Chip-scale two-dimensionai optical phased array with simplified controls

Description (excerpt)

CHIP-SCALE TWO-DIMENSIONAL OPTICAL. PHASED ARRAY WITH SIMPLIFIED CONTROLS CROSS-REFERENCE TO RELATED APPLICATIONS [0001 } The present application claims priority to U.S. Provisional Patent ' Application Serial No. 62/302,248, which was filed on 2 Match 2016. FIELD OF THE INVENTION [Θ0Θ2] The present invention relates in general to optical phased arrays, and in particular to chip-scale optical phased arrays used for optical beam steering (where light is emitted) as well as for optical receivers, imagers and/or scanners (where light is received), BACKGROUND OF THE INVENTION Mechanical Beam Steering Using Gimbals and Fast Steering Mirrors 0 1 The simplest method of steering an optical beam is by use of mechanical means. An example of such standard mechanical means includes a standard, macro-scale gimbal 10, such as shown in FIG. L A light source and lens mounted on the gimbal 10 enables steering in. any direction provided that the gimbal allows for rotation about the two primary axes. Macro-scale gimbals 10 are generally heav (e\g., - : 20 lbs.), require significant power (e.g.,, -48 W) and are slow (e.g., -<10Hz); although -smaller gimbals with improved performance are available, they are still macro-scale devices. For some applications (e.g. on board ships or fixed building mstellations), the Size, Weight, & .Power (''SWAP") of macro-scale gimbals is not prohibitive. However, in other applications, the large SWAP is prohibitive and other non-niechanical beam steering solutions are needed. [0004] While gimbals are generally used to coarsely point the FSQ terminal, stand rd fast steering mirrors. ("FSM") or standard piezo-controlied ("PZ") mirrors are often used for fine pointing of both the transmit and the receive beams. FSMs (e.g. Newport FSM-300 FSM) and PZs (e.g., C0HEX-AG-M 100D PZ) typically operate by controlling the beam reflection from a 1" mirror. The FSM deflects the beam by ±3°, whereas a $¾. deflects the beam by ±0,75°. Because one FSM or PZ is needed for both transmit and receive beams, two units and controllers are required in each interrogator. The- weight of the FSM. mirror is --· I lb. and weight of the PZ is only --85 g. Each needs additional controller electronics. For larger scale motions (e.g., 25 mrad), the FSM can operate at u t 50 Hz and, for very small (0.1 ttiracl) control. loop motions, at up to 5 0 Hz. The PZ controlled pitch yaw mount is generally regarded as a slower ( 10 Hz) system but with absolute position encoding it has a ver stable and reproducible pointing capability. C p-scaie Mechanical Beam Steering Using MEMS [0005] Another method of steering an optical beam ' is by use of standard .micro-electromechanical systems ("MEMS"). An example of a standard MEM ' S device for beam steering is a standard MEMS-based iip/tiii/piston mierornirror 20, such as shown in FIG. 2. In general MEMS approaches simply implement, mechanical beam steering similar te a girnhai, but at the micro-scale (i.e. characteristic lengths ' of hundreds of micrometers). MEM S mirrors are often preferred over lenses due to significant previous research and development by Texas instruments (e.g., Texas Instraments* digital mierornirror device ("DMD") for movie projectors) and Lucent Technologies (e.g., Lucent's optical cross-connect switch for optical networks). By fabricating a micro-mirror on 7 a tip/ti!t/pistoii actuator, the mirror can be positioned to reflect any incident light i a desired direction. Limitations of MEMS microrairrors. include the limited response time (typically, in the 1 microsecond to millisecond-range) and modest fill-factor (e.g. 30% ft!l-iactor and 7 d.B insertion loss) due to th complicated actuator design which requires motion along several axes. For large- angle beam steering, a high fill-factor is essential since the steering angle is a direct function of the mirror separation and the .amount of optical power in a steered beam depends on the mirror size and Fill factor. Many optical MEMS components also only function as switches with two stable states (e.g. Texas Instruments' D D) and are therefore not suitable for beam steering which requires continuously variable devices. Chip-Scale Non-Mechanical- Beam Steering Using Liquid Crystals {0006} Another method of steering an optical beam is by use of standard liquid crystals ("LCs*). LCs are materials that can change their refractive index upon application of an electric field. For itematic LCs, the .time-averaged field needs to be zero; otherwise, the LC will experience permanent Io migration and damage, initial applications of liquid crystals to chip-scale beam steering.