Polarization-maintaining multicore optical fiber and method for manufacturing polarization-maintaining multicore optical fiber

Abstract

A polarization-maintaining multicore optical fiber (1) comprises: a plurality of cores (2) disposed side by side in a first direction (X) orthogonal to an axial direction (Z); a plurality of optical claddings (3) respectively provided around the plurality of cores (2); a plurality of low refractive index parts (4) provided so as to sandwich each of the plurality of cores (2) therebetween in the first direction (X); and a common physical cladding (5) having a lower refractive index than the refractive index of the plurality of cores (2) and surrounding the plurality of cores (2), the plurality of optical claddings (3), and the plurality of low refractive index parts (4). The plurality of low refractive index parts (4) are disposed side by side alternately with the plurality of cores (2) in the first direction (X), at least a part of the outer periphery of each of the plurality of low refractive index parts (4) is provided in contact with the core (2), and the distance between the low refractive index parts (4) adjacent to each other in the first direction (X) is shorter than the length of each of the plurality of cores (2) in a second direction (Y) orthogonal to the axial direction (Z) and the first direction (X).

Description

Technical Field

[0001] The present disclosure relates to a polarization-maintaining multi-core optical fiber and a method for manufacturing the polarization-maintaining multi-core optical fiber. This application claims priority based on Japanese Application No. 2023-106126 filed on June 28, 2023, and incorporates all the descriptions described in the above Japanese application.

Background Art

[0002] Patent Document 1 describes a polarization-maintaining multi-core optical fiber (hereinafter, polarization-maintaining MCF) including a polarization-maintaining core having a core and a pair of low refractive index portions, an optical cladding, and a common physical cladding, and a method for manufacturing the polarization-maintaining MCF.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] The polarization-maintaining according to one aspect of the present disclosure Multicore optical fiber includes a plurality of cores arranged side by side in a first direction orthogonal to the axial direction, a plurality of optical claddings having a refractive index lower than that of the plurality of cores and provided around each of the plurality of cores, a plurality of low refractive index portions having a refractive index lower than that of the plurality of cores and provided so as to sandwich each of the plurality of cores in the first direction, and a common physical cladding having a refractive index lower than that of the plurality of cores and surrounding the plurality of cores, the plurality of optical claddings, and the plurality of low refractive index portions. The plurality of low refractive index portions are arranged alternately with the plurality of cores in the first direction, and at least a part of the outer periphery of each of the plurality of low refractive index portions multiple is provided in contact with the core at least one of and the distance between adjacent low refractive index portions in the first direction is shorter than the length of each of the plurality of cores in a second direction orthogonal to the axial direction and the first direction. [Brief explanation of the drawing]

[0005] [Figure 1] Figure 1 shows a cross-section perpendicular to the axial direction of the polarization-maintaining MCF according to the first embodiment. [Figure 2] Figure 2 shows a cross-section perpendicular to the axial direction of the polarization-maintaining MCF according to the second embodiment. [Figure 3] Figure 3 shows a cross-section perpendicular to the axial direction of the polarization-maintaining MCF according to the third embodiment. [Figure 4] Figure 4 shows a cross-section perpendicular to the axial direction of the polarization-maintaining MCF according to the fourth embodiment. [Figure 5] Figure 5 is a process diagram showing the manufacturing method of the polarization-maintaining MCF according to the second embodiment. [Figure 6] Figure 6 is a cross-sectional view illustrating the method for manufacturing a polarization-maintaining MCF according to the second embodiment. [Figure 7] Figure 7 is a cross-sectional view illustrating the method for manufacturing a polarization-maintaining MCF according to the second embodiment. [Figure 8] Figure 8 is a cross-sectional view illustrating the manufacturing method of the polarization-maintaining MCF according to the second embodiment. [Figure 9] Figure 9 is a cross-sectional view illustrating the manufacturing method of the polarization-maintaining MCF according to the second embodiment. [Figure 10] Figure 10 is a cross-sectional view illustrating the manufacturing method of a polarization-maintaining MCF according to the second embodiment. [Figure 11] Figure 11 is a cross-sectional view illustrating the manufacturing method of a polarization-maintaining MCF according to the second embodiment. [Figure 12] Figure 12 is a cross-sectional view illustrating the manufacturing method of a polarization-maintaining MCF according to the second embodiment. [Figure 13] Figure 13 is a cross-sectional view illustrating the manufacturing method of a polarization-maintaining MCF according to the second embodiment. [Figure 14] Figure 14 is a cross-sectional view illustrating the manufacturing method of a polarization-maintaining MCF according to the second embodiment. [Modes for carrying out the invention]

[0006] [Issues this disclosure aims to address] In the polarization-maintaining MCF described in Patent Document 1, since two low refractive index sections are provided for each core, a sufficient distance between cores is required, which greatly restricts the core density.

