Professor Chi-Kuang Sun

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

台湾大学光电所 孙启光教授

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

台湾大学光电所 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：陈于堂   指导教授：林晃岩教授

论文题目：铟镓系氧化物相变化内存与薄膜晶体管组件之研制

姓名：王菘豊   指导教授：彭隆瀚教授

— 数据提供：影像显示科技知识平台 (DTKP, Display Technology Knowledge Platform) —

— 整理：林晃岩教授、陈圣灏 —

奈米微影术—使用传递与消散波 

奈米级的微影术(lithography)技术至今依旧是一大挑战，虽然有不少方法与实验测试被提出，此一问题仍尚未解决，根据Kosei Ueno和他在北海道大学(Hokkaido University)以及日本科技技术中心(Japan Science and Technology Agency)的同事最新的研究结果指出( Appl. Phys. Lett. 99,011107; 2011)，利用光阻的双光子化学反应配合电浆辅助蚀刻(plasmon-assisted lithography aided by two photon chemical reaction of photoresist)可能会是一有用之解决工具。

利用电子束以及10 nm的金薄膜所制作成的奈米结构光罩如下图左所示，此光罩被直接贴合在正光阻上，由于光罩上许多结构使得入射光在光罩中产生了复杂的电磁反应，其中包含了在波长为780 nm的共振(此研究中采用中心波长为800 nm的飞秒fs激光)。

虽然电浆蚀刻技术并非一全新技术，但Ueno指出在他们的实验中特别的地方在于曝光光源的使用上选择了高阶多偶极电浆共振( higher-order multiple plasmon resonance)所产生之具指向性散射成分而非局域的消散场(evanescent fields)。

Ueno表示在过去的电浆蚀刻系统中，利用金属奈米结构上之电浆偶极(dipole plasmon)所产生的近场光，虽然可以在光阻上产生(平面方向)奈米级的凹洞，但这些被蚀刻出的奈米图样受限于近场光的穿透深度，于是蚀刻出的凹槽并不深，同时Ueno也指出这些由电浆蚀刻出的图样并不能完全符合光罩预期产生之图样 。

Ueno: 「以上所提到的缺点指出了，要建构出一个实用的电浆蚀刻系统应该要解决的问题，为了克服这些问题，我们提出了一个新的电浆辅助蚀刻技术。」由于使用与多偶极电浆共振辐射模态耦合的具指向性散射成分(非近场光)，因此可以在光阻上得到较深的奈米图样。

其团队指出由于光阻图样与光罩上的图样非常类似，且10 nm的宽度都能被明显地蚀刻出，上图右为30 μm × 30 μm的范围内蚀刻的瓶颈状组成之链接图样，结构上的误差约为4 nm。

从实用观点上，此技术主要缺点在于本身为一种直接碰触式( direct contact exposure)的曝光方式(虽然在许多电浆式蚀刻系统中很常见)，此团队表示未来将会改良发展成为一套无须直接接触曝光的光蚀刻技术。