transmitter array

Abstract

In a light emitter device, when point emitters are placed on a focal plane of a lens system, each point emitter will point to a specific free space angle depending on its position relative to a longitudinal center axis of the lens system. A plurality of point emitters is arranged in an array comprising a plurality of rows of point emitters and a plurality of columns of point emitters. Each of the plurality of point emitters comprises a grating coupler configured to emit a respective light beam in a respective transmission direction. Each grating coupler comprises a plurality of periodically spaced first optical waveguide grating structures, at least some of the optical waveguide grating structures comprising a notch, whereby a first portion of each optical waveguide grating structure extends to a different height compared to a second portion.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a transmitter array, and in particular to a transmitter array for a LIDAR system. BACKGROUND

[0002] Conventional integrated optical phased arrays emit and receive light beams at various controllable angles for various applications including free-space communications, holography, and light detection and ranging (LIDAR), among others. LIDAR sensors are optical remote sensors that measure distance to a target by illuminating the target with a pulse or modulated signal from a laser and measuring the time taken for the light to return to a receiver of the LIDAR sensor. When a reflected pulse or modulated signal is detected, the time of flight of the pulse or modulated signal corresponds to the distance to the sensed target. LIDAR sensors are important components in autonomous vehicles, drone navigation systems, and robot interactions, but are currently costly and relatively large.

[0003] Conventional approaches to achieve large-aperture on-chip non-mechanical beam steering, such as phased arrays, can have one or more of the following problems: 1) high power consumption, 2) limited to one-dimensional steering, 3) complex beamforming algorithms, and 4) stringent requirements on manufacturing process uniformity.

[0004] To overcome some of the above problems, a one- or two-dimensional array of point emitters is arranged on a chip. As described in WO2020 / 0506307, entitled “Beam Steering and Receiving Method Based on an Optical Switch Array,” published on March 19, 2020, incorporated herein by reference, when a point emitter is placed on the focal plane of a lens system, depending on the position of the point emitter relative to the longitudinal center axis of the lens system, the individual point emitter will point to a specific free-space angle. However, point emitters that can be manufactured at commercially available silicon photonics foundries are typically grating couplers, which can have one or more of the following problems: 1) low emission efficiency, 2) non-uniformity of the manufacturing process, 3) strong wavelength dependence, and 4) inability to utilize light polarization to achieve a low-loss monostatic system. SUMMARY

[0005] Accordingly, the present disclosure relates to an optical transmitter device comprising:

[0006] a plurality of point emitters arranged in an array comprising a plurality of rows of point emitters and a plurality of columns of point emitters, each of the plurality of point emitters comprising:

[0007] grating coupler configured to emit a respective light beam in a respective transmission direction;

[0008] Each grating coupler comprises a plurality of periodically spaced first optical waveguide grating structures, at least some of the optical waveguide grating structures comprising a gap, whereby a first portion of each optical waveguide grating structure extends to a different height compared to a second portion. BRIEF DESCRIPTION OF DRAWINGS

[0009] The present application will be explained in more detail with reference to the drawings representing preferred embodiments of the application, in which:

[0010] Figure 1 is a side view of a light emitter device according to an embodiment of the present disclosure;

[0011] Figure 2 is a side view of a light emitter device according to an embodiment of the present disclosure; Figure 1 is a plan view of a portion of the emitter array of the device of

[0012] Figure 3A is a plan view of a portion of the emitter array of the device of Figure 2

[0013] Figure 3B is an end view of a portion of the emitter array of the device of Figure 3A

[0014] Figure 3C is a cross-sectional view of a portion of the emitter array of the device of Figure 3A

[0015] Figure 3D is a cross-sectional view of a portion of the emitter array of the device of Figure 3A

[0016] Figure 4A is a plan view of a portion of another embodiment of the emitter array of the device of Figure 2

[0017] Figure 4B is an end view of a portion of the emitter array of the device of Figure 4A

[0018] Figure 4C is a cross-sectional view of a portion of the emitter array of the device of Figure 4A

[0019] Figure 4D is a cross-sectional view of a portion of the emitter array of the device of Figure 4A

[0020] Figure 5 ​​​​​​​​It has a steering base plate Figure 2 A cross-sectional view of the point emitter in the transmitter array;

[0021] Figure 6 yes Figure 5 A top view of the point emitter;

