Ultralarge and Thermally Stable Electro‐optic Activities from Diels–Alder Crosslinkable Polymers Containing Binary Chromophore Systems

Abstract

Poled electro-optic (EO) polymers have enabled many advances in the exploration of high-speed and broadband information technologies.[1] Polymer based EO devices have been demonstrated to have large bandwidths (over 110 GHz), low driving voltages, and sustain their performance in a flexible form [2] or under extreme environmental conditions. [3,4] For optical circuits, EO polymers can be easily integrated with stripline-or ring-structured waveguides made of sol-gels, [5] low-loss fluorinated polymers, [6] silicon slots, [7] conducting oxides, [8] and photonic crystals. [9] Recently, EO polymers have also been utilized for the generation/detection of a gap-free pulsed THz system with a bandwidth up to ca. 12 THz.[10]Large numbers of discrete photonic components need to be inserted into integrated systems of telecommunication and silicon microphotonics, especially where an extreme amount of data is required to travel in a very small space.[11] Therein lies the great challenge for polymer-based EO technologies: to have thermally stable EO coefficients (r 33 ) of around 500 pm V -1 at wavelengths of 1.31 or 1.55 lm.[11b]Currently, the most commonly used materials for polymeric EO devices are based on poled polymers with r 33 values around 50-80 pm V -1 at wavelengths of 1.31 or 1.55 lm. In these materials, dipolar nonlinear optical (NLO) chromophores have been doped or incorporated at a level of ca. 20-25 wt % to reach their maximum r 33 values. [5][6][7][8][9][10] Beyond such a moderate loading of chromophores, strong intermolecular electrostatic interactions severely limit the poling-induced polar order and cause phase-separation problems between chromophores and polymers.To further improve EO activity, research efforts have focused on developing shape-engineered chromophores with high molecular optical nonlinearities (lb), [12] where lb is a product of first hyperpolarizability and the dipole moment of the NLO chromophore, and increasing order within the matrices by controlling the nanoscale architecture of macromolecules. [13] In our recent study we have demonstrated, using Diels-Alder (DA) "click chemistry" to post-functionalize NLO chromophores onto polymers, that high chromophore loading levels (up to 35 wt %) and large r 33 values (up to 110 pm V -1 ) could be achieved in in situ generated side-chain dendronized NLO polymers with non-reacted chromophores as guest dopants. [14] This opens a new avenue to explore optimal host-guest combinations and to develop an efficient way to control lattice hardening in these hybrid polymers. The ultimate goal is to simultaneously achieve very large EO activity, good thermal stability, high optical transparency, and excellent mechanical properties within the same material via molecular design and facile processing. In this paper, we report a novel method to disperse a highly efficient secondary chromophore into in situ crosslinked NLO polymer networks, leading to both enhanced EO activity (> 260 pm V -1 at 1.31 lm) and alignment stability at 85°C. In photorefractive (PR) po...

Organic Broadband TeraHertz Sources and Sensors

“…Thanks to more than twenty years of intensive study driven by the telecommunication industry crying for cheap EO devices and easy integration, EO polymers with both high EO coefficients and high glass transition temperature (good thermal stability) are available now. [69][70][71] With certain material modification, THz technology can also benefit from this advancement. An example to show the necessity of the material modification is that most existing NLO chromophores that lead to EO polymers with high EO coefficients cannot be processed into the thick films required by freestanding THz emitters or sensors.…”

Enhancement of bulk second-harmonic generation from silicon nitride films by material composition

“…One of the limitations of many nonlinear materials for CMOS-compatible platforms is the lack of second-order nonlinearity due to centrosymmetry. The problem can be overcome by poling [4,5], straining the material [3] or by using multilayer composites [6][7][8]. Unexpectedly, CMOS-compatible amorphous silicon nitride films (SiN) have been shown to possess a bulk second-order nonlinearity by measuring strong second-harmonic generation (SHG) from thin films [9][10][11].…”

Molecular Design and Supramolecular Organization of Highly Efficient Nonlinear Optical Chromophores for Exceptional Electro-Optic Properties

“…The origin of this enhancement is still under investigation (48,49). To further understand these results, we applied the measurement of the order parameters based on linear optical dichroism of intramolecular charge transfer bands.…”