Other Adaptive Liquid Lenses
In the past two decades, besides membrane lens, electrowetting lens, and dielectrophoretic lens, several other approaches for adaptive liquid lenses have been developed. The focal length of those lenses can be tuned by either changing refractive index or changing geometrical shape. Similar to PDMS lenses, some lenses are operated by pressure control but without employing PDMS membrane. Some lenses are actuated by external voltage, but some work based on the principles of magnetic control, thermo control, electro-optic control or other physical effects. Each approach has its own pros and cons. The common features of these lenses are polarization independence, broad spectral range, and wide focal length tunability.
In this chapter, we briefly introduce six other scientifically interesting adaptive lenses. Their operation principles include mechanical wetting, magnetic control, electromagnetic, hydrogels, acoustic field, and electrochemical control. In each category, we will describe the device structure, operation mechanism, and lens performances.
As we mentioned in Chapter 4, when the size of a liquid droplet is small enough, the effect of gravity force on the droplet shape is negligible. For an oil droplet (SL-5267, γ ∼ 50 dyn/cm) with aperture ∼ 0.2 mm, its surface profile is free from gravity distortion (1). If the glycerol is replaced by water, then the water droplet's ...