[0022] Figure 7 yes Figure 2 A cross-sectional view of another embodiment of the point transmitter of the transmitter array;

[0023] Figure 8 yes Figure 7 A top view of the point emitter;

[0024] Figure 9A It is used for Figure 1 A side view of an exemplary embodiment of the steering substrate of the light emitter device;

[0025] Figure 9B yes Figure 9A Top view of the steering base plate;

[0026] Figure 9C yes Figure 9A A bottom view of the steering base plate;

[0027] Figure 10 yes Figure 1 A plan view of another embodiment of the transmitter array of the device;

[0028] Figure 11A yes Figure 10 A cross-sectional view of an implementation scheme for a point transmitter in a transmitter array;

[0029] Figure 11B yes Figure 11A A top view of the point emitter;

[0030] Figure 12A yes Figure 10 A cross-sectional view of an implementation scheme for a point emitter in a transmitter array; and

[0031] Figure 12B yes Figure 12A A top view of the point emitter. Detailed Implementation

[0032] While this teaching has been illustrated with various embodiments and examples, it is not intended to limit this teaching to these embodiments. Rather, as those skilled in the art will understand, this teaching encompasses various alternatives and equivalents.

[0033] Long-range LiDAR systems rely on the efficient transmission and reception of highly focused or collimated beams at different angles. While lenses are typically associated with imaging, they can also be used for beamforming and beam steering. (See reference...) Figure 1 The light emitter device 1 includes an emitter array 2 and a beam steering lens system 3. For beamforming, when the point emitter 5 from the emitter array 2... 11 Up to 5 nm When placed on the focal plane F of the lens system 3, it can emit a highly collimated output beam 4. o (Infinite conjugate). Based on the reciprocity theorem, the same applies to backpropagation, thus the parallel input beam 4 illuminating the lens system 3. i Focus will be placed on point-and-shoot transmitter 5 11 Up to 5 nm At one of the captured light spots, there is a slight spread limited by lens aberrations and diffraction. For beam steering, the shaped (e.g., substantially collimated or focused) far-field beam angle α depends on the point emitter 5 11 Up to 5 nm The output beam 4 is positioned on the focal plane F relative to the longitudinal central optical axis OA of the lens system 3. o The beam angle α is determined by the following equation: α = arctan(d / f), where d is the distance from the center of the focal plane (i.e., the point where the optical axis OA coincides with the focal plane F), and f is the focal length of lens system 3. Therefore, by using point emitter 5... 11 Up to 5 nm The transmitter array 2 is placed on or near the focal plane F of the lens system 3, and then the point transmitters 5 are selectively turned on and off. 11 Up to 5 nm To enable one or more output beams 4 o A full LIDIA system is achieved by steering in the desired direction at the desired beam angle α. This method differs fundamentally from optical phased arrays because it does not require controlling the relative optical phase between transmitters and only requires activating one point transmitter at a time. 11 Up to 5 nm In addition, multiple point emitters can be activated simultaneously. 11 Up to 5 nm To transmit in different directions (i.e., with different beam angles α) 11 To α nm ) has multiple output beams 40.

[0034] As described below, the transmitter array 2 may include: for supporting point transmitters 5 11 Up to 5 nmThe optical waveguide structure 8 includes a main substrate 7 and an upper steering substrate 9 for supporting beam-directing and / or beam-shaping elements. Ideally, the point emitter 5... 11 Up to 5 nm Arranged to include multiple (n) rows of point emitters 5 11 Up to 5 nm and multiple (m) column point transmitters 5 11 Up to 5 nm Point launcher 5 11 Up to 5 nm An array of point emitters. Typically, point emitters in rows are aligned, and point emitters in columns are aligned, but the rows and / or columns of point emitters can be offset. Point emitters 51 to 5... n There are many methods, including end-fire cones, end-fire cones with steering mirrors, single-layer grating couplers, and double-layer grating couplers.

