Structural Color and Mueller Matrix Analysis in a Ferrocell

The brightest colorations observed in nature are the result of structural colour, a physical phenomenon relying not on pigments but on the interactions of light with nanostructured materials. Research on structural colour in seaweeds has been growing and hints that the phenomenon is considerably more widespread in these organisms than previously understood. In this review, we combine information from published literature, herbarium specimens and our own observations to clearly outline and reframe the current state of knowledge on the phenomenon in red seaweeds (Rhodophyta). We describe structural colour and the structures responsible for it in rhodophytes, identifying clear categories and their variations. Through an overview of the phylogenetic, geographic and ecological distribution of the phenomenon, we confirm that it is more widespread and diverse than had been indicated by casual recording. We finally discuss hypotheses on the biological significance of structural colour for red seaweeds. Our investigation emphasizes the need for more extensive research in order to fully assess the evolutionary mechanisms at play, the development of the nanostructures and their relation to environmental conditions. This review provides a framework for understanding and classifying structural colour in red algae to encourage a more comprehensive reporting of the phenomenon.

Traditional textile dyeing uses chemical pigments and dyes, which consumes a large amount of water and causes serious environmental pollution. Structural color is an essential means of achieving green dyeing of textiles, and thin-film interference is one of the principles of structural coloring. In the assembly of structural color films, it is necessary to introduce dark materials to suppress light scattering and improve the brightness of the fabric. In this study, the conditions for the generation of nanofilms of catechin (CC) at the gas-liquid interface were successfully investigated. At the same time, environmentally friendly colored silk fabrics were novelly prepared using polycatechin (PCC) structural color films. In addition, it was found that various structural colors were obtained on the surface of silk fabrics by adjusting the time. Meanwhile, the color fastness of the structural colored fabrics was improved by introducing polyvinylpyrrolidone (PVP) to form a strong hydrogen bond between the fabric and catechin. PCC film is uniform and smooth, with a special double-layer structure, and can be attached to the surface of silk fabrics, giving the fabrics special structural colors. Through the thin-film interference formed between the visible light and the PCC film, the silk fabrics obtain bright, controllable, and uniform structural colors. This method is easy to operate and provides a new way of thinking for environmental-protection-oriented coloring of fabrics.

Structural color occurs by the interaction of light with regular structures and so generates colors by completely different optical mechanisms to dyes and pigments. Structural color is found throughout the tree of life but has not, to date, been reported in the fungi. Here we give an overview of structural color across the tree of life and provide a brief guide aimed at stimulating the search for this phenomenon in fungi.

Structural color is a unique optical property of nano- or microstructured materials with periodic dimensions similar to the wavelength of visible light. Characteristic color is produced through reflectance, interference, scattering, diffraction or refraction of incident light of a specific wavelength in visible spectrum, thereby producing a specific color or so-called structural color. Structural color is seen throughout nature, notably Morpho butterflies and opals present a striking sheen and accompanying vivid hue. Prior analysis of minerals and organisms that produce these distinctive colors allows for continuing analysis of color developing mechanisms [1]. Recently, with improvements in micro-fabrication, trial reproduction of these naturally occurring structural colors is proceeding across the field of Biomimetics [2]. Mono-dispersed micro-particles, structured in an ordered arrangement, are called colloidal crystals. Through Bragg reflection they exhibit structural color with a vivid hue. Colloidal crystals are relatively easy to produce by self-organization, and since dielectric periodic structures can be used as a photonic crystal for controlling electromagnetic waves, it has been extensively studied as a structural color element and photonic crystal. Some of the methods for manufacturing colloidal crystals include capillary method, electric electrophoresis, spin coating, spray coating, and substrate raising [3 - 6]. The color developing mechanism for structural color differs from pigment and does not absorb a specific wavelength, therefore in principle, fading from UV rays should be reduced. These materials can be used in applications that require pigments with excellent light-resistance and durability. In addition, since these colored micro-particle aggregates are non-toxic with a high level of safety, they show promise for wide use in printed materials. Here we present research results involving the formation of a pattern of stable colloidal crystals on various substrates and exploring their suitability for use in printed materials. Monodisperse silica nano-particles with a diameter of 300 nm were dispersed in a highly polar solvent. As the solvent evaporates the particles self-assemble into colloidal crystals. By depositing this dispersed suspension as an ink with a direct write printer (aerosol jet) we confirmed the ability to print colloidal crystals with structural color in any pattern. The cohesion of self-assembled colloidal crystals relies on electrostatic attraction making them extremely brittle with limited practical use. As such, a polymer was added to the suspension to reinforce the colloidal crystal structure with limited influence on the self-assembly mechanism. Thus, a strong coating is produced while also producing the desired color effect. Printed colloidal crystals produced by this method are difficult to reproduce by color copying and traditional printing methods considering the color and gloss change depending on the viewing angle. Figure 1 shows a feature printed using the colloidal crystal ink under various lighting/viewing conditions. Also, since it is possible to direct print any pattern, the method is amenable to variable data printing, providing a tamper prevention effect. Thus, these materials are attractive for use in security printing applications.

