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Analysis of Design Principle of Optical Fiber Ribbon Cable Sleeve

2022-09-07
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I. Overview

Optical fiber communications technology stands out from optical communications and has become one of the main pillars of modern communications, playing a pivotal role in modern telecommunication networks. As an emerging technology, optical fiber communication has developed rapidly and has a wide range of applications in recent years, which is rare in the history of communication. It is also an important symbol of the world's new technology revolution and the main transmission tool for various information in the future information society.

 

In my country, optical fiber communication has been used since the late 1970s, and it has been more than 20 years now. Especially in recent years, the large-scale adoption of optical fiber and cable is more significant. The promotion and pilot development of IPTV networks in cities, on the other hand, the rapid expansion of operators' business capacity, and the continuous development of rich and diverse business content. At the same time, operators continue to build and improve their The basic physical fiber network has both the necessity of its development and the need to maintain a competitive position. Therefore, the massive demand from the two aspects of infrastructure construction and business development has directly led to the rapid growth of operators' demand for optical fibers and cables.

 

Due to the limited increase of urban underground pipe network resources for laying optical cables in a long period of time and within a certain space, and has the characteristics of exclusivity and scarcity. The optical fiber ribbon optical fiber cable has the characteristics of high optical fiber density, small optical cable outer diameter, and easy laying. Over the years, the use of optical fiber ribbon cables by operators has become more and more common, and the application areas have become more and more extensive. The network level of operation has gradually spread from the core layer to the key access layer, and the number of cores is also increasing. The large-core-count fiber optic ribbon cable in operation has reached 432 cores. Based on the development of fiber optic ribbon cable, this paper introduces the structure design principle of manufacturing layered fiber optic ribbon cable. The experiment verifies the performance change of the fiber optic ribbon cable when different materials are used for the fiber optic ribbon sleeve.

ftth cable

Principles of Optical Fiber Communication

The principle of optical fiber communication is: at the transmitting end, the transmitted information (such as voice) is first converted into an electrical signal, and then modulated onto the laser beam emitted by the laser, so that the intensity of the light changes with the amplitude (frequency) of the electrical signal. And sent out through the optical fiber; at the receiving end, the detector converts the optical signal into an electrical signal after receiving it, and restores the original information after demodulation.

 

Development of Optical Fiber Communication

Optical fiber communication is the main transmission means of modern communication network. Its development history is only ten or twenty years, and it has gone through three generations: short-wavelength multimode fiber, long-wavelength multimode fiber and long-wavelength single-mode fiber. The adoption of optical fiber communication is a major change in the history of communication. More than 20 countries, including the United States, Japan, Britain, and France, have announced that they will no longer build cable communication lines, and are committed to the development of optical fiber communication. China's optical fiber communication has entered a practical stage.

 

The birth and development of optical fiber communication is an important revolution in the history of telecommunications, and satellite communication and mobile communication are listed as technologies in the 1990s. After entering the 21st century, due to the rapid development of Internet services and the growth of audio, video, data, and multimedia applications, there is a more urgent need for large-capacity (ultra-high-speed and ultra-long-distance) optical wave transmission systems and networks.

 

Optical fiber communication is a latest communication technology that uses light waves as carrier waves to transmit information, and uses optical fibers as transmission media to realize information transmission and achieve the purpose of communication.

 

The development process of communication is the process of continuously increasing the carrier frequency to expand the communication capacity. The optical frequency as the carrier frequency has reached the upper limit of the communication carrier. Because light is an electromagnetic wave with a very high frequency, the communication capacity of using light as a carrier is extremely large. It is thousands of times more attractive than the past communication methods. Optical communication is the goal that people have long pursued, and it is also the inevitable direction of communication development.

 

Compared with the previous electrical communication, the main difference between optical fiber communication is that it has many advantages: it has a large transmission frequency bandwidth and large communication capacity; low transmission loss and long relay distance; It is conducive to the rational use of resources; it has strong insulation and anti-electromagnetic interference performance; it also has the advantages of strong corrosion resistance, strong radiation resistance, good windability, no sparks, small leakage, and strong confidentiality. It can be used in special environments or military use on.

 

fiber optic cable

2. Theoretical analysis of fiber optic cable sleeve design

1. Dimensional design of optical fiber tape sleeve

Optical fiber ribbons can be divided into two structures, namely edge bonding type and integral cladding type. Compared with the edge bonding type, the overall cladding type structure has a correspondingly larger thickness and width of the optical fiber ribbon. Considering the actual production and use of fiber optic ribbon cables, in order to improve the lateral pressure resistance and torsion resistance of fiber optic ribbons, domestic fiber optic cable manufacturers currently choose to produce fiber optic ribbons with an overall cladding structure.

 

For the identification of the optical fibers in the optical fiber ribbon, it is generally recommended to select the full chromatographic method for identification, so as to facilitate the on-site management of engineering connection and future optical fiber distribution. Fiber ribbons can be superimposed to form a fiber ribbon matrix.

