Two-dimensional optical phased array and method of forming a two-dimensional optical phased array

Abstract

There is provided a two-dimensional optical phased array and a method of forming a two-dimensional optical phased array. The two-dimensional optical phased array including: antenna arrays, each antenna array comprising one or more antennas; a plurality of bus waveguides, a portion of each bus waveguide positioned adjacent a respective one of the antenna arrays; a plurality of first phase shifters, each phase shifter integrated along a portion of one of the bus waveguides that is adjacent the respective one of the antenna arrays, the first phase shifters steer the light beam in a longitudinal direction; and a plurality of second phase shifters, each second phase shifter is situated along a portion of one of the bus waveguides that precedes the portion of the bus waveguide that is adjacent the respective one of the antenna arrays, the second phase shifters steer the light beam in a transverse direction.

Description

TWO-DIMENSIONAL OPTICAL PHASED ARRAY AND METHOD OF FORMING A TWO- DIMENSIONAL OPTICAL PHASED ARRAYTECHNICAL FIELD

[0001] The following relates generally to optical antennas, and more specifically, to a two- dimensional optical phased array and method of forming a two-dimensional optical phased array.BACKGROUND

[0002] Optical phased arrays (OPAs) are an integral part for chip-based beam forming and scanning. They are used with various optical applications, such as for light detection and ranging (LIDAR) and optical satellite communication, among others. These applications require high scanning resolution, large beam scanning range, and low insertion loss of optical power. The ability to control (i.e. , to transmit, steer and receive) optical waves in different directions out of the chip plane is an important prerequisite for integrated (i.e., on-chip) OPAs.SUMMARY

[0003] In an aspect of the present invention, there is provided a two-dimensional optical phased array comprising: antenna arrays, each antenna array comprising one or more antennas; a plurality of bus waveguides, a portion of each bus waveguide positioned adjacent a respective one of the antenna arrays; a plurality of first phase shifters, each phase shifter integrated along a portion of one of the bus waveguides that is adjacent the respective one of the antenna arrays, the first phase shifters steer the light beam in a longitudinal direction; and a plurality of second phase shifters, each second phase shifter is situated along a portion of one of the bus waveguides that precedes the portion of the bus waveguide that is adjacent the respective one of the antenna arrays, the second phase shifters steer the light beam in a transverse direction.

[0004] In a particular case of the two-dimensional optical phased array, the antenna arrays are arranged in rows.

[0005] In another case of the two-dimensional optical phased array, the first phase shifter induces a phase gradient along the bus waveguide.

[0006] In yet another case of the two-dimensional optical phased array, the first phase shifter is segmented.

[0007] In yet another case of the two-dimensional optical phased array, each antenna array comprises a single antenna.

[0008] In yet another case of the two-dimensional optical phased array, each antenna array comprises a plurality of antennas.

[0009] In yet another case of the two-dimensional optical phased array, each antenna comprises a diffraction grating.

[0010] In yet another case of the two-dimensional optical phased array, light is distributed to the one or more antennas from the bus waveguide via a slab waveguide that feeds the one or more antennas through evanescent coupling.

[0011] In yet another case of the two-dimensional optical phased array, each of the first phase shifters are integrated with the respective bus waveguide and provide light-distribution to the antenna arrays in addition to steering in the longitudinal direction.

[0012] In yet another case of the two-dimensional optical phased array, the bus waveguides comprise an optical waveguide controlled by a microelectromechanical system.

[0013] In yet another case of the two-dimensional optical phased array, the optical waveguide comprises a slot bus waveguide as the bus-integrated phase shifter, the slot bus waveguide comprising fixed structures and moveable structures, the moveable structures moved by the microelectromechanical system relative to the fixed structures to adjust a gap width that alters a phase gradient of the optical waveguide.

[0014] In another aspect, there is provided a method for forming a two-dimensional optical phased array, the method comprising: arranging antenna arrays into a plurality of rows on a substrate, each antenna array comprising one or more antennas; placing bus waveguides with a portion of each bus waveguide positioned adjacent a respective one of the antenna arrays; integrating a plurality of first phase shifters, each phase shifter positioned along a portion of one of the bus waveguides, the portion being adjacent the respective one of the antenna arrays, the first phase shifter steers the light beam in a longitudinal direction; and placing a plurality of second phase shifters, each second phase shifter positioned along a portion of one of the bus waveguides that precedes the portion of each bus waveguide that is adjacent the respective one of the antenna arrays, the second phase shifter steers the light beam in a transverse direction.

