Mid-Infrared Silicon Photonics and Waveguide Technologies

Mid-infrared silicon photonics exploits the optical transparency of silicon beyond the near-infrared telecommunications window, extending functionality into the 2–20 µm band. This spectral region overlaps with strong molecular absorption features, enabling on-chip spectroscopic sensing of gases and liquids, environmental monitoring, and biochemical analysis. Silicon’s mature fabrication infrastructure offers high-volume scalability, while alternative cladding materials and suspended structures mitigate absorption losses intrinsic to silicon dioxide. Waveguide designs range from silicon-on-insulator strips to suspended nanomembranes and silicon-germanium hybrid platforms, each engineered to balance confinement, propagation loss and fabrication tolerance. Key active components include microring resonators, modulators and phase shifters, which benefit from high quality factors and efficient nonlinear interactions. Integration strategies encompass monolithic approaches on silicon substrates and heterogeneous integration with nonlinear crystals or quantum cascade sources, paving the way for fully integrated photonic circuits that combine light generation, modulation and detection in the mid-infrared.

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Research from all publishers

A suspended nanomembrane silicon photonic integrated circuit architecture has been demonstrated for short-wavelength mid-infrared operation, achieving deep-subwavelength waveguide thickness and high compatibility with multi-project wafer foundry processes. Grating couplers, waveguide arrays and micro-resonators fabricated on this platform exhibit low back reflections, broad bandwidths and quality factors competitive with telecommunication-band devices, offering a scalable route to mid-infrared sensing and nonlinear optics.

A comprehensive review of integrated mid-infrared electro-optic modulators has catalogued material platforms and modulation mechanisms, highlighting advances in free-carrier depletion, Pockels-effect heterointegration and all-optical modulation. Unique strengths and limitations of silicon, germanium and lithium-niobate–on-silicon devices are compared, revealing emerging designs that deliver high extinction ratios, low drive voltages and broad modulation bandwidths suitable for spectral scanning and on-chip communication.

A silicon–germanium ring resonator platform has achieved loaded quality factors exceeding 2×10^5 at 4.18 µm, with combined propagation and bending losses below 0.2 dB/cm. Dispersion engineering in the waveguide cross-section supports efficient nonlinear processes, while the high Q-factor performance underpins sensitive refractive index sensing and low-threshold optical parametric oscillation, illustrating the dual utility of this hybrid platform in sensing and mid-infrared photonic signal processing.

Mid-Infrared Silicon Photonics and Waveguide Technologies publication trend

The graph below shows the total number of articles in mid-infrared silicon photonics and waveguide technologies across all publications each year (not limited to Nature Index journals).

Technical terms

Mid-infrared: Electromagnetic spectrum from approximately 2 µm to 20 µm, where many molecular vibrations yield strong absorption.

Photonic integrated circuit (PIC): A chip-scale device combining multiple optical functions—such as guiding, modulation and detection—using waveguides and passive/active elements.

Waveguide: A structure that confines and directs light within a specific path, defined by refractive index contrast between core and cladding materials.

Quality factor (Q-factor): A dimensionless parameter that describes the energy storage versus loss rate in a resonator; higher values indicate lower intrinsic loss.

Electro-optic modulator: A device that alters the phase or amplitude of light in response to an electric field, enabling high-speed signal encoding.

References

1. Suspended nanomembrane silicon photonic integrated circuits. Chip (2024).
2. Mid-infrared integrated electro-optic modulators: a review. Nanophotonics (2023).
3. Mid-infrared integrated silicon–germanium ring resonator with high Q-factor. APL Photonics (2023).
4. Mid-infrared integrated photonics on silicon: a perspective. Nanophotonics (2017).
5. Quantum cascade laser on silicon. Optica (2016).