Patent Publication Number: US-2023152571-A1

Title: Micro-electromechanical system (mems) based tunable polarization rotator

Description:
TECHNICAL FIELD 
     The present disclosure relates to managing the polarization of light that has traveled via, e.g., an optical fiber or waveguide. 
     BACKGROUND 
     An optical receiver processes an optical signal received over a fiber optic cable. The optical signal may have been modulated, by a transmitter, in amplitude, phase, polarization, or a combination thereof. At the receiver end, the optical signal is typically demodulated using a transducer (e.g., a photodiode or photodetector) that converts the optical (light) signal into a corresponding electrical signal. The corresponding electrical signal is then processed to extract information that was contained in the original optical signal. Modern communication systems use complex modulation schemes, e.g., quadrature modulation, to increase the communication channel efficiency. 
     The optical receiver, typically implemented as a Photonic Integrated Circuit (PIC), is often designed to operate in transverse electric (TE) polarization mode. Notably, however, when light is propagated in an optical fiber over a distance, the transverse electric/transverse magnetic (TE/TM) polarization fraction of the light undergoes a change. This change may detrimentally impact how well the optical receiver can properly demodulate the optical signal and extract the intended information. One way to minimize the polarization change is to use polarization maintaining fibers (PMFs). However, PMFs can be very expensive and may thus not be a practical option in many implementations. 
     Traditional polarization splitter rotators (PSRs) can also rotate light to a desirable polarization prior to optical receiver processing, but such devices tend to occupy a lot of area (˜200 um in length). In any event, PSRs are not tunable across wavelength and polarization. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  shows a micro-electromechanical system (MEMS)-based tunable polarization rotator, according to an example embodiment. 
         FIGS.  1 B and  1 C  depict different approaches for electrodes to drive MEMS cantilevers of the MEMS-based tunable polarization rotator, according to an example embodiment. 
         FIG.  2    shows a high-level feedback mechanism for controlling the MEMS-based tunable polarization rotator, according to an example embodiment. 
         FIG.  3 A  shows an approach to detect a phase, and thus TE/TM polarization fraction, of an optical signal to use as part of the feedback mechanism for controlling the MEMS-based tunable polarization rotator, according to an example embodiment. 
         FIG.  3 B  shows the use of a polarization splitter to sense TE/TM polarization fraction, of an optical signal to use as part of the feedback mechanism for controlling the MEMS-based tunable polarization rotator, according to an example embodiment. 
         FIG.  4    shows a slotted waveguide that can be used to dampen TM polarization to calibrate the MEMS-based tunable polarization rotator, according to an example embodiment. 
         FIG.  5    shows a flowchart for controlling the MEMS-based tunable polarization rotator, according to an example embodiment. 
         FIG.  6    is a flowchart for operating the MEMS-based tunable polarization rotator, according to an example embodiment. 
         FIG.  7    illustrates a hardware block diagram of a computing device that may leverage the MEMS-based tunable polarization rotator as part of its I/O function, according to an example embodiment. 
     
    
    
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Overview 
     Presented herein is a method of rotating polarization of light travelling in a waveguide. In an embodiment, the method includes receiving an optical signal having a first polarization state at a first section of the waveguide, the first section of the waveguide being disposed on a plane of a substrate, using a micro-electromechanical system (MEMS) device, angling a second section of the waveguide out of the plane of the substrate, and outputting the optical signal with a second polarization state, different from the first polarization state, on a third section of the waveguide, the third section of the waveguide also being disposed on the plane of the substrate . . . . 
     In another embodiment, an apparatus is provided. The apparatus includes a substrate, a waveguide disposed on the substrate, at least one micro-electromechanical system (MEMS) cantilever disposed under a portion of the waveguide, and configured, when actuated, to displace the portion of the waveguide outside of a plane of remaining portions of the waveguide disposed on the substrate, and a control loop configured to actuate the at least one MEMS cantilever, responsive to polarization of light traveling in the waveguide. 
