CN117581060A - Waveguide array illuminator with light scattering mitigation - Google Patents

Abstract

A waveguide illuminator (100) includes an input waveguide (106), a waveguide splitter (112) coupled to the input waveguide (106), and a waveguide array (116) coupled to the waveguide splitter (112). The waveguide array (116) includes an array of out-coupling gratings (120) that couple out portions (122) of the split light beam to form an array of out-coupling beam portions for illuminating the display panel. The out-coupling grating (120) may be apodized to reduce light scattering through the grating. Furthermore, the gaps between these out-coupling gratings along the waveguide may be filled by gap gratings and/or etched trenches extending parallel to the waveguide.

Description

Waveguide array illuminator with light scattering mitigation

Technical Field

The present disclosure relates to luminaires, visual display devices, and related components and modules.

Background

Visual displays provide information to one or more viewers, including still images, video, data, and the like. Visual displays find application in a variety of fields including entertainment, education, engineering, science, professional training, advertising, to name a few. Some visual displays (e.g., televisions) display images to multiple users, while some visual display systems (e.g., near-eye displays (NED)) are intended for use by a single user.

An artificial reality system typically includes a NED (e.g., a headset) or a pair of glasses configured to present content to a user. The near-eye display may display or combine images of real objects with images of virtual objects, as in a Virtual Reality (VR) application, an augmented reality (augmented reality, AR) application, or a Mixed Reality (MR) application. For example, in an AR system, a user may view an image (e.g., a computer-generated image (CGI)) of a virtual object superimposed with the surrounding environment through a perspective "combiner" component. The combiner of the wearable display is typically transparent to external light, but includes some light routing optics to direct the display light into the field of view of the user.

Because the display of an HMD or NED is typically worn on the head of a user, a large, bulky and heavy, unbalanced and/or heavy display device with heavy batteries would be cumbersome and uncomfortable for the user to wear. Accordingly, head mounted display devices may benefit from a compact and efficient construction that includes efficient light sources and illuminators that provide illumination of the display panel, as well as high flux eyepieces and other optical elements in the image forming system.

Disclosure of Invention

According to a first aspect of the present disclosure, there is provided a waveguide illuminator comprising: an input waveguide for guiding an input light beam therein; a waveguide splitter coupled to the input waveguide, the waveguide splitter for splitting the input optical beam into a plurality of sub-beams; a waveguide array coupled to the waveguide splitter, the waveguide array for propagating the plurality of beamlets in the waveguide array, a plurality of waveguides in the waveguide array extending parallel to each other, each waveguide configured to guide one of the plurality of beamlets; and an out-coupling grating array comprising a plurality of rows of out-coupling gratings, each row coupled to a corresponding waveguide in the waveguide array along a length of the corresponding waveguide, wherein the plurality of out-coupling gratings of each row are configured to couple out portions of a beamlet propagating in the corresponding waveguide such that, in operation, a two-dimensional array of portions of the beamlet is coupled out of the waveguide array.

The plurality of out-gratings of each row of the out-grating array may have an increasing out-coupling efficiency with distance from the waveguide splitter for flattening (flat) the spatial distribution of the optical power of the two-dimensional array of the coupled-out portions of the beamlets.

The out-coupling gratings in the out-coupling grating array may be apodized (apodized) in the length direction of the corresponding waveguide such that at least one of the following is present: the duty cycle of each out-coupling grating at opposite ends of the out-coupling grating is less than 0.1 or greater than 0.9, and the duty cycle between the opposite ends of the out-coupling grating is greater than 0.1 and less than 0.9; or the depth of the grooves of each out-coupling grating at opposite ends of the out-coupling grating is smaller than the depth of the grooves at the middle of the out-coupling grating.

The waveguide array may comprise a ridge waveguide array; the out-coupling grating array may be formed in the ridge waveguide array; the out-coupling gratings of each row may include being etched to a grating etch depth D in a corresponding ridge waveguide in the array of ridge waveguides _Grating Is a groove of (a); and the gaps between adjacent outcoupled gratings of each row may be uniformly etched to a gap etch depth D _{Gap of} ＝aD _Grating Wherein 0 is<a<1。

a may be less than 0.5.

The waveguide array may comprise a ridge waveguide array; the out-coupling grating array may be formed in the ridge waveguide array; the out-coupling gratings of each row may be included in corresponding ones of the array of ridge waveguides at a grating pitch P _Grating A groove is arranged; and the gaps between adjacent outcoupling gratings of each row may comprise gap gratings.

The gap grating may include a gap pitch P extending non-parallel to the waveguides of the waveguide array _{Gap of} ＝bP _Grating A groove is provided, wherein 0<b<0.5。

The gap grating may include grooves extending parallel to the waveguides of the waveguide array.

According to a second aspect of the present disclosure, there is provided a display device including a waveguide illuminator and a display panel, the waveguide illuminator comprising: an input waveguide for guiding an input light beam therein; a waveguide splitter coupled to the input waveguide, the waveguide splitter for splitting the input optical beam into a plurality of sub-beams; a waveguide array coupled to the waveguide splitter, the waveguide array for propagating the plurality of beamlets in the waveguide array, a plurality of waveguides in the waveguide array extending parallel to each other, each waveguide configured to guide one of the plurality of beamlets; and an out-coupling grating array comprising a plurality of rows of out-coupling gratings, each row coupled to a corresponding waveguide in the waveguide array along a length of the corresponding waveguide, wherein the plurality of out-coupling gratings of each row are configured to couple out portions of a beamlet propagating in the corresponding waveguide such that, in operation, a two-dimensional array of portions of the beamlet is coupled out of the waveguide array; the display panel includes an array of display pixels arranged and configured to receive a two-dimensional array of coupled portions of the beamlets.

The plurality of out-gratings of each row in the out-grating array may have an increasing out-coupling efficiency with distance from the waveguide splitter for flattening the spatial distribution of the optical power of the two-dimensional array of coupled-out portions of the beamlets.

