Patent Description:
Head mounted displays (HMD), helmet mounted displays, near-eye displays (NED), and the like are being used increasingly for displaying virtual reality (VR) content, augmented reality (AR) content, mixed reality (MR) content, etc. Such displays are finding applications in diverse fields including entertainment, education, training and biomedical science, to name just a few examples. The displayed VR / AR / MR content can be three-dimensional (3D) to enhance the experience and to match virtual objects to real objects observed by the user. To provide better optical performance, display systems and modules may include a large number of components such as lenses, waveguides, display panels, etc. Because a display of an HMD or NED is usually worn on the head of a user, 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 desirable. <NPL>, discloses integrated optical phased arrays for one-dimensionally steering of a beam in an on-chip single-mode waveguide.

A device according to the claimed invention is defined in appended claims <NUM>, <NUM> and <NUM>. In accordance with a first aspect of the present disclosure, there is provided a device for providing a line of an image in angular domain. The device comprises a low-mode waveguide. The low-mode waveguide comprises: an in-coupler for coupling image light into the low-mode waveguide; a 1xN splitter for splitting the image light coupled by the in-coupler into N linear waveguides; N phase shifters each coupled to a particular one of the N linear waveguides for delaying image light portions propagating therein by a controllable amount; an array of N linear waveguide emitters each coupled to a particular one of the N phase shifters for emitting the image light portions delayed thereby; and a slab waveguide portion coupled to the array of N linear waveguide emitters for propagating therein the delayed image light portions emitted by corresponding emitters of the array of N linear waveguide emitters, wherein N is an integer.

In some embodiments, the slab waveguide portion comprises a singlemode slab waveguide.

In some embodiments, the slab waveguide portion comprises a few-mode slab waveguide supporting no more than <NUM> lateral modes of propagation.

The 1xN splitter may preferably comprise a binary tree of tunable Mach-Zehnder interferometers for providing a controllable distribution of optical power of the image light between the N linear waveguides.

In accordance with the first aspect, the slab waveguide portion comprises a field of view (FOV) expander in the slab waveguide portion, the FOV expander comprising a tunable cladding portion evanescently coupled to a core of the slab waveguide portion and shaped to deviate light propagated in the core of the slab waveguide portion by a controllable amount.

The tunable cladding portion comprises an array of triangular-shaped liquid crystal cladding portions, the array extending laterally w. an optical path of the image light in the core of the slab waveguide portion, wherein at least some triangular-shaped liquid crystal cladding portions have a side extending at an acute angle w. the optical path.

In some embodiments, the slab waveguide portion further comprises a hologram configured to reflect a collimated beam portion of the image light at a plurality of locations along an optical path of the collimated beam portion in the hologram, such that the collimated beam portion reflected by the hologram is wider than the collimated beam portion impinging onto the hologram.

In accordance with a second aspect of the present disclosure, there is provided a device for providing a line of an image in angular domain, the device comprising a low-mode waveguide comprising: an in-coupler for coupling image light into the low-mode waveguide; a tunable 1xN splitter for distributing optical power of the image light coupled by the in-coupler between linear waveguides of an array of N linear waveguides; and a slab waveguide portion comprising a collimating element for converting a lateral position of a linear waveguide of the array of n linear waveguides into a beam angle of an image light portion propagated in the linear waveguide of the array of n linear waveguides, wherein N is an integer.

In some embodiments, the 1xN splitter comprises a binary tree of Mach-Zehnder switches for switching the image light between the n linear waveguides.

In accordance with the second aspect, the slab waveguide portion further comprises a field of view (FOV) expander in the slab waveguide portion, the FOV expander comprising a tunable cladding portion evanescently coupled to a core of the slab waveguide portion and shaped to deviate light propagated in the core of the slab waveguide portion by a controllable amount.

The slab waveguide portion may preferably further comprise a hologram configured to reflect a collimated beam portion of the image light at a plurality of locations along an optical path of the collimated beam portion in the hologram, such that the collimated beam portion reflected by the hologram is wider than the collimated beam portion impinging onto the hologram.

In accordance with a third aspect of the present invention, there is provided a device for providing a line of an image in angular domain, the device comprising: a microelectromechanical system (MEMS) beam scanner comprising a tiltable reflector for scanning image light in a first plane; a low-mode slab waveguide in the first plane, for propagating the image light scanned by the MEMS beam scanner; and a coupler for receiving the image light scanned by the MEMS beam scanner and coupling the image light to the low-mode slab waveguide.

The low-mode slab waveguide may be a singlemode slab waveguide.

The low-mode slab waveguide may be a few-mode slab waveguide supporting no more than <NUM> lateral modes of propagation.

In accordance with the third aspect, the low-mode slab waveguide further comprises a field of view (FOV) expander in the slab waveguide portion, the FOV expander comprising a tunable cladding portion evanescently coupled to a core of the low-mode slab waveguide and shaped to deviate light propagated in the core of the slab waveguide portion by a controllable amount.

The tunable cladding portion comprises an array of triangular-shaped liquid crystal cladding portions, the array extending laterally w. an optical path of the image light in the core of the low-mode slab waveguide, wherein at least some triangular-shaped liquid crystal cladding portions have a side extending at an acute angle w. the optical path.

In some embodiments, the low-mode slab waveguide further comprises a hologram configured to reflect a collimated beam portion of the image light at a plurality of locations along an optical path of the collimated beam portion in the hologram, such that the collimated beam portion reflected by the hologram is wider than the collimated beam portion impinging onto the hologram.

Exemplary embodiments will now be described in conjunction with the drawings, in which:.

While the present teachings are described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives and equivalents, as will be appreciated by those of skill in the art. All statements herein reciting principles, aspects, and embodiments of this disclosure, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof.

As used herein, the terms "first", "second", and so forth are not intended to imply sequential ordering, but rather are intended to distinguish one element from another, unless explicitly stated. Similarly, sequential ordering of method steps does not imply a sequential order of their execution, unless explicitly stated. In <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>, similar reference numerals denote similar elements.

Near-eye displays (NEDs) may use pupil-replicating waveguides to expand a projected image over an eyebox of the display, i.e. over an area where user's eye may be located during normal operation, e.g. when the display is worn by the user. A pupil-replicating waveguide is typically a parallel slab of a transparent material propagating image light in a zigzag pattern by total internal reflection (TIR) from the waveguide's top and bottom surfaces. Such waveguides may be prone to diffraction effects that cause color dispersion as function of field angle, and are generally unsuitable for curved substrates and present ghost images for real-world up-close objects.

In accordance with this disclosure, single mode (SM) or few-mode (FM) waveguides, termed herein collectively as "low-mode" waveguides, may be used to deliver light to the eyebox and form an image. An advantage of low-mode waveguides is that light interacts with gratings several orders of magnitude more often compared to a regular multimode light guide. As a result, the diffraction efficiency of the grating for every single interaction may be made small enough to lessen or eliminate see-through artifacts such as rainbow and improve conspicuity of the display. Additionally, single mode waveguides enable more precise control of light distribution across the eyebox, which leads to better uniformity and efficiency.

A challenge of using a single mode waveguide is that it only has capacity to transmit 1D information, e.g. horizontal resolution but not vertical resolution, or vice versa. This limitation may be overcome by encoding the other component of 2D image in a non-spatial characteristic of light such as wavelength, for example. The wavelength range used for each color channel may be made small enough to not reduce the color gamut significantly.

In accordance with this disclosure, there is provided a device for providing a line of an image in angular domain. The device includes a low-mode waveguide comprising an in-coupler for coupling image light into the low-mode waveguide; a 1xN splitter for splitting the image light coupled by the in-coupler into N linear waveguides; N phase shifters each coupled to a particular one of the N linear waveguides for delaying image light portions propagating therein by a controllable amount; an array of N linear waveguide emitters each coupled to a particular one of the N phase shifters for emitting the image light portions delayed thereby; and a slab waveguide portion coupled to the array of N linear waveguide emitters for propagating therein the delayed image light portions emitted by corresponding emitters of the array of N linear waveguide emitters, wherein N is an integer. The slab waveguide portion may include e.g. a singlemode slab waveguide, or a few-mode slab waveguide supporting no more than <NUM> lateral modes of propagation. The 1xN splitter may include a binary tree of tunable Mach-Zehnder interferometers for providing a controllable distribution of optical power of the image light between the N linear waveguides.

