The Effect of the Coherence of UV Laser on the Fabrication of Polymer Fiber Probe

• Main Author: 郭嘉竣
• Other Authors: 許芳文
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/99129817757253554066

碩士 === 國立嘉義大學 === 電子物理學系光電暨固態電子研究所 === 103 === In this study, a 355-nm ultraviolet (UV) laser beam is expanded and then focused on a diffuser plate through a series of lenses. The scattered lights passing through the diffuser plate are first collected by a collimator and then a focusing lens is used to throw the partially incoherent laser light into three types of optical fibers to be tested. Next, negative resists are coated at the end of the fiber for a lithography process. The plan is to fabricate polymer fiber tips. To figure out the effect of the coherence of the UV laser on the fabrication of the polymer fiber tip, we adjust the degree of coherence of the light source by changing the position of both the non-rotating diffuser plate and the collimator. We focus the lights on three types of optical fibers and acquire the fiber cross-sectional image. Then, we make the cross-correlation analysis in the image, calculating the degree of coherence of the UV laser light source. Next, we use these different coherence lights to fabricate fiber tips, and we compare the surface topography of the fiber tips. We know that the fiber tips made by the high-coherence UV laser have more defects because of the centralized distribution of optical power, and the mode pattern images show bigger and brighter speckles. Moreover, the rotating diffuser plate can be used to convert the laser light into a lower coherence light and investigate the effect of low-coherence transformed UV laser lights on the fabrication of polymer fiber tips. We find that the fiber tips made by the low-coherence transformed UV laser light have better quality surface topography. Furthermore, we produce polymer fiber tips of varying lengths by controlling the amount of the negative resists coated on the fiber endface. Finally, the different shapes of polymer fiber tips are utilized for measuring the change of a liquid refractive index. When we immerse the polymer fiber tip into deionized water and gradually add saltwater of a specified concentration to change its refractive index, we find that a change in the interference spectra can be observed, proving that the fiber tips produced using the low-coherence transformed UV laser lithography has the capability of refractive index sensing. Simultaneously, we verify that the shorter fiber tip has a better capability for refractive index sensing.