2208 in slab waveguide portion 2256 (i.e., the X direction), thereby causing outcoupled image light 2208 to diverge or converge in the XZ plane. By varying the applied voltage, the divergence / convergence (collectively, "divergence") of outcoupled image light 2208 can be controlled. In some examples, LC cell 2288 can be parallel to slab waveguide portion 2256 and can be pixelated to impart a refractive index variation profile along the propagation direction of image light 2208 (i.e., along the X direction).

[0118] Now refer to Figure 23 Zoom adjuster 2330 includes a low-mode slab waveguide portion 2356 for propagating light (e.g., image light 2308). Slab waveguide portion 2356 includes a core layer 2307 and an outcoupler 2310 configured to outcouple image light 2308 at an angle relative to the plane of the slab waveguide portion. Core layer 2307 is made of a material having a refractive index that depends on an applied electric field. For example, core layer 2307 can be made of LiNbO3, AlN, SiC, or other materials with a high electro-optic coefficient.

[0119] Electrodes 2383 are positioned above and below the core layer 2307 to apply an electric field 2386 to the core layer 2307. The electrodes 2383 can be positioned at an acute angle to one another, forming a wedge shape. When a voltage is applied to the electrodes 2383, the electric field 2386 varies spatially along the direction of propagation of the image light 2308 in the core 2307 of the slab waveguide portion 2356 (i.e., along the X direction). This causes the direction of the image light 2308 outcoupled from the slab waveguide portion 2356 to vary along the direction of propagation of the light in the low-mode slab waveguide, effectively causing the outcoupled image light 2308 to diverge or converge in the XZ plane. By varying the applied voltage, the degree of convergence / divergence of the outcoupled image light 2308 can be controlled.

[0120] Spatial modulation of the refractive index can be achieved by a DC or AC electric field that propagates through the material and optical mode 2390 of the slab waveguide portion 2356. Depending on the crystal axis and element design required for refractive modulation, the electrodes can be placed above / below the upper / lower cladding layers, respectively, or in only one of these layers. In the case where the electrodes sandwich the core of the waveguide, the electric field 2386 will be as follows Figure 23 23. The electrodes 2382 extend vertically as shown. The relative amplitude of the electric field 2386 along the propagation of the image light 2308 (which is the one that needs to be controlled to achieve focus) can be specified by varying the distance between the electrodes 2382. A larger distance will produce a weaker electric field 2386. By doing so, a predetermined wedge-shaped profile electric field 2386 can be embedded that is proportional to the local refractive index change. When the applied voltage V = 0, the image light 2308 is collimated (i.e., the image is at infinity). As the applied voltage V increases, the focal plane of the system will become closer.

[0121] exist Figure 24 A similar principle is employed in the zoom adjuster 2430 of FIG. , where an electric field 2486 is parallel to the core 2407 of the minority-mode slab waveguide 2456. This orientation of the electric field 2486 is defined by a floating electrode 2482 that extends along the direction of propagation of the image light 2408 in the low-mode slab waveguide 2456 between a pair of end electrodes 2485 to which a voltage V can be applied. The floating electrode 2482 is configured to provide an amplitude distribution of the electric field 2486 that matches the refractive index profile required for focusing the outcoupled image light 2408. In some examples, a set of independently controlled electrodes may be provided to further control the amplitude distribution of the electric field 2486.

[0122] Now refer to Figure 25The zoom adjuster 2530 includes a low-mode slab waveguide portion 2506 supporting a grating structure 2510 comprising an array of grating fringes 2511 having a first refractive index and surrounded by a substrate 2512 between individual grating fringes 2510 having a second refractive index. The grating structure 2510 outcouples image light 2508 from the low-mode slab waveguide portion 2506. At least one of the first or second refractive indices is tunable to provide a gradient of at least one of the first or second refractive indices for focusing or defocusing the image light 2508 outcoupled from the slab waveguide portion by an outcoupler. To this end, an array of heating elements 2570 can be coupled to the waveguide 2506 for providing non-uniform, spatially selective heating to the grating structure 2510. The spatially selective heating generates a refractive index gradient that can modify the local diffraction angle for the image light 2508, thereby enabling focusing or defocusing of the image light 2508 outcoupled from the waveguide 2506. As a non-limiting example, to achieve a 1 m focal length for a 16 mm eyebox length, a maximum Δn = 0.008 is required for the effective refractive index. If a slow light waveguide is used instead of waveguide 2506, this number will be proportionally smaller. In some examples, substrate 2510 can include a liquid crystal (LC) layer to provide the required refractive index gradient by tuning the LC layer with an applied electric field. Because the layer in which the refractive index is modified is very thin, it will only affect the display optical path and not the see-through optical path.