[0007] This disclosure enables improvements in core density 、 The objective is to provide polarization-maintaining MCF and a method for manufacturing polarization-maintaining MCF.

[0008] [Effects of this disclosure] This disclosure provides a polarization-maintaining MCF capable of improving core density and a method for manufacturing a polarization-maintaining MCF.

[0009] [Description of Embodiments of this Disclosure] First, the embodiments of this disclosure will be listed and described. (1) Polarization maintenance relating to one aspect of the present disclosure Multicore optical fiber The device comprises a plurality of cores arranged side by side in a first direction perpendicular to the axial direction, a plurality of optical claddings having a refractive index lower than that of the plurality of cores and provided around each of the plurality of cores, a plurality of low refractive index portions having a refractive index lower than that of the plurality of cores and provided so as to sandwich each of the plurality of cores in the first direction, and a common physical cladding having a refractive index lower than that of the plurality of cores and surrounding the plurality of cores, the plurality of optical claddings and the plurality of low refractive index portions, wherein the plurality of low refractive index portions are arranged alternately with the plurality of cores in the first direction, and at least a portion of the outer circumference of each of the plurality of low refractive index portions is multiple core at least one of The low refractive index portion is provided in contact with the first direction, and the distance between adjacent low refractive index portions in the first direction is shorter than the length of each of the multiple cores in the axial direction and in the second direction perpendicular to the first direction. In this polarization-maintaining MCF, one low refractive index portion provided between two adjacent cores is also used for polarization maintenance of the two cores. Therefore, it is possible to improve the core density as compared with a configuration in which two dedicated low refractive index portions are provided for each core. Since the low refractive index portion is in contact with the core, it is also possible to improve the core density. Since the distance between the low refractive index portions is shorter than the length of the core in the second direction, it is also possible to improve the core density. Further, since the distance between the low refractive index portions is shorter than the length of the core in the second direction, polarization maintenance of the core is realized due to the shape of the core.

[0010] (2) In (1) above, the plurality of low refractive index portions include a first low refractive index portion disposed between adjacent cores in the first direction and two second low refractive index portions disposed outside the plurality of cores in the first direction, and the size of the second low refractive index portion may be smaller than the size of the first low refractive index portion. In this case, further improvement in core density is possible.

[0011] (3) In (1) above, the plurality of low refractive index portions include a first low refractive index portion disposed between adjacent cores in the first direction and two second low refractive index portions disposed outside the plurality of cores in the first direction, and the size of the second low refractive index portion may be equal to the size of the first low refractive index portion. In this case, since no tool change is required when opening the holes of the first low refractive index portion and the second low refractive index portion, manufacturing is easier as compared with a configuration having different sizes. hole and the second low refractive index portion of drilling ru is unnecessary, and manufacturing is easier than a configuration with different sizes.

[0012] (4) In any one of (1) to (3) above, the plurality of low refractive index portions include a first low refractive index portion disposed between adjacent cores in the first direction and two second low refractive index portions disposed outside the plurality of cores in the first direction, and the refractive index of the second low refractive index portion may be lower than the refractive index of the first low refractive index portion. In this case, further improvement in core density is possible.

[0013] (5) In any one of (1) to (3) above, the plurality of low refractive index portions include a first low refractive index portion arranged between adjacent cores in a first direction, and two second low refractive index portions arranged outside the plurality of cores in a first direction, wherein the refractive index of the second low refractive index portions may be equivalent to that of the first low refractive index portion. In this case, since it is not necessary to change the composition of the base material that will become the first low refractive index portion and the second low refractive index portion, manufacturing is easier compared to configurations with different refractive indices.