[0035] The design of lens system 3 is critical to the system's performance. Lens system 3 may include multiple lens elements if desired. Much of the design of lens system 3 involves trade-offs between F-number, field of view, and aperture size. However, several design priorities are possible: for example, a) a design with a telecentric image plane, where the image space originates from point emitter 5. 11 Up to 5 nm a) The principal rays are all parallel to the optical axis OA; b) the diffraction limit is reached across the entire field of view; and c) the image spatial numerical aperture (NA) of lens system 3 is essentially matched to that of point emitter 5. 11 Up to 5 nm The NA. The principal ray parallel to the optical axis OA will cause the point emitter 5 11 Up to 5 nm Designed to be perfectly vertical. Minimizing lens curvature aberrations enables an output beamwidth of 4. o Minimum spread and receive input beam 4 i The best possible focus. Point emitter 5 11 Up to 5 nm Preferably, the output beam 4 is emitted at a beam angle α that can be completely captured by the lens system 3. o For example, if point emitter 5 11 Up to 5 nm If one or more of the NA values ​​in the lens system 3 are greater than the image space NA of the lens system 3, then the emission from the point emitter 5... 11 Up to 5 nm A portion of the emitted light will not pass through lens system 3, thus causing a loss.

[0036] Reference Figure 2 The light emitter device 1 may further include at least one light source, preferably an array of light sources, and at least one photodetector, preferably optically connected to a corresponding point emitter 5 of the emitter array 2.11 to 5 nm optical detector array. Preferably, the array of light sources and the array of light detectors comprise an array of transceivers 111 to 11 n . Each transceiver 111 to 11 n may comprise a laser generating at least one of the output beams 4 o and an optical detector detecting at least one of the input beams 4 i . The selective transmission of light to the point emitters 5 n to 5 11 and the selective reception of light from the point emitters 5 nm to 5 11 may be provided by a switching matrix 12 between the transceivers 111 to 11 nm and the array of emitters 2. Thus, in order to select a desired point emitter 5 11 to 5 nm corresponding to a desired beam angle a, the controller 13 can select one of the light sources in one of the transceivers 111 to 11 11 corresponding to one of the rows (e.g. 1 to n) of point emitters 5 nm to 5 n and then select one of the point emitters 5 11 to 5 nm in that row by opening and / or closing individual switches 14 in the switching matrix 12. For example, for 4 point emitters 5 11 to 5 nm in each row, the switching matrix 12 can have a single input port (e.g. a 2x2 on-chip Mach-Zehnder interferometer (MZI)) optically connected to a switch tree comprising (m-1 = 3) switches 14 which can be selectively activated to output the output beam 4 o to the desired output port. A plurality of optical waveguide cores 15 extend parallel to each other between the output ports of the switching matrix 12 to the point emitters 5 n to 5 11 . Each optical waveguide core 15 can comprise a curved portion, e.g. a 90° curve, at its end portion, each curved portion having a different radius of curvature configured to align to each point emitter 5 nm to 5 11 in a row. Each row of point emitters 5 nm to 5 11 may be aligned with other rows of columns of point emitters 5 nm to 5 11 forming the n x m emitter array 2 of point emitters 5 nm to 5 11 . Ideally, the point emitters 5 nm to 5The pitch of the point emitters 5

[0037] Pitch = Resolution / (2 * arctan(L / 2f)) * L

[0038] Similarly, when one of the incident beams 4 i is received at the same point emitter 5 n , the incident beam 4 i is back-transmitted through the corresponding optical waveguide core 15 to the switching matrix 12 back to the corresponding photodetector of the corresponding transceiver 11 n .

[0039] Referring to Figures 3A-4D , the point emitters 5 11 to 5 nm may each comprise an end-fire taper 21 in combination with a turning reflector 22 (e.g. a mirror) and optionally a microlens 23 (for more details, refer to Figure 5 and Figure 6 ). Unlike a grating coupler, the end-fire taper 21 enables uniform broadband transmission of light with all possible polarization states. The turning reflector 22 can be arranged in a cavity or trench 24 provided in the optical waveguide structure 8 to direct the light emitted from the end-fire taper 21 parallel to the optical axis OA of the lens system 3, e.g. vertically upwards from the upper surface of the emitter array 2 and perpendicular to the upper surface of the emitter array 2, which both enables a two-dimensional point emitter array 2 and a more simplified assembly process.

[0040] A single trench 24 can be provided for a plurality of point emitters, the ends of the plurality of end-fire tapers 21 located in the vicinity of the trench being directed into the trench. Ideally, one trench 24 is provided for an entire row of point emitters (e.g. 5 11 to 5 14 ); however, it is also possible that one trench 24 is provided for each point emitter (e.g. point emitter 5 34 ), or for a group (e.g. 2 or 3) of point emitters (e.g. point emitters 5 23 and 5 24 ). Each trench 24 is configured to receive one or more respective turning reflectors 22 aligned with the ends of the end-fire tapers 21, and can have a depth of between 2 pm and 150 pm, e.g. extending beyond the end-fire tapers, or preferably extending to the bottom of the optical waveguide structure 8 to the main substrate 7, and / or more preferably extending into the main substrate 7 (shown in dashed lines).

