Effect of intensity noise of semiconductor lasers on the digital modulation characteristics and the bit error rate of optical communication systems

Abstract

This paper presents theoretical evaluation of the digital modulation performance of semiconductor lasers in digital communication systems with gigabit rates. The study is based on numerical integration of the rate equations augmented by a nonreturn-to-zero ͑NRZ͒ bit generator. For solitary semiconductor lasers, the performance is evaluated in terms of the eye diagram, turn-on delay jitter ͑TOJ͒, and signal-to-noise ratio. In communication systems, the performance is evaluated by the bit error rate ͑BER͒ and power penalty induced by the laser noise. Contributions of both the intrinsic fluctuations and bit pattern to the TOJ and BER are assessed. The results show that when the modulation current is low and the semiconductor laser is biased relatively above threshold, the power penalty decreases although the eye diagram is not well open. When the modulation current is high enough, biasing the semiconductor laser far-above threshold achieves both lower power penalty and higher eye-diagram quality.

Performance analysis of a digital fiber optic link incorporating gain‐levered laser diode transmitter

“…The result shows that the distortion increases as the number of bits transmitted per second is increased, leading to reduced eye opening. These results coincide with theory …”

“…These results coincide with theory. [3][4][5][6][7] For the unlevered laser diode, an equal current is provided to both regions. The current pulse of magnitudes 15.25 and 17.25 mA is given for bit 0 and bit 1, respectively.…”

“…This noise is due to photons that are generated from spontaneous emission and coupled into lasing mode. [3][4][5][6][7][8][9] Coding techniques generally used to represent digital data are return to zero (RZ) and non-return to zero (NRZ) formats; however, NRZ is preferred because of its simple implementation. Further, the NRZ signal requires bandwidth less than that of RZ case.…”

“…4 Performance of directly modulated laser diode in the digital fiber link is reported by many researchers in the recent past. [3][4][5][6][7][8][9] Dynamics of laser diode are analyzed by Ahmed et al 5 for gigabit rates. The same author group has also analyzed the influence of transmission bit rate in the fiber optic link.…”

“…All the literatures available till now have analyzed the performance of digital fiber link, by considering a normal single-section laser diode-based transmitter. [3][4][5][6][7][8][9] Pocha et al 10 have envisaged that gain-levered laser diode can be used for digital switching applications. However, gain-levered-based direct modulation and link analysis have not been investigated earlier.…”