A Novel Photonic Clock and Carrier Recovery Device

As data communication rates climb toward ten Gbls, clock recovery and synchronization become more dificult, if not impossible, using conventional electronic circuits. We present in this article experimental results of a high speed clock and carrier recovery using a novel device called the photonic oscillator that we recently developed in our laboratory. T h i s device is capable of recovering clock signals up to 70 GHz. To recover the clock, the incoming data is injected into the photonic oscillator either through the optieal injection port or the electrical injection port. The free running photonic oscillator is tuned to oscilhte at a nominal frequency equal to t h ~ clock frequency of the incoming data. With the injection of the data, the photonic oscillator wiU be quickly locked to the to the clock frequency of the data stream while rejecting other frequency components associated with the data. Consequently, the outpul of the lacked photonic oscillator is a continuous periodical wave synchronized with the incoming data or simply the recovered clock. We have demonstrated a clock to spur ralio of more than 60 dB of the recovered clock using this technique. Similar to the clack recovery, the photonic oscillator can be used to recover a high frequency carrier degraded by noise and an improvement of about 50 dB in signal-to-noise-ratio was demonstrated. The photonic oscillator has both elemical and optical inputs and outputs and can be directly interfaced with a photonic system without signal conversion. In addition to clock and carrier recovery, the photonic oscillator can also be used for 1) stable high frequency clock signal generation, 2) frequency mukipltcation, 3)square wave and comb frequency generation, and 4) photonic phase locked loop.