Transmission of 100-Gb/s PAM-6 Signal by Using DML Wavelength-Locked to Delay Interferometer

We experimentally demonstrate the transmission of 100-Gb/s 6-ary pulse amplitude modulation signal over 2-km standard single-mode fiber using a 1.55-μm directly-modulated laser (DML) wavelength-locked to a delay interferometer (DI). The DI, serving as an optical equalizer, not only improves the extinction ratio, but also compensates for the waveform distortions induced by fiber chromatic dispersion. Thus, no nonlinear electrical equalizer is employed in our experiment. The DML's wavelength is locked to the transmittance curve of the DI so that the system operates in a stable manner under external perturbations. The experimental results show that we achieve a decent receiver sensitivity of -2.4 dBm after the transmission. We also demonstrate a long-term stable operation even when the DI is subject to temperature variations or frequency dithering by a sinusoidal wave.