Optical fiber

An optical fiber is a flexible, transparent fiber made of very pure glass (silica) not much wider than a human hair that acts as a waveguide.
Optical fibers are widely used in fiber-optic communications,which permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communication.
This allows long distances to be spanned with few repeaters. Additionally,the per-channel light signals propagating in the fiber have been modulated at rates as high as 111 gigabits per second by NTT although 10 or 40 Gbit/s is typical in deployed systems.
Fibers have many uses in remote sensing.In most cases,the sensor is itself an optical fiber. In other cases,fiber is used to connect a non-fiberoptic sensor to a measurement system.Depending on the application, fiber may be used because of its small size,or the fact that no electrical power is needed at the remote location, or because many sensors can be multiplexed along the length of a fiber by using different wavelengths of light for each sensor,or by sensing the time delay as light passes along the fiber through each sensor.
Time delay can be determined using a device such as an optical time-domain reflectometer.