56 Gb/s direct-detection polarization multiplexing multi-band CAP transmission

Carrierless amplitude and phase(CAP) modulation is generating increasing interest for short-reach optical communications. Polarization multiplexing(Pol Mux) is a good way to improve the CAP system’s data rate further with the limited bandwidth of electrical devices. In this Letter, we experimentally demonstrate a 56 Gb/s directdetection Pol Mux CAP system over a 15 km fiber link for the first time, to our best knowledge. Two-band CAP modulation with different modulated orders for each band is employed. An optical filter at the receiver is utilized to realize the polarization separation. No extra digital signal processing for polarization-dependent distortion is required.