Optic Fiber Contact

A pair of optics fibers can be optically coupled by forming lenses at the ends of the optic fibers and positioning the lenses substantially in alignment and at approximately a predetermined spacing. One technique for accomplishing this is to insert the fiber through a hole in a contact so the end of the fiber lies in a cross-aperture in the end portion of the contact. A pair of electrodes are placed on either side of the fiber, in line with the cross-aperture, and an electric arc is established between the electrodes to melt the fiber end to form a nearly spherically shaped lens thereon.

Fiber optic contacts can be formed of stainless steel for high precision, or of molded plastic for lower cost production. When using such contacts, care must be taken to assure that the electric arc is not short-circuited and does not melt the contact. Japanese patent No. 58-102911 by Takashima describes a technique wherein the electrodes have flat ends and lie closely on either side of the fiber. Such closely spaced electrodes appear to confine the arc to just the fiber, which could avoid short-circuiting the arc through a metal contact or melting a plastic, or polymer, contact. When only a small arc current is used, to splice a pair of fibers to join them, such close spacing of the electrodes works well. However, when a larger arc current is used to melt the end of a fiber into a lens of greater diameter than the fiber, it is found that the electrodes become degraded after repeated use, so the arcs become erratic. An arrangement which enabled the forming of a fiber end into a lens of greater diameter than the fiber, in a cross-aperture of a contact end, in a consistent manner, would be of considerable value.

In accordance with one embodiment of the present invention, an optic fiber connection apparatus is provided which facilitates the repeatable formation of an enlarged lens at the end of an optical fiber. The contact has a hole extending along its axis for receiving the optic fiber, and includes a cross aperture at the front of the contact along which an electric arc can be established between a pair of electrodes lying on opposite sides of the fiber. The contact includes a forward end portion formed of a ceramic or other high melting temperature material in which the cross-aperture is formed. The arc electrodes are widely spaced, which avoids an erratic arc over a period of time when lenses are repeatedly formed, while avoiding short circuiting of the arc by the contact or melting of the contact.

The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.

FIG. 1 is a perspective view of a contact of the present invention, showing the manner in which a lens is formed on an optic fiber.

FIG. 2 is a sectional view of the apparatus of FIG. 1.

FIG. 3 is a view taken on the line 3--3 of FIG. 2.

FIG. 4 is a sectional view of a connection assembly which includes the contact and optic fiber shown in FIG. 2.

FIG. 5 is an enlarged partial sectional view of the apparatus of FIG. 2.

FIG. 6 is a sectional view of an optic fiber connection assembly constructed in accordance with another embodiment of the invention.

FIG. 7 is a view taken on the line 7--7 of FIG. 6.

FIG. 8 is a partial perspective view of the connector of FIG. 6.

FIG. 2 illustrates an optic fiber connection apparatus 10 which includes a contact 12 which has a longitudinal passage or hole 14 extending along its axis 16, for receiving an optic fiber 18. The optic fiber is part of an optic fiber assembly 20 which includes a buffer 22 whose front end has been stripped off. The contact 12 includes a ferrule 24 and a bushing 25 mounted on the front end of the ferrule. In order to effectively couple the front end of the optic fiber to another similar optic fiber, a lens or bead 26 is formed at the end of the fiber, by heating the fiber end into a bead having a rounded and optically clear end. The contact 12 may be used to couple the optic fiber 18 to an external optical device, such as to another similar optic fiber as described above, or to a light source (not shown) or light detector (not shown). One method for heating the optic end is to position a pair of electrodes 30, 32 on opposite sides of the optic fiber end on an imaginary line 36 that extends along a cross-aperture through the optic fiber, and applying a voltage between the electrodes to establish an arc between them that passes across the optic fiber to heat it. This heating method has been found to produce nearly spherical lenses of diameters that are predictable within about three percent. The contact is formed with a cross-aperture 34 that provides access to the optic fiber end to form the lens thereon.

The cross-aperture 34 extends along a direction 36 that is largely perpendicular to the axis 16 of the contact along which the hole extends. This enables the lens 26 to be initially formed at a location rearward of the front end 40 of the contact. The optic fiber therefore does not have to be pulled rearwardly after the lens is formed. A typical optic fiber has a diameter of about 125 .mu.m (about 5 thousandths inch), while the lens 26 on such a fiber may have a diameter of about 200 .mu.m (about 8 thousandths inch).

The lens 26 is preferably formed so upon its formation it lies at the final position it is to assume for coupling to another optic fiber. As shown in FIG. 5, this can be accomplished by locating the tip 18t of the unlensed optic fiber end, at a position where it will form a lens whose end 26e is spaced at a predetermined distance D from the contact end. The tip 18t is located so the volume of the unlensed fiber between the fiber tip 18t and the desired position of the root 26r of the bead, equals the volume of the lens 26 to be formed. Prior to the lens 26 being formed, the optic fiber assembly can be permanently fixed in position in the connection 12, without the need to slide the optic fiber 18 along its length after the lens 26 has been formed. Avoidance of the need to slide the lensed fiber, especially in the rearward direction, minimizes the danger of damage to the lens. In the final position, the lens root 26r is spaced a distance w forward of the end walls 47 of the hole.