[0123] refer to Figure 26 And further reference Figure 1A , a method 2600 for providing an image in an angular domain ( Figure 26 ) includes image light that includes a spectral component at a first wavelength (e.g., Figure 1A The image light is coupled (2602) to a 1D redirector / imager using an inner coupler (e.g., inner coupler 103). The image light may be redirected using any horizontal FOV 1D redirector / imager disclosed herein, e.g., Figure 9 The phased array 1D imager 904 includes Figures 10A to 10E Any PIC example of Figure 11 A hybrid 1D imager 1104, or Figure 12 FSO 1D scanner 1204. The 1D imager is in a first plane (e.g., Figure 1AThe image light is redirected (2604) in the XY plane (which is the plane of the low-mode slab waveguide portion 107) by the ID imager. The image light 108 redirected by the ID imager propagates in the low-mode slab waveguide portion 107 (2606). A spectral component at a first wavelength is outcoupled from the low-mode slab waveguide by an outcoupler 110 (e.g., any grating outcoupler contemplated herein) at an angle that depends on the first wavelength (2608). The low-mode slab waveguide portion can include a single-mode slab waveguide or a low-mode (no more than 10 modes) slab waveguide.

[0124] Go to Figure 27 , method 2700 is Figure 26 An example of method 2600. For example, Figure 27 Method 2700 uses a monochromatic tunable source of image light (such as Figure 5 tunable laser source 502). Method 2700 includes setting (2702) the emission wavelength of the monochromatic tunable source and redirecting (2704) the image light coupled into the 1D imager in the XY plane. In other words, the wavelength of the tunable light source is not shifted when the 1D imager redirects the image light in the first plane, whereby the image light redirected in the first plane is outcoupled at the same angle. Then, the next wavelength is set (2706) and the process is repeated with its own value of the output power of the light source corresponding to the desired brightness of the pixels of the displayed image. The redirection in the XY plane includes angularly scanning (2708) the collimated light beam in the XY plane or simultaneously forming an angular distribution of brightness (2710).

[0125] Now refer to Figure 28 , method 2800 is Figure 26 An example of method 2600. Figure 28 The method 2800 uses a spectrally tunable light source, for example, Figure 6A A spectrum-adjustable light source 602 is provided. Figure 28 The method 2800 includes using a spectrally tunable light source to provide (2802) image light having multiple spectral components corresponding to a vertical FOV of an image to be displayed. The image light having multiple spectral components is redirected (2804) in the XY plane by providing an angular distribution of brightness in the XY plane, which can be achieved by scanning (2808) or forming an instantaneous angular distribution (2810). The angularly dispersed multi-wavelength image light is outcoupled (2806) from a low-mode slab waveguide, with the angular distribution corresponding to the spectral composition of the image light.

[0126] Go to Figure 29, an augmented reality (AR) near-eye display 2900 includes a frame 2901 having the form factor of a pair of glasses. The frame 2901 supports a light engine 2908 for each eye, the light engine 2908 including the tunable spectrum light source described herein, and a low mode (i.e., single mode or few mode waveguide 2910 disclosed herein) optically coupled to the light engine 2908. The AR near-eye display 2900 may also include an eye tracking camera 2904, a plurality of illuminators 2906, and an eye tracking camera controller 2907. The illuminator 2906 may be supported by the waveguide 2910 for illuminating an eye box 2912. The light engine 2908 provides a light beam having a spectrum representing a vertical 1D FOV for projection into the user's eyes. The waveguide 2910 receives the light beam and expands the light beam above the eye box 2912. The horizontal 1D FOV may be provided by a 1D imager disclosed herein, for example, Figure 4A PIC-based imager 436, Figure 9 The phased array 1D imager 904 of FIG. 1 , the hybrid 1D imager 1104 of FIG. 1 , or Figure 12 MEMS-based scanner 1204.

[0127] The purpose of the eye tracking camera 2904 is to determine the position and / or orientation of the user's eyes. Once the position and orientation of the user's eyes are known, the gaze convergence distance and direction can be determined. The displayed image can be dynamically adjusted to take into account the user's gaze so that the user can be more realistically immersed in the displayed augmented reality scene, and / or to provide specific functions that interact with the augmented reality. In operation, the illuminator 2906 illuminates the eye at the corresponding eye box 2912 so that the eye tracking camera can obtain an image of the eye and provide a reference reflection (i.e., glint). The glint can be used as a reference point in the captured eye image to facilitate eye gaze direction determination by determining the position of the eye pupil image relative to the glint image. In order to avoid distracting the user's attention with illumination light, the illumination light can be made invisible to the user. For example, infrared light can be used to illuminate the eye box 2912.

