Flattened optical frequency-locked multi-carrier generation by cascading one directly modulated laser and one phase modulator

We propose a novel scheme for optical frequency-locked multi-carrier generation based on a directly modulated laser (DML) and a phase modulator (PM) in cascade through synchronous sinusoidal radio frequency (RF) signal. The optimal operating zone for the cascaded DML and PM scheme is determined via theoretical analysis and numerical simulation. We demonstrate 16 optical subcarriers can be successfully generated based on the cascaded DML and PM scheme in the optimal zone. The generated 16 optical subcarries have frequency spacing of 12.5 GHz and power difference of less than 3 dB. These results agree well with those of the numerical simulation. We also demonstrate intensity modulation and direct detection (IM-DD) based on one of the 16 generated optical subcarriers. After 20-km single-mode fiber-28 (SMF-28) transmission, the bit-error ratio (BER) of 1 \times 10-9 can be attained for both 3.125- and 12.5-Gb/s bit rates.