Switchable positive and negative microlens

The microlens array is a useful component for optical interconnections, optical fiber switches, shutters of optical super-resolution devices, light deflection devices, and image processing. In 3-D display systems based on integral photography, the microlens array with dynamically 

As shown in Equation (12.5), the focal length of an LC lens depends on the lens radius, LC layer thickness, and its gradient refractive index. Normally, a lens can either have a positive or negative focal length. In this section, an LC microlens array whose focal length can be switched from positive to negative or vice versa by the appUed voltage is introduced. 

ITO electrode and then flattened by a polymer film. For phase-only modulation, homogeneous LC alignment should be used. Thus, the polymer surface and the bottom ITO glass substrate with a thin polyimide alignment layer are rubbed in anti-parallel directions. The cell gap is controlled at 18 pm by Mylar spacers and hermetically sealed using ultraviolet-curable glue. To achieve a fast response time, a dual-frequency liquid crystal (DFLC) is used. The physical properties of the DFLC mixture are summarized as follows crossover frequency / , 5 kHz, An 0.285 (at X=633nmand T=22°C), and dielectric anisotropy Ae = 4.73 at/= 1 kHz, and Ae = -3.93 at 50 kHz. 

To explain this focal length transition phenomenon quantitatively, we need to calculate the voltage-induced LC director reorientation numerically. First, we calculate the voltage-dependent refractive index change for a symmetric, uniform LC layer and use that to predict 

The tilt angle profile G z) can be used to calculate the average refractive index, n, of the liquid crystal at different applied voltages. For a given tilt angle, the refractive index is given by the index ellipsoid equation [54]  

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