本所吴育任教授与校同仁荣获「大专校院2024年度教职员工慢速垒球锦标赛」冠军，特此恭贺！

Noise Reduction Through Square Aperture Array in Integral Imaging-based 3D Light-Field Display

Professor Hoang-Yan Lin

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

台湾大学光电所 林晃岩教授

The integral-imaging based 3D light field display can restore its light-field information, reconstruct different images in different depth planes, and realize the floating projection effect. In the metaverse, AR/VR wearable devices, HUD for smart cockpits, medical care, entertainment, art performance and other scenarios, naked-eye 3D display is one of the most crucial requirements for the coming future.

We have created 3D floating images with an integral imaging-based 3D light field display. However, noise is an annoying problem after restoring information in 3D light field displays. In this study, we proposed a square aperture array to be added to the original light field display to solve the noise problem and find out that an aperture array can effectively decrease the noise. Also, the light intensity will be decreased a lot for the circle aperture array case but will not be decreased for our square aperture array design. Finally, we created naked-eye 3D images with very little noise and also without light intensity sacrifice.

Firstly, we show a light-emitting angle = 90 degrees for the sample, we will create a picture at different depths (z) as shown in Fig. 1. Looking closely at Figs. 1 (a)(b)(c), we can find out that there are 4 dim letters A around the bright letter A and the same situation in letters B and C. We regard those dim letters as noise and it is produced by a light ray that does not obey the principle of CGEI.

After knowing the best position of the aperture array, we have shown the restored image in different depths (z) in Fig. 2 when aperture array X=7 mm. We set parameter X for the distance between the aperture array and the display panel. We can discover that there isn’t any dim letter next to the bright letter, which means that we successfully eliminate the noise!

Reference:

Chia-Yuan Chang and Hoang-Yan Lin, Noise Reduction Through Square Aperture Array in Integral Imaging-based 3D Light-Field Display, SID Display Week 2023.

Photonic Mixing Sub-THz Carrier for Wireless Data Link with Single-Chip Dual-Wavelength DFBLD

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

Sub-THz wireless communication technology has emerged as a promising candidate to extend the carrier frequency toward previously unexplored bands to enable the ultra-wide-band short-range data link beyond 6G. The optical heterodyned generation of millimeter-wave wireless carriers via discrete laser sources is intriguing in view of the currently available technologies for carrier synthesis because of its flexibility on frequency tunability. However, finite modal linewidth and residual wavelength drift are two main concerns that raise the noise background to degrade the signal-to-noise ratio of the data encoded onto the heterodyned carrier. Maintaining the difference and stability of wavelength and phase between two independent lasers usually relies on additional controlling and feedback schemes such as a phase-locked loop. This inevitably induces systematic complexity and alternative solution needs to be considered for simplification. In this work, a dual-mode distributed feedback laser diode (DFBLD) is demonstrated as a monolithic wireless sub-THz carrier synthesizer with absolute wavelength (frequency) differentiation and phase synchronization between two lasing longitudinal modes. By directly encoding the DFBLD with QAM-OFDM data format, the wireless data link can be performed via such a compact and simplified sub-THz wireless transmitter.

The dual-mode-lasing DFBLD is designed by slightly tilting the DFB mirror structure by an angle f to the surface normal of the output end-face at one side of the resonant cavity, which enables the concurrent lasing of both longitudinal modes inside the DFBLD cavity. Such a design combined with a short cavity results in a mode spacing of 2-3 nm to cause a frequency difference tunable from 320 to 330 GHz. The dual-mode-lasing DFBLD exhibits two distinct longitudinal modes centered at 1545-1546 nm and 1547-1548 nm, respectively. The back-to-back sub-THz wireless link is demonstrated by transmitting the NRZ-OOK data stream at 5 GBaud, revealing the quality factor and bit-error ratio of nearly 4 and 5e-5, respectively. By amplifying the 16-QAM DMT data amplitude, the received constellation plot of the down-converted baseband DMT data shows a blurred spot with an increased EVM. The signal-to-noise ratio remains above 15 dB over 95% of the encoding bandwidth, providing a BER of 2.3x10^-3 of the broadened 16-QAM formats at allowable data rates of 12 Gbit/s. The fully integrated dual-mode-lasing DFBLD chip can serve as a novel compact sub-THz transmitter as compared to those using individual laser sources and external data modulators.

