Optical Device Including a Buried Grating With Air Filled Voids and Method For Realising It
An optical device includes a waveguide, the waveguide having a core surrounded by a cladding, the cladding including a lower cladding, the core being placed above the lower cladding, a lateral cladding adjacent to a first and a second opposite lateral sides of the core, and an over-cladding, the over-cladding being positioned above the core and lateral cladding. The core and lateral cladding define a guiding layer. A grating structure is formed in the guiding layer, which includes a plurality of empty trenches. The over-cladding includes a cap layer, the cap layer having a first refractive index and being in contact with the grating structure. The first refractive index of the cap layer is substantially identical to the refractive index of the lateral cladding in contact with the cap layer. Additionally, the cap layer is located above the trenches and forms bridges connecting each couple of adjacent trenches of the plurality, so that voids are formed in the trenches.
1 - 39 . (canceled)
40 . An optical device comprising a waveguide, said waveguide comprising
a core surrounded by a cladding, said cladding comprising a lower cladding, the core being placed above the lower cladding, a lateral cladding adjacent to a first and a second opposite lateral sides of the core, and an over-cladding, said over-cladding being positioned above said core and lateral cladding, wherein said core and lateral cladding define a guiding layer and said over-cladding comprises a cap layer, said cap layer having a first refractive index; and
a grating structure formed in said guiding layer, said grating structure comprising a plurality of empty trenches, and said cap layer being in contact with said grating structure,
wherein said first refractive index of said cap layer is substantially identical to the refractive index of the lateral cladding in contact with said cap layer, said cap layer being located above said trenches and forming bridges connecting each couple of adjacent trenches of said plurality so that the material forming said cap layer does not enter into said trenches.
41 . The optical device according to claim 40 , wherein said over-cladding comprises an upper cladding layer on top of said cap layer.
42 . The optical device according to claim 40 , wherein said cap layer comprises silicon oxide.
43 . The optical device according to claims 40 , wherein said cap layer comprises a silicon oxide-based material doped with fluorine.
44 . The optical device according to any of claim 40 , wherein said cap layer comprises a silicon oxide-based material doped with carbon.
45 . The optical device according to claim 40 , wherein said cap layer comprises a silicon oxide-based material doped with nitrogen.
46 . Optical device according to claim 40 , wherein the thickness of said cap layer is 500 nm to 1500 nm.
47 . The optical device according to claim 46 , wherein the thickness of said cap layer is 700 nm to 1000 nm.
48 . The optical device according to claim 40 , wherein the thickness of said lower cladding is substantially equal to the thickness of said over-cladding.
49 . The optical device according to claim 40 , wherein the thickness of said over-cladding is 7 μm to 10 μm.
50 . The optical device according to claim 41 , wherein the refractive index of said upper cladding layer is substantially identical to the refractive index of said cap layer.
51 . The optical device according to claim 40 , wherein the refractive index of said lower cladding is substantially identical to the refractive index of said cap layer.
52 . The optical device according to 41 , wherein said upper cladding layer comprises silicon oxide.
53 . The optical device according to claim 41 , wherein said upper cladding layer comprises a silicon oxide-based material doped with fluorine.
54 . The optical device according to claim 41 , wherein said upper cladding layer comprises a silicon oxide-based material doped with carbon.
55 . The optical device according to claim 41 , wherein said upper cladding layer comprises a silicon oxide-based material doped with nitrogen.
56 . The optical device according to claim 40 , wherein said grating trenches are filled with air.
57 . The optical device according to claim 40 , wherein said core comprises doped silicon-based material.
58 . The optical device according to claim 40 , wherein the refractive index of said core is 1.448 to 3.5.
59 . The optical device according to claim 40 , wherein the refractive index of said cladding is 1.446 to 3.5.
60 . The optical device according to claim 40 , wherein said cap layer has low stress properties.
61 . A method for making a waveguide on a substrate, comprising the steps of:
depositing a lower cladding layer on said substrate;
forming at least one core over said lower cladding layer;
depositing a lateral cladding layer over said core and/or over said lower cladding layer, wherein said lateral cladding and said core form a guiding layer;
forming a plurality of empty trenches in said guiding layer; and
depositing in a process chamber a cap layer on top of said plurality of empty trenches using a plasma chemical vapour apparatus, said deposition step comprising the substeps of:
introducing a silicon source into the process chamber; and
selecting the power to form the plasma and the depositing pressure in such a way that the material forming said cap layer is inhibited from filling said trenches.
62 . The method according to claim 61 , wherein the deposition of said cap layer is a plasma enhanced chemical vapour deposition.
63 . The method according to claim 61 , comprising the step of introducing a fluorine source in said process chamber during said cap layer deposition step and wherein the step of depositing said cap layer comprises the sub-steps of selecting a power of 80 W to 150 W to form the plasma and selecting a depositing pressure of 900 Mtorr to 1200 Mtorr.
64 . The method according to claim 61 , wherein said cap layer comprises undoped silicon compound material and the step of depositing said cap layer comprises the sub-steps of selecting a power of 50 W to 100 W to form the plasma and selecting a depositing pressure of 600 Mtorr to 900 Mtorr.
65 . The method according to 61 , comprising the step of introducing a carbon source and/or a nitrogen source in said process chamber during said cap layer deposition step.
66 . The method according to claim 61 , wherein the temperature in said process chamber during said cap layer deposition step is 250° C. to 350° C.
67 . The method according to claim 61 , comprising the step of introducing an oxygen source in said process chamber during said cap layer deposition step.
68 . The method according to claim 67 , wherein said oxygen source is N 2 O.
69 . The method according to claim 61 , comprising the step of introducing an inert gas in said process chamber during said cap layer deposition step.
70 . The method according to claim 61 , comprising the step of depositing an upper cladding layer over said cap layer.
71 . The method according to claim 61 , wherein said silicon source comprises a silane compound.
72 . The method according to claim 63 , wherein said fluorine source is CF 4 .
73 . The method according to claim 61 , comprising the step of terminating said cap layer deposition process when the thickness of said cap layer is 500 nm to 1500 nm.
74 . The method according to claim 73 , comprising the step of terminating said cap layer deposition process when the thickness of said cap layer is 700 nm to 1000 nm.
75 . The method according to claim 70 , comprising the step of terminating the deposition process of said upper cladding layer when the sum of the thickness of said cap layer and of said upper cladding layer is substantially equal to the thickness of said lower cladding layer.
76 . The method according to claim 61 , comprising the step of selecting said power to form the plasma and said deposition pressure and the temperature of the deposition chamber in such a way that the refractive index of said cap layer is substantially identical to the refractive index of said lateral cladding layer.
77 . The method according to claim 61 , comprising the step of selecting said power to form plasma in such a way that said cap layer has low stress properties.
78 . An optical device containing a waveguide made according to the method of claim 61 .