Patent Publication Number: US-2023145261-A1

Title: Compact micro electrical mechanical actuated ring-resonator

Description:
TECHNICAL FIELD 
     Embodiments presented in this disclosure generally relate to optical devices. More specifically, embodiments disclosed herein provide for optical power splitters, optical power combiners, and signal re-routers for optical signals using a ring resonator and selectively coupled waveguides controlled by mechanically actuated cantilevers. 
     BACKGROUND 
     Optical power splitters often use Y-branched designs, multi-mode interferometers (MMIs), and tap couplers (e.g., 2:1 splitters/combiners) to split optical power to multiple different waveguides, which are bulky, wavelength sensitive, and fixed in their splitting arrangement (e.g., 50:50, 60:40, 90:10). Accordingly, developers seeking to split or combine optical signals in a Photonic Integrated Circuit (PIC) often make compromises in the design and layout of the PIC to account for tolerance margins due to the fabrication techniques, thus resulting in over-engineered components that take up more space in the design, with little flexibility in reacting to changing signaling needs, and that require additional signal processing elements to support the optical splitter/combiner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate typical embodiments and are therefore not to be considered limiting; other equally effective embodiments are contemplated. 
         FIG.  1    illustrates a first layout of an optical device for splitting or combining optical signals, according to embodiments of the present disclosure. 
         FIG.  2    illustrates a second layout of an optical device for splitting or combining optical signals, according to embodiments of the present disclosure. 
         FIG.  3    illustrates a third layout of an optical device for splitting or combining optical signals, according to embodiments of the present disclosure. 
         FIG.  4    illustrates details of the piezoelectric cantilever for an optical device for splitting or combining optical signals, according to embodiments of the present disclosure. 
         FIGS.  5 A- 5 F  illustrate cross-sectional views of an optical device for splitting or combining optical signals in various configurations to selectively couple and decouple selective waveguides with a ring resonator, according to embodiments of the present disclosure. 
         FIG.  6    illustrates wavelength tuners in relation to the ring resonator, according to embodiments of the present disclosure. 
         FIG.  7    is a flowchart for using an optical device for splitting optical signals, according to embodiments of the present disclosure. 
         FIG.  8    is a flowchart for using an optical device for combining optical signals, according to embodiments of the present disclosure. 
         FIG.  9    illustrates hardware of a computing device, according to embodiments of the present disclosure. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially used in other embodiments without specific recitation. 
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Overview 
     One embodiment presented in this disclosure is a system, comprising: a bus waveguide disposed on a platform; a ring resonator disposed on the platform, including at least a first optical coupler, wherein the ring resonator is optically coupled with the bus waveguide; and a selective waveguide disposed on a piezoelectric cantilever mounted in a trench defined in the platform, wherein the selective waveguide includes a second optical coupler and is controllable to selectively adjust a coupling ratio between the first optical coupler with the second optical coupler by physically changing a distance between the first optical coupler and the second optical coupler. 
     One embodiment presented in this disclosure is a device, comprising: a platform, defining a first trench and a second trench; a first piezoelectric cantilever connected on one end to the platform within the first trench; a second piezoelectric cantilever connected on one end to the platform within the second trench; a ring resonator connected to the platform between the first trench and the second trench; a first selective waveguide disposed on the first piezoelectric cantilever and the platform; a second selective waveguide disposed on the second piezoelectric cantilever and the platform; and a bus waveguide disposed on the platform and optically coupled with the ring resonator. 
     One embodiment presented in this disclosure is an optical signal processor, comprising: a bus waveguide disposed in a first plane; a ring resonator disposed in the first plane and optically coupled with the bus waveguide, the ring resonator including a plurality of first optical couplers; and a plurality of selective waveguides, wherein each selective waveguide of the plurality of selective waveguides comprises: a second optical coupler corresponding to one first optical coupler of the plurality of first optical couplers; and a piezoelectric cantilever configured to adjust a relative alignment between the second optical coupler and the corresponding one first optical coupler to selectively adjust a coupling efficiency between each selective waveguide with the ring resonator. 
     EXAMPLE EMBODIMENTS 
     The present disclosure provides systems and devices for optical signal processing that use smaller footprints on the photonic die (taking up less physical space), with less sensitivity to variations in signal wavelength, and with an adjustable splitting/combining arrangement (e.g., from X:Y, where X+Y=100%), among other benefits compared to previous optical power splitters, optical power combiners, and optical power re-routers (generally referred to as splitters, combiners, and re-routers or signal splitters, combiners, and re-routers). that will become apparent on a detailed examination of the present disclosure. 
     The systems and devices described herein use Micro-Electrical-Mechanical (MEM) actuation to physically change an alignment between two optical couplers (one in a waveguide and one in a ring resonator) to change how strongly coupled the waveguide is to the ring resonator. By including multiple such actuated waveguides, an operator can configure on the fly the splitting arrangement (e.g., how much of a split input signal waveguide one receives vs. waveguide two). Each of the waveguides are defined on piezoelectric cantilevers that can move up/down, left/right, or twist to change the alignment and/or distance between the ring and an associated waveguide, thereby changing how strongly the waveguide is coupled to the ring resonator. 
