Optical cable, optical fiber structure and type

Optical cable, optical fiber structure and type

Optical fiber structure and type:

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 62.5 μm), the middle is the low refractive index silica glass cladding (the diameter is generally 125 μm), 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. Optical fibers produced by different manufacturers have different numerical apertures.

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 should be narrower and the stability should be 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: 50/12

5μm, European standard 62.5/125μm, American standard

Industrial, Medical and Low Speed ​​Networks: 100/140μm, 200/230μm

Plastic: 98/1000μm for car control

Optical fiber manufacturing and attenuation:

1) Optical fiber manufacturing:

At present, optical fiber manufacturing methods mainly include: in-tube CVD (chemical vapor deposition) method, in-rod CVD method, PCVD (plasma chemical vapor deposition) method and VAD (axial vapor deposition) method.

2) Attenuation of fiber:

The main factors that cause fiber attenuation are: intrinsic, bending, extrusion, impurities, non-uniformity and butt joint.

Intrinsic: It is the inherent loss of the fiber, including: Rayleigh scattering, intrinsic absorption, etc.

Bending: When the fiber is bent, part of the light in the fiber will be lost due to scattering, resulting in loss.

Squeeze: Loss caused by tiny bends in an optical fiber when it is squeezed.

Impurities: Losses caused by impurities in the fiber absorbing and scattering light propagating in the fiber.

Non-uniformity: Loss caused by non-uniform refractive index of the fiber material.

Docking: The loss generated when the optical fiber is docked, such as: different axes (the coaxiality of single-mode fiber is required to be less than 0.8μm), the end face is not perpendicular to the axis, the end face is not flat, the butt core diameter does not match and the welding quality is poor.

The advantages of optical fiber:

1) The passband of the optical fiber is very wide. Theoretically, it can reach 3 billion megahertz.

2) The length of the non-relay section is tens to more than 100 kilometers, and the copper wire is only a few hundred meters.

3) Not affected by electromagnetic fields and electromagnetic radiation.

4) Light weight and small size. For example: 900 pairs of twisted-pair cables with 21,000 voice channels, the diameter is 3 inches, and the weight is 8 tons/KM. The optical fiber cable with ten times the communication capacity has a diameter of 0.5 inches and a weight of 450P/KM.

5) Optical fiber communication is not electrified, and can be used in flammable and violent places for safe use.

6) The use of a wide range of ambient temperature.

7) Chemical corrosion, long service life.

Optical cable

1. Manufacture of optical cable:

The manufacturing process of optical cable is generally divided into the following processes:

1) Screening of optical fibers: select optical fibers with excellent transmission characteristics and qualified tension.

2) Dyeing of optical fibers: use standard full chromatogram to identify, requiring high temperature not fading and not migrating.

3) Secondary extrusion: Use plastic with high elastic modulus and low linear expansion coefficient to extrude into a certain size tube, incorporate the optical fiber and fill it with moisture-proof and waterproof gel, and store it for a few days (not less than two days) .

4) Optical fiber cable twisting: twist several extruded optical fibers and strengthening units together.

5) Squeeze the outer sheath of the optical cable: add a layer of sheath to the twisted optical cable.

Types of optical cables:

1) According to the laying method, there are: self-supporting overhead optical cable, pipeline optical cable, armored buried optical cable and submarine optical cable.

2) According to the optical cable structure, it is divided into: bundled optical cable, layered optical cable, tightly hugged optical cable, ribbon optical cable, non-metallic optical cable and branchable optical cable.

3) According to the use, it is divided into: optical cable for long-distance communication, short-distance outdoor optical cable, hybrid optical cable and optical cable for building.

Construction of optical cable:

Over the years, the construction of optical cables has enabled us to have a set of mature methods and experience.

Outdoor construction of optical cable:

The most important thing for long-distance cable laying is to choose a suitable path. The shortest path is not necessarily the best, but also pay attention to the right to use the land, the possibility of erection or burial, etc.

There must be very complete design and construction drawings for convenient and reliable construction and future inspections. During construction, be careful not to put the optical cable under heavy pressure or be punctured by hard objects.

When the optical cable turns, its turning radius is 20 times larger than the diameter of the optical cable itself.