We propose and experimentally demonstrate a coherent receiver based on simplified heterodyne detection for 100 G polarization division multiplexing (PDM) signal. Compared to the conventional homodyne detection, only two balanced photo detectors (PDs) and two analog-to-digital converters (ADCs) are used in the simplified heterodyne detection. Compared to the conventional hybrid for homodyne detection, the polarization-diversity hybrid here is also simplified. The in-phase/quadrature (I/Q) separation and corresponding digital signal processing (DSP) following downconversion are realized in digital domain after ADCs. Using this scheme, we successfully demonstrated 8 × 112-Gb/s wavelength-division-multiplexing (WDM) polarization-division-multiplexing 16-ary quadrature amplitude modulation (PDM-16QAM) over 720-km single-mode fiber (SMF)-28 with heterodyne detection based on DSP and erbium-doped fiber amplifier (EDFA)-only amplification. Although the required analog bandwidth and sampling speed of the PDs and ADCs are significantly increased for heterodyne detection, the benefits from the simplified coherent receiver architecture and effective DSP in digital frequency domain are experimentally demonstrated.
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