       FIG.  1    illustrates a first layout of an optical device for splitting or combining optical signals, according to embodiments of the present disclosure.  FIG.  2    illustrates a second layout of an optical device for splitting or combining optical signals, according to embodiments of the present disclosure.  FIG.  3    illustrates a third layout of an optical device for splitting or combining optical signals, according to embodiments of the present disclosure. Although the examples given herein generally related to one of splitting or combining optical signals, the described optical device may operate as an optical signal processor in either capacity based on the direction of signal flow through the optical device. 
     In each of  FIGS.  1 - 3   , a platform  110  of a photonic die is shown on which the other elements are grown or bonded. In various embodiments, the platform  110  may include one or more layers of a dielectric material, such as Silicon Carbide (SiC), III-V materials, Silicon Dioxide (SiO 2 ), etc., that the various other elements are fabricated on (e.g., via epitaxial growth) or affixed to (e.g., via an epoxy) after being fabricated elsewhere, and may include various layers of different materials grown or affixed to a base substrate. 
     A ring resonator  120  and a bus waveguide  130  are disposed on the platform  110 , and are optically coupled with one another. In various embodiments, the bus waveguide  130  provides an input signal to the ring resonator  120  that is split as output signals to one or more selective waveguides  140   a - c  (generally or collectively, selective waveguide  140 ). Alternatively, the bus waveguide  130 , receives and carries an output signal from the ring resonator  120  that is made of several input signals received from the one or more selective waveguides  140 . 
     In various embodiments, the number and arrangement of the selective waveguides  140  included in the optical device can be different from what is shown in  FIGS.  1 - 3   . Accordingly,  FIGS.  1 - 3    illustrate various layouts and numbers of the elements, which are provided as non-limiting examples of the optical device of the present disclosure. 
     In  FIGS.  1  and  2   , each selective waveguide  140   a - c  is disposed on a corresponding piezoelectric cantilever  150   a - c  (generally or collectively, piezoelectric cantilever  150 ) that is mounted, on a connected side, to the platform  110  in a corresponding trench  111   a - c  (generally or collectively, trench  111 ) defined in the platform  110 . In various embodiments, such as with the second selective waveguide  140   b  in  FIG.  3   , one or more selective waveguides  140  may be mounted in a fixed position (e.g., as a fixed waveguide), and is disposed on the platform  110  rather than on a piezoelectric cantilever  150  in a trench  111 . Additionally or alternatively, some or all of the trenches  111  may extend through each layer of the platform  110  or a subset of the layers of the platform  110  (e.g., the trenches  111  may define through holes or cavities closed on one end by a layer of the platform  110 ). 
     Several electrodes  160   a - f  (generally or collectively, electrode  160 ) are provided at the side of the associated piezoelectric cantilevers  150  mounted to the platform  110  to control an orientation and position of the associated piezoelectric cantilevers  150  relative to the ring resonator  120 , as is discussed in greater detail in regard to  FIGS.  5 A- 5 F . The piezoelectric cantilevers  150  are made of various piezoelectric materials, including, but not limited to, quartz, Lithium Niobate (LiNbO 3 ), Lead Ziconate Titantate (PZT), Potassium Niobate (KNbO 3 ), Sodium Tungstate (Na 2 WO 3 ), group III-V semiconductors, group II-VI semiconductors, etc., that move or deform when an electric field is applied by the electrodes  160 . 
     The piezoelectric cantilevers  150  are mounted on one side to the platform  110  (e.g., a connected end) where the electrodes  160  are co-located, and have another end (e.g., a distal end to the connected end that is otherwise unconnected or held in free space) that is free to move based on the electrical fields imparted by the electrodes  160 . When the electrodes  160  impart an electrical field to the piezoelectric cantilevers  150 , the piezoelectric cantilevers  150  physically move (e.g., by pitching, yawing, or rotating) the selective waveguides  140  disposed thereon closer to or further from the ring resonator  120  to adjust a coupling strength between a given selective waveguide  140  and the ring resonator  120 . 
     The ring resonator  120  includes a plurality of first optical couplers  121   a - c  (generally or collectively, first optical couplers  121 ) that correspond to the second optical couplers  141   a - c  (generally or collectively, second optical couplers  141 ). 
     As the corresponding couplers move closer to, further from, and in/out of alignment with one another based on the piezoelectric actuation of the piezoelectric cantilevers  150 , an operator can adjust a coupling strength between the ring resonator  120  and one or more of the selective waveguides  140 . Accordingly, the coupling ratio can be adjusted to account for manufacturing tolerances, changes in operational needs for power splitting ratios or power combining ratios. In various embodiments, the first optical couplers  121  and the second optical couplers are Distributed Bragg Gratings (DBG). 