[0014] (6) Polarization maintenance relating to one aspect of the present disclosure Multicore optical fiber The manufacturing method comprises: a plurality of core portions arranged side by side in a first direction perpendicular to the axial direction; a plurality of optical cladding portions having a refractive index lower than that of the plurality of core portions and provided around each of the plurality of core portions; and a common physical cladding portion having a refractive index lower than that of the plurality of core portions and surrounding the plurality of core portions and the plurality of optical cladding portions. fiber optic The process involves forming multiple holes in the base material so as to sandwich each of the central axes of the multiple core parts in a first direction, and inserting one by one multiple low-refractive-index base material into each of the multiple holes, each having a refractive index lower than that of the multiple core parts. fiber optic The process includes a step of drawing lines after integrating the base material and a plurality of low refractive index base materials by heating, or while integrating them by heating, wherein the plurality of holes may be formed alternately with the central axes of the plurality of core parts in a first direction, and in positions that overlap the plurality of core parts and the plurality of optical cladding parts. In this polarization-maintaining MCF manufacturing method, one low-refractive-index region is formed between two adjacent cores, allowing this single region to be used for polarization maintenance of both cores. Therefore, compared to a configuration in which two dedicated low-refractive-index regions are formed for each core, an improvement in core density is possible. The formation of the holes in a position overlapping with the core also contributes to the improvement in core density. Furthermore, because the holes are formed in a position overlapping with the core, polarization maintenance of the core is achieved due to the shape of the core.

[0015] [Details of the embodiments of this disclosure] Specific examples of polarization-maintaining MCFs and methods for manufacturing polarization-maintaining MCFs according to this embodiment will be described with reference to the drawings as necessary. This disclosure is not limited to these examples, but is indicated by the claims, and all modifications within the meaning and scope of the claims are intended to be included. In the following description, the same elements in the drawings are denoted by the same reference numerals, and redundant descriptions are omitted.

[0016] (Polarization-maintaining MCF) Figure 1 shows a cross-section perpendicular to the axial direction of a polarization-maintaining MCF according to the first embodiment. As shown in Figure 1, the polarization-maintaining MCF 1 according to the first embodiment comprises a plurality of cores 2, a plurality of optical claddings 3, a plurality of low refractive index sections 4, and one common physical cladding 5. The axial direction (or longitudinal direction) of the polarization-maintaining MCF 1 is the Z-axis direction. In this embodiment, the number of cores 2 is 3, the number of optical claddings 3 is 3, and the number of low refractive index sections is 4.

[0017] Multiple cores 2 are arranged side by side in the X-axis direction, which is perpendicular to the Z-axis direction. In a cross-section (hereinafter simply referred to as "cross-section") perpendicular to the axial direction of the polarization-maintaining MCF1, the multiple cores 2 are arranged on a straight line m that passes through the central axis C of the polarization-maintaining MCF1 and extends in the X-axis direction. The multiple cores 2 are spaced apart from each other.

[0018] Core 2 has a shape that is symmetric with respect to line m in cross-section. Multiple cores 2 have the same shape in cross-section. In cross-section, the length (maximum length) of core 2 in the X-axis direction is shorter than the length (maximum length) of core 2 in the Z-axis direction and the Y-axis direction which is perpendicular to the X-axis direction. Polarization retention of core 2 is achieved due to this shape of core 2. Core 2 has polarization retention axes in the X-axis direction and the Y-axis direction. Core 2 is made of glass. Multiple cores 2 have the same composition. Multiple cores 2 have the same refractive index.

[0019] Multiple optical claddings 3 are provided around each of the multiple cores 2. One optical cladding 3 is provided for each core 2. The number of optical claddings 3 is equal to the number of cores 2. Each optical cladding 3 is divided into two regions in the Y-axis direction by multiple low refractive index sections 4. That is, each optical cladding 3 contains two regions provided so as to sandwich the core 2 in the Y-axis direction.

[0020] The two regions of each optical cladding 3 are configured to be symmetrical with respect to a line m in cross-section. Multiple optical claddings 3 are spaced apart from each other. The optical claddings 3 are provided in contact with both ends of the core 2 in the Y-axis direction. The optical claddings 3 are made of glass with a different composition than the core 2. Multiple optical claddings 3 have the same composition as each other. Multiple optical claddings 3 have the same refractive index as each other. The optical claddings 3 have a refractive index lower than that of the multiple cores 2.

[0021] Multiple low refractive index sections 4 are provided so as to sandwich each of the multiple cores 2 in the X-axis direction. The multiple low refractive index sections 4 are arranged alternately with the multiple cores 2 in the X-axis direction. The number of low refractive index sections 4 is equal to the number of cores 2. to 1 The number of additions The multiple low refractive index portions 4 are arranged on a straight line m in cross-section. The multiple low refractive index portions 4 are spaced apart from each other. The multiple low refractive index portions 4 have the same shape in cross-section. The multiple low refractive index portions 4 have a circular shape in cross-section.

[0022] The multiple low refractive index sections 4 include a first low refractive index section 4A and two second low refractive index sections 4B. In this embodiment, the number of first low refractive index sections 4A is 2 The first low refractive index section 4A is located between adjacent cores 2 in the X-axis direction. The two second low refractive index sections 4B are located outside the multiple cores 2 in the X-axis direction. The two second low refractive index sections 4B are located at both ends of the multiple low refractive index sections 4 in the X-axis direction. The first low refractive index section 4A is located between the two second low refractive index sections 4B.

