This paper introduces modeling and simulation of the harmonic and intermodulation distortions of semiconductor laser radiating an optical fiber link. The study is based on the rate equation model of semiconductor lasers excited by injection current with two sinusoidal tones separated by a radio frequency. The modulated laser signal is modeled in both the time and frequency domains. The laser signal distortions include the 2nd and 3rd harmonic distortion (2HD and 3HD), and the third-order intermodulation distortion IMD3. The laser is assumed to be modulated around its relaxation frequency. Influence of the modulation depth on the signal distortion is investigated when the laser is free running and when it is radiating a fiber link. In the latter case, influences of the attenuation and chromatic dispersion on the signal dispersion are elucidated when the fiber length increases up to 10 km. The results show that the fiber attenuation does not affect the signal distortion, whereas the chromatic dispersion affects both the harmonic distortions and intermodulation distortion. Sending the laser signal down an optical fiber of length ~ 5km can help in minimizing 2HD which is the dominant harmonic distortion of the modulated signal. This range of optical fiber is also characterized with intermodulation distortion less than 0dBc.
Noise caused by semiconductor lasers in high-speed fiber-optic links