     For example, when operating the optical device as a signal splitter, by changing the alignment and/or distance between a first corresponding pair of couplers (e.g., the first optical coupler  121   a  and the second optical coupler  141   a  of the first selective waveguide  140   a ) and leaving the alignment and/or distance between a second corresponding pair of couplers (e.g., the first optical coupler  121   b  and the second optical coupler  141   b  of the first selective waveguide  140   b ) unchanged, an operator can alter the splitting ratio. For example, a first selective waveguide  140   a  and a second selective waveguide  140   b  may each nominally receive half of the optical power of an input signal (e.g., a 50:50 split), but due to the optical power needs of downstream devices, manufacturing imperfections, etc., an operator can adjust the first selective waveguide  140   a  to receive a greater share of the optical power (e.g., a 60:40 split) or a lesser share of the optical power (e.g., a 30:70 split) that is different from the nominal split. The operator may move one or more of the selective waveguides  140  to change the splitting ratio between the selective waveguides  140 . Additionally or alternatively, an operator may change the alignments and/or distances between two or more pairs of corresponding couplers at the same time to affect the relative coupling strengths of those pairs and any unchanged pairs. 
     In some embodiments, the coupling ratio with a given selective waveguide  140  may be set to zero, to thereby de-couple (at least temporarily) the given selective waveguide  140  from the ring resonator  120 . For example, when the first selective waveguide  140   a  is connected to a first destination and the second selective waveguide  140   b  is connected to a second destination, an operator can selectively decouple one of the selective waveguides  140  from the ring resonator  120  to direct the optical signal to one of the first destination or the second destination. Accordingly, in some embodiments, the optical device may be operated as a signal router in addition to or instead of a signal splitter or combiner. 
     In various embodiments, the ring resonator  120 , the bus waveguide  130 , and the selective waveguides  140  may be made of various materials for directing light along a defined pathway, including, but not limited to, Silicon (Si) and Silicon Nitride (SiN). Additionally, although not illustrated, the bus waveguide  130  and the selective waveguides  140  may be connected to other waveguides or continue past where the individual elements are shown in the Figures to further directed optical signals to the ring resonator  120  or away from the ring resonator  120 . 
     In various embodiments, the bus waveguide  130  may be mounted to the platform  110  as a static waveguide, or may be mounted to a carrier  180  disposed in a carrier trench  112  defined in some or all of the layers of the platform  110  to allow for adjustable coupling strength with the ring resonator  120 . In various embodiments, the carrier  180 , like the piezoelectric cantilevers  150 , is made of a piezoelectric material that allows for various bus electrodes  170   a - d  (generally or collectively, bus electrodes  170 ) to impart an electrical field to physically move the carrier  180  (e.g., by pitching or rotating) and thereby adjust the bus waveguide  130  to be closer or further from the ring resonator  120 . In various embodiments, bus waveguide  130  may be evanescently coupled with the ring resonator  120  (as is illustrated in  FIGS.  1 - 3   ) or may be coupled via additional pairs of optical couplers like the selective waveguides  140  are couple with the ring resonator  120 . 
     Although each of  FIGS.  1 - 3    illustrate the respective selective waveguides  140  and piezoelectric cantilevers  150  as having curved sections (where the second optical couplers  141  are located) that are concentric to the ring resonator  120  (e.g., where the curvature of the selective waveguides  140  and piezoelectric cantilevers  150  are matched to an outer curvature of the ring resonator  120 ), the selective waveguides  140  and piezoelectric cantilevers  150  may have various shapes including straight-side quadrilaterals. Similarly, although each of  FIGS.  1 - 3    illustrate the respective selective waveguides  140  and the bus waveguide  130  as being evenly spaced around the ring resonator  120  (e.g., at approximately (±5%) the same arc distance clockwise and counterclockwise to the adjacent coupling locations), in some embodiments, the waveguides may be unevenly spaced around the ring resonator  120 . In various embodiments, the initial distance between the waveguide/cantilever and the ring resonator  120  can also be different in a given fabricated device and across devices to provide a “bias” point for further tuning. 
       FIG.  4    illustrates details of the piezoelectric cantilever  150  for an optical device for splitting or combining optical signals, according to embodiments of the present disclosure. The optical device illustrated in  FIG.  4    includes three piezoelectric cantilevers  150   a - c , similarly to the layout illustrated in  FIG.  1   , although more or fewer piezoelectric cantilevers  150  may be included in other layouts. 
     Each piezoelectric cantilever  150  is attached to the platform  110  at one end, and has a free end at the opposite side that is configured to move the second optical coupler  141  of the selective waveguide  140  associated with that piezoelectric cantilever  150  relative to the corresponding first optical couplers  121  of the ring resonator  120 . 