The out-coupling gratings in the out-coupling grating array may be apodized along the length of the waveguides in the waveguide array to reduce light scattering through the out-coupling grating array.

The pitch of the display pixels may be substantially equal to the pitch of the out-coupling grating array.

The display device may further comprise a light source for providing an input light beam to the input waveguide.

The light source may be a polarized light source, wherein the input light beam and the coupled-out portion of the beamlets may be polarized; and the array of display pixels may comprise an array of tunable polarization rotators for tuning the polarization of portions of the respective beamlets.

The light source may comprise a monochromatic light source, wherein the input light beam may have a wavelength of the first color channel.

According to a third aspect of the present disclosure, there is provided a method for reducing light scattering in a waveguide luminaire, the waveguide luminaire comprising: a waveguide splitter for splitting an input optical beam into a plurality of sub-beams; a waveguide array coupled to the waveguide splitter, the waveguide array for propagating the plurality of beamlets in the waveguide array, each waveguide configured to guide one beamlet of the plurality of beamlets; and an out-coupling grating array comprising a plurality of rows of out-coupling gratings formed in the corresponding waveguides for coupling out portions of the beamlets propagating in the corresponding waveguides, the method comprising: the impedance of the plurality of out-coupling gratings in a row of out-coupling gratings is matched to the impedance of the gaps between the out-coupling gratings in the row of out-coupling gratings.

Matching the impedances of the out-coupling gratings may include apodizing the out-coupling gratings in the out-coupling grating array along the length of the corresponding waveguide such that the duty cycle of each out-coupling grating at opposite ends of the out-coupling grating is less than 0.1 or greater than 0.9 and the duty cycle between the opposite ends of the out-coupling grating is between 0.1 and 0.9.

The waveguide array may comprise an array of ridge waveguides and may be etched by etching the ridge waveguides to a grating etch depth D _Grating Forming the coupling-out grating array in the array of ridge waveguides; and wherein matching the impedance of the outcoupling gratings may comprise uniformly etching the gaps between adjacent outcoupling gratings of each row to a gap etch depth D _{Gap of} ＝aD _Grating Wherein 0 is<a<1。

The waveguide array may include a ridge waveguide array, and the out-coupling grating array may be formed in the ridge waveguide array; and wherein matching the impedances of the outcoupling gratings may comprise forming gap gratings in the gaps between adjacent outcoupling gratings at a pitch that is at least twice smaller than the pitch of the outcoupling gratings.

The waveguide array may comprise a ridge waveguide array, and the coupling-out grating arrays may be formed in the ridge waveguide array; and wherein matching the impedances of the out-coupling gratings may include forming gap gratings in gaps between adjacent out-coupling gratings, which may include grooves extending parallel to the ridge waveguides in the ridge waveguide array.

Drawings

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

FIG. 1 is a schematic plan view of a waveguide illuminator of the present disclosure;

FIG. 2A is a graph of the coupling-out efficiency and the coupled-out optical power combined with the distance light travels in the waveguide of the luminaire of FIG. 1 for the case of spatially uniform coupling-out efficiency;

FIG. 2B is a graph of the coupling-out efficiency and the coupled-out optical power combined with the distance light travels in the waveguide of the luminaire of FIG. 1 for the case of spatially non-uniform coupling-out efficiency;

FIG. 3 is an enlarged side cross-sectional view of a waveguide illuminator illustrating forward scattering by a grating coupler of the waveguide illuminator of the present disclosure;

FIG. 4A is an enlarged side cross-sectional view of an embodiment of a waveguide illuminator in which the grating coupler has an apodization duty cycle (apodized duty cycle);

FIG. 4B is an enlarged side cross-sectional view of an embodiment of the waveguide illuminator in which the grating coupler has an apodized grating depth (apodized grating depth);

FIG. 5 is an enlarged side cross-sectional view of an embodiment of a waveguide illuminator with etched gaps between grating couplers;

FIG. 6A is an enlarged side cross-sectional view of an embodiment of a waveguide illuminator in which a gap grating is formed between grating couplers;

FIG. 6B is a top view of the waveguide illuminator of FIG. 6A;

FIG. 7 is an enlarged side cross-sectional view of an embodiment of a waveguide illuminator in which a waveguide parallel gap grating is formed between grating couplers;

fig. 8 is a schematic diagram of a near-eye display using the waveguide illuminator of the present disclosure.

FIG. 9 is a diagram of an embodiment of a method for reducing light scattering in a waveguide illuminator according to the present disclosure;

FIG. 10 is a view of an Augmented Reality (AR) display of the present disclosure having a form factor of a pair of glasses; and

fig. 11 is a three-dimensional view of a Head Mounted Display (HMD) of the present disclosure.

Detailed Description

While the present teachings are described in connection with various embodiments and examples, the present teachings are not intended to be limited to these 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 the disclosure, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Furthermore, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.

As used herein, unless explicitly stated otherwise, the terms "first" and "second," etc. are not intended to imply a sequential order, but rather to distinguish one element from another element. Similarly, the sequential order of the method steps does not imply a sequential order of their execution unless explicitly stated. In fig. 3 to 7, like reference numerals denote like elements.

In a visual display comprising an array of pixels coupled to an illuminator, the light utilization efficiency depends on the ratio of the geometric area occupied by the pixels to the total area of the display panel. For micro-displays, which are typically used in near-eye displays and/or head-mounted displays, this ratio may be below 50% due to the small pixel size. Color filters on the display panel (which on average transmit no more than 30% of the incident light) may further hinder efficient use of the backlight. In addition, for polarization-based display panels (e.g., liquid Crystal (LC) display panels), there may be a 50% loss of polarization. All of these factors can greatly reduce the light utilization and overall photoelectric conversion efficiency of the display (wall plug efficiency), which is undesirable.