[0015] In a particular case of the method, each antenna array comprises a single antenna.

[0016] In another case of the method, each antenna array comprises a plurality of antennas.

[0017] In yet another case of the method, light is distributed to the antennas from the bus waveguide via a slab waveguide that feeds the antennas through evanescent coupling.

[0018] In yet another case of the method, the first phase shifters are integrated with the respective bus waveguide and provide light-distribution to the antenna arrays in addition to steering in the longitudinal direction.

[0019] In yet another case of the method, the method further comprising installing a microelectromechanical system to control an optical waveguide, the bus waveguides comprising the optical waveguide.

[0020] In yet another case of the method, the optical waveguide comprises a slot bus waveguide as the bus-integrated phase shifter, the slot bus waveguide comprising fixed structures and moveable structures, the moveable structures moved by the microelectromechanical system relative to the fixed structures to adjust a gap width that alters a phase gradient of the optical waveguide.

[0021] In yet another case of the method, the method further comprising providing a slab waveguide between the bus waveguide and a diffraction grating of the one or more antennas to distribute light to the diffraction grating of the one or more antennas through evanescent coupling of an optical mode from the bus waveguide to the slab waveguide.

[0022] These and other embodiments are contemplated and described herein. It will be appreciated that the foregoing summary sets out representative aspects of certain embodiments to assist skilled readers in understanding the following detailed description.DESCRIPTION OF THE DRAWINGS

[0023] A greater understanding of the embodiments will be had with reference to the Figures, in which:

[0024] FIG. 1 illustrates an example of a one-dimensional optical phased array;

[0025] FIG. 2 illustrates an example of a two-dimensional optical phased array;

[0026] FIG. 3A illustrates a two-dimensional optical phased array, in accordance with an embodiment of the present invention;

[0027] FIG. 3B illustrates a two-dimensional optical phased array, in accordance with another embodiment of the present invention;

[0028] FIG. 4 illustrates an example embodiment of an approach for index changing for the embodiments of FIGS. 3A and 3B using microelectromechanical systems (MEMS);

[0029] FIG. 5 illustrates an example case for the embodiments of FIGS. 3A and 3B using a slab waveguide;

[0030] FIG. 6 is a flowchart illustrating a method of forming a two-dimensional optical phased array, in accordance with an embodiment;

[0031] FIG. 7A illustrates a two-dimensional optical phased array with a segmented bus- integrated phase shifter, in accordance with an embodiment of the present invention; and

[0032] FIG. 7B illustrates a two-dimensional optical phased array with a segmented bus- integrated phase shifter, in accordance with another embodiment of the present invention.DETAILED DESCRIPTION

[0033] For simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the Figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein may be practised without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the embodiments described herein. Also, the description is not to be considered as limiting the scope of the embodiments described herein.

[0034] Various terms used throughout the present description may be read and understood as follows, unless the context indicates otherwise: “or” as used throughout is inclusive, as though written “and / or”; singular articles and pronouns as used throughout include their plural forms, and vice versa; similarly, gendered pronouns include their counterpart pronouns so that pronouns should not be understood as limiting anything described herein to use, implementation, performance, etc. by a single gender. Further definitions for terms may be set out herein; these may apply to prior and subsequent instances of those terms, as will be understood from a reading of the present description.

[0035] Generally, OPAs are used to control the phase and amplitude of light waves radiated, reflected, or captured (i.e. , received) by an array of optical antenna. Most implementations of on- chip OPAs have focused on one-dimensional (1 D) arrays, generally consisting of long 1 D antennas. These antennas are typically arranged in parallel direction, where beam steering is achieved by wavelength scanning in the longitudinal direction and phase control in the direction transverse to the antennas. To eliminate the undesirable beam lobes formed by high-order grating diffraction, the antennas are generally required to be packed closely; for example, with center-to-center pitch down to approximately half optical wavelength. This condition can be nearly met in 1 D arrays as the antennas are lined up in one direction.

