Abstract
Purpose :
Attenuators are basic ophthalmic optical elements. They have wide applications such as sunglasses, treatment of amblyopia, ophthalmic imaging systems, etc. The majority of the attenuators has a fixed transmission coefficient and they are usually made of dielectric, semiconductor, or metallic coatings based on optical interference or absorption effects. Variation of the transmission requires use of different coatings. Photochromic materials can change the transmission based on the light condition of the environment, but it is slow as it may take a couple minutes to change the transmission from bright to dark light conditions. Electrochromic materials can be used to change the transmission continuously. However, its contrast ratio (the ratio of the highest transmission to the lowest transmission) is limited to about 10. The purpose of this study is to investigate a new technique that can continuously tune the transmission with a contrast ratio much higher than 100 while keeping the device transparent and also with high speed.
Methods :
In order to achieve the above goal, we have made a liquid crystal device with large tunability of the transmission. A liquid crystal mixture including nematic liquid crystal, chiral dopant, and dichroic dye is sandwiched between two glasses each coated with transparent conductive thin film. The thickness of the liquid crystal mixture is only about 20 mm. An electrical field is applied to the device by applying a voltage less than 20 Vrms. The variable transmission is due to change of scattering and absorption affected by the orientations of the liquid crystals and the dye, which are tailored by the applied electric field.
Results :
The transmission of the new electro-optic device can be tuned across a very large range, and a contrast over 200 has been achieved, much higher than the concurrent technologies. The spectrum in the whole visible range is almost flat, which is good. The response time is fast and it is around 200 milliseconds. The device is polarization-independent, i.e., it responds equally to the light with any polarization and it is suitable for vision care.
Conclusions :
A tunable optical device with the highest contrast ratio while maintaining its transparency has been reported. It is promising for a lot of ophthalmic applications, including treatment of amblyopia, sunglass, imaging, etc.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.