Fiber Bragg gratings are made by laterally exposing the core of single-mode fiber to a periodic, intense laser mode. Exposure causes the refractive index to permanently increase in the core of the fiber, generating a fixed exponential modulation according to the exposure mode. This fixed exponential modulation is called grating. FBG is a technology basis, on which T&S Communications developed a series of sensors for optical sensing and ID reflectors for fiber trouble shooting, among which, sensors mainly include a temperature sensor, vibration sensor, FBG strain sensor and pressure sensor.
During each periodic change in refraction, a small amount of light is reflected. When the grating is periodic, all the reflected light signals form a large reflection at a particular wavelength. This is called the Bragg condition, and the wavelength at which this reflection occurs is called the Bragg wavelength. The length of the phase mismatch is essentially transparent except for the Bragg wavelength of the optical signal at the wavelength.