Microlens arrays

‡Bell Laboratories, Lucent Technologies, 600 Mountain Avenue, Murray Hill, NJ 07974, USA E-mail: [email protected] Microlenses are important optical components that image, detect, and couple light. But most synthetic microlenses have fixed position and shape once they are fabricated, so their possible range of tunability and complexity is rather limited. By comparison, biology provides many varied, new paradigms for the development of adaptive optical networks. Here, we discuss inspirational examples of biological lenses and their synthetic analogs. We focus on the fabrication and characterization of biomimetic microlens arrays with integrated pores, whose appearance and function are similar to highly efficient optical elements formed by brittlestars. The complex design can be created by three-beam interference lithography. The synthetic lens has strong focusing ability for use as an adjustable lithographic mask and a tunable optical device coupled with the microfluidic system. Replacing rigid microlenses with soft hydrogels provides a way of changing the lens geometry and refractive index continuously in response to external stimuli, resulting in intelligent, multifunctional, tunable optics. Clear vision is an important adaptation to biological organisms, which in most cases rely on eyes as their photosensory organs for focusing, detection, and imaging. Millions of years of evolution have perfected the design of the lenses used for image formation, resulting in optical structures whose multifunctional and hybrid characteristics are unparalleled in today’s technology1. For example, the human eye has a flexible lens that changes focus and gain dynamically. In contrast, the muscles in an octopus eye move the lens in and out within the shell to focus on close and distant objects, respectively. An insect eye consists of mesh-like divisions, which split into many identical imaging units called ommatidia. Each ommatidium has a corneal lens that can create a field-of-view (FOV) on its own and vary over an angle. Ommatidia then overlap to provide a composite image of the world to the insect brain. A dragonfly eye contains about 28 000 ommatidia, which cover a 70° horizontal and 90° vertical range of view. Some vertebrates that need to spend their lives in both air and water have developed amphibious eyes, allowing them to see clearly in both media. One particular example is the ‘four-eyed fish’ Analeps, which uses an ovoid lens with different curvatures on different axes, resulting in two focal lengths and two foveas.