# Wavephotonics YAMLs: component
Below is the breakdown of an exemplary YAML file for a component, a 1x2 MMI, which has one input and two output ports, all optical. The original component file can be found [here](../../Si_220nm_active/components/SOI220nm_1310nm_TE_RIB_2x1_MMI.yaml)
First, let's define the name of the file.
``` yaml
name: SOI220nm_1310nm_TE_RIB_2x1_MMI
```
This should be identical to the GDS file name (without the file extension). Continuing with the component type,
``` yaml
component_type: MMI1x2
```
`component_type` is not allowed to be arbitrary within the Wavephotonics' YAML format - these are specified in the [allowed list of components](../references/components_list.md) . Another requirement from Wavephotonics is explicit specification of the modes going through the ports.
``` yaml
modes:
- mode_numbers:
- 0
- 0
polarisation: TE
wavelength: 1310
```
Here, we have defined `modes`, which has only one mode entry, TE_00 mode at 1310nm wavelength. When defined globally for the component this way, the `modes` field will be assigned to all the ports of the component. We move on to defining the ports:
``` yaml
ports:
- name: o1
port_type: optical
center:
- 0
- 0
orientation: 180
cross_section: rib_1310nm_TE
- name: o2
port_type: optical
center:
- 123.6
- 1.52500
orientation: 0
cross_section: rib_1310nm_TE
- name: o3
port_type: optical
center:
- 123.6
- -1.525
orientation: 0
cross_section: rib_1310nm_TE
```
Here, we defined the three ports within this MMI. First port `o1` is the input port, and is facing the -x direction, hence its `orientation` is 180. It has a cross-section `rib_1310nm_TE`, which will be described in `*/cross-sections/cross_sections.yaml` - it will be presented as a cross-section example later on. Ports `o2` and `o3` are outputs, they face +x direction (0 degree orientation), with their centres offset by `1.525 um` from `y=0` line.
Below we demonstrate port-level mode definition within a grating coupler's YAML. The component is a 1D grating coupler for c-band operation in SiN - the original component file can be found [here](../../SiN_300nm/components/SiN300nm_1550nm_TE_STRIP_Grating_Coupler_v1p2.yaml)
``` yaml
name: SiN300nm_1550nm_TE_STRIP_Grating_Coupler_v1p2
component_type: GratingCoupler1D
ports:
- center:
- 0.0
- 0.0
name: o1
orientation: 180
port_type: optical
cross_section: strip_1550nm_TE
modes:
- mode_numbers:
- 0
- 0
polarisation: TE
wavelength: 1550
```
We defined the first port, an optical port with cross-section `strip_1550nm_TE` and facing -x. It is defined for TE_00 mode at 1550nm: `modes` went a level down in hierarchy to be a field of `ports`. The second port is a vertical port, which requires a different set of fields
``` yaml
ports: # Kept here to display the indentation - this line does not exist in the original file
- center:
- 325.81
- 0
name: vertical_te
port_type: vertical_te
orientation: 0.0
width: 10.0
coupling_angle_cladding: 13.659
fibre_modes:
- fibre_type: SMF-28
wavelength: 1550
```
- Here, `port_type` is specified as `vertical_te` from the [allowed list of ports](../references/ports_list.md) .
- For vertical ports, we are allowed to define a `width` instead of a `cross-section` - e. g. `10.0` here.
- Another important parameter is `coupling_angle_cladding` - this is the relative angle of the light travelling within the cladding. This component was designed for a 20 degree fibre angle over SiO2 cladding, hence `coupling_angle_cladding = arcsind(sind(20)*n_air/n_siox) = 13.659`. If the device had been air-clad, `coupling_angle_cladding` would have been set to `20.0`.
- Lastly, we defined `fibre_modes` to specify the possibly different fibres to be used across different settings; i. e. it is possible to use `780HP` for 780nm operation and `SMF-28` for 1550nm operation over the same grating coupler by defining an additional entry to `fibre_modes`, using the fibres listed in the [allowed list of fibres](../references/fibres_list.md).