JP2008032993A - Optical fiber body and mode converter using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suggest a method of connection of single mode fibers having different mode field diameters with low loss. <P>SOLUTION: The optical fiber body is composed by providing: a first single mode fiber 11; a second single mode fiber 12 having a mode field diameter smaller than the mode field diameter W1 of the first single mode fiber 11; and a grated index fiber 13 of which the one end part is connected to the one end part of the first single mode fiber 11 and the other end part is connected to the one end part of the second single mode fiber 12 for matching the mode field diameters of the respective connected single mode fibers. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to connection between optical fibers used in optical communication equipment and the like.

Optical fibers are largely classified into single mode fibers and multimode fibers, but single mode fibers are mainly used for long-distance transmission. This single mode fiber is most frequently used with a mode field diameter of about 10 μm defined by the diameter of the region where the light intensity attenuates to 1 / e ² with respect to the maximum intensity.

  In recent years, the amount of communication has increased due to the diversification of communication contents, and the necessity of drawing an optical fiber into each home or office has arisen. When optical fibers are drawn into a house or office, it is recommended that the allowable bending radius be as small as possible for ease of wiring and construction. This allowable bending radius is the radius at which the single-mode fiber can be bent and used, and if it is bent to a radius smaller than the allowable bending radius, the transmission loss of light increases at the bending location, so it is larger than the allowable bending radius. It is necessary to install a single mode fiber so as to have a radius. In general, the smaller the mode field diameter of a single mode fiber, the smaller the allowable bending radius. The mode field diameter of such a single mode fiber is about 6 μm to 8 μm.

  However, the mode field diameter of the single mode fiber already wired from the base station to just before the house is about 10 μm, whereas the mode field diameter of the single mode fiber wired to the house or office is about 6 to 8 mm. Therefore, it is necessary to connect single mode fibers having different mode field diameters.

  Conventionally, methods such as fusion splicing, connector connection, or mechanical splicing have been used to connect single mode fibers having different mode field diameters. However, in any of the connection methods, there is a problem that connection loss increases due to a difference in mode field diameter of the single mode fiber. For example, when the mode field diameter of one single-mode fiber is 10.5 μm and the mode field diameter of the other single-mode fiber is 6 μm, a theoretical loss of 1.3 dB occurs due to the difference in mode field diameter. Since a factor such as shaft misalignment is further added, a loss of about 1.8 dB occurs. In general, the connection loss due to a single mode fiber having the same mode field diameter is 0.5 dB or less for connector connection (see JIS C5971) and about 0.1 dB for fusion connection.

  In connection of such single mode fibers having different mode field diameters, a method has been proposed in which single mode fibers having different mode field diameters are fusion-bonded to each other, and then the fusion-bonding point is heated and drawn (patent). Reference 1). In this method, as shown in FIG. 8, after the first single mode fiber 111 and the second single mode fiber 112 are fusion-spliced, the fusion point 101 is heated and stretched, thereby the vicinity of the fusion point 101. The first single mode fiber 111 and the second single mode fiber 112 can be reduced in diameter, and the mode field diameters W11 and W12 can be reduced. Therefore, the mode field diameter W11 of the first single mode fiber 111 at the fusion point 101 is reduced. And the difference in mode field diameter W12 of the second single mode fiber 112 can be reduced. Therefore, this method makes it possible to reduce the difference in mode field diameter and reduce the connection loss between the fibers, compared to the case where the single mode fibers having different mode field diameters are brought into direct contact and fused. It was.