[0128] The function of the eye tracking camera controller 2907 is to process the images obtained by the eye tracking camera 2904 to determine the eye gaze direction of the user's eyes in real time. In some examples, the image processing and eye position / orientation determination functions can be performed by a central controller (not shown) of the AR near-eye display 2900. The central controller can also provide control signals to the light engine 2908 based on the determined eye position, eye orientation, gaze direction, eye vergence, etc.

[0129] Now refer to Figure 30, HMD 3000 is an example of an AR / VR wearable display system that surrounds a user's face for greater immersion in an AR / VR environment. The function of HMD 3000 is to augment the view of a physical, real-world environment with computer-generated imagery, or to generate a completely virtual 3D image. HMD 3000 may include a front body 3002 and a strap 3004. The front body 3002 is configured to be placed in front of the user's eyes in a secure and comfortable manner, and the strap 3004 may be stretched to secure the front body 3002 on the user's head. A display system 3080 may be disposed in the front body 3002 for presenting AR / VR images to the user. Sides 3006 of the front body 3002 may be opaque or transparent.

[0130] In some examples, the front body 3002 includes a positioner 3008 and an inertial measurement unit (IMU) 3010 for tracking the acceleration of the HMD 3000, as well as a position sensor 3012 for tracking the position of the HMD 3000. The IMU 3010 is an electronic device that generates data indicating the position of the HMD 3000 based on measurement signals received from one or more position sensors 3012, which generate one or more measurement signals in response to the movement of the HMD 3000. Examples of the position sensor 3012 include one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor that detects movement, a type of sensor used for error correction of the IMU 3010, or some combination thereof. The position sensor 3012 can be located external to the IMU 3010, internal to the IMU 3010, or some combination thereof.

[0131] The localizer 3008 is tracked by an external imaging device of the virtual reality system, allowing the virtual reality system to track the position and orientation of the entire HMD 3000. The information generated by the IMU 3010 and the position sensor 3012 can be compared with the position and orientation obtained by tracking the localizer 3008 to improve the tracking accuracy of the position and orientation of the HMD 3000. As the user moves and rotates in 3D space, accurate position and orientation are important for presenting the user with an appropriate virtual scene.

[0132] The HMD 3000 may also include a depth camera assembly (DCA) 3011 that captures data describing depth information of a local area surrounding some or all of the HMD 3000. To this end, the DCA 3011 may include a laser radar (LIDAR) or similar device. The depth information may be compared with information from the IMU 3010 to more accurately determine the position and orientation of the HMD 3000 in 3D space.

[0133] The HMD 3000 may also include an eye tracking system 3014 for determining the orientation and position of the user's eyes in real time. The position and orientation of the eyes obtained also allow the HMD 3000 to determine the user's gaze direction and adjust the image generated by the display system 3080 accordingly. In one example, vergence (i.e., the convergence angle of the user's eye gaze) is determined. The determined gaze direction and vergence angle can also be used to compensate for visual artifacts that depend on the viewing angle and eye position in real time. In addition, the determined vergence and gaze angle can be used to interact with the user, highlight objects, bring objects to the foreground, create additional objects or pointers, etc. An audio system can also be provided, which includes, for example, a group of small speakers built into the front body 3002.

[0134] Embodiments and examples of the present disclosure may include or be implemented in conjunction with an artificial reality system. The artificial reality system adjusts sensory information about the external world obtained through sensing such as visual information, audio, touch (body) information, acceleration, balance, etc. in some manner before presenting it to the user. As non-limiting examples, artificial reality may include virtual reality (VR), augmented reality (AR), mixed reality (MR), hybrid reality, or some combination and / or derivative thereof. Artificial reality content may include fully generated content or generated content combined with captured (e.g., real-world) content. Artificial reality content may include video, audio, body or tactile feedback, or some combination thereof. Any of the content may be presented in a single channel or multiple channels, such as in a stereoscopic video that produces a three-dimensional effect for the viewer. In addition, in some embodiments and examples, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof for, for example, creating content in artificial reality and / or otherwise using it in artificial reality (e.g., performing activities in artificial reality). Artificial reality systems that provide artificial reality content can be implemented on a variety of platforms, including wearable displays such as HMDs connected to a host system, standalone HMDs, near-eye displays with eyeglass form factors, mobile devices or computing systems, or any other hardware platform capable of providing artificial reality content to one or more viewers.

