Method of fixing optical fiber array to substrate

Abstract: In the case of fixing an optical fiber array to a substrate (1), wherein the optical fiber array includes a V-groove substrate (11) having at least one V-groove (13) used for arranging an optical fiber, a fix substrate (14) for fixing the optical fiber in the V-groove, and a pair of guide grooves (15) arranged at both ends of the V-groove through which a guide pin (31) used for a connection is arranged, the guide pin is arranged in the guide groove and the optical fiber array is fixed to the substrate under such a condition that one point of the guide pin (31) is brought into contact with the substrate (1).

Description: The present invention relates to a method of fixing an optical fiber assembly to a substrate, with the aim of fixing the optical fiber assembly to the substrate precisely in a thickness direction. The optical fiber assembly comprises a V-groove body having one or more V-grooves each receiving an optical fiber, and is also known in the art as an optical fiber array, which term will also be used in the following description. Fig. 6 is a schematic view for explaining a known method of fixing an optical fiber array to a substrate. In Fig. 6, the optical fiber array 57 comprises a V-groove body 54 having a plurality of V-grooves 53 used for fixing optical fibers 52, a fixing body 55 for fixing the optical fibers 52 in the V-grooves 53, and a pair of guide grooves 56 arranged at both ends of the V-grooves 53 of the V-groove body 54. When the optical fiber array 57 having the construction mentioned above is fixed to an element mount substrate 51, it is necessary to set precisely a position of the optical fiber 52 with respect to the element mount substrate 51 i.e. a distance A in a thickness direction. This is because, as shown in Fig. 6, the optical fiber array 57 and an optical element 58 such as an optical waveguide or the like must be fixed on the element mount substrate 51 in such a manner that optical axes of the optical element 58 are optically made identical with those of the optical fibers 52 of the optical fiber array 57. In the known embodiment mentioned above, in order to set precisely the distance A in the thickness of the optical fiber array 57 and a distance B in the thickness direction of the optical element 58, they are worked with reference to the surfaces, to which the element mount substrate 51 is contacted, in such a manner that distances from those reference surfaces are made equal to the distances A and B. In this case, the distance B in the thickness direction of the optical element 58 can be worked relatively easily to a precise value since a shape to be worked is simple. However, it is difficult to work the distance A in the thickness direction of the optical fiber array to a precise value, since a shape to be worked is complicated. Therefore, the optical axes of the optical fiber array 57 and the optical element 58 are made identical with each other in such a manner that a light transmitted through both of the optical fiber array 57 and the optical element 58 is monitored while they are moved relatively on the element mount substrate 52 and they are fixed to the element mount substrate 51 at which a power of the monitored light is largest. In this case, if the distance A in the thickness direction of the optical fiber array 57 is inaccurate as mentioned above, a space is generated between the element mount substrate 51 and the optical element 58 or the optical fiber array 57, and thus it is necessary to fill adhesives into the space. Therefore, a stress due to a shrinkage or expansion of the adhesives is generated in the thickness direction, and thus it is feared that a reliability of the optical connection is deteriorated. DE-A-3902022 shows a connector in which two optical fiber assemblies, having fibers held between V-grooved plates, are located relative to each other on a substrate by means of guide pins. Springs hold these assemblies against the guide pins. An object of the present invention is to eliminate the drawbacks mentioned above and to provide a method of fixing an optical fiber assembly to a substrate, which can fix the optical fiber assembly to the substrate precisely in a thickness direction. According to the present invention, there is provided a method of fixing an optical fiber assembly to a substrate, as set out in claim 1. In the method of the invention, the guide pins are arranged in the guide grooves alongside the V-groove, and the optical fiber assembly is preferably fixed to the substrate under such a condition that the guide pins are in line contact with the substrate. In this case, the V-groove can be worked precisely to an extent such that a relative positional relation between a center of the guide pin and a center of the optical fiber becomes in an order of sub-microns if the guide pin and the optical fiber are set in the guide groove and the V-groove. Therefore, it is possible to set a distance from a surface of the substrate on which the element is mounted to the optical fiber precisely in an order of sub-microns. Accordingly, since the optical axes of the optical element and the optical fiber assembly are identical with each other in a thickness direction thereof, it is possible to perform easily an optical axis adjusting operation between the optical element and the optical fiber assembly when they are fixed to the same substrate. Fig. 1 is a schematic view showing one embodiment for performing a method of fixing an optical fiber array to a substrate according to the invention; Fig. 2 is a schematic view illustrating another embodiment for performing the method of fixing the optical fiber array to the substrate according to the invention; Fig. 3 is a schematic view depicting still another embodiment for performing the method of fixing the optical fiber array to the substrate according to the invention; Figs. 4a to 4d are schematic views