[0023] Multiple low refractive index sections 4 are provided in contact with multiple cores 2. Each low refractive index section 4 is provided in contact with at least one adjacent core 2 in the X-axis direction. The first low refractive index section 4A is provided in contact with two adjacent cores 2 in the X-axis direction. The second low refractive index section 4B is provided in contact with one adjacent core 2 in the X-axis direction. In cross-section, the outer circumference of the core 2, excluding the portion in contact with the low refractive index section 4, forms a part (arc) of a first virtual circle, and the low refractive index section 4 is located inside the first virtual circle. In cross-section, the outer circumference of the optical cladding 3, excluding the portion in contact with the low refractive index section 4 and the core 2, forms a part (arc) of a second virtual circle with a larger diameter than the first virtual circle, and the low refractive index section 4 is also located inside the second virtual circle.

[0024] The distance between adjacent low-refractive-index sections 4 in the X-axis direction (shortest distance) is shorter than the length of each of the multiple cores 2 in the Y-axis direction (maximum length). The low-refractive-index sections 4, together with the optical cladding 3, cover the entire circumference of the core 2. The low-refractive-index sections 4 are made of glass with a different composition than the core 2. Multiple low-refractive-index sections 4 have the same composition as each other. Multiple low-refractive-index sections 4 have the same refractive index as each other. The low-refractive-index sections 4 have a lower refractive index than the refractive index of the multiple cores 2. Considering radial refractive index variations, even if there is a refractive index variation of less than 0.05% among the multiple low-refractive-index sections 4, the multiple low-refractive-index sections 4 can be considered to have equivalent refractive indices. If the difference between the refractive index of the first low-refractive-index section 4A and the refractive index of the second low-refractive-index section 4B is less than 0.05%, then the refractive indices of the first low-refractive-index section 4A and the second low-refractive-index section 4B are equivalent.

[0025] The common physical cladding 5 encloses multiple cores 2, multiple optical claddings 3, and multiple low refractive index sections 4. Together with the multiple optical claddings 3, the common physical cladding 5 constitutes the cladding of the polarization-maintaining MCF1. The common physical cladding 5 is provided in contact with each of the multiple optical claddings 3 and the multiple low refractive index sections 4. The common physical cladding 5 is not in contact with the multiple cores 2. The common physical cladding 5 is a glass with a different composition than the cores 2. The common physical cladding 5 has a refractive index lower than that of the multiple cores 2.

[0026] The core 2, optical cladding 3, low refractive index section 4, and common physical cladding 5 are composed of, for example, silica glass. The core 2, optical cladding 3, low refractive index section 4, and common physical cladding 5 are configured such that, for example, the refractive index of core 2 > the refractive index of common physical cladding 5 > the refractive index of optical cladding 3 ≥ the refractive index of low refractive index section 4. With such refractive index relationships, the silica glass constituting the core 2, optical cladding 3, low refractive index section 4, and common physical cladding 5 may contain trace amounts of germanium (Ge), chlorine, or fluorine.

[0027] As explained above, in the polarization-maintaining MCF1, one first low refractive index section 4A, located between two adjacent cores 2, is used for polarization maintenance of both cores 2. In other words, one common first low refractive index section 4A is provided for two adjacent cores 2. Therefore, compared to a configuration where each core has two dedicated low refractive index sections, the distance between cores can be shortened. As a result, core density can be improved. Furthermore, fiber optic Base material of This avoids increasing the size (base material diameter).

[0028] During the manufacturing process of the polarization-maintaining MCF1, there are limitations on the diameter of the drilling tool and the distance between holes that can be drilled. From this perspective, the polarization-maintaining MCF1 allows for shorter inter-core distances compared to a configuration where each core has two dedicated low-refractive-index sections. Multiple low-refractive-index sections 4 are provided in contact with multiple cores 2. Therefore, further improvements in core density are possible.

[0029] In this embodiment, the multiple low refractive index sections 4 have the same refractive index, but the refractive index of the second low refractive index section 4B may be lower than the refractive index of the first low refractive index section 4A. In this case, Core 2 The externally positioned second low refractive index section 4B further reduces the leakage loss of core 2. Therefore, core 2 can be positioned further outward, i.e., closer to the outer surface 5a of the common physical cladding 5. As a result, a further improvement in core density is possible.