As another method, as shown in FIG. 9, the mode field diameter W22 is smaller than the mode field diameter W21 of the first single mode fiber 211 and the first single mode fiber 211, and the core portion dopant concentration. The second single mode fiber 212 having a large size is opposed to each other and fusion-bonded, and after the fusion-bonding, the fusion point 201 is heated at a temperature lower than the fusion-connection temperature, It has been proposed to make the mode field diameter W32 substantially coincide with the mode field diameter W31 on the fusion point 201 side of the first single-mode fiber (see Patent Document 2). According to this method, since the size of the mode field diameter at the connection portion of the first single mode fiber 111 and the second single mode fiber 112 can be made equal, the connection loss can be reduced.
JP-A-4-219706 Japanese Patent Laid-Open No. 5-215931

  However, in the method disclosed in Patent Document 1, since it is necessary to heat and stretch the fusion point 101 until the difference in mode field diameter becomes small, the fiber diameter in the vicinity of the fusion point 101 is extremely small. Thus, there is a problem that the mechanical strength is lowered. Furthermore, in this method, it is difficult to manage the heating conditions for stretching the fusion point 101, and there is a problem that the single mode fiber breaks during heating.

  Further, in the method disclosed in Patent Document 2, a mode of two single mode fibers is obtained by thermally diffusing a dopant such as Ge previously added to the core portion of the single mode fiber by heating and expanding the mode field diameter. The field diameter is matched. However, the thermal diffusion of the dopant differs in the diffusion speed depending on the type of the single mode fiber, and it is difficult to manage the thermal diffusion by heating. Therefore, the mode field diameters of the first single mode fiber 211 and the second single mode fiber 213 are the same. It was difficult to make. Furthermore, in this method, since it is necessary to heat the single mode fiber while entering light and monitoring the connection loss, the manufacturing process becomes complicated and a long time is required for production.

  In view of the above problems, the optical fiber body of the present invention includes a first single mode fiber, a second single mode fiber having a mode field diameter smaller than the mode field diameter of the first single mode fiber, and one end portion A graded index fiber connected to one end of the first single-mode fiber and having the other end connected to one end of the second single-mode fiber to match the mode field diameter of each connected single-mode fiber It is provided with.

 In the optical fiber body of the present invention, the length of the graded index fiber is 0.22 to 0.28 + 0.5n (n is an integer of 0 or more) times the pitch length of the graded index fiber. Features.

 The mode converter of the present invention is characterized by comprising a support having a through hole and the optical fiber body inserted into and fixed to the through hole.

In the mode converter of the present invention, the optical fiber body includes the first single-mode fiber and the second single-mode fiber that are fusion-bonded to the graded index fiber, and the fusion portion is the first- The mode converter according to the present invention is characterized in that one end side is an outer peripheral portion at one end portion of the support body. And an optical fiber having a mode field diameter equivalent to the mode field diameter of the first single mode fiber or the second single mode fiber of the optical fiber body exposed from one end surface of the support from the other end side. A cylindrical sleeve into which the held plug is inserted is provided It is characterized by

  According to the optical fiber body of the present invention, by connecting two single mode fibers having different mode field diameters via a graded index fiber, the mode field diameter of each connected single mode fiber is determined as a graded index fiber. Therefore, it is possible to reduce the connection loss of light generated between the first single mode fiber and the second single mode fiber.

  Furthermore, in the present invention, if the length of the graded index fiber is 0.22 to 0.28 + 0.5n (n is an integer of 0 or more) times the pitch length of the graded index fiber, the first single mode fiber And the second single-mode fiber can be matched in mode matching conditions, and can be connected with the lowest loss.

  Further, according to the mode converter of the present invention, the optical fiber body can be easily held by inserting and fixing the optical fiber body of the present invention into the through hole of the support. .

  Furthermore, in the mode converter of the present invention, the first single mode fiber and the second single mode fiber of the optical fiber body are fusion-bonded with the graded index fiber, and the outer diameter of the fusion portion is the first single-mode fiber, By making it smaller than the outer diameter of the second single mode fiber and the graded index fiber, the connection loss between the fibers is reduced, and the optical fiber body is easily inserted and fixed in the through hole of the support. be able to.

