title: Temperature-insensitive optical fiber refractometer based on multimode interference in two cascaded no-core square fibers.
abstract: A temperature-insensitive optical fiber refractometer, based on multimode interference in no-core square fibers, has been proposed and experimentally demonstrated. The refractometer is formed by a single-mode fiber sandwiched between two segments of no-core square fibers through cleaving and fusion splicing. The transmission spectra characteristic of refractive index (RI) and environmental temperature have been investigated. Experimental results show that a transmission dip exhibits a redshift as large as about 25 nm when the ambient RI increases from 1.3424 to 1.4334. Within the RI range of 1.4033 to 1.4334, the RI sensitivity reaches 474.8189  nm/RIU. A temperature sensitivity of 0.00639  nm/°C is experimentally acquired between 20°C and 85°C, showing a low temperature cross-sensitivity of about 1.35×10⁻⁵  RIU/°C. The proposed refractometer has several advantages, such as low cost, simple structure, and compact size. Therefore, it is also expected to be employed in chemical and multi-parameter sensing applications.
authors.forename: Jixuan
authors.initials: J
authors.lastname: Wu
authors.forename: Yinping
authors.initials: Y
authors.lastname: Miao
authors.forename: Binbin
authors.initials: B
authors.lastname: Song
authors.forename: Kailiang
authors.initials: K
authors.lastname: Zhang
authors.forename: Wei
authors.initials: W
authors.lastname: Lin
authors.forename: Hao
authors.initials: H
authors.lastname: Zhang
authors.forename: Bo
authors.initials: B
authors.lastname: Liu
authors.forename: Jianquan
authors.initials: J
authors.lastname: Yao