 

1.1 The inner diameter of the casing usually adopts the following approximate formula

The equivalent size of the fiber ribbon matrix is ​​shown in Figure 2, where the width and height of the fiber ribbon matrix determine the length of the diagonal of the matrix, and its length is the basis for us to design the size of the sleeve.

 

The formula for the inner diameter of the casing is as follows:

The K value is related to the production process control. If the K value is considered large, the space for the optical fiber stack to move in the sleeve will be larger, and the quality of the fiber stack in the sleeve will be more guaranteed. If the diameter is too large, the cost of the optical cable will increase significantly.

 

The inner diameter of the sleeve determined by the above formula is designed based on a completely ideal rectangular optical fiber ribbon, but from the anatomical results of the actual optical fiber ribbon cable, the optical fiber ribbon is diamond-shaped in the sleeve, and there is a certain gap between the ribbons. . Therefore, the model of the modified optical fiber stack should be the deformed stack.

 

1.2 Design of casing wall thickness

The design of casing wall thickness needs to take into account the crushing resistance, torsion resistance and bending performance of the casing. The test results of these properties are related to the lateral pressure, bending and torsion that the casing is subjected to during processing where it passes over runners, stranding heads, etc. Industry standards have specified corresponding test methods.

 

In order to facilitate the design, the relationship between the wall thickness of the casing and the lateral compression strength and bending strength can be theoretically estimated by the structural strength factor and material strength factor of the casing. The structural strength factor of the casing is related to the inner space and wall thickness of the casing, and different materials have different material strength factors. The material strength factor has a linear relationship with the compressive modulus and bending modulus of the material.

 

According to experience, the casing wall thickness is generally designed to be 5% to 10% of the casing diameter, and the casing wall thickness is generally controlled at 0.45 to 0.85mm in the actual production process. As long as the casing designed in this way can withstand the crushing force greater than 400N, it is relatively safe in the actual production process.

 

Therefore, according to the above design of the inner diameter and wall thickness of the casing, the outer diameter of the casing can be obtained.

 

2. Selection of fiber optic ribbon sleeve material

Fiber paste needs to be filled in the fiber optic ribbon sleeve. The filling of the fiber paste can ensure the change of the roundness of the inner diameter of the casing, and can also meet the water blocking requirements of the casing. Non-polar filling fiber paste is used for polar polymer sleeve material, and polar filling fiber paste is used for non-polar polymer sleeve material to ensure good compatibility between sleeve plastic material and filling fiber paste.

 

At present, the commonly used optical fiber tape sleeve materials are modified polypropylene (PP) and polybutylene terephthalate (PBT). Major foreign cable manufacturers in Europe and the United States choose PP materials, and domestic cable manufacturers mostly use PBT materials. .

 

The PP optical fiber ribbon sleeve material is generally a high-impact copolymer non-polar polypropylene modified by adding a nucleating agent. During the nucleation process of PP crystallization, the polymer segment forms more by adsorbing PP molecules on the surface of the nucleating agent. , Thermodynamically stable microcrystalline nucleus; this microcrystalline structure makes the crystallinity of the PP material larger, resulting in better impact resistance properties of the product. The quality of this kind of crystallization can be evaluated by measuring the post-shrinkage phenomenon of the casing after extrusion. The material with serious post-shrinkage phenomenon has a small proportion of crystallites, which corresponds to the impact resistance, tensile yield strength and pressure resistance of the casing. Poor performance. PBT is a polar polyester polymer material, which is formed by polycondensation of terephthalic acid monomer with hard segment structure and 1,4-butanediol monomer with soft segment structure. The hard segment structure provides sufficient tensile strength and flexural strength of the material, and the soft segment structure provides a certain flexibility. Its crystallization process is very fast, which makes the sleeve have better surface gloss and dimensional stability, but crystallization under different cooling rates will form crystals with different densities and structures, resulting in changes in the mechanical properties and shrinkage characteristics of the sleeve.

 

Two different material casings have been described in many literatures, and the main comparison results are: assuming the same structural design, PBT casing will have better tensile mechanical strength, impact resistance, flexural strength and Flattening strength, but sensitive to bending radius. The non-modified PP has poor thermal oxygen aging performance, and PBT has a serious hydrolysis reaction under high temperature and humidity conditions.

 

The sleeves processed from the two materials are actually in a state of incomplete crystallization, and will have a certain degree of shrinkage after crystallization; but it is worth noting that the temperature of the cooling water in the front section of the production process and the position between the coupling point of the optical fiber ribbon and the traction wheel All will seriously affect the post-retraction index of the PBT sleeve at the glass transition temperature (about 60 degrees). Generally speaking, the higher the cooling temperature of the casing into the water, the greater the shrinkage of the casing, and the smaller the shrinkage after crystallization; on the contrary, the lower the cooling water temperature, the smaller the casing shrinks, but the shrinkage after crystallization will be very large, Even 1 to 2 times the retraction of the casing, which will adversely affect the final performance of the product, so this post-retraction phenomenon should be avoided in production. On the contrary, the degree of shrinkage of PP after crystallization is relatively less affected by the cooling water temperature and is easier to control.

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