     Example Embodiments 
       FIG.  1 A  shows a micro-electromechanical system (MEMS)-based tunable polarization rotator  100 , according to an example embodiment. A silicon oxide (SiO 2 ) layer  110  is disposed on a substrate  105  (e.g., silicon) and supports an input waveguide  120 , a connecting waveguide  130 , an output waveguide  140 , a first MEMS cantilever  150 , and a second MEMS cantilever  160 . First MEMS cantilever  150  is attached to SiO 2  layer  110  at a first flexible joint  152 , and second MEMS cantilever  160  is attached to SiO 2  layer  110  at a second flexible joint  162 . From a fabrication standpoint, first MEMS cantilever  150  and second MEMS cantilever  160  may be grown on top of a buffer which is then etched away via, e.g., reactive ion etching (RIE) to create an under-cut  180  in SiO 2  layer  110 , as seen in  FIG.  1 A . Further, first MEMS cantilever  150  and second MEMS cantilever  160  may be fabricated from piezoelectric material such as, e.g., aluminum nitride, which also happens to be CMOS compatible, thus facilitating fabrication of a PIC with the functionality described herein. 
     A first curved waveguide section  154  is disposed on a surface of first MEMS cantilever  150 , and a second curved waveguide section  164  is disposed on a surface of second MEMS cantilever  160 . First curved waveguide section  154  is optically coupled to input waveguide  120  and to one end of connecting waveguide  130 . Second curved waveguide section  164  is optically coupled to output waveguide  140  and to another end of connecting waveguide  130 . The several waveguides may be fabricated from silicon, for example. 
     A first electrode  156  straddles first flexible joint  152 , and a second electrode  166  straddles second flexible joint  162 . Other electrodes (i.e., anodes, which are not shown in  FIG.  1 A ) oppose first electrode  156  and second electrode  166 , respectively, and are disposed underneath first MEMS cantilever  150  and second MEMS cantilever  160 . When a control voltage is applied, respectively, between the anodes (not shown) and their corresponding first MEMS cantilever  150  and second MEMS cantilever  160 , first MEMS cantilever  150  and second MEMS cantilever  160  will displace by tilt angles θ 1   1 , θ 2 . It is noted that the voltage applied to move, angle, or actuate each of first MEMS cantilever  150  and second MEMS cantilever  160  need not be the same. Likewise, the tilt angles θ 1 , θ 2  can be controlled to be different from one another. 
     The position and the geometry of the electrodes are not critical as long as they function to deform first MEMS cantilever  150  and second MEMS cantilever  160  to attain a desired tilt angle θ 1   1 , θ 2 , described further below. Hence, several examples of electrode placement can be implemented, as shown in  FIGS.  1 B and  1 C . 
     In  FIG.  1 B , electrodes  166 ,  167  sandwich the piezo cantilever only on a flat portion of the piezoelectric material. This design may be advantageous when electrodes  166 ,  167  are made of inflexible materials. 
     In  FIG.  1 C , the electrodes extend onto a portion of the MEMS cantilever  160  which bends. This design makes more sense when electrodes are flexible (polymer, doped III-V etc.). In this embodiment, electrode  167  lies flat, but could also be flexible. 
     The discussion above is also applicable to electrode  156 , and its corresponding anode (not shown). 
     It is noted the stack up used for the platform described above can vary. For example, the MEMS-based tunable polarization rotator  100  can be implemented with different materials. For instance, the substrate  105  could be SiC, III-V materials, etc. This would then be accompanied by a change in the cladding from SiO 2  to another III-V material, a polymer, perovskite, air, etc. The waveguides may then be fabricated from a material with high refractive index such as Lithium Niobate, BaTiO 3 , III-V materials, etc. The piezoelectric material used could also vary to include quartz, Lithium Niobate (LiNbO 3 ), Lead Zirconate Titanate (PZT), Potassium Niobate (KNbO 3 ), Sodium Tungstate (Na 2 WO 3 ), group III-V semiconductors, group II-VI semiconductors, etc. The primary requirement for the piezoelectric material is that it exhibits a mechanical deformation when subjected to an electric field. 
     Further, the fabrication of MEMS-based tunable polarization rotator  100  may vary depending on the materials involved. Generally, the materials may be grown in epitaxial layers or with a portion of a material stack grown separately and transferred onto a primary stack by techniques such as bonding, transfer printing, etc. 
     The operation of the MEMS-based tunable polarization rotator  100  may be understood as follows: 
     One or both of the first MEMS cantilever  150  and the second MEMS cantilever  160  are angled or actuated via first electrode  156  and/or second electrode  166  (and corresponding anodes) to control the tilt angles θ 1 , θ 2 . 
