Patent
1986-03-12
1988-05-17
Wan, Gene
350 9615, G02B 630
Patent
active
047446196
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to arrangements for and methods of connecting waveguides, and in particular to connecting optical waveguides of dissimilar structure.
BACKGROUND AND SUMMARY OF THE INVENTION
The invention has an important application in connecting single mode optical fibres to optical components comprising waveguides formed on substrates.
Successful introduction into optical communications systems of optical components on planar substrates, such as, for example, optical waveguides on lithium niobate substrates, often depends among other criteria on the ability to provide interconnection of such components with optical fibres. The interconnection should not only have low losses and be capable of withstanding reasonable mechanical shocks, but should also be advantageously simple and reliable to make.
Where the optical component concerned is, or is similar in structure to, an optical waveguide on a substrate, such an interconnection is particularly difficult to provide. The waveguide is embedded in a surface of the substrate, the end-faces of the substrate being co-planar with the terminations of the waveguide. Because there is no close structural similarity between an optical fibre end and the end-portion of a substrate, the two components being of substantially differing dimensions and cross-sections, special techniques have been developed for making the interconnections.
An arrangement which has produced acceptably low losses between an optical fibre and a waveguide on a substrate is that called "end-fire" coupling. In this arrangement the fibre core is physically aligned with the waveguide and optically coupled directly thereto with no intervening components. Such an arrangement is disclosed by:
ALFERNESS, R. C., RAMASWAMY, V. R., KOROTKY, S. K., DIVINO, M. D., and BUHL, L. L.: "Efficient single-mode fibre to titanium diffused lithium niobate waveguide coupling for I=1.32 .mu.m". IEEE J. Quantum Electron., 1982, QE-18, pp 1807-1813. The technique achieves low losses not only through precise alignment of the fibre end with the waveguide end but also by closely matching the mode-pattern of the wave guide to that of the fibre.
The above technique does not however address the problem of how to fix the fibre end relative to the waveguide while preserving the low losses, and how to do so in a manner suitable for component packaging.
The absence of a readily usable manner of providing the connections between the fibre and waveguide presents, in fact, a major obstacle to the use of the end-fire coupling technique in the packaging of waveguide components, because misalignment resulting in a significant increase in the coupling loss, can easily occur. It should be borne in mind that the fibre cores of single-mode fibres typically have diameters of between 0.005 and 0.01 mm. The waveguides are of similar dimensions, and consequently misalignment of only a few micrometres is sufficient to cause a serious increase in the connection loss.
The search for techniques of providing satisfactory connection has attracted a considerable amount of effort as witnessed by the following disclosures, all of which refer to techniques for connecting the fibre end to a waveguide in the correct spatial relationship:
SHEEM S. K., GIALLEORANI T. G.: "Two-dimensional silicon grooves for altitudinal alignment in fibre end-butt coupling". Optics Letts., 1978, 3, pp 73-752.
BULMER C. H., SHEEM S. K., MOELLER R. P., and BURNS W. K.: "Fabrication of flip-chip optical couplers between single-mode fibre and lithium niobate channel waveguides". IEEE Trans. on Comps. Hybrids and Manuf. Tech., 1981, CHMT-4, pp 350-355.
HSU H. P., MILTON A. F., and BURNS W. K.: "Multiple fibre end fire coupling with single-mode channel waveguides". Appl. Phys. Lett., 1978, 33(7), pp 603-605.
RAMER O. G., NELSON C., and MOHR C.: "Experimental integrated circuit losses and pigtailing of chips" IEEE J. Quantum Electron., 1981, QE-17, pp 970-974.
ARDITTY H. J., BETTINI J. P., GRAINDORGE P., LEFEVRE H. C., PAPUCHON M., BOURBIN Y.,
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British Telecommunications public limited company
Lee James C.
Wan Gene
LandOfFree
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