Patent Description:
If there are any contradictions or inconsistencies in language between this application and the cases that have been incorporated by reference that might affect the interpretation of the claims in this case, the claims in this case should be interpreted to be consistent with the language in this case.

This invention was made with Government support under Contract No. DEAR0000849 awarded by the Advanced Research Projects Agency-Energy (ARPA-E). The Government has certain rights in the invention.

The present disclosure relates to free-space optics in general, and, more particularly, to free-space beam-steering.

Agile beam-steering devices are needed for free-space optical communications as well as LiDAR (light detection and ranging), 3D imaging, sensing, and microscopy applications. They provide scanning and acquisition/pointing/tracking (ATP) functions. Traditional beam-steering apparatuses use motorized mechanical gimbals to rotate the entire optical systems. Unfortunately, motorized gimbals are bulky, heavy, and consume a great deal of power.

Integrated beam-steering systems have shown great utility in portable or mobile platforms, and have become key elements of "solid-state LiDAR". For example, collimation and beam-steering has been demonstrated in the prior art using a light source positioned at the focal plane of a lens (e.g., telecentric lens, telescope, etc.) and changing the arrangement of the position of the optical axis of the lens and the position of the light source within the focal plane of the lens. This has been done in various ways, such as by moving a macro light source relative to the optical axis, moving an optical fiber located in the focal plane, and moving the lens relative to a fixed-position light source.

Unfortunately, the mechanical systems required to move the lens and/or light source have limited frequency response due to the weight/stiffness of the loads, are too slow for LiDAR and/or free-space communications between fast moving vehicles, and are bulky, complex, slow, and expensive.

Other prior-art beam-steering systems are based on electronic crossbar switches that selectively energize individual elements of a two-dimensional (2D) array of vertical cavity surface-emitting lasers (VCSEL). However, such an approach requires large arrays of lasers. In addition, such systems require VCSEL sources, which are not well suited for some communication or sensing applications.

Still other prior-art beam-steering systems have used silicon-photonic-based thermo-optic switches to activate surface-emitting grating couplers. Unfortunately, thermo-optic switches are temperature sensitive, have limited steering capability, have high power consumption and do not scale well to large-scale beam-steering devices.

<CIT> discloses a steerable optical transmit and receive terminal including a MEMS-based Nxl optical switching network. Each optical switch in the switching network uses an electrostatic MEMS structure to selectively position a translatable optical grating close to or far from an optical waveguide. In the close ("ON") position, light couples between the translatable optical grating and the optical waveguide, whereas in the far ("OFF") position, no appreciable light couples between the translatable optical grating and the optical waveguide. The translatable optical grating is disposed at or near a surface of the optical switching network. Thus, the translatable optical grating emits light into, or receives light from, free space. The steerable optical transmit and receive terminal also includes a lens and can steer a free space optical beam in a direction determined by which port of the Nxl optical switching network is ON.

<CIT> refers to a system serving as a transmitter and comprising an optics system, a plurality of source elements positioned on the focal plane, and a small angle beam steerer. The plurality of source elements are each capable of providing a point source of radiation to the optics system. The optics system provides a collimated output. The small angle beam steerer receives the collimated output and redirects the collimated output through a small angular deviation. The redirected output is transmitted in a desired direction without a need for mechanical gimbals and is capable of covering a large angular range with respect to the optical axis of the optics system. The system can also be implemented as a receiver.

<CIT> discloses a programmable electro-optically controlled optical delay device providing multiple optical outputs where the optical propagation delay increases at each port. An incident optical beam is propagated within electro-optically active material within the device, so that the propagation delay at each output port may be varied according to an applied voltage. In an optical beam steering system, the present invention provides true-time delay for multiple optical beams, allowing the beams radiated by the beam steering system to be time-coincident. The present invention provides for one or two dimensional beam steering.

Practical beam-steering technology remain, as yet, unavailable in the prior art.

The present disclosure is directed to a beam-steering apparatus comprising an integrated-optics-based, programmable, two-dimensional (2D) array of mechanically active vertical-grating couplers (i.e., couplers) that is located in the focal plane of a lens. The lens is arranged to convert free-space light emitted by any of the couplers into a collimated, free-space light beam. The programmable coupler array is monolithically integrated on a substrate and includes a switching network that controls which coupler (or couplers) is energized (i.e., receives light and launches it into free space). The switching network is configured to mitigate leakage to non-energized couplers, thereby mitigating optical crosstalk. The propagation direction of each free-space light beam (i.e., its output angle with respect to the optical axis of the lens) is a function of the x and y coordinates of its respective coupler relative to the optical axis of the lens. Embodiments in accordance with the present disclosure are particularly well suited for use in LiDAR systems, optical communications systems, optical coherence tomography and other medical imaging systems, three-dimensional imaging and sensing applications, and the like.

An illustrative embodiment in accordance with the present disclosure is a beam-steering system that includes a lens and a programmable vertical coupler array that includes (<NUM>) a 2D array of mechanically active integrated-optics-based couplers and (<NUM>) an integrated-optics-based switching network for controlling which coupler is energized.

