HAROLD

HAROLD is a Schrödinger/drift/diffusion QW laser model and gain function calculator that be used to add detailed hetero-structure modelling to PICWAVE, or as a stand alone product.

In 1D mode, HAROLD solves the appropriate differential equations in the vertical direction for a quantum well laser with arbitrary vertical multiple-structure and composition. Both single and multiple quantum well lasers can be modelled. A state of the art capture/escape model for carriers in quantum wells is implemented. Both pulsed (isothermal) and CW (self-heating) operation conditions can be simulated. Materials include ternary and quaternary alloys.

In 2D mode, Harold will model longitudinal effects as well for simple Fabry-Perot cavities.


XY Laser Module

Harold's XY Laser Module extends Harold’s algorithm so that the lateral structure of laser devices is accounted for. It uses the same physical model as a Harold 1d simulation but solves the electrical/optical/thermal problem on a 2D (XY) grid, the starting point being a 2D cross-section, rather than a single 1D epilayer stack. In addition, it supports insulating layers and graded etching and allows n and p-contacts can be on the top of the structure. All this makes it ideal for the detailed modelling of simple ridge waveguide and SOI hybrid laser structures alike.


Platforms

PC: x86+x64: Win2000/XP/Vista, 1GB RAM, 2GHz or better recommended.


Features

Electrical model - Self consistent solution of Poisson Equation, drift-diffusion, and capture/escape for both holes and electrons.
Thermal model - Full vertical-longitudinal solution of the heat flow equation, including the substrate, the metal contacts and the heat sinks. Power dissipation is treated locally and includes Joule, non-radiative recombination, free carrier absorption, excess power distribution, mirror scattering and mirror absorption.
Optical model - Photon distribution according to the optical mode of the laser cavity. The total photon density is determined considering the gain/loss balance in the full cavity.
Capture/escape - In QW regions, thermal equilibrium between confined and unconfined carriers is not assumed, but described by means of appropriate capture/escape balance equations.
Quaternary alloys - Utilization of quaternary alloys is fully supported through the material database.
Gain model - Material gain for quantum well lasers is computed as a function of the wavelength and carrier concentration, using a parabolic band approximation.
Recombination - Shockley-Read-Hall, Auger, stimulated and spontaneous recombination processes are included. Advanced features, such as arbitrary specification of deep trap levels, are allowed on a layer-per-layer basis.
Surface recombination - Recombination at the facets is included via deep trap levels at the mirror.
Bandgap narrowing - Carrier-induced band-gap narrowing is included.
Quantum well - The program will determine the energy levels by solving Schrödinger's equation; this data is then used in the gain computations.
Strain - The effect of strain on the quantum well levels is included.
Thermal overhang - Heat-sink overhang is implemented.
Non-injecting mirror - Suppression of current injection at the mirrors is implemented.
Absorbing mirror - Photon absorption attenuation at the mirrors is implemented


Example: – Facet Heating


The adjacent figure presents the results of a 2D Harold simulation showing the temperature rise towards the facet of a high power laser.


Example 2 – Heating mechanisms in high power laser


The adjacent figure is an analysis of the main heating mechanisms in a high power pump laser:


P-exc : excess power - spontaneously emitted photons and scattered stimulated emission.
P-nr : non-radiative recombination
P-joule : joule heating
P-fc : free-carrier absorption