Pitch converter and optical fiber connector

Abstract

To provide a pitch converter and optical fiber connector that suppress inter-core crosstalk while increasing core density. [Solution] The pitch converter comprises a plurality of core portions, a cladding portion surrounding the outer circumference of the plurality of core portions and having a refractive index lower than the maximum refractive index of the core portions, and a first end face and a second end face perpendicular to the longitudinal direction and facing each other in the longitudinal direction. The plurality of core portions and the cladding portion have a tapered diameter portion that narrows in the longitudinal direction from the first end face to the second end face to a diameter of 2 / 3 or less, the core pitch of the first end face is 30 μm or more, and the core pitch of the second end face is 20 μm or less. The plurality of core portions have a step-type refractive index profile, the core diameter of the core portion at the first end face is 3.2 μm or more and 3.7 μm or less, and the relative refractive index difference Δ1 of the maximum refractive index of the core portion to the refractive index of the cladding portion is 1.9% or more and 2.3% or less.

Description

[Technical Field]

[0001] The present invention relates to a pitch converter and an optical fiber connector. [Background Art]

[0002] As a new technology for increasing transmission capacity at relatively low cost, technological development of space division multiplexing is progressing. One of the space division multiplexing technologies is Multi-Core Fiber (MCF) (see Non-Patent Document 1). In the type of multi-core fiber disclosed in Non-Patent Document 1, increasing the number of core portions reduces the distance between cores, so inter-core crosstalk (XT) becomes a problem.

[0003] Further, as another type of multi-core fiber, a multi-core fiber called coupled multi-core fiber is disclosed (see Non-Patent Document 2). A coupled multi-core fiber is a multi-core fiber that allows inter-core crosstalk to occur, and achieves high core density by narrowing the distance between cores. When a coupled multi-core fiber is used for signal transmission, it is premised that MIMO (Multiple Input Multiple Output) DSP (Digital Signal Processing) is performed when processing transmitted signal light. Note that a multi-core fiber in which inter-core crosstalk does not occur or inter-core crosstalk is small may be referred to as an uncoupled multi-core fiber. [Prior Art Documents] [Non-Patent Documents]

[0004] [Non-Patent Document 1] Takashi Matsui, Taiji Sakamoto, Yukihiro Goto, Kotaro Saito, Kazuhide Nakajima, Fumihiko Yamamoto, Toshio Kurashima, “Design of 125 um cladding multi-core fiber with full-band compatibility to conventional single-mode fiber”, European Conference on Optical Communication 2015, We.1.4.5. [Non-Patent Document 2] Tetsuya HAYASHI, Yoshiaki TAMURA, Takemi HASEGAWA, Tetsuya NAKANISHI, and Toshiki TARU, “Coupled Multi-Core Optical Fiber Suitable for Long-Haul Transmission”, SEI TECHNICAL REVIEW · NUMBER 85 OCTOBER 2017 p.19-23. [Overview of the project] [Problems that the invention aims to solve]

[0005] However, multi-core fibers that increase core density while suppressing inter-core crosstalk have not been sufficiently studied, and there is room for improvement.

[0006] The present invention has been made in view of the above, and its object is to provide a pitch converter and an optical fiber connector in which intercore crosstalk is suppressed while increasing core density. [Means for solving the problem]

[0007] To solve the above-mentioned problems and achieve the objective, one aspect of the present invention is a pitch converter comprising: a plurality of core portions; a cladding portion surrounding the outer circumference of the plurality of core portions and having a refractive index lower than the maximum refractive index of the core portions; and a first end face and a second end face perpendicular to the longitudinal direction and facing each other in the longitudinal direction, wherein the plurality of core portions and the cladding portion have a tapered diameter portion that narrows in the longitudinal direction from the first end face to the second end face to a diameter of 2 / 3 or less, the core pitch which is the distance between the centers of the nearest adjacent core portions at the first end face is 30 μm or more, the core pitch which is the distance between the centers of the nearest adjacent core portions at the second end face is 20 μm or less, the plurality of core portions have a step-type refractive index profile, the core diameter of the core portion at the first end face is 3.2 μm or more and 3.7 μm or less, and the relative refractive index difference Δ1 of the maximum refractive index of the core portion to the refractive index of the cladding portion is 1.9% or more and 2.3% or less.

[0008] One aspect of the present invention comprises a plurality of core portions, a cladding portion surrounding the outer circumference of the plurality of core portions and having a refractive index lower than the maximum refractive index of the core portions, and a first end face and a second end face perpendicular to the longitudinal direction and facing each other in the longitudinal direction, wherein the plurality of core portions and the cladding portion have a tapered diameter portion that narrows in the longitudinal direction from the first end face to the second end face to a diameter of 2 / 3 or less, the core pitch which is the distance between the centers of the nearest adjacent core portions at the first end face is 30 μm or more, and the core pitch which is the distance between the centers of the nearest adjacent core portions at the second end face is 20 μm or less, The pitch converter is characterized in that the core portion has a W-shaped refractive index profile, the core portion is composed of a center core with a diameter of 2a, and a depressed layer surrounding the outer circumference of the center core, the depressed layer having a refractive index smaller than that of the cladding portion, an inner diameter of 2a, and an outer diameter of 2b, and at the first end face, the relative refractive index difference Δ1 of the center core with respect to the cladding portion is 1.8% or more and 2.3% or less, the relative refractive index difference Δ2 of the depressed layer with respect to the cladding portion is -0.67% or more and -0.53% or less, 2a is 3.5 μm or more and 4.1 μm or less, and 2b is 9.5 μm or more and 10.1 μm or less.

