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1. Ultrathin WS 2 ‐on‐Glass Photonic Crystal for Self‐Resonant Exciton‐Polaritonics

   https://doi.org/10.1002/adom.201901988  

   Zhang, Xingwang ; Zhang, Xiaojie ; Huang, Wenzhuo ; Wu, Kedi ; Zhao, Mengqiang ; Charlie Johnson, A. T. ; Tongay, Sefaattin ; Cubukcu, Ertugrul ( February 2020 , Advanced Optical Materials)

   Room temperature stable excitons in layered two‐dimensional (2D) transition metal dichalcogenides (TMDs) offer a unique route for engineering light and matter interactions. Due to the strong optical dispersion near the excitonic transitions, a high refractive index arises in these ultrathin semiconductors.^[1,2]Utilizing this behavior, strongly confined Fano type optical resonances in an ultrathin (i.e., ≈12 nm) tungsten disulfide (WS₂) photonic crystal (PhC) directly fabricated on a TMD‐on‐glass platform are reported. In this approach, Fano‐type WS₂photonic resonances strongly couple to the WS₂excitonic dispersion engender self‐resonant exciton‐polaritons with an out‐of‐plane optical confinement exceeding that provided by surface plasmon polaritons in the visible. The large spatial light‐matter overlap endowed by this unique monolithic self‐coupling scheme is utilized for steering of enhanced 2D WSe₂excitonic photoluminescence in a truly TMD integrated system. It is envisioned that the strong light matter interaction on the TMD‐on‐glass platform will unfold the prospects of ultrathin exciton‐polaritonic resonators.

    

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2. Highly Sensitive, Affordable, and Adaptable Refractive Index Sensing with Silicon‐Based Dielectric Metasurfaces

   https://doi.org/10.1002/admt.201800567  

   Ollanik, Adam J. ; Oguntoye, Isaac O. ; Hartfield, George Z. ; Escarra, Matthew D. ( December 2018 , Advanced Materials Technologies)

   A sensing platform is presented that uses dielectric Huygens source metasurfaces to measure refractive index changes in a microfluidic channel with experimentally measured sensitivity of 323 nm RIU⁻¹, a figure of merit (FOM) of 5.4, and a response of 8.2 (820%) change in transmittance per refractive index unit (T/RIU). Changes in the refractive index of liquids flown through the channel are measured by single‐wavelength transmittance measurement, requiring only a simple light source and photodetector, significantly reducing device expense in comparison to state‐of‐the‐art refractive index sensing technologies. A technoeconomic analysis predicts a device costing ≈$2400 that is capable of detecting refractive index changes of the order of 2*10⁻⁸. The metasurfaces utilized are low profile, scalable, and use materials and fabrication processes compatible with CMOS and other technologies making them suitable for device integration. The Huygens metasurface system, characterized by spectrally overlapping electric and magnetic dipole modes, offers a high degree of customizability. Interplay between the two resonances may be controlled via metasurface geometry, leading to tunability of device sensitivity and measurement range. Ultrahigh sensitivity of 350 nm RIU⁻¹with FOM of 219, corresponding to single‐wavelength sensitivity of 360 RIU⁻¹, is demonstrated computationally through use of antisymmetric resonances of a Huygens metasurface illuminated at small incidence angles.

    

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3. Microsphere photolithography patterned nanohole array on an optical fiber

   https://doi.org/10.1109/ACCESS.2021.3059439  

   Liu, Jiayu ; Jasim, Ibrahem ; Zhu, Chen ; Roman, Muhammad ; Huang, Jie ; Kinzel, Edward ; Almasri, Mahmoud ( February 2021 , IEEE Access)

   null (Ed.)

