Albert M. Young

Design and analysis of an ARROW-waveguide-based silicon pressure transducer

We present the design and analysis of a microfabricated silicon pressure transducer. The operating principle for this device is based on the evanescent modulation of power in an integrated optical waveguide. A silicon diaphragm attenuator is initially separated from the waveguide by a precise microfabricated gap spacing. When external pressure is applied to the sensor, the silicon attenuator is moved into closer proximity with the waveguide, and light is coupled out of the waveguide into the attenuator. Thus, by monitoring the light intensity at the output of the waveguide, one can deduce the pressure applied to the silicon diaphragm. Packaging considerations have played an important role in the development of the device and have led to the use of anti-resonant reflecting optical waveguides (ARROWs), which are etched down to form a rib in order to provide confinement in the lateral direction. These waveguides provide good spatial and index matches to single-mode optical fibers. Numerical simulations of device performance have provided information critical to the design of the sensor.

A twin-interferometer fiber-optic readout for diaphragm pressure transducers

A twin-interferometer fiber-optic readout scheme has been developed to monitor the deflection of pressure transducer diaphragms. This technique has a potential advantage at high temperatures, since the circuitry is kept at room temperature and is coupled to the sensor head via optical fibers. The interference scheme used differs from conventional interferometry in that: light is carried forward to the diaphragm and backwards to the photodetectors using a single fiber; and the cleaved fiber end-face itself acts as the reference plane for the interference cavity. A single interferometer cannot uniquely determine the direction of motion, but two such interferometers in parallel, i.e. the twin-interferometer, do provide the necessary information to measure both the magnitude and direction of deflection. Prototype sensor assemblies and detection circuitry have been developed and tested in an industrial setting. Limiting factors on sensor performance have been identified. This technique should also be applicable to other mechanical sensors in which deflections must be monitored.<<ETX>>