Diffractive Optical Elements (DOE)
What are DOE’s
Diffractive Optical Elements (DOE’s) are thin optical microstructured components designed to utilize light propagation physics to create a desired light pattern, by “encoding” phase information in the beam. This phase distribution leads to constructive and destructive self-interference, forming the pattern at the required distance. Contrary to LED-based, mask-type pattern-forming devices which have inherent optical power loss, DOE uses light physics to redirect intensity from where it’s not required to where it is, therefore minimizing power losses. A DOE can also be designed to act as a lens, or function as a lens combined with pattern generator.
Capabilities and limitations
- DOE’s are designed for a specific wavelength, and can function within a certain spectral range around it.
- The angular span a DOE can project can reach above 90 degrees.
- A DOE can be designed to project to a large distance (tens of cm and above) or a finite distance (few mm). The pattern would appear sharp within a range of distances around the nominal distance (focal plane).
- A single DOE can also be designed to project patterns at objects located at different distances or inclined planes.
DOE’s are designed to work with coherent light sources, commonly with edge-emitting laser diodes and VCSELs. Some DOE’s are designed to have a collimated beam as input, therefore there would be some optics between light source and DOE. Some DOE’s are positioned directly after light source, e.g. edge-emitter laser chip or VCSEL chip.
A DOE pattern projector is designed to deliver a sharp pattern over a range of distances. For certain applications, such as keyboard projection, it is advantageous to design the DOE to project onto a tilted plane.
In some applications such as automotive, it is required to project the pattern at an oblique angle.
It is also possible to design a DOE to project multiple patterns, each focused to different distance.