EDF laser displacement sensor based on bending characteristics of polarization-independent double-pass cascaded-chirped long-period fiber grating

Abstract

In this study, we propose an Erbium-doped fiber (EDF) laser displacement sensor using bending characteristics of a cascadedchirped long-period fiber grating (C-CLPG), in which the C-CLPG assisted by a Faraday rotator mirror (FRM), namely double-pass C-CLPG, shows a channeled spectrum and plays both the roles of wavelength tunable filter and sensor element. In the sensing scheme, the spectral shift of the channeled spectrum due to the displacementinduced bending deformation is utilized. Due to the FRM reflection, the double-pass C-CLPG has characteristics suitable for sensing: the polarization-independent channeled spectrum and the compensation effect for polarization variation in the sensor section. In the experiment, it is successfully demonstrated that the EDF laser in a sigma-type cavity configuration (EDFσL) using the double-pass C-CLPG enables precise displacement measurement based on the oscillation wavelength shift corresponding to the spectral shift of the double-pass C-CLPG. Further, the advantage of this EDFσL is confirmed by comparison with the conventional EDF ring laser using the single-pass C-CLPG.

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Amplified-spontaneous-emission feedback circuit with wide operating bandwidth and dynamic range

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