According to the present disclosure, the light utilization efficiency and the photoelectric conversion efficiency of a backlight type display can be improved by providing a waveguide illuminator as follows: the waveguide illuminator includes an array of couplers aligned with pixels of the display panel. In displays where the illuminator emits primary colors (e.g., red, green, and blue) of light, the color of the illumination light may be matched to the color filter, or the color filter may be omitted entirely. For polarization-based displays, the polarization of the emitted light may be matched to a predefined input polarization state. Matching the spatial distribution, transmission wavelength and/or transmission polarization characteristics of the pixels of the display panel can increase the useful portion of the display light (which is not absorbed or reflected by the display panel on its way to the observer's eye) and thus increase the photoelectric conversion efficiency of the display.

Single-mode waveguides or few-mode waveguides (e.g., ridge waveguides that propagate light in up to several lateral propagation modes) allow for efficient control of light characteristics such as color and directivity, particularly in conjunction with laser illumination. Since light propagates in a single spatial mode, the output light can be diffraction limited and highly directional. Single mode propagation also allows light to be coupled out at specific points on the waveguide, even in combination with focusing pixels that can focus light into pixels of the display panel and avoid scattering in the inter-pixel regions. The narrow spectrum of laser illumination enables large color gamut display. Furthermore, the single mode waveguide may maintain polarization, which results in a highly polarized output from the backlight unit of the polarization selective display without the need for a polarizer.

Single mode waveguides or few mode waveguides may use diffraction gratings to couple light out at specific points of a ridge waveguide array. These gratings couple out light by diffraction. A small portion of the light may also scatter, especially in the forward direction. Due to the coherent nature of the illumination light, the scattered light may undergo optical interference. Optical interference may interfere with the output illumination pattern. According to the present disclosure, scattering of the diffraction grating coupler may be reduced by matching the impedance of the gratings to the impedance of the inter-grating waveguide region. Impedance may be matched by, for example, apodizing the gratings, etching the inter-grating regions, filling the inter-grating regions with grating structures, and by other methods as disclosed herein.

According to the present disclosure, there is provided a waveguide illuminator comprising: an input waveguide for guiding an input light beam therein; a waveguide splitter coupled to the input waveguide, the waveguide splitter for splitting the input optical beam into a plurality of sub-beams; and a waveguide array coupled to the waveguide splitter, the waveguide array for propagating the plurality of beamlets in the waveguide array. A plurality of waveguides in the waveguide array extend parallel to each other, each waveguide configured to guide one of the plurality of beamlets. The waveguide illuminator further includes an out-coupling grating array including a plurality of rows of out-coupling gratings. Each row is coupled to a corresponding waveguide in the waveguide array along the length of the corresponding waveguide. The plurality of outcoupling gratings of each row is configured to couple out a plurality of portions of the beamlet propagating in the corresponding waveguide, such that in operation, a two dimensional array of portions of the beamlet is coupled out of the waveguide array.

The plurality of out-gratings of each row of the out-grating array may have an increasing out-coupling efficiency with distance from the waveguide splitter for flattening the spatial distribution of the optical power of the two-dimensional array of the portions of the sub-beams that are coupled out. In some embodiments, the out-coupling gratings in the out-coupling grating array are apodized in a length direction of the corresponding waveguide such that at least one of the following conditions is met: the duty cycle of each out-coupling grating at opposite ends of the out-coupling grating is less than 0.1 or greater than 0.9, and the duty cycle between the opposite ends of the out-coupling grating is greater than 0.1 and less than 0.9; or the depth of the grooves of each out-coupling grating at opposite ends of the out-coupling grating is smaller than the depth of the grooves at the middle of the out-coupling grating.

In embodiments where the waveguide array comprises a ridge waveguide array, the outcoupling grating array may be formed in the ridge waveguide array. The out-coupling gratings of each row may include being etched to a grating etch depth D in a corresponding ridge waveguide in the array of ridge waveguides _Grating Is formed in the substrate. To balance the impedance, the gaps between adjacent outcoupling gratings of each row may be uniformly etched to a gap etch depth D _{Gap of} ＝aD _Grating Wherein 0 is<a<1, e.g. a<0.5. In some embodiments, the out-coupling gratings of each row are included in the corresponding ridge waveguide of the ridge waveguide array at a grating pitch P _Grating And a groove is arranged. To balance the impedance, the gap between adjacent out-coupling gratings of each row may comprise a gap grating. The gap gratings may include a gap pitch P extending non-parallel to the waveguides in the waveguide array _{Gap of} ＝bP _Grating A groove is provided, wherein 0<b<0.5, or in some embodiments, the gap gratings may include grooves extending parallel to the waveguides in the waveguide array.

According to the present disclosure, there is provided a display device comprising a waveguide illuminator of the present disclosure and a display panel comprising an array of display pixels arranged and configured to receive a two-dimensional array of portions of coupled beamlets. The pitch of the display pixels may be substantially equal to the pitch of the out-coupling grating array.

In some embodiments, the display device further comprises a light source for providing an input light beam to the input waveguide. The light source may be, for example, a polarized light source providing a polarized input light beam and a polarized portion of the coupled-out beamlets. The light source may also be a monochromatic light source, wherein the input light beam has a wavelength of a certain color channel. The input beam may comprise a plurality of color channels.

In accordance with the present disclosure, there is also provided a method for reducing light scattering in a waveguide illuminator as disclosed herein. The method includes matching the impedance of a plurality of out-coupling gratings in a row of out-coupling gratings with the impedance of gaps between the out-coupling gratings in the row of out-coupling gratings.

In some embodiments of the method, matching the impedance of the out-coupling gratings comprises apodizing the out-coupling gratings of the out-coupling grating array over the length of the corresponding waveguide such that the duty cycle of each out-coupling grating at opposite ends of the out-coupling grating is less than 0.1 or greater than 0.9 and the duty cycle between the opposite ends of the out-coupling grating is between 0.1 and 0.9.