[0036] As illustrated in the example of FIG. 1 , 1 D arrays typically use long diffraction grating as antenna. The antennas are typically arranged in an 1 D mesh. External phase shifters are used to control beam steering in an array direction (i.e., transversely) and a tunable laser is used to control emission angle for beam steering in a grating direction (i.e., longitudinally)

[0037] As illustrated in the example of FIG. 2, conventional two-dimensional (2D) OPAs use micro / nano-antennas arranged in a 2D mesh. Each antenna is independently controlled using a phase shifter for beam steering in 2D space, whereby wavelength tuning is generally not required. For 2D arrays, which typically consist of small individual antenna elements that each require individual phase control, the ability to have close packing, such as in the 1 D array, is conventionally considered not feasible. Particularly because typical implementations of 2D arrays use routing waveguides and phase control for individual antenna elements. Having the routing waveguides and the phase control for each individual antenna elements means it is extremely challenging to achieve the required density due to space considerations.

[0038] Typically, 2D OPAs are placed in two-dimensional grids and spaced by a relatively considerable distance, up to tens of the wavelength, to allow for the placement of routing waveguides and, in some cases, also phase shifters. Due to the large distances and spacing between antennas to accommodate the waveguides and phase shifters, typical 2D periodic OPAs will inevitably generate a set of grating lobes; even where efficient phase shifters with small footprints are successfully integrated within the array. There have been various attempts to produce small-scale 2D aperiodic and sparse OPAs through suppression of the grating lobes, using, for example, genetic algorithms and artificial intelligence. However, these attempts have generally failed at the scalability required for practical applications. Moreover, such a sparse array generally has very low antenna filling factor (antenna area divided by the optical aperture of the entire array), which dramatically reduces the optical power collection efficiency of the OPA when used as a receiver.

[0039] Accordingly, conventional on-chip 2D OPAs fail to simultaneously provide, at least, (1) a dense integration of optical antennas with wavelength scale pitch and high antenna filling factor, (2) flexibility in beam steering in orthogonal directions, and (3) sufficient scalability.

[0040] In contrast, the 2D OPA provided in the present embodiments advantageously achieves, at least, dense integration of optical antennas, with center-to-center pitch mainly limited by theantenna dimensions. The 2D OPA of the present embodiments archives these significant advantages by, at least, (1) a coupling approach that distributes optical power from a bus waveguide to the optical antennas, and (2) integration of a phase shifter directly into the bus waveguide. The phase shifter can be used to steer the optical beam in a longitudinal direction relative to the bus waveguide by means of control of an optical phase in the bus waveguide.

[0041] Embodiments of the present disclosure use evanescent coupling to directly couple a bus waveguide optical mode to a slab waveguide optical mode, to efficiently distribute the received light to an antenna in ultra-short distance. Advantageously, such approach does away with having to use the conventional taper structures and permits packing of antennas into an array with antenna pitch that is, for example, less than a few wavelengths. The density of such a 2D array yields a significantly higher antenna filling factor than other approaches. Furthermore, embodiments of the present disclosure integrate a phase shifter into a bus waveguide in order to steer the received optical beam in a longitudinal direction of the bus waveguide by controlling an optical phase in the bus waveguide. Advantageously, such approach dramatically reduces the number of phase shifters required because an entire row of antennas that are fed by the same bus waveguide is controlled using only one phase shifter. As an example, for an array of N x N antennas, only 2 x N phase shifters are required; a significant reduction compared to prior approaches.

[0042] FIGS. 3A and 3B illustrate two respective embodiments of the 2D OPA 300 of the present invention. FIG. 3A illustrates a first embodiment (informally referred to as ‘Structure T) that includes a single antenna 301 per row and a bus waveguide 302 associated with each antenna 301 . Each bus waveguide 302 includes an external phase shifter 303 located prior to the antenna 301. Additionally, each bus waveguide 302 includes a bus-integrated phase shifter 304 associated therewith. FIG. 3B, in contrast, illustrates a second embodiment (informally referred to as ‘Structure 2’) that includes multiple antennas 301 packed closely per row. This embodiment likewise includes a bus waveguide 302 associated with each row of antennas 301 . Again, each bus waveguide 302 includes an external phase shifter 303 located prior to the row of antennas 301. Additionally, each bus waveguide 302 also includes a bus-integrated phase shifter 304 associated therewith. The insert shown in FIGS. 3A and 3B is an illustration of light being steered from the bus waveguide 302 into the antenna 301. Note that a substrate is present but not illustrated for clarity.