[0030] Figure 2 shows a cross-section perpendicular to the axial direction of the polarization-maintaining MCF according to the second embodiment. As shown in Figure 2, the polarization-maintaining MCF1A according to the second embodiment differs from the polarization-maintaining MCF1 in that, in cross-section, the size of the second low refractive index section 4B is smaller than the size of the first low refractive index section 4A. In the polarization-maintaining MCF1A, the number of cores 2 is 4, the number of optical cladding 3 is 4, and the number of low refractive index sections 4 is 5. Both the first low refractive index section 4A and the second low refractive index section 4B are circular in cross-section.

[0031] The size of the second low refractive index section 4B is its diameter, and the size of the first low refractive index section 4A is its diameter. The diameter of the second low refractive index section 4B is shorter than the diameter of the first low refractive index section 4A. In cross-section, the size of the low refractive index section 4 is defined as the maximum length of the low refractive index section 4. For example, if the low refractive index section 4 is elliptical in cross-section, the size of the low refractive index section 4 is the length of its major axis.

[0032] In polarization-maintaining MCF1A, the small size of the second low refractive index section 4B makes it easier to maintain the distance between the second low refractive index section 4B and the outer surface 5a of the common physical cladding 5. Therefore, the core 2 can be positioned further outward, i.e., closer to the outer surface 5a of the common physical cladding 5. As a result, further improvement in core density is possible.

[0033] Figure 3 shows a cross-section perpendicular to the axial direction of the polarization-maintaining MCF according to the third embodiment. As shown in Figure 3, the polarization-maintaining MCF1B according to the third embodiment differs from the polarization-maintaining MCF1A in that the multiple cores 2 are arranged in two rows on lines m1 and m2, which are parallel to line m. In the cross-section, lines m1 and m2 are lines that are symmetric to each other with respect to line m. The number of cores 2 arranged on lines m1 and m2 is equal to the number of cores 2. Four cores 2, four optical cladding 3, and five low refractive index sections 4 are arranged side by side on lines m1 and m2, respectively. In the polarization-maintaining MCF1B, since the multiple cores 2 are arranged in two rows, further improvement of core density is possible. Note that in the cross-section, the size of the second low refractive index section 4B may be the same as the size of the first low refractive index section 4A. 「 equivalent 」 This includes manufacturing variations of less than 1 μm. The diameter of the drilling tool used when forming the polarization-maintaining MCF matrix varies from lot to lot, but the same drilling tool can be used when forming holes of the same size. Therefore, the manufacturing variation in hole size can be reduced, and as a result, the manufacturing variation in the size of the first low refractive index section 4A and the second low refractive index section 4B after fiberization can be reduced. In addition, the refractive index of the second low refractive index section 4B may be lower than the refractive index of the first low refractive index section 4A.

[0034] Figure 4 shows a cross-section perpendicular to the axial direction of the polarization-maintaining MCF according to the fourth embodiment. As shown in Figure 4, the polarization-maintaining MCF1C according to the fourth embodiment differs from the polarization-maintaining MCF1 in that the multiple cores 2 are arranged in four rows at equal intervals on lines m1, m2, m3, and m4, which are parallel to line m. In the cross-section, lines m1 and m2 are lines that are symmetric to each other with respect to line m, and lines m3 and m4 are lines that are symmetric to each other with respect to line m. Line m1 is located between line m and line m3. Line m2 is located between line m and line m4. Two cores 2, two optical claddings 3, and three low refractive index sections 4 are arranged on lines m1, m2, m3, and m4, respectively. In the polarization-maintaining MCF1C, since the multiple cores 2 are arranged in four rows, further improvement of core density is possible.

[0035] The size of the second low refractive index portion 4B on lines m3 and m4 is smaller than the size of the first low refractive index portion 4A. Both the first low refractive index portion 4A and the second low refractive index portion 4B on lines m3 and m4 are circular in cross-section, and the diameter of the second low refractive index portion 4B is smaller than the diameter of the first low refractive index portion 4A. This makes it easier to maintain the distance between the second low refractive index portion 4B on lines m3 and m4 and the outer surface 5a of the common physical cladding 5. Therefore, the core 2 can be placed further outward, i.e., in a region closer to the outer surface 5a of the common physical cladding 5. As a result, further improvement in core density is possible. Note that in cross-section, the size of the second low refractive index portion 4B on lines m3 and m4 may be the same as the size of the first low refractive index portion 4A. 「 equivalent 」 This includes manufacturing variations of less than 1 μm. The diameter of the drilling tool used when forming the polarization-maintaining MCF matrix varies from lot to lot, but the same drilling tool can be used when forming holes of the same size. Therefore, the manufacturing variation in hole size can be reduced, and as a result, the manufacturing variation in the size of the first low refractive index section 4A and the second low refractive index section 4B after fiberization can be reduced. In addition, the refractive index of the second low refractive index section 4B may be lower than the refractive index of the first low refractive index section 4A.