Each vertical coupler of the 2D array includes a grating structure formed in an integrated-optics waveguide, where the waveguide and grating are configured such that the optical energy of a light signal propagating through the waveguide is launched into free space by the grating.

The switching network receives a light signal at an input port of a bus waveguide that is optically couplable with each of a plurality of row waveguides via a different MEMS-based optical switch that has an OFF state and an ON state. In its OFF state, a light signal received at the switch remains in the bus waveguide and passes through the switch with substantially no optical energy being lost. In its ON state, the light signal is completely transferred from the bus waveguide to its respective row waveguide. Each switch is configured such that the bus and row waveguides are optically isolated from one another when the switch is in its OFF state to mitigate leakage between them at the switch.

Each row waveguide is also optically couplable with each coupler in a corresponding row of the coupler array by another MEMS-based optical switch. In the OFF state of each row-waveguide switch, a light signal propagating through the row waveguide remains in the row waveguide and passes through the switch with substantially no optical energy being lost. In its ON state, the light signal is completely transferred from the row waveguide to its respective coupler.

The lens is arranged to receive the optical energy launched into free-space by each coupler and convert the received optical energy into a collimated free-space output beam. The output beam is directed along a propagation direction that is based on the x and y coordinates of the vertical coupler relative to the optical axis of the lens.

In some embodiments, only a single vertical coupler can be energized at a time. In some embodiments, the switching network enables a plurality of vertical couplers to be energized at a given time. In some embodiments, the switching network is completely non-blocking, thereby enabling each vertical coupler to be energized regardless of the state of any other vertical coupler.

In some embodiments the arrangement of the lens and coupler array is controllable.

An embodiment in accordance with the present disclosure is a beam-steering system (<NUM>) comprising: a lens (<NUM>) and a programmable vertical coupler array (<NUM>) comprising: a substrate (<NUM>); an array of couplers (<NUM>) that is a two-dimensional array characterized by a center point (CP1) and having a plurality of coupler rows (CR) and a plurality of coupler columns (CC), each coupler of the array thereof including a coupler waveguide (<NUM>) and a vertical-coupling element (<NUM>) that is configured to launch optical energy received from the coupler waveguide into free space; a bus waveguide (<NUM>) disposed on the substrate, the bus waveguide having a first input port (IP1) for receiving a first light signal (<NUM>); a first plurality of row waveguides (<NUM>) disposed on the substrate; and a switching network (<NUM>) that is operative for controlling the propagation of a first light signal (<NUM>) from the first input port to any coupler of the array thereof; wherein the lens and programmable vertical coupler array are arranged such that the lens receives the optical energy launched by each vertical-coupling element of the plurality thereof and directs the optical energy in a direction that is based on the position of that vertical-coupling element within the programmable vertical coupler array and a relative position of the lens and the programmable vertical coupler array, characterized in that each coupler of the plurality thereof is optically couplable with a row waveguide of the first plurality thereof; and coupler waveguide of the coupler array has a movable end (<NUM>-<NUM>) and a fixed end (<NUM>-<NUM>) that includes its respective vertical-coupling element, wherein the fixed end has a fixed height relative to its respective row waveguide.

<FIG>depict schematic drawings of side and top views of an illustrative embodiment of a beam-steering system in accordance with the present disclosure. Beam-steering system <NUM> includes lens <NUM>, programmable coupler array <NUM>, and controller <NUM>. System <NUM> is configured to receive input light signal <NUM>, collimate its optical energy as free-space output beam <NUM>, and steer the output beam through a three-dimensional volume. In the depicted example, light signal <NUM> is a continuous wave (CW) signal; however, system <NUM> is operative for virtually any light signal (e.g., frequency-modulated continuous wave (FMCW) signals, LiDAR signals, light pulses, and the like).

Lens <NUM> is a simple convex-convex refractive lens having optical axis A1 and focal length, f, which defines focal plane FP1. In some embodiments, lens <NUM> is a different type of lens, such as a compound lens (e.g., a telecentric lens, etc.) or other multielement lens configured to, for example, correct one or more aberrations or otherwise improve optical performance. In some embodiments, lens <NUM> is a plano-convex lens. In some embodiments, lens <NUM> is a cellphone lens, which are typically low cost and can enable mobile systems. In some embodiments, lens <NUM> is a diffractive element, such as a diffractive lens, holographic element, metasurface lens, and the like.

Programmable coupler array <NUM> (hereinafter referred to as coupler array <NUM>) includes switching network <NUM> and vertical couplers <NUM>(<NUM>,<NUM>) through <NUM>(M,N) (referred to, collectively, as couplers <NUM>). Vertical couplers <NUM> are arranged in a two-dimensional array comprising coupler rows CR-<NUM> through CR-M (referred to, collectively, as coupler rows CR) and coupler columns CC-<NUM> through CC-N (referred to, collectively, as coupler columns CC).