Including an array of ridge waveguides therein, and by etching the ridge waveguides to a grating etch depth D as disclosed herein _Grating While in embodiments where an array of out-coupling gratings is formed in a ridge waveguide array, matching the impedance of these out-coupling gratings may include uniformly etching the gaps between adjacent out-coupling gratings of each row to a gap etch depth D _{Gap of} ＝aD _Grating Wherein 0 is<a<1, and/or adjacent outcoupling gratings at a pitch at least twice smaller than the pitch of the outcoupling gratings A gap grating is formed in the gap between them. The gap grating may comprise grooves extending parallel to the ridge waveguides in the ridge waveguide array.

Referring now to fig. 1, a waveguide illuminator 100 includes a substrate 101 supporting an input waveguide 106 for guiding an input light beam 108 provided by a light source 110 (e.g., a laser source). In this context, the term "waveguide" means a light guiding structure as follows: the light guiding structure restricts light propagation in two dimensions like a light guide beam (light wire) and guides light in a single transverse mode (transversal mode) or several transverse modes (e.g. up to 12 propagation modes). The waveguide may be straight, curved, etc. One example of a linear waveguide is a ridge waveguide. The waveguide illuminator 100 may be implemented in a photonic integrated circuit (photonic integrated circuit, PIC).

The waveguide splitter 112 is coupled to the input waveguide 106. The function of the waveguide splitter 112 is to split the input optical beam 108 into a plurality of sub-beams 114. An array of waveguides 116 is coupled to the waveguide splitter 112, the array of waveguides being used to guide the beamlets 114 in the waveguides 116 of the array. As shown, these waveguides 116 extend parallel to each other. Each waveguide 116 is configured to direct one of the plurality of beamlets 114 from the waveguide splitter 112 to an end 129 of the waveguide 116.

The array of out-coupling gratings 120 is supported by the substrate 101 of the waveguide illuminator 100 or may be formed in the waveguide 116 itself. Each row 119 of the out-coupling grating 120 is coupled to the waveguide 116 along the length of the waveguide 116 of the waveguide array for coupling out portions 122 of one of the beamlets 114 propagating in the waveguide 116. These portions 122 coupled out by all rows 119 of the coupling-out grating 120 form a two-dimensional array of beamlet portions 122. These portions 122 are coupled out of the waveguide array and exit the waveguide illuminator 100 at an angle (e.g., acute or right angle) relative to the substrate 101. The X-pitch and Y-pitch of these out-coupling gratings 120 that couple out the two-dimensional array of beamlet portions 122 may be selected to match the X-pitch and Y-pitch of the display panel to be illuminated by the waveguide illuminator 100 to ensure that each beamlet portion 122 illuminates a particular pixel (not shown) of the display panel.

When the outcoupling efficiency of all the outcoupling gratings 120 is the same along any row 119 (as indicated by the straight solid line 201A in fig. 2A), the outcoupled optical power of the beamlet section 122 decreases exponentially with the distance from the waveguide splitter 112, as indicated by the exponential dashed line 202A. This occurs because with each out-coupling, the beamlets 114 lose power and, therefore, the same percentage of out-coupling of less power results in less out-coupling optical power for the next beamlet portion 122.

In many applications, it is desirable that the optical power of all beamlet portions 122 be at the same level. To this end, the outcoupling grating 120 of each row 119 of the outcouplers may be made to have a coupling-out efficiency (as shown by the curved solid line 201B in fig. 2B) that gradually increases with the distance from the waveguide splitter 112 for flattening or flattening the spatial distribution of the optical power of the two-dimensional array of outcoupled beamlet portions 120, as shown by the straight dashed line 202B.

Depending on the type of coupling-out, a gradual increase of the coupling-out efficiency can be achieved in various ways. As a non-limiting example, the grating duty cycle, length, height and/or width may be varied between gratings to achieve spatial uniformity of the optical power of the beamlet portion 120 of the outcoupler.

Referring to fig. 3, waveguide illuminator 300 is an embodiment of waveguide illuminator 100 of fig. 1 and includes elements similar to those of waveguide illuminator 100 of fig. 1. Specifically, the waveguide illuminator 300 of fig. 3 includes an array of waveguides 316 supported by a substrate 301. Similar to waveguide illuminator 100 of fig. 1, an array of out-coupling gratings 320 is coupled to the array of waveguides 316, the array of out-coupling gratings being used to couple out a two-dimensional array of portions 322 of beamlets 314. For simplicity, fig. 3 shows one of the plurality of waveguides 316 of the waveguide illuminator 300, and three out-coupling gratings 320 formed in the waveguide 316 and configured to couple out portions 322 of the beamlets 314 propagating in the waveguide 316.

A portion of the energy of beamlet 320 is coupled out as forward scattered light 333. This is because the impedance of the out-coupling gratings 320 does not match the impedance of the inter-grating regions or gaps 321 (the inter-grating regions or gaps being the portions of the waveguide 316 between the out-coupling gratings 320). Such light scattering may be undesirable because the scattered light may experience optical interference due to the coherent nature of the input beam 108. Optical interference can distort the desired pattern of outcoupling spots 122, resulting in undesirable and unpredictable local optical power density variations.

The scattering shown in fig. 3 may be reduced by matching the impedance of the out-coupling grating 320 with the impedance of the gap 321 between the out-coupling gratings 320. Impedance matching may be achieved in a variety of ways, as described in detail below.

