Optical transmission system with a receiver using full optical clock recovery

摘要

In an optical transmission system a transmitter (2) generates a sequence of time domain division multiplexed pulses and transmits them via an optical transmission medium (4) to a receiver (6). In the receiver (6) the received optical multiplex signal is applied to an optical demultiplexer (30) and to a clock recovery element (48). The clock recovery element (48) generates optical clock pulses which are used to control optically controlled optical switches (32 . . . 38) which demultiplex the optical signal. The optical clock recovery circuit is based on a laser which is mode locked by the received optical signal. The mode locked laser comprises an optical amplifier (50) having its output coupled to its input by a feedback loop comprising a polarization controller (52), a saturable absorber (61), a coupling element (56) and a adjustable delay (51). The received optical signal is coupled into the feedback loop by means of the coupling element (56). The saturable absorber (61) comprises a 3 dB, 90° coupling element (54) being coupled to a secondary loop. Said secondary loop comprises an attenuator (60) and an amplifier (62). The amplifier (62) is placed asymmetrically in the secondary loop. Due to the non-linearity in the secondary loop, the optical pulses propagating in the secondary loop interfere destructively for low signal levels, and interfere constructively for high signal levels.