Multicore fiber connector

Abstract

This disclosure aims to enable low-loss fan-in / fan-out of multicore fibers and to reduce the thickness of the MCF-FIFO to within 1 mm. [Solution] The present disclosure provides a multicore fiber connector comprising: a plurality of double-core fibers each having a first core at the center, a second core arranged around the first core, and a cladding arranged around the second core; and a capillary that holds the plurality of double-core fibers in an arrangement corresponding to the cores of the multicore fiber, wherein the cladding on the plurality of double-core fibers is welded to the capillary, the capillary has a tapered portion whose outer diameter decreases from the tip to the rear end, and the difference in relative refractive index between the second core and the cladding is 0.3% or more and 1.0% or less.

Description

Technical Field

[0001] The present disclosure relates to a multi-core fiber connection component capable of fan-in / fan-out of a multi-core fiber.

Background Art

[0002] In a data center, multi-core fibers (hereinafter sometimes abbreviated as "MCF") are expected for optical fiber wiring to converge and for further increased capacity. Therefore, miniaturization of an MCF-FIFO that performs fan-in / fan-out of multi-core fibers is expected.

[0003] Multi-core fiber connection components that meet such requirements have been proposed (see, for example, Patent Document 1). In Patent Document 1, a plurality of double-core fibers arranged in accordance with the core arrangement of an MCF are fixed with a capillary, and one end of the capillary is reduced in diameter together with the capillary. Thereby, the inner first core arranged at one end of the capillary can be connected to the core of a single-core fiber, and the outer second core arranged at the other end of the capillary can be connected to the core of the MCF.

[0004] In Patent Document 1, in order to shorten the length of the MCF-FIFO, the taper length during diameter reduction is shortened. Therefore, the relative refractive index difference Δ1 between the first core and the second core is 0.32 or more and 0.36 or less, and the relative refractive index difference Δ2 between the second core and the cladding is 0.4 or more and 0.6 or less.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] While there is a desire to make mechanically transferable (MTs) that bundle single-core fibers thinner, Patent Document 1 shows that depending on the reduction ratio, the thickness of the MCF-FIFO exceeds 1 mm. Therefore, this disclosure aims to enable low-loss fan-in / fan-out of multi-core fibers and to keep the thickness of the MCF-FIFO within 1 mm. [Means for solving the problem]

[0007] The multicore fiber connection component of this disclosure is A plurality of double-core fibers comprising a first core located in the center, a second core arranged around the first core, and a cladding arranged around the second core, A capillary that holds the plurality of double-core fibers in an arrangement corresponding to the core of the multi-core fiber, Equipped with, The cladding provided on the plurality of double core fibers is welded to the capillary, The aforementioned capillary has a tapered section in which the outer diameter decreases from the tip to the rear end. The difference in relative refractive index between the second core and the cladding is 0.3% or more and 1.0% or less.

[0008] The MFD of the first core at the leading edge and the MFD of the second core at the trailing end are approximately 9 μm. This value corresponds to the MFD of the core of a single-mode fiber and can be any value between 8.6 μm and 9.2 μm. When the connection loss with this approximately 9 μm MFD was examined, it was found that the connection loss becomes 0.3 dB or less when the opposing MFD is between 7.5 μm and 11.5 μm. Therefore, this disclosure provides a value between 0.3% and 1.0% that is the relative refractive index difference between the second core and the cladding such that the connection loss with the MCF is 0.3 dB or less.

[0009] When the wavelength is 1.55 μm, the difference in relative refractive index between the second core and the cladding can be any value between 0.4% and 1.0%. This allows the connection loss with the MCF to be reduced to 0.3 dB or less. Furthermore, the reduction ratio of the tapered portion can be any value between 5.5 and 8.0.

[0010] When the wavelength is 1.31 μm, the difference in relative refractive index between the second core and the cladding can be any value between 0.3% and 0.75%. This allows the connection loss with the MCF to be reduced to 0.3 dB or less. Furthermore, the reduction ratio of the tapered portion can be any value between 6.5 and 8.0.

