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Principles Of Optics Electromagnetic Theory Of Propagation Interference And Diffraction Of Light

Through billions of years of evolution and natural selection, biological systems have developed strategies to achieve advantageous unification between structure and bulk properties. The discovery of these fascinating properties and phenomena has triggered increasing interest in identifying characteristics of biological materials, through modern characterization and modeling techniques. In an effort to produce better engineered materials, scientists and engineers have developed new methods and approaches to construct artificial advanced materials that resemble natural architecture and function. A brief review of typical naturally occurring materials is presented here, with a focus on chemical composition, nano-structure, and architecture. The critical mechanisms underlying their properties are summarized, with a particular emphasis on the role of material architecture. A review of recent progress on the nano/micro-manufacturing of bio-inspired hybrid materials is then presented in detail. In this case, the focus is on nacre and bone-inspired structural materials, petals and gecko foot-inspired adhesive films, lotus and mosquito eye inspired superhydrophobic materials, brittlestar and Morpho butterfly-inspired photonic structured coatings. Finally, some applications, current challenges and future directions with regard to manufacturing bio-inspired hybrid materials are provided.

Nano/Micro-Manufacturing of Bioinspired Materials: a Review of Methods to Mimic Natural Structures

The surprising properties of biomaterials are the results of billions of years of evolution. Generally, biomaterials are assembled under mild conditions with very limited supply of constituents available for living organism, and their amazing properties largely result from the sophisticated hierarchical structures. Following the biomimetic principles to prepare manmade materials has drawn great research interests in materials science and engineering. In this review, we summarize the recent progress in fabricating bioinspired materials with the emphasis on mimicking the structure from one to three dimensions. Selected examples are described with a focus on the relationship between the structural characters and the corresponding functions. For one-dimensional materials, spider fibers, polar bear hair, multichannel plant roots and so on have been involved. Natural structure color and color shifting surfaces, and the antifouling, antireflective coatings of biomaterials are chosen as the typical examples of the two-dimensional biomimicking. The outstanding protection performance, and the stimuli responsive and self-healing functions of biomaterials based on the sophisticated hierarchical bulk structures are the emphases of the three-dimensional mimicking. Finally, a summary and outlook are given.

Bioinspired materials: from low to high dimensional structure.

Current trends, challenges, and perspectives of anti-fogging technology: Surface and material design, fabrication strategies, and beyond

Bio-Inspired Photonic Materials: Prototypes and Structural Effect Designs for Applications in Solar Energy Manipulation

In nature, optical structures in the subwavelength range have been evolved over millions of years. For example, in the form of ‘moth-eye’ structures they show a strong anti-reflective effect on the compound eyes of night-active insects and therefore offer a successful protection over predators. In this contribution the advantages and challenges to transfer this natural concept of subwavelength structured optical interfaces to high-end optical systems are discussed. Here, in comparison to alternative conventional multilayer systems, the bioinspired anti-reflective structures offer a wide wavelength range and a broad angle dependency. Additionally, adhesion problems are reduced drastically. Simultaneously to the theoretical consideration of the best profile form of the subwavelength structures, appropriate realization technologies have been developed in recent years, where both top-down and bottom-up approaches have been investigated. Depending on the choice of the structuring technique, anti-reflective subwavelength structures are applicable to a wide spectrum of optical elements ranging from micro-optical components to aspheres for applications in imaging and also illumination setups of high-end optical instruments.

Lessons from nature: biomimetic subwavelength structures for high-performance optics

A solid immersion lens based on diffraction (dSIL) is proposed as an alternative to the conventional design based on refraction. A design analogous to a Fresnel zone plate is derived in accordance with the Huygens–Fresnel principle. Fabrication of a binary dSIL is achieved by electron-beam lithography and reactive-ion etching on LaSF35, with index n=2.014. Measurement of the point-spread function is performed with near-field optical microscopy. The results are in accord with the expected resolution enhancement of a factor n with respect to the diffraction limit.

Diffraction-based solid immersion lens

Blazed transmission gratings have become crucial components in many hybrid optical systems. Shadowing effects are known to occur at their passive blaze facets, which may impair the system's efficiency performance. For optical designs, it is desirable to have a simple but accurate description of this phenomenon. We show that the efficiency reduction in low diffraction orders is dominated by a linear dependence on the ratio of wavelength to grating period rather than a quadratic dependence as proposed in extended scalar theory. The strength of the electromagnetic shadowing will be determined using rigorous diffraction methods and discussed with respect to imaging optical components. Results are compared to existing ray-optical models.

Rigorous analysis of shadowing effects in blazed transmission gratings

The polarization beam splitter has an optically transparent carrier substrate (1) provided with an array of parallel grid lines (2,3) formed by a multi-layer system, for splitting an unpolarized light beam (UP) received at a given incidence angle into reflected and transmitted polarized beams (TE,TM). The individual layers (H,L) of the multi-layer system are provided by non-metallic dielectric materials with differing optical characteristics in alternation with one another.

Polarization beam splitter for microscopy or projection system or UV lithography using grid array with parallel grid lines formed by multi-layer system with alternating non-metallic dielectric layers with differing optical characteristics

The performance predictions and optimization of blazed diffraction gratings are key issues for their application in hybrid optical systems, both in the case of imaging and analyzing systems. Scalar and vectorial theories are often used for a first performance estimation whenever applicable. However, in the intermediate structure regime, characterized by a grating period within the transition from the validity of the scalar to the fully electromagnetic theory, rigorous numerical simulations are inevitable for accurate modeling of blaze structures with sawtooth-shaped profiles. A variety of electromagnetic algorithms exists to determine the diffraction efficiency, such as integral equation methods, finite element methods or rigorous coupled-wave analyses. An effect known as shadowing occurs and has a significant influence on the diffraction efficiency of the blazed grating. A simple but accurate model describing the shadowing phenomena would be of enormous practical importance for the optical design of hybrid systems. Commonly, dielectric transmission gratings are regarded, when the efficiency behavior due to shadowing is discussed. We succeeded in filling the modeling gap in the intermediate structure regime and have derived a rigorous-based semi-analytical model for dielectric gratings. We are able to extend this model to the case of metallic reflection gratings. For both types of gratings, we find that the blaze efficiency obeys a linear dependence on the ratio of blaze wavelength to grating period, which dominates the performance in the first diffraction order. We define the linear coefficient of shadowing strength and discuss its dependence on the material properties.

Oliver Sandfuchs

Papers

Lessons from nature: biomimetic subwavelength structures for high-performance optics

Diffraction-based solid immersion lens

Rigorous analysis of shadowing effects in blazed transmission gratings

Polarization beam splitter for microscopy or projection system or UV lithography using grid array with parallel grid lines formed by multi-layer system with alternating non-metallic dielectric layers with differing optical characteristics

Rigorous modeling of dielectric and metallic blaze gratings in the intermediate structure regime