Photonic Crystal Cavity IQ Modulators in Thin-Film Lithium Niobate

Thin-Film Lithium Niobate is an emerging integrated photonic platform showing great promise due to its large second-order nonlinearity at microwave and optical frequencies, cryogenic compatibility, large piezoelectric response, and low optical loss at visible and near-infrared wavelengths. These properties enabled Mach-Zehnder interferometer-based devices to demonstrate amplitude- and in-phase/quadrature (IQ) modulation at voltage levels compatible with complementary metal-oxide-semiconductor (CMOS) electronics. Maintaining low-voltage operation requires centimeter-scale device lengths, making it challenging to realize the large-scale circuits required by ever-increasing demands for information density in communications as well as classical- and quantum information processing. Reduced device sizes reaching the 10 mu m scale are possible with photonic crystal cavities. So far, their operation has been limited to amplitude modulation and required circulators or lacked cascadability. Here, we demonstrate a compact IQ modulator using two photonic crystal cavities operating as phase shifters in a Fabry-Perot-enhanced Michelson interferometer configuration. It supports cascadable amplitude and phase modulation at GHz bandwidths with CMOS-compatible voltages.