Different methods have already been developed to measure the magnetic field with fiber Bragg gratings (FBGs). They are based on the use of a magnetic fluid or magnetostrictive materials. In addition to these methods, a direct measurement of the magnetic field is also possible by determining the circular birefringence created by the magnetic field inside the fiber. In standard optical fiber, this circular birefringence is of the same order as the intrinsic fiber birefringence or even below. The polarization properties of FBGs are therefore used to perform such measurement since they allow to determine weak birefringence with higher accuracy than standard read-out techniques. However, the obtained accuracy is usually low due to the influence of the intrinsic fiber birefringence. To mitigate this issue, we study in this work the use of the diattenuation vector. This parameter is obtained from the Mueller matrix and we show that it evolves in response to a magnetic field. In practice, we analyze its response by both simulation and experiment. In our simulations, we solve numerically the coupled mode equations of the FBG. For the experiments, the Mueller matrix is measured by an optical vector analyzer for the gratings connected in transmission. We apply an increasing magnetic field on different Bragg gratings photo-written in SMF28 fibers. The rotation of the diattenuation vector is then used to retrieve the magnetic field induced circular birefringence. A linear increase of the reconstructed circular birefringence is reported for increasing magnetic field values in the range 0-1T.

Mueller matrix analysis of light depolarization by a linear optical medium

The multresponsive photonic hydrogels (MRPHs) based on Fe3O4@C NPs and Acrylamide-N-isopropylacrylamide (AM-NIPAM) was prepared by UV polymerization process with the help of magnetic field. This work is mainly about the long-term stability of MRPHs. The mechano-response performance of MRPHs after being remained in water for a year has been measured and discussed in details. The result shows that the MRPHs were still very sensible and exhibit brilliant structure color. The reflectance peak of MRPHs changed markedly (from 700 nm to 550 nm) as increasing compression from 0 to 1N and the structure color change can be made reversible for ∼100 times or even more if necessary. Besides, the structure color of MRPHs was broken after being natural air-dried for 3 months and it can recover when dried MRPHs were immerged in water for 10 hours. So the MRPHs have good stability and the structure color can persevere for long time without fading, which contributes to the piratical application of MRPHs used as sensors.

We report on a light-dispersing device consisting of two transmission gratings and a waveplate. The gratings separate two orthogonal polarization components of light incident at the Bragg angle. The waveplate, which is sandwiched between the gratings, functions as a polarization converter for oblique light incidence. With these optical parts suitably integrated, the resulting device efficiently diffracts unpolarized light with high spectral resolution. Using coupled-wave theories and Mueller matrix analysis, we constructed a device for a wavelength range of 680±50 nm with a 400 nm grating period. From the characterization of this optical device, we validated the proposed polarization-independent, light-dispersing concept.

Surveys of the natural world reveal an extensive array of optical effects in a broad range of animal and insect species. While the aesthete may simply take delight in such phenomena, students of photonics have increasingly been prepared to look more closely; deriving understanding and inspiration from nature's optical ingenuity. By describing specific structural color examples in detail, within a general context of Lepidopteran microstructure classification, this review paper seeks to present an introduction to current work on butterfly photonics. Additionally, new but preliminary results and analysis are presented, that describe the structural color of a butterfly that exhibits a distinct 3D photonic crystal structure.

