Study On Wavelength-Shift Detection Of Optic Fiber Grating

Wavelength-shift detection is the key technology of fiber Bragg grating (FBG) sensor. It is a conventional way that demodulate the wavelength-shift of FBG with spectrometer. However, for a practical system, the measurement of a small Bragg wavelength shift with spectrometer is not a good solution because it is both costly and bulky. Several techniques have been developed for demodulation of these sensors such as: interferometric detection, use of Fabry-Perot filter, wavelength matched grating pairs, etc.This thesis focuses on the theoretical analysis and experimental research about the wavelength detection of fiber Bragg grating(FBG).Two approaches for demodulating the wavelength shift signal of FBG called unbalanced-interferometric demodulation and wavelength maximum scanning with tunable narrow-linewidth laser demodulation are studied.The way to form a demodulator employing scanning by tunable narrow-linewidth laser is described. The wavelength detection sensitivity of the system is demonstrated to be 0.00965nm/°C ,the temperature resolution was observed to be 0.2°C, while the wavelength resolution was superior to 2.08pm.A demodulator based on unbalanced Mach-Zehnder interferometer is put up. The experiment result demonstrates that the wavelength sensitivity is 0.00117nm/με ,the wavelength resolution is 0.00185pm ,the strain resolution is 3.23ne ,the detection range is ±68με. High frequency vibration sensing with fiber grating is achieved with unbalanced Mach-Zehnder interferometer. A vibration signal at 40 kHz frequency is detected successfully by our system.fiber Bragg grating; wavelength-shift detection;...