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Folded thin-film lithium niobate modulator based on a poled Mach-Zehnder interferometer structure.

The thin-film lithium niobate structure has been used recently to construct compact and high-performance electro-optical modulators. Due to the moderate electro-optical coefficient of the lithium niobate material, the device length of such a modulator is still long, a few centimeters usually. Here, a folded Mach-Zehnder interferometer based modulator on x-cut thin-film lithium niobate is demonstrated. An effective poling procedure is developed to activate the device. The proposed modulator structure can shorten the device length without affecting its performance. The measured VπL product of a fabricated and completely poled folded modulator is about 2.74V⋅cm, and the 3 dB electro-optical bandwidth is about 55 GHz. They are close to those of a conventional Mach-Zehnder modulator with a straight modulation section.