高速光子晶體發光二極體應用於可見光通訊系統

由於近日科技的進步，氮化鎵發光二極體已變成可見光通訊的物理傳輸層中，頗具發展潛力的光傳輸器，然而其調變頻寬通常受限於系統前端發光二極體中的多層量子井其較長的自發性輻射復合生命週期。目前有許多研究團隊正致力於元件結構的改善以解決較長輻射復合生命週期此一問題。在本論文中我們將闡述如何利用光子晶體結構的特性，在發光二極體中加入光子晶體的結構，探討光子晶體發光二極體於可見光通訊系統當中之應用。在本篇論文的第一部份中，我們設計了四種不同光子晶體排列方式之光子晶體發光二極體，討論其小訊號行為的表現。可以發現到由於光子晶體奈米結構之特性，其元件中侷限的模態可產生較快的輻射性載子復合，因此達到更快的調變速度。另外在室溫下的時間解析光致螢光光譜及拉曼散射頻譜中，我們可以驗證光子晶體可造成更快速的暫態響應及高效率的偶合出光。最後在最佳化的光子晶體排列設計之下，我們可以得到光子晶體中有著較大的晶格周期及較大的空氣孔比例之光子晶體發光二極體可以達到347 MHz 的調變速度，相當於55%的普通發光二極體的頻寬增加量。接下來第二部分的實驗中，我們著重於討論光子晶體發光二極體應用於可見光通訊系統之可行性。在可見光通訊的應用當中，往往必須在元件大小以及出光強弱之間取捨，越小的元件可以達到更高速的訊號傳輸，但是將會犧牲了出光的表現。在調變速度以及出光強度兩者的取捨之下，我們的研究顯示，使用光子晶體發光二極體於開關鍵控的調變之下，可以觀察到400Mbit/s傳輸速度之眼圖。此外，為了提升元件訊號傳輸量的表現，我們使用正交分頻多工的調變技術進行訊號的傳輸，在此調變方法之下，光子晶體發光二極體可以達到2Gbit/s的傳輸速度，並且誤碼率為3.8 x 10^(-3)，這也表示著我們的光子晶體發光二極體具備極大的潛力應用於高速傳輸的可見光通訊系統當中。

關鍵字

可見光通訊；頻率響應；發光二極體；光子晶體；輻射復合；數位調變；正交分頻多工

並列摘要

Recently, GaN based light-emitting-diodes (LEDs) have attracted a lot of attention as they can be applied to visible light communication (VLC) as the transmitter. However, the modulation bandwidth of LEDs is usually limited by the spontaneous carrier lifetime in the multiple quantum wells. Nowadays, much research has been investigated to solve this problem. In this thesis, we discuss the photonic crystal (PhC) structure embedded in LED (PhCLED) which can improve the performance of the devices on high-speed operation due to its unique spatial and temporal management. In the first part of this thesis, we compare four kind of various PhC structures with corresponding dynamic behaviors in the small signal modulation. Faster transient responses and higher efficiency of the out-coupled modes were obtained in the room-temperature time-resolved photoluminescence (TRPL) and Raman scattering measurement. For the best performance, an optimal design of PhCs, with a larger period and a larger air-hole portion characterizes PhCLEDs achieved the highest f-3dB bandwidth of 347 MHz, which corresponds a 55% enhancement of modulation bandwidth compared to a convention LED. For LEDs on visible light communication applications, there is generally a trade-off of high-speed performance of the LEDs. By shrinking the mesa area, LEDs can achieve higher bandwidth but at the cost lower light output, which is unfavorable when the signal-to-noise ratio (SNR) is the concern for large-signal modulation. In the second part of our work, we demonstrated data transmission capability of our devices. The eye pattern up to 400Mb/s using on-off keying (OOK) modulation is observed. Moreover, VLC with 16-quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) transmission capacity up to 2Gbit/s is achieved from the LEDs with PhC with an error vector magnitude (EVM) of 8.4%, signal-to-noise ratio (SNR) of 17.05dB and bit-error-rate (BER) of 3.8 x 10^(-3) passes the forward error correction (FEC) criterion. The results reveals the advantages of LEDs with PhC for achieving higher data rate transmission.

並列關鍵字

visible light communication ； frequency response ； light emitting diodes ； photonic crystals ； radiative recombination ； digital modulation ； OFDM

參考文獻

[3] L. De Nardis and M.-G. Di Benedetto, "Overview of the IEEE 802.15. 4/4a standards for low data rate Wireless Personal Data Networks," in Positioning, Navigation and Communication, 2007. WPNC'07. 4th Workshop on, 2007, pp. 285-289: IEEE.

[5] J. J. McKendry et al., "Visible-light communications using a CMOS-controlled micro-light-emitting-diode array," Journal of lightwave technology, vol. 30, no. 1, pp. 61-67, 2012.

[6] D. Tsonev et al., "A 3-Gb/s single-LED OFDM-based wireless VLC link using a gallium nitride μLED," IEEE Photon. Technol. Lett., vol. 26, no. 7, pp. 637-640, 2014.

[7] H. Haas, L. Yin, Y. Wang, and C. Chen, "What is LiFi?," Journal of Lightwave Technology, vol. 34, no. 6, pp. 1533-1544, 2016.

[8] S. Rajbhandari et al., "A Multi-Gigabit/sec Integrated Multiple Input Multiple Output VLC Demonstrator," Journal of Lightwave Technology, 2017.

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高速光子晶體發光二極體應用於可見光通訊系統

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