Optical interface utilizing polymer assisted strain relief

Details Optical interface utilizing polymer assisted strain relief Optical interface utilizing polymer assisted strain relief

2002-11-27

2004-11-09

Ullah, Akm Enayet (Department: 2874)

Optical waveguides

With disengagable mechanical connector

Optical fiber/optical fiber cable termination structure

C385S147000

Reexamination Certificate

active

06814500

ABSTRACT:

This application is a U.S. National filing under 35 U.S.C. §119 hereby claiming priority to GB Application No. 0128619.4, filed Nov. 29, 2001, the contents of which are incorporated herein by reference for all purposes.
INTRODUCTION
The present invention relates to the provision of an interface between an optical fibre and an optical source. In particular, the invention relates to a method of manufacture of a fibre-to-butterfly-casing interface that utilises polymer assisted strain relief.
The proliferation of laser diodes in the areas of optical networking, medical and spectroscopic instruments have placed greater demands on the way laser diodes are packaged and interfaced to fibre. The trends in delivering laser light into fibres for more efficient connectivity will put cost of packaging as the primary consideration for packaging laser diodes. Current methods of laser fibre interface demand that the fibres be fixed to the laser diodes' emitter facets by a compliant clip restraining V groove. These methods will fix the end tip of an optical fibre to a sub-mount or substrate near the laser diode. In the scheme of packaging, the fibre has to be interfaced to a package casing, commonly designed as a “butterfly” package. The fibre is constructed with a ferrule interface, which is gold plated and pre-coated with solder. The butterfly casing interface wall has a snout with a concentric hole bored to fit the ferrules on the fibre. Upon assembly, the ferrules are soldered to the casing wall and snout bore by applying a series of solder joint seals. At the exit of the snout bore, thick epoxy is applied to the fibre to cover the external fibre ferrule to the harness, cladding overlay and fibre cladding. A rubberized sleeve is pulled over the epoxy and fibre harness before the epoxy is cured. This rubberized sleeve forms the initial part of the stiffness measure to prevent stress point fibre failure at the snout interface. A rubber boot is then pulled over the rubber sleeve as a final assembly to complete the device interface. The boot, together with the rubber sleeve, constitutes the full strain relief in the interface design. The boot helps maintain a minimum bend radius when forces are applied at the connector and distributes strain forces to the connector housing instead of the fibre.
This method of butterfly casing interfacing requires fibres and ferrules that are very expensive. The epoxy joints and sleeve processes are very messy, curing times are relatively long, and the curing process often leads to non-uniform stress formation. There is a need to reduce cost of component, cost of assembly, and to reduce failures due to stresses induced during assembly.
Strain relief in electrical wire plugs and connectors has typically been achieved using moulded polymer materials. Fibre optic interfaces are however more fragile and making conventional moulding techniques undesirable. Furthermore, sealing and hermetic proofing requirements have also discouraged the use of moulded polymer interfaces.
In accordance with the present invention, there is provided a strain relief interface for connecting a packaged optical device and an optical fibre, the optical fibre passing through a snout bore extending from a side wall of the package, comprising: a first moulded jacket, said first moulded jacket surrounding and affixed to a sheathed section of optical fibre from which a fibre jacket has been removed, a first end of the first moulded jacket affixed to a fibre jacket encasing an adjacent section of optical fibre, a second end of the first moulded jacket affixed to the snout bore and to a ferrule located within the snout bore; and a second moulded jacket, said second moulded jacket surrounding and affixed to the first moulded jacket, a portion of the fibre jacket, and the snout bore.
The strain relief interface of the invention has a reduced part count and assembly time when compared to prior art strain relief interfaces.
The first moulded jacket may comprise a quick-curing epoxy compound. The epoxy compound preferably has a similar coefficient of thermal expansion to the optical fibre.
Advantageously, the second moulded jacket comprises a thermoplastic elastomer.
An outer surface of the second moulded jacket may be ridged to provide strain relief.
The strain relief interface may further comprise a rubber boot pulled over the second moulded jacket.
The packaged optical device is preferably a butterfly packaged optical device.
In accordance with a further aspect of the present invention, there is provided a method for fabricating a strain relief interface that connects a packaged optical device and an optical fibre, the optical fibre passing through a snout bore extending from a side wall of the package, comprising the steps of:
locating over a bezel a sheathed section of optical fibre adjacent the snout bore, said sheathed section comprising a portion stripped of a fibre jacket and an adjacent portion with a fibre jacket;
placing the package, optical fibre and bezel into a mould cavity, the mould cavity including an insert seat on which the snout bore is located, thereby facilitating mould material flow and mould chamber sealing;
injecting a first material into the mould to form a first moulded jacket, said first moulded jacket surrounding the sheathed portion of optical fibre stripped of a fibre jacket and affixed to: the fibre jacket encasing the adjacent portion of optical fibre, the snout bore, and a ferrule located within the snout bore; and,
injecting a second material into the mould to form a second moulded jacket, said second moulded jacket surrounding and affixed to the first moulded jacket, a portion of the fibre jacket and the snout bore.
Since the first stage seals the optical fibre, the strain relief can then be fabricated outside a fibre shop. A predetermined minimum fibre optic radius can be designed into the polymer relief structure.
The method may further comprise the step of curing the first material by a polymerisation process. The first material is preferably a quick-curing epoxy compound. In which case, the epoxy compound may advantageously be cured at low temperature.
The second material is conveniently a thermoplastic elastomer.
The method may further comprise the step of pulling a rubber boot over the second moulded jacket.
The packaged optical device connected by the strain relief interface may comprise a butterfly packaged optical device.


REFERENCES:
patent: 5199095 (1993-03-01), Iapicco
patent: 5889910 (1999-03-01), Igl et al.
patent: 6431904 (2002-08-01), Berelsman
patent: 2003/0133673 (2003-07-01), Lam et al.
patent: WO 99/05553 (1999-02-01), None

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