Bio-Inspired Optics

Burgess IB, Aizenberg J, Loncar M. Creating bio-inspired hierarchical 3D–2D photonic stacks via planar lithography on self-assembled inverse opals. Bioinspiration & Biomimetics. 2013;8 :045004. Publisher's VersionAbstract
Structural hierarchy and complex 3D architecture are characteristics of biological photonic designs that are challenging to reproduce in synthetic materials. Top–down lithography allows for designer patterning of arbitrary shapes, but is largely restricted to planar 2D structures. Self-assembly techniques facilitate easy fabrication of 3D photonic crystals, but controllable defect-integration is difficult. In this paper we combine the advantages of top–down and bottom–up fabrication, developing two techniques to deposit 2D-lithographically-patterned planar layers on top of or in between inverse-opal 3D photonic crystals and creating hierarchical structures that resemble the architecture of the bright green wing scales of the butterfly, Parides sesostris. These fabrication procedures, combining advantages of both top–down and bottom–up fabrication, may prove useful in the development of omnidirectional coloration elements and 3D–2D photonic crystal devices.
Kim P, Hu Y, Alvarenga J, Kolle M, Suo Z, Aizenberg J. Rational Design of Mechano-Responsive Optical Materials by Fine Tuning the Evolution of Strain-Dependent Wrinkling Patterns. Adv. Optical Mater. 2013;1 (5) :381-388. Publisher's VersionAbstract
Rational design strategies for mechano‐responsive optical material systems are created by introducing a simple experimental system that can continuously vary the state of bi‐axial stress to induce various wrinkling patterns, including stripes, labyrinths, herringbones, and rarely observed checkerboards, that can dynamically tune the optical properties. In particular, a switching of two orthogonally oriented stripe wrinkle patterns from oxidized polydimethylsiloxane around the critical strain value is reported, as well as the coexistence of these wrinkles forming elusive checkerboard patterns, which are predicted only in previous simulations. These strain‐induced wrinkle patterns give rise to dynamic changes in optical transmittance and diffraction patterns. A theoretical description of the observed pattern formation is presented which accounts for the residual stress in the membrane and allows for the fine‐tuning of the window of switching of the orthogonal wrinkles. Applications of wrinkle‐induced changes in optical properties are demonstrated, including a mechanically responsive instantaneous privacy screen and a transparent sheet that reversibly reveals a message or graphic and dynamically switches the transmittance when stretched and released.