Patent ID: 7330666

Claim:
A method of controlling modulator phase alignment for a transmitter of an optical communication system, said method comprising: generating a modulated optical signal with two cascaded modulators included in the transmitter; filtering the modulated optical signal generated by the two cascaded modulators in the transmitter to extract a narrowband of wavelengths from the modulated optical signal at and around an optical carrier frequency of the modulated optical signal, said filtering step extracting a band of wavelengths having a bandwidth equal to or less than approximately 75% of a data rate of the transmitter; monitoring an output of said filtering step to determine power spectral density at and around an optical carrier frequency of the modulated optical signal, wherein the monitoring step only monitors at and around the optical carrier frequency; adjusting phase of one of the cascaded modulators of the transmitter only as a function of the monitored power spectral density tracked over time at and around the carrier frequency of the modulated optical signal; and repeating said monitoring and adjusting steps until said modulator phase of said transmitter is in alignment.