Shockproof optical waveguide device

Abstract: An optical waveguide device has a casing (3), a base member (1) housed in the casing, at least one input optical fiber cable (8) and at least one output optical fiber cable (9) which are introduced into the casing, an optical waveguide substrate (2) mounted on the base member (1) and connected to respective ends of the input and output optical fiber cables for transmitting a light signal from the input optical fiber cable (8) to the output optical fiber cable. Support bases (6) and holders (7) are fixed to the base member (1) for holding end portions (81,91) of the input and output optical fiber cabled on the base member, and a bushing (4) or bushings in the casing (3) are for introducing the input and output optical fiber cables into the casing. The optical waveguide substrate (2) has an optical waveguide (2a) branched into a plurality of waveguide paths, and input and output optical fiber cables are coupled to each other through the optical waveguide.

Description: The present invention relates to an optical waveguide device for use in optical communications, and more particularly to a shock-resistant optical waveguide device capable of keeping input and output optical fibres stably connected to an optical waveguide without causing an axial mis-alignment therebetween. One such device is shown in EP-A-0277390. Known optical waveguide devices have a casing in the shape of a rectangular parallelepiped, a base member supporting an optical waveguide substrate with an optical waveguide formed therein, the base member being fixedly mounted in the casing through a support member of resin, and input and output optical fibres extending into the casing through a bushing on the casing. The conventional optical waveguide devices are dis-advantageous in that they are unable to sufficiently resist external forces such as shocks, tensile forces, or the like, i.e., the optical waveguide and the optical fibres tend to be disconnected or axially misaligned when subjected to external forces. In many prior optical waveguide devices, the optical waveguide and the optical fibres are spliced by directly bonding and fixing a flat end face of the optical waveguide to flat end faces of the optical fibres, such as is shown in EP-A-0283301. According to one splicing process, it has been necessary to position the optical waveguide and the optical fibres three-dimensionally along X, Y, and Z axes, and then adjust the angles of the optical axes of the optical fibres with respect to the optical axis of the optical waveguide along the X, Y, and Z axes so that the optical waveguide and the optical fibres are axially aligned for higher optical propagation efficiency. If the flat end faces of the optical waveguide and the optical fibres are not sufficiently bonded to each other, however, they can easily be axially misaligned under external forces. The gap between the bushing and the optical fibres which extend through the bushing into the casing is filled with an adhesive that is simply applied from outside of the casing, thus hermetically sealing the casing. If the adhesive contains air bubbles or the bushing and the optical fibres are bonded through an insufficient adhesive area at the time the casing is shocked, then the casing may not be kept hermetically sealed well. The present invention therefore seeks to provide an optical waveguide device which can sufficiently withstand external forces such as shocks thereby to prevent an optical waveguide and optical fibres from being disconnected or axially misaligned. According to the present invention, there is provided:- An optical waveguide device comprising: a casing; a base member housed in said casing; at least one input optical fibre cable and at least one output optical fibre cable which are introduced into said casing; an optical waveguide comprising a substrate mounted on said base member and having therein at least one optical waveguide path through which respective ends of said input and output optical fibre cables are interconnected for transmitting a light signal from said input optical fibre cable to said output optical fibre cable; holding means fixed to said base member for holding end portions of said input and output optical fibre cables on said base member; and introducing means in said casing for introducing said input and output optical fibre cables into said casing; characterised in that said at least one waveguide path has a spherical end face exposed at an end of said optical waveguide substrate, at least one of said input and output optical fibre cables having a complementary spherical end face butted to said waveguide spherical end face. The spherical end face of the waveguide path may be concave and the spherical end face of the optical fibre cable may be convex or vice versa. The invention will now be described in greater detail, by way of example, with reference to the drawings, in which: Fig. 1 is a horizontal cross-sectional view of an optical waveguide device according to a first embodiment of the present invention; Fig.2 is a vertical cross-sectional view of the optical waveguide device shown in Fig. 1; Fig.3 is a side elevational view, partly in cross section, of an optical waveguide (substrate) and an optical fibre, before they are spliced, for use in an optical waveguide device according to the present invention; Fig.4 is a side elevational view, partly in cross section, of the optical waveguide and the optical fibre, after they are spliced, shown in Fig.3; Fig.5 is a side