What are the structures and types of fiber optic cables

What are the structures and types of optical fiber cables? It is still very necessary to understand optical fibers. Let's take a look at the structure and types of optical fibers.

1) Fiber structure:

Bare optical fiber is generally divided into three layers: the central high-refractive index glass core (core diameter is generally 50 or 62.5 μm), the middle is low-refractive index silica glass cladding (diameter is generally 125 μm), and the outermost is resin coating for reinforcement. layer.

2) Numerical aperture:

Not all the light incident on the end face of the fiber can be transmitted by the fiber, but only the incident light within a certain angle range. This angle is called the numerical aperture of the fiber. The larger numerical aperture of the fiber is beneficial for the butt joint of the fiber.

3) Types of optical fibers:

A. According to the transmission mode of light in the optical fiber, it can be divided into: single-mode optical fiber and multi-mode optical fiber.

Multimode fiber: The central glass core is thicker (50 or 62.5μm), which can transmit light in multiple modes. However, its intermodal dispersion is relatively large, which limits the frequency of digital signal transmission, and it will be more serious with the increase of distance. For example: 600MB/KM optical fiber has only 300MB bandwidth at 2KM. Therefore, the transmission distance of multimode fiber is relatively short, generally only a few kilometers.

Single-mode optical fiber: The central glass core is 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 should be narrow and the stability should be good. .

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: Fiber optic manufacturers optimize the fiber transmission frequency on two wavelengths of light, such as: 1300nm and 1550nm.

C. According to the distribution of refractive index: abrupt and graded optical 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. Suitable for short-distance low-speed communication, such as: industrial control. However, due to the small inter-modal dispersion of single-mode fibers, all single-mode fibers are of abrupt type.

Gradient optical fiber: The refractive index from the center core of the fiber to the glass cladding is gradually reduced, which can make the high-mode light propagate in a sinusoidal form, which can reduce inter-modal dispersion, increase the bandwidth of the fiber, and increase the transmission distance, but the cost is high. Most mode fibers are 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 network: 100/140μm, 200/230μm

Plastic: 98/1000μm for automotive controls