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We present a model for the description of the dynamical behavior of Quantum Dot (QD) based Semiconductor Optical Amplifiers (SOAs) under injection of optical pulses. The model uses a Time Domain Traveling Wave (TDTW) approach to describe the optical field in the amplifier, and allows us to consider chirped QD materials by the inclusion of a set of rate equations modeling the occupation probability of the QD confined states in each active layer. The results of the numerical simulations are validated against experimental measurements of a two-contact chirped QD SOA with ground state emissions in the 1200 nm to 1300 nm range. When the single-pass configuration is compared to the double-pass setup, both the numerical simulations and the experimental results show that a clear improvement can be obtained with the latter configuration in terms of output power and signal amplification; for the majority of biasing conditions, the double-pass amplifier presents a gain approximately 3 dB greater than the single-pass without evident saturation of the gain and pulses broadening.

We introduce a rate equation based numerical model suitable for the description of the wide spectral asymmetry experimentally observed at the two facets of multi-electrode tapered superluminescent diode based on Quantum Dot material. Numerical simulations carried out with this model were able to quantitatively reproduce the behavior of a two-section SLD and explain the reported spectral asymmetry in terms of non-uniform filling of the QD confined states under non-uniform current injection.

A wide spectral asymmetry between the wide and narrow facets of a two-section tapered quantum dot (QD) superluminescent diode (SLD) emitting around 1240 nm was observed and investigated. This asymmetry, as characterized by the mismatch in the center wavelengths of the wide and narrow facet spectra, was found to be tunable and had some dependence on the magnitude of the difference in current densities applied to each section of the device. A maximum spectral mismatch of 14 nm was observed when the current density difference between the two SLD sections was 1.5 kAcm2.This spectral asymmetry presents an unexplored degree of freedom which could be exploited via multiplexing from a single device to optimize spectral bandwidth. Furthermore, potentially useful output powers of up to 50 mW were observed from the narrow facet of the SLD, which could again be exploited via single device multiplexing to increase output power, with little to no cost to spectral bandwidth. The experimental findings were analyzed using a rate-equation based QD model considering the QD ensemble inhomogeneous broadening, the multilayer chirped active material, the spatial distribution of the QD carriers and the spectral and spatial distribution of the photons in the SLDs. The numerical simulations were able to predict the asymmetric output powers extracted from the SLD facets, mainly to due to different equivalent material losses experienced by the forward and backward fields in the weakly gain guided tapered device. Simulations were also able to predict the spectral distribution of the optical fields at the output facets.

A high-power quantum-dot superluminescent diode is demonstrated under continuous-wave operation, with an output power of 137.5 mW and a corresponding spectral bandwidth of 21 nm. This represents not only the highest output power, but also a record-high power spectral density of 6.5 mW/nm for a CW-operated superluminescent diode in the 1.1 - 1.3 μm spectral region, marking more than a 6-fold increase with respect to the state of the art. The two-section contact layout of the reported device introduces additional degrees of freedom, which enable a wide tunability of the bandwidth and power depending on the desired application. A maximum bandwidth of 79 nm was recorded, with an output power of 1.4 mW. The high-power continuous-wave operation of this device would be particularly relevant for continuous, high-speed, high-sensitivity spectroscopy, imaging and sensing applications, as well as in optical communications.

A wide spectral asymmetry between the front and rear facets of a tapered chirped quantum dot multi-section superluminescent diode is reported. The spectral asymmetry between the two facet outputs was found to be tunable and highly dependent on the bias asymmetry between the two contact sections, with a spectral mismatch of up to 14 nm. Numerical simulations confirmed a relationship between this spectral asymmetry and the non-uniform filling of the quantum dots’ confined states when different current densities are applied to the device electrodes. The results from this investigation open up an additional degree of freedom for multi-section superluminescent diodes, which could pave the way for optical bandwidth engineering via multiplexing the spectral output from both facets, using only a single device.

A novel passively mode-locked semiconductor edge-emitting laser is reported, based on an AlGaAs multi-quantum-well structure. Ultra short pulses are generated at 752 nm, with a 19.4-GHz repetition rate and a pulse duration of 3.5 ps.

A deep-red semiconductor monolithic mode-locked laser is demonstrated. Multi-section laser diodes based on an AlGaAs multi-quantum-well structure were passively mode-locked, enabling the generation of picosecond optical pulses at 752 nm, at pulse repetition rates of 19.37 GHz. An investigation of the dependence of the pulse duration as a function of reverse bias revealed a predominantly exponential decay trend of the pulse duration, varying from 10.5 ps down to 3.5 ps, which can be associated with the concomitant reduction of absorption recovery time with increasing applied field. A 30-MHz-tunability of the pulse repetition rate with bias conditions is also reported. The demonstration of such a compact, efficient and versatile ultrafast laser in this spectral region paves the way for its deployment in a wide range of applications such as biomedical microscopy, pulsed terahertz generation as well as microwave and millimeter-wave generation, with further impact on sensing, imaging and optical communications.

We demonstrate the first semiconductor mode-locked lasers for ultrashort pulse generation at the 760 nm waveband. Multi-section laser diodes based on an AlGaAs multi-quantum-well structure were passively mode-locked, resulting in the generation of pulses at around 766 nm, with pulse durations down to ~4 ps, at pulse repetition rates of 19.4 GHz or 23.2 GHz (with different laser cavity lengths of 1.8 mm and 1.5 mm, respectively). The influence of the bias conditions on the mode-locking characteristics was investigated for these new lasers, revealing trends which can be ascribed to the interplay of dynamical processes in the saturable absorber and gain sections. It was also found that the front facet reflectivity played a key role in the stability of mode-locking and the occurrence of self-pulsations. These lasers hold significant promise as light sources for multi-photon biomedical imaging, as well as in other applications such as frequency conversion into the ultraviolet and radio-over-fibre communications.

We will present our recent results, harnessing the flexibility of quantum dot materials towards the development of increasingly versatile regimes of ultrashort pulse generation and amplification in edge-emitting devices.