[0041] Furthermore, one trench 24 can be provided for a row of point emitters (e.g. 5 11 to 5 14) set of end-fire tapers 21 output beams 4 o ( and input beams 4 i ) are directed to the point emitters. Ideally, one steering reflector 22 is provided for the entire row of point emitters (e.g., 5 11 to 5 14 ); however, it is also possible to provide one steering reflector 22 for each point emitter (e.g., point emitter 5 34 ), or for a group (e.g., 2 or 3) of point emitters (e.g., point emitters 5 23 and 5 24 ). As described below with reference to Figures 9A to 9C , some or all of the steering reflectors 22 can be mounted on a steering substrate 9 Figure 3C and Figure 4C ), or mounted (e.g., deposited or etched) in the trench 24 Figure 3D and Figure 4D . The width and height of the steering reflectors 22 are about 5 pm to 100 pm, i.e., larger than the near-field mode size of the end-fire tapers 21 divided by cos(45°).

[0042] Figure 3A A top view of a portion of the point emitter array 2 with the steering substrate 9 removed is shown, i.e., showing a row of point emitters 5 11 to 5 14 . Four point emitters are shown; however, additional point emitters are also within the scope of the invention. Figure 3B A cross-sectional view of a portion of the emitter array 2 taken along section B-B is shown. Figure 3C and Figure 3D is taken along section C-C (i.e., the outer optical waveguide core 15 to the fourth point emitter 5 14) cross-sectional view of a transmitter array 2 with another turning reflector 22. The transmitter array 2 can include a lightguide structure 8 composed of one or more lightguide layers configured to form a lightguide core 15 and end-fire tapers 21 surrounded by cladding (i.e., a material with a lower refractive index). The lightguide core 15 and end-fire tapers 21 can be composed of silicon (Si) or silicon nitride (SiN) or both Si and SiN or any other suitable lightguide core material. The lightguide structure 8 can be mounted on an upper portion of a host substrate 7, for example, grown on an upper portion of the host substrate, with upper and lower cladding layers 32 and 33 surrounding the lightguide core 15 and end-fire tapers 21. The upper and lower cladding layers 32 and 33 can be composed of an oxide material such as silicon dioxide (SiO2), for example, 2-5 pm thick, and the host substrate 7 can be composed of silicon, quartz, or any suitable material. The length of at least some of the end-fire tapers 21 can be 100 pm to 400 pm and taper from the original width of the lightguide core 15 (e.g., 400 nm to 500 nm wide) by 200 nm to 250 nm thick, for example, by 25% to 75%, preferably by about 50%, down to a tip having a width of 50 nm to 300 nm and the original thickness (e.g., 200 nm to 250 nm), but the thickness can also taper to less than the lightguide core 15 if desired. Preferably, the end of the end-fire tapers 21 can be symmetrical, for example, square (200 nm x 200 nm). At least some of the end-fire tapers 21, for example, point transmitters 5 11 , can include a reverse taper that expands from the original dimensions (e.g., width) of the lightguide core 15 at least in width to a wider width, for example, 2x to lOx wider or 1 mm to 4 mm wide. The thickness can also expand if desired. The width of some of the end-fire tapers 21 can narrow while the width of some of the end-fire tapers 21 can widen. Some of the end-fire tapers 21 can be narrower than others or wider than others.

[0043] Upon transmission from the end of the end-fire taper 21, the guided light mode propagating in the feed lightguide core 15 expands. Mode expansion controls beam divergence and emission efficiency through the lens system 3. The minimum achievable NA for a bare silicon end-fire taper in, for example, air around the lens system 3 is about 0.38, which is difficult for the design of the lens system 3 because a portion of the output beam 4 i may expand beyond the NA of the lens system 3 and be lost. Alternatively, even if the lens system 3 has a high enough NA, optical aberrations that are typically present in high-NA lenses can degrade the performance of the LIDAR system. Aberration-free high-NA systems are typically expensive to manufacture and sensitive to misalignment and environmental disturbances such as shock and temperature.