elevational view, partly in cross section, of the optical waveguide and the optical fibre shown in Fig.4 with an adhesive applied; Fig.6 is a perspective view of an optical waveguide substrate for use in the optical waveguide device according to the present invention; Fig.7 is a fragmentary cross-sectional view of a photomask fixed to a side of an optical waveguide substrate for forming the substrate structure shown in Fig.3; Fig.8 is a vertical cross-sectional view of a hermetically sealed bushing; Fig.9 is a front elevational view of the bushing shown in Fig.8; Fig.10 is a horizontal cross-sectional view of an optical waveguide device according to a second embodiment of the present invention, which incorporates the bushing shown in Fig.8; Fig. 11 is a vertical cross-sectional view of the optical waveguide device shown in Fig. 10; Fig.12 is a horizontal cross-section view of the optical waveguide device according to a further embodiment of the present invention; and Fig.13 is a vertical cross-sectional view of the optical waveguide device shown in Fig.12. Like or corresponding parts are denoted by like or corresponding reference characters throughout views. As shown in Figs. 1 and 2, an optical waveguide device according to a first embodiment of the present invention comprises a closed casing 3 in the shape of a rectangular parallelepiped composed of an upper casing member 3a and a lower casing member 3b, a flat base member 1 fixedly housed in the casing 3, a flat optical waveguide substrate 2 fixedly mounted on the base member 1 and having an optical waveguide 2a formed therein, successively spaced support bases 6a, 6b, 6c, 6d fixedly mounted on the base member 1 and supporting ends of input and output optical fibre cables 8, 9, successively spaced holders 7a, 7b, 7c, 7d mounted on the respective support bases 6a, 6b, 6c, 6d and holding the ends of the optical fibre cables 8, 9, and a bushing 4 mounted on the casing 3 and through which the optical fibre cables 8, 9, extend into the casing 3. The base member 1 is fixed to an inner surface of the lower casing 3b. However, the base member 1 may be mounted in the casing 3 in any of various other fashions. The input optical fibre cable 8 has an end portion extending into the casing 3 through the bushing 4, i.e., an optical fibre introducing means, that is disposed in a boundary between the upper and lower casing members 3a, 3b. The end portion of the input optical fibre cable 8 is supported on the base member 1 by the support base 6a and the holder 7a. The end portion of the input optical fibre cable 8 has its cover layer peeled off, exposing an optical fibre 81 that is supported by the support base 6b and the holder 7b. The optical fibre 81 has a distal end mechanically spliced to an end face of the optical waveguide 2a at one end of the optical waveguide substrate 2 and bonded in position by an adhesive 82. The four output optical fibre cables 9 have respective end portions extending into the casing 3 through the bushing 4. The end portion of each of the output optical fibre cables 9 is supported on the base member 1 by the support base 6c and the holder 7c. The end portion of each of the output optical fibre cables 9 has its cover layer peeled off, exposing an optical fibre 91 that is supported by the support base 6d and the holder 7d. The optical fibres 91 have respective distal ends mechanically spliced to an end face of the optical waveguide 2a at the other end of the optical waveguide substrate 2 and bonded in position by an adhesive 92. The optical waveguide 2a is branched from a single waveguide path into a plurality of (four in the illustrated embodiment) output waveguide paths for transmitting a single light signal from the input optical fibre cable 8 as four light signals into the respective output optical fibre cables 9. The optical waveguide 2a is formed as a region having a higher refractive index than the surrounding region by the ion exchange process, for example. However, the optical waveguide 2a may be formed in any of various other manufacturing processes. The optical waveguide 2a may have one or more input waveguide paths and may have four or more or less output waveguide paths. The major components of the optical waveguide device, i.e.,the optical waveguide substrate 2, the end portions of the input and output optical fibre cables 8,9, the support bases 6a - 6d and the holders 7a - 7d, are placed on the base member 1 and fixedly housed in the closed casing 3. Therefore, external forces such as shocks are prevented from being directly applied to the optical waveguide substrate 2 and the exposed optical fibres 81, 91, or the spliced and bonded joints 82, 92, therebetween. Even when the optical fibre cables 8, 9, are subjected to tensile forces, since the optical fibre cables 8, 9, are securely held on the base member 1 by the support bases 6a - 6d and the holders 7a - 7d, the spliced and bonded joints 82, 92 are prevented form being damaged. Consequently, the optical waveguide device is of a shock-resistant structure capable of sufficiently withstanding external forces such as shocks and tensile forces. Inasmuch as the input and output optical fibre cables 8, 9, introduced into the casing 3 are disposed on one side within the casing 3, the optical waveguide device may be of a low profile. Therefore, the optical waveguide device may be installed in a relatively small space, e.g., may be inserted into a small space through an end thereof. Since the input and output optical fibre cables 8, 9, can be