Low-voltage tunable liquid crystal lens fabricated with self-assembled polymer gravel arrays

A novel approach for fabricating liquid crystal (LC) lenses is presented. The approach involves the use of a photocurable prepolymer dispersed in a cell fabricated with vertically aligned substrates. A radial gradient UV irradiation intensity distribution is produced using a radial variable neutral density filter. Under UV irradiation, the prepolymer diffuses and is then polymerized on the substrate surfaces owing to vertical phase separation. After polymerization, the diameter of the self-assembled polymer gravel on the substrates has a radial gradient distribution, causing a radial gradient pretilt angle (RGPA) distribution on the substrates and producing LC lenses. By numerical simulation, RGPA LC lens has significantly lower supplied voltage than conventionally hole-patterned electrode (HPE) LC lens, and higher lens power. In the experiment, the fabricated RGPA LC lens with aperture size of 5 mm possesses a simple planar electrode structure, low operation voltage (< 4 V), small root mean square wavefront error (< 0.08 λ), and acceptable focusing quality. By the overdriving scheme, the switched-off time of the fabricated RGPA LC lens reaches 0.27 s. With the novel approach, low-voltage LC lenses with different optical aperture sizes can be easily fabricated.