In some embodiments, the slab waveguide portion further includes a field of view (FOV) expander in the slab waveguide portion. The FOV expander may include a tunable cladding portion evanescently coupled to a core of the slab waveguide portion and shaped to deviate light propagated in the core of the slab waveguide portion by a controllable amount. The tunable cladding portion may include an array of triangular-shaped liquid crystal cladding portions, the array extending laterally w. an optical path of the image light in the core of the slab waveguide portion. At least some triangular-shaped liquid crystal cladding portions may have a side extending at an acute angle w. the optical path.

In some embodiments, the slab waveguide portion further includes a hologram configured to reflect a collimated beam portion of the image light at a plurality of locations along an optical path of the collimated beam portion in the hologram, such that the collimated beam portion reflected by the hologram is wider than the collimated beam portion impinging onto the hologram.

In accordance with the present disclosure, there is provided a device for providing a line of an image in angular domain. The device may include a low-mode waveguide comprising an in-coupler for coupling image light into the low-mode waveguide; a tunable 1xN splitter for distributing optical power of the image light coupled by the in-coupler between linear waveguides of an array of N linear waveguides; and a slab waveguide portion comprising a collimating element for converting a lateral position of a linear waveguide of the array of n linear waveguides into a beam angle of an image light portion propagated in the linear waveguide of the array of n linear waveguides, where N is an integer.

The slab waveguide portion may include e.g. a singlemode slab waveguide or a few-mode slab waveguide supporting no more than <NUM> lateral modes of propagation. The 1xN splitter may include a binary tree of Mach-Zehnder switches for switching the image light between the n linear waveguides. In some embodiments, the slab waveguide portion further comprises a field of view (FOV) expander in the slab waveguide portion. The FOV expander may include a tunable cladding portion evanescently coupled to a core of the slab waveguide portion and shaped to deviate light propagated in the core of the slab waveguide portion by a controllable amount. The tunable cladding portion may include an array of triangular-shaped liquid crystal cladding portions, the array extending laterally w. an optical path of the image light in the core of the slab waveguide portion. At least some triangular-shaped liquid crystal cladding portions may have a side extending at an acute angle w. the optical path. The slab waveguide portion may further include a hologram configured to reflect a collimated beam portion of the image light at a plurality of locations along an optical path of the collimated beam portion in the hologram, such that the collimated beam portion reflected by the hologram is wider than the collimated beam portion impinging onto the hologram.

In accordance with the present disclosure, there is further provided a device for providing a line of an image in angular domain. The device may include a microelectromechanical system (MEMS) beam scanner comprising a tiltable reflector for scanning image light in a first plane; a low-mode slab waveguide in the first plane, for propagating the image light scanned by the MEMS beam scanner; and a coupler for receiving the image light scanned by the MEMS beam scanner and coupling the image light to the low-mode slab waveguide. The low-mode slab waveguide may include e.g. a singlemode slab waveguide or a few-mode slab waveguide supporting no more than <NUM> lateral modes of propagation. The low-mode slab waveguide may further include a field of view (FOV) expander in the slab waveguide portion. The FOV expander may include a tunable cladding portion evanescently coupled to a core of the low-mode slab waveguide and shaped to deviate light propagated in the core of the slab waveguide portion by a controllable amount.

In some embodiments, the tunable cladding portion comprises an array of triangular-shaped liquid crystal cladding portions, the array extending laterally w. an optical path of the image light in the core of the low-mode slab waveguide. At least some triangular-shaped liquid crystal cladding portions may have a side extending at an acute angle w. the optical path. The low-mode slab waveguide may further include a hologram configured to reflect a collimated beam portion of the image light at a plurality of locations along an optical path of the collimated beam portion in the hologram, such that the collimated beam portion reflected by the hologram is wider than the collimated beam portion impinging onto the hologram.

Referring now to <FIG>, a device <NUM> provides an image in angular domain. The image may be defined by a light field having a two-dimensional (2D) angular distribution of brightness I(α,β). The angles α,β are ray angles of the image light defining the ray angle in 3D space, as shown in <FIG>. More generally, the device <NUM> is usable for redirecting light in two dimensions or along two non-parallel planes or surfaces, e.g. for 2D beam rastering, remote sensing, depth sensing, LIDAR applications, etc. Herein, the term "redirecting" includes rastering of a collimated light beam, as well as providing instantaneous distributions of light in one or two dimensions or planes.

The device <NUM> includes a light source <NUM>, an 1D redirector <NUM> coupled to the light source <NUM>, and a low-mode waveguide <NUM> coupled to the 1D redirector <NUM> by a coupler <NUM>. The low-mode waveguide <NUM> includes a slab waveguide portion <NUM>. Herein, the term "slab waveguide" denotes a waveguide that limits the light propagation only in one dimension, i.e. vertical direction or Z-direction perpendicular to the waveguide plane, allowing the light to freely propagate in plane of the waveguide, e.g. in XY plane in the example of <FIG>. The light source <NUM> provides light <NUM> having a tunable optical spectrum, which is a function of the desired distribution of brightness I(α,β). For example, the tunable optical spectrum may have a plurality of spectral components; in some embodiments, one spectral component may be provided at a tunable wavelength.

The 1D redirector <NUM> receives the light <NUM> from the light source <NUM> and redirects, e.g. angularly disperses, the light <NUM> in XY plane, i.e. the plane of the low-mode waveguide <NUM>, in accordance with the desired distribution of brightness I(α,β). In display applications, the 1D redirector <NUM> functions as a 1D imager providing a line of a 2D image. The slab waveguide portion <NUM> is a singlemode waveguide or a few-mode waveguide configured for propagating the light <NUM> in XY plane but confining and guiding the light propagation along Z-axis. The slab waveguide portion <NUM> includes an out-coupler <NUM> that out-couples the image light <NUM> at angle(s) to the low-mode waveguide <NUM> plane (XY plane), the angle depending on the wavelength(s) of the spectral component(s) of the light <NUM>. In some embodiments, a single tunable spectral component may be out-coupled by the out-coupler <NUM> at an angle depending on its wavelength, in a plane disposed at an angle to the plane of the low-mode waveguide <NUM>, that is, XY plane; and in some embodiments, a plurality of spectral components is out-coupled simultaneously, or instantaneously, at a distribution of angles corresponding to the distribution of the wavelengths of the spectral components. The distribution of the out-coupling angles is defined by the tunable optical spectrum of the light <NUM>. The angular distribution of brightness in both X- and Y-directions may be controlled to provide the image in angular domain having the the desired distribution of brightness I(α,β), for direct observation by a viewer.

<FIG> shows an embodiment of the low-mode waveguide <NUM> in a side cross-sectional view. The low-mode waveguide <NUM> includes a substrate <NUM> supporting a thin waveguide layer <NUM> in which the light <NUM> propagates. Depending on refractive index contrast and thickness of the waveguide layer <NUM>, only one mode or several, e.g. up to <NUM> modes, may propagate in the thin waveguide layer <NUM>. Thus, the term "low-mode" waveguide is defined herein to mean a waveguide supporting up to <NUM> different lateral modes of propagation. The light <NUM> propagates in plane of the waveguide <NUM> i.e. XY plane, but is constrained, or guided, in Z-direction.

The wavelength-selective out-coupler <NUM> out-couples the image <NUM> at different angles depending on wavelength. For example, a first spectral <NUM> component at a wavelength λ<NUM> is out-coupled at a straight angle to the low-mode waveguide <NUM>, and a second spectral component <NUM> at a wavelength λ<NUM> is out-coupled at an acute angle to the low-mode waveguide <NUM>. The spectral composition of the light <NUM> provided by the light source <NUM>, as well as the angular dispersion of the wavelength-selective out-coupler <NUM>, are selected so as to provide the desired angular distribution of brightness I(α,β(λ)). By way of a non-limiting example, referring to <FIG>, an entire image <NUM> in angular domain may be formed. The image <NUM> is represented by the angular distribution of brightness I(α,β(λ)).

Referring to <FIG>, a device <NUM> is an example implementation of the device <NUM> of <FIG>. The display device <NUM> of <FIG> includes serially optically coupled: a spectrally tunable singlemode light source <NUM>, an in-coupler <NUM>, an 1D imager <NUM>, the following optional modules: 1D FOV expander <NUM>, 1D lateral beam expander <NUM>, and angular dispersion enhancer <NUM>; and an out-coupler <NUM>. Other elements may also include a varifocal adjuster <NUM>, a stray light filter <NUM>, and a distributed temperature sensor <NUM>. Optional elements are shown in dashed round-corner rectangles. All or some of the elements may be a part of a low-mode waveguide <NUM>, e.g. may be formed in or on the low-mode waveguide <NUM>. It is to be noted that the low-mode waveguide <NUM> may include a section with linear waveguides, i.e. straight or curved ridge-type waveguides guiding light in two dimensions, and a slab waveguide section, guiding light in only one dimension, i.e. Z-direction in <FIG>, while allowing free propagation in XY plane. The order of coupling of the elements shown in <FIG> may vary.

