OPTICAL TRANSMITTER

PROBLEM TO BE SOLVED: To provide an optical transmitter wide in dynamic range and capable of obtaining stable distortion and noise characteristic even when conditions of an optical transmission line are changed by controlling the level of an auxiliary signal in response to a detected input signal level, adding the auxiliary signal from an auxiliary signal level variable means to the input signal, and converting an electric output of an auxiliary signal addition means into an optical signal and outputting it. SOLUTION: Electric signals given to input terminals 4-1,..., 4-N are synthesized by a multiplexer 5. A signal from an auxiliary signal oscillator 6 is added to the electric signals from the input terminals 4-1,..., 4-N by an adder 7, and the sum signal is given to an electrooptic converter 8, where intensity modulation is connected. The optical signal is sent up to a receiver side through an optical transmission line 3, a photoelectric converter 11 converts the optical signal into an electric signal and a demultiplexer 12 distributes the electric signals to output terminals 13-1,...,13-n. An input signal level detector 9 detects a reception level from the input terminals 4-1,..., 4-N to change a level of the signal given to the adder 7.