Device for forming and detecting fingerprint images with valley and ridge structure

摘要

A method and ultra-compact system has been developed for illuminating and detecting the surface topography of an object such as the finger of an individual. The system is capable of producing high- contrast images which can be electronically transmitted in real-time, or stored using electronic or photographic recording devices. Light traveling within a light transmitting substrate is redirected by a slanted-fringe light diffractive grating preferably embodied within a volume hologram. The volume hologram, either of the reflection or transmission type, is attached to the light transmitting substrate, and functions to diffract light striking thereupon and illuminate an object having topographical surface structure. After being spatially and intensity modulated in accordance with topographical details of the illuminated object, the modulated light passes back through the light transmitting substrate and the volume hologram, onto an image detection array, for subsequent analysis. Each of the disclosed embodiments has a compact geometry suitable for use in diverse object identification applications.