Dip-and-bake low-cost high-performance lenses for smartphone-based microscopy

Aspherical optical lenses are known for high performance and aberration free imaging. They are increasingly in demand for developing simple and compact high quality optical systems. The conventional methods of production of aspherical lenses are complex and time-consuming. There is a need for a simple, inexpensive and robust method of fabrication of such lenses. Here, we present a novel, low cost and simple approach to fabricate aspherical lenses reproducibly. The two-step process involves 1) controlled wetting of a curved surface with a transparent, cross-linkable polymer by dipping, and 2) pulling the wetted curved surface from the polymer solution. The curvature of the lens is dependent on the area of wetting, speed of pulling and the curvature of the curved surface. The lenses are produced with less than 5% error, and hence, the approach is reproducible in comparison to the previously reported techniques. A smartphone microscope developed using one of the fabricated lenses is found to have a resolution of ~1.7 μm. In addition, we show an application of these lenses as a means to check for the authenticity of Indian currency notes by a common man. The micro-patterns on the currency note are imaged using the smartphone microscope in ambient light. Also, the lenses have potential applications in developing compact and portable high quality optical systems, such as, endoscopes and microscopes.