Lithium Niobate Meta-Optics

Abstract

The rapid development of optical metasurfaces, 2D ensembles of engineered nanostructures, is presently underpinning a steady drive toward the miniaturization of many optical functionalities and devices. The list of material platforms for optical metasurfaces is rapidly expanding as, over the past few years, we have witnessed a surge in establishing meta-optical elements from high-index, highly transparent materials with strong nonlinear and electro-optic properties. In particular, crystalline lithium niobate (LiNbO 3 ), already a prime material for integrated photonics, has shown great promise for novel meta-optical components, thanks to its large electro-optical coefficient and secondorder nonlinear response and its broad transparency window ranging from the visible to the mid-infrared. Recent advances in nanofabrication technology have indeed marked a new milestone in the miniaturization of LiNbO 3 platforms, hence enabling the first demonstrations of LiNbO 3 -based metasurfaces. These seminal works set a steppingstone toward the realization of ultrathin monolithic nonlinear light sources, efficient quantum sources of correlated photon pairs, as well as electro-optical modulators. Here, we review these recent advances by providing a perspective on their potential applications and examining the possible setbacks and limitations of these emerging technologies.

Nonlinear THz Generation through Optical Rectification Enhanced by Phonon–Polaritons in Lithium Niobate Thin Films

“…Noteworthy, its value is up to 2 orders of magnitude larger than the one achieved at optical frequencies. 16,21 A similar frequency-dependent behavior is observed for the d 31 element describing a resulting THz nonlinear polarization that is oriented along the e-axis.…”

“…This element of the nonlinear tensor is enhanced by a phonon resonance at 7.45 THz. Noteworthy, its value is up to 2 orders of magnitude larger than the one achieved at optical frequencies. , A similar frequency-dependent behavior is observed for the d 31 element describing a resulting THz nonlinear polarization that is oriented along the e -axis. Nonlinear mixing generating a nonlinear THz polarization oriented along one of the ordinary ( o ) axes, which is accounted for by the d 22 and d 15 elements, is instead enhanced by the o -axis phonon resonance at 4.5 THz.…”

“…The complex permittivity of LN is modeled according to eq 1 in the THz band and with a Sellmeier equation for the optical band. 16 The nonlinear polarization generated at the frequency Ω by optical rectification of a pulse centered at frequency ω 0 is given by…”

Synergetic Peroxidase-Mimic Catalytic Activity of Noble-Metal-Decorated Lithium Niobate Nanozymes for Potential Biological Applications

“…To this end, LiNbO 3 (LN) is an interesting material as it has a noncentrosymmetric structure that confers outstanding nonlinear optics, and pyroelectric and piezoelectric properties, making it ideal for numerous applications in optics, batteries, and optical communications. − At the nanoscale, LN NPs present low toxicity and lack phase-matching conditions, making them excellent candidates for bio-imaging and photo-triggered drug delivery. , Other features include its semiconducting and ferroelectric properties that enhance catalysis and photocatalysis, especially in redox reactions. These properties favor charge separation and polarization-induced facile adsorption .…”

Polarization Engineering of Entangled Photons from a Lithium Niobate Nonlinear Metasurface

“…Metasurfaces based on the LiNbO 3 -on-insulator platform were recently developed for various applications including electro-optic modulation, classical optical frequency conversion, and photon-pair generation . With this platform, we engineer and multiplex polarization state of photon pairs generated from a metasurface where periodic SiO 2 metagratings are fabricated on top of a subwavelength-thin layer of LiNbO 3 .…”