[0036] (Manufacturing method for polarization-maintaining MCF) Figure 5 is a process diagram showing the manufacturing method of polarization-maintaining MCF according to the second embodiment. Figures 6 to 14 are cross-sectional views illustrating the manufacturing method of polarization-maintaining MCF according to the second embodiment. The manufacturing method of polarization-maintaining MCF1A includes a preparation step S1, a first hole drilling step S2, a first insertion step S3, a first heating and integration step S4, a second hole drilling step S5, a second insertion step S6, a second heating and integration step S7, a third hole drilling step S8, a third insertion step S9, a third heating and integration step S10, and a line drawing step S11. Polarization-maintaining MCF1A is manufactured, for example, by performing these steps in this order, but the order of the steps may be changed as appropriate. Each step will be described below.

[0037] Preparation step S1 is the process of preparing the core base material 12 (see Figure 7) which will become core 2, the first cladding base material 10 (see Figure 6) which will become optical cladding 3, the second cladding base material 14 (see Figure 9) which will become common physical cladding 5, and the low refractive index base materials 19,20 (see Figure 13) which will become low refractive index section 4. Each base material is cylindrical and made of silica glass. For each base material, the refractive index of core base material 12 > refractive index of second cladding base material 14 > refractive index of first cladding base material 10 ≥ low refractive index Department The base materials are configured to have refractive indices of 19 and 20. Within this refractive index relationship, the silica glass constituting each base material may contain trace amounts of germanium (Ge), chlorine, or fluorine.

[0038] The first drilling step S2 is a step in which a hole 11 is formed in the first clad base material 10 for inserting the core base material 12 (see Figure 7), as shown in Figure 6. The hole 11 has a circular cross-section. The hole 11 has a central axis parallel to a predetermined axis (for example, the central axis) of the first clad base material 10. The hole 11 does not protrude from the first clad base material 10, and the entire inner surface of the hole 11 is composed of the first clad base material 10. The hole 11 is formed coaxially with the first clad base material 10.

[0039] The first insertion step S3 is the step of inserting the core material 12 into the hole 11 of the first clad material 10, as shown in Figure 7. The insertion of the core material 12 is performed with the outer diameter of the core material 12 appropriately adjusted to match the inner diameter of the hole 11. The outer diameter of the core material 12 is adjusted so that the core material 12 can be inserted into the hole 11. A predetermined axis (for example, the central axis) of the first clad material 10 and the central axis of the core material 12 are parallel to each other.

[0040] The first heating and integration step S4 is a step in which the first clad base material 10 and the core base material 12 are integrated by heating, as shown in Figure 8. This gives rise to the first base material 13. The first base material 13 comprises a core portion formed by the core base material 12 and an optical clad portion formed by the first clad base material 10.

[0041] The second drilling step S5 is a step in which a plurality of holes 15 are formed in the second clad base material 14 for inserting the first base material 13 (see Figure 8), as shown in Figure 9. The plurality of holes 15 are formed side by side in the X-axis direction perpendicular to the axial direction (Z-axis direction) of the second clad base material 14. The holes 15 have a circular cross-section. The holes 15 have a central axis parallel to a predetermined axis (for example, the central axis) of the second clad base material 14. The holes 15 do not protrude from the second clad base material 14, and the entire inner circumferential surface of the holes 15 is composed of the second clad base material 14.

[0042] The second insertion step S6 is the step of inserting the first base material 13 one by one into the holes 15 of the second clad base material 14, as shown in Figure 10. The insertion of the first base material 13 is performed with the outer diameter of the first base material 13 appropriately adjusted to match the inner diameter of the holes 15. The outer diameter of the first base material 13 is adjusted so that the first base material 13 can be inserted into the holes 15. The predetermined axis (for example, the central axis) of the second clad base material 14 and the central axis of the first base material 13 are parallel to each other.

[0043] The second heating and integration step S7 is a step in which the second clad base material 14 and the first base material 13 are integrated by heating, as shown in Figure 11. This gives rise to the second base material 16. The second base material 16 comprises a core portion formed by the core base material 12, an optical clad portion formed by the first clad base material 10, and a common physical clad portion formed by the second clad base material 14. In the second base material 16, the multiple core portions are arranged in a line along the X-axis direction, which is perpendicular to the axial direction (Z-axis direction) of the second base material 16. The optical clad portion has a refractive index lower than that of the multiple core portions and is provided around each of the multiple core portions. The common physical clad portion surrounds the multiple core portions and the multiple optical clad portions. The second base material 16 comprises a clad portion formed by the optical clad portion and the common physical clad portion.

