Annual Report 2011–12

26 開拓人類知識的版圖 Breakthrough in Ultrahigh-speed Optical Communication Prof. Liu Renbao of the Department of Physics and his collaborators Prof. Mark Sherwin and Ben Zaks at the University of California Santa Barbara (UCSB) made a key breakthrough in ultrahigh-speed optical communication that has potential to speed up the current Internet by 10,000 times. Optical communication has been the backbone of information technology. The speed of optical communication is determined by how fast one can turn the light on and off, measured in the number of bits per second. The commercially available lithium niobate modulators can modulate the brightness of light at 10 Gb/s rate, i.e., 10 billion times per second. The research by Professor Liu and his co-workers demonstrates a scheme 100 times faster, i.e., modulation of light at Tb/s rate or one trillion times per second. About five years ago, Professor Liu and co-worker Prof. Zhu Bangfen of Tsinghua University proposed the idea of modulating light in a semiconductor by a strong THz (trillion Hertz) laser. Recently, experiments on Professor Liu’s proposal were conducted at UCSB, which had free electron lasers that produced strong electric field at THz frequencies. The researchers at UCSB used the THz free electron lasers to irradiate a semiconductor device. The observed THz frequency comb indicates light modulation at THz frequency, demonstrating a key element in future optical communication at Tb/s rate. If such high-speed communication comes into being, one could transfer a whole quadruple-layer blue-ray disc or an electronic library of one million books in only one second. This new technology has the potential to transfer data 10,000 times faster than copper cables, on which the current Internet is widely based. Researchers at the Centre of Optical Sciences of CUHK will continue to work with its collaborators at UCSB to conduct research. The study was recently published in the April 2011 issue of the prestigious journal Nature . 超高速光學通信新進展 物理系劉仁保教授與他的實驗夥伴──加州 大學聖芭芭拉分校的 Prof. Mark Sherwin 及 博士研究生 Ben Zaks ，在超高速光學通信研 究取得重大突破，可望將現有的互聯網速度 提升上萬倍。 光學通信是現代資訊技術的基礎，其速度取 決於開關光的頻率，稱之為位率。目前，最快 的鈮酸鋰調製器可以 10 Gb/s 的速度──即 每秒一百億次的頻率調製光的亮度；而劉仁 保教授與夥伴研究出的新方案較之還要快 一百倍，即達到每秒萬億次的調製頻率。 約五年前，劉仁保教授和清華大學的合作夥 伴朱邦芬教授預言，強交流電場可在半導體 中以太赫茲（每秒萬億次）的極高頻率調製 光束。最近加州大學聖芭芭拉分校研究員利 用自由電子激光照射半導體裝置，觀察到劉 教授等人預言的光梳現象。劉教授的理論 充分解釋了實驗中顯示的現象，為邁向高達 Tb/s （每秒萬億位）的高速光通信奠定了重 要基礎。 若有關技術應用於現實，傳輸一張四層的藍 光碟或一個包含百萬冊圖書的電子圖書庫只 需一秒，較現時互聯網廣泛採用的銅纜傳輸 技術快上萬倍。中大將以物理系光學科學中 心為基地，與加州大學繼續合作該項研究。 該研究已於國際權威學術期刊《自然》 2011 年 4 月號發表。 Photo by Ben Zaks 劉仁保教授 Prof. Liu Renbao