Holographic filter with a wide angular field of view and a narrow spectral bandwidth
View Patent ↗A holographic optical filter that includes an optical recording medium for storing several multiplexed reflection holograms that are formed by successive interference between two or more collimated object beams with a common collimated reference beam. The object beams are incident to the recording material at a series of angles chosen to provide reflection efficiency over the desired filed of view at the specified wavelength.
1. A holographic optical filter, comprising:
an optical recording medium that stores a multiplexed reflection hologram, the hologram being formed by successive interference between two or more collimated object beams and a common collimated reference beam,
the object beams being coherent with the common reference beam and being incident to the optical recording medium at a series of angles chosen to provide reflection efficiency over a selected angular field of view, wherein any light with the same wavelength as the object beams that is incident to the optical recording medium is reflected in a direction parallel to the common reference beam.
2. The holographic filter of claim 1 , wherein any light with wavelength different from the object beams that is incident to the optical recording medium is reflected in a direction at an angle different from that of the common reference beam.
3. The holographic filter of claim 1 , further comprising a filter that selects a reflected light signal of a desired wavelength and blocks reflected light of undesired wavelengths.
4. The holographic filter of claim 3 , wherein the filter is a spatial filter.
5. The holographic filter of claim 4 , wherein the spatial filter includes a lens that focuses the reflected light.
6. The holographic filter of claim 4 , wherein the spatial filter includes a pin hole.
7. The holographic filter of claim 1 , wherein the angular field of view includes angles in a single incident plane.
8. The holographic filter of claim 1 , wherein the angular field of view includes a cone of incident angles.
9. A method of forming a holographic filter, comprising:
providing an holographic recording medium; and
transmitting two or more collimated object beams at the medium from one side of the medium while transmitting a common collimated reference beam from an opposite side of the medium in a manner in which each of the multiple object beams and the reference beam forms a hologram within the holographic recording medium by successive interference of the respective object beam and the reference beam so that the interference patterns are superimposed to form a multiplexed holographic filter, the multiplexed hologram configured to reflect light of a specified wavelength from at least one angle along a common reference beam direction.
10. The method of claim 9 , wherein the multiple object beams are incident to the medium over a series of angles chosen to provide reflection efficiency over the desired angular field of view.
11. The method of claim 10 , wherein the angular field of view includes angles in a single incident plane.
12. The method of claim 10 , wherein the angular filed of view includes a cone of incident angles.
13. The method of claim 9 , wherein the holographic recording medium is made of a photopolymerizable material.
14. The method of claim 13 , wherein the holographic recording medium has a thickness of about between 50 μm and 5 mm.