Optical fiber Bragg grating (FBG) was invented in the late 70's, when refractive index of the fiber core was found changed by light propagating in the fiber.

FBG is one-dimensional grating. It has a periodical pattern of index change. The period of the grating determines the center wavelength of the reflected spectrum, which is called Bragg wavelength. The light at Bragg wavelength (and within a certain bandwidth) is reflected by the FBG. The grating can be designed to have different Bragg wavelength, bandwidth, reflectivity, etc.

In addition to standard FBG, there are other types of gratings, such as chirped gratings, long period gratings, superstructure gratings, etc. FBG provides a flexible way to manipulate the wavelength, dispersion, power of the optical signals.

The most common method to fabricate FBG is using a photomask. The mask is made with the same pattern of the grating. The pattern of the mask is directly written onto the fiber using strong UV light. Chirped gratings are usually made in this way. FBG can also be made using interference pattern generated by two laser beams. Changing the interference setting can easily change the Bragg wavelength of the grating.

FBG is widely used in optical fiber telecommunication networks as a filter component. DWDM modules can be made using gratings. However, the environmental sensitivity of the gratings must be addressed. Gratings are also used in fiber lasers or semiconductor laser diodes, to achieve narrow linewidth laser output, or stabilizing the laser power.

Another important application for FBG is optical sensor. The Bragg wavelength is affected by temperature and strain on the fiber. Hence FBG can be used as temperature sensor or pressure/vibration/strain/mechanical force sensors.