Temperature insensitive refractive index sensor based on single-mode micro-fiber Sagnac loop interferometer

A single-mode micro-fiber Sagnac loop interferometer (SMSLI) based on single-mode micro-fiber with a diameter of wavelength scale is demonstrated theoretically and experimentally. The influence of structure parameters in SMSLI on its transmission spectra has been investigated by both experimental and theoretical analysis. The sensor responses to the ambient refractive index (RI) and temperature are also investigated experimentally. Experimental results show that the proposed sensor exhibits quite high sensitivity to the ambient RI, which is found to be ∼12 500 nm/RIU. In addition, the sensitivity of SMSLI to ambient temperature is also demonstrated to be only ∼3 pm/ °C by experiments.