     When light travels via the input waveguide  120 , first curved waveguide section  154 , connecting waveguide  130 , second curved waveguide section  164 , and output waveguide  140 , the light will travel out of plane (i.e., out of a plane of substrate  105 ) on one or both of first curved waveguide section  154  and/or second curved waveguide section  164  such that, due to the principle known as Berry&#39;s phase, the polarization of the light will shift by up to 90° if the total out of plane tilt angle θ 1  plus tilt angle θ 2  is 45°. That is, as light passes along first curved waveguide section  154  and/or second curved waveguide section  164 , which is/are arranged to be out-of-plane, the polarization of the light in the waveguide may convert fully from TM mode to TE mode (assuming the light entering the input waveguide  120  is in TM mode). The light may also be converted to TM mode from TE mode, and combinations of TE/TM ratios, as desired, based on the selection of tilt angles θ 1 , θ 2  and the polarization of the light input to MEMS-based tunable polarization rotator  100 . In other words, by operating or actuating, i.e., angling, the first MEMS cantilever  150  and/or the second MEMS cantilever  160 , it is possible to control the polarization of the light signal to a desired state. 
     In an embodiment, and as shown in  FIG.  1 A , two MEMS cantilevers, i.e., first MEMS cantilever  150  and second MEMS cantilever  160 , are employed to achieve, in combination, a full 45° (θ 1  plus θ 2 ), e.g., 22.5° each. However, those skilled in the art will appreciate that a single MEMS cantilever and associated curved waveguide may be sufficient, in some implementations, to achieve the desired polarization rotation. 
     Theoretically, by controlling tilt angles θ 1  and θ 2  with first MEMS cantilever  150  and second MEMS cantilever  160 , tuning over the entire Poincaré sphere is possible. 
       FIG.  2    shows a high-level feedback mechanism or control loop for controlling the MEMS-based tunable polarization rotator  100 , according to an example embodiment. Specifically,  FIG.  2    shows an input  210  for a light signal, MEMS-based tunable polarization rotator  100 , an intermediate output  220  that feeds a sensing circuit  230 , and an output  240  via which the light signal is passed to follow-on optical components. A feedback loop  250  connects sensing circuit  230  to MEMS-based tunable polarization rotator  100 , and provides, e.g., voltage signal(s) to drive first MEMS cantilever  150  and/or second MEMS cantilever  160  to the desired tilt angles θ 1  and θ 2 . That is, sensing circuit  230  is configured to sense the TE/TM ratio of the light signal carried by intermediate output  220 , and further configured to, responsively, send feedback signals to MEMS-based tunable polarization rotator  100  to cause MEMS-based tunable polarization rotator  100  to adjust the polarization of the light signal by actuating first MEMS cantilever  150  and/or second MEMS cantilever  160 . Dynamic polarization variations can be handled in real time with a transient response bandwidth limited mainly by the MEMS cantilever actuation time. 
     Thus, a control loop, including feedback loop  250 , is meant to sense the polarization state of the incoming optical mode from the MEMS-based tunable polarization rotator  100  and determine the amount of shift needed to correct the polarization based on a given desired polarization state (e.g., 100% TE, 100% TM, a combination of both, etc.). The polarization state can be sensed in several ways, including using birefringent waveguides and a polarization splitter. 
       FIGS.  3 A and  3 B  show approaches to detect a phase, and thus TE/TM polarization fraction, of an optical signal to use to as part of the feedback mechanism for controlling the MEMS-based tunable polarization rotator, according to an example embodiment. The structures shown in  FIGS.  3 A and  3 B  may be used as part of an initial calibration of the system. Using the result as a “bias” point, a control loop, like that shown in  FIG.  2   , can then fine tune the polarization in real time. Thus, the circuits of  FIGS.  3 A and  3 B  could be one aspect of an implementation of sensing circuit  230  in  FIG.  2   . 
     As suggested in  FIG.  3 A , the optical mode from the rotator enters the control loop circuit shown below and passes through an adiabatic 2×2 (i.e., power splitter  310 ). The power splitter  310  splits incoming power in the ratio of 1:9 or 1:19 etc. Instead of power splitter  310 , a multi-mode interferometer (MMI), Y-branch, tap coupler, etc. could also be used. 
     Most of the power is directed to the optical circuit downstream. A small fraction is then directed into a Y-branch  315 , which divides the signal power into two waveguides (50% each). A transition  317  is then employed to match the modes in the input waveguide and the birefringent waveguide used in the next stage. The purpose of this is to prevent any energy loss by adiabatically transforming the optical mode in the input waveguide to the mode in the birefringent waveguide and minimize scattering and back reflections. 
