AMBIENT LIGHT REJECTION FILTER

• US 20070280514A1
• Filed: 02/21/2007
• Published: 12/06/2007
• Est. Priority Date: 02/22/2006
• Status: Active Grant

• Current Assignee: Wasatch Photonics, Inc.
• Original Assignee: Wasatch Photonics, Inc.
• Inventors: Heidt, Gerald
• Granted Patent: US 8,077,929 B2
• Time in Patent Office: Days
• US Class Current: 382/124
• CPC Class Codes: G06V 40/1324 by using geometrical optics, e.g. using prisms G06V40/1312 takes precedence

Abstract

A fingerprint reader is described. The fingerprint reader includes an illumination source that produces light and a camera. An optical window is also part of the reader. The window is positioned so that light from the illumination source passes through the optical window and then is reflected to the camera for imaging a person'"'"'s fingerprint. A filter may be positioned on or proximate to the optical window. The filter prevents ambient light from reaching the camera. In some situations, the filter will be a dielectric mirror, a dielectric filter, a holographic mirror, a holographic filter, a dichroic mirror or a dichroic filter.

Claims

1. A fingerprint reader comprising:

an illumination source that produces light;

a camera;

an optical window, wherein light from the illumination source is reflected by the optical window to the camera for imaging a fingerprint; and

a filter on or proximate to the optical window, wherein the filter prevents ambient light from reaching the camera.

2. The fingerprint reader as in claim 1, wherein the filter is selected from the group consisting of dielectric elements, holographic elements, and diachronic elements.

3. The fingerprint reader as in claim 1 wherein the reader further comprises a holographic optical element, and wherein light from the illumination source passes through the holographic optical element prior to contacting the filter.

4. The fingerprint reader as in claim 1 wherein the surface of the filter is curved.

5. The fingerprint reader as in claim 1 wherein the filter is a holographic element that creates a curved wave front that effectively operates as a curved filter surface.

6. The fingerprint reader as in claim 1 wherein the filter is used in conjunction with a holographic optical element, and wherein the filter deflects zero order light that is produced by holographic optical element away from the camera.

7. The fingerprint reader as in claim 1 wherein the camera is a CCD (charge-coupled device) that includes at least one camera filter.

8. The fingerprint reader as in claim 1 wherein the filter operates to block ambient light based upon the angle upon which the ambient light strikes the filter.

9. The fingerprint reader of claim 1 wherein the filter is a thin film added to the top of the optical window.

10. The fingerprint reader of claim 1 wherein the reader digitally communicates a fingerprint image to a computing device.

11. The fingerprint reader of claim 1 further comprising a prism or glass block, wherein light from the source passes through the prism or glass block prior to reaching the optical window.

12. The fingerprint reader of claim 11 wherein the filter is added to a surface of the prism or glass block.

13. A method for increasing the sensitivity of a fingerprint reader, the method comprising:

obtaining a fingerprint reader, wherein the reader comprises;

an illumination source that produces light;

a camera;

an optical window, wherein light from the illumination source passes through the optical window and then is reflected to the camera for imaging a fingerprint; and

a filter on or proximate the optical window; and

using the filter to block ambient light from reaching the camera.

14. The method as in claim 13, wherein the filter is selected from the group consisting of dielectric elements, holographic elements, and dichroic elements.

15. An optical window that may be used on a fingerprint reader having a camera, the optical window comprising a filter that prevents ambient light from reaching the camera, wherein light from an illumination source passes through the filter and then is reflected by the optical window.