Fiber optic connector hermetically terminated

An arrangement for sealing an optical fiber within a fiber optic connector. The fiber optic connector includes a ferrule having an outside diameter and a throughbore. An exposed portion of the optical fiber is positioned within the throughbore of the ferrule, and a metal seal is added between the ferrule and the outer diameter of the optical fiber, forming a bond between the ferrule and the optical fiber. The disclosed method includes the steps of heating the ferrule wherein the ferrule has a throughbore. The optical fiber is then placed within the throughbore. A molten metal is added between the ferrule and the exposed region of the optical fiber. A bond is formed between the ferrule and the optical fiber during cooling of the molten metal.

TECHNICAL FIELD 
The present invention relates to fiber optic connectors, specifically an 
arrangement for sealing an optical fiber within a fiber optic connector. 
BACKGROUND ART 
A typical prior art connector including a ferrule assembly is illustrated 
in FIG. 1. As is well known, standard fiber connectors lack the 
male-female polarity common in electronic connectors. Instead, fiber 
connectors 150 mate in an adaptor 152 that fit between two fiber 
connectors. A cable 154 has an exposed region 156 where the cladding is 
exposed. The region 156 is mounted in a long, thin cylinder called a 
ferrule 158 with a hole to match the fiber cladding diameter. The ferrule 
158 centers and aligns the exposed region 156 and protects it from 
mechanical damage. Surrounding a portion of exposed region 156 is a 
connector body 160 which is attached to the ferrule 158. A strain-relief 
boot 162 is attached to the cable 154 and the connector body 160 and 
shields the junction of the connector body 160 and the cable 154. 
The ferrules 158 are typically made of metal or ceramic, but some are made 
of plastics. The hole through the ferrule 158 must be large enough to fit 
the clad fiber and tight enough to hold it in a fixed position. An end 164 
of the ferrule 158 and the exposed region 156 protrudes beyond the 
connector body 160. 
The connector 150 slips into the left side of the adaptor 152. A second 
connector (not shown) slips into the right side of the connector 150. One 
connector is an emitter and the other a receptor. There are numerous 
problems with the prior art connectors. End losses between connectors 
occur due to many different factors including misalignment between 
emitters and receptors, the core being elliptical and the cladding 
thickness being inconsistent in the radial direction. 
The above described fiber optic connector may be fastened to the ferrule by 
an adhesive, for example a light-curable acrylic. If exposed to the 
environment, the adhesive can absorb moisture from the atmosphere and 
change dimensions and rigidity, lowering the precision alignment of the 
optical fiber connector and increasing signal loss. 
An epoxy may be used as the adhesive. The use of such epoxy, however, is 
still susceptible to moisture and chemicals. Hence, the epoxy may still 
break down upon exposure to moisture. Moreover, epoxy does not form a good 
bond with the optical fiber, and has relatively poor thermal 
characteristics, resulting in expansion or contraction due to changes in 
temperature. 
Another proposed technique uses hermetically-sealed optical fibers having a 
metal coating instead of the conventional plastic coating. The proposed 
method removes the metal coating layer from the metal-coated optical 
fibers, fuses together the exposed portions of the optical fibers, and 
immediately after fusing, forms a metal reinforcing layer on the coupled 
portion of the optical fibers under an anhydrous atmosphere. The metal 
reinforcing layer is formed by applying a primary layer of metal on the 
exposed portion of the fibers by sputtering or vacuum vapor deposition in 
a reaction container having an inert gas. A secondary layer of metal is 
then applied over the primary layer for mechanical strength. Such a 
technique, however, is cumbersome because it requires sputtering or vapor 
deposition equipment. Alternative techniques include encapsulating optical 
fibers and the corresponding fiber coating in molten metal having a low 
melting point. The low melting point is necessary to prevent damage to 
organic material within the optical fiber assembly, for example glass or 
adhesive. Moreover, such techniques are difficult to control, especially 
since components less dense than the molten material may tend to float to 
the top of a mold and move off-center within the mold. 
DISCLOSURE OF THE INVENTION 
There is a need for an arrangement (apparatus and method) for hermetically 
terminating a fiber optic device without the necessity of adhesives that 
are subject to degradation upon exposure to air or moisture. 
There is also a need for attaching a fiber to a ferrule in a reliable and 
controllable manner. 
There is also a need for an arrangement for hermetically terminating a 
fiber optic device using metal bonded directly to the optical fiber to 
hermetically seal the fiber optic device. 
There is also a need for an arrangement for forming a compressive and/or 
chemical seal in an efficient manner to hermetically seal a fiber optic 
device. 
There is also a need to terminate an optical fiber that reliably provides a 
hermetic seal for the terminated optical fiber. 
These and other needs are attained by the present invention where an 
optical fiber is hermetically sealed within a fiber optic connector. 
These and other needs are also achieved by the present invention, where a 
metal seal forms a compressive and/or chemical bond with an optical fiber 
and also forms a bond with a ferrule. 
