Versatile meta-structured waveguides for photonic integrated circuits and beyond

Allying subwavelength photonic structures with diverse waveguide platforms to develop meta-devices for tailoring guided waves and massive emergent applications.

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The concept of metasurfaces and metamaterials have catalyzed fruitful results in the realm of meta-optics by leveraging the judiciously engineered microscopic photonic architectures with subwavelength features. Previous research attentions on meta-optics are mainly centered around tailoring light in free space and develop free-space optical elements and its relevant applications. However, recent years are witnessing ever-increasing interest in synergizing various functional subwavelength photonic structures with diverse optical waveguide platforms to enable novel photonic meta-devices.

In a recent article published by 'Light: Science & Applications', an international team of scientists comprehensively reviewed recent advances on subwavelength meta-structured optical waveguides, encompassing a broad class of photonic devices and systems that ally metamaterials and metasurfaces with diverse optical waveguides platforms. As illustrated in Fig. 1a, meta-waveguides can be classified via either design methods or underpinning waveguide platforms. (1) If classified by design method, meta-waveguides can be conceived either by physics intuition-based forward design or computer optimizations-based inverse design, as shown in Fig. 1b. (2) If categorized by waveguide platforms, meta-optics can be saddled with dielectric waveguides, optical fibers and plasmonic waveguides. 

Photonic structures with subwavelength devised details are crucial to meta-waveguides. Taking two-dimensional periodic silicon segments as an instance (see Fig. 1c), the meta-waveguides should be treated as a designer effective medium, which is physically distinctive from the photonic bandgap theory found in photonic crystals or scalar diffraction theory used in conventional gratings.

Fig. 1
Figure 1. Meta-waveguide features and attributes. a, Meta-waveguides can be classified via either design methods or underpinning waveguide platforms. b, Two general directions to design meta-waveguides: physics intuition-based forward designs and inverse design methods. c, Comparisons of light propagating in structured planar waveguides with different periodic feature size (The left panel in c is reproduced from Ref: Subwavelength integrated photonics, Nature, 2018). 

In this review article, foundational results and representative applications are comprehensively summarized. Brief physical models with explicit design tutorials, either physical intuition-based design methods or computer algorithms-based inverse designs, are cataloged as well. The authors highlight how incorporating the concepts of meta-optics with waveguide technologies may propel photonic integrated circuits into new heights, by infusing new degrees of freedom to the available waveguide landscapes to provide versatile efficient coupling interfaces, novel on-chip optical signal processing paradigms and diverse platforms for sensing, imaging and artificial intelligence.

Fig. 2
Figure 2. Outlook on photonic integrated “meta-circuits”. Diverse meta-waveguide-based photonic devices may potentially revolutionize conventional integrated optical scenarios with compact footprint, enhanced efficiency and multifunctionality.

Despite the concept of meta-waveguides is still in its infancy, exciting progress are hatching with bright perspectives and profound potential applications. As conceptually illustrated in Fig. 2, the advancement of meta-waveguides can not only extend meta-optics to the realm of guided electromagnetic waves and waveguide technology, but may also prototype a plethora of emergent applications on this versatile playground in devising artificial optical nanostructures. We believe that meta-waveguides may further venture photonic integrated circuits and many relevant applications into new territories, such as biomedical sensing, imaging, and detection. Massive novel emerging device functions will still await exploring in this vibrant field and beyond.

For more information, please refer to this recent publication: Y. Meng, Y. Chen, L. Lu, et al, "Optical meta-waveguides for integrated photonics and beyond", Light: Science & Applications, 10, 235, 2021.

DOI: 10.1038/s41377-021-00655-x

Yuan Meng

PhD, Tsinghua University