Patent ID: 7515834

Claim:
A method for upgrading a wavelength division multiplexed (WDM) optical communication system, comprising: replacing an installed transmitter operable to transmit payload data over a channel at a defined bit rate with an M-ary phase shift keying (mPSK) transmitter operable to transmit the payload data at a system designed bit rate and at least one other payload data at the system designed bit rate together in an mPSK signal having a combined bit rate at least double the system designed bit rate and a symbol rate approximately equal to the system designed bit rate; replacing an installed receiver operable to receive the payload data at the defined bit rate with an mPSK receiver operable to recover the payload data at the system designed bit rate and the at least one other payload at the system designed bit rate from the mPSK signal; and maintaining a multiplexer used in connection with the replaced transmitter, a demultiplexer used in connection with the replaced receiver, and a fiber and in-line optical amplifiers between the replaced transmitter and receiver.