MICROLENS SYSTEM FORMED ON THE END OF A SINGLE MODE FIBER FOR LASER APPLICATIONS (MICROBEAM, MICROPTICS, SPOTSIZE, COUPLING, PHOTOLITHOGRAPHY).

摘要

In this thesis microlenses on the end of single mode fibers were designed, fabricated and tested. In designing this Microlens-ended single mode fiber (MSMF) system for laser applications the focusing beam parameters such as minimum spot size W(,o2), minimum spot size position Z(,m), Rayleigh range Z(,R) and maximum intensity position Z(,p) are very important.; Using the paraxial and diffraction theories, MSMF systems were designed for laser applications. These theories state that the focusing beam parameters depend on the lens system parameters and change due to the finite size of the incident beam, finite size of the lens aperture and aberrations.; The various types of photoresist microlenses were fabricated on the ends of single mode optical fibers as well as multimode optical fibers using the photolithographic process. The microlenses fabricated on the ends of single mode fibers are 2.6 (TURN) 20 (mu)m in radius of curvature, 0.7 (TURN) 9 (mu)m in thickness and 5.9 (TURN) 15 (mu)m in diameter.; The thickness and the radius of curvature of microlenses developed depend on the total exposing energy in the photolithographic process. The developed microlenses were tested by measuring the focusing beam parameters and the intensity distribution near the waist position. The measured focusing beam parameters of microlenses closely follow those expected from the paraxial theory or from the diffraction theory. The shape of the lens also roughly matches the lens shape predicted under some assumptions. Both measured and expected values for (at 830 nm) W(,o2), Z(,M) and Z(,R) are 0.75 (TURN) 3.0 (mu)m, 3.5 (TURN) 20 (mu)m and 0.9 (TURN) 13 (mu)m, respectively.; Various testing apparatus for the spot size measurement, waist position measurement, examination of the intensity distribution and study of the lens surface were built. The minimum spot sizes and minimum spot size positions were measured using the interferometric knife-edge scaning system. The sizes of microlenses were determined by using the scanning electron microscope.; Finally, tolerance criteria for the degree of aperturing and spherical aberration in MSMF systems (cutoff wavelength of optical fiber = 690 nm, wavelength of an incident beam = 830 nm ) are a/W(,o) (GREATERTHEQ) 0.95, a(,2) (GREATERTHEQ) -0.4 x 10('-3)(lamda). These tolerance criteria were obtained from the Modified Strehl intensity.