Referring first to fig. 4A, waveguide illuminator 400A is an embodiment of waveguide illuminator 100 of fig. 1 and includes elements similar to those of waveguide illuminator 100. Specifically, waveguide illuminator 400A of fig. 4A includes an array of waveguides 416 (e.g., ridge waveguides) supported by substrate 401. The array of waveguides 416 receives beamlets 414 from a splitter (e.g., splitter 112 of waveguide illuminator 100 of fig. 1). Similar to waveguide illuminator 100 of fig. 1, an array of outcoupling gratings 420A (fig. 4A) for coupling out a two-dimensional array of portions 422 of beamlet 414 is coupled to the array of waveguides 416. Fig. 4A shows an enlarged view of one of the plurality of waveguides 416 and three out-coupling gratings 420A formed in the waveguide 416 and configured to couple out portions 422 of the beamlet 414 propagating in the waveguide 416.

The out-coupling grating 422A is apodized at opposite ends 431, 432 in the length direction of the waveguide 416 (i.e., left to right along the waveguide 416 in fig. 4). The grating coupler 422A is apodized on the duty cycle. The duty cycle is defined as the ratio of the width W of the grating grooves or stripes to the pitch P of the grating. For example, the duty cycle of each out-coupling grating 422A at the opposite ends 431, 432 of the out-coupling grating 422A may be less than 0.1 or greater than 0.9, and the duty cycle between the opposite ends 431, 432 of the out-coupling grating 422A may be greater than 0.1 and less than 0.9.

Turning to fig. 4B, waveguide illuminator 400B is similar to waveguide illuminator 400A of fig. 4A. The difference between waveguide illuminator 400B of fig. 4B and waveguide illuminator 400A of fig. 4A is that: in waveguide illuminator 400B of fig. 4B, out-coupling grating 422B is apodized at depth D instead of duty cycle W/P. As shown, the depth D of the out-coupling grating 422B varies along the corresponding waveguide 416, being minimal at opposite ends 431, 432 of the out-coupling grating 422B and maximal near or in the middle of the out-coupling grating 422B. In some embodiments, the out-coupling grating may be apodized over both the depth D and the duty cycle W/P.

Referring to fig. 5, waveguide illuminator 500 is an embodiment of waveguide illuminator 100 of fig. 1 and includes elements similar to those of waveguide illuminator 100. In particular, the waveguide illuminator 500 of fig. 5 includes an array of waveguides 516 (e.g., ridge waveguides) located on a substrate 501. The array of waveguides 516 receives sub-beams 516 from a splitter (e.g., splitter 112 of waveguide illuminator 100 of fig. 1). Similar to waveguide illuminator 100 of fig. 1, an array of outcoupling gratings 520 (fig. 5) for coupling out a two-dimensional array of portions 522 of beamlets 514 is coupled to the array of waveguides 516. Fig. 5 shows an enlarged view of one of the waveguides 516 and three out-coupling gratings 520 of a row of coupling gratings 520 formed in the waveguide 516 and configured to couple out portions 522 of the beamlet 514 propagating in the waveguide 516.

The out-coupling gratings 520 of each row include a grating etched to a grating etch depth D in the corresponding ridge waveguide 516 in the ridge waveguide array _Grating Is formed in the substrate. The gaps 521 between adjacent outcoupling gratings 520 of each row may be uniformly etched to a gap etch depth D _{Gap of} ＝aD _Grating Wherein 0 is<a<1. In other words, the gap 521 is etched uniformly to a depth D that is greater than the depth D of the grooves of the outcoupling grating _Grating Smaller depth D _{Gap of} . Etch depth D of gap 521 _{Gap of} Depending on the duty cycle of the out-coupling grating 520, and may be selected to match the impedance of the gap to the impedance of the out-coupling grating 520, thereby reducing forward scattering of the beamlets 514. In some embodiments, parameter a<0.5, i.e. gap etch depth D _{Gap of} Less than the grating etching depth D _Grating Half of (a) is provided.

Turning to fig. 6A, waveguide illuminator 600 is an embodiment of waveguide illuminator 100 of fig. 1 and includes similar elements. In particular, the waveguide illuminator 600 of fig. 6 includes an array of waveguides 616 (e.g., ridge waveguides) located on a substrate 601. The array of waveguides 616 receives beamlets 616 from a splitter (e.g., splitter 112 of waveguide illuminator 100 of fig. 1). Similar to waveguide illuminator 100 of fig. 1, an array of outcoupling gratings 620 (fig. 6A) for coupling out a two-dimensional array of portions 622 of beamlet 614 is formed in the array of waveguides 616. Fig. 6A shows an enlarged view of one of the waveguides 616 and three out-coupling gratings 620 of a row of coupling gratings 620 formed in the waveguide 616 and configured to couple out portions 622 of the beamlet 614 propagating in the waveguide 616.

The out-coupling gratings 620 of each row include trenches etched into the corresponding ridge waveguide 616 of the ridge waveguide array. The gaps 621 between adjacent outcoupling gratings 620 of each row include a gap grating 630. Gap grating 630 may have a sufficiently fine pitch to prevent diffraction of beamlet portion 622. The purpose of the gap grating 630 is to match the impedance of the gap to the impedance of the out-coupling grating 620, thereby reducing forward scattering of the beamlets 614. For example, pitch P of gap grating 630 _{Gap of} Can be equal to bP _Grating Wherein 0 is<b<0.5. In other words, the pitch of the gap grating 630 may be less than half the pitch of the out-coupling grating 620. Fig. 6B shows that gap grating 630 may have grooves that are angled with respect to coupling-out grating 620. The grooves of the gap grating 630 may not extend parallel to the waveguides 616 of the waveguide array.

Referring to fig. 7, a waveguide illuminator 700 is similar to the waveguide illuminator 600 of fig. 6A and 6B and includes similar elements, such as an array of waveguides 716 supported by a substrate 701, and an array of out-coupling gratings 720 coupled to the array of waveguides 716 (e.g., formed in the waveguides 716). The difference between waveguide illuminator 700 of fig. 7 and waveguide illuminator 600 of fig. 6A and 6B is that: in the waveguide illuminator 700 of fig. 7, the gap grooves 737 of the gap grating 730 extend parallel to the waveguide 716. This orientation of the gap trenches 737 ensures that light propagating in the waveguide 716 does not diffract on the gap grating 730. The purpose of the gap grating 730 is to reduce forward scatter.

