Chromatic-dispersion monitoring using an optical delay-and-add filter

A novel postdetection method based on an optical delay-and-add filter (DAF) is proposed for dispersion monitoring at 40 Gb/s or beyond. The proposed method can be used with or without a pilot tone and works well even when there exists a residual chirp due to the finite direct current (DC) extinction ratio of a Mach-Zehnder (MZ) modulator or self-phase modulation (SPM). Several modulation formats, including conventional nonreturn to zero (NRZ), return to zero (RZ), carrier-suppressed RZ (CSRZ), RZ differential phase shift keying (RZ-DPSK), and CSRZ-DPSK are used to numerically demonstrate the feasibility of this technique without using a pilot tone.