Molecular Bandgap Engineering of Organic Electro-Optic Materials for Achieving Ultralarge Near-Resonance Optical Nonlinearities Guided by Spectroscopic Electromodulation and Ellipsometry

Description

The performance of organic electro-optic (EO) materials and hybrid devices have increased remarkably over the past decade, making them an exciting potential componentry for future 5G/6G technologies. However, recent research and development of organic EO (OEO) materials have been limited by the lack of reliable EO characterization techniques and an in-depth understanding of the structure-property relationships, and the frequent occurrence of incorrect and unreliable data-reporting of ultrahigh EO coefficients risks damaging the credibility and reliability of the field. Since the active dimension of hybrid nanoscale photonic devices has continued to shrink with footprints of tens of square micrometers, it offers a great opportunity to explore the possibility of maximizing the nonlinearities of OEO materials by operating at thewavelengths near the material absorption without significantly increasing optical losses. However, the study of the resonance-enhanced nonlinear coefficients of OEO materials has not been well supported by common measurement techniques for characterizing the EO coefficients of OEO materials include Teng–Man (TM) simple reflection, attenuated total reflectance (ATR), and Mach–Zehnder interferometric (MZI) technique, which are applicable only at discrete near-infrared (NIR) wavelengths in the low absorbing regions of poled films, with relative advantages and disadvantages of each method. This project aims to use the latest developments in electromodulation spectroscopy and spectroscopic ellipsometry, with the assistance of the ATR technique, to study the complex EO coefficients of poled polymers and molecular glasses. The selected OEOmaterials are the newly developed high-performance EO polymers and self-assembled molecular glasses exhibiting large EO coefficients at the telecom wavelengths, albeit with little understanding of their near-resonance properties and the origin of their largenonlinearities. Based on transmission-mode Stark effect EM spectroscopy and Kramers-Kronig analysis, we will study the electric-field-induced full spectral changes in optical absorption and refraction of materials and quantify their near-band-edge opticalnonlinearities from electroabsorption and electrorefraction effects of poled films. Our approach would overcome the limitation of the classic qualitative two-level model and provide a quantitative understanding of near-resonance optical nonlinearities of organicEO materials. By analyzing the dispersion of complex EO coefficients of poled polymers in the NIR region, we expect that our study provides ample insight into molecular bandgap engineering of OEO materials for achieving performance breakthroughs ofnear-resonance optical nonlinearities greater than 10,000 pm/V in the second NIR window. It can inspire the exploration of high-speed, absorptive, or phase-shifting light-modulators for on-chip applications.