The correct answer is option 4: total internal reflection of light.

Total internal reflection is a phenomenon that occurs when a light ray traveling in a medium reaches a boundary with another medium where the angle of incidence is larger than the critical angle. In this case, the light ray is completely reflected back into the original medium, instead of being refracted or transmitted into the second medium.

In an optical fiber, light is transmitted by utilizing total internal reflection. The fiber consists of a core material with a high refractive index surrounded by a cladding material with a lower refractive index. When a light ray enters the core of the fiber at an angle larger than the critical angle, it undergoes total internal reflection at the boundary between the core and cladding. This allows the light to propagate through the fiber, bouncing off the core-cladding boundary, and ultimately reaching its destination.

It is important to note that total internal reflection allows light to travel through the fiber regardless of its shape. The light will continue to be reflected and guided within the fiber as long as the angle of incidence remains larger than the critical angle.