Applications of high birefringent fiber in sensor and demodulation

Abstract

First, the actuality of fiber sensors in homeland and abroad are outlined in this paper. And the characteristics and transfer matrix of high birefringent fiber (HBF) are introduced. After deduction of transfer matrix of the HBF Sagnac loop mirror, a conclusion that the frequency of optical transmissibility will not change with the wavelength change basically is obtained, and it is proportional to the length of the HBF in the loop mirror.After the theoretical conclusion is verified by spectrometer, the HBF Sagnac loop mirror application to sensor and demodulation are discussed. Because the frequency of optical transmissibility is not change following the wavelength change, and it is proportional to the length of the HBF in the loop mirror, we adopt the counting method for wavelength demodulation. Using a long HBF Sagnac loop mirror, through the recording number of changed periods of the optical transmissibility, the wavelength variation can be judged. This method gets high resolution, it even can be better than 0.01nm which is the higher precision of spectrometers.The HBF is also more sensitive to temperature. If changing the temperature of the HBF in the loop mirror and keeping the wavelength of input light invariable, the intensity of output light also changes in period. For a short HBF Sagnac loop mirror, the period gets longer, and the range of temperature change is included in its half period. Using the short HBF Sagnac loop mirror, we have achieved the temperature measurement. The material and devices including HBF, Pin, circuit of amplification and Mega8 A/D converter are only used in the two methods as mentioned above. The structure is simple and the cost is low.