[0009] One aspect of the present invention comprises a plurality of core portions, a cladding portion surrounding the outer circumference of the plurality of core portions and having a refractive index lower than the maximum refractive index of the core portions, and a first end face and a second end face perpendicular to the longitudinal direction and facing each other in the longitudinal direction, wherein the plurality of core portions and the cladding portion have a tapered diameter portion that narrows in the longitudinal direction from the first end face to the second end face to a diameter of 2 / 3 or less, the core pitch which is the distance between the centers of the nearest adjacent core portions at the first end face is 30 μm or more, the core pitch which is the distance between the centers of the nearest adjacent core portions at the second end face is 20 μm or less, the plurality of core portions have a trench-type refractive index profile, and the core portions have a diameter The pitch converter comprises a center core of 2a, an intermediate layer surrounding the outer circumference of the center core, having a refractive index smaller than that of the cladding portion and having an inner diameter of 2a and an outer diameter of 2b, and a trench layer surrounding the outer circumference of the intermediate layer, having a refractive index smaller than that of the cladding portion and having an inner diameter of 2b and an outer diameter of 2c, wherein at the first end face, the relative refractive index difference Δ1 of the center core with respect to the cladding portion is 1.8% or more and 2.3% or less, the relative refractive index difference Δ2 of the intermediate layer with respect to the cladding portion is -0.05% or more and 0.05% or less, 2a is 3.3 μm or more and 3.7 μm or less, 2b is 6.0 μm or more and 6.5 μm or less, and 2c is 9.6 μm or more and 10.0 μm or less.

[0010] The diameter of the second end face may be 70 μm or more and 125 μm or less.

[0011] One aspect of the present invention is an optical fiber connector comprising: a pitch converter; and a connecting multicore fiber connected to the second end face of the pitch converter, the multicore fiber having a plurality of core portions and a cladding portion surrounding the outer periphery of the plurality of core portions and having a refractive index lower than the maximum refractive index of the core portions.

[0012] One aspect of the present invention is an optical fiber connector comprising: a pitch converter; a first multicore fiber which is a coupled multicore fiber, connected to the second end face of the pitch converter, and comprising: a plurality of core portions; a cladding portion surrounding the outer circumference of the plurality of core portions and having a refractive index lower than the maximum refractive index of the core portions, wherein the core pitch, which is the distance between the centers of the nearest adjacent core portions in a cross section perpendicular to the longitudinal direction, is 20 μm or less, and the cladding diameter at the second end face of the pitch converter and the cladding diameter of the first multicore fiber are substantially the same. [Effects of the Invention]

[0013] According to the present invention, a pitch converter and an optical fiber connector can be realized that suppress inter-core crosstalk while increasing core density. Furthermore, since the core pitch can be widened all at once, it is easy to connect a multi-core fiber with a relatively narrow core pitch to a multi-core fiber with a relatively wide core pitch, and the optical fiber connector can be easily constructed. As a result, the handling of the multi-core fiber with a narrow core pitch and the optical fiber connector can be made easier, and the operability is also improved. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a schematic diagram showing a multicore fiber according to Embodiment 1. [Figure 2A] Figure 2A is a schematic diagram of a refractive index profile that can be used in a multicore fiber. [Figure 2B] Figure 2B is a schematic diagram of a refractive index profile that can be used in a multicore fiber. [Figure 2C] Figure 2C is a schematic diagram of a refractive index profile that can be used in a multicore fiber. [Figure 3] Figure 3 is a schematic diagram showing a multicore fiber according to Embodiment 2. [Figure 4] Figure 4 is a schematic diagram showing a pitch converter according to Embodiment 3. [Figure 5] FIG. 5 is a schematic diagram illustrating a pitch converter according to Embodiment 3. [Figure 6] FIG. 6 is a schematic exploded view illustrating an optical fiber connector according to Embodiment 4. [Figure 7] FIG. 7 is an explanatory diagram illustrating an example of the relationship between core diameter and mode field diameter. [Figure 8] FIG. 8 is a schematic exploded view illustrating an optical fiber connector according to Embodiment 5. [Figure 9] FIG. 9 is a schematic exploded view illustrating an optical fiber connector according to Embodiment 6. [Figure 10] FIG. 10 is a schematic exploded view illustrating an optical fiber connector according to Embodiment 7. DESCRIPTION OF EMBODIMENTS

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that the present invention is not limited by these embodiments. In addition, in the description of the drawings, the same or corresponding elements are appropriately assigned the same reference numerals. It should also be noted that the drawings are schematic, and the dimensional relationships and proportions of each element may differ from those in actual situations. Even between the drawings, there may be portions where the dimensional relationships and proportions differ from one another. In the present specification, the cutoff wavelength refers to the effective cutoff wavelength, and means the cable cutoff wavelength defined in ITU-T (International Telecommunication Union) G.650.1. In addition, terms not specifically defined in the present specification shall follow the definitions and measurement methods set forth in G.650.1 and G.650.2.

[0016] (Embodiment 1) FIG. 1 is a schematic diagram showing the multi-core fiber according to Embodiment 1. The multi-core fiber 10 includes a plurality of core portions 11 and a clad portion 12 that surrounds an outer circumference of the plurality of core portions 11 and has a refractive index lower than a maximum refractive index of the plurality of core portions 11, and extends in a longitudinal direction. This multi-core fiber 10 has a structure in which four core portions 11 are arranged inside the clad portion 12 in a square lattice pattern in a cross section orthogonal to the longitudinal direction. The core portion 11 is an example of four or more core portions arranged in a square lattice pattern.

[0017] The core portion 11 is made of, for example, silica-based glass to which a refractive index adjusting dopant such as germanium or fluorine is added. The clad portion 12 is made of, for example, pure silica glass. Here, pure silica glass is extremely high-purity silica glass that does not substantially contain a dopant for changing the refractive index and has a refractive index of about 1.444 at a wavelength of 1550 nm.

[0018] The core portion 11 of the multi-core fiber has, for example, a refractive index profile as shown in FIGS. 2A, 2B, and 2C.

[0019] FIG. 2A shows a step-type refractive index profile. In FIG. 2A, a profile P11 shows the refractive index profile of the core portion 11 which is a center core, and a profile P12 shows the refractive index profile of the clad portion 12. Note that the refractive index profile is represented by a relative refractive index difference (Δ) with respect to the clad portion 12. In the step-type refractive index profile shown in FIG. 2A, the diameter (core diameter) of the core portion 11 is 2a, and the relative refractive index difference of the core portion 11 with respect to the clad portion 12 is Δ1.

