Method of producing an optical fiber terminus for high temperature use

A fiber optic terminus is provided in which a deformable material (37), such as an elastomer, is compressed and grips an optical fiber (34) along a substantial length of a terminus body (10). In accomplishing this, an opening (15, 16, 18) in a front terminus body (10) receives a liquid material (37) which can be cured to a solid consistency. An optical fiber (34) then is extended through an opening (24, 25, 26) in a rear terminus body (20) and through the passageway (15, 16, 18) in the front terminus body (10), emerging at the forward end of the latter. The rear terminus body (20) then is forced a short distance into the passageway (15) in the front connector body (10) and the material (37) is cured to a solid consistency. After this, the rear connector body (20), which has a press fit within the passageway (15), is moved to a second position causing compression of the material (37) in the passageway ( 15, 16, 18) so that it grips the optical fiber (34).

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The field of this invention is that of optical fiber connectors and is 
particular to the retention of an optical fiber in a terminus. 
2. Description of Related Art 
In the design of optical fiber connectors, the connection of a fiber in a 
terminus has presented various difficulties. In such a connection it is 
necessary to hold the fiber securely without damaging the fiber or 
creating an incorrect orientation of the fiber relative to the terminus 
body. For full service capability, the fiber should be retained over a 
wide temperature range, including elevated temperatures. There should be 
the ability to compensate for temperature changes which the connector may 
encounter. In addition, the terminus should be capable of economical 
manufacture and be of uncomplicated construction. 
Through one approach, an adhesive is used to hold an optical fiber within a 
terminus body. The adhesives used for this purpose have only limited 
tolerance for temperature changes and typically fail at elevated 
temperatures which many connectors may encounter. The retention force on 
the fiber also could be improved. 
When crimping against an optical fiber to hold it within a terminus body, 
the retention force may be localized which can cause damage to the optical 
fiber. The position of the fiber can be altered such that the fiber will 
not align properly and the efficiency of light transmission suffers. 
Retention forces may not be adequate to retain the fiber under all 
conditions and temperature compensation may not be possible. In some 
designs, the complexity of springs to allow dimensional changes with 
temperature variations becomes necessary. 
SUMMARY OF THE INVENTION 
The present invention provides an improved arrangement for attaching a 
fiber to a terminus body overcoming the difficulties of the prior art. The 
fiber is retained securely without damage and temperature extremes may be 
encountered without loss of retention force. The construction is simple 
and the terminus can be produced economically. 
The fiber retention system of this invention makes use of a deformable 
material occupying substantially the entire length of the optical terminus 
body, which is compressed so as to be forced against the optical fiber 
along its length to frictionally retain the fiber. A material may be 
selected which will withstand high temperatures. 
In producing the optical fiber connector a front optical terminus body is 
constructed as an elongated tubular element having a restricted opening at 
its forward end, generally complementary to the periphery of the bare 
optical fiber. The remainder of the passageway is of larger diameter than 
the optical fiber. A deformable material is introduced into the passageway 
so as to fill most of it. Preferably this material is a viscous liquid 
which can cure to a solid material capable of withstanding high 
temperatures. An elastomer such as a silicone rubber is an example of such 
a material. The liquid may be introduced into the passageway in the front 
terminus body by a syringe. 
An optical fiber, with the buffer stripped from its end, then is fed 
through a rear terminus body and through the passageway in the front body 
to emerge from the front end of the latter terminus body. The rear body 
then is forced into the rearward end of the passageway in the front body 
where it engages the wall of the passageway with a press fit. The rear 
body is advanced only a short distance into the passageway initially. 
After this, the material in the passageway is cured to a solid condition. 
When the material is heat-curable, the application of heat is provided. 
After the cure, the rear body is forced longitudinally further into the 
passageway to a second position, exerting a force on the deformable 
material in the passageway such that this material tightly grips the 
optical fiber throughout a major portion of the length of the passageway. 
This secures the fiber to the terminus body with the force being 
distributed over a great length in the passageway in the front connector 
body. Damage to the fiber is avoided. The material in the passageway may 
be selected to withstand variations in temperature so that the retention 
force will be adequate under all service conditions. When temperature 
changes occur, the material can act as a spring and compensate for the 
small dimensional variations caused by the temperature change.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The front body 10 of an optical fiber terminus, shown in FIG. 1, is an 
elongated tubular element, exteriorly contoured to cooperate with the 
other components of an optical fiber connector. The forward end portion 11 
of the front body 10 has a relatively small exterior diameter and is 
received within an end bushing 12 with a press fit. Interiorly, the 
forward end of the bushing 12 tapers to a relatively small bore 13, which 
is generally complementary to the periphery of an optical fiber from which 
the buffer has been removed. 
A bore extends through the front body 10 from the rearward end 14 to the 
forward end at the bushing 12. The portion 15 of the bore leading inwardly 
from the rearward end 14 is cylindrical and of relatively large diameter. 
A frustoconical wall 16 connects to the inner end of the bore portion 15, 
extending to a relatively narrow cylindrical passageway 18 that is longer 
than the portions 15 and 16 and occupies the remainder of the front body 
10. The bore portion 18 is larger than the opening 13 through the bushing 
12, being of greater diameter than an optical fiber that includes its 
buffer coating. 
