Electro-Optical Chromophores and Polymers for Short NIR-Wavelengths – Materials to Application

The development of photonics in communication and sensing, particularly in integrated circuits, relies heavily on functional optical materials. These materials play a central role in converting external impulses into optical signals and vice versa. Examples include piezo-optic, elasto-optic, magneto-optic, acousto-optic, and electro-optic materials, which find applications in modulators, sensing resonators, and beam steering devices.<br/>In the field of electro-optics (EO), traditionally dominated by periodically poled LiNbO3, there is an ongoing demand for alternative materials with distinct properties to cater to specialized applications. Organic electro-optic chromophores, as part of composite polymer materials, exhibit the Pockels effect. This effect occurs when electrons move along the molecular axis within a donor-acceptor structure in response to external stimuli in an electric field. These chromophores can be easily integrated into waveguides using common spin-coating and molding techniques, offering convenient fabrication.<br/>This work specializes on the 980 nm wavelength at the short end of the NIR spectrum. The active component of such materials are electro optical (EO) chromophores, which are integrated in a suitable host polymer, mostly amorphous polycarbonate (APC) and methacrylate polymers/copolymers and are electropoled to achieve the parallel orientation necessary for a strong electro-optic effect. A range of chromophores has previously been synthesized, guided by DFT calculations, with consideration on high-dipole moments µ, good hyperpolarizability β, optical transmission in the desired spectral window and shielded side-groups that improve electropoling quality due to decreased intermolecular interactions. These materials also exhibit strong solvatochromism with differences in absorption maxima ranging between 60 nm and 90 nm depending on solvent polarity. The materials are characterized regarding their optical and materials property, specifically the electro-optical coefficient r₃₃, which is measured using Teng-Man ellipsometry.<br/>These materials have been successfully used in electro-optical Fabry-Pérot switches in a cooperation with the Laser Zentrum Hannover e.V. to translate an electrical field-shift into a transmission wavelength shift of up to 20 nm with the desired application of miniaturized optical switches.<br/>With the transition from materials research towards device applications, long-term stability has come into focus. Different polymer host-materials and covalently integrated chromophore polymer composite materials have been exposed to high-temperature aging experiments to compare their ability to maintain the parallel chromophore orientation that was obtained during the electropoling step.