Design and Fabrication of an Optical-MEMS Sensor
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1052-DD04-08
Design and Fabrication of an Optical-MEMS Sensor Vaibhav Mathur, Jin Li, and William D. Goodhue Photonics Center,Department of Physics and Applied Physics, University of Massachusetts,Lowell, 720,Suffolk St., Lowell, MA, 01854 ABSTRACT A novel optical-MEMS sensor based on the AlGaAs material system is designed and fabricated. The device consists of micro-beam waveguides butt-coupled with their ends separated by approximately 2 to 4 µm. The device works on the principle that when acoustically driven by an external source, the waveguides misalign, leading to coupling loss. The device design parameters were determined using FEM (Finite Element Method) modeling. The dielectric waveguide beams were designed for single mode propagation at 785 nm and longer wavelengths. A combination of dry and wet etching process followed by precision laser cutting was used to fabricate the suspended beams. Beams ranging from 100 µm to 400 µm with fundamental frequencies of 50 KHz to 200 KHz were successfully fabricated. Initial uncut waveguide test results will be discussed along with the plan for characterizing the devices using an acoustically coupled piezoelectric driver. These devices may be utilized for vibration sensing, or optical intensity modulation. INTRODUCTION Micro-electro-mechanical System (MEMS) based sensors have been used in the past decade for a variety of applications ranging from pressure sensing, bio-sensing and accelerometers. Most vibration sensors in use today are accelerometers in which the suspended structure oscillates harmonically. For sinusoidal vibrations, the displacement, velocity and acceleration amplitudes are related directly to the frequency. For example, the iMEMS family of accelerometers developed by Analog Devices is widely used in the automobile industry [1]. Most of these devices work on the principle of capacitance changes induced in a parallel plate capacitor type configuration due to the movement of a proof mass with respect to the substrate. The device presented here employs a novel technique based on the change in the optical signal which could potentially have faster response and higher sensitivity. In addition, conventional MEMS devices have relied heavily on the use of silicon as the substrate material. Developing MEMS based on III-V semiconductor materials offers the great potential of integration with opto-electronic devices such as lasers and photodetectors. The AlGaAs/GaAs based MEMS devices reported here work on the principle of change in the optical coupling due to micro-cantilever waveguide misalignment when driven acoustically with a piezo chip. The device design parameters were determined using FEM (Finite Element Method) modeling. The dielectric waveguide beams were designed for single mode propagation at 785 nm and longer wavelengths. A combination of dry and wet etching process followed by precision laser cutting was used to fabricate the suspended beams. Beams ranging from 100 µm to 400 µm with fundamental frequencies of 50 KHz to 200 KHz were successfully fabric
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