Picosecond pulse amplification up to a peak power of 42 W by a quantum-dot tapered optical amplifier and a mode-locked laser emitting at 1.26 µm.

We experimentally study the generation and amplification of stable picosecond-short optical pulses by a master oscillator power-amplifier configuration consisting of a monolithic quantum-dot-based gain-guided tapered laser and amplifier emitting at 1.26 µm without pulse compression, external cavity, gain- or Q-switched operation. We report a peak power of 42 W and a figure-of-merit for second-order nonlinear imaging of 38.5 W2 at a repetition rate of 16 GHz and an associated pulse width of 1.37 ps.

Two-state semiconductor laser self-mixing velocimetry exploiting coupled quantum-dot emission-states: experiment, simulation and theory.

We exploit the coupled emission-states of a single-chip semiconductor InAs/GaAs quantum-dot laser emitting simultaneously on ground-state (λ(GS) = 1245 nm) and excited-state (λ(ES) = 1175 nm) to demonstrate coupled-two-state self-mixing velocimetry for a moving diffuse reflector. A 13 Hz-narrow Doppler beat frequency signal at 317 Hz is obtained for a reflector velocity of 3 mm/s, which exemplifies a 66-fold improvement in width as compared to single-wavelength self-mixing velocimetry. Simulation results reveal the physical origin of this signal, the coupling of excited-state and ground-state photons via the carriers, which is unique for quantum-dot lasers and reproduce the experimental results with excellent agreement.

Tapered InAs/InGaAs quantum dot semiconductor optical amplifier design for enhanced gain and beam quality.

In this Letter, a design for a tapered InAs/InGaAs quantum dot semiconductor optical amplifier is proposed and experimentally evaluated. The amplifier's geometry was optimized in order to reduce gain saturation effects and improve gain efficiency and beam quality. The experimental measurements confirm that the proposed amplifier allows for an elevated optical gain in the saturation regime, whereas a five-fold increase in the coupling efficiency to a standard single mode optical fiber is observed, due to the improvement in the beam quality factor M² of the emitted beam.

P-i-n junction quantum dot saturable absorber mirror: electrical control of ultrafast dynamics.

We report on nonlinear optical properties of a p-i-n junction quantum dot saturable absorber based on InGaAs/GaAs. Absorption recovery dynamics and nonlinear reflectivity are investigated for different reverse bias and pump power conditions. A decrease in absorption recovery time of nearly two orders of magnitude is demonstrated by applying a voltage between 0 and -20 V. The saturable absorber modulation depth and saturation fluence are found to be independent from the applied reverse bias.

VECSEL gain characterization.

We present the first full gain characterization of two vertical external cavity surface emitting laser (VECSEL) gain chips with similar designs operating in the 960-nm wavelength regime. We optically pump the structures with continuous-wave (cw) 808-nm radiation and measure the nonlinear reflectivity for 130-fs and 1.4-ps probe pulses as function of probe pulse fluence, pump power, and heat sink temperature. With this technique we are able to measure the saturation behavior for VECSEL gain chips for the first time. The characterization with 1.4-ps pulses resulted in saturation fluences of 40-80 µJ/cm2, while probing with 130-fs pulses yields reduced saturation fluences of 30-50 µJ/cm2 for both structures. For both pulse durations this is lower than previously assumed. A small-signal gain of up to 5% is obtained with this technique. Furthermore, in a second measurement setup, we characterize the spectral dependence of the gain using a tunable cw probe beam. We measure a gain bandwidth of over 26 nm for both structures, full width at half maximum.

Femtosecond high-power quantum dot vertical external cavity surface emitting laser.

We report on the first femtosecond vertical external cavity surface emitting laser (VECSEL) exceeding 1 W of average output power. The VECSEL is optically pumped, based on self-assembled InAs quantum dot (QD) gain layers, cooled efficiently using a thin disk geometry and passively modelocked with a fast quantum dot semiconductor saturable absorber mirror (SESAM). We developed a novel gain structure with a flat group delay dispersion (GDD) of ± 10 fs2 over a range of 30 nm around the designed operation wavelength of 960 nm. This amount of GDD is several orders of magnitude lower compared to standard designs. Furthermore, we used an optimized positioning scheme of 63 QD gain layers to broaden and flatten the spectral gain. For stable and self-starting pulse formation, we have employed a QD-SESAM with a fast absorption recovery time of around 500 fs. We have achieved 1 W of average output power with 784-fs pulse duration at a repetition rate of 5.4 GHz. The QD-SESAM and the QD-VECSEL are operated with similar cavity mode areas, which is beneficial for higher repetition rates and the integration of both elements into a modelocked integrated external-cavity surface emitting laser (MIXSEL).

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

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.

Dual-wavelength mode-locked quantum-dot laser, via ground and excited state transitions: experimental and theoretical investigation.

We report a dual-wavelength passive mode locking regime where picosecond pulses are generated from both ground (lambda = 1263 nm) and excited state transitions (lambda = 1180 nm), in a GaAs-based monolithic two-section quantum-dot laser. Moreover, these results are reproduced by numerical simulations which provide a better insight on the dual-wavelength mode-locked operation.

2.5 W orange power by frequency conversion from a dual-gain quantum-dot disk laser.

We report a disk laser using two quantum-dot semiconductor gain elements, resulting in what we believe is the first demonstration of intracavity frequency conversion with these active media. Output power of 6 W has been obtained in dual-gain configuration at a wavelength of 1180 nm, while single-gain lasers produced up to 3 and 4 W individually, limited by thermal rollover in the output characteristics. The gain enhancement achieved with two active elements comprising 39 layers of Stranski-Krastanov InGaAs quantum dots allows for intracavity frequency doubling delivering 2.5 W of orange radiation.

Optically pumped semiconductor quantum dot disk laser operating at 1180 nm.

We demonstrate an optically pumped semiconductor disk laser using 39 layers of Stranski-Krastanov InGaAs quantum dots self-assembled during epitaxial growth on a monolithic GaAs/AlAs distributed Bragg reflector. The gain structure bonded to an intracavity diamond crystal heat spreader allows 1.75 W single-transverse-mode output (M(2)<1.2) with circular beam shape operating at 1180 nm in a disk laser geometry.

Static gain saturation in quantum dot semiconductor optical amplifiers.

Measurements of saturated amplified spontaneous emission-spectra of quantum dot semiconductor optical amplifiers demonstrate efficient replenishment of the quantum-dot ground state population from excited states. This saturation behavior is perfectly modeled by a rate equation model. We examined experimentally the dependence of saturation on the drive current and the saturating optical pump power as well as on the pump wavelength. A coherent noise spectral hole is observed with which we assess dynamical properties and propose optimization of the SOA operating parameters for high speed applications.