基於聲光效應下的光頻調變分析

Optical Frequency Modulation Based on Acoustic-Optical Effect

賴立展(Li-Chan Lai)

指導教授 ： 黃建璋

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202102665

摘要

至今，可見光通訊（VLC）系統已廣泛應用於我們的日常生活中。由於能夠與一般照明結合，VLC 系統作為替代的通訊方式有著強大的潛力。近年來，隨著無線通訊的需求不斷增加，提升元件速率變得越來越重要。藍光發光二極體（LED）已逐漸取代傳統燈泡成為主要的發光源。然而，其調變頻寬仍然受到自發性載子壽命週期的限制。因此，提高LED的操作速率是本論文的主要目標。
近年來，III-V族半導體材料非常流行，尤其是具有壓電特性的相關半導體，引來更多學者關注。本文中利用不同頻率的表面聲波可以觀察到發光二極體不同強度的光輸出，這取決於thickness-shear 振動模態。而隨著外加於二極體的電壓提升，額外的溫度上升造成的熱擾動也影響表面聲波的傳輸特性，進而影響發光二極體的光學響應。了解聲波的作用機制後，不僅可以於常溫下達到超過1 GHz的光學振盪，更可以透過施加不同的外加偏壓於LED上實現可調式光學頻率響應裝置。
除此之外，光頻調變在過去幾年中已經有很廣泛的研究。在本論文中，我們提供一種新的方法是通過千兆赫頻率下的表面聲波經頻率上轉換導致的光頻調變現象。透過此方式，可以從帶通濾波器中消除低頻雜訊後，再經下轉換得到降噪後的訊號，這是傳統方法無法實現的。因此，對於長距離的傳輸下可以實現更高的訊雜比。我們的方法提供了一個新的可見光通訊指向其具有更好的長距離傳輸品質。

關鍵字

發光二極體 ； 可見光通訊 ； 表面聲波 ； 光學振盪 ； 上轉換 ； 頻率響應

並列摘要

Nowadays, visible light communication (VLC) system has been widely used in our daily life. Due to the ability to integrate with the lighting infrastructure, VLC system shows a strong potential as an alternative choice of radio source. In recent years, an topic to improve the bandwidth of components has become more and more important with the increasing demand for data content. The blue-light light-emitting diode (LED) luminaires have gradually replaced traditional bulbs as the major light-emitting source. However, its modulation bandwidth is still limited by the spontaneous carrier lifetime. Therefore, improving the bandwidth of LEDs is the main goal of this thesis.
In recent years, the materials of III-V semiconductors are very popular, especially with piezoelectric characteristics. In this thesis, SAW with different frequencies can be used to observed the different light output of LEDs, which depends on the thickness-shear vibration mode. With the increase of the bias voltage, the corresponding increase of optical output leads to the rise of junction temperature, which may cause the thermal disturbance and further change the properties of SAW and the electro-optic frequency response of LED. After understanding the above mechanism of SAW-modulated LED, not only can the gigahertz optical oscillation achieve at room temperature but also the tunable optical frequency response device can be realized by the varying bias voltage.
Optical frequency modulation has been widely studied in recent years. Here, we experimentally demonstrate that the electrical data signal can be intermixed with surface acoustic waves in the LED cavity, resulting in frequency up-conversion. Also, we indicate that this kind of acoustic-optical frequency modulation possesses advantageous of the frequency modulation to suppress the low-frequency noise, leading to better transmission quality over a long distance in visible light communication (VLC) system.

並列關鍵字

light-emitting diode ； visible light communication ； surface acoustic wave ； optical oscillation ； up-conversion ； frequency response

參考文獻

[1] Statista, " Global mobile data traffic from 2017 to 2022", ed, 2019.

[2] F. Deicke, W.-J. Fisher, and M. Faulwaßer, "Optical wireless communication to eco-system." pp. 1-8.

[3] S. Rajbhandari, J. J. McKendry, J. Herrnsdorf, H. Chun, G. Faulkner, H. Haas, I. M. Watson, D. O’Brien, and M. D. Dawson, “A review of gallium nitride LEDs for multi-gigabit-per-second visible light data communications,” Semiconductor Science and Technology, vol. 32, no. 2, pp. 023001, 2017.

[4] A. Kerans, D. Vo, P. Conder, and S. Krusevac, "Pricing of spectrum based on physical criteria." pp. 223-230.

[5] R. X. Ferreira, E. Xie, J. J. McKendry, S. Rajbhandari, H. Chun, G. Faulkner, S. Watson, A. E. Kelly, E. Gu, and R. V. Penty, “High bandwidth GaN-based micro-LEDs for multi-Gb/s visible light communications,” IEEE Photonics Technology Letters, vol. 28, no. 19, pp. 2023-2026, 2016.