According to one aspect of the present invention, a fiber optic connector 
includes a ferrule having an outside diameter and a throughbore. An 
exposed portion of the optical fiber is positioned within the throughbore 
and a metal seal is added between the ferrule and the outer diameter of 
the optical fiber, forming a bond between the ferrule and the optical 
fiber. The metal seal provides an hermetic seal between the optical fiber 
and the ferrule and aligns the optical fiber within the ferrule without 
distorting the optical fiber. 
Another aspect of the present invention provides a method of forming a 
fiber optic connector. A ferrule having a throughbore is heated. An 
exposed region of an optical fiber is placed within the throughbore. A 
molten metal is added between the ferrule and the exposed region. A bond 
is formed between the optical fiber and the ferrule during the cooling of 
the molten metal. 
Additional objects, advantages and novel features of the invention will be 
set forth in part in the description which follows, and in part will 
become apparent to those skilled in the art upon examination of the 
following or may be learned by practice of the invention. The objects and 
advantages of the invention may be realized and attained by means of the 
instrumentalities and combinations particularly pointed out in the 
appended claims.

BEST MODE FOR CARRYING OUT THE INVENTION 
The present invention provides an arrangement (apparatus and method) for 
hermetically sealing an optical fiber within a fiber optic connector. As 
described below, a metal seal hermetically seals the optical fiber to the 
fiber optic connector. The metal seal bonds to the optical fiber 
chemically and/or compressively to ensure a hermetic seal. Hence, a 
hermetic seal may be easily implemented, without the necessity of 
adhesives. 
FIG. 2 is a diagram illustrating an overall system for automated 
fabrication of a fiber optic device according to an embodiment of the 
present invention. The system 10 enables the automated fabrication of 
fiber optic devices, for example, fiber optic connectors, etc., without 
operator intervention. The method of the automatic fabrication of a fiber 
optic device may be summarized as follows. 
During fabrication of a fiber optic device, lengths of optical fiber are 
removed from a device carrying a length of optical fiber, for example an 
optical fiber spool 12. The optical fiber is removed from the spool 12 in 
a manner that prevents twisting of the optical fiber in order to prevent 
any stresses from being induced on polarization-sensitive fibers, for 
example birefringent fibers. When the optical fiber spool 12 is initially 
set up for providing optical fiber, the end of the optical fiber on the 
spool 12 is secured into a stationary gripping device 14. As described 
below, the gripping device has at least an open and closed position, where 
the optical fiber may move freely when the gripping device 14 is in an 
open position, and where the fiber is securely positioned when the 
gripping device 14 is in a closed position. 
Once the optical fiber from the spool 12 is secured into the stationary 
gripping device, the system 10 is able to maintain control over the end of 
the optical fiber and the path of the optical fiber. Specifically, the end 
of the optical fiber is controlled at all times to be at a specified 
position in order to maintain an accurate relationship between the optical 
fiber used during fabrication and the associated devices operating on the 
optical fiber. For example, control of the end of the optical fiber 
enables the system to automatically clamp the end of the optical fiber and 
perform automated fusion splicing, automated termination of the optical 
fiber to a ferrule, automated packaging for shipping in a container that 
secures the end for future use, etc. In addition, the length optical fiber 
is controlled as it is moved along a prescribed path, enabling the optical 
fiber to be positioned for clamping and collected for formation of fiber 
optic leads on each end of a fiber optic device. Hence, the disclosed 
embodiment provides a completely automated system for the fabrication of 
fiber optic devices by maintaining at all times precise control over the 
length of the optical fiber from the spool 12a and the corresponding fiber 
end. 
Once the end of the optical fiber is secured to the stationary gripping 
device 14a, the optical fiber can be moved along a prescribed path in 
order to thread additional devices onto the optical fiber, or to position 
the optical fiber with respect to clamping devices. Once the optical fiber 
is moved through any devices to be threaded, the optical fiber is moved 
along the path of clamp assemblies 16 and 18 mounted on movable stages 20 
and 22, respectively. The optical fiber is moved in a manner to provide an 
optical fiber lead 24 and 26 on each end of the clamp assemblies 16 and 
18. The optical fiber leads 24 and 26 are placed in a lead container 28 
and 30, respectively, for example trays. 
Once the first optical fiber 10a is clamped for fabrication, a fiber optic 
device may be formed using the optical fiber 10a, for example by heating 
the optical fiber using a movable heat source 32 and pulling the heated 
optical fiber using the movable stages 20 and 22. Additional details 
regarding the automated fabrication of a fiber optic device according to 
FIG. 2 are disclosed in co-pending application 08/763,122, filed of even 
date herewith entitled "Arrangement for Automated Fabrication of Fiber 
Optic Devices," the disclosure of which is incorporated in its entirety 
herein by reference. FIG. 2 corresponds to FIG. 1 of that application. 
After formation of the fiber optic device, the optical fibers 10a, 10b may 
be terminated using a movable terminating assembly 17, described below. 
FIGS. 3a and 3b are diagrams illustrating the details of the terminating 
assembly 170 according to the present invention. The terminating assembly 
includes a splicer/cutter 172, a ferrule feeder 174, a clamp 176 and an 
alignment collar 178. After an optical fiber 10a, 10b has been positioned 
as shown in FIG. 2, the optical fiber can be terminated and a ferrule 200 
attached thereto so that the terminated optical fiber can be connected 
through a coupler to another terminated optical fiber. 
