Multimode Interference Devices in Photonic Systems

Multimode interference (MMI) devices form a cornerstone of integrated photonics by harnessing the natural self-imaging of multiple guided modes in a broad waveguide region. When light from one or more input channels propagates through an MMI section, the modal superposition recreates one or more intensity images at predetermined distances. This principle enables compact power splitters, combiners, demultiplexers and interferometric sensors without reliance on resonant cavities or long coupling lengths. Advances in fabrication and material platforms—from silicon and silicon nitride to lithium niobate on insulator and emerging chalcogenides—have driven performance gains in insertion loss, uniformity and wavelength tolerance. Modern MMI components occupy footprints of only a few tens of micrometres, offering low back-reflection, wide bandwidth and fabrication tolerance suitable for dense wavelength-division multiplexing in data-centre interconnects, on-chip quantum circuits and mid-infrared sensing. Integration with active elements such as modulators or detectors has further extended MMI utility, supporting reconfigurable routing, nulling interferometry for exoplanet imaging and temperature or biochemical sensing. Continued optimisation of geometry and refractive-index contrast promises ever more versatile and energy-efficient photonic circuits that underpin global optical communications and emerging sensing technologies.

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Multimode Interference Devices in Photonic Systems publication trend

The graph below shows the total number of articles in multimode interference devices in photonic systems across all publications each year (not limited to Nature Index journals).

Technical terms

Multimode interference (MMI): The phenomenon by which multiple guided modes in a broad waveguide interfere to recreate input field patterns at specific propagation distances.

Self-imaging principle: The underlying mechanism of MMI in which an input beam profile reproduces itself periodically along the propagation axis due to modal beating.

Insertion loss: The optical power reduced when a device is inserted into a waveguide path, typically expressed in decibels (dB).

Crosstalk: Unwanted coupling or leakage of optical power between adjacent channels in a multiplexed device, impacting channel isolation.

Waveguide: A structure that confines and directs light, defined by a core region of higher refractive index surrounded by lower-index cladding.

References

1. Design of thin-film lithium niobate power splitters and combiners based on multimode interference. Optical and Quantum Electronics (2025).
2. An Optical 1×4 Power Splitter Based on Silicon–Nitride MMI Using Strip Waveguide Structures. Nanomaterials (2023).
3. 1 × 4 Wavelength Demultiplexer C-Band Using Cascaded Multimode Interference on SiN Buried Waveguide Structure. Materials (2022).
4. Fabrication tolerant chalcogenide mid-infrared multimode interference coupler design with applications for Bracewell nulling interferometry.. Optics Express (2017).
5. All-silicon optical temperature sensor based on Multi-Mode Interference.. Optics Express (2003).