High efficiency optical diffraction device

• US 7,454,103 B2
• Filed: 04/22/2005
• Issued: 11/18/2008
• Est. Priority Date: 04/23/2004
• Status: Active Grant

• Current Assignee: Olivier M. Parriaux
• Original Assignee: Olivier M. Parriaux
• Inventors: Parriaux, Olivier M.
• Primary Examiner(s): Connelly-Cushwa; M. R.
• Assistant Examiner(s): Rahll; Jerry T
• Application Number:
  US11/568,135
• Publication Number:
  US 20080138013A1
• Time in Patent Office: 1,306 Days
• Field of Search: 385/37, 359/369
• US Class Current: 385/37
• CPC Class Codes: G02B 2006/12164 Multiplexing; Demultiplexing
• CPC Class Codes: G02B 5/1814 structurally combined with one or more further optical elements, e.g. lenses, mirrors, prisms or other diffraction gratings G02B5/189 takes precedence
• CPC Class Codes: G02B 5/1828 having means for producing variable diffraction controlling the direction of light by means of one or more diffracting elements G02B26/0808; acousto-optical elements G02F1/11, G02F1/33; electro- or magneto-optical diffraction G02F1/292, G02F1/2955
• 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 5/289 Rugate filters
• CPC Class Codes: G02B 5/32 Holograms used as optical elements
• CPC Class Codes: G02B 6/0016 Grooves, prisms, gratings, scattering particles or rough surfaces
• CPC Class Codes: G02B 6/124 Geodesic lenses or integrated gratings
• CPC Class Codes: G02B 6/34 utilising prism or grating G02B6/293 takes precedence
• CPC Class Codes: G03H 1/0408 Total internal reflection [TIR] holograms, e.g. edge lit or substrate mode holograms
• CPC Class Codes: G03H 2250/42 Reflective layer G03H2250/36 takes precedence

Abstract

Lightwave diffraction device formed of a dielectric layer (4), a mirror (12) arranged at the lower face (10) of said layer, a semi-reflective structure (13) arranged at the upper face (100) of said layer, and a diffractive structure (8) arranged in said layer or on its faces. The height (H) of the layer is chosen so as to substantially satisfy the resonance condition for at least one leaky mode propagating in said layer for at least one given incident wave having a determined wavelengthλ and a determined incidence angle θ_c. Next, the diffractive structure is arranged so that there is no propagating positive diffracted order, and so that all negative orders other than the −1^st propagating order have zero or a relatively small diffraction efficiency, the reflected −1^st order propagating in a direction non-parallel to the incident wave. This diffraction device allows a high diffraction efficiency of up to 100% for the −1^st order.

Claims

1. An optical diffraction device comprising:

a layer defining a general plane and arranged for propagating locally at least one local leaky mode which is excited by refraction of a locally incident electromagnetic wave having a given vacuum wavelength λ and

reaching said layer from a cover medium of refractive index n_c under a local incidence angle θ

_c relative to the normal to said general plane, said layer having a local mean thickness H and a local refractive index profile n_f substantially satisfying the resonance condition for said at least one local leaky mode;

a highly reflective structure at the lower side of said layer for said at least one local leaky mode;

a diffractive element in the form of a corrugation or/and of an index modulation arranged in, or/and at the upper side of, or/and above, or/and at the lower side of, or/and under said layer for diffracting said locally incident electromagnetic wave into the reflected −

1^st order in a direction non-parallel to the direction of this locally incident electromagnetic wave;

said locally incident electromagnetic wave reaching said layer with a local incidence direction defining together with said normal to the general plane a local incidence plane, said diffractive element having a local grating vector K_g making an angle β

with said local incidence plane which is larger than or equal to zero and smaller than or equal to 90 degrees, the diffractive element having, where said locally incident electromagnetic wave reaches said layer, no positive propagating diffraction order and all negative propagating orders with substantially zero diffraction efficiency except the −

1^st order when said angle β

is smaller than 90 degrees and all propagating diffraction orders except the two first diffraction orders with substantially zero diffraction efficiency when said angle β

is equal to 90 degrees, wherein the diffraction device comprises a semi-reflective structure for said locally incident electromagnetic wave which is arranged between the upper side of said layer and said cover medium, this semi-reflective structure being arranged for increasing the −

1^st order diffraction efficiency when said angle β

is smaller than 90 degrees and the two first diffraction order efficiencies when said angle β

is equal to 90 degrees.

2. A device according to claim 1 wherein said layer has a local refractive index n_f and a local mean thickness H substantially satisfying the leaky mode dispersion equation

kH(n_f²−

n_c² cos² α

)^1/2=m_lmπ

−

φ

/2−

φ

_c/2,

where k=2π

/λ

, m_lm is an integer number larger or equal to zero, α

=π

/2−

φ

_c, φ and

φ

_c are the reflection phase shifts at the lower side and at the upper side of said layer.

3. The device according to claim 1 wherein said index profile n_f of said layer is continuous or/and varies by index steps.

4. The device according to claim 1 wherein the sole propagating negative diffraction order in at least a region of said diffractive element is the −

1^st order.

5. The device according to claim 4 wherein at least a region of said diffractive element is formed by a grating of substantially sinusoidal profile and small amplitude, or of substantially sinusoidal index modulation with a small amplitude.

6. The device according to claim 4 wherein the refractive index of the cover medium is larger than the refractive index of said layer and where the angle of incidence θ

_c of said electromagnetic wave is smaller than arcsin(n_f/n_c).