[0044] The third drilling step S8 is a step in which a plurality of holes 17, 18 are formed in the second base material 16 for inserting the low refractive index base materials 19, 20 (see Figure 13), as shown in Figure 12. The plurality of holes 17, 18 are formed so as to sandwich each of the central axes 12C of the plurality of core base materials 12 in the X-axis direction. The plurality of holes 17, 18 are formed alternately with the central axes 12C of the plurality of core base materials 12 in the X-axis direction. The plurality of holes 17, 18 are formed in positions that overlap with the plurality of core base materials 12 and the plurality of first cladding base materials 10. In other words, the holes 17, 18 are formed so as to partially cut away the core base materials 12 and the first cladding base materials 10.

[0045] The holes 17 and 18 have a circular cross-section. The holes 17 and 18 have a central axis parallel to a predetermined axis (for example, the central axis 16C) of the second base material 16. The holes 17 and 18 do not protrude from the second base material 16, and the entire inner surface of the holes 17 and 18 is composed of the second base material 16.

[0046] Hole 17 is formed so that its central axis is located midway between the central axes 12C of two adjacent core base materials 12 in the X-axis direction. Hole 18 is formed at positions that sandwich multiple core base materials 12 in the X-axis direction. Holes 17 and 18 are arranged alternately with the multiple core base materials 12. The size (diameter) of hole 18 is smaller than the size (diameter) of hole 17. Hole 18 is formed such that, in the X-axis direction, the distance from the central axis 12C of the core base material 12 to hole 18 is equal to the distance from the central axis 12C of the core base material 12 to hole 17. When two holes 17 are adjacent, the two holes 17 are formed so that they are point-symmetric with respect to the central axis 12C of the core 2. The minimum lengths of the multiple core base materials 12 in the X-axis direction are equal to each other.

[0047] The third insertion step S9 is the step of inserting the low refractive index base materials 19 and 20 one by one into the holes 17 and 18 of the second base material 16, as shown in Figure 13. The low refractive index base material 19 is inserted into hole 17, and the low refractive index base material 20 is inserted into hole 18. The insertion of the low refractive index base materials 19 and 20 is performed with the outer diameter of the second base material 16 appropriately adjusted to match the inner diameter of holes 17 and 18. The outer diameters of the low refractive index base materials 19 and 20 are: Low refractive index base material 19, 20 It is adjusted so that it can be inserted into holes 17 and 18. The predetermined axis of the second base material 16 (for example, the central axis 16C) and the central axes of the low refractive index base materials 19 and 20 are parallel to each other.

[0048] The third heating and integration step S10 is a step in which the second base material 16 and the low refractive index base materials 19 and 20 are integrated by heating, as shown in Figure 14. This gives rise to the polarization-maintaining MCF base material 21. The polarization-maintaining MCF base material 21 comprises a core portion formed by the core base material 12, an optical cladding portion formed by the first cladding base material 10, a common physical cladding portion formed by the second cladding base material 14, and a low refractive index portion formed by the low refractive index base materials 19 and 20.

[0049] The drawing process S11 is a process of drawing polarization-retaining MCF 1A from polarization-retaining MCF base material 21. In the drawing process, polarization-retaining MCF 1A is manufactured by heating and melting the polarization-retaining MCF base material 21 and stretching it.

[0050] As explained above, in this manufacturing method, only one hole 17 is formed between two adjacent core base materials 12. Since one common hole 17 is formed for two core base materials 12, the number of drilling steps can be reduced. Therefore, manufacturing becomes easier and costs can be reduced. According to this manufacturing method, one low refractive index section 4 is formed between two adjacent cores 2 of the polarization-holding MCF1A, so one low refractive index section 4 can be used for polarization holding of both cores 2. Therefore, compared to a configuration in which two dedicated low refractive index sections 4 are formed for each core 2, it is possible to improve the core density. In the third drilling step S8, the multiple holes 17, 18 are formed in positions that overlap with the multiple core base materials 12 and the multiple first cladding base materials 10. Therefore, polarization holding of the cores 2 is achieved due to the shape of the cores 2 in which the length in the X-axis direction is shorter than the length in the Y-axis direction.

