A Microwave Photonics Equalizer for Overcoming Dispersion-Induced Distortions on Wideband Signals in Radio-Over-Fiber Links

Chromatic dispersion (CD) has been considered as a significant issue that needs to be addressed over the past decades. Nowadays, as the bandwidth of radio frequency signals has expanded to multi-gigahertz, CD becomes increasingly troublesome for some wideband signals such as linear frequency modulated waveform (LFMW), which requires a flat amplitude response and a linear phase response. In this paper, we first investigate the CD-induced amplitude distortion and phase distortion that a wideband signal will suffer in traditional double-sideband (DSB) modulated and single-sideband (SSB) modulated radio-over-fiber (RoF) links with an emphasis on the LFMW. The detrimental impacts of the CD-induced distortions are subsequently discussed based on the pulse compression performance. Then, a two-tap microwave photonics equalizer (MPE) model is proposed and its operating principle for overcoming the CD-induced distortions is demonstrated. Based on the model, we design the MPE, which is mainly composed of an integrated dual-polarization dual-parallel Mach–Zehnder modulator and a differential group delay module. In the proof-of-concept experiment, the RoF link utilizing the proposed MPE is built, and a 1–10 GHz LFMW is transmitted over the 66.3-km single-mode fiber. Thanks to the MPE, both CD-induced amplitude distortion and phase distortion are successfully compensated. Pulse compression results show that the pulse, compared with the signal transmitted in the SSB-based link.