Optical fiber sensing is a technology which provides one with a technique to measure strain/temperature along the fiber optic route. In this technology, two laser beams, a pump pulse, of unique wave profile, and a continuous wave probe light, are injected into an optical fiber from both its ends. The interaction of these two laser beams excites acoustic waves, due to their different frequencies. The pump pulse is backscattered by the phonons, and part of its energy is transferred to the CW. The power gain of the CW, which is called the Brillouin Gain Spectrum (BGS), as a function of frequency difference between the two laser beams, is measured at the output end of the probe light while the frequency of the probe light is scanned. The value of the strain/temperature can be estimated by measuring the peak frequency of BGS (Brillouin frequency), whilst its position calculated from the light round-trip time.

The small size of the fiber and, most of all, the fact that no electrical power is needed at the remote location, gives fiber optic sensors advantages to conventional electrical sensor in many industrial applications.

• real time monitoring without stopping the system
• especially suitable for overall monitoring of large structures
• precise distributed measurements along the fiber to detect the location of changes in strain/temperature profiles
• explosion-safe (can be directly installed even in the flammable liquids / gases)
• insensitive to interface from electromagnetic wave / lightning / electric power surge
• can be simultaneously used as a communication wire and sensor
• reduce total maintenance inspection cost