[0044] Figure 4AA partial top view of another embodiment of the dot emitter array 2 with the steering substrate 9 removed is shown, specifically, a row of dot emitters 5 is shown. 11 Up to 5 14 . Figure 4B A cross-sectional view of a portion of the transmitter array 2 taken along section BB is shown. Figure 4C and Figure 4D It is along the section CC (i.e., from the outer double-layer waveguide core 15' to the fourth point transmitter 5) 14 The image shows a cross-sectional view of the transmitter array 2 with another deflector 22. The transmitter array 2 may include an optical waveguide structure 8, which consists of two optical waveguide layers configured to form a double-layered waveguide core 15' and a double-layered end-cone 21'. The inclusion of the second waveguide layer enables mode profile engineering, which also allows for a change in the NA of the transmitter array 2; that is, emitting light into a coupled mode with a wider mode spread results in a smaller NA. The double-layered waveguide core 15' and the double-layered end-cone 21' may be made of two similar waveguide materials with similar refractive indices, such as silicon (Si) or silicon nitride (SiN), or two different waveguide materials with different refractive indices (e.g., a first refractive index (e.g., Si) greater than a second refractive index (e.g., SiN)), or any other suitable waveguide core material. The waveguide layer can be mounted on the upper part of the main substrate 7, for example, grown on the upper part of the main substrate, wherein the upper and lower cladding layers 32 and 33 surround the dual-waveguide core 15' and the end-emitting taper 21'. The upper and lower cladding layers 32 and 33 can be made of oxide materials, such as silicon dioxide (SiO2), for example, 2 μm thick, and the main substrate 7 can be made of silicon or any suitable material.

[0045] Figure 5 and Figure 6 Cross-sectional and top views are shown, respectively, of the steering reflector 22 and optional microlens 23 (if desired) combined with end-projection cone 21 or double-ended projection cone 21'. The steering reflector 22 can be formed (e.g., etched) from a separate (e.g., silicon or quartz) steering substrate 9, having angled wall corners, for example, at 45° to the longitudinal axis of the end-projection cone 21 defining the transmission direction, and can be coated or configured with a reflective layer or coating 42, such as silver, copper, aluminum, gold, or Bragg grating. If the steering reflector 22 has a sufficiently high refractive index n... reflector For example, silicon, and trench 24 has a sufficiently low refractive index r. reflector For example, air, making beam 4 o Most of them are greater than the critical angle arcsin(n reflector / n trench If the angle of impact on the inclined wall is such that coating 42 can be omitted, and beam 4o The turning reflector 22 can be reflective by total internal reflection. The flat vertical sidewalls of the end-fire cones 21 or 21' facing the turning reflector 22 can be coated with an anti-reflective (AR) coating 43 to minimize Fresnel reflections therefrom. Similarly, the top surface of the micro-lens 23 or the turning substrate 9 can be coated with an AR coating. The output beams 40 from the end-fire cones 21 or 21' adjacent to the trench 24 o pass through the air gap to expand, for example, 1 pm to 10 pm, and pass through the vertical sidewalls, i.e., the AR coating 43, and then impinge on and reflect off of the tilted reflective layer or coating 42 which re- orients the optical path substantially perpendicular to the original transmission direction in the end-fire cone 21 and the upper surface of the point emitter array 2 upward. The emission pattern of each output beam 40 (and input beam 4 i ) can then be reshaped, e.g., collimated or focused, by the corresponding micro-lens 23. The goal of the micro-lens 23 is to convert the NA of the point emitters to a smaller value, e.g., less than 0.2, and preferably less than 0.15 for more practical lens designs. The diameter of each micro-lens 23 can be 25 pm to 200 pm. Each turning reflector 22 can have an edge with a length between 6 pm to 90 pm. The gap and / or trench 24 can include a refractive index matching material, e.g., a material with a refractive index between the effective refractive index of the mode of the end-fire cone 21 and the refractive index of the turning reflector 22, between the end-fire cone 21 and the gap and / or between the gap and the turning reflector 22 to at least reduce back reflections at the interfaces.

