Imagine a square prism made from some material with such an index of refraction and surrounded by a substance of such index of refraction so that light rays entering the prism and hitting one of the internal sides of the prism at an angle of incidence 45° experience total internal reflection. And since the internally reflected light rays reflect at an angle of also 45°, and the prism is a square one (90°) ,they also get internally reflected at the adjacent side of the square prism. And this goes on until all the light is slowly absorbed by the material of the prism. I know it's the same idea as the optical fibers, but I am wondering what we would see in such a prism. Will light going in a loop show interference patterns? and if it doesn't, How bright are the trapped rays going to be combined before the first of them is absorbed ?