     The two arms containing the birefringent waveguide function as a VOA (variable optical attenuator)  320 . One of the arms is equipped with a heater  325  and when a current is passed through this heater (basically a resistor made of metal traces  326 , doped Si etc.), the temperature of one arm increases. This causes a shift in the refractive index as compared to the other identical arm. A birefringent waveguide essentially means that the waveguide material exhibits different refractive indices for TE and TM modes in the absence of geometric dispersion (waveguide is wide and tall enough (square cross section)). 
     The temperature increase further causes a variation in these indices via the thermo optic coefficient of the material. Thus, the phase of the mode changes. At the output of the VOA  320 , the mode passes through transitions  318  and is combined in a y-combiner  327  (e.g., MMI, 2×2, tap coupler, etc.) and the amplitude is measured using a photodiode  330 . A transimpedance amplifier (TIA)  335  converts the output current of photodiode  330  into a sizable voltage which the electrical circuit can then process. 
     Knowing the output amplitude, one can estimate the phase shift observed. And knowing the phase shift and the temperature increase (using a temp. sensor/calculating estimate based on electrical power input), one can determine the change in the material refractive index. Since the thermo-optic coefficient is well-known, it is then possible to calculate the relative percentage of TE/TM fields in the optical mode. For example, knowing the phase difference between the legs, it is possible to calculate ΔΦ=λ/2Δη eff . Therefore, Δη eff =λ/2ΔΦ. With Δη eff  it is then possible to estimate η eff  (effective refraction). Using η eff , one can then estimate polarization. 
     The 100% TE/ 100% TM reference  305  at the input of is meant for calibration of this control loop (characterizing the birefringence etc.) if a suitable laser source is available. 
       FIG.  3 B  shows the use of a polarization splitter to sense TE/TM polarization fraction, of an optical signal to use as part of the feedback mechanism for controlling the MEMS-based tunable polarization rotator  100 , according to an example embodiment. As shown, the optical mode from the MEMS-based tunable polarization rotator  100  enters the control loop circuit and passes through adiabatic 2×2 power splitter  310 . Power splitter  310  splits incoming power in the ratio of 1:9 or 1:19 etc. Instead of a 2×2 power splitter, an MMI, Y-branch, tap coupler, etc. can be used. 
     Most of the power is directed to the optical circuit downstream. A small fraction is then directed into a 2×2 power splitter  350  which divides the signal power into two waveguides (50% each). One of the arms is terminated using a photodiode  355  to measure the optical intensity (as a reference). Photodiode  355  should have the same responsivity across different polarizations. 
     The other arm is directed into a polarization splitter  360  which separates the TE and TM fields and each of these waveguides is then terminated with a respective photodiode  362 ,  364  to measure the optical power in the TE fields and the TM fields. Outputs of photodiodes  362 ,  364  are provided to TIAs  372 ,  374 . This directly provides the TE/TM ratio. 
     The bandwidth of the control loop depends on the photodiode bandwidth, any propagation delay in the electrical circuit and the settling time of the MEMS cantilever. 
       FIG.  4    shows a slotted waveguide  410  (cross section) that can be used to dampen TM mode polarization to calibrate the MEMS-based tunable polarization rotator  100 , according to an example embodiment. More specifically, for purposes of calibration, polarization of a light signal is varied to calibrate, initially, based on amplitude detected at, e.g., a photodiode. Since the slotted waveguide dampens TM mode, and passes TE mode, it can be discerned that the mode is 100% quasi-TE when the amplitude detected is maximum. 
       FIG.  5    shows a flowchart for controlling the MEMS-based tunable polarization rotator  100 , according to an example embodiment. At  510 , TE/TM light is input to the MEMS-based tunable polarization rotator  100 . At  520 , initial polarization is tuned based on tilt angles θ 1  and θ 2 . At  530 , a polarization shift for desired polarization state is sensed, i.e., determined. Stated alternatively, at  530 , the current polarization is sensed to determine a desired shift to be applied by the EMS-based tunable polarization rotator  100 . And, at  540 , one or more MEMS cantilevers are actuated to achieve the desired polarization rotation. 
     Thus, those skilled in the art will appreciate that the embodiments described herein provide a MEMS actuated, tunable, chip-scale polarization converter based on out-of-plane waveguides and Berry&#39;s phase. The MEMS-based tunable polarization rotator  100  is wavelength insensitive, has a small form factor and can be used to eliminate the use of PMFs in data center switches and to design chip-scale sensors. 
