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1. Mode-Selective Frequency Conversion in a Three-Mode Fiber

   https://doi.org/10.1364/CLEO_SI.2020.SM3P.3  

   Shamsshooli, Afshin ; Guo, Cheng ; Parmigiani, Francesca ; Li, Xiaoying ; Vasilyev, Michael ( January 2020 , CLEO 2020 Conference Proceedings)

   We present a scheme for spatial-mode-selective frequency conversion in a few-mode fiber and experimentally demonstrate upconversion of either of two signal modes from C-band to fundamental mode in S-band with crosstalk below –15.5 dB. 

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2. Selective active resonance tuning for multi-mode nonlinear photonic cavities

   https://doi.org/10.1364/OE.512048  

   Logan, Alan D. ; Yama, Nicholas S. ; Fu, Kai-Mei C. ( March 2024 , Optics Express)

   Resonant enhancement of nonlinear photonic processes is critical for the scalability of applications such as long-distance entanglement generation. To implement nonlinear resonant enhancement, multiple resonator modes must be individually tuned onto a precise set of process wavelengths, which requires multiple linearly-independent tuning methods. Using coupled auxiliary resonators to indirectly tune modes in a multi-resonant nonlinear cavity is particularly attractive because it allows the extension of a single physical tuning mechanism, such as thermal tuning, to provide the required independent controls. Here we model and simulate the performance and tradeoffs of a coupled-resonator tuning scheme which uses auxiliary resonators to tune specific modes of a multi-resonant nonlinear process. Our analysis determines the tuning bandwidth for steady-state mode field intensity can significantly exceed the inter-cavity coupling rategif the total quality factor of the auxiliary resonator is higher than the multi-mode main resonator. Consequently, over-coupling a nonlinear resonator mode to improve the maximum efficiency of a frequency conversion process will simultaneously expand the auxiliary resonator tuning bandwidth for that mode, indicating a natural compatibility with this tuning scheme. We apply the model to an existing small-diameter triply-resonant ring resonator design and find that a tuning bandwidth of 136 GHz ≈ 1.1 nm can be attained for a mode in the telecom band while limiting excess scattering losses to a quality factor of 10⁶. Such range would span the distribution of inhomogeneously broadened quantum emitter ensembles as well as resonator fabrication variations, indicating the potential for the auxiliary resonators to enable not only low-loss telecom conversion but also the generation of indistinguishable photons in a quantum network.

    

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3. 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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4. Scalable non-mode selective Hermite–Gaussian mode multiplexer based on multi-plane light conversion

   https://doi.org/10.1364/PRJ.411529  

   Wen, He ; Zhang, Yuanhang ; Sampson, Rachel ; Fontaine, Nicolas K. ; Wang, Ning ; Fan, Shengli ; Li, Guifang ( January 2021 , Photonics Research)

   Non-mode-selective (NMS) multiplexers (muxes) are highly desirable for coherent power combining to produce a high-power beam with a shaped profile (wavefront synthesis) from discrete, phase-locked emitters. We propose a design for a multi-plane light conversion (MPLC)-based NMS mux, which requires only a few phase masks for coherently combining hundreds of discrete input beams into an output beam consisting of hundreds of Hermite–Gaussian (HG) modes. The combination of HG modes as a base can further construct a beam with arbitrary wavefront. The low number of phase masks is attributed to the identical zero-crossing structure of the Hadamard-coded input arrays and of the output HG modes, enabling the practicality of such devices. An NMS mux supporting 256 HG modes is designed using only seven phase masks, and achieves an insertion loss of$-1.6\mathrm{dB}$, mode-dependent loss of 4.7 dB, and average total mode crosstalk of$-4.4\mathrm{dB}$. Additionally, this design, featuring equal power for all input beams, enables phase-only control in coherent power combining, resulting in significant simplifications and fast convergence compared with phase-and-amplitude control.

    

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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)

   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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