Mechanism of variable structural colour in the neon tetra: quantitative evaluation of the Venetian blind model

Abstract

The structural colour of the neon tetra is distinguishable from those of, e.g., butterfly wings and bird feathers, because it can change in response to the light intensity of the surrounding environment. This fact clearly indicates the variability of the colour-producing microstructures. It has been known that an iridophore of the neon tetra contains a few stacks of periodically arranged light-reflecting platelets, which can cause multilayer optical interference phenomena. As a mechanism of the colour variability, the Venetian blind model has been proposed, in which the light-reflecting platelets are assumed to be tilted during colour change, resulting in a variation in the spacing between the platelets. In order to quantitatively evaluate the validity of this model, we have performed a detailed optical study of a single stack of platelets inside an iridophore. In particular, we have prepared a new optical system that can simultaneously measure both the spectrum and direction of the reflected light, which are expected to be closely related to each other in the Venetian blind model. The experimental results and detailed analysis are found to quantitatively verify the model.

Alignment of crystal orientations of the multi-domain photonic crystals in Parides sesostris wing scales

“…A microscatterometer was used to examine the direction of reflected light from a single domain of the photonic crystal. The optical set-up for the microscatterometer was previously described in detail [32]. In brief, the back focal plane of the objective lens in the optical microscope (Olympus BX51) was observed by a CCD camera through a macro zoom lens, because the light intensity pattern from this plane is considered to be the far-field pattern of reflection.…”

Membrane invaginations facilitate reversible water flux driving tunable iridescence in a dynamic biophotonic system

“…A lthough structural color is widespread across both the animal and plant kingdoms (1)(2)(3)(4), there are very few cases in which the photonic structures are tunable and adaptive (5)(6)(7). Many cephalopods exhibit iridescence, but only a few squid species can tune this iridescence for adaptive camouflage and communication (8,9) by modulating the periodicity of multilayer reflectors (7) in specialized cells classically called iridocytes.…”

Mechano-actuated ultrafast full-colour switching in layered photonic hydrogels

“…Many tropical fishes show bright structural colour that can undergo dramatic and lightning-quick transformations in response to environmental stimuli. In these fish scales, many rigid platelets of B10 mm are periodically embedded in soft matrix to reflect light, and the quick colour change is caused by the spacing or angle variation between the reflective platelets 22,23 (Fig. 1a).…”