There are many applications where the coupling of light between devices is required. In this video lesson, we will demonstrate how to calculate the overlap and power coupling of a certain mode with another mode or a beam.

The Frequency Sweep tool allows you to calculate and plot the following results as a function of frequency:

Effective index $\left ( n_{eff} \right )$ : Effective index of the calculated mode(s)

Loss: Modal loss (in dB/cm of propagation)

Gain: Modal gain (in dB/cm of propagation)

Group index $\left ( n_{g} \right )$: Ratio of the speed of light to the group velocity, $n_{g} = \frac{c}{v_{g}}$

Group Velocity $\left ( v_{g} \right )$: Rate at which the peak of a temporal pulse will propagate in the absence of non-linearities (in m/s), $v_{g} = \frac{\mathrm{d} \omega }{\mathrm{d} \beta }$

Group delay (t): $t = \frac{1}{v_{g}}$ (in ps/km)

Dispersion: Rate of change of the group delay with respect to the wavelength (in ps/nm/km), $D =\frac{\mathrm{d} t}{\mathrm{d} \lambda }$

Beta $\left ( \beta \right )$: Propagation constant, where $\lambda _{0}$ is the free-space wavelength (in 1/m), $\beta = \frac{2\pi n_{eff}}{\lambda _{0}}$

When the “track selected mode” option is selected, the solver will use the best overlap to track the modes and not just their effective index.