Referring now to fig. 8 and with further reference to fig. 1, a display device 800 includes the waveguide illuminator 100 of fig. 1 or any other waveguide illuminator disclosed herein coupled to a display panel 802 (fig. 8). A light source 801 (e.g., a monochromatic light source and/or a polarized light source at the wavelength of the color channel) may be optically coupled to the illuminator 100, the light source being used to provide a light beam 108 to the illuminator 100. The display panel 802 includes an array of display pixels 820 that are arranged and configured to receive an array of coupled-out beamlet portions 122 from the illuminator 100. To ensure efficient use of beamlet portions 122, the pitch of display pixels 820 may be matched to the pitch of the array of outcouplers 120 in the X-direction and the Y-direction. For example, the pitch of the display pixels 820 may be equal to the pitch of the array of couplers 120, thereby enabling each beamlet section 122 to propagate through the corresponding display pixel 820.

The display panel 802 may include a Liquid Crystal (LC) layer 804 in which display pixels 820 are configured to controllably convert or tune the polarization states of the respective beamlet portions 122 (e.g., rotate the linear polarization states). In this embodiment, the light source 801 may be a polarized light source that emits linearly polarized light. The linear polarizer 828 may be arranged to convert the polarization distribution imparted by the display pixels 820 of the beamlet section 122 into an optical power density distribution representing an image to be displayed. The image is in the linear domain, which means that the pixel coordinates of the image being displayed correspond to the XY coordinates of the display pixel 820. Eyepiece 830 may be used to convert an image in the linear domain into an image in the angular domain at eyebox 826 for direct viewing by eye 880. Herein, the term "image in the angular domain" refers to such an image: the pixel coordinates of the image being displayed correspond to the ray angles of beamlet portion 122. In embodiments with a tunable polarization rotator, light source 801 may emit polarized light and waveguide illuminator 100 may maintain that polarization state. It is also noted that any of the waveguide illuminators disclosed herein may be used in place of waveguide illuminator 100 of display device 800. Waveguide illuminator 100 can be made transparent to external light 814.

Referring to FIG. 9 and with further reference to FIGS. 1 and 3, a method 900 for reducing light scattering in a waveguide illuminator (e.g., waveguide illuminator 100 of FIG. 1 or waveguide illuminator 300 of FIG. 3) includes matching an impedance of an out-coupling grating (e.g., out-coupling grating 120 (FIG. 1) in out-coupling grating row 119) to an impedance of a gap between out-coupling gratings (e.g., gap 321 (FIG. 3) in out-coupling grating 320 row) (FIG. 9; 901) to reduce an optical power of scattered light (e.g., forward scattered light 333).

Impedance matching 901 for reducing the amount of scattered light may be achieved using a variety of methods, either alone or in combination. In one embodiment, matching the impedance of the out-coupling gratings includes apodizing (902) the out-coupling gratings in the array of out-coupling gratings in a length direction of the corresponding waveguide such that a duty cycle of each out-coupling grating at opposite ends 431, 432 (fig. 4A) of the out-coupling grating 420A is less than 0.1 or greater than 0.9, and a duty cycle between the opposite ends 431, 432 of the out-coupling grating 420A is between 0.1 and 0.9; and/or each out-coupling grating 420B has an etch depth D at opposite ends 431, 432 of the out-coupling grating 420B that is less than the etch depth in the middle of the out-coupling grating 420B (fig. 4B). In embodiments in which the waveguide array comprises a ridge waveguide array and the array of out-coupling gratings may be formed in the ridge waveguide array by uniformly etching the ridge waveguides (e.g., waveguide illuminator 500 of FIG. 5), matching the impedance of the out-coupling gratings may comprise uniformly etching (FIG. 9; 904) gaps between adjacent out-coupling gratings of each row, the gap etch depth D _{Gap of} ＝aD _Grating Wherein 0 is<a<1 and D _Grating Is the grating etch depth. Matching the impedance may also include forming a gap grating (FIG. 9; 906) in the gap between adjacent out-coupling gratings, e.g., at least twice the pitch less than the pitch of the out-coupling gratings, as with gap grating 621 between out-coupling gratings 620 in waveguide illuminator 600 of FIGS. 6A and 6B. Matching the impedance may also include forming (FIG. 9; 908) a gap grating having grooves extending parallel to the ridge waveguides in the ridge waveguide array, as in, for example, waveguide illuminator 700 in FIG. 7.

Turning to fig. 10, a Virtual Reality (VR) near-eye display 1000 includes a frame 1001 that supports for each eye: a light source 1002; a waveguide illuminator 1006 operatively coupled to the light source 1002 and comprising any of the waveguide illuminators disclosed herein; a display panel 1018 comprising an array of display pixels, wherein the position of the out-coupling grating in the waveguide illuminator 1006 is coordinated with the position of the polarization tuning pixels of the display panel 1018; and an eyepiece 1032 for converting an image in the linear domain produced by display panel 1018 into an image in the angular domain for direct viewing at eyebox 1026. A plurality of eyebox illuminators 1062 (shown as black dots) may be disposed on a side of the waveguide illuminator 1006 facing the eyebox 1026. An eye tracking camera 1042 may be provided for each eye-ward 1026.

The purpose of eye tracking camera 1042 is to determine the position and/or orientation of the user's two eyes. The eyebox illuminator 1062 illuminates the eye at the corresponding eyebox 1026, allowing the eye tracking camera 1042 to obtain an image of the eye and provide a reference reflection, i.e., glint. Flicker may be used as a reference point in the acquired eye image to facilitate the determination of the eye gaze direction by determining the position of the eye pupil image relative to the flicker image. To avoid distracting the user's light from the eyebox illuminator 1062, the eyebox illuminator may be caused to emit light that is not visible to the user. For example, infrared light may be used to illuminate the eyebox 1026.

