High modulation efficiency thin-film lithium niobate modulator using a three-mode folded phase shifter [Invited]

In this study, we proposed and experimentally demonstrated an electro-optic modulator with a small footprint and high modulation efficiency, achieved through the utilization of a mode-folded phase shifter with lumped electrodes. The three-mode phase shifter recycles the light three times with different waveguide modes while leading to a pronounced tightening of the optical field confinement. We experimentally obtained a 3.7-times improvement in the modulation efficiency. A low V pi L for thin-film lithium niobate (TFLN) Mach-Zehnder modulators of 1 V<middle dot>cm is realized with a device footprint of 2.7 mm x 0.6 mm (0.5 mm for the phase shifter). Even greater improvements in modulation efficiency can be expected through the incorporation of additional modes.