[0020] Figure 2B shows a W-type refractive index profile. In Figure 2B, profile P21 shows the refractive index profile of the core portion 11, and profile P22 shows the refractive index profile of the cladding portion 12. In the W-type refractive index profile, the core portion 11 consists of a center core with a diameter of 2a and a depressed layer surrounding the outer circumference of the center core, with a refractive index smaller than that of the cladding portion 12, an inner diameter of 2a, and an outer diameter of 2b. The difference in specific refractive index of the center core relative to the cladding portion 12 is Δ1. The difference in specific refractive index of the depressed layer relative to the cladding portion 12 is Δ2.

[0021] Figure 2C shows a trench-type refractive index profile. In Figure 2C, profile P31 shows the refractive index profile of the core portion 11, and profile P32 shows the refractive index profile of the cladding portion 12. In the trench-type refractive index profile, the core portion 11 consists of a center core with a diameter of 2a, an intermediate layer surrounding the outer circumference of the center core with a refractive index smaller than that of the center core and an inner diameter of 2a and an outer diameter of 2b, and a trench layer surrounding the outer circumference of the intermediate layer with a refractive index smaller than that of the cladding portion 12 and an inner diameter of 2b and an outer diameter of 2c. The relative refractive index difference of the center core with respect to the intermediate layer is Δ1. The relative refractive index difference of the intermediate layer with respect to the cladding portion 12 is Δ2. Note that Δ2 is usually set to 0% or near 0%, for example, in the range of -0.2% to 0.2%. The relative refractive index difference of the trench layer with respect to the cladding portion 12 is Δ3.

[0022] Returning to Figure 1, in the multicore fiber 10, the core pitch d1 is the distance between the centers of the nearest adjacent core portions 11 in a cross section perpendicular to the longitudinal direction. In the multicore fiber 10, the core pitch d1 is 20 μm or less.

[0023] Furthermore, in the multicore fiber 10, the intercore crosstalk is the crosstalk between the two nearest core sections 11 at a wavelength of 1625 nm. In the multicore fiber 10, the intercore crosstalk for each core section 11 is -20 dB / km or less. In other words, the multicore fiber 10 is an uncoupled multicore fiber.

[0024] Furthermore, in the multicore fiber 10, the macrobend loss at a wavelength of 1550 nm when each core portion 11 is bent with a radius of 5 mm is 0.1 dB / m or less.

[0025] The multicore fiber 10 configured as described above has a core density that is increased so that the core pitch d1 is 20 μm or less, while suppressing intercore crosstalk to -20 dB / km or less. Furthermore, because the multicore fiber 10 has high bending resistance, it is also suitable for relatively short-distance connection applications such as wiring within equipment.

[0026] In order to achieve a core pitch d1 of 20 μm or less and intercore crosstalk of -20 dB / km or less in the multicore fiber 10, it is preferable that, for example, the mode field diameter (MFD) at a wavelength of 1550 nm for each core portion 11 is 5 μm or less, and that the relative refractive index difference between the refractive index of the cladding portion 12 and the maximum refractive index of each core portion 11, i.e., Δ1, is 2% or more.

[0027] The multicore fiber 10 can be manufactured using various known methods for producing multicore fibers, such as the perforation method.

[0028] According to the simulation calculation results performed by the inventors, in a step-type refractive index profile, when Δ1 is 2.0%, the mode field diameter at a wavelength of 1550 nm is 4.4 μm, 2a (core diameter) is 3.5 μm, and the core pitch is 20 μm, an intercore crosstalk (XT) of -51.5 dB per meter, or -21.5 dB / km, is obtained. Furthermore, in order to suppress intercore crosstalk to -20 dB / km or less when the core pitch is 20 μm, it is desirable that the mode field diameter at a wavelength of 1550 nm is in the range of 4.0 μm to 4.8 μm, the core diameter (2a) is in the range of 3.2 μm to 3.7 μm, and Δ1 is in the range of 1.9% to 2.3%.

[0029] Furthermore, according to the simulation calculation results, in the W-type refractive index profile, Δ1 is 2.0%, Δ2 is -0.55%, the mode field diameter at a wavelength of 1550 nm is 4.1 μm, 2a is 3.8 μm, 2b is 9.8 μm, and with a core pitch of 20 μm, an intercore crosstalk of -54.4 dB per meter, or -24.4 dB / km, is obtained. Furthermore, in order to suppress intercore crosstalk to -20 dB / km or less when the core pitch is 20 μm, it is desirable that the mode field diameter at a wavelength of 1550 nm be in the range of 4.0 μm to 4.4 μm, Δ1 be in the range of 1.8% to 2.3%, Δ2 be in the range of -0.67% to -0.53%, the core diameter (2a) be in the range of 3.5 μm to 4.1 μm, and 2b be in the range of 9.5 μm to 10.1 μm.

[0030] Furthermore, according to the simulation calculation results, in a trench-type refractive index profile, Δ1 is 2.0%, Δ2 is 0%, Δ3 is -0.55%, the mode field diameter at a wavelength of 1550 nm is 4.1 μm, 2a is 3.5 μm, 2b is 6.3 μm, and 2c is 9.8 μm, and with a core pitch of 20 μm, an intercore crosstalk of -54.4 dB per meter, or -24.4 dB / km, is obtained. Furthermore, in order to suppress intercore crosstalk to -20 dB / km or less when the core pitch is 20 μm, it is desirable that the mode field diameter at a wavelength of 1550 nm be in the range of 4.0 μm to 4.3 μm, Δ1 be in the range of 1.8% to 2.3%, Δ2 be in the range of -0.05% to 0.05%, the core diameter (2a) be in the range of 3.3 μm to 3.7 μm, 2b be in the range of 6.0 μm to 6.5 μm, and 2c be in the range of 9.6 μm to 10.0 μm.

