We present high-power surface-emitting second-order distributed feedback quantum-cascade lasers in GaAs and InP material systems. The GaAs device, grown by molecular-beam epitaxy, showed single-mode peak output powers of 3 W at 78 K in pulsed operation. With the InP-based devices, which are grown by metalorganic vapor phase epitaxy, we obtained single-mode peak output powers of 1 W at room temperature. These are the highest output powers for surface emission of quantum-cascade lasers reported so far. The InP-based distributed feedback lasers also have very low threshold current densities and are working well above room temperature.
Intervalley carrier transfer in short-wavelength InP-based quantum-cascade laser Appl. Phys. Lett. 93, 071109 (2008); 10.1063/1.2973212 Short-wavelength ( λ ≈ 3.05 μ m ) InP-based strain-compensated quantum-cascade laser Appl. Phys. Lett. 90, 051111 (2007); 10.1063/1.2437108 Short-wavelength ( λ ≈ 3.3 μ m ) InP-based strain-compensated quantum-cascade laserThe effect of doping concentration on the performance of short-wavelength quantum-cascade lasers based on the strain-compensated InGaAs/InAlAs/AlAs heterostructure on InP, emitting at 3.8 m, is investigated for average doping concentrations between 0.3 and 3.9ϫ 10 17 cm −3 ͑sheet densities between 1.6 and 20.9ϫ 10 11 cm −2 ͒. Although the threshold current density is rather independent of doping concentration, the maximum current density increases with doping and exhibits a saturation for the highest doping level. Other important performance characteristics such as differential quantum efficiency, peak optical emission power, slope efficiency, and maximum operating temperature are observed to be maximized for structures with an average doping of 2 − 3 ϫ 10 17 cm −3 , corresponding to a sheet density of about 1.5ϫ 10 12 cm −2 .
A monolithic coupling scheme in which two active waveguides merge into a single waveguide is presented for a GaAs∕AlGaAs quantum cascade laser. The evolving fields interfere and a constant phase is observed in the Y-shaped laser cavity, resulting in a far field pattern of a double slit. The mode distribution is comprehensively derived by matching the far field profiles to simulated values and shows a weak current dependence. The device demonstrates the feasibility of coherent laser resonators with prospective applications in interferometric sensing and high power laser arrays.
Time-resolved transmission spectroscopy of a mid-infrared quantum cascade laser emitting at 11.7 mum allows us to iteratively retrieve the effective refractive index and the extinction coefficient of the gain medium in a broad spectral range with an accuracy of +/-7x10(-3). Besides a 3% slowdown of the group velocity we find a large induced group-velocity dispersion with changing signs in the vicinity of the gain maximum, disclosing implications for self-pulse formation in quantum-cascade lasers. Additionally we measured the temperature in the active region by exploiting the thermo-optic effect. A linear behavior with respect to the current and the duty cycle was observed.
A hybrid GaAs quantum cascade laser system obtained by Au–Au thermocompression bonding epilayer down onto gold coated silicon substrates is presented in this paper. The performance of the hybrid laser in low-duty-cycle pulsed operation in comparison to an unbonded one was not deteriorated. The lasers run with a threshold of 4.6kA∕cm2, emit around 12μm, and with a maximum optical output power of 550mW at cryogenic temperatures. The key advantage of such hybrid chips is the possibility of integrating III-V cascade lasers with established silicon photonics technology, such as silicon-on-insulator waveguides, V-groove fiber coupling and microfluidics.
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