Optical system for an image acquisition device

Patent metadata

Field	Value
Publication number	US-10467469-B2
Application number	US-201615053863-A
Country	US
Kind code	B2
Filing date	Feb 25, 2016
Priority date	Feb 27, 2015
Publication date	Nov 5, 2019
Grant date	Nov 5, 2019

Abstract

An optical system for an image acquisition device comprises an image sensor comprising an array of pixels including pixels sensitive to IR wavelengths for acquiring an image. A lens assembly includes a collecting lens surface with an optical axis, the lens assembly being arranged to focus IR light received from a given object distance on the sensor surface. The lens assembly includes at least a first reflective surface for reflecting collected light along an axis transverse to the optical axis so that a length of the optical system along the optical axis is reduced by comparison to a focal length of the lens assembly.

First claim

The invention claimed is:

1. An optical system for an image acquisition device comprising:
an image sensor comprising an array of pixels including pixels sensitive to IR wavelengths for acquiring an image; and
multiple optical components formed in a single piece of plastic material, comprising a prism shape having first and second opposing surfaces and third and fourth opposing surfaces, formed along the prism shape to provide a lens assembly having a predetermined focal length, the lens assembly including:
a collecting lens having a convex surface positioned along the first surface to initially transmit light received from a scene along a first optical axis and then along a second axis transverse to the first optical axis for focusing on the image sensor, the lens assembly arranged to focus IR light received from a given object distance on a surface of the image sensor, the lens assembly further including:
a first reflective coating formed along the third surface for reflecting collected light along the second axis transverse to said first optical axis;
a second reflective coating formed along the fourth surface for further reflecting the collected light along a third axis parallel to the first optical axis; and
a second lens positioned along the second surface to focus the collected light on the image sensor so that said optical system has a length, as measured along the first optical axis and the third axis, less than the predetermined focal length of the lens assembly.

2. The optical system according to claim 1 where the second reflective coating is positioned parallel spaced apart relationship to the first reflective coating and arranged to reflect light reflected from the first reflective coating toward the image sensor.

3. An optical system according to claim 2 wherein the second reflective coating is arranged to reflect light reflected from the first reflective coating through an image side surface, the image sensor being disposed in parallel spaced apart relationship to the fourth surface.

4. An optical system according to claim 2 wherein the collecting lens and the first surface are integrally formed in a first prism.

5. An optical system according to claim 4 wherein the third surface and the fourth surface are integrally formed in the first prism.

6. The optical system according to claim 4 wherein the third surface and the fourth surface are integrally formed in a second prism connected to the first prism, there being a gap formed between a portion of the first and second prisms.

7. An optical system according to claim 6 wherein said first and second prisms are integrally formed in a single mold.

8. An optical system according to claim 1 , wherein said discrete lens is moveable along said transverse axis to focus said optical system.

9. An optical system according to claim 1 wherein the image sensor is moveable along one of the first optical axis or the third axis to focus the optical system.

10. An optical system according to claim 1 wherein an aperture stop diameter for the collecting lens is approximately 3 mm and wherein the optical system extends a depth of less than 5.5 mm from a front surface of the collecting lens to the image sensor.

11. A camera module including the optical system of claim 1 .

12. An image acquisition system including a camera module according to claim 11 and further including a software application which is operable to determine if an image acquired by said camera module is in focus and, responsive to said image not being in focus, to direct a user to move the acquisition device to a correct focal distance from their face.

13. An image acquisition device including the camera module of claim 11 and an infra-red light source.

14. An image acquisition device according to claim 13 including a first polarizer mounted in front of said infra-red light source and a second polarizer mounted in front of said camera module.

15. An image acquisition device according to claim 14 , wherein said polarizers are linear, each having respective polarization axes at 90 degrees to one another.

16. An image acquisition device according to claim 14 , wherein said polarizers are circular, each having opposite polarization senses.

17. An image acquisition device according to claim 16 further comprising a mechanism for adjustably rotating said second polarizer.

18. A biometric recognition system including an image acquisition device comprising an optical system according to claim 1 and wherein the image sensor comprises X columns of Y pixels, said biometric recognition system further comprising:
a buffer operatively connected to the image sensor for selectively acquiring images from the sensor in one of landscape mode, where said images comprise A columns of B pixels, and portrait mode, where said images comprise C columns of D pixels, where X≥A>B, Y≥D>C, X>C and Y>B; and
a biometric recognition application operatively connected to said buffer for acquiring one or more images in portrait mode at a first distance of the image acquisition device from a subject sufficient to obtain an image of the subject's face for facial recognition and at a second distance, less than said first distance, of the image acquisition device from the subject sufficient to obtain at least one image of at least one of said subject's irises for iris recognition.

19. A biometric recognition system including an image acquisition device comprising an optical system according to claim 1 wherein said image sensor comprises X columns of Y pixels, and a buffer operatively connected to the image sensor for selectively acquiring images from the sensor in one of a landscape mode, where said images comprise A columns of B pixels, and a portrait mode, where said images comprise C columns of D pixels, where X≥A>B, Y≥D>C, X>C and Y>B and a biometric recognition application operatively connected to said buffer for acquiring one or more images in portrait mode at a first distance of the image acquisition device from a subject sufficient to obtain an image of the subject's face for facial recognition and at a second distance, less than said first distance, of the image acquisition device from the subject sufficient to obtain at least one image of at least one of said subject's irises for iris recognition.

20. A biometric recognition system as claimed in claim 19 comprising an optical system arranged to focus images at distances of between 30 cm and 40 cm between said image acquisition device and said subject on said image sensor.

21. A biometric recognition system as claimed in claim 19 comprising a fixed focus optical system.

22. A biometric recognition system as claimed in claim 19 wherein said image sensor comprises a 4 MP sensor and images captured in said landscape and said portrait modes comprises 2 MP images.

23. A biometric recognition system as claimed in claim 19 further comprising an infra-red illumination source.

Assignees

• Fotonation Ltd

Inventors

• Goncharov Alexander
• Dainty Christopher
• Andorko Istvan
• Corcoran Peter

Classifications

• G02B17/0856

  comprising a refractive element with a reflective surface, the reflection taking place inside the element, e.g. Mangin mirrors · CPC title

• G02B13/007 Primary

  the beam folding prism having at least one curved surface · CPC title

• G02B13/008

  designed for infrared light · CPC title

• A61B5/117

  Identification of persons (methods or arrangements for recognising patterns, e.g. fingerprints, G06F18/00, G06V40/00; identification of persons by analysing their voice or speech G10L17/00) · CPC title

• H04N23/67

  Focus control based on electronic image sensor signals · CPC title