Building up Two Exposure Systems of Optical Fiber Interference Lithography to Make Micro Polarizers
在二元相位光柵全光纖雙光干涉曝光系統中，關鍵元件是光纖端面二元相位光柵。為了要先行確認光纖端面二元相位光柵的製做參數，我們會先在石英玻璃上製作二元相位光柵，並量測其繞射效率。我們藉由此參數，利用酸化玻璃(acid soluble glass)，改善了光纖集束(fiber bundle)製程，製做出光纖端面二元相位光柵。我們接著會介紹二元相位光柵全光纖雙光干涉曝光系統。由公式推導及實驗驗證，可得知以雷射通過二元相位光柵的繞射光為光源，在光阻上曝光時，光阻光柵圖案的周期將會是二元相位光柵周期的一半。藉由適當地調整曝光劑量，可以由二元相位光柵全光纖雙光干涉曝光系統製造出完整的光阻圖案。在此光阻光柵圖案均勻地鍍上金後，由實驗及模擬佐證，此圖案可以被視為是反射式偏振片。藉由調整二元相位光柵全光纖雙光干涉曝光系統中的曝光平台，我們可以在同一片基板上製做具有不同光柵方向的四個曝光區域的方型圖樣，此圖樣是微偏振片陣列的基礎。
To date, fabricating submicron structures on an optical fiber facet has drawn a lot of attentions which has brought many applications have been developed. One particular optical component based on submicron structures on optical fiber facets, binary phase grating (BPG), is the main focus of this work. In this work, two-beam fiber interference lithography is first demonstrated to show how the fibers can play a role in interference lithography, and acts as a transition from the traditional interference lithography to an all-fiber one. Then an all-fiber two-beam interference exposure system based on the optical fiber patterned with BPG is introduced.
Two-beam fiber interference exposure system is composed of two subsystems, a beam steering system to stabilize laser beam in free space due to possible environment variations, and a fiber interference lithography system to fabricate interference patterns on a substrate. The experimental results of PR patterns by two-beam fiber interference lithography will be shown, along with the MATLAB simulation results. From the simulation, interference patterns by two Gaussian beams of which the centers are matched are hyperbolic shape. The SEM images one show that interference patterns at the center of single exposure area have the best contrast. By adjusting the incident angle of exposure beams, fabrication of interference patterns with variable periods are presented. While fabricating multiple exposure areas on the same chip, moire patterns and overexposure areas will occur due to distance effect.
Two-beam interference exposure system by using optical fiber ends patterned with BPGs is introduced. To obtain the process parameters of optical fiber ends patterned with BPGs, BPG fabricated on quartz substrate is fabricated first, and diffraction efficiency is measured. Using these parameters, we will demonstrate the procedure to fabricate optical fiber ends patterned with BPGs by a modified fiber bundle process using acid soluble glass. We then introduce the setup of two-beam interference exposure system by using an optical fiber ends patterned with BPGs. By adjusting the exposure dose properly, complete PR grating patterns are fabricated by this system. The period of these PR grating patterns is a half of the BPG structure, verified by exposure results and equation deviations. These PR grating patterns deposited with a chromium layer and a silver layer are lifted-off, and the left metal grid structures are confirmed to be wire grid polarizers in simulation and measurements. By adjusting the exposure platform in two-beam interference exposure system by using optical fiber ends patterned with BPGs, four adjacent exposure areas with different grating directions arranged in a square pattern can be fabricated on the same substrate, which is the base of micro-polarizer array.
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