In the depicted example, switching network <NUM> and couplers <NUM> are monolithically integrated on substrate <NUM>; however, in some embodiments, one or more elements of programmable coupler array <NUM> are located on substrate <NUM> using a different integration method, such as bump bonding, multi-chip module packaging, etc..

In the depicted example, substrate <NUM> is a silicon substrate. The use of a silicon substrate enables the straight-forward inclusion of integrated circuits and/or other circuitry that can augment the capabilities of coupler array <NUM>. In some embodiments, such on-chip capability includes electronics for signal modulation, phase shifting, photodetectors, processing, memory, signal conditioning, pre-amplification, energy scavenging and/or storage, and the like. In some embodiments, the entire electronics functionality of a LiDAR system is monolithically integrated on substrate <NUM>.

Controller <NUM> is a conventional controller that is configured to control the positions of lens <NUM> and coupler array <NUM> in each of the x-, y-, and z-dimensions via a positioning system, such as a high-precision, multi-axis positioning system, voice coils, piezoelectric actuators, MEMS actuators, and the like. Controller <NUM> is also operative for controlling the state of switching network <NUM> and, therefore which coupler or couplers of the coupler array are energized. In some embodiments, controller <NUM> is at least partially integrated on coupler array <NUM>.

It should be noted that, although the present disclosure is directed toward beam steering applications, the teachings disclosed herein are also applicable to steerable receivers (i.e., receivers whose receiving direction is controllable), as well as transceivers that comprise both a beam-steering transmitter and a steerable receiver.

In the depicted example, lens <NUM> and coupler array <NUM> are arranged such that they are concentric and the separation, s1, between them is equal to the focal length, f, of lens <NUM>. As a result, the plane of couplers <NUM> is substantially located at focal plane FP1 and optical axis A1 is centered on the arrangement of couplers <NUM>, thereby defining center point CP1. In some embodiments, lens <NUM> is located such that the lens and coupler array are separated by a distance other than the focal length of the lens and/or such that optical axis A1 is not centered on the arrangement of couplers <NUM> of the coupler array.

In the depicted example, controller <NUM> is optionally configured to scan lens <NUM> along scan direction SD1 to control the lateral alignment of lens <NUM> and coupler array <NUM> in each of the x- and y-dimensions. Such lateral scanning capability enables output beam <NUM> to be smoothly moved between angles dictated by the fixed positions of each coupler within the coupler array, thereby realizing a greater number of resolvable spots than possible with a fixed-position system. In some embodiments, controller <NUM> is further configured to control the vertical separation, s1, between the lens and coupler array, thereby enabling output beam <NUM> to be focused at different points in space. It should be noted that the lateral alignment between the lens and coupler array can be controlled by moving only lens <NUM>, only coupler array <NUM>, or by moving both the lens and coupler array.

Switching network <NUM> includes row switch <NUM> and column switch <NUM>, which collectively control the distribution of the optical energy of light signal <NUM> throughout the programmable coupler array. In the depicted example, switching network <NUM> is configured to direct all of the optical energy of light signal <NUM> to only one coupler <NUM>. Switching network <NUM> is described in more detail below and with respect to <FIG>.

Each of couplers <NUM>(i,j), where i=<NUM> through M and j=<NUM> through N, comprises a diffraction grating that is integrated into the structure of an integrated-optics waveguide (i.e., a "coupler waveguide") in coupler array <NUM> and configured such that its output light signal <NUM>' is characterized by output axis A2, which is substantially aligned with a geometric line between its respective coupler and the center of lens <NUM>. In some embodiments, it is preferable that at least one diffraction grating of couplers <NUM> is a blazed grating to achieve high efficiency. In addition, in the depicted example, each of couplers <NUM> is characterized by a large dispersion angle such each of light signals <NUM>' substantially fills the clear aperture of lens <NUM>. It should be noted that the design of each coupler <NUM> is typically based on its position with coupler array <NUM>.

By virtue of the alignment of output axis A2 with the center of lens <NUM>, light signal <NUM>' illuminates a larger portion of the aperture of the lens, which mitigates the divergence angle of output beam <NUM> in the far field and increases the resolution with which output beam <NUM> can be steered.

Each coupler <NUM>(i,j) is configured such that it can be switched between an ON state and an OFF state. In its ON state, coupler <NUM>(i,j) is optically coupled with input port IP1 such that its grating structure receives light signal <NUM> and scatters its optical energy into free space as light signal <NUM>'(i,j). In its OFF state, coupler <NUM>(i,j) is optically decoupled from input port IP1 and its grating structure does not receive light signal <NUM>. Preferably, each coupler <NUM> is designed to correct for aberrations of lens <NUM>. It should be noted that many different designs for the grating element of coupler <NUM> are within the scope of the present invention, including one-dimensional gratings or two-dimensional gratings.

