All-Fiber Refractometer Based on Core Mismatch Structure¹

F. Xu^{a, b}, D. Chen^{a, b,} *, B. Peng^{a, b}, J. Xu^{a, b}, and G. Wu^{a, b}

^a Institute of Information Optics, Zhejiang Normal University, Jinhua, 321004 China

^b Joint Research Laboratory of Optics of Zhejiang Normal University and Zhejiang University, Jinhua, 321004 China

*e-mail: daru@zjnu.cn

Received April 27, 2012; published online September 3, 2012

Abstract—We demonstrate a novel all-fiber refractometer which is a multimode-single mode-multimode
(MM-SM-MM) fiber structure formed by splicing a section of uncoated single mode fiber (SMF) with two short
sections of multimode fibers (MMFs). Owing to the core mismatch at the splicing points of the SMF with two
sections of MMFs, part of the guided light propagates in the cladding of the SMF, which makes the SMF sen-
sitive to the external refractive index (RI). RI sensing is achieved by measuring the wavelength shift of the inter-
ference pattern of the cladding mode and the core mode of the SMF. A RI sensor with an average sensitivity of
412 nm/RUI (refractive index unit) for a RI range from 1.333 to 1.400 is presented.

DOI: 10.1134/S1054660X12100271

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