       FIG.  6    is a flowchart for operating the MEMS-based tunable polarization rotator  100 , according to an example embodiment. At  602 , an operation includes receiving an optical signal having a first polarization at a first section of a waveguide, the first section of the waveguide being disposed on a plane of a substrate. At  604 , an operation includes, using a micro-electromechanical system (MEMS) device, angling a second section of the waveguide out of the plane of the substrate. And, at  606 , an operation includes outputting the optical with a second polarization, different from the first polarization, on a third section of the waveguide, the third section of the waveguide also being disposed on the plane of the substrate. 
       FIG.  7    illustrates a hardware block diagram of a computing device that may leverage the MEMS-based tunable polarization rotator  100  as part of its I/O function, according to an example embodiment. In at least one embodiment, the computing device  700  may include one or more processor(s)  702 , one or more memory element(s)  704 , storage  706 , a bus  708 , one or more network processor unit(s)  710  interconnected with one or more network input/output (I/O) interface(s)  712 , one or more I/O interface(s)  714 , and control logic  720 . In various embodiments, instructions associated with logic for computing device  700  can overlap in any manner and are not limited to the specific allocation of instructions and/or operations described herein. MEMS-based tunable polarization rotator  100  could be implemented in, e.g., network (I/O) interface(s)  712 . 
     In at least one embodiment, processor(s)  702  is/are at least one hardware processor configured to execute various tasks, operations and/or functions for computing device  700  as described herein according to software and/or instructions configured for computing device  700 . Processor(s)  702  (e.g., a hardware processor) can execute any type of instructions associated with data to achieve the operations detailed herein. In one example, processor(s)  702  can transform an element or an article (e.g., data, information) from one state or thing to another state or thing. Any of potential processing elements, microprocessors, digital signal processor, baseband signal processor, modem, PHY, controllers, systems, managers, logic, and/or machines described herein can be construed as being encompassed within the broad term ‘processor’. 
     In at least one embodiment, memory element(s)  704  and/or storage  706  is/are configured to store data, information, software, and/or instructions associated with computing device  700 , and/or logic configured for memory element(s)  704  and/or storage  706 . For example, any logic described herein can, in various embodiments, be stored for computing device  700  using any combination of memory element(s)  704  and/or storage  706 . Note that in some embodiments, storage  706  can be consolidated with memory element(s)  704  (or vice versa), or can overlap/exist in any other suitable manner. 
     In at least one embodiment, bus  708  can be configured as an interface that enables one or more elements of computing device  700  to communicate in order to exchange information and/or data. Bus  708  can be implemented with any architecture designed for passing control, data and/or information between processors, memory elements/storage, peripheral devices, and/or any other hardware and/or software components that may be configured for computing device  700 . In at least one embodiment, bus  708  may be implemented as a fast kernel-hosted interconnect, potentially using shared memory between processes (e.g., logic), which can enable efficient communication paths between the processes. 
     In various embodiments, network processor unit(s)  710  may enable communication between computing device  700  and other systems, entities, etc., via network I/O interface(s)  712  to facilitate operations discussed for various embodiments described herein. In various embodiments, network processor unit(s)  710  can be configured as a combination of hardware and/or software, such as one or more Ethernet driver(s) and/or controller(s) or interface cards, Fibre Channel (e.g., optical) driver(s) and/or controller(s), and/or other similar network interface driver(s) and/or controller(s) now known or hereafter developed to enable communications between computing device  700  and other systems, entities, etc. to facilitate operations for various embodiments described herein. In various embodiments, network I/O interface(s)  712  can be configured as one or more Ethernet port(s), Fibre Channel ports, and/or any other I/O port(s) now known or hereafter developed. Thus, the network processor unit(s)  710  and/or network I/O interface(s)  712  may include suitable interfaces for receiving, transmitting, and/or otherwise communicating data and/or information in a network environment. 
     I/O interface(s)  714  allow for input and output of data and/or information with other entities that may be connected to computing device  700 . For example, I/O interface(s)  714  may provide a connection to external devices such as a keyboard, keypad, a touch screen, and/or any other suitable input and/or output device now known or hereafter developed. In some instances, external devices can also include portable computer readable (non-transitory) storage media such as database systems, thumb drives, portable optical or magnetic disks, and memory cards. In still some instances, external devices can be a mechanism to display data to a user, such as, for example, a computer monitor, a display screen, or the like. 
