Preface
Now the communication with the class A and class B single-mode fiber multimode fiber is made of quartz glass manufacturing. Quartz glass optical fibers in the process of making the glass matrix inevitably exists a tiny inhomogeneities, high temperature melt quenching drawing surface to allow formation of nonuniform stress distribution, and environmental dust, mechanical damage cause of fiber surface some micro-cracks. These cracks in high-speed wire drawing, the drawing under tension, will generate further expansion, resulting in reduced fiber strength. With the current drawing speed increase, how to ensure the strength of the optical fiber to be concerned. In this paper, from the angle of technology on the preform, furnace temperature, coating process and drawing environment on fiber strength effect.
A preform for optical fiber strength, influence
Fiber in the production process of low strength fracture is mainly composed of optical defects caused by. These defects can be divided into internal flaws and surface defects, the internal defects of preform with the bubbles and inclusions. Surface defect is the main form of microcracks and dust contamination, it and preform surface damage, drawing furnace and environmental cleanliness, coating quality and other factors are closely related. To further illustrate these factors on fiber strength effect, the following are respectively discussed and analysis:
Effect of 1.1 internal defect
Preform production process, inevitable existence of bubbles and inclusions. The preform inside diameter of bubbles, drawing in the process of rupture may occur, or reduced to tiny gas line and have a serious impact on optical fiber strength. For internal impurity defects, drawing process not only can make its healing and reduce the, opposite such impurities in natural quartz raw materials are mixed in a high melting point metal oxides, due to its expansion coefficient and vitreous exists bigger difference, so in the high temperature melting, impurities and vitreoretinal interface crack. Crack in drawing process will continue to grow, the crack size is much larger than the size of impurity itself, therefore these impurities on the strength of the optical fiber is more serious than bubble sort of much bigger effect. Preform in the presence of bubbles and inclusions for optical fiber drawing, is inevitable, if the preform quality is not good, will not be able to wire drawing process to improve the strength of. Therefore, when the optical fiber preform quality effect of the main factors of influencing strength.
1.2 surface defects in rats
Surface defects are mainly micro crack and surface contamination. Preform surface micro cracks, during the drawing process inevitably into smaller fiber surface micro crack. When the fiber is subjected to an external stress is larger than the small crack growth threshold stress, small cracks increased, eventually lead to the breaking of the optical fiber. While the surface contamination can reduce the surface of the bare optical fiber and coated in a coating combining. Because the inner coating and bare fiber between voids, when subjected to some external force, the coating is first broken, causing the bare fiber fracture.
The surface defects are of two main methods: one is the flame polishing, the HF acid treatment. Flame polishing can be effectively cured preform surface micro cracks, HF acid can wash away the attachment in the preform surface impurity. Therefore, in the actual production of the preform, HF pickling and flame polishing is treated for two times, thereby improving the fiber strength. We on untreated preform and preform processing after drawing the fiber strength statistics, results as shown in the table:
Screen tension preform fiber length breakpoint number
9.0N treated with 1000KM 14
9.0N 1000KM 8
Table 1 preform surface treatment on fiber strength effect
As you can see from table 1, after treated two times of the preform, the drawn fibers strength improves obviously. Need to pay attention to, HF pickling must control the pickling time, if overlong pickling time, cracks will produce apparent expansion. And the flame polishing, to control the flame combustion gas purity and environmental cleanliness, prevent polishing have two pollution.
Two, the effect of temperature on strength of optical fibers
High temperature wire drawing process occurring in point defects will cause the optical fiber mechanical strength deterioration, has been found to be the most important point defects of E ′Si-O defect is the chain fracture generation, Si-O strand breaks and to chain when dynamic changes, E defect depends on the concentration of Si-O strand breaks and to balance the results chain. E defect concentration with drawing furnace heating zone length increases, with the drawing speed increased, leading to preform heating area in the high temperature zone time lengthened, thereby causing the Si-O strand breaks produced by higher frequency. Studies have shown that, when the heating furnace temperature is increased from 2200K to 3000K, just from the heater of the bare fiber defect concentration will increase by two orders of magnitude.
