Research on High and Low Temperature Resistance Performance of Multi-mode Miniature Tele-Optical Cable

I. Introduction

With the development of 4G and 5G communication networks, the number of base stations is rapidly increasing, and the amount of outdoor remote optical cables is increasing. The current remote technology generally adopts a distributed base station architecture. In the base station signal transmission system, the cable from the baseband unit BBU (Base Band Unit) to the remote radio unit RRU (Remote Radio Unit) is called the radio frequency cable. Cable for remote unit (RRU). Since the base station is mainly laid in the field, the remote optical cable needs a wide operating temperature range, generally -40 to 85°C. Therefore, this article analyzes and studies the factors that affect the high and low temperature resistance of the remote optical cable.

2. Brief description of optical cable structure and test conditions

The remote optical cable is generally composed of tight-buffered optical fiber or tight-buffered sub-units, possible reinforcements, and low-smoke, halogen-free, flame-retardant polyolefin outer sheath. As shown in Figure 1, Figure 2. In addition, there are armored telescopic cables, generally steel tape or spiral armor as the main compression component

The high and low temperature resistance of the optical cable discussed in this article mainly refers to the attenuation change of the optical cable under the high and low temperature cycle test. It is carried out in accordance with the method F1 "temperature cycle" in GB/T 7424.2-2018. The specific provisions are as follows: the test length is not less than 1km, the test The lower limit of the temperature range is -40℃ and the upper limit is 85℃, each temperature holding time is not less than 8h, and the number of cycles is 2 times. According to the qualified conditions of YD/T 2289.1-2011, it is the attenuation change of the multimode fiber in the test at the wavelength of 1300nm Not higher than 1.0db/km.

3. Factors affecting high and low temperature resistance

We take the 4-core miniature remote optical cable shown in Figure 2 as an example, and carry out the research on the high and low temperature resistance of the optical cable from three aspects: the raw material of the optical cable, the production process of the optical cable, and the structure of the optical cable.

First， Raw materials for optical cable

The raw materials for optical cables can be subdivided into sheath materials, reinforcements, and optical fibers. The impact of the reinforcements on the high and low temperature resistance of the optical cable in this study is negligible. Therefore, this time the research is mainly on optical fiber materials and sheath materials. The sheath material mainly considers the attenuation change of the optical cable caused by the shrinkage of the sheath in the temperature cycle test of the optical fiber cable, and the optical fiber material mainly considers the attenuation change of the optical cable caused by the bending of the optical fiber in the temperature cycle test of the optical fiber cable. On the premise that there is only one variable, we have selected three materials and three optical fiber coating materials, and trial-produced samples to verify the relationship between the optical cable material

The test results show that the sheath material B and the coating A have obviously better effects on the high and low temperature resistance of the optical cable than other materials. Therefore, these two materials should be selected when selecting materials.

Second. Optical cable production process

When the optical cable is produced, the production process of the product is the influencing factor of the high and low temperature resistance of the optical cable. For this type of optical cable, the stranding pitch of the optical cable and the pay-off tension of the tight sleeve are the main influencing factors. The size and pay-off tension of the tight sleeve can control the excess length of the optical cable and prevent the excess length of the optical cable from being too large and leading to poor high and low temperature resistance. Similarly, three sets of data are taken to verify the relationship between the optical cable production process and the high and low temperature resistance of the optical cable.

The test results show that the smaller the tight-sleeve stranding pitch and the increase of the pay-off tension, the smaller the attenuation change of the optical cable during the high and low temperature test. However, a high-speed twisting cage is required to meet the requirements of small pitch. The twisting pitch is limited by the production speed and the twisting cage rotation speed. The smaller the excess length, the tensile performance of the optical cable will be affected. The number of pieces must be comprehensively considered based on the equipment capabilities and product design of each manufacturer.

4. Optical cable structure

As we all know, the compactness of the optical cable structure will affect the space of the optical fiber, which in turn affects the high and low temperature resistance of the optical cable. By adjusting the tightness of the optical cable (with the outer diameter unchanged, reduce the wall thickness), verify the structure of the optical cable and the resistance of the optical cable. The relationship between high and low temperature performance is shown in Figure 7.The test results show that the more compact the structure of this optical cable is, the relatively lower the high and low temperature resistance of the optical cable. This conclusion is only for the design verification of this optical cable, and does not represent all remote optical cables.