  In the mode converter of the present invention, the first single mode fiber or the second single of the optical fiber body, one end side of which is inserted into the outer peripheral portion of the one end portion of the support and exposed from the one end surface of the support from the other end side. By providing a cylindrical sleeve into which a plug holding an optical fiber having a mode field diameter equivalent to the mode field diameter of the mode fiber is inserted, the plugs having single mode fibers having different mode feel diameters are sleeved together. Can be connected through.

  Hereinafter, an optical fiber body 1 according to an embodiment of the present invention will be described in detail with reference to the drawings. In addition, in each figure, about the same member, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  As shown in FIG. 1A, an optical fiber body 1 according to an embodiment of the present invention is fused in the order of a first single mode fiber 11, a graded index fiber 13, and a second single mode fiber 12. Connected.

  The first single-mode fiber 11 is formed by forming a core portion 11a having a refractive index of 1.460 to 1.470 and a clad portion 11b having a refractive index of 1.450 to 1.460 so as to cover the core portion 11a. For example, it is made of glass such as quartz. The mode field diameter of the first single mode fiber is about 9 to 11 μm.

  The second single mode fiber 12 is formed by forming a core portion 12a having a refractive index of 1.460 to 1.470 and a cladding portion 12b having a refractive index of 1.450 to 1.460 so as to cover the core portion 12a. For example, it is made of glass such as quartz. The mode field diameter of the second single mode fiber is about 6 to 8 μm, which is smaller than the mode field diameter of the first single mode fiber.

  The graded index fiber 13 has a refractive index profile in which the refractive index gradually decreases from the central axis of the fiber (the central axis of the core portion 13a) toward the outer peripheral surface of the cladding portion 13b. Fiber, generally used for multimode transmission. Since the refractive index distribution of the graded index fiber 13 has a lens effect similar to that of the GRIN lens, a coupled optical system can be configured by using the graded index fiber 13 with an appropriate length.

In various optical fibers, the core portion is a region having a higher refractive index than the cladding portion, and has an effect of confining light. In general, light is not transmitted only through the core portion of the optical fiber, but also oozes out slightly into the cladding portion, so that the light transmission region is substantially larger than the core region. Therefore, when considering the behavior of light in an optical fiber, it is generally necessary to consider it in the mode field, not the core of the optical fiber. The mode field is defined as a region where the light intensity is attenuated to 1 / e ² with respect to the maximum light intensity of the optical fiber, and the diameter is referred to as a mode field diameter. Therefore, in the following description, it demonstrates using a mode field and a mode field diameter.

  FIG.1 (b) is the schematic diagram which showed the mode field of the optical fiber body 1 of this invention. Here, the mode field of each optical fiber is indicated by a dotted line in the figure. As shown in FIG. 1B, the mode field diameter W2 of the second single mode fiber 12 is smaller than the mode field diameter W1 of the first single mode fiber 11.

  FIG. 2 is a schematic diagram showing the behavior of the light beam transmitted through the graded index fiber. As shown in FIG. 2, the light beam transmitted through the graded index fiber 13 exhibits a sine curve behavior, and the length of the graded index fiber is represented by a pitch (P) corresponding to the period of the light beam behavior. Here, in FIG. 2, the horizontal axis represents the pitch, the vertical axis represents the position of the light beam in the graded index fiber, and the portion where the light spreads most is relatively illustrated as 1 or −1 on the vertical axis. It is. Note that P = 1 corresponds to one period (2π) of the sine curve. For example, P = 0.25 to make the light emitted from the graded index fiber parallel light, and P = 0... To converge the light at the light emitting part of the graded index fiber. 5 may be used. Here, when P = 0.25, light is emitted as parallel light (collimated light), and the graded index fiber acts like a GRIN lens. The pitch length P of the graded index fiber 13 is as follows, assuming that the length of the graded index fiber is L, the radius of the core part is r, and the relative refractive index of the core part and the clad part having the highest refractive index is Δ. It is expressed by the following formula.

