Question

The optical path length is equal to _____?

Answer 1

Optical path length:

1. The optical path length is the actual path length times the refractive index. The actual path length measures the distance covered or traveled by the light with the medium being a vacuum. The optical path length measures the distance covered or traversed by the light with a medium other than a vacuum.
2. The most significant distinction between the optical and the actual path length would be that the optical path length is used when light passes through a substrate other than a vacuum. In contrast, the actual path length should be used when light passes other than vacuum.

Therefore,

$\mathrm{Optical}\mathrm{path}\mathrm{length}=\mathrm{Refractive}\mathrm{index}\times \mathrm{d}$ where ‘d’ is the distance covered.