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Waveguide simulation for integrated photonics

Full-wave waveguide simulation shows where light goes in your waveguides, rings and couplers, so you can check a design before it costs you a mask set.

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What waveguide simulation answers

  • 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.

  • 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.

  • 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.

Explore XSim Photonics

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

See photonics and optoelectronics applications

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.

Published photonics work

  • FTCO Webinar June 2026

    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.

    Watch the webinar

  • 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.

    Browse the examples

Further reading on optical simulation

Browse the Simulation Standard

Test it on the device you're stuck on

  • Talk to an engineer

    Bring the layer stack, the wavelength and the coupler that underperforms its simulation. A Silvaco application engineer will go through it with you.

    Talk to our Technical Experts

  • Read the documentation

    The XSim user guide, reference material and examples are public on txcorp.com, with no login.

    Read the XSim user guide

  • Get support

    Licensed XSim users open cases through the Tech-X support portal. For Silvaco's other tools, start at Support and Downloads.

    Tech-X support portal Support and Downloads

Questions engineers ask about XSim Photonics

It solves Maxwell's equations through the actual device geometry to predict where light goes, rather than tracing rays. Integrated photonic structures measure only a few wavelengths, which means computing the field at every point in the domain. XSim Photonics does it with full-wave FDTD, from a single straight waveguide up to a full coupler.

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.

Closely. The optical methods in Victory Device, from ray tracing and beam propagation to transfer matrix, mode solving and FDTD, sit inside the same simulator that handles the electrical device. A modulator or photodiode needs both behaviors in one model, and Victory Device is where they meet.

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.

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. VSim, Tech-X's plasma tool, came over in the same deal and is part of Silvaco's Plasma family.

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.

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