Effect of gain switching frequency on ultrashort pulse generation from laser diodes

Abstract

In this work, the effects of gain switching frequency on ultrashort pulse generation are investigated using a model based on the multi-mode rate equations. In addition to the commonly used laser diode parameters, the key parameters corresponding to the different laser diode materials and structures are included in the model. Effects of some laser diode parameters, and d.c. and RF drive conditions on the full width at half-maximum (FWHM) of gain switched pulses are investigated for the 1–15 GHz gain switching frequency range. Multi-pulse generation and the cut-off frequency of gain switching are also determined for this frequency range. It is found that the FWHM of pulses decrease as the RF current is increased, at a constant frequency. However, the FWHM of pulses either decrease or increase as the d.c. bias is increased, depending especially on the gain compression and gain peak. As the frequency is increased, pulse widths start to decrease or increase depending on the laser diode parameters. The FWHM of pulses for shorter cavity lasers are found to be almost insensitive to the frequency. Among the parameters affecting the multi-pulse generation and cut-off, gain compression, gain constant, and d.c. and RF current amplitudes are found to be the most effective. All calculations are also carried out using single-mode rate equations and results of multi-mode and single-mode solutions are compared.