Modern life is increasingly shaped by light. Optical devices exist in smartphone cameras, medical sensors, and emerging quantum technologies. As these technologies become more powerful, they are also expected to become smaller, lighter, and more energy efficient. One promising solution comes from metasurfaces—ultrathin layers patterned with nanoscale structures ("meta-atoms") that offer unprecedented control over light within a flat, chip-compatible platform. When integrated with optoelectronic platforms, these metasurfaces give rise to so-called metadevices, offering new ways to control light on a chip. For many applications, trapping light so that it interacts more with active media is a key requirement, and this is where a photonic bound states in the continuum (BIC) enters the picture.
Despite this promise, designing BICs for practical use remains challenging. Unlike traditional optical cavities that rely on light bouncing back and forth between two mirrors, BICs trap light through destructive interference between light waves. This mechanism allows light to remain confined in open systems like BIC metasurfaces. In theory, BICs are bound, non-radiative states that can trap light indefinitely, although practical limitations inevitably cause some leakage. Even so, these "quasi-BICs" retain exceptionally strong light confinement, making them among the most promising optical resonators available today. As the demand for more sophisticated functionalities grows, highly symmetric nanostructures are no longer sufficient, making the design more challenging and increasing the need for more flexible design strategies.
In a review article, that was made available online on March 15, 2026, and later published in Volume 9, Issue 3 of the journal Opto-Electronic Advances on March 24, 2026, first author Thi Thu Ha Do and corresponding author Son Tung Ha, from the Advanced Optical Technologies department at the Agency for Science, Technology and Research (A*STAR), Singapore, discuss how far photonic BICs have come and where they are headed next. The review provides a comprehensive overview of the field, beginning with the foundations of BIC physics and moving through recent advances in design strategies, material platforms, and device concepts.
The authors guide readers through the foundations of BIC physics and provide a library of materials to design BICs across a broad range of the electromagnetic spectrum, from deep ultraviolet, visible, and infrared to terahertz and microwave wavelengths. This diversity in materials is matched by a significant evolution in how these structures are conceived.
Another striking feature of BICs is their intrinsic topological nature, which allows these states to split or merge in a controlled manner. This tunability gives rise to a range of extraordinary photonic states, such as super-BICs, chiral BICs, and flatband BICs, as well as emergent physical phenomena, such as BIC polariton condensation, ultrafast optical switching, and exceptional points. The review also provides a clear discussion of the deeper physical principles that give BICs their unusual and robust behaviour, helping to connect these advances to broader themes in modern photonics and condensed matter physics.
One especially valuable aspect of the review is its comprehensive survey of low-loss all-dielectric materials that can support BICs across a wide range of wavelengths, from the ultraviolet to the microwave regime. By gathering this information into a single, curated resource, the authors make it easier for researchers to identify suitable material platforms for specific applications. This practical focus is further strengthened by discussions of emerging design strategies, including machine-learning and inverse-design approaches, which are becoming essential as the demands on metasurfaces grow more complex.
These advances translate directly into practical opportunities, with immediate implications for applications in lasing, sensing, nonlinear optics, wavefront shaping, and imaging. Beyond summarizing past achievements, the review looks firmly toward the future of the field, outlining key challenges such as scaling fabrication to wafer-level production and integrating BIC metasurfaces with active electronic systems.
