The development of compact systems operating in the mid-infrared wavelength range is of high interest for spectroscopic and sensing applications. Interestingly, graded index Silicon Germanium (SiGe) photonic circuits possessed unique properties for the development of a complete photonic integrated platform in this wavelength range, which are their transparency in a wide spectral range together with the strong non linear index and ability to fine tune both the electronic bandgap and refractive index of SiGe alloys.
In the last year major achievements have been obtained across different fundamental building blocks :
• High speed optical modulators based on carrier depletion in SiGe photonic circuits have been demonstrated [1]. By using the free-carrier plasma absorption effect, the device achieves an extinction ratio of up to 1.9 dB at a wavelength of 9 µm. High-speed operation up to 7 GHz is obtained, while the optical bandwidth is estimated to be around 3 GHz.
• As the development of on-chip spectroscopic systems require broadband mid-infrared sources, supercontinuum generation has been improved, targeting a reduction of the required input power. Octave spanning supercontinuum generation at a record-low peak power of 311 W in this wavelength range has thus been demonstrated [2].
• Compact integrated resonators have also been demonstrated. Two designs have been developed and compared based on racetrack with Euler bends and wrapped ring resonators. In each case the ring radius is 100 µm. Q factors above 40,000, with over 10 dB of extinction ratio have been demonstrated at 7.5 m wavelength [3].
Interestingly, each of these results represent a significant step forward in the performance of mid-IR integrated photonics, paving the way for high-performance on-chip spectroscopic systems.
References :
[1] J. Huertas-Pedroche, V. Turpaud, L. Lucia, A. Bousseksou, T.H.N. Nguyen, H. Dely, G.L. Ngo, S. Calcaterra, D. Impelluso, A. de Cerdeira Oliveira, E. Herth, D. Bouville, S. Edmond, J.R. Coudevylle, V. Merupo, E. Peytavit, J.F. Lampin, S. Barbieri, J. Frigerio, R. Colombelli, G. Isella, D. Marris-Morini, High-speed integrated Silicon Germanium optical modulator with 3 GHz bandwidth in the 5-9 µm wavelength range, Optics Express, 33(20), 42408-42419 (2025), https://doi.org/10.1364/OE.572563, https://hal.science/hal-05287436
[2] V. Turpaud, Y. Yang, H. Dely, A. Bricout, T.H.N. Nguyen, N. El Bouchikhi, S. Calcaterra, D. Impelluso, J-M. Hartmann, S. Edmond, C. Alonso-Ramos, L. Vivien, J. Frigerio, G. Isella, and D. Marris-Morini, Low-power supercontinuum generation in Ge-rich SiGe waveguides from 4 to 13 µm wavelength, APL Photonics (invited paper)10, 090804 (2025) https://doi.org/10.1063/5.0270228, https://hal.science/hal-05268510v1
[3] H. Dely, V. Turpaud, A. Bricout, S. Edmond, J.R. Coudevylle, D. Bouville, E. Herth, J. Frigerio, D. Impelluso, S. Calcaterra, G. Isella, C. Alonso Ramos, L. Vivien, D. Marris-Morini, Compact silicongermanium microresonators for longwave infrared frequencies Optics Express, 33 (19), 39715 (2025). https://doi.org/10.1364/OE.570083 , https://hal.science/hal-05249546
Contact : Delphine Marris-Morini
Funding. This work was partly supported by the French RENATECH network. This project has received funding from the European Union’s Horizon Europe research and innovation program (101128598 - UNISON) and from the European Research Council (101097569 - Electrophot).
Figure :(a) Integrated electro optical modulator : a Schottky diode is embedded in a SiGe waveguide, and free carrier absorption is used to achieve high speed optical modulation (b) : Compact ring resonator. A thermal phase modulator is used to retrieve the resonance linewidth (c) : Supercontinuum generation within SiGe waveguide. Dispersion engineering allow a flat – more than one octave– super continuum generation.