[0011] Furthermore, the above disclosures can be combined as much as possible. [Effects of the Invention]

[0012] The multicore fiber connector component of this disclosure enables low-loss fan-in / fan-out of multicore fibers and allows the thickness of the MCF-FIFO to be within 1 mm. [Brief explanation of the drawing]

[0013] [Figure 1] This is an example of the configuration of a multicore fiber connection component according to an embodiment of the present invention. [Figure 2] This is an example of the configuration of a multicore fiber connection component according to an embodiment of the present invention. [Figure 3] This diagram illustrates the refractive index of a single-core double-core fiber. [Figure 4] This is an explanatory diagram of a capillary according to one embodiment of the present invention. [Figure 5] An example of MCF connection loss is shown. [Figure 6] An example of an MFD for a specific refractive index difference Δ2 that satisfies the single-mode condition at a wavelength of 1.55 μm is shown. [Figure 7]An example of the MFD with respect to the value of the relative refractive index difference Δ2 that satisfies the single-mode condition when the wavelength is 1.31 μm is shown. [Figure 8] It is an explanatory diagram of the manufacturing process of an embodiment of the present invention.

Embodiments for Carrying out the Invention

[0014] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These examples are merely illustrative, and the present disclosure can be implemented in various modified forms based on the knowledge of those skilled in the art. In the present specification and drawings, components with the same reference numerals indicate the same components as each other.

[0015] (First Embodiment) FIG. 1 is a diagram showing an embodiment of a multi-core fiber connection component according to the present invention. The multi-core fiber connection component of this embodiment is a fan-in / fan-out component for MCF that connects light from each core provided in the MCF to a single-mode fiber. The multi-core fiber connection component of the present invention includes an MPO connector 95, a double-core fiber 94, a capillary 93, and a multi-core fiber connector 96.

[0016] FIG. 2 is a diagram showing an embodiment of a multi-core fiber connection component according to the present invention. This figure shows a state where the capillary 93 is housed in the housing 83. The MT (Mechanically Transferable) ferrule 92 housed in the housing of the MPO connector 95 and the capillary 93 in the housing 83 are connected by a double-core fiber 94.

[0017] In this embodiment, an example is shown in which the MCF86 in the multicore fiber connector 96 has four cores and is equipped with four double-core fibers 94. The tip of each double-core fiber 94 is positioned at the connection end of the MT ferrule 92. Thus, the multicore fiber connector of the present invention can connect the light from each core of the MCF86 to the single-mode fibers by connecting four single-mode fibers to the MT ferrule 92.

[0018] Figure 3 shows an example of the refractive index distribution of a double-core fiber 94. The double-core fiber 94 is a double-core fiber in which a second core 94b with refractive index n2 is arranged around a first core 94a with refractive index n1, and a cladding 94c with refractive index n3 is arranged around the second core 94b.

[0019] The relative refractive index difference Δ1 between refractive index n1 and refractive index n2 can be set to a value similar to the relative refractive index difference between the core and cladding of single-mode fibers used in the 1.55 μm and 1.31 μm wavelength bands, for example, between 0.3% and 0.36%. This allows the first core 94a to be connected to the single-mode fiber with a connection loss of 0.5 dB or less. Furthermore, the relative refractive index difference Δ2 can be set to a value larger than Δ1, and as will be described later, a value between 0.3% and 1.0% can be used.

[0020] Figure 4 shows an example of the configuration of the capillary 93 and double core fiber 94. Each double core fiber 94 extending from the MT ferrule 92 is housed in the capillary 93. The capillary 93 and double core fiber 94 are integrally formed by welding, and the outer diameter from the tip 31 to the rear end 32 is φ 31 From φ 32 It has a tapered section 33 that narrows towards the end.

[0021] Here, the capillary 93 holds multiple double-core fibers 94 in an arrangement corresponding to the core of the MCF86. The four double-core fibers 94 are tapered into four cores by the tapered portion 33, resulting in an MCF structure with a uniform outer diameter at the rear end 32. This allows each second core 94b at the rear end 32 to be connected to each core of the MCF86. The rear end 32 may be fitted with a multi-core fiber connector 96 for connection to the MCF86, or it may be fusion-spliced ​​to the MCF86.

[0022] In this disclosure, the first core 94a at the tip 31 and the second core 94b at the trailing end 32 have an MFD (Mode Field Diameter) of approximately 9 μm, similar to the core of a single-mode fiber. The value of approximately 9 μm can be any value between 8.6 μm and 9.2 μm. When the MFD of the core in the MCF86 is approximately 9 μm, the reduction ratio after stretching can be any value between 5.5 and 8.0.

[0023] When the reduction ratio from the tip 31 to the rear end 32 is set to 5.5, the MFD of the first core 94a, which is 8.6 μm at the tip 31, becomes 1.56 μm at the rear end 32. Therefore, when the wavelength is 1.55 μm, the connection loss with the MCF86 can be reduced by setting the reduction ratio from the tip 31 to the rear end 32 to 5.5 or higher.

