Single Section Quantum Dot Lasers Research Articles

Multimode description of self-mode locking in a single-section quantum-dot laser.

This paper describes a theory for mode locking and frequency comb generation by four-wave mixing in a semiconductor quantum-dot active medium. The derivation uses a multimode semiclassical laser theory that accounts for fast carrier collisions within an inhomogeneous distribution of quantum dots. Numerical simulations are presented to illustrate the role of active medium nonlinearities in mode competition, gain saturation, carrier-induced refractive index and creation of combination tones that lead to locking of beat frequencies among lasing modes in the presence of cavity material dispersion.

All Optical Integrate and Fire Neuromorphic Node Based on Single Section Quantum Dot Laser

In this work we provide numerical results concerning an all-optical inhibitory integrate and fire neuron based on a single section quantum-dot InAs/GaAs laser. The numerical model employs a detailed multi-population approach that accommodates electron-hole dynamics and can efficiently describe waveband transitions from both the ground and excited energy state. The underlying physical mechanism of waveband switching in an inhibitory neuron is unveiled and is attributed to hole-electron's transport time asymmetries. A detailed dynamical analysis allowed the identification of suitable optical injection regimes so as to trigger highly sought neuro-computational behaviors such as rate encoding and neural spikes with picosecond temporal resolution.

Indications on self mode-locking in a broad area single-section quantum dot laser

Broad-area edge-emitting monolithic mode-locked semiconductor quantum dot lasers emitting at 1.26 μm could potentially serve as ideal sources for the generation of high power broad optical frequency combs for short-reach inter and intra data-center links. In this contribution, the inter-mode beat frequency of a 2 mm long InAs/InGaAs quantum dot laser with a broad-ridge waveguide are studied experimentally. Laser output power, radio-frequency and spectral domain analysis is performed. -3 dB spectral widths ranging from 2nm to 5.3 nm and the existence of an inter-mode beat frequency at 20.4 GHz with a signal-to-noise ratio from 2 dB up to 11 dB are experimentally confirmed for injection currents from 0.225 A to 1 A. Our results indicate a potential way towards high output power optical frequency comb generation by electrically injected monolithic semiconductor lasers.

Dynamic Intermode Beat Frequency Control of an Optical Frequency Comb Single Section Quantum Dot Laser by Dual-Cavity Optical Self-Injection

Dynamic frequency tuning of the 40.67 GHz intermode beat frequency of a 1255 nm emitting 1 mm long monolithic self mode-locked single section optical frequency comb InAs/InGaAs quantum dot laser across 70 MHz is experimentally demonstrated by fine-delay dual-cavity controlled all optical self-injection. Fiber-based macroscopic optical delay lengths are 9.4 m (round-trip time of 62.7 ns) and 16.5 m (round-trip time of 110.1 ns), the maximum studied microscopic delay tuning times are 40 ps and the optical self-injection strengths are below 0.02%. For selected delay times, the lowest intermode beat frequency line width amounts to 2 kHz indicating an improvement of carrier phase coherence by a factor of 700 as compared to the free-running laser. We validate these experimental results by a simple and universal stochastic time-domain model which is applied for the first time to model a self mode-locked quantum dot laser subject to optical self-injection. Modeling results are in good quantitative agreement.

