Numerical modeling of mode-locking stability and repetition rate transitions in monolithic multi-section semiconductor lasers

摘要

Passively mode-locked lasers are compact photonic sources delivering high-repetition rate (RR) pulse trains and picosecond short optical pulses. An excellent stability of the generated optical pulse train is crucially important towards their application in optical communications, optical sampling or as photonic clocks. Controlled RR transitions in a multi-section monolithic quantum-dot (QD) laser have been experimentally demonstrated by a reconfigurable absorber placement or a double-interval technique. In this contribution, we study the optical pulse train stability improvement and higher harmonic RR transitions in a monolithic semiconductor laser with interdigilal absorber placement by the simulation tool FreeTWM. The laser under investigation is 4 mm long, corresponding to a fundamental RR of 10 GHz, and consists of 2 gain and 2 absorber sections. All gain sections are biased with the same current density and the absorber sections are equally reverse biased. The total absorber lengths contribute with 10 % to the total cavity length. One absorber is placed at the high reflective facet, the second at 1/3 of the total cavity length with one gain section in between and the second gain section following the second absorber. Numerically transitions from fundamental mode-locking (n=1; 10 GHz) to higher harmonic mode-locking (n=3; 30 GHz) occur by increasing the injected current density using numerical continuation. Associated with that transition is an improved timing stability by a factor of 333. Simulations confirm experimental results obtained by timing stability and RR transition studies.