     In various embodiments, control logic  720  can include instructions that, when executed, cause processor(s)  702  to perform operations, which can include, but not be limited to, providing overall control operations of computing device; interacting with other entities, systems, etc. described herein; maintaining and/or interacting with stored data, information, parameters, etc. (e.g., memory element(s), storage, data structures, databases, tables, etc.); combinations thereof; and/or the like to facilitate various operations for embodiments described herein. 
     In various embodiments, entities as described herein may store data/information in any suitable volatile and/or non-volatile memory item (e.g., magnetic hard disk drive, solid state hard drive, semiconductor storage device, random access memory (RAM), read only memory (ROM), erasable programmable read only memory (EPROM), application specific integrated circuit (ASIC), etc.), software, logic (fixed logic, hardware logic, programmable logic, analog logic, digital logic), hardware, and/or in any other suitable component, device, element, and/or object as may be appropriate. Any of the memory items discussed herein should be construed as being encompassed within the broad term ‘memory element’. Data/information being tracked and/or sent to one or more entities as discussed herein could be provided in any database, table, register, list, cache, storage, and/or storage structure: all of which can be referenced at any suitable timeframe. Any such storage options may also be included within the broad term ‘memory element’ as used herein. 
     Note that in certain example implementations, operations as set forth herein may be implemented by logic encoded in one or more tangible media that is capable of storing instructions and/or digital information and may be inclusive of non-transitory tangible media and/or non-transitory computer readable storage media (e.g., embedded logic provided in: an ASIC, digital signal processing (DSP) instructions, software (potentially inclusive of object code and source code), etc.) for execution by one or more processor(s), and/or other similar machine, etc. Generally, memory element(s)  704  and/or storage  706  can store data, software, code, instructions (e.g., processor instructions), logic, parameters, combinations thereof, and/or the like used for operations described herein. 
     In some instances, software of the present embodiments may be available via a non-transitory computer useable medium (e.g., magnetic or optical mediums, magneto-optic mediums, CD-ROM, DVD, memory devices, etc.) of a stationary or portable program product apparatus, downloadable file(s), file wrapper(s), object(s), package(s), container(s), and/or the like. In some instances, non-transitory computer readable storage media may also be removable. For example, a removable hard drive may be used for memory/storage in some implementations. Other examples may include optical and magnetic disks, thumb drives, and smart cards that can be inserted and/or otherwise connected to a computing device for transfer onto another computer readable storage medium. 
     Variations and Implementations 
     Embodiments described herein may include one or more networks, which can represent a series of points and/or network elements of interconnected communication paths for receiving and/or transmitting messages (e.g., packets of information) that propagate through the one or more networks. These network elements offer communicative interfaces that facilitate communications between the network elements. A network can include any number of hardware and/or software elements coupled to (and in communication with) each other through a communication medium. Such networks can include, but are not limited to, any local area network (LAN), virtual LAN (VLAN), wide area network (WAN) (e.g., the Internet), software defined WAN (SD-WAN), wireless local area (WLA) access network, wireless wide area (WWA) access network, metropolitan area network (MAN), Intranet, Extranet, virtual private network (VPN), Low Power Network (LPN), Low Power Wide Area Network (LPWAN), Machine to Machine (M2M) network, Internet of Things (IoT) network, Ethernet network/switching system, any other appropriate architecture and/or system that facilitates communications in a network environment, and/or any suitable combination thereof. 
     Networks through which communications propagate can use any suitable technologies for communications including wireless communications (e.g., 4G/5G/nG, IEEE 802.11 (e.g., Wi-Fi®/Wi-Fi6®), IEEE 802.16 (e.g., Worldwide Interoperability for Microwave Access (WiMAX)), Radio-Frequency Identification (RFID), Near Field Communication (NFC), Bluetooth™ mm.wave, Ultra-Wideband (UWB), etc.), and/or wired communications (e.g., T1 lines, T3 lines, digital subscriber lines (DSL), Ethernet, Fibre Channel, etc.). Generally, any suitable means of communications may be used such as electric, sound, light, infrared, and/or radio to facilitate communications through one or more networks in accordance with embodiments herein. Communications, interactions, operations, etc. as discussed for various embodiments described herein may be performed among entities that may directly or indirectly connected utilizing any algorithms, communication protocols, interfaces, etc. (proprietary and/or non-proprietary) that allow for the exchange of data and/or information. 