Adaptive infrared radiation modulator using reversible metal electrodeposition with silicon carbide-based fabry-perot cavity

Structural colors can be generated by metasurfaces with the capability of spectrum manipulation at subwavelength. In general, the optimization of specific color designs and iterative geometric parameters is computationally time-consuming, so obtaining thousands of different structural colors can be challenging. Deep learning methods offer a new approach to the efficient design of nanophotonic devices, as it revolutionizes the way nanophotonic devices are designed. Here, we trained a deep learning method, which can predict the colors by random geometries in the forward modeling process. The forward design model is good at processing data, which is an effective way to design nanophotonic devices.

In this study, we investigated a color-tunable carboxyl-rich carbon inverse photonic ball (CIPB) ink, which was fabricated using a polymeric photonic ball (PB) as a template, with characteristic self-assembled opalline structures from monodisperse polystyrene (PS) microspheres. The PBs were prepared on a large scale via an optimized diffusive drying method using an aqueous dispersion of polystyrene microspheres. Via acid-catalyzed thermal dehydration of monosaccharides within the interstitial space of PB followed by template removal, iridescent CIPB, which is insoluble in water or organic solvents because the crosslinked structure is similar to a naturally occurring humin, was obtained. The use of PS microspheres of different sizes for the preparation of the respective PBs resulted in CIPBs with different structural colors. Optical characterization revealed that the individual CIPB particles exhibit specific colors on the basis of the angular dependence of the Bragg condition for each particle. The overall structural color of the CIPB ink was sensitively tuned by changing dispersing media with different indices of refraction. Spectroscopic analysis confirmed the presence of carboxyl groups within CIPB due to the light thermal condensation of sugar, and the osmotic swelling/deswelling of the charged CIPB at pH values above/below the pKa of the bound carboxylate drove the reversible pH-responsive changes in structural color, indicating the promising applicability of CIPB as a colorimetric chemical sensor.

The effect of magnetic field (MF) exposure on melatonin production was studied in female CD(2)F(1)(BALB/c x DBA/2) mice. The mice were exposed to a 50 Hz MF at 100 microT for 52 days and nocturnal urine was collected 1, 3, 7, 14, 16 and 23 days after the beginning of MF exposure. The animal room was illuminated for 12 h daily at 200 lux. To study the circadian rhythm of melatonin production, night and day samples of urine were collected once, at about 40 days after the beginning of MF exposure. Urinary 6-hydroxy melatonin sulfate (6-OHMS) was determined to assess melatonin production. The pineal glands were analyzed for melatonin content at the middle of the dark period. No statistically significant peak of melatonin was observed in either group. The light-regulated natural melatonin rhythm was absent in sham-exposed mice. The MF exposure caused a significant day-night difference in the 6-OHMS levels, but did not affect the total excretion of 6-OHMS during the 24-hour period. A possible interpretation of the findings is that MF exposure increases the sensitivity of the pineal gland to light in this strain normally insensitive to the circadian light variations. Further studies on interaction of light and MF exposure might help in understanding the inconsistencies of earlier research on MFs and melatonin.

Optical imaging and photostimulation have been widely used in biological and medical applications. Penetration of light is limited by the scattering and absorption in tissue. Moreover, studying neural circuits using optogenetics to identify and isolate specific pathways and projections requires individual or simultaneous stimulation of multiple regions within the brain, which is not easily possible using existing optrodes. Here, we present a novel technique for guiding and steering of light deep in scattering tissue using non-invasive ultrasound. We show that a tunable virtual optical graded-index (GRIN) lens can be sculpted in tissue by using reconfigurable ultrasonic interference patterns, enabling bidirectional light delivery without implanting any physical light guide. The interaction of ultrasound and light is mediated through the tissue itself. We show that the ultrasonically sculpted tunable GRIN lenses can be used for light delivery as well as relaying images of the underlying structures within tissue, thus providing a noninvasive alternative for invasive implantable endoscopes. Using a custom-designed cylindrical ultrasonic array, complex patterns of light can be sculpted in the medium, including dipole and quadrupole shapes for multisite illumination. Finally, we demonstrate that this technique can be used to define spatial patterns of light to selectively target neurons in a mouse brain slice.

Smartphone-based colorimetric analysis of structural colors from pH-responsive photonic gel