OPTICAL CONNECTOR AND PROCESS FOR PRODUCING THE SAME

Abstract: An optical connector comprises an optical fiber connector ferrule which comprises a substrate plate (111) having at least one optical fiber groove (113) and pin grooves (114) each being formed at one surface thereof, and a cover plate (112) joined to the substrate plate to form at least one optical fiber groove holes into which an optical fiber is inserted; a guide pin means (102) to be inserted into the pin grooves for coupling the optical fiber connector ferrule with another; and means for absorbing the variation in the diameter of the guide pin means. A process for producing an optical connector comprises the steps of: preparing a substrate plate wafer and a cover plate wafer; forming a plurality of optical fiber grooves on a top surface of said substrate plate wafer and a plurality of windows in said cover plate wafer; stacking the cover plate wafer on the substrate plate wafer; heating the cover and substrate plate wafers at an elevated temperature to join them into a unitary assembly; cutting the unitary assembly in a direction that is parallel to the plurality of optical fiber grooves and in a direction that is perpendicular to the plurality of optical fiber grooves and in traversing the centers of the plurality of windows in the cover plate wafer to produce a plurality of chips of optical fiber connector ferrule having a cutout in the rear portion of each cover plate; and fixing a plurality of optical fibers in a fiber array in position in a plurality of optical fiber holes.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a wire material positioning connector and in particular, to an optical connector comprising the features as set out in the preamble of claim 1. An optical connector comprising similar features is, for example, known from FR-A-2406211. The optical connector of the present invention employs the use of guide pins to couple optical connector plugs together for fixing optical fibres in position in lightwave communications systems. Prior Art Fig. 1 is a sketch of a typical example of the prior art optical connector. In Fig. 1, the numeral 10 denotes an optical connector plug formed by resin molding; a ribbon fiber (A) contains five optical fibers 15 which are fixed in position side by side at a pitch of, say, 0.3 mm, and guide pin holes 16 are formed on both sides of the ribbon fiber at a pitch of 3.6 mm. Indicated by 17 is a guide pin having a diameter of, say, 0.7 mm. Two such guide pins 17 are inserted into guide pin holes 16 formed in one optical connector plug 10, then inserted into the corresponding holes in the other plug which is positioned in registry with the first plug, and the two optical connectors are coupled together. In the present invention, the term "optical connector plug" is used to designate the most important basic member of an optical connector which fixes optical fibres in position so as to couple them together. When coupling multi-fiber optical connectors 10, it is necessary that the optical fibers in one connector should abutt in a very precise manner against those in the other connector in order to minimize the coupling loss. This requirement is particularly stringent when coupling single-mode fibers which have a core diameter of only about 10 µm and even an axial displacerent of no more than about 1 µm between fibers will cause a great coupling loss. To avoid this problem optical fibers to be mounted on an optical connector must be positioned in the proper place with vary high precision; in coupling two optical connectors, it is also necessary that they should be positioned with high precision by means of guide pins. In order to realize low-loss coupling of multi-fiber optical connectors of the type described above, it is first of all necessary that optical fiber guide holes and guide pin holes should be provided at designed positions by precision machining. But even if this requirement is met, some clearance still remains both between the optical fiber guide holes and optical fibers and between the guide pin holes and guide pins and because of the existence of such clearance, it is not always possible to achieve low coupling loss. Even if the clearance is only about 0.5 µm both between optical fibre guide holes and optical fibres and between guide pin holes and guide pins, optical fibres will experience an axial offset of about 1 µm in an extreme situation. Therefore, in order to realize low coupling loss, it is essential that each of these clearances be entirely eliminated or reduced to thew nearest of zero. However, in consideration of the variation in the inside diameters of optical fiber guide holes and guide pin holes, as well as the variation in the outside diameters of optical fibers and guide pins, it is by no means easy to reduce these clearances. If an optical fiber guide hole should have an inside diameter smaller than the outside diameter of an optical fiber to be inserted thereinto, not only is it impossible to insert the optical fiber but also the fiber itself may break. If the inside diameter of a guide pin hole is smaller than the outside diameter of a guide pin to be inserted thereinto, the guide pin, which must be forced into the guide pin hole, will break either itself or the guide pin hole. Suppose here the case where guide pins are to be inserted into guide pin holes in a multi-fiber optical connector. If the precision Of machining is within ± 1 µm both for the guide pin diameter which should be 0.700 mm and for the inside diameter of the guide pin hole which should be 0.701 mm, there is a high likelihood that some of the guide pins have an outside diameter of 0.701 mm while some guide pin holes have an inside