微結構高分子光纖的製作與分析

Abstract

本研究藉由自行組裝的簡易型抽製設備達到製作微結構高分子光纖(microstructured polymer optical fiber, MPOF)的目的。首先製作單孔的微結構光纖，並量測光纖的空氣孔直徑(dmpof)，並以相同抽絲比(draw ratio, DR)但搭配不同抽絲速度(draw speed, Ud)條件下，探討光纖空氣孔與毛細數(capillary number, Ca)間的關係，實驗結果並利用3-parameter Chapman-Richards function計算空氣孔直徑的極限值。接著製作單層(6孔)的微結構光纖，同樣地，量測其空氣孔直徑與孔距(hole spacing)，並比較其與單孔型態的尺寸，以應用在三層微結構光纖的製作。 實驗結果方面：(1) 以Ca = 1.5 × 105為界，將實驗範圍區分為表面張力區(Ca < 1.5 × 105)及平衡區(Ca > 1.5 × 105)。(2) 在表面張力區，由於表面張力作用較明顯，使得空氣孔直徑隨Ca變化；在平衡區，表面張力與黏滯力達到平衡，所以空氣孔直徑會趨近一定值。(3) 當改變抽絲溫度，但仍以相同Ca 抽製光纖，實驗結果顯示：光纖空氣孔直徑幾乎相同；但若改以相同抽絲速度製作，則溫度越高，空氣孔直徑會減少，因為溫度高，黏滯力快速的下降。(4) 在相同的實驗條件下，單孔與單層(6孔)微結構光纖的空氣孔直徑幾乎相同，這項結果將可應用及驗證於三層的微結構光纖實驗中。(5) 若使用臨界值d/Λ = 0.45，微結構高分子光纖在Ca < 2×104或縮孔率在33%以上時，可製作出endless single mode的微結構光纖。 誤差分析方面：(1) 低抽絲速度條件下可製作空氣孔直徑較小的光纖，但相對地其對熱電耦及溫控器的精度要求相當高。在成本及光纖尺寸的均勻度方面，高抽絲速度應是較佳的選擇。(2)在低抽絲速度時( < 20 mm/sec)，抽絲溫度是影響光纖空氣孔直徑的主因，在較高抽絲速度時( > 20 mm/sec)，預型體本身的空氣孔直徑誤差則是誤差的主要來源。 三層微結構光纖製作方面：依據單孔與單層型態的實驗結果，建立三層空氣孔型態的空氣孔直徑與孔距的迭代(iteration)運算流程，並依據相同抽製條件，微結構光纖空氣孔直徑相同的結論，以相同條件抽製單孔光纖並驗證其結果。

In this study, a plain drawing apparatus was assembled to fabricate the microstructured polymer optical fibers (MPOFs). We first drew the one-hole MPOFs and measured the air hole diameter (dmpof). Then, the one-layer (six-hole) MPOFs were fabricated with the same drawing conditions. The relationship between dmpof and capillary number (Ca) was illustrated. The limit of dmpof was calculated using the 3-parameter Chapman-Richards function, Furthermore, the analysis and comparison between the one-hole and six-hole patterns were conducted to fabricate the three-layer MPOFs. For one-hole MPOF, the experimental results are listed as follows: (1) Two draw regimes: surface-tension-dominated and force-balanced were separated with the critical capillary number of Ca = 1.5 × 105. The draw regime is surface-tension-dominated for Ca < 1.5 × 105 and force-balanced for Ca > 1.5 × 105. (2) In surface-tension-dominated regime, the air hole diameter changes with Ca and reaches a limit in the force-balanced regime. (3) When MPOFs were fabricated at different Td with the same DR, the air hole diameter changes with Ca. When MPOFs were fabricated with the same draw speed (Ud) and draw ratio, the dmpof drawn from high draw temperature is smaller than that drawn from low draw temperature due to large loss of viscosity at high draw temperature. (4) With considering the experimental results, the air hole diameters of one-hole and six-hole patterns conduct to the similar values at the same draw conditions. This result was utilized in fabricating the three-layer MPOFs. (5) An endless single mode MPOF can be produced for Ca < 2×104 (collapse ratio > 33%) provided that the critical value of d/Λ = 0.45 is applied. In error analysis, the results are list as follows: (1) At low draw speed, a MPOF with small air hole diameter can be produced. However, highly precise thermal couples and thermal controllers are required. Therefore, high draw speed is a better choice with considering the cost and fiber uniformity. (2) For low draw speed (< 20 mm/sec), Td is the major cause on the error of dmpof. For high draw speed (> 20 mm/sec), dpreform is the major cause on the error of dmpof. In the fabrication of 3-layer MPOFs: an iteration process has be derived to determine the air hole diameter and hole spacing. The numerical results are coordinated with the experimental results. Furthermore, the air hole diameter of one-hole MPOFs fabricated with the same draw conditions is similar to the results of 3-layer MPOFs.