Application of Fiber Bragg Grating in Fiber Communication System As a new optical device, Fiber Bragg Grating is mainly used in fiber communication, fiber sensing and optical information processing. In optical fiber communication, many special functions are realized and widely used. Active and passive optical fiber devices can be composed of:

Active devices: fiber laser (grating narrowband reflector for DFB and other structures, wavelength tunable, etc.); semiconductor laser (fiber grating as feedback external cavity and used to stabilize 980 nm pumping light source); EDFA fiber amplifier (fiber grating to achieve flat gain and residual pumping light reflection); Ramam fiber amplifier (Bragg grating resonator);

Passive devices: filters (narrowband, broadband and band-stop; reflective and transmissive); WDM wavelength division multiplexer (waveguide grating array, grating/filter combination); OADM upstream and downstream add-drop multiplexer (grating selection); dispersion compensator (linear chirped fiber grating realizes single channel compensation, sampling fiber grating realizes multi-channel compensation in WDM system); wavelength converter OTDM delayer OCDMA Encoder Fiber Bragg Grating Encoder.

Fiber Bragg Grating (FBG) has been widely used in the field of optical fiber sensing since its advent. Fiber Bragg Grating (FBG) sensors have attracted more and more attention due to their advantages of anti-electromagnetic interference, anti-corrosion, electrical insulation, high sensitivity and low cost, and good compatibility with ordinary optical fibers. Because the resonant wavelength of FBG is sensitive to the change of stress and strain and temperature, it is mainly used to measure temperature and stress and strain. The sensor acquires sensing information by modulating the central wavelength of Bragg FBG with external parameters (temperature or stress and strain). Therefore, the sensor has high sensitivity, strong anti-interference ability, low requirement for energy and stability of light source, and is suitable for precise and accurate measurement. Fiber Bragg Grating (FBG) sensors now account for 44.2% of the materials mainly consisting of optical fibers. Fiber Bragg Grating (FBG) sensors have been used in various aspects, such as monitoring of highways, bridges, dams, mines, airports, ships, earth technology, railways, oil or gas depots. One of the development directions of sensors is multi-point and distributed sensors, which mainly use the combination of WDM, TDM, SDM and CDMA.

Fiber filter is an important passive device in optical fiber communication. The emergence of fiber grating really realizes all-fiber filter. Fiber Bragg Grating (FBG) filter is an ideal device in optical communication system because of its low cost, compatibility with optical fibers and easy integration. With the maturity of the fabrication technology of FBG and the abundance of various wavelength adjustment methods, the single-channel and multi-channel wide-band, high reflectivity band-stop filters and narrow-band and low-loss band-pass filters can be realized from 1520 to 1560 nm. In addition, FBG filters with flat gain have attracted wide attention. In addition, FBG is also used in SDH system. Dispersion compensation and add-drop multiplexing of WDM system.

For ordinary single-mode G.652 fibers, the dispersion value is positive at 1550 nm. When the optical pulse propagates in it, the short-wavelength light ("blue light") propagates faster than the long-wavelength light ("red light"). After a certain distance of transmission, the pulse is broadened and the dispersion of the fiber material is formed. If the grating period is large, the long-wavelength light will be reflected at the front of the grating, while the short-wave will be reflected at the front of the grating. The long light reflects at the end of the grating, so the short wavelength light travels 2 L longer than the long wavelength light (L is the grating length). Thus, the time delay difference between the long and short wavelength light is produced, and the dispersion of the grating is formed. When the light pulse passes through the grating, the time delay of the short wavelength light is longer than that of the long wavelength light, which just plays the role of dispersion equalization and achieves dispersion compensation.