diameter of 0.700 mm. In this situation, none of the guide pins can be inserted into any guide pin hole. As described above, the efforts so far made to minimize the clearance that exists between guide holes and wire materials when the latter are to be fixed in position in the former have been limited by the precision of machining and this means that there is a certain limit on the effort toward reducing the coupling loss that occurs in coupling connectors such as multi-fiber optical connectors. Therefore, these problems have been a major obstacle to the goal of achieving low-loss coupling of optical connectors. With an optical connector of the type shown in Fig. 1, some clearance (g), as shown in Fig. 2, is necessary for permitting a guide pin 17 to be smoothly inserted into a guide pin hole 16 in an optical connector plug 10. However, the provision of this clearance (g) causes the problem that the coupling loss occurring in coupling optical connectors, in particular, those optical connectors which are used to achieve precise positioning of single-mode fibres with a core diameter of 10 µm, will vary as a result of repeated connect-disconnect cycles. Stated more specifically, if a variation of 0.5 µm occurs on account of the clearance (g) as a result of repeated connect/disconnect cycles, the optical connectors that were initially connected to produce a coupling loss of 0.5 dB will eventually produce a variation of about ± 0.3 dB after repeated connect and disconnect operations. This amount of variation is greater than the initial value of coupling loss. It is therefore clear that in order to realize low-loss and stable coupling of single-mode fibers, the connect/disconnect variation resulting from the clearance (g) for guide pins 17 must be reduced. However, if the clearance (g) is reduced, it becomes difficult to smoothly insert the guide pin 17 into the guide pin hole 16. These problems could be solved by employing a guide pin that is in the form of an elastic slit pipe 18 which has a longitudinal slit 18a as shown in Fig. 3. However, in order to fabricate a slit pipe having an outside diameter of 0.7 mm with a wall thickness of 0.1 mm, the pipe must be worked to have an inside diameter of 0.5 mm and it is difficult and very expensive to achieve by such micro-machining the precise working of the pipe to attain perfect roundness in its outside diameter and accuracy in other shape parameters. In order to reduce the size of an optical connector, the size of guide pins must also be reduced but to this end, the diameter of each guide pin has to be decreased to 0.5 mm and even to 0.3 mm, making the machining of an elastic slit pipe 18 more and more difficult. SUMMARY OF THE INVENTION An object of the invention is to provide an optical fibre connector that is free from the aforementioned problems. Another object of the invention is to provide an optical fibre connector which is equipped with guide pins that are reduced in diameter and which ensures high dimensional precision and can be produced in large quantities. A further object of the invention is to provide an optical fibre connector that tolerates a certain dimensional variation in working due to the limited percision of machining skill and that enables a wire material to be precisely positioned with reduced clearance. The aforementioned object of the present invention can be achieved by providing an optical fibre connector comprising the features as set out in claim 1. Further embodiments of the present invention are described in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sketch showing a typical example of the prior art optical connector; Fig. 2 illustrates the problem that affects the optical connector shown in Fig. 1; Fig. 3 is a perspective view showing an elastic slit pipe used as a guide pin; Fig. 4 is a perspective view of an optical connector according to the present invention; Fig. 5 is a front view of an optical fibre guide member in the optical connector of the present invention; Fig. 6 is a longitudinal section of two units of the optical connector shown in Fig. 4 Fig. 7 is a cross section of an optical connector according to the present invention; Detailed Description of the Preferred Embodiments Fig. 4 is a perspective view of an optical connector according to an embodiment of the present invention. Fig. 5 is a front view of an optical fiber guide member in the optical connector of the present invention. Fig. 6 is a longitudinal section of two coupled units of the optical connector shown in Fig. 4. The construction of the optical fiber guide member 101 in the optical connector of the present invention is shown in Fig. 5; a grooved substrate 111 provided in its top surface with optical fiber guide grooves; 113 for fixing optical fibers in position and guide pin grooves 114 is overlaid with a flat plate 112 that is joined to said grooved substrate 111 with a thin layer of an adhesive 115 being interposed, and the flat plate 112 covers only the optical fibre guide grooves 113 in such a way that the guide ping grooves 114 are exposed. As shown in Figs. 4 and 6, two optical connectors are coupled together, with a clamp 103 having a resilient compressive force being attached from the rear end of the optical fiber guide member 101 while guide pins 102 are inserted from the front end of the guide member 101. As a result, the guide pins 102 are secured in the guide pin grooves 114 by the resilient compressive force of the clamp 103. Each of the guide pins 102 is provided with at least two small-diameter portions 121 and that portion of the underside of the grooved substrate 111 where the small-diameter portions 121 are situated is provided with a clamping groove 116 that runs in a