Folded Sub-1V Vπ Thin Film Lithium Niobate Phase Modulator

This work reports a sub-1 volt drive voltage (V $_{\pi } $ ) folded phase modulator utilizing capacitor-loaded traveling wave electrodes (CLTWEs). The implementation employs a low-loss CLTWE on a quartz (Qz) substrate, facilitating both broadband index matching and minimal RF loss. A series of phase modulators of varying lengths have been fabricated and subjected to experimental characterization. The measured loss for straight CLTWEs is 0.21 dB/(cm $\cdot $ GHz $^{1/2}$ ). The experimentally determined DC V $\pi $ is 0.52 V for a modulation length of 7.5 cm.