In this study, passively mode-locked semiconductor lasers with a central wavelength of 1550 nm are theoretically investigated, consisting of gain and absorption sections. Variation of carrier density with time and pulse profiles of the laser outputs are obtained. Comparative results are obtained for different lengths of the gain sections and absorber sections. In addition, the results are also examined while the absorption section is located between two gain sections and at the far end. It has been found that the devices with two gain sections have higher power and shorter pulse width when the absorber section is located between the two gain sections. Finally, ultrashort stable optical pulses with nearly 800 mW peak power and 1.57 ps duration have been obtained from mode-locked laser diodes with two gain sections and one absorber section located between.

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Transient and steady-state characteristics of 1550 nm AlGaInAs/InP and 980 nm InGaAs/GaAs diode lasers were comparatively modeled using rate equations. The variations of the number of electrons (N-t) and the output power (P out -t) with time were examined in the transient regime for the both lasers. In addition steady-state characteristics, the number of electrons (N-I) and the output power versus current (L-I), was also investigated for different values of cavity length, stripe-width and active layer thickness. We also verified for both of the lasers that L-I simulation results are well agreed with the experimental results.