[0031] (Embodiment 2) Figure 3 is a schematic diagram showing a multicore fiber according to Embodiment 2. The multicore fiber 20 comprises a plurality of core portions 21 and a cladding portion 22 surrounding the outer periphery of the plurality of core portions 21 and having a refractive index lower than the maximum refractive index of the plurality of core portions 21, and extends in the longitudinal direction. This multicore fiber 20 has a structure in which seven core portions 21 are arranged in a hexagonal close-packed grid inside the cladding portion 22 in a cross section perpendicular to the longitudinal direction. The core portion 21 is an example of three or more core portions arranged in a hexagonal close-packed grid.

[0032] The constituent materials of the core portion 21, the constituent materials of the cladding portion 22, and the refractive index profile are the same as those of the corresponding elements in the multicore fiber 10, so their explanation is omitted.

[0033] In a multicore fiber 20, the core pitch d2 is the distance between the centers of the nearest adjacent core portions 21 in a cross-section perpendicular to the longitudinal direction. In a multicore fiber 20, the core pitch d2 is 20 μm or less.

[0034] Furthermore, in the multicore fiber 20, the intercore crosstalk for each core 21 is -20 dB / km or less.

[0035] Furthermore, in the multicore fiber 10, the macrobend loss at a wavelength of 1550 nm when each core portion 21 is bent with a radius of 5 mm is 0.1 dB / m or less.

[0036] The multicore fiber 20 configured as described above has a core density that is increased so that the core pitch d2 is 20 μm or less, while suppressing intercore crosstalk to -20 dB / km or less. Furthermore, because the multicore fiber 20 has high bending resistance, it is also suitable for relatively short-distance connection applications such as wiring within equipment.

[0037] In order to achieve a core pitch d2 of 20 μm or less and intercore crosstalk of -20 dB / km or less in the multicore fiber 20, it is preferable that, for example, the mode field diameter at a wavelength of 1550 nm for each core portion 21 is 5 μm or less, and that the relative refractive index difference between the refractive index of the cladding portion 22 and the maximum refractive index of each core portion 21, i.e., Δ1, is 2% or more.

[0038] This multi-core fiber technology, which increases core density while suppressing inter-core crosstalk, can be applied to pitch converters and optical fiber connectors, as described in the embodiments below.

[0039] (Embodiment 3) Figures 4 and 5 are schematic diagrams showing a pitch transducer according to Embodiment 3. The pitch transducer 30 comprises a plurality of core portions 31 and a cladding portion 32 surrounding the outer circumference of the plurality of core portions 31 and having a refractive index lower than the maximum refractive index of the core portions 31, and extends in the longitudinal direction. Furthermore, the pitch transducer 30 has a first end face 30a and a second end face 30b that are perpendicular to the longitudinal direction and face each other in the longitudinal direction. The core portions 31 and cladding portion 32 are exposed at the first end face 30a and the second end face 30b.

[0040] This pitch converter 30 has a structure in which four core parts 31 are arranged in a square grid pattern in a cross section perpendicular to the longitudinal direction inside the cladding part 32.

[0041] The constituent materials of the core portion 31, the constituent materials of the cladding portion 32, and the refractive index profile are the same as those of the corresponding elements in the multicore fiber 10, so their explanation is omitted.

[0042] Each core portion 31 and clad portion 32 has a tapered diameter section in the longitudinal direction from the first end face 30a to the second end face 30b, where the diameter tapers to 2 / 3 or less. In this embodiment, the entire section from the first end face 30a to the second end face 30b is the tapered diameter section. That is, the diameter Db of the clad portion 32 at the second end face 30b is 2 / 3 or less of the diameter Da of the clad portion 32 at the first end face 30a. The diameter Db of the clad portion 32 at the second end face 30b is, for example, 70 μm or more and 125 μm or less.

[0043] In the pitch converter 30, the core pitch d3a at the first end face 30a is 30 μm or more, and the core pitch d3b at the second end face 30b is 20 μm or less.

[0044] The pitch converter 30 can be suitably used to connect multicore fibers with different core pitches. For example, the pitch converter 30 may be configured such that each core portion 31 and cladding portion 32 is tapered in the longitudinal direction from the first end face 30a to the second end face 30b, with the core pitch d3a being 30 μm and the core pitch d3b being 20 μm. This makes the pitch converter 30 suitable for connecting a multicore fiber with a core pitch of 30 μm and a multicore fiber with a core pitch of 20 μm.

[0045] The pitch converter 30 can be manufactured, for example, as follows. That is, a multicore fiber having the same configuration as the multicore fiber 10 according to Embodiment 1, but differing in that its core pitch is 30 μm, is heated and stretched into a tapered shape to form the pitch converter 30. If the length of the pitch converter is to be shortened, the tapered portion may be cut out to form the pitch converter 30. In this case, it is preferable that the multicore fiber has a mode field diameter of 5 μm or less at a wavelength of 1550 nm for each core portion, and that Δ1 is 2% or more. In the pitch converter 30 manufactured from such a multicore fiber, Δ1 is 2% or more for each core portion.

[0046] (Embodiment 4) Figure 6 is a schematic exploded view showing an optical fiber connector according to Embodiment 4. The optical fiber connector 100 is formed by connecting the end face 10a of the multicore fiber 10 according to Embodiment 1 to the second end face 30b of the pitch converter 30 according to Embodiment 3, and connecting the four core sections 11 and the four core sections 31, respectively. This connection is, for example, a fusion splice, but may also be a physical contact. The multicore fiber 10 is an example of a connected multicore fiber.

[0047] Such an optical fiber connector 100 can connect to both of two multicore fibers having different core pitches. For example, the optical fiber connector 100 can connect to both a multicore fiber with a core pitch of 30 μm and a multicore fiber with a core pitch of 20 μm.