[0043] In both of the above embodiments, empty space between antennas is advantageously minimized. The insert shown in FIGS. 3A and 3B is an illustration of light being coupled from thebus waveguide 302 to the antenna 301 through direct evanescent coupling, without any additional coupler and taper structures. In most cases, there is only one phase shifter for each bus waveguide in the row (i.e. , co-located with the antenna array) by way of the bus-integrated phase shifter (Bl PS) 304. As illustrated in FIGS. 7A and 7B, in some cases, the Bl PS 304 for each bus waveguide 302 can be segmented into several independent phase shifting sections; where FIG. 7A shows such case for a single antenna per row and FIG. 7B shows such case for an array of multiple antennas per row. Additionally, beam steering in the x-direction, illustrated in FIGS. 3A and 3B (i.e., longitudinal), is controlled by the BIPS 304, which controls the phase gradient along the bus waveguide. Beam steering in the y-direction, illustrated in FIGS. 3A and 3B (i.e., transverse), is controlled by the external phase shifters 303 associated with each row and which reside outside of the area of the single antenna 301 or the antenna array 301.

[0044] The Bl PS 304 acts as an optical bus waveguide; for example, in the form of a channel waveguide, slot waveguide, SWG waveguide, slow light waveguide, or the like. The Bl PS 304 can include additional metallic structures to act as an electrode to control the optical mode index of the bus waveguide through one of several possible mechanisms. These mechanisms include, but are not limited to, thermo-optic effect, electro-optic effect, plasma dispersion effect, waveguide cross-section deformation (which is illustrated in the example embodiment of FIG. 4).

[0045] Optical beam forming is achieved by controlling the relative phase between adjacent antennas 301. Since the antennas 301 are periodically placed, the relative phase between each pair adjacent antennas 301 is constant for a beam radiated at a specific angle. In the embodiments of FIGS. 3A and 3B, a desired relative phase can be generated by controlling the phase gradient along the bus waveguide with the Bl PS 304 and coupling the light to a slab waveguide feeding antenna 301. In this way, the BIPS 304 serves simultaneously as a lightdistribution component and a phase-control component. As light propagates in the bus waveguide 302, an optical phase gradient is accumulated along the propagation direction. By controlling the optical mode index in the Bl PS 304, the phase gradient along the bus waveguide can be controlled; and therefore, the beam forming angle can be controlled.

[0046] Thus, the Bl PS 304 controls the phase gradient along the bus waveguide 302, and therefore, the relative phase between adjacent antennas 301 on the same row. Using the Bl PS 304 to change the phase gradient in the longitudinal direction permits the steering of the optical beam along the same direction. In contrast, the external phase shifter 303 is used to control the phase at the entry of each respective bus waveguide 302 and to control the relative phase between adjacent rows of antennas. The external phase shifters 303 permits the steering of theoptical beam along the transverse direction. The external phase shifter 303 and the Bl PS 304 can use the same or different structures and mechanisms. However, light in the Bl PS 304 propagates in the waveguide 302 and, in some cases, simultaneously couples to the adjacent slab waveguides feeding antennas 301 ; while light in the external phase shifters 303 accumulate a specific phase shift.

[0047] In some cases, the bus-integrated phase shifter (BIPS) 304 can be implemented using efficient index changing, including and not limited to, thermo-optic effect, electro-optic effect, plasma dispersion effect, slow-light effect, microelectromechanical systems (MEMS), or any other suitable approach.

[0048] In some cases, further phase shifters (not shown), that steer the beam in the transverse direction, can be placed between adjacent antennas 301 on the same row of the antenna array; for example, placed after every nthantenna on the row.

[0049] FIG. 4 illustrates an example embodiment of an approach for efficient index changing using MEMS. In this example embodiment, a MEMS-controlled the optical waveguide 302 is used as a phase shifter. The optical waveguide 302 forms a slot bus waveguide that is comprised of fixed structures 401 , that includes the substrate and antennas 301 , and moveable structures 402. The MEMS, as illustrated in the example embodiment of FIG. 4, allows the use of electrical drives to move structures attached to them. In a particular case, the MEMS can include two arms. A first arm is attached to the fixed structures 401 and a second arm attached to the movable structures 402, whose position in space is controlled by the MEMS. The arms are typically used to suspend structures in the air; for example, the movable structures 402 are connected to a MEMS actuator, while the fixed structures 401 remain still.

