Phase gratings with odd symmetry for high-resolution lensed and lensless optical sensing
A sensing device with an odd-symmetry grating projects near-field spatial modulations onto a closely spaced photodetector array. Due to physical properties of the grating, the spatial modulations are in focus for a range of wavelengths and spacings. The spatial modulations are captured by the array, and photographs and other image information can be extracted from the resultant data. Used in conjunction with a converging optical element, versions of these gratings provide depth information about objects in an imaged scene. This depth information can be computationally extracted to obtain a depth map of the scene.
1. A camera for sensing incident light over a wavelength band of interest, the camera comprising:
a photodetector array in a path of the incident light; and
a phase grating overlying the photodetector array and disposed in the path to illuminate a pattern area at the photodetector array, the phase grating including:
curved boundaries of odd symmetry, intersecting to form a spiral, separating stepped features on opposite sides of each boundary, the stepped features on the opposite sides of each boundary offset from the array by one half of one of the wavelengths of the wavelength band of interest, plus an integer number of the one of the wavelengths, to produce curtains of destructive interference that extend to the photodetector array.
2. The camera of claim 1 , the phase grating having a minimum separation from the photodetector array of no more than 400 times a maximum wavelength of interest.
3. The camera of claim 1 , the features on opposite sides of each boundary including at least two segments of different widths in a dimension perpendicular to the path.
4. The camera of claim 1 , the photodetector array operable to capture a pattern of the curtains from a scene incident the phase grating, the camera further comprising a processor coupled to the photodetector to invert the pattern to recover an image of the scene.
5. The camera of claim 1 , wherein the phase grating comprises tessellated ensembles of sub-elements operable to induce the curtains, wherein the sub-elements extend between adjacent ones of the ensembles.
6. The camera of claim 1 , wherein the wavelength band of interest comprises the visible spectrum.
7. The camera of claim 1 , further comprising an optical element operable to converge incident light from a point source.
8. The camera of claim 1 , the stepped features are separated by spacings that increase away from a center of the spiral.
9. The camera of claim 8 , wherein the spacings include discontinuities.
10. The camera of claim 1 , wherein the curtains extend toward the photodetector array over a distance greater than ten times the one of the wavelengths.
11. The camera of claim 1 , wherein the curtains extend toward the photodetector array over a distance greater than twenty times the one of the wavelengths.
12. A camera for sensing incident light over a wavelength band of interest, the camera comprising:
a photodetector array in a path of the incident light; and
a phase grating overlying the photodetector array and disposed in the path to illuminate a pattern area at the photodetector array, the phase grating including:
curved boundaries of odd symmetry separating stepped features on opposite sides of each boundary, the stepped features on the opposite sides of each boundary offset from the array by one half of one of the wavelengths of the wavelength band of interest, plus an integer number of the one of the wavelengths, to produce curtains of destructive interference that pattern spiral point spread functions on the photodetector array.
13. The camera of claim 12 , the features on opposite sides of each boundary including at least two segments of different widths in a dimension perpendicular to the path.
14. The camera of claim 12 , the stepped features are separated by spacings that increase away from a center of the spiral.
15. The camera of claim 14 , wherein the spacings include discontinuities.
16. The camera of claim 12 , wherein the curtains extend toward the photodetector array over a distance greater than twenty times the one of the wavelengths.