Skew mirrors, methods of use, and methods of manufacture

Patent metadata

Field	Value
Publication number	US-10185069-B2
Application number	US-201715849532-A
Country	US
Kind code	B2
Filing date	Dec 20, 2017
Priority date	Aug 24, 2015
Publication date	Jan 22, 2019
Grant date	Jan 22, 2019

Abstract

An optical reflective device referred to as a skew mirror, having a reflective axis that need not be constrained to surface normal, is described. Examples of skew mirrors are configured to reflect light about substantially constant reflective axes across a relatively wide range of wavelengths. In some examples, a skew mirror has substantially constant reflective axes across a relatively wide range of angles of incidence. Exemplary methods for making and using skew mirrors are also disclosed. Skew mirrors include a grating structure, which in some examples comprises a hologram.

First claim

We claim:

1. Apparatus comprising:
a grating medium;
a grating structure residing in the grating medium, wherein:
the grating structure is configured to reflect first incident light, the first incident light being incident upon the grating medium at a specific site and having a first wavelength and a first internal angle of incidence relative to a grating medium surface normal;
the first incident light is principally reflected by the grating medium as first reflected light, the first reflected light having the first wavelength and a first internal angle of reflection relative to the surface normal;
the first incident light and the first reflected light are bisected by a first reflective axis having a first reflective axis angle relative to the surface normal;
the grating structure is further configured to reflect second incident light, the second incident light being incident on the grating medium at the specific site and having a second wavelength and a second internal angle of incidence relative to the surface normal;
the second incident light is principally reflected by the grating medium as second reflected light, the second reflected light having the second wavelength and a second internal angle of reflection relative to the surface normal;
the second incident light and the second reflected light are bisected by a second reflective axis having a second reflective axis angle relative to the surface normal;
the first internal angle of incidence is the same as the second internal angle of incidence;
the first reflective axis is non-zero relative to the surface normal;
the first wavelength differs from the second wavelength; and
the first reflective axis angle differs from the second reflective axis angle.

2. The apparatus of claim 1 , wherein the first reflective axis angle differs from the second reflective axis angle by 0.25 degrees or less.

3. The apparatus of claim 2 , wherein the first incident light is offset from the first reflective axis by at least 1.0 degree.

4. The apparatus of claim 1 , wherein the first wavelength differs from the second wavelength by a wave fraction of at least 0.005.

5. The apparatus of claim 1 , wherein:
the grating structure comprises a plurality of volume holograms;
each of the volume holograms in the plurality of volume holograms spatially overlaps at least one other volume holograms in the plurality of volume holograms; and
the grating medium is at least 70 μm thick.

6. The apparatus of claim 5 , wherein:
the plurality of volume holograms includes at least four holograms; and
each of the volume holograms in the plurality of volume holograms at least partially spatially overlaps all others of the plurality of volume holograms.

7. The apparatus of claim 6 , wherein adjacent |ΔK G | for the at least four holograms has a mean value that resides between 5.0×10 3 and 1.0×10 7 radians per meter (rad/m).

8. The apparatus of claim 1 , wherein:
the grating structure comprises at least 9 volume holograms;
each of the at least 9 volume holograms at least partially spatially overlaps at least one other of the at least 9 volume holograms; and
the grating medium is at least 200 μm thick.

9. The apparatus of claim 1 , wherein the first reflective axis differs from the surface normal by at least 4.0 degrees.

10. The apparatus of claim 9 , wherein the first reflective axis differs from the surface normal by at least 9.0 degrees.

11. A method of making the apparatus of claim 1 , the method comprising:
creating the grating structure by recording multiple volume holograms in the grating medium, wherein:
each of the multiple volume holograms is recorded using a first recording beam and a second recording beam, each of the first and second recording beams including a collimated, plane wave beam, and the first recording beam having the same wavelength as the second recording beam;
each of the multiple volume holograms is recorded with the first recording beam being incident upon the grating medium at a unique first recording beam internal angle relative to the surface normal and the second recording beam being incident upon the grating medium at a unique second recording beam internal angle relative to the surface normal;
each of the multiple volume holograms is recorded with the first recording beam and the second recording beam being symmetrical about a skew axis;
each of the multiple volume holograms at least partially spatially overlaps at least one other of the multiple holograms;
the skew axes of the multiple volume holograms have substantially constant skew angles relative to the surface normal; and
the skew axes of the multiple volume holograms have a mean skew angle that is substantially identical to both the first reflective axis angle and the second reflective axis angle.

12. The method of claim 11 , wherein each of the multiple volume holograms at least partially spatially overlaps all others of the multiple volume holograms.

13. A method of making an apparatus, the method comprising:
creating a grating structure in a grating medium by recording multiple volume holograms in the grating medium, wherein:
each of the multiple volume holograms is recorded using a first recording beam and a second recording beam, each of the first and second recording beams including a collimated, plane wave beam, and the first recording beam having a same wavelength as the second recording beam;
each of the multiple volume holograms is recorded with the first recording beam being incident upon the grating medium at a unique first recording beam internal angle relative to a surface normal of the grating medium and the second recording beam being incident upon the grating medium at a unique second recording beam internal angle relative to the surface normal;
each of the multiple volume holograms is recorded with the first recording beam and the second recording beam being symmetrical about a skew axis, the skew axis having a skew axis angle relative to the surface normal;
each of the multiple volume holograms at least partially spatially overlaps at least one other of the multiple holograms; and
the skew axes of the multiple volume holograms are substantially constant and have a non-zero mean skew axis angle relative to the surface normal.

14. The method of claim 13 , wherein each of the multiple volume holograms at least partially spatially overlaps all others of the multiple volume holograms.

15. The method of claim 14 , wherein:
the multiple volume holograms includes at least 9 holograms; and
all of the unique first recording beam internal angles collectively span a range of at least 6.4 degrees.

16. The method of claim 15 , wherein:
adjacent |ΔK G | for the at least 9 holograms has a mean value that resides between 5.0×10 3 and 1.0×10 7 rad/m.

17. The method of claim 15 , wherein:
adjacent |ΔK G | for the at least 9 holograms has a mean value that resides between 1.0×10 4 and 1.0×10 6 rad/m.

18. The method of claim 13 , wherein:
the grating structure is configured to reflect first incident light, the first incident light being incident upon the grating medium at a specific site and having a first wavelength and a first internal angle of incidence relative to grating medium surface normal;
the first incident light is principally reflected by the grating medium as first reflected light, the first reflected light having the first wavelength and a first internal angle of reflection relative to the surface normal;
the first incident light and the first reflected light are bisected by a f

Assignees

• Akonia Holographics Llc
• Akonia Holographics Llc

Inventors

• Ayres Mark R
• Anderson Kenneth
• Urness Adam
• Schlottau Friso

Classifications

• G03H2001/2265

  Achromatic holobject · CPC title

• G03H2001/266

  Wavelength multiplexing · CPC title

• G03H2001/0439

  for recording Holographic Optical Element [HOE] · CPC title

• G03H1/0248

  Volume holograms · CPC title

• G03H2001/264

  One hologram being a HOE · CPC title