Patent ID: 8090269

Claim:
A data transmission system for transmitting an optical signal converted from data of transmitting, comprising: a transmitter; and a receiver, wherein the transmitter and the receiver are coupled to each other through a transmission path, wherein the transmitter comprises: a laser oscillator serving as a source of light with a wavelength of λ; a phase encoder for selecting usable signal points, from among signal points having an N-ary phase, where N is a natural number larger than three, set in one symbol, by excluding signal points having overlapping variance values of a phase noise included in a carrier generated by the laser oscillator corresponding to a predefined symbol error rate, and for sequentially converting consecutive data of at least one bit into corresponding signal points having one of one symbol and a set of symbols by confining use of signal points only to the usable signal points, in order to output the signal points thus converted as phase information; a differential pre-coder for obtaining a phase difference between the phase information output by the phase encoder and a signal point which has been output 1 symbol before, and outputting the phase difference as phase difference information; and a phase modulator for generating an N-ary carrier from light output from the laser oscillator and outputting an optical signal of a phase corresponding to the phase difference information for each symbol, and wherein the receiver comprises: a demodulator for detecting a phase difference from the received optical signal and outputting phase information including the phase difference; and a phase decoder for converting, into data of least one bit, the phase information output by the demodulator which includes at least one symbol.