Focusing Polarization Diversity Grating Couplers in Silicon-on-Insulator

We report on compact focusing polarization diversity grating couplers in silicon-on-insulator, which can be used to overcome the polarization dependence of nanophotonic integrated circuits. The minimum fiber-to-fiber polarization dependent loss is 0.4 dB and the focusing grating couplers are as performant as standard 2-D-grating couplers without focusing. In addition, the focusing property of the gratings results in an 8-fold length reduction of the coupling structure as compared to standard nonfocusing 2-D-grating versions.     

Compact Focusing Grating Couplers for Silicon-on-Insulator Integrated Circuits

We report experimental results on compact and broadband focusing grating couplers, both in silicon-on-insulator (SOI) and gold on SOI. An eight-fold length reduction of the coupling structure from fiber to photonic wire in SOI, as compared to a linear grating and adiabatic taper, is obtained, without performance penalty. A proof of principle is given for a focusing grating coupler in gold on SOI, with 20% fiber-to-focus efficiency.     

太赫兹3D打印透镜综述

太赫兹波由于其独特的电磁特性可应用于超高速率无线通信、生物化学物质检测以及高分辨率成像等领域。但由于太赫兹波的物理波长小,传统适用于低频的加工工艺难以满足其加工精度的要求;而微纳米加工工艺又具有加工复杂、成本高等缺点。3D打印技术的发展为太赫兹器件的加工提供了新的选择和更多的设计灵活度。文章介绍了香港城市大学太赫兹与毫米波国家重点实验室在3D打印太赫兹透镜方面的最新研究动态和实验研究新成果,包括基于3D打印的太赫兹高增益圆极化透镜、近场聚焦圆极化透镜、贝塞尔波束生成透镜的设计,高精度3D打印方法的探索以及太赫兹天线测试方法等。太赫兹3D打印透镜天线具有低成本、低损耗、能快速成型等特点,可应用于不同的太赫兹场景中。     

倾斜耦合的光栅耦合器研究进展

近年来,片上光子集成技术备受关注并飞速发展,但在光纤与芯片、芯片与芯片上实现高效、高可靠性的光耦合仍是难题。光栅因其制作简单,位置灵活,对准容差大及可实现片上测试等一系列优点而备受研究者的关注。目前在绝缘体上硅(SOI)平台和绝缘体上铌酸锂(LNOI)平台上已开发出大量的光栅耦合器件,并获得较高的耦合效率和大带宽。该文主要介绍光栅耦合器的工作原理和主要性能指标,阐述了均匀光栅、倾斜光栅、闪耀光栅和切趾光栅耦合的特点及现阶段进展,并对具有代表性的一维光栅性能指标进行了比较。结果表明,分布式布喇格反射镜和金属反射镜可有效地提升光栅耦合效率。此外,该文还介绍了基于LNOI平台的几种光栅耦合器,其可帮助研究者们梳理光栅耦合器的发展历程、研究现状及各耦合器的特点,为未来研究提供一定的参考。     

3-D Printed Anti-Reflection Structures for the Terahertz Region

Terahertz radiation has a growing number of applications in material characterization, where spectral fingerprinting and diffractive effects are the carriers of information. On the other hand, electromagnetic waves in the range of millimeters exhibit strong unwanted specular reflections, resulting in uncontrolled interferences. This problem is especially disturbing in the goniometric time-domain spectroscopy (TDS) configuration, where angular distribution of the field modified by the sample is altered by unwanted reflections. For this reason, low-cost anti-reflection layers are desired. Here, we present a simple way of designing and manufacturing one-sided and two-sided anti-reflection polyamide layers for the THz range. The structures were fabricated using 3-D printers based on selective laser sintering. We demonstrate experimentally in the goniometric time-domain spectroscopy the significant reduction of wavelength-dependent oscillations in Fabry-Perot configuration in the range between 0.1 and 0.3 THz. We also examine the influence of the anti-reflection layers on the distribution of THz energy in reflected, transmitted, and diffracted fields.     

Feasibility and Characterization of Common and Exotic Filaments for Use in 3D Printed Terahertz Devices

Recent years have seen an influx of applications utilizing 3D printed devices in the terahertz regime. The simplest, and perhaps most versatile, modality allowing this is Fused Deposition Modelling. In this work, a holistic analysis of the terahertz optical, mechanical and printing properties of 17 common and exotic 3D printer filaments used in Fused Deposition Modelling is performed. High impact polystyrene is found to be the best filament, with a useable frequency range of 0.1–1.3 THz, while remaining easily printed. Nylon, polylactic acid and polyvinyl alcohol give the least desirable terahertz response, satisfactory only below 0.5 THz. Interestingly, most modified filaments aimed at increasing mechanical properties and ease of printing do so without compromising the useable terahertz optical window.     

