| 摘要 |
PURPOSE:To obtain an exact measured value of an absolute length by deciding the polarity of an instruction of a phase measuring system for sweeping successively and displaying a modulation section which has set the upper limit and the lower limit, counting the number of times which has exceeded 2pi, and deriving an absolute phase quantity. CONSTITUTION:A modulating part A fetches a reference signal and a signal for passing through a transmission line to be measured, from a front light and a back light of a semiconductor laser. Subsequently, in a demodulating part B, a signal which has passed through an optical fiber 3 is converted to an electric signal by an optical-electric transducer 4, and thereafter, mixed with an output frequency of the second wave oscillator 10, a hybrid 11 of 3dB branch, and a directional coupler 12 by a frequency mixer 13. This intermediate frequency fIF passes through BPF5 and becomes a signal to be measured VS. Also, the reference signal is dropped as well to the intermediate frequency fIF by an optical-electric transducer 4' and a frequency mixer 13', and becomes a reference signal VR through a BPF5'. A measuring part C is constituted of a phase measuring instrument 7, and displays a phase quantity not exceeding 2pi. Also, a display of the phase measuring instrument 7 of every sweep frequency is read to a control part D.
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