Abstract

The optical fiber curvature sensor is an important device that is widely used in the field of medical instruments. In this paper, we proposed a high sensitivity curvature sensor based on a long period fiber grating (LPFG), which is inscribed in the two-mode fiber (TMF) by ${{\rm{CO}}_2}$ laser pulses. Unlike the traditional LPFG in the single-mode fiber, TMF-LPFG couples the high-order mode ${{\rm{LP}}_{11}}$ in the core with the modes in the cladding. From the experiment results, the wavelength shifts to the short-wave direction as the sensor bends. This sensor offers a high curvature sensitivity of ${-}{23.67}\;{\rm{nm/}}{{\rm{m}}^{- 1}}$ in the range of ${{1.137 - 4}.{684}}\;{{\rm{m}}^{- 1}}$ and ${-}{18.95}\;{\rm{nm/}}{{\rm{m}}^{- 1}}$ in the range of ${{4.766 - 6}.{132}}\;{{\rm{m}}^{- 1}}$, respectively. Moreover, this sensor has the advantage of low transmission loss, which is less than ${-}{{4}}\;{\rm{dB}}$.

© 2021 Optical Society of America

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