  Images recorded below the surface of a finger can have more details and be of
higher quality than the conventional surface fingerprint images. This is
particularly true when the quality of the surface fingerprints is compromised
by, for example, moisture or surface damage. However, there is an unmet need
for an inexpensive fingerprint sensor that is able to acquire high-quality
images deep below the surface in short time. To this end, we report on a
cost-effective full-field optical coherent tomography (FF-OCT) system comprised
of a silicon camera and a powerful near-infrared LED light source. The system,
for example, is able to record 1.7 cm x 1.7 cm en face images in 0.12 s with
the spatial sampling rate of 2116 dots per inch and the sensitivity of 93 dB.
We show that the system can be used to image internal fingerprints and sweat
ducts with a good contrast. Finally, to demonstrate its biometric performance,
we acquired subsurface fingerprint images from 240 individual fingers and
estimated the equal-error-rate to be ~0.8 %. The developed instrument could
also be used in other en face deep-tissue imaging applications because of its
high sensitivity, such as in vivo skin imaging.
