Bias-taper based hybrid modal interferometer for simultaneous triple-parameter measurement with joint wavelength and intensity demodulation

An in-fiber hybrid modal interferometer (HMI) is theoretically and experimentally demonstrated in a section of bias-tapered multimode fiber only fabricated by arc-discharge technique, which consists of multimode interferometer (MMI) and Mach-Zehnder interferometer (MZI). The MZI has the sensitivity as high as −31.08 nm/RIU, but the MMI presents the immunity of both wavelength and intensity to ambient refractive index (RI). In strain test, MMI has a 9.8-dB intensity deduction and MZI shows high wavelength sensitivity (−6.31 pm/ $\mu \varepsilon$ ). Thus, our HMI shows a strong multi-parameter discriminative proficiency and simultaneous measurement of RI, strain and temperature is achieved by the means of joint wavelength and intensity demodulation-based inversion-matrix method. Such a compact and low-cost sensor, without the crosstalk from the temperature and the light source, is very promising for the applications of biochemical sensing and structural health monitoring.