Travelling‐wave modelling of the modulation dynamic performance of wavelength‐tunable laser diodes using the integrated VPI and PICS3D software

The modulation dynamic performance of a three-section bulk InGaAsP/InP tunable laser diode (TLD) operating at 1550-nm under direct intensity modulation during discontinuous tuning is investigated with the travelling-wave approach, using commercial software tools VPI and PICS3D. The authors demonstrate a strong effect of the gain spectra shape on the modulation response of the TLDs. Two models have been developed for simulation of the modulation response which incorporate real gain spectra of TLDs obtained either from experiment or ab-initio calculations: (i) the VPI + PICS3D integrated model, and (ii) the fitted parabolic shape gain model. The results obtained for both models are in good agreement. A significant ~3 times increase of the relaxation oscillation frequency and the corresponding modulation bandwidth was observed under blue wavelength tuning of the TLD over a 21-nm range from the initial 1550-nm lasing wavelength. The authors show that the main physical reason for this increase is a dispersion of the differential gain which increases about 4 to 5 times when the lasing wavelength decreases over the above tuning range. The reported enhancement of the modulation response of TLDs is important for their practical applications.