Researchers in China have developed an adaptive liquid lens based on dibutyl adipate (DBA), a new electrically responsive liquid that changes the focal length when a voltage is applied.
According to the team, the lens is suitable for mobile phone cameras, endoscopes, glasses and machine vision applications because it is light, compact and easy to manufacture.
“The human eye can arbitrarily focus on objects at different distances at incredibly high speeds,” said study team leader Miao Xu of Hefei University of Technology. “Inspired by this functionality, we developed an eye-like adaptive fluid lens that can be used to diverge or converge light by changing the shape of the DBA fluid.”
In Optics Letters, the researchers describe their new DBA-based adaptive liquid lens, which weighs a few grams, and show that it exhibits high optical performance with good stability. Due to the electronegative molecular structure of DBA, an applied voltage can be used to quickly change the shape of the lens to change the focal length. DBA is also said to be transparent, non-volatile and inexpensive, making it a candidate for use in adaptive fluid lenses.
“This type of adaptive liquid lens could one day replace conventional fixed lens systems,” Xu said in a statement. “This would enable a cell phone camera that can quickly change focal lengths while still being as thin as the phone itself.” Because it requires no mechanical elements, this type of lens can be used for years without wearing out, the team added.
Tension brings new metals into view
The researchers created the new liquid lens by filling an electrode with DBA liquid, which forms a dome shape because the inner surface of the electrode is covered with a water-repellent layer. Applying a direct current causes the DBA molecules to accumulate at the anode, changing the shape of the dome in a way that depends on the applied voltage, changing the focal length. Removing the electric field causes the DBA liquid to return to its original shape.
The DBA lens offers a ‘significant improvement’ over the electrowetting adaptive liquid lenses available on the market. Electrowetting liquid lenses use a liquid, such as salt water, which requires a dielectric film to separate the conductive liquid from the metal electrode.
“Our DBA liquid lens is not prone to volatilization or electrolysis, and because the DBA liquid comes in direct contact with the electrode, no insulating layer is needed,” says Xu. “This gives the DBA lens a simpler structure and better stability compared to an electrowetting liquid lens.”
Analysis of the new DBA-based liquid lenses showed that they exhibit about 95 percent optical transmission at visible wavelengths between 390 and 780 nm and that performance remains stable at temperatures ranging from room temperature to over 200°F. The researchers showed also notes that increasing the applied voltage from 0 to 100V changed the focal length from 7.5mm to 13.1mm and that the resolution of the lens can reach nearly 29 lines per millimeter.
The researchers will continue to work on making the new lenses more practical by developing ways to reduce the voltage needed to drive the DBA-based liquid lens, increase resolution and improve response speed on the order of milliseconds. . They also want to reduce the effects of gravity on the DBA fluid so that larger lenses can be made.