     Various cathodes  410   a - f  (generally or collectively, cathodes  410 ) and anodes  420   a - f  (generally or collectively, anodes  420 ) form electrode pairs (e.g., a first cathode  410   a  and a first anode  420   a  are first electrodes  160   a ). These electrode pairs apply a voltage supplied from a corresponding voltage source  430   a - f  (generally or collectively voltage source  430 ) to cause the piezoelectric cantilever  150  to deflect, bend, or twist. The electrode pairs produce an electric field in the piezoelectric cantilever  150  that causes the deflectable/bendable/twistable piezoelectric cantilever  150  to physically change location from a base state, and thereby move the optical couplers relative to one another. 
     In various embodiments, the voltage sources  430  may be set to a given value during test and calibration by a test and calibration system external to the optical device including the voltage sources  430  that is removed after test/calibration are complete, such as computing device  900  described in relation to  FIG.  9   . In some embodiments, a microcontroller, such as computing device  900  described in relation to  FIG.  9   , that is part of the optical device or otherwise connected to the optical device during regular operations (e.g., after test/calibration) may maintain the set voltage values or adjust the voltage values occasionally to alter the position of the piezoelectric cantilevers  150  to maintain a desired splitting or combining ratio, or change the desired splitting or combining ratio. 
     Each of the pairs of electrodes (e.g., paired cathodes/anodes  410 / 420 ) may be controlled separately from one another by individually controlling the voltage supplied by the corresponding voltage source  430 . For example, when applying a voltage of X via the first voltage source  430   a  to the first cathode  410   a  and first anode  420   a  and a voltage of 2× via the third voltage source  430   c  to the third cathode  410   c  and third anode  420   c , and operator may cause (ceteris paribus) greater movement in the second piezoelectric cantilever  150   b  than in the first piezoelectric cantilever  150   a . In various embodiments, the relative orientations of some or all the cathodes  410  and the anodes  420  above or below the platform  110  may be reversed from what is illustrated in  FIG.  4   . 
       FIGS.  5 A- 5 F  illustrate cross-sectional views of an optical device for splitting or combining optical signals in various configurations to selectively couple and decouple selective waveguides  140  with a ring resonator  120 , according to embodiments of the present disclosure. 
       FIG.  5 A  illustrates a first state of the piezoelectric cantilevers  150  that evenly positions a first selective waveguide  140   a  and a second selective waveguide  140   b  relative to the ring resonator  120 . The piezoelectric cantilevers  150  are shown in-plane with the platform  110  and in the middle of the void defined in the platform  110 . In various embodiments,  FIG.  5 A  may represent a “resting” or “base” state for the piezoelectric cantilevers  150  when no electric field is applied by the electrodes  160 . The discussion of  FIGS.  5 B- 5 F  use  FIG.  5 A  as a base state as a point of comparison for the purpose of highlighting the different positions shown in  FIGS.  5 A- 5 F  that the piezoelectric cantilevers  150  can move between. However, the piezoelectric cantilevers  150  may be constructed to be in various positions as a resting state or base state. 
       FIG.  5 B  illustrates a second state of the piezoelectric cantilevers  150  in which the first piezoelectric cantilever  150   a  is pitched downward from the plane of the platform  110  and the second piezoelectric cantilever  150   b  is pitched upward from the plane of the platform  110  relative to  FIG.  5 A . When pitching the piezoelectric cantilevers  150 , the electrodes  160  apply an electric field that adjusts the relative alignment and/or distance between the respective optical couplers by causing the respective piezoelectric cantilever  150  to move a free distal end of the piezoelectric cantilever  150  away from the plane of the platform  110  relative to the end of the piezoelectric cantilever  150  connected to the platform  110 , effectively moving far end of the piezoelectric cantilever  150  up or down in the Z direction. 
       FIG.  5 C  illustrates a third state of the piezoelectric cantilevers  150  in which the first piezoelectric cantilever  150   a  and second piezoelectric cantilever  150   b  are yawed outward from the ring resonator  120  (relative to  FIG.  5 A ) while remaining in the plane of the platform  110 . Similarly,  FIG.  5 D  illustrates a fourth state of the piezoelectric cantilevers  150  in which the first piezoelectric cantilever  150   a  and second piezoelectric cantilever  150   b  are yawed inward towards the ring resonator  120  (relative to  FIG.  5 A ) while remaining in the plane of the platform  110 . When yawing the piezoelectric cantilevers  150 , the electrodes  160  apply an electric field that adjusts the relative alignment and/or distance between the respective optical couplers by causing the respective piezoelectric cantilever  150  to move a free distal end of the piezoelectric cantilever  150  within the plane of the platform  110  relative to ring resonator  120 , effectively moving far end of the piezoelectric cantilever  150  left or right in the X direction. 
