Fiber Optic Terminus

1. Field of the Invention

This invention relates to a fiber optic terminus which facilitates the coupling of optical fibers, both in the field and in the factory.

2. Description of Related Art

In military situations, it is often necessary for personnel operating under field conditions to reterminate optical fibers. In the past, this has been accomplished by injecting an epoxy into the terminus using a hypodermic needle and inserting the optical fiber. When the epoxy cures, the fiber is retained in position within the terminus. The fiber is then cut and polished flush with an outer surface of the terminus.

This technique has a number of disadvantages which are particularly acute for field terminations. For example, mixing of the components of the epoxy is time consuming and somewhat difficult under field conditions. Also, to remove tiny air bubbles known as micro bubbles from the epoxy, it is necessary to apply vacuum to the epoxy. If this is not done, these micro bubbles can induce miniature bends in the optical fiber and cause losses in the optical energy transmitted by the fiber.

Although it does not require substantial skill to carry out the field termination procedure, it would be desirable to further reduce the skill level and the consequent chances of error. It would also be desirable to eliminate the need to cut and polish the fiber in the field. Finally, it would be desirable to eliminate some of the equipment, e.g., the vacuum equipment, polishing tools, epoxy and hypodermic needle, that must be transported into the field or carried aboard ship in order to obtain the fiber optic termination.

This invention generally overcomes the problems identified above with the prior art. With this invention, the vacuum equipment and hypodermic needle, as well as the mixing of epoxy, are eliminated, and the required skill level is reduced. In addition, the need for polishing the fiber in the field is eliminated.

This invention provides a fiber optic terminus which includes a body having a passage therein and an outer surface. The passage has an opening at the outer surface for receiving an optical fiber. Means is provided in the passage for guiding the optical fiber.

An important feature of this invention is that a temperature-activated adhesive is carried by the body. The adhesive is flowable when its temperature is raised to a predetermined level. By raising the temperature of the temperature-activated adhesive to the predetermined level, the optical fiber can be adhered in the passage of the body.

Because the temperature-activated adhesive is carried by the body, the hypodermic needle employed heretofore and the field mixing of the epoxy are eliminated. In addition, because all that is required is to heat the adhesive to the desired temperature, the skill level for carrying out the coupling of the optical fibers is considerably reduced, and the likelihood of error in obtaining the fiber optic termination is correspondingly reduced.

To solve the problem of the micro bubbles referred to above without the need for separate evacuation equipment, this invention provides means for applying a compressive force to the adhesive. When the temperature of the adhesive is raised to the predetermined level, the adhesive flows under the influence of the force applying means, and the micro bubbles are forced out of the adhesive.

The adhesive can be of any temperature-activated type which is capable of adhering an optical fiber in the passage of the body. For example, the adhesive may be hot melt glue, a B-staged epoxy pellet or wax. Preferably, the adhesive is solid at ambient temperatures and becomes flowable at a temperature well above ambient, such as 300 degrees F. or above. For better adhesion, the adhesive preferably completely surrounds the optical fiber, and for this purpose, has a passage extending through it which is adapted to receive the optical fiber.

Although the force-applying means can take different forms, it preferably includes a tubular plunger having a passage extending therethrough which is also adapted to receive the optical fiber. Although the plunger can be moved in different ways, this can be simply, accurately and inexpensively accomplished using biasing means, such as a spring.

The means for guiding the optical fiber can take various different forms, but preferably it includes a fiber guide in the passage of the body and having a passage extending through it. With this construction, the passages of the fiber guide, the adhesive and the plunger are preferably all in registry so that the optical fiber can be extended through all of them. Also, the adhesive is preferably sandwiched between the fiber guide and the plunger so that the adhesive is compressively loaded between the plunger and the fiber guide.

Another feature of this invention, which can be used with or without the temperature-activated adhesive feature, is that the fiber optic terminus may be provided with one optical fiber permanently retained in the passage of the body with an outer end face of the optical fiber polished and essentially flush with an outer surface of the terminus. This eliminates cutting and polishing of the fiber in the field. An inner end face of the optical fiber is exposed in the passage of the fiber guide. When so constructed, the fiber optic terminus is adapted to optically couple the inner end face and the optical fiber which is receivable through the opening. In addition, the adhesive can be activated in the factory or elsewhere to attach the optical fiber.

The invention, together with additional features and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying illustrative drawing.

In the accompanying drawings:

FIG. 1 is an axial sectional view through a fiber optic terminus constructed in accordance with the teachings of this invention with the adhesive in a deactivated state.

FIG. 2 is a sectional view similar to FIG. 1 with the adhesive activated and cured.

FIG. 1 shows a fiber optic terminus 11 which includes a body 13 having an axial passage 15 extending therethrough, means, including a fiber guide 17 in the passage 15 for guiding an optical fiber 19 (FIG. 2), a temperature-activated adhesive 21 and means for applying a compressive force to the adhesive in the form of a plunger 23 and a spring 25.