In operation, the spectrally tunable singlemode light source <NUM> provides image light <NUM> having a tunable optical spectrum, which is a function of the desired angular distribution of brightness I(α,β(λ)) as explained above. The coupler <NUM> couples the image light <NUM> into the 1D imager <NUM>. The 1D imager <NUM> receives the image light <NUM> from the light source <NUM> and redirects or angularly disperses the image light <NUM>, scans a collimated beam of the image light <NUM>, etc. The 1D FOV expander <NUM> may be configured to switch the image light <NUM> between a plurality of conterminous FOV portions to enhance or broaden the spread of light. The 1D lateral beam expander <NUM> increases a width of collimated portions of the image light in the XY plane, i.e. broadens the image light <NUM> beam in plane of the low-mode waveguide <NUM> thereby increasing the lateral size of the eyebox of the display device <NUM>. Herein, the term "eyebox" means a geometrical area where an image of acceptable quality may be observed by a user of the display device <NUM>. The angular dispersion enhancer <NUM> increases the spectral dispersion of the image light <NUM>, to arrive at the desired second 1D angular distribution of brightness I(β) when out-coupled by the wavelength-selective out-coupler <NUM>. The varifocal adjuster <NUM> may adjust convergence or divergence of the out-coupled image light to vary the perceived depth of focus. The stray light filter <NUM> may remove or lessen portions of the image light out-coupled not to the eyes of the user but outwards to the external world. The distributed temperature sensor <NUM> may obtain a temperature distribution across the low-mode waveguide <NUM> to provide corrections and to operate thermally-driven optical elements and components. More details will be given below.

Referring to <FIG>, a display device <NUM> is an implementation of the device <NUM> of <FIG> or the device <NUM> of <FIG>. The display device <NUM> of <FIG> is a near-eye display device having a form factor of a pair of eyeglasses <NUM>, with a low-mode waveguide <NUM> occupying a lens area of the eyeglasses. The display device <NUM> of <FIG> includes serially optically coupled: a light source <NUM>, a coupler <NUM>, an 1D imager <NUM>, a 1D FOV expander <NUM>, a 1D lateral beam expander <NUM>, an angular dispersion enhancer <NUM>, an out-coupler <NUM>, and a varifocal adjuster <NUM>. All elements may be implemented in the low-mode waveguide <NUM>. The light source <NUM> may be disposed separately, as shown.

Referring to <FIG>, a display device <NUM> is an implementation of the device <NUM> of <FIG>, the device <NUM> of <FIG>, or the display device <NUM> of <FIG>. The display device <NUM> of <FIG> is a near-eye display device having a form factor of a pair of eyeglasses <NUM>, with active components/features implemented in a PIC portion <NUM> of a waveguide <NUM>. The PIC portion <NUM> may be driven by an integrated circuit (IC) driver unit <NUM>. The display device <NUM> includes a light source <NUM> having a tunable emission spectrum, coupled to the PIC portion <NUM> via an optical fiber <NUM>. The PIC portion <NUM> may include, for example, a 1D imager and/or a 1D FOV expander. Light beams 408A, 408B, and 408C (collectively <NUM>) formed in the LC portion <NUM> are expanded by in-waveguide optical elements 426A, 426B, and 426C respectively, having optical power (i.e. focusing/defocusing power) for collimating/redirecting the light beams 408A, 408B, and 408C towards a highly dispersive output grating <NUM>. The function of the highly dispersive output grating <NUM> is to provide the out-coupling of image light <NUM> at different vertical angles to provide a vertical FOV, as illustrated in <FIG>. The horizontal FOV shown in <FIG> is provided by the PIC portion spreading the image light <NUM> in-plane of the waveguide <NUM>.

Various implementations of different modules depicted in <FIG>, <FIG>, <FIG> will now be considered.

Referring first to <FIG>, a tunable laser source <NUM> may be used as a wavelength-tunable light source for a display device of this disclosure. The tunable laser source <NUM> includes an optical cavity formed by a pair of mirrors <NUM>, a gain medium <NUM>, and a wavelength-selective intracavity element <NUM> having a transmission peak tunable within a gain spectral band of the gain medium <NUM>. The transmission peak of the wavelength-selective element <NUM> may be scanned in coordination with scanning an 1D angle of a collimated beam of light <NUM> to provide the required 2D FOV of the display device, with e.g. horizontal FOV provided by the beam scanning, and vertical FOV provided by the output wavelength scanning of the tunable laser source <NUM>.

Turning to <FIG>, a tunable-spectrum light source <NUM> may be used as a wavelength-tunable light source for a display device of this disclosure. The tunable spectrum light source <NUM> includes a broadband source <NUM> of light <NUM> coupled to a dynamic spectral filter <NUM> having a selectable arbitrary spectral shape. Emission spectrum <NUM> of the broadband source <NUM> is illustrated in <FIG>, where it is overlapped with an example broadband spectral shape <NUM> of the dynamic spectral filter <NUM>, or an example narrowband (single-wavelength) spectral shape <NUM> of the dynamic spectral filter <NUM>.

Dynamic spectral filter <NUM> may be configured to independently adjust transmission of a single or a plurality of adjacent narrow spectral bands or channels. For example, the dynamic spectral filter <NUM> may adjust the shape of the broadband spectral shape <NUM> in accordance with the desired angular distribution of brightness at the output of the display device. In some embodiments, the narrowband spectral shape <NUM> may be scanned in wavelength, which results in the output light beam being scanned angularly in accordance with the dispersion function of the out-coupler of the display device.

Resulting output spectra are shown in <FIG>. For example, the broadband spectral shape <NUM> results in a broadband emission spectrum <NUM>, and the narrowband spectral shape <NUM> accordingly results in a narrowband emission spectrum <NUM>, the emission wavelength being tunable by the dynamic spectral filter <NUM>.

Referring to <FIG>, a free-space grating coupler <NUM> may be used to couple light from a tunable-spectrum light source 702A, such as the tunable laser source <NUM> of <FIG> or a tunable-spectrum light source <NUM> of <FIG>, into a waveguide or PIC of a display disclosed herein. The free-space grating coupler <NUM> includes a plurality of grating lines <NUM> that receive image light <NUM> and couple the image light <NUM> into a core <NUM> of a waveguide <NUM>. The grating lines <NUM> run parallel to each other and may be straight or curved, e.g. may have shapes of concentric arc sections running perpendicular to the plane of <FIG>. The concentric arc shape provides focusing of the image light <NUM>, matching its mode size to a size of an optical mode <NUM> that can propagate in the core <NUM> of the waveguide <NUM>.

Turning to <FIG>, a waveguide coupler <NUM> may be used to couple light from a tunable-spectrum, waveguide-based or fiber-coupled light source into a waveguide or PIC of a display of this disclosure. The waveguide coupler <NUM> includes a tapered section <NUM> where a tapered core <NUM> of a source optical fiber <NUM> is disposed in close proximity and parallel to a tapered waveguide core <NUM> of a waveguide <NUM> having a waveguide core <NUM>. The tapered section <NUM> may be long enough to ensure an adiabatic transition of optical energy from the source optical fiber <NUM> into a waveguide core <NUM> of the waveguide <NUM>.

Referring to <FIG>, a phased array 1D imager <NUM> is an embodiment of the 1D redirector / imager <NUM> of <FIG>, the 1D imager <NUM> of <FIG>, or the 1D imager <NUM> of <FIG>. The phased array 1D imager <NUM> of <FIG> includes a 1xN power splitter <NUM>, N phase shifters <NUM> coupled to the power splitter <NUM>, and an array of N linear waveguide emitters <NUM> coupled to the phase shifters <NUM>. Throughout this specification, the term "linear waveguide" denotes a waveguide that bounds the light propagation in two dimensions, like a light wire. A linear waveguide may be straight, curved, etc.; in other words, the term "linear" does not mean a straight waveguide section. One example of a linear waveguide is a ridge-type waveguide. All elements of the phased array 1D imager <NUM> may be implemented in a low-mode waveguide <NUM> including a slab waveguide portion <NUM>. The number N may vary between <NUM> and <NUM>,<NUM>, for example.

