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- FIBER-OPTIC SILICON FABRY-PEROT INTERFEROMETERS FOR HIGH-SPEED ANEMOMETER AND HIGH-SENSITIVITY BOLOMETER APPLICATIONS
- Uddin, Nezam
- Electronic Theses & Dissertations
Fiber-optic silicon Fabry-Perot interferometric temperature sensor offers the advantage of high-speed and high-resolution to characterize the ocean turbulence in oceanographic research. Compared to silica, the material that makes the optical fiber, silicon has a thermo-optic coefficient ten times higher and a thermal conductivity sixty time higher. Silicon is highly transparent in the infrared wavelength range and can be easily processed with the mature microfabrication technology. All of...
Show moreFiber-optic silicon Fabry-Perot interferometric temperature sensor offers the advantage of high-speed and high-resolution to characterize the ocean turbulence in oceanographic research. Compared to silica, the material that makes the optical fiber, silicon has a thermo-optic coefficient ten times higher and a thermal conductivity sixty time higher. Silicon is highly transparent in the infrared wavelength range and can be easily processed with the mature microfabrication technology. All of these make silicon a very attractive material for high-speed and high-resolution turbulence measurement. We attached a small silicon pillar to the end of an optical fiber to make fiber-optic Fabry-Perot interferometric sensor demodulated by a white light system for fast turbulence measurement. We studied the two modes of fiber-optic hot wire anemometer operation for turbulence measurement theoretically and experimentally. The constant temperature operation of the fiber-optic hot wire anemometer was introduced for the first time to reduce the time constant significantly. The anemometer used for demonstration is based on a silicon low-finesse Fabry-Perot interferometer (FPI) attached to the tip of a single mode fiber. Turbulent flow measurement method based on constant temperature operation offers high measuring speed, because the wire temperature is kept constant, the effect of thermal inertia of the wire is suppressed. We also investigated a new sensor structure experimentally and theoretically for the measurement of water flow with reduced directivity. This sensor consists of a laser heated silicon FPI embedded in a metal microsphere. Herein, the spherical shape of the outside metal shell gives a symmetric response to water flow direction; thus, the directivity is reduced greatly. Moreover, the water flow measurement by the hot wire fiber-optic water flow sensor based on laser heated silicon FPI need to compensate the effect of water temperature variation. We reported a technique to compensate the effect of water temperature change in the flow measurement by using another sensor which will track the temperature of the water. By using the information of the water temperature change, baseline can be defined which will provide unique wavelength change for the flow. Finally, the wavelength change corresponding to the flow speed were calibrated using the sensor pair after compensating the effect of water temperature variation. We expanded the use of silicon Fabry-Perot interferometric sensor in the measurement of plasma radiation by modifying the structure with gold coated silicon and multimode graded index fiber between the single mode fiber (SMF) and silicon. We reported the design, fabrication, and characterization of a fiber-optic bolometer (FOB) with improved noise equivalent power density (NEPD) performance and increased absorption to high energy photons by engineering the absorber of the FOB. We also have developed a multichannel fiberoptic bolometry system with five bolometers connected to each channel of the coarse wavelength division multiplexer (CWDM), a single light source of super luminescent LED (SLED) and a single I-MON 512 OEM spectrometer. Easy sensor fabrication, significantly enhanced measurement range compared to the previous high-finesse FPI bolometer system for measuring radiation are some of the advantages. Moreover, utilization of the FOB in the vacuum for radiation measurement with reduced time constant was also studied which is practically required in the fusion devices. This was done by adding a heat sink with the current FOB structure and using the deconvolution method to get better temporal resolution. Finally, the FOB with the heat sink was tested in the vacuum condition to measure the radiation using the deconvolution method. Experimental results are presented to support the idea of heat sink and deconvolution method for plasma radiation measurement.