Lens <NUM> receives light signal <NUM>'(i,j) at a distance from optical axis A1 that depends on the position of signal <NUM>(i,j) within coupler array <NUM>. As a result, every light signal emitted by a different vertical coupler is collimated and steered along a different output axis A2(i,j) by lens <NUM>.

<FIG>depict schematic drawings of perspective views of an exemplary beam-steering system in accordance with the present disclosure in different beam-steering states. Beam-steering system 100A is an example of beam steering system <NUM> in which programmable coupler array <NUM> includes only nine couplers 112A (i.e., couplers 112A(<NUM>,<NUM>) through 112A(<NUM>,<NUM>)), which are arranged in a 3x3 array. Furthermore, it should be noted that, in <FIG>, each of couplers 112A(<NUM>,<NUM>) through 112A(<NUM>,<NUM>)) is an example of an alternative coupler - specifically, a conventional vertical grating coupler - having an emission pattern that realizes a relatively narrower lights signal propagating along a propagation direction that is substantially normal to the plane of coupler array <NUM>, as discussed below and with respect to <FIG>.

<FIG> shows system 100A in a beam-steering state in which only coupler <NUM>(<NUM>,<NUM>) is in its ON state. As a result, coupler <NUM>(<NUM>,<NUM>) receives light signal <NUM> and launches it into free space as light signal <NUM>'(<NUM>,<NUM>). Lens <NUM> receives light signal <NUM>'(<NUM>,<NUM>), collimates it, and directs it along output axis A2(<NUM>,<NUM>) as output beam <NUM>(<NUM>,<NUM>). Output beam <NUM>(<NUM>,<NUM>) propagates along output axis A2(<NUM>,<NUM>), which is oriented at angles θx1 and θy1. Angles θx1 and θy1 are angles in the x-z and y-z planes, respectively, relative to optical axis A1. Angles θx1 and θy1 are given by the formulas: θx = <MAT> and <MAT>, where f is the focal length of lens <NUM> and (x,y) is the coordinate of the energized grating coupler in the x-y plane (i.e., the focal plane of the vertical coupler array) relative to center point CP1.

<FIG> shows system 100A in a beam-steering state in which only coupler <NUM>(<NUM>,<NUM>) is in its ON state. As a result, coupler <NUM>(<NUM>,<NUM>) receives light signal <NUM> and launches it into free space as light signal <NUM>'(<NUM>,<NUM>). Lens <NUM> receives light signal <NUM>'(<NUM>,<NUM>), collimates it, and directs it along output axis A2(<NUM>,<NUM>) as output beam <NUM>(<NUM>,<NUM>). Output beam <NUM>(<NUM>,<NUM>) propagates along output axis A2(<NUM>,<NUM>), which is oriented at angles θx2 and θy2.

<FIG> depicts an operational schematic drawing of a coupler array in accordance with the illustrative embodiment. Coupler array <NUM> includes switching network <NUM>, couplers <NUM>, bus waveguide <NUM>, and row waveguides <NUM>-<NUM> through <NUM>-M.

As depicted in <FIG>, coupler array <NUM> in an exemplary switch configuration in which MEMS optical switch <NUM>-<NUM> and column switch array <NUM>-<NUM> are each in their ON states, while all other MEMS optical switches <NUM> and column switch arrays <NUM> are in their OFF states (as discussed below). As a result, light signal <NUM> is diverted from bus waveguide <NUM> into row waveguide <NUM>-<NUM> by MEMS optical switch <NUM>-<NUM> and then from row waveguide <NUM>-<NUM> into coupler <NUM>(<NUM>,<NUM>) by column switch array <NUM>-<NUM>.

Each of bus waveguide <NUM> and row waveguides <NUM>-<NUM> through <NUM>-M (referred to, collectively, as row waveguides <NUM>) is a single-mode ridge waveguide having a core of single-crystal silicon. In the depicted example, the bus and row waveguides are coplanar. In some embodiments, at least one of the bus and row waveguides is a multimode waveguide. In some such embodiments, the multi-mode waveguide includes a large width and is configured such that its fundamental mode can be excited to reduce optical loss.

Although the depicted example includes bus and row waveguides (and shunt and coupling waveguides, as discussed below) that are silicon-based ridge waveguides, in some embodiments, a different waveguide structure (e.g., rib waveguides, etc.) and/or a different waveguide material system is used for at least one waveguide. For example, the use of dielectric-based waveguides, such as silicon-nitride-core waveguides, can realize systems having lower optical loss and/or increased optical power-handling capability (peak or average), which can mitigate nonlinear effects, and the like.

Switching network <NUM> includes row switch <NUM> and column switch <NUM>.

Row switch <NUM> is a 1xM switch that includes MEMS optical switches <NUM>-<NUM> through <NUM>-M (referred to, collectively, as MEMS optical switches <NUM>), which are independently controllable 1x2 integrated-optics-based MEMS switches for controlling the optical coupling between bus waveguide <NUM> and row waveguides <NUM>-<NUM> through <NUM>-M, respectively.

<FIG> depicts a schematic drawing of a top view of MEMS optical switch <NUM>.

