| 摘要 |
PROBLEM TO BE SOLVED: To inexpensively detect an illegal intrusion by utilizing a characteristic of an optical fiber. SOLUTION: An external force detecting apparatus is provided with: a light source 1; an optical modulation means 2 for intensity-modulating a light emitted from the light source 1 with a modulated signal, and outputting an intensity-modulated light; an optical transmission path 4 installed at a predetermined location, transmitting the intensity-modulated light entering from the optical modulation means 2 as a measurement light, and having an end as a reflection end 4a for reflecting the measurement light and generating a reflection light; an optical sensor 5 installed in the middle of the optical transmission path 4, and switched between a light transmission state and a light absorption state by the existence of an action from an external force; a phase detector 7 for detecting a phase difference between an envelope of the reflection light and the modulated signal or an envelope of the measurement light; and a determination section 8 for determining the existence of the action from the external force based on a phase detection signal from the phase detector 7. COPYRIGHT: (C)2008,JPO&INPIT
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