respectively showing a step of the method of fixing the optical fiber array to the substrate according to the invention; Fig. 5 is a schematic view illustrating still another embodiment for performing the method of fixing the optical fiber array to the substrate according to the invention; and Fig. 6 is a schematic view depicting one embodiment of a known method of fixing an optical fiber array. Fig. 1 is a schematic view showing one embodiment of 1×4 optical splitter utilizing a method of fixing an optical fiber array to a substrate according to the invention. In the embodiment shown in Fig. 1, a numeral 1 is an element mount substrate, a numeral 2 is an optical fiber array arranged on the element mount substrate 1 at its light incident side, a numeral 3 is an optical fiber array arranged on the element mount substrate 1 at its light emitting side, and a numeral 4 is an optical waveguide element arranged between the optical fiber arrays 2 and 3. The optical fiber array 2 has a construction such that a V-groove 13 for fixing an optical fiber 12, a fixing body 14 used for fixing the optical fiber 12 arranged in the V-groove 13, and a pair of guide grooves 15 arranged at both ends of the V-groove 13, in which a guide pin not shown is arranged, are arranged on a V-groove body 11. The optical fiber array 3 has the same construction as that of the optical fiber array 2 except that four V-grooves 13 are arranged in the V-groove body 11. Then, the optical fiber array 2 and the optical fiber array 3 are fixed on the element mount substrate 1 via adhesive layers 16 and 17 respectively. Moreover, the optical waveguide element 4 is fixed on the element mount substrate 1 via an adhesive layer in such a manner that an optical axis thereof at its light incident side is made identical with that of the optical fiber 12 of the optical fiber array 2 and optical axes thereof at its light emitting side are made identical with those of the optical fibers 12 of the optical fiber array 3. Figs. 2 and 3 are schematic views respectively showing one embodiment of a photoelectric converting module utilizing the method of fixing the optical fiber array to the substrate according to the invention. In Figs. 2 and 3, portions similar to those of Fig. 1 are denoted by the same reference numerals, and the explanation thereof is omitted here. In the embodiment shown in Fig. 2, the photoelectric converting module has a construction such that the optical fiber array 2 of the light incident side is arranged on the element mount substrate 1 and a light receiving element 21 is-arranged correspondingly to the optical fibers 12 of the optical fiber array 2. In the embodiment of Fig. 3 showing a variation of Fig. 2, the guide groove 15 is constructed by a guide groove portion 22 formed in the optical fiber-array and a guide groove portion 23 formed in the element mount substrate 1. It should be noted that the construction of the guide groove 15 shown in Fig. 3 can be applied to the embodiment shown in Fig. 1. Moreover, as for the optical element, use may be made of a light emitting element instead of the light receiving element. Figs. 4a to 4d are schematic views respectively showing a step of the method of fixing the optical fiber array to the substrate according to the invention. At first, as shown in Fig. 4a, the V-grooves 13 and the guide grooves 15 are formed in the V-groove body 11 in an order of sub-micrometer. In this case, it is necessary to set a distance Z equal to a distance between the element mount substrate 1 and an optical axis of the optical element such as the optical waveguide element 4 and the light receiving element 21. Here, the distance Z means the vertical distance between an optical axis of the optical fiber 12 and the line of contact of the pin 31 at the substrate 1, under such a condition that the optical fibers 12 and the guide pins 31 are arranged in the V-grooves 13 and the guide grooves 15 respectively. Moreover, an end portion lla of the V-groove body 11 is worked by a distance X from a position at which the element mount substrate 1 arranged so as to form the adhesive layers 16, 17. Further, it is not necessary to set the optical axis of the optical fiber 12 equal to a center position of the guide pin 31 precisely in the thickness direction. However, in the case that the optical fiber array 2 is directly connected to the optical connector having a single optical fiber or a plurality of optical fibers via the guide pin 31, it is preferred to make identical the optical axis of the optical fiber 12 with the center position of the guide pin 31 in the thickness direction as shown in Fig. 4a, since a position of the optical fiber 12 of the optical fiber array 2(3) can be arranged relatively equal to a position of the optical fiber of the optical connector not shown. Then, as shown in Fig. 4b, the optical fibers 12 are arranged in the V-grooves 13 of the V-groove body 11 and are fixed by the fix substrate 14 via adhesives. In this case, it is necessary to set a thickness of the fix substrate 14 thinner than the distance Z mentioned above so as to always contact the guide pin 31 with the element mount substrate 1. After that, as shown in Fig. 4c, both end surfaces of the optical fiber array 2(3), to which the optical fiber 12 is exposed, are optically ground to obtain the optical fiber array 2(3) as manufactured articles. Finally, the thus obtained optical fiber array 2(3) is fixed on the element mount substrate 1 to obtain the optical module. That is to say, as shown in Fig. 4d, the optical fiber array 2(3) is arranged on the element mount substrate 1 under such a condition that the guide pin 31 is arranged in the guide groove 15. In this case, a space of the distance X is formed between the end portion 11a of the V-groove substrate 11 and the element mount substrate 1. Under such a condition, an optical axis adjustment between the optical fiber array 2(3) and the optical element such as the