Linear demodulation of intensity-modulated analog photonic link based on polarization modulator

We propose and experimentally demonstrate a linearization approach for a novel type of intensity-modulated directly-detected (IM-DD) analog photonic link based on digital processing technique. In our scheme, the analog signal is intensity and orthogonally modulated on a pair of co-propagated photonic links, i.e. one of the two intensity modulations has a bias angle which is 90 degree difference from the other. At the remote end, the analog signal can be linearly recovered by a digital signal processing based on the direct detections of the link pair. We experimentally demonstrate our concept through a piece of polarization maintained fiber (PMF), a polarization modulator (PolM), a polarizer, and the dual-channel wavelength division multiplexing (WDM) technology. The PMF, PolM, and the polarizer constitute an asymmetric mach-zehnder modulator (A-MZM), whose bias angle can be tuned easily by tuning the input optical carrier wavelength. Experiment results show 26.8 dB suppression of the third-order intermodulation distortion (IMD3) compared with the traditional quadrature-biased IM-DD link is achieved. Compared with the previously-reported linearized phase- or polarization-modulated, in-phase/quadrature demodulation (PM-IQD or PolM-IQD) analog photonic links, our scheme has the advantage that neither the highly-coherent optical local oscillation nor the precise polarization alignment is required in the remote end.