Published the April 18, 2024

On-Chip Electro-Optic Frequency-Comb Generation at 8 µm wavelength

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.
In this context, researchers from C2N in collaboration with Politecnico Di Milano have experimentally demonstrated for the first time electro-optic comb generation in the deep mid-IR wavelength range.
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 to demonstrate the generation of electro-optical combs spanning
over 2.4 GHz around 8 µm wavelength.

References :
V. Turpaud1, T.-H-N. Nguyen1, N. Koompai1, J. Peltier1, J. Frigerio2, S. Calcaterra2, J-R. Coudevylle1, D. Bouville1, C. Alonso-Ramos1, L. Vivien1, G. Isella2, D. Marris-Morini1
Tunable on-chip electro-optic frequency-comb generation at 8 µm wavelength,
Laser and Photonics Review, 2300961 (2024)

1 Centre de Nanosciences et de Nanotechnologies, CNRS, Université Paris-Saclay, Palaiseau, 91120 France
2 L-NESS, Dipartimento di Fisica, Politecnico di Milano, Polo di Como, Via Anzani 42, Como, 22100 Italy

Contacts : Victor Turpaud, Delphine Marris-Morini

Légende: top : Electro-optical frequency comb generation principle. A CW laser source is sent to the modulator, driven by a periodic electrical signal, which modifies both the light amplitude and instantaneous phase and frequency, leading to optical pulses at the output corresponding to frequency comb in the spectral domain. bottom : Example of measured beatnote signal showing frequency comb operation.