J. Wykes

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.

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.

Hot-cavity modelling of high-power tapered laser diodes using wide-angle 3D FD-BPM

The effective design of high power tapered laser diodes requires a detailed understanding of the coupled nonlinear optical, electrical and thermal processes which take place in the cavity. These nonlinearities result in phenomena such as spatial hole burning, self-focussing and filamentation, all of which play a significant role at higher output powers. Consequently, care must be taken in optimising the design of these devices to maximise the output power whilst maintaining good beam quality. Simulation gives the device designer the ability to experiment with the numerous degrees of freedom available in the design of these laser diodes, thus minimising the expense and time incurred for fabrication.

Design of high power pump lasers for C-band EDFA amplifiers

High performance fibre EDFA amplifiers for dense WDM systems require efficient and economic pumping devices. One way of providing high pumping power to an EDFA amplifier at low cost is to use tapered semiconductor lasers. The development of a software package for the design and optimisation of these high power tapered laser diodes is described. Cold cavity modelling enables the influence of the laser geometry on the overall performance of the cavity to be investigated along with the beam spoiler design. A 2.5D hot cavity laser model also takes into account effects such as spatial hole burning, carrier diffusion and current spreading. This enables detailed investigation of the laser design and the factors limiting beam quality to be carried out. Our present research aims to incorporate a 3D model of the optical propagation into the laser model using wide-angle FD-BPM schemes, novel finite difference techniques, and modem matrix solvers to minimize memory usage and calculation time.

Numerical simulations of 3D micro-resonators

Micro-resonators are critical optical components that have many exciting applications in fields such as telecommunications, quantum cryptography and optical signal processing. Fabrication techniques allow many different designs of micro-resonator to be realised, but at present their optimisation and simulation remain firmly entrenched in 2D. The geometrical complexity of many micro-resonators mitigates against analytic study. Thus there is a strong demand for comprehensive 3D numerical simulations. We discuss some of the difficulties and challenges when modelling micro-resonators and recent progress towards their 3D modelling using time-domain codes.

Simulation methodologies for electromagnetic compatibility (EMC) and signal integrity (SI) for system design

Current technology trends require the utilisation of very high clock rates which have a broad electromagnetic spectrum. Electronic equipment designers require accurate characterisation and optimisation of electrical components, sub-systems and complete systems at frequencies that extend well into the microwave spectrum. This paper aims to assess the state-of-the-art in full field solvers in system and sub-system design and in doing so identify the trends in simulation techniques that are targeted towards the development of complex designs which operate at high speeds. Particular emphasis is placed on the treatment of multiscale problems, the development of macronodes containing sub-wavelength features and optimal meshing techniques. Developments in these areas are illustrated with results typical of EMC and SI design issues

Towards numerical vector Helmholtz solutions in integrated photonics

Much present day simulation and design for optoelectronics involves approximations due to the limitations of todays computer resources. For example, finite difference beam propagation (FD-BPM) methods assume that the propagation takes the form of an envelope function multiplied by a propagation factor. These approximations can limit the utility of present methods. The next generation of software must aim to eliminate these limitations, ideally correctly solving the vector Helmholtz equation subject to open boundary conditions. In this paper we will address how advances in our understanding, novel approaches and computer power are moving us towards this goal.

Desensitization of unstructured transmssion line modeling simulations to mesh characteristics

Flexible simulation solvers are paramount for the development of a wide range of modern technologies. Numerical techniques complement computationally efficient analytical approaches and offer ease of use and applicability to a wide range of applications. The Transmission Line Modeling Method has recently been extended to the domain of tetrahedral mesh descriptions of structure geometry and this presentation discusses a number of recent advances that affect its practical deployment.