In the prior art, the entire contact 12 has been constructed of stainless steel, to provide high rigidity and strength, although a high strength plastic could be used. With the line 36 connecting the tips of the arc electrodes extending through the cross-aperture 34, care must be taken to avoid either short-circuiting the arc through the closely-surrounding cross-aperture walls, or the melting of such cross-aperture walls. One approach would be to place the tips of the electrodes 30, 32 closely on either side of the optic fiber, to prevent the arc from passing to the walls of the cross-aperture or from melting such walls. Such close spacing of the electrodes works well where a low arc current is sufficient, as when splicing the ends of a pair of fibers wherein the fiber ends only have to be softened. However, where a much larger arc current and/or duration (e.g. 30 milliampers for 3 to 6 seconds for a 125 .mu.m to 250 .mu.m fiber) is required, to melt the fiber end to form a molten ball that becomes a lens larger than the fiber, applicant has found that such close electrode spacing is unsatisfactory. It is found that the arc becomes erratic after the electrodes have been used several times, so that it is difficult to produce lenses of consistent size. Applicant believes the degradation of the electrodes is due to silica vapor from the molten fibers depositing of the electrode tips.

Applicant avoids degradation of the electrodes with their repeated use to form lenses at the ends of optic fibers, by spacing the electrode tips far apart compared to the fiber diameter. The spacing A (FIG. 2) of the electrode tips is preferably equal to more than half the length of the cross-aperture through which the arc passes. The spacing is preferably at least eight times the fiber diameter (i.e. for a 125 .mu.m diameter fiber the spacing is preferably at least 0.040 inch, or one-twentieth of an inch). To prevent the arc from short-circuiting through the contact wall that forms the cross-aperture, the front end of the contact, formed by the bushing 25, is formed of a dielectric. To prevent the arc from melting the bushing, the bushing is formed of a high melting temperature dielectric material. A ceramic, which is a material formed of a nonmetallic mineral at high temperatures that are above the melting temperature of the optic fiber and which have a melting temperature above the softening temperature of the optic fiber, and preferably above its melting temperature, is used. Optic fibers include a cladding and a core within the cladding. Typical optic fibers have claddings that soften at 1040.degree. C., and have cores that soften at 1600.degree. C. and melt at 2200.degree. C. to 2400.degree. C. Thus, the bushing material is a dielectric which softens and melts only at a temperature of over 1600.degree. C., and preferably at over 2200.degree. C.

The optic fiber assembly can be fixed in place, as by applying epoxy 45 (FIG. 2) between the buffer 22 and holder 24, or by crimping the optic fiber assembly in place. The fact that the optic fiber does not have to be pulled back results in avoiding the danger that the lens will be broken off by being pulled against the end walls 47 (FIG. 5) of the end of the narrow contact hole.

FIG. 4 illustrates a connection system where the optic fiber 18 is optically coupled to another similarly mounted optic fiber 50. The contacts 12 which hold the two optic fibers are mounted in a housing 52 which holds the connectors in alignment, with their ends 40 in abuttment. A transparent intermediate sheet 54 is sometimes placed between the lenses to facilitate their coupling. Although the lenses at the ends of the two optic fibers provide good coupling over a range of separations, it is still important to maintain their separation within such a range.

FIGS. 6-8 illustrate another optic fiber connector 60 which includes a hole 62 extending through the entire length of the contact between its opposite end portions 64, 66, along the axis 68 of the connector. A cross-aperture 70 of greater width C than the diameter H of the hole extends between opposite sides 72, 74 of the contact along a direction of axis 76 which is substantially perpendicular to the axis 68 of the hole. Electrodes can be positioned in line with the cross-aperture 70 on opposite sides of the hole axis 68 to create an arc that passes through the cross-aperture to melt an optic fiber whose tip initially lies at the position 80. The resulting lens 82 lies within the cross-aperture 70.

As mentioned above, the diameter of the lens formed by an arc extending between electrodes can be closely predicted. The diameter C of the cross hole is preferably no more than 50% greater than the diameter of the bead or lens 82. Also, the diameter of the hole 62 is less than the diameter of the lens. The final position of the lens is the same as the position at which the lens is formed, so the optic fiber does not have to be moved axially after the lens is formed and before the optic fiber assembly is fixed in place.

Thus, the invention provides an optic fiber connection apparatus and method, which enables the consistent forming of a lens of greater diameter than an optical fiber at the end of the fiber. A contact having a hole through which the fiber extends, includes a cross-aperture at its end through which an arc can extend between a pair of electrode tips, to melt the fiber end into an enlarged lens. The contact end is preferably formed of a ceramic material to enable the arc electrodes to be widely spaced to provide for consistent lensing, without short circuiting the arc or melting the contact end.

Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art, and consequently, it is intended that the claims be interpreted to cover such modification and equivalents.