Evident from more than 50 years of table-top nonlinear optics, utilizing strong quadratic nonlinearities in integrated photonics can significantly expand the potentials of photonics for applications ranging from sensing to computing. In the past few years, nanophotonic lithium niobate (LN) has emerged as one of the most promising integrated photonic platforms with strong quadratic nonlinearity. In this talk we present some of our recent experimental results on realization and utilizing of dispersion-engineered and quasi-phase-matched devices in nanophotonic LN for intense optical parametric amplification, ultrafast ultra-low-energy all-optical switching, and ultra-low-energy broadband sources in the mid-infrared. We also present some recent experimental and numerical results on how resonators with only strong quadratic nonlinearities exhibit phase transitions in the spectral domain, and pulse compression. We show a path for realization of such nonlinear resonators at the wavelength-scale and discuss how networks of such resonators can lead to topological and non-Hermitian dynamics in the classical and quantum regimes.
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