In operation, an in-coupler, e.g. the free-space grating coupler <NUM>, receives image light <NUM> from a wavelength-tunable laser source, not shown in <FIG>, and couples the image light <NUM> into the power splitter <NUM>. The power splitter <NUM> distributes the image light <NUM> between N linear waveguides <NUM> of the low-mode waveguide <NUM>, each linear waveguide <NUM> carrying a portion of the image light <NUM>. Each image light portion is shifted in phase, or delayed, by a corresponding phase shifter <NUM>, based on a control signal provided by a controller <NUM>. The image light portions are emitted by the array of N linear waveguide emitters <NUM> with a phase profile corresponding to a desired beam angle ϑ, forming an output beam <NUM> having a phase front <NUM>. The output beam <NUM> propagates in a slab waveguide portion <NUM>. In some embodiments, the phase profile in <NUM> may be controlled to suppress all diffraction orders but one, such that all energy is concentrated into a single steered beam.

Turning to <FIG>, a PIC phased array 1D imager <NUM> is an example implementation of the phased array 1D imager <NUM> of <FIG>. The PIC phased array 1D imager <NUM> of <FIG> includes a Mach-Zehnder interferometers array (MZIA) <NUM> operating as the splitter <NUM>, a PIC phase shifter array (PSA) <NUM> coupled to the MZIA <NUM>, and a waveguide concentrator <NUM> coupled to the PIC phase shifter array <NUM>. Ends of output linear waveguides <NUM> of the waveguide concentrator <NUM> operate as the antennae <NUM> (<FIG>) emitting light that propagates freely in plane of the slab waveguide portion (XY plane in <FIG>), while remaining bound in a direction perpendicular to the slab waveguide (Z-direction in <FIG>).

The MZIA <NUM> may include a binary tree of passive Y-splitters and/or active Mach-Zehnder interferometers (MZIs) <NUM>, as shown in <FIG>. Each MZI may include one input <NUM> and two outputs <NUM>, <NUM> of an evanescent coupler <NUM> as illustrated in <FIG>, or two inputs (one of which is idle) and two outputs, being two waveguide sections coupled by evanescent couplers at two locations. The function of the MZIA <NUM> is to split the image light into N portions. In embodiments where passive Y-splitters are used, the PSA <NUM> may be used to scan a collimated beam. In implementations where active MZIs are used, phase shifters <NUM> in at least one of the two branches of the MZI (<FIG>) may be used to control optical power distribution at the outputs to not equal optical powers if required, e.g. to provide apodization of the scanned collimated beam, or even create a full desired 1D angular profile.

Referring to <FIG>, the phase shifter array <NUM> may include a plurality of phase shifters <NUM> providing a controllable amount of phase shift, or delay, to light propagating therein. The phase shifters <NUM> may be, for example, thermo-optic shifters based on thermo-optic effect, electro-optic shifters based on Pockels and/or Kerr effect, and/or electro-absorption phase shifters based on electro-absorption effect in semiconductors, and accordingly may include heaters and/or electrodes over the waveguides, as required.

Turning to <FIG>, the waveguide concentrator <NUM> includes an array of waveguides fanning in or out to achieve a required output pitch. Typically, the output pitch needs to be small enough to enable large FOV. The FOV is approximately equal to a ratio of emission wavelength to pitch of the output linear waveguides <NUM>.

Referring to <FIG>, a hybrid 1D imager <NUM> is an example implementation of the 1D redirector <NUM> of <FIG>, the 1D imager <NUM> of <FIG>, or the 1D imager <NUM> of <FIG>. The hybrid 1D imager <NUM> of <FIG> includes a MZIA <NUM>, a waveguide concentrator <NUM> coupled to the MZIA <NUM>, and an FOV collimator <NUM> coupled to the waveguide concentrator <NUM> implemented in a low-mode waveguide <NUM>. The MZIA <NUM> functions as 1xN distributor or switch, where N is the number of output MZIA waveguides <NUM>. The MZIA <NUM> may include, for example, a binary tree of Mach-Zehnder switches for switching image light <NUM> between N linear output waveguides. The waveguide concentrator <NUM> brings its output linear waveguides <NUM> closer together than the output MZIA waveguides <NUM>. Ends of the output linear waveguides <NUM> of the waveguide concentrator <NUM> are disposed at a focal plane of the FOV collimator <NUM>, which is located in a slab waveguide portion <NUM> of the few-mode waveguide <NUM>. The FOV collimator <NUM> is a collimating element disposed one focal length away from the ends of the output linear waveguides <NUM> of the waveguide concentrator <NUM>. The function of the FOV collimator <NUM> is to convert position, or Y-offset, of the ends of the output linear waveguides <NUM> of the waveguide concentrator <NUM> into a beam angle of a corresponding output light beam <NUM> propagating in the slab waveguide portion <NUM>. In other words, the FOV collimator <NUM> operates as an offset-to-angle optical element converting an offset, or the Y-position, of a selected one of the output waveguides <NUM> carrying a portion of the image light <NUM> into an angle of the output light beam <NUM> originating from the image light portion propagated in the selected output waveguide.

The FOV collimator <NUM> may be a single element such as lens or mirror, or may include a plurality of lenses <NUM>, <NUM>, as shown in <FIG>. The lenses <NUM>, <NUM> may be formed in the low-mode waveguide <NUM> by etching, and may have s folded configuration such as a pancake lens configuration, for example. Output light beam <NUM> may be reshaped, focused, collimated, etc., in the plane of the waveguide (XY plane), while remaining guided by the slab waveguide portion <NUM>, i.e. while remaining constrained in Z-direction. The lens surfaces may include a plurality of tapers <NUM> with subwavelength periodicity to facilitate an adiabatic transition between etched and non-etched part of the waveguide and in so doing prevent an out of plane light scattering.

Referring to <FIG>, a free-space optics (FSO) 1D scanner <NUM> includes a microelectromechanical system (MEMS) beam scanner <NUM> with a tiltable reflector <NUM> and a cylindrical lens <NUM>. In operation, a multi-wavelength light source, such as a wavelength-swept laser source <NUM>, emits a light beam <NUM> at a tunable, e.g. linearly swept, emission wavelength. The light beam <NUM> is focused by the cylindrical lens <NUM> onto the MEMS tiltable reflector <NUM>. The cylindrical lens <NUM> functions as a coupler receiving the image light <NUM> scanned by the MEMS beam scanner <NUM> and coupling the image light <NUM> to a low-mode slab waveguide <NUM>. The cylindrical lens <NUM> may be refractive or diffractive, for example. Other types of couplers such as mirrors, for example, may be used. The MEMS tiltable reflector <NUM> reflects the light beam <NUM> at a variable angle, as shown by a doubleheaded arrow. The cylindrical lens <NUM> has focusing power in XZ plane, while propagating the light beam <NUM> substantially without focusing in XY plane. The cylindrical lens <NUM> focuses the light beam <NUM> onto an edge of the low-mode slab waveguide <NUM> or onto a grating coupler formed in the low-mode slab waveguide <NUM>. The light beam <NUM> gets coupled into the low-mode slab waveguide <NUM> and propagates freely in the low-mode slab waveguide <NUM> in XY plane, being confined in Z-direction perpendicular to a plane of the low-mode slab waveguide <NUM>. The cylindrical lens <NUM> needs to be precisely parallel to the low-mode slab waveguide <NUM> for efficient coupling.

Turning to <FIG>, a liquid crystal (LC) 1D FOV expander <NUM> is an embodiment of the 1D FOV expander <NUM> of <FIG> and the 1D FOV expander <NUM> of <FIG>. The LC 1D FOV expander <NUM> of <FIG> includes a slab waveguide <NUM> having a core <NUM> for guiding image light <NUM> in the core <NUM> while allowing the image light <NUM> to freely propagate in XY plane, as depicted. A top cladding <NUM> includes tunable cladding portions <NUM>, <NUM> evanescently coupled to the core <NUM> of the slab waveguide <NUM> and shaped to deviate light propagated in the core <NUM> of the slab waveguide <NUM> by a controllable amount. In the embodiment shown in <FIG>, the tunable cladding portions <NUM>, <NUM> have saw-tooth shapes in XY plane, e.g. an array of triangular shapes, as shown in <FIG>. The array extends laterally w. an optical path of the image light in the core <NUM> of the slab waveguide <NUM>. At least some triangular-shaped tunable cladding portions have a side 1339A, 1340A extending at an acute angle w. the optical path represented by horizontal arrows in <FIG>. An underlayer <NUM> (<FIG>) may be provided under the tunable cladding portions <NUM>, <NUM> to avoid a direct contact between the tunable cladding portions <NUM>, <NUM> and the waveguide core <NUM>. The underlayer <NUM> may be thin enough to ensure the evanescent coupling of the light propagating in the core <NUM> with the tunable cladding portions <NUM>, <NUM>.

