Jin Sung Choi

Fabrication of a graded-index polymer optical fiber preform by using a centrifugal force

We have investigated a fabricating method for a graded index polymer optical fiber preform using a centrifugal force. When two monomers with different densities and refractive indices are polymerized under a centrifugal force, a concentration gradient is generated due to their density difference. Therefore, a graded refractive index can be obtained according to the concentration gradient. When a monomer is polymerized under a centrifugal force, a preform with a hollow is obtained because of volume shrinkage. To compensate for this practically, additional monomer should be filled into the hollow. Monomer should be fed to obtain a continuous gradient of refractive index at the interface before the first polymerized product is perfectly glassified. Two different types of feeding additional monomer were experimented with: monomer-monomer pair (case I) and monomer-polymer pair (case II). The graded index profile with a proper δn (about 0.01) was successfully obtained in either case.

Fabrication of a graded-index polymer optical fiber preform without a cavity by inclusion of an additional monomer under a centrifugal force field

When two or more monomers with different densities and refractive indices are polymerized under a centrifugal force field, a radially varying refractive index is generated owing to the difference in density of the monomers. After the polymerization is completed, a cavity is generated about the rotational axis as a result of inherent volume shrinkage during bulk radical polymerization. Therefore it is necessary to feed an additional monomer into the cavity to compensate for the undesirable volume shrinkage. We have successfully fabricated a preform with graded indices for polymer optical fiber without a cavity by adding another monomer during rotation of the reactor. One can control the overall refractive-index profile by changing the rotation speed. Furthermore, the refractive-index profile can be predicted as a function of rotating speed by use of a simple mathematical model.