Phase Modulation in Amplified Circulating Loop

sons. Firstly, it demonstrates that injection locking is not a necessary condition for effective timing extraction. It also demonstrates that timing extraction can be accompanied by a change in the wavelength of the synchronized clock signal. Such a wavelength change for an optical clock could find applications in hybrid optical switching systems based on time and wavelength switching. These aspects of timing extraction will be considered in a future publica-tion. CONCLUSION We have demonstrated that it is possible to extract a timing signal from a random data signal at either the bit rate frequency or at half the bit-rate frequency, using the same twin section self-pulsating laser diode. It is possible to switch between these two timing extraction states by altering only the dc biases applied to the self-pulsating laser diode. We have also proposed that injection locking of the self-pulsating laser diode is not a necessary condi-tion for timing extraction. ACKNOWLEDGMENT The authors would like to thank M. J. Robertson of British Telecom Laboratories for providing the lasers used in this work and D. McCaughan of Northern Tele-com for the use of the line codec