A Compact Sagnac Loop Based on a Microfiber Coupler for Twist Sensing

We present a compact highly sensitive microfiber coupler-based twist sensor formed by fusing and tapering two optical fibers and then connecting two of the pigtails to form a Sagnac loop. The device is miniature, low cost, and easily fabricated. The sensor has high twist sensitivities of $\sim 0.9$ nm/° when measuring wavelength shift and $\sim 0.16$ dB/° when measuring transmission power, both of which confirm that the sensor has good potential for application in the structural health monitoring and other areas.