Polymer Deformable Mirror for Optical Auto Focusing

Abstract

A low-stress organic polymer membrane is proposed as a deformable mirror that can be incorporated into a cellular phone camera to achieve auto focusing without motor-type moving parts. It is demonstrated that our fabricated device has an optical power of 20 diopters and can switch focus in 14 ms. The surface roughness of the organic membrane is measured around 15 nm, less than λ/20 of the visible light. With curve fitting, we found that the actuated membrane is almost parabolic in shape, which leads to less aberration than spherical surfaces. It is suitable for reflective- optics systems. fulfill the two requirements of large refractive index contrast and small density difference. Another solution is the use of liquid crystal lenses (4), (5), but the incident light must be linearly polarized. It was also proposed in (6) and (7) to adopt deformable mirrors in a reflective optics configuration. Recently, reflective optics has attracted more attention as a means of achieving a long lightpath in thin products because of the folded light-path design. Deformable mirrors have an advantage of low color dispersion, but the optical power of silicon-based deformable mirrors (8) is relatively small. We propose an organic polymer deformable mirror which can be operated over a large optical power range of up to 20 diopters, which is one order of magnitude higher than the range of previously reported devices. Experimental results of its actuated shape and surface roughness will also be discussed.