installed on the base member 1 with the upper casing member 3a removed, they can be mounted in place from one side of the casing 3. Thus, any space required for the worker to install the input and output optical fibre cables 8, 9, in the casing 3 may be relatively small. Figs.3 through 7 show the special splicing structure of the invention for allowing an optical waveguide and an optical fibre to be spliced easily and quickly while maintaining a desired optical propagation efficiency in the waveguide device of Figures 1 and 2. In Figs. 3 through 5, only one set of an optical waveguide, an optical fibre, and a positioning hole are shown for the sake of brevity. As shown in Fig. 3, an optical waveguide substrate 2' has an optical waveguide 2a with an exposed end face 2c in the form of a concave spherical surface having a radius R of curvature, and an optical fibre 91 includes a core 94 having a distal end face 93b in the form of a convex spherical surface having a radius R of curvature and a cladding 94 having a tapered distal end face 94b. To splice the optical waveguide substrate 2' and the optical fibre 91, as shown in Fig.4, the distal end face 93b of the core 93 of the optical fibre 91 is fitted into the end face 2c of the optical waveguide 2a, so that they are mechanically spliced to each other. The optical waveguide 2a and the optical fibre 91 can thus easily axially aligned with each other by simply fitting the distal end face 93b in the end face 2c. As shown in Fig.5, an adhesive 95, e.g.,an ultraviolet-curing resin, may be filled between the end of the optical waveguide substrate 2' and the distal end face 94b of the cladding 94 around the distal end face 93b of the core 93 to bond the optical waveguide 2a and the optical fibre 91 to each other. The splicing structure is used on the flat optical waveguide substrate 2' with the optical waveguide 2a for dividing a single light signal into four light signals as shown in Fig.6. The end face 2c of each of the waveguide paths of the optical waveguide 2a is shaped to a concave spherical end surface irrespective of whether it may be spliced to the input optical fibre 81 or each of the output optical fibres 91. The concave spherical end face 2c of the optical waveguide 2a may be formed by holding a photomask 22 (see Fig.7) having a hole of a predetermined diameter against the end of the optical waveguide substrate 2' to expose the end face 2c of the optical waveguide 2a through the hole in the photomask 22, and then shaping the end face 2c into a concave spherical surface having a radius R of curvature according to the photolithographic or etching process. The end face 2c of the optical waveguide 2a is in the shape of a concave spherical surface having a radius R of curvature and the end face 93b of the core 93 of the optical fibre 91 is in the shape of a convex spherical surface having a radius R of curvature. However, the end face 2c of the optical waveguide 2a may be in the shape of a convex spherical surface having a radius R of curvature and the end face 93b of the core 93 of the optical fibre 91 may be in the shape of a concave spherical surface having a radius R of curvature. In the above embodiment and also following embodiments, a single light signal from the input optical fibre cable 8 is divided into four light signals which are transmitted into the respective output optical fibre cables 9. However, there may be employed four input optical fibre cables and a single output optical fibre cable, so that four light signals from the respective four input optical fibre cables are combined or coupled into a single light cable that is transmitted into the single output optical fibre cable. An optical waveguide device according to a second embodiment of the present invention will be described below with reference to Figs. 8 through 11. The optical waveguide device according to the second embodiment employs a hermetically sealed bushing. Figs. 8 and 9 show, at an enlarged scale, a hermetically sealed bushing 40 for use in an optical waveguide device. As shown in Figs. 8 and 9, the bushing 40 is of a hollow structure composed of a cover 41 and a case 42 which are interfitted, defining a space 40S between. The cover 41 and the case 42 have respective through holes 41a, 42a defined in confronting positions and through which four output optical fibre cables extend. The cover 41 also has a through hole 41b defined in a side panel thereof for filling a resin 40R into the space 40S, and a through hole 41C for letting air go out of the space 40S. For filling the space 40S with the resin 40R, the output optical fibre cables 9 are inserted through the holes 41a, 42a in the bushing 40, directing the hole 41b downwardly and the hole 41c upwardly, and the resin 40R, which may be a low-viscosity thermosetting adhesive resin, is injected through the hole 41b into the space 40S. Since the resin 40R is low in viscosity, it fills the space 40S and the holes 41a, 42a, 41b, 41c while forcing air bubbles from the resin 40R and air from the space 40S. When the resin 40R starts being discharged from the holes 41a, 42a, 41c, the injection of the resin 40R from the hole 41b is stopped. Then, the bushing 40 is heated to thermoset the resin 40R. When the resin 40R is thermoset, the bushing 40 and the optical fibre cables 9 are intimately coupled to each other by the resin 40R in the holes 41a, 42a, and the space 40S. The optical waveguide device according to the second embodiment which incorporates the bushing 40 is shown in Figs. 10 and 11. In