Photonics
Photonics Simulation for integrated photonic design
What is photonics simulation?
Electromagnetic Fields
Index contrast holds light in a silicon waveguide. Part of the guided mode rides outside the core, in the cladding. That tail decides how well a coupler transfers power and how much a tight bend leaks. At these dimensions rays don’t describe the light. You have to solve the field.
Virtual Prototyping
Testing each design change on silicon means another fab run. Simulation takes that sweep off the wafer, as long as the model matches what gets built. Sidewall angle, line-edge roughness, CD shifts and corner rounding all pull a real device away from its as-drawn numbers.
Design-Ready Results
That sets the bar for a solver. It should return broadband results from one run, carry dispersion properly and mesh curved geometry without stair-steps. It should end in S-parameters a circuit-level tool can use, and run fast enough for a sensitivity sweep. XSim Photonics was built to that bar.
XSim Photonics
Full-wave FDTD for photonic and electromagnetic design, developed at Tech-X and now a Silvaco product. The same model runs on a laptop, a GPU cluster or AWS, so a bigger sweep becomes a hardware decision.
Geometry
Imports GDS, STEP and STL, or build it in the Composer 3D geometry builder
Solver
Constant or variable gridding, conformal conductors, conformal dispersive dielectrics and resistive materials
Sources and boundaries
Launch and exit ports, broadband or monochromatic input, total-field/scattered-field sources, adiabatic absorbers and phase-shifted periodic boundaries
Analysis
Mode solver, S-parameters versus wavelength, far-field and Fourier transforms, and your own analyzers
Workflow
Scriptable from setup through analysis and visualization
It handles RF and antenna design as well, antenna arrays included.
The methods behind the solver
FDTD with conformal, dispersive materials
One time-domain run returns the whole spectrum, so a broadband source replaces a sweep across wavelengths. Conformal meshing follows the curve of a bend or ring, and dispersive dielectrics carry wavelength-dependent behavior through the solve.
Mode solving
Solve the cross-section first to see which modes it supports and each one’s effective index. Launch that guided mode into the FDTD run and the transmission you measure belongs to the device.
Far-field and S-parameter extraction
S-parameters versus wavelength give you insertion loss and coupling ratio in a form circuit simulators accept. Far-field transforms show what the light does after it exits the structure.
GPU and cloud execution
Split one job across CPUs and GPUs. When a sensitivity study outgrows one machine, scale from a workstation to a supercomputer, or out to AWS through Tech-X CloudCompute.
What you can simulate
Waveguides
Straight, bent, tapered and multi-material, with roughness if you need it.
Modulators
The optical side, with Victory Device solving the electrical device underneath.
Resonators
Microrings, where free spectral range and extinction hinge on a coupling gap tens of nanometers wide.
Couplers and splitters
Adiabatic tapers and inter-layer transitions between guides, layers and fiber.
Full photonic circuits
Built up from per-component S-parameters, since a whole-circuit FDTD solve is rarely practical.
Coming to Silvaco from Tech-X
XSim has been part of Silvaco since the Tech-X acquisition closed on April 29, 2025.
It keeps its name, its public user guide and its examples. John Cary, who founded Tech-X, now works at Silvaco as Senior Director and Fellow.
Support portal
Licensed XSim users open cases through the Tech-X support portal. For Silvaco’s other tools, start at Support and Downloads.
Read the documentation
The XSim user guide, reference material and examples are public on txcorp.com, with no login.
Silvaco Support and Downloads
Open a case under a current maintenance contract and follow it through to resolution. Your downloads sit in the same portal.
License and Support
You’ll find XSim support, licensing and documentation on txcorp.com.
Published photonics work
What has actually been published, and by whom. No photonics customer has been named publicly by either company, so nothing here is presented as one.
FTCO
Webinar
Simulating photonic devices as manufactured
Silvaco’s FTCO flow feeds your fab’s process parameters into the model, so you catch fabrication-driven losses in a passive device before tapeout. Victory Process builds the fabricated geometry, Victory Device runs GPU-accelerated FDTD on it, and Victory DoE and Victory Analytics handle sweep and optimization. Presented by John Sembower, Field Application Engineer.
Tech-X
Worked examples
Nine XSim photonics examples
Mode calculations for dielectric, three-material and cylindrical waveguides, plus dispersion, a microring launched two ways, an adiabatic tapered splitter and an inter-layer slope coupler. One of them models a rough waveguide.
Further reading on optical simulation
Webinar
April 2020
Optoelectronic Simulation of Solar Cells, Waveguides, and LEDs
Silvaco's time-domain optical methods, FDTD included, across three device classes.
Presentation · PDF
Optical simulations
The optical methods deck, from ray tracing to FDTD, with a view on which suits which problem.
Questions engineers ask about XSim Photonics
How does photonic simulation connect to process and device simulation?
Closely. Photonic performance depends on both the structure that is manufactured and the physics that occurs within that structure. Victory Process can generate realistic, process-aware 3D geometries that capture fabrication effects such as sidewall angle, critical-dimension variation, and thickness changes. These structures can then be transferred directly into photonic simulation for optical analysis and into Victory Device for coupled electro-optical simulation. This creates a continuous workflow from virtual fabrication to photonic device and circuit design
When should I use FDTD and when a mode solver?
A mode solver tells you what a waveguide cross-section can carry: how many modes, what effective index each has, and how far each reaches into the cladding. FDTD covers structures that change along their length, such as bends, tapers and coupling gaps. Most projects run the mode solver first, then hand its mode to FDTD for propagation.
Can photonic simulation run on GPUs or in the cloud?
Yes. XSim Photonics runs on NVIDIA GPUs and x86 CPUs, under Windows, Linux or Mac, from a single laptop to a cluster, with AWS available through Tech-X CloudCompute. Inside Silvaco's FTCO photonics flow, Victory Device runs its FDTD on GPUs as well.
What happened to Tech-X and XSim?
Silvaco bought Tech-X Corporation in April 2025, and XSim now sits in its AI-Driven Manufacturing portfolio. Documentation, examples, licensing and the support portal remain on txcorp.com.
Which layout formats can photonic simulation import?
It reads GDS, STEP and STL. For integrated photonics GDS is the one that counts, because your layout already lives in it, and Silvaco's FTCO photonics flow also begins with a GDS import. If you'd rather build geometry by hand, XSim includes a Composer 3D geometry builder.