Recognition of Bragg Wavelength Disturbed by Time Delay of Fiber Length in Prepositive Tunable Filter

摘要

The wavelength shift in fiber Bragg grating does not depend directly on the total light levels, losses in the connecting fibers and couplers, or source power. However, if the tunable Fabry-Perot filter is place on the end of incident fiber, the detected time delay of modulation light is occurred due to the unmatch between the scanning time and light transmission time in the transmission fiber. Consequently, the detected peak wavelength shifts with the length of transmission fiber. Thus, the peak wavelength shift effect of Bragg reflective light transmitted in fiber with different fiber length can be obvious in the demodulator with a prepositive tunable Fabry-Perot filter. The experiment indicates the shift rates of 0.109 - 0.126 nm/km increase approximately linearly with the original peak wavelength of 1532.917 - 1560.300 nm at the fiber length of 0 - 6 km. To certify the consistency of measurement data, the criterion correction is introduced. By using the differential method of two fiber Bragg gratings with an optical path, the differential worth is compensated from the disturbance modulated by the time delay of fiber length.