The body 13 can be of any desired configuration, and in this embodiment, the body 13 is elongated and is constructed of a suitable metal. The passage 15 has openings 27 and 29 at its opposite ends.

A number of accessories may be mounted on the body 13 to form a body assembly for various purposes, such as mounting of the body into a housing (not shown). These accessories are conventional and may include, for example, an O-ring seal 31, a contact retention clip 33, a series of belleville washers 35 mounted to form a spring and acting against a washer 37, a floating spacer 39 and a guide bushing 41 pressed onto one end of the body 13 and having a orifice 43. A length of heat-shrink tubing 45 is slid over the other end of the body 13, and such other end may have a series of grooves 47 in its outer surface to strengthen the attachment between the tubing 45 and the body 13 when the former is shrunk onto the body.

The fiber guide 17 is suitably fixedly mounted within the passage 15 and, in the illustrated embodiment, is pressed into a region of the passage 15. The fiber guide 17 has an axial passage 49 extending completely through it. The passage has flared conical end portions 51 and 53. The fiber guide 17 is preferably constructed of a ceramic.

The adhesive 21 is carried by the body 13 and must be able to flow into the passage 15 when activated. Preferably, the adhesive 21 is retained within the passage 15 and, in this embodiment, is sandwiched between and engages the plunger 23 and the fiber guide 17. In this embodiment, the adhesive 21 is a hot-melt glue which becomes flowable at about 300 degrees F. and is in the form of a cylindrical ring having a cylindrical passage 55 extending axially through it.

The plunger 23 has an axial cylindrical passage 57 extending completely through it. The plunger 23 is slidable axially in the passage 15 of the body 13 and is biased toward the adhesive 21 by the spring 25, which acts between a rear fiber guide 59 and an annular shoulder 61 on the plunger 23. For example, the spring 25 may apply a load of about 100 psi to the adhesive 21.

The rear fiber guide 59 is mounted in the passage 15 and, in this embodiment, is pressed into the passage 15. The rear fiber guide 59 has an axial passage 63 extending through it with the lefthand or entrance end of the passage flared conically outwardly. The passages 49, 55, 57 and 63 are all in registry and, in this embodiment, are in axial alignment so they can receive the optical fiber 19 as described hereinbelow.

In this embodiment, an optical fiber 65 comprising a core and cladding extends through the orifice 43 and into the passage 49 of the fiber guide 17. The optical fiber 65 may be attached in any suitable manner, and in this embodiment, it is bonded to the guide bushing 41 at the orifice 43. The optical fiber 65 terminates in an inner end face 67 in the passage 49 of the fiber guide 17 and in an outer end face 69, which is ground and polished flush with an end surface 71 of the body assembly and, more specifically, the guide bushing 41. This can be done during manufacture to eliminate field polishing of the outer end face 69. The radial position of the inner end face 67 is accurately controlled by the passage 49 of the fiber guide 17. A layer of index matching material may be applied to the inner end face 67. Of course, an optical component other than the end face 67 of the optical fiber 65 may be retained by the fiber guide for purposes of being optically coupled to the optical fiber 19.

In use of the fiber optic terminus 11, a region of a jacket 73 (FIG. 2) is stripped away to expose the optical fiber 19 which comprises a core and cladding. The optical fiber 19 is then inserted through the opening 27 and the passages 63, 57 and 55 and into the passage 49 of the fiber guide. The optical fiber 19 is advanced until its end face 75 engages the end face 67 of the optical fiber 65 as shown in FIG. 2. In this position, the end faces 67 and 75 are accurately aligned, and the jacket 73 is within the lefthand end portion of the passage 15 and within the tubing 45.

With the optical fiber 19 in this position, the body 13 and the tubing 45 may be heated in any suitable manner, such as by a small forced air heater to elevate the temperature of the adhesive to the level at which the adhesive becomes flowable. When the adhesive becomes flowable, it is forced to flow by the force of the spring 25 acting on the plunger 23 to reduce the axial length of the adhesive and to cause it to flow radially in both directions such that it engages the wall of the passage 15 of the body 13 and completely surrounds and tightly engages the optical fiber 19 as shown in FIG. 2. The adhesive can be expected to flow into the enlarged end portion 53 of the passage 49 and into any openings presented. Of course, the adhesive remains quite viscous even when flowable. The adhesive is then allowed to cure to strongly couple the optical fiber 19 to the body 13 with the end faces 67 and 75 coaxial and in contact, or essentially in contact.

The temperature to which the fiber optic terminus 11 is exposed is preferably sufficient to activate the shrink tubing 45 to cause it to contract around the body 13 and the jacket 73 as shown in FIG. 2. However, it could be activated at a higher temperature, if desired. Th shrink tubing 45 holds the jacket 73 in the position shown in FIG. 2.

Although exemplary embodiments of the invention have been shown and described, many changes, modifications and substitutions may be made by one having ordinary skill in the art without necessarily departing from the spirit and scope of this invention.