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1. Second Harmonic Amplification

   https://doi.org/10.1364/NP.2020.NpM4D.6  

   Flemens, Noah; Swenson, Nicolas; Moses, Jeffrey (January 2020, OSA Advanced Photonics Congress (AP) 2020 (IPR, NP, NOMA, Networks, PVLED, PSC, SPPCom, SOF))

   null (Ed.)

   Hybridized OPA and idler SHG suppresses back-conversion in OPA, dramatically improving efficiency. Spatiotemporal analysis of CSP and LNB-based devices demonstrates up to 55% energy conversion to signal and efficient fractional harmonic pump upconversion. 

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2. Non-Hermitian Dynamics Mimicked by a Fully Parametric Hybrid Nonlinear Optical System

   https://doi.org/10.1364/NP.2020.NpM3E.2  

   Flemens, Noah; Moses, Jeffrey (January 2020, OSA Advanced Photonics Congress (AP) 2020 (IPR, NP, NOMA, Networks, PVLED, PSC, SPPCom, SOF))

   null (Ed.)

   We demonstrate that hybridization of OPA and idler SHG produces desirable nonlinear dynamics equivalent to OPA with idler loss, despite being a fully conservative system. Both systems take the form of a damped Duffing oscillator. 

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3. On-chip non-Hermitian optical parametric amplifiers with a large bandwidth

   https://doi.org/10.1364/JOSAB.426956  

   Ahmed, Asif; Meng, Xiang; Zhong, Qi; El-Ganainy, Ramy; Osgood, Richard_M; Dadap, Jerry_I (June 2021, Journal of the Optical Society of America B)

   Recently, our groups have introduced the notion of optical parametric amplification based on non-Hermitian phase matching wherein the incorporation of loss can lead to gain in this nonlinear optical process. Previous simulation results using second-order nonlinear optical coupled-mode theory have demonstrated the potential of this technique as an alternative to the stringent phase-matching condition, which is often difficult to achieve in semiconductor platforms. Here we fortify this notion for the case of third-order nonlinearity by considering parametric amplification in silicon nanowires and illustrate the feasibility of these devices by employing rigorous finite-difference time-domain analysis using realistic materials and geometric parameters. Particularly, we demonstrate that by systematic control of the optical loss of the idler in a four-wave mixing process, we can achieve efficient unidirectional energy conversion from the pump to the signal component even when the typical phase-matching condition is violated. Importantly, our simulations show that a signal gain of $\sim <\#comment/>9\mathrm{d}\mathrm{B}$for a waveguide length of a few millimeters is possible over a large bandwidth of several hundreds of nanometers ( $\sim <\#comment/>600\mathrm{n}\mathrm{m}$). This bandwidth is nearly 2 orders of magnitude larger than what can be achieved in the conventional silicon-photonics-based four-wave mixing process. 

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4. 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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5. 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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