[0050] In the example embodiment of FIG. 4, the optical waveguide 302 is formed by the fixed first arm and the movable second arm with air in between. This kind of waveguide is commonly referred to as a “slot waveguide”. The optical mode index is determined by the slot waveguide cross-section and therefore the distance between these two arms. With the movable second arm attached to the slot waveguide, the optical mode index of the slot waveguide can be modified; and therefore, the phase gradient along the longitudinal (x) direction can be modified. Therefore, the beam forming angle in the same direction can likewise be changed and controlled by applying different voltages to the MEMS.

[0051] In example embodiment of FIG. 4, a gap is formed as the edge-to-edge distance between the fixed first arm and the movable second arm. Using the bus waveguide 302 illustrated in FIG.4, the gap impacts the optical mode index. This leads to a large variation of the gap, which results in a large variation of the optical mode index and a large change of the phase gradient along the longitudinal direction; which therefore results in a large beam steering range. The gap size is subject to the beam forming angle along the x-direction and controlled by the MEMS. Advantageously, in the example embodiment of FIG. 4, large mode index variation, and therefore, a large steering angle in the x-direction can be obtained by changing the gap size; for example, during experimentation it was determined that a mode index variation of 0.2 is possible for a gap width variation of 100 nm.

[0052] FIG. 5 illustrates a portion of a particular case of the 2D OPA 300 that includes a slab waveguide 501 and a diffraction grating 502. In this case, light from the light source can be distributed to the antennas 301 through evanescent coupling of an optical mode from the bus waveguide 302 to the slab waveguide 501. In such cases, the bus waveguide 302 distributes the optical power to the antennas 301 and the slab waveguide 501 can be considered as affixed to, or as a portion of, the antenna 301 ; whereby the antenna 301 structure is typically dominated by the diffraction grating 502 structure. Such slab waveguides 501 can be particularly useful because antennas 301 typically have a width that is greater than the bus waveguide 302. In this way, the slab waveguide 501 will generally have a width that is significantly larger than its height. In conventional OPA structures, a relatively larger access waveguide, in “S” shape or other shapes, and a taper structure is used to take the light from the bus waveguide and feed the diffraction grating structure. In contrast, the present embodiments that use the slab waveguide 501 do not use access waveguide in “S” shapes or other shapes and do not use taper structures; and therefore, the placement of the antennas 301 can be significantly more compact and the density of the diffraction grating 502 can be significantly higher.

[0053] FIG. 6 illustrates a method 600 for forming a two-dimensional optical phased array, in accordance with an embodiment. At block 602, an antenna array, of one or more antennas 301 , are each arranged on a substrate into two or more rows. At block 604, each bus waveguide 302 is placed such that a portion of the waveguide 302 is positioned adjacent a respective one of the antenna arrays 301. The bus waveguide 302 have a bus-integrated phase shifter 304 integrated thereon on the portion of each waveguide that is adjacent the respective one of the antenna arrays. At block 606, the external phase shifter 303 is positioned at the bus waveguide 302 preceding each row of antenna arrays (i.e. , along a portion of each waveguide that precedes the portion of each waveguide that is adjacent the respective one of the antenna arrays). In use, each of the bus waveguides 302 receive light that is passed through the external phase shifter 303,then direct the light into the antenna(s) 301 of the antenna array that are positioned adjacent the respective bus waveguide 302, through the bus-integrated phase shifter 304. The external phase shifter 303 steers the optical beam in the transverse direction, and the bus-integrated phase shifter 304 steers the optical beam in the longitudinal direction.

[0054] Advantageously, the present embodiments enable dense integration of antennas and provide a substantially high antenna filling factor (antenna area per optical aperture of the entire array) of up to 50%; which is particularly beneficial for receivers. An array of N*M antennas will need only 2N phase shifters; i.e. , N external phase shifters and N bus-integrated phase shifters. Additionally, antenna center-to-center pitch is substantially small; for example, no more than approximately 3 times of wavelength. Further advantageously, no complex optical routing is generally needed.

[0055] Moreover, in the optical far-field, the present embodiments advantageously suppress most or all of the grating lobes due to the small pitch. An array of optical antennas forms an optical beam in the space comprising the central lobe, which is desired, and sidelobes, which are undesired. The number of undesired sidelobes can be reduced by minimizing the center-to-center (C2C) separation (i.e., pitch) between adjacent antennas. When the C2C pitch is no larger than half of the wavelength of the light, then only one optical beam is generated. As the C2C pitch increases, more undesired sidelobes will emerge. Due to the density of the adjacent antennas 301 in the present embodiments, undesired grating lobes are significantly reduced or eliminated all together.

