On-chip mirror beamforming

Abstract

The present invention discloses a system and architecture for sending and receiving collimated light beams directly from a photonic chip via an on-chip mirror beamforming device to reduce manufacturing difficulties and optical aberrations. More specifically, elliptical or parabolic mirrors can be used in a photonic chip to collimate the light beam emitted from a waveguide port and further enable techniques such as wavefront error correction and beam steering without moving parts.

Description

Technical Field

[0001] The present disclosure relates to systems and architectures for sending and receiving collimated light beams directly from a photonic chip, and more particularly to applications in photonics, such as for LIDAR, spectroscopy, and other remote sensing. Background Art

[0002] There are many applications in photonics that require the use of photonic integrated circuit (PIC) chips to send and receive wide, low-divergence, collimated beams, for example, with a diameter of more than one millimeter. Typical methods for generating collimated beams of millimeter-scale diameter involve the use of external lenses, i.e., off-chip lenses. For example, a divergent beam is emitted from the PIC chip by using a waveguide brought to the edge of the chip, using an inverted cone, or using a small grating. The divergent beam then passes through an external lens, which is manufactured according to specific parameters and is positioned / aligned to collimate the beam. However, the use of external lenses is problematic because the lenses: i) are expensive, ii) must be aligned very accurately at high assembly costs, iii) are misaligned due to vibration or movement, and iv) need to be operated at a high numerical aperture.

[0003] Therefore, monolithic on-chip designs that do not require external optics are preferred for emitting collimated beams. Some designs have been proposed in which light is coupled from a waveguide to a dielectric slab, allowed to diverge as it propagates, and then collimated by a single in-plane lens element. However, these designs are very difficult to manufacture and produce due to the tiny tolerances involved. More specifically, these designs vary the thickness of the slab or add a cover layer of material with a different refractive index to vary the effective refractive index, thereby forming an optical element by defining an area of ​​such a slab or cover material of varying thickness. The focal length of the lens, and thus the defocus aberration of the system, is very sensitive to the effective refractive index of both the lens and the slab area. The tolerances on the effective refractive index mean that the thickness and etching depth of these layers must be controlled to an unrealistic nanometer level. In addition, monolithic lenses like these are subject to optical aberrations including chromatic aberration and higher-order aberrations, such as spherical, astigmatism, coma, etc., which are difficult to correct even with complex aspheric or aplanatic lenses.

[0004] The object of the present invention is to overcome the disadvantages of the prior art by providing a photonic chip having a monolithic on-chip design for sending and receiving collimated light beams that is easy to manufacture and does not have any optical aberrations. Summary of the invention

[0005] Therefore, the present invention relates to a beamforming device, comprising:

[0006] a first input port for emitting a first output light beam;

[0007] a slab waveguide for confining the first light beam in a first dimension while diverging the first output light beam in a second perpendicular dimension; and

[0008] A reflector is coupled to the slab waveguide for redirecting and substantially collimating the first output beam for output.

[0009] The reflector may include an elliptical reflector defining a segment of an ellipse including a first focus and a second focus; wherein the first focus is proximate the input port; and wherein the second focus is located outside the beamforming device.

[0010] Ideally, the second focal point is far enough away that the first output beam appears substantially collimated at the output end.

[0011] The reflector may include a spherical surface or any aspherical shape. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The present invention will be described in more detail with reference to the accompanying drawings showing preferred embodiments of the invention, in which:

[0013] Figure 1 is a diagram illustrating the basic principles used in a mirror-based beamforming device according to an embodiment of the present disclosure.

[0014] Figure 2A is a top view of an implementation of a mirror-based beamforming device according to an embodiment of the present disclosure.

[0015] Figure 2B is a top view of an implementation of a mirror-based beamforming device according to an embodiment of the present disclosure.

[0016] Figure 3 is a top view of an implementation of a mirror-based beamforming device according to an embodiment of the present disclosure.

[0017] Figure 4A is a vertical cross-sectional view of an on-chip mirror-based beamforming device according to an embodiment of the present disclosure.

[0018] Figure 4B is a vertical cross-sectional view of an on-chip mirror-based beamforming device according to an embodiment of the present disclosure.

[0019] Figure 4C is a vertical cross-sectional view of an on-chip mirror-based beamforming device according to an embodiment of the present disclosure.

[0020] Figure 4D is a vertical cross-sectional view of an on-chip mirror-based beamforming device according to an embodiment of the present disclosure.

[0021] Figure 5is a top view of an implementation of a mirror-based beamforming device with wavefront error correction according to an embodiment of the present disclosure.

[0022] Figure 6 is a top view of an implementation of a mirror-based beamforming device with wavefront error correction according to an embodiment of the present disclosure.

[0023] Fig. 7A is a vertical cross-sectional view of mirror-based beamforming with wavefront error correction according to an embodiment of the present disclosure.

[0024] Figure 7B is a vertical cross-sectional view of a mirror-based beamforming device with wavefront error correction according to an embodiment of the present disclosure.

