Patent ID: 7580629

Claim:
An optical repeater for receiving an optical signal from an upstream node and for transmitting a regenerated copy of the received optical signal to a downstream node, the repeater comprising: an optical to electrical converter for generating an electrical domain signal in accordance with the received optical signal; a clock recovery device for recovering a clocking signal from the electrical domain signal; a framer for reframing the electrical domain signal in accordance with input and output domain clocking signals; an electrical to optical converter for converting the reframed electrical domain signal into an optical signal, and for transmitting the optical converted signal for a downstream node; a local clock for generating a local clocking signal; a beat detector having a multiplier for multiplying the recovered clock signal with the local clocking signal, a trigger for receiving the multiplied clock signals from the multiplier and for generating an output having first value when a component of the multiplied clock signals exceeds a threshold, and a second output value distinct from the first value when the component of the multiplied clock signal does not exceed a threshold, and a window detector for receiving the output of the trigger and for generating a signal indicative of drift in the recovered clock signal when the frequency in change between the first value and second value of the trigger is outside of a predefined window; and a switch for providing the framer with one of the recovered clocking signal and the local clocking signal as the input domain clocking signal in accordance with the signal indicative of drift.