A high-efficiency tunable refractive lens based on liquid crystals with concentric electrode rings and a simple unique design of a resistor network is reported, and used to assess the performance of an optimized electrically tunable lens. It has a large number of phase control points to be able to accurately control the phase profile and produce high efficiency. The lens design uses resistors between neighboring electrodes to minimize external connections. The lens optical path difference is measured as a near perfect parabolic shape and the Strehl ratio of about 80% is obtained (comparing to a high-quality glass lens). Image evaluations show a good image quality with diffraction limited resolution, but the contrast is lowered by a large-area haze. The lens design also shows a good switching speed, and adjustable power, allowing it to be used in many applications. An example lens with a diameter of 2.4 mm and a 5 diopter tunable range is used in the evaluations.
We show the modeling, design and fabrication for a tunable refractive lens based on liquid crystals. The lens has about
80 rings of transparent ITO conductor with an inter-ring resistor network. The width of each electrode is calculated to
have maximum phase step within each electrode region about 1/8 λ. The gap between any 2 adjacent electrodes is 3 μm.
The active diameter is about 4.7 mm, and our lens has a substrate gap of 10 μm, filled with a LC material of a large
birefringence of Δn = 0.27. Through a via in a SiO2 layer deposited on the ITO pattern, we run metal lines to every 10th ring electrode for establishing the voltage profile, which is calculated by our simulation, taking into account the details
of the electrode structure, the properties of the LC material used, and the desired focal length. To characterize the optical
performance: we use a Mach-Zehnder interferometer to obtain the actual phase profile across the lens aperture, which
fits the calculation very well in parabolic shape. An eye chart image through the lens is also taken, which shows very
good resolution and contrast.