Method of forming an optical fibre connector

Abstract: A fibre optic connector (20) includes a retaining section (26) for receiving a retaining clip (28), and a severable section (30). The connector (20) has a cable receiving bore (35) which receives a fibre cable (2). The fibre cable (2) is receivable in the bore (35) such that the fibre (6) projects beyond a front face (50) of the severable portion (30). The severable end portion (30) is removable adjacent to a notch (32) to form a clean end face.

Description: The invention relates to a connector for terminating fibre optic cables. The optical qualities of a fibre optic electrical connector are often dependent upon the ability to cut the optical fibre without destroying the surrounding cladding. It is easy to cut an optical fibre including the surrounding jacket, as the jacket supports the inner cladding and fibre for cutting. However most optical connectors require a bare fibre, including the core and cladding, to be inserted through a rear side of a fibre connector. Thus it is usually required to strip the outer insulating jacket from the fibre cable, in a manner similar to stripping the insulation from a metal conductor of an insulated wire. However, when the fibre core and cladding are bared and the fibre end is cut, the cladding is often times chipped and severed at the free end, and it is this end face which is used as the mating interface with the complementary connector or other optical device. Thus, much time and effort has been spent trying to perfect methods for notching and cutting fibre ends so as to reduce the destruction to the fibre cladding at the fibre free end. An object of the invention then is to provide a method of termination to enhance the mating interface of a fibre optical electrical connector. The present invention consists in a method, as defined in claim 1, of forming an optical fibre connector. US-A-4 084 308 discloses a method according to the preamble of claim 1. A resin housing is molded about the fibre cable. JP-A-62 118 306 discloses a method of severing an optical fibre cable, in which the fibre cable is inserted through a pipe. A blade is used to sever the pipe and the fibre cable, after which the severed length of the pipe which remains on the fibre cable is removed. US-A-4 333 705 discloses a similar method to that of US-A-4 084 308 but in which a notch is formed in the housing back from its forward end and the forward end and the fibre cable are snapped off at the notch. The preferred embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which:- Figure 1 shows a standard fibre cable including the bared fibre and jacket; Figure 2 shows a free end of the bared fibre showing at the free end, the destroyed cladding; Figure 3 is a top view showing an electrical connector in accordance with the preferred embodiment of the invention; Figure 4 is a side plan view of the connector shown in Figure 3; Figure 5 is a front plan view of the connector viewed in Figure 4; Figure 6 is an end view of the connector as shown in Figure 4; Figure 7 is a cross sectional view taken through lines 7-7 of Figure 3; Figure 8 is a view of a fibre cable with the jacketing stripped to the proper length; Figure 9 is a partial cross sectional view similar to that of Figure 7 showing the fibre cable of Figure 8 inserted into the connector; Figure 10 shows the downward movement of the retainer clip which holds the fibre cable in a longitudinally fixed position; Figure 11 shows the final movement of the retainer into its final position as well as the initial movement of a cutting blade to severe the front end of the fibre connector; Figure 12 shows the complete severing of the front end of the connector; Figure 13 shows the front end of the connector falling free of the complete fibre connector; Figure 14 shows the front mating end as completed; Figure 15 shows a diagrammatical view of the knife which is used for the cutting operation; Figure 16 is an end view of the cutting knife shown in Figure 15; Figure 17 shows a view through lines 17-17 of Figure 15 and; Figure 18 is a diagrammatical view of the cutting operation. With respect first to Figure 1, a fibre cable is shown generally at 2 which includes an outer insulating jacket at 4 which covers a fibre cable 6. The fibre 6 is shown in Figure 2 as including an inner core 8 and an outer cladding at 10. As mentioned before, when a fibre cable is cut through the outer jacket 4, there is no shattering of the outer cladding material, as the jacket material protects the cladding through the cutting operation. However most fibre connectors, require that the fibre cable be prepared as shown in Figure 1 where the outer jacket 4 is stripped at 12 and pulled forward (leftward as viewed in Figure 1) to expose the bared fibre 6. The next step in preparing the cable is to cut the free end 12 of the fibre cable to provide an exposed bared cable of a specific length, and to provide a mating fibre end at 14. Cutting the fibre without the insulative jacket 4 however causes chattering and destruction of the cladding material 10 towards the free end 12 as shown by reference numeral 16 in Figure 2. When this fibre free end 12 is now inserted into a fibre connector, light loss occurs by the destroyed cladding material at the free end 12. With respect now to Figures 3-7, an improved connector will be described for use with a cable similar to that as shown in Figure 1. With reference first to Figure 3 and 4, a fibre connector is shown generally at 20 which is provided by an insulating housing generally comprised of a relatively soft material such as a polyvinylchloride (PVC) or a polyester material. The connector 20 includes a front mating end 22 having an outer diameter 24 which is generally received in the bore of a mating connector, or like electronic device. The connector 20 further includes a terminating section at 26 including a U-shaped retaining clip 28 which is relatively conventional but will be described in greater detail herein. Finally the connector 20 includes a severable section at 30 forwardly located of a notch at 32. With reference now to Figures 3-7, the connector 20 will be described in greater detail. The connector housing 20 includes a cable receiving end at 34 having a receiving bore shown 35, defined by a lead-in section 36 and a cylindrical bore at 38. The retaining clip 20 is positioned in a transverse clip receiving groove at 40 which intersects with the bore 38, but it should be appreciated that when the clip is in the position shown in Figures 4 and 7, that the free end of the clip does not interfere with the bore 38 such that a fibre cable can be inserted without hitting the clip ends. This is best shown in Figure 6 where the end of one of the clip retaining arms 42 is shown in phantom where the end of the clip arm 42 is above the periphery of the bore 38. The bore 38 extends forwardly to a frusto-conical section 44 which narrows down to a fibre receiving bore 46 which extends forwardly beyond the notch through the severable portion 30 and to an end 50 of the severable portion. It should be understood that the diameter of the bore 38 is profiled to receive the outside diameter of the fibre jacket 4 whereas the inside diameter 46 is profiled to receive the fibre, including the core and cladding 6. As shown in Figures 3 and 4, the housing 20 further includes latching members 52 and a forwardly facing shoulder at 54. With respect now to Figures 8-13, the method of assembling the connector and fibre will be described in greater detail. As shown in Figure 8 a fibre cable 2 is shown which is similar to that in Figure 1, except that the cable has not been cut to length at its free end thus that the fibre 6 has a rough end at 7. The outer jacket 4 is stripped to expose the fibre cable 6 to a length L which is somewhat greater than the distance from the leading edge of the frusto conical portion 44 and the front face 50 of the severable portion 30. Said differently, enough fibre core 6 is exposed such that when the fibre cable 2 is inserted through the bore 35, to a position where the end face 12 of the insulation abuts the shoulder formed by frusto-conical portion 44, a sufficient length of fibre cable 6 is exposed beyond the front edge of the face 50 as shown in Figure 9. When the fibre cable 2 is in its fully forward position as it is described above, a force F1 may be applied to the retainer clip 28 as shown in Figure 10 to a first locked position which will retain the cable from axial movement during the transport of the connector housing 20 and cable 6 to a cutting station. With reference now to Figures 11-13, the connector housing 20 and fibre cable 2 are moved to a position where the severable portion 30 can be removed. As shown in Figure 11 a cutting knife 60 is shown positioned proximate to the notch 32, and a force F2 can be subjected to the retainer 28, and the knife member 60 can be projected downwardly to begin severing the end portion 30. As shown in Figure 12, the knife member 60 is protruding through the section 30 and through the fibre cable 6 whereas in Figure 13 the section 30 is completely severed from the connector member 20 leaving a clean end face at 70. By providing the notch at 32, and by cutting through the mating end portion 32 at the notch, a champered lead-in section 72 is thereby formed. Advantageously, it has been shown that by cutting through the cable and through the connector end portion 22 as described above, the light loss can be kept to a minimum of 2.2 dB, without any polishing of the free end. If this optical quality is not adequate, the free end can also be polished to achieve a light loss of only one dB. Also advantageously, if polishing is necessary, the polishing time required is merely seconds, as the connector end face and the fibre are cut to such a clean end face, and as the connector end 22 and the fibre 6 are cut simultaneously such that they are at the exact same axial length. It should also be appreciated that this type of connector assembly could be utilized in a mass production operation, an automatic harness making apparatus could feed lengths of fibre cable to a specific length, and then strip the ends of the insulation a distance L. The end portion 7 could be automatically inserted into the receiving bore 35 of the connector housing 20 whereupon the retainer 28 is moved to a partially retaining position as described with respect to Figure 10. The assembly as shown in Figure 10 of the connector housing 20 and the fibre cable 2 could then be moved to a cutting station where the knife member 60 is automatically registered by distance X from the shoulder 54 as viewed in Figure 11. In the preferred embodiment of the invention the cutter member 60 is a ceramic blade having an angled cutting edge 62 where in the preferred embodiment of the invention, the angle α is 45°. Also preferably the cutting edge 62 is a symmetrical sharpened tip where in the preferred embodiment of the invention, β = 20°. It should be appreciated that the combination of the sharpened tip 62 and the angle α, in combination, provide for a cutting and slicing action. The sharpened tip 62 provides for the cutting through of the connector housing 20 and through the fibre cable 6 but also through the connector end portion 22. Furthermore the angled cutting edge at an angle α provides for relative movement of the cutting edge with respect to the connector 20 and fibre 6 providing a simulated slicing action.