       FIG.  5 E  illustrates a fifth state of the piezoelectric cantilevers  150  in which the first piezoelectric cantilever  150   a  and second piezoelectric cantilever  150   b  are rolled outward from the ring resonator  120  (relative to  FIG.  5 A ) while remaining in the plane of the platform  110  and equidistant from the edges of the platform  110 . Similarly,  FIG.  5 F  illustrates a sixth state of the piezoelectric cantilevers  150  in which the first piezoelectric cantilever  150   a  and second piezoelectric cantilever  150   b  are rolled inward towards the ring resonator  120  (relative to  FIG.  5 A ) while remaining in the plane of the platform  110  and equidistant from the edges of the platform  110 . When rolling the piezoelectric cantilevers  150 , the electrodes  160  apply an electric field that adjusts the relative alignment and/or distance between the respective optical couplers by causing the respective piezoelectric cantilever  150  to move a first side of the piezoelectric cantilever  150  closer to the ring resonator  120  and move a second side (opposite to the first side) of the piezoelectric cantilever  150  further from the ring resonator  120  relative to the plane of the platform  110 . Stated differently, the piezoelectric cantilever  150  rotates about the Y axis when rolled. 
     Although  FIGS.  5 A- 5 F  illustrate how an operator may pitch, yaw, or roll a piezoelectric cantilever  150  to adjust the coupling strength between a given selective waveguide  140  and the ring resonator by changing the associated alignment and/or distance or amount of overlap between the pair of optical couplers, combinations of two or more of yawing, pitching, and rolling a given piezoelectric cantilever  150  are contemplated. Similarly, although  FIGS.  5 A- 5 F  illustrate two piezoelectric cantilevers  150  performing similar movements (e.g., both yawing, both pitching, both rolling), an operator may move each piezoelectric cantilever  150  independently of the other piezoelectric cantilevers  150 , and a given piezoelectric cantilever  150  may remain stationary, yaw, pitch, or roll while another piezoelectric cantilever  150  may move (or not move) according to a different movement pattern. 
     Additionally or alternatively, when the optical device includes an adjustable bus waveguide  130  (e.g., mounted to piezoelectric carrier  180  controllable by bus electrodes  170 ), the operator may pitch, roll, or pitch and roll the piezoelectric carrier  180  to move the bus waveguide  130  closer to or further from the ring resonator  120  such as in  FIGS.  5 C- 5 F . 
       FIG.  6    illustrates wavelength tuners  610   a - b  (generally or collectively, wavelength tuner  610 ) in relation to the ring resonator  120 , according to embodiments of the present disclosure. In various embodiments the wavelength tuners  610  are metallic resistors that are defined in a plane above or below the ring resonator  120  (in the Z direction) in the optical device that are supplied with a controllable current to generate heat. The generated heat is radiated to the ring resonator  120  to change the temperature of the ring resonator  120  and thereby change the refractive index of the ring. The operator may control the amount of current supplied to the wavelength tuners  610  to ensure that critical coupling is met at the interface between the bus waveguide  130  and the ring resonator  120  to enable the optical device to operate across a wide range of wavelengths. 
       FIG.  7    is a flowchart of a method  700  for using an optical device for splitting optical signals, according to embodiments of the present disclosure. Method  700  begins with block  710 , where the optical device determines coupling percentages for a given pair of optical couplers for an optical device. In various embodiments, the determined coupling percentages can be specified by a human operator to define a desired splitting ratio, a microcontroller on the optical device or a calibration system external to the optical device (such as a computing device  900  described in relation to  FIG.  9   ) that recalibrates a desired splitting level based on manufacturing variability in the optical device, or combinations thereof. 
     For example, a human operator may specify that a given optical device with three selective waveguides  140  should have a splitting ratio of 1:1:1, and each selective waveguide  140  is therefore nominally set to receive one third of the input optical power. However, if during test and calibration, variations in the ring resonator  120 , the selective waveguides  140 , or various components that receive signals from the selective waveguides  140  indicate that the nominal coupling percentages provide too much optical power or not enough optical power to various downstream components, the microcontroller or calibration system can bring the effects back into tolerance by further adjusting the splitting ratio. 
     For example, when the first selective waveguide  140   a  and second selective waveguides  140   b  receive too strong of a signal, or the third selective waveguide  140   c  receives too weak of a signal, the microcontroller or calibration system adjusts the splitting ratio from 1:1:1 to 1:1:2. To change the splitting ratio, the nominal coupling efficiency may be increased or decreased in one or more pairs of optical couplers. In various embodiments, the microcontroller may adjust one or more of the selective waveguides to have stronger or weaker coupling efficiencies to respectively accept a greater or lesser percentage of the incoming signal power. Consider then that two otherwise identical selective waveguides  140 , when set to equal coupling efficiencies (with no other selective waveguides  140  coupled with the ring resonator  120 ), each receive 50% of the incoming optical signal strength. However, when a first selective waveguide  140   a  of the two otherwise identical selective waveguides  140  is set at half of its original coupling efficiency, the first selective waveguide  140   a  receives 33% of the incoming optical signal strength and the second selective waveguide  140   b  receives 66% of the incoming optical signal strength. 
