Browsing by Author "Li, Tao"

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    Characterizations of two-photon absorption process induced by defects in aluminum nitride using Z-scan method
    (IOP Publishing, 2024) Zhou, Jingan; Li, Tao; Zhao, Xuan; Zhang, Xiang; Doumani, Jacques; Xu, Mingfei; He, Ziyi; Luo, Shisong; Mei, Zhaobo; Chang, Cheng; Robinson, Jacob T.; Ajayan, Pulickel M.; Kono, Junichiro; Zhao, Yuji; Smalley-Curl Institute
    In this work, we reported two-photon absorption (TPA) measurements for aluminum vacancies in Aluminum nitride single crystals. We measured the linear transmission and identified the defect levels. Using the Z-scan method, we measured the TPA coefficients of the transitions between defect levels from 380 nm to 735 nm. The transition occurs between the aluminum vacancies defect levels. Furthermore, the power dependence shows good linear fitting, confirming the TPA mechanism. These results will be helpful for the design and fabrication of ultra-low loss waveguides and integrated photonics in the ultraviolet spectral range.
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    SARS-CoV-2 Exposure in Norway Rats (Rattus norvegicus) from New York City
    (American Society for Microbiology, 2023) Wang, Yang; Lenoch, Julianna; Kohler, Dennis; DeLiberto, Thomas J.; Tang, Cynthia Y.; Li, Tao; Tao, Yizhi Jane; Guan, Minhui; Compton, Susan; Zeiss, Caroline; Hang, Jun; Wan, Xiu-Feng
    Millions of Norway rats (Rattus norvegicus) inhabit New York City (NYC), presenting the potential for transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from humans to rats. We evaluated SARS-CoV-2 exposure among 79 rats captured from NYC during the fall of 2021. Our results showed that 13 of the 79 rats (16.5%) tested IgG- or IgM-positive, and partial SARS-CoV-2 genomes were recovered from all 4 rats that were qRT-PCR (reverse transcription-quantitative PCR)-positive. Genomic analyses suggest these viruses were associated with genetic lineage B, which was predominant in NYC in the spring of 2020 during the early pandemic period. To further investigate rat susceptibility to SARS-CoV-2 variants, we conducted a virus challenge study and showed that Alpha, Delta, and Omicron variants can cause infections in wild-type Sprague Dawley (SD) rats, including high replication levels in the upper and lower respiratory tracts and induction of both innate and adaptive immune responses. Additionally, the Delta variant resulted in the highest infectivity. In summary, our results indicate that rats are susceptible to infection with Alpha, Delta, and Omicron variants, and wild Norway rats in the NYC municipal sewer systems have been exposed to SARS-CoV-2. Our findings highlight the need for further monitoring of SARS-CoV-2 in urban rat populations and for evaluating the potential risk of secondary zoonotic transmission from these rat populations back to humans. IMPORTANCE The host tropism expansion of SARS-CoV-2 raises concern for the potential risk of reverse-zoonotic transmission of emerging variants into rodent species, including wild rat species. In this study, we present both genetic and serological evidence for SARS-CoV-2 exposure to the New York City wild rat population, and these viruses may be linked to the viruses that were circulating during the early stages of the pandemic. We also demonstrated that rats are susceptible to additional variants (i.e., Alpha, Delta, and Omicron) that have been predominant in humans and that susceptibility to infection varies by variant. Our findings highlight the reverse zoonosis of SARS-CoV-2 to urban rats and the need for further monitoring of SARS-CoV-2 in rat populations for potential secondary zoonotic transmission to humans.
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    Topological Photonic Devices in the UV-visible Spectrum Based on the III-N Wide Bandgap Semiconductor Platform
    (2024-04-19) Li, Tao; Zhao, Yuji; Huang, Shengxi; Chen, Songtao
    Topological photonics, renowned for the edge/interface states resistant to local defects and back-scattering, can be a promising solution for ensuring the stability in integrated photonic platforms and has already found applications in lasers and quantum photonic circuits. However, existing topological photonic demonstrations have primarily operated in the microwave or near-infrared spectrum due to material and nanofabrication limitations. In this thesis, we break through this wavelength barrier and extend the limit into UV-visible spectrum by implementing topological photonics on the III-N wide bandgap semiconductor platform. In the first part of the thesis, we devise a 1D topological photonic cavity fabricated from a gallium nitride on silicon (GaN-on-Si) wafer. The designed cavity has a single resonance mode around the wavelength of 800 nm and shows a simulated quality factor (Q) around 1600. Based on the non-zero second-order susceptibility of the GaN, we further demonstrate the second harmonic generation (SHG) from the 1D topological photonic cavity and reveal the power dependence and polarization dependence of the cavity-based SHG. The second part of the thesis focuses on the design of topological photonic routing devices in the visible spectrum based on 2D photonic crystals (PC) made of hexagonal boron nitride (h-BN). Interfacing 2D h-BN PCs with distinct topological phases gives rise to topological edge states supporting polarization-resolved unidirectional propagation. Through meticulous design of the interfaces’ shape, we demonstrate ultra-compact topological photonic routers. These routers feature 6 input/output ports within a 10 µm × 10 µm footprint and showcase a simulated crosstalk extinction ratio exceeding 15 dB. The results from this thesis underpin the UV-visible topological photonics based on the III-N wide bandgap semiconductor platform and can potentially benefit the design of high-performance integrated photonic devices in the UV-visible spectrum by leveraging the unique properties of photonic topology.