Active nanophotonic structure in iridoplasts of begonias

So-called ‘iridoplasts’ found in certain species of the genus Begonia are alike to common chloroplasts found in most plants, but with a modified, periodic internal structure reminiscent of a 1D photonic crystal. Modelling indicates that this structure gives the Begonias their iridescent blue leaves, while also enhancing the absorption of photosynthetically active radiation. We will present an overview of the nano-optical theory underlying the model of iridoplasts, contrasting the design goals and constraints of biological and artificial systems. We use a simplified optical model based on Lorentz oscillators to answer the question of if the measured structure parameters of the iridoplasts are photonically optimised or if they reflect other biological constraints. Our results show that optimised photonic absorbers will not necessarily have high reflectance, raising the possibility that photonic structures for light harvesting in nature are more common than previously believed.