Patent ID: 7113708

Claim:
A data communication link comprising a data transmitter station coupled by an optical communication channel to a data receiver station, wherein the data transmitter station includes a multi-power-level optical source connected to receive data words of n digital bits, wherein said data transmitter encodes different value words in the data word into different power levels of a signal having m optical power levels, where m is greater than two, wherein different sequences of bits comprised of more than one bit are encoded into different power levels of the signal, wherein said data transmitter transmits the multi-power-level output signal of the optical source along the optical communications channel to the data receiver station, said data receiver station including a data-decoding receiver arranged to receive and decode said multi-power level signal into n bit digital words, and wherein said receiver station further comprises a received-signal condition monitor coupled by a control channel to a control device located in the data transmitter station, said condition monitor being arranged to sense the level of a predetermined characteristic of each of the power levels of the multi-power-level output signal received by the data-decoding receiver and consequently to transmit control signals along the control channel to the control device to adjust the laser drive current for each of the power levels to provide adequate bit error rate for each of the power levels used to transmit the multi-Power-level output signal, said control device being adapted to control the power output of the optical source for each power level consistent with achieving a predetermined sensed level of said predetermined characteristic for each power level used to transmit the multi-power-level output signal.