We published a review article on flatband fine-tuning and its photonic applications in Nanophotonics last week! This follows up on our earlier perspective on photonic flatbands published in APL Photonics in 2018.
How has the field changed in 6 years?
In 2018, we identified promising areas for future research where flatbands had not yet been extensively explored yet: coupled resonator lattices, circuit QED, and photonic crystals.
For the case of coupled resonators, the idea of synthetic dimensions (considering coupling in the frequency domain rather than space) has since emerged as a new direction for non-Hermitian and topological photonics, with the ability to fine-tune short- and long-range hoppings to realize flat band lattices using coupled optical fiber loops.
Circuit QED now sees broad interest as a platform for quantum simulation, especially for studying lattices on hyperbolic space.
Flatband photonic crystals have received a great amount of attention, driven especially by the rise of moire materials which exhibit flat bands at "magic" twist angles. This breakthrough in condensed matter physics inspired the development of theory (see Phys. Rev. Lett. 126, 136101 (2021), Phys. Rev. Lett. 126, 223601 (2021), and Phys. Rev. Research 4, L032031 (2022), for example), with applications to photonic crystal lasers and shaping free electron radiation being actively explored.
The huge growth of interest in flat bands in photonic crystals and related platforms such as metasurfaces has been quite remarkable. It is driven by the realization that one does not need to carefully control symmetries or suppress long range couplings, guided by simple tight binding models for flat bands, to design them. Rather, a sufficiently complex system supporting parameter fine-tuning is all that you need to realize flat bands! Equipped with this knowledge, our latest review is timely in that it covers novel phenomena that can emerge in fine-tuned flat band systems.
