Wikipedia
The path that light takes in traversing an optical is often called the optical path. The physical length of an optical device can be reduced to less than the length of the optical path by using folded optics. The optical path length as defined in optics is the length of the path multiplied by the index of refraction of the medium.
Usage examples of "optical path".
This had roiled the air, disturbing the optical path, moving the beam on and off the target and also spreading the beam wider than its intended diameter.
His eyes appeared to be surmising the existence of an optical path along which might travel any number of topics neither generated nor perceived in the usual manner.
Scanlon's thought was that if a laser were aimed at the roof from the ground inside, its beam ought to trace the same optical path, but in the opposite direction.
Isaac NEWTON, professor of mathematics in the university of Cambridge, improving on previous telescopes by contracting the optical path.