Dynamics Of Passively Mode-locked Lasers With Optical Injection

Semiconductor passively mode-locked (ML) lasers are of particular interest due to their compactness, cost-efficiency and ease of operation. However, outside optimal parameter range these lasers suffer waveform instabilities, large chirp and significant timing jitter, which makes them ineffective in highspeed applications. In this work we model monolithic passively mode-locked lasers using delay differential equations. We study laser dynamics under external optical injection. We demonstrate that optical injection can improve the properties of mode-locked lasers in terms of the time-bandwidth product, noise and pulse stability. Also this work provides the estimate of locking range for a passively ML semiconductor laser subjected to single frequency optical injection. Using two time scale method we calculate the asymptotic width of the locking range. Our simple analytical expression is in good agreement with direct numerical simulations of the full model equations and can be considered as an analog of the formula estimating the locking range width in a cw laser subjected to a coherent optical injection |68|. Finally, a cascade of quantum dot mode-locked lasers is utilized in order to (i) clone coherence and performance characteristics of the master source and (ii) to obtain high quality wider frequency combs resulting in pulses of short duration. Quantum- dot (QD) mode-locked lasers (MLL) are excellent candidates for applications such as optical sampling, microwave photonics and optical time division multi-plexed communication. Studies have indicated however that they are subject to a waveform instability that impacts negatively upon their time-bandwidth product (TBP) |95]. This said, QD continuous-wave lasers have shown very stable optical injection locking characteristics, with no instabilities observed at zero detuning frequency over a wide range of master powers |21]. This observation then suggests that QD-MLL characteristics could be further improved and controlled through optical injection locking, for example for applications such as remote coherent receivers |61]. This has previously been explored through the injection of two tone coherent master light, which can be thought of as a form of optical injection in combination with hybrid modulation [26].