Optical Domain Down-Conversion of Microwave Signals for High Dynamic Range Microwave Fiber Optic Links

Optical downconversion of microwave signals offers the potential for reduced noise and higher dynamic range over electronic downconversion. A novel downconversion scheme is introduced which allows for remote reception of microwave signals and downconversion to intermediate frequencies or baseband in the optical domain. Experiments show low noise and intermodulation effects. Further extensions of the optical downconverter and potential gains are also discussed

I. Introduction

Microwave fiber-optic links have been extensively pursued to replace bulky coax cables in antenna remoting and signal distribution in phased array antennas because they possess higher bandwidth, lower attenuation, and immunity to electromagnetic interference. However, unlike fiber-optic links for data communication, the analog microwave fiber-optic link in the past enjoyed limited success principally because of its inadequate dynamic range due to the nonlinear distortion incurred in the optical modulation/demodulation processes. Conversely, at the present, linearized links can provide a spurious free dynamic range (SFDR) around 115dB·Hz^2/3 [1]–[3]. Critical applications, such as radar and channelized EW receivers, call for an SFDR several orders of magnitude higher than that.