Nontrivial phase matching in helielectric polarization helices: Universal phase matching theory, validation, and electric switching

Abstract

Second-order optical nonlinearity is the essential concept for realizing modern technologies of optical wavelength conversion. The emerging helical polarization fluid, dubbed helielectric nematic, now makes it possible to design and easily fabricate various polarization structures and control their optical responses. The matter family is demonstrated as an ideal liquid platform for nonlinear optical conversion and amplification with electric-reconfigurable tunability. We here develop a universal phase matching theory and reveal a nonclassic chirality-sensitive phase-matching condition in the polarization helices through both the numerical calculation and the experimental validations. The nonlinear optical amplification can be dramatically modulated with a contrast ratio of >100:1 by an in-plane electric field. Furthermore, we employ the director relaxation under electric fields coupled with nonlinear optical simulation to clarify the topology–light interactions.

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“…Recently, the ferroelectric nematic mesophase, expected since at least 1916, has been uncovered [37] . This phase possesses ferroelectricity, huge low-frequency dielectric constants, and spontaneous polar ordering [38,39] . A series of studies have reported self-assembled helical polar structures by doping chiral additives, which will open up new opportunities for polar fingerprints and introduce new physical properties to fingerprints, such as electro-optic, electromechanical, and nonlinear optical effects.…”

Roadmap on nonlinear optics–focus on Chinese research

“…Unlike traditional confocal microscopy techniques, the SH signal in a 3D volume depends on not only the orientation of polarity but also the optical phase between fundamental and SHG lights. The optical simulation and data fitting methodologies should be established and further improved [69]. Moreover, there is a limit of structural size above nearly-micron-scale dominated by the diffraction limit.…”

High-g-factor phase-matched circular dichroism of second harmonic generation in chiral polar liquids

“…48,49 Appropriate polarization periodicities in the HN* state can significantly improve nonlinear optical conversion efficiency through a unprecedented phase-matching mechanism. 50 In contrast to the traditional quasi-phase-matching (QPM) conditions of W = 2L c = l/2(n o À n 2o ), 51 the amplification of SHG occurs when the polarization helical pitch p is in the range L c -1.7L c . The periodicity of the periodic rectangular structure W equals twice the optical coherence length L c , and n o and n 2o are the refractive indices at the wavelengths of the fundamental and SH waves.…”