Robert P. Sarzała

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.

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.

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.

Double-diamond high-contrast-gratings vertical external cavity surface emitting laser

A new design of vertical external cavity surface emitting laser (VECSEL) with diamond-based high contrast gratings is proposed. The self-consistent model of laser operation has been calibrated based on experimental results and used to optimize the new proposed device and to perform comparative thermal and optical analysis of conventional and double-diamond high-contrast-grating VECSELs. The proposed design considerably reduces the dimensions and complexity of the device and provides up to 80% increase of the maximum emitted power as compared with the conventional design.

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.

Separate-confinement-oxidation vertical-cavity surface-emitting laser structure

In the present paper, a comprehensive self-consistent three-dimensional model is used to analyze physical aspects of the operation of oxide-confined vertical-cavity surface-emitting diode lasers (VCSELs) and to optimize their structures. The impact of the built-in radial confining mechanisms created by oxide apertures, i.e., the influence of their diameters and localizations on radial confinements of both the current injection into VCSEL active regions and electromagnetic fields of successive cavity modes, has been investigated. Basically, there are two extreme cases: the index-guided (IG) VCSELs with the aperture localized at the antinode position of the optical standing wave, characterized by a very low lasing threshold but exhibiting rather poor mode selectivity, and the gain-guided (GG) VCSELs with the aperture shifted to the node position, ensuring usually the single-fundamental-mode operation, but at the expense of much higher lasing threshold. In the present paper, the separate-confinement-oxidatio...

Microthermography of diode lasers: The impact of light propagation on image formation

We analyze the effect of propagating infrared thermal radiation within a diode laser on its thermal image taken by a thermocamera. A ray-tracing analysis shows that this effect substantially influences image formation on a spatial scale of 10 μm, i.e., in the domain of microthermography. The main parameter affecting the thermal radiation spread in the semitransparent semiconductor structure is the free carrier concentration in the substrate, governing its absorption. Two applications are presented: a quantum dot laser and a quantum-well laser, where independent thermal models are developed using the finite element method (FEM). Our ray-tracing analysis verifies the FEM simulated temperature profiles by interlinking them to experimental temperature maps obtained through microthermography. This represents a versatile experimental method for extracting reliable bulk-temperature data from diode lasers on a microscopic scale.

Photonic Crystal VCSELs: Detailed Comparison of Experimental and Theoretical Spectral Characteristics

We present a detailed comparison of experimental and simulated optical spectra obtained from a 980-nm photonic-crystal (PhC) VCSEL. We demonstrate good qualitative agreement of the experimental spectra with the calculated emitted wavelengths for number of VCSEL structures with different PhC designs. We show the statistical analysis which reveals that strong confinement introduced by the photonic crystal contributes to the conformity between experiment and theory. For shallow etching of the photonic crystal holes, narrow optical aperture, and large diameter air-holes, we observe that diffraction and mode leakage through the PhC holes becomes the dominating phenomena, and then any fabrication imperfection may contribute to discrepancy between theory and experiment.

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.

Thermal management of GaInNAs/GaAs VECSELs

Different methods used to reduce temperature increase within the active region of vertical-external-cavity surface-emitting lasers (VECSELs) are described and compared with the aid of the self-consistent thermal finite-element method. Simulations have been carried out for the GaInNAs/GaAs multiple-quantum-well (MQW) VECSEL operating at room temperature at 1.31 μm. Main results are presented in form of ‘thermal maps’ which can be simply used to determine maximal temperature of different structures at specified pumping conditions. It has been found that these maps are also appropriate for some other GaAs-based VECSELs and can be very helpful especially during structure designing. Moreover, convective and thermal radiation heat transfer from laser walls has been investigated.