FM MODULATOR

摘要

PROBLEM TO BE SOLVED: To provide an FM modulator to generate no deterioration of waveform in FM demodulation by removing an average value fluctuation component of a wide band FM modulation signal. SOLUTION: A modulation signal is divided into two branches so that a mutual phase relation becomes opposite phase and one of the branches is inputted in an FM laser 102 and the other is inputted in an IM suppression laser 110 after propagation delay amount and amplitude are adjusted by a branching part 107. Intensity of outputted light of the FM laser 102 is modulated and an optical frequency modulation signal centering around wavelength λ1 is simultaneously outputted by the FM laser 102. The light with wavelength λ0 which is different from the oscillation wavelength λ1 of the FM laser 102 by Δλ is outputted by a station light emitting source 104. The optical intensity modulation signal is outputted by the IM suppression laser 110. The three kinds of light are multiplexed and inputted in a light detecting part 106. Beat signals of two kinds of light are outputted, the optical intensity modulation signal from the IM suppression laser 110 is directly detected and converted into an electric signal again in frequency corresponding to a difference Δλ of the wavelength between the outputted optical signal from the FM laser 102 and the outputted light from the station light emitting source 104 by performing heterodyne conversion to the inputted light by the light detecting part 106.