Compact Slow-Wave Electrode Design for High-Index Photonic Devices

This work presents a method for the development of traveling slow-wave metallic electrodes to provide widely tunable structures for applications in integrated photonic devices. The method is particularly useful for index-matching of radio-frequency (RF) signals with optical waves in photonic devices based on waveguide structures with large group indices. The proposed electrode design provides greater flexibility when devising impedance-matched, low-loss, and compact RF transmission lines by including planar T-electrodes with interleaved conductive digits. The addition of these two microstructures permits modification of the capacitance and inductance of a standard ground-signal-ground coplanar waveguide. This independent design of the reactive values provides engineering control of the RF index in a wide range of $\sim {2}$ to $\sim {6}$, while ensuring the structure maintains a 50 $\Omega$ impedance for integration with standard RF equipment. Although the proposed electrode geometry provides an agnostic design solution for substrate materials, this work focuses on applications in thin-film lithium niobate on silicon.