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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. Mode conversion of hyperbolic phonon polaritons in van der Waals terraces

   https://doi.org/10.1038/s41467-025-68030-7  

   Noh, Byung-Il; Jafari_Ghalekohneh, Sina; Chen, Mingyuan; Shen, Jialiang; Janzen, Eli; Zhou, Lang; Chen, Pengyu; Edgar, James_H; Zhao, Bo; Dai, Siyuan (December 2025, Nature Communications)

   Abstract Electromagnetic hyperbolicity has driven key functionalities in nanophotonics, including super-resolution imaging, efficient energy control, and extreme light manipulation. Central to these advances are hyperbolic polaritons—nanometer-scale light-matter waves—spanning multiple energy-momentum dispersion orders with distinct mode profiles and incrementally high optical momenta. In this work, we report the mode conversion of hyperbolic polaritons across different dispersion orders by breaking the structure symmetry in engineered step-shape van der Waals (vdW) terraces. The mode conversion from the fundamental to high-order hyperbolic polaritons is imaged using scattering-type scanning near-field optical microscopy (s-SNOM) on both hexagonal boron nitride (hBN) and alpha-phase molybdenum trioxide (α-MoO₃) vdW terraces. Our s-SNOM data, augmented with electromagnetics simulations, further demonstrate the alteration of polariton mode conversion by varying the step size of vdW terraces. The mode conversion reported here offers a practical approach toward integrating previously independent different-order hyperbolic polaritons with ultra-high momenta, paving the way for promising applications in nano-optical circuits, sensing, computation, information processing, and super-resolution imaging. 

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5. 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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