     Accordingly, a microcontroller may make various adjustments to the coupling efficiencies of the selective waveguides  140  to affect various desired signal optical power splitting ratios. For example, when in a base state each pair of optical couplers is coupled at X % of nominal coupling efficiency to each nominally receive 33% of the incoming signal power, the microcontroller or calibration system can adjust the first selective waveguide  140   a  and second selective waveguides  140   b  to Y % efficiency (where Y&lt;X, to receive 25% of the incoming signal power) and leave the third selective waveguide coupled at X % efficiency (to now receive the remaining 50% of the incoming signal power) to affect a 1:1:2 splitting ratio instead of a 1:1:1 splitting ratio. In another example, the microcontroller or calibration system can leave the first selective waveguide  140   a  and second selective waveguides  140   b  to X % coupling efficiency and adjust the third selective waveguide to 2*X % coupling efficiency to affect a 1:1:2 splitting ratio instead of a 1:1:1 splitting ratio. In a further example, the microcontroller or calibration system can adjust the first selective waveguide  140   a  and second selective waveguides  140   b  to 0.8*X % coupling efficiency and adjust the third selective waveguide to be 1.6*X % coupling efficiency to affect a 1:1:2 splitting ratio instead of a 1:1:1 splitting ratio. 
     In another example, an optical device may nominally provide a 1:1:1 splitting ratio, and the user may desire 1:1 splitting ratio; omitting one of the selective waveguides  140  as an output path (e.g., 1:1:0). Accordingly, the human operator may designate one selective waveguide  140  to have zero coupling efficiency with the ring resonator  120  and leave the other two selective waveguides  140  coupled at a nominal coupling percentage. 
     As will be appreciated, the examples given for 1:1:1 nominal splitting ratios and 1:1:2 and 1:1:0 effective splitting ratios are provided as non-limiting illustrations of the capabilities of the optical device described herein. Various different nominal splitting ratios using more or fewer coupling pairs at different relative values may be adjusted to various different effective splitting ratios. Additionally or alternatively, the adjustments to coupling efficiencies may be used to correct for out-of-tolerance components that would nominally use a first splitting ratio at an initial coupling efficiency, but are adjusted to provide a second splitting ratio that accounts for the out-of-tolerance components to bring the performance of those components back into tolerance for downstream components that receive inputs from the out-of-tolerance components. 
     At block  720 , the optical device adjusts one or more piezoelectric cantilevers  150  according to the coupling efficiencies identified per block  710 . In various embodiments, a microcontroller or calibration system translates the desired (or adjusted) coupling efficiency to one or more voltages that one or more respective voltage sources  430  apply to the electrodes  160  of the associated piezoelectric cantilevers  150  for the selective waveguides  140 . By moving the associated piezoelectric cantilevers  150 , the second optical coupler  141  included in the selective waveguide  140  changes location relative to the first optical coupler  121  included in the ring resonator  120 . Thus the ring resonator  120  and the moved selective waveguide  140  form a stronger or weaker coupled connection relative to when the piezoelectric cantilever  150  is in a resting state. 
     In various embodiments, the microcontroller or calibration system may move the piezoelectric cantilever  150  from the resting state to adjust the effective coupling efficiency by one or more of yawing, pitching, or rolling the piezoelectric cantilever  150  to change a relative alignment and/or distance or overlapping surface area of the first optical coupler  121  with the second optical coupler  141 . Similarly, the microcontroller or calibration system may move the piezoelectric carrier  180  from the resting state to adjust the effective coupling efficiency by one or more of pitching or rolling the piezoelectric carrier  180  to change a relative alignment and/or distance or overlapping surface area of the evanescently coupled regions of the bus waveguide  130  and the ring resonator  120 . 
     In various embodiments, after moving the piezoelectric cantilevers  150  and/or carrier  180  into desired positions, the fabricator may fix the positions of the various MEMS actuated components by applying an epoxy or other material in the trenches  111  and bus trench  112  to hold the piezoelectric cantilevers  150  and carrier  180  in place. Once held in place by the epoxy or other material, the fabricator may remove the applied voltages from the respective electrodes. Accordingly, the fabricator may define specific morphologies for the various waveguides to couple with the ring resonator  120  and hold those morphologies in place after an initial calibration without having to continuously supply voltage to affect the actuation. Beneficially, the application of the epoxy or other material consumes less power, and reduces noise in the optical signals (e.g., due to minor mechanical movement of the piezoelectric cantilevers  150  or carrier  180 ) compared to active control of the MEMS actuated components during operations, while still allowing the fabricator to adjust a base design of an optical device for specific use cases or to compensate for manufacturing tolerances. 
     At block  730 , the optical device receives an input signal from a bus waveguide  130  at the ring resonator  120 . 
     At block  740 , the optical device outputs the split signals from the ring resonator  120  according to the coupling percentages onto the selective waveguides  140 . Depending on the coupling percentages set for the individual selective waveguides  140 , each waveguide may receive between 0-100% of the input signal, which is then carried to any downstream devices that receive inputs from the respective selective waveguides  140 . 
