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1. Reconfigurable mode-selective frequency conversion in a three-mode fiber

   https://doi.org/10.1109/IPC47351.2020.9252379  

   Shamsshooli, Afshin; Guo, Cheng; Vasilyev, Michael; Parmigiani, Francesca; Li, Xiaoying (October 2020, IEEE Photonics Conference 2020)

   null (Ed.)

   We present a scheme for spatial-mode-selective frequency conversion in a few-mode fiber and experimentally demonstrate upconversion of arbitrary superpositions of two signal modes from C-band to the fundamental mode in S-band with conversion efficiencies within 1 dB range of one another. 

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2. Emerging applications of wavelength conversion

   https://doi.org/10.1109/IPC48725.2021.9592892  

   Shamsshooli, Afshin; Guo, Cheng; Vasilyev, Michael; Parmigiani, Francesca; Li, Xiaoying; Akasaka, Youichi; Palacharla, Paparao (October 2021, 2021 IEEE Photonics Conference (IPC))

   We discuss three emerging applications of wavelength conversion: 1) hybrid amplification outside of EDFA band, based on a combination of two wavelength converters and an EDFA, 2) spatial-mode-selective wavelength conversion, and 3) generation of spatial-mode-entangled photon pairs. 

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3. Direct imaging of magnetohydrodynamic wave mode conversion near a 3D null point on the sun

   https://doi.org/10.1038/s41467-024-46736-4  

   Kumar, Pankaj; Nakariakov, Valery M; Karpen, Judith T; Cho, Kyung-Suk (December 2024, Nature Communications)

   Abstract Mutual conversion of various kinds of magnetohydrodynamic (MHD) waves can have profound impacts on wave propagation, energy transfer, and heating of the solar chromosphere and corona. Mode conversion occurs when an MHD wave travels through a region where the Alfvén and sound speeds are equal (e.g., a 3D magnetic null point). Here we report the direct extreme ultraviolet (EUV) imaging of mode conversion from a fast-mode to a slow-mode MHD wave near a 3D null point using Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) observations. An incident fast EUV wavefront associated with an adjacent eruptive flare propagates laterally through a neighboring pseudostreamer. Shortly after the passage of the fast EUV wave through the null point, a slow-mode wave appears near the null that propagates upward along the open structures and simultaneously downward along the separatrix encompassing the fan loops of the pseudostreamer base. These observations suggest the existence of mode conversion near 3D nulls in the solar corona, as predicted by theory and MHD simulations. Moreover, we observe decaying transverse oscillations in both the open and closed structures of the pseudostreamer, along with quasiperiodic type III radio bursts indicative of repetitive episodes of electron acceleration. 

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4. Efficient Conversion to Very High Order Modes in Silicon Waveguides

   https://doi.org/doi.org/10.1364/CLEO_SI.2019.SM3J.6  

   Dave, Utsav D; Lipson, Michal (May 2019, Conference on Lasers and Electrooptics)

   We demonstrate robust mode conversion up to the 12th higher order mode in silicon waveguides by using an optimized adiabatic directional coupler and using subwavelength waveguides. The conversion efficiency is better than -1.5 dB over a 75 nm bandwidth and tolerating ±30 nm fabrication variations. 

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5. On‐Demand Mode Conversion and Wavefront Shaping via On‐Chip Metasurfaces

   https://doi.org/10.1002/adom.202200910  

   Deng, Lin; Xu, Yihao; Jin, Renchao; Cai, Ziqiang; Liu, Yongmin (September 2022, Advanced Optical Materials)

   Abstract In this work, mode conversion and wavefront shaping by integrating a metallic metasurface on top of a planar waveguide are proposed and demonstrated. The metasurface consists of C‐shaped nanoantennas. By controlling the orientation of each nanoantenna, mode conversion and focusing effect for the cross‐polarized electric fields inside the waveguide are achieved. The design and simulation results of 16 scenarios of wideband transverse‐magnetic to transverse‐electric mode converters with the mode purity up to 98%, and on‐chip lenses at the wavelength of 1550 nm are reported. It is worth noting that the dimension of the devices along the propagation direction is only 9.6 µm. This work manifests the potential application of mode division multiplexing systems and on‐chip optical interconnections based on metasurfaces. 

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