Macrobending Characteristics of a Hetero-Core Splice Fiber Optic Sensor for Displacement and Liquid Detection

Kazuhiro WATANABE  Kaori TAJIMA  Yuzuru KUBOTA  

IEICE TRANSACTIONS on Electronics   Vol.E83-C   No.3   pp.309-314
Publication Date: 2000/03/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Optical Fiber Sensors)
Category: Physical and Mechanical Sensors
fiber optic sensor,  macrobending,  hetero-core,  damage monitoring,  liquid detection,  

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Macrobending characteristics of a newly developed hetero-core splicing sensor is investigated from the viewpoint of the practical use intended both for relatively large distortion monitoring and for liquid adhesion detection. The hetero-core sensor can be simply fabricated by fusion splicing of a hetero-core fiber portion as short as approximately 5 mm in length, which is inserted in a typical low-transmission-loss single mode fiber with a 9-µm core diameter for the wavelength of 1.3 µm as a fiber network line. Two types of the sensor are typically realized in terms of the core diameters of 3 and 5 µm for the inserted hetero-core portion which are referred to as 9-3-9 and 9-5-9 types, respectively , with showing their distinct bending loss characteristics. This paper deals with the explorative applications of the two types of hetero-core sensors in which a bending-to-linear displacement converter and a liquid adhesion sensor are successfully examined using a 9-5-9 structure with its low insertion loss and a cladding interactive 9-3-9 structure with its high sensitivity, respectively. The low-insertion loss 9-5-9 sensor has shown the capability of monitoring millimeters-order distortion in low transmission loss fiber networks. On the other hand, the 9-3-9 type has found to be a prospective sensor for liquid adhesion detection. Operational mechanisms for these two sensors are also discussed in terms both of optical leaks occurring at the hetero-core interfaces and of the build-up of cladding modes which might interrogate the outer cladding boundary conditions of the hetero-core sensor.