초정밀 레이저를 이용한 렌즈일체형 광섬유 제작연구

Abstract

Recently, the studies to simplify complex optical systems have been done in the fields such as an interferometer, a fiber laser, etc. using optical fibers. When the light beam traveling through an optical fiber exits from the optical fiber core, the light beam diverges according to a numerical aperture (NA) value of the optical fiber. Therefore, to converge the light, a lens is installed in front of the fiber. In order to overcome this complexity, researches have been conducted to fabricate a lens-integrated optical fiber that allows light beams emitted from the optical fiber to converge. Femtosecond and CO2 lasers which can cleave precisely and melt easily a silica-based optical fiber, respectively were used. A lens-integrated optical fiber can be fabricated by attaching a single mode optical fiber to core less silica fiber (CSF) with the radius curvature at the end of the CSF. For a converging lensed optical fiber, the length between the end of the single mode optical fiber and the CSF end and the radius of curvature are important. In order to fabricate a lensed optical fiber with a focal length, experiments cleaving a single mode optical fiber using a femtosecond laser have been done. In addition to these experiments, experiments to melt the end of the optical fiber using a CO2 laser to generate a radius of curvature depending on CO2 laser powers and exposure times were carried out. We get conditions for Lc(the distance from the front surface of the lens to the single-mode fiber core) and the radius curvature R using a MATLAB program. Using those parameters a lensed fiber was fabricated. We measured the focal length of the lens-integrated fiber using the power density of the light beam returning to the lens-integrated optical fiber from a circulator and a mirror. The comparisons between theoretically estimated and measured focal length has been done.