[0046] Referring to Figure 7 and Figure 8 , to further reduce the NA of the point emitters 5 11 to 5 nm , a suspended optical waveguide structure 50 can be provided which is optically connected to the end of some or each end-fire cone 21 or 21'. The suspended optical waveguide structure 50 can be composed of a cladding material (e.g., Si02) which now forms the core of the optical waveguide which is surrounded by a pocket (e.g., air) of a material with a lower refractive index which forms the cladding. The suspended optical waveguide structure 50 can be suspended above the main substrate 7 by removing (e.g., etching) the cladding material from the one or more substrate materials of the main substrate 7 and / or the turning substrate 9 and / or from the upper and lower cladding layers 32 and 33 which form the pocket or chamber 51 around the suspended optical waveguide structure 50 below and / or around the suspended optical waveguide structure 50. Ideally, each trench 24 can be enlarged to extend below and / or around the suspended optical waveguide structure 50 to form the pocket or chamber 51. As shown in Figure 8 , the turning substrate 9 can also be etched in selected areas above the suspended waveguide structure 50 to form channels 52 Figure 9C), so that the optical mode of the overhanging optical waveguide structure 50 does not leak into the host substrate 7 and / or the turning substrate 9. Thus, the NA of the overhanging waveguide structure 50 / end-fire taper 21 or 21'can be reduced to less than about 0.25, preferably less than 0.2, so that the microlens 23 is able to convert the NA of the point emitter to less than 0.20, preferably less than 0.15. The overhanging optical waveguide structure 50 can extend 2 pm to 50 pm into the chamber 51 or trench 24, while the end-fire taper 21 or 21'can extend slightly into the chamber 51 or trench 24, but less than the full length of the overhanging optical waveguide structure 50. The overhanging optical waveguide structure 50 can have a thickness of, for example, 6 pm to 8 pm, the same as the entire optical waveguide structure 8, or can be made thinner than the optical waveguide structure by locally removing some of the upper cladding layer 32. The overhanging optical waveguide structure 50 can have a constant width, approximately the same as the thickness, for example, 6 pm to 8 pm. The overhanging optical waveguide structure 50 can taper, i.e., narrow in width and / or height, towards its outer free end (dashed line), or can taper in reverse, i.e., widen in width and / or height, towards its outer free end. Ideally, the end-fire taper 21 is centered vertically and horizontally within the waveguide structure 50.

[0047] Further, in some or all of the above embodiments, the turning reflector 22 can include an integrated curved reflective surface 53 on or forming its tilted surface to further reduce the NA of the point emitter 5 11 to 5 nm . For example, a spherical, conical or aspherical surface with a radius of curvature of, for example, 0.1 mm to 1.0 mm can be provided (e.g., etched or deposited) on the tilted surface of the turning reflector 22. In embodiments with or without the curved reflective surface 53, the microlens 23 can not be needed and can be omitted.

[0048] Referring to Figures 9A to 9C , the turning reflector 22 and the microlens 23 can be fabricated on the same turning substrate 9, whereby multiple turning reflectors 22 and multiple microlenses 23 can be configured on the same turning substrate 9, which can then be bonded to the upper portion of the photonic chip including the emitter array 2. Thus, the reflective layer or coating 42, the AR coating 43 and the AR coating on the respective microlenses 23 can be provided (e.g., coated) onto the corresponding features of the turning substrate 9 in a manufacturing process separate from the manufacturing of the optical waveguide structure 8. Further, the multiple turning reflectors 22 can comprise a single monolithic structure extending the length of the turning substrate 9 for reflecting the multiple output beams 4 14 from the point emitters (e.g., 5 24 , 5 34 , 5 44 and 5 n4 ) in a column of the emitter array 2. oand reflect the input beam 41 to a point transmitter (e.g. 5 14 , 5 24 , 5 34 , 5 44 , and 5 n4 ) in a column of the transmitter array 2.

