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1. Snapshot multifocal light field microscopy

   https://doi.org/10.1364/OE.390719  

   He, Kuan ; Wang, Xiaolei ; Wang, Zihao W. ; Yi, Hannah ; Scherer, Norbert F. ; Katsaggelos, Aggelos K. ; Cossairt, Oliver ( April 2020 , Optics Express)

   Light field microscopy (LFM) is an emerging technology for high-speed wide-field 3D imaging by capturing 4D light field of 3D volumes. However, its 3D imaging capability comes at a cost of lateral resolution. In addition, the lateral resolution is not uniform across depth in the light field dconvolution reconstructions. To address these problems, here, we propose a snapshot multifocal light field microscopy (MFLFM) imaging method. The underlying concept of the MFLFM is to collect multiple focal shifted light fields simultaneously. We show that by focal stacking those focal shifted light fields, the depth-of-field (DOF) of the LFM can be further improved but without sacrificing the lateral resolution. Also, if all differently focused light fields are utilized together in the deconvolution, the MFLFM could achieve a high and uniform lateral resolution within a larger DOF. We present a house-built MFLFM system by placing a diffractive optical element at the Fourier plane of a conventional LFM. The optical performance of the MFLFM are analyzed and given. Both simulations and proof-of-principle experimental results are provided to demonstrate the effectiveness and benefits of the MFLFM. We believe that the proposed snapshot MFLFM has potential to enable high-speed and high resolution 3D imaging applications.

    

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2. Additives for Ambient 3D Printing with Visible Light

   https://doi.org/10.1002/adma.202104906  

   Ahn, Dowon ; Stevens, Lynn M. ; Zhou, Kevin ; Page, Zachariah A. ( November 2021 , Advanced Materials)

   With 3D printing, the desire is to be “limited only by imagination,” and although remarkable advancements have been made in recent years, the scope of printable materials remains narrow compared to other forms of manufacturing. Light‐driven polymerization methods for 3D printing are particularly attractive due to unparalleled speed and resolution, yet the reliance on high‐energy UV/violet light in contemporary processes limits the number of compatible materials due to pervasive absorption, scattering, and degradation at these short wavelengths. Such issues can be addressed with visible‐light photopolymerizations. However, these lower‐energy methods often suffer from slow reaction times and sensitivity to oxygen, precluding their utility in 3D printing processes that require rapid hardening (curing) to maximize build speed and resolution. Herein, multifunctional thiols are identified as simple additives to enable rapid high‐resolution visible‐light 3D printing under ambient (atmospheric O₂) conditions that rival modern UV/violet‐based technology. The present process is universal, providing access to commercially relevant acrylic resins with a range of disparate mechanical responses from strong and stiff to soft and extensible. Pushing forward, the insight presented within this study will inform the development of next‐generation 3D‐printing materials, such as multicomponent hydrogels and composites.

    

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3. High‐Speed 3D Printing of High‐Performance Thermosetting Polymers via Two‐Stage Curing

   https://doi.org/10.1002/marc.201700809  

   Kuang, Xiao ; Zhao, Zeang ; Chen, Kaijuan ; Fang, Daining ; Kang, Guozheng ; Qi, Hang Jerry ( January 2018 , Macromolecular Rapid Communications)

   Design and direct fabrication of high‐performance thermosets and composites via 3D printing are highly desirable in engineering applications. Most 3D printed thermosetting polymers to date suffer from poor mechanical properties and low printing speed. Here, a novel ink for high‐speed 3D printing of high‐performance epoxy thermosets via a two‐stage curing approach is presented. The ink containing photocurable resin and thermally curable epoxy resin is used for the digital light processing (DLP) 3D printing. After printing, the part is thermally cured at elevated temperature to yield an interpenetrating polymer network epoxy composite, whose mechanical properties are comparable to engineering epoxy. The printing speed is accelerated by the continuous liquid interface production assisted DLP 3D printing method, achieving a printing speed as high as 216 mm h⁻¹. It is also demonstrated that 3D printing structural electronics can be achieved by combining the 3D printed epoxy composites with infilled silver ink in the hollow channels. The new 3D printing method via two‐stage curing combines the attributes of outstanding printing speed, high resolution, low volume shrinkage, and excellent mechanical properties, and provides a new avenue to fabricate 3D thermosetting composites with excellent mechanical properties and high efficiency toward high‐performance and functional applications.

    

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4. In-situ transfer vat photopolymerization for transparent microfluidic device fabrication

   https://doi.org/10.1038/s41467-022-28579-z  

   Xu, Yang ; Qi, Fangjie ; Mao, Huachao ; Li, Songwei ; Zhu, Yizhen ; Gong, Jingwen ; Wang, Lu ; Malmstadt, Noah ; Chen, Yong ( February 2022 , Nature Communications)

   While vat photopolymerization has many advantages over soft lithography in fabricating microfluidic devices, including efficiency and shape complexity, it has difficulty achieving well-controlled micrometer-sized (smaller than 100 μm) channels in the layer building direction. The considerable light penetration depth of transparent resin leads to over-curing that inevitably cures the residual resin inside flow channels, causing clogs. In this paper, a 3D printing process — in-situ transfer vat photopolymerization is reported to solve this critical over-curing issue in fabricating microfluidic devices. We demonstrate microchannels with highZ-resolution (within 10 μm level) and high accuracy (within 2 μm level) using a general method with no requirements on liquid resins such as reduced transparency nor leads to a reduced fabrication speed. Compared with all other vat photopolymerization-based techniques specialized for microfluidic channel fabrication, our universal approach is compatible with commonly used 405 nm light sources and commercial photocurable resins. The process has been verified by multifunctional devices, including 3D serpentine microfluidic channels, microfluidic valves, and particle sorting devices. This work solves a critical barrier in 3D printing microfluidic channels using the high-speed vat photopolymerization process and broadens the material options. It also significantly advances vat photopolymerization’s use in applications requiring small gaps with high accuracy in theZ-direction.

    

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5. Ultrafast modulation of terahertz waves using on-chip dual-layer near-field coupling

   https://doi.org/10.1364/OPTICA.469461  

   Zhang, Yaxin ; Ding, Kesen ; Zeng, Hongxin ; Kou, Wei ; Zhou, Tianchi ; Zhou, Hongji ; Gong, Sen ; Zhang, Ting ; Wang, Lan ; Liang, Shixiong ; et al ( November 2022 , Optica)

   As a key potential component of future sixth-generation (6G) communication systems, terahertz (THz) technology has received much attention in recent years. However, a lack of effective high-speed direct modulation of THz waves has limited the development of THz communication technology. Currently, most high-speed modulators are based on photonic systems that can modulate electromagnetic waves with high speed using sophisticated optoelectronic conversion techniques. Yet, they usually suffer from low conversion efficiency of light to the THz range, resulting in low output power of the modulated THz waves. Here, we describe a guided-wave modulator for THz signals whose performance nearly matches that of existing in-line fiber-optic modulators. Our results demonstrate a maximum modulation depth greater than 20 dB (99%) and a maximum sinusoidal modulation speed of more than 30 GHz, with an insertion loss around 7 dB. We demonstrate the capabilities of this modulator in a point-to-point communication link with a 25 Gbit/s modulation speed. Our modulator design, based on near-field coupling of a THz transmission line to a single resonant meta-element, represents a powerful improvement for on-chip integrated high-performance THz devices.

    

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