Optical fibre光纖的原理

If you want to ask how to ensure the incident angle is greater than the critical one, then I would say,

if the final signal you receive at the other end of the optical fiber is very weak, that means there is energy loss, and such loss must due to the loss of light and how can the light beam get losed? Then it must be because the total internal reflection does not occur at somewhere along the fiber.

So, a way to know it is to test it by inputting a light beam and measure the efficiency of the light travel (as far as people won't check the fibre meter by meter and it costs time).

2008-06-26 17:05:19 補充：
Yes, there is chance of information loss, but that is not important provided that such loss is not sufficient. The longer the light path, the more chance the information will lose. So I suppose the light path of endoscope is so short that the loss is not significant.

2008-06-26 17:05:26 補充：
For network purpose, people would overcome this problem by establishing a number of mid-way amplifier to cover the loss part.

Ofcourse, the signal generator is so designed that the majority incident on the interior glass by s good angle.