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1. Mechanical Control of the Optical Bandgap in One-Dimensional Photonic Crystals

   https://doi.org/10.3390/mi13122248  

   Stinson, V. Paige; Shuchi, Nuren; McLamb, Micheal; Boreman, Glenn D.; Hofmann, Tino (December 2022, Micromachines)

   Over the last several years, two-photon polymerization has been a popular fabrication approach for photonic crystals due to its high spatial resolution. One-dimensional photonic crystals with photonic bandgap reflectivities over 90% have been demonstrated for the infrared spectral range. With the success of these structures, methods which can provide tunability of the photonic bandgap are being explored. In this study, we demonstrate the use of mechanical flexures in the design of one-dimensional photonic crystals fabricated by two-photon polymerization for the first time. Experimental results show that these photonic crystals provide active mechanically induced spectral control of the photonic bandgap. An analysis of the mechanical behavior of the photonic crystal is presented and elastic behavior is observed. These results suggest that one-dimensional photonic crystals with mechanical flexures can successfully function as opto-mechanical structures. 

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2. Photonic metacrystal: design methodology and experimental characterization

   https://doi.org/10.1364/OE.448151  

   Hu, S.; Khater, M.; Kratschmer, E.; Engelmann, S.; Green, W_M_J; Weiss, S_M (February 2022, Optics Express)

   We report a design methodology for creating high-performance photonic crystals with arbitrary geometric shapes. This design approach enables the inclusion of subwavelength shapes into the photonic crystal unit cell, synergistically combining metamaterials concepts with on-chip guided-wave photonics. Accordingly, we use the term “photonic metacrystal” to describe this class of photonic structures. Photonic metacrystals exploiting three different design freedoms are demonstrated experimentally. With these additional degrees of freedom in the design space, photonic metacrystals enable added control of light-matter interactions and hold the promise of significantly increasing temporal confinement in all-dielectric metamaterials. 

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3. Light Confinement in Twisted Single-Layer 2D+ Moiré Photonic Crystals and Bilayer Moiré Photonic Crystals

   https://doi.org/10.3390/photonics11010013  

   Kamau, Steve; Hurley, Noah; Kaul, Anupama B; Cui, Jingbiao; Lin, Yuankun (January 2024, Photonics)

   Twisted photonic crystals are photonic analogs of twisted monolayer materials such as graphene and their optical property studies are still in their infancy. This paper reports optical properties of twisted single-layer 2D+ moiré photonic crystals where there is a weak modulation in z direction, and bilayer moiré-overlapping-moiré photonic crystals. In weak-coupling bilayer moiré-overlapping-moiré photonic crystals, the light source is less localized with an increasing twist angle, similar to the results reported by the Harvard research group in References 37 and 38 on twisted bilayer photonic crystals, although there is a gradient pattern in the former case. In a strong-coupling case, however, the light source is tightly localized in AA-stacked region in bilayer PhCs with a large twist angle. For single-layer 2D+ moiré photonic crystals, the light source in Ex polarization can be localized and forms resonance modes when the single-layer 2D+ moiré photonic crystal is integrated on a glass substrate. This study leads to a potential application of 2D+ moiré photonic crystal in future on-chip optoelectronic integration. 

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4. Iterative eigensolver using fixed-point photonic primitive

   https://doi.org/10.1364/OL.506704  

   Klein, Andrew_B; Zhu, Zheyuan; Saiham, Dewan; Li, Guifang; Pang, Shuo_S (January 2024, Optics Letters)

   Photonic computing has potential advantages in speed and energy consumption yet is subject to inaccuracy due to the limited equivalent bitwidth of the analog signal. In this Letter, we demonstrate a configurable, fixed-point coherent photonic iterative solver for numerical eigenvalue problems using shifted inverse iteration. The photonic primitive can accommodate arbitrarily sized sparse matrix–vector multiplication and is deployed to solve eigenmodes in a photonic waveguide structure. The photonic iterative eigensolver does not accumulate errors from each iteration, providing a path toward implementing scientific computing applications on photonic primitives. 

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5. Photonic Band Gaps and Resonance Modes in 2D Twisted Moiré Photonic Crystal

   https://doi.org/10.3390/photonics8100408  

   Alnasser, Khadijah; Kamau, Steve; Hurley, Noah; Cui, Jingbiao; Lin, Yuankun (October 2021, Photonics)

   The study of twisted bilayer 2D materials has revealed many interesting physics properties. A twisted moiré photonic crystal is an optical analog of twisted bilayer 2D materials. The optical properties in twisted photonic crystals have not yet been fully elucidated. In this paper, we generate 2D twisted moiré photonic crystals without physical rotation and simulate their photonic band gaps in photonic crystals formed at different twisted angles, different gradient levels, and different dielectric filling factors. At certain gradient levels, interface modes appear within the photonic band gap. The simulation reveals “tic tac toe”-like and “traffic circle”-like modes as well as ring resonance modes. These interesting discoveries in 2D twisted moiré photonic crystal may lead toward its application in integrated photonics. 

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