[0024] Furthermore, if the reduction ratio from the tip 31 to the rear end 32 is set to 6.5, the MFD of the first core 94a becomes 8.6 μm at the tip 31 and 1.32 μm at the rear end 32. Therefore, when the wavelength is 1.31 μm, the connection loss with the MCF86 can be reduced by setting the reduction ratio from the tip 31 to the rear end 32 to 6.5 or higher.

[0025] On the other hand, when the reduction ratio after stretching is 8.0, the second core 94b at the rear end 32 is 9.2 μm. diameter However, at the tip 31 it becomes 73.6 μm. Second core 94b diameter To make it 73.6 μm, the outer diameter φ cThis needs to be close to 1000 μm. For this reason, in order to make the thickness of the MCF-FIFO 1 mm or less, it is preferable that the reduction ratio from the front end 31 to the rear end 32 be 8.0 or less.

[0026] Figure 5 shows an example of connection loss with an MFD around 9 μm. The horizontal axis represents the MFDs positioned opposite each other. It can be seen that when the MFDs positioned opposite each other are between 7.5 μm and 11.5 μm, the connection loss with MFDs between 8.6 μm and 9.2 μm is 0.3 dB or less. Therefore, by setting the MFD of the second core 94b at the rear end 32 to between 7.5 μm and 11.5 μm, the connection loss with the MCF 86 can be reduced to 0.3 dB or less.

[0027] The relative refractive index difference Δ2 is determined such that the second core 94b at the rear end 32 satisfies the single-mode condition with respect to the core of the MCF86. Specifically, it is defined that the V number V, expressed by the following equation, is 2.405 or less. (Math 1) V = 2π / λ·a·n√2Δ (1) λ is the wavelength, a is the core radius, n is the core refractive index, and Δ is the relative refractive index difference.

[0028] Δ can be expressed using n as follows: (Math 2) Δ=(n-n0) / n In this embodiment, the refractive index of quartz glass was used for n0.

[0029] In this embodiment, the condition for the second core 94b to connect with the core of MCF86 is obtained by changing Δ in equation (1) to Δ2 and calculating the second core 94b from a. diameter This can be determined by comparing it with the MFD of the core equipped in the MCF86.

[0030] Figure 6 shows an example of a specific refractive index difference Δ2 value that satisfies the single-mode condition when the wavelength is 1.55 μm. For the calculation of Δ2, n0 = 1.444 was used when the wavelength is 1.55 μm. When the specific refractive index difference Δ2 was between 0.4% and 1.0%, the MFD of the second core 94b at the rear end 32 was between 7.5 μm and 11.5 μm.

[0031] Figure 7 shows an example of a specific refractive index difference Δ2 value that satisfies the single-mode condition when the wavelength is 1.31 μm. For the calculation of Δ2, n0 = 1.447 was used when the wavelength is 1.31 μm. When the specific refractive index difference Δ2 was between 0.3% and 0.75%, the MFD of the second core 94b at the rear end 32 was between 7.5 μm and 11.5 μm.

[0032] In this embodiment, both the connection of the first core 94a to the core of the single-mode fiber and the connection of the second core 94b to the core of the multi-core fiber are designed to satisfy the single-mode condition. Therefore, the multi-core fiber connection component of this embodiment can reduce the connection loss of the MCF-FIFO.

[0033] Furthermore, the multicore fiber connector component of this embodiment is designed to reduce the thickness of the MCF-FIFO to 1 mm or less. Therefore, the multicore fiber connector component of this embodiment enables low-loss fan-in / fan-out of the multicore fiber, and the thickness of the MCF-FIFO can be reduced to 1 mm or less.

[0034] (Second embodiment) The method for manufacturing the multicore fiber connection component of the present invention will be described with reference to Figure 8. (Welding process) A double-core fiber 94 is inserted into the void of the capillary 93 (Figure 8(a)), and the double-core fiber 94 and the capillary 93 are welded together (Figure 8(b)). Welding can be performed, for example, by reducing the pressure of the entire system or the void of the capillary 93 and using an arc discharge with multiple electrodes 81. A cross-sectional view of the capillary 93 after welding corresponds to the left diagram in Figure 4.

