Simultaneous Measurement of RI and Temperature Based on a Composite Interferometer

A novel double-parameter sensor based on a composite interference structure has been designed and implemented in this letter. It can be regarded as a cascade of the conventional single-mode fiber (SMF)-multimode fiber-photonic crystal fiber-SMF structure, which forms a reflected Fabry-Perot interferometer and a transmitted Mach-Zehnder interferometer at the same time. In addition, a simultaneous measurement of temperature and refractive index has been achieved by monitoring the correlative moves of reflected spectrum and transmitted spectrum. The fact that these two spectra do not interfere with each other makes it easier to obtain a demodulation method that does not involve complex fast Fourier transform and matrix computation. The sensitivities of temperature and refractive index can reach up to 27.5 pm/°C and 108 nm/RIU, respectively.