GRINDER FOR CORE OF OPTICAL CONNECTOR AND CORE GRINDING METHOD

Abstract: Technique for grinding an end surface of a core (2) of an optical connector used for connecting an optical fiber (11), to grind the same into a convex surface. A grinder (3) is prov­ ided with at least a layer (4) of a low-elasticity material, and a grinding layer (6) laminated unitarily on the upper surface of the layer (4). The JIS-A hardness and Shore hardness of the layer (4) of the low-elasticity material are set to be not less than 50° and not more than 60°, respectively. When the sur­ face of such a grinder and the end surface of the core (2) of an optical connector are brought into contact with each other with a suitable pressing force, the surface of the grinder (3) is recessed to form a concave surface. Accordingly, the end sur­ face of the core (2) of the connector can be ground into a convex surface by utilizing this recession.

Description: This invention relates to a grinder for grinding to a convex spherical shape the end face of a ferrule of an optical connector which is used to connect one optical fiber to another or to connect an optical connector to another optical component. The invention also relates to a method for grinding the end face of the ferrule to convex spherical shape. Optical connectors have been used to connect, in a reproducible manner, one optical fiber to another or an optical fiber to another optical component. In general, an optical connector has a ferrule and another component in combination. When this optical connector is attached to an optical fiber, the ferrule is attached to the end of the optical fiber, the end face of the ferrule is then ground together with the end of the optical fiber, and they are then mounted to the other connector component. In this case, the end face of the ferrule and the end of the optical fiber are ground to reduce coupling losses. A method which has recently been noted includes the step of directly physically contacting only the ferrules of the optical fibers when connecting the optical fibers using an optical connector, to reduce the coupling losses to a minimum value. To perform this method, it is necessary to grind the end face of the ferrule to a convex spherical shape, when grinding the end face of the ferrule together with the end of the optical fiber. Figure 7 shows a representative example of apparatus for grinding the end face of the ferrule of an optical connector to a convex spherical shape. A grinder 1 having a recessed grinding surface 1A is rotated by a grinder rotating unit (not shown), the ferrule 2 of the optical connector is rotated by a ferrule rotating unit (not shown), the ferrule is rocked (in a pendulum motion) by a ferrule rocking unit (not shown), and the end face of the ferrule 2 is then ground to a convex spherical shape as it is pressed against the grinding surface 1A of the grinder 1. In the conventional example described above, not only the grinder rotating unit and the ferrule rotating unit are required, but also the ferrule rocking unit is required. Thus, the cost of the grinding apparatus is increased, in that means for rotating the grinder, means for rotating the ferrule, means for rocking the ferrule and means for pressing the ferrule against the grinder must all be provided and controlled. Therefore, the control difficulties are enhanced, yet accurate control is required for the rocking motion of the ferrule in order to ensure that the desired convex spherical surface is formed on the end face of the ferrule. EP-A-0 147633 discloses a grinder which comprises a layer of low-elasticity material and grinding material laminated on the surface of the low-elasticity material layer: in particular, hard blocks of abrasive material are embedded into the surface of an elastomer substrate with gaps between adjacent blocks, the blocks of abrasive material being thick (8 to 15 mm). In accordance with this invention there is provided a grinder which comprises a layer (4) of low-elasticity material and grinding material (5) laminated on the surface of the low-elasticity material layer (4), characterised in that , for grinding the end face of a ferrule of an optical connector, the grinding material (5) is formed as a flexibly deformable layer laminated in the surface of the low-elasticity layer (4), and the hardness of the low-elasticity layer (4) is equal to or greater than 18° of Shore hardness and equal to or less than 60° of Shore hardness. When the end face of the ferrule is pressed against the surface of the grinder, the surface of the grinder is flexibly deformed owing to the pressure of the end face of the ferrule, and as a consequence the end face of the ferrule is ground to a predetermined convex spherical shape. More specifically, since the grinding material layer and the low-elasticity material layer are flexibly deformed into a recess of spherical shape, at the location of the end face of the ferrule, this end face of the ferrule is ground to a complementary shape i.e. of convex spherical form. The radius of the convex spherical surface, to which the end face of the ferrule is formed, is determined mainly according to the hardness of the low-elasticity material layer and the force by which the end face of the ferrule is pressed against the surface of the grinder, and since the hardness of the low-elasticity material layer is chosen within the range defined above, the convex spherical surface can be formed reliably as will be described in more detail. A hard layer may be laminated to the rear of the low-elasticity material layer. This gives strength to the grinder, such that it can be readily attached to or detached from a grinder rotating unit. Preferably a