Scale-invariant, resolution-invariant iris imaging using reflection from the eye
View Patent ↗An optical system includes an active focus element that maintains an image in focus over a range of object distances. The active focus element and aperture stop are positioned such that the image scale and the image spatial resolution are also invariant (or at least have a reduced sensitivity) with respect to object distance.
1. An iris imaging system comprising a camera that captures images of irises within a predefined capture volume with sufficient resolution for biometric identification, the camera including:
an optical system including an objective lens, and an adaptive optics loop that auto-focuses an image of an iris onto an image plane located at a fixed position based on a reflection of light from an eye containing the iris, with an image scale and an image spatial resolution that is constant regardless of a standoff distance to the iris, the adaptive optics loop comprising:
a deformable mirror that adjusts a wavefront of the eye reflected light;
a wavefront sensor that senses the wavefront of the eye reflected light; and
a controller coupled between the deformable mirror and the wavefront sensor that adjusts the deformable mirror based on the sensed wavefront; and
a sensor array located at the image plane.
2. The iris imaging system of claim 1 , wherein the deformable mirror is located one focal length behind the objective lens.
3. The iris imaging system of claim 1 , wherein the deformable mirror is located at an optical conjugate to the infinite focus of the optical system.
4. The iris imaging system of claim 1 , wherein an aperture stop is located at the deformable mirror.
5. The iris imaging system of claim 1 , wherein a size of an entrance pupil of the optical system is linearly proportional to a distance from the entrance pupil to the iris.
6. The iris imaging system of claim 1 , wherein the deformable mirror is a deformable curvature mirror based on applying different voltages across different areas of a piezoelectric material.
7. The iris imaging system of claim 1 , wherein the deformable mirror is circular deformable mirror mounted by its circumference and driven by one or more annular forces.
8. The iris imaging system of claim 1 , wherein the wavefront sensor is a wavefront curvature sensor based on defocused pupil images.
9. The iris imaging system of claim 1 , wherein the iris imaging system has a speed to acquire and image at least one iris per second.
10. The iris imaging system of claim 1 , wherein the camera captures images of
irises with a spatial resolution of 200 microns or better.
11. The iris imaging system of claim 1 , wherein the camera captures images of
irises with a spatial resolution of 100 microns or better.
12. The iris imaging system of claim 1 , wherein the camera captures images of
irises with a spatial resolution of 75 microns or better.
13. The iris imaging system of claim 1 , wherein the iris imaging system can cover a capture volume of at least 1 cubic meter.
14. The iris imaging system of claim 1 , wherein the camera can capture iris images at a standoff of at least 2.5 m.
15. The iris imaging system of claim 1 , wherein the camera can capture iris images at a standoff of at least 5 m.
16. The iris imaging system of claim 1 , wherein image brightness is constant for constant object brightness.
17. The iris imaging system of claim 1 , wherein a required focus adjustment is used to determine a measurement of iris standoff distance.