Digital Modulation Characteristics of High-Speed Semiconductor Laser for Use in Optical Communication Systems

We introduce modeling and simulation of digital modulation characteristics of high-speed semiconductor laser and evaluates its performance for use in 40 Gbps communication systems. The study is applied for both the return to zero (RZ) and non-return to zero (NRZ) formats of the modulation current. The modulation characteristics include the waveform of the modulated signal, eye diagram, and frequency chirp. The receiver sensitivity and power penalty associated with the increase in the transmission bit rate are evaluated in the back to back configuration of an optical communication system. The results showed that under 40 Gbps modulation, the modulated laser signal is broadened within the modulation bits as a pseudorandom bit-pattern effect. The laser chirp is in the range of 34–72 GHz, which is expected to combine with fiber dispersion, degrading the performance of high-speed fiber communication systems. Under both the NRZ and RZ modulations, the receiver sensitivity of the communication system increases with the increase in the bit rate. Except for the bit rate of 40 Gbps, the receiver sensitivity is larger under the NRZ modulation than under the RZ modulation. The power penalty associated with increase of the bit rate from 2 to 40 Gbps ranges between 2 and 14 dB.