[0056] Although the foregoing has been described with reference to certain specific embodiments, various modifications thereto will be apparent to those skilled in the art without departing from the spirit and scope of the invention as outlined in the appended claims.

Claims

CLAIMS1 . A two-dimensional optical phased array comprising: antenna arrays, each antenna array comprising one or more antennas; a plurality of bus waveguides, a portion of each bus waveguide positioned adjacent a respective one of the antenna arrays; a plurality of first phase shifters, each phase shifter integrated along a portion of one of the bus waveguides that is adjacent the respective one of the antenna arrays, the first phase shifters steer the light beam in a longitudinal direction; and a plurality of second phase shifters, each second phase shifter is situated along a portion of one of the bus waveguides that precedes the portion of the bus waveguide that is adjacent the respective one of the antenna arrays, the second phase shifters steer the light beam in a transverse direction.

2. The two-dimensional optical phased array of claim 1 , wherein the antenna arrays are arranged in rows.

3. The two-dimensional optical phased array of claim 1 , wherein the first phase shifter induces a phase gradient along the bus waveguide.

4. The two-dimensional optical phased array of claim 1 , wherein the first phase shifter is segmented.

5. The two-dimensional optical phased array of claim 1 , wherein each antenna array comprises a single antenna.

6. The two-dimensional optical phased array of claim 1 , wherein each antenna array comprises a plurality of antennas.

7. The two-dimensional optical phased array of claim 1 , wherein each antenna comprises a diffraction grating.

8. The two-dimensional optical phased array of claim 1 , wherein light is distributed to the one or more antennas from the bus waveguide via a slab waveguide that feeds the one or more antennas through evanescent coupling.

9. The two-dimensional optical phased array of claim 1 , wherein each of the first phase shifters are integrated with the respective bus waveguide and provide light-distribution to the antenna arrays in addition to steering in the longitudinal direction.

10. The two-dimensional optical phased array of claim 1 , wherein the bus waveguides comprise an optical waveguide controlled by a microelectromechanical system.

11. The two-dimensional optical phased array of claim 10, wherein the optical waveguide comprises a slot bus waveguide as the bus-integrated phase shifter, the slot bus waveguide comprising fixed structures and moveable structures, the moveable structures moved by the microelectromechanical system relative to the fixed structures to adjust a gap width that alters a phase gradient of the optical waveguide.

12. A method for forming a two-dimensional optical phased array, the method comprising: arranging antenna arrays into a plurality of rows on a substrate, each antenna array comprising one or more antennas; placing bus waveguides with a portion of each bus waveguide positioned adjacent a respective one of the antenna arrays; integrating a plurality of first phase shifters, each phase shifter positioned along a portion of one of the bus waveguides, the portion being adjacent the respective one of the antenna arrays, the first phase shifter steers the light beam in a longitudinal direction; and placing a plurality of second phase shifters, each second phase shifter positioned along a portion of one of the bus waveguides that precedes the portion of each bus waveguide that is adjacent the respective one of the antenna arrays, the second phase shifter steers the light beam in a transverse direction.

13. The method of claim 12, wherein each antenna array comprises a single antenna.

14. The method of claim 12, wherein each antenna array comprises a plurality of antennas.

15. The method of claim 14, wherein light is distributed to the antennas from the bus waveguide via a slab waveguide that feeds the antennas through evanescent coupling.

16. The method of claim 12, wherein the first phase shifters are integrated with the respective bus waveguide and provide light-distribution to the antenna arrays in addition to steering in the longitudinal direction.

17. The method of claim 12, further comprising installing a microelectromechanical system to control an optical waveguide, the bus waveguides comprising the optical waveguide.

18. The method of claim 17, wherein the optical waveguide comprises a slot bus waveguide as the bus-integrated phase shifter, the slot bus waveguide comprising fixed structures and moveable structures, the moveable structures moved by the microelectromechanical system relative to the fixed structures to adjust a gap width that alters a phase gradient of the optical waveguide.

19. The method of claim 12, further comprising providing a slab waveguide between the bus waveguide and a diffraction grating of the one or more antennas to distribute light to the diffraction grating of the one or more antennas through evanescent coupling of an optical mode from the bus waveguide to the slab waveguide.

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