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 an 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 3dB, 90 DEG 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.