Simultaneous measurement of RI and temperature based on compact U-shaped interferometer

A compact U-shaped interferometer with high refractive index (RI) sensitivity based on bent single-mode fiber is proposed and demonstrated experimentally. The sensor is fabricated by roasting a balloon-shaped single-mode optical fiber to form a U-shaped modal interferometer. Since the spectral dips show different sensitivities to both the surrounding RI and temperature, simultaneous measurement of RI and temperature can be achieved by demodulating the shifts of the different resonance dips without cascading additional components. The sensitivity of RI reaches up to −1705.66 nm/RIU in the range of 1.3330-1.3581, which is about 10 times as the reported arts. The proposed compact U-shaped interferometer is a potentially effective sensor for chemical and biological applications where an accurate RI measurement of a temperature-changing liquid is required.