Optical waveguides – Planar optical waveguide
Patent
1999-04-12
2000-03-28
Healy, Brian
Optical waveguides
Planar optical waveguide
385 14, 385 42, 385130, 385131, 385132, 65385, 65386, 65391, G02B 610, C03B 37023
Patent
active
060441925
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND TO THE INVENTION
The present invention relates to dielectric waveguide pairs made by plasma enhanced chemical vapour deposition (PECVD) upon planar substrates. Such deposition involves depositing and patterning material to form cores of material having a slightly greater refractive index than that of buffer layer material upon which those cores are supported and that of cladding material with which those cores are covered. Typically these waveguide pairs are designed for guiding light in the 1 to 2 .mu.m for optical communication systems.
SUMMARY OF THE INVENTION
The invention is particularly concerned with waveguide pairs in which their waveguide cores approach close enough together to provide a significant amount of cross coupling either from the cores, or between the cores, without undue losses. Such losses can arise from irregularities or discontinuities in the intervening medium.
Embodiments of the invention aim to provide cladding for the cores produced by PECVD which maintain good and low-loss optical coupling between the two waveguide cores.
According to the invention there is provided a cladded waveguide pair assembly obtainable by plasma enhanced chemical vapour deposition (PECVD), comprising a substrate, a buffer layer of dielectric material on said substrate, a pair of elongate dielectric waveguide cores deposited on the buffer layer and of higher refractive index than that of the buffer layer, and a cladding layer of boron and phosphorus doped silica glass (BPSG) arranged over the pair of cores and adjoining regions of the buffer layer including the interval between the cores of the pair, said BPSG cladding layer having a lower refractive index than that of the material of the cores and a lower flowing temperature than that of the materials of the cores and the buffer, wherein said BPSG cladding layer is obtainable in multiple stages each stage consisting of a PECVD deposition step and a subsequent annealing step by which the deposited material is flowed.
When the buffer is pure silica, its refractive index is matched by that of a BPSG cladding, and the buffer's flowing temperature satisfactorily exceeds that of a BPSG cladding.
A feature of preferred embodiments is that the cladding is in a layer constructed in stages. It is believed that, in combination with the choice of material for the cladding, namely BPSG, the use of a multi-deposit process minimises the creation of air voids or other physical imperfections that may cause discontinuities and accordingly reduces the undesirable lossy wave coupling between the cores which otherwise tends to occur.
The use of twin dielectric cores on a buffer of silica or other material, and enveloped in dielectric cladding, is known in planar waveguide techniques.
The invention also resides in a method of producing a cladded waveguide pair assembly by plasma enhanced chemical vapour deposition (PECVD), comprising depositing a buffer layer of dielectric material on a substrate, depositing a pair of spaced dielectric waveguide cores on the buffer layer, which cores are of a material of higher refractive index than that of the buffer layer, and producing a layer of cladding over the pair of cores and adjoining region of the buffer layer including the interval between the cores of the pair, the material of said cladding layer having a lower refractive index than that of the material of the cores and a lower flowing temperature than that of the materials of the cores and buffer, wherein said cladding layer is produced in multiple stages, each stage including a PECVD deposition step followed by a step of annealing in which the deposited material is flowed.
BRIEF DESCRIPTION OF THE DRAWING
The invention will be further explained with reference to an embodiment by way of example, in conjunction with the accompanying drawing, which shows a transverse section across a dielectric waveguide pair produced by PECVD on a planar substrate illustrating schematically an undesirable fault which is largely eradicated by the use of the invention.
DETAILED
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Day Stephen
Grant Michael Francis
Healy Brian
Nortel Networks Corporation
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