[0048] According to the simulation calculation results performed by the inventors, the optical fiber connector 100 has characteristics as shown in Table 1, for example. In Table 1, HΔMCF is the multicore fiber 10, and the pitch converter is the pitch converter 30. In the pitch converter 30, the small pitch side is the side of the second end face 30b, and the large pitch side is the side of the first end face 30a. Furthermore, both the multicore fiber 10 and the pitch converter 30 were set to a step-type refractive index profile.

[0049] In a multicore fiber 10 (HΔMCF), when Δ1 is 2.0%, the mode field diameter at a wavelength of 1550 nm is 4.4 μm, the core diameter (2a) is 3.5 μm, and the core pitch is 20 μm, an intercore crosstalk of -51.5 dB per meter, or -21.5 dB / km, is obtained. The cutoff wavelength λc is 1239 nm.

[0050] The pitch converter 30 is a multicore fiber with a Δ1 of 2.0%, a mode field diameter of 4.4 μm at a wavelength of 1550 nm, a core diameter (2a) of 3.5 μm, and a core pitch of 30 μm. The diameter is tapered from the first end face 30a (large pitch side) to the second end face 30b (small pitch side) to 2 / 3 of its original diameter, resulting in a core pitch d3a of 30 μm and a core pitch d3b of 20 μm. In this case, on the large pitch side, the core diameter (2a) is 3.5 μm, the mode field diameter is 4.4 μm, the cutoff wavelength λc is 1239 nm, and an intercore crosstalk of -115.9 dB per meter is obtained. On the small pitch side, the core diameter (2a) is 2.3 μm, the mode field diameter is 4.6 μm, the cutoff wavelength λc is 894 nm, and an intercore crosstalk of -22.7 dB per meter is obtained.

[0051] However, in the multicore fiber 10 (HΔMCF) and the first end face 30a (large pitch side), the core diameter (2a) may be in the range of 3.2 μm or more and 3.7 μm or less, and Δ1 may be in the range of 1.9% or more and 2.3% or less.

[0052] [Table 1]

[0053] Incidentally, when a multicore fiber is heated and tapered, the relationship between the core diameter and the mode field diameter, which was as shown at point A in Figure 7 before stretching, may decrease as shown at point B due to the reduction in core diameter. However, if the core diameter is further reduced, the light confinement force by the core decreases, and the mode field diameter actually expands. The pitch converter in Table 1 reduces the core diameter to the extent that the mode field diameter expands as the core diameter decreases on the small pitch side. This makes it possible to suppress the increase in connection loss due to mode field mismatch between the small pitch side of the pitch converter 30 and the multicore fiber 10 (HΔMCF).

[0054] (Embodiment 5) Figure 8 is a schematic exploded view showing an optical fiber connector according to Embodiment 5. The optical fiber connector 200 is formed by connecting the end face 10a of the multicore fiber 10 according to Embodiment 1 to the second end face 30b of the pitch converter 30 according to Embodiment 3, and further connecting the end face 10b of the multicore fiber 10 to the end face 40a of the coupled multicore fiber 40. These connections are, for example, fusion splices, but may also be physical contacts.

[0055] The coupled multicore fiber 40 comprises a plurality of core portions 41 and a cladding portion 42 surrounding the outer periphery of the plurality of core portions 41, having a refractive index lower than the maximum refractive index of the plurality of core portions 41, and extends in the longitudinal direction. This coupled multicore fiber 40 has a structure in which four core portions 11 are arranged in a square grid pattern in a cross section perpendicular to the longitudinal direction inside the cladding portion 42. The core portion 41 is an example of four or more core portions arranged in a square grid pattern.

[0056] The constituent materials of the core portion 41, the constituent materials of the cladding portion 42, and the refractive index profile are the same as those of the corresponding elements in the multicore fiber 10, so their explanation is omitted.

[0057] In the coupled multicore fiber 40, the core pitch d4 is the distance between the centers of the nearest adjacent core portions 41 in a cross-section perpendicular to the longitudinal direction. In the coupled multicore fiber 40, the core pitch d4 is 20 μm or less. Also, the core pitch d1 of the multicore fiber 10 and the core pitch d4 of the coupled multicore fiber 40 are the same.

[0058] In the optical fiber connector 200, four core sections 11 and four core sections 31 are connected to each other, and four core sections 11 and four core sections 41 are connected to each other.

[0059] Furthermore, the multicore fiber 10 and the coupled multicore fiber 40 are connected to form an optical fiber connector. The coupled multicore fiber 40 is an example of a first multicore fiber. The multicore fiber 10 is an uncoupled multicore fiber and is an example of a second multicore fiber.

[0060] It is preferable that the cladding diameters of the multicore fiber 10 and the coupled multicore fiber 40 are approximately the same. For example, the cladding diameters of both are 125 μm ± 1 μm (1 μm is a tolerance), and a difference of about 2 μm is acceptable.

[0061] When connecting a multicore fiber 10 and a coupled multicore fiber 40, it is preferable to fusion splice the multicore fiber 10 and the coupled multicore fiber 40, and then further heat the fusion spliced ​​portion to bring the mode field diameter of the core portion 11 of the multicore fiber 10 and the mode field diameter of the core portion 41 of the coupled multicore fiber 40 closer together. This reduces the connection loss between the multicore fiber 10 and the coupled multicore fiber 40.

[0062] According to the simulation calculation results performed by the inventors, the optical fiber connector 200 has characteristics as shown in Table 2, for example. In Table 2, HΔMCF is the multicore fiber 10, C-MCF is the coupled multicore fiber 40, and pitch converter is the pitch converter 30. Furthermore, the multicore fiber 10, the coupled multicore fiber 40, and the pitch converter 30 were all set to a step-type refractive index profile.

[0063] In a multicore fiber 10 (HΔMCF), when Δ1 is 2.0%, the mode field diameter at a wavelength of 1550 nm is 4.4 μm, the core diameter (2a) is 3.5 μm, and the core pitch is 20 μm, an intercore crosstalk of -51.5 dB per meter, or -21.5 dB / km, is obtained. The cutoff wavelength λc is 1239 nm.

