光柵式側向耦光技術應用於高功率半導體雷射陣列之研究

Study of Grating Based Side-coupling Technology for High Power Laser Diode Array

楊松蒲(Song-Pu Yang)

指導教授 ： 黃升龍

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.01632

摘要

近年來，利用半導體雷射激發之光纖雷射逐漸成為高功率雷射主流，藉由光纖輸出，此種雷射具有極佳的光束品質、窄線寬及高電光轉換效應等優點。半導體雷射陣列是一種可靠的高功率雷射激發光源，並且廣泛地使用在各種雷射幫浦應用上。本實驗室於2011年提出半導體雷射陣列之側向式光柵耦光系統，將976-nm 半導體雷射陣列耦入內纖衣尺寸為400 μm光纖，其輸出功率為21瓦並達到50%耦光效率，但該研究提及第二次繞射效應所造成之耦光效率損耗，將使得光源要耦入更小內纖衣尺寸之光纖更為困難。
因此在本論文中，主要將光柵週期改變至675 nm，在內纖衣尺寸為400 μm時，可以減少第二次繞射效應以提高耦光效率達至67.63%，將光纖內纖衣尺寸縮小至250 μm，其耦光效率可接近光源以680-nm光柵耦入400-μm內纖衣光纖，因此提升光纖輸出亮度2.36倍；另外引用基因演算法方式，可以提供設計光柵及優化之方向，如解決第二次繞射損耗及折射率匹配液損耗等問題。在本論文中，利用基因演算法設計出光柵之±1st 階繞射效率呈現非對稱型態，並以增強+1st 階繞射效率解決折射率匹配液帶來之損耗。此外，本論文將討論系統結構參數與光學架構因素損耗之關係，以達到高亮度、高功率輸出之光纖雷射側向耦光系統。

關鍵字

高功率光纖雷射 ； 半導體雷射陣列 ； 光柵 ； 光柵耦合器 ； 繞射

並列摘要

In recent years, diode-pumped fiber lasers have become main-stream in the high-power laser field, owing to their superior beam quality, narrow linewidth, and high electrical-optical conversion efficiency. Besides, laser diode array (LDA) is a reliable high-power pump source, and it has been widely used in many applications. In 2011, we have demonstrated a side-coupling scheme, a 50% coupling efficiency was achieved by using 680-nm period gold-embedded grating to couple 21-W, 976-nm LDA pump source into a 400-μm double-clad passive fiber. But in such a system, there was coupling loss caused by the secondary diffraction. The issue made it harder to couple pump source into a small cladding fiber.
In this work, we achieve 67.63% coupling efficiency into a 400-μm fiber by using a 675-nm grating. In addition, even using the fiber with the cladding diameter to 250 μm, the coupling efficiency is as good as the above mentioned case. In this result, the brightness has been enhanced by a factor of 2.36. Secondly, we introduce a genetic algorithm to optimize the grating coupling efficiency by eliminating the secondary diffraction and index-matching-gel coupling loss. We design an asymmetrical ±1st-order-diffraction-efficiency grating to increase +1st order diffraction efficiency, and reduce the coupling loss caused by the use of index-matching gel. Finally, we discuss the correlation between coupling loss issues and system structure parameters to achieve a high brightness, high power fiber laser output with a compact side coupling system.

並列關鍵字

high-power fiber laser ； laser diode array ； grating ； grating coupler ； diffraction

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