半導體雷射與半導體光放大器的特性研究和應用

Characteristics and Applications of Semiconductor Lasers and Semiconductor Optical Amplifiers

張維哲(Wei-Che Chang)

指導教授 ： 林清富

國立臺灣大學/電機資訊學院/電子工程學研究所/碩士(2006年)

https://doi.org/10.6342/NTU.2006.00741

摘要

隨著光通訊領域的發展，以及因應網路的需求和資訊傳輸量的增加，在本論文中我們利用設計過的量子點與量子井結構，來開發具有更寬發光頻寬特性，以及擁有更高直接調變速度、更寬調變頻寬的半導體雷射與半導體光放大器。
首先我們提出一種新的量測寬頻增益的方法，設計出新型的兩段式波導的量子點光放大器，使其可以在不需要外部雷射以及複雜的實驗架設之下，便可以量測到量子點光放大器的增益頻譜，並且得到一個正的增益值超過480nm以上的極寬頻增益，並且最大的增益值可以超過42.83cm-1。
另外，我們也透過實驗上的量測發現了具有第二量子化能階的量子點雷射，因其自由電子在本身傳導帶內部的量子化能階做躍遷，又這兩個能帶間的能隙很小，所以可以放出遠紅外光波段的波長，而目前在遠紅外光這個波段正是欠缺便宜且穩定的波源，想必在未來的發展性勢必相當大。
除此之外，我們藉由控制減短共振腔的長度，增加材料的損耗，或是降低斷面的反射量等方法，使得元件可以在第二量子化能階發出雷射光。我們利用這種發光機制，在實驗結果上發現，操作在第二量子化能階的元件，其頻寬可達2.78GHz，比第一量子化能階的元件高出約2.6倍。這個研究結果對於量子點雷射在直接調變上的應用來講是一個很重要的突破，有助於未來光通訊市場的發展和普及。然而我們更進一步的針對元件內部的載子與放光機制，去做理論上的研究與分析，發展出一套動態模型來解釋實驗結果，關於這部分目前也是尚未被研究討論過的。
最後，我們繼續量測非對稱量子井兩段式波導雷射的頻率響應，因為載子在不同量子井間互相轉移的過程，造成共振波長的快速切換，使得此結構雷射的直接調變速率可以達到更寬的調變頻寬，約6.04GHz，希望藉此來因應將來光通訊市場的發展和普及的需要。

關鍵字

量子點 ； 量子井 ； 半導體 ； 雷射 ； 光放大器 ； 增益 ； 頻譜 ； 調變

並列摘要

With the increase of blooming information and data transmission of internet, the perspective of fiber-optic communication becomes more and more prospect in the future. In this dissertation, we focus on the use and design of quantum well (QW) and quantum dot (QD) devices to achieve broadband emission characteristics and higher modulation bandwidth of semiconductor laser diodes (LD) and semiconductor optical amplifiers (SOA).
First, we propose a new simple method to measure the broadband gain spectrum with a two-section device. Without any other external tunable lasers and complicated setup, we measured broadband gain spectrum of quantum-dot amplifiers. The quantum dots give positive gain for the spectral range near 480nm, covering from 950nm to 1400nm. The maximum gain could be 42.83cm-1.
Besides, we find out the infrared emission in the second quantized state device. The reason is supposed to be the free electron’s intersubband transition in the conduction band. By the small energy band gap, the emission of the QDs has the infrared wavelength.
In Addition, we propose a new mechanism for direct modulation of laser diode by using second quantized state device. Lasing at the second quantized state can be induced by increasing the total cavity loss, which can be practically accomplished either by decreasing the length of cavity, increasing the material loss, or by decreasing the facet reflectivity. In our experiment, the bandwidth of the QD device lasing at the second quantized state highest could achieve 2.78GHz. Furthermore, it also enhanced the modulation speed over 2.6 times more than the first quantized state. In addition, we also analysis this result using theoretical model. It helps us to figure out the mechanism of the carriers and the photons.
Finally, we continue to measure the direct modulation of laser diode by using carrier redistribution inside nonidentical multiple quantum wells (MQWs). With proper design of the nonidentical MQW structure, a device with two-section waveguide Fabry-Perot laser diodes can be switched between two widely separated lasing wavelengths at high frequency. The switched intensity can have extinction ratio of 20dB within 5mA of current variation. Carriers redistribute inside nonidentical MQWs and contribute to different lasing wavelengths. Because the transport time between quantum wells is much smaller than the diffusion and drift time in SCH layer of carriers, the modulation bandwidth of two-section laser is expected to surpass the relaxation frequency of conventional laser diode. This new mechanism will greatly improve the transmitter speed and lower the cost in optical communication system.

並列關鍵字

Quantum-dot ； Quantum-well ； Semiconducter ； Laser Diodes ； Optical Amplifiers ； Gain ； Spectrum ； Modulation

參考文獻

broadband tunable semiconductor lasers for optical communication,”

[1] J. L. Baird, British Patent 285, 739, 1927.

[4] A. C. S. van Heel, Nature 173, 39, 1954.

Gastro-enterology 35, 50, 1958.

Press, San Diego, CA, 1967.