[0135] The present disclosure is not limited to the scope of the specific embodiments or examples described herein. In fact, based on the foregoing description and drawings, in addition to those embodiments, examples and modifications described herein, various other embodiments, examples and modifications will be apparent to those of ordinary skill in the art. Therefore, these other embodiments, examples and modifications are intended to fall within the scope of the present disclosure. In addition, although the present disclosure has been described herein in the context of specific embodiments in a specific environment for a specific purpose, those skilled in the art will recognize that its usefulness is not limited thereto, and the present disclosure can be advantageously implemented in any number of environments for any number of purposes. Therefore, the claims set forth below should be interpreted in light of the full scope of the present disclosure as described herein.

Claims

1. A wearable AR head-mounted device for providing lines of imagery in an angular domain, the device comprising: a wavelength-tunable light source for providing image light including a spectral component at a first wavelength; as well as A low-mode waveguide supporting no more than 10 lateral propagation modes, the low-mode waveguide comprising: an inner coupler for coupling the image light into the low-mode waveguide; and a slab waveguide portion, configured to propagate the image light coupled by the inner coupler; Wherein the slab waveguide portion comprises an outcoupler configured to outcouple the spectral component of the image light at an angle to a plane of the slab waveguide portion, wherein the angle depends on the first wavelength.

2. The apparatus of claim 1, wherein the slab waveguide portion comprises a single-mode slab waveguide.

3. The apparatus of claim 1 or 2, wherein the slab waveguide portion comprises a core and a top cladding, the top cladding being supported by the core, wherein the inner coupler comprises a diffraction grating formed in the core of the slab waveguide portion.

4. The apparatus according to claim 1 or 2, wherein the slab waveguide portion comprises a first core and a first cladding, the first cladding being supported by the first core, the first core and the first cladding being configured for single-mode propagation of the image light, and the outcoupler comprises a first diffraction grating formed in the first core; The first diffraction grating is configured to outcouple the spectral component of the redirected image light at a first angle dependent on the first wavelength, wherein the first angle is within a first angular range corresponding to a tunable range of the wavelength tunable light source.

5. The apparatus of claim 4 , wherein the slab waveguide portion further comprises a second core and a second cladding, the second core being supported by the first cladding, the second cladding being supported by the second core, the second core and the second cladding being configured for single-mode propagation of the image light, the outcoupler further comprising a second diffraction grating formed in the second core; wherein the second diffraction grating is configured to outcouple the spectral component of the redirected image light at a second angle different from the first angle, wherein the second angle is within a second angular range corresponding to the tunable range of the wavelength tunable light source, wherein the second angular range is different from the first angular range.

6. The apparatus according to claim 5 further comprises a multimode interference (MMI) coupler in an optical path between the inner coupler and the first and second cores of the slab waveguide, for coupling the image light into at least one of the first and second cores of the slab waveguide portion.

7. The apparatus of claim 6 , further comprising a 1×2 optical switch and a vertical mode converter, the vertical mode converter being downstream of the 1×2 optical switch in the optical path between the inner coupler and the MMI coupler; wherein an input port of the 1×2 optical switch is coupled to the inner coupler, and a first output port and a second output port of the 1×2 optical switch are coupled to a first input port and a second input port of the vertical mode converter, respectively; and The vertical mode converter is configured to couple light at the first input port of the vertical mode converter to the first core of the slab waveguide portion, and to couple light at the second input port of the vertical mode converter to the second core of the slab waveguide portion.

8. The apparatus of any one of claims 1 to 2 and 5 to 7, further comprising a focusing grating supported by the slab waveguide portion, the focusing grating comprising: a grating stripe array having a first refractive index; as well as a substrate between individual stripes of the grating stripe array, the substrate having a second refractive index; At least one of the first refractive index or the second refractive index is adjustable to provide a gradient of at least one of the first refractive index or the second refractive index for focusing or defocusing the image light outcoupled from the slab waveguide portion by the outcoupler.

9. The apparatus of claim 8, wherein the substrate comprises liquid crystal.

10. The apparatus of claim 8, wherein the apparatus further comprises a spatially selective heater coupled to the focusing grating and configured to generate a temperature gradient across the focusing grating to provide the gradient of the at least one of the first refractive index or the second refractive index.

