Thin film lithium niobate on sapphire for integrated mid-infrared modulator

The mid-infrared spectrum, spanning from 3 to 14 µm, holds great promise for molecular spectroscopy and free space optical communication, benefiting from strong molecular absorption and reduced atmospheric attenuation. While progress in MIR photonics has accelerated due to improved sources and detectors, integrated low-loss, high -performance modulators remain limited. In order to address this gap, we demonstrate a broadband, high speed lithium niobate on sapphire Mach Zehnder electro optic modulator operating from 3.95 to 4.5 µm. The device shows a 3 dB bandwidth above 20 GHz, 17 dB extinction ratio, and V_πL = 22 V ⋅ cm, with optical output power at the half milliwatt level. We demonstrate 10 Gbit s^-1 data transmission and a 70 GHz broad frequency comb, uniquely combining integration, low propagation loss, extinction ratio and high-speed operation.