Pablo Moreno

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.

Ultraviolet and infrared femtosecond laser induced periodic surface structures on thin polymer films

This work demonstrates the formation of femtosecond laser induced periodic surface structures (LIPSS) by multipulse irradiation with the fundamental and 3rd harmonic of a linearly polarized Ti:sapphire laser (795 and 265u2009nm) on thin films of the polymers poly (ethylene terephthalate), poly (trimethylene terephthalate), and poly (carbonate bisphenol A) prepared by spin-coating. LIPSS, inspected by atomic force microscopy, are formed upon multiple pulse UV and IR irradiation with wavelength-sized period in a narrow range of fluences below the ablation threshold. Control and tunability of the size and morphology of the periodic structures become thus possible ensuring photochemical integrity of polymer films.

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.

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.

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.

Beam filamentation and maximum optical power in high-brightness tapered lasers

In this work we use a numerical model to analyze the beam filamentation in tapered lasers with the goal of optimizing the epitaxial structure. The model self-consistently solves the steady state electrical and optical equations for the flared unstable resonator. This model has been applied to simulate the performance of InGaAs/InGaAsP tapered lasers emitting at 975 nm. We investigate the role of the active material properties (carrier induced index change, differential gain) and of the epitaxial design (optical confinement factor) on the filamentation process and on the maximum achievable power.

High-power and high-brightness lasers with an Al-free active region at 915 nm

We have developed Al-free broad area lasers with low optical losses of 0.5 cm-1 and T0 = 171 K. Clarinet lasers deliver 0.65 W cw with an M2 of less than 1.3 at 1/e2. (2 pages)