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Research Of Fiber Sensing Technique Based On Fabry-Perot Tunable Filter And Erbium-Doped Fiber Amplifier

Posted on:2010-07-08Degree:DoctorType:Dissertation
Country:ChinaCandidate:K LiuFull Text:PDF
GTID:1118360302995123Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
- II - Optical fiber sensing system is developed in this dissertation, using Fabry-Perot (F-P) type tunable optical filter (TOF) and Erbium-doped fiber amplifier (EDFA). Further study has been done in theory, systems and experiments. The system has two configurations of open loop and closed loop, which can be used to realize strain and gas sensing respectively with quasi-distributed ability and high sensitivity.The relationship between the detected spectra of the gratings and the 3-dB bandwidth of the F-P type TOF in the open loop optical fiber sensing system is deduced mathematically. The nonlinearity of the F-P type TOF is investigated theoretically and experimentally, which can be compensated. The optics, mechanics, hardware and data processing of the system had been designed and realized. And the tolerance extension of the system had been also discussed. The system can be used to realize strain sensing with demodulation sensitivity less than 3μεand scan rate close to 6 0 Hz.Based on closed loop optical fiber sensing system, the gas sensing model is established using rate equations and transmission equations respectively. The influences of pump power and system loss on the gas sensing sensitivity are analyzed. The optics, mechanics and data processing of the system had been designed and realized. Using wavelength sweep technique, the system can be used to realize acetylene sensing with sensitivity less than 100 ppm. And the sensitivity can be enhanced to 75 ppm by use of wavelength modulation technique, with probability of gas recognition at the same time.Major innovations of this dissertation:1. The model of F-P type TOF is established based on multiple-beam interference. And the nonlinearity characteristic of F-P type TOF and its source are analyzed. The investigation of F-P type TOF nonlinearity using the open loop optical fiber sensing system is put forward. And the wavelength-voltage relationship and its polynomial fit are adopted to model the nonlinearity and analyze the random error of wavelength measurement. The nonlinearity of F-P type TOF can be compensated by use of two methods respectively.2. Transmission equations are used to model the gas sensing system and investigate the sensitivity. The influences of pump power and system loss on the gas sensing sensitivity are analyzed, which can be validated experimentally. And the detection limit of the gas sensing system is deduced theoretically.3. Wavelength sweep technique and wavelength modulation technique are introduced into the gas sensing system. The scheme of wavelength modulation/2nd harmonic components calculation based on virtual instrument technique is put forward. By using these techniques, the gas sensing sensitivity is improved remarkably, and the gas recognition can be also realized.
Keywords/Search Tags:fiber sensing, Fabry-Perot type tunable optical filter, Erbium-doped fiber amplifier, quasi-distributed, wavelength sweep, wavelength modulation
PDF Full Text Request
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