Four-Dimensional Modulation and Stokes Direct Detection of Polarization Division Multiplexed Intensities, Inter Polarization Phase and Inter Polarization Differential Phase

Abstract

We propose and experimentally demonstrate modulation and Stokes space direct-detection (DD) of four orthogonal dimensions or degrees of freedom (DOF) of a single laser being the intensity on two orthogonal polarizations, the inter-polarization phase and the inter-polarization differential phase. At the transmitter, a dual-polarization in-phase quadrature-phase (DP-IQ) modulator driven by a 4-channel digital-to-analog converter is employed to imprint the transmitted data onto the aforementioned four DOF. Transmitted symbols for each polarization are drawn from multi-ring/multi-phase constellations, e.g., 2-ring/4-ary phase shift keying (PSK) or 2-ring/8PSK, resulting in a polarization division multiplexed (PDM) format with intensity, inter-polarization phase, and inter-polarization differential phase modulation (PDM-IM-IPM-IDPM). At the receiver, a novel DD front-end 1 1 A direct-detection front-end refers to a family of receivers that employ a self-beating mechanism in which the received signal beats with itself or its polarization tributaries beat with themselves. Unlike a coherent front-end, a direct-detection front-end does not incorporate a local oscillator (LO) laser.