高頻寬850nm波段面射型雷射之研究

Abstract

隨著行動裝置的普及和線上服務與社群網路的蓬勃，全球網路資訊流量以驚人的速度成長，傳統低頻寬、壽命低與易受電磁波干擾的電纜線漸漸被光纖所取代，而面射型雷射應用於光通訊中有耗能低、光纖耦合損耗低、調變效率高與封裝整合容易等特點，所以發展出高速的面射型雷射將會提升光通訊系統中的傳輸頻寬。 首先我們會先藉由理論模擬改善現有商規的標準雷射結構，探討腔體長度、氧化孔徑的幾何結構和分散式布拉格反射鏡(DBR)的設計對於雷射調製頻寬的影響，並模擬設計出具有24 GHz頻寬的高速雷射。隨後我們將模擬的結構製成元件並和商用雷射結構傳輸表現比較，我們得到較小的元件電阻值76 Ω 和較高的傳輸頻寬18 GHz，有助於提升光互聯網的傳輸效率。 第二部分，我們由模擬分析使用鋅擴散達到模態控制的單模雷射傳輸特性，單模態雷射在長距離傳輸下沒有色散的問題，但是在文獻中所發表的元件在小訊號傳輸表現上有頻寬飽和在低頻響應差等現象。我們先成功模擬出新擴散對模態控制的特性，再更進一步模擬小訊號頻率響應和注入電流與光場分布，推測鋅擴散有較差的高速表現和大電流下注入載子與光場重疊差有關。

The proliferation of mobile devices and the concept of cloud computing has drastically change the way we use the Internet like streaming videos and social networking, which greatly skyrocketed the global internet traffic. By using optical interconnects instead of traditional copper cables we will get larger bandwidth and immune to electro-magnetic interference. The use of high speed vertical cavity surface emitting lasers (VCSELs) can increase the modulation efficiency and enhance the speed limit of the system. In the first part of this study, we will focus on enhancing the bandwidth of the VCSEL by numerically simulating the effect of cavity length, oxide aperture geometry and Distributed Bragg Reflector (DBR) with different design. We finally came up with a structure that has a 24 GHz bandwidth in our simulation. Next we fabricate our simulated VCSEL structure into real device and compared with the IQE reference samples. We found a resistance reduction in our design from 91 Ω to 76 Ω and a bandwidth enhancement form 17 GHz to 18GHz. The second part is about the high speed performance of Zn-diffused single mode VCSELs. Single mode VCSELs doesn’t suffer from dispersion at long distance transmission, however, researches show that there is a degraded high-speed characteristic such as bandwidth saturation and low frequency roll-off. By numerically observed the effect of Zn-diffused aperture on mode control, we successfully simulated the single-mode VCSEL with Zn-diffusion and further discussed the high-speed performance. We found out the injected current has poor overlap with optical modes at high injection current, which will cause the modulation bandwidth to saturate.