direction perpendicular to the axial direction of each guide pin 102. The pressure-applying portions of the clamp 103 serve to compress and fix the guide pins 102 in position, with one pressure-applying portion being situated in the small-diameter portions of the guide pins 102 while the other pressure-applying portion is situated in the groove 116 on the underside of the grooved substrate 111. The width of the clamp 103 is made equal to or slightly greater thatn the width of the grooved substrate 111 of the optical fibre guide member 101, and the height of the clamp 103 is so set that its maximum dimension is greater than the height of the optical fibre guide member 101. Fig. 7 is a cross section of an optical connector according to another embodiment of the present invention. In this embodiment, the clamp 103 is divided into two separate members which are so constructed that they can be connected or disconnected from the lateral side of the optical fiber guide member 101. In this case, clamping grooves 117 are formed on the grooved substrate 111 in such a way that they run parallel to the axial direction of the guide pins 102, and the clamp 103 is provided with a projection where it contacts each of the small-diameter portions 121 of a guide pin, so that said projection is situated in the associated small-diameter portion 121 of a guide pin. In the optical connector of the present invention, the guide pin grooves 114 in the optical fiber guide member 1 are not covered with the flat plate 112 and are directly exposed to the outside. Therefore, guide pins 102 inserted into these grooves 114 will be supported by means of contact at only two points of each groove 114 and the upper side of each guide pin 102 which contacts the clamp 103 is compressed toward the bottom of the groove 114 so that it can be fixed therein. In this connection, it should be emphasized that since the clamp 103 is capable of elastic deformation, any slight variation in the diameter of guide pins can be effectively absorbed by the elastic of the clamp 103. In practice, a variation of about 0.1 mm in the guide pin diameter from a prescribed value of, say, 0.7 mm can be completely absorbed by the clamp without any difficulty and even a guide pin having a diameter of 1.0 mm could be effectively inserted into a guide pin groove. As a further advantage, two optical connectors can be coupled together without any difficulty even if the two guide pins used have slightly different diameters. In the optical connector of the present invention, guide pins 102 are compressed toward the bottom of guide pin grooves 114 by means of clamp 103 and this has the advantage that if an external force is applied to the guide pins 102, the stress will not be transmitted to the grooved substrate 111 but instead will be absorbed by the deforming clamp 103. In order to attain this result, the clamp 103 must deform elastically to absorb the stress acting on the guide pins 102 before it is exerted on the grooved substrate 111 to damage part of it. The resilient compressive force of the clamp 103 can be easily adjusted by changing the material or thickness of the clamp and it is easy to set a value that accommodates the stress tolerated by the grooved substrate 111 before it fails. Another feature of the optical connector of the present invention is that the small-diameter portions of each of the guide pins 102 that are held in position by the clamp 103 are in registry with the clamping groove 116 in the grooved substrate 111. This feature is effective in reducing the slippage that might occur between the guide pins 102 and the grooved substrate 111 and because of this anti-slip effect, resistance is provided against the force that acts to pull apart coupled optical connectors, thereby enhancing the reliability of coupling of two connectors. This resistive force against separation between connectors is dependent upon the force of friction between the guide pins 102 and the grooved substrate 111 and enhanced friction can be easily produced either by increasing the compressive force of the clamp 103 or by roughening the surface of the guide pins. An experiment has shown that optical connectors fabricated according to the present invention can withstand a pulling force of up to 2.8 kg without causing slippage between the guide pins and the grooved substrate. They could theoretically be improved to withstand a pulling force of up to 4 - 5 kg and for practical purposes, a strength that withstands a pulling force of about 2 kg would be sufficient to ensure reliable operation of coupling two optical connectors. In a preferred embodiment of the present invention, the clamp 103 has such dimensions that its width is equal to or greater than the width of the grooved substrate 111 and that its maximum height is greater than the height of the optics fiber guide member 101, and the clamp having these dimensions serves to protect the optical fiber guide member 101 against any external force such as impact that is exerted upon the optical connector. In particular, in the case where the grooved substrate 111 and the flat plate 112 are made of a hard and brittle material such as silicon, the clamp 103 will serve as an effective protector against nicking of the silicon material upon application of impact. As described above, the clamp used in the optical connector of the present invention is responsible for a great variety of actions and the optical connector adopts an optical fiber guide member and guide pins that are constructed to elicit such actions from the clamp in an effective and efficient manner. Example: An optical connector having the construction shown in Fig. 4 was fabricated. the grooved substrate and the flat plate