<FIG>depict schematic drawings of perspective views of a representative MEMS optical switch <NUM> in its "off" and ON states, respectively.

MEMS optical switch <NUM> includes a portion of bus waveguide <NUM>, a portion of row waveguide <NUM>, shunt waveguide <NUM> and MEMS actuator <NUM> (not shown in <FIG>).

In the depicted example, the portions of bus waveguide <NUM> and row waveguide <NUM> are arranged such that there is no waveguide crossing between them. As a result, very low optical insertion loss can be achieved, as well as substantially zero optical cross-talk between the waveguides. In some embodiments, however, the two waveguide portions intersect at a crossing point, preferably such that they are orthogonal to mitigate leakage of bus waveguide <NUM> into row waveguide <NUM> when MEMS optical switch <NUM> is in its OFF state. In some embodiments, bus waveguide <NUM> includes multi-mode interference (MMI) region and tapers leading into and out of the MMI region. In some embodiments, bus waveguide <NUM> and row waveguides <NUM> are formed in different planes above their common substrate.

Shunt waveguide <NUM> is a waveguide portion that extends between ends <NUM>-<NUM> and <NUM>-<NUM>. Shunt waveguide <NUM> is analogous to bus waveguide <NUM> and row waveguides <NUM>; however, shunt waveguide <NUM> is configured to be movable relative to the bus and row waveguides.

Ends <NUM>-<NUM> and <NUM>-<NUM> (referred to, collectively, as ends <NUM>) are aligned directly above waveguide portions <NUM>-<NUM> and <NUM>-<NUM>, respectively, where waveguide portions <NUM>-<NUM> and <NUM>-<NUM> (referred to, collectively, as waveguide portions <NUM>) are portions of bus waveguide <NUM> and row waveguide <NUM>, respectively.

Although not depicted in <FIG> for clarity, typically, shunt waveguide <NUM> also includes projections that extend from its bottom surface to establish a precise vertical spacing between ends <NUM> and waveguide portions <NUM> when MEMS optical switch <NUM> is in its ON state.

MEMS actuator <NUM> is an electrostatic MEMS vertical actuator that is operative for controlling the vertical position of shunt waveguide <NUM> and ends <NUM> relative to waveguide portions <NUM>-<NUM> and <NUM>-<NUM>. MEMS actuator <NUM> is described in more detail below and with respect to <FIG>.

Although MEMS optical switch <NUM> includes an electrostatic MEMS vertical actuator in the illustrative embodiment, it will be clear to one skilled in the art, after reading this Specification, how to specify, make, and use any actuator suitable for controlling the separation between ends <NUM> and waveguide portions <NUM>. Actuators suitable for use in the present invention include, without limitation, vertical actuators, lateral actuators, and actuators that actuate both vertically and laterally. Further, actuators in accordance with the present invention include, without limitation, electrothermal, thermal, magnetic, electromagnetic, electrostatic comb-drive, magnetostrictive, piezoelectric, fluidic, pneumatic actuators, and the like.

When MEMS optical switch <NUM> is in its unswitched (i.e., "off") state, shunt waveguide <NUM> is held at a first position in which ends <NUM>-<NUM> and <NUM>-<NUM> are separated from waveguide portions <NUM>-<NUM> and <NUM>-<NUM> by distance d1. Distance d1 has a magnitude that is sufficient to ensure that substantially no optical energy transfers between ends <NUM> and their respective waveguide portions. As a result, light signal <NUM> bypasses MEMS optical switch <NUM> and continues to propagate, substantially unperturbed, through bus waveguide <NUM>.

When MEMS optical switch <NUM> is in its switched (i.e., "on") state, shunt waveguide <NUM> is moved to a second position in which ends <NUM> are separated from waveguide portions <NUM> by distance d2, thereby defining directional couplers <NUM>-<NUM> and <NUM>-<NUM>. Distance d2 is determined by the height of the projections on the bottom of the shunt waveguide and has a magnitude that enables the optical energy of light signal <NUM> to substantially completely transfer from waveguide portion <NUM>-<NUM> into end <NUM>-<NUM> at directional coupler <NUM>-<NUM> and from end <NUM>-<NUM> into waveguide portion <NUM>-<NUM> at directional coupler <NUM>-<NUM>. As a result, light signal <NUM> is substantially completely switched from bus waveguide <NUM> into row waveguide <NUM>.

It should be noted that MEMS optical switch <NUM> is merely one example of an integrated-optics-based MEMS optical switch. Additional examples of MEMS switches suitable for use in accordance with the teachings of the present disclosure are described by <NPL>, as well as in <CIT> and International Publication No. <CIT>. MEMS switches such those described in these publications offer many advantages for programmable coupler arrays in accordance with the present disclosure relative to prior-art beam-steering systems. In particular, such switches have significant lower optical loss than conventional electro-optic or thermo-optic switches, their optical crosstalk (< -<NUM> dB) and power consumption (~ <NUM> microwatts) are several orders of magnitude lower than conventional switches, and they can operate in digital mode. These advantages enable beam-steering devices having relatively higher throughput (i.e., lower optical insertion loss) and relatively higher resolution (i.e., greater density of grating couplers) than possible in the prior art, as well as simple digital control.

