Nyquist 4-ary pulse amplitude modulation scheme based on electrical Nyquist pulse shaping and fiber Bragg grating filter

Intensity modulation and direct detection signal are sensitive to power fading and nonlinear inter-symbol interference (ISI) induced by modulator chirp, fiber dispersion, and square-law photo-detection. We propose and experimentally demonstrate a Nyquist 4-ary pulse amplitude modulation and direct detection scheme relying on pulse-shaping with an electrical filter and optical equalization with a vestigial-sideband (VSB) filter in the transmitter. The power fading could be eliminated by using the VSB filter. Compared with conventional 4-ary pulse amplitude modulation, the Nyquist signal has a stronger resistance to nonlinear ISI. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)