Professor Chi-Kuang Sun

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所 孫啟光教授

Terahertz (THz) technology has high potential in a wide variety of applications ranging from high-speed telecommunications to bio-imaging. To facilitate THz applications, it is essential to develop low-loss and low-cost THz waveguides. Recently, we proposed a dielectric circular air-core pipe for low-loss THz waveguiding. The pipe waveguide is the simplest pipe with a large air core region surrounded by thin and low-index dielectric cladding. Without complex fabrication, we used commercial Teflon pipes to demonstrate that the circular pipe waveguides not only possess low attenuation constants (< 0.001 cm^-1) and high coupling efficiency (> 80%), but also suffer low bending loss. By modifying the circular pipe waveguides into rectangular ones, we further removed the transmission degeneracy of two orthogonal polarizations. It is expected that these easily available, low loss, low bending loss, and polarization-sensitive THz waveguides would have a high potential for THz sensing, communication, and imaging applications.

Fig. 1. Structure of the pipe waveguide. (n1 = 1, air).	Fig. 2. Attenuation spectra of straight Teflon pipe waveguides for t = 0.5 mm and 1.0 mm. The core diameters were the same (D = 9 mm).
Fig. 3. Bending loss spectra of the pipe waveguide for bending radius of curvature (R) = 75 and 60 cm.	Fig. 4. Attenuation spectra of PE rectangular pipe waveguides for different polarizations.

 Professor Gong-Ru Lin

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所 林恭如教授

A TO-46-can packaged VCSEL with a finite bandwidth of only 3 GHz has been employed to demonstrate a 10-Gbit/s all-optical NRZ-to-RZ data-format convertor, as shown in Fig. 1. This approach is based on the injection-locking induced gain-switching and the beyond-bandwidth electrical-pulse modulation of the TO-46-can packaged VCSEL biased at nearly lasing condition. To support 10-Gbit/s RZ data pulse generation, the resonant relaxation oscillation frequency of this TO-46-can packaged VCSEL is increased through direct modulation by an electrical-pulse at 10 GHz and external NRZ optical injection from 2 to at least 7.3 GHz. The optimized 10-Gbit/s RZ data-stream exhibits the signal to noise ratio, the timing jitter, and the pulsewidth of 7.2 dB, 2.9 ps, and 27 ps, respectively. The peak-to-peak chirp and corresponding chirp parameter are slightly raised to 4.3 GHz and 122 MHz/ps by increasing the injection power and the biased current. Owing to carrier accumulation and gain variation, the RZ data pulsewidth gets reduced by increasing the optical NRZ injection power and concurrently increasing the DC biased current.

A higher DC biased current further promotes the RZ data with greater modulation depth and sharper shape. A BER of 10^-9 at 10 Gbit/s is achieved at a receiving power of -19.5 dBm, and an improvement of receiving power penalties up to 16 dB is observed when the DC biased current is reduced to only 10% of its lasing threshold, as shown in Fig. 2. In particular, the slope of the BER versus receiving power significantly changes at a receiving power of >-19 dBm. The major reason for the slope change in the BER curves is crosstalk between the reflected incoming optical NRZ injection and the output of the VCSEL converted RZ data-stream. With a limited receiving sensitivity of the 10-Gbit/s lightwave receiver (Agilent 83434A), the VCSEL converted RZ data-stream inevitably introduces a noise floor in its BER response. Despite the finite bandwidth set by the homemade VCSEL, this work demonstrates the feasibility of operating the TO-can packaged VCSEL based RZ generator beyond its intrinsic modulation bandwidth with the aid of electrical-pulse modulation and externally optical injection. Most concerns regarding the noisy data-stream output can be addressed if the VCSEL can tolerate a larger bias and thereby achieve a better SNR before breakdown.

