Integrated microphotonic-MEMS inertial sensors

The objective of this thesis is to design, simulate, fabricate and characterize high sensitive low cost in-plane photonic-band-gap (PBG)-micro electromechanical systems (MEMS)-based miniature accelerometers and rotational rate sensors (gyroscopes) on a silicon-on-insulator (SOI) substrate in order to enable the integration of an array of two-axis of these sensors on a single SOI platform. Use of guided-wave optical devices integrated with MEMS on SOI for multichannel/multifunction sensor systems allows the use of multiple sensors to extend the measurement range and accuracy. This provides essential redundancy which makes long-term reliability in the space environment possible therefore reducing the possibility of system failure. The navigator microchip also represents the ability of accommodating diverse attitude and inertial sensors on the same microchip to eliminate the need of many separate sensors. The end product exhibits orders of magnitude reduction in system mass and size. Furthermore, redundancy improves the net performance and precision of the navigation measurement systems.;Two classes of optical accelerometers/gyroscopes are considered in this thesis for application in smallsats navigation, one based on tunable Fabry-Perot (FP) filter, where the sensor is actuated by the applied acceleration providing a shift in the operating wavelength that varies linearly with the applied acceleration and the other one based on variable optical attenuator (VOA), where the sensor is actuated by the applied acceleration providing a linear change for small displacements around the waveguide propagation axis in the relative signal intensity with the applied acceleration. In the case of FP-based sensors, the FP microcavity consists of two distributed Bragg reflectors (DBR) in which one DBR mirror is attached to the proof mass of the system. As a consequence of acceleration/rotation, the relative displacement of the movable mirror with respect to the fixed mirror changes the cavity length and modifies the FP resonance. In the case of VOA-based sensors, a shutter modulation method is used to modulate the coupled light intensity to a multimode strip silicon waveguide. A DBR mirror that is attached to the system proof mass of the sensor is positioned in the gap between two input and output multimode waveguides. The displacement of the Bragg mirror in the presence of acceleration/rotation modulates the intensity of the transmitted optical signal between the input and the output strip waveguides. The sensor sensitivity is inversely proportional to both waveguides widths at the VOA junction and system resonant frequency.;The main differences between FP-based and VOA-based sensors presented here is that the FP filter enables a highly sensitive optical detection of displacement at a nanometer scale but requires more complex optical sources and detectors, whereas VOA-based sensors do not require high spectral quality sources and the detection is much simpler since the intensity of light is measured at the output instead of the wavelength. However to obtain a high sensitive sensor, displacements at the level of micrometer are required.;For gyroscopes, the sensor uses a MEMS electrostatic comb-drive with interdigital fingers to oscillate the MEMS proof mass along the x-axis at rates of about 500 to 1000 Hz. An applied rotation in the z-axis causes the proof mass and the VOA sensing actuator/FP movable mirror to be linearly displaced along the perpendicular y-axis, proportional to the rotation rate. This displacement is ac modulated by the x-axis oscillations, modulating the VOA actuator/FP gap and the resultant transmitted optical signal/wavelength. The MEMS electrostatic oscillator requires about 100 V ac to deflect the proof mass periodically by about +/- 3 microns, as validated experimentally. This displacement is not enough to provide high modulation on the transmitted optical signal in the case where VOA is used. Therefore a compliant microleverage mechanism is introduced to amplify the displacement of the VOA sensing device. A two stage micro-lever mechanism is proposed, providing 7 x displacement amplification. In the instance of the FP-based sensor, a compliant structure is not required since even nano-displacement can significantly shift the transmission peak of the FP. Due to the symmetrical design of all inertial sensors presented here, they have the potential to be designed as two-axis sensors. (Abstract shortened by UMI.).