Patent ID: 7340182

Claim:
A multiplexer comprising: a time-division multiplexing unit that multiplexes a plurality of digital signals into two signals each having a first transmission rate; an encoder that generates a ternary electric signal from the two signals; a light source; and an optical modulator that modulates light, emitted from the light source, with the ternary electric signal, and transmits the light modulated as an optical signal having a second transmission rate twice the first transmission rate, wherein the encoder includes: a first flip-flop circuit that holds one of the two signals at a frequency of the first transmission rate; a second flip-flop circuit that holds the other of the two signals at the frequency; a delay unit that delays a signal output from the second flip-flop circuit by a time of the reciprocal of the second transmission rate, with respect to a signal output from the first flip-flop circuit; and an adder that adds signals output from the first flip-flop circuit and delayed signals output form the delay unit, and transmits a resultant signal to the optical modulator.