光學同調斷層掃描技術 (optical coherence tomography; OCT) 為一新穎性的光學顯微系統，是一種及時、具備非侵入性切片能力及高解析度的掃描技術，其縱向與橫向掃描相互獨立，縱向解析度與光源的頻寬成反比，橫向解析度取決於光源於聚焦平面上光點大小。本實驗室所研製的摻鉻鎂橄欖石晶體光纖，具寬頻的自發輻射頻譜，且避開水吸收的波段，故適合做為光學同調斷層掃描技術的光源。
本論文為研製摻鉻鎂橄欖石雙纖衣晶體光纖，利用雷射加熱基座生長法，將原始晶棒拉提成直徑為 69μm 之單晶棒，並置於兩種不同材料的玻璃毛細管內，再拉提成雙纖衣晶體光纖，進行超寬頻自發輻射放大光源功率量測，相較於先前單纖衣晶體光纖之光源功率提升 5成之多。
為了提升晶體光纖的自發輻射放大光源功率，我們嘗試幾種方法提升晶體光纖內之 Cr2O3 及 Cr4+ 的濃度：(1) 直徑 290μm 之單晶棒周邊蒸鍍 Cr2O3 再加熱擴散進入，(2) 直徑 69μm 之單晶棒於氧環境下，進行 800℃ 之退火實驗， (3) 使用離子佈植的方式，將氧離子佈植於晶體內。最有成效的是周邊蒸鍍 Cr2O3。當蒸鍍厚度為 109nm，鉻離子濃度提升為 0.011 ± 0.003 wt%，於幫浦功率為 1.33W 時，產生 CW 1.04mW 的 ASE 寬頻光源。相較於無周邊蒸鍍之單纖衣晶體光纖，其功率提升至少 1 倍。

Optical coherence tomography (OCT) is a novel real-time non-invasive optical scanning technique with ultrahigh resolution. OCT axial resolution is inversely proportional to the bandwidth of the light source and the lateral resolution depends on the spot size of the light at the focal plane. Cr:forsterite crystal has broad bandwidth and appropriate wavelengths away from water absorption peaks. It′s ideal for OCT application.
This study is on the fabrication of Chromium ions doped Forsterite double-clad crystal fiber. By the means of laser heated pedestal growth (LHPG) method, single crystal fibers of 69μm in diameter were produced first. They were inserted into two capillary tubes of different refractive index and matched size, and then were grown into Cr:forsterite double-clad crystal fiber. Compared with the single-clad crystal fiber, the amplified spontaneous emission (ASE) power was increased up to 50%.
In order to increase the ASE power, we tried several methods to increase the concentration of Cr2O3 and Cr4+ as follows: (1) Using electron gun to deposit Cr2O3 on 290μm-diameter single crystal fiber which was then laser-heated to in-diffuse Chromium, (2) Annealing 69μm-diameter single crystal fiber at 800℃ in oxygen environment, and (3) Using ion implantation to implant oxygen ions into crystal fibers. The most effective method was Cr2O3 deposition. When a thickness of 109nm was deposited, the Chromium ion concentration was raised up to 0.011 ± 0.003 wt%. When pumped with 1.33W incident power, CW 1.04mW ASE power was generated that was twice as much as that of crystal fibers without Cr2O3 deposition.

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