     In various example implementations, entities for various embodiments described herein can encompass network elements (which can include virtualized network elements, functions, etc.) such as, for example, network appliances, forwarders, routers, servers, switches, gateways, bridges, load balancers, firewalls, processors, modules, radio receivers/transmitters, or any other suitable device, component, element, or object operable to exchange information that facilitates or otherwise helps to facilitate various operations in a network environment as described for various embodiments herein. Note that with the examples provided herein, interaction may be described in terms of one, two, three, or four entities. However, this has been done for purposes of clarity, simplicity and example only. The examples provided should not limit the scope or inhibit the broad teachings of systems, networks, etc. described herein as potentially applied to a myriad of other architectures. 
     Communications in a network environment can be referred to herein as ‘messages’, ‘messaging’, ‘signaling’, ‘data’, ‘content’, ‘objects’, ‘requests’, ‘queries’, ‘responses’, ‘replies’, etc. which may be inclusive of packets. As referred to herein and in the claims, the term ‘packet’ may be used in a generic sense to include packets, frames, segments, datagrams, and/or any other generic units that may be used to transmit communications in a network environment. Generally, a packet is a formatted unit of data that can contain control or routing information (e.g., source and destination address, source and destination port, etc.) and data, which is also sometimes referred to as a ‘payload’, ‘data payload’, and variations thereof. In some embodiments, control or routing information, management information, or the like can be included in packet fields, such as within header(s) and/or trailer(s) of packets. Internet Protocol (IP) addresses discussed herein and in the claims can include, but not limited to, any IP version 4 (IPv4) and/or IP version 6 (IPv6) addresses. 
     To the extent that embodiments presented herein relate to the storage of data, the embodiments may employ any number of any conventional or other databases, data stores or storage structures (e.g., files, databases, data structures, data or other repositories, etc.) to store information. 
     Note that in this Specification, references to various features (e.g., elements, structures, nodes, modules, components, engines, logic, steps, operations, functions, characteristics, etc.) included in ‘one embodiment’, ‘example embodiment’, ‘an embodiment’, ‘another embodiment’, ‘certain embodiments’, ‘some embodiments’, ‘various embodiments’, ‘other embodiments’, ‘alternative embodiment’, and the like are intended to mean that any such features are included in one or more embodiments of the present disclosure, but may or may not necessarily be combined in the same embodiments. Note also that a module, engine, client, controller, function, logic or the like as used herein in this Specification, can be inclusive of an executable file comprising instructions that can be understood and processed on a server, computer, processor, machine, compute node, combinations thereof, or the like and may further include library modules loaded during execution, object files, system files, hardware logic, software logic, or any other executable modules. 
     It is also noted that the operations and steps described with reference to the preceding figures illustrate only some of the possible scenarios that may be executed by one or more entities discussed herein. Some of these operations may be deleted or removed where appropriate, or these steps may be modified or changed considerably without departing from the scope of the presented concepts. In addition, the timing and sequence of these operations may be altered considerably and still achieve the results taught in this disclosure. The preceding operational flows have been offered for purposes of example and discussion. Substantial flexibility is provided by the embodiments in that any suitable arrangements, chronologies, configurations, and timing mechanisms may be provided without departing from the teachings of the discussed concepts. 
     As used herein, unless expressly stated to the contrary, use of the phrase ‘at least one of’, ‘one or more of’, ‘and/or’, variations thereof, or the like are open-ended expressions that are both conjunctive and disjunctive in operation for any and all possible combination of the associated listed items. For example, each of the expressions ‘at least one of X, Y and Z’, ‘at least one of X, Y or Z’, ‘one or more of X, Y and Z’, ‘one or more of X, Y or Z’ and ‘X, Y and/or Z’ can mean any of the following: 1) X, but not Y and not Z; 2) Y, but not X and not Z; 3) Z, but not X and not Y; 4) X and Y, but not Z; 5) X and Z, but not Y; 6) Y and Z, but not X; or 7) X, Y, and Z. 
     Additionally, unless expressly stated to the contrary, the terms ‘first’, ‘second’, ‘third’, etc., are intended to distinguish the particular nouns they modify (e.g., element, condition, node, module, activity, operation, etc.). Unless expressly stated to the contrary, the use of these terms is not intended to indicate any type of order, rank, importance, temporal sequence, or hierarchy of the modified noun. For example, ‘first X’ and ‘second X’ are intended to designate two ‘X’ elements that are not necessarily limited by any order, rank, importance, temporal sequence, or hierarchy of the two elements. Further as referred to herein, ‘at least one of’ and ‘one or more of’ can be represented using the ‘(s)’ nomenclature (e.g., one or more element(s)). 
