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Photonics

Ultrathin waveguides for 2D photonic integrated circuits

Nature Reviews Physics volume 5, page 634 (2023)Cite this article

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Photonic integrated circuits (PICs) are chips housing diverse optical components that operate with photons, identical to miniatures of free-space optics. Many designs for PICs use waveguides to confine, direct and modulate light waves. However, as these circuits become more miniaturized, challenges arise due to absorption losses and limits on the integration density for waveguides. These factors often limit light propagation to mere micrometres or even less, diminishing the performance of the PICs. A possible solution to these challenges is to make waveguides out of 2D materials that have high refractive index and low loss. Two recent papers demonstrate progress on this front: one reporting the millimetre-scale light transport in a 2D waveguide and the other showing how optical anisotropy perpendicular to the layers of a van der Waals material can benefit 2D PICs.

Writing in Nano Letters, Andrey A. Vyshnevyy and colleagues demonstrate a way to shorten the crosstalk distance — a measure of how far the interference from one waveguide extends into neighbouring waveguides — by taking advantage of the difference in in-plane and out-of-plane refractive indices of WS2, a van der Waals material. The high in-plane refractive index of the van der Waals waveguide strengthens the effective index (which measures how confined the light is in the waveguide) of its fundamental mode, while the low out-of-plane refractive index weakens the effective indices of high-order modes. As a result, the waveguide favours single-mode propagation with a larger cross-sectional area, which is beneficial for high-performance optical communication. This work highlights the correlation between the known waveguiding characteristics of WS2 layers and their unique optical anisotropy, which is important to overcome the possible crosstalk limitation in practical parallel waveguides in PICs.

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References

Original articles

  • Lee, M. et al. Wafer-scale δ waveguides for integrated two-dimensional photonics. Science 381, 648–653 (2023)

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  • Vyshnevyy, A. A. et al. van der Waals materials for overcoming fundamental limitations in photonic integrated circuitry. Nano Lett. 23, 8057–8064 (2023)

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  1. Nature Reviews Electrical Engineering https://www.nature.com/natrevelectreng/

    Lishu Wu

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  1. Lishu Wu
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Correspondence to Lishu Wu.

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Wu, L. Ultrathin waveguides for 2D photonic integrated circuits. Nat Rev Phys 5, 634 (2023). https://doi.org/10.1038/s42254-023-00657-1

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  • DOI: https://doi.org/10.1038/s42254-023-00657-1

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