そして、本発明の一実施形態に係る光ファイバ体１は、グレイテッドインデックスファイバ１３のピッチ長Ｐ、コア部の半径ｒ、屈折率差Δが、第１シングルモードファイバ１１のモードフィールド径Ｗ１と、第２シングルモードファイバ１２のモードフィールド径Ｗ２のモードの整合が取れるように調整されている。そのため、グレイテッドインデックスファイバ１３におけるモードフィールド１６は、接続部１４における直径がモードフィールド径Ｗ１と一致し、一方、接続部１５における直径がモードフィールド径Ｗ２に一致している。

In the optical fiber body 1 according to the embodiment of the present invention, the pitch length P of the graded index fiber 13, the radius r of the core portion, and the refractive index difference Δ are the same as the mode field diameter W1 of the first single mode fiber 11. The mode of the mode field diameter W2 of the second single mode fiber 12 is adjusted so as to be matched. Therefore, the mode field 16 in the graded index fiber 13 has a diameter at the connection portion 14 that matches the mode field diameter W1, while a diameter at the connection portion 15 matches the mode field diameter W2.

  At this time, the length of the graded index fiber 13 is preferably set so that the pitch length of the graded index fiber is 0.22 to 0.28. This is because light is emitted as collimated light when the pitch length is closer to 0.25, and therefore mode matching with the mode field diameters W1 and W2 of the first and second single mode fibers 12 is reduced to reduce light loss. realizable.

  Next, a specific form of the optical fiber body 1 will be described. FIG. 3 shows that the mode field diameter W1 of the first single mode fiber 11 is 10.5 μm, the mode field diameter W2 of the second single mode fiber 12 is 6 μm, and the relative refractive index Δ of the graded index fiber 13 is 0.05. It is a graph which shows the calculation result of the mode field diameter in the optical fiber body 1 in case the pitch length is P = 0.25 and the radius of a core part is 15.5 micrometers.

  FIG. 3 shows the relationship between the length of the graded index fiber 13 and the mode field diameter of each optical fiber, where the horizontal axis is distance (the length of the optical fiber) and the vertical axis is the mode field diameter of the optical fiber. ing. In FIG. 3, the region of less than 0 μm is the first single mode fiber 11, the region of 0 to 77 μm is the graded index fiber 13, and the region of 77 μm or more is the second single mode fiber 12. That is, in the optical fiber body 1 having the mode field diameters W1 and W2 described above, if the graded index fiber 13 is 77 μm, the connection loss is small and the mode matching of the first single mode fiber 11 and the second single mode fiber 12 is achieved. Can do.

  FIG. 4 is a graph showing the calculation result of the mode field diameter in another form of the optical fiber body 1. In FIG. 4, the first single mode fiber 11 and the second single mode fiber 12 have the mode field diameter shown in FIG. 3, and the pitch length of the graded index fiber 13 is P = 0.75. In this case, the length of the graded index fiber 13 is calculated.

  In FIG. 4, the region of less than 0 μm is the first single mode fiber 11, the region of 0 to 77 μm is the graded index fiber 13, and the region of 231 μm or more is the second single mode fiber 12. That is, in the optical fiber body 1 having the mode field diameters W1 and W2 described above, if the graded index fiber 13 is 231 μm, the connection loss is small and the mode matching of the first single mode fiber 11 and the second single mode fiber 12 is achieved. Can do.

As described above, the graded index fiber 13 returns to the original position every 0.5 pitches with respect to the period of the pitch length P = 1, as shown in FIG. It may be 22 to 0.28 + 0.5n times (n is an integer of 0 or more). However, the refractive index distribution in the graded index fiber 13 may be slightly different from the ideal distribution in manufacturing. For this reason, when n increases, the possibility of being affected by an error increases. Therefore, it is preferable that n is small. Further, as n increases, the length of the graded index fiber 13 increases, and the optical fiber body increases in size. Therefore, the pitch length of the graded index fiber 13 is 0.22 to 0.28, preferably 0. It is good to set to 24-0.26.

