Ambient light rejection filter

• US 8,077,929 B2
• Filed: 02/21/2007
• Issued: 12/13/2011
• Est. Priority Date: 02/22/2006
• Status: Active Grant

• Current Assignee: Wasatch Photonics, Inc.
• Original Assignee: Wasatch Photonics, Inc.
• Inventors: Heidt, Gerald Lee
• Primary Examiner(s): Ahmed, Samir
• Assistant Examiner(s): HU, FRED H.
• Application Number:
  US11/677,459
• Publication Number:
  US 20070280514A1
• Time in Patent Office: 1,756 Days
• Field of Search: None
• US Class Current: 382/115
• 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;

an ambient light filter in contact with the optical window;

wherein the light from the illumination source enters the optical window at a total internal reflection angle, such that the light is reflected off a surface of the optical window by total internal reflection;

wherein when a person'"'"'s finger is placed on the optical window, the light from the illumination source is frustrated by oils on ridges of the finger and is not reflected off the optical window;

wherein the filter allows the light from the illumination source to pass through the filter at the total internal reflection angle inside the optical window while reflecting ambient light coming from outside of the optical window so that the ambient light does not reach the camera;

wherein the ambient light can cancel or diminish the quality of a desired fingerprint to be imaged;

wherein the illumination source and the filter are designed so that the light from the illumination source contacts the filter within a desired range of angles, so that the light from the illumination source is not affected by the filter; and

wherein the filter is designed so that the ambient light contacts the filter outside of the desired range of angles, so that the filter rejects the ambient light.

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

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

10. 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.

11. The fingerprint reader of claim 10 wherein the filter is added to a surface of the prism or glass block.

12. 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;

an ambient light filter in contact with the optical window;

wherein the light from the illumination source enters the optical window at a total internal reflection angle, such that the light is reflected off a surface of the optical window by total internal reflection;

wherein when a person'"'"'s finger is placed on the optical window, the light from the illumination source is frustrated by oils on ridges of the finger and is not reflected off the optical window;

wherein the filter allows the light from the illumination source to pass through the filter at the total internal reflection angle inside the optical window while reflecting ambient light coming from outside of the optical window so that the ambient light does not reach the camera;

wherein the ambient light can cancel or diminish the quality of a desired fingerprint to be imaged;

wherein the illumination source and the filter are designed so that the light from the illumination source contacts the filter within a desired range of angles, so that the light from the illumination source is not affected by the filter; and

wherein the filter is designed so that the ambient light contacts the filter outside of the desired range of angles, so that the filter rejects the ambient light;

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

13. The method as in claim 12, wherein the filter is selected from the group consisting of dielectric elements, holographic elements, and dichroic elements.