The DBA liquid lens was made by filling an annular electrode with DBA liquid. The liquid forms a dome that changes shape when a direct current is applied. Removing the electric filed causes the DBA liquid to recover its initial shape. [Image: Miao Xu, Hefei University of Technology]
Inspired by the human eye, researchers in China have developed a new type of adaptive liquid lens that can change its focal length with the application of an electric field (Opt. Lett., doi: 10.1364/OL.447182).
The lens is based on a novel, electrically responsive fluid and achieves the functionality of a conventional lens system without the bulk, weight or complexity. Given these advantages, potential applications for the lens include mobile electronics, endoscopes and optical waveguides, according to the study authors.
Inspired by nature
As opposed to a solid lens, a liquid lens can alter its shape at will (see “Lenses Go Liquid,” OPN, March 2021). For example, an electrowetting lens consists of a droplet of conductive liquid such as salt water on the surface of an electrically insulating dielectric layer. When an external voltage is applied to the device, the surface profile of the droplet changes along with the focal length of the lens.
Scientists from Hefei University of Technology looked to nature to develop a liquid lens with simpler structure and more stable optical performance than traditional electrowetting lenses. Instead of a conductive liquid, their lens is based on dibutyl adipate (DBA), a transparent, inexpensive and electrically responsive liquid.
“The human eye is a naturally formed adaptive lens, which can arbitrarily vary its focal length at incredibly fast speeds,” said research team leader Miao Xu. “Inspired by the functionality of a human eye, we developed an eye-like adaptive liquid lens, which can diverge or converge light by the shape deformation of the DBA liquid.”
Demonstrating the lens
The DBA lens was made by filling an annular electrode with DBA liquid, which forms a dome shape due to a hydrophobic coating on the inner surface. When an electric field is applied, the electronegative DBA molecules migrate to the anode and accumulate there, changing the shape of the dome—and subsequently, the focal length of the lens. When the electric field is removed, the DBA liquid recovers its initial shape.
The researchers demonstrated their concept with a DBA lens that increased its focal length from 7.5 mm to 13.1 mm when the voltage goes from 0 to 100 V. It exhibited a high transmittance of around 95% at visible wavelengths between 390 and 780 nm, as well as stable optical performance at temperatures ranging from 20 °C to 100 °C. Unlike the conductive liquids found in electrowetting lenses, DBA has the advantages of no volatilization or electrolysis, which leads to greater stability.
Wide range of applications
Overall, the results suggest that DBA could be a promising candidate for fabricating the next generation of adaptive liquid lenses, the researchers argued. The DBA lens weighs only a few grams, does not require an insulating layer, and uses low-cost materials. The researchers are working on the next steps, which include reducing the driving voltage of the lens and increasing the response time to the order of milliseconds.
“Tunable-focal adaptive liquid lenses have potential applications in cellular phone cameras, machine vision, eyeglasses, endoscopes and other lab-on-a-chip devices,” said Xu. “There is no doubt that adaptive liquid lenses will play an increasingly more important role in the era of optical technology.”