This is because infrared can travel farther with less distortion, i.e., it has less attenuation.

Infrared is used for wireless user input devices like mice and keyboards. It may also be used for fiber optic audio and even Internet technology. The biggest thing now with DSL is fiber optic to premises technology. That supposedly cuts a major bottleneck since the copper wire portion is very short. So more than likely, infrared light is used for that.

Fiber optic cables use wavelengths of visible light to transmit data. (Some use infrared as well.) They use red and above with the higher wavelengths being of higher speed and quality. The higher the wavelengths of light used, the more expensive the equipment is.

Monica A Starnes has written:

'Infrared thermography for nondestructive evaluation of fiber reinforced polymer composites bonded to concrete' -- subject(s): Thermography, Nondestructive testing, Testing, Fiber-reinforced concrete

A spectrophotometer is used for a lot of things in forensic. It can be used to identify certan kinds of cemicals in drugs and it can be used to identify fiber colors.