11. The apparatus of any one of claims 1 to 2, 5 to 7, and 9 to 10, wherein the slab waveguide portion comprises a photonic crystal slab layer supporting a cladding layer and having a group refractive index of at least 10, wherein the outcoupler comprises a diffraction grating supported by the cladding layer for outcoupling the image light propagating in the photonic crystal slab layer.

12. The apparatus of any one of claims 1 to 2, 5 to 7, and 9 to 10, wherein the slab waveguide portion comprises a few-mode slab waveguide supporting no more than 10 transverse propagation modes, the few-mode slab waveguide comprising a core, wherein the outcoupler comprises a diffraction grating formed in or on the core; wherein the diffraction grating is configured to outcouple the spectral component of the redirected image light at an angle that depends on the first wavelength, wherein the angle is within an angular range corresponding to a tunable range of the wavelength tunable light source, and wherein the angular range is different for different lateral propagation modes of the few-mode slab waveguide.

13. The apparatus according to claim 12, further comprising a multi-mode interference (MMI) coupler in an optical path between the inner coupler and the few-mode slab waveguide portion, for coupling the image light into at least one propagation mode of the few-mode slab waveguide.

14. The apparatus of claim 13, further comprising a 1×N optical switch and a vertical mode converter, the vertical mode converter being downstream of the 1×N optical switch in the optical path between the inner coupler and the MMI coupler; wherein an input port of the 1×N optical switch is coupled to the inner coupler, and each of the N output ports of the 1×N optical switch is coupled to a specific one of the N input ports of the vertical mode converter, wherein N is an integer; as well as The vertical mode converter is configured to couple light received at its input port to a corresponding propagation mode of the few-mode slab waveguide portion.

15. The apparatus of any one of claims 1 to 2, 5 to 7, 9 to 10, and 13 to 14, wherein the outcoupler comprises a diffraction grating configured to outcouple the spectral components of the image light at an angle exceeding 90 degrees relative to a propagation direction of the image light in the slab waveguide, the apparatus further comprising a corrugated reflector supported by the slab waveguide portion for reflecting the image light diffracted by the diffraction grating through the slab waveguide portion and to an exterior of the low-mode waveguide.

16. The apparatus of claim 15 , wherein the corrugated reflector comprises a polarization-selective reflector configured to reflect light at a first polarization and transmit light at a second polarization orthogonal to the first polarization, the apparatus further comprising: a quarter-wave plate (QWP) supported by the slab waveguide portion on a side of the slab waveguide portion opposite to the polarization-selective reflector and configured to receive the image light reflected by the polarization-selective reflector, the image light having the first polarization; as well as a diffractive structure supported by the quarter-wave plate and configured to reflect the image light propagating through the QWP back for a second propagation through the QWP, converting the polarization of the image light to the second polarization, through the slab waveguide portion, and through the polarization-selective reflector.

17. A low-mode waveguide supporting no more than 10 lateral propagation modes, the low-mode waveguide comprising: a slab waveguide portion for propagating light therein, the slab waveguide portion comprising an outcoupler configured to outcouple the light at an angle to a plane of the slab waveguide portion; as well as a liquid crystal LC cell evanescently coupled to the slab waveguide portion; wherein, in operation, the LC cell defines an effective refractive index for the light propagating in the slab waveguide portion, wherein the effective refractive index varies in a propagation direction of the light in the slab waveguide portion, whereby a direction of the light outcoupled from the slab waveguide portion by the outcoupler varies along the propagation direction of the light in the slab waveguide portion.

18. The low mode waveguide of claim 17, wherein the LC unit forms an acute angle with the slab waveguide portion.

19. A low-mode waveguide supporting no more than 10 lateral propagation modes, the low-mode waveguide comprising: a slab waveguide portion for propagating light therein, the slab waveguide portion comprising a core layer and an outcoupler configured to outcouple the light at an angle to a plane of the slab waveguide portion, wherein the core layer has a refractive index that depends on an applied electric field; as well as electrodes above and below the core layer for applying the electric field to the core layer so that the electric field varies spatially along the propagation direction of light in the core of the slab waveguide portion; Thus, in operation, the effective refractive index of the light propagating in the slab waveguide portion varies in the propagation direction of the light in the slab waveguide portion, whereby the direction of the light outcoupled from the slab waveguide portion varies along the propagation direction of the light in the slab waveguide portion.

20. The low mode waveguide of claim 19, wherein the electrodes are disposed at acute angles to each other.

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