Microwave Photonic Link With Improved Dynamic Range Using a Polarization Modulator

A microwave photonic link (MPL) using a single polarization modulator (PolM) with an improved spurious free dynamic range (SFDR) is proposed and experimentally demonstrated. The proposed MPL is designed based on the destructive combination of the distortion signals in the electrical domain, which is realized using a PolM with its output split into two channels. In the upper channel, the PolM, a polarization controller (PC), and a polarization beam splitter (PBS) form an equivalent Mach-Zehnder modulator (MZM) that is biased at the quadrature point. The optical carrier is suppressed using a phase-shifted fiber Bragg grating (PS-FBG). In the lower channel, the PolM, another PC, and the PBS form a second equivalent MZM that is also biased at the quadrature point but at the opposite slope of the transfer function. The signals from the two channels are sent to a photodetector (PD). If the optical powers into the two channels are identical, the third-order intermodulation terms are completely suppressed. An experiment is performed. An enhancement in SFDR of 10 dB is achieved. The insertion loss of the proposed MPL is also estimated, which is 9.5 dB smaller than a phase modulator based MPL.