grinder in accordance with this invention is used in a method of grinding the end face of a ferrule of an optical connector to a convex spherical shape, comprising the steps of: rotating the grinder (3) and the ferrule (2) about the respective axes, the ferrule (2) being held perpendicular to the grinding material layer (5) of the grinder, and pressing the end face of the ferrule (2) against the grinding material layer (5) to flexibly deform the latter and so form a concave recess therein. The surface of the rotating grinder may be contacted under a suitable contacting pressure by the end face of the ferrule, and it is not necessary to move the ferrule in any special manner while grinding, but the contact pressure of the ferrule against the rotating grinder may be controlled in simple manner to grind the end of the ferrule to a predetermined convex spherical shape. Embodiments of the present invention will now be described by way of examples only and with reference to the accompanying drawings, in which: FIGURE 1 is a sectional view through a first embodiment of grinder according to the present invention; FIGURE 2 is a sectional view through a second embodiment of grinder according to the invention; FIGURES 3 and 4 are side and plan views respectively showing an embodiment of grinding apparatus using the grinder of the invention; FIGURE 5 is a graph showing the relationship between the radius of the convex spherical surface formed on the end face of the ferrule and the hardness of the low-elasticity material layer of the grinder; FIGURE 6 is a graph showing the relationship between the radius of the convex spherical surface and the contact or coupling loss; and FIGURE 7 is an explanatory view of a conventional grinding apparatus. A grinder 3 shown in Figure 1 comprises a low-elasticity material layer 4 and a layer 5 of grinding material laminated integrally on the surface of the low-elasticity material layer 4, and being flexibly deformable. The layer 4 is formed of a low-elasticity material such as a soft rubber, a soft plastic or a composite material thereof, and has a hardness equal to or greater than 50° of JIS-A hardness (18° Shore hardness) and equal to or less than 60°of Shore hardness. The grinding layer 5 comprises, for example, a diamond lapping film. The low-elasticity material layer 4 and the grinding material layer 5 are integrally laminated by suitable means, including for example, bonding using a bonding agent, thermal fusion-bonding using a hot press or hot melt, clamping means using a clamp such as a bolt and a nut, or a clip e.g. spring clip or a calking clip. The bonding method and the thermal fusion-bonding method suitably employ known techniques. When the clamping means employs the bolt and the nut, the low-elasticity material layer 4 and the grinding material layer 5 are integrally laminated by passing the bolt through the layers 4 and 5 and the nut which is threaded onto the bolt: when the clip is used, both layers 4 and 5 are engaged at the edges thereof by the clip. A plate-like layer of hard material may be detachably laminated to the lower surface of the low-elasticity material layer 4 in the grinder 3. In this grinder 3, when the end face of the ferrule 2 of the optical connector is pressed against the surface of the grinder 3, the grinder 3 is locally recessed or depressed by the pressing force applied to it by the end face of the ferrule 2, so that the end face of the ferrule is ground to a convex spherical shape. The grinder 3 shown in Figure 2 not only comprises a low-elasticity material layer 4 and a grinding material layer 5 integrally laminated together, but also comprises a hard layer 20 integrally laminated to the back surface of the low-elasticity material layer 4. The low-elasticity material layer 4 and the grinding material layer 5 in Figure 2 correspond with the layers 4,5 of Figure 1: in particular the hardness of the low-elasticity material of layer 4 is equal to or higher than 50° of JIS-A (18° of Shore) and equal to or less than 60° of Shore. The hard layer 20 comprises for example metal, hard rubber, hard plastic, fiber reinforced plastic, reinforced glass, ceramics, or a composite of such materials. The low elasticity material layer 4, the grinding material layer 5 and the hard layer 20 may be integrally laminated by bonding thermal fusion-bonding means, or clamping, for example. Figures 3 and 4 show a modified grinding machine in which the grinder 3 of Figure 1 is used. The grinding machine comprises a rotary disc 6 which is disposed in a horizontal plane and is rotated on a vertical shaft 7 by a motor (not shown) and its transmission system (not shown). The grinder 3 is mounted to the upper surface of the rotary disc 6. A supporting plate 9 extends over the grinder 3 and reciprocates in an arc in a horizontal plane. The supporting plate 9 is mounted on a vertical stand 8 disposed adjacent the disc 6. The plate 9 rotatably supports a ferrule holder 10 and a mechanism 12 for rotating the ferrule holder 10 around its vertical axis on the plate 9. The ferrule rotating mechanism 12 has a motor 14 supported by a bracket 13 on the plate 9, a pulley 16 mounted to the output shaft 15 of the motor 14, and an endless belt 17 engaged over the pulley 16 and a pulley 10A of the holder 10. The ferrule 2 of the optical connector is mounted on the end of the optical fiber 11, and pressed against the surface of the grinder 3 once it has been detachably attached to the center of the ferrule holder 10. The end face of the ferrule 2 to be ground is pressed to the surface of the grinder 3, and the surface of the grinder 3 is flexibly deformed into a depression under the end face of the ferrule, owing to the