Patent ID: 8917998

Claim:
A method implemented in a transmission apparatus used in an optical fiber communications system for a polarization switched differential quaternary phase-shift keying (DQPSK) signal, the method comprising: splitting data into two or more data streams; inputting said two or more data streams to 1-bit DQPSK precoders to perform 1-bit DQPSK precoding; multiplexing inphase outputs of the 1-bit DQPSK precoders to generate a first output; and multiplexing quadrature outputs of the 1-bit DQPSK precoders to generate a second output, wherein an operation speed of the 1-bit DQPSK precoders is set to half of a total data rate to perform differential encoding of the two of more data streams, wherein the first and second outputs 1 and 2 have the following signals: output 1 : x 1 y 1 x 3 y 3 x 5 y 5 . . . output 2 :x 0 y 0 x 2 y 2 x 4 y 4 . . . where xn and yn represent nth data from odd and even channels, and each output has at least part of two independent data streams x and y and when performing 2-bit differential detection (x 3 -x 1 , y 3 -yl, x 5 -x 3 , y 5 -y 3 , . . . ) on a receiver side, precoded data in each data can be correctly decoded.