Diffractive optical elements
Techniques for designing diffractive optical elements (DOEs) such as diffusers and other optical beam shaping elements can include designing a DOE unit cell on a smaller area than the overall area of the DOE, and then distributing the unit cell across the entire surface for the DOE. Height translations are introduced for at least some of the unit cells distributed across the surface, where the height translations correspond to respective phase translations for the intended operational wavelength of the DOE. In some instances, phase wrapping is introduced to translate the height variations among the unit cells into unit cells having sub-unit structures whose heights fall within a range that corresponds to a specified phase range at the operational wavelength.
1. An apparatus comprising a diffractive optical element comprising:
a plurality of unit cells distributed over a common plane and composed of an optical material, each unit cell within the plurality of unit cells including a respective plurality of subunit cells, wherein the subunit cells are arranged to cause an optical effect to incident light of a predetermined operational wavelength, and wherein each of the subunit cells in each particular one of the unit cells has a respective subunit height that differs from the respective heights of adjacent ones of the subunit cells in the same unit cell,
wherein the plurality of unit cells includes at least one base unit cell and other unit cells that are not a base unit cell, and wherein each of the unit cells that is not a base unit cell is a phase-wrapped version of the base unit cell.
2. The apparatus of claim 1 , wherein a difference in height between any two of the subunits in the diffractive optical element corresponds to a respective phase shift of no more than 2π at the operational wavelength.
3. The apparatus of claim 2 , wherein each of the respective phase shifts is a respective whole number multiple of (½)π at the operational wavelength.
4. The apparatus of claim 1 , wherein the subunit heights span four discrete levels relative to the common plane.
5. The apparatus of claim 1 , wherein the subunit heights span eight discrete levels relative to the common plane.
6. The apparatus of claim 1 , wherein the subunit heights span sixteen discrete levels relative to the common plane.
7. The apparatus of claim 1 wherein the respective heights of adjacent ones of the subunit cells that are in the same unit cell differ by an amount that corresponds to a respective phase shift that is equal to an integer multiple of (½)π at the operational wavelength.
8. The apparatus of claim 1 , wherein the optical effect is a substantially diffuse illumination.
9. The apparatus of claim 1 further comprising:
a light emitting component,
wherein the light emitting component is mounted to direct the incident light to the plurality of unit cells, the light emitting component being operable to emit the incident light of the operational wavelength.
10. The apparatus of claim 9 , wherein the light emitting component includes at least one of a light-emitting diode, a laser diode, or a vertical-cavity surface-emitting laser.
11. The apparatus of claim 9 further comprising:
a light-sensitive component,
wherein the light-sensitive component is operable to collect reflected light from a scene or object, wherein the reflected light is generated by illuminating the scene or object with the optical effect.
12. The apparatus of claim 1 wherein the operational wavelength is in an infrared part of the electromagnetic spectrum.