[0025] Fig. 8A is a top view of a photonic chip and waveguide assembly for LIDAR sensing according to an embodiment of the present disclosure.

[0026] Figure 8B is a top view of a photonic chip and waveguide assembly for LIDAR sensing according to an embodiment of the present disclosure.

[0027] Figure 8C is a top view of a photonic chip and waveguide assembly for LIDAR sensing according to an embodiment of the present disclosure.

[0028] Fig.9A is a top view of a photonic chip and waveguide assembly for beam steering in LIDAR sensing according to an embodiment of the present disclosure.

[0029] Fig. 9B is a top view of a photonic chip and waveguide assembly for beam steering in LIDAR sensing according to an embodiment of the present disclosure.

[0030] Fig. 9C is a top view of a photonic chip and waveguide assembly for beam steering in LIDAR sensing according to an embodiment of the present disclosure.

[0031] Fig.9D is a top view of a photonic chip and waveguide assembly for LIDAR sensing according to an embodiment of the present disclosure.

[0032] Fig.10 is a top view of an implementation of a mirror-based beamforming device with a stray light attenuation structure according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0033] Although the present teaching is described in conjunction with various embodiments and examples, the present teaching is not limited to these embodiments. On the contrary, as those skilled in the art will appreciate, the present teaching encompasses various alternatives and equivalents.

[0034] Embodiments of the photonic chip disclosed herein attempt to address these problems by implementing on-chip collimated beamforming using a mirror-based design. Notably, the focal length and optical aberrations of a curved mirror (e.g., an elliptical or parabolic mirror) are independent of the refractive index surrounding the mirror, completely eliminating sources of defocus and aberrations. In addition, multiple elements - fully planar mirrors, fully planar lenses, or some combination of planar mirrors and planar lenses, i.e., a catadioptric design - can be used to improve imaging performance and reduce high-order aberrations. The design of these planar optical elements can be performed using ray tracing of multi-element systems and standard optical design principles using the effective refractive index of a layer stack with any covering material, such as the thickness of a slab, as the refractive index of the optical element.

[0035] Thus, embodiments of photonic chips with different designs are disclosed herein that utilize mirror-based beamforming to send and receive wide, low-divergence collimated beams, such as beams with widths from fifty microns to one or two centimeters, directly from the photonic chip. Embodiments and other considerations for implementing them are disclosed below.

[0036] Figure 1 The reflective characteristics of the elliptical reflector 108 are shown. The elliptical reflector 108 has two focal points 106 and 110, and when light leaves one of the focal points, such as the focal point 106, and reflects from a point on the elliptical reflector 108, the light will be reflected from that point of the elliptical reflector 108 to the other focal point, such as the focal point 110, and pass through the focal point. For example, for the elliptical reflector 108 including the first focal point 106 and the second focal point 110 and the inner surface having mirror-like characteristics, when the end of the input waveguide 102 of the photonic chip 104, i.e., the input port, is located at the first focal point 106 of the elliptical reflector 108, the light beam leaving the end of the waveguide 102 will be reflected from the inner surface of the elliptical reflector 108 to the second focal point 110, and finally pass through the second focal point 110.

[0037] Thus, an elliptical reflector can provide perfect (aberration-free) focusing between two foci. This can be applied, for example, to a photonic chip for sensing or LIDAR by positioning one focus of the ellipse at the output of the waveguide, terminating in a slab, such as a silicon slab, and the other focus being an off-chip target. As the distance to the target increases, for example in an infinite target range, the beam reflected from the ellipse becomes more collimated, and the ellipse becomes a parabolic reflector. In other terms, for example, a target distance of 5m would specify an ellipse with foci at (-5m, 0) and (0, y), where (0, y) are the coordinates of the waveguide output, which may be (0, -5mm). The non-zero y in the case of an ellipse or parabola produces an off-axis reflector where the output light is not blocked by the waveguide or any circuitry around it. In LIDAR applications, the reflected light from the target is refocused into the waveguide via a reflector, for example, the light is received via the same path as the light followed when it was emitted from the waveguide. For certain target distance ranges near the design target distance, an acceptable amount of light is received back into the waveguide because the defocus aberration is small enough. Therefore, as referenced Figure 2A and Figure 2B As shown and described, an elliptical or parabolic reflector can collimate light into a beam for a functional LIDAR system.

[0038] exist Figure 2A In the figure, a reflector-based beamforming device 200 arranged on a simple photonic integrated circuit (PIC) chip 201 is shown, which includes a slab waveguide 204 with a reflector 208, such as a mirror, such as dielectric silicon, which reflector 208 represents a portion of an ellipse, for example, the reflector 208 can be manufactured to have a specific curvature as if it is a portion of a larger elliptical reflector with two foci. Although various curved embodiments of the elliptical reflector 208 can be used, the elliptical reflector 208 provides better results for point-to-point imaging. If the selected ellipse parameters correspond to a very elongated ellipse, only a small portion of the entire ellipse may be required as the elliptical reflector 208, for example, for a target located 50 meters away, the elliptical reflector 208 may have a width of less than 1 cm.

