METHOD TO OPTIMIZE A LIGHT COUPLING WAVEGUIDE
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Abstract
The present invention concerns a method for constructing a light coupling system wherein a grating is manufactured on the surface of a multimode waveguide and defines the entrance of the waveguide for an incident light beam, said grating comprising a repetition of patterns. The grating is defined by a set of parameters comprising: •grating period (P), separating two adjacent patterns, •grating depth (d) between the highest and the lowest point of the pattern, •incident angle mean value (θ) of the incident light with respect to the waveguide. The method comprises a step of optimization of the set of parameters to obtain an optimized second set of parameters, in order to obtain a transmission efficiency (Ce) of the incident light into said waveguide for the first or the second diffractive order exceeding 35% for unpolarized light, or exceeding 50% for polarized light, at a given wavelength of the incident light.
22 Citations
40 Claims
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1-16. -16. (canceled)
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17. A method for constructing a light coupling system wherein a grating is manufactured on the incident light surface of a multimode waveguide, said grating defining the entrance of the multimode waveguide for an incident light beam, said grating comprising a repetition of patterns, said method comprising a step of choosing a first set of parameters comprising
wavelength distribution of the incident light to be transmitted by the multimode waveguide, said wavelength distribution being at least 40 nm polarized or unpolarized nature of said incident light, incident angle standard deviation of the incident light with respect to the multimode waveguide, shape of the patterns, which is designed to have its local surface normal (Ns), in any location of said shape, making an angle (α - ) with respect to the average normal (N) of the surface of the multimode waveguide, said angle (α
) being comprised between α
=−
90° and
α
=90°
, refractive index (n1) of the medium surrounding the multimode waveguide,multimode waveguide refractive index (n3), said grating being defined by a second set of parameters comprising grating period (P), separating two adjacent patterns, grating depth (d) between the highest and the lowest point of the pattern, incident angle mean value (θ
) of the incident light with respect to the normal to said entrance of the multimode waveguide,said method comprises a step of optimization of the second set of parameters to obtain an optimized second set of parameters, said step of optimization being performed to obtain a transmission efficiency (Ce) of the incident light crossing through the grating into said multimode waveguide for the first or the second diffractive order exceeding 35% for unpolarized light, or exceeding 50% for polarized light, over at least the wavelength distribution of the incident light beam as defined in the chosen first set of parameters, said grating having a length (D) measured on the incident light surface of the multimode waveguide in the direction of the diffracted beam, said length (D) being related to the thickness (WT) of the multimode waveguide and to the angle β
between the multimode waveguide surface normal and the light beam inside the multimode waveguide, said length D being defined by the following inequality;
D≦
2·
WT·
tanβsaid method comprising a step of manufacturing the grating on the surface of the multimode waveguide according to the chosen first set of parameters and to said optimized second set of parameters. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40)
wherein said grating has a length (D), measured on the incident light surface of said multimode waveguide in the direction of the diffracted beam, said length (D) being related to the thickness (WT) of the multimode waveguide and to the angle β
between the multimode waveguide surface normal and the light beam inside said multimode waveguide, said length D being defined by the following inequality;
D≦
2·
WT·
tanβand said set of parameters is optimized to obtain a transmission efficiency (Ce) of the incident light beam into said waveguide for the first or the second diffractive order that exceeds 35% for unpolarized light or that exceeds 50% for polarized light over at least the wavelength distribution of the incident light beam as defined in the chosen first set of parameters, said incident light beam having a wavelength distribution being at least 40 nm.
- ) with respect to the average normal (N) of the surface of the multimode waveguide, said angle (α
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24. The light coupling system of claim 23, wherein the multimode waveguide is made of Glass, or Quartz, or Polymer, or SolGel.
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25. The light coupling system of claim 23, wherein the multimode waveguide is made of Polycarbonate (PC) or Polymethyl methacrylate (PMMA) or Polyethylene terephthalate (PET).
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26. The light coupling system according to claim 23, wherein the shape of the pattern is rectangular and wherein the fill factor (A/P), defined as the width of a rectangle (A) compared to the grating period (P), is comprised between 10% and 90%, preferably between 40% and 60%.
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27. The light coupling system according to claim 23, comprising
an enhancement layer with refractive index n2, wherein n2-n1 is greater or equal to 0.3, preferably greater or equal to 0.5 preferably greater or equal to 0.8, and wherein n2-n3 is greater or equal to 0.3, preferably greater or equal to 0.5 preferably greater or equal to 0.8, and wherein said enhancement layer thickness (L) is optimized as an additional parameter in said parameter set in order to obtain a transmission efficiency for the first or the second diffractive order exceeding 50% preferably exceeding 70% preferably exceeding 90% at a given wavelength of the incident light beam. -
28. The light coupling system according to claim 27, wherein the enhancement layer comprises at least one of ZnS, or TiO2, or HfO2, or Ta2O5, or ZrO2, or AlN, or Al2O3 or ZnO or any combination of these materials.
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29. Light coupling system according to claim 23, wherein said grating depth (d) between the highest and the lowest point of the pattern is comprised between 10 nm and 100 nm, preferably between 20 nm and 400 nm.
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30. Light coupling system according to claim 27, wherein said grating depth (d) between the highest and the lowest point of the pattern is comprised between 10 nm and 100 nm, preferably between 20 nm and 400 nm.
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31. Light coupling system according to claim 23, wherein the grating is manufactured on the waveguide top surface and wherein the waveguide thickness (WT) is larger or equal to 1 micron, preferably larger or equal to 10 microns, preferably larger or equal to 0.5 mm.
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32. Light coupling system according to claim 27, wherein the grating is manufactured on the waveguide top surface and wherein the waveguide thickness (WT) is larger or equal to 1 micron, preferably larger or equal to 10 microns, preferably larger or equal to 0.5 mm.
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33. Light coupling system according to claim 23, wherein the thickness (L) of the enhancement layer is comprised between 10 nm and 500 nm, preferably between 100 nm and 200 nm.
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34. Light coupling system according to claim 27, wherein the thickness (L) of the enhancement layer is comprised between 10 nm and 500 nm, preferably between 100 nm and 200 nm.
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35. Light coupling system according to claim 23, for coupling light with a wavelength comprised between 400 nm and 700 nm, wherein the grating period (P), separating two adjacent patterns, is comprised between 230 nm and 840 nm.
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36. Light coupling system according to claim 27, for coupling light with a wavelength comprised between 400 nm and 700 nm, wherein the grating period (P), separating two adjacent patterns, is comprised between 230 nm and 840 nm.
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37. Light coupling system according to claim 23, for coupling light with a wavelength comprised between 700 nm and 2500 nm, wherein the grating period (P), separating two adjacent patterns, is comprised between 580 nm and 3000 nm.
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38. Light coupling system according to claim 27, for coupling light with a wavelength comprised between 700 nm and 2500 m, wherein the grating period (P), separating two adjacent patterns, is comprised between 580 nm and 3000 nm.
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39. Light coupling system according to claim 23, for coupling light with a wavelength comprised between 250 nm and 400 nm, wherein the grating period (P), separating two adjacent patterns, is comprised between 180 nm and 560 nm.
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40. Light coupling system according to claim 27, for coupling light with a wavelength comprised between 250 nm and 400 nm, wherein the grating period (P), separating two adjacent patterns, is comprised between 180 nm and 560 nm.
Specification