    Next, a first embodiment of the mode converter of the present invention will be described. As shown in FIG. 2A, the mode converter 20 includes an optical fiber body 1 and a support body 21.

  The support body 21 is a member for holding the optical fiber body 1 inserted into the through hole, and is constituted by, for example, a cylindrical body, a prismatic body having a through hole, or the like. If the support 21 is formed of a cylindrical body and the outer diameter of the optical fiber body 1 is 0.125 mm, for example, the support 21 has a diameter of φ1.24 to φ2.6 mm and a diameter of the through hole of φ0. It is composed of about 125 to φ0.128 mm. The material of the support 21 is not particularly limited as long as the optical fiber body 1 can be fixed. However, zirconia ceramics are preferable from the viewpoints of workability and toughness. Further, the one end portion 21a of the support 21 may be formed into a spherical shape by polishing or the like in order to favorably connect the optical fiber by contact with the plug 40 described later.

  The mode converter 20 inserts the optical fiber body 1 into the through hole of the support body 21 and bonds the optical fiber body 1 with an adhesive such as epoxy resin interposed between the support body 21 and the optical fiber body 1. It is produced by fixing.

  Further, as shown in FIG. 2A, the mode converter 20 may adhere the covering portion 11c of the first single-mode fiber 11 to the other end portion 21b of the support 21, while metal or plastic is used. It may be a structure that is bonded to the covering portion 11c via a housing (not shown) formed by, for example.

  Furthermore, as shown in FIG. 2A, the mode converter 20 may include a sleeve 31 inserted into the outer peripheral portion of the one end portion 21a of the support 21. The sleeve 31 is a member into which the plug 40 is inserted from the opening of the through hole located on the other end side opposite to the one end side where the support body 21 is inserted, and is configured by a cylindrical body. . As the material of the sleeve 31, for example, a metal such as phosphor bronze or a ceramic such as zirconia can be used.

  In such a mode converter 20, a plug 40 having an optical fiber equivalent to the mode field diameter of the second single mode fiber 12 is inserted from the other end side of the sleeve 31, and from the end face of the one end 21 a of the support 21. By connecting to the exposed second single mode fiber 12 of the optical fiber body 1, the mode field of the optical fiber of the plug 40 can be converted to the mode field diameter of the first single mode fiber via the graded index fiber 13. it can.

  Further, the mode converter 20 may be a fiber stub type in which the optical fiber body 1 is accommodated in the through hole of the support body 21 as shown in FIG. In the mode converter 20, the second single mode fiber 12 is disposed on the one end 21 a side of the support 21, but the first single mode fiber 11 is disposed on the one end 21 a side of the support 21. Also good.

  In such a mode converter 20, a plug (not shown) including an optical fiber having a mode field diameter equivalent to that of the second single mode fiber 12 is brought into contact with the end surface of the one end 21 a of the support 21. The light emitted from the optical fiber of the plug is incident on the second single mode fiber 12 of the optical fiber body 1, mode matching is performed via the graded index fiber 13, and the mode field diameter W 1 of the first single mode fiber 11 is set. It has a function to convert.

    Here, the optical fiber body 1 used for the mode converter 20 includes a connection portion 14 between the first single mode fiber 11 and the graded index fiber 13 and a connection portion 15 between the graded index fiber 13 and the second single mode fiber 12. It is desirable that the fusion splicing (fusion splicing portion) be smaller than the outer diameters of the first single mode fiber 11, the second single mode fiber 12, and the graded index fiber 13. This is because if the optical fibers constituting the optical fiber body 1 are fused and connected, the connection loss of light generated between the optical fibers can be reduced.

