Wideband ambient light rejection
Optical apparatus includes an image sensor and objective optics, which are configured to collect and focus optical radiation over a range of wavelengths along a common optical axis toward a plane of the image sensor. A dispersive element is positioned to spread the optical radiation collected by the objective optics so that different wavelengths in the range are focused along different, respective optical axes toward the plane.
1. Optical apparatus, comprising:
an image sensor; and
objective optics, which are configured to collect and focus optical radiation over a range of wavelengths within at least one of an infrared and a visible part of the optical spectrum toward a plane of the image sensor, and which comprise a dispersive element configured so that the optics have a chromatic aberration within the range in excess of one micrometer per nanometer of wavelength at the plane.
2. The apparatus according to claim 1 , wherein the optics are configured so that the chromatic aberration causes different wavelengths in the range originating from a given object point to focus at different, respective image points along an axis perpendicular to the plane.
3. The apparatus according to claim 1 , wherein the optics are configured so that the chromatic aberration causes different wavelengths in the range originating from a given object point to focus along different, respective axes.
4. The apparatus according to claim 1 , wherein the dispersive element is configured to cause the image sensor to capture a sharp image of the optical radiation emitted from an object at a target wavelength within the range, while spreading broadband background radiation within the range across the plane.
5. The apparatus according to claim 4 , and comprising a projection assembly, which is configured to project the optical radiation at the target wavelength onto the object, so that the emitted optical radiation collected by the objective comprises the projected optical radiation that is reflected from the object.
6. The apparatus according to claim 5 , wherein the projected optical radiation comprises a predetermined radiation pattern, and wherein the sharp image captured by the image sensor comprises an image of the pattern projected onto the object.
7. The apparatus according to claim 4 , and comprising a processor, which is configured to process the sharp image captured by the image sensor while rejecting interference caused by the background radiation.
8. The apparatus according to claim 7 , wherein the processor is configured to construct a 3D map of the object by processing the sharp image.
9. The apparatus according to claim 1 , wherein the dispersive element comprises a diffractive element.
10. The apparatus according to claim 9 , wherein the diffractive element comprises a grating.
11. The apparatus according to claim 10 , wherein the grating is configured to direct a selected diffraction order onto the image sensor, and wherein the apparatus comprises an interference filter positioned between the grating and the image sensor so as to block stray diffraction orders, other than the selected diffraction order, from reaching the image sensor.
12. The apparatus according to claim 1 , wherein the dispersive element comprises a refractive element.
13. Optical apparatus, comprising:
an image sensor; and
objective optics, which are configured to collect and focus optical radiation over a range of wavelengths toward a plane of the image sensor, and which comprise a dispersive element configured so that the optics have a chromatic aberration in excess of one micrometer per nanometer of wavelength at the plane,
wherein the dispersive element has a first tilt relative to an optical axis of the objective optics, and wherein the apparatus comprises a wedged lens, which is configured to focus the optical radiation with a second tilt, opposite to the first tilt.
14. The apparatus according to claim 13 , wherein the wedged lens comprises a section of an axially-symmetrical lens.
15. A method for imaging, comprising:
collecting and focusing optical radiation over a range of wavelengths within at least one of an infrared and visible part of the optical spectrum along an optical path toward a plane of an image sensor; and
positioning a dispersive element in the optical path so that the radiation is focused with a chromatic aberration within the range in excess of one micrometer per nanometer of wavelength at the plane.
16. The method according to claim 15 , wherein the chromatic aberration causes different wavelengths in the range originating from a given object point to focus at different, respective image points along an axis perpendicular to the plane.
17. The method according to claim 16 , wherein the chromatic aberration causes different wavelengths in the range originating from a given object point to focus along different, respective axes.