Optical fingerprint imaging using holography

1. An electronic device comprising:

a biometric sensor, the biometric sensor comprising:

an illuminator;

a mirror;

a biometric sensor array; and

a beam splitter, the beam splitter configured to:

split a beam received from the illuminator into a first beam incident on a biometric sensing area and a second beam incident on the mirror; and

combine a reflected first beam reflected from the biometric sensing area and a reflected second beam reflected from the mirror into a third beam incident on the sensor array, wherein the reflected first beam and the reflected second beam are combined off-axis with respect to each other in the third beam;

a processing system coupled to the sensor array, the processing system configured to:

transform pixel data from the sensor array into a frequency spectrum, the frequency spectrum including a zeroth order image, a real image, and a virtual image;

filter the frequency spectrum outside of a frequency range corresponding to the real image; and

reconstruct the filtered frequency spectrum into a biometric image.

2. The electronic device of claim 1 , wherein the biometric sensor is a fingerprint sensor.

3. The electronic device of claim 1 , further comprising a protective layer disposed over the beam splitter, wherein the biometric sensing area is at an upper surface of the protective layer.

4. The electronic device of claim 3 , wherein the protective layer is a cover lens of a display.

5. The electronic device of claim 3 , wherein the beam splitter is mounted to a surface of the protective layer.

6. A biometric sensor comprising:

an illuminator;

a mirror;

a biometric sensor array; and

a beam splitter, the beam splitter configured to:

split a beam received from the illuminator into a first beam incident on a biometric sensing area and a second beam incident on the mirror; and

combine a reflected first beam reflected from the biometric sensing area and a reflected second beam reflected from the mirror into a third beam incident on the sensor array, wherein the reflected first beam and the reflected second beam are combined off-axis with respect to each other in the third beam, and wherein the first beam is reflected by the beam splitter to the biometric sensing area and the second beam is transmitted by the beam splitter to the mirror.

7. The biometric sensor of claim 6 , wherein the biometric sensor is a fingerprint sensor.

8. The biometric sensor of claim 6 , further comprising a protective layer disposed over the beam splitter, wherein the biometric sensing area is at an upper surface of the protective layer.

9. The biometric sensor of claim 8 , wherein the protective layer is a cover lens of a display.

10. The biometric sensor of claim 8 , wherein the beam splitter is a polarizing beam splitter having a first quarter wave plate disposed between the biometric sensing area and the polarizing beam splitter, and a second quarter wave plate disposed between the mirror and the polarizing beam splitter.

11. The biometric sensor of claim 6 , further comprising a second beam splitter, wherein each of the beam splitters is configured to split a beam received from a corresponding illuminator into a first beam incident on the biometric sensing area and a second beam incident on a corresponding mirror.

12. The biometric sensor of claim 11 , wherein the mirror is disposed between each of the beam splitters, and each of the beam splitters share the mirror.

13. The biometric sensor of claim 6 , wherein the mirror is a discrete mirror mounted proximate to the beam splitter.

14. The biometric sensor of claim 6 , wherein the mirror is coated on a face of the beam splitter.

15. The biometric sensor of claim 6 , wherein the illuminator comprises a light source and a pinhole, wherein the pinhole is disposed in an optical path between the light source and the beam splitter.

16. The biometric sensor of claim 6 , wherein the sensor array has a pixel pitch, the illuminator is configured to emit light of a first wavelength, and wherein a relative angle between the face of the mirror and the normal of the sensing plane is less than the inverse sine of the first wavelength divided by the twice the pixel pitch.

17. An electronic device comprising:

a biometric sensor, the biometric sensor comprising:

a plurality of illuminators;

a mirror;

a biometric sensor array; and

a plurality of beam splitters, each beam splitter configured to:

split a beam received from one of the plurality of illuminators into a first beam incident on a biometric sensing area and a second beam incident on the mirror; and

combine a reflected first beam reflected from the biometric sensing area and a reflected second beam reflected from the mirror into a third beam incident on the sensor array, wherein the reflected first beam and the reflected second beam are combined off-axis with respect to each other in the third beam;

a processing system coupled to the sensor array, for each of the plurality of beam splitters the processing system configured to:

transform pixel data from the sensor array into a frequency spectrum, the frequency spectrum including a zeroth order image, a real image, and a virtual image;

filter the frequency spectrum outside of a frequency range corresponding to the real image; and

reconstruct the filtered frequency spectrum into a biometric image; and

combine each of the biometric images from each of the beam splitters into a single combined biometric image.

18. The electronic device of claim 17 , wherein the biometric sensor is a fingerprint sensor.

19. The electronic device of claim 17 , further comprising a protective layer disposed over the beam splitter, wherein the biometric sensing area is at an upper surface of the protective layer.

20. A biometric sensor comprising:

an illuminator;

a mirror;

a biometric sensor array;

a beam splitter, the beam splitter configured to:

split a beam received from the illuminator into a first beam incident on a biometric sensing area and a second beam incident on the mirror; and

combine a reflected first beam reflected from the biometric sensing area and a reflected second beam reflected from the mirror into a third beam incident on the sensor array, wherein the reflected first beam and the reflected second beam are combined off-axis with respect to each other in the third beam; and

a protective layer disposed over the beam splitter, wherein the biometric sensing area is at an upper surface of the protective layer, and wherein the beam splitter is a polarizing beam splitter having a first quarter wave plate disposed between the biometric sensing area and the polarizing beam splitter, and a second quarter wave plate disposed between the mirror and the polarizing beam splitter.

21. A biometric sensor comprising:

an illuminator;

a mirror;

a biometric sensor array;

a first beam splitter, the first beam splitter configured to:

combine a reflected first beam reflected from the biometric sensing area and a reflected second beam reflected from the mirror into a third beam incident on the sensor array, wherein the reflected first beam and the reflected second beam are combined off-axis with respect to each other in the third beam; and

a second beam splitter, wherein each of the beam splitters is configured to split a beam received from a corresponding illuminator into a first beam incident on the biometric sensing area and a second beam incident on a corresponding mirror.

22. A biometric sensor comprising:

an illuminator;

a mirror;

a biometric sensor array; and

a beam splitter, the beam splitter configured to:

split a beam received from the illuminator into a first beam incident on a biometric sensing area and a second beam incident on the mirror; and

combine a reflected first beam reflected from the biometric sensing area and a reflected second beam reflected from the mirror into a third beam incident on the sensor array, wherein the reflected first beam and the reflected second beam are combined off-axis with respect to each other in the third beam, and

wherein the mirror is coated on a face of the beam splitter.