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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. Principles of leaky-mode photonic lattices: Band flips and Bloch mode dynamics

   https://doi.org/10.1117/12.2508984  

   Magnusson, Robert; Lee, Sun G.; Lee, Kyu J.; Hemmati, Hafez; Carney, Daniel J.; Bootpakdeetam, Pawarat; Ko, Yeong H. (March 2019, Proceedings Volume 10921, Integrated Optics: Devices, Materials, and Technologies XXIII; 109211E (2019))

   García-Blanco, Sonia M.; Cheben, Pavel (Ed.)

   We present principles of leaky-mode photonic lattices explaining key properties enabling potential device applications. The one-dimensional grating-type canonical model is rich in properties and conceptually transparent encompassing all essential attributes applicable to two-dimensional metasurfaces and periodic photonic slabs. We address the operative physical mechanisms grounded in lateral leaky Bloch mode resonance emphasizing the significant influence imparted by the periodicity and the waveguide characteristics of the lattice. The effects discussed are not explainable in terms of local Fabry-Perot or Mie resonances. In particular, herein, we summarize the band dynamics of the leaky stopband revealing principal Bragg diffraction processes responsible for band-gap size and band closure conditions. We review Bloch wave vector control of spectral characteristics in terms of distinct evanescent diffraction channels driving designated Bloch modes in the lattice. 

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3. Experimental band flip and band closure in guided-mode resonant optical lattices

   https://doi.org/10.1364/OL.463350  

   Razmjooei, Nasrin; Magnusson, Robert (June 2022, Optics Letters)

   We demonstrate band flip in one-dimensional dielectric photonic lattices presenting numerical and experimental results. In periodic optical lattices supporting leaky Bloch modes, there exists a second stop band where one band edge experiences radiation loss resulting in guided-mode resonance (GMR), while the other band edge becomes a nonleaky bound state in the continuum (BIC). To illustrate the band flip, band structures for two different lattices are provided by calculating zero-order reflectance with respect to wavelength and incident angle. We then provide three photonic lattices, each with a different fill factor, consisting of photoresist gratings on Si₃N₄sublayers with glass substrates. The designs are fabricated using laser interferometric lithography. The lattice parameters are characterized and verified with an atomic force microscope. The band transition under fill-factor variation is accomplished experimentally. The measured data are compared to simulation results and show good agreement. 

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4. Two Topologies of Balanced Dual-Band Bandpass Filters with Extended Common-Mode-Suppression Bandwidth

   https://doi.org/10.1109/RWS.2019.8714386  

   Gomez-Garcia, Roberto; Munoz-Ferreras, Jose-Maria; Feng, Wenjie; Psychogiou, Dimitra (March 2019, 2019 IEEE Radio and Wireless Symposium (RWS))

   Two architectures of fully-planar differential-mode dual-band bandpass filters (DB-BPFs) with enlarged common-mode-suppression bandwidth are reported. The first one, which aims at designs with broadly-separated wide passbands, exploits the loading of extra lines in its balanced symmetry plane. Thus, multiple common-mode transmission zeros (TZs) are created to make wider the DB-BPF common-mode-rejection range. The second one can be used for realizations with closely-spaced passbands and employs a properly-balanced quasi-bandpass-type DB-BPF topology. In this case, the common-mode-mitigation bandwidth broadening is performed by adequately selecting the type of implementation for the short-circuit terminations of its resonating lines- i.e., virtual or physical short circuits in the differential-mode operation-. For experimental-validation purposes, two microstrip DB-BPF prototypes are manufactured and tested. 

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5. A Compact Mm-Wave Multi-Band VCO Based on Triple-Mode Resonator for 5G and Beyond

   Chahardori, Mohammad; Hoque MD Aminul; Mokri Mohammad Ali; Heo, Deukhyoun Heo (July 2022, IEEE RFIT 2022)

   We present a low phase noise four-core triple-band voltage controlled-oscillator (VCO) with reconfigurable oscillator cores and multi-mode resonator. By activation/deactivation of oscillator cores and change of resonator impedance in three modes of operations, the proposed VCO provides complete freedom in selecting the resonance frequency for three operation bands in the mm-wave range. Compared to VCOs using switch-capacitor-bank for multi-band operation, the proposed VCO does not use any series switches with passive components in the resonator to provide a low phase noise in all three bands of operation. As a proof of concept, the proposed four-core triple-band VCO is implemented in a 65 nm CMOS process using four class-D oscillators with tail switches and a compact high-Q triple-mode resonator. The VCO oscillation frequencies center at 19, 28, and 38 GHz while providing good phase noise and low power consumption in all bands. Measured results show the total frequency tuning range (FTR) of 38.5% while the PN at 1MHz offset varies from -100.3 dBc/Hz to -106.06dBc/Hz resulting in an excellent FoMT of 199.8 dBc/Hz. 

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