L. Borruel

Nonlinear properties of tapered laser cavities

The nonlinear phenomena accompanying the process of light generation in high-power tapered semiconductor lasers are studied using a combination of simulation and experiment. Optical pumping, electrical overpumping, filamentation, and spatial hole burning are shown to be the key nonlinear phenomena influencing the operation of tapered lasers at high output powers. In the particular tapered laser studied, the optical pumping effect is found to have the largest impact on the output beam quality. The simulation model used in this study employs the wide-angle finite-difference beam propagation method for the analysis of the optical propagation within the cavity. Quasi-three-dimensional (3-D) thermal and electrical models are used for the calculation of the 3-D distributions of the temperature, electrons, holes, and electrical potential. The simulation results reproduce key features and the experimental trends.

Quasi-3-D simulation of high-brightness tapered lasers

We present a simulation tool useful to optimize the design of semiconductor tapered lasers and to study the physical processes inside of them. This is achieved by using a state-of-the-art quasi-three-dimensional (quasi-3-D) electrical and thermal model, coupled to a two-dimensional (2-D) wide-angle beam propagation method optical model. A calibration procedure of model parameters is proposed to contribute to the development of reliable simulation tools. Different laser diodes with a tapered gain section, emitting at 735 and 975 nm, are used to validate the model through the extensive comparison of experimental and simulated results. The suitability of 2-D and 3-D electrical, thermal, and optical models is discussed in terms accuracy and computational effort.

Beam Properties of 980-nm Tapered Lasers With Separate Contacts: Experiments and Simulations

The beam properties of 980-nm tapered lasers with separate current drives for the ridge waveguide and tapered sections are analyzed by means of a comparison between simulations and experimental results. The simulations are performed with a new model for this type of tapered lasers, providing a good qualitative agreement with experiments. The observed improvement in the beam quality by a stronger pumping of the ridge waveguide section with respect to the tapered section is attributed to the reduction of the backward field intensity. The simulations show that this improvement, far from being a general rule, depends on the details of the device geometry.

Modeling of patterned contacts in tapered lasers

We study the influence of a patterned contact design on the beam properties of high-brightness tapered lasers. A simple approach to simulate patterned injection has been developed and introduced into a quasi-three-dimensional tapered laser model. The method is applied to tapered lasers, whose performance is limited by two different mechanisms: self-focusing and poor modal filtering. The results show an improvement in beam quality in comparison to standard devices.

Self-consistent electrical, thermal, and optical model of high-brightness tapered lasers

A quasi-3D model has been developed with the aim of studying the different factors limiting the performance of high-brightness high-power tapered lasers. The model solves the complete semiconductor and thermal equations, neglecting the flow of carriers and heat along the cavity ax is, together with a 2D Wide-Angle Beam Propagation method solving the optical propagation. The coupling between electrical, thermal and optical equations yields a stable solution which incorporates carrier and temperature induced perturbations of the refractive index. Although tapered lasers have already demonstrated superior beam quality performance in comparison with broad area devices, they still suffer of beam filamentation at high power levels. We analyze the influence of the different competing factors in the self-focusing process for 980 nm lasers with a gain guided taper section. The simulation results indicate that the lasers with the longest taper section provide the highest output power before the filamentation process is triggered, and that the backward propagating field plays a crucial role in the stability of the output beam.

Clarinet laser: Semiconductor laser design for high-brightness applications

High-power and high-brightness continuous-wave (cw) operation has been achieved with an optimized design of fully index-guided tapered laser emitting at 975 nm. The device achieves simultaneously negligible astigmatism and stable low divergence in the lateral axis at high-power operation. By using a quasi-three-dimensional simulation model, the different mechanisms modifying the slow axis beam divergence at high power have been carefully balanced in the clarinet design, easing the use of collective optics in laser bars. The devices consist of a relatively long ridge-waveguide filtering section coupled to a relatively short tapered section with an aperture angle of 2°. InGaAs∕InGaAsP lasers were fabricated with this design, demonstrating an output power of 1 W cw, a maximum wall-plug efficiency of 50%, negligible astigmatism, a slow-axis far-field divergence (measured at 1∕e2) of 5° at 1 W and beam quality parameter M2<3.

Measurement of gain spectra, refractive index shift, and linewidth enhancement factor in Al-free 980-nm lasers with broadened waveguide

Measurements of the optical gain, differential refractive index and linewidth enhancement factor ((alpha) parameter) in 980 nm InGaAs/InGaAsP broad area lasers diodes are presented. Two different experimental configurations for the measurement of the Amplified Spontaneous Emission spectra, both using a spatial filtering technique, are compared. A new procedure for extracting the modal index change in the case of low optical confinement factor laser structures is proposed. We present and discuss the influence of the experimental technique, and of the data processing on the extracted value of the gain and ß parameter as a function of injection level.

A Self-Consistent CW Model of Unstable Cavity Semiconductor Lasers including Symmetrical and Antisymmetrical Solutions

We present a quasi-three dimensional (3D) CW simulation model for unstable cavity semiconductor lasers which propagates simultaneously a symmetrical and an antisymmetrical optical field along the cavity until a stable solution is found.

High brightness tapered lasers at 732 nm and 975 nm: experiments and numerical analysis

The 732 nm laser structure consists of a tensile strained GaAsP QW with AlGaAs confinement and cladding regions. The 975 nm structure comprises a strained InGaAs QW embedded in an Al-free optical cavity Both designs employ a large optical cavity to reduce the fast axis divergence and to decrease the tendency to filamentation, with similar values for the vertical confinement factor.

Quasi-3D optoelectronic modelling of 730 nm tapered laser diodes

Summary from only given. For the design and optimisation of laser structures predictive models are needed. Previous models which have the potential to reproduce results have been obtained experimentally. However the accuracy and generality of these models are limited by the use of the paraxial approximation in the beam propagation algorithms and reliance on a phenomenological electronic model based on 1D lateral carrier diffusion in the active region. In the laser model presented in this paper, both limitations have been addressed. The simulation results are shown to agree well with experiment. The model solves consistently the optical, electrical and thermal equations for tapered lasers, taking into account the carrier and temperature induced refractive index changes.