At the same time due to high temperature in the furnace, graphite piece volatile produces the following reaction:
Reaction of SiC is a kind of high hardness of the particles, in the heating furnace if the bare fiber is SiC particles touch, fiber surface defects and cracks. When the heating furnace temperature is high, SiC reacts to the number of fine particles are more, so the surface of the bare optical fiber by the collision probability is higher, the optic fiber surface defects produced more, fiber strength is lower. Three, coating and curing on strength
3.1 coating effect
Optical fiber coating 's role is to protect the fiber surface will not be subjected to mechanical damage and tidal effects and maintains its original strength, if the coating is too thin or eccentric lose mechanical protection function. Coating concentricity in drawing process easy to change, so in the drawing of need to pay attention to. Below is the actual drawing according to the statistics of the coating concentricity of optical fiber intensity influence.
A coating concentricity of optical fiber intensity influence
According to the above, when the coating concentricity of less than 8, every 1000KM fiber breakpoint number at around 10, in the screening of fiber strength will not cause too big effect influence. When the fiber concentricity amounts to 10, breakpoint number 15.5. Therefore, the fiber concentricity of less than 8, can effectively reduce the eccentricity caused by coating the fiber strength reduction.
The coating process, the influence of another optical fiber strength factor is coated in bubbles. Bubble formation is mainly because the drawing of optical fiber in the mold, excursion, the coating forming a half-moon shaped surface tilt angle, smaller side under increased pressure, gas easily fiber into the coating or coating; coating temperature changes, pressure fluctuations and other factors will generate bubbles in the coating. Bubbles in the coating, reduce the coating and the coating as well as between the coating and the binding force between the bare fiber. And the existence of gas increases the coating under tensile condition, the possibility of crack producing, eventually leading to fiber strength reduction.
3.2 effect of curing system
According to the actual optical fiber production method, widely used photopolymerization technique. Using UV radiation makes the photo-initiator excitation survival body ( radical and cationic ). The active body and the prepolymer and the monomer of C=C double bond formation reaction, growing chain. The growing chain further reaction, forming longer polymer chains. If there are multiple energy polymer or monomer, crosslinking structure will produce, last active body coupled with the disproportionation reaction termination.
As the technology improved, the production of wire drawing speed has been increased 20m/s~30m/s, optical fiber in curing furnace residence time is only 0.1s~0.2s. In order to ensure the coated fiber curing effect, required curing oven is capable of providing sufficient UV light, meet the photoinitiator activated into the active body the energy needed. At the same time, in the curing oven inlet in a certain proportion of inert gas, preventing oxygen on polymer chain growth inhibition, improve the curing effect.
Figure two and figure three
Figure 2 and figure 3 on different curing degree of optical fiber and as oxygen levels caused by overhigh fiber surface sticky hair fiber strength statistics. From the chart to see, when the fiber curing degree higher than 80%, the fiber strength with fiber curing degree increases, rather than a random distribution. While the map, curing furnace caused by high oxygen content in the surface sticky fiber, fiber compared with normal, every 1000KM breakpoint number from 12.1 up to 12.8, did not appear big rise.
Four, environmental and other factors influence on the strength of
In the preform transport process and drawing preform is alignment, are likely to cause preform surface abrasion. When the cover is poor, the surface of the bare optical fiber can also be easily scratch coating mouth. But in general, these mechanical injury in the operation of careful case, can effectively avoid.
In addition to the mechanical damage, another effect of fiber strength is an important factor in dust in the environment as well as the graphite furnace of volatiles in drawing. The dust can not only adhered to the surface of the bare optical fiber preform and, even in the stove to form small particles, hit the preform in melting zone, produced larger defects. Therefore in the drawing furnace in addition to the use of high volatile small high pure graphite material, also must be of high purity argon forced exhaust, ensure the local keeping a cleanliness. For drawing environment, in addition to ensure the whole drawing workshop clean out, in drawing tower air filter device to ensure that the local magnitude about 100 purification zone.
Five, summary
The preform, drawing furnace, coating and curing and environment and other factors on fiber strength analysis, can see, the effect of fiber strength is a major factor in the quality of prefabricated rod. Through the wand surface treatment can improve the strength of the optical fiber drawing furnace temperature, stable, good coating quality and good curing degree can improve the strength of the optical fiber. In the wire drawing production to keep drawing environment clean, strengthen production operations for the specification, selection of quality and reliable production of auxiliary materials, to prevent these recessive factors on fiber strength influence.
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