Claims: A method of forming an optical fibre connector, comprising the steps of retaining an end portion (6) of an optical fibre cable (2) in a connector housing (20), adjacent to a front mating end (22) of the housing (20) and cutting off a portion (30) of said front mating end (22) and the optical fibre cable (2) therein by means of a knife blade to provide a planar mating face (70); characterised by the steps of providing in the front mating end (22) of the housing (20) a notch (32) and a bore (46) extending beyond the notch into the housing (20) and dimensioned to receive the optical fibre cable (2), inserting the optical fibre cable (2) into the cable receiving end of the bore (38,46) until an end portion (6) of the cable (2) is adjacent to the front mating end of the housing (20), and cutting off said portion (30) of said front mating end (22) at the notch (32). The method of claim 1, characterised in that the fibre cable (2) extends beyond the front mating end (22) prior to the cutting step. The method of claim 1 or 2, characterised in that the notch (32) provides a chamfered edge (72) at the planar face (70) after said cutting step. The method of claim 1, 2 or 3, characterised in that the cutting step is accomplished with a ceramic knife blade (60). The method of claim 4, characterised in that the ceramic knife blade (60) has a cutting edge (62) which has an oblique angle relative to the blade movement direction, and in that the ceramic knife blade has a sharpened cutting edge. The method of claim 5, characterised in that the oblique angle is 45° to the perpendicular to the blade movement direction. The method of claim 5 or 6, characterised in that the cutting edge has a symmetrically sharpened tip of 20°.

Inventors: VAN WOESIK EGBERTUS THEODORUS, VAN WOESIK, EGBERTUS THEODORUS CONSTANTIUS MARIA
Applicants: WHITAKER CORP, THE WHITAKER CORPORATION
Application year: 1993
Main classification: G02B6
IPC codes: G02B6