A liquid crystal (LC) lens is prepared by controlling the alignment of a LC using a homogeneous polyimide (PI) layer and a homeotropic PI layer. The rubbed homogeneous PI layer has a concave surface and the homeotropic PI layer is flat. The LC sandwiched between the two PI layers obtains a hybrid alignment which has the largest gradient of refractive index (GRIN) distribution. The LC layer exhibits a lens character because of its convex shape. Since the effective refractive index of the LC is larger than that of the homogeneous PI, the LC lens can focus a light with the shortest focal length in the voltage-off state. By applying an external voltage, the LC molecules can be reoriented along the electric field. As a result, the focal length of the LC lens is reduced. The focal length of the LC lens can be tuned from ~30 to ~120 μm when the voltage is changed from 0 to 7 Vrms. This LC lens has the advantages of no threshold, low operating voltage, and simple fabrication.
We prepared a lenticular microlens array (LMA) using a polyvinyl chloride (PVC) gel and an interdigitated electrode. By applying a DC voltage to the electrode, the surface of the PVC gel can be waved with an LMA character. When the voltage is removed, the wavy PVC gel can recover its flat surface gradually. With the aid of a polarity-inverted voltage, the recovering time can be largely reduced. The LMA can present a stable dynamic response when it is repetitively impacted by a pulse voltage. The experimental results are given, and the mechanism of reducing the dynamic response time is explained. Our LMA with improved response time has potential applications in sensing, beam steering, biometrics, and displays.
A tunable-focus liquid crystal (LC) lens is prepared. The orientation of the LC is controlled using a homeotropic polyimide (PI) layer and a homogeneous PI layer. The homeotropic PI layer has a concave shape. The LC in the concave space presents a hybrid alignment and has a convex shape. As a result, the LC has a lens character with the shortest focal length in the voltage-off state. The focal length can be tuned from 9 to 15 cm when an applied voltage is changed from 0 to 8 Vrms. Our LC lens has no threshold voltage, and the fabrication procedure is relatively simple.
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