The tunable cladding portions <NUM>, <NUM> of the top cladding <NUM> include liquid crystal (LC) LC material that changes its refractive index for light of a certain polarization upon application of electric field to the tunable cladding portions <NUM>, <NUM>. When refractive index of the LC tunable cladding portions <NUM>, <NUM> of the top cladding <NUM> changes, the effective refractive index of the slab waveguide <NUM> changes as well, causing the image light <NUM> to deviate from the original direction of propagation due to a Fresnel refraction on the tilted faces of the LC tunable cladding portions <NUM>, <NUM>. The magnitude of the deviation depends on the angle of the tilted faces and the vertical pitch (in Y-direction) of the LC tunable cladding portions <NUM> and <NUM>. The distribution of energy in directions <NUM> and <NUM> depends on the switching state of the LC tunable cladding portions <NUM> and <NUM>, which may be operated in binary mode, ON/OFF. Each array of the LC tunable cladding portions <NUM> and <NUM> may offset the 1D FOV by a discrete amount when the LC tunable cladding portions <NUM> and <NUM> are not be continuously tunable. Therefore, a cascade of m LC elements would yield <NUM>m combinations of 1D FOV offsets. By energizing different triangular LC tunable cladding portions <NUM>, <NUM>, the image light <NUM> may be deviated at different angles. For example, energizing larger triangular shapes <NUM> deviates the image light <NUM> to propagate at an angle as shown at <NUM>, and energizing shallower triangular shapes <NUM> deviates the image light <NUM> to propagate at a steeper angle, as shown at <NUM>. More arrays of LC portions with different deviation angles may enable a more precise angle control. When different triangular shapes of the LC tunable cladding portions1339, <NUM> are energized in coordination with operating the 1D imager or scanner, the image light is switched between a plurality of conterminous FOV portions, enabling effective controllable light spread and associated horizontal FOV to be expanded, or enhanced.

Referring to <FIG>, a holographic beam expander <NUM> includes a hologram <NUM> in a low-mode slab waveguide <NUM> enabling propagation of image light in plane of the slab waveguide <NUM> in two dimensions, i.e. in XY plane. The hologram <NUM> is configured to receive image light <NUM> including at least one collimated beam portion, e.g. first (<NUM>; dotted lines) and second (<NUM>; dashed lines) collimated beam portions propagating at an angle to each other, and to reflect each collimated beam portion at a plurality of locations along an optical path of the collimated beam portion in the hologram <NUM>. For example, the first collimated beam portion <NUM> is reflected at a plurality of locations 1451A, 1451B, 1451C at a first angle, producing a first output beam (<NUM>; dotted lines); and the second collimated beam portion <NUM> is reflected at a plurality of locations 1452A, 1452B, 1452C at a second angle, producing a second output beam (<NUM>; dashed lines). Any other light beams are reflected at beam angles between the first and second angles, propagating in a plurality of directions between the directions of the first <NUM> and second <NUM> output beams. To that end, the hologram <NUM> may include a plurality of fringes configured to ensure reflection in the desired directions, depending on the impinging beam angles. It is seen from <FIG> that such a reflection geometry leads to expansion of the light beams <NUM>, <NUM>.

Turning to <FIG>, a wide-beam PIC phased array 1D imager <NUM> is similar to the PIC phased array 1D imager <NUM> of <FIG>, but includes many more linear waveguides in a MZIA <NUM> and a PSA <NUM> (<FIG>). An output waveguide array coupler or beam expander <NUM> is similar to the concentrator <NUM>, but includes many more output linear waveguides <NUM>, e.g. <NUM>,<NUM>; <NUM>,<NUM>; <NUM>,<NUM> or more waveguides spanning over <NUM>; <NUM>; or <NUM> of lateral distance, as the case may be. The output beam may be as wide as the width of the linear waveguide <NUM> array, and thus may not require any subsequent beam expansion and collimation to expand the output beam over an eyebox of a near-eye display, simplifying the overall design.

Referring now to <FIG>, a slab waveguide <NUM> supports a diffraction grating <NUM> for diffracting out a portion of image light <NUM> propagating in the XY plane of the slab waveguide <NUM>. A K-vector of the diffraction grating <NUM> is aligned with the x-component of the K-vector of the image light <NUM>. A diffraction angle θ of the image light <NUM> follows the equation
<MAT>
where n is refractive index, T is grating period and λ is the wavelength of light in the propagation medium. Accordingly,
<MAT>
where ngr is a group index. In a regular waveguide with small dispersion, ngr = n; therefore,
<MAT>.

It follows from Eq. (<NUM>) that at normal incidence and T = λ/n that
<MAT>
for n =<NUM> at wavelengths ranging from <NUM> to <NUM>. In accordance with this disclosure, the angular range may be increased to some extent by increasing the angle of diffraction θ. For example, by reducing the grating pitch to <NUM>, one may achieve the range of diffraction angles dθ to <NUM> degrees.

The angular dispersion range may be increased e.g. by using a multi-layer output waveguide. Referring to <FIG>, a dual-core slab waveguide <NUM> extends in XY plane. The dual-core slab waveguide <NUM> includes first <NUM> and second <NUM> cores running parallel to one another in XY plane of a substrate <NUM> surrounded by first <NUM> and second <NUM> claddings respectively. The first core <NUM> and the first cladding <NUM> are configured for singlemode propagation of a first beam (solid arrows; <NUM>) of image light. Similarly, the second core <NUM> and the second cladding <NUM> are configured for singlemode propagation of a second beam (dashed arrows; <NUM>) of image light.

The first <NUM> and second <NUM> cores have first <NUM> and second <NUM> diffraction gratings formed in or on the first <NUM> and second <NUM> cores, respectively. The first diffraction grating <NUM> is configured to out-couple spectral component(s) of the redirected image light at a first angle dependent on the first wavelength. The first angle is within a first angle range corresponding to a tuning range of a wavelength-tunable light source used. Similarly, the second diffraction grating <NUM> is configured to out-couple spectral component(s) of the redirected image light at a second angle different from the first angle. The second angle is within a second angle range corresponding to the tuning range of the wavelength-tunable light source.

Different angles and angular ranges of diffraction from different cores <NUM>, <NUM> of the dual-core waveguide <NUM> can be attained by changing the thickness or refractive index of the cores <NUM> and <NUM>, refractive index of the claddings <NUM> and <NUM>, or pitch of the diffraction gratings <NUM> and <NUM>, for the same wavelength of the image light represented by the first <NUM> and second <NUM> light beams. To simplify fabrication, a single grating can be etched into the first core <NUM> layer, and the second core <NUM> layer or any subsequent layer(s) may reproduce this grating simply through a directional material deposition. In the latter case, the FOV may be adjusted by varying the thickness of the layers and, therefore, the effective refractive index.

Different angles of diffraction may be used to expand the corresponding "vertical" 1D FOV by tiling smaller angular ranges from separate layers. Herein, the term "vertical" is meant to differentiate from the 1D FOV by redirecting the image light in plane of the low-mode waveguide, i.e. XY plane, which is termed "horizontal". It is to be noted that the terms "horizontal" and "vertical" in this context are meant as mere differentiators to distinguish in-plane 1D FOV from wavelength dispersion 1D FOV, and do not imply the actual orientation of the devices when in use. The switching between the first <NUM> and second <NUM> cores can be achieved, for example, using Mach-Zehnder interferometers and directional couplers. More details on possible switching configurations will be provided further below.

Turning to <FIG>, an angular dispersion module <NUM> provides enhanced wavelength dispersion of image light to obtain the required vertical 1D FOV. The angular dispersion module <NUM> includes serially coupled: a MZIA <NUM> coupled to a vertical mode converter <NUM>, e.g. a non-symmetrical directional coupler, a multimode interference (MMI) coupler <NUM> receiving light from the vertical mode converter <NUM>, and a few-mode slab waveguide portion <NUM> receiving light from the MMI coupler <NUM>. The number of transversal modes of propagation of image light that may propagate in a core of the few-mode slab waveguide portion <NUM> may be <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>, for example, or more generally no more than <NUM> modes. A diffraction grating <NUM> disposed in or on the core of the few-mode slab waveguide portion <NUM> operates as an out-coupler, out-coupling the image light at an angle dependent on wavelength. The diffraction grating <NUM> is configured to out-couple each spectral component of the redirected image light at an angle dependent on the wavelength of the spectral component. The out-coupling angle is within an out-coupling angle range corresponding to a tuning range of the wavelength-tunable light source used. The out-coupling angle range is different for different lateral modes of propagation of the few-mode slab waveguide portion <NUM>, because each mode of propagation has a different effective refractive index.

