Analysis of ADSS fiber optic cable drawing and polishing process
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Analysis of ADSS fiber optic cable drawing and polishing process

The polishing process of optical fiber for ADSS cable

Polishing definition: In the process of optical fiber production, the docking of the preform and the tailpipe is called polishing.

Polishing process: Fix the preform and the tailpipe to the machine separately, align the cut surface as much as possible, continue heating for 1 hour at high temperature, melt, and weld, then smooth the welded joint, and finally cool enough (more than 2 hours) to remove.

Drawing process of optical fiber for ADSS cable

1 bare fiber

The smaller the outer diameter of the fiber, the better. The fluctuation of the fiber diameter can cause the backscattering power loss and the fiber connection loss of the fiber. The fluctuation of the outer diameter of the fiber causes the core diameter and the mode field diameter to fluctuate, resulting in an increase in fiber scattering loss and connection loss. Assuming that the fiber core diameter fluctuation is proportional to the outer diameter fluctuation, when the two outer diameter fibers are connected, the loss at the fiber connection point can be seen as:

A (diameter fluctuation) ≈ 20log{2/(a1/a2+a2/a1)} (dB)

Let a1 = 126 μm, a2 = 124 μm, then A = 0.001 (dB); let a1 = 127C a2 = 123 μm then A = -0.0045 (dB). Therefore, it is preferable to control the outer diameter fluctuation of the optical fiber to ±1 μm. Increase the drawing speed, properly reduce the drawing temperature, and reduce the residence time of the preform in the high-temperature furnace. Reducing the diffusion of water in the cladding to the new region is beneficial to reduce the additional attenuation of the fiber drawing. Increasing the drawing speed and increasing the drawing tension can reduce the fluctuation of the outer diameter and also help to reduce the occurrence of E’ defects. It also contributes to the increase in fiber strength. However, high-speed wire drawing requires a higher furnace temperature heating power, which is more likely to cause an uneven temperature field. It has a large influence on the warpage of the fiber (the warp is the radius of curvature corresponding to the bending of the bare fiber without any external stress). The main reason for the influence of the warpage is that the optical fiber is unevenly heated in the temperature field, which causes the fiber to shrink in the neck direction, resulting in a decrease in fiber warpage. The warpage of the optical fiber is one of the indicators that the cable used is more concerned about, especially in the optical fiber. If the fiber warpage is too small, it will have adverse consequences for the connection.

Due to the following basic requirements for high-speed fiber drawing furnaces:

  1. Design the ideal temperature zone distribution and air path design to produce the ideal preform neck shape.
  2. The furnace temperature is stable and adjustable, which is convenient for precise control of the tension of the wire.
  3. Furnace component selection and airflow design ensure that the fiber surface is as less polluted as possible.

Therefore, the structure of the drawing furnace components is improved, and the airflow process in the furnace is improved. Get the following results:

  1. Finally, the amplitude of the F-path change of the fiber during the drawing process is controlled to be about 0.3 μm.
  2. Fiber warpage control is above 10m
  3. Good attenuation characteristics of each wavelength of the fiber

2 fiber coating

The coating is a very special process in the production of optical fibers. The quality of the coating has a great influence on the strength and loss of the fiber. The bare fiber enters the mold at a high speed and is drawn into the coating liquid. Since the fiber itself is heated, the viscosity of the coating on the top of the mold is lower than the viscosity of the coating in the coating tank. This difference in viscosity between the coatings creates a pressure differential that pushes the coating up. The coating liquid level in the mold is kept stable by a certain coating pressure. If the bare fiber temperature is too high (increasing the drawing speed), the coating liquid level balance will be out of control, the coating will be unstable, and the coating will be abnormal. Affects coating quality and fiber performance. A good stable coating state should include the following aspects: a no bubbles or impurities in the coating layer; b good coating concentricity; c small coating diameter change. In the case of high-speed drawing, in order to achieve a good and stable coating state, it is necessary to keep the fiber at a constant and sufficiently low temperature (generally considered to be around 50 ° C) when entering the coating die. As the drawing speed increases, the probability of air being mixed into the coating during fiber coating is greatly increased. At the same time, at the time of high-speed drawing, the drawing tension is also greatly improved, and the result of the interaction of the centripetal force and the drawing tension generated by the coating die determines the stability of the coating state. This requires a higher centripetal mold and a more precise mold base tilt adjustment system for high-speed drawing to ensure coating stability.

After high-speed fiber drawing, the following fiber coating failure occurred:

  1. The coating diameter changes greatly when drawing on the wire and the coating is eccentric;
  2. The coating has bubbles
  3. Layering between the coating and the cladding

Poor curing of the coating is optimized by some of the following process improvements and equipment adjustments:

  1. Optimize the coating process for the case where the coating diameter changes greatly, and finally, make the coating diameter variation amplitude and coating concentricity reach the desired state.
  2. Bubbles are applied to the coating, the cooling device is optimized, and the cooling efficiency is modified to achieve a uniform and effective cooling of the bare fiber during the production process.
  3. For poor curing of the coating, delamination between the coating and the cladding. The fiber-coated UV curing system has been modified to achieve excellent air tightness; the positioning of the retrofit system ensures optimal positioning of the fiber in the UV-cured quartz tube.

After the above improvements to the relevant process parameters and facilities, the excellent coating quality is obtained to ensure the stability and reliability of the fiber performance.

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