The terminus also includes a rear body 20, seen in FIG. 2, which is shorter 
than the front body. A bore extends through the rear body between its 
forward end 21 and its rearward end 22. The portion 24 or the bore 
extending inwardly from the rearward end 22 is of relatively large 
diameter. This part of the bore connects, through a frustoconical surface 
25, to the forward portion 26 of the bore which is considerably smaller. 
The bore portion 26 has a diameter slightly larger than that of an optical 
fiber. 
Exteriorly, the rear connector body 20 includes an enlarged flange portion 
28 at one end of which is a forwardly facing radial shoulder 29. The 
exterior circumferential surface 30 that extends from the shoulder 29 to 
the forward end 21 is of relatively small diameter. This surface is 
interrupted near the forward end 21 by a portion 32 of slightly larger 
diameter. The diameter of the portion 32 is such that it can enter the 
rearward bore portion 15 of the front body 10 with a press fit. 
The optical fiber 34 to be associated with the terminus is prepared by 
stripping the buffer 35 from one end portion of the fiber. The bare fiber 
36 at that end and a portion of the buffer 35 then are cleaned. 
A material 37 is introduced into the bore in the front body 10, 
substantially filling it. The material 37 is in liquid form, but is of a 
nature such that it will cure to a solid deformable material. Preferably 
the cured material 37 possesses resilience such as that of a resilient 
elastomer. When the optical fiber connector is to be subjected to 
variations in temperature a material 37 should be selected which will 
maintain its properties throughout the anticipated temperature range. It 
is possible to select a material that will withstand elevated temperatures 
so that the optical fiber connector can be subjected to an environment 
having higher temperatures than those which can be withstood by a 
connector of conventional design. The material 37 may be, for example, a 
heat curable silicone rubber of approximately 35 duromaters when cured. 
Such a material may have an operating temperature range of -55 degrees 
Centigrade to +200 degrees Centigrade. 
In its liquid form, the material 37 may be injected into the front body 10 
with a syringe. Because of its high viscosity the liquid material 37 will 
not run out of the body 10 through the opening 13 in the front bushing 12. 
Enough liquid material 37 is introduced to substantially fill the 
passageway through the front connector body 10, as seen in FIG. 1. 
An O-ring 39 is positioned around the cylindrical surface 30 of the rear 
connector body 20 adjacent the radial shoulder 29. The cleaned end of the 
optical fiber 34 is extended through the passageway in the rear connector 
body 20 from the rearward end 22 to the forward end 21. The optical fiber 
end then is fed through the passageway in the front connector body 10 from 
the rearward end 14 so as to emerge through the aperture 13 and project a 
short distance beyond the end face 40 of the bushing 12. Although the 
material 37 is viscous it can be displaced readily to permit the fiber 34 
to be pushed through the front connector body. 
After this, the forward end of the rear connector body 20 is inserted into 
the passageway 15 at the rearward end of the front connector body. As this 
occurs the surface 32 near the forward end 21 of the rear connector body 
20 makes a press fit with the wall of the passageway 15 in the front 
connector body 10. The rear connector body 20 is advanced forwardly in the 
front body 10 a short distance longitudinally to assure an absence of any 
significant voids in the material 37. This position is shown in FIG. 2 and 
will be retained frictionally because of the press fit of the rear body 
into the front body. As the rear body 20 is moved to this position some of 
the material 37 may be displaced rearwardly around the fiber 34 through 
the passageways 26, 25 and 24 in the rear body. The presence of the fiber 
36 in the opening 13 blocks extrusion of the material 37 through that 
opening. 
The material 37 then is cured to a solid consistency. For a heat-curable 
material the assembly is subjected to an elevated temperature sufficient 
to effect the curing. 
After the curing of the material 37 is complete, the rear connector body 20 
is pushed further into the front connector body 10 to its final position 
shown, in FIG. 3. By virtue of the press fit in the passageway 15, the 
rear connector body 20 will be retained in this position. The forward 
movement of the rear connector body 20 causes it to exert a compressive 
force on the material 37. This causes the material 37 to exert an equal 
force against the connector body and the optical fiber 34. As a result, 
the fiber 34 is gripped securely along most of the length of the 
passageway through the front connector body 10. This force is uniform 
throughout the length of the optical fiber engaged by the material 34 and 
is the same on the buffer 35 as on the bare fiber 36. This creates a high 
frictional force locking the optical fiber to the terminus. There are no 
localized stress concentrations with the uniformly applied force against 
the fiber, which avoids damage to the fiber or undesired movement of it. 
To complete the terminus, the protruding end of the bare fiber 36 is 
severed and it is ground and polished flush with the end face 40 of the 
bushing 12. To construct a socket terminus, a socket sleeve 42 is fitted 
over the forward end portion of the front connector body 10 to provide a 
socket opening beyond the end face 40 of the front bushing 12. For a pin 
terminus, of course, the sleeve 42 is omitted. 
The optical fiber 34 will be retained in the terminus over a wide range of 
temperatures reflecting the temperature range of the material 37 selected, 
which can be far greater than that of adhesives normally used. As 
temperatures change and expansion or contraction occurs the material 37 
will act as a spring compensating for the minute dimensional changes 
encountered. No auxiliary spring is needed. 
The foregoing detailed description is to be clearly understood as given by 
way of illustration and example only, the spirit and scope of this 
invention being limited solely by the appended claims.