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1. Fano resonance in metallic grating via strongly coupled subwavelength resonators

   https://doi.org/10.1017/S0956792520000200  

   LIN, JUNSHAN; ZHANG, HAI (January 2021, European Journal of Applied Mathematics)

   We investigate the Fano resonance in grating structures using coupled resonators. The grating consists of a perfectly conducting slab with periodically arranged subwavelength slit holes, where inside each period, a pair of slits sit very close to each other. The slit holes act as resonators and are strongly coupled. It is shown rigorously that there exist two groups of resonances corresponding to poles of the scattering problem. One sequence of resonances has imaginary part in the order of ε , where ε is the size of the slit aperture, while the other sequence has imaginary part in the order of ε 2 . When coupled with the incident wave at resonant frequencies, the narrow-band resonant scattering induced by the latter will interfere with the broader background resonant radiation induced by the former. The interference of these two resonances generates the Fano-type transmission anomaly, which persists in the whole radiation continuum of the grating structure as long as the slit aperture size is small compared to the incident wavelength. 

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2. Merging mechanical bound states in the continuum in high-aspect-ratio phononic crystal gratings

   https://doi.org/10.1038/s42005-024-01692-9  

   Tong, Hao; Liu, Shengyan; Fang, Kejie (December 2024, Communications Physics)

   Abstract Mechanical bound states in the continuum (BICs) present an alternative avenue for developing high-frequency, high-Qmechanical resonators, distinct from the conventional band structure engineering method. While symmetry-protected mechanical BICs have been realized in phononic crystals, the observation of accidental mechanical BICs—whose existence is independent of mode symmetry and tunable by structural parameters—has remained elusive. This challenge is primarily attributed to the additional radiation channel introduced by the longitudinal component of elastic waves. Here, we employ a coupled wave theory to predict and experimentally demonstrate mechanical accidental BICs within a high-aspect-ratio gallium arsenide phononic crystal grating. We observe the merging process of accidental BICs with symmetry-protected BICs, resulting in reduced acoustic radiation losses compared to isolated BICs. This finding opens up new possibilities for phonon trapping using BIC-based systems, with potential applications in sensing, transduction, and quantum measurements. 

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3. Integration of plasmonic heating and on‐chip temperature sensor for nucleic acid amplification assays

   https://doi.org/10.1002/jbio.202000060  

   Monshat, Hosein; Wu, Zuowei; Pang, Jinji; Zhang, Qijing; Lu, Meng (March 2020, Journal of Biophotonics)

   Abstract Nucleic acid tests have been widely used for diagnosis of diseases by detecting the relevant genetic markers that are usually amplified using polymerase chain reaction (PCR). This work reports the use of a plasmonic device as an efficient and low‐cost PCR thermocycler to facilitate nucleic acid‐based diagnosis. The thermoplasmonic device, consisting of a one‐dimensional metal grating, exploited the strong light absorption of plasmonic resonance modes to heat up PCR reagents using a near‐infrared laser source. The plasmonic device also integrated a thin‐film thermocouple on the metal grating to monitor the sample temperature. The plasmonic thermocycler is capable of performing a PCR amplification cycle in ~2.5 minutes. We successfully demonstrated the multiplex and real‐time PCR amplifications of the antibiotic resistance genes using the genomic DNAs extracted fromAcinetobacter baumannii,Klebsiella pneumonia,Escherichia coliandCampylobacter. 

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4. Polarization-independent photonic Bragg grating filter with cladding asymmetry

   https://doi.org/10.1364/OL.479600  

   Pimbi, Daniel; Hasan, Mehedi; Borhan_Mia, Md; Jaidye, Nafiz; Kim, Sangsik (February 2023, Optics Letters)

   A photonic Bragg grating is a fundamental building block that reflects the direction of wave propagation through spatial phase modulation and can be implemented using sidewall corrugation. However, due to the asymmetric aspect ratio of a waveguide cross section, typical Bragg gratings exhibit a strong polarization sensitivity. Here, we show that photonic Bragg gratings with cladding asymmetry can enable polarization-independent notch filters by rotating input polarizations. Such Bragg gratings strongly couple transverse electric (TE) and transverse magnetic (TM) modes propagating in opposite directions, filtering the input signal and reflecting the rotated mode. We analyzed this polarization-rotating Bragg grating using the coupled-mode theory and experimentally demonstrated it on a silicon-on-insulator platform. Our device concept is simple to implement and compatible with other platforms, readily available as polarization transparent Bragg components. 

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5. High-efficiency 2D grating design for the magneto-optical trap: enhancing intensity balance and reducing optical complexity

   https://doi.org/10.1117/1.OE.64.8.085106  

   Karooby, Elaheh; Li, Jiazhen; Agrawal, Amit; Gu, Qing (August 2025, Optical Engineering)

   Integrated diffraction gratings offer a compact route to magneto-optical traps (MOTs) for atom cooling and trapping, thus preparing MOTs for future scalable quantum systems. While segmented tri-gratings ensure axial radiation pressure balance, they are limited in optical trapping volume. Planar 2D gratings, though offer larger trapping regions, suffer from low diffraction efficiency and the resulting axial pressure imbalance, necessitating the use of a neutral density (ND) filter to achieve this balance. We present a numerically optimized 2D diffraction grating design that overcomes these limitations and satisfies the required optical conditions for laser cooling, namely, radiation pressure balance, specular reflection cancellation, and circular polarization handedness reversal upon diffraction, thus achieving an optical molasses – a necessary condition in MOT. Using Rigorous Coupled Wave Analysis (RCWA) and a Genetic Algorithm (GA), we design a grating for (_ ^87)Rb grating MOT (GMOT) that achieves a 24% first-order diffraction efficiency, of which 99.7% have the correct circular handedness. These properties enable efficient atom cooling without an ND filter when used with a flat-top beam inside the vacuum chamber. Our design simplifies optical alignment, reduces system footprint, and advances the integration of GMOTs into compact quantum devices. 

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