Semiconductor lasers are convenient and compact sources of light, offering highly efficient operation, direct electrical control and integration opportunities. In this review we describe how semiconductor quantum-dot structures can provide an efficient means of amplifying and generating ultrafast (of the order of 100 fs), high-power and low-noise optical pulses, with the potential to boost the repetition rate of the pulses to beyond 1 THz. Such device designs are opening up new possibilities in ultrafast science and technology.

Mode-locked quantum-dot lasers

This paper summarizes recent advances on InAs/InP quantum dash (QD) materials for lasers and amplifiers, and QD device performance with particular interest in optical communication. We investigate both InAs/InP dashes in a barrier and dashes in a well (DWELL) heterostructures operating at 1.5 mum. These two types of QDs can provide high gain and low losses. Continuous-wave (CW) room-temperature lasing operation on ground state of cavity length as short as 200 mum has been achieved, demonstrating the high modal gain of the active core. A threshold current density as low as 110 A/cm2 per QD layer has been obtained for infinite-length DWELL laser. An optimized DWELL structure allows achieving of a T0 larger than 100 K for broad-area (BA) lasers, and of 80 K for single-transverse-mode lasers in the temperature range between 25degC and 85degC. Buried ridge stripe (BRS)-type single-mode distributed feedback (DFB) lasers are also demonstrated for the first time, exhibiting a side-mode suppression ratio (SMSR) as high as 45 dB. Such DFB lasers allow the first floor-free 10-Gb/s direct modulation for back-to-back and transmission over 16-km standard optical fiber. In addition, novel results are given on gain, noise, and four-wave mixing of QD-based semiconductor optical amplifiers. Furthermore, we demonstrate that QD Fabry-Perot (FP) lasers, owing to the small confinement factor and the three-dimensional (3-D) quantification of electronic energy levels, exhibit a beating linewidth as narrow as 15 kHz. Such an extremely narrow linewidth, compared to their QW or bulk counterparts, leads to the excellent phase noise and time-jitter characteristics when QD lasers are actively mode-locked. These advances constitute a new step toward the application of QD lasers and amplifiers to the field of optical fiber communications

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Recent Advances on InAs/InP Quantum Dash Based Semiconductor Lasers and Optical Amplifiers Operating at 1.55 $\mu$ m

Accurate conversion of wideband multi-GHz analog signals into the digital domain has long been a target of analog-to-digital converter (ADC) developers, driven by applications in radar systems, software radio, medical imaging, and communication systems. Aperture jitter has been a major bottleneck on the way towards higher speeds and better accuracy. Photonic ADCs, which perform sampling using ultra-stable optical pulse trains generated by mode-locked lasers, have been investigated for many years as a promising approach to overcome the jitter problem and bring ADC performance to new levels. This work demonstrates that the photonic approach can deliver on its promise by digitizing a 41 GHz signal with 7.0 effective bits using a photonic ADC built from discrete components. This accuracy corresponds to a timing jitter of 15 fs - a 4-5 times improvement over the performance of the best electronic ADCs which exist today. On the way towards an integrated photonic ADC, a silicon photonic chip with core photonic components was fabricated and used to digitize a 10 GHz signal with 3.5 effective bits. In these experiments, two wavelength channels were implemented, providing the overall sampling rate of 2.1 GSa/s. To show that photonic ADCs with larger channel counts are possible, a dual 20-channel silicon filter bank has been demonstrated.

/pdf/photonic-adc-overcoming-the-bottleneck-of-electronic-jitter-fnlt3u426z.pdf

Photonic ADC: overcoming the bottleneck of electronic jitter.

https://www.ulp.ethz.ch/content/dam/ethz/special-interest/phys/quantum-electronics/ultrafast-laser-physics-dam/publications_awards/publications/2006/248__PhysRep_429__67__2006_.pdf

Passively modelocked surface-emitting semiconductor lasers

In this paper, we review the current status of the hybrid silicon photonic integration platform with emphasis on its prospects for increased integration complexity. The hybrid silicon platform is maturing fast as increasingly complex circuits are reported with tens of integrated components including on-chip lasers. It is shown that this platform is well positioned and holds great potential to address future needs for medium-scale photonic integrated circuits.

/pdf/hybrid-silicon-photonic-integrated-circuit-technology-1988farjec.pdf

Hybrid Silicon Photonic Integrated Circuit Technology

We demonstrate mode locking in a two-section quantum-dot laser that produces output powers up to 45 mW at 1260 nm. The pulse duration could be varied from 2 ps to as short as 400 fs at the 21 GHz pulse repetition rate.

High-power picosecond and femtosecond pulse generation from a two-section mode-locked quantum-dot laser

A record broadly tunable high-power external cavity InAs/GaAs quantum-dot diode laser with a tuning range of 202 nm (1122 nm-1324 nm) is demonstrated. A maximum output power of 480 mW and a side-mode suppression ratio greater than 45 dB are achieved in the central part of the tuning range. We exploit a number of strategies for enhancing the tuning range of external cavity quantum-dot lasers. Different waveguide designs, laser configurations and operation conditions (pump current and temperature) are investigated for optimization of output power and tunability.

http://eprints.aston.ac.uk/22911/1/Broadly_tunable_high_power_InAs_GaAs_quantum_dot_external_cavity_diode_lasers.pdf

Broadly tunable high-power InAs/GaAs quantum-dot external cavity diode lasers

The authors demonstrate stable mode locking that involves transitions within either the ground state (1260nm) or the excited state (1190nm) in a two-section quantum-dot laser, at repetition frequencies of 21 and 20.5GHz, respectively. The average power of the mode-locked output was in excess of 35mW for operation in the ground state and 25mW in the excited state. The selection of pulse generation between these states in the mode-locking regime is controlled by the electrical biasing conditions.

Stable mode locking via ground- or excited-state transitions in a two-section quantum-dot laser

We examine the surface recombination rate in quantum-dot semiconductor lasers and determine the diffusion length (1.0 mum) and, for the first time, provide a value for surface recombination velocity (5times104 cm/s) in quantum-dot material. As a result of strong carrier confinement in the dots, these values are much lower than in comparable quantum-well lasers (5times105 cm/s and 5 mum, respectively) allowing the creation of narrow (2-3 mum wide) lasers with comparable threshold currents to those of broad area devices

Maria Ana Cataluna

Papers

Mode-locked quantum-dot lasers

High-power picosecond and femtosecond pulse generation from a two-section mode-locked quantum-dot laser

Broadly tunable high-power InAs/GaAs quantum-dot external cavity diode lasers

Stable mode locking via ground- or excited-state transitions in a two-section quantum-dot laser

Reduced surface sidewall recombination and diffusion in quantum-dot lasers