[0035] Here, the double-core fiber 94 has an outer diameter φ so that it can connect to the single-mode fiber to which the MT ferrule 92 is connected. c The diameter is 125 μm, and the MFD of the first core 94a should be between 8.6 μm and 9.2 μm. The second core 94b diameter This is determined by the reduction ratio of the MFD of the first core 94a. Any value between 5.5 and 8.0 can be used for the reduction ratio. For example, when the reduction ratio is 7 times, the second core 94b diameter This becomes 60.2 μm.

[0036] (Stretching process) The tip 31 of the capillary 93 is left intact, and the capillary 93 is extended from the middle (Figure 8(c)). For example, 10 mm is left from the tip 31 and the extension is formed to create a tapered portion 33 (Figure 8(c)). The extension can be performed, for example, by arc discharge using multiple electrodes 81, and the extended portion is between 5 mm and 20 mm in length. The length of the rear end 32 can be any length that the multicore fiber connector 96 can connect to, for example, 10 mm and 20 mm in the case of fusion splicing.

[0037] The cross-sectional view of the rear end portion 32 after stretching corresponds to the right diagram in Figure 4. The tip portion 31 is formed by inserting a double-core fiber 94 into the void inside the capillary 93 and welding it under reduced pressure by arc discharge heating. The tapered portion 33 is formed by further stretching the welded capillary 93 by arc discharge heating, resulting in a state similar to MCF, and the rear end portion 32 has an MCF structure.

[0038] In this embodiment, an arc discharge is used as the heat source, but other heat sources may be used instead. For example, a carbon heater, ceramic heater, or oxyhydrogen burner may be used. However, when considering miniaturization, a heat source that can reach the desired melting point with a short heating distance is desirable.

[0039] Furthermore, to obtain specific refractive index differences Δ1 and Δ2, it is desirable to prepare the materials by adding germanium oxide as an additive to quartz glass, specifically to the first core 94a and the second core 94b.

[0040] (MT ferrule connection process) Each double-core fiber 94 is connected to the MT ferrule 92 (Figure 8(d)). This makes it possible to manufacture a multi-core fiber connection component according to the present invention, as shown in Figure 2.

[0041] Furthermore, a coating material may be applied to each double-core fiber 94 after the welding process. This preserves the optical fiber strength of the double-core fiber 94 before the coating is removed. Here, multiple double-core fibers 94 may be arranged within the coating. For example, all double-core fibers 94 may be protected with a common coating so that a bending radius greater than or equal to the allowable radius of curvature R is maintained.

[0042] Furthermore, although the above-described embodiment shows an example of a multicore fiber with four cores, each core being equidistant from the central axis of the multicore fiber, the present invention is not limited to this. The number of cores may be five or more, and the arrangement of each core does not have to be equidistant from the central axis of the multicore fiber.

[0043] [Examples from experiments] The multicore fiber connector of this disclosure was fabricated based on the following design, and the trailing end 32 and MCF86 were fusion-spliced. The insertion loss of the MCF-FIFO was measured to be 0.5 dB or less. The crosstalk was measured to be -45 dB or less. • Specific refractive index difference Δ1: 0.3% • Specific refractive index difference Δ2: 1.0% • First core 94aMFD at tip 31: 8.6μm • MFD of the first core 94a at the rear end 32: 1.2 μm • Second core 94b at tip 31 diameter : 60.2 μm • MFD of the second core 94b at the rear end 32: 8.6 μm • Reduction ratio from tip 31 to rear end 32: 7 [Explanation of symbols]

[0044] 31:Tip 32: Rear end 33: Tapered section 81: Electrode 83: Housing 86: Multicore fiber 92: MT ferrule 93: Capillary 94: Double Core Fiber 94a: First Core 94b: Second core 94c: Clad 95: MPO connector 96: Multicore fiber connector

Claims

1. A plurality of double-core fibers comprising a first core located in the center, a second core arranged around the first core, and a cladding arranged around the second core, A capillary that holds the plurality of double-core fibers in an arrangement corresponding to the core of the multi-core fiber, Equipped with, The cladding provided on the plurality of double core fibers is welded to the capillary, The aforementioned capillary has a tapered section in which the outer diameter decreases from the tip to the rear end. The wavelength is 1.55 μm, The difference in relative refractive index between the second core and the cladding is 0.4% or more and 1.0% or less. The MFD of the first core at the tip and the MFD of the second core at the rear end are 8.6 μm or more and 9.2 μm or less. Multicore fiber connector.

2. The reduction ratio of the tapered portion is 5.5 or more and 8.0 or less. The multicore fiber connection component according to claim 1.

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