Method and apparatus for beam control with optical MEMS beam waveguide
A high density, low power, high performance information system, method and apparatus are described in which perpendicularly oriented processor and memory die stacks ( 130, 140, 150, 160, 170 ) include integrated deflectable MEMS optical beam waveguides (e.g., 190 ) at each die edge (e.g., 151 ) to provide optical communications ( 184 ) in and between die stacks by using a beam control method and circuit to maintain and adjust alignment over time by calibrating and updating X and Y counter values stored in deflection registers ( 541 - 542 ) to control DAC circuitry ( 546, 548 ) which generates and supplies deflection voltages to charging capacitors ( 551, 552 ) connected to deflection electrodes ( 195 - 197 ) positioned on and around each MEMS optical beam waveguide ( 193 - 194 ) to provide two-dimensional alignment and controlled feedback to adjust beam alignment and establish optical communication links between die stacks.
1. An apparatus comprising:
beam control circuitry for controlling deflection of a first cantilevered MEMS optical beam waveguide, comprising:
a plurality of separate deflection electrodes positioned to control deflection of the first cantilevered MEMS optical beam waveguide, the separate deflection electrodes comprising a vertical deflection electrode positioned above the first cantilevered MEMS optical beam waveguide and a plurality of separate lateral deflection electrodes positioned on at least a first side of the first cantilevered MEMS optical beam waveguide; and
a bias circuit connected to provide separately controllable bias voltages to the plurality of separate deflection electrodes, thereby generating controlled, two-dimensional deflection of the first cantilevered MEMS optical beam waveguide.
2. The apparatus of claim 1 , where the plurality of separate deflection electrodes comprises a plurality of vertical deflection electrodes positioned above and below the first cantilevered MEMS optical beam waveguide to control vertical deflection of the first cantilevered MEMS optical beam waveguide.
3. The apparatus of claim 1 , where the bias circuit generates a first bias voltage for electrical connection to a first deflection electrode located near an anchored base of the first cantilevered MEMS optical beam waveguide, and generates a second bias voltage having a greater magnitude for electrical connection to a second deflection electrode located near a distal end of the first cantilevered MEMS optical beam waveguide.
4. The apparatus of claim 1 , where the bias circuit generates a first polarity bias voltage for electrical connection to a first deflection electrode located near an anchored base of the first cantilevered MEMS optical beam waveguide, and generates a second, opposite polarity bias voltage for electrical connection to a second deflection electrode located near a distal end of the first cantilevered MEMS optical beam waveguide.
5. The apparatus of claim 1 , where the bias circuit comprises:
a programmable register for storing a digital deflection value;
a digital-to-analog converter for converting the digital deflection value to an analog voltage value;
a driver circuit for generating a first bias voltage from the analog voltage value; and
a multi-tap resistive circuit for generating a plurality of bias voltages for connection to the plurality of separate deflection electrodes.
6. The apparatus of claim 1 , where the bias circuit comprises:
a plurality of programmable registers for storing lateral and vertical deflection values for each of a plurality of cantilevered MEMS optical beam waveguides;
control logic for processing the lateral and vertical deflection values to select a pair of lateral and vertical deflection values for the first cantilevered MEMS optical beam waveguide; and
one or more digital-to-analog converter circuits for converting the pair of lateral and vertical deflection values to a pair of lateral and vertical bias voltages.
7. The apparatus of claim 6 , further comprising a plurality of switched capacitor circuits for storing the pair of lateral and vertical bias voltages, where each switched capacitor circuit is respectively connected between a digital-to-analog converter circuit and a corresponding separate deflection electrode.
8. The apparatus of claim 7 , where each switched capacitor circuit comprises a control switch connected between a digital-to-analog converter circuit and a corresponding beam alignment capacitor to thereby couple a lateral or vertical bias voltage to the corresponding separate deflection electrode.
9. The apparatus of claim 1 , where the bias circuit comprises one or more storage devices for storing one or more calibrated digital deflection values to compensate for beam deflections at the first cantilevered MEMS optical beam waveguide resulting from manufacturing stresses or defects.