  In the fusion splicing of the optical fiber, since the glass constituting the optical fiber is melted and connected by, for example, heat due to electric discharge, the outer diameters of the connecting portion 14 and the connecting portion 15 are larger than the outer diameter of each optical fiber to be connected. . However, when the outer diameter of the connection portions 14 and 15 of the optical fiber body 1 is increased, it is difficult to insert the support body 21 into the through hole. Along with this, if the diameter of the through hole of the support body 21 is increased, the optical fiber body 1 is misaligned, and the possibility that the connection loss of light with the plug increases. Therefore, at the time of fusion splicing of the optical fibers, when the optical fibers are connected to each other by melting, it is preferable that each optical fiber is pulled and stretched to reduce the outer diameter at the connection portion. Note that the fusion drawing at this connecting portion does not require an outer diameter unlike the optical fiber body in which the vicinity of the fusion point 101 is extremely long until the mode field diameter shown in FIG. 8 is matched. The outer diameter may be reduced by stretching only the portion that has been increased. Therefore, the length of the fusion-stretched portion in the connection portions 14 and 15 of the optical fiber body 1 is extremely small, and hardly affects the strength of the optical fiber.

  Next, a mode converter 30 according to another embodiment of the present invention will be described. As shown in FIG. 6, the mode converter 30 includes the above-described mode converter 20 and a sleeve 31, and the mode converter 20 is accommodated in the through hole of the sleeve.

  The sleeve 31 is a member that holds the mode converter 20 in the through hole and into which the plugs 40 and 40 ′ are inserted from the openings of the through holes located at both ends, and is configured by a cylindrical body.

As the material of the sleeve 31, for example, a metal such as phosphor bronze or a ceramic such as zirconia can be used.

  The mode converter 30 is a member for connecting the plug 40 and the plug 40 ′ having optical fibers having different mode field diameters by matching the mode of light and reducing the loss of light. Specifically, the sleeve 31 so that the plug 40 including an optical fiber having a mode field diameter equivalent to the mode field diameter W1 of the first single mode fiber 11 is in contact with the end surface of the other end 21b of the support 21. On the other hand, the plug 40 ′ having an optical fiber having a mode field diameter equivalent to the mode field diameter W 2 of the second single mode fiber 12 is brought into contact with the end face of the one end portion 21 a of the support 21. Into the sleeve 31. Thereby, in the mode converter 30, the plug 40 and the plug 40 'having optical fibers having different mode field diameters can be easily optically connected with little connection loss.

  Below, the manufacturing method of the optical fiber body 1 and the mode converter 20 of this invention is demonstrated. First, the first single mode fiber 11 and the graded index fiber 13 are fusion-bonded by discharge, and then the graded index fiber 13 is cut at a predetermined pitch length (for example, P = 0.25) using cleavage. . Thereafter, the second single mode fiber 12 is fusion spliced to the graded index fiber 13, whereby the optical fiber body 1 can be manufactured.

  In addition, the mode converter 20 inserts the optical fiber body 1 into the support body 21, and is bonded and fixed using, for example, an epoxy-based adhesive, and then, using a polishing sheet such as diamond powder particles, It is produced by polishing the end portions 21a and 21b. The mode converter 30 including the sleeve 31 can be manufactured by press-fitting or inserting the mode converter 20 into a cylindrical sleeve 31 made of metal, ceramics, or the like, and then bonding and fixing.

  A first embodiment of the present invention will be described. In the first embodiment, single mode fibers having mode field diameters different from 10.5 μm and 6 μm were fusion spliced by the present invention and the conventional method, and the connection loss was measured.

  First, a first embodiment of the present invention will be described. First, the mode field diameter W1 of the first single mode fiber 11 is 10.5 μm, the mode field diameter W2 of the second single mode fiber 12 is 6 μm, the relative refractive index Δ of the graded index fiber 13 is 0.05, A fiber having a radius of 15.5 μm was prepared. The graded index fiber 13 having a pitch length of 0.18 to 0.22, 0.22 to 0.28, and 0.28 to 0.32 is used as the first single mode fiber. Five optical fiber bodies 1 each having a fusion spliced connection with the 11 and second single mode fibers 12 were produced, and used as samples according to the examples of the present invention.

