Focus-tunable micro-reflective lens: Design and fabrication feasibility with deformable micromirror

This paper presents a novel design and fabrication concept for a fully reflective architecture-based focus-tunable micromirror lens without translating constituent mirrors. The lens system consists of two mirror elements: a microelectromechanical-system varifocal spherically deformable convex micromirror and a fixed-focal spherical concave micromirror. After the fabrication and optical characterization of the two individual mirrors, they are vertically integrated 4 cm apart, with their own optical-axis alignment, for the realization of the lens system. The mirror lens system, comprising a 20-mm-diameter concave primary micromirror with a fixed focal length of 70.8 mm and 4-mm-diameter deformable convex secondary micromirror actuated by electromagnetic force as the driving component of the entire system, allows a focal-length tunability of ~74 mm via the application of an input controlling current of 0.8 A to the solenoid. The focusing performance of the realized micromirror lens system is evaluated. Despite speckle noise in the focused images, which possibly originates from the geometry of the mirror components, the varifocal micromirror lens is demonstrated to be feasible with regard to fully reflective and non-movable mirrors.