PURPOSE: To obtain a circuit for stably operating even if a slight deviation exists between a central frequency of an FSK signal and a peak frequency of transmission characteristics of an MZI and so controlling that both the frequencies always coincide by controlling the amplitude of a digital signal in response to the low band frequency component of a differential detection signal of an MZI output light.
CONSTITUTION: An optical transmitter for generating an FSK signal light by directly modulating a current to be applied to a laser diode 71 according to the digital signal has a Mach-Zehnder interferometer (MZI) 73 inputting the FSK signal for period-varying its permeability, and differential detecting means 74a, 74b for differentially detecting output lights obtained from the two output terminals (a), (b) of the MZI 72. Further, the transmitter has a low pass filter 11 inputting the differential detection signals for passing only the low band frequency components, and frequency deviation control means 75 for controlling the amplitude of the digital signal in response to the output signal of the filter 11 and controlling a current to be applied to the diode 71.
TOBA HIROSHI
ODA KAZUHIRO
NAKANISHI KENJI