Editorial

Chris Toumazou 2018 was another year of exciting development for Electronics Letters. The subjects of its published papers continued to diversify, reflecting the expansion of its editorial board – the board now numbers in excess of 250, with 103 new members joining in 2018. 22 countries are represented, and we are certainly hoping to expand further, given that over sixty countries are numbered amongst the 4000 submissions to the journal. As mentioned, these submissions span the entire scope of electrical and electronic engineering, from numerous applications of liquid metal to signal processing for biomedical applications; or cover-song identification, and single-photon diodes to quantum computing. The intriguing world of memristors was the subject of this year's IET Premium Award winner: ‘Extreme Multistability In A Memristive Circuit’, by Bo-Cheng Bao, Quan Xu, Han Bao, and Mo Chen, [Electronics Letters, 2016, 52, (12), pp. 1008–1010]. The judges were impressed by, and excited to see, “a paper on a ‘proper’ memristor, not an RRAM device called a memristor. The circuit produces a very interesting dynamic response that includes chaos, here called extreme multistability – it is an intriguing concept which provides nonlinearity and very complex circuit behaviour.” From memristors, we move onto photonic crystal fibres, with ‘High Numerical Aperture, Highly Birefringent Novel Photonic Crystal Fibre For Medical Imaging Applications', by J. Sultana, Md.S. Islam, M.R. Islam, and D. Abbott, [Electronics Letters, 2018, 54, (2), pp. 61–62]. The fibre they present can be manufactured using 3D printing and possesses low effective material loss and negligible confinement loss in the terahertz frequency band. Their technique overcomes the problem that terahertz wave transmission is largely limited to free-space applications due to the lack of suitable waveguides. Electronics Letters has been at the forefront of silicon photonics research since its development in the 1980s, and this continued in 2018 with ‘490 Fs Pulse Generation From Passively Mode-Locked Single Section Quantum Dot Laser Directly Grown On On-Axis GaP/Si’ by S. Liu, D. Jung, J. C. Norman, M. J. Kennedy, A. C. Gossard, and J. E. Bowers, [Electronics Letters, 2018, 54, (7), pp. 432–433]. This fascinating work presents the first experimental demonstration of a 31 GHz single section Quantum-dot-mode-locked semiconductor lasers directly grown on on-axis (001) GaP/Si substrate using molecular beam epitaxy. The laser shows a threshold current of 34 mA with a cavity length of 1330 μm at 20°C. 490 fs pulse generation with a narrow 3 dB RF linewidth of 100 kHz is obtained when the laser is forward biased around 470 mA. With continued research into the behaviour and decoherence of qubits, quantum computing and communication is slowly moving into the realm of engineering: ‘Qubit State Detection And Enhancement By Quantum Thermal Noise’, by N. Gillard, E. Belin, and F. Chapeau-Blondeau, [Electronics Letters, 2018, 54, (1), pp. 38–39]. Reading the state of a qubit is, for obvious reasons, one of the main concerns in the field, and the authors address the problem of detecting or discriminating between two noisy quantum states. Crucially, regimes are found where higher noise temperatures are more favourable to detection, with relation to stochastic resonance effects where noise becomes beneficial to information processing. These highlights, as well as the hundreds of papers published each year by Electronics Letters, represent the great journey ahead for the journal and for the subject as a whole. Finally, we would like to thank the editorial and production teams at the IET, the editorial board, and of course the many thousands of peer-reviewers who make the journal possible. That the reviewers take the time out of their busy schedules and roles to support the community is hugely appreciated, and is one of the reasons that the community, not just Electronics Letters, is flourishing.

Injection-induced, tunable all-optical gating in a two-state quantum dot laser.

We demonstrate a tunable all-optical gating phenomenon in a single-section quantum dot laser. The free-running operation of the device is emission from the excited state. Optical injection into the ground state of the material can induce a switch to emission from the ground state with complete suppression of the excited state. If the master laser is detuned from the ground-state emitting frequency, a periodic train of ground-state dropouts can be obtained. These dropouts act as gates for excited-state pulsations: during the dropout, the gate is opened and gain is made available for the excited state, and the gate is closed again when the dropout ends. Numerical simulations using a rate equation model are in excellent agreement with experimental results.

All-optical switching with a dual-state, single-section quantum dot laser via optical injection.

An all-optical switching mechanism via optical injection of an InAs/GaAs quantum dot laser is presented. Relative state suppression in excess of 40dB is achieved, and experimental switching times of the order of a few hundred picoseconds are demonstrated.

Random Population Model for Self Pulsation in Single-Section Quantum-Dot Lasers

A new mechanism of self-pulsation in single section Fabry-Pérot (F-P) quantum-dot (QD) lasers is studied in this letter. Since Fermi-Daric statistics are not readily applicable to QD lasers for picosecond pulse generation, we use a random population model to simulate single-section QD F-P lasers. It is demonstrated that some QDs contribute as gain media, while others can still be absorptive, even though the overall device is biased above lasing threshold. This can lead to pulse generation without the typical nonlinear effects, such as four-wave mixing, Kerr nonlinearity, and spatially inhomogeneous current distribution, previously reported in single section self-pulsating semiconductor lasers.

Low-frequency self-pulsing in single-section quantum-dot laser diodes and its relation to optothermal pulsations

Self-sustained pulsations in the output of an InAs quantum dot laser diode in the MHz range are reported. The characteristics (shape, range, and frequency) are presented for the free-running laser and when optical feedback in the Littrow configuration is applied. Bistability in the light-current characteristics is observed for operating wavelengths smaller than the gain peak, but it is not present for wavelengths above the gain peak and for the free-running laser, except at elevated temperatures. The temporal evolution of the envelopes of the optical spectra is very different for operation below, around, and above the gain peak, which might be related to a change of phase-amplitude coupling across the gain maximum, in agreement with the expectation for a two-level system. The time scale and the bifurcation scenario, supported by an initial blueshift of the emission wavelength of each longitudinal mode in time-resolved optical spectra, suggests that these are optothermal pulsations similar to those reported in quantum well amplifiers [Phys. Rev. E 68, 036209 (2003)]. The mechanism of pulsation seems to be a destabilization of bistable states (due to saturable absorption in the beam wings) by a slow thermal change in the waveguiding properties.