Microlenses on Bragg Reflectors to Create Iridescent Colors
In nature strong colors play an important role in scaring away predators or finding a mate. Often, the strongest and brightest colors arise from coherent scattering and reflection on periodic structures on a length scale of several micro- or nanometers. Until recently, many theoretical combinations of diffractive structure and interference layers have been investigated and nearly nothing has been done on combinations of refractive structures and multilayer interferences. Only a few realizations have been achieved. We constructed and studied optical systems that mimic nature and are fabricated completely from organic materials. In this study we concentrate on combinations of Bragg reflectors and microlenses. Fabrication was carried out by spin-coating of organic interference layers and soft replication of microlenses. We studied reflection properties of such structures and discuss herein their behavior under different illumination conditions. To provide deeper insight, a model based on ray tracing is used that allows simulation of main characteristics. Particular optical configurations exist where the reflected color is insensitive to observation angles, while others have only one preferred direction of response.