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Abstract: The Nicobar pigeon (Caloenas Nicobarica) belongs to the extinct dodo‐bird family and has been declared as an endangered species. Here, microscopic and spectroscopic measurements are carried out on the bird's feathers to study the structural coloration originating from the barbule nanostructures. A range of color shades is recorded with changing viewing and illumination angles at different locations of the feathers. A spectacular variation in colors is generated by photonic structures; red, green, and blue and their blends are observed. Hydrophobicity of the optical material is also investigated. A contact angle of ≈156° is observed demonstrating it to be superhydrophobic. Experimental observations of the optical properties are analyzed on these feathers for sensing made possible due to the material and structural properties at the interface between barbule's surface and solution. An optical response is observed with a redshift in optical spectra with increasing refractive index of the solution, which is correlated with concentration values. The structural coloration in Nicobar pigeon can be adopted for many practical applications such as color selective filters, nonreflecting coatings, and refractive index‐based sensing. [ABSTRACT FROM AUTHOR]

Abstract: Optical waveguides allow propagating light through biological tissue in optogenetics and photomedicine applications. However, achieving efficient light delivery to deep tissues for long‐term implantation has been limited with solid‐state optical fibers. Here, a method is created to rapidly fabricate flexible, functionalized soft polymer optical fibers (SPOFs) coupled with silica fibers. A step‐index core/cladded poly(acrylamide‐co‐poly(ethylene glycol) diacrylate)/Ca alginate SPOF is fabricated through free‐radical polymerization in a mold. The SPOF is integrated with a solid‐state silica fiber coupler for efficient light delivery. The cladded SPOF shows ≈1.5‐fold increase in light propagation compared to the noncladded fiber. The optical loss of the SPOF is measured as 0.6 dB cm−1 at the bending angle of 70° and 0.28 dB cm−1 through a phantom tissue. The SPOF (inner Ø = 200 µm) integrated with a 21 gauge needle (inner Ø = 514 µm) is inserted within a porcine tissue. The intensity of light decreases ≈60%, as the SPOF is implanted as deep as 2 cm. Doped with fluorescent dye and gold nanoparticles, the SPOF fiber exhibits yellow‐red and red illumination. Living cells can also be incorporated within the SPOF with viability. The flexible SPOFs may have applications in photodynamic light therapy, optical biosensors, and photomedicine. [ABSTRACT FROM AUTHOR]

The wing scales of Morpho butterflies contain 3D nanostructures that produce blue iridescent colors. Incident light is diffracted from multilayered nanostructures to create interference effects and diffract narrow‐band light. The intensity of the diffracted light remains high over a wide range of viewing angles. Structural coloration originating from the scales of Morpho wing nanostructures has been studied to analyze its optical properties and to produce scalable replicas. This review discusses computational and experimental methods to replicate these nanoarchitectures. Analytical and numerical methods utilized include multilayer models, the finite element method, and rigorous coupled‐wave analysis, which enable the optimization of nanofabrication techniques involving biotemplating, chemical vapour deposition, electron beam lithography, and laser patterning to mimic the wing scale nanostructure. Dynamic tunability of the morphology, refractive index, and chemical composition of the Morpho wing scales allows the realization of a numerous applications. [ABSTRACT FROM AUTHOR]

Thermochromic materials (TCMs) change their color in response to temperature variations. Here, presented is a rare combination of TCMs with conventional corner‐cube retroreflectors (CCRs) that are widely used in industry for their ability to return an incident beam of light directly back toward its source. The TCM quoted CCR (TCR sensor) allows remote measurements of the quantitative thermal information of the environment to which the TCR sensor is subjected. Two different commercially available thermochromic systems, a leuco dye and liquid crystals, are utilized as sensing materials. Since the incident (probe) beam and reflected (sensing) beam always follow the opposite directions 180°, this allows the probing and sensing to be carried out remotely from the same spot. Therefore, such remote sensing mechanism is virtually independent of the incident and detection beam angles. The TCR sensor has potential application in the space research, mining, power generation facilities, radioactive environments, and other industries where remote temperature sensing is a stringent requirement. A remote temperature sensor is developed by applying thermochromic materials on three mutually perpendicular planes of a corner cube retroreflector. Beams of visible monochromatic or broadband light are used as probes, which contain temperature information from the reflecting planes. The sensor is capable of measuring temperature virtually from any angle. [ABSTRACT FROM AUTHOR]