| 摘要 |
PURPOSE:To effectively compensate variation such as the change in a phase due to temp. characteristic, in a signal detection circuit, by extracting a reference signal for synchronous detection from a light receiving signal. CONSTITUTION:The laser beam from a beam emitting element 10 is split into two beams by a beam splitter 14 to be coupled with both ends of an optical fiber 18. The laser beams inputted to the fiber 18 generate phase difference in a sensor coil 20 and subjected to phase modulation in a phase modulator 24 driven at angular frequency omegam. The laser beams propagated through the fiber 18 right-handedly and left-handedly are gathered by the splitter 14 to be incident to a beam receiving element 26. The output of the element 26 is amplified by a beam signal amplifier 32 to be inputted to a synchronous detector 34 through BPF 36 permitting the passage of the component of the angular frequency omegam. The output of the element 26 further passes through BPF 37 permitting the passage of a component of angular frequency 2omegam to be further divided in frequency by a 1/2 frequency divider 42 and inputted to the detector 34 as a reference signal through a phase correction circuit 40. The detector 34 synchronously detects a receiving signal on the basis of the reference signal to output the same.
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