Now is the era of optical fiber transmission, and it is very necessary to understand the optical fiber. Let's take a look at the structure and types of optical fibers.
1) Optical fiber structure:
The bare fiber is generally divided into three layers: the central high-refractive-index glass core (the core diameter is generally 50 or 62.5μm), the middle is the low-refractive-index silica glass cladding (the diameter is generally 125μm), and the outermost is the resin coating for reinforcement. Floor.
2) Numerical aperture:
The light incident on the end face of the fiber cannot be all transmitted by the fiber, only the incident light within a certain angle range can. This angle is called the numerical aperture of the fiber. A larger numerical aperture of the optical fiber is advantageous for the butt-joining of the optical fiber.
3) Types of optical fibers:
A. According to the transmission mode of light in the fiber, it can be divided into: single-mode fiber and multi-mode fiber.
Multimode fiber: The central glass core is thicker (50 or 62.5μm) and can transmit light in multiple modes. But its intermodal dispersion is large, which limits the frequency of transmitting digital signals, and it will be more serious with the increase of distance. For example: 600MB/KM fiber has only 300MB bandwidth at 2KM. Therefore, the distance of multimode fiber transmission is relatively short, generally only a few kilometers.
Single-mode fiber: The central glass core is relatively thin (the core diameter is generally 9 or 10 μm), and only one mode of light can be transmitted. Therefore, its intermodal dispersion is very small, which is suitable for long-distance communication, but its chromatic dispersion plays a major role, so the single-mode fiber has higher requirements on the spectral width and stability of the light source, that is, the spectral width is narrower and the stability is better. .
B. According to the optimal transmission frequency window: conventional single-mode fiber and dispersion-shifted single-mode fiber.
Conventional type: The optical fiber manufacturer optimizes the optical fiber transmission frequency on a single wavelength of light, such as 1300nm.
Dispersion-shifted type: Optical fiber manufacturers optimize the transmission frequency of optical fibers at two wavelengths of light, such as: 1300nm and 1550nm.
C. According to the distribution of refractive index, it is divided into: abrupt and graded fibers.
Abrupt type: The refractive index from the central core of the fiber to the glass cladding is abrupt. It has low cost and high intermodal dispersion. It is suitable for short-distance low-speed communication, such as industrial control. However, due to the small intermodal dispersion of single-mode fiber, the single-mode fiber adopts abrupt type.
Graded fiber: The refractive index from the center core of the fiber to the glass cladding is gradually reduced, so that the high-mode light can propagate in a sinusoidal form, which can reduce the dispersion between modes, improve the bandwidth of the fiber, and increase the transmission distance, but the cost is high. Mode fibers are mostly graded fibers.
4) Common fiber specifications:
Single mode: 8/125μm, 9/125μm, 10/125μm
Multimode: 50/125μm, European standard 62.5/125μm, American standard
Industrial, Medical and Low Speed Networks: 100/140μm, 200/230μm
Plastic: 98/1000μm for car control
The above is the introduction to the structure and types of optical fibers. I hope it can help you. If you have needs for optical fiber cabling products, you can contact us.