[0049] In another embodiment, illustrated in Figure 10 , Figure 11A and Figure 11B , the light transmitter device 101 comprises a transmitter array 102 and a beam steering lens system 3. As described above with reference to Figure 1 , for beam shaping, when the point transmitters 5 11 to 5 nm from the transmitter array 102 are placed on or near the focal plane F of the lens system 3, highly focused or collimated output light beams 4 o (infinite conjugate) can be emitted. Based on the reciprocity theorem, the reverse is also true, where a parallel beam 4i impinging on the lens system 3 will be focused at a point with a slight spread limited by lens aberrations and diffraction. In addition to the point transmitters 5 11 to 5 nmA very small grating coupler 81 (length and width of about a few pm) can be included that is connected to the feed optical waveguide core 15, which can be provided (e.g., fabricated) entirely in a silicon layer on a silicon-on-insulator (SOI) wafer, in addition to all other features of the light emitter device 101 being similar to the light emitter device 1, e.g., the main substrate 7 for supporting the optical waveguide structure 8. The grating coupler 81 can include an expansion optical waveguide section 82 and a corrugated grating section 83 that includes periodically spaced optical waveguide grating structures 84 that extend laterally (i.e., perpendicular to the direction of transmission), with a gap 85 that extends partially through the optical waveguide grating structures 84. The grating section 83 can include a width that is as wide as the wider outer end of the expansion optical waveguide section 82. The gap in the optical waveguide grating structures 84 can form a step, so that a first portion of each optical waveguide grating structure 84 extends a different depth in the grating section 83 than a second portion of each optical waveguide grating structure 84. For example, the first portion can be the entire thickness of the grating section 83, which can have the same thickness as the expansion optical waveguide section 82, which can have the same thickness as the optical waveguide core 15. The second portion can extend only partially (e.g., 40% to 60%) through the grating section 83. The corrugated grating coupler 81 can add additional momentum to the incident waveguide mode, which then connects to a free-space emission. The pitch and depth of the optical waveguide grating structures 84 can be configured so that a) the emission angle is as close to normal, i.e., perpendicular to the original direction of transmission and the upper surface of the emitter array 2, as possible, and b) the grating coupler strength is strong enough to emit almost all of the light. Ideally, the grating coupler 81 has a thickness of 50 nm to 500 nm, a length of 5 pm to 20 pm, and a width of 5 pm to 20 pm, and a grating period of 0.5 pm to 1 pm.

[0050] In Figure 12A and Figure 12B Another embodiment is shown in FIGS. 1A-1C, where the point emitters 5 11 to 5 nmA very small grating coupler 91 (length and width of about a few pm, e.g. 2-5 pm) can be included, which is connected to the feed optical waveguide core 15, which can be entirely provided (e.g. fabricated) in a silicon layer on a silicon-on-insulator (SOI) wafer. The grating coupler 91 can include an extended optical waveguide section 92 and a corrugated grating section 93, which includes periodically spaced optical waveguide grating structures 94 extending laterally (i.e. perpendicular to the transmission direction), with a gap 95 partially extending through the optical waveguide grating structures 94. The grating section 93 can include the same width as the wider outer end of the extended optical waveguide section 92. The grating section 93 can be composed of a double layer structure, which includes a bottom layer 96 of a first optical waveguide material (e.g. silicon) and a top layer 97 of a different material (which has a lower refractive index than the first material, e.g. silicon nitride (SiN)), which is entirely surrounded by the upper and lower cladding layers 32 and 33 (e.g. silicon dioxide). The gap 95 in the optical waveguide grating structures 94 in the bottom layer 96 can form a step, so that a first portion of each optical waveguide grating structure 94 extends a different depth in the grating section 93 than a second portion of each optical waveguide grating structure 94. For example, the first portion can be the entire thickness of the grating section 93, which can have the same thickness as the extended optical waveguide section 92, which can have the same thickness as the optical waveguide core 15. The second portion of the optical waveguide grating structures 94 can extend partially (e.g. 40-60%) through the grating section 93. The bottom layer 96 and the top layer 97 of the grating section 93 can have a translational offset, i.e. are laterally offset from each other, so that the grating structures in the top layer 97 spatially overlap, i.e. are superimposed on, the optical waveguide grating structures 94 in the bottom layer 96, and the spaces in the top layer 97 overlap the optical waveguide grating structures 94 in the bottom layer 96. This offset breaks the symmetry of the grating coupler 91 in the emission direction. Ideally, the grating coupler 91 has a length of 5-20 pm and a width of 5-20 pm, and a grating period of 0.5-1 pm. The pitch and depth of the optical waveguide grating structures 94 can be configured so that a) the emission angle is as close to normal, i.e. perpendicular to the original transmission direction and the upper surface of the emitter array 2, as possible, and b) the grating coupler strength is strong enough to emit almost all light. Preferably, the thickness of the top layer 97 (e.g. SiN) is 0.05-0.5 pm, the spacing between the bottom layer 96 and the top layer 97 is between 0-0.2 pm, preferably 0.05-0.2 pm. An example offset between the grating material in the bottom layer 96 and the top layer 97 is between 0-0.5 pm, preferably 0.01-0.05 pm.

