In this letter, we proposed a self-temperature-compensation approach for fiber specklegram sensor (FSS) based on polarization specklegram analysis. The temperature compensation is achieved by comparing the variation difference of the two specklegrams with vertical linear polarization state. We designed a fiber specklegram magnetic field sensor employing this method and the magneto-birefringence effect of magnetic fluid. The measurement of magnetic field with high stability and good repeatability has been successfully achieved, which demonstrated the effectiveness of the proposed method. Due to the merits of low cost, ease of implement and system simplicity, the proposed method can promote the practical use of the FSS in long term monitoring.
KEYWORDS: Single mode fibers, Ceramics, Control systems, Raster graphics, Free space optics, Optical fibers, Photodetectors, Sensors, Free space optical communications, Detection and tracking algorithms
The adaptive coupling of making laser beam into single-mode fiber(SMF) plays an important role in free space optical communication. It’s the key point to the coupling of spatial light and single-mode fiber that finding the best position in the transverse plane of fiber precisely. An adaptive coupling system is proposed, which mainly comprises two-dimensional piezoelectric nanopositioning stage, driver, controller, photoelectric detector, coupling lens which is a closed loop control system. The adaptive coupling system uses optimized raster scanning algorithm to confirm the best position accurately. Theories of optimized raster scanning algorithm are expounded. Analysis results of experiment show that the adaptive coupling system proposed can search the best position automatically based on the power of the light which is coupled into the single-mode fiber. At the same time, it can correct the numerical deviation which is caused by atmospheric turbulence, and maintain high coupling efficiency which can improve the performance of the receiver.
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