[0039] The end of the input waveguide 202, i.e., the input port, is positioned relative to the elliptical reflector 208 such that the end of the input waveguide 202 is located at a first focus of the entire ellipse of which the elliptical reflector 208 is a segment. Diverging light rays 206 exiting the input waveguide 202 enter the slab waveguide 204 and propagate until they hit the elliptical reflector 208. More specifically, the slab waveguide 204 confines the light rays 206 in a first dimension (e.g., vertically) while enabling the light rays 206 to diverge in a second perpendicular dimension (e.g., horizontally).

[0040] Within the slab waveguide 204, the elliptical reflector 208 reflects the light 206 toward the chip face 210 and collimates the light 206 at the same time. The light 206 then leaves the chip 201 by exiting through the chip face 210, such as the edge of the chip 201, toward a target (not shown) located at the second focus of the ellipse containing the elliptical reflector 208. In this edge emission case, the light 206 can diverge perpendicular to the plane of the slab waveguide 204, and one or more off-chip cylindrical lenses or mirrors 220 can be placed after the chip 201 to collimate the beam of light 206. The light reflected from the target at the second focus can return to the chip 201 along the same path in the opposite direction and can be re-focused in the waveguide 202 via the elliptical reflector 208.

[0041] The above-described reflector-based beamforming device 200 can generate highly efficient return light for LIDAR applications, which is simpler to implement and less expensive. In addition, since the elliptical reflector 208 is in the chip 201, the durability is increased because there are no issues associated with a lens separate from the chip 201 and any air gap therebetween, which may cause misalignment offsets, etc.

[0042] Figure 2B The mirror-based beamforming device 250 shown includes a photonic integrated circuit (PIC) chip 251, which is similar to Figure 2AThe chip 201 shown is different in that the chip 251 includes an additional grating 260 in or near the slab waveguide 254, which changes the output path of the light 256 once the light 256 hits the elliptical reflector 258. More specifically, the photonic chip 251 includes a slab waveguide 254, such as a dielectric silicon slab, having an elliptical reflector 258, such as a mirror, representing a segment of the entire ellipse. The end of the input waveguide 252 is positioned relative to the elliptical reflector 258 so that the end of the input waveguide 252 is located at the first focus of the entire ellipse of which the elliptical reflector 258 is a segment. The divergent light rays 256 leaving the input waveguide 252 enter the slab waveguide 254 and propagate until they are reflected by the elliptical reflector 258. The output grating 260 is located in a portion of the slab waveguide 254 through which the light 256 passes after reflecting from the elliptical reflector 258. The light 256 can then leave the chip 251 from the output grating 260 at an acute angle to the plane of the slab waveguide 254, e.g., in a direction out of the paper, in the XZ plane defined by the coordinate system 262, and the chip 251 is already collimated or focused depending on the design of the output grating 260. The grating 260 can steer the beam in one axis, e.g., in the XZ plane, around the Y axis, by changing the wavelength of the emitted light. Additional steering in an axis perpendicular to the grating 260 can be performed by emitting the beam from the waveguide at a different position in the (XY) plane of the slab waveguide 254, e.g., in the XZ plane, and with reference to Figure 3 An embodiment with this design is shown and discussed. Thus, beam steering can be achieved in two directions using the output grating 260 in conjunction with the use of a waveguide array to change the wavelength of light. In either case, further steering can be accomplished by placing external tilted or moving off-chip mirrors in the beam path. Beam steering is important for LIDAR applications, where the beam can be moved and imaging of the surrounding environment can be achieved, such as reflecting light from various targets, without moving any physical parts, such as moving the chip itself with a rotating motor.

[0043] refer to Figure 3 , a reflector-based beamforming device 300 includes a photonic integrated circuit (PIC) chip 301 with an output grating 312, which can utilize more than one waveguide in a waveguide array 302 in the plane of a slab waveguide 304 to achieve beam steering on an axis perpendicular to the grating 312. The photonic chip 301 includes a waveguide slab 304 with an elliptical reflector 310, such as an elliptical reflector, representing a segment of a whole ellipse. The waveguide array 302 may include a plurality of waveguides positioned relative to the elliptical reflector 310 such that the ends of the waveguides in the waveguide array 302, i.e., the input ports, are located at the focus of the whole ellipse of which the elliptical reflector 310 is a segment. Figure 3The example shown in shows two different sets of light rays, namely, light rays 306 and light rays 308, emanating from two different waveguides of the waveguide array 302. Because the two different sets of light rays are emitted from slightly different locations, they have slightly different paths as they reflect from the elliptical reflector 310 and pass through the output grating 312. In other words, after striking the elliptical reflector 310, the light from each waveguide of the waveguide array 302 is collimated, but propagates out of the output grating 312 at different angles. Therefore, the angle at which the light leaves the output grating 312 can be controlled based on which waveguide in the waveguide array 302 the light is emitted from. Although not shown, this concept of beam steering using the waveguide array 302 can also be used without the output grating 312, for example as shown in FIG. Figure 2A As shown, the light beam leaves the edge or chip face 210 of the chip 201. In some embodiments, light can be emitted from different waveguides of the waveguide array 302 simultaneously, or sequentially, and can be switched quickly so that the light beam can be used to obtain an image of the surrounding environment, such as for LIDAR applications. Because the elliptical reflector is only aberration-corrected for light passing through its two focal points and not for off-axis light, at most one waveguide of the waveguide array 302 will emit an aberration-free light beam. Waveguides that are not in focus will experience various aberrations, especially coma. In some embodiments, the reflector 310 can have a non-elliptical shape, such as a spherical or arbitrary aspherical shape, thereby improving the aberrations of multiple waveguides.