[0064] In a coupled multicore fiber 40 (C-MCF), the characteristics of the coupled multicore fiber were obtained when Δ1 was 0.38%, the mode field diameter at a wavelength of 1550 nm was 9.0 μm, 2a was 8.6 μm, and the core pitch was 20 μm. Since the mode field diameter per core cannot be defined in a coupled multicore fiber, the above mode field diameter represents the mode field diameter of a single-core fiber having the same core diameter, Δ1, and refractive index profile as above. The cutoff wavelength λc is 1230 nm.

[0065] The pitch converter 30 is a multicore fiber with a Δ1 of 2.0%, a mode field diameter of 4.4 μm at a wavelength of 1550 nm, a core diameter (2a) of 3.5 μm, and a core pitch of 30 μm. The fiber is tapered from the first end face 30a (large pitch side) to the second end face 30b (small pitch side) to reduce the diameter to 2 / 3, resulting in a core pitch d3a of 30 μm and a core pitch d3b of 20 μm. In this case, on the large pitch side, 2a is 3.5 μm, the mode field diameter is 4.4 μm, the cutoff wavelength λc is 1239 nm, and an intercore crosstalk of -115.9 dB per meter is obtained. On the small pitch side, 2a is 2.3 μm, the mode field diameter is 4.6 μm, the cutoff wavelength λc is 894 nm, and an intercore crosstalk of -22.7 dB per meter is obtained.

[0066] However, at the first end face 30a (large pitch side) of the multicore fiber 10 (HΔMCF) and the pitch converter 30, the core diameter (2a) may be in the range of 3.2 μm to 3.7 μm, and Δ1 may be in the range of 1.9% to 2.3%.

[0067] [Table 2]

[0068] Furthermore, according to the simulation calculation results, the optical fiber connector 200 has characteristics such as those shown in Table 3. Both the multicore fiber 10 and the pitch converter 30 were set to a W-type refractive index profile.

[0069] In a multicore fiber 10 (HΔMCF), when Δ1 is 2.0%, Δ2 is -0.55%, the mode field diameter at a wavelength of 1550 nm is 4.1 μm, 2a is 3.8 μm, 2b is 9.8 μm, and the core pitch is 20 μm, an intercore crosstalk of -54.4 dB per meter, or -24.4 dB / km, is obtained. The cutoff wavelength λc is 1218 nm.

[0070] The coupled multicore fiber 40 (C-MCF) is the same as in Table 2, so the explanation is omitted.

[0071] The pitch converter 30 is a multicore fiber with a Δ1 of 2.0%, a Δ2 of -0.55%, a mode field diameter of 4.1 μm at a wavelength of 1550 nm, 2a of 3.8 μm, 2b of 9.8 μm, and a core pitch of 30 μm. The diameter of the multicore fiber is tapered from the first end face 30a (large pitch side) to the second end face 30b (small pitch side) to 2 / 3 of its original diameter, resulting in a core pitch d3a of 30 μm and a core pitch d3b of 20 μm. In this case, on the large pitch side, 2a is 3.8 μm, 2b is 9.8 μm, the mode field diameter is 4.1 μm, the cutoff wavelength λc is 1218 nm, and an intercore crosstalk of -124.1 dB per meter is obtained. On the small pitch side, 2a is 2.5 μm, 2b is 6.5 μm, the mode field diameter is 4.3 μm, the cutoff wavelength λc is 817 nm, and an intercore crosstalk of -23.6 dB per meter is obtained. In the pitch converter shown in Table 3, the core diameter is also reduced on the small pitch side to the extent that the mode field diameter expands as the core diameter decreases.

[0072] However, at the first end face 30a (large pitch side) of the multicore fiber 10 (HΔMCF) and the pitch converter 30, Δ1 may be in the range of 1.8% to 2.3%, Δ2 may be in the range of -0.67% to -0.53%, the core diameter (2a) may be in the range of 3.5 μm to 4.1 μm, and 2b may be in the range of 9.5 μm to 10.1 μm.

[0073] [Table 3]

[0074] Furthermore, according to the simulation calculation results, the optical fiber connector 200 has characteristics such as those shown in Table 4. Both the multicore fiber 10 and the pitch converter 30 were set to trench-type refractive index profiles.

[0075] In a multicore fiber 10 (HΔMCF), when Δ1 is 2.0%, Δ2 is 0%, Δ3 is -0.55%, the mode field diameter at a wavelength of 1550 nm is 4.1 μm, 2a is 3.5 μm, 2b is 6.3 μm, 2c is 9.8 μm, and the core pitch is 20 μm, an intercore crosstalk of -54.4 dB per meter, or -24.4 dB / km, is obtained. The cutoff wavelength λc is 1218 nm.

[0076] The coupled multicore fiber 40 (C-MCF) is the same as in Table 2, so the explanation is omitted.

[0077] The pitch converter 30 is a multicore fiber with Δ1 = 2.0%, Δ2 = 0%, Δ3 = -0.55%, a mode field diameter of 4.1 μm at a wavelength of 1550 nm, 2a = 3.5 μm, 2b = 6.3 μm, 2c = 9.8 μm, and a core pitch of 30 μm. The diameter of the multicore fiber is tapered from the first end face 30a (large pitch side) to the second end face 30b (small pitch side) to 2 / 3 of its original diameter, resulting in a core pitch d3a of 30 μm and a core pitch d3b of 20 μm. In this case, on the large pitch side, 2a = 3.5 μm, 2b = 6.3 μm, 2c = 9.8 μm, a mode field diameter of 4.1 μm, a cutoff wavelength λc of 1218 nm, and an intercore crosstalk of -124.1 dB per meter. On the small pitch side, 2a is 2.3 μm, 2b is 4.1 μm, and 2c is 6.4 μm, resulting in a mode field diameter of 4.3 μm, a cutoff wavelength λc of 817 nm, and an intercore crosstalk of -23.6 dB per meter. In the pitch converter shown in Table 4, the core diameter is reduced to the extent that the mode field diameter expands as the core diameter decreases on the small pitch side.