Initially, only a fundamental mode of image light is coupled by an in-coupler <NUM> into the MZIA <NUM>. The MZIA <NUM> functions as 1xN optical switch, switching the image light between its output waveguides. At the end of each MZIA <NUM> output waveguide, the image light is converted into a different vertical mode by the vertical mode converter <NUM>. The image light from all the waveguides is combined into the few-mode slab waveguide portion <NUM> using the MMI coupler 1851In this manner, the in-plane image encoder layout, i.e. horizontal 1D imager circuitry disclosed above with reference to <FIG>, may be shared between different modes of propagation of image light in the FMW <NUM>.

Different vertical modes have different effective refractive indices and, therefore, will diffract at the diffraction grating <NUM> at different angles for the same wavelength. The overall vertical 1D FOV may be expanded using diffraction ranges of the separate modes in a time-sequential manner, that is, switching to a particular core providing a corresponding vertical 1D FOV portion, then switching to another core providing a different vertical 1D FOV portion, and so on, until all the vertical 1D FOV is covered. The MMI coupler <NUM> may be optimized for the required coupling of vertical modes using a physical design software by defining an optimization function (also termed merit function) to have operands representing optical insertion loss of the MMI coupler for each vertical mode having predefined vertical coordinates, and letting the physical design software run the optimization.

The coupling configuration of <FIG>, i.e. the MZIA <NUM> coupled to the vertical mode converter <NUM> coupled to the MMI <NUM>, may be used to couple the image light received by the in-coupler <NUM> into different vertical modes of any waveguide component supporting several vertical modes. Such a configuration may be used, for example, to couple image light into cores of the dual-core slab waveguide <NUM> of <FIG>. In case of the dual-core slab waveguide <NUM>, only one Mach-Zehnder interferometer, operating as 1x2 optical switch, may be used instead of the MZIA <NUM>. A multi-core slab waveguide may include a plurality of cores, and the coupling configuration of <FIG> may be used to couple the image light into any of the cores of the multi-core slab waveguide.

Referring to <FIG>, an angular dispersion enhancer <NUM> is based on a slow-light slab waveguide <NUM> extending in XY plane and supporting a cladding <NUM> with a diffraction grating structure <NUM> for out-coupling image light form the slow-light waveguide <NUM>. The slow-light waveguide <NUM> may include a uniform 2D photonic crystal, a multilayer structure, or a combination of the two, for increasing a group velocity refractive index by a factor of <NUM>, for example, or at least by a factor of <NUM>. Then, it follows from Eqs. (<NUM>) - (<NUM>) than the FOV may be increased tenfold, e.g. from <NUM> degrees to <NUM> degrees for the slowing factor of <NUM>. In some embodiments, the slow-light waveguide <NUM> may include an array of linear photonic crystal waveguides.

Referring to <FIG>, an angular dispersion enhancer 2028A includes a low-mode waveguide <NUM> having a slab waveguide portion <NUM> disposed in XY plane, and a corrugated reflector 2070A supported by the slab waveguide portion <NUM>. Image light <NUM>, carrying image information encoded in its spectrum, propagates in the slab waveguide portion <NUM>. A diffraction grating <NUM>, e.g. a Bragg grating, in the slab waveguide portion <NUM> out-couples different spectral components of image light <NUM> at different angles exceeding <NUM> degrees w. a direction of propagation of the image light <NUM> in the slab waveguide portion <NUM>. For example, a first spectral component <NUM> is out-coupled at a first angle θ<NUM>, and a second spectral component <NUM> is out-coupled at a second, larger angle θ<NUM>. The corrugated reflector 2070A reflects the first <NUM> and second <NUM> spectral components of the image light <NUM> diffracted by the diffraction grating <NUM> through the slab waveguide portion <NUM> and outside of the low-mode waveguide <NUM>.

The angular dispersion of the out-coupled image light <NUM> is largest when the image light <NUM> is out-coupled almost directly back, i.e. the angle θ approaches <NUM> degrees. For example, assuming a regular waveguide grating with refractive index of <NUM>, changing the wavelength from <NUM> to <NUM> causes <NUM>°shift if the averaged diffraction angle θ is zero, but <NUM>° shift if the average diffraction angle θ is ~<NUM>°. In this configuration, the diffraction grating <NUM> out-couples the image light <NUM> backwards to maximize the angular dispersion and, therefore, increase the FOV of a display. The corrugated reflector 2070A may include a plurality of prisms <NUM> with reflective coating <NUM> supported by the slab waveguide portion <NUM>, which redirect the image light <NUM> in the direction normal to the slab waveguide portion <NUM> to make sure that the central field angle is perpendicular to the slab waveguide portion <NUM>, i.e. is parallel to Z-axis. By way of a non-limiting example, the reflective layer <NUM> can be made of either one of the following or a combination of: (<NUM>) a lower refractive index material for total internal reflection (TIR), (<NUM>) a thin metal layer forming a semi-reflective mirror, or (<NUM>) a narrow-spectrum multilayer mirror coating or a reflective polarizer, such as a wire grid polarizer or a dual brightness enhancement film (DBEF).

Turning to <FIG>, an angular dispersion enhancer 2028B is a polarization-selective embodiment of the angular dispersion enhancer 2028A of <FIG>. In the angular dispersion enhancer 2028B of <FIG>, the corrugated reflector includes a polarization-selective reflector 2070B configured to reflect light at a first polarization and transmit light at a second polarization orthogonal to the first polarization. The angular dispersion enhancer 2028B further includes a quarter-wave waveplate (QWP) <NUM> supported by the slab waveguide portion <NUM> on an opposite side of the slab waveguide portion <NUM> from the polarization-selective reflector 2070B. The QWP <NUM> is configured to receive the image light components <NUM>, <NUM> reflected by the polarization-selective reflector 2070B. The image light components <NUM>, <NUM> are in the first polarization state.

A diffractive structure <NUM>, e.g. a reflective surface-relief diffraction grating, is supported by the QWP <NUM> and configured to reflect the image light components <NUM>, <NUM> propagated through the QWP <NUM> back to propagate through the QWP <NUM> for a second time converting the polarization of the image light components <NUM>, <NUM> from the first polarization to the second polarization. Then, the components <NUM>, <NUM> propagate through the slab waveguide portion <NUM>, and through the polarization-selective reflector 2070B, which transmits them through because they are in the second polarization state. The purpose of the diffractive structure <NUM> is to further increase the angular dispersion of the image light <NUM>.

Referring to <FIG>, a principle of varifocal adjustment (i.e. adjusting the convergence/divergence) of the out-coupled image light is illustrated. A low-mode slab waveguide portion 2156A in <FIG> includes a grating out-coupler with a uniform refractive index. An image light component <NUM> is out-coupled vertically, i.e. perpendicular to the plane of the slab waveguide portion 2156A, as a parallel beam focused at infinity. A slab waveguide portion 2156B in <FIG> includes a grating out-coupler with a controllable non-uniform refractive index to cause the image light component <NUM> to be out-coupled vertically, i.e. perpendicular to the plane of the slab waveguide portion 2156B, with a convergence as shown, as a focused beam at a focal distance equal to an inverse of the optical power (focusing power) of the grating out-coupler. Assuming a desired size of an eyebox <NUM> of <NUM>, a <NUM> refractive delta is required to focus the image light component <NUM> from the slab waveguide portion 2156B into a focal spot <NUM> two meters away for the eyebox <NUM>. To achieve this focusing function, the effective refractive index neff of the grating out-coupler needs to vary linearly from a <NUM> to -<NUM> in going across the eyebox <NUM>. This principle may be used in any dispersion enhancer considered herein. For a dispersion enhancer with a resonating structure, any change in the physical refractive index of the materials in the stack would generate a larger change in neff, thus facilitating the focusing or defocusing due to the change of refractive index along an out-coupler. Illustrative example of varifocal adjusters based on this principle are considered below with reference to <FIG>.

Referring first to <FIG>, a varifocal adjuster <NUM> includes a low-mode slab waveguide portion <NUM> for propagating light, e.g. image light <NUM>. The slab waveguide portion <NUM> includes an out-coupler <NUM>, e.g. a Brag grating, configured to out-couple the image light <NUM> at an angle to the XY plane of the slab waveguide portion <NUM>. A liquid crystal (LC) cell <NUM> is evanescently coupled to the slab waveguide portion <NUM>. The thickness of an upper cladding <NUM> of the slab waveguide portion <NUM> is selected such that a tail of a guided mode <NUM> of the image light <NUM> travelling in the core of the mode slab waveguide portion <NUM> overlaps the LC cell <NUM>, reaching an LC layer <NUM> of the LC cell <NUM> through an upper cladding <NUM> supporting the LC cell <NUM>. The LC layer <NUM> is disposed between a pair of electrodes <NUM>. The guided mode <NUM> overlaps the LC layer <NUM> of the LC cell <NUM>.