Referring now to fig. 11, hmd 1100 is an example of an AR/VR wearable display system that encloses a user's face in order to more immerse the user in an AR/VR environment. HMD 1100 may generate a fully virtual 3D image. HMD 1100 may include a front body 1102 and a strap 1104 that may be secured around the user's head. The front body 1102 is configured for placement in front of the eyes of a user in a reliable and comfortable manner. A display system 1180 may be provided in the front body 1102 for presenting AR/VR images to a user. The display system 1180 may include any of the display devices and illuminators disclosed herein. The side 1106 of the front body 1102 may be opaque or transparent.

In some embodiments, the front body 1102 includes a locator 1108, an inertial measurement unit (inertial measurement unit, IMU) 1110 for tracking acceleration of the HMD 1100, and a position sensor 1112 for tracking a position of the HMD 1100. The IMU 1100 is an electronic device that generates data representing a position of the HMD 1100 based on received measurement signals from one or more of the plurality of sensors 1112, wherein the one or more position sensors generate one or more measurement signals in response to movement of the HMD 1100. Examples of the position sensor 1112 include: one or more accelerometers, one or more gyroscopes, one or more magnetometers, other suitable types of sensors that detect motion, a type of sensor for error correction of the IMU 1110, or some combination thereof. The position sensor 1112 may be located external to the IMU 1110, internal to the IMU 1110, or some combination thereof.

The locator 1108 is tracked by an external imaging device of the virtual reality system so that the virtual reality system can track the position and orientation of the entire HMD 1100. The information generated by the IMU 1110 and the position sensor 1112 may be compared to the position and orientation obtained by the tracking locator 1108 to improve the tracking accuracy of the position and orientation of the HMD 1100. As the user moves and rotates in 3D space, the exact position and orientation is important for presenting the user with the proper virtual scene.

The HMD 1100 may also include a depth camera assembly (depth camera assembly, DCA) 1111 that collects data describing depth information of a local area surrounding part or all of the HMD 1100. The depth information may be compared to information from IMU 1110 in order to more accurately determine the position and orientation of HMD 1100 in 3D space.

HMD 1100 may also include an eye-tracking system 1114 for determining the orientation and position of a user's eyes in real-time. The acquired position and orientation of the eyes also allows the HMD 1100 to determine the gaze direction of the user and adjust the image generated by the display system 1180 accordingly. The determined gaze direction and vergence angle may be used to adjust the display system 1180 to reduce vergence adjustment conflicts. As disclosed herein, the direction and vergence may also be used for exit pupil steering of the display. Further, the determined vergence angle and gaze angle may be used to interact with a user, highlight an object, bring an object to the foreground, create additional objects or pointers, and so forth. An audio system may also be provided, including, for example, a set of small speakers built into the front body 1102.

Embodiments of the present disclosure may include or be implemented in conjunction with an artificial reality system. The artificial reality system adjusts sensory information (e.g., visual information, audio, touch (somatosensory) information, acceleration, balance, etc.) about the outside world obtained through the sense of sense in some way, and then presents to the user. As non-limiting examples, artificial reality may include Virtual Reality (VR), augmented Reality (AR), mixed Reality (MR), mixed reality (hybrid reality), or some combination and/or derivative thereof. The artificial reality content may include entirely generated content, or generated content combined with collected (e.g., real world) content. The artificial reality content may include video, audio, physical or tactile feedback, or some combination thereof. Any of these content may be presented in a single channel or in multiple channels (e.g., in stereoscopic video that produces a three-dimensional effect to the viewer). Further, in some embodiments, the artificial reality may also be associated with applications, products, accessories, services, or some combination thereof, for creating content in the artificial reality and/or otherwise for use in the artificial reality (e.g., performing an activity in the artificial reality), for example. The artificial reality system providing artificial reality content may be implemented on a variety of platforms including a wearable display (e.g., an HMD connected to a host computer system), a stand-alone HMD, a near-eye display with a form factor of glasses, a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers.

The scope of the present disclosure is not limited by the specific embodiments described herein. Indeed, various other embodiments and modifications in addition to those described herein will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Accordingly, such other embodiments and modifications are intended to fall within the scope of this disclosure. Furthermore, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that the usefulness of the present disclosure is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Therefore, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.

Claims (20)

1. A waveguide illuminator, the waveguide illuminator comprising:

an input waveguide for guiding an input light beam therein;

a waveguide splitter coupled to the input waveguide, the waveguide splitter for splitting the input optical beam into a plurality of sub-beams;

a waveguide array coupled to the waveguide splitter, the waveguide array for propagating the plurality of beamlets in the waveguide array, a plurality of waveguides in the waveguide array extending parallel to each other, each waveguide configured to guide one of the plurality of beamlets; and

An out-coupling grating array comprising a plurality of rows of out-coupling gratings, each row being coupled to a corresponding waveguide in the waveguide array along a length of the corresponding waveguide, wherein the plurality of out-coupling gratings of each row are configured to couple out portions of a beamlet propagating in the corresponding waveguide such that, in operation, a two-dimensional array of portions of beamlets is coupled out of the waveguide array.

2. The waveguide illuminator of claim 1, wherein the plurality of out-coupling gratings of each row of the out-coupling grating array have progressively increasing out-coupling efficiency with distance from the waveguide splitter for flattening the spatial distribution of optical power of the two-dimensional array of portions of the sub-beams that are coupled out.

3. The waveguide illuminator of claim 1 or 2, wherein the out-coupling gratings in the out-coupling grating array are apodized in a length direction of the corresponding waveguide such that there is at least one of:

the duty cycle of each out-coupling grating at opposite ends of the out-coupling grating is less than 0.1 or greater than 0.9, and the duty cycle between the opposite ends of the out-coupling grating is greater than 0.1 and less than 0.9; or alternatively

The depth of the grooves of each out-coupling grating is smaller at opposite ends of the out-coupling grating than at the middle of the out-coupling grating.

