OPTICAL FIBER DEVICE

PURPOSE:To obtain a genuine modulation signal by calculating a ratio of a modulation optical signal modulated by a modulation signal to a reference signal whose frequency is the same as that of the modulation signal generated from a reference signal generator and calculating a ratio of the calculated ratio to the modulation optical signal so as to eliminate noise. CONSTITUTION:A signal from an optical fiber 3 is converted into an electric signal by a photo diode(PD) 11 and amplified by an amplifier 15. A reference signal generator 16 generates a reference signal whose frequency is the same as a frequency of a voltage to be measured. The generator 16 provides the frequency when it is known and the measured frequency without noise in advance when the frequency of the voltage is unknown. The reference signal is led to a phase shifter 17, in which the phase is made the same as that of a measured signal and the amplitude is made equal. The signals are led to a 1st divider 18a, in which a ratio of both the signals is calculated to obtain a noise (AC component by vibration) signal not including the signal to be measured. An section from the divider 18a and the signal to be measured are led to a 2nd divider 18b, in which a ratio of the both is calculated. Thus, AC optical intensity fluctuation, that is, noise of optical fiber vibration is eliminated from the signal to be measured.