[0051] The foregoing description of one or more implementations of the application has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the application to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the application be limited not by this detailed description, but rather by the claims appended hereto.

Claims

1. A light emitter device comprising: a plurality of point emitters arranged in an array comprising a plurality of rows of point emitters and a plurality of columns of point emitters, each of the plurality of point emitters comprising: a grating coupler configured to receive light along a transmission direction and emit a respective light beam in an emission direction; each grating coupler comprising: a plurality of periodically spaced first optical waveguide grating structures forming a directional grating for asymmetrically emitting light in the emission direction, at least some of the plurality of periodically spaced first optical waveguide grating structures comprising a gap, whereby a first portion of each of the plurality of periodically spaced first optical waveguide grating structures extends a different height compared to a second portion; and 2. The optical transmitter apparatus of claim 1, wherein, a plurality of periodically spaced second optical waveguide grating structures superimposed over the plurality of periodically spaced first optical waveguide grating structures, the plurality of periodically spaced second optical waveguide grating structures being spaced apart from the directional grating in the emission direction.

3. The optical transmitter apparatus of claim 2, wherein, the plurality of periodically spaced second optical waveguide grating structures are laterally offset from the plurality of periodically spaced first optical waveguide grating structures.

4. The optical transmitter apparatus of claim 1, wherein, the plurality of periodically spaced second optical waveguide grating structures are laterally offset from the plurality of periodically spaced first optical waveguide grating structures by 0.1 pm to 0.5 pm.

5. The optical transmitter apparatus of claim 1, wherein, the plurality of periodically spaced second optical waveguide grating structures are composed of a different material than the plurality of periodically spaced first optical waveguide grating structures.

6. The optical transmitter apparatus of claim 5, wherein, the plurality of periodically spaced second optical waveguide grating structures are composed of a different material having a lower refractive index than the plurality of periodically spaced first optical waveguide grating structures.

7. The optical transmitter apparatus of claim 1, wherein, the plurality of periodically spaced second optical waveguide grating structures are composed of silicon nitride and the plurality of periodically spaced first optical waveguide grating structures are composed of silicon.

8. The optical transmitter apparatus of claim 1, wherein, the plurality of periodically spaced second optical waveguide grating structures are 0.05 pm to 0.5 pm thick.

9. The optical transmitter apparatus of claim 1, wherein, the plurality of periodically spaced second optical waveguide grating structures are spaced apart from the plurality of periodically spaced first optical waveguide grating structures by 0 to 0.2 pm.

10. The optical transmitter apparatus of claim 1, wherein, each grating coupler is 2 pm to 5 pm in length and 2 pm to 5 pm in width.

11. The optical transmitter apparatus of claim 1, wherein, the second portion extends only 40% to 60% of the height of the first portion.

12. The optical transmitter apparatus of claim 1, wherein, a pitch and depth of each grating coupler are configured such that the emission direction is substantially perpendicular to the transmission direction.

13. The optical transmitter apparatus of claim 1, wherein, each grating coupler is 5 pm to 20 pm in length and 5 pm to 20 pm in width.

14. The optical transmitter apparatus of claim 1, wherein, each grating coupler is 2 pm to 5 pm in length and 2 pm to 5 pm in width.

15. The optical transmitter apparatus of claim 1, wherein, the plurality of periodically spaced first optical waveguide grating structures comprise a grating period of 0.5 pm to 1 pm. each grating coupler comprises an extended optical waveguide portion extending into a respective one of the plurality of periodically spaced first optical waveguide grating structures.

16. The light emitter device of claim 1, further comprising: a host substrate for supporting the plurality of point emitters; and an optical waveguide structure comprising: a plurality of optical waveguide cores, each of the plurality of optical waveguide cores extending to a respective one of the plurality of point emitters with an extended optical waveguide portion therebetween; and a cladding surrounding the plurality of optical waveguide cores.

17. The optical transmitter apparatus of claim 1, further comprising a lens system including a focal length and an optical axis, configured to re-direct the respective light beams at respective beam angles as a function of a position of each of the plurality of point emitters relative to the optical axis.

18. The optical transmitter apparatus of claim 1, further comprising: at least one light source for generating the light; and a switching matrix for selectively directing at least a portion of the light to one of the plurality of point emitters.

19. The optical transmitter apparatus of claim 18, further comprising at least one photodetector for detecting an incident light beam received by the plurality of point emitters.

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