Large SNR Enhanced Fast Non-repetitive Event Detection by an Improved Spectral Cloning Receiver

An improved spectral cloning receiver assisted by coherent Optical Frequency Combs (OFCs) to detect a fast, non-repetitive event hidden in noise is presented. In the proposed approach, the modulated signal OFC and local OFC are both divided into $M$ paths by using an optical coupler. M-1 Acousto-Optic Frequency Shifters (AOFSs) are used to upshift the local OFC and then these local OFCs combine with the signal OFCs, resulted in $M$ times increase in the number of sub-channels over before. Then the spectrum of the received signal is extracted in these channels and superimposed positively by a digital signal processor, which can realize a large SNR enhancement. For a single-instance signal, the detection gains of a 9 lines OFC based spectral cloning receiver (9.54 dB detection gain) can be increased to 12.55 dB and 15.56 dB by using one or three AOFSs.