       FIG.  8    is a flowchart of a method  800  for using an optical device for combining optical signals, according to embodiments of the present disclosure. Method  800  begins with block  810 , where the optical device determines coupling percentages for a given pair of optical couplers for an optical device. In various embodiments, the determined coupling percentages can be specified by a human operator to define a desired combining ratio, a microcontroller on the optical device or a calibration system external to the optical device (such as a computing device  900  described in relation to  FIG.  9   ) that recalibrates a desired combining level based on manufacturing variability in the optical device, or combinations thereof. 
     For example, a human operator may specific that a given optical device with three selective waveguides  140  should have a combining ratio of 1:1:1, and each selective waveguide  140  is therefore nominally set to provide one third of the input optical power to the ring resonator  120 . However, if during test and calibration, variations in the ring resonator  120 , the selective waveguides  140 , or various components that provide signals to the selective waveguides  140  indicate that the nominal coupling percentages provide too much optical power or not enough optical power to various downstream components from the bus waveguide  130 , the microcontroller or calibration system can bring the effects back into tolerance by further adjusting the splitting ratio. 
     In various embodiments, the microcontroller may adjust one or more of the selective waveguides  140  to have stronger or weaker coupling efficiencies to respectively provide a greater or lesser percentage of the outgoing signal power. Consider then that two otherwise identical selective waveguides  140 , when set to equal coupling efficiencies (with no other selective waveguides  140  coupled with the ring resonator  120 ) and carrying input signals at an equal strength, each input 50% of the outgoing optical signal strength provided to the bus waveguide  130 . However, when a first selective waveguide  140   a  of the two otherwise identical selective waveguides  140  is set at half of its original coupling efficiency, the first selective waveguide  140   a  inputs 33% of the outgoing optical signal strength and the second selective waveguide  140   b  inputs 66% of the outgoing optical signal strength. 
     Accordingly, a microcontroller may make various adjustments to the coupling efficiencies of the selective waveguides  140  to affect various desired signal optical power splitting ratios. For example, when the first selective waveguide  140   a  and second selective waveguides  140   b  input too strong of signals, or the third selective waveguide  140   c  inputs too weak of a signal, the microcontroller or calibration system adjusts the combining ratio from 1:1:1 to 1:1:2. To change the combining ratio, the nominal coupling efficiency may be increased or decreased in one or more pairs of optical couplers. For example, when in a base state each pair of optical couplers is coupled at X % coupling efficiency, the microcontroller or calibration system can adjust the first selective waveguide  140   a  and second selective waveguides  140   b  to 0.5*X % coupling efficiency and leave the third selective waveguide coupled at X % coupling efficiency to affect a 1:1:2 combining ratio instead of a 1:1:1 combining ratio. In another example, the microcontroller or calibration system can leave the first selective waveguide  140   a  and second selective waveguides  140   b  at X % coupling efficiency and adjust the third selective waveguide to 2*X % coupling efficiency to affect a 1:1:2 combining ratio instead of a 1:1:1 combining ratio. In a further example, the microcontroller or calibration system can adjust the first selective waveguide  140   a  and second selective waveguides  140   b  to 0.8*X % coupling efficiency and adjust the third selective waveguide to 1.6*X % coupling efficiency to affect a 1:1:2 combining ratio instead of a 1:1:1 combining ratio. Accordingly, by adjusting one or more coupling efficiencies from a baseline coupling efficiency to produce a 1:1:2 combining ratio, the microcontroller or calibration system induces the optical device to produce the intended effects of a 1:1:1 combining ratio when the optical device would otherwise be out of tolerance. 
     In another example, an optical device may nominally provide a 1:1:1 combining ratio, and the user may desire 1:1 combining ratio; omitting one of the selective waveguides  140  as an input path (e.g., 1:1:0). Accordingly, the human operator may designate one selective waveguide  140  to have zero coupling efficiency with the ring resonator  120  and leave the other two selective waveguides  140  coupled at a nominal coupling efficiency. 
     As will be appreciated, the examples given for 1:1:1 nominal combining ratios and 1:1:2 and 1:1:0 effective combining ratios are provided as non-limiting illustrations of the capabilities of the optical device described herein. Various different nominal combining ratios using more or fewer coupling pairs at different relative coupling efficiency values may be adjusted to various different effective combining ratios. 
     At block  820 , the optical device adjusts one or more piezoelectric cantilevers  150  according to the coupling percentages identified per block  810 . In various embodiments, a microcontroller or calibration system translates the desired (or adjusted) coupling percentage to one or more voltages that one or more respective voltage sources  430  apply to the electrodes  160  of the associated piezoelectric cantilevers  150  for the selective waveguides  140 . By moving the associated piezoelectric cantilevers  150 , the second optical coupler  141  included in the selective waveguide  140  changes location relative to the first optical coupler  121  included in the ring resonator  120 . Thus the ring resonator  120  and the moved selective waveguide  140  form a stronger or weaker coupled connection relative to when the piezoelectric cantilever  150  is in a resting state. Similarly, the microcontroller or calibration system may move the piezoelectric carrier  180  from the resting state to adjust the effective coupling efficiency by one or more of pitching or rolling the piezoelectric carrier  180  to change a relative alignment and/or distance or overlapping surface area of the evanescently coupled regions of the bus waveguide  130  and the ring resonator  120 . 
