Development Of Multi-Focal Fresnel Lens Using Magnetroheological Fluid

The purpose of this study is to design a diffraction optical element using magnetorheological fluid for a switchable object lens used in optical pickup head. The micro fresnel structure was fabricated using micro-molding of silica wafer and made of PDMS.
Switchable lens was consists of a PDMS fresnel zone plate and a PDMS convex lens. The channels of the micro fresnel plate were filled with magnetorheological fluid. The light transmittance of the switchable lens will varied depends on the existence of the vertical magnetic field applied to the lens. The focus of the PDMS lens were measured when with or without magnetic field. MATLAB software was used to simulate the intensity distribution on the fresnel zone plate and to control the movement of two stepping motors in controlling the position of the focusing screen.
An electromagnetic controlled focus-switchable lens was developed in this study. The results showed that the focus of PDMS lens will change from 35.7 mm to 35.1 mm when a 240 gauss magnetic field was applied.