Tomasz Czyszanowski

Monolithic high-index contrast grating: a material independent high-reflectance VCSEL mirror

In this paper we present an extensive theoretical and numerical analysis of monolithic high-index contrast grating, facilitating simple manufacture of compact mirrors for very broad spectrum of vertical-cavity surface-emitting lasers (VCSELs) emitting from ultraviolet to mid-infrared. We provide the theoretical background explaining the phenomenon of high reflectance in monolithic subwavelength gratings. In addition, by using a three-dimensional, fully vectorial optical model, verified by comparison with the experiment, we investigate the optimal parameters of high-index contrast grating enabling more than 99.99% reflectance in the diversity of photonic materials and in the broad range of wavelengths.

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.

Optimal photonic-crystal parameters assuring single-mode operation of 1300 nm AlInGaAs vertical-cavity surface-emitting laser

We present a self-consistent analysis of InP-based 1300 nm AlInGaAs photonic-crystal vertical-cavity surface-emitting lasers (PhC VCSELs) and tunnel-junction PhC VCSELs, and analyze the influence of the electrical confinement, the PhC hole diameter and etching depth, and the size of the single defect optical aperture on the threshold current and the transverse mode discrimination. We also investigate the thermal performance of the two VCSEL configurations. As a result we determine the optimal PhC parameters assuring stable, single-mode operation in a broad range of driving currents.

Numerical Self-Consistent Analysis of VCSELs

Vertical-cavity surface-emitting lasers (VCSELs) yield single-longitudinal-mode operation, low-divergence circular output beam, and low threshold current. This paper gives an overview on theoretical, self-consistent modelling of physical phenomena occurring in a VCSEL. The model has been experimentally confirmed. We present versatile numerical methods for nitride, arsenide, and phosphide VCSELs emitting light at wavelengths varying from violet to near infrared. We also discuss different designs with respect to optical confinement: gain guidance using tunnel junctions and index guidance using oxide confinement or photonic crystal and we focus on the problem of single-transverse-mode operation.

Wafer-Fused Optically Pumped VECSELs Emitting in the 1310-nm and 1550-nm Wavebands

1300-nm, 1550-nm, and 1480-nm wavelength, optically pumped VECSELs based on wafer-fused InAlGaAs/InP-AlGaAs/GaAs gain mirrors with intracavity diamond heat spreaders are described. These devices demonstrate very low thermal impedance of 4 K/W. Maximum CW output of devices with 5 groups of quantum wells shows CW output power of 2.7 W from 180  μm apertures in both the 1300-nm and the 1550-nm bands. Devices with 3 groups of quantum wells emitting at 1480 nm and with the same aperture size show CW output of 4.8 W. These VECSELs emit a high-quality beam with 𝑀 2 beam parameter below 1.6 allowing reaching a coupling efficiency as high as 70% into a single-mode fiber. Maximum value of output power of 6.6 W was reached for 1300 nm wavelength devices with 290  μm aperture size. Based on these VECSELs, second harmonic emission at 650 nm wavelength with a record output of 3 W and Raman fiber lasers with 0.5 W emission at 1600 nm have been demonstrated.

Precise Lateral Mode Control in Photonic Crystal Vertical-Cavity Surface-Emitting Lasers

We demonstrate an oscillatory behavior of resonant wavelengths and threshold gains of the fundamental and first-order transverse mode of photonic crystal vertical-cavity surface-emitting laser (PhC VCSEL) with the PhC etching depth. To this aim we use a full vectorial, 3-D optical model (plane wave admittance method) combined with a thermal model and an exemplary 1300 nm quantum-dot VCSEL structure. Such oscillatory behavior poses a strong restriction on the etching depth precision: about 0.1 μm in order to achieve a threshold gain not higher than 10% the threshold gain minimum and twice higher precision for simultaneous strong discrimination of the first-order transverse mode.

Transverse mode control in high-contrast grating VCSELs

This paper presents an extensive numerical analysis of a high-contrast grating VCSEL emitting at 0.98 μm. Using a three-dimensional, fully vectorial optical model, we investigate the influence of a non-uniform grating with a broad range of geometrical parameters on the modal behavior of the VCSEL. Properly designed and optimized, the high-contrast grating confines the fundamental mode selectively in all three dimensions and discriminates all higher order modes by expelling them from its central region. This mechanism makes single mode operation possible under a broad range of currents and could potentially enhance the single-mode output power of such devices. The high-contrast grating design proposed here is the only design for a VCSEL with three-dimensional, selective, optical confinement that requires relatively simple fabrication.

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.

Monolithic Subwavelength High-Index-Contrast Grating VCSEL

In this letter, we propose and numerically investigate a new vertical-cavity surface-emitting laser (VCSEL) structure consisting of a nearly lambda-thick active optical cavity sandwiched between two planar monolithic subwavelength high-index-contrast gratings (MHCGs) etched directly into the semiconductor layers surrounding the optical cavity. The structure allows the reduction of the vertical thickness of the subsequent MHCG VCSEL to roughly 0.6 μm for emission at 980 nm. Compared with a conventional all-semiconductor VCSEL with distributed Bragg reflector mirrors, the MHCG VCSEL has a shorter effective cavity length and thus a shorter roundtrip cavity time. Our proposed design enables the fabrication of VCSELs with lattice-matched mirror layers in all common semiconductor optoelectronic material systems, or alternatively VCSELs with hybrid HCGs.

Comparison of Exactness of Scalar and Vectorial Optical Methods Used to Model a VCSEL Operation

In the paper, a comparison between results of the optical scalar and vectorial optical methods, using the scalar effective frequency method and the vectorial method of lines, respectively, as their typical examples, applied for simulating an operation of vertical-cavity surface-emitting diode lasers (VCSELs) is presented. Both optical approaches has been applied to simulate an operation of the standard 1.3-mum GaAs-based oxide-confined GaInAsN double quantum-well VCSEL, but comparison conclusions seem to be more general and concerns all VCSELs. Validity limits of the simplified scalar approach have been determined by comparing its approximate results with more exact ones obtained with the aid of the accurate vectorial model. The scalar model has been found to be quite exact in the case of a determination of the wavelength of emitted radiation, whereas its exactness in the lasing threshold analysis is much worse, especially in the case of higher order modes, smaller aperture diameters and/or weak radial optical guidance. Our analysis leads also to more general designing conclusions concerning the optimal position and the thickness of the oxide layer assuring, respectively, the stable single mode operation and the lowest threshold gain