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We review results on the optical injection of dual state InAs quantum dot-based semiconductor lasers. The two states in question are the so-called ground state and first excited state of the laser. This ability to lase from two different energy states is unique amongst semiconductor lasers and in combination with the high, intrinsic relaxation oscillation damping of the material and the novel, inherent cascade like carrier relaxation process, endows optically injected dual state quantum dot lasers with many unique dynamical properties. Particular attention is paid to fast state switching, antiphase excitability, novel information processing techniques and optothermally induced neuronal phenomena. We compare and contrast some of the physical properties of the system with other optically injected two state devices such as vertical cavity surface emitting lasers and ring lasers. Finally, we offer an outlook on the use of quantum dot material in photonic integrated circuits.

One of the defining characteristics of excitability is the existence of an excitable threshold: the minimum perturbation amplitude necessary to produce an excitable response. We analyze an optically injected dual state quantum dot laser, previously shown to display a dual state stochastic excitable dynamic. We show that deterministic triggering of this dynamic can be achieved via optical phase perturbations. Further, we demonstrate that there are in fact two asymmetric excitable thresholds in this system corresponding to the two possible directions of optical phase perturbations. For fast enough perturbations, an excitable interval arises, and there is a limit to the perturbation amplitude, above which excitations no longer arise, a phenomenon heretofore unobserved in studies of excitability.

We derive and apply a numerical model for the description of optically injected long-cavity Fabry-P\'erot (FP) quantum-dot (QD) lasers, based on a multisection delay-algebraic-equation approach. In conjunction with experimental measurements, we characterize the multimode dynamics of the free-running laser as well as under external optical injection. We investigate the dynamics of the spatial hole burning (SHB) in the charge-carrier distribution, which is significant in QD lasers and is furthermore a driving mechanism for the emergence of multimode dynamics. In the injected laser, we focus on the transition between the locking regions of neighboring FP modes, which could not be described using traditional multimode rate-equation models. For very strong injection, the individual locking cones are found to converge. For intermediate injection strength, an additional dynamic boundary between the unlocked states is found in a narrow dynamical region in between two neighboring locking cones. This region is characterized by a further unlocking of all laser modes. Furthermore, we find the SHB to impose a threshold in the locking strength which must be overcome to lock a laser mode.

Optically injected quantum dot lasers display many unique nonlinear phenomena and are in particular, excellent testbeds for different forms of excitability. We analyse the recent discovery of Type II excitability in such devices. An optothermal instability leads to the phenomenon and while an underlying Hopf bifurcation is ultimately responsible for the observation, intriguingly there are two potential routes: One via a subcritical bifurcation and an associated bistable region and the other via a supercritical bifurcation and an associated canard explosion.

Excitable pulses are one of the necessary building blocks in achieving a functional neuromorphic photonic system. Many different semiconductor devices have been arranged in various configurations to produce excitable pulses [1]. Of these, Quantum Dot (QD) lasers in a unidirectional optical injection set-up are great candidates for future applications. The optically injected QD laser is shown to be a truly unique set up producing a plethora of different non linear dynamics, many of which are potentially useful in neuromorphic applications. In particular, there are several different excitable regimes: Both Type I [2] and Type II excitability [3] can be produced. In fact, both types are produced with exactly the same master-slave configuration. By simply adjusting the control parameters only — injection strength and detuning — it is easy to navigate between these two types of excitability.

Quantum dot (QD) lasers display the unique ability to lase from multiple energy states [1]. Depending on pump current a QD laser can lase from the ground state (GS), from the first excited state (ES), or simultaneously from both. Although a lot of work has been done investigating the neuromorphic dynamics for the GS state, very little has been done involving the ES. In [2] antiphase ES and GS bursting intensity oscillations were reported while in [3], a novel Type I dual state excitable dynamic was reported. Here we show that we can controllably produce GS dark pulses and an associated ES bright pulse using sufficiently large perturbations to deterministically trigger them. We also identify and show techniques that can be used to control the number of spikes in the bursts and the refractory time in the dual state excitability.

Quantum dot lasers have proven to be extremely interesting in terms of nonlinear dynamics. One of the key benefits is their highly damped relaxation oscillations. In this work we take advantage of this stability in a master slave configuration. We find a novel, dual state excitable dynamic resulting in antiphase operation between two lasing states in the device. We interpret the behaviour as a non-Adler but still Type I excitability. Phase measurements bolster our interpretation.

Quantum dot lasers display many unique dynamic phenomena when optically injected. Bistability has been predicted in a region of high injection strength. We show experimentally, rather than a phase-locked bistability, a square wave phenomenon is observed in this region. The squares can manifest as a periodic train but also as noise driven Type II excitable events. We interpret the appearance of the square waves as a thermally induced breaking of the bistability. Indeed we find experimentally that over the duration of a square the relative detuning between the master and the slave evolves deterministically. A relatively simple, physically motivated, rate equation model is presented and displays excellent agreement with the experiment., Comment: 8 pages, 5 figures, preprint