optical waveguide element 4 and the light receiving element 21 by passing a light therethrough as is the same as the known method. According to the present invention, since the optical axes thereof in the thickness direction are precisely identical with each other, it is possible to perform the optical axis adjustment only by adjusting a variation of a surface parallel to the element mount substrate and a variation of a rotation angle with respect to the surface mentioned above. Then, when the optical axis adjustment mentioned above is completed, the optical fiber array 2(3) is fixed to the element amount substrate 1 by forming the adhesive layer 16(17) in the space of the distance X therebetween. In the embodiment mentioned above, the V-groove substrate 11 can be worked precisely to be the distance Z between the optical fiber 12 and the element mount substrate 1 in an order of sub-micrometer i.e. Z ± 0.5 µm. Therefore, if the optical fiber array 2(3) is fixed to the element mount substrate 1 under the condition such that the guide pin 31 is brought into line contact with the element mount substrate 1 and two points of the guide pin 31 are brought into line contact with the guide groove 15, it is possible to perform the optical axis adjustment between the optical fiber array 2(3) and the optical element easily, since their optical axes in the thickness direction are made identical with each other. Moreover, also in the case that use is made of the other optical fiber array 3 as shown in Fig. 1, the optical fiber array 3 can be fixed to the element mount substrate 1 in the same manner after the optical fiber array 2 is fixed. In this case, as shown in Fig. 5, if the same guide pins 15 are used for connecting the optical fiber array 2, the optical axes of the optical fiber array 3 are automatically identical with those of the optical element 4. Therefore, it is not necessary to perform the optical axis adjustment for the optical fiber array 3, and thus it is possible to make ease an assembling operation extraordinarily. The present invention is not limited to the embodiments mentioned above, and various variations can be effected. In the embodiments mentioned above, the present invention is applied to the optical axis adjustment between the optical fiber array and the optical element, but it should be noted that the present invention can be applied to a fixing of only one optical fiber array to the substrate. If the present invention is applied to the fixing of only one optical fiber array, the same advantages mentioned above can be obtained. As mentioned above in detail, according to the invention, since the optical fiber array is fixed to the element mount substrate under the condition such that the guide pin is arranged in the guide groove of the V-groove body and one point of the guide pin is brought into contact with the element mount substrate, it is possible to set a distance in an order of sub-micrometer between an upper surface of the element mount substrate and the optical fiber. Therefore, when the optical axis adjustment between the optical fiber of the optical fiber array and the optical element, both of which are fixed on the same element mount surface, is performed, it is possible to perform the optical axis adjustment easily, since the optical axes thereof are made identical with each other precisely in the thickness direction.

Claims: A method of arranging a first optical element in the form of an optical fiber assembly (2,3) and a second optical element (4) having at least one optical axis on a substrate (1) having a reference surface, said optical fiber assembly (2,3) including a V-groove body (11) having at least one V-groove (13) receiving an optical fiber (12), a fixing body (14) fixing said optical fiber (12) in said V-groove (13), and a pair of guide grooves (15) in said V-groove body (11) alongside said V-groove (13) for receiving guide pins (31), the method comprising the steps of (i) bringing said fiber assembly (2,3) to a desired position relative to said reference surface with guide pins (31) arranged in said guide grooves (15) and contacting said reference surface, and fixing said fiber assembly to said substrate by means of adhesive (16,17) so as to maintain said desired position, and (ii) fixing said second optical element (4) at a desired position directly on said substrate reference surface with one of its surfaces on said substrate reference surface, wherein the depth of the guide grooves (15) and the diameter of the guide pins (31) are selected such that the optical axes of the optical fiber (12) in the V-groove and of the second optical element (4) are at the same level above the substrate reference surface. The method according to claim 1, wherein said guide pins (31) make line contact with said substrate (1) (1) in said step (i). The method according to claim 1 or claim 2, wherein said pair of guide grooves (15) are parallel to said V-groove (13) for said optical fiber (12). The method according to any one of claims 1 to 3, wherein said second optical element (4) is an optical waveguide element, a light receiving element or a light emitting element. The method according to any one of claims 1 to 4, wherein at least two of said optical fiber assemblies (2,3) are fixed to said substrate (1) by said step (i) with said guide pins (31) located in said guide grooves (15), so as to align said optical fiber assemblies with said second optical element (4). The method according to any one of claims 1 to 5, wherein, when said guide pins (31) are in said guide grooves (15) and in contact with said substrate the level relative to said substrate (1) of the optical axis of said optical fiber (12) is identical with the level of centers of said guide pins (31).

Inventors: FUKUYAMA MASASHI, OTA TAKASHI, FUKUYAMA, MASASHI, OTA, TAKASHI
Applicants: NGK INSULATORS LTD, NGK INSULATORS, LTD.
Application year: 1995
Main classification: G02B6
IPC codes: G02B6