Optical waveguides – Optical fiber waveguide with cladding – Utilizing multiple core or cladding
Patent
1992-09-21
1994-04-19
Gonzalez, Frank
Optical waveguides
Optical fiber waveguide with cladding
Utilizing multiple core or cladding
385 84, 385138, G02B 610
Patent
active
053054130
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to optical fibre feedthroughs.
2. Related Art
A device package that incorporates an optical or opto-electronic component has an aperture for a feedthrough feeding one or more optical fibres that conduct light to or from inside of the package. One approach is to seal the optical fibres hermetically within a metallic sleeve with glass solder, which sleeve is, in turn, mounted in the aperture.
Generally `single mode` optical fibre supports two orthogonally polarized He.sub.11 modes. Because of the near-degeneracy of the propagation constants B.sub.X and B.sub.y, for the x and y axes respectively, any small perturbations along the length of the fibre lifts this degeneracy and thus the state of polarization (SOP) will evolve unpredictably. Any linearly polarized light injected into the fibre will thus become elliptically polarized after a short distance.
Many applications, e.g. lithium niobate components and coherent optical transmission systems, require a stable SOP output from the fibre. One solution is to use High Birefringence Polarization Maintaining (HB-PM) fibre.
PM fibres maintain the state of polarization by introducing a large intrinsic birefringence arising from asymmetry in the core or stress effects due to the fibre cladding. The latter of the two methods includes, for example, the formation of high stress regions by means of circular rods along the length of the fibre either side of the core. When launched into one or other of the principal modes, light will propagate unchanged along the length of the fibre provided no external perturbations exceed the internal intrinsic stresses, otherwise the SOP will be unpredictable. When using circular profile tubes it is imperative that the fibre is concentric within the tube, that the tube wall thickness is uniform and that no air bubbles or contaminants interfere with the glass seal. Any significant deviation from a symmetrical structure, both longitudinally and axially, will destroy the symmetry of the stresses external to the fibre and could therefore act to destroy the fibres PM properties. Keeping the symmetry accurate to such an extent can pose difficult problems if large-quantity production is envisaged.
BRIEF SUMMARY OF THE INVENTION
The present invention provides an optical fibre feedthrough assembly comprising a metallic sleeve, at least one polarization maintaining fibre, and a glass seal completely surrounding the or each fibre and sealing the or each fibre to the sleeve, the seal applying asymmetric stresses to the or each fibre, and the or each fibre being orientated so that the stresses act to reinforce the polarization maintaining properties of that fibre.
Because the feedthrough is designed to apply stresses to the fibre via the glass seal reinforcing the polarization maintaining properties of the fibre, small manufacturing deviations from the ideal will not result in a net stress to the fibre acting to destroy its polarization maintaining properties.
The asymmetric stresses can be achieved by use of a metallic sleeve having an asymmetric inner cross-section. These may be made by metal injection moulding due to the difficulty of machining a metallic sleeve with an asymmetric inner cross-section to have a circular external profile. 304L and 316L stainless steels are expected to be suitable materials for such moulding. In this case the outer cross-section is preferably circular to simplify fixing within the aperture of the device package. Alternatively rod elements can be introduced into an otherwise circularly symmetric seal to provide the required asymmetric stresses. These rod elements could be standard, bare, single-mode fibres, for example.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention and a method of manufacturing them will now be described, by way of example only, with reference to the accompanying drawings of which:
FIG. 1 is perspective, part cut-away, view of a metallic sleeve suitable for the present invention;
FIG. 2 is a cross-sec
REFERENCES:
patent: 4407561 (1983-10-01), Wysocki et al.
patent: 4418984 (1983-12-01), Wysocki et al.
patent: 4504113 (1985-03-01), Baak
patent: 4610506 (1986-09-01), Tokunaga et al.
patent: 4708429 (1987-11-01), Clark et al.
patent: 4818047 (1989-04-01), Takuma et al.
patent: 4904052 (1990-02-01), Rand et al.
patent: 4997260 (1991-03-01), Honjo et al.
patent: 5074643 (1991-12-01), Petisce
Chu et al., Journal of Lightwave Technology, vol. LT-2, No. 5, Oct., 1984, pp. 650-662.
Patent Abstracts of Japan, vol. 12, No. 194, Jun. 7, 1988, and JP A 62299918 (Nippon Telegr. & Teleph. Corp.) Dec. 26, 1987.
BT & D Technologies Limited
Gonzalez Frank
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