Publication

Backward Wave Second-Harmonic Generation in X-Cut Thin Film Lithium Niobate

2025

Abstract

Thin-film lithium niobate (TFLN) is of particular interest for nonlinear wave mixing processes thanks to its high refractive index, high second-order nonlinearity and ferroelectricity enabling efficient quasi-phase-matching (QPM). Nonlinear wave mixing in x-cut TFLN also offers cointegration with other nonlinear components such as high-speed electrooptic modulators. Although there are many demonstrations of forward second-harmonic generation (FSHG) in x-cut TFLN, the SH-peak position shifts severely with respect to the intrinsic fluctuations in waveguide dimensions [1, 2]. Alternatively, QPM in backward-wave second-harmonic generation (BWSHG) is intrinsically more tolerant to such fluctuations as the QPM wavelength is only dependent on the effective refractive index of the second harmonic (λQPM = 2n2ωΛ) [3]. It also enables novel nonlinear effects such as mirrorless optical parametric oscillation [4]. Here, we demonstrate for the first time BWSHG in x-cut TFLN.

Official source

https://infoscience.epfl.ch/entities/publication/a7a1fe9f-bece-49e8-8375-fa6b91fbb4f4

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2025

Abstract

Official source

https://infoscience.epfl.ch/entities/publication/a7a1fe9f-bece-49e8-8375-fa6b91fbb4f4

About this result

Related concepts (32)

Nonlinear optics

Nonlinear optics (NLO) is the branch of optics that describes the behaviour of light in nonlinear media, that is, media in which the polarization density P responds non-linearly to the electric field E of the light. The non-linearity is typically observed only at very high light intensities (when the electric field of the light is >108 V/m and thus comparable to the atomic electric field of ~1011 V/m) such as those provided by lasers. Above the Schwinger limit, the vacuum itself is expected to become nonlinear.

Second-harmonic generation

Second-harmonic generation (SHG, also called frequency doubling) is a nonlinear optical process in which two photons with the same frequency interact with a nonlinear material, are "combined", and generate a new photon with twice the energy of the initial photons (equivalently, twice the frequency and half the wavelength), that conserves the coherence of the excitation. It is a special case of sum-frequency generation (2 photons), and more generally of harmonic generation.

Nonlinear metamaterial

A nonlinear metamaterial is an artificially constructed material that can exhibit properties not yet found in nature. Its response to electromagnetic radiation can be characterized by its permittivity and material permeability. The product of the permittivity and permeability results in the refractive index. Unlike natural materials, nonlinear metamaterials can produce a negative refractive index. These can also produce a more pronounced nonlinear response than naturally occurring materials.

Related publications (1)

Backward Wave Second-Harmonic Generation in X-Cut Thin Film Lithium Niobate

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