[0044] In some embodiments, it may be preferred to use Figure 6 More than one reflector 208, 258 or 310 are arranged in sequence so that the light 206, 256 or 308 bounces off multiple reflectors before leaving the chip 201, 251 or 301 via the chip face 210 or the grating 260 or 312. These reflectors can be of various spherical or aspherical shapes to correct aberrations, flatten the focal field or change the intensity distribution of the emitted light beam, i.e., apodization.

[0045] Figures 4A-4D 2 shows a vertical cross-sectional view of various mirror-based beamforming devices in which on-chip elliptical reflectors 208, 258, or 310 may be used in their fabrication, e.g. Figure 2A , 2B and the elliptical reflector shown in 3 . Figures 4A-4CSome layers that may be deposited in, for example, a mirror-based beamforming device 400 similar to the mirror-based beamforming devices 200, 250, and 300 are shown, including (from top to bottom) an upper cladding 402, for example, an oxide such as silicon dioxide; a slab waveguide 404, for example, composed of a suitable waveguide material such as silicon or silicon nitride; a lower cladding 406, for example, composed of an oxide such as silicon dioxide or a dielectric; and a handle wafer or substrate 408, for example, composed of silicon. Figure 4D In the embodiment of the present invention, the slab waveguide 404 may not occupy the entire layer, which means that the upper cladding layer 402 and the lower cladding layer 406 may fill a portion of the layer occupied by the slab waveguide 404 and thus form a single continuous layer.

[0046] exist Figure 4A In the embodiment of the present invention, the reflector-based beamforming device 400 includes a photonic integrated circuit (PIC) chip 401, which includes an elliptical reflector 410, such as an elliptical reflector, which can be provided by etching a trench 409 through the upper cladding, the slab waveguide 404 and into the lower cladding 406, and then filling or coating the sidewalls of the trench 409 with a reflective material such as a deposited metal to form an elliptical reflective surface (e.g., the elliptical reflector 410). The trench 409 must extend sufficiently below the slab waveguide 404 into the lower cladding 406 to reflect the entire mode area of ​​the light. Various metals can be used for the elliptical reflector 410, including silver, aluminum, copper, and gold.

[0047] Or, if Figure 4B As shown, a reflector-based beamforming device 400' includes a photonic chip 401' that includes a deposited Bragg reflector 420, which can be provided by etching a trench 409 through a slab waveguide 404 and depositing alternating layers of low-refractive index and high-refractive index materials to form a reflector for a wavelength of interest, i.e., Bragg reflector 420. The layers of low-refractive index and high-refractive index materials typically have a thickness of λ / (4n), where λ is the vacuum wavelength of light and n is the refractive index of the layer.

[0048] Or, in Figure 4C In the present invention, a reflector-based beamforming device 400" includes a photonic integrated circuit (PIC) chip 401", which includes a similar Bragg reflector concept, which can be configured by patterning the slab waveguide 404 itself, for example, alternating the effective refractive index seen by the slab mode, rather than a groove and fill technique, to form alternating low and high refractive index layers to produce an etched slab Bragg mirror 430.

[0049] Finally, reference Figure 4D, a reflector-based beamforming device 400'' includes a photonic integrated circuit (PIC) chip 401'', where a slab waveguide 404 simply terminates at a desired shape of a reflective surface, such as a reflector 440, and therefore, the upper cladding 402 and the lower cladding 406 can be a single unit of the cladding 412. The method utilizes total internal reflection at the junction between the higher refractive index material in the slab waveguide 404 and the lower refractive index material in the cladding 412. The reflector design in this embodiment can cause all light impinging on the reflector 440 to impinge at a grazing angle greater than the critical angle for total internal reflection.

