Research On Temperature Compensation Of Orthogonal Dual Frequency Fiber Laser Sensors

The drift of beat frequency generated by orthogonally polarized laser can be used to realize the measurement of external parameters, which is the principle of orthogonal dual fiber laser sensor. These sensors have high signal to noise ratio, narrow linewidth, mature electrolytic adjustment programs and low cost demodulation, etc., and thus subject to more and more attention.The physical quantities measured by orthogonally polarized dual frequency fiber laser include stress, displacement, pressure, electric field, magnetic field and the acceleration, which all characterized through the beat frequency signal drift. Since the beat frequency is sensitive to temperature and strain at the same time, single beat frequency change will not effectively distinguish temperature and stress variation. Therefore, to effectively eliminate its temperature cross-sensitivity effects is significant.In this thesis, a temperature compensation technology based on cleave-rotatesplice is proposed according to the deep analysis of the temperature response mechanism of the orthogonal dual frequency optical fiber laser. The specific research work is as follows:Temperature compensation of dual-frequency fiber lasers: Unlike conventional temperature compensation methods, we propose a method that cleaving the laser cavity into two segments with comparable lengths, one of them aligning with a rotated angle of 90 degrees and then fusion splicing the two halves, based on birefringence and optical sensing principle of dual frequency fiber laser. After the operation of the new fiber laser, the fast axis of the left laser cavity aligns with the slow axis of the right laser cavity while the slow axis of the left laser cavity aligns with the fast axis of the right laser cavity, which leads to the offset of the temperature effect for both sides. It makes dual fiber laser temperature response coefficient reducing from-1.99 MHz/0C to-0.3 MHz/0C with its maximum transverse strain sensitivity unchanged and better noise performance acquired.In addition, a method to prepare single-frequency single polarization fiber laser through heat treatment is proposed, according to the feature that both polarized directions of orthogonally polarized laser have laser output. With experimental heat treatment being controlled, one polarized direction loss is greater than the doped fiber gain, while in the other direction of polarization losses introduced as small as possible so as to output laser. Since the laser output is suppressed in the polarized direction which introduced loss greater than the gain, the fiber laser will be in the singlefrequency fiber laser single polarization state eventually. Experiments show that due to this technology, the fiber laser can produce single-frequency single polarization laser with stable output.