To solve the problem wherein Fiber Bragg Grating (FBG) sensors may incorrectly detect wavelength shifts as an external force due to intruders etc. since changes in diffractive index due to variations in ambient temperature and disturbances such as winds easily occur in FBG sensors, which is a property of optical fibers, to prevent them from having a prescribed diffractive index at all times and cause wavelength shifts to occur in reflected light by FBG sensors not due to an external force.
Light is made incident onto an optical fiber having a plurality of Bragg grating sensors having different Bragg grating intervals to receive a spectrum of every wavelength of reflected light reflected by each Bragg grating sensor. Primary detected spectra of which an absolute value of the difference between the wavelength of each received spectrum and a reference wavelength of resonance reflection are detected. After the primary detected spectra are detected, the number of times by which the primary detected spectra are continuously detected from the Bragg grating sensor corresponding to the primary detected spectra, is computed to detect secondary detected spectra of which this number of times exceeds a specific number of times.
COPYRIGHT: (C)2007,JPO&INPIT
NAGASHIMA MASAHIRO
MOGI ATSUSHI
Tadahiko Inaba
Kanako Murakami
Nakatsuru Kazutaka
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