Enhancement of refractive index sensitivity for rectangular-microfiber Sagnac loop sensors

We demonstrate a method for obtainment of high refractive index sensitivity by inserting a highly-birefringent bow-tie fiber into a rectangular-microfiber Sagnac loop. The sensitivity is enhanced significantly when a certain condition is satisfied. The maximum absolute sensitivity reaches 34772 nm/refractive-index unit (RI-unit), which is around five times of the value, i.e. 7069nm/RI-unit, without bow-tie fiber.