Record-high near-band-edge optical nonlinearities and two-level model correction of poled polymers by spectroscopic electromodulation and ellipsometry  

作　　者：Taili Liu Di Zhang Md Rashedul Huqe Wen Wang Juan Antonio Zapien Sai-Wing Tsang Jingdong Luo 

机构地区：[1]Shenzhen Research Institute,City University of Hong Kong,Shenzhen 518057,China [2]Department of Chemistry,City University of Hong Kong,Hong Kong SAR,China [3]Department of Materials Science and Engineering,City University of Hong Kong,Hong Kong SAR,China [4]Center of Super-Diamond and Advanced Films(COSDAF),City University of Hong Kong,Hong Kong SAR,China

出　　处：《Science China Chemistry》2022年第3期584-593,共10页中国科学（化学英文版）

基　　金：supported by the Fundamental Research Project Funding from Shenzhen Science & Technology Innovation Committee (JCYJ20180507181718203);the National Natural Science Foundation of China (21975213);the Research Grants Council (RGC) of Hong Kong (11306320, 11303618, 11210218);the City University of Hong Kong (9610389, 9680263, 9610454);the Innovation and Technology Commission of Hong Kong (ITS/461/18)。

摘　　要：The determination of nonlinearities near the band edge of organic and polymeric electro-optic(EO)materials is important from the viewpoint of molecular nonlinear optics(NLO)and photonic device applications.Based on transmission-mode Stark effect electromodulation(EM)spectroscopy,we study the electric-field-induced changes in optical absorption and refraction of newly developed EO polymers from the visible to near-infrared(NIR)wavelengths and report record-high near-band-edge complex EO effects from poled thin films.Values ofΔn andΔk up to 10^(-3) and 10^(-2) are found at an applied electric field of 2.0×10^(5)-3.0×10^(5)V/cm.The study of linear optical properties of poled films by spectroscopic ellipsometry shows large polinginduced birefringence and a nearly two-fold increase in the extinction coefficients at the extraordinary polarization.Through the Kramers-Kronig analysis,we obtained the real and imaginary second-order nonlinear coefficients up to~3,500 and~5,600 pm/V,respectively,which are believed to be the highest NLO coefficients of poled polymers through the resonance enhancement.Our approach goes beyond the previous works,applicable only to several discrete wavelengths,to a full-spectral analysis with independent verification of slab waveguide measurements.By considering both the electroabsorption and electrorefraction effects,our study overcomes the limitation of the classic qualitative two-level model and provides a quantitative understanding of near-resonance optical nonlinearities of organic EO materials.It can inspire the exploration of high-speed,absorptive,or phase-shifting light-modulators using EO polymers for on-chip applications.

关 键 词：poled polymers ELECTROABSORPTION electro-optic effect second-order nonlinear susceptibilities 

分 类 号：O631[理学—高分子化学]