Plastic optical fiber compared with quartz optical fiber, low cost, simple manufacturing process, and the advantages of large numerical aperture, in cars, a local area network (LAN), has been widely used in such fields as health care and sensor, plastic optical fiber with polymethyl methacrylate (PMMA) as the core, the cladding needs low refractive index (1.4 z) of fluorine resin} to polystyrene hexene (Ps)/styrene acrylic ester copolymer as the fiber core, because of the Ps higher refractive index (1.59), can use the acrylic resin (refractive index of 1.49) as cladding.

Plastic optical fiber cladding can use different methods to make _]]. If the coating is solid, core material, coating material can be used at the same time extrusion forming ways of producing plastic optical fiber (coating a core plastic optical fiber), the method of equipment requires higher} or secondary extrusion method, namely again by extrusion method evenly on the optical fiber core wrapped a layer of coating material, but in the use of molten coating squeeze onto the fiber core, a larger temperature difference between coating and fiber core, made from fiber, tend to form in the optical fiber core is a pack of layer interface residual thermal stress, affect the properties of the fiber, and it is difficult to make coating and core work. If the coating is liquid, can take soaking method, is adopted by the law on the optical fiber core through put liquid of coating material, coating, so that it can be on the core materials evenly coated with a layer of coating.

For PS core plastic optical fiber, liquid coating material is general by has dissolved in solvent, polymerization good PMMA coating on the fiber core, after bake, make solvent evaporation, get a uniform layer on fiber optic core cladding. The author made of PS - MMA core plastic optical fiber attenuation has been reduced to 180 dB/km or so.

1 solvent thermal polyester

Using ontology polymerization polymerization of PMMA, by controlling the dosage of molecular chain regulator to making different relative molecular mass of PMMA, and soluble in methyl methacrylate (MMA) made from different liquid viscosity of coating, coating on the PS/MMA copolymer fiber core, after bake, make MMA volatilization, get a uniform PMMA on fiber core cladding.

From the effect of coating, high relative molecular mass, the viscosity of the membrane with high intensity, on the contrary, relatively small molecular weight, low viscosity small film strength. But high relative molecular mass, coating liquid viscosity, easy to cause hard to uniform coating, surface has property of plastic optical fiber particles. This is because the relative molecular mass is big, coating layer molecular chain length, asked the entanglement of molecular chain, formation of the cladding strength is high; But when high relative molecular mass, molecular chain in the coating layer asked tangles is overmuch, may form a molecular chain, unable to dissolve to the solvent, equably clad surface is caused by particles.

By experimental comparison, solvent thermal coating of plastic optical fiber coated with liquid on molecular mass should be in 10 ~ 150000, the resulting surface cladding

No particles appeared, and has enough strength.

Plastic optical fiber core of solvent thermal coating process has obvious flaws, due to high coating liquid viscosity can't bake, glassy state by the fiber core temperature transition temperature limit too much, so from the fiber core coated with the coating to coating solidified completely need a longer time (usually for a few minutes), before coating curing fiber adhesion on various kinds of particles, affect the performance of the fiber. And the volatilization of solvents on the operating environment pollution also nots allow to ignore.

2 uv-curing optical fiber cladding

Uv-curing coatings is studied, the method of the fiber core by contain light initiator, monomer coating liquid coating slot, and then under the protection of nitrogen, using ultraviolet light together form the cladding coating monomer, plastic optical fiber. This kind of uv curing process has simple equipment, core ask no residual thermal stress, a pack of layer coating curing quickly, without solvent volatilization, etc.

2.1 the experiment

Light initiator for benzoin ethyl ether in the experiments, the comparison of the monomer MMA and methyl acrylate (MA) coating ultraviolet curing coating effect. Cause MMA benzoin ethyl ether, for example, the first is excitation energy after benzoin ethyl ether absorbs uv light to three line excited states, photosensitive is decomposed into two kinds of free radicals. Then, free radicals react with MMA monomer, formed activated monomers.

2.2 the result of the experiment and analysis

Under the same content of initiator, polymerization by uv irradiation required more time than MA, MMA coating may be due to the effect of 1, 1, 2 to replace of the MMA. The formation of macromolecular chain caused by the interaction between substituent polymer Shan space tension lead to gather the energy of reaction is reduced, which reduces the light MMA polymerization reaction rate, polymerization of acrylic acid methanol heat is 78.9 kJ/tool], far more than the heat polymerization of methyl acrylic acid methanol 57.9 kJ/too1. In addition, the light curing time increased with the increase of initiator content decreased, but when the content of the initiator to a certain extent, decreasing light curing time become slow,

Because of the low concentration of light initiator coating, free radicals are uniform, high light initiator coating, close to the source of the surface of the coating. Easy to produce high levels of free radicals, and at the interface between coating a core, photochemical activity is small, so the whole coating completely cure time drop becomes slow. Light polymerization of MMA and MA monomer coating while heat coating speed, but for plastic optical fiber coating curing, curing time, the less the better. Therefore, this paper studies the MMA polymerization by uv irradiation and MA performed system (monomer heat causes the performed to the required viscosity plus light initiator, after mixing, vacuum). The monomer performed, not only because it has been part of the polymerization process, so as to reach the time at the end of solidification completely reduced; And because the viscosity of the system increases, oxygen solubility decreased, oxygen effect on polymerization of polymerization process less E (although have nitrogen protection, but there are still a small amount of oxygen into the reaction system), as shown in figure 1 (b), coating curing speed significantly improved.

Coating light initiator concentration and the plastic optical fiber attenuation relationship (632.8 rim in nitrogen neon laser wavelength light by using the truncation method measuring attenuation); Figure 3 for light initiator concentration and PMMA coating material through rate diagram (also in the same light, the ratio of initiator to make a batch of preform and measure them in 632.8 the transmittance of 5 cm thick rim wavelength). In figure 3, with the improvement of light initiator concentration, the light transmittance of coating materials have obvious decline. Because: (1) the initiator efficiency, is not the ideal l [5, the higher the content of initiator, and the smaller, the cured coating material as impurities in the more residue; (2) the higher the reaction system of initiator content, reaction product of macromolecular chain initiator end group, the more the end group and molecular structure of macromolecular chain is different, also has the scattering light effect. However,

Figure 2, the attenuation of plastic optical fiber is not subsequently and increase significantly. This is because the plastic optical fiber in the transmission of light, most of the light transmission by the plastic optical fiber core, the cladding of the fiber transmission only few percent of the light, so the optical fiber cladding optical transmittance of plastic optical fiber attenuation.