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Fiber optic low coherence interferometry technology research

Author: JinZuo
Tutor: ZhongHongJie
School: Tianjin Polytechnic University
Course: Physical Electronics
Keywords: Spectral domain Phase domain Center stripe Centroid algorithm
CLC: TN256
Type: Master's thesis
Year: 2006
Downloads: 247
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Abstract


The fiber-optic interferometer sensor may be using a new technique , i.e. low coherence , broadband light source, such as a light emitting diode ( LED ) , the multi-mode laser diode or a halogen . Sensing method referred to as \Optical fiber sensing technology until 1983 was reported , but the operating principle of the first to use single-mode fiber and multimode fiber in 1975 proved that can be used in potential communication system . Like all the interference method , the lightwave through the optical path length changes in the interferometer fringe pattern analysis. Here study using two different methods in the fiber optic sensor system to observe such a stripe pattern , i.e. the spectral domain processing method , and the phase -domain processing methods . Spectral domain technology , the spectrum analyzer is used for optical processing elements . Optical processing element can be used in the phase domain techniques Michelson, to constitute a Fabry -Perot or a Mach-Zehnder interferometer . In this method must make the optical path difference is greater than the coherence length of the light source of the sensing chamber such that the less the output of the interference effect observed in the normal state . The return of the light waves from the sensing interference cavity is incoherent time . The second treatment function of the interferometer is the reconstruction of the interference effect , the restoration of radiation components time-coherency . LED or multimode laser diode interference analyzer system in the main difficulty is the identification of the center stripe . A simple but very effective way , using a centroid algorithm to the authentication center stripe . The second method to enhance the fringes discernment dual wavelength variation of the method , to obtain a wide spectrum using a dual wavelength intervals in the order of magnitude of 100 nm . Lateral movement of the stripes through space is converted to a time on the detector plane streaks through the grating element . The adjustment of the position of the two grating elements , such that their periodic structure difference of π / 2 radians . The change in the length of the sensing interferometer cavity causes the lateral displacement of the spatial fringe static grating element , a phase difference of π / 2 , so that the two photodiodes respectively generated output of the sinφ and cosφ . By such cross- I signal reflects the change and the direction of change in the sensing chamber of the optical path difference (OPD) .

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CLC: > Industrial Technology > Radio electronics, telecommunications technology > Photonics technology,laser technology > Optical waveguide and integrated optics > Integrated optical devices
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