Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
2001-06-29
2003-09-02
Ullah, Akm E. (Department: 2874)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C385S088000, C385S092000, C385S138000
Reexamination Certificate
active
06612752
ABSTRACT:
The present invention relates to a container for optical components. In particular, active and/or passive optical components such as, for example, laser sources, optical splitters, components made with integrated optics and fibre devices can be contained inside a container. In general, for the purposes of the present invention, optical components are considered as being passive or active optical device, for example electrooptic and/or acousto-optic devices which require one or more connections with optical fibres.
In general, these components suffer from contact with particles of water contained in humidity and with other atmospheric agents, for example corrosive agents, which can give rise to a decline in the performance of the component, up to the point at which its correct functioning is compromised. In addition, in certain components, for example lasers, it is necessary-that a defined gas composition inside the container remain unaltered for reasons of reliability.
Examples of optical components which require sealing are, for example, electrooptic modulators made on lithium niobate substrates, and acousto-optic devices. The materials inside the container which suffer most from contact with humidity are, for example, the adhesives used to attach the components and the fibres inside the container.
Thus, what is required is containers which have good sealing, allowing the environment inside them to be kept free of humidity and of other external agents, thus allowing all the components present therein to function correctly. In general, these containers are made of a metallic material, for example stainless steel, Kovar™, metal alloys such as copper-tungsten, for example, and, more generally, materials which do not allow humidity to penetrate into the container, The points at which the passage of humidity or of other agents into the container can take place are the regions in which the electrical and optical connections, referred to hereinbelow as electrical feedthroughs and optical feedthroughs, respectively, with the components present inside the container are located.
Another region in which humidity or other external agents can penetrate into the container, when the said container comprises a base and a lid, is the region of the closure between the lid and the base. In order to ensure sealing in this case, the lid is generally closed using a known technique of brazing along the entire peripheral region of contact. This brazing is carried out, for example, by subjecting the said region of contact to an electrical discharge. The metallic material both of the lid and of the base in the said region fuses and hermetically fixes the two parts together.
For the passage of optical fibres into the container from the outside, the optical feedthroughs are sealed using various techniques.
An optical fibre has a portion made of glass with a core and cladding; generally, the dimensions (diameter) are about 10 &mgr;m for the core and about 125 &mgr;m for the cladding for monomodal optical fibres. In all the types of fibre, the said portion made of glass has a coating made, for example, of acrylate (acrylic resins) or of elastomeric material in general, which has a minimum diameter of about 250 &mgr;m and a maximum diameter of about 400 &mgr;m in the case of fibres with maintained polarization. A description of fibres with maintained polarization is given in patent application 98EP-100185.2 in the name of the Applicant.
This coating has pores such that they allow humidity to pass into it and thus, when this coating is not removed in making a feedthrough, they also allow humidity to pass into the container and contact the various optical components. The only portion of the optical fibre which ensures sealing is the portion made of glass, which does not allow any passage of humidity or of other agents.
Thus, in order to seal an optical feedthrough, it is necessary to remove the fibre's acrylate coating in the region which will be inserted through the optical feedthrough, thus exposing the “naked” fibre, i.e. the portion made of glass only.
A technique which effects the sealing involves metallizing the fibre, i.e. coating the naked fibre with a metallic layer which is in direct contact with the glass.
An example of metallization of a fibre is described in U.S. Pat. No. 4,779,788, in which the metallization process takes place after the outer surface of the fibre has been cleaned thoroughly by immersing it, for example, in hot sulphuric acid and washing it with deionized water. The subsequent metallization takes place by means of a process of evaporating metal particles, which settle on the glass of the fibre and become firmly attached thereto, without allowing any humidity to pass between the fibre and the metal.
An example of this technique for sealing an optical feedthrough is described in European patent application EP 690,322, which describes a method for generating a sealed feedthrough, in which a length of the fibre is first stripped of its acrylate coating. The fibre is placed in a cylindrical body having a first portion in which is placed the length of metallized fibre and a second portion, which has a larger diameter than the first portion, in which is placed the length of fibre following the section stripped of coating. The portion of metallized fibre is soldered inside the said first portion of the cylindrical body using a metallic soldering alloy and the portion of fibre with the coating is attached in the second portion of the cylindrical body by means of an adhesive. Next, the cylindrical body, with the fibre attached inside it, is placed in a feedthrough hole appropriately made on a wall of the container and is fixed therein by soldering around the circumference of the feedthrough hole.
The Applicant has found that this technique is expensive, mainly due to the preparation of the metallized fibre, which is a particularly intricate process, since the naked fibre is very fragile and can thus be damaged during the metallization. In addition, the process is carried out using complex machinery. The metallization must be carried outside the container and before the fibre is connected to any of the components housed in the container.
Another technique for sealing an optical feedthrough is described in U.S. Pat. No. 5,177,806, which relates to an optical feedthrough in which the fibre, stripped of the acrylate protective layer, is soldered into a tube by means of glass powder (“glass solder”). In particular, that patent describes an optical feedthrough in which a fibre is maintained in a fixed position in a metal sleeve, while a glass powder is brought to high temperature and then cooled to form a solder inside this sleeve on the naked fibre.
The Applicant has observed that, although this solution eliminates the problems associated with metallization of the fibre, it introduces a high risk of damage to the components inside the container. In fact, the glass powders have relatively high melting points (350° C.-500° C.) and the components generally must not be taken up to such high temperatures. In this case also, it is necessary to carry out the soldering inside the sleeve before connecting the fibre to the components and mounting these components in the container.
When the fibres are of the type with maintained polarization, the “glass solder” in contact with the said fibre can bring about a reduction of the polarization extinction ratio of this fibre.
Another technique for sealing an optical feedthrough, described in patent application EP 469,853, involves using an epoxy resin to prevent humidity from passing into the feedthrough.
In particular, that patent application describes a light guide with an optical fibre for guiding light from an external source into a closed space. The optical fibre is placed in a feedthrough hole formed in a fixing support for the said light guide. The said support has an inlet hole which communicates with the said feedthrough hole. The optical fibre is coated with a surface layer throughout the feedthrough hole, except for the portion which communic
Gobbi Luigi
Schiattone Francesco
Corning Oti SpA
Doan Jennifer
Oliver Kevin A.
Short Svetlana Z.
Ullah Akm E.
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