[0050] It should be noted that in all of the previously shown embodiments, the wavefront of the emitted light beam may be distorted because it accumulates phase errors as it propagates through the slab waveguide 404 or gratings 420 or 430. For example, variations in slab thickness, refractive index, or temperature may cause a portion of the light beam to be delayed in phase relative to the rest of the beam. The resulting wavefront error can result in a loss of resolution in imaging and reduce the amount of return light that can be coupled back into the single-mode waveguide for LIDAR applications. This wavefront error may need to be corrected by a number of different methods, and Figure 5 , Figure 6 and Figure 7A-7B Various such methods are shown and discussed.

[0051] Figure 55 is a top view of a mirror-based beamforming device 500 on a photonic integrated circuit (PIC) chip 501 including wavefront error correction according to an embodiment of the present disclosure. As previously described, a light beam 506 is emitted from an input port, such as the end of a waveguide 502, located at a first focus of the entire ellipse, and diverges and propagates through a slab waveguide 504 before reflecting from an elliptical reflector 508, such as an elliptical mirror, that forms a segment of the entire ellipse. The second focus of the entire ellipse may be far enough away, such as greater than 4 m, so that the wavefront of the light leaving the chip appears flat within a certain tolerance range (e.g., 1 / 20 of the wavelength), i.e., the beam appears substantially collimated. Typically, for light to appear collimated, the second focus may be located in the Fraunhofer far field, i.e., farther than W2 / λ, where W is the beam width and λ is the operating wavelength. The portion of the slab waveguide 504 that the light beam passes through after being incident on, for example, reflected from, the elliptical reflector 508 can be heated in two or more segments by placing a resistive heating element 510, such as a thermal phase shifter, near the slab waveguide 504 and running an adjustable current through each heating element 510. Each heating element 510 is locally heated, thereby adjusting the refractive index of the slab waveguide 504 below, which causes a phase shift in the portion of the light propagating below the heating element 510. Any form of emitting light from the chip 501 can be utilized, including any of the above-described devices, such as the chip facet 210, the output grating 260 or 312.

[0052] Figure 6 600 is a top view of another reflector-based beamforming device 600 on a photonic integrated circuit (PIC) chip 601 including wavefront error correction according to an embodiment of the present disclosure. For the photonic chip 601, a beam splitter, such as a 1x4 beam splitter, is used to split the input beam into a plurality of, for example, four sub-beams. An elliptical reflector, such as an elliptical reflector, is divided into a plurality of parts 608, 618, 628, and 638, and each part of the reflector is arranged with a separate corresponding waveguide 602, 612, 622, and 632. Each elliptical reflector part 608, 618, 628, and 638 is configured to have a focus at the corresponding waveguide 602, 612, 622, and 632, and a second focus at the target. The second focus of the entire ellipse may be far enough away, such as greater than 4m, so that the beam appears to be collimated, as defined above. In particular, when the entire focus is far away, each of 608, 618, 628, and 638 will have the same shape. Each phase shifter 604, 614, 624 and 634 is placed above each respective waveguide 602, 612, 622 and 632 before emitting the respective sub-beam toward the respective elliptical reflector portion 608, 618, 628 and 638, which enables the phase shifting of each sub-beam. Figure 5 As with the embodiment shown, a phase shift pattern can be applied via a voltage or current applied to phase shifters 604, 614, 624, and 634. Phase shifting can be used to pre-distort the output wavefront of a sub-beam so that the sub-beam leaves the chip 601 correctly aligned after picking up the phase error in the slab waveguide 605 or grating 640 (if included). Since most phase errors encountered vary slowly in space, a relatively coarse correction is sufficient to fully correct the beam. For example, two to sixteen phase shifters, such as heating elements 604, 614, 624, and 634 and / or reflector portions 608, 618, 628, and 638 can be used to achieve effective wavefront error correction.

[0053] More specifically, in Figure 6 , light from waveguide 602 passes through phase shifter 604 before being emitted at reflector portion 608, light in waveguide 612 passes under phase shifter 614 before being emitted at reflector portion 618, light in waveguide 622 passes under phase shifter 624 before being emitted at reflector portion 628, and light in waveguide 632 passes under phase shifter 634 before being emitted at reflector portion 638. The net result is a wavefront error correction that is similar to Figure 5 Wavefront error correction is obtained in the illustrated embodiment, except that the phase shift occurs before the light is reflected by reflector portions 608, 618, 628 and 638 rather than after.

[0054] Although Figure 5 and Figure 6 A method of dynamically correcting or at least partially compensating for wavefront errors by electronically controlling phase shifts is shown, but another method is to physically correct the wavefront error. The correction can be accomplished by fabricating a static corrector layer 706 on top of a photonic integrated circuit (PIC) chip 701. In some embodiments, the corrector layer 706 can be a corrector plate mounted on top of the chip 701. The corrector layer 706 can have a patterned variable depth or thickness so that light in different parts of the beam receives different phase delays. The appropriate pattern for the corrector layer 706 can be determined by first fabricating a photonic chip 701, which includes a slab waveguide 404, a grating 704, and layers of an upper cladding 402 and a lower cladding 406 on a substrate 408, and then measuring the emitted wavefront. Wavefront measurements can be accomplished using standard techniques such as interferometry or Shack-Hartmann sensors. A reverse correction pattern can be calculated to be patterned into the corrector layer 706 so that the optical path length difference nL cancels the measured phase error, where n is the refractive index of the corrector layer 706 and L is the local thickness along the propagation direction. The correction pattern is then defined in the corrector layer 706. Fig. 7A and Figure 7BVarious ways of implementing this corrector layer are shown in .

