GHz-rate optical phase shift in light matter interaction-engineered, silicon-ferroelectric nematic liquid crystals

TL;DR

This paper demonstrates GHz-rate optical phase shifting using ferroelectric nematic liquid crystals integrated with silicon photonics, enabling fast, efficient, and CMOS-compatible electro-optic devices without poling issues.

Contribution

It introduces a novel ferroelectric nematic liquid crystal device with GHz-speed phase shifting, overcoming limitations of traditional electro-optic materials and simplifying fabrication.

Findings

Achieved >4.18 GHz electro-optic bandwidth.

Demonstrated low insertion loss (~2.6 dB).

Reported high Pockels effect modulation efficiency (~25.7 V·mm).

Abstract

Organic electro-optic materials have demonstrated promising performance in developing electro-optic phase shifters. Their integration with other silicon photonic processes, nanofabrication complexities, and durability remains to be developed. While the required poling step in electro-optic polymers limits their potential and utilization on a large scale, devices made of paraelectric nematic liquid crystals suffer from slow bandwidth. In ferroelectric nematic liquid crystals, we report an additional GHz-fast phase shift that ultimately allows for significant second-order nonlinear optical coefficients related to the Pockels effect. It avoids poling issues and can pave the way for hybrid silicon-organic systems with CMOS-foundry compatibility. We report DC and AC modulation efficiencies of $\approx$~0.25 V$\cdot$mm (from liquid crystal orientation) and $\approx$~25.7 V$\cdot$mm (from Pockels effect), respectively, an on-chip insertion loss of $\approx$~2.6 dB, and an electro-optic bandwidth of $f_\text{-6dB}$>4.18 GHz, employing improved light-matter interaction in a waveguide architecture that calls for only one lithography step.