Why light does not leave the optical fiber from the sides?

Light does not leave the optical fiber from the sides due to a phenomenon called total internal reflection. This occurs when light travels from a medium with a higher refractive index (the glass or plastic of the fiber) to a medium with a lower refractive index (the surrounding air or cladding) at an angle greater than the critical angle. As a result, the light is reflected back into the fiber rather than escaping, allowing it to travel long distances with minimal loss. The fiber's design ensures that light remains confined within its core, maximizing efficiency in data transmission.