As shown in FIG. 3A, clamp 176 is movable in three axes and is moved to 
clamp onto the optical fiber 10a. The clamp 176 then moves optical fiber 
10a into engagement with splicer/cutter 172 as shown by the dotted lines 
in FIG. 3A. Splicer/cutter 172 then cuts optical fiber 10a as shown in 
FIG. 3B and the remaining portion of optical fiber 10a to the right of the 
splicer/cutter 172 is removed. The ferrule 200 is moved by a clamp 180 
from the ferrule feeder 174 into a receiving position adjacent to and 
aligned with splicer/cutter 172. The alignment collar 178 is then moved 
into position for receiving and guiding the cut optical fiber 10a into the 
ferrule 200. The clamp 176 is repositioned and clamped onto the optical 
fiber to the left of splicer/cutter 172. Splicer/cutter 172 releases the 
optical fiber loa thereby allowing the clamp 176 to move the cut end of 
optical fiber 10a through the alignment collar 173 and into a throughbore 
204 of the ferule 200. 
A self centering mold 202 and an injector 206 are moved into position as 
shown in FIG. 4. It should be understood that although the invention as 
depicted in FIG. 4 shows the longitudinal axis of optical fiber 10a 
extending in a vertical direction, it should be understood that the method 
according to the present invention can be performed in other directions 
such as a horizontal orientation. 
The ferrule 200 is made from stainless steel or ceramic. The self centering 
mold 202 is preferably formed of a material which does not adhere to 
molten metal is positioned around the ferrule 200 as shown in FIG. 4. The 
ferrule 200 is heated to approximately 900.degree. C., a temperature 
corresponding to the melting point of pure aluminum. If other metals are 
used, the ferrule should be heated to the melting point of that metal. The 
ferrule is also heated so that it will expand making the optical fiber 10a 
easier to insert, and so the throughbore 204 of the ferrule 200 can 
accommodate the molten metal to be added as described below. The heating 
also prevents the added molten metal from prematurely solidifying. 
After heating the ferrule, molten metal is provided between the exposed 
optical fiber and the cylindrical throughbore 204 while in an inert 
environment. The bore 204 is just slightly larger than the exposed region 
205 of the optical fiber 10a. The molten metal is provided by adding 
(e.g., pouring) molten metal into the throughbore 204 and inserting the 
optical fiber into the throughbore 204, by dipping the exposed region 205 
into molten metal and then inserting the dipped optical fiber into the 
throughbore 204, or by injecting molten aluminum between the throughbore 
204 and the exposed region 205 using the injector 206. 
The ferrule 200 and molten metal are then allowed to cool, during which the 
ferrule 200 will compress the molten metal, and wherein a chemical and/or 
compressive bond will form between the solidifying metal 208 and the 
exposed region 205. If pure aluminum is used, the pure aluminum will cool 
faster than the ferrule 200. Hence, the exposed region 205 will be 
centered within ferrule 200 as the pure aluminum cools and shrinks around 
the exposed region 205 of the optical fiber 10a within three microns or 
less forming a metal seal 208 with the exposed region 24 and the ferrule 
200. The metal seal 208 may preferably extend the entire axial length of 
the ferrule 200, or as shown, may only extend for part of the axial length 
of the ferrule 200. 
After hermetically sealing the optical fiber within the ferrule, the 
resulting structure provides a hermetically terminated optical fiber 
leaving an optical fiber end surface 210 extending beyond ferrule 200 or 
flush therewith which is not encapsulated by the molten metal. 
The ferrule 200 has been illustrated having a cylindrical exterior surface. 
The exterior surface of the ferrule 200 serves as a structural interface 
to a connector, an adaptor and the like. Thus, the exterior surface may be 
any shape that mates with a corresponding adaptor or connector to 
interface with another terminated optical fiber. The exterior surface may 
also be coated with a soft deformable metal so that the exterior of the 
ferrule 200 can be hermetically sealed to a connector. 
As shown in FIG. 5, a sealant 212 is applied covering the exposed portion 
205 between ferrule 200 and the covered region 207 of optical fiber 10a. 
The sealant 212 may be an RTV (room temperature vulcanizing) silicon 
coating, or a UV-cured acrylate. A strain-relief boot 214 is attached to 
the covered portion 207 and the ferrule 200 and shields the sealant 212 
and exposed portion 205. 
Although the invention has been described preferably using pure aluminum, 
other materials having a melting point below that of the ferrule may also 
be used. Preferably the metal layer forms a compressive shrink fit bond on 
the optical fiber because the metal has a higher coefficient of thermal 
expansion than does the optical fiber, although it is important that the 
metal is soft and ductile so as to not overstress the optical fiber. Other 
possible metals include gold and lead. 
While this invention has been described in connection with what is 
presently considered to be the most practical and preferred embodiment, it 
is to be understood that the invention is not limited to the disclosed 
embodiment, but, on the contrary, is intended to cover various 
modifications and equivalent arrangements included within the spirit and 
scope of the appended claims.