Tunable On‐Chip Electro‐Optic Frequency‐Comb Generation at 8 μm$\umu {\rm m}$ wavelength

Abstract

The development of compact systems operating in the long‐wave infrared wavelength range is of high interest for spectroscopic and sensing applications. There is currently a wide interest toward the development of optical frequency‐combs to enhance the performances of these systems. Amongst the different techniques to obtain optical frequency‐combs, electro‐optic frequency‐comb generation presents major advantages thanks to the tunable repetition rate only limited by the bandwidth of the used electro‐optical modulator. However, the development of integrated and efficient electro‐optical modulators operating in a wide long‐wave infrared spectral band is still at its infancy, and electro‐optical frequency‐comb has not been demonstrated so far beyond 3 wavelength. In this work, a Schottky‐based modulator embedded in a Ge‐rich graded SiGe waveguide is used for electro‐optic frequency‐comb generation. Considering the limited efficiency of the modulator, harmonically‐rich RF signals are used to enhance the generation of comb lines around the optical carrier. Interestingly, this allows us to demonstrate the generation of electro‐optical combs spanning over 2.4 GHz around 8 wavelength. This paves the way toward fully integrated and tunable mid‐infrared electro‐optic frequency‐comb generation systems.