I need to understand the concept of bright mode and dark mode completely. I know that by the destructive interference of bright and dark modes we achieve PIT but what is exactly bright and dark mode?
Hi there,
First of all, bright and dark modes are some kinds of resonators in a classical structures (as in your case, in a metamaterial structure).
The bright mode is the one that interacts directly with the incident light, whereas the dark mode does not couple directly with the latter, hence the word "dark" to describe it.
Another way of looking at it is that the bright mode will induce a large transmission dip when coupled alone (dark mode not present in the structure) to the incident wave. Specifically, the induced transmission dip has got a high FWHM (or low Q-factor).
Conversely, the dark mode when coupled alone (bright resonator not present) with the incoming light induces a high Q-factor transmission dip or nothing at all as it is quite weakly coupled (or not at all depending on the system configuration) to the incident wave.
You may look at the literature (there is a plenty) to get a deeper insight on this.
Good luck.
Adnane
Usually, the polarization of incident light and the placement method of resonators determine which is the bright mode resonator (coupled to incident waves directly), and which is the dark mode resonator (coupled to bright mode resonators but could not be excited by incident light directly). When we usually use Lorentz oscillator model to analyze the phenomenon.
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