Włodzimierz Nakwaski

Effective masses of electrons and heavy holes in GaAs, InAs, A1As and their ternary compounds

Abstract A comparative survey of known experimental and theoretical values of heavy-hole and electron effective mass in GaAs, InAs, and A1As is presented in this work. Recommended room-temperature values of these parameters are given for the above binary solutions and for their ternary compounds.

Transient thermal properties of high-power diode laser bars

The transient thermal properties of high-power diode laser bars with active and passive cooling are analyzed experimentally with thermal imaging and through their thermal wavelength tuning behavior and modeled with the finite element method.

Thermal analysis of GaAs-AlGaAs etched-well surface-emitting double-heterostructure lasers with dielectric mirrors

A comprehensive self-consistent thermal-electrical model is described and used to investigate thermal properties of GaAs-AlGaAs etched-well double-heterostructure vertical-cavity surface-emitting lasers (VCSELs) with dielectric mirrors. Special attention is paid to effects of varying the active-region diameter on thermal behavior of the device. The active-region diameter is optimized with the goal of reducing the relative power loss due to heating and maximizing the optical output power. The optimal diameter, at which the excess of pumping current over the CW lasing threshold at the corresponding active-region temperature is maximum, is 16 mu m. >

Transverse modes in gain-guided vertical-cavity surface-emitting lasers

An analytical approximate form of the lowest-order transverse modes is proposed for gain-guided vertical-cavity surface-emitting lasers for the first time. Central intensity maxima of higher-order modes are found to disappear. Therefore the number of intensity maxima on experimental near-field intensity profiles cannot be used as an indicator of the mode order.

Thermal analysis of the catastrophic mirror damage in laser diodes

A new thermal analysis of a catastrophic mirror damage in laser diodes is presented in the present paper. Three‐dimensional heat spreading and temperature dependence of a thermal conductivity is taken into account in the model. Both an active layer heating and a nonradiative recombination of carriers generated by absorbed radiation in an active area close to a facet mirror are considered as heat sources. The model is strictly correct for times ranging from 6.2 to 500 nsec for a standard stripe laser diode, i.e., for currents not higher than 4.5 A and not lower than 0.8 A. The analytical solution of the thermal conduction equation gives a dependence of a catastrophic‐degradation time, i.e., a permissible length of current pulses from a point of view of the catastrophic mirror damage, on the amplitude of the pulses for the standard stripe laser diode.

Room-temperature continuous-wave operation of the In(Ga)As/GaAs quantum-dot VCSELs for the 1.3 µm optical-fibre communication

Efficient room-temperature (RT) continuous-wave (CW) lasing operation of the 1.3 µm MBE (molecular-beam epitaxy) In(Ga)As/GaAs quantum-dot (QD) top-emitting oxide-confined vertical-cavity surface-emitting diode lasers (VCSELs) for the second-generation optical-fibre communication has been achieved. In their design, a concept of a QD inside a quantum well (QW) has been utilized. The proposed In(Ga)As/GaAs QD active region is composed of five groups of three 8 nm In0.15Ga0.85As QWs, each containing one InAs QD sheet layer. In each group located close to successive anti-node positions of the optical standing wave within the 3λ cavity, QWs are separated by 32 nm GaAs barriers. Besides, at both active-region edges, additional single InGaAs QWs are located containing single QD layers. For the 10 µm diameter QD VCSELs, the RT CW threshold current of only 6.2 mA (7.9 kA cm−2), differential efficiency of 0.11 W A−1 and the maximal output power of 0.85 mW have been recorded. The experimental characteristics are in excellent agreement with theoretical ones obtained using the optical-electrical-thermal-recombination self-consistent computer model. According to this, for the 10 µm devices, the fundamental linearly polarized LP01 mode remains the dominating one up to the current of 9.1 mA. The lowest RT CW lasing threshold below 5 mA is expected for 6 µm devices.

III: Thermal Properties of Vertical-Cavity Surface-Emitting Semiconductor Lasers

Publisher Summary This chapter reviews the temperature-dependent phenomena in vertical-cavity surface-emitting lasers (VCSELs). Compared to edge-emitting lasers (EELs), VCSELs have a number of unique features that make them potentially more immune to damage caused or accelerated by external ambient. The chapter discusses various comprehensive approaches used to model thermal properties of VCSELs. The chapter focuses on the main differences between properties of VCSELs and EELs and discusses the experimental data on various device characteristics affected by temperature. The chapter presents temperature-related effects on VCSEL performance, including the temperature dependence of the longitudinal mode spectra, the transverse-mode structure, the threshold current, and the output power. The basics of thermal VCSEL modeling are also illustrated in the chapter. The chapter describes comprehensive analytical and numerical thermal models of VCSELs, which are especially important if device design needs to be optimized.

