Abstract
In this work, a linear birefringence measurement method is proposed for an optical fiber current sensor (OFCS). First, the optical configuration of the measurement system is presented. Then, the elimination method of the effect of the azimuth angles between the sensing fiber and the two polarizers is demonstrated. Moreover, the relationship of the linear birefringence, the Faraday rotation angle and the final output is determined. On these bases, the multi-valued problem on the linear birefringence is simulated and its solution is illustrated when the linear birefringence is unknown. Finally, the experiments are conducted to prove the feasibility of the proposed method. When the numbers of turns of the sensing fiber in the OFCS are about 15, 19, 23, 27, 31, 35, and 39, the measured linear birefringence obtained by the proposed method are about 1.3577, 1.8425, 2.0983, 2.5914, 2.7891, 3.2003 and 3.5198 rad. Two typical methods provide the references for the proposed method. The proposed method is proven to be suitable for the linear birefringence measurement in the full range without the limitation that the linear birefringence must be smaller than π/2.
Highlights
An optical fiber current sensor (OFCS) has a number of advantages over the conventional current sensor, such as high precision, high sensitivity, wide dynamic range and immunity to electro-magnetic interference
The elimination method of the effect of the azimuth angles between the sensing fiber and the two polarizers is demonstrated based on the orthogonal modulation and a Faraday rotator
The relationship of the linear birefringence, the Faraday rotation angle and the final output is determined based on the Jones matrix calculus and the heterodyne method
Summary
An optical fiber current sensor (OFCS) has a number of advantages over the conventional current sensor, such as high precision, high sensitivity, wide dynamic range and immunity to electro-magnetic interference. The sensing fibers wound along the cylindrical [8] and toroidal [13] spiral paths have been proposed based on the geometrical rotation effect In these sensing fibers, the produced circular birefringence only depends on the geometrical parameters of the path rather than the stress, which provides the effective method to eliminate the linear birefringence in the low-birefringent sensing fiber. The produced circular birefringence only depends on the geometrical parameters of the path rather than the stress, which provides the effective method to eliminate the linear birefringence in the low-birefringent sensing fiber In this method, the accurate measurement of the linear birefringence can help to optimize the design of the geometrical path. The first one of the typical measurement methods of the linear birefringence has been proposed by Ren, who applied the isotropy of circularly polarized light to measure the linear birefringence of the low-birefringent sensing fiber [14]. When the linear birefringence is not greater than π/2, the typical methods proposed by Ren [14] and Tentori [15] provide the references for our proposed method
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