Returning now to <FIG>, column switch <NUM> is a 1xN switch that includes column switch arrays <NUM>-<NUM> through <NUM>-N (referred to, collectively, as column switch arrays <NUM>).

In the depicted example, each column switch array <NUM> includes M substantially identical MEMS optical switches <NUM>, each of which is analogous to MEMS optical switch <NUM>; however, each MEMS optical switch <NUM> is configured to control the optical coupling between a respective coupler <NUM> and a row waveguide <NUM>. Each MEMS optical switch <NUM> and its associated coupler <NUM> collectively defines a MEMS-controlled vertical coupler <NUM>.

In the depicted example, all of the MEMS optical switches <NUM> of each column switch array <NUM> are "ganged together" such that they are all controlled with the same control signal. As a result, each column switch array <NUM> simultaneously controls the optical coupling between all M couplers <NUM> in its respective column of coupler arrays <NUM> and their respective row waveguides. Such a switch array configuration is particularly advantageous for beam steering system having large numbers of couplers (e.g., an MxN array where each of M and N is <NUM> or more), which would require MxN control signals if each coupler were addressed individually. For large systems, the number of electrical input/output (I/O) would quickly exceed standard electrical packaging limits. The use of switch arrays, such as column switch arrays <NUM>, however, can significantly reduce the number of electrical control signals required by enabling a "row-column" addressing scheme that reduces the number of control signals from MxN to M+N.

In the ON state of each MEMS-controlled vertical coupler <NUM>, its MEMS optical switch <NUM> optically couples its respective row waveguide <NUM> with its respective coupler <NUM>. As a result, when light signal <NUM> is propagating through that row waveguide, its optical energy is diverted to its coupler <NUM>. In the OFF state of each MEMS-controlled vertical coupler <NUM>, its MEMS optical switch <NUM> does not optically couple its respective row waveguide and coupler; therefore, light signal <NUM> remains in the row waveguide and bypasses that coupler.

<FIG> depicts a schematic drawing of a top view of an exemplary MEMS-controlled vertical coupler in accordance with the illustrative embodiment. MEMS-controlled vertical coupler <NUM> comprises MEMS optical switch <NUM> and coupler <NUM>.

<FIG>depict schematic drawings of a sectional view of MEMS-controlled vertical coupler <NUM> in its "off" and ON states, respectively. The sectional views shown in <FIG> are taken through line a-a depicted in <FIG>.

MEMS optical switch <NUM> includes a portion of coupler waveguide <NUM>, which is operatively coupled with MEMS actuator <NUM>.

Coupler waveguide <NUM> is analogous to shunt waveguide <NUM> and is configured to convey light from movable end <NUM>-<NUM> to fixed end <NUM>-<NUM>, where vertical-coupling element <NUM> is located, thereby defining coupler <NUM>. In the depicted example, vertical-coupling element <NUM> is a diffraction grating that is configured to direct its optical energy toward the center of lens <NUM> when optical axis A1 is aligned with center point CP1. In some embodiments, at least one of vertical-coupling element <NUM> includes a different optical element suitable for providing a desired output light signal <NUM>'. Optical elements suitable for use in vertical-coupling element <NUM> includes, without limitation, prisms, holograms, two-dimensional grating structures, diffractive lenses, diffraction-grating elements, refractive lenses, angle-etched waveguide-facet mirrors, angle-etched waveguides, angled mirrors, and the like.

At movable end <NUM>-<NUM>, coupler waveguide <NUM> is attached to MEMS actuator <NUM>.

At fixed end <NUM>-<NUM>, coupler waveguide <NUM> is physically attached to a pair of anchors <NUM>, which are rigid elements that project up from underlying substrate <NUM>. Since the coupler waveguide is affixed to rigid structural elements in this region, its height above the row waveguide <NUM> is fixed.

MEMS actuator <NUM> is analogous to MEMS actuator <NUM>, described above, and includes struts <NUM>, electrodes <NUM>, and tethers <NUM>, which are connected to another pair of anchors <NUM>.

Struts <NUM> are substantially rigid elements that connect movable end <NUM>-<NUM> to each of electrodes <NUM>.

Electrodes <NUM> are located above a matching pair of electrodes disposed on substrate <NUM> (not shown) such that a voltage applied between the two pairs of electrodes give rise to an electrostatic force that pulls the electrodes, struts, and movable end toward the substrate, thereby reducing the separation between coupler waveguide <NUM> and row waveguide <NUM>.

Tethers <NUM> are "spring-like" elements that are flexible in the z-direction but substantially rigid along the x- and y-directions. The flexibility of tethers <NUM> enable the motion of movable end <NUM>-<NUM> relative to row waveguide <NUM>.

