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1. Effective χ(𝟐) in a Rb-Filled Hollow-Core Photonic Bandgap Fiber for Coherent Photon Conversion

   https://doi.org/10.1364/CLEO_QELS.2018.FM3G.5  

   Zhao, Yun; Donvalkar, Prathamesh; Joshi, Chaitali; Kim, Bok Young; Gaeta, Alexander L. (July 2018, Conference on Lasers and Electro-Optics OSA Terchnical Digest (online) (Optical Society of America, 2018))

   We demonstrate a large effective χ(2) in a rubidium-filled photonic bandgap fiber by an spontaneous parametric down conversion process. This system can be used for the coherent photon conversion scheme in quantum information processing. 

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2. Back-conversion suppressed parametric frequency conversion for ultrawide bandwidth and ultrahigh efficiency devices

   https://doi.org/10.1117/12.2548361  

   Moses, Jeffrey; Flemens, Noah; Ding, Xiaoyue; Schunemann, Peter G.; Schepler, Kenneth L. (March 2020, SPIE LASE, 2020, San Francisco, California, United States)

   For as widely used a tool as nonlinear optical frequency conversion is for both science and industry, it remains widely limited in eciency and bandwidth (and ultimately also in cost) due to the fundamental problem of backconversion in the nonlinear evolution dynamics. This review paper covers new developments and capabilities in frequency conversion devices, including optical up- and down-converters and ampli ers, based on nonlinear evolution dynamics in which back-conversion is suppressed. One such approach is adiabatic frequency conversion, in which the dynamics of rapid adiabatic passage replace the regular cyclic conversion evolution in phase-matched sum- and dierence-frequency generation. This approach has enabled devices far surpassing the conventional eciency-bandwidth trade-o. For example, in chirped quasi-phase matched quadratic crystals, microjouleenergy single-cycle mid-infrared pulses were generated with arbitrary pulse shaping capability, presenting a source with unique features for nonlinear spectroscopy and strong- eld physics applications. We review new developments in the use of optical bers as a cubic nonlinear platform for the same concept, utilizing a tapered core diameter or a pressure gradient to allow up- and down-conversion with ultra-wide bandwidth and high eciency. We also review a newly introduced concept for high eciency optical parametric ampli cation, via a novel approach for suppressing back-conversion in optical parametric ampli cation by simultaneously phasematching the idler wave for second harmonic generation. Keywords: Adiabatic wave mixing, ecient optical parametric ampli cation, octave-spanning 

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3. Experimental Demonstration of Efficient OPA via Simultaneous SHG

   https://doi.org/10.1364/CLEO_AT.2022.JTh6B.4  

   Flemens, Noah; Heberle, Dylan; Zheng, Jiaoyang; Davis, Connor; Zawilski, Kevin; Schunemann, Peter G.; Moses, Jeffrey (January 2022, Conference on Lasers and Electro-Optics, OSA Technical Digest (Optica, 2022))

   We demonstrate dramatic parametric amplifier conversion efficiency enhancement simply by arranging for simultaneously phase-matched idler second-harmonic generation, with 44% pump-to-signal energy conversion (68% pump depletion) in a 48-dB-gain bulk-crystal mid-IR amplifier stage with Gaussian beams. 

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4. Ultra-low-power second-order nonlinear optics on a chip

   https://doi.org/10.1038/s41467-022-31134-5  

   McKenna, Timothy P.; Stokowski, Hubert S.; Ansari, Vahid; Mishra, Jatadhari; Jankowski, Marc; Sarabalis, Christopher J.; Herrmann, Jason F.; Langrock, Carsten; Fejer, Martin M.; Safavi-Naeini, Amir H. (December 2022, Nature Communications)

   Abstract Second-order nonlinear optical processes convert light from one wavelength to another and generate quantum entanglement. Creating chip-scale devices to efficiently control these interactions greatly increases the reach of photonics. Existing silicon-based photonic circuits utilize the third-order optical nonlinearity, but an analogous integrated platform for second-order nonlinear optics remains an outstanding challenge. Here we demonstrate efficient frequency doubling and parametric oscillation with a threshold of tens of micro-watts in an integrated thin-film lithium niobate photonic circuit. We achieve degenerate and non-degenerate operation of the parametric oscillator at room temperature and tune its emission over one terahertz by varying the pump frequency by hundreds of megahertz. Finally, we observe cascaded second-order processes that result in parametric oscillation. These resonant second-order nonlinear circuits will form a crucial part of the emerging nonlinear and quantum photonics platforms. 

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5. Multi-modality deep learning for pulse prediction in homogeneous nonlinear systems via parametric conversion

   https://doi.org/10.1063/5.0252720  

   Zhang, Hao; Sun, Linshan; Hirschman, Jack; Carbajo, Sergio (May 2025, APL Photonics)

   In this Letter, we introduce FusionNet, a multi-modality deep learning framework designed to predict and analyze output pulses in high-power rare-earth-doped laser systems driving parametric conversion in homogeneous guided nonlinear media. FusionNet integrates temporal, spectral, and physical experimental conditions to model ultrafast nonlinear phenomena, including parametric nonlinear frequency conversion, self-phase modulation, and cross-phase modulation in homogeneous guided systems such as gas-filled hollow-core fibers. These systems bridge physical models with experimental data, advancing our understanding of light-guiding principles and nonlinear interactions while expediting the design and optimization of on-demand high-power, high-brightness systems. Our results demonstrate a 73% reduction in prediction error and an 83% improvement in computational efficiency compared to conventional neural networks. This work establishes a new paradigm for accelerating parametric simulations and optimizing experimental designs in high-power laser systems, with further implications for high-precision spectroscopy, quantum information science, and distributed entangled interconnects. 

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