Abstract
Purpose :
Tunable attenuators may play an important role in treatment of amblyopia, smart sunglass, head-mounted displays, and various ophthalmic imaging systems. Photochromic materials are slow as it takes a couple minutes to change the transmission from bright to dark conditions. Electrochromic materials have a limited contrast ratio (the ratio of the highest transmission to the lowest transmission, only about 10). Last year we reported a tunable liquid crystal (LC) attenuator with unprecedented contrast ratio (> 200) and fast response (200 milliseconds). It is also critical to maintain the operation voltages below the safe voltage (24 volts) for wearable devices. The purpose of this study is to investigate a new tunable LC attenuator with large contrast ratio, fast response, and low operation voltages.
Methods :
For LC devices, one way to reduce the operation voltages is to use LC materials with high dielectric anisotropy. The LCs used in the work reported last year were E7, which has a positive dielectric anisotropy value of 11.4. In this implementation, we chose the LC material (LC-1) with a higher dielectric anisotropy of 31.8. Tunability of the transmission of the electro-optic device is based on light scattering and absorption of the LC mixture and the change of the orientations of the LC droplets under the influence of the applied electric field. The LC mixture is composed of nematic LC, chiral dopant, and dichroic dye. The mixture is sandwiched between two glasses each coated with transparent conductive thin film. The thickness of the LC mixture is only 20 microns.
Results :
By applying a voltage in the range of 0-22 Vrms, the transmission of the new electro-optic device can be tuned across a very large range, and a contrast over 250 has been achieved, much higher than the concurrent technologies (typically around 100). 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 responds equally to the light with any polarization and it is suitable for vision care.
Conclusions :
A low-voltage, high-contrast ratio, broadband tunable attenuator based on liquid crystal materials has been achieved. It is promising for many ophthalmic applications, including treatment of amblyopia, smart sunglass, head-mounted displays, eye imaging, etc.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.