[0078] However, at the first end face 30a (large pitch side) of the multicore fiber 10 (HΔMCF) and the pitch converter 30, Δ1 may be in the range of 1.8% to 2.3%, Δ2 may be in the range of -0.05% to 0.05%, the core diameter (2a) may be in the range of 3.3 μm to 3.7 μm, 2b may be in the range of 6.0 μm to 6.5 μm, and 2c may be in the range of 9.6 μm to 10.0 μm.

[0079] [Table 4]

[0080] (Embodiment 6) Figure 9 is a schematic exploded view showing an optical fiber connector according to Embodiment 6. The optical fiber connector 300 is formed by connecting the end face 40a of the coupled multicore fiber 40 of Embodiment 5 to the second end face 30b of the pitch converter 30 according to Embodiment 3, and connecting the four core sections 41 to the four core sections 31. These connections are, for example, fusion splices, but may also be physical contacts. The coupled multicore fiber 40 and the pitch converter 30 may also be directly connected, as in this optical fiber connector 300.

[0081] It is preferable that the cladding diameter at the second end face 30b of the pitch converter 30 and the cladding diameter of the coupled multicore fiber 40 are approximately the same. For example, the cladding diameters of both are 125 μm ± 1 μm (1 μm is a tolerance), and there may be a difference of about 2 μm.

[0082] According to the simulation calculation results performed by the inventors, the optical fiber connector 300 has characteristics as shown in Table 5, for example. In Table 5, C-MCF is a coupled multicore fiber 40, and pitch converter is a pitch converter 30. Furthermore, both the coupled multicore fiber 40 and the pitch converter 30 were set to a step-type refractive index profile.

[0083] In Table 5, the coupled multicore fiber 40 (C-MCF) and the pitch converter 30 are the same as in Table 2, so the explanation is omitted.

[0084] However, at the first end face 30a (large pitch side) of the pitch converter 30, the core diameter (2a) may be in the range of 3.2 μm or more and 3.7 μm or less, and Δ1 may be in the range of 1.9% or more and 2.3% or less.

[0085] [Table 5]

[0086] Furthermore, according to the simulation calculation results, the optical fiber connector 300 has characteristics such as those shown in Table 6. The pitch converter 30 was set to a W-type refractive index profile.

[0087] In Table 6, the coupled multicore fiber 40 (C-MCF) and the pitch converter 30 are the same as in Table 3, so the explanation is omitted.

[0088] However, at the first end face 30a (large pitch side) of the pitch converter 30, Δ1 may be in the range of 1.8% to 2.3%, Δ2 may be in the range of -0.67% to -0.53%, the core diameter (2a) may be in the range of 3.5 μm to 4.1 μm, and 2b may be in the range of 9.5 μm to 10.1 μm.

[0089] [Table 6]

[0090] Furthermore, according to the simulation calculation results, the optical fiber connector 300 has characteristics such as those shown in Table 7. The pitch converter 30 was set to a trench-type refractive index profile.

[0091] In Table 7, the coupled multicore fiber 40 (C-MCF) and the pitch converter 30 are the same as in Table 4, so the explanation is omitted.

[0092] However, at the first end face 30a (large pitch side) of the pitch converter 30, Δ1 may be in the range of 1.8% to 2.3%, Δ2 may be in the range of -0.05% to 0.05%, the core diameter (2a) may be in the range of 3.3 μm to 3.7 μm, 2b may be in the range of 6.0 μm to 6.5 μm, and 2c may be in the range of 9.6 μm to 10.0 μm.

[0093] [Table 7]

[0094] (Embodiment 7) Figure 10 is a schematic diagram showing an optical fiber connector according to Embodiment 7. The optical fiber connector 400 is formed by further connecting the end face 50a of an optical fiber fan-in / fan-out 50 to the first end face 30a of the pitch converter 30 of the optical fiber connector 300 according to Embodiment 6. These connections are, for example, fusion splices, but may also be physical contacts.

[0095] The optical fiber fan-in / fan-out 50 comprises a glass capillary 51 and four optical fibers 52. The four optical fibers 52 are, for example, single-mode optical fibers, each comprising a core portion 52a and a cladding portion 52b. The four optical fibers 52 are bundled together such that the core portions 52a at the end face 50a are arranged in a square grid pattern that coincides with the core portion 31 at the first end face 30a of the pitch converter 30, and are inserted and fixed into the glass capillary 51. The four core portions 52a and the four core portions 31 are then connected to each other.

[0096] Optical fiber fan-in / fan-out connectors are generally manufactured by bundling optical fibers and inserting and fixing them into a glass capillary. However, when manufacturing an optical fiber fan-in / fan-out connector for a multicore fiber with a small core pitch, such as a coupled multicore fiber 40, the bundled optical fibers must be very thin, such as 20 μm in diameter. In this case, thin optical fibers are difficult to insert into a glass capillary, making the manufacturing of optical fiber fan-in / fan-out connectors challenging.

[0097] In contrast, the optical fiber connector 400 connects the optical fiber fan-in / fan-out 50 to the coupled multicore fiber 40 via a pitch converter 30. This makes it possible to construct an optical fiber connector 400 that is easier to manufacture and implement, equipped with an optical fiber fan-in / fan-out 50 using a wider diameter optical fiber 52 such as 30 μm.

[0098] In the above embodiment, the multicore fiber, coupled multicore fiber, and pitch converter have their cores arranged in a square grid or a hexagonal close-packed grid, but they may be arranged in other shapes, such as a ring shape.

[0099] Furthermore, in the above embodiment, the entire pitch converter from the first end face to the second end face is a reduced diameter section. However, a portion of the section from the first end face to the second end face may be a reduced diameter section, and the remaining portion may be a constant diameter section with a constant cladding diameter.

