Fundamental limits on the electro-optic device figure of merit

TL;DR

This paper analyzes the fundamental limits of the electro-optic device figure of merit, linking microscopic material properties to device performance, and highlights that optimal figures of merit do not always correlate with high nonlinearity.

Contribution

It introduces a method to calculate the electro-optic figure of merit based on half-wave voltage and loss, relating it to microscopic properties and identifying fundamental limits.

Findings

Large figure of merit does not always mean high nonlinearity.

Low loss can compensate for low nonlinearity in device materials.

Resonance can enhance nonlinear response despite high loss.

Abstract

Device figures of merit are commonly employed to assess bulk material properties for a particular device class, yet these properties ultimately originate in the linear and nonlinear susceptibilities of the material which are not independent of each other. In this work, we calculate the electro-optic device figure of merit based on the half-wave voltage and linear loss, which is important for phase modulators and serves as the simplest example of the approach. This figure of merit is then related back to the microscopic properties in the context of a dye-doped polymer, and its fundamental limits are obtained to provide a target. Surprisingly, the largest figure of merit is not always associated with a large nonlinear-optical response, the quantity that is most often the focus of optimization. An important lesson to materials design is that the figure of merit alone should be optimized. The best device materials can have low nonlinearity provided that the loss is low; or, near resonance high loss may be desirable because it is accompanied by resonantly-enhanced, ultra-large nonlinear response so device lengths are short. Our work shows which frequency range of operation is most promising for optimizing the material figure of merit for electro-optic devices.