4. The waveguide illuminator according to any preceding claim, wherein,

the waveguide array comprises a ridge waveguide array;

the out-coupling grating array is formed in the ridge waveguide array;

the out-coupling gratings of each row include a grating etched to a grating etch depth D in a corresponding ridge waveguide in the array of ridge waveguides _Grating Is a groove of (a); and is also provided with

The gaps between adjacent outcoupled gratings of each row are uniformly etched to a gap etch depth D _{Gap of} ＝aD _Grating Wherein 0 is<a<1。

5. The waveguide illuminator of claim 4, wherein a <0.5.

6. The waveguide illuminator according to any one of claims 1 to 3,

the waveguide array comprises a ridge waveguide array;

the out-coupling grating array is formed in the ridge waveguide array;

the out-coupling gratings of each row are included in corresponding ones of the array of ridge waveguides at a grating pitch P _Grating A groove is arranged; and is also provided with

The gaps between adjacent outcoupling gratings of each row comprise gap gratings.

7. The waveguide illuminator of claim 6, wherein the gap grating comprises a gap pitch P extending non-parallel to waveguides in the waveguide array _{Gap of} ＝bP _Grating A groove is provided, wherein 0<b<0.5。

8. The waveguide illuminator of claim 6, wherein the gap grating comprises grooves extending parallel to waveguides in the waveguide array.

9. A display device, the display device comprising:

a waveguide illuminator, the waveguide illuminator comprising:

an input waveguide for guiding an input light beam therein;

a waveguide splitter coupled to the input waveguide, the waveguide splitter for splitting the input optical beam into a plurality of sub-beams;

a waveguide array coupled to the waveguide splitter, the waveguide array for propagating the plurality of beamlets in the waveguide array, a plurality of waveguides in the waveguide array extending parallel to each other, each waveguide configured to guide one of the plurality of beamlets; and

a coupling-out grating array comprising a plurality of rows of coupling-out gratings, each row being coupled to a corresponding waveguide in the waveguide array along a length of the corresponding waveguide, wherein the plurality of coupling-out gratings of each row are configured to couple out a plurality of portions of beamlets propagating in the corresponding waveguide, such that in operation a two-dimensional array of portions of beamlets is coupled out of the waveguide array; and

A display panel comprising an array of display pixels arranged and configured to receive a two-dimensional array of coupled-out portions of the beamlets.

10. The display device of claim 9, wherein the plurality of out-gratings of each row in the out-grating array have an increasing out-efficiency with distance from the waveguide splitter for flattening the spatial distribution of optical power of the two-dimensional array of coupled-out portions of the beamlets.

11. The display device of claim 9 or 10, wherein the out-coupling gratings in the out-coupling grating array are apodized in a length direction of the waveguides in the waveguide array to reduce light scattering through the out-coupling grating array.

12. The display device of any one of claims 9 to 11, wherein a pitch of the display pixels is substantially equal to a pitch of the out-coupling grating array.

13. The display device of any one of claims 9 to 12, further comprising a light source for providing the input light beam to the input waveguide.

14. The display device of claim 13, wherein the light source is a polarized light source, wherein the input light beam and the portion of the sub-beams that are coupled out are polarized; and is also provided with

Wherein the array of display pixels comprises an array of tunable polarization rotators for tuning the polarization of portions of the respective beamlets.

15. The display device of claim 13, wherein the light source comprises a monochromatic light source, wherein the input light beam has a wavelength of a first color channel.

16. A method for reducing light scattering in a waveguide illuminator, the waveguide illuminator comprising: a waveguide splitter for splitting an input optical beam into a plurality of sub-beams; a waveguide array coupled to the waveguide splitter, the waveguide array for propagating the plurality of beamlets in the waveguide array, each waveguide configured to guide one beamlet of the plurality of beamlets; and an out-coupling grating array comprising a plurality of rows of out-coupling gratings formed in a corresponding waveguide for coupling out portions of beamlets propagating in the corresponding waveguide, the method comprising:

the impedance of a plurality of out-coupling gratings in a row of out-coupling gratings is matched to the impedance of the gaps between the plurality of out-coupling gratings in the row of out-coupling gratings.

17. The method of claim 16, wherein matching the impedance of the plurality of out-coupling gratings comprises apodizing the out-coupling gratings in the array of out-coupling gratings in a length direction of the corresponding waveguide such that a duty cycle of each out-coupling grating at opposite ends of the out-coupling grating is less than 0.1 or greater than 0.9 and a duty cycle between the opposite ends of the out-coupling grating is between 0.1 and 0.9.

18. The method of claim 16, wherein the waveguide array comprises a ridge waveguide array and the grating etching depth D is achieved by etching the ridge waveguide to _Grating And forming said out-coupling grating array in said ridge waveguide array; and is also provided with

Wherein matching the impedance of the plurality of out-coupling gratings comprises uniformly etching gaps between adjacent out-coupling gratings of each row to a gap etch depth D _{Gap of} ＝aD _Grating Wherein 0 is<a<1。

19. The method of claim 16, wherein the waveguide array comprises a ridge waveguide array and the out-coupling grating array is formed in the ridge waveguide array; and is also provided with

Wherein matching the impedance of the plurality of out-coupling gratings comprises forming a gap grating in the gap between adjacent out-coupling gratings at a pitch that is at least twice smaller than the pitch of the out-coupling gratings.

20. The method of claim 16, wherein the waveguide array comprises a ridge waveguide array and the out-coupling grating array is formed in the ridge waveguide array; and is also provided with

Wherein matching the impedance of the plurality of out-coupling gratings comprises forming a gap grating in a gap between adjacent out-coupling gratings, the gap grating comprising grooves extending parallel to ridge waveguides in the ridge waveguide array.