本文为与台湾大学电机系郑宇翔教授合作之成果。

Reference:

1. C.-Y. Lin, Y.-C. Chi, C.-T. Tsai, H.-Y. Wang, and G.-R. Lin, “39-GHz millimeter-wave carrier generation in dual-mode colorless laser diode for OFDM-MMWoF transmission,” IEEE J. Sel. Top. Quantum Electron., vol. 21, pp. 609-618, Nov.-Dec. 2015

2. C.-T. Tsai, C.-H. Lin, C.-T. Lin, Y.-C. Chi, and G.-R. Lin, “60-GHz millimeter-wave over fiber with directly modulated dual-mode laser diode,” Sci. Rep. vol. 6, no. 27919, Jun. 2016.

论文题目：硅奈米结构与芯片本质特性对高效率单多晶与硅/有机异质结太阳能电池的影响

姓名：薛丞智   指导教授：林清富教授

摘要

本论文深入探讨了硅奈米结构以及芯片本质特性对于单晶与多晶硅/无机异质结太阳能电池高效转换性能的贡献。综述了当前高效太阳能电池的技术发展趋势，关注于硅基太阳能电池在降低成本与提升转换效率方面的研究重点。透过创新的实验设计，深入分析了硅奈米结构对于提升太阳能电池效率的关键贡献。利用改良的金属辅助化学蚀刻技术，在6英寸的单晶与多晶硅芯片上成功制造了均匀的硅奈米线数组，如图一所示，整体呈现黑色，而图二显示了硅奈米线数组的SEM图，采用硅奈米线数组的P型多晶铝背面场电池相比于传统粗化技术制作的多晶电池显著提升了组件效能，光电转换效率（PCE）达17.83%，并有效解决了P型多晶硅由于钻石线切割产生的光滑表面难以粗化的问题。接着专注于硅芯片本质特性研究，探讨了金属杂质与光衰减（硼氧）对于P型高效能多晶硅芯片质量的影响，以及电阻率对于钝化射极与背面太阳能电池效率的影响。其中N型材料在减少金属杂质影响和提升少数载子体寿命与电池效率方面的潜力。最后专注于N型单晶硅奈米线结构与有机材料PEDOT:PSS结合制作异质结太阳能电池的研究，最后通过两阶段硝酸银蚀刻制备的高密度硅奈米洞结构与DMSO混合的PEDOT:PSS相结合，降低了接触角，使有机溶剂更有效覆盖奈米洞，提升了载子传输效率，最终Jsc为36.80 mA/cm²，Voc为524.15mV，FF为66.50%，因此PCE达到了12.82%。 图一、单多晶硅芯片蚀刻前(a)(c)与蚀刻后(b)(d) 图二、单晶硅芯片蚀刻后(a)(b)、多晶硅芯片蚀刻后SEM图

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

— 整理：林晃岩教授、黄茂恺 —

铁电中的全光极化切换

使用窄带宽可调红外激光脉冲进行的超快光学实验，在接近零介电常数（epsilon-near-zero, ENZ）的状态下，使钛酸钡（BaTiO₃）中的铁电极化实现了非挥发性的全光切换。

鉴于提升数据记录速度的重要性，数十年来，利用单一超短激光脉冲在固态系统中探索非挥发性全光切换有序参数的途径，仍然是热门研究主题。根本问题在于朝向最终状态的转变，受到超快的飞秒至微秒时间尺度上之多种非平衡动力学的影响。在铁磁系统中，透过微小的磁光效应来微调激光与材料的交互作用，能够阐明主要的切换机制。