   Microsphere Photolithography (MPL) is a nanopatterning technique that utilizes a self-assembled monolayer of microspheres as an optical element to focus incident radiation inside a layer of photoresist. The microspheres produces a sub-diffraction limited photonic-jet on the opposite side of each microsphere from the illumination. When combined with pattern transfer techniques such as etching/lift-off, MPL provides a versatile, low-cost fabrication method for producing hexagonal close-packed metasurfaces. This article investigates the MPL process for creating refractive index (RI) sensors on the cleaved tips of optical fiber. The resonant wavelength of metal elements on the surface is dependent on the local dielectric environment and allows the refractive index of an analyte to be resolved spectrally. A numerical study of hole arrays defined in metal films shows that the waveguide mode provides good sensitivity to the analyte refractive index. This can be readily tuned by adjusting the MPL exposure and the simulation results guide the fabrication of a defect tolerant refractive index sensor on the tip of a fiber tip with a sensitivity of 613 nm/RIU. The conformal nature of the microsphere monolayer simplifies the fabrication process and provides a viable alternative to direct-write techniques such as Focused Ion Beam (FIB) milling 

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4. Active and Passive Tuning of Ultranarrow Resonances in Polaritonic Nanoantennas

   https://doi.org/10.1002/adma.202104954  

   Duan, Jiahua ; Alfaro‐Mozaz, Francisco Javier ; Taboada‐Gutiérrez, Javier ; Dolado, Irene ; Álvarez‐Pérez, Gonzalo ; Titova, Elena ; Bylinkin, Andrei ; Tresguerres‐Mata, Ana Isabel F. ; Martín‐Sánchez, Javier ; Liu, Song ; et al ( January 2022 , Advanced Materials)

   Optical nanoantennas are of great importance for photonic devices and spectroscopy due to their capability of squeezing light at the nanoscale and enhancing light–matter interactions. Among them, nanoantennas made of polar crystals supporting phonon polaritons (phononic nanoantennas) exhibit the highest quality factors. This is due to the low optical losses inherent in these materials, which, however, hinder the spectral tuning of the nanoantennas due to their dielectric nature. Here, active and passive tuning of ultranarrow resonances in phononic nanoantennas is realized over a wide spectral range (≈35 cm⁻¹, being the resonance linewidth ≈9 cm⁻¹), monitored by near‐field nanoscopy. To do that, the local environment of a single nanoantenna made of hexagonal boron nitride is modified by placing it on different polar substrates, such as quartz and 4H‐silicon carbide, or covering it with layers of a high‐refractive‐index van der Waals crystal (WSe₂). Importantly, active tuning of the nanoantenna polaritonic resonances is demonstrated by placing it on top of a gated graphene monolayer in which the Fermi energy is varied. This work presents the realization of tunable polaritonic nanoantennas with ultranarrow resonances, which can find applications in active nanooptics and (bio)sensing.

    

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5. Direct Light‐Writing of Nanoparticle‐Based Metallo‐Dielectric Optical Waveguide Arrays Over Silicon Solar Cells for Wide‐Angle Light Collecting Modules

   https://doi.org/10.1002/adom.201900661  

   Biria, Saeid ; Wilhelm, Thomas S. ; Mohseni, Parsian K. ; Hosein, Ian D. ( August 2019 , Advanced Optical Materials)

   Here presented are the properties and performance of a new metallo‐dielectric waveguide array structure as the encapsulation material for silicon solar cells. The arrays are produced through light‐induced self‐writing combined with in situ photochemical synthesis of silver nanoparticles. Each waveguide comprises a cylindrical core consisting of a high refractive index polymer and silver nanoparticles homogenously dispersed in its medium, all of which are surrounded by a low refractive index common cladding. The waveguide array‐based films are processed directly over a silicon solar cell. Arrays with systematically varied concentration of AgSbF₆as the salt precursor are explored. The structures are tested for their wide‐angle light capture capabilities, specifically toward enhanced conversion efficiency and current production of encapsulated solar cells. Observed are increases in the external quantum efficiency, especially at wide incident angles up to 70°, and nominal increases in the short circuit current density by 1 mA cm⁻²(relative to an array without nanoparticles). Enhanced light collection is explained in terms of the beneficial effect of scattering by the nanoparticles along the waveguide cores. This is a promising approach toward solar cell encapsulants that aid to increase solar cell output over both the course of the day and year.

    

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