When MEMS actuator <NUM> is in its unactuated state, movable end <NUM>-<NUM> is separated from row waveguide <NUM> by distance d1. As a result, the two waveguides are not optically coupled, as discussed above and coupler <NUM> is in its OFF state.

When MEMS actuator <NUM> is in its actuated state, movable end <NUM>-<NUM> is forced downward such that it becomes separated from row waveguide <NUM> by distance d2, which is determined by the height of projections <NUM>. As a result, the two waveguides collectively define directional coupler <NUM>, which enables substantially all of light signal <NUM> to evanescently couple into coupler waveguide <NUM> and propagate to grating element <NUM>. The optical energy of the light signal is then launched into free-space by grating element <NUM> and coupler <NUM> is in its ON state.

It should be noted that the MEMS-controlled vertical coupler <NUM> is merely exemplary and that myriad alternative designs for MEMS-controlled vertical coupler <NUM> are within the scope of the present disclosure.

For example, in some embodiments, no coupler waveguide is included in MEMS-controlled vertical coupler <NUM> and grating element is disposed on a MEMS actuator <NUM> itself.

<FIG> depicts a schematic drawing of a top view of an alternative embodiment of a MEMS-controlled vertical coupler in accordance with the present disclosure. MEMS-controlled vertical coupler 212A includes MEMS actuator <NUM>, grating element <NUM>, platform <NUM>, and coupler waveguide <NUM>.

Platform <NUM> is a substantially rigid structural element formed at the center of the MEMS actuator. Platform <NUM> includes coupler waveguide <NUM>, which is analogous to the movable portion of coupler waveguide <NUM>.

<FIG>depict schematic drawings of MEMS-controlled vertical coupler 212A in its OFF and ON states, respectively. The sectional views shown in <FIG> are taken through line b-b depicted in <FIG>.

When MEMS actuator <NUM> is in its unactuated state, movable end <NUM>-<NUM> is separated from row waveguide <NUM> by distance d1. As a result, the two waveguides are not optically coupled and coupler <NUM> is in its OFF state.

When MEMS actuator <NUM> is in its actuated state, row waveguide <NUM> and coupler waveguide <NUM> collectively define directional coupler <NUM>, which couples optical energy from the row waveguide directly into grating element <NUM>, which then emits the energy into free space.

In some embodiments, MEMS-controlled vertical coupler <NUM> includes a row waveguide and coupling waveguide that lie in the same plane and switching is realized using a movable shunt waveguide, as described above.

<FIG> depicts a schematic drawing of a top view of another alternative MEMS-controlled vertical coupler in accordance with the present disclosure. MEMS-controlled vertical coupler 212B includes MEMS actuator <NUM>, row waveguide <NUM>, coupler waveguide <NUM>, shunt waveguide <NUM>, and coupler <NUM>. MEMS-controlled vertical coupler 212B is analogous to MEMS optical switch <NUM> described above and with respect to <FIG>.

When MEMS actuator <NUM> is in its unactuated state, shunt waveguide is held well above row waveguide <NUM> and coupler waveguide <NUM>. As a result, the two waveguides are not optically coupled and coupler <NUM> is in not energized.

When MEMS actuator <NUM> is in its actuated state, shunt waveguide <NUM> is optically coupled with each of row waveguide <NUM> and coupler waveguide <NUM>, thereby defining directional couplers at each end of the shunt waveguide. As a result, optical energy couples from the row waveguide into the shunt waveguide and then from the shunt waveguide into the coupling waveguide. The optical energy is conveyed by the coupling waveguide into coupler <NUM>, thereby energizing it such that it emits the optical energy into free space.

<FIG> depicts an alternative programmable coupler array in accordance with the present disclosure. Coupler array <NUM> is analogous to coupler array <NUM>; however, coupler array <NUM> is configured to direct multiple light signal to multiple couplers <NUM>, thereby enabling beam-steering systems that can simultaneously form and steer multiple output beams.

Coupler array <NUM> includes switching network <NUM> and vertical couplers <NUM>, bus waveguide <NUM>, and row waveguides <NUM>-<NUM> through <NUM>-M.

Switching network <NUM> includes row switch <NUM> and column switches <NUM>-<NUM> through <NUM>-M.

Row switch <NUM> is an LxM switch that is operative for directing any of input signals <NUM>-<NUM> through <NUM>-L to a different one of row waveguides <NUM>-<NUM> through <NUM>-M.

Each of column switches <NUM>-<NUM> through <NUM>-M is 1xN optical switch that includes N switches <NUM>. Column switch <NUM>-<NUM> directs the light signal it receives from row switch <NUM> to one of couplers <NUM>(<NUM>,<NUM>) through <NUM>(<NUM>,N), column switch <NUM>-<NUM> directs light signal <NUM>-<NUM> to one of couplers <NUM>(<NUM>,<NUM>) through <NUM>(<NUM>,N), and so on.