[0055] refer to Fig. 7A , a mirror-based beamforming device 700 fabricated on a photonic integrated circuit (PIC) chip 701 includes a corrector layer 706, such as a corrector plate, for wavefront error correction. The corrector layer 706 can be fabricated on top of the upper cladding layer 402 by spin coating the upper layer of the PIC chip 701 with a photosensitive material or photoresist (such as SU-8 epoxy resin, etc.), and then grayscale lithography can be used to pattern the variable thickness of the deposited material. The laser beam can be raster scanned on the corrector layer 706, changing the dwell time or power of the laser beam to produce different thicknesses. The SU-8 3D patterned corrector layer 706 is used as a corrector plate placed on top of the chip 701 so that the emitted light 702 passing through the grating 704 passes through the corrector layer 706.

[0056] Figure 7B A mirror-based beamforming device 750 is shown integrated in a photonic integrated circuit (PIC) chip 751, which includes an etched corrector facet 708 for wavefront error correction. Grayscale lithography can be used to form Fig. 7A 706, except that the photoresist material is not left as a permanent part of the PIC chip 751, which can be used as a mask to etch the correction pattern on the etched corrector facet 708 into the upper cladding of the PIC chip 751. Therefore, the emitted light 702 passing through the grating 704 passes through the etched corrector facet 708 etched directly into the upper cladding 402, which performs the wavefront error correction. The elliptical reflector can be any of the elliptical reflectors described above, such as the elliptical reflectors 410, 420, 430, and 440.

[0057] The mirror-based beamforming devices described herein for beam collimation and wavefront correction, such as 200, 250, 300, 400, 500, 600, 700, 750, and the mirror-based beamforming device 804 described below, can be combined with a LIDAR core 801 to form a LIDAR (Light Detection and Ranging) sensing device 800. The LIDAR core 801 composed of related waveguide components can be optically coupled to a transmitting waveguide 802 forming the LIDAR sensing device 800. Figures 8A-8C One such arrangement is shown and described.

[0058] refer to FIG. 8A to FIG. 8C, the launch waveguide 802 of any of the aforementioned mirror-based beamforming devices (e.g., 200, 250, 300, 400, 500, 600, 700, 750) can be connected to a first output 831 of a beam director 810 (e.g., a first beam splitter such as a 2x2 coupler). The first input 821 of the beam director 810 can be connected to a laser source 812 that generates and provides a beam. The second input 822 and the second output 832 of the beam director 810 can be connected to first and second inputs 841 and 842 of a second beam splitter 814 (e.g., a 2x2 coupler). The first and second outputs of the second beam splitter 814 can be connected to one or more photodetectors, such as a first photodetector 816 and a second photodetector 816, respectively. Optionally, one of the first and second photodetectors 816 can be omitted. The difference in laser return time and wavelength can then be used by a controller 845 connected to the photodetector 816 to make a digital 3-D representation of the target according to any known technique commonly used. This arrangement of beam director 810 and beam splitter 814, laser source 812, and photodetector 816 may be referred to as a "LIDAR core."

[0059] Special References Figure 8C The above arrangement can also realize optical homodyne detection of light received in a reflector-based beamforming device (e.g., 200, 250, 300, 400, 500, 600, 700, 750). The second output end 832 of the beam director 810 provides a portion of the light from the light source 812 as local oscillator (LO) light to the second beam splitter 814 ( Figure 8B ) for comparison with the returned input light. The second input end 822 of the beam director 810 carries the input light received from the mirror-based beamforming device to be sensed ( Figure 8C ). Typically, the optimal splitting ratio of the beam director 810 is 50:50. In the case of two photodetectors 816, the typical optimal splitting ratio of the second beam splitter 814 is 50:50. In the case of one photodetector 816, the typical optimal splitting ratio of the second beam splitter 814 is close to 90:10, coupling 90% of the received light and 10% of the LO to the single photodetector 816. The laser source 812 can be a tunable laser, whereby the angle of the light emitted via the grating varies depending on the wavelength of the laser source 812.

[0060] Figure 8BThe exit path of light propagation generated by the laser source 812 is shown by arrows. Light propagates from the laser source 812 to the beam director 810. As described in the previous embodiment, some of the light output from the beam director 810 exits the launch waveguide 802 and exits the mirror-based beamforming device 804 toward the target. The remainder of the light output from the beam director 810 enters the second beam splitter 814 as LO where it is split into outputs that are sent to a pair of photodetectors 816.

