Hermetically sealed package and method of assembly

Details Hermetically sealed package and method of assembly Hermetically sealed package and method of assembly

1998-08-25

2001-04-24

Sanghavi, Hemang (Department: 2874)

Optical waveguides

With disengagable mechanical connector

Optical fiber to a nonfiber optical device connector

C385S138000, C385S080000

Reexamination Certificate

active

06220766

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a hermetically sealed package and a method of assembly therefor. The invention is particularly concerned with the provision of a hermetically sealed package for a fibre optic device.
FIELD OF THE INVENTION
Packaging of fibre optic devices is driven by the need to achieve low cost while at the same time maintaining high reliability for extended operational life, for example in excess of 20 years. It is particularly important to achieve hermeticity around the fibre optic cable as it enters the device package. In this context, the hermetic seal is required to provide a good barrier to the ingress of moisture which can cause damage to the fibre optic devices within the package.
According to one method for hermetically sealing of fibre optic cables, a glass to metal seal is formed between the fibre optic cable and its supporting tube or sleeve. This involves locally heating a stripped portion of the fibre optic cable to around 500° C. to reflow a precision solder glass bead, positioned at an appropriate place to form the seal. At the same time, the fibre jacket, or protective outer coating, must be maintained to below 90° C. to avoid damage to the coating. Control of the reflow profile is quite critical as high stress concentrations can lead to damage to the optical fibre and subsequent light attenuation in use.
According to another method, the fibre optic cable is coated with metal (for example titanium/platinum/gold or titanium/tungsten/gold) and then soldered to its support tube. This approach involves costly metal deposition processes to coat the fibre. It is also difficult to maintain adhesion of the coating to the fibre. In addition, as with the first method mentioned above, a heat process is required which can lead to stress and deformation of the fibre optic cable.
Thus, although these known methods do give reliable hermetic seals, they have inherent assembly difficulties and also compromise the cost objectives of packaging.
SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided a hermetically sealed structure comprising an outer sleeve of a material resistant to moisture ingress; an insert located within the sleeve at one end portion thereof, the insert having a bore therethrough, and an optical fibre extending through said bore and beyond the end portion of the sleeve, wherein respective adhesive films secure respectively the insert to the sleeve and the optical fibre to the insert.
According to another aspect of the present invention there is provided a method of assembling a hermetically sealed package comprising the following steps:
a) inserting an insert into a distal portion of a sleeve, the insert having a bore extending therethrough;
b) guiding an optical fibre along said sleeve from a remote portion thereof and through said bore;
c) applying a quantity of adhesive to a remote end of the optical fibre; and
d) drawing the optical fibre through the sleeve whereby the adhesive is caused to flow between the insert and the sleeve and between the bore and the optical fibre to form respective seals therewith.
It will be understood that with a small gap available between the insert and the sleeve, and between the optical fibre and the bore, the adhesive flows due to capillary action. According to the example described herein, an epoxy resin is used to form a hermetic seal. This resin thus replaces the solder glass or metal solders which were used in the known techniques outlined above, and thus negates the need for high temperature processing. It is somewhat surprising that an epoxy resin provides an adequate hermetic seal, because epoxy resins in their bulk form have a tendency to permeate moisture and are not normally considered to be completely hermetic. However, by providing a thin film of epoxy resin at the interface between the insert and the sleeve on the one hand, and the optical fibre and the bore within the insert on the other hand, a fully hermetic seal can be established.
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.


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Perryman, A.J., et al. “Packaging Considerations For Semiconductor Laser Diodes”, Laser Diode Technology and applications, vol. 1043 (Jan. 18-20, fc1989), pp. 330-337.

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