DC-to-GHz Modulation In Microring Modulators Using Ferroelectric Nematic Liquid Crystal-on-Silicon in a Foundry Photonic Process
Silicon-organic hybrid (SOH) platforms exhibit exceptional electro-optic (EO) properties, including high-speed operation, low energy consumption, and compact footprints. However, the absence of a scalable poling method for EO polymers, combined with the slow switching speeds characteristic of liquid crystals, has impeded the integration and compatibility of these materials with commercial silicon photonic foundries. On the other hand, the realization of very-large-scale photonic integrated circuits (PICs) in the native silicon photonics platform itself is impeded by the complexities associated with the wavelength and thermal stabilization for microring modulators (MRMs). This study establishes the foundation for a poling-free, CMOS-compatible SOH MRM platform by exploiting simultaneous AC phase shifts in ferroelectric nematic liquid crystals (FN-LCs). We present the first demonstration of an MRM coated with FN-LC, with both the RF signal and the DC bias applied to the same electrodes, taking advantage of the dual phase shift uniquely available in FN-LC. An EO bandwidth of f$_{-6dB}\approx$ 7.8 GHz is achieved \textendash~ the highest reported value for an SOH MRM to date. As a proof of concept, we demonstrate an approximately linear resonance shift across the full width at half maximum ($\approx$ 150 pm/V), with a static power efficiency of $\approx$ 4.5 nW/$\pi$ for an MRM occupying a total footprint of $\approx$ 0.084 mm$^2$ and exhibiting an on-chip optical insertion loss of $\approx$ 0.78 dB. Successful infiltration of FN-LC, selectively patterned on top of phase shifters, along with optical input/output channels established using free-form photonic wire bonds, is demonstrated in the proposed PIC.