# Modes

Modes — MC Grating documentation for Modal Collinear and Modal Conical. This page provides the user with the possibility to calculate the lamellar modes and…

Canonical: https://mcgrating.com/docs/modal/modes.html


Written by Nikolay M. LyndinLast revised 2017-12-30

This documentation was written for releases up to 2018 and is being revised. Some dialogs have changed since. If something does not match what you see, write to [mc@mcgrating.com](mailto:mc@mcgrating.com).

This page provides the user with the possibility to calculate the lamellar modes and overlapping/scattering matrix parameters or Fourier modes and scattering matrix parameters of a grating structure, and to analyze their values as well as to draw the eigenmode field distributions. Most of the controls of this page have an obvious meaning; only a few deserve an explanation:

- The ***Output Type*** control allows choosing the appropriate type of displayed coupling coefficients (*Overlapping* or *Scattering *for Lamellar and only *Scattering* for Fourier modes).
- The ***Incidence Layer*** edit window provides the possibility to select a layer of the structure where from an incident mode propagates towards one of the layer interfaces, and the ***Mode N*** edit windows provide the possibility to select the order of an incident mode whose effective index/permittivity is displayed under ***Mode Propagation ***control.
- The ***Output Layer*** edit window provides the possibility to choose which one of the adjacent layers or the layer itself contains the scattered mode and the ***Mode M*** edit window provides the possibility to select the order of this mode.
- The ***Output*** control informs which part (up or down) of the ***Overlapping***/***Coupling N to M mode Coefficient*** is displayed. If the ***Incidence Layer*** and the ***Output Layer*** is the same, the ***Up*** choice means the scattering from a bottom interface the ***Down*** choice corresponds to the scattering from a top interface.
- The ***Polarization*** control (in the conical mount version) provides the possibility to select a mode polarization type. In this case, the mode polarization is defined as TE if the mode has only the Y component of the electric field and as TM if the mode has only the Y component of the magnetic field.
- The ***Save Modes*** button provides the possibility to save in a text or data file an effective index and permittivity table of all modes for the selected ***Incidence Layer*** and optionally to save a ***N to M mode*** ***Overlapping/Scattering Coefficient* **table.

**Note 1 **If the layer index is *0* or *N+1* (where *N* is the number of layers), this index corresponds to the cover or substrate media respectively.

**Note 2** Modes of a simple (without grating) layer are enumerated as Raleigh modes including positive and negative indexes. Lamellar/Fourier modes of a grating layer are enumerated in decreasing effective refractive index for positive real part value.

From the in-application help of Modal Collinear and Modal Conical, documented through 2018. If you publish results computed with MC Grating, see [how to cite it](https://mcgrating.com/references.html#cite).