SKEW MIRRORS, METHODS OF USE, AND METHODS OF MANUFACTURE

• US 20170059759A1
• Filed: 06/06/2016
• Published: 03/02/2017
• Est. Priority Date: 08/24/2015
• Status: Active Grant

• Current Assignee: Akonia Holographics, LLC (Apple Inc.)
• Original Assignee: Akonia Holographics, LLC (Apple Inc.)
• Inventors: Urness, Adam, Ayres, Mark R., Anderson, Kenneth E., Sissom, Bradley J.
• Granted Patent: US 10,180,520 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G02B 2027/0174 holographic
• CPC Class Codes: G02B 27/0172 characterised by optical features
• CPC Class Codes: G02B 5/1857 using exposure or etching means, e.g. holography, photolithography, exposure to electron or ion beams
• CPC Class Codes: G02B 5/1861 Reflection gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials G02B5/1809, G02B5/1828, G02B5/1833, G02B5/1838 and G02B5/1847 take precedence
• CPC Class Codes: G02B 5/32 Holograms used as optical elements
• CPC Class Codes: G03H 1/0248 Volume holograms
• CPC Class Codes: G03H 1/0465 Particular recording light; Beam shape or geometry G03H1/06 takes precedence
• CPC Class Codes: G03H 1/265 Angle multiplexing; Multichannel holograms G03H1/268 takes precedence
• CPC Class Codes: G03H 1/28 superimposed holograms only
• CPC Class Codes: G03H 2001/0415 for recording reflection holograms
• CPC Class Codes: G03H 2001/0439 for recording Holographic Optical Element [HOE]
• CPC Class Codes: G03H 2001/0473 Particular illumination angle between object or reference beams and hologram
• CPC Class Codes: G03H 2001/0482 Interference based printer
• CPC Class Codes: G03H 2001/2265 Achromatic holobject
• CPC Class Codes: G03H 2001/2615 in physical contact, i.e. layered holograms
• CPC Class Codes: G03H 2001/264 One hologram being a HOE
• CPC Class Codes: G03H 2001/266 Wavelength multiplexing

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 a constant reflective axis across a relatively wide range of wavelengths. In some examples, a skew mirror has a constant reflective axis 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.

Claims

1. A skew mirror comprising:

a grating structure residing in a 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 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 angle differs from the surface normal by at least 2.0 degrees;

the first wavelength differs from the second wavelength by a wave fraction equal to 0.010;

the first reflective axis angle differs from the second reflective axis angle by 0.10 degree or less; and

each of the first internal angle of incidence and the second internal angle of incidence includes multiple angles spanning a range of 4.0 degrees and being spaced at angle intervals of approximately 0.67 degree.

2. The skew mirror of claim 1, wherein the first reflective axis angle differs from the second reflective axis angle by 0.025 degree or less.

3. The skew mirror of claim 1, wherein the first wavelength differs from the second wavelength by a wave fraction equal to 0.030.

4. The skew mirror of claim 2, wherein the first wavelength differs from the second wavelength by a wave fraction equal to 0.030.

5. The skew mirror of claim 1, wherein the first incident light is offset from the first reflective axis by at least 1.0 degree.

6. The skew mirror of claim 1, wherein:

the grating structure comprises multiple volume holograms;

each of the multiple volume holograms spatially overlaps at least one other of the multiple holograms; and

the grating medium is at least 70 μ

m thick.

7. The skew mirror of claim 6, wherein:

the multiple volume holograms includes at least 9 holograms; and

each of the multiple volume holograms at least partially spatially overlaps all others of the multiple holograms.

8. The skew mirror of claim 4, wherein:

the grating structure comprises at least 9 volume holograms;

each of the at least 9 volume holograms at least partially spatially overlaps all others of the multiple holograms; and

the grating medium is at least 200 μ

m thick.

9. A method of making the skew mirror 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 such that a first recording beam internal angle relative to the skew axis is equal to 180°

minus a second recording beam angle relative to the skew axis;

each of the multiple volume holograms at least partially spatially overlaps at least one other of the multiple holograms; and

the skew axis has a skew axis angle relative to the surface normal that is substantially identical to both the first reflective axis angle and the second reflective axis angle.

