Fiber birefringence measurement by an external applied strain method and a polarimetric fiber laser sensor

In this work, a high-sensitivity and low-cost sensing scheme for measuring intrinsic and induced fiber birefringence change is reported based on a polarimetric fiber laser sensor interrogated by the beat frequency technique. The fiber birefringence measurement is achieved by an external applied strain method. A detailed theoretical analysis of the principle for fiber birefringence measurement is carried out. Two alternative equations are given for determining the change of fiber birefringence, which make it very convenient for users to choose different order beat signals. To verify the performance of the sensing system, the external applied strain-induced fiber birefringence change is measured experimentally. The experiment result shows that the fiber birefringence experiences a linear increase with the increase of applied strain. A strain response coefficient of 4.646×10^-11/μϵ is obtained. Furthermore, the repeatability and stability performances of the polarimetric fiber laser sensor are also investigated.