Patent ID: 7398023

Claim:
An apparatus for transmitting an optical signal, said apparatus comprising: a modulator for modulating data on an optical signal with a modulation format having a periodic intensity modulation and a differential phase shift keying (DPSK) data modulation, said modulator comprising a Mach-Zehnder RZ modulator for imparting said periodic intensity modulation in response to a RZ bias signal, and a Mach-Zehnder NRZ modulator for imparting said DPSK data modulation in response to a NRZ bias signal; a phase shifter for selectively aligning said periodic intensity modulation and said data modulation in response to a phase bias signal; a low speed photo-detector, said low speed photo-detector having a bandwidth of at least one order of magnitude less than a data rate of said data and being configured to detect light scattered at an output of said NRZ modulator and provide an output representative of power in said light scattered at said output of said NRZ modulator; and a controller for providing at least one of said RZ bias signal, said NRZ bias signal, or said phase bias signal, in response to said output of said low speed photodetector.