10. The method of claim 9, wherein each of the multiple volume holograms at least partially spatially overlaps all others of the multiple volume holograms.

11. A method of making the skew mirror of claim 1, the method comprising:

creating the grating structure by recording a volume hologram in the grating medium, wherein;

the volume hologram 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;

the volume hologram is recorded with the first recording beam being incident upon the grating medium at a first recording beam internal angle relative to the surface normal and the second recording beam being incident upon the grating medium at a second recording beam internal angle relative to the surface normal;

the first recoding beam and the second recording beam are symmetrical about a skew axis such that an internal angle of the first recording beam relative to the skew axis is equal to 180°

minus an internal angle of the second recording beam relative to the skew axis; and

the skew axis has a skew axis angle relative to the surface normal that is substantially identical to both the first reflective axis angle and the second reflective axis angle;

changing the first recording beam internal angle relative to the surface normal while recording the volume hologram; and

changing the second recording beam internal angle relative to the surface normal while recording the volume hologram, wherein the symmetry of the first recording beam and the second recording beam about the skew axis is maintained during said changing the first and second recording beam internal angles.

12. A method of making the skew mirror of claim 1, the method comprising:

creating the grating structure by recording a volume hologram in the grating medium, wherein;

the volume hologram 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;

the volume hologram is recorded with the first recording beam being incident upon the grating medium at a first recording beam internal angle relative to the surface normal and the second recording beam being incident upon the grating medium at a second recording beam internal angle relative to the surface normal;

the first recoding beam and the second recording beam are symmetrical about a skew axis such that an internal angle of the first recording beam relative to the skew axis is equal to 180°

minus an internal angle of the second recording beam relative to the skew axis; and

the skew axis has a skew axis angle relative to the surface normal that is substantially identical to both the first reflective axis angle and the second reflective axis angle;

changing the first recording beam wavelength while recording the volume hologram; and

changing the second recording beam wavelength while recording the volume hologram, wherein the first recording beam wavelength remains the same as the second recording beam wavelength during said changing of the first and second recording beam wavelengths.

13. A method of making a skew mirror 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 such that a first recording beam internal angle relative to the skew axis is equal to 180°

minus a second recording beam angle relative to the skew axis, the skew axis having a skew axis angle relative to surface normal;

each of the multiple volume holograms at least partially spatially overlaps at least one other of the multiple holograms; and

the skew axis has a skew axis angle relative to the surface normal of at least 2.0 degrees.

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;

all of the unique first recording beam internal angles collectively span a range of at least 4.0 degrees; and

all of the unique second recording beam internal angles collectively span a range of at least 4.0 degrees.

16. The method of claim 13, wherein:

the grating structure exhibits a line segment-like Δ

n({right arrow over (k)}) distribution.

17. 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 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;

both the first reflective axis angle and the second reflective axis angle are substantially identical to the skew axis angle; and

the first wavelength differs from the second wavelength by a wave fraction equal to 0.010.

18. The method of claim 17, wherein:

the first wavelength differs from the second wavelength by a wave fraction equal to 0.030.

19. A skew mirror comprising:

a grating structure residing in a 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 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 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 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 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 incident light, the first reflected light, the second incident light, and the second reflected light have the same wavelength as each other;

the first internal angle of incidence differs from the second internal angle of incidence by 20 times Δ

θ

_B;

the first reflective axis angle differs from the surface normal by at least 2.0 degrees; and

the first reflective axis angle differs from the second reflective axis angle by 0.25 degree or less.

20. The skew mirror of claim 19, wherein:

the first reflective axis angle differs from the second reflective axis angle by 0.10 degree or less.

21. The skew mirror of claim 20, wherein:

the first reflective axis angle differs from the second reflective axis angle by 0.025 degree or less.

22. The skew mirror of claim 19, wherein:

each of the first incident light and the second incident light are offset from the first reflective axis by at least 5.0 degrees.

23. The skew mirror of claim 19, wherein:

each of the first incident light and the second incident light are offset from the first reflective axis by at least 9.0 degrees.

24. The skew mirror of claim 21, wherein:

each of the first incident light and the second incident light are offset from the first reflective axis by at least 5.0 degrees.