Highly Linear Microwave Photonic Link Using a Polarization Modulator in a Sagnac Loop

We propose a highly linear microwave photonic link (MPL) using a single polarization modulator (PolM) incorporated in a Sagnac loop. For the counter clockwise optical signal, the joint use of the PolM, a polarization controller, and a polarizer is equivalent to an intensity modulator, while the optical signal cannot be modulated in the clockwise direction due to the velocity mismatch. An intensity-modulated optical signal plus an optical carrier is thus generated. The third-order intermodulation distortion (IMD3) is reduced by properly adjusting the parameters of the system, i.e., the power ratio and the phase difference between the clockwise and counter clockwise optical signals and the bias point of the equivalent intensity modulator. The proposed scheme is theoretically analyzed and experimentally verified. The IMD3 reduction of 45 dB has been achieved, giving a spurious-free dynamic range of 98.85 dB·Hz^2/3. This result is 15 dB more than that in a conventional PolM-based MPL.