Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
1998-10-20
2001-11-06
Healy, Brian (Department: 2874)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C385S092000, C385S014000, C385S049000, C385S139000, C385S080000
Reexamination Certificate
active
06312165
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of making an optics package, in particular one of the type in which a length of optical fibre is fixed to an integrated optics device.
BACKGROUND OF THE INVENTION
The present invention is particularly, but not exclusively, concerned with the packaging of integrated opto-electronic devices which comprise a silicon-on-insulator wafer in which are monolithically formed optical waveguides. These waveguides are defined in the surface of the silicon itself. The integrated optics device can also include electronic or optoelectronic components which are secured to the surface of the wafer. The optical fibre acts as a conduit for light onto and off the integrated optics device. It is supported within the package by an entry ferrule and extends from that to a fixing point on the integrated optics device. The design of reliable optoelectronics devices requires that the end fixtures of the optical fibre do not experience excessive forces during package temperature changes nor that the optical fibre experiences excessive strain levels.
The present invention seeks to provide a method of manufacture which attains these objectives.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a method of making an optics package in which an exposed length of optical fibre extends between a supported location and a fixing point on an integrated optics device wherein the relationship between the exposed length (L) of the optical fibre and a distance (&Dgr;h) between the supported location and the fixing point on a mutually perpendicular axis is determined taking into account the induced strain in the optical fibre so that, on assembly, a predetermined bend is introduced into the exposed length of optical fibre.
The package includes a casing which has a part holding an integrated optics device and an entry part within which the optical fibre is supported at the supported location. In a situation where the casing is manufactured first, the method comprises the step of determining the vertical offset (&Dgr;h) inherent in the casing between the fixing point on the integrated optics device and the supported location. The required exposed length (L) of optical fibre is then calculated taking into account the induced strain limitations.
According to the described embodiment, the method also comprises assembling a fibre optics structure by inserting a length of optical fibre through a supporting element, cutting the length of optical fibre to the required exposed length (L), receiving the fibre optics structure in the casing which holds the integrated optics device, and fixing the optical fibre to the fixing point. The supporting element is termed herein a ferrule and comprises in the preferred embodiment a metallic outer casing housing a ceramic insert through which the optical fibre extends, as described for example in our earlier British Application No. 9814643.4.
It has been found that it is possible to design a package wherein the maximum induced strain &egr;
max
is kept to 0.3% or below, where:
&egr;
max
=r/R×
100,
R being the minimum bending radius, even when small longitudinal displacements are incurred in use due to thermal expansion and/or assembly errors.
One way of achieving this is to utilise a design technique which relies on an empirically determined design strain &egr;
des
as discussed in more detail in relation to the preferred embodiment. Another way of achieving this for packages of the approximate dimensions discussed herein is to rely on the following equation:
L
Δ
h
lies
in
the
range
100
×
3
r
10
to
100
×
3
r
where r is the fibre radius. This has been found in practice to be a robust guide for the relationship between the exposed length L and the distance &Dgr;h in an optoelectronic package.
The optical fibre can be fixed to the integrated optics device by inserting the fibre optics structure into the casing, with the free end of the optical fibre located just above the integrated optics device held in the casing, and then pushing the free end of the optical fibre downwards into a groove at the fixing point on the integrated optics device. The optical fibre can be secured by epoxy resin at the fixing point. This provides a so-called positive S-bend which eases assembly and produces a downwards force at the tip of the fibre in front of the fixing point.
The integrated optics device can be located within the casing on a base component such as a ceramic wafer.
According to the specific embodiment described herein, a design method is disclosed in which the optical fibre is intentionally assembled with a vertical offset &Dgr;h between the end fixing points thereby forcing the fibre to take up a gentle positive S bend shape of known geometry. The important aspect of the S bend is that, despite the small additional strain induced in the fibre due to the bending moment from the vertical offset, compressive or tensile forces experienced by the end fixing points remain substantially constant and at a known level. This is important as the end fixings, particularly to the integrated optics device, can be relatively weak because of the limited surface area that is available to form bond surfaces. Moreover, the expected strain can be predetermined to be below a level at which short term failure would occur, that is preferably no greater than 0.3%.
For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made by way of example to the accompanying drawings.
REFERENCES:
patent: 4997243 (1991-03-01), Aiki et al.
patent: 5018817 (1991-05-01), Suzuki et al.
patent: 5268986 (1993-12-01), Kakii et al.
patent: 5694506 (1997-12-01), Kobayashi et al.
patent: 5991487 (1999-11-01), Sugiyama
patent: 2313676 (1997-12-01), None
patent: 11-202155 (1999-07-01), None
UK search report re application No. GB 9817562.3, dated Jan. 26, 1999.
International Search Report for application No. PCT/GB99/01494, dated Aug. 9, 1999.
Mitachi, S. et al, “Trend in the Technology and Prospects for Reducing the Cost for Fiber Optic Connectors,”NTT Review, vol. 9, No. 2, pp. 52-57, Mar., 1997.
Iwano, S. et al, “Novel Flexible Fine Ferrule for Optical Fiber Connectors,”The Transactions of the IEICE, vol. E71, No. 4, pp. 406-413, Apr., 1998.
1) PCT International Preliminary Examination Report re application No. PCT/GB99/01494; dated Sep. 14, 2000.
2) Patent Abstracts of Japan re JP 11-202155, published Jul. 30, 1999.
Cornish Andrew Paul
Yeandle Jonathan Charles
Bookham Technology plc
Cook Alex McFarron Manzo Cummings & Mehler, Ltd.
Healy Brian
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