pressing force. The ferrule 2, held by the ferrule holder 10 as described above, is rotatably reciprocated through an angle of 360° or more by the ferrule rotating mechanism 12, and at the same time the grinder 3 is rotated in a selected direction, e.g. the counterclockwise direction. The end face of the ferrule is ground while partly depressing the surface of the grinder 3, so that the edge of the end face of the ferrule 2 is not ground by the recessed surface, and the depression in the surface gradually changes in shape, and the end face of the ferrule 2 is eventually ground to a convex spherical shape. It is preferable to move the supporting plate 9 to alter the position of the ferrule 2 on the grinder 3 during grinding, and thus prevent the grinding surface of the grinder 3 from local, concentric wear. When grinding the ferrule the radius R of the end face (convex spherical surface) of the ferrule is determined by the hardness of the low-elasticity material layer 4 and the pressing force of the ferrule 2 against the grinder. Figure 4 shows the relationship between the hardness of the low-elasticity material layer 4 made of urethane of 1mm thick and the radius R of the convex spherical surface which is formed on the ferrule. In Figure 5, the plot defined by small circles represents a plastic ferrule and the plot defined by triangles represents a metal-ceramic composite ferrule. The range of the hardness of the low-elasticity material layer 4 can be expressed reliably on the JIS-A hardness and Shore hardness scales. Accordingly, in the example of Figure 5, the hardness of the low-elasticity material layer 4 is indicated according to both hardness scales. Figure 6 shows the relationship between the radius R of the convex spherical surface formed on the ferrule, and the coupling or contact losses of the connector. As apparent with reference to Figure 6, it is understood that stable physical contact is provided with R = 250mm or less in the case of the plastic ferrule, and with R = 150mm or less in the case of the metal-ceramic composite ferrule. As apparent by referring to Figure 5, the preferred values of the radius R for the convex spherical surface on the end face of the ferrule are achieved when the low-elasticity material layer 4 has a hardness equal to or greater than 50° of JIS-A (18° Shore) and equal to or less than 60° Shore. If the hardness of the low-elasticity material layer 4 is less than 50° of JIS-A (18° Shore), it was found that the end face of the optical fiber was not ground to a sufficient radius. When the apparatus of Figures 3 and 4 is used, stable physical contact is achieved between the end face of the ferrule and the grinder. The grinder is provided with good strength and the handling is easy. In use of the apparatus of Figures 3 and 4, grinder 3 is held at a predetermined position and the end face of the ferrule 2 is pressed against the surface of the grinder 3 whilst the latter is disposed at a predetermined position. However, modifications may be made: for example, the surface of the grinder 3 may be pressed against the end face of the ferrule 2 whilst the latter is disposed at a predetermined position, or pressing forces may be applied to both the ferrule 2 and the grinder 3.

Claims: A grinder which comprises a layer (4) of low-elasticity material and grinding material (5) laminated on the surface of the low-elasticity material layer (4), characterised in that, for grinding the end face of a ferrule of an optical connector, the grinding material (5) is formed as a flexibly deformable layer laminated in the surface of the low-elasticity layer (4), and the hardness of the low-elasticity layer (4) is equal to or greater than 18° of Shore hardness and equal to or less than 60° of Shore hardness. A grinder according to claim 1, characterised in that the low elasticity material layer (4) and the flexibly deformable grinding layer (5) are integrally laminated by a bonding agent. A grinder according to claim 1, characterised in that the low-elasticity material layer (4) and the flexibly deformable grinding layer (5) are integrally laminated by thermal fusion-bonding. A grinder according to claim 1, characterised in that the low-elasticity material layer (4) and the flexibly deformable grinding layer (5) are held together by a clamp. A grinder according to any one of claims 1 to 4, characterised in that said low-elasticity material comprises rubber, plastics or a composite thereof. A grinder according to any one of claims 1 to 5, characterised in that a hard layer (20) is laminated to a rear surface of the low-elasticity material layer (4). A grinder according to claim 6, characterised in that the material of said hard layer (20) comprises metal, hard rubber, hard plastics, fiber reinforced plastics, reinforced glass, ceramic, or a composite thereof. A method of grinding the end face of a ferrule of an optical connector to a convex spherical shape using a grinder as claimed in any preceding claim, comprising the steps of: rotating the grinder (3) and the ferrule (2) about the respective axes, the ferrule (2) being held perpendicular to the grinding material layer (5) of the grinder, and pressing the end face of the ferrule (2) against the grinding material layer (5) to flexibly deform the latter an dso form a concave recess therein.

Inventors: OCHIAI, TOSHIHIRO FURUKAWA ELECTRIC CO. LTD., OHTAKE, AKIHIRO FURUKAWA ELECTRIC CO. LTD., SANKAWA, IZUMI NIPPON TELEGRAM & TELEPHONE CO. LTD, SANKAWA, Izumi Nippon Telegram &amp; Telephone Co. Ltd
Applicants: NIPPON TELEGRAM & TELEPHONE CO. LTD., THE FURUKAWA ELECTRIC CO., LTD.
Application year: 1986
Main classification: B24B11
IPC codes: G02B6, B24D9, B24B19, B24B7, B24B11