Igor L. Krestnikov

The role of Auger recombination in the temperature-dependent output characteristics (T0=∞) of p-doped 1.3 μm quantum dot lasers

Temperature invariant output slope efficiency and threshold current (T0=∞) in the temperature range of 5–75 °C have been measured for 1.3 μm p-doped self-organized quantum dot lasers. Similar undoped quantum dot lasers exhibit T0=69K in the same temperature range. A self-consistent model has been employed to calculate the various radiative and nonradiative current components in p-doped and undoped lasers and to analyze the measured data. It is observed that Auger recombination in the dots plays an important role in determining the threshold current of the p-doped lasers.

High power temperature-insensitive 1.3 µm InAs/InGaAs/GaAs quantum dot lasers

We report on GaAs-based broad area (100 µm) 1.3 µm quantum dot (QD) lasers with high CW output power (5 W) and wall-plug efficiency (56%). The reliability of the devices has been demonstrated beyond 3000 h of CW operation at 0.9 W and 40 °C heat sink temperature with 2% degradation in performance. P-doped QD lasers with a temperature-insensitive threshold current (T0 > 650 K) and differential efficiency (T1 = infinity) up to 80 °C have been realized.

Gain studies of (Cd, Zn)Se quantum islands in a ZnSe matrix

By inserting stacked sheets of nominally 0.7 monolayer CdSe into a ZnSe matrix we create a region with strong resonant excitonic absorption. This leads to an enhancement of the refractive index on the low-energy side of the absorption peak. Efficient waveguiding can thus be achieved without increasing the average refractive index of the active layer with respect to the cladding. Processed high-resolution transmission electron microscopy images show that the CdSe insertions form Cd-rich two-dimensional (Cd, Zn)Se islands with lateral sizes of about 5 nm. The islands act as quantum dots with a three-dimensional confinement for excitons. Zero-phonon gain is observed in the spectral range of excitonic and biexcitonic waveguiding. At high excitation densities excitonic gain is suppressed due to the population of the quantum dots with biexcitons.

Quantum dot laser with 75 nm broad spectrum of emission

We report on a quantum dot laser having an emission spectrum as broad as 74.9 nm at 25 degrees C in the 1.2-1.28 wavelength interval with a total pulsed output power of 750 mW in single lateral mode regime and the average spectral power density of >10 mW/nm. A significant overlap and approximate equalization of the ground-state and the excited-state emission bands in the lasers spectrum is achieved by means of intentional inhomogeneous broadening of the quantum dot energy levels.

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).

Single-mode submonolayer quantum-dot vertical-cavity surface-emitting lasers with high modulation bandwidth

Single-mode vertical-cavity surface-emitting lasers based on dense arrays of stacked submonolayer grown InGaAs quantum dots, emitting near 980nm, demonstrate a modulation bandwidth of 10.5GHz. A low threshold current of 170μA, high differential efficiency of 0.53W∕A, and high modulation current efficiency factor of 14GHz∕mA are realized from a 1μm oxide aperture single-mode device with a side mode suppression ratio of >40dB and peak output power of >1mW. The lasers are also suitable for high temperature operation.

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.

InGaAs/GaAs Quantum Dot Lasers with Ultrahigh Characteristic Temperature (T 0= 385 K) Grown by Metal Organic Chemical Vapour Deposition

Low threshold current density (AlInGa)As/GaAs lasers based on InGaAs quantum dots (QDs) are grown by metal organic chemical vapour deposition (MOCVD). Quantum dots deposited at 490° C and covered with GaAs are directly revealed in the active region. On a transmission electron microscopy (TEM) image of the laser structure no large clusters or dislocations are found over a macroscopic distance. We show that the properties of QD lasers can be strongly improved if the QDs are confined by Al0.3Ga0.7As barriers and the cladding layers are grown at high temperature. Optimisation of the laser structure geometry allows extension of the range of ultrahigh temperature stability (T0=385 K) of the threshold current to 50° C.

1.3 µm luminescence and gain from defect-free InGaAs-GaAs quantum dots grown by metal-organic chemical vapour deposition

Annealing of InGaAs quantum dots (QDs) fabricated by metal-organic chemical vapour deposition and covered with a very thin GaAs cap layer completely eliminates large dislocated InGaAs clusters and remarkably improves the optical properties of the structures. A modal gain of ~4 cm-1 is achieved in the 1.35 µm range. The elimination of defects allows the stacking of QDs emitting at 1.3 µm without deterioration of their optical and structural properties and reduces the QD density in the upper sheets.

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.