     In various embodiments, after moving the piezoelectric cantilevers  150  and/or carrier  180  into desired positions, the fabricator may fix the positions of the various MEMS actuated components by applying an epoxy or other material in the trenches  111  and bus trench  112  to hold the piezoelectric cantilevers  150  and carrier  180  in place. Once held in place by the epoxy or other material, the fabricator may remove the applied voltages from the respective electrodes. Accordingly, the fabricator may define specific morphologies for the various waveguides to couple with the ring resonator  120  and hold those morphologies in place after an initial calibration without having to continuously supply voltage to affect the actuation. Beneficially, the application of the epoxy or other material consumes less power, and reduces noise in the optical signals (e.g., due to minor mechanical movement of the piezoelectric cantilevers  150  or carrier  180 ) compared to active control of the MEMS actuated components during operations, while still allowing the fabricator to adjust a base design of an optical device for specific use cases or to compensate for manufacturing tolerances 
     In various embodiments, the microcontroller or calibration system may move the piezoelectric cantilever  150  from the resting state to adjust the effective coupling percentage by one or more of yawing, pitching, or rolling the piezoelectric cantilever  150  to change a relative alignment and/or distance or overlapping surface area of the first optical coupler  121  with the second optical coupler  141 . 
     At block  830 , the optical device receives one or more input signals according to the coupling percentages from the selective waveguides  140 . 
     At block  840 , the optical device outputs the combined output signals from the ring resonator  120  onto the bus waveguide  130 . Depending on the coupling percentages set for the individual selective waveguides  140 , each waveguide may input between 0-100% of optical power that is provided in the combined signal output to the bus waveguide  130 . The bus waveguide  130  receives the combined signal and carries the combined signal to any downstream devices that receive inputs from the bus waveguide  130 . 
       FIG.  9    illustrates hardware of a computing device  900  such as can be included as a microcontroller for the optical device or as a calibration and test system for an optical device, as described herein. The computing device  900  includes a processor  910 , a memory  920 , and communication interfaces  930 . The processor  910  may be any processing element capable of performing the functions described herein. The processor  910  represents a single processor, multiple processors, a processor with multiple cores, and combinations thereof. The communication interfaces  930  facilitate communications between the computing device  900  and other devices. The communication interfaces  930  are representative of wireless communications antennas (both omnidirectional and directional), various steering mechanisms for the antennas, and various wired communication ports including out-pins and in-pins to a microcontroller. The memory  920  may be either volatile or non-volatile memory and may include RAM, flash, cache, disk drives, and other computer readable memory storage devices. Although shown as a single entity, the memory  920  may be divided into different memory storage elements such as RAM and one or more hard disk drives. 
     As shown, the memory  920  includes various instructions that are executable by the processor  910  to provide an operating system  921  to manage various functions of the computing device  900  and one or more applications  922  to provide various functionalities to users of the computing device  900 , which include one or more of the functions and functionalities described in the present disclosure. 
     In the current disclosure, reference is made to various embodiments. However, the scope of the present disclosure is not limited to specific described embodiments. Instead, any combination of the described features and elements, whether related to different embodiments or not, is contemplated to implement and practice contemplated embodiments. Additionally, when elements of the embodiments are described in the form of “at least one of A and B,” it will be understood that embodiments including element A exclusively, including element B exclusively, and including element A and B are each contemplated. Furthermore, although some embodiments disclosed herein may achieve advantages over other possible solutions or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the scope of the present disclosure. Thus, the aspects, features, embodiments and advantages disclosed herein are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s). Likewise, reference to “the invention” shall not be construed as a generalization of any inventive subject matter disclosed herein and shall not be considered to be an element or limitation of the appended claims except where explicitly recited in a claim(s). 
     As will be appreciated by one skilled in the art, the embodiments disclosed herein may be embodied as a system, method or computer program product. Accordingly, embodiments may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, embodiments may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon. 
     Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing. 
     Computer program code for carrying out operations for embodiments of the present disclosure may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The program code may execute entirely on the user&#39;s computer, partly on the user&#39;s computer, as a stand-alone software package, partly on the user&#39;s computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user&#39;s computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). 
     Aspects of the present disclosure are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments presented in this disclosure. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the block(s) of the flowchart illustrations and/or block diagrams. 
     These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other device to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the block(s) of the flowchart illustrations and/or block diagrams. 
     The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable apparatus or other device to produce a computer implemented process such that the instructions which execute on the computer, other programmable data processing apparatus, or other device provide processes for implementing the functions/acts specified in the block(s) of the flowchart illustrations and/or block diagrams. 
     The flowchart illustrations and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments. In this regard, each block in the flowchart illustrations or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the Figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustrations, and combinations of blocks in the block diagrams and/or flowchart illustrations, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions. 
     In view of the foregoing, the scope of the present disclosure is determined by the claims that follow.