The LC cell <NUM> defines an effective refractive index for the guided mode <NUM> of the image light <NUM> propagating in the slab waveguide portion <NUM>. The effective refractive index neff varies in a direction of propagation of the image light <NUM> in the low-mode slab waveguide <NUM>, that is, X-direction in <FIG>. The varying effective refractive index neff causes a direction of the out-coupled image light <NUM> portions to vary in going along X-axis, which causes the out-coupled image light <NUM> to focus or defocus, as explained above with reference to <FIG>. The thickness profile of the upper cladding <NUM> (<FIG>) may be selected so that a change of the refractive index of the LC layer <NUM> would cause a linear change of the effective refractive index neff for the propagating waveguide mode <NUM>. This will cause the out-coupled image light <NUM> to be focused or defocused. The absolute value of the change and, therefore, the focal length, can be controlled by a voltage applied to the LC cell <NUM>. The thickness profile of the upper cladding <NUM> may be made linear, i.e. the LC cell <NUM> may form an acute angle with the slab waveguide portion <NUM>, thereby varying the effective refractive index neff for the waveguide mode <NUM>.

The refractive index of the LC layer <NUM> is varied by applying voltage to the LC cell <NUM>. As explained above, this causes a direction of propagation of the out-coupled image light <NUM> to vary along the direction of propagation (i.e. X-direction) of the image light <NUM> in the slab waveguide portion <NUM>, causing the out-coupled image light <NUM> to diverge or converge in XZ plane. By varying the applied voltage, the divergence / convergence of the out-coupled image light <NUM> (collectively termed "divergence") may controlled. In some embodiments, the LC cell <NUM> may be parallel to the slab waveguide portion <NUM>, and may be pixelated to impart a refractive index change profile along the direction of propagation of the image light <NUM>, that is, along the X-direction.

Referring now to <FIG>, a varifocal adjuster <NUM> includes a low-mode slab waveguide portion <NUM> for propagating light, e.g. image light <NUM>. The slab waveguide portion <NUM> includes a core layer <NUM> and an out-coupler <NUM> configured to out-couple the image light <NUM> at an angle to a plane of the slab waveguide portion. The core layer <NUM> is made of a material having a refractive index dependent on an applied electric field. For example, the core layer <NUM> may be made of LiNbO3, AlN, SiC, or another material with a high electro-optic coefficient.

Electrodes <NUM> are disposed above and below the core layer <NUM> for applying an electric field <NUM> to the core layer <NUM>. The electrodes <NUM> may be disposed at an acute angle to each other, forming a wedge. When a voltage is applied to the electrodes <NUM>, the electric field <NUM> spatially varies along the direction of propagation of the image light <NUM> in the core <NUM> of the slab waveguide portion <NUM>, i.e. along X-direction. This causes a direction of the image light <NUM> out-coupled from the slab waveguide portion <NUM> to vary along the a direction of propagation of the light in the low-mode slab waveguide, effectively causing the out-coupled image light <NUM> to diverge or converge in XZ plane. By varying the applied voltage, the degree of convergence/divergence of the out-coupled image light <NUM> may be varied in a controllable manner.

The spatial modulation of refractive index may be achieved by a DC or AC electric field that passes through the materials of the slab waveguide portion <NUM> and a propagating optical mode <NUM>. Depending on the crystal axis in which the refractive modulation is desired and the component design, electrodes can be placed either above/below the upper/lower cladding respectively, or just in one of these layers. In case where the electrodes sandwich the core of the waveguide, the electric field <NUM> will run vertically as shown in <FIG>. The relative magnitude of the electric field <NUM> along the propagation of the image light <NUM> (which is the one that needed to be controlled to achieve focusing) can be assigned by changing the distance between electrodes <NUM>. Larger distance will yield a weaker electric field <NUM>. By doing so, one can embed a pre-determine wedge profile electric field <NUM> that proportionally correlates with local refractive index change. When the applied voltage V =<NUM>, the image light <NUM> is collimated, i.e. the image is at infinity. As the applied voltage V is increased, the focal plane of the system will get closer.

A similar principle is applied in a varifocal adjuster <NUM> of <FIG>, where an electric field <NUM> is parallel to a core layer <NUM> of a few-mode slab waveguide <NUM>. Such orientation of the electric field <NUM> is defined by floating electrodes <NUM> extending along a direction of propagation of the image light <NUM> in the low-mode slab waveguide <NUM> between a pair of end electrodes <NUM>, to which the voltage V may be applied. The floating electrodes <NUM> are disposed so as to provide a magnitude distribution of the electric field <NUM> that matches a refractive index distribution required for focusing of the out-coupled image light <NUM>. In some embodiments, a set of independently controlled electrodes might be provided to have a better control of the magnitude distribution of the electric field <NUM>.

Referring now to <FIG>, a varifocal adjuster <NUM> includes a low-mode slab waveguide portion <NUM> supporting a grating structure <NUM> including an array of grating fringes <NUM> having a first refractive index and surrounded by a substrate <NUM> between individual grating fringes <NUM> having a second refractive index. The grating structure <NUM> out-couples image light <NUM> form the low-mode slab waveguide portion <NUM>. At least one of the first or second refractive index is tunable to provide a gradient of the at least one of the first or second refractive index for focusing or defocusing of the image light <NUM> out-coupled from the slab waveguide portion by the out-coupler. To that end, an array of heating elements <NUM> may be coupled to the waveguide <NUM> for providing a non-uniform, spatially selective heating to the grating structure <NUM>. The spatially selective heating creates a refractive index gradient, which may modify local diffraction angle for the image light <NUM>, thereby enabling focusing or defocusing of the image light <NUM> out-coupled from the waveguide <NUM>. By way of a non-limiting example, to achieve a <NUM> focal distance for <NUM> eyebox length one needs a maximum Δn=<NUM> for the effective refractive index. This number will become proportionally smaller if a slow light waveguide is used instead of the waveguide <NUM>. In some embodiments, the substrate <NUM> may include a liquid crystal (LC) layer to provide a required refractive index gradient by tuning the LC layer with an applied electric field. Since the layer in which the refractive index is modified is thin, it will only affect the display optical path but not the see-through optical path.

Referring to <FIG> with further reference to <FIG>, a method <NUM> (<FIG>) for providing an image in angular domain includes coupling (<NUM>) image light, e.g. the light <NUM> in <FIG>, including a spectral component at a first wavelength, to a 1D redirector/imager using an in-coupler, e.g. the in-coupler <NUM>. The image light may be redirected using any of the horizontal FOV 1D redirectors/imagers disclosed herein, e.g. the phased array 1D imager <NUM> of <FIG> including any of the PIC embodiments of <FIG>, the hybrid 1D imager <NUM> of <FIG>, or the FSO 1D scanner <NUM> of <FIG>. The 1D imager redirects (<NUM>) the image light in a first plane, e.g. in the XY plane (which is the plane of the low-mode slab waveguide portion <NUM>) in <FIG>. The image light <NUM> redirected by the 1D imager is propagated (<NUM>) tin a in a low-mode slab waveguide portion <NUM>. The spectral component at the first wavelength is out-coupled (<NUM>) from the low-mode slab waveguide by the out-coupler <NUM>, e.g. any of the grating out-couplers considered herein, at an angle dependent on the first wavelength. The low-mode slab waveguide portion may include a singlemode slab waveguide or a few-mode (no greater than <NUM> modes) slab waveguide.

Turning to <FIG>, a method <NUM> is an embodiment of the method <NUM> of <FIG>. The method <NUM> of <FIG> uses a monochromatic tunable source of image light, such as the tunable laser source <NUM> of <FIG>, for example. The method <NUM> includes setting (<NUM>) an emission wavelength of the monochromatic tunable source and redirecting (<NUM>) 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 while the 1D imager redirects the image light in the first plane, whereby the image light redirected in the first plane is out-coupled at the same angle. Then, next wavelength (<NUM>) is set and the process repeats, at its own value of output power of the light source corresponding to a desired brightness of a pixel of an image being displayed. The redirection in XY plane includes angularly scanning (<NUM>) a collimated light beam in XY plane, or forming the angular distribution of brightness simultaneously (<NUM>).

