ALL-OPTICAL CLOCK EXTRACTION USING 2-CONTACT DEVICES

A comprehensive summary of the operation of two-contact semiconductor self-pulsating laser diode (SP-LD) in both return-to-zero (RZ) and non -return-to-zero (NRZ) optical transmission systems is presented. Resul ts demonstrate that this type of device has great potential as the bas is for all-optical clock recovery circuits at multi-Gbits rates for sw itching applications. Results describe the basic device behaviour show ing how zinc doping the shorter (absorber) region of the device enable s repeatable and controlled GHz pulsations, within the range similar t o 0.6 to > 5.5 GHz and tunability (via the DC gain current) over many GHz, to be achieved. Experimental results show that the SP-LD can be l ocked with mu W of incident power to produce a locked oscillator with a linewidth of < 10 Hz at 5 GHz and with 20 dB power gain across the d evice. New results, addressing the pattern dependence, demonstrate tha t long breaks (up to similar to 30 'zeros') in the clock can be accomm odated without significant degradation of the locked clock purity; the length of break being dependent on the initial state of locking. Othe r new results show that the lock-up time for such circuits is of the o rder of 100 clock cycles. System performance is investigated using the se devices within a 20 Gbit/s (4 x 5 Gbit/s) optical-time-division-mul tiplexed demonstrator; the results showing no significant degradation of the bit-error-ratio performance. Other system results at 3.2 Gbit/s show that this technique can be applied to NRZ systems when also util ising a nonlinear effect within a similar device biased below threshol d, and identifying the differences from RZ operation. These results sh ow that such an approach could provide major benefits in developing th e next generation of telecommunications networks.