Jarosław Walczak

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.

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.

Numerical model of capacitance in vertical-cavity surface-emitting lasers

In this paper we present a model of impedance and modulation time constants for vertical-cavity surface-emitting lasers (VCSELs) operating above threshold current. A 3D numerical model of potential distribution in the device under a constant bias is used to determine resistances and capacitances of an appropriate equivalent circuit. The model has been verified by comparing the theoretical and measured impedance as a function of frequency Z(f). The measured Z(f) is determined from S 11 small signal modulation experiments. The comparison has been performed for frequencies up to 40 GHz and a wide range of above threshold currents, for two oxide-confined VCSELs of different aperture diameters. We obtained a very good quantitative agreement for frequencies up to about 15 GHz and qualitative agreement over the entire range of currents and frequencies.

Transverse mode discrimination in long-wavelength wafer-fused vertical-cavity surface-emitting lasers by intra-cavity patterning

Transverse mode discrimination is demonstrated in long-wavelength wafer-fused vertical-cavity surface-emitting lasers using ring-shaped air gap patterns at the fused interface between the cavity and the top distributed Bragg reflector. A significant number of devices with varying pattern dimensions was investigated by on-wafer mapping, allowing in particular the identification of a design that reproducibly increases the maximal single-mode emitted power by about 30 %. Numerical simulations support these observations and allow specifying optimized ring dimensions for which higher-order transverse modes are localized out of the optical aperture. These simulations predict further enhancement of the single-mode properties of the devices with negligible penalty on threshold current and emitted power.

Numerical Analysis of Mode Discrimination by Intracavity Patterning in Long-Wavelength Wafer-Fused Vertical-Cavity Surface-Emitting Lasers

This paper presents an extensive numerical analysis of 1.3-μm wavelength wafer-fused vertical-cavity surface-emitting lasers (VCSELs) incorporating intracavity patterning. Using a 3-D, self-consistent model of the physical phenomena in VCSELs, supported by experimental results used for parameter calibration, we investigate the influence of arch-and ring-shaped intracavity features with a broad range of geometrical parameters on the modal behavior of the VCSEL. To design and optimize the devices, we used intracavity patterning that provides very strong discrimination of higher order modes, pushing them out from the active region. This mechanism makes possible single mode operation under a broad range of currents and could potentially enhance the single-mode output power of these devices.

High-power 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/InPAlGaAs/ GaAs gain mirrors with intra-cavity diamond heat-spreaders demonstrate very low thermal impedance of 4 K/W. Maximum CW output of devices with5 groups of quantum wells show CW output power of 2.7 W from 180μm apertures in both 1300-nm and 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 devices emit a high quality beam with M² beam parameter below 1.6 allowing reaching a coupling efficiency into a single mode fiber as high as 70 %. Maximum value of output power of 6.6 W was reached for 1300nm wavelength devices with 290μm aperture size.

Improved single-mode emission characteristics of long-wavelength wafer-fused vertical-cavity surface-emitting lasers by intra-cavity patterning

We report on transverse mode discrimination in long-wavelength wafer-fused vertical-cavity surface-emitting lasers (VCSELs) incorporating ring-shaped air gap patterns at the fused interface between the active region and the top distributed Bragg reflector (DBR). These 60-nm deep patterns were implemented with the aim of favoring the fundamental mode while preserving high output power. The VCSELs under consideration emit in the 1310-nm band and incorporate an AlGaInAs-based quantum well active region, a regrown circular tunnel junction and undoped GaAs/AlGaAs DBRs. A large batch of devices with varying pattern dimensions was investigated by on-wafer mapping, allowing significant statistical analysis leading to conclusions on their typical behavior. We observe experimentally a dependence of the side-mode suppression ratio on the geometrical parameters of the patterns. In particular, we identified a design that statistically increases the maximal single-mode emitted power by more than 20%. Numerical simulations of the patterned-cavity VCSELs based on our fully three dimensional electrical, thermal and optical VCSEL computational model support these observations. They show that patterns with a large inner diameter actually confine the first-order transverse mode and enhance its modal gain. In smaller devices, this mode is pushed out of the optical aperture and suffers larger losses. Optimized parameters were found numerically for enhancing the single-mode properties of the devices with negligible penalty on emitted power and threshold current.

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.

VCSEL modeling with self-consistent models: From simple approximations to comprehensive numerical analysis

In the talk we show the process of modeling complete physical properties of VCSELs and we present a step-by-step development of its complete multi-physics model, gradually improving its accuracy. Then we introduce high contrast gratings to the VCSEL design, which strongly complicates its optical modeling, making the comprehensive multi-physics VCSEL simulation a challenging task. We show, however, that a proper choice of a self-consistent simulation algorithm can still make such a simulation a feasible one, which is necessary for an efficient optimization of the laser prior to its costly manufacturing.

Electrically Pumped Vertical-External-Cavity Surface-Emitting Lasers With Patterned Tunnel Junction for Single Transversal-Mode Emission

This paper reports on a numerical analysis of methods for current injection into AlInGaAs/InP tunnel-junction electrically pumped vertical-external-cavity surface-emitting lasers. The tunnel junction is patterned to minimize the current crowding effect and support the fundamental transverse modes. Optimization of the tunnel junction radius predicts 9-mW emission and 4% wall-plug efficiency in the single-mode regime. Additional patterning of the tunnel junction in the form of a coaxial ring, without modifying its total radius but reducing its area, maintains or improves the emitted power and in addition enhances wall-plug efficiency by around 60%. A design of E-VECSEL is proposed which offers five times larger emitted power and wall-plug efficiency in the single-mode regime in comparison to recently reported experimental devices.