High-Quality Optical Frequency Comb by Spectral Slicing of Spectra Broadened by SPM

This paper introduces a spectral slicing technique that extends the useful spectral range of frequency combs generated through self-phase modulation (SPM) of mode-locked laser pulses. When generating frequency combs by SPM, the spectral range with high-quality carriers is usually limited due to spectral minima carrying too little power. To overcome these limitations, we combine suitable slices of broadened and nonbroadened spectra. The concept was experimentally verified: A total number of 325 consecutive equidistant subcarriers span a bandwidth of 4 THz. All subcarriers have an optical carrier-power-to-noise-power-density ratio (OCNR) larger than 25.8 dB (0.1 nm) and were derived from one mode-locked laser with a mode linewidth of approximately 1 kHz. The signal quality of the comb and in particular of each subcarrier was ultimately tested in a terabit-per-second communication experiment. The comb quality allowed us to transmit 32.5 Tb/s over 225 km with 100 Gb/s dual polarization 16-ary quadrature amplitude modulation (16QAM) signals on each of the subcarriers.