BROAD BAND FM MODULATOR

PROBLEM TO BE SOLVED: To suppress noise caused by frequency fluctuation of an FM modulation semiconductor laser and a local oscillation layer in the broad band FM modulator that applies frequency modulation to video signals of a multi-channel subject to frequency division multiplex. SOLUTION: A modulator uses a photocoupler 13 to combine an output of an FM modulation semiconductor laser 11 that applies FM modulation to a signal with a frequency shift larger than a required frequency shift and an output of a local oscillation laser 12 that converts the output of the laser 11 to a frequency higher than a required intermediate frequency. Then an output of the photocoupler 13 is photoelectric-converted by a light receiving element, the result is amplified by an amplifier circuit 15, the amplified signal is frequency-divided by a frequency divider circuit 16 to obtain a required frequency shift, then the frequency fluctuation is frequency-divided simultaneously and then noise is suppressed.