Introduction to Optical fiber

Optical fiber, short for optical fiber, is a fiber made of glass or plastic that can be used as a tool for conducting light. Communication fiber is a medium for transmitting light, and its main component is silicon dioxide. Its structure can be divided into high refractive index core, low refractive index cladding and surface coating.

So how does light travel through optical fibers?

Optical fiber as the transmission channel of light mainly uses the principle of total reflection of light to realize the transmission of optical signals in it. Cladding refractive index. Fiber core refractive index n1, when the Angle of the incident light reach or exceed a certain Angle, the refracted light will disappear, all incident light is reflected, ray of light in the fiber core and cladding interface of total reflection, and form the light blocking in the spread of the fiber core internal forward necessary condition, even after bending routing light does not penetrate optical fiber.

According to the different transmission modes, it can be divided into multi-mode fiber and single-mode fiber.

Single-mode optical fibers allow only one mode of optical signal transmission at a time, the loss is relatively small, can be used in long-distance transmission. At present, FTTx deployments in access networks are all single-mode optical fibers.

Multi-mode optical fiber refers to the transmission of optical signals in multiple modes at the same time, which is easy to cause interference with each other, large loss, and short transmission distance. It is mainly used for fiber-optic communication over short distances, such as in buildings or on campuses, and the cost (transmitter and receiver) of multi-mode fiber-optic transmission systems is lower.

The main parameters that affect the transmission performance of optical fiber are attenuation and chromaticity dispersion.

The attenuation coefficient of the optical fiber varies with the wavelength. The smaller the attenuation coefficient is, the longer the transmission distance without relay is.

Chromaticity dispersion refers to the phenomenon of optical pulse broadening caused by different wavelength components in the light source spectrum at different speeds in the optical fiber, which limits the size of the transmission capacity and transmission distance. The smaller the dispersion, the longer the transmission distance without relay.

Different types of single-mode fibers are classified according to their attenuation range, dispersion value, etc.

According to the optical fiber performance, combined with the PON network optical fiber transmission distance is not more than 20km, the last kilometer of the characteristics of many turning points, we recognize several commonly used single-mode optical fiber types.

G.652D type

G.652D fiber is the most widely used single-mode fiber in China. It is mainly used for feeder segment and distribution segment of PON network.

G.657 type

The most important characteristic of g. 657 fiber is its good bending resistance. G.657 optical fibers are divided into two subclasses: A and B. The performance and application environment of G.657A optical fibers are similar to that of G.652D optical fibers, and they can be interconnected with G.652D optical fibers. Its bending radius can reach 7.5mm, suitable for FTTH information transmission, installed in indoor or building and other narrow places.

The lower limit of the mode field diameter of g. 657B optical fiber is smaller than that of G.652A and G.652D, but the upper limit is the same. It is different from that of G.652D, so the connection loss may be large and the application is limited.

G.654E type

G.654E optical fiber is a new type of optical fiber, this optical fiber has the characteristics of large effective area and low loss coefficient, 200G, 400G and the future Tbit/s ultra-high speed transmission technology preferred optical fiber.