[0051] In addition, in the third insertion step S9, the first ends of the holes 17 and 18 of the second base material 16 are sealed, and the low refractive index base materials 19 and 20 are inserted from the open second ends of the holes 17 and 18. Furthermore, instead of the third heating and integration step S10 and the line drawing step S11, a step of drawing lines may be performed while integrating the second base material 16 and the low refractive index base materials 19 and 20 by heating.

[0052] Here, we have described the manufacturing method for polarization-maintaining MCF1A, but the same applies to polarization-maintaining MCF1,1B, and1C. Drilling holes By adjusting the processing location and hole diameter, the same manufacturing process can be achieved.

[0053] Although embodiments and modifications have been described above, this disclosure is not necessarily limited to the embodiments and modifications described herein, and various modifications are possible without departing from the spirit thereof. Furthermore, the above embodiments and modifications may be combined as appropriate. [Explanation of Symbols]

[0054] 1,1A,1B,1C…Polarization maintaining MCF 2... Core 3…Optical クラッド 4…low refractive index part 4A…First Low Refractive Index Section 4B…Second Low Refractive Index Section 5…Common physics クラッド 5a…outer peripheral surface 10…1st クラッド base material 11…hole 12…コアbase material 12C…Central Axis 13…First parent material 14…2nd クラッド base material 15…holes 16…Second parent material 16C…Central axis 17, 18… Kong 19…low refractive index base material 20...low refractive index base material 21…Polarization maintaining MCF base material C… central axis m, m1, m2, m3, m4… (straight line)

Claims

1. Multiple cores arranged side by side in a first direction perpendicular to the axial direction, A plurality of optical claddings having a refractive index lower than that of the plurality of cores, provided around each of the plurality of cores, A plurality of low refractive index portions having a refractive index lower than that of the plurality of cores, and provided so as to sandwich each of the plurality of cores in a first direction, A common physical cladding having a refractive index lower than that of the plurality of cores, comprising the plurality of cores, the plurality of optical claddings, and the plurality of low refractive index portions, The plurality of low refractive index portions are arranged alternately with the plurality of cores in the first direction, At least a portion of the outer circumference of each of the plurality of low refractive index portions is provided in contact with at least one of the plurality of cores, The distance between adjacent low refractive index portions in the first direction is shorter than the length of each of the plurality of cores in the axial direction and in the second direction perpendicular to the first direction. Polarization-maintaining multicore optical fiber.

2. The plurality of low refractive index portions include a first low refractive index portion arranged between adjacent cores of the plurality of cores in the first direction, and two second low refractive index portions arranged outside the plurality of cores in the first direction. The size of the second low refractive index portion is smaller than the size of the first low refractive index portion. Polarization-maintaining multicore optical fiber according to claim 1.

3. The plurality of low refractive index portions include a first low refractive index portion arranged between adjacent cores in the first direction, and two second low refractive index portions arranged outside the plurality of cores in the first direction. The size of the second low refractive index portion is equivalent to the size of the first low refractive index portion. Polarization-maintaining multicore optical fiber according to claim 1.

4. The plurality of low refractive index portions include a first low refractive index portion arranged between adjacent cores in the first direction, and two second low refractive index portions arranged outside the plurality of cores in the first direction. The refractive index of the second low refractive index region is lower than the refractive index of the first low refractive index region. Polarization-maintaining multicore optical fiber according to any one of claims 1 to 3.

5. The plurality of low refractive index portions include a first low refractive index portion arranged between adjacent cores in the first direction, and two second low refractive index portions arranged outside the plurality of cores in the first direction. The refractive index of the second low refractive index region is equivalent to the refractive index of the first low refractive index region. Polarization-maintaining multicore optical fiber according to any one of claims 1 to 3.

6. An optical fiber matrix comprising: a plurality of core portions arranged side by side in a first direction perpendicular to the axial direction; a plurality of optical cladding portions having a refractive index lower than that of the plurality of core portions and provided around each of the plurality of core portions; and a common physical cladding portion having a refractive index lower than that of the plurality of core portions and surrounding the plurality of core portions and the plurality of optical cladding portions, wherein a plurality of holes are formed so as to sandwich each of the central axes of the plurality of core portions in the first direction; The process involves inserting one low-refractive-index base material into each of the aforementioned multiple holes, the base material having a refractive index lower than that of the aforementioned multiple core portions. The process includes a step of drawing a line after integrating the optical fiber base material and the plurality of low refractive index base materials by heating, or while integrating them by heating. The plurality of holes are formed in the first direction, alternately aligned with the central axes of the plurality of core portions, and in positions that overlap with the plurality of core portions and the plurality of optical cladding portions. A method for manufacturing polarization-maintaining multicore optical fibers.

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