Fingerprint sensor using a polymer dispersed liquid crystal holographic lens.

Abstract

We used a polymer dispersed liquid crystal material holographic lens in a fingerprint sensor, which reduced the total size of the sensor and improved image quality. The beam carrying fingerprint information was diffracted by the holographic lens and converged onto the complementary metal-oxide semiconductor image sensor directly, which omitted the traditional lens or fiber taper. The phenomenon that the image quality is poor when the finger is too dry or wet was explained based on the evanescent wave theory. The total size of the device was $50\mathrm{mm}\times 25\mathrm{mm}\times 30\mathrm{mm}$. The fingerprint image had a contrast of $250\text{:}1$ and a resolution of $800\mathrm{dots}$/in.