Question

When launching light down an optical fiber, why is it important to exceed the critical angle?

Answer 1

Light pulses move easily down thefiber-optic line because of a principle known as total internal reflection.
This principle of total internal reflection states that when the angle of
incidence exceeds a critical value, light cannot get out of the glass; instead,
the light bounces back in. When this principle is applied to the construction
of the fiber-optic strand, it is possible to transmit information down fiber
lines in the form of light pulses.