Multipoint measurement based on hetero-core structured optical fiber SPR sensor employing OTDR equipment

Abstract

In this paper, multipoint refractive index measurement is described using surface plasmon resonance (SPR) sensors based on hetero-core structured fiber optic technique. The sensor simply consists of two different core diameters fibers, which are connected by thermal fusion splicing, in order to deliberately leak the transmitted light wave into the cladding layer of the sensing fiber region. Chromium film and gold film were uniformly deposited around the cladding surface with a layer thickness of 5 nm and 45 nm, respectively, for SPR excitation. Multipoint measurement system consists of three SPR sensors, whose hetero-core insertion length are employed as 2-mm, located in a single transmission optical fiber and an optical time domain reflectometer (OTDR) to be used to measure refractive index. As a result, a hetero-core insertion length has trade off between sensitivity for refractive index and the number of sensors in tandem. The proposed multipoint refractive index measurement has been successfully demonstrated using three hetero-core SPR sensors and OTDR.