A 10 Gb/s coherent detection system with feed-forward equalizers for optical duobinary transmission

This paper presents a 10-Gb/s coherent detection system incorporating feed-forward equalizers (FFEs) and an optical duobinary modulation scheme in order to increase the transmission distance limited by chromatic dispersion in standard single-mode fibers up to 400-km without signal regeneration and optical dispersion compensation. The FFE structure is based on a finite impulse response (FIR) filter with 9 taps and 100-ps tap spacing. The FFE employs capacitor-degenerated differential pairs for the delay block implementation in order to meet the system bandwidth requirement. The coherent system also incorporates a squarer for phase-diversity detection. Both the FFE and squaring circuits are fabricated in 0.18-mum CMOS technology.