Research On Spectrum Interrogation For FBG Sensing Signals Based On Real-time Data Format Conversion

The spectrum interrogation of fiber Bragg grating (FBG) is the key technology ofFBG sensing applications. This paper proposes and studies the spectruminterrogation for FBG sensing signals based on real-time data format conversion.We obtain the multi-wavelength signals by sampling FBG reflection spectra the usingcomb source. By using all-optical wavelength conversion technology for real-timedata format conversion on the sampling information, multi-wavelength signals areconverted to the time domain signal on the same specific wavelength, and thendetected by a photodetector. The advantages of the program are the same spectrumresources sharing by each sub-link in the same bus network, efficient opticalinterrogation in real time, the intelligent management of the links, and so on.The main contents of this paper are summarized as follows:1. The theory studies on FBG sensor1). The coupled-mode theory of optical fiber Bragg grating is analyzed, and thespectrum characteristics of FBG are simulated using MATLAB.2). The sensing characteristics of FBG sensors are analyzed in theory. Thetemperature and strain sensing properties of FBG sensor are analyzed theoretically.The temperature sensitive coefficient is10.9pm oC and stress sensitive coefficientare obtained1.21nm m.2. Studies on real-time data format conversion for spectrum interrogation intheory.1). The basic principle and technology solutions of spectrum interrogation basedon real-time data format conversion is introduced, and analyzes the characteristics andadvantages of the scheme.2). The working principle of the key components which are used in the spectruminterrogation is analyzed theoretically. Analysis of the switching principle andcharacteristics of LiNbO3intensity modulator; the time delay unit and its advantages;the wavelength conversion theoretical model and working principle based on thecross-absorption modulation in an electro-absorption modulator (EAM) are analyzed.3. Studies on real-time data format conversion for spectrum interrogation in experiment.1). The working characteristics of the key components which are used in thespectrum interrogation are experimentally researched. The switching property ofLiNbO3intensity modulator, which is driven by electrical signals with differentfrequency and pulse width, is studied in experiment. The wavelength conversioncharacteristics of electric-absorption modulator has carried on the experiment and itsworking bandwidth is30nm. The temperature characteristics of the three FBGsensors are tested in experiment, and the temperature sensitivity is10pm oC with adifference of0.9pm oC comparing with the theoretical value.2). The experimental studies on the spectrum interrogation for temperaturevariation of single FBG sensor. The wavelength shift amount are obtained atdifferent temperature variation. Linear fit degree using least squares linear fitting is0.9965.3). The experiment studies on the spectrum interrogation for three cascaded FBGsensors. By using the spectrum interrogation, the variation of corresponding pulseintensity is detected, when the temperature of one FBG sensor is changed.