An Integrated Fiber Michelson Interferometer Based on Twin-Core and Side-Hole Fibers for Multiparameter Sensing

An integrated fiber Michelson interferometer (MI) based on an asymmetrical twin-core fiber (TCF) cascaded with a side-hole fiber (SHF) for multiparameter sensing is proposed and demonstrated. The asymmetrical TCF consists of a centric core and an eccentric core with same refractive index. The centric core of the TCF is aligned with the core of the SHF and the eccentric core is aligned with one air hole of the SHF. Because the eccentric core of the TCF is off the axis of the fiber, a bend or twist will cause a variation of the optical path difference of the MI, which makes the MI structure be suitable for twist and vector curvature measurements. Experimental results show that the bending sensitivities of the sensor are −6.968 and 6.978 nm/m −1 at the bending directions of 0° and 180° in the curvature ranges of 0–10.708 m −1 , respectively, and the twist sensitivity of the sensor is 0.639 nm/(rad/m) in the twist ranges of 0–7.44 rad/m. The structure is also sensitive to strain and temperature, and the strain and temperature sensitivities of the interferometer are 1.36 pm/ ${{\mu \varepsilon }}$ and 10.37 pm/°C, respectively.