  Next, as a comparative example, a sample in which the mode field diameter at the connection portion of the optical fiber shown in FIG. The first single mode fiber 211 has a mode field diameter W31 of 10.5 μm, and the second single mode fiber 212 has a mode field diameter W32 of 6 μm. 5 were repeated, and five optical fiber bodies with enlarged mode field diameters in the vicinity of the connection portion were produced, and used as samples for comparative examples.

The light produced from the LD (laser diode) light source was input to the first single mode fiber 11 and the light output from the second single mode fiber 12 was measured with a power meter. As the LD light source, a wavelength of 1550 nm was used. When the power input to the first single mode fiber 11 is Po and the power output from the second single mode fiber 12 is P, the connection loss is obtained by −10 Log (P / Po). Table 1 shows the results of measurement of splice loss in all samples.

  As shown in Table 1, in the sample of the comparative example, the optical connection loss was an average of 0.47 dB, whereas in the sample of the present invention, the optical connection loss was an average of 0.22 to 0.31 dB. The connection loss could be reduced. Furthermore, in the embodiment of the present invention, the average connection loss when the pitch length is 0.22 to 0.28 is 0.24 dB, whereas the average connection loss when the pitch length is 0.18 to 0.22 is The average connection loss is 0.31 dB when the pitch length is 0.31 dB and the pitch length is 0.28 to 0.32, and the connection loss is the smallest when the pitch length is 0.22 to 0.28. .

  From the above results, according to the optical fiber body 1 of the present invention, the first single mode fiber 11 and the second single mode fiber 18 having the mode field diameter W2 smaller than the mode field diameter W1 of the first single mode fiber 11. And one end is connected to one end of the first single mode fiber 11 and the other end is connected to one end of the second single mode fiber 12 to match the mode field diameter of each connected single mode fiber. Since the graded index fiber 13 is provided to match the modes of the first single mode fiber 11 and the second single mode fiber 12, the first single mode fiber 11 and the second single mode The connection loss of the fiber 12 can be reduced.

  The length of the graded index fiber 13 is most preferably 0.22 to 0.28 + 0.5n (n is an integer of 0 or more) times the pitch length of the graded index fiber 13. .

  Next, as a second embodiment of the present invention, a mode converter 30 in which a mode converter 20 in which an optical fiber body 1 is inserted and fixed to a support 21 is housed in a sleeve 31 is manufactured, and its connection loss is produced. Evaluated.

  In the second embodiment of the present invention, as the optical fiber body, the mode field diameter W1 of the first single mode fiber 11 is 10.5 μm, the mode field diameter W2 of the second single mode fiber 12 is 6 μm, and the graded index fiber 13 is used. A graded index fiber having a refractive index difference Δ of 0.5% and a core radius of 15.5 μm was used. Further, the pitch length of the graded index fiber 13 was set to 0.22 to 0.28. The optical fiber body 1 is inserted into a support 21 made of zirconia having an outer diameter of φ2.499 ± 0.0005 μm, an inner diameter of φ0.126 ± 0.0005 μm, and a length of 10.5 mm, and is bonded and fixed using an epoxy adhesive. Then, after polishing the end faces 21a and 21b of the support 21, five mode converters 30 are prepared by being inserted and fixed to a sleeve 31 having a total length of 20 mm. Further, the mode field diameter with optical connector plugs at both ends is 10 Five sets each of a single mode fiber of .5 μm and a single mode fiber having an optical connector plug at both ends and a mode field diameter of 6 μm were prepared. Using these, the connection loss was evaluated with or without the mode converter 30 interposed between the optical connector plugs.

  Specifically, the measurement was performed according to the following procedure using the connection loss method shown in FIG. First, as shown in FIG. 7A, an incident-side single mode fiber 73 having a mode field diameter of 10.5 μm is connected to an LD light source 71 that emits light of 1550 nm, and light emitted from an optical connector plug 74 at the opposite end. Was read by the power meter 72, and the output at this time was Po. Next, as shown in FIG. 7B, an optical connector using a conventional method in which an optical connector plug 75 of an outgoing-side single mode fiber 77 having a mode field diameter of 6 μm is brought into contact with the optical connector plug 74 and connected. The light emitted from the plug 76 was read by the power meter 72, and the output at that time was P1. When the output is P1, the connection loss is obtained by −10 Log (P1 / Po).

