Timbert
Member
You got a good memory, uptown.Just as a side note... I did a fibre installation course many many moons ago (about 25 years ago) and I remember that the Optical Time Domain Reflectometer (OTDR) used to use a principle called Fresnell Reflection in order to determine where the break/bad bend is in a fibre.
Going to pedantic for a moment. The speed of light in vacuum is a constant. Speed of light in fiber is not. It depends on the construction of the fiber and wavelength of light. Typical index of refraction in a fiber is about 1.45, so the speed of light in a fiber is only about 2/3 of the speed of light in vacuum. Knowing the index of refraction is important to be able to use an OTDR accurately.So, because the speed of light is a constant, the OTDR fires light down the fibre.