77 K operation of AlGaAs/GaAs quantum cascade laser at 9 um

The paper presents the way that colour can serve solving the problem of calibration points indexing in a camera geometrical calibration process. We propose a technique in which indexes of calibration points in a black-and-white chessboard are represented as sets of colour regions in the neighbourhood of calibration points. We provide some general rules for designing a colour calibration chessboard and provide a method of calibration image analysis. We show that this approach leads to obtaining better results than in the case of widely used methods employing information about already indexed points to compute indexes. We also report constraints concerning the technique. Nowadays we are witnessing an increasing need for camera geometrical calibration systems. They are vital for such applications as 3D modelling, 3D reconstruction, assembly control systems, etc. Wherever possible, calibration objects placed in the scene are used in a camera geometrical calibration process. This approach significantly increases accuracy of calibration results and makes the calibration data extraction process easier and universal. There are many geometrical camera calibration techniques for a known calibration scene [1]. A great number of them use as an input calibration points which are localised and indexed in the scene. In this paper we propose the technique of calibration points indexing which uses a colour chessboard. The presented technique was developed by solving problems we encountered during experiments with our earlier methods of camera calibration scene analysis [2]-[3]. In particular, the proposed technique increases the number of indexed points points in case of local lack of calibration points detection. At the beginning of the paper we present a way of designing a chessboard pattern. Then we describe a calibration point indexing method, and finally we show experimental results. A black-and-white chessboard is widely used in order to obtain sub-pixel accuracy of calibration points localisation [1]. Calibration points are defined as corners of chessboard squares. Assuming the availability of rough localisation of these points, the points can be indexed. Noting that differences in distances between neighbouring points in calibration scene images differ slightly, one of the local searching methods can be employed (e.g. [2]). Methods of this type search for a calibration point to be indexed, using a window of a certain size. The position of the window is determined by a vector representing the distance between two previously indexed points in the same row or column. However, experiments show that this approach has its disadvantages, as described below. * E-mail: A.Nowakowski@ire.pw.edu.pl Firstly, there is a danger of omitting some points during indexing in case of local lack of calibration points detection in a neighbourhood (e.g. caused by the presence of non-homogeneous light in the calibration scene). A particularly unfavourable situation is when the local lack of detection effects in the appearance of separated regions of detected calibration points. It is worth saying that such situations are likely to happen for calibration points situated near image borders. Such points are very important for the analysis of optical nonlinearities, and a lack of them can significantly influence the accuracy of distortion modelling. Secondly, such methods may give wrong results in the case of optical distortion with strong nonlinearities when getting information about the neighbouring index is not an easy task. Beside this, the methods are very sensitive to a single false localisation of a calibration point. Such a single false localisation can even result in false indexing of a big set of calibration points. To avoid the above-mentioned problems, we propose using a black-and-white chessboard which contains the coded index of a calibration point in the form of colour squares situated in the nearest neighbourhood of each point. The index of a certain calibration point is determined by colours of four nearest neighbouring squares (Fig.1). An order of squares in such foursome is important. Because the size of a colour square is determined only by the possibility of correct colour detection, the size of a colour square can be smaller than the size of a black or white square. The larger size of a black or white square is determined by the requirements of the exact localisation step which follows the indexing of calibration points [3]. In this step, edge information is extracted from a blackand-white chessboard. This edge information needs larger Artur Nowakowski, Wladyslaw Skarbek Institute of Radioelectronics, Warsaw University of Technology, Nowowiejska 15/19, 00-665 Warszawa, A.Nowakowski@ire.pw.edu.pl Received February 10, 2009; accepted March 27, 2009; published March 31, 2009 http://www.photonics.pl/PLP

Thermal analysis of closely-packed two-dimensional etched-well surface-emitting laser arrays

A self-consistent thermal-electrical model of etched-well surface-emitting GaAs-AlGaAs lasers is applied to study thermal properties of two-dimensional (2-D) arrays. Temperature profiles across small- and moderate-size arrays are generated. Thermal problems associated with integration of vertical-cavity surface-emitting lasers (VCSELs) into closely packed 2-D arrays are addressed. In particular, thermal crosstalk between elements of the array is investigated. The results indicate severe thermal crosstalk, even at relatively low pumping currents, with strong individual-element temperature-profile nonuniformities. The asymmetry of individual waveguides caused by skewed temperature distributions can be exploited for controlling supermode structure in phase-locked arrays. Optimization of 2-D etched-well laser array designs is presented, aimed at maximizing the optical output power density from the array. We find that the highest output power density is strongly increasing for arrays of small diameter emitters, and that the optimal center-to-center spacing between emitters is equal to /spl sim/2.5-3 times their diameter. >

Self-consistent model of 650 nm GaInP/AlGaInP quantum-well vertical-cavity surface-emitting diode lasers

A comprehensive fully self-consistent model of oxide-confined GaAs-based vertical-cavity surface-emitting diode lasers (VCSELs) with GaInP/AlGaInP quantum-well active regions to simulate their room-temperature (RT) continuous-wave (CW) operation is presented. The model takes into consideration all observed or expected special features of GaInP/AlGaInP VCSELs. A complete set of model parameters is given. The model enables a deeper understanding of a VCSEL operation with full complexity of many inter-related physical phenomena taking place within its volume. It may also be used to design and optimize the above VCSEL structures for their numerous applications, in particular as sources of the 650 nm carrier wave in communication systems using plastic optical fibres. With the aid of this model, anticipated VCSEL RT CW performance characteristics may be determined.