[0061] Figure 8C The incoming path of light reflected from the target and received by the mirror-based beamforming device 804 in the reverse path is shown by the blue arrows. The received light propagates along the waveguide 802 to the beam director 810 which splits the light. Part of the light enters the laser source 812 and this part is ignored. Another part of the light enters the second beam splitter 814 which further splits the received light into outputs sent to a pair of photodetectors 816. As previously mentioned, this arrangement allows for very sensitive detection of the received light.

[0062] Figures 9A-9D Additional components of the waveguide assembly of the LIDAR sensing device 900 for implementing beam steering are shown. Fig.9A 802, a wavelength division multiplexing element (WDM) 904 is connected to the launch waveguide 802. The WDM 904 connects one output, such as the launch waveguide 802, to two or more input waveguides that are each connected to a separate corresponding LIDAR core 801. Each LIDAR core 801 can be associated with light of a different wavelength, and the WDM 904 routes the light according to its wavelength so that all wavelengths share the same launch waveguide 802, but each separate wavelength is routed to a separate input waveguide from a separate LIDAR core 801. This configuration allows for simultaneous ranging at multiple output angles of a grating, such as the grating 260, 312, 640, or 704, each angle being accessed by one of the separate LIDAR cores 801 at a separate wavelength.

[0063] refer to Fig. 9B , the LIDAR sensing device 950 includes a reflector-based beamforming device 804 and a waveguide array 912, such as Figure 3 Each waveguide in the waveguide array 912 can be attached to a separate LIDAR core 801.

[0064] refer to Fig. 9C , Fig.9A and Fig. 9B The basic concepts of are combined to produce a beamforming device including a mirror-based beamforming device 804 and a waveguide array 912 (e.g., similar to Fig. 9BThe LIDAR sensing device 980 is composed of each waveguide of the waveguide array 302 connected to a different wavelength division multiplexing element (WDM) 904. Each WDM 904 receives a light beam of a different wavelength routed through a separate input waveguide, each of which is attached to a separate LIDAR core 801.

[0065] exist Figures 8A-8C and Figures 9A-9C In either configuration shown, the beam director 810 of the LIDAR core 801 may include a circulator 934 so that: 1) output from the laser source 812 may propagate to the launch waveguide 802 or 912; 2) light returning from the launch waveguide 802 or 912 may propagate to the photodetector 816; and 3) propagation in the reverse direction is prevented. Fig.9D shows a structure with a launch waveguide placed in the Figures 8A-8C 814 of the LIDAR core 801. For example, before the signal reaches the circulator 934, the local oscillator is tapped from the laser output using an asymmetric 1x2 splitter 940.

[0066] In all of the aforementioned reflector-based beam shaping structures (referred to as 1000), such as 200, 250 or 300, 400, 500 or 600, some of the light 1006 exiting the output waveguide 1002 will diverge beyond the physical extent of the reflector 1008, continue through its edges and not be reflected. Any portion of the beam that does not hit the reflector 1008 falls outside the aperture of the optical system and is intended to be discarded. As with any optical system, special care must be taken to ensure that unwanted light 1006 does not enter the optical path and exit the chip 1001 via the facet 1010 or enter the grating structure 1060 via various unexpected reflections. Such a situation may result in the generation of unwanted beam sidelobes and unwanted ghost images. Aperture beam stops or attenuation structures 1012 can be strategically placed, for example, beside, around or behind the reflector 1008 or grating structure 1060 to attenuate or reduce the unwanted light 1006 entering the optical system, but without attenuating or cutting off the desired light 1007. In some embodiments, the attenuation structure 1012 can be placed adjacent to but not intersecting the beam path of the expanded desired light ray 1007 before it strikes the reflector 1008, for example on either side of the reflector 1008. In some embodiments, the attenuation structure 1012 can be formed by doping a portion of the waveguide slab 1004, for example at its edge. The light must pass through a sufficiently long attenuation region so that its intensity is attenuated to an acceptable minimum level, typically less than -20 dB. By doping, such as by implantation of boron, phosphorus, or arsenic ions, a portion of the waveguide slab 1004 may have a concentration greater than 1e19 cm -3, typically a length of 250 μm is sufficient for such attenuation. This doping level also allows for minimal back reflections at the boundary between doped and undoped waveguide materials (e.g., silicon) because the refractive index change caused by the doping is small. Such attenuated light may eventually re-enter the optical system through stray reflections, but will be sufficiently attenuated by structure 1012 so as not to adversely affect system performance.

[0067] The foregoing description of one or more embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many variations and changes may be made in accordance with the above teachings. The scope of protection of the present invention is not limited to specific embodiments, but is defined by the appended claims.

Claims

1. A beamforming device, comprising: a first input port for emitting a first output light beam; an output end, used for outputting the first output light beam; a slab waveguide for confining the first output beam in a first dimension while diverging the first output beam in a second perpendicular dimension; and a reflector coupled to the slab waveguide for redirecting and substantially collimating the first output beam at the output end, the reflector comprising an elliptical reflector defining a segment of an ellipse including a first focus proximate the first input port and a second focus external to the beamforming device and at a sufficiently distant position that the first output beam is substantially collimated at the output end.

