Analysis on the Design and Manufacture of Remote Optical Cable

1. Introduction

As the country vigorously develops new infrastructure construction; 5G communication has entered the final sprint stage. As the four major operators compete for market share, the construction of 5G-LTE base stations is in full swing. The base station mode generally follows the 4G BBU (radio remote module )+RRU (baseband processing unit) station building mode (see Figure 1), RRU and BBU need to be connected by optical fiber, and one BBU can support multiple RRUs, which can well solve the problem of covering large venues and complex buildings, and extending optical cables Plays an important role in mobile communication.

Figure 1 BBU+RRU mode

2. Pull out the optical cable

Since the BBU+RRU mode is generally used in short-distance and indoor coverage scenarios, optical cables must pass through corridors, indoor wiring pipes, shafts, etc., and air blowing may be used in some places, so this type is different from ordinary optical cables. In the field of special optics, optical cables generally require light weight, small outer diameter, small bending radius, dry structure, flame retardant, and tensile strength. We generally call this type of optical cable a remote optical cable; it consists of a single-core flexible optical cable , aramid armor and a low – smoke halogen -free sheath.

Single core flexible optical cable                                    Remote fiber optic cable

Photoelectric composite remote optical cable

The remote optical cable is usually in the form of all dielectrics, that is, non-metallic strength members are used. Since the BBU+RRU remote base station requires a small number of cores in the optical cable, the combination method is flexible and changeable, and a photoelectric hybrid structure can also be used in some scenarios.

3. Design
4. Structural design

In order to reduce the diameter of the optical cable, the remote optical cable generally adopts a tight-sleeved optical fiber, which can further improve the tensile and pressure-resistant performance of the optical fiber, and is convenient for terminal processing with the quick connector . Short-term tensile strength and flexibility. Considering that the optical cable is mostly used indoors, the sheath is made of LZSH sheathing material. At the same time, it can be considered to add water-blocking yarn when placing the aramid yarn, which can effectively avoid the occurrence of the optical cable. Potential for water seepage.

2. Selection of aramid yarn

In order to improve the tensile performance of the optical cable, the strengthening member is generally made of aramid fiber. Since this type of optical cable requires low short-term tensile force, the model used is generally aramid fiber below 1670dtex, and the maximum tensile force of the optical cable is 200

4. 4. Processing technology of remote optical cable
5. Single-core flexible optical cable subunit process control

The sheath layer of the sub-unit single-core flexible optical cable can be distinguished by color or surface printing according to the needs. During the production process, special attention should be paid to the control of the outer diameter of the optical cable and the aftershrinkage of the sheath. The aftershrinkage is required to be less than 3‰, so The selection of the sheath material and the selection of the mold size in the production process must be strictly controlled to ensure the normal use of the product and the processing and process control of subsequent products.

Before the sheath extrusion of the single-core soft optical cable , according to the design requirements, it is necessary to consider the wiring method of the aramid fibers and choose to place directly around the tight-sleeved optical fiber or helically twisted and wrapped. It should be uniform 2-3N. If helical twisting is required for wrapping, the pitch is generally required to be controlled between 500-600mm to avoid uneven stress on the aramid fiber during the stretching process, resulting in excessive cable strain and strain of the optical cable. The pay-off tension of the single-core tight- buffered fiber should also be uniform, and it is required to be controlled at 6-8N, otherwise, the optical fiber strain will be uneven.

2. Remote structure cabling process control

The cabling process control of remote optical cables is different from that of ordinary optical cables. Generally, tight sleeve optical fibers or subunit soft optical cables are twisted around a non-metallic center reinforcement (may not have a central reinforcement) to make a cable core. In order to ensure the roundness and structural stability of the cable core, helical twisting is generally used to form a cable. The cable core in front of the sheath is usually wrapped with water-blocking tape or polyester tape to protect the cable core, so as to avoid the connection between the sheath material and the tight sleeve or subunit structure. , affecting the use of stripping; secondly, pay attention to the influence of the yarn tension on the cable core when forming a cable.

3. Process control of remote optical cable outer sheath

According to the use environment and conditions of the remote optical cable, the general sheath is made of low-smoke halogen -free flame-retardant material (LSZH), and other materials (polyurethane TPU) can also be used according to the special requirements of users.

The processing temperature of low-smoke and halogen -free materials should not be too high, and the screw needs a special low-smoke and halogen-free screw. The recommended temperature is as follows:

Considering the post-shrinkage of the finished optical cable, controlling the take-up tension can effectively reduce the post-shrinkage. The take-up tension is generally controlled at 30-40N; at the same time, it is necessary to ensure sufficient cooling of the optical cable and the speed of the production line during the production process to avoid excessive post-shrinkage. Large, abnormal sound fiber optic performance indicators.

5. Conclusion

At present, with the widespread application of distributed base stations, the market demand for remote optical cables is increasing, but the environment in which they are used is very complicated. Therefore, due to the particularity of the structure of remote optical cables, there may be differences in theoretical design and test structures. If there is a large difference, it is necessary to continuously debug, compare the experimental data with the theory, and adjust various parameters in the design calculation, so as to summarize a set of theoretical design schemes suitable for oneself.