Referring now to <FIG>, a method <NUM> is an embodiment of the method <NUM> of <FIG>. The method <NUM> of <FIG> uses a tunable-spectrum light source, e.g. the tunable-spectrum light source <NUM> of <FIG>. The method <NUM> of <FIG> includes using the tunable-spectrum light source to provide (<NUM>) image light having a plurality of spectral components corresponding to the vertical FOV of the image to be displayed. The image light with the plurality of spectral components is redirected (<NUM>) in XY plane by providing angular distribution of brightness in XY plane, which may be done by scanning (<NUM>) or forming the instantaneous angular distribution (<NUM>). The angularly dispersed, multi-wavelength image light is out-coupled (<NUM>) from the low-mode slab waveguide with an angular distribution corresponding to the spectral composition of the image light.

Turning to <FIG>, an augmented reality (AR) near-eye display <NUM> includes a frame <NUM> having a form factor of a pair of eyeglasses. The frame <NUM> supports, for each eye, a light engine <NUM> including a tunable-spectrum light source described herein, and a low-mode, i.e. a singlemode or few-mode waveguide <NUM> disclosed herein, optically coupled to the light engine <NUM>. The AR near-eye display <NUM> may further include an eye-tracking camera <NUM>, a plurality of illuminators <NUM>, and an eye-tracking camera controller <NUM>. The illuminators <NUM> may be supported by the waveguide <NUM> for illuminating an eyebox <NUM>. The light engine <NUM> provides a light beam having a spectrum representative of the vertical 1D FOV to be projected into a user's eye. The waveguide <NUM> receives the light beam and expands the light beam over the eyebox <NUM>. The horizontal 1D FOV may be provided by a 1D imager disclosed herein, e.g. the PIC-based imager <NUM> of <FIG>, the phased array 1D imager <NUM> of <FIG>, the hybrid 1D imager <NUM> of <FIG>, or MEMS-based scanner of <NUM> <FIG>.

The purpose of the eye-tracking cameras <NUM> is to determine position and/or orientation of both eyes of the user. Once the position and orientation of the user's eyes are known, a gaze convergence distance and direction may be determined. The imagery displayed may be adjusted dynamically to account for the user's gaze, for a better fidelity of immersion of the user into the displayed augmented reality scenery, and/or to provide specific functions of interaction with the augmented reality. In operation, the illuminators <NUM> illuminate the eyes at the corresponding eyeboxes <NUM>, to enable the eye-tracking cameras to obtain the images of the eyes, as well as to provide reference reflections i.e. glints. The glints may function as reference points in the captured eye image, facilitating the eye gazing direction determination by determining position of the eye pupil images relative to the glints images. To avoid distracting the user with illuminating light, the latter may be made invisible to the user. For example, infrared light may be used to illuminate the eyeboxes <NUM>.

The function of the eye-tracking camera controllers <NUM> is to process images obtained by the eye-tracking cameras <NUM> to determine, in real time, the eye gazing directions of both eyes of the user. In some embodiments, the image processing and eye position/orientation determination functions may be performed by a central controller, not shown, of the AR near-eye display <NUM>. The central controller may also provide control signals to the light engines <NUM> depending on the determined eye positions, eye orientations, gaze directions, eyes vergence, etc..

Referring now to <FIG>, an HMD <NUM> is an example of an AR/VR wearable display system which encloses the user's face, for a greater degree of immersion into the AR/VR environment. The function of the HMD <NUM> is to augment views of a physical, real-world environment with computer-generated imagery, or to generate the entirely virtual 3D imagery. The HMD <NUM> may include a front body <NUM> and a band <NUM>. The front body <NUM> is configured for placement in front of eyes of a user in a reliable and comfortable manner, and the band <NUM> may be stretched to secure the front body <NUM> on the user's head. A display system <NUM> may be disposed in the front body <NUM> for presenting AR/VR imagery to the user. Sides <NUM> of the front body <NUM> may be opaque or transparent.

In some embodiments, the front body <NUM> includes locators <NUM> and an inertial measurement unit (IMU) <NUM> for tracking acceleration of the HMD <NUM>, and position sensors <NUM> for tracking position of the HMD <NUM>. The IMU <NUM> is an electronic device that generates data indicating a position of the HMD <NUM> based on measurement signals received from one or more of position sensors <NUM>, which generate one or more measurement signals in response to motion of the HMD <NUM>. Examples of position sensors <NUM> include: one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor that detects motion, a type of sensor used for error correction of the IMU <NUM>, or some combination thereof. The position sensors <NUM> may be located external to the IMU <NUM>, internal to the IMU <NUM>, or some combination thereof.

The locators <NUM> are traced by an external imaging device of a virtual reality system, such that the virtual reality system can track the location and orientation of the entire HMD <NUM>. Information generated by the IMU <NUM> and the position sensors <NUM> may be compared with the position and orientation obtained by tracking the locators <NUM>, for improved tracking accuracy of position and orientation of the HMD <NUM>. Accurate position and orientation is important for presenting appropriate virtual scenery to the user as the latter moves and turns in 3D space.

The HMD <NUM> may further include a depth camera assembly (DCA) <NUM>, which captures data describing depth information of a local area surrounding some or all of the HMD <NUM>. To that end, the DCA <NUM> may include a laser radar (LIDAR), or a similar device. The depth information may be compared with the information from the IMU <NUM>, for better accuracy of determination of position and orientation of the HMD <NUM> in 3D space.

The HMD <NUM> may further include an eye tracking system <NUM> for determining orientation and position of user's eyes in real time. The obtained position and orientation of the eyes also allows the HMD <NUM> to determine the gaze direction of the user and to adjust the image generated by the display system <NUM> accordingly. In one embodiment, the vergence, that is, the convergence angle of the user's eyes gaze, is determined. The determined gaze direction and vergence angle may also be used for real-time compensation of visual artifacts dependent on the angle of view and eye position. Furthermore, the determined vergence and gaze angles may be used for interaction with the user, highlighting objects, bringing objects to the foreground, creating additional objects or pointers, etc. An audio system may also be provided including e.g. a set of small speakers built into the front body <NUM>.

Embodiments of the present disclosure may include, or be implemented in conjunction with, an artificial reality system. An artificial reality system adjusts sensory information about outside world obtained through the senses such as visual information, audio, touch (somatosensation) information, acceleration, balance, etc., in some manner before presentation to a user. By way of non-limiting examples, artificial reality may include virtual reality (VR), augmented reality (AR), mixed reality (MR), hybrid reality, or some combination and/or derivatives thereof. Artificial reality content may include entirely generated content or generated content combined with captured (e.g., real-world) content. The artificial reality content may include video, audio, somatic or haptic feedback, or some combination thereof. Any of this content may be presented in a single channel or in multiple channels, such as in a stereo video that produces a three-dimensional effect to the viewer. Furthermore, in some embodiments, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof, that are used to, for example, create content in artificial reality and/or are otherwise used in (e.g., perform activities in) artificial reality. The artificial reality system that provides the artificial reality content may be implemented on various platforms, including a wearable display such as an HMD connected to a host computer system, a standalone HMD, a near-eye display having a form factor of eyeglasses, a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers.

Claim 1:
A device (<NUM>) for providing a line of an image in angular domain, the device comprising a low-mode waveguide (<NUM>) comprising:
an in-coupler (<NUM>) for coupling image light from a light source into the low-mode waveguide;
a 1xN splitter (<NUM>) for splitting the image light coupled by the in-coupler into N linear waveguides (<NUM>);
N phase shifters (<NUM>) each coupled to a particular one of the N linear waveguides for delaying image light portions propagating therein by a controllable amount;
an array of N linear waveguide emitters (<NUM>) each coupled to a particular one of the N phase shifters for emitting the image light portions delayed thereby; and
a slab waveguide portion (<NUM>) coupled to the array of N linear waveguide emitters for propagating therein the delayed image light portions emitted by corresponding emitters of the array of N linear waveguide emitters, wherein N is an integer;
wherein the slab waveguide portion comprises a single mode slab waveguide or a few-mode slab waveguide supporting no more than <NUM> lateral modes of propagation;
characterized in that
the slab waveguide portion further comprises a field of view, FOV, expander (<NUM>) in the slab waveguide portion;
the FOV expander comprises a tunable cladding portion (<NUM>, <NUM>) evanescently coupled to a core (<NUM>) of the slab waveguide portion and shaped to deviate light propagated in the core of the slab waveguide portion by a controllable amount; and
the tunable cladding portion (<NUM>, <NUM>) comprises an array of triangular-shaped liquid crystal cladding portions, the array extending laterally w.r.t. an optical path of the image light in the core of the slab waveguide portion, wherein at least some triangular-shaped liquid crystal cladding portions have a side (1339A, 1340A) extending at an acute angle w.r.t. the optical path.