As a result, a beam-steering system comprising coupler array <NUM> can provide a plurality of independently steerable collimated output beams <NUM>-<NUM> through <NUM>-L.

As noted above, the number of electrical signals required can become problematic for a beam system having independently controllable switches. For example, in system <NUM>, the number of electrical signals required is NxM+LxM. In some embodiments, however, integrated electrical addressing circuits are included to mitigate electrical packaging problems. Such integration can be achieved via any of a wide range of known techniques, such as monolithic integration, hybrid integration, flip-chip bonding, and the like.

It should be noted that the architecture of system <NUM> is blocking in the sense that only one coupler <NUM> per row can receive a light signal from row switch <NUM>.

<FIG> depicts another alternative programmable coupler array in accordance with the present disclosure. Programmable coupler array <NUM> is a non-blocking coupler array suitable for use in a beam-steering system configured to provide a plurality of independently steerable output beams. Programmable coupler array <NUM> is analogous to programmable coupler array <NUM>; however, switching network <NUM> includes a row switch that is an LxM optical switch and M column switches that are PxN optical switches.

Coupler array <NUM> includes switching network <NUM>, vertical couplers <NUM>, bus waveguide <NUM>, and row waveguides <NUM>-<NUM> through <NUM>-MxP.

Row switch <NUM> is an Lx(MxP) switch that is operative for directing any of input signals <NUM>-<NUM> through <NUM>-L to a different one of bus waveguides <NUM>-<NUM> through <NUM>-MxP.

Each of column switches <NUM>-<NUM> through <NUM>-M is PxN optical switch capable of directing a light signal received on each of P row waveguides <NUM> to any of N coupler <NUM>. Column switch <NUM>-<NUM> directs the light signal it receives on each of row waveguides <NUM>(<NUM>,<NUM>) through <NUM>(<NUM>,P) to any one of couplers <NUM>(<NUM>,<NUM>) through <NUM>(<NUM>,N), column switch <NUM>-<NUM> directs the light signal it receives on each of row waveguides <NUM>(<NUM>,<NUM>) through <NUM>(<NUM>,P) to one of couplers <NUM>(<NUM>,<NUM>) through <NUM>(<NUM>,N), and so on.

In other words, each row of couplers <NUM> is connected to Lx(MxP) switch <NUM> through P waveguides and a PxN switch <NUM>. As a result, any of P input signals can simultaneously access the grating couplers in the same row.

<FIG> depicts a schematic drawing of a side view of an alternative beam-steering system in accordance with the present disclosure. Beam-steering system <NUM> is analogous to beam steering system <NUM>; however, beam-steering system <NUM> includes coupler array <NUM>, which includes couplers that are conventional vertical-grating couplers.

Coupler array <NUM> includes switching network <NUM> and vertical couplers <NUM>(<NUM>,<NUM>) through <NUM>(M,N) (referred to, collectively, as couplers <NUM>).

Couplers <NUM> are analogous to couplers <NUM>; however, in the depicted example, couplers <NUM> are conventional vertical-grating couplers configured to provide direct their free-space emission (i.e., light signal <NUM>) as a relatively small-divergence light signal that propagates along a propagation direction that is substantially normal to focal plane FP1. As a result, light signal <NUM> interacts with only a relatively small portion of the clear aperture of lens <NUM>.

Lens <NUM> receives light signal <NUM> and collimates it as output beam <NUM> and diverts the output beam such that it propagates along output axis A3. As discussed above and with respect to <FIG>, the angle of output axis A3, relative to optical axis A1, depends on the position of coupler <NUM>(i,j) within coupler array <NUM>.

Claim 1:
A beam-steering system (<NUM>) comprising:
a lens (<NUM>); and
a programmable vertical coupler array (<NUM>) comprising:
a substrate (<NUM>);
an array of couplers (<NUM>) having a plurality of coupler rows (CR) and a plurality of coupler columns (CC), each coupler of the array including a coupler waveguide (<NUM>) and a vertical-coupling element (<NUM>) that is configured to launch optical energy received from the coupler waveguide into free space;
a bus waveguide (<NUM>) disposed on the substrate, the bus waveguide having a first input port (IP1) configured to receive a first light signal (<NUM>);
a first plurality of row waveguides (<NUM>) disposed on the substrate; and
a switching network (<NUM>) that is operative for controlling the propagation of the first light signal (<NUM>) from the first input port to any coupler of the array;
wherein the lens and programmable vertical coupler array are arranged such that the lens receives the optical energy launched by each vertical-coupling element and directs the optical energy in a direction that is based on the position of that vertical-coupling element within the programmable vertical coupler array and a relative position of the lens and the programmable vertical coupler array;
characterized in that
each coupler of the plurality thereof is optically couplable with a row waveguide of the first plurality thereof; and
each coupler waveguide of the coupler array has a movable end (<NUM>-<NUM>) and a fixed end (<NUM>-<NUM>) that includes its respective vertical-coupling element, wherein the fixed end has a fixed height relative to its respective row waveguide.