Study on the temperature characteristic of tapered twin-core fiber working at dispersion turning point

We present a study on the spectral characteristics and ultrahigh sensitivity near the dispersion turning point (DTP) of tapered twin-core fiber (TCF). The tapered TCF with the DTP can be fabricated by the one-step taper method by the flame taper machine. Numerical simulations reveal that DTP exists when the group effective refractive index difference between the HE11 mode and the HE21 mode equals zero, where ultrahigh sensitivities can be achieved. The position of the DTP is dependent on the diameter of the taper waist and the refractive index of the external environment. We experimentally demonstrate the temperature characteristic of tapered TCF with DTP in the air, and its maximum sensitivity is − 994 pm/ºC. Finally, by coating polydimethylsiloxane (PDMS) material with the high refractive index and the high thermal-optical coefficient on the tapered TCF, not only the DTP can be achieved in large diameter, but also ultra-high temperature sensitivity can be obtained. The measured temperature sensitivity of the tapered TCF coated with PDMS is as high as 36.71 nm/ºC.