of this connector were made of silicon, and optical fibre guide grooves and guide pin grooves were formed in the top surface of the substrate by a cutting operation. In the optical connector sample fabricated in this example, twelve optical fiber guide grooves were formed at a pitch of 0.25 mm. The guide pins used with this optical connector had a diameter of 0.7 mm and were each provided with small-diameter portions having a diameter of 0.4 mm. As shown in Fig. 4 , the clamp was so designed that it could be connected or disconnected from the rear end of the optical fiber guide member whereas the guide pins were capable of insertion from the front end of the guide member. A clamping groove was formed in the underside of the grooved substrate in such a way that it ran perpendicularly to the axial direction of each guide pin. The pressure-applying portions of the clamp were situated both in the clamping groove and in the small-diameter portions of the guide pins so that they would compress and fix the guide pins in position. The optical connector of the present invention described above affords the following advantages. (1) A clamp capable of elastic deformation is positioned over guide pin grooves, so the stress that is exerted upon the grooved substrate by guide pins when they are inserted into guide pin grooves is absorbed by the clamper to protect the grooved substrate. (2) Since the clamp deforms elastically when guide pins are inserted into guide pin grooves, any variation in the diameter of guide pins can be effectively absorbed by the clamp so that two optical connectors can be coupled together without any difficulty. Furthermore, the diameters of two guide pins that are to be inserted into the guide pin grooves on both lateral sides of the optical fiber guide member need not be equal to each other and this eliminates the need to perform strict control over the diameter of guide pins for use with the optical connector of the present invention. (3) The clamp is held in position by both the groove formed in the underside of the grooved substrate and the small-diameter portions of each guide pin. This is effective in reducing the slippage that might occur between the guide pins and the guide pin grooves, and resistance is provided against the force that acts to pull apart coupled optical connectors, thereby ensuring reliable coupling of two connectors. (4) The clamp is designed to have larger dimensions than the optical fiber guide member, so it has a capability of protecting the optical fibre guide member against damage. (5) Each of the guide pins used in the optical connector of the present invention is provided with small-diameter portions, which serve as grips for the guide pins and permit them to be easily inserted into guide pin grooves of readily extracted the refrom. In the above described embodiments, the material of the guide pin may be preferably made of ceramics, particularly of zirconia. The zirconia is tougher than alumina, and the outer diameter of the crystal thereof is not larger than 0.5 µm so that the surface thereof is smooth and slidable. Further, according to the present invention, at least one of the substrate and the holding plate may be made of silicon, ceramics or plastics, in which the former may be different from the latter in material In one specific embodiment of the present invention, optical fiber guide holes are formed by simply joining a grooved substrate and a cover plate. Therefore, optical fibers can be easily inserted and assembled to provide a coupling member that is capable of positioning optical fibers with dimensional precision. As described above, according to the present invention, the clearance that would occur between the guide pins and the guide pin holes which are to be coupled thereto is entirely eliminated or reduced to a very small value, thereby realizing low-loss coupling of optical fibers in a consistent manner. Further, the optical connector plugs of the present invention can be precisely and easily disconnected or connected.

Claims: An optical connector comprising: an optical fiber connector plug including a substrate plate (101) having at least one optical fiber groove and a plurality of pin grooves (114) each groove being formed in one surface thereof and a cover plate (112) joined to said substrate plate to form at least one optical fiber groove hole into which an optical fiber is inserted; and further comprising a corresponding plurality of pins (102) so positioned in said pin grooves as to enable coupling of said optical fiber connector plug with another plug; and resiliently compressive clamping means for holding said pins in their groove despite variations in the diameter of said pin means, characterised in that said clamping means comprises a corresponding plurality of individual clamps each clamp pressing on a respective pin and acting independently of the other clamp(s) each pin being exposed and not covered by the cover plate such that the associated clamp can act directly on its associated pin. An optical connector as claimed in claim 1, in which said pin means is made of a ceramic material. An optical connector as claimed in claim 1, in which said pin means is made of zirconia. An optical connector as claimed in claim 1, in which at least one of said substrate and cover plates is made of silicon. An optical connector as claimed in claim 1, in which at least one of said substrate and cover plates is made of ceramic material.

Inventors: KAKII, TOSHIAKI C/O YOKOHAMA WORKS SUMITOMO, SAITO, KAZUHITO C/O YOKOHAMA WORKS SUMITOMO, SUZUKI, SHUZO C/O YOKOHAMA WORKS SUMITOMO
Applicants: SUMITOMO ELECTRIC INDUSTRIES LIMITED
Application year: 1987
Main classification: G02B6
IPC codes: G02B6