Understanding of light sensing organs in biology creates opportunities for the development of novel optic systems that cannot be available with existing technologies. The insect’s eyes, i.e., compound eyes, are particularly notable for their exceptional interesting optical characteristics, such as wide fields of view (FOV) and nearly infinite depth of field. The construction of man-made sensing systems with these characteristics is of interest due to potential for applications in micro air vehicles (MVAs), security cameras, clinical endoscopes, and new approaches to navigation and sensing. Mimicking of such compound eyes has been evolving for the last few decades, which starts from simple fabrication of stand-alone microlens arrays (MLAs). Recent work has yielded significant progress in the realization of artificial compound eyes, including multiple lens arrays together with sensing pixel arrays with a hemispherical geometry. In this chapter, we discuss a complete set of materials, design layouts, integration schemes, and operating principles for sensing systems that mimic compound eyes. Certain concepts extend recent advances in flexible electronics that provide previously unavailable options in design.

Artificially Engineered Compound Eye Sensing Systems

In this study, 4.5 μm thick GaN films with graded AlxGa1−xN/AlN buffer and SiNx interlayer were prepared on 6H–SiC substrates by metal–organic chemical vapor deposition. To determine the effects of SiNx interlayer on epitaxial quality and stress state of GaN films, a series of comparative experiments were carried out by changing the deposition time and the insert location of SiNx interlayer. 
By optimizing growth conditions of SiNx interlayer, the full width at half maximum values of $$ (0002) $$
 and $$ (10\bar{1}2) $$
 rocking curves of GaN films were improved to 142 and 170 arcsec, respectively. A crack-free GaN film with a small root-mean-squared roughness of 0.21 ± 0.02 nm was achieved. Simultaneously, the reduction in threading dislocation density of GaN films was confirmed by using wet etching method. In addition, stress values in GaN films were investigated by Raman and low-temperature photoluminescence spectra, which indicated that the lower tensile stress in GaN film, the higher the film’s crystallinity.

Improvements of epitaxial quality and stress state of GaN grown on SiC by in situ SiNx interlayer

We present disordered moth eye structures on curved surfaces fabricated by dry etching of thermally dewetted metal nanoparticles. This lithography-free fabrication allows the formation of subwavelength scale nanostructures on the strongly inclined surfaces such as ball lens as well as on the microlens arrays with low curvature. In particular, we found that the size and average distance of nanostructures are closely related to the inclined angle of the surface. Experimental results on oblique angle deposition of metal thin films followed by thermal dewetting also support these effects.

Fabrication of Disordered Subwavelength Structures on Curved Surfaces by Using a Thermal Dewetting Process

A multiscale model that enables quantitative understanding and prediction of the size effect on the scattering properties of micro- and nanostructures is crucial for the design of light-emitting diode (LED) surface textures optimized for high light extraction efficiency (LEE). In this paper, a hybrid process for combining full-wave finite-difference time-domain simulation and a ray-tracing technique based on a bidirectional scattering distribution function model is proposed. We apply this method to study the influence of different pattern sizes of a patterned sapphire substrate on GaN-based LED light extraction from the micro-scale to the nano-scale. The results show that near-wavelength–scale patterns with strong diffraction are not expected to enhance the LEE. By contrast, micro-scale patterns with optical diffusion behavior have the highest LEE at a specific aspect ratio, and subwavelength-scale patterns that have antireflection properties show a marked enhancement of the LEE for a wide range of aspect ratios.

Scale-Dependent Light Scattering Analysis of Textured Structures on LED Light Extraction Enhancement Using Hybrid Full-Wave Finite-Difference Time-Domain and Ray-Tracing Methods

Artificial antireflective nanostructured surfaces, inspired by moth eyes, effectively reduce optical losses at interfaces, offering significant advantages in enhancing optical performance in various optoelectronic applications, including solar cells, light-emitting diodes, and cameras. However, their limited flexibility and low surface hardness constrain their broader use. In this study, we introduce a universal antireflective film by integrating nanostructures on both sides of a thin polycarbonate film. One side was thinly coated with Al2O3 for its high hardness, enhancing surface durability while maintaining flexibility. The opposite side was coated with SiO2 to optimize antireflective properties, making the film suitable for diverse environments (i.e., air, water, and adhesives). This dual-coating strategy resulted in a mechanically robust and flexible antireflective film with superior optical properties in various conditions. We demonstrated the universal capabilities of our antireflective film via optical simulations and experiments with the fabricated film in different environments. 

Dual-Coated Antireflective Film for Flexible and Robust Multi-Environmental Optoelectronic Applications

We demonstrate the hierarchical micro- and subwavelength-structures on the surface of GaN based green vertical light-emitting diodes (VLEDs) to enhance the light extraction efficiency. Hierarchical structures (HSs), which were fabricated by simple two-step process consisting of pattern transfer of reflowed photoresist for micro structures (MSs) and self-masked dry etching method for subwavelength structures (SWSs), play an important role in enhancing the light extraction efficiency by reducing both the total internal reflection and the Fresnel reflection. HSs lead to an enhancement of optical output power of ~200% compared to the conventional VLEDs with flat surface as a result of reflection suppression and transmittance enhancement, without any serious degradation of electrical characteristics and a change of peak emission wavelength as function of injection current. Furthermore, optical simulations by ray-tracing and the rigorous coupled-wave analysis methods provide design guidelines for MSs and SWSs, respectively.

Improved light extraction efficiency of GaN-based vertical LEDs using hierarchical micro/subwavelength structures

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Improved light extraction efficiency of GaN-based vertical LEDs using hierarchical micro/subwavelength structures