Lukasz Piskorski

Comparison of Usability of Oxide Apertures and Photonic Crystals Used to Create Radial Optical Confinements in 650-nm GaInP VCSELs

Threshold characteristics of GaAs-based 650-nm gallium indium phosphide (GalnP) vertical-cavity surface-emitting diode lasers (VCSELs) with two different optical confinement structures are investigated with the aid of a self-consistent, fully-physical VCSEL model. Efficacy of the optical confinement introduced by the oxide aperture is compared with an alternative single-defect photonic-crystal design with holes etched throughout the whole VCSEL. Initially, photonic-crystal VCSEL reveals 10% lower threshold electrical power than that of the analogous oxide-confined VCSEL. Further optimization of the current injection allows for an additional 20% threshold reduction. The photonic-crystal confinement concept appears to be a very prospective solution for VCSEL configurations, for which oxidation is unfeasible, e.g., for possible nitride or phosphide VCSELs.

A Possibility to achieve emission in the mid-infrared wavelength range from semiconductor laser active regions

In the present paper the results of the computer analysis of the arsenide-based (GaInNAs/AlGaInAs) and antimonide-based (GaInAsSb/AlGaAsSb) active regions emitting in the mid-infrared wavelength region are presented. Quantum well material contents and strain dependencies on the maximal gain are investigated. It is shown that above 3 μm the maximal gain obtained for arsenide-based active region is very low, irrespective of the nitrogen content and compressive strain in GaInNAs. Much higher optical gain in this wavelength range can be obtained for antimonide-based active region, which offers relatively high gain even at 5 μm, when the indium content in GaInAsSb and compressive strain in this layer are higher than 80% and 1.5%, respectively.

Automated self-consistent approach to modeling of photonic devices

In the talk a new automated and self-consistent approach to modeling photonic devices is presented. Is is based on a new software being developed at Lodz University of Technology and its main idea is automated consideration of mutual interactions between various physical phenomena taking place in photonic devices. The software consists of several solvers that can model temperature distribution within the investigated structure, the electric current flow and carriers diffusion, the optical eigenmodes of the analyzed cavity or waveguide and the light-matter interaction. Results of the modeling performed with one solver are automatically provided as the input state of another one, and the calculations are performed in a user-controlled self-consistent loop. In the talk the basic idea of the approach is presented and it is supported by examples of simulation results of semiconductor lasers.

Transverse-mode selectivity in antimonide-based vertical-cavity surface-emitting lasers

In this work results of a threshold operation of antimonide-based tunnel-junction (TJ) VCSEL have been presented with the aid of the comprehensive fully self-consistent optical-electrical-thermal-recombination numerical model. Calculations have been carried out for the structure with GaInAsSb/GaSb active region emitting at 2.6 μm. In order to suppress higher-order transverse modes in the device three different methods have been used. It has been shown that each of these methods allows us to achieve lasing with the LP01 mode for structure with TJ diameter of 8 μm, which has not been possible for the structure without modifications. Although using these methods leads to higher values of the threshold current, the drop of the maximal operating temperature for the structure with TJ diameter of 7 μm has not been higher than 10 K.

Concept of the CW GaN-based VECSEL

A concept and numerical study of a continuous-wave (CW) nitride-based vertical-external-cavity surface-emitting laser (VECSEL) with an InGaN/GaN active region is presented. The structure is designed to generate radiation around 450 nm. An array of nitride-based continuous-wave laser diodes is proposed to pump directly the quantum wells in the active region. We expect that it enables CW operation of the presented laser, in contrast to the GaN-based VECSELs demonstrated so far. Moreover, employing in-well pumping instead of barrier pumping reduces pump-laser quantum defect, which contributes to better thermal properties of the device. An external efficiency as high as 26% can be theoretically achieved by using a special multi-pass pump setup.

Optical simulations of blue and green semipolar InGaN/GaN lasers

III-N-based edge-emitting lasers suffer from low refractive index contrast between GaN, AlGaN and InGaN layers, conventionally used in their epitaxial structures. This issue becomes more severe with an increase in wavelength at which those devices operate when tuning from blue-violet to real blue and green light. To overcome this issue and to increase the refractive index contrast other materials must be employed within the epitaxial structures replacing the standard nitride layers with materials with lower refractive index. We demonstrate results of effective-index numerical calculations performed for the state-of-the-art semipolar real blue (471 nm) and green (518 nm) edge-emitting lasers with structural modifications that include ITO, AlInN, plasmonic GaN:Ge and nanoporous GaN layers. Such solutions are extensively investigated for III-N-based EELs operating in blue-violet region but only separately. Using combination of these solutions we managed to increase optical confinement factor over twice in blue- and over 3.5-times in green-EELs.

Numerical analysis of suppression of the higher order modes in nitride VCSELs using an inverted surface relief

This paper presents a comprehensive numerical study on the surface relief technique implemented in nitride Vertical-Cavity Surface-Emitting Laser (VCSEL) emitting in the 414-nm range. We calculated the threshold currents and optical modes in VCSEL structures with and without a surface relief. A standard structure was based on the first continuous-wave nitride VCSEL reported to operate at room temperature. We analysed the effect of higher order modes suppression in such devices.

Performance characteristics of GaSb-based TJ-VCSELs with emission wavelength above 2.6 µm

In this paper we present the results of the computer simulation of the GaSb-based multi-quantum-well GaInAsSb/GaSb vertical-cavity surface-emitting lasers (VCSELs) with the emission wavelength above 2.6 μm. Calculations have been performed with the aid of the comprehensive fully self-consistent numerical model developed by our group. The model combines electrical, thermal, gain, and optical effects, together with the mutual interactions between individual physical processes. For the selected active regions with various material contents and strains the influence of the ambient temperature and tunnel-junction diameter on continuous-wave performance characteristics has been taken into account. The results of the numerical analysis show that with the use of optimised active region it is possible to obtain stable single-fundamental-mode low-threshold operation of VCSEL with emission close to 2.8 μm. This wavelength is 0.2 μm longer than values reported so far for similar devices.

Simulation and optimization of 2.6–2.8 μm GaSb-based vertical-cavity surface-emitting lasers

We present the simulation results of threshold operation of mid-infrared GaSb-based vertical-cavity surface-emitting lasers obtained with the use of comprehensive fully self-consistent optical-electrical-thermal-recombination numerical model. The results show that by a proper design of the active region it is possible to achieve the stable single-fundamental-mode low-threshold operation with emission wavelengths longer than those reported so far for similar devices.

Numerical study of the influence of pumping beam parameters on VECSEL performance

In the paper we present results of our simulations of the influence of pumping beam parameters on power transfer characteristics of an optically pumped vertical-external-cavity surface-emitting laser (VECSEL). Calculations have been done with the aid of the comprehensive, fully self-consistent numerical model developed by our group. The research has focused mainly on an influence of the pumping beam size and shape on thermal and optical properties as well as power scaling of the modelled laser. Various beam profiles, such as: Gaussian, super-Gaussian and top-hat, have been investigated. An analysis of the optimal width of the emitted beam within the structure volume for pumping beams of different shapes has been also carried out.