Mode Conversion Techniques in Silicon Photonics

Mode conversion techniques play a pivotal role in managing and tailoring the spatial distribution of optical fields within silicon photonic circuits. These techniques enable efficient coupling between distinct guided modes—whether fundamental or higher-order—facilitating advanced functionalities such as mode-division multiplexing, switching and on-chip signal processing on a silicon-on-insulator platform. A variety of strategies have been explored, including adiabatic tapers that gradually transform waveguide geometry to redistribute optical power, engineered Bragg gratings that harness phase-matched reflections for selective mode exchange, and metamaterials providing subwavelength perturbations for arbitrary spatial mode manipulation. Recent advances in computational topology optimisation and inverse design algorithms have miniaturised device footprints while maintaining high conversion efficiencies, even for complex transformations. Integration of dynamic control elements—such as liquid-crystal infiltration or thermo-optic phase shifters—introduces reconfigurability essential for adaptable optical networks. Complementary approaches using three-dimensional photonic lanterns have bridged fibre-chip interfaces, enabling seamless mode-and-polarisation multiplexing in hybrid systems. Collectively, these developments underpin the scalability of high-capacity data links, compact sensor arrays and programmable photonic processors.

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Mode Conversion Techniques in Silicon Photonics publication trend

The graph below shows the total number of articles in mode conversion techniques in silicon photonics across all publications each year (not limited to Nature Index journals).

Technical terms

Adiabatic taper: A gradually varying waveguide structure that transitions the effective mode index to redistribute optical power between modes with minimal reflection.

Bragg grating: A periodic refractive-index modulation used to couple light between forward and backward propagating modes or different guided modes via phase matching.

Inverse design: A computational technique that optimises device geometry by defining target optical performance and iteratively adjusting structures, often via adjoint methods.

Metamaterial: An artificial subwavelength structure engineered to produce desired optical properties, enabling tailored wavefront and mode control within a compact footprint.

Photonic lantern: A three-dimensional waveguide assembly that adiabatically converts multimode fibre inputs into multiple single-mode outputs on chip, or vice versa.

Mode-division multiplexing: A scheme that transmits multiple data channels simultaneously by encoding signals onto distinct spatial modes within a multimode waveguide or fibre.

References

1. Handling mode and polarization in fiber by fs-laser inscribed (de)multiplexer and silicon switch array. PhotoniX (2023).
2. Tunable on-chip mode converter enabled by inverse design. Nanophotonics (2023).
3. Metamaterial-enabled arbitrary on-chip spatial mode manipulation. Light: Science & Applications (2022).