Method of manufacturing planar optical waveguides
First Claim
1. The method of manufacturing planar optical waveguides, which comprisesforming upon a substrate selected from a group consisting of silicon and silica a lower cladding layer comprising silica having a first index of refraction,forming upon the lower cladding layer at least one waveguiding ridge comprising silica having a second index of refraction which is higher than said first index of refraction,forming on said at least one waveguide ridge and on exposed regions of the lower cladding layer an upper cladding layer comprising particles of silica having an index of refraction which is lower than said second index of refraction, said upper cladding layer is formed by depositing a layer of soot particles comprising silica and sintering the soot particles in a helium-containing atmosphere into a glassy layer,wherein, said sintering is conducted by heating the soot layer in a helium atmosphere containing a gaseous additive selected from the group consisting of BCl3 and BF3 at temperatures of from 800°
- to 900°
C., sintering the heated soot layer at a temperature ranging from 1000°
to 1100°
C. in absence of said gaseous additive, annealing the sintered structure in a steam-and-oxygen atmosphere at a temperature of from 1000°
to 1150°
C., and allowing the annealed layer to cool to room temperature.
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Abstract
A novel planar waveguide structure has been constructed by sintering substantially pure SiO2 layers in a He2 /BCl3 atmosphere. This results in the generation of a liquid phase of substantially lower viscosity than that of the deposited silica by itself. Since viscous sintering is enhanced by the presence of this liquid, consolidation occurs at lower temperature, e.g. 1000°-1100° C., than those used in the prior art, e.g. 1350°-1500° C. Much of the B2 O3 remains unreacted with the silica particles it helps to sinter, acting like a flux to bring about consolidation. This remaining B2 O3 is removed at the conclusion of the consolidation procedure by steam treatment at temperatures of 900°-1100° C. Some boron is incorporated into the silica layer, changing its CTE without substantially increasing its index. Thus, this method improves both structure and processing of planar waveguides by reducing the processing temperature and producing a glass which does not bow the substrate and essentially eliminates birefringence resulting in polarization dependent losses. This greatly benefits sophisticated circuits such as those intended for wavelength diversion multiplexing and allows narrow and precisely positional pass bands.
21 Citations
18 Claims
-
1. The method of manufacturing planar optical waveguides, which comprises
forming upon a substrate selected from a group consisting of silicon and silica a lower cladding layer comprising silica having a first index of refraction, forming upon the lower cladding layer at least one waveguiding ridge comprising silica having a second index of refraction which is higher than said first index of refraction, forming on said at least one waveguide ridge and on exposed regions of the lower cladding layer an upper cladding layer comprising particles of silica having an index of refraction which is lower than said second index of refraction, said upper cladding layer is formed by depositing a layer of soot particles comprising silica and sintering the soot particles in a helium-containing atmosphere into a glassy layer, wherein, said sintering is conducted by heating the soot layer in a helium atmosphere containing a gaseous additive selected from the group consisting of BCl3 and BF3 at temperatures of from 800° - to 900°
C., sintering the heated soot layer at a temperature ranging from 1000°
to 1100°
C. in absence of said gaseous additive, annealing the sintered structure in a steam-and-oxygen atmosphere at a temperature of from 1000°
to 1150°
C., and allowing the annealed layer to cool to room temperature. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
- to 900°
-
10. The method of producing a silica cladding layer on a structure comprising a substrate selected from the group consisting of silicon and silica, which comprises
forming on said substrate a silica soot layer by flame hydrolysis deposition, placing the structure into a furnace, purging the furnace with helium at a low temperature, adding an additive selected from the group consisting of BCl3 and BF3 into the helium stream, raising the temperature over a period of 1.5 to 2.5 hours to a heating temperature of 900° - C. or less,
sintering the heated soot layer in absence of said gaseous additive by raising the temperature to from 1000°
to 1100°
C. over a period of from 1.5 to 2.5 hours and maintaining the sintering temperature over a period of about one hour,annealing the sintered structure in a steam-and-oxygen atmosphere at a temperature ranging from 1000°
to 1150°
C. for a period of from 5 to 7 hours, andallowing the annealed structure to cool to the room temperature. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18)
- C. or less,
Specification