在铁电材料的特定案例中，铁电畴（ferroelectric domain）与独特的原子配置有关联，这表明需要对单位晶胞内的原子配置进行超快控制。早期的理论研究建议，利用适当场形的太赫兹（THz）脉冲电场，可以将铁晶体管中的离子从初始畴方向中的位置，沿着明确的微观路径移动到新畴中的位置。近年来，透过激发锂铌酸盐（LBO）中的大振幅红外活性声子，已足以创造出接近切换区的瞬态原子配置。

尽管非挥发性铁电切换无法在这个实验中展示，这项工作明确突显了在此类实验中由光学声子介导的非线性光学交互作用的重要性。在使用MHz重复频率激光光源进行扫描飞秒激光写入实验中，已经实现了锂铌酸盐中的永久性与可重构性之极化切换，然而切换主要受到沿激光扫描方向引起的热电场影响。迄今为止，尚不清楚这些不同机制中哪一个是实现使用单一超短激光脉冲随选进行非挥发性铁电切换的关键。

现在，Kwaaitaal及其同事在《Nature Photonics》上发表文章，探讨了由自由电子激光（在Nijmegen的FELIX设备）超短红外脉冲之爆发辐照下，钛酸钡这种钙钛矿型材料之铁电极化的动态研究。该实验处于类单次脉冲的状态，因为每个样品位置都被8微秒（μs）长的中红外窄带宽脉冲辐照，这些脉冲由间隔40奈秒（ns）的200皮秒（ps）脉冲组成。自由电子激光在7到28微米（μm）的波长范围内具有广泛的可调性，并且脉冲能量高达几微焦（μJ），这是研究激光驱动铁电极化动态的理想条件，跨越两个光学声子共振点，分别位于14和21微米波长。

在这项研究中，特别注意了发展不同的实验方法，以清晰且明确地识别铁电畴。偏振显微镜足以识别90度畴（见图一(b)），而产生二次谐波显微镜则必须用于观察180度畴（见图一(c)）。

这些显微镜影像的定量分析使得能够测量切换区随激发波长变化的情况（见图一(d)）。值得注意的是，研究人员能够将切换效率的最大值与介电函数的零点相关联。也就是说，与钛酸钡特有的声子性质自然产生的ENZ条件相对应。因此，研究人员一方面显示，钛酸钡实现了他们所定义的自然「声子」ENZ材料，另一方面，在ENZ条件下，光与物质的强烈放大交互作用导致了长期以来所追求且迄今难以实现的非挥发性全光切换其铁电极化。

具体的微观切换机制仍然存在较大的不明确性。初步的时间解析研究似乎表明铁电畴的超快重新定向。在应用了几种仪器限制时间解析的时间解析技术后，研究人员估计切换时间的上限大约在3奈秒左右。

为了进一步探索切换现象的光子学面向，需要更加理解ENZ材料独特且独有的光学性质。图一(f) 显示在两个共振点上的强烈色散效应，其中光速群指数在激发辐射中高达40倍增加，这表明光速的明显减慢。在这样的慢光区域中，中红外脉冲与铁电材料的交互作用时间可以大大超过真空中的脉冲持续时间。这一卓越的特性确实有望透过相干控制或非线性光学模型的透镜来理解导致切换现象的机制。除了这些已确立的理论概念外，作者还发展了一个简单的理论模型，解释样品的激光加热如何产生温度应变的准静态高斯分布，进而生成与切换畴匹配的极化分布。尽管有这些令人兴奋的观察，寻找铁电切换的极限速度仍然是一个引人入胜的课题。考虑到桌面型低重复率μJ能量中红外光参数放大器（OPA）基于飞秒激光源的可用性，可以透过光学飞秒时间解析极化敏感显微技术来解决在真正单次脉冲制度中超快铁电切换的确切途径。

晶格、电荷、自旋和轨道等自由度之间的强耦合，提供了新的视野和广泛的研究领域，这些领域可能展现出各种异常和具有技术意义的性质，这些性质可以以相同的方式调控。这个一般概念本身即材料固有的ENZ条件的发生，使得可以实现有序参数的超快全光切换潜力巨大，能够远远超越这里所示的铁电材料的特定案例，前提是能够找到ENZ材料，其中使得ENZ条件发生的性质直接或间接地与需要调控的有序参数耦合。