History of Microlenses

The history of microlenses with fixed focal length may be traced back to the seventeenth century. Hooke melted small filaments of glass and allowed the surface tension in the molten glass to form the smooth spherical surfaces required for lenses [1]. The principle is very simple and has now been repeated by melting other patterned materials such as photoresists and ultraviolet light (UV)-curable epoxies, and making them reflow at high temperatures to form lenses or lens arrays [2-7]. 

Advances in technology have enabled microlenses to be designed and fabricated by a variety of methods. Biebuyck et al. introduced a method to form microlenses, also by utilizing surface tensions [8]. Self-assembled monolayers (SAMs) are used to pattern hydrophobic and hydrophilic regions. Water and immiscible hydrocarbon fluids (oils) exhibit different wettability characteristics in these two regions. Water droplets are segregated from hydrocarbon fluid at the surface of the SAM and thus form lenses. 

Pan et al. utilized melted plastics to fabricate microlenses. At the melting temperature, the hot melted plastic is intruded into circularly shaped holes and stopped at the desired depth under elevated temperature and pressure. After cooling down, the microlenses are formed. This is called a hot intrusion process [9]. 

Choo et al. used a different method. Microlenses are printed by a commercial inkjet printer. By controlling the volume of each droplet spread from a nozzle in the printer, the liquid microlenses can be printed onto most surfaces or structures [10]. 

Another approach involved etching silicon or glass at the same speed along different directions to form a master with hemispherical holes. Microlenses 

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The history of microlenses spans more than 400 years. With the development of microscale fabrication methods, microlenses have in the past decades drawn a lot of interest and found many applications, many of which are unique. The intriguing feature of most of these microlenses is that they all involve liquids some are formed directly from liquids some use liquids during operation some are solid but their fabrication involves liquids. Therefore, in this book, we aim to examine the recent progress in the emerging and fascinating field of liquid-based microlenses. 

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