2. The beamforming device according to claim 1, wherein: The reflector includes a plurality of reflective surfaces arranged in sequence.

3. The beamforming device of claim 1, further comprising an output grating for directing the first output beam at a first angle relative to the slab waveguide.

4. The beamforming device of claim 3, further comprising a second input port for transmitting a second output beam comprising a different wavelength than the first output beam; in, The output grating is configured to direct the second output beam at a second angle relative to the slab waveguide.

5. The beamforming device according to claim 3, wherein: The first input port is configured to emit a second output beam comprising a different wavelength than the first output beam; Wherein, the output grating is configured to direct the second output light beam at a second angle relative to the slab waveguide.

6. The beamforming device of claim 1, further comprising a second input port for emitting a second output beam directed at a different angle.

7. The beamforming device according to claim 1, wherein: The reflector includes a metal coating on an edge of the slab waveguide.

8. The beamforming device according to claim 1, wherein: The reflector includes a Bragg reflector on an edge of the slab waveguide.

9. The beamforming device according to claim 1, wherein: The reflector includes a Bragg grating in the slab waveguide.

10. The beamforming device according to claim 1, wherein: The reflector comprises a junction between the slab waveguide comprising a first material having a first refractive index and a cladding comprising a second material having a second refractive index lower than the first refractive index, whereby the first output beam is incident on the junction at a grazing angle greater than a critical angle for total internal reflection.

11. The beamforming device according to claim 1, wherein: Also included is an attenuation structure arranged near the optical path of the output light beam, which is used to reduce stray light.

12. The beamforming device according to claim 11, wherein: The attenuation structure includes a doped portion of the slab waveguide.

13. The beamforming device according to claim 1 further includes a wavefront error corrector, which includes a plurality of tunable phase shifters adjacent to or inside the slab waveguide, each corresponding phase shifter of the plurality of tunable phase shifters being configured to locally tune the refractive index of a portion of the slab waveguide, thereby shifting the phase of a portion of the first output light beam traveling adjacent to each corresponding phase shifter to compensate for the phase error in the first output light beam.

14. The beamforming device according to claim 1, further comprising: A beam splitter, configured to split the first output beam into a plurality of sub-beams; and a plurality of phase shifters, a corresponding phase shifter being used for each sub-beam, each corresponding phase shifter being used to locally tune the phase of one of the plurality of sub-beams, thereby controlling the wavefront of the plurality of sub-beams reflected from the reflector; The reflector comprises a plurality of reflector parts, and corresponding reflector parts are used for each sub-beam respectively.

15. The beamforming device according to claim 1, further comprising: A wavefront error correction layer located in the path of the first output beam includes a 3-D pattern for compensating for phase error in the first output beam propagating through the slab waveguide.

16. The beamforming device according to claim 15, further comprising: a cladding layer above the slab waveguide; Wherein, the wavefront error correction layer is in the cladding.

17. The beamforming device according to claim 15, further comprising: a cladding layer above the slab waveguide; an additional corrector layer above the cladding; Wherein, the wavefront error correction layer is in the additional corrector layer.

18. A LIDAR sensing device, comprising: A beamforming device, comprising: a first input port for emitting a first output light beam and for receiving a first input light beam; a slab waveguide configured to confine the first output beam in a first dimension while diverging the first output beam in a second perpendicular dimension; an elliptical reflector coupled to the slab waveguide and configured to redirect and collimate the first output beam for output and to redirect and focus the first input beam onto the first input port; wherein the elliptical reflector defines a segment of an ellipse including a first focus and a second focus; wherein the first focus is close to the first input port; and wherein the second focus is outside the beamforming device and is sufficiently far away so that the first output beam is substantially collimated at the output end; and The first LIDAR core, which includes: a first laser for generating the first output beam; a first photodetector for detecting the first input light beam; and A first beam director is configured to direct the first output beam to the first input port and is configured to direct the first input beam to the first photodetector.

19. The device according to claim 18, wherein: The beam director is also configured to direct a portion of the first output beam to the photodetector for comparison with the first input beam.

20. The apparatus of claim 18, further comprising a second LIDAR core comprising: a second laser for generating a second output beam having a different wavelength than the first output beam; a second photodetector for detecting a second input light beam; a second beam director configured to direct the second output beam to the first input port and configured to direct the second input beam to the second photodetector; and A first wavelength division multiplexer is configured to combine the first output beam and the second output beam for emission from the first input port.

21. The device according to claim 18, wherein The beamforming device comprises a second input port; and Also included is a second LIDAR core, which includes: a second laser for generating a second output beam having a different wavelength than the first output beam; a second photodetector for detecting a second input light beam; A second beam director is configured to direct the second output beam to the second input port and is configured to direct the second input beam to the second photodetector.

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