     In sum, a method is provided. The method may include receiving an optical signal having a first polarization state at a first section of a waveguide, the first section of the waveguide being disposed on a plane of a substrate, using a micro-electromechanical system (MEMS) device, angling a second section of the waveguide out of the plane of the substrate, and outputting the optical signal with a second polarization state, different from the first polarization state, on a third section of the waveguide, the third section of the waveguide also being disposed on the plane of the substrate. 
     In the method, the first polarization state is a first transverse electric (TE) mode and transverse magnetic (TM) mode ratio, and the second polarization state is a second TE mode and TM mode ratio. 
     The method may further include angling the second section of the waveguide by actuating a piezo-electric material on which the second section of the waveguide is disposed. 
     The angling may be up to 22.5 degrees, or up to 45 degrees. 
     The method may further include angling a fourth section of the waveguide out of the plane of the substrate. 
     In the method, a sum of a first angle of the second section of the waveguide and a second angle of the fourth section of the waveguide is up to at least 45 degrees. 
     In the method, angling the second section of the waveguide out of the plane of the substrate may be executed during a calibration operation. 
     The method may further include leveraging waveguide birefringence as part of the calibration operation. 
     The method may also include receiving a feedback signal indicative of polarization state, and angling the second section of the waveguide out of the plane of the substrate in response to the feedback signal. 
     In another embodiment, an apparatus is provided. The apparatus may include a substrate, a waveguide disposed on the substrate, a micro-electromechanical system (MEMS) cantilever disposed under a portion of the waveguide, and configured, when actuated, to displace the portion of the waveguide outside of a plane of remaining portions of the waveguide disposed on the substrate, and a control loop configured to actuate the MEMS cantilever, responsive to polarization of light traveling in the waveguide. 
     The substrate may be comprised of silicon. 
     The MEMS cantilever may be comprised of piezoelectric material. 
     The piezoelectric material may be comprised of aluminum nitride, quartz, Lithium Niobate (LiNbO 3 ), Lead Zirconate Titanate (PZT), Potassium Niobate (KNbO 3 ), Sodium Tungstate (Na 2 WO 3 ). 
     The MEMS cantilever may be configured to be displaced out of the plane of remaining portions of the waveguide by up to at least 22.5 degrees. 
     The apparatus may further include a second MEMS cantilever having disposed thereon another portion of the waveguide, and configured, when actuated, to displace the another portion of the waveguide outside of the plane of remaining portions of the waveguide disposed on the substrate. 
     In still another embodiment, an apparatus is provided and includes a substrate, a waveguide disposed on the substrate, a first micro-electromechanical system (MEMS) cantilever disposed under a first curved portion of the waveguide, and configured, when actuated, to displace the first curved portion of the waveguide outside of a plane of remaining portions of the waveguide disposed on the substrate, a second MEMS cantilever disposed under a second curved portion of the waveguide, and configured, when actuated, to displace the second curved portion of the waveguide outside of the plane of remaining portions of the waveguide disposed on the substrate, and electrodes disposed on the first MEMS cantilever and the second MEMS cantilever via which a voltage may be applied to actuate the first MEMS cantilever and the second MEMS cantilever. 
     The apparatus may also include a control loop configured to actuate the first MEMS cantilever and the second MEMS cantilever, responsive to a polarization state of light traveling in the waveguide. 
     In the apparatus, the first MEMS cantilever and the second MEMS cantilever may be comprised of piezoelectric material. 
     The piezoelectric material may be comprised of aluminum nitride, quartz, Lithium Niobate (LiNbO 3 ), Lead Zirconate Titanate (PZT), Potassium Niobate (KNbO 3 ), Sodium Tungstate (Na 2 WO 3 ). 
     One or more advantages described herein are not meant to suggest that any one of the embodiments described herein necessarily provides all of the described advantages or that all the embodiments of the present disclosure necessarily provide any one of the described advantages. Numerous other changes, substitutions, variations, alterations, and/or modifications may be ascertained to one skilled in the art and it is intended that the present disclosure encompass all such changes, substitutions, variations, alterations, and/or modifications as falling within the scope of the appended claims.