How does an optical fibre transfer light?

To understand how an optical fibre transfers light, we must first understand the concept of 'total internal reflection'. Whenever light is refracted from one medium to another, the refractive index of the second medium with respect to the first along with the angle of incidence determines what the refracted angle will be. Generally during this process, most of the light is refracted and some small portion is reflected. When light strikes at a certain angle of incidence greater than the mediums' 'critical angle', all of the light is reflected and no refraction occurs. This phenomenon is called total internal reflection (I would draw the standard diagram here to explain). An optical fibre is a long thin strand of glass with an outer plastic coating which works on this principle.

Follow up question to test understanding: Is total internal reflection possible for light moving from an optically denser to optically rarer medium, the other way around, or both?