Electro-optically tunable optical delay line with a continuous tuning range of ∼220 fs in thin-film lithium niobate

We demonstrate fabrication of a 30-cm-long thin-film lithium niobate (TFLN) optical delay line (ODL) incorporated with segmented microelectrodes of 24-cm total length using the femtosecond laser lithography technique. The transmission spectra of the unbalanced Mach-Zehnder interferometers (MZIs) reveal an ultra-low propagation loss of 0.025 dB/cm. The device exhibits a low half-wave voltage of 0.45 V, corresponding to a voltage-length product of 10.8 V·cm, which is equivalent to 5.4 V·cm in the push-pull configuration. We also demonstrate a high electro-optic (EO) tuning efficiency of 3.146 fs/V and a continuous tuning range of 220 fs in the fabricated ODL.