# MMI with GDSFactory FDTD

Configure a 3D MMI simulation, inspect its geometry, and calculate one broadband S-matrix column.

**Requirements:** [GDSFactory+](<https://gdsfactory.com>) cloud simulation access.

**You will:** build the component, configure the solver, preview the 3D setup, run one cached cloud simulation, and inspect its wavelength response.

## 1\. Build the component

```python
import gdsfactory as gf

from gsim import fdtd

gf.gpdk.PDK.activate()
component = gf.get_component("mmi1x2")
component
```

## 2\. Configure the simulation

```python
simulation = fdtd.Simulation()
simulation.materials(background="SiO2", overrides={"si": 3.4757})
simulation.geometry(component)
simulation.source(
    port="o1",
    wavelength_um=1.55,
    wavelength_span_um=0.1,
    num_wavelengths=101,
)
simulation.domain(padding=1)
simulation.solver(cell_size_nm=60, energy_decay_fraction=1e-5)
```

```text
Solver(cell_size_nm=60.0, max_timesteps=None, energy_decay_fraction=1e-05, max_wall_seconds=3600.0)
```

Preview the resolved layer stack, ports, and simulation domain before submitting the job.

```python
simulation.plot_3d()
```

```text
3488129338.py:1: UserWarning: Material dispersion is not sent to GDSFactory FDTD; these materials use their index at the source wavelength across the 1500 to 1600 nm band: SiO2 (0.1 % permittivity change). materials(dispersion=True) sends dispersive models instead.
  simulation.plot_3d()
```

## 3\. Run and inspect the result

```python
result = simulation.run(check_cache=True)
```

```text
  fdtd-eb03ee90  [####################] 100%  complete  elapsed 0m 00s


Extracting results.tar.gz...
Downloaded 2 files to sim-data-fdtd-eb03ee90
```

```python
result.s_parameters.plot_plotly()
```

```python

```