Basic cabling knowledge and practical case analysis (1)

Part 1 optical fiber theory and optical fiber structure

I. Light and its features:

1. Light is an electromagnetic wave

Visible light wavelength range: 390 ~ 760nm (MB ). The part greater than 760nm is infrared light, and the part smaller than 390nm is ultraviolet light. Three types of optical fiber are used: 1550, and.

2. refraction, reflection, and total reflection of light.

Because the propagation speed of light in different substances is different, when light emits from one substance to another, it will produce refraction and reflection at the interface of the two substances. In addition, the angle of the refraction light changes with the angle of the incident light. When the angle of the incident light reaches or exceeds a certain angle, the refraction light disappears and all the incident light is reflected back. This is the total reflection of the light. Different materials have different optical refractive indexes for the same wavelength of light. The same material has different refractive indexes for different wavelengths of light. Optical fiber communication is based on the above principles.

Ii. optical fiber structure and types:

1. optical fiber structure:

The raw fiber is generally divided into three layers: The Center High Refractive Index Glass core diameter is generally 50 or 62.5 μm), the middle is low refractive index silicon glass package layer diameter is generally 125 μM ), the outermost layer is a reinforced resin coating.

2. numerical aperture:

The light incident to the end of the optical fiber cannot be transmitted by the optical fiber. Only the incident light within a certain angle can be transmitted. This angle is called the numerical aperture of the optical fiber. The larger numerical aperture of the optical fiber is advantageous for the interconnection of the optical fiber. What is the difference between the numerical aperture of optical fiber produced by different manufacturers ?? CORNING ).

3. optical fiber types:

A. optical fiber transmission modes can be divided into single touch optical fiber and multi-mode optical fiber.

Multi-Mode Optical Fiber: the center glass core is coarse 50 or 62.5 μm, and can transmit light in multiple modes. However, the color difference between them is large, which limits the frequency of digital signal transmission and increases with the increase of distance. For example, 600 MB/KM optical fiber only has 2KM MB of bandwidth. Therefore, multimode optical fiber transmission distance is relatively close, generally only a few kilometers.

Single-Mode Optical Fiber: the diameter of the center glass core is usually 9 or 10 μm), and only one mode of light can be transmitted. Therefore, it is suitable for remote communication, but its color dispersion plays a major role. In this way, the single-mode optical fiber has a high requirement on the spectral width and Stability of the light source, that is, the spectral width must be narrow, good stability.

B. According to the Optimal Transmission frequency window: conventional single-mode optical fiber and dispersion displacement single-mode optical fiber.

Conventional: Optical Fiber manufacturers optimize the optical fiber transmission frequency on a single wavelength, for example, 1300nm.

Dispersion Displacement Type: Optical Fiber Production experts optimize the optical fiber transmission frequency on two wavelengths of light, such as 1300nm and 1550nm.

C. Distribution by refractive index: Mutant and gradient optical fiber.

Mutating: The refractive index from the core to the glass package layer in the optical fiber is mutating. The cost is low, and the image color is high. Suitable for short-distance and low-speed communication, such as industrial control. However, single-mode optical fiber adopts mutant type because of its small color dispersion.

Gradient Optical Fiber: The refractive index from the core to the glass package layer of the optical fiber gradually decreases, which can make the High-Mode Optical Fiber transmit in the form of sine, which can reduce the gray mode and increase the bandwidth of the optical fiber, the transmission distance is increased, but the cost is high. Currently, most multimode optical fibers are gradient optical fibers.

4. Common Optical Fiber specifications:

Single Mode: 8/125 μm, 9/125 μm, 10/125 μm

Multimode: 50/125 μm, European Standard
62.5/125 μM, US standard
Industrial, medical and low-speed networks: 100/140 μm, 200/230 μm

Plastic: 98/1000 μm for Vehicle Control

3. optical fiber manufacturing and attenuation:

1. optical fiber manufacturing:

The optical fiber manufacturing methods include tube CVD chemical vapor deposition, Rod CVD, PCVD plasma chemical vapor deposition, and VAD axial vapor deposition.

2. attenuation of Optical Fiber:

Factors that cause attenuation of optical fibers include intrinsic, bending, extrusion, impurity, non-uniformity, and interconnection.

Intrinsic: it is the inherent loss of the optical fiber, including the secondary scattering and the inherent absorption.

Bending: the loss of light in some optical fibers due to scattering.

Extrusion: the loss caused by slight bending when the optical fiber is squeezed.

Impurity: the loss caused by the absorption and scattering of impurities in the optical fiber.

Uneven: Loss Caused by uneven refractive index of the optical fiber.

Interconnection: The loss produced when the optical fiber is docked. For example, the coaxial degree of single-mode optical fiber with different axes must be less than 0.8 μm. The end face is not perpendicular to the axis, and the end face is uneven, mismatch of connection cores and poor weld quality.

