Harold

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.

Harold’s XY supports insulating layers, graded etching, and allows n and p-contacts to both be on the top of the structure. Its non-uniform simulation grid allows rigorous and efficient simulation of lateral current and heat spreading in the region below and either side of the active region/optical mode, which may extend for 100s of microns. In addition, it can simulate multimode operation and can simulate the change in the optical mode properties with increasing bias (hot-cavity effects). All this makes it ideal for the detailed modelling of a variety of laser designs, from simple ridge waveguide lasers to SOI hybrid lasers, high-power lasers with asymmetric waveguides and p-n blocking buried het lasers.

The XY Laser Module uses the Harold’s existing layers editor, trap definition editor and mesh policy editor, making it easy to adapt and use existing Harold projects to set up XY simulations. The XY Laser Module also has the same execution modes as a Harold 1D simulation: Test mode (for quick diagnostics), Isothermal (pulsed), and Self-Heating (CW) modes.

Cross-section editor

The XY Laser Module’s cross-section editor allows you to fully define a laser’s 2D cross-section. A cross-section is composed of a number of vertical slices, of varying widths, each of which uses its own (or a shared) epitaxial layer structure. Slices can be etched to varying depths and can also have graded etching. Each slice can have its top or bottom connected to the bias contact, the ground contact, or no contact at all.

The cross-section editor incorporates our powerful FDM Mode Solver which allows for detailed mode analysis including our Farfield Calculator. 

XY Cross-section Editor: A ridge waveguide structure with graded etching: in this case, all slices share a common layer structure; the bias contact is attached to top of ridge, ground contact extends across the bottom of all slices

Simulations results

In addition to Per Bias results (i.e. vs. bias current/voltage/current density), Harold XY produces 2D lateral-vertical profiles of various quantities, including: 

• Electrostatic potential and electric field (vector plot)

• Electron and hole Fermi energies

• Conduction and valence band edges

• Electron and hole densities (in bulk and QWs)

• Electron and hole current densities (vector field plots)

• Recombination rates: SRH, Auger, spontaneous emission, stimulated

• Temperature profile

• Optical mode

Optical mode of graded etch ridge waveguide as computed by Harold XY’s FDM Solver

Temperature profile in region around ridge waveguide, illustrating how Harold XY can efficiently model a large spatial region around the waveguide so as to obtain a realistic temperature profile. The temperature peaks in the 4-um wide ridge waveguide on the top of the structure where current is injected and most of the heating takes place. Heat then flows out into the substrate and side regions until reaching the ambient/heatsink temperature.

Current spreading in a heterostructure laser. Current takes a path through the active region, contributing to heating.

Profile of Auger recombination in QW of ridge waveguide laser – showing reduced Auger rate
in centre of waveguide where mode intensity, and therefore stimulated recombination, is large

Laser LI curve results from a 2-mode, self-heating simulation exhibiting thermal-rollover. Curves show the total output power (blue) and the individual output powers of fundamental (green) and first order (red) waveguide modes.

Laser LI curve results from a 2-mode, self-heating simulation exhibiting thermal-rollover. Curves show the total output power (blue) and the individual output powers of fundamental (green) and first order (red) waveguide modes.

Comparison with PICWave, Harold and Harold EAM

Please see here for a comparison of the active component (laser diode, SOA, modulators etc.) modelling capabilities of PICWave, Harold, Harold XY and Harold QCSE.