Method and apparatus for generating a modulated optical return to zero signal

摘要

The present invention generally relates to the field of signal generation and particularly to a method and an apparatus for generating a modulated RTZ signal from a RTZ signal by driving an modulator with a non-RTZ signal. For the transmission of optical high bit-rate signals over a fibre mainly intensity modulated optical signals are used. To intensity modulate an optical signal with data formed by a bit sequence the optical power of an optical carrier is switched on and off according to the bit sequence. There are non-RTZ signals having a constant high power level for consecutive bits of the bit sequence having a high level, and RTZ signals for which the power level is set back to zero within each bit interval. To correctly modulate the RTZ signal with the electrical non-RTZ signal a fixed phase relation between the two signals is necessary. The invention under consideration provides a method and an apparatus for automatically aligning the phases of the RTZ signal and the non-RTZ signal by phase modulation of one of the signals with an auxiliary signal and analysing the modulated RTZ signal generated from the signals. The analysis and the phase alignment are based on deviations in the mean signal power of the modulated RTZ signal.