Measurement of Constellation Diagrams for 40-Gb/s DQPSK and 60-Gb/s 8ary-DPSK Using Sampled Orthogonal Differential Direct- Detection

We demonstrate the reconstruction of constellation diagrams for 40-Gb/s DQPSK and 60-Gb/s 8ary-DPSK signals using orthogonal differential direct-detection and high-speed analog-to-digital conversion. The recovered differential-phase variance clearly manifests various transmission impairments including noise and nonlinearity.