Electrowetting variable-focus optics span visible to mid-IR
The 400 to 5000 nm spectral region is useful in adaptive optics for imaging, spectroscopy, microscopy, lidar, and surveillance.
|An electrowetting steering prism is based on fluids with transmission from the visible to the MWIR. (Image: John Wallace)|
A type of electrically focusable, no-moving-parts type of lens (and a steering prism as well) developed by researchers at the University of Colorado (Boulder, CO) has a spectral band of 400 to 5000 nm and has been experimentally demonstrated at wavelengths of 588, 1550, and 3000 nm. The lenses are based on electrowetting, where varying a voltage changes the wettability and thus the contact angle of a fluid lens, also changing its shape. While the electrowetting concept itself isn’t new, the wide spectral range is. Uses include adaptive optics for imaging, spectroscopy, microscopy, lidar, and persistent surveillance.
The lens contains two fluids with differing refractive indices. The fluids are a room-temperature ionic liquid (RTIL) called N-Propyl-N- methylpyrrolidinium Bis(fluorosulfonyl)imide (Pyr133a) and dodecane.
An electrowetting lens with an indium tin oxide (ITO) substrate was made for visible-to-2000-nm applications, while a lens on a silicon substrate was fabricated for midwave-IR (MWIR) applications. The lenses had a focal range of about 7, 19, and 23 diopters at 588, 1550, and 3000 nm, respectively.
An electrowetting steering prism operating at 1550 nm was also fabricated that steered a beam over a 1.12° angle (which can easily be amplified with additional conventional optics, or by using a different nonpolar liquid in place of dodecane).
1. Alexander M. Watson et al., arXiv:1603.00421v1 (1 March 2016)