[0100] Furthermore, in the above embodiment 5, the pitch converter, multicore fiber, and coupled multicore fiber are connected in this order, but they may also be connected in the order of pitch converter, coupled multicore fiber, and multicore fiber.

[0101] Furthermore, the present invention is not limited by the embodiments described above. For example, the present invention also includes configurations that appropriately combine the above-described components. In addition, further effects and modifications can be easily derived by those skilled in the art. Therefore, broader aspects of the present invention are not limited to the embodiments described above, and various modifications are possible. [Industrial applicability]

[0102] The present invention is particularly suitable for application to pitch converters and optical fiber connectors. [Explanation of Symbols]

[0103] 10, 20: Multicore fiber 10a, 40a, 50a: End surface 11, 21, 31, 41, 52a: Core section 12, 22, 32, 42, 52b: Clad section 30: Pitch Converter 30a: 1st end surface 30b: Second end surface 40: Coupled multicore fiber 50: Fiber optic fan in / out 51: Glass capillary 52: Optical fiber 100, 200, 300, 400: Optical fiber connectors P11, P12, P21, P22, P31, P32: Profile d1, d2, d3a, d3b, d4: Core pitch

Claims

1. Multiple core sections, A cladding portion surrounds the outer circumference of multiple core portions and has a refractive index lower than the maximum refractive index of the core portion, A first end face and a second end face that are perpendicular to the longitudinal direction and face each other in the longitudinal direction, Equipped with, Each of the multiple core portions and cladding portions has a tapered diameter portion in which the diameter is reduced to 2 / 3 or less in the longitudinal direction from the first end face to the second end face. The core pitch, which is the distance between the centers of the nearest adjacent core portions on the first end face, is 30 μm or more. The core pitch, which is the distance between the centers of the nearest adjacent core portions on the second end face, is 20 μm or less. Multiple of the core portions have a step-type refractive index profile. At the first end face, the core diameter of the core portion is 3.2 μm or more and 3.7 μm or less, and the relative refractive index difference Δ1 of the maximum refractive index of the core portion to the refractive index of the cladding portion is 1.9% or more and 2.3% or less. Pitch converter.

2. Multiple core sections, A cladding portion surrounds the outer circumference of multiple core portions and has a refractive index lower than the maximum refractive index of the core portion, A first end face and a second end face that are perpendicular to the longitudinal direction and face each other in the longitudinal direction, Equipped with, Each of the multiple core portions and cladding portions has a tapered diameter portion in which the diameter is reduced to 2 / 3 or less in the longitudinal direction from the first end face to the second end face. The core pitch, which is the distance between the centers of the nearest adjacent core portions on the first end face, is 30 μm or more. The core pitch, which is the distance between the centers of the nearest adjacent core portions on the second end face, is 20 μm or less. The multiple core portions have a W-shaped refractive index profile. The core portion consists of a center core with a diameter of 2a and a depressed layer surrounding the outer circumference of the center core, with a refractive index smaller than that of the cladding portion, an inner diameter of 2a, and an outer diameter of 2b. At the first end face, the relative refractive index difference Δ1 of the center core with respect to the cladding portion is 1.8% or more and 2.3% or less, the relative refractive index difference Δ2 of the depressed layer with respect to the cladding portion is -0.67% or more and -0.53% or less, 2a is 3.5 μm or more and 4.1 μm or less, and 2b is 9.5 μm or more and 10.1 μm or less. Pitch converter.

3. Multiple core sections, A cladding portion surrounds the outer circumference of multiple core portions and has a refractive index lower than the maximum refractive index of the core portion, A first end face and a second end face that are perpendicular to the longitudinal direction and face each other in the longitudinal direction, Equipped with, Each of the multiple core portions and cladding portions has a tapered diameter portion in which the diameter is reduced to 2 / 3 or less in the longitudinal direction from the first end face to the second end face. The core pitch, which is the distance between the centers of the nearest adjacent core portions on the first end face, is 30 μm or more. The core pitch, which is the distance between the centers of the nearest adjacent core portions on the second end face, is 20 μm or less. Multiple of the aforementioned core portions have a trench-type refractive index profile. The core portion is composed of a center core with a diameter of 2a, an intermediate layer surrounding the outer circumference of the center core, having a refractive index smaller than that of the cladding portion, an inner diameter of 2a, and an outer diameter of 2b, and a trench layer surrounding the outer circumference of the intermediate layer, having a refractive index smaller than that of the cladding portion, an inner diameter of 2b, and an outer diameter of 2c. At the first end face, the relative refractive index difference Δ1 of the center core with respect to the cladding portion is 1.8% or more and 2.3% or less, the relative refractive index difference Δ2 of the intermediate layer with respect to the cladding portion is -0.05% or more and 0.05% or less, 2a is 3.3 μm or more and 3.7 μm or less, 2b is 6.0 μm or more and 6.5 μm or less, and 2c is 9.6 μm or more and 10.0 μm or less. Pitch converter.

4. The diameter of the second end face is 70 μm or more and 125 μm or less. A pitch converter according to any one of claims 1 to 3.

5. A pitch converter according to any one of claims 1 to 3, A connecting multicore fiber is connected to the second end face of the pitch converter and comprises a plurality of core portions and a cladding portion surrounding the outer circumference of the plurality of core portions and having a refractive index lower than the maximum refractive index of the core portions. A fiber optic connector equipped with the following features.

6. A pitch converter according to any one of claims 1 to 3, A first multicore fiber is a coupled multicore fiber connected to the second end face of the pitch converter, comprising a plurality of core portions and a cladding portion surrounding the outer circumference of the plurality of core portions and having a refractive index lower than the maximum refractive index of the core portions, wherein the core pitch, which is the distance between the centers of the nearest adjacent core portions in a cross section perpendicular to the longitudinal direction, is 20 μm or less, Equipped with, The cladding diameter at the second end face of the pitch converter and the cladding diameter of the first multicore fiber are substantially the same. Optical fiber connector.

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