Abstract
Aiming to equip commercial camera modules, such as the optical imaging systems with a CMOS sensor module in 3 Mega pixels, an ultra thin liquid crystal lens with designed hole-and-ring electrodes is proposed in this study to achieve high focusing power. The LC lens with proposed electrodes improves the central intensity of electric field which leads to better focusing quality. The overall thickness of the LC lens can be as thin as 1.2 mm and the shortest focal length of the 4 mm-aperture lens occurs at 20 cm under an applied voltage of 30 V at 1 KHz. The inner ring electrode requires only 40% of applied voltage of the external hole electrode. The applied voltages for this internal ring and external hole electrodes can simply be realized by a pre-designed parallel resistance pair and a single voltage source. Experiments are conducted for validation and it shows that the designed LC lens owns good image clearness and contrast at the focal plane. The proposed design reduces the thickness of LC lens and is capable of achieving relative higher focusing power than past studies with lower applied voltage.
Highlights
In the applications of optical lens for commercial imaging systems or communication devices such as cell phones, a desirable feature is to dynamically control the optical properties of the lens; in this way, the functions of focusing and/or zooming can be realized
Several studies are presented in designing the stacked planar electrode geometry [5] or forming a certain electric field [6,7,8,9] by spherical electrode, to lead LC lens acting as a gradient index (GRIN) lens
Several studies on different LC material instead of nematic type are proposed by using polymer-separated composite film (PSCOF) as a Fresnel zone plate [16], polymer stabilized liquid crystal (PSLC) [17] and polymer-dispersed liquid crystal (PDLC) [3]
Summary
In the applications of optical lens for commercial imaging systems or communication devices such as cell phones, a desirable feature is to dynamically control the optical properties of the lens; in this way, the functions of focusing and/or zooming can be realized. Conventional LC lens with large aperture size [19] usually required high applied voltage, about 50 V, to form the electric field but the focal length is too far, 760 mm, to be applied in the camera applications. In the conventional hole type electrode LC lens, a trade-off exists between the high focusing power and low driving voltage This trade-off problem becomes more serious as a large-aperture lens (> 4 mm) is considered, which is required to be implemented in commercial CCMs for mobile devices. This study is proposed a hole-and-ring type electrode to improve the distribution of electric field, which only requires lower applied voltage than the conventional one and meet the required optical performance, i.e. the minimum focal length. It is preceded that the intensity of electric field will be enhanced at the central hole which means that the focusing power will be higher due to the central LC are affected by higher electric field
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