Gigantic electric-field-induced second harmonic generation from an organic conjugated polymer enhanced by a band-edge effect

Shumei Chen,Guixin Li,Shuang Zhang,King Fai Li,Kok Wai Cheah

doi:10.1038/s41377-019-0128-z

Abstract

Electric-field-induced second harmonic generation (EFISH), a third-order nonlinear process, arises from the interaction between the electric field of an external bias and that of two incident photons. EFISH can be used to dynamically control the nonlinear optical response of materials and is therefore promising for active nonlinear devices. However, it has been challenging to achieve a strong modulation with EFISH in conventional nonlinear materials. Here, we report a large tunability of an EFISH signal from a subwavelength-thick polymer film sandwiched between a transparent electrode and a metallic mirror. By exploiting the band-edge-enhanced third-order nonlinear susceptibility of the organic conjugated polymer, we successfully demonstrate a gigantic EFISH effect with a modulation ratio up to 422% V−1 at a pumping wavelength of 840 nm. The band-edge-enhanced EFISH opens new avenues for modulating the intensity of SHG signals and for controlling nonlinear electro-optic interactions in nanophotonic devices.

Highlights

In nonlinear optics, it is well-known that the frequency conversion processes depend on both the chemical composition of the material and the spatial symmetry of the optical crystal[1,2]
The inversion symmetry of conventional optical crystals can be broken by introducing a stressor layer[3], the modulation depth of the nonlinear
second harmonic generation (SHG) can be generated in homogenous PFO film under the condition of broken inversion symmetry from an oblique incidence of the fundamental wave (FW)

Summary

Introduction

It is well-known that the frequency conversion processes depend on both the chemical composition of the material and the spatial symmetry of the optical crystal[1,2]. Symmetry is especially important for second-order nonlinear processes. Second harmonic generation (SHG) has been widely explored in natural crystals with broken inversion symmetry. The inversion symmetry of conventional optical crystals can be broken by introducing a stressor layer[3], the modulation depth of the nonlinear optical susceptibility of the hybrid system is very limited. With artificial photonic structures, such as liquid crystals, photonic crystals, metamaterials and metasurfaces[4,5,6], both local and global symmetries can be readily engineered to boost the SHG efficiency through quasi-phase matching[7,8,9,10], plasmonic and magnetic resonances[11,12,13,14,15], and continuous control of nonlinearity phase[16]

Methods

Results

Conclusion