Iv. Advantages of Optical Fiber:

1. The optical fiber channel is very wide and theoretically can reach 3 billion m Hz.

2. No relay section is long. Dozens to 100 kilometers, and the copper line is only several hundred meters.

3. It is not affected by the electromagnetic field and electromagnetic radiation.

4. light weight, volume School For example: 20 thousand pairs of twisted pair wires with a diameter of 900 and a weight of 8 tons/KM. The optical cable with 10 times the communication volume has a diameter of 0.5 inch and a weight of 450 P/KM.

5. The optical fiber communication is not electrified and safe to use can be used in inflammable and violent places.

6. Wide ambient temperature range.

7. Chemical Corrosion and long service life.

Part 2 optical cable

I. Optical Cable Manufacturing:

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

1. Optical Fiber Screening: Select optical fiber with excellent transmission characteristics and qualified tension.

2. Optical Fiber Dyeing: It is identified by standard full chromatography and requires high temperature without fading and no migration.

3. secondary extrusion: Choose high elastic modulus, low linear expansion coefficient of plastic extrusion into a certain size of the tube, the optical fiber into and fill in the moisture-proof waterproof gel, the last storage for a few days not less than two days ).

4. Cable twisting: The cables squeezed out by several cables are twisted together with the reinforcing unit.

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

Ii. Types of optical cables:

1. The laying methods include: Self-bearing overhead optical cable, pipeline optical cable, armored buried optical cable and submarine optical cable.

2. According to the optical cable structure, there are: bundle-pipe optical cable, layer-twisted optical cable, tension-type optical cable, belt optical cable, non-metallic optical fiber cable and branch optical cable.

3. Optical Cables for long-distance communication, short-distance outdoor cables, hybrid cables, and optical cables for buildings are used by purpose.

Iii. Optical Cable Construction:

Over the years, we have established a mature method and experience in cable construction.

1) Outdoor construction of optical cables:

For long-distance optical fiber cables, the most important thing is to select a proper path. Here, not necessarily the shortest path is the best, but also pay attention to the right to use the land, the possibility of erection or burial.

Complete Design and construction drawings must be provided to facilitate construction and future inspection. During construction, be sure not to make the optical cable under heavy pressure or be hurt by hard objects.

When a optical cable turns, its turning radius must be 20 times greater than its own diameter.

1. Outdoor overhead Optical Cable Construction:

A. It is A simple and inexpensive method for hanging the cable tray. It is the most widely used method in China, but it is time-consuming to add and sort the hooks.

B. Wire-wound overhead mode. This mode is relatively stable and has less maintenance work. However, a dedicated machine is needed.

C. Self-bearing overhead mode, which has high requirements on line drying, difficulty in construction and maintenance, and high cost. It is rarely used in China at present.

D. A guide device must be added to the trunk line of the optical cable during overhead, and the cable can be dragged to the ground. Reduce the friction during Optical Cable traction. The remaining optical cable used for scaling is required on each worker.

E. Pay attention to the reliable grounding of metal objects in optical cables. Especially in mountainous areas, high-voltage power grids, and multi-region areas, there are usually three grounding points per kilometer, and even non-metallic optical cables are used.

2. Construction of optical fiber cables for outdoor pipelines:

A. Check the pipe occupation before construction, clean and place the plastic sub-pipes, and put them in the lead wires.

B. Make sure that the reserved length is sufficient when calculating the layout length. See the table below:

Increase in natural Bending Length m/km)	Bending inside a manhole Increase the length of m/hole)	Joint Overlapping length M/side)	Intra-Bureau reservation Length m)	Note
5	0.5 ~ 1	8 ~ 10	15 ~ 20	Other remaining security Design reservation

C. The length of a single deployment should not be too long, generally 2 KM). The wiring should start from the middle and lead to both sides.

D. The cable traction is generally not greater than 120 kg, and the Strengthening center of the optical cable should be pulled, and the waterproofing and strengthening treatment of the optical cable head should be completed.

E. The introduction and source of optical fiber cables must be added to the Guide Device and cannot be directly dragged to the ground.

F. Pay attention to reliable grounding for pipe cables.

3. Directly Buried Optical Cable Laying:

A. The depth of the Directly Buried Optical Cable trench should be mined according to standards. The standards are shown in the following table:

B. Place where troughs are not allowed can be laid on an overhead or drill-down pre-Buried Pipeline.

C. The trench bottom should be kept stable and sturdy. You can pre-fill a part of sand, cement or support materials when necessary.

D. manual or mechanical traction is available for laying, But guidance and lubrication should be paid attention.

E. After laying is completed, the soil should be covered and consolidated as soon as possible.

4. Laying of optical cables in buildings:

A. Pay special attention to the load-bearing problem of optical fiber cables during Vertical Laying. Generally, the optical fiber cables must be fixed once for each two layers.

B. When the optical cable goes through a wall or floor, add a plastic tube with a protection port and fill the tube with a flame retardant filler.

C. A certain amount of plastic pipes can be laid in advance in the building, and a certain amount of plastic pipes can be laid. After that, the optical fiber cables will be laid with traction or vacuum cables.