Frequency comb-based analog coherent receiver for multi-wavelength optical links

Abstract

Coherent wavelength division multiplexing is provided using frequency comb sources for both the transmitter and the local oscillator (LO) in the receiver. The local oscillator is made phase coherent with the received multifrequency optical signal using two analog control loops. One of the control loops locks an optical frequency of the local oscillator to an optical frequency of the received frequency comb. The other control loop locks a microwave frequency of the local oscillator (i. e. LO the comb spacing) to the comb spacing of the received frequency comb. As a result, coherent detection is enabled in all channels with just two analog control loops. Control signals for the two loops can be derived from two of the received channels individually (asymmetric carrier recovery), or they can be derived from sum and difference signals from two of the received channels (symmetric carrier recovery).