7. The device according to claim 1 wherein at least a region of said diffractive element is formed by a grating of substantially sinusoidal profile and small amplitude, or of substantially sinusoidal index modulation with a small amplitude.

8. The device according to claim 7 wherein said diffraction grating is created by a surface acoustic wave generated by a transducer.

9. The device according to claim 7 wherein said diffractive element is generated by an electrically actuated viscoelastic material.

10. The device according to claim 1 wherein the reflective structure is a resonant waveguide grating.

11. The device according to claim 1 wherein the semi-reflective structure is a resonant waveguide grating.

12. The device according to claim 1 wherein said semi-reflective structure is formed by a single high refractive index layer.

13. The device according to claim 1 wherein said semi-reflective structure is formed by a multilayer.

14. The device according to claim 13 wherein said semi-reflective structure is formed by a resonance broadening chirped multilayer.

15. The device according to claim 1 wherein said semi-reflective structure comprises a transparent electrode.

16. The device according to claim 1 wherein said semi-reflective structure is formed by a low index trench.

17. The device according to claim 1 wherein said semi-reflective structure is formed by a thin metallic film.

18. The device according to claim 1 wherein the reflective structure between said layer and said substrate is a total internal reflector for said at least one local leaky mode and/or for the transmitted −

1^st diffraction order in said layer.

19. The device according to claim 1 wherein the difference between the reflection phase shift sum φ

+φ

_c of TE and TM polarizations is an integer multiple of 2π

, φ and

φ

_c being the reflection phase shifts at the lower side and at the upper side of said layer.

20. The device according to claim 1 wherein said semi-reflective structure or said reflective structure is formed by two phase shifted corrugations.

21. The device according to claim 1 wherein the thickness of said layer has spatial variations in said general plane.

22. The device according to claim 1 wherein the transmitted −

1^st diffracted order in said layer corresponds to a leaky mode of this layer of order and/or of polarization differing from said leaky mode.

23. The device according to claim 1 performing as a high visibility hologram comprising a polymer cover medium, a high index leaky mode field enhancement semi-reflective structure, said layer, a metal mirror and a diffractive element embossed at the surface of substrate.

24. The device according to claim 1 performing as a notch filter filtering out diffracted waves and wherein the cover medium has a refractive index larger than the one of the substrate and incident wave experiences total internal reflection at the interface between layer and substrate.

25. The device according to claim 1 performing as a dispersion compensator and comprising two opposite optical diffraction elements.

26. The device according to claim 1 performing as an external mirror rendering a wide stripe semiconductor laser single transverse mode and comprising a substrate with two oblique side mirrors, said mirror, said layer and said semi-reflective structure being normal to the wide stripe laser axis.

27. The device according to claim 1 performing as a lighting window or back illumination panel comprising a finite thickness cover medium and a mirror, wherein the incident wave propagates in zigzags in this cover medium and is diffracted out of said cover medium, the average thickness H of said layer propagating at least one leaky mode at the spectral components composing the diffracted wave.

28. The device according to claim 1 performing as a high efficiency diffractive element in a monolithic optical interconnect wherein the incident beam propagates in zigzags in the cover medium having a finite thickness, the diffractive optical element associated with said layer being placed at any side of the said finite thickness cover medium.

29. The device according to claim 1 performing as a high efficiency input and output port of an optical back-plane wherein incident waves propagating in a thick waveguide on a substrate reach output/input port comprising a mirror, a leaky mode propagating layer and a grating diffracting a beam essentially normally to its general plane.

30. The device according to claim 1 performing as an electro-optic frequency sweeper in a Littman-Metcalf mounting comprising a lens and a spatial light modulator.

31. The device according to claim 1 performing as a displacement sensor and comprising a grating rule with sinusoidal grating profile, a leaky mode propagating layer, a mirror and a swapping grating element with sinusoidal grating profile, a leaky mode propagating layer and a mirror.

32. The device according to claim 1 performing as a high efficiency dynamic hologram wherein said layer is composed of a light activated photochromic or photorefractive material.

33. The device according to claim 1 wherein said layer is composed of a liquid crystal or polymer dispersed liquid crystal actuated by a metal electrode and a transparent electrode.

34. The device according to claim 1 wherein said diffraction grating is created by a surface acoustic wave generated by a transducer.

35. The device according to claim 1 wherein the sole propagating negative diffraction orders in at least a region of said diffractive element are the −

1^st and −

2^nd orders, the −

2^nd order having a diffraction efficiency substantially equal to zero.

36. The device according to claim 35 wherein the diffractive element in said at least a region is a binary grating made of substantially rectangular grooves of substantially 50/50 line/space ratio and relatively shallow depth.

37. The device according to claim 1 wherein said diffractive element is generated by an electrically actuated viscoelastic material.

38. The device according to claim 1 performing as a disk pickup head wherein said diffractive element defines a focusing grating.

39. The device according to claim 1 performing light extraction from a light emitting layer into an external medium, said light emitting layer defining said cover medium and being arranged between this device and said external medium.

40. The device according to claim 1 performing from an external medium pump light trapping into a lasing or amplifying layer, said lasing or amplifying layer defining said cover medium and being arranged between this device and said external medium.

41. The device according to claim 1 performing as a high efficiency axicon in reflection wherein said diffractive element is a grating of non intersecting closed grating lines and is arranged so that an essentially collimated incident beam experiences conical diffraction.