3D Printed Bioelectronic Microwells

The in-house and on-demand fabrication of electrochemical integrated biosensors is a great challenge, especially in the field of modern point-of-care diagnostics. 3D printing technology allows the production of specialized electronic devices adapted to the required conditions, and 3D printed thermoplastic electrodes have shown hopeful achievements mainly in enzymatic bioassays. This work describes a novel configuration of integrated all-3D-printed electrochemical microtitration wells (e-wells) for direct quantum dot-based (QDs) and enzymatic bioassays. The e-wells enable the in situ development of complete bioassays, that is, from sample addition to biomarker detection, without the need for external equipment other than a micropipette and a detector. The bioanalytical capability of the 3D e-wells is demonstrated through the voltammetric bioassay of C-reactive protein employing biotinylated reporter antibody and streptavidin-conjugated CdSe/ZnS QDs. In addition, in order to extend their scope to enzymatic biosensing, e-wells are applied to the amperometric determination of hydrogen peroxide by-products, demonstrating their universal applicability in electrochemical bioassays.     

3D Printed Neural Regeneration Devices

Neural regeneration devices interface with the nervous system and can provide flexibility in material choice, implantation without the need for additional surgeries, and the ability to serve as guides augmented with physical, biological (e.g., cellular), and biochemical functionalities. Given the complexity and challenges associated with neural regeneration, a 3D printing approach to the design and manufacturing of neural devices can provide next‐generation opportunities for advanced neural regeneration via the production of anatomically accurate geometries, spatial distributions of cellular components, and incorporation of therapeutic biomolecules. A 3D printing‐based approach offers compatibility with 3D scanning, computer modeling, choice of input material, and increasing control over hierarchical integration. Therefore, a 3D printed implantable platform can ultimately be used to prepare novel biomimetic scaffolds and model complex tissue architectures for clinical implants in order to treat neurological diseases and injuries. Further, the flexibility and specificity offered by 3D printed in vitro platforms have the potential to be a significant foundational breakthrough with broad research implications in cell signaling and drug screening for personalized healthcare. This progress report examines recent advances in 3D printing strategies for neural regeneration as well as insight into how these approaches can be improved in future studies.     

Focused-Ion-Beam Fabrication of Slanted Grating Couplers in Silicon-on-Insulator Waveguides

We have designed and fabricated an efficient grating coupler for coupling light between optical fibers and silicon-on-insulator waveguides. The coupler consists of 88-nm-wide slits, etched at an angle of 58deg to the surface normal. They are defined by direct etching with a focused ion beam, using iodine gas and an alumina hard mask. The measured efficiency is 46%     

光纤光栅耦合器在光通信中的应用

光纤光栅耦合器综合了光纤光栅良好的波长选择和光纤耦合器多端口特性的特点,是一种低插入损耗、应用简便的全光纤器件。介绍了光纤光栅的基本结构和功能,重点分析了它在插分复用、全光交换、改善EDFA的信噪比和监测EDFA增益等方面的应用。     

3D Printed Microstructures Erasable by Darkness

To advance the applications of direct laser writing (DLW), adaptability of the printed structure is critical, prompting a shift toward printing structures that are comprised of different materials, and/or can be partially or fully erased on demand. However, most structures that contain these features are often printed by complex processes or require harsh developing techniques. Herein, a unique photoresist for DLW is introduced that is capable of printing 3D microstructures that can be erased by exposure to darkness. Specifically, microstructures based on light-stabilized dynamic materials are fabricated that remain stable when continously irradiated with green light, but degrade once the light source is switched off. The degradation and light stabilization properties of the printed materials are analyzed in-depth by time-lapse scanning electron microscopy. It is demonstrated that these resists can be used to impart responsive behavior onto the printed structure, and –critically– as a temporary locking mechanism to control the release of moving structural features.     

3D Printed Anatomical Nerve Regeneration Pathways

A 3D printing methodology for the design, optimization, and fabrication of a custom nerve repair technology for the regeneration of complex peripheral nerve injuries containing bifurcating sensory and motor nerve pathways is introduced. The custom scaffolds are deterministically fabricated via a microextrusion printing principle using 3D models, which are reverse engineered from patient anatomies by 3D scanning. The bifurcating pathways are augmented with 3D printed biomimetic physical cues (microgrooves) and path‐specific biochemical cues (spatially controlled multicomponent gradients). In vitro studies reveal that 3D printed physical and biochemical cues provide axonal guidance and chemotractant/chemokinetic functionality. In vivo studies examining the regeneration of bifurcated injuries across a 10 mm complex nerve gap in rats showed that the 3D printed scaffolds achieved successful regeneration of complex nerve injuries, resulting in enhanced functional return of the regenerated nerve. This approach suggests the potential of 3D printing toward advancing tissue regeneration in terms of: (1) the customization of scaffold geometries to match inherent tissue anatomies; (2) the integration of biomanufacturing approaches with computational modeling for design, analysis, and optimization; and (3) the enhancement of device properties with spatially controlled physical and biochemical functionalities, all enabled by the same 3D printing process.     