the optical waveguide device according to the second embodiment, the input optical fibre cable 8 is introduced into the casing 3 through a bushing 43 that is located on an end of the casing 3 opposite to the bushing 40 through which the output optical cables 9 are introduced into the casing 3. Except for the bushing 43, the internal structure of the casing 3 is essentially the same as the casing 3 according to the first embodiment described above. The bushing 43 is substantially identical in structure to the bushing 40. The bushings 40, 43, are held in contact with outer surfaces of the casing 3, and any gaps therebetween are filled with respective adhesives 40A, 43A, thus keeping the casing 3 hermetically sealed. In the second embodiment, external moisture and air are prevented from entering the casing 3 through the bushings 40, 43. While the resin 40R is being filled into the space 40S between the cover 41 and the case 42, air bubbles entrapped in the resin 40R can be discharged through the hole 41c which is positioned upwardly. The bushings 40, 43, are therefore hermetically sealed, and hence no hole is formed through the bushings 40, 43, between the ambient space and the casing 3. Consequently, the casing 3 is highly hermetically sealed. Furthermore, since the optical cables and the bushings are unitized by the filled resin, they can easily and quickly be installed on and removed from the casing 3. The hermetically sealed bushing shown in Figs.8 and 9 may be incorporated in the optical waveguide device according to the first embodiment and any other optical waveguide devices according to any other embodiments described below. The optical waveguide device, according to a further embodiment is illustrated in Figs. 12 and 13. The major components of the optical waveguide device according to that embodiment are substantially identical to those of the optical waveguide devices according to the first and second embodiments. The input and output optical fibre cables 8, 9 are introduced into the casing 3 from respective opposite ends of the casing 3 as with the second embodiment. The optical waveguide device according to that embodiment has bushings 40', 43' which may be of the hermetically sealed structure as with the bushings 40, 43 according to the second embodiment. With the optical waveguide device according to that embodiment, the optical waveguide and the optical fibres can easily and quickly be spliced to each other. The splicing structure can sufficiently withstand external forces such as shocks, thus minimizing the risk of axial misalignment between the optical waveguide and the optical fibres. Although there have been described what are at present considered to be the preferred embodiments of the invention, it will be understood that the invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative, and not restrictive. The scope of the invention is indicated by the appended claims rather than by the foregoing description.

Claims: An optical waveguide device comprising: a casing (3); a base member (1) housed in said casing (3); at least one input optical fibre cable (8) and at least one output optical fibre cable (9) which are introduced into said casing (3); an optical waveguide (2) comprising a substrate (2') mounted on said base member (1) and having therein at least one optical waveguide path (2a) through which respective ends of said input and output optical fibre cables (8, 9) are interconnected for transmitting a light signal from said input optical fibre cable (8) to said output optical fibre cable (9); holding means (7a-7d) fixed to said base member (1) for holding end portions of said input and output optical fibre cables (8, 9) on said base member (1), and introducing means (4) in said casing (3) for introducing said input and output optical fibre cables (8, 9) into said casing (3), characterised in that said at least one waveguide path (2a) has a spherical end face (2c) exposed at an end of said optical waveguide substrate (2'), at least one of said input and output optical fibre cables (8, 9) having a complementary spherical end face (93b) butted to said waveguide spherical end face (2c). An optical waveguide device according to Claim 1, wherein spherical end face (2c) of said waveguide path (2a) is concave and the spherical end face (93b) of said optical fibre cable (8, 9) is convex. An optical waveguide device according to Claim 1, wherein the spherical end face (2c) of said waveguide path (2a) is convex and the spherical end face (93b) of said optical fibre cable (8, 9) is concave. An optical waveguide device according to Claim 1, 2, or 3, wherein said at least one of said input and output optical fibre cables (18, 19) has a core (93) and a cladding (94) surrounding said core (93), said cladding (94) having a tapered end (94b), further comprising an adhesive filling (95) between said end of said optical waveguide substrate (2') and said tapered end (94b) of the cladding (94) around said spherical end faces (2c, 93b) butted together. An optical waveguide device according to any one of Claims 1 to 4, wherein said optical waveguide (2) is branched into a plurality of waveguide paths (2a), each of the waveguide paths (2a) including a spherical end face (2c) exposed at the end of said optical waveguide substrate (2').

Inventors: IKEDA MTSUAKIRA, IKEDA, MTSUAKIRA, Ikeda, Mtsuakira, c/o Nippon Sheet Glass Co., Ltd.
Applicants: NIPPON SHEET GLASS CO LTD, NIPPON SHEET GLASS CO., LTD.
Application year: 1993
Main classification: G02B6
IPC codes: G02B6