Fig. 1. VCSEL based 10-Gbit/s NRZ-to-RZ convertor. Amp: microwave amplifier; MZM: Mach-Zehnder modulator; OC: optical circulator; PC: polarization controller; TL: tunable laser; Att: attenuator; DSO: Digital Sampling Oscilloscope; BER: bit error rate tester; OSA: optical spectrum analyzer.	Fig. 2 BER analysis of the optical NRZ from a externally modulated VCSEL without injection (black), and the generated RZ at 10 Gbit/s from the injection-locked VCSEL at DC bias of 1.2, 1.3, and 1.4 mA.

Reference:
Chia-Chi Lin, Yu-Chieh Chi, Hao-Chung Kuo, Peng-Chun Peng, Connie Chang-Hasnain, and Gong-Ru Lin, “Beyond-Bandwidth Electrical-Pulse Modulation of a TO-can Packaged VCSEL for 10 Gbit/s Injection-Locked NRZ-to-RZ Transmission,” Journal of Lightwave Technology, Vol. 29, Issue 6, pp. 830-841, Mar. 2011.

姓名：陳于堂   指導教授：林晃巖教授

論文題目：銦鎵系氧化物相變化記憶體與薄膜電晶體元件之研製

姓名：王菘豊   指導教授：彭隆瀚教授

— 資料提供：影像顯示科技知識平台 (DTKP, Display Technology Knowledge Platform) —

— 整理：林晃巖教授、陳聖灝 —

奈米微影術—使用傳遞與消散波 

奈米級的微影術(lithography)技術至今依舊是一大挑戰，雖然有不少方法與實驗測試被提出，此一問題仍尚未解決，根據Kosei Ueno和他在北海道大學(Hokkaido University)以及日本科技技術中心(Japan Science and Technology Agency)的同事最新的研究結果指出( Appl. Phys. Lett. 99,011107; 2011)，利用光阻的雙光子化學反應配合電漿輔助蝕刻(plasmon-assisted lithography aided by two photon chemical reaction of photoresist)可能會是一有用之解決工具。

利用電子束以及10 nm的金薄膜所製作成的奈米結構光罩如下圖左所示，此光罩被直接貼合在正光阻上，由於光罩上許多結構使得入射光在光罩中產生了複雜的電磁反應，其中包含了在波長為780 nm的共振(此研究中採用中心波長為800 nm的飛秒fs雷射)。

雖然電漿蝕刻技術並非一全新技術，但Ueno指出在他們的實驗中特別的地方在於曝光光源的使用上選擇了高階多偶極電漿共振( higher-order multiple plasmon resonance)所產生之具指向性散射成分而非局域的消散場(evanescent fields)。

Ueno表示在過去的電漿蝕刻系統中，利用金屬奈米結構上之電漿偶極(dipole plasmon)所產生的近場光，雖然可以在光阻上產生(平面方向)奈米級的凹洞，但這些被蝕刻出的奈米圖樣受限於近場光的穿透深度，於是蝕刻出的凹槽並不深，同時Ueno也指出這些由電漿蝕刻出的圖樣並不能完全符合光罩預期產生之圖樣 。

Ueno: 「以上所提到的缺點指出了，要建構出一個實用的電漿蝕刻系統應該要解決的問題，為了克服這些問題，我們提出了一個新的電漿輔助蝕刻技術。」由於使用與多偶極電漿共振輻射模態耦合的具指向性散射成分(非近場光)，因此可以在光阻上得到較深的奈米圖樣。

其團隊指出由於光阻圖樣與光罩上的圖樣非常類似，且10 nm的寬度都能被明顯地蝕刻出，上圖右為30 μm × 30 μm的範圍內蝕刻的瓶頸狀組成之鏈結圖樣，結構上的誤差約為4 nm。

從實用觀點上，此技術主要缺點在於本身為一種直接碰觸式( direct contact exposure)的曝光方式(雖然在許多電漿式蝕刻系統中很常見)，此團隊表示未來將會改良發展成為一套無須直接接觸曝光的光蝕刻技術。