3D Printed Graphene-Based 3000 K Probe

High-temperature heating is ubiquitously utilized in material synthesis and manufacturing, which often features a rapid production rate due to the significantly improved kinetics. However, current technologies generally provide overall and steady-state heating, thereby limiting their applications in micro/nano-manufacturing that require selective patterning and swift heating. Herein, significantly improved control over small-scale heating is reported by utilizing 3D printed reduced-graphene-oxide (RGO) probe triggered by electrical Joule heating, which enables precise heating with high spatial (sub-millimeter scale) and temporal (milliseconds) resolutions. The block copolymer-modified aqueous-based RGO ink enabled 3D printing of high-precision structures, and a bio-inspired cellular microstructure is constructed to achieve control of the electrical conductivity and maximize structure robustness (benefit for efficient heating and operability). In particular, a thermal probe featuring a microscale tip with excellent heating capabilities (up to ≈3000 K, ultra-fast ramping rate of ≈10⁵ K s⁻¹, and durations in milliseconds) is fabricated. This thermal probe is ideal for surface patterning, as it is demonstrated for the selective synthesis of patterned metal (i.e., platinum and silver) nanoparticles on nano-carbon substrates, which is not possible by traditional steady-state heating. The material construction and heating strategy can be readily extended to a range of applications requiring precise control on high-temperature heating.     

用微光学技术制作位相型聚焦光栅

根据菲涅耳衍射理论,采用微光学制作技术通过3次套刻,将8位相台阶的菲涅耳波带片和平面光栅组合制作在同一块基片上,构成同时具有色散分光和聚焦光谱线功能的位相型光栅.这种光栅具有较高的光谱分辨本领和衍射效率,而且光路简单,调节方便.实验测出的衍射效率大于71%.     

Tailoring 3D Printed Micro-Structured Carbons for Adsorption

The manufacture of tailored carbon-based adsorbent structures with exceptionally low-pressure drops and improved kinetics using stereolithographic 3D printing is presented. Adsorbent structures are printed from commercial resins with square, circular, and hexagonal cross-sectional microchannels. These structures can reduce energy use by 50–95% compared to conventional carbon-packed beds. The activated 3D printed carbon achieves Brunauer–Emmett–Teller surface areas over 1000 m² g⁻¹ and shows outstanding butane adsorption capacities, over twice the capacity of a commercial carbon and a comparable capacity to phenolic-based carbons. The structures also show excellent uptakes of cyclohexane, up to 0.62 g g⁻¹ in a saturated feed. The introduction of complex axial geometries including spirals and chevrons enable superior adsorption kinetics and premature breakthrough of contaminants at high gas flow rates. These results demonstrate the success of intelligent manufacturing of low-pressure drop, high-capacity micro-structured adsorbents, allowing for the development of gas separation technologies for applications such as greenhouse gas removal and respiratory protection.     

Customizable Supercapacitors via 3D Printed Gel Electrolyte

New manufacturing strategies toward customizable energy storage devices (ESDs) are urgently required to allow structural designability for space and weight-sensitive electronics. Besides the macroscopic geometry customization, the ability to fine-tune the ESD internal architectures are key to device optimization, allowing short and uniform electrons/ions diffusion pathways and increased contact areas while overcoming the issues of long transport distance and high interfacial resistance in conventional devices with planar thick electrodes. ESDs with 2D or 3D electrodes filled with liquid or gel-like electrolyte have been reported, yet they face significant challenges in design flexibility for 3D ESD architectures. Herein, a novel method of assembling ESDs with the ability to customizing both external and internal architectures via digital light processing (DLP) technique and a facile sequential dip-coating process is demonstrated. Using supercapacitors as prototype device, the 3D printing of ESDs with areal capacity of 282.7 mF cm⁻² which is higher than a reference device with same mass loading employing planar stacked configuration (205.5 mF cm⁻²) is demonstrated. The printed devices with highly customizable external geometry conveniently allow the ESDs to serve as structural components for various electronics such as watchband and biomimetic electronics which are difficult to be manufactured with previously reported strategies.     

Terahertz Polarization Detector Based on PMMA Grating Pipe

In this paper, we propose and experimentally demonstrate a method to realize a polarization detector by using a commercially available polymethyl methacrylate (PMMA) pipe. An asymmetric polarization-related structure is fabricated by etching different grating structures on the external surface of the pipe. The results show that when the pipe rotates up to 90, the peak of the transmission spectrum can evidently shift towards the low frequency, which means the pipe with grating structures can serve as a polarization detector. This design possesses the merits of a simple structure and easy fabrication.     

基于表面等离子波耦合的流体波导光栅耦合器

提出了一种由金属光栅和流体光波导结构组成的,基于表面等离子波耦合的光栅耦合器。利用光栅的衍射效应,将金属光栅与介质分界面之间产生的表面等离子波耦合到流体光波导中,并且能够沿着流体光波导稳定地向前传播。通过采用基于有限时域差分算法的FDTD Solutions软件对光栅耦合器进行了参数优化及特性分析,通过优化使该结构在650 nm波长下的耦合效率达到56%。此外,由于该结构对TE偏振光和TM偏振光的选择比达到70∶1,因此具有偏振器的功能。同时由于TE偏振光耦合频谱的频带宽度仅为20 nm,该结构还具有窄带滤波的作用。此外,还研究了光栅结构参数、入射角以及流体折射率对耦合频谱的影响。