A coherent fiber-optic link with optical-domain down-conversion and digital demodulation

Frequency down-conversion is an essential element of radar signal processing. Classical electronic down-conversion using heterodyne mixing, however, introduces unavoidable non-linearities resulting in inter-modulation distortion and conversion loss. In this paper we describe a hybrid optical/digital downconversion technique that is free of distortion and conversion loss. Experimental results are presented showing proof-of-concept operation limited to the dynamic range of the A/Ds that were available for the experiment. The ultimate goal is to attain an SFDR of 150 dB-Hz2/3 or higher across an instantaneous bandwidth of 1 GHz for a microwave carrier up to 100 GHz.