8 Jul 2025

PCSEL Design Flow - Combine laser simulations with FDTD

Decades of laser simulations and crystal FDTD calculations combine for simulating PCSELs and PCLs, a growing interest for research and comercial applications

Photon Design is the home of Photonic Crystal Laser simulations. Our market leading laser simulations in software Harold can combine with FDTD Omnisim which was created specifically for designing crystal structures.

This page details the features our tools offer to support an ‘out-of-the-box-ready’ design flow.

1. Building your Epitaxy + Gain Models

Laser simulation software Harold is where designers build their epitaxy structure and perform thorough laser simulations to find the gain spectra of the material stack.

Results such as the gain spectra are then sent to OmniSim where a surrogate model is created, allowing the active FDTD simulation to use a Dynamic Gain Model. This sophisticated model treats gain as a function of carrier density, modelled by the rate equations including carrier diffusion, spontaneous recombination, stimulated recombination, and current injection.

An epitaxial layer structure defined in Harold. Shown here are the core layers of a 4QW InGaAsP structure.

Material gain spectra for a set of carrier densities from a simulation of an AlGaAs SQW epilayer structure - note the second gain peak which occurs at higher carrier densities. Such material gain spectra can be exported to the simulator: PICWave

Hint: You could use Python Scripting to reproduce the epitaxy stack built in Harold as a set of layers in OmniSim.

2. Building Your Crystal

A crystal lattice is attached to an OmniSim object where lattice angles and separations are defined. ‘Atoms’ are then added to the lattice; individual atoms can be moved, replaced with other atoms, or removed to create a cavity. Atoms can be customised using a set of 2D and 3D shapes (ellipses, polygons, ellipsoids) which can be coated with materials from the expandable database.

3. Band Analyser

OmniSim’s Band Analyser produces band diagrams of photonic crystals, allowing designers to tune their structure to disrupt propagation in the bulk of the crystal at the desired lasing wavelength, confining light to the central cavity.

From here we can also see the Bloch Modes of the structure.

4. Kallistos - Automatic Opimiser

Optimers excel in the frequency domain for rapid iterative design. Pairing automatic optimiser Kallistos with the Band Analyser allows for variables of the lattice, atoms, or created cavity (size, shape, position) to be quickly tuned to create the structure that’s ideal for supporting the desired lasing wavelength.

Click here to learn more about Kallistos and its set of local and global optimisation methods.

5. Run Active FDTD Simulations + Q-Factor Calculator

OmniSim’s Q-factor calculator allows early insight to the results of your Active FDTD simulation. Conventionally an active FDTD simulation will require most of the light has left the cavity to determine the Q-Factor; a long run-time for high Q-Factor lasers.

The Q-Factor calculator will accurately provide the operating wavelength and linewidth of the laser far earlier than the conventional Fourier transform approach. Our investigations show an 85% reduction in calculation time while results remain accurate within a single percent.