Multimode Waveguide Design in Silicon Photonics

Multimode waveguide design in silicon photonics addresses the need to carry multiple optical modes within a single on-chip channel, thereby multiplying data capacity and enabling efficient mode-division multiplexing. By exploiting higher-order transverse modes, integrated circuits can route several signals in parallel without expanding chip real estate. Critical design considerations include minimising insertion loss and inter-mode crosstalk, particularly around sharp bends and waveguide transitions. Advances in fabrication allow tight confinement in silicon-on-insulator platforms, while novel geometry optimisation techniques ensure smooth mode evolution. Applications span high-bandwidth data interconnects, optical switching matrices and compact photonic routers, all of which benefit from increased integration density and reduced power consumption. The global push towards data-centric computing and AI is driving the development of robust, low-loss multimode circuits compatible with standard CMOS processes.

Research from Nature Portfolio

Recent studies have applied topology optimisation to design ultra-compact multimode waveguide bends on a 220 nm silicon-on-insulator platform. By algorithmically shaping L- and U-bend structures, footprints were reduced to as little as 1 µm × 1 µm for L-bends and 1.5 µm × 1.5 µm for U-bends, achieving insertion losses below 1 dB across a broad 1450–1650 nm wavelength range. Experimental verification of dense meander lines confirmed averaged losses around 1.2 dB for multiple cascaded bends, representing a more than 50 % improvement over conventional arc-type bends. These findings demonstrate the potential to dramatically increase circuit density while maintaining low loss and fabrication tolerance.

Multimode Waveguide Design in Silicon Photonics publication trend

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

Technical terms

Multimode waveguide: A waveguide that supports propagation of multiple transverse optical modes simultaneously.

Insertion loss: The optical power loss incurred when light passes through a component or connection.

Inter-mode crosstalk: Undesired coupling between different guided modes within a multimode structure.

Topology optimisation: Computational methods to determine the optimal material distribution for a given performance objective in photonic structures.

Mode-division multiplexing: A multiplexing technique that uses different optical modes as parallel data channels within the same waveguide.

Silicon-on-insulator (SOI): A silicon substrate separated from a top silicon layer by an insulating oxide, offering high index contrast for photonic integration.

Adiabatic bend: A waveguide curvature designed to change mode shape gradually, minimising mode coupling and radiation loss.

References

1. Ultra-compact and efficient photonic waveguide bends with different configurations designed by topology optimization. Scientific Reports (2024).
2. Demultiplexing-free ultra-compact WDM-compatible multimode optical switch assisted by mode exchanger. Nanophotonics (2024).
3. Ultra-compact multimode waveguide bend with shallowly etched grooves.. Optics Express (2021).
4. Multimode silicon photonic waveguide corner-bend.. Optics Express (2020).