Photonic topological insulators harness the principles of topology and quantum mechanics to manipulate light in unique ways, giving rise to a lot of potential applications in various fields. This article discusses photonic topological insulators, their construction, applications and recent relevant research.
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Photonic Topological Insulators
In materials science, topological insulators are referred to as materials that conduct electricity on their surface while insulating their interior due to the non-trivial topology of the electronic wave functions, preventing the backscattering of electrons within the bulk.
Similarly, photonic topological insulators use the same concept in optics, where the flow of light is manipulated rather than the flow of electrons. Photonic topological insulators (PTIs) are designed to exhibit edge states that confine light waves along their boundaries, preventing the scattering of light within the bulk.
How are Photonic Topological Insulators Constructed?
Photonic topological insulators are constructed using dielectric materials with specific refractive indices, allowing light manipulation without significant absorption. It involves creating a two-dimensional photonic crystal lattice, where the periodic arrangement of dielectric materials creates bandgaps affecting light propagation.
Topological insulators are characterized by the breaking of time-reversal symmetry achieved by incorporating non-reciprocal elements like magneto-optical materials into the photonic structure, introducing a directional preference for the propagation of light.
The topological edge states, which are immune to backscattering and other types of disturbances, are crucial for light transportation along the boundaries of the material. The construction may also involve mathematical concepts like topological invariants (e.g., Chern numbers) to predict the topological properties of the photonic material.
After fabrication, the photonic topological insulator is characterized to confirm its topological properties by measuring the transmission and reflection of light at different frequencies and angles.
Applications of Photonic Topological Insulators
Photonic topological insulators have several applications in various fields. For instance, photonic topological insulators are used in photonic circuits that can be employed in various applications, including communication systems, sensing devices, and quantum optics experiments.
The main advantage of using photonic topological insulators in photonic circuits is the inherent topological protection that ensures stability even in the presence of imperfections or external disturbances.
The edge states created by photonic topological insulators can be harnessed to create and manipulate quantum bits or qubits. The protection against scattering ensures the integrity of quantum information, which helps in developing topologically protected quantum gates.
Similarly, topological lasers exhibiting unidirectional light emission use photonic topological insulators. Compared to traditional lasers, these topological lasers are prone to backscattering and other forms of interference, which opens up new possibilities for highly stable and efficient lasers with applications in communication, sensing, and imaging.
Breakthrough in Nonlinear Photonic HOTIs
In a 2021 study, researchers have achieved a breakthrough in the field of photonic topological insulators. The study focuses on higher-order topological insulators (HOTIs), a novel phase of matter exhibiting unique boundary modes.
While prior research in PTIs has predominantly explored the linear evolution of topological states, this study introduces nonlinear dynamics to HOTIs. The researchers experimentally demonstrated nonlinear higher-order topological corner states using a photonic platform with a kagome lattice.
These states exhibit intriguing features such as soliton formation and remain topological even in the presence of nonlinearity. This advancement will help researchers explore topological properties of matter in the nonlinear regime, paving the way for the development of compact devices leveraging the aspects of topology.
Fractal Topological Insulators
In another recent study, researchers investigated fractal photonic topological insulators characterized by scatter-free edge states surrounding an insulating bulk. Unlike conventional topological insulators, which rely on the presence of an insulating bulk, these fractal topological insulators are composed exclusively of edge sites.
The study focused on a fourth-generation Sierpinski gasket, an exact fractal, and experimentally demonstrated that photonic lattices of helical waveguides with Sierpinski geometry support topologically protected chiral edge states.
Despite the absence of bulk bands, the system exhibited increased velocities in light transport compared to a corresponding honeycomb lattice. The findings challenge the conventional understanding of topological insulators, paving the way for exploring new dimensions of topological fractals in various applications, including photonics and beyond.
Photonic topological insulators face challenges like scalability, fabrication complexity, and limited bandwidth. For example, large-scale integration of topological photonic devices is challenging due to intricate design requirements.
]Similarly, achieving topological protection in the presence of disorder or environmental variations is another significant challenge. These limitations hinder the integration of photonic topological insulators into some real-world applications; however, with continuous research and developments like the ones mentioned above, it is expected that researchers will come up with appropriate solutions for every challenge.
In conclusion, photonic topological insulators represent an evolving field in optics based on topological principles and quantum mechanics. These materials exhibit robust edge states, preventing light scattering within the bulk and finding applications in photonic circuits, quantum information processing, and topological lasers.
Recent breakthroughs, such as the exploration of nonlinear dynamics in higher-order topological insulators and the study of fractal topological insulators, demonstrate the potential of photonic topological insulators for compact devices with topological properties.
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References and Further Reading
Biesenthal, T., Maczewsky, L. J., Yang, Z., Kremer, M., Segev, M., Szameit, A., & Heinrich, M. (2022). Fractal photonic topological insulators. Science. https://doi.org/10.1126/science.abm2842
Christiansen, R. E., Wang, F., Sigmund, O., & Stobbe, S. (2019). Designing photonic topological insulators with quantum-spin-Hall edge states using topology optimization. Nanophotonics. https://doi.org/10.1515/nanoph-2019-0057
Davis, R., Zhou, Y., Bandaru, P., & Sievenpiper, D. (2021). Photonic Topological Insulators: A Beginner's Introduction [Electromagnetic Perspectives]. IEEE Antennas and Propagation Magazine. https://doi.org/10.1109/MAP.2021.3069276
Khanikaev, A. B., Hossein Mousavi, S., Tse, W. K., Kargarian, M., MacDonald, A. H., & Shvets, G. (2013). Photonic topological insulators. Nature materials. https://doi.org/10.1038/nmat3520
Kirsch, M. S., Zhang, Y., Kremer, M., Maczewsky, L. J., Ivanov, S. K., Kartashov, Y. V., ... & Heinrich, M. (2021). Nonlinear second-order photonic topological insulators. Nature Physics. https://doi.org/10.1038/s41567-021-01275-3
Politano, A., Viti, L., & Vitiello, M. S. (2017). Optoelectronic devices, plasmonics, and photonics with topological insulators. APL Materials. https://doi.org/10.1063/1.4977782