The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

This paper reviews the current status of instruments for measuring the full 4×1 Stokes vector S, which describes the state of polarization (SOP) of totally or partially polarized light, and the 4×4 Mueller matrix M, which determines how the SOP is transformed as light interacts with a material sample or an optical element or system. The principle of operation of each instrument is briefly explained by using the Stokes-Mueller calculus. The development of fast, automated, imaging, and spectroscopic instruments over the last 50 years has greatly expanded the range of applications of optical polarimetry and ellipsometry in almost every branch of science and technology. Current challenges and future directions of this important branch of optics are also discussed.

Stokes-vector and Mueller-matrix polarimetry [Invited].

Precise optical and thermal regulatory systems are found in nature, specifically in the microstructures on organisms' surfaces. In fact, the interaction between light and matter through these microstructures is of great significance to the evolution and survival of organisms. Furthermore, the optical regulation by these biological microstructures is engineered owing to natural selection. Herein, the role that microstructures play in enhancing optical performance or creating new optical properties in nature is summarized, with a focus on the regulation mechanisms of the solar and infrared spectra emanating from the microstructures and their role in the field of thermal radiation. The causes of the unique optical phenomena are discussed, focusing on prevailing characteristics such as high absorption, high transmission, adjustable reflection, adjustable absorption, and dynamic infrared radiative design. On this basis, the comprehensive control performance of light and heat integrated by this bioinspired microstructure is introduced in detail and a solution strategy for the development of low-energy, environmentally friendly, intelligent thermal control instruments is discussed. In order to develop such an instrument, a microstructural design foundation is provided.

Bioinspired Microstructured Materials for Optical and Thermal Regulation.

/pdf/absence-of-circular-polarisation-in-reflections-of-butterfly-3y5q9h6gsc.pdf

Absence of circular polarisation in reflections of butterfly wing scales with chiral gyroid structure

Soft, mechanically deformable materials and systems that can, on demand, manipulate light propagation within both the visible and infrared (IR) regions of the electromagnetic spectrum are desirable for applications that include sensing, optoelectronics, robotics, energy conservation, and thermal management. However, the development of such technologies remains exceptionally difficult, with relatively few examples reported to date. Herein, this challenge is addressed by engineering cephalopod-inspired adaptive camouflage platforms with multispectral functionality. First, stretchable copolymer membranes that feature outstanding unstrained protonic conductivities of up to ≈90 mS cm-1 , demonstrate increases of ≈80% in their conductivities at strains of 200%, and exhibit no loss in electrical performance even under extreme elongations of 500% are described. Next, the membranes are used for the fabrication of mechanically and electrically actuated camouflage devices that function over an unprecedented spectral window; can simultaneously modulate their visible and IR specular-to-diffuse transmittance ratios by >3000-fold and >4-fold, respectively; feature rapid response times of ≈0.6 s; and exhibit good performance after repeated actuation. These findings may afford new scientific and technological opportunities not only for adaptive optics and photonics but also for any platform that can benefit from simultaneously controlling visible light and heat.

Stretchable Cephalopod-Inspired Multimodal Camouflage Systems.

Polarization effects in reflection from the cuticle of scarab beetles studied by spectroscopic Mueller-matrix ellipsometry H. Arwin*, T. Berlind, J. Birch, L. Fernandez Del Rio, J. Gustafson, J. La ...

Polarization effects in reflection from the cuticle of scarab beetles studied by spectroscopic Mueller-matrix ellipsometry

Important properties for camouflage materials can be summarized in six criteria: (1) spectrally selective reflectance, (2) low gloss, (3) low degree of polarization, (4) low infrared emissivity, (5) non-destructive effect on radar properties and (6) color adaptivity. We have studied a collection of natural materials for potential use as camouflage surfaces for the arctic region. The four first camouflage criteria are analyzed using spectrometry, scatterometry and spectroscopic ellipsometry techniques. The materials involved in the study are diffuse white nature-inspired surfaces: Cuticles of the beetle Cyphochilus insulanus, and foams of freeze-casted cellulose nanofibrils. We present data that partly fulfills the addressed camouflage criteria. An adequate reflectance is achieved in the spectral range of 400–1600 nm for both samples. Scattering data show that near-Lambertian properties are achieved at 633 nm for both surfaces but at 1550 nm for only the beetle cuticle. The degree of polarization is low for unpolarized light incident near the surface normal for both surfaces.

Optical studies of white organic materials for camouflage applications in Arctic environments

With the increased threat from advanced sensor systems using several wavelength bands and sensor fusion, the requirements on camouflage increase. Consequently, in order to reduce the risk of EU soldiers being detected, identified and engaged, adaptive camouflage prototypes have been developed, implemented and demonstrated. Several active and passive adaptation mechanisms were integrated into a textile-based soldier camouflage system. The prototypes address several wavelength bands, including visual, thermal infrared and radar. Military needs on sensing, fire power, mobility, compatibility with other equipment and wearing endurance were considered. The demonstration, at TRL5, took place in a relevant environment, an area adjacent to vegetation and buildings close to Paris, France. The reduction in detection range and hence the increase in survivability, as established in field trials previously conducted in Portugal and France, was made clear during the demonstration. The demonstrated technology comprised actively controlled light emitting diodes and thermochromic materials for visible signature adaptation, phase change materials and biologically degradable insulating cellulose cells (cork) for thermal camouflage and radar absorbing coatings with conjugated polymer compositions. Two suits were shown with soldiers walking along a treeline and in front of buildings. Prior to the public demonstration laboratory tests of the materials and components had been performed as well as ergonomic tests, signature measurements in different backgrounds and light conditions and radar cross section measurements at an outdoor test range. Production technologies were studied and production cost estimated. It was concluded that a similar system can be produced at a reasonable cost and the production scaled up to larger volumes. Throughout the project, dialogue with military end-users was upheld concerning requirements and applicable environments and tactical situations in order to ensure relevance. Military end-users from Sweden, Portugal, Germany, France, Lithuania and the Netherlands were invited to the final workshop and technical demonstration.

Christina Åkerlind

Papers

Polarization effects in reflection from the cuticle of scarab beetles studied by spectroscopic Mueller-matrix ellipsometry

Optical studies of white organic materials for camouflage applications in Arctic environments

Demonstration of adaptive camouflage for the soldier