Frequency-to-time mapping by a phase-modulated frequency-shifting loop

Photonic processing of microwave signals may offer higher bandwidth than conventional electronic methods [1]. Among various functions achievable by optical means, optical real-time Fourier transformation (RTFT) has received special attention because of its high processing speed, which is far beyond conventional digital signal processing methods. In this respect, the frequency-shifting loop (FSL) shows high performance, as compared to dispersion-based methods, by analyzing MHz-range bandwidth signals with a frequency resolution of a few kHz [2]. FSLs up to now mainly rely on the use of acousto-optic frequency shifters, with inherent limitations in efficiency when seeking a high bandwidth. To overcome this limitation, the use of electro-optic modulators inside FSLs was theoretically studied [3]. It was shown that phase modulators could be an alternative for realizing RF-photonic frequency-to-time mapping (FTM). Here we give some experimental support to the predictions of Ref. [3] , opening a new route to fully integrated microwave-photonic signal analyzers.