Biologically inspired optical surfaces for miniaturized optical systems
Mining smartness from vision organs found in nature becomes of much interest in optical applications such as imaging, display, or lighting. Unlike conventional bulk optics, miscellaneous hierarchical structures at micro- or nanoscale deliver highly efficient light management with a small form factor. For example, natural species have evolved their eyes to obtain all necessary visual information from surrounding environment. Natural imaging schemes can be chiefly classified by three different types of pinholes, camera, and compound eyes. Pinhole eyes found in clam are sensitive enough to allow the animals to protect themselves from dangerous environment but not so sensitive to collect all visual inputs. Unlike other types, the pinhole eye as one of natural eyes with the simplest and thinnest optical configurations is well known for infinite depth-of-field, i.e., no blurred imaging depending on object distance and thus these unique features have been implemented on early-stage simple camera imaging systems. Besides, advanced pinhole eyes are also found in viper snakes of Crotalinae and some python of Boidae, which combine both pinhole eye and ordinary camera eye in order to confer infrared (IR) as well as visible imaging for warm-blooded preys. Compound eyes found in arthropods exhibit many intriguing features for wide field-of-view (FOV), fast motion detection, polarization sensing, color imaging, or high-resolution imaging with compact optical configuration unlike other types. They comprise arrays of integrated optical units called ommatidia. The individual component consists of a facet lens, a crystalline cone, a light-guiding rhabdom, and photoreceptor cells. Furthermore, nature exhibits ten different optical schemes of compound eyes, which have some attractive figures-of-merits for sustainable life style in visual acuity, photon collection efficiency, and polarization or spectral sensitivity. Such biological inspiration recently and actively provides new opportunities for improving optical capability of conventional imaging systems by incorporating nano- and microfabrication methods and furthermore it delivers technical solutions for miniaturized optical systems in medical, industrial, and military fields. In this chapter, we will review engineering approach inspired from diverse biological organs, which can be utilized for miniaturized optical systems in diverse optical applications.