On the other hand, as an embodiment of the present invention, as shown in FIG. 7C, the mode converter 30 is inserted between the optical connector plug 74 and the optical connector plug 75, and the light emitted from the optical connector plug 76 is supplied with power. Read by meter 72. If the output at this time is P2, the connection loss in the connection method using the mode converter 30 of the present invention is obtained by −10 Log (P2 / Po). For each of the five, connection loss was compared with the conventional connection method and the connection method using the mode converter of the present invention. The results are shown in Table 2.

  As shown in Table 2, in the conventional connection method, the average connection loss is 1.51 dB, and in the connection method using the mode converter of the present invention, the average connection loss is 0.50 dB. By using a converter, connection loss could be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an embodiment of an optical fiber body of the present invention, in which (a) is a cross-sectional view and (b) is a schematic diagram showing a mode field of the optical fiber body. It is a schematic diagram which shows the aspect of the light of a graded index fiber. It is a graph which shows the aspect of the light which permeate | transmits the optical fiber body which concerns on one Embodiment of this invention. It is a graph which shows the aspect of the light which permeate | transmits the optical fiber body which concerns on other embodiment of this invention. It is sectional drawing which shows the mode converter which concerns on one Embodiment of this invention. It is sectional drawing which shows the mode converter which concerns on other embodiment of this invention. It is the schematic for demonstrating the measuring method of the connection loss of light, (a) is a reference value measurement, (b) is an outgoing light measurement by the conventional connection method (c) is the mode converter of this invention. The outgoing light measurement is shown. It is the schematic which shows the conventional optical fiber body. It is the schematic which shows the conventional optical fiber body.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical fiber body 2 ... Mode converter 11 ... 1st single mode fiber 11a ... Core part 11b ... Cladding part 11c ... Covering part 12 ... 2nd single mode fiber 12a ... Core portion 12b ... Cladding portion 13 ... Graded index fiber 13a ... Core portion 13b ... Cladding portions 14, 15 ... Connection portion 16 ... Mode field 21 ... Support 71 ... Light source 72 ... Power meter 73 ... Incident side single mode fibers 74 to 76 ... Optical connector plug 77 ... Outgoing side single mode fibers W1, W2, W11, W12, W21, W22 ... Mode field diameter

Claims (5)

A first single mode fiber;
A second single mode fiber having a mode field diameter smaller than the mode field diameter of the first single mode fiber;
One end is connected to one end of the first single mode fiber, the other end is connected to one end of the second single mode fiber, and a gray for matching the mode field diameter of each connected single mode fiber. An optical fiber body including a ted index fiber.   The length of the graded index fiber is 0.22 to 0.28 + 0.5n (n is an integer equal to or greater than 0) times the pitch length of the graded index fiber. Optical fiber body. A support having a through hole;
A mode converter comprising: the optical fiber body according to claim 1, wherein the optical fiber body is inserted into the through hole and fixed by adhesion.   In the optical fiber body, the first single mode fiber and the second single mode fiber are fusion-connected to the graded index fiber, and the fusion part is the first single mode fiber and the second single mode. The mode converter according to claim 3, wherein the mode converter is smaller than an outer diameter of a fiber and the graded index fiber. The mode field diameter of the first single mode fiber or the second single mode fiber of the optical fiber body, one end side of which is inserted into the outer peripheral portion at one end portion of the support and exposed from the one end surface of the support from the other end side. 5. The mode converter according to claim 3, further comprising a cylindrical sleeve into which a plug holding an optical fiber having a mode field diameter equivalent to that of a cylindrical sleeve is inserted.

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