10. The apparatus of claim 1 , where beam control circuitry further comprises control logic for processing a control feedback signal from the plurality of separate deflection electrodes to adjust the controlled, two-dimensional deflection of the first cantilevered MEMS optical beam waveguide over time.
11. A method comprising:
providing an integrated circuit die comprising a cantilevered MEMS optical beam and a plurality of deflection electrodes positioned to control deflection of the cantilevered MEMS optical beam;
retrieving digital calibration values for compensating for an initial beam deflection in the cantilevered MEMS optical beam;
generating deflection bias voltages from the digital calibration values for storage, where each deflection bias voltage is stored on a storage capacitor that is connected to a corresponding one of the plurality of deflection electrodes; and
transferring an optical signal along the cantilevered MEMS optical beam which is deflected by electric field forces exerted on the cantilevered MEMS optical beam in response to deflection bias voltages applied to the plurality of deflection electrodes.
12. The method of claim 11 , where the initial beam deflection in the cantilevered MEMS optical beam results at least in part from manufacturing stresses or defects in the cantilevered MEMS optical beam.
13. The method of claim 11 , where retrieving digital calibration values comprises retrieving one or more digital calibration values from one or more programmable fuses or flash memory storage.
14. The method of claim 11 , further comprising computing digital beam deflection values from the digital calibration values by:
computing digital deflection values representing an adjusted beam deflection for the cantilevered MEMS optical beam;
adding the digital calibration values and digital deflection values to compute digital beam deflection values; and
storing the digital beam deflection values in a plurality of registers.
15. The method of claim 14 , where generating deflection bias voltages comprises loading the digital beam deflection values into corresponding digital-to-analog converters for conversion into deflection bias voltages.
16. The method of claim 11 , where transferring an optical signal comprises transferring a dummy signal along the cantilevered MEMS optical beam for reception at a target MEMS optical beam waveguide for use in generating a feedback control signal that is processed to adjust alignment of the cantilevered MEMS optical beam.
17. A system comprising:
a first integrated circuit device comprising an optical transmitter, a first cantilevered MEMS optical beam waveguide, and a first plurality of deflection electrodes positioned to control deflection of the first cantilevered MEMS optical beam waveguide;
a second integrated circuit device comprising an optical receiver, a second cantilevered MEMS optical beam waveguide, and a second plurality of deflection electrodes positioned to control deflection of the second cantilevered MEMS optical beam waveguide;
beam control circuitry for controlling two-dimensional deflection of the first cantilevered MEMS optical beam waveguide into alignment with the second cantilevered MEMS optical beam waveguide by generating a plurality of deflection bias voltages which are coupled to the first and second plurality of deflection electrodes to exert electric field forces on the first and second cantilevered MEMS optical beam waveguides; and
a plurality of storage capacitors for storing the deflection bias voltages, where each storage capacitor is connected to a corresponding one of the plurality of deflection electrodes.
18. The system of claim 17 , further comprising:
a feedback system including a non-optical communication link for receiving feedback information regarding optical signal information transmitted over the first cantilevered MEMS optical beam waveguide to the second cantilevered MEMS optical beam, where the beam control circuitry uses the feedback information to generate a plurality of adjusted deflection bias voltages which are coupled to the first and second plurality of deflection electrodes.
19. The system of claim 17 , where the beam control circuitry comprises:
memory for storing digital calibration values to compensate for an initial beam deflection in the cantilevered MEMS optical beam;
a plurality of registers for storing digital beam deflection values;
control logic for transforming the digital calibration values into digital beam deflection values; and
bias generator circuits for generating deflection bias voltages from the digital beam deflection values.
20. The system of claim 19 , where the memory comprises programmable fuses or flash memory storage for storing digital calibration values to compensate for initial beam deflections in the first and second cantilevered MEMS optical beams resulting from manufacturing stresses or defects, thereby zeroing deflection in the first and second cantilevered MEMS optical beams.