Optical fiber, optical device, and method of manufacturing optical device

Abstract

Realized is an optical fiber which has a helical core and in which a change in core position at an end surface thereof, possibly occurring due to end surface polishing, is suppressed. An optical fiber (1) includes a helical section (I0) in which a non-center core (12) is helical, and a first non-helical section (I1) which includes a first end of the optical fiber (1) and in which the non-center core (12) is linear.

Description

[Technical Field]

[0001] The present invention relates to an optical fiber having a helical core, and to an optical device comprising such an optical fiber. [Background technology]

[0002] In recent years, progress has been made in the development of optical fibers in which polarization mode dispersion and the like are suppressed by making the cores spiral. In particular, multicore fibers in which at least one core is spiral are also called spun multicore fibers, and are used, for example, in contact sensors, shape sensors, medical applications, communications applications, etc. Patent Document 1 listed below discloses a conventional spun multicore fiber. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 8,773,650 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, when an optical fiber having a spiral core is subjected to end face polishing and / or excess length processing in a state where rotation is impossible or difficult, the position (circumferential position) of the core at the end face changes. The amount of change in the core position at the end face is determined by the amount of change in fiber length due to end face polishing and / or excess length processing and the number of times the core is spiraled per unit length. For example, when a first optical fiber and a second optical fiber having a spiral core are connected via connectors attached to the ends of the respective optical fibers in a state where rotation is impossible or difficult, particularly when end face polishing and / or excess length processing are performed, the change in the core position at the end face is determined by the amount of change in fiber length due to end face polishing and / or excess length processing and the number of times the core is spiraled per unit length. or If the excess length is treated after the connector is attached, the optical loss at the connection point may increase. This is because, in conventional optical fibers, the number of spirals per unit length is constant over the entire length, and therefore, the end face is polished and / or or This is because the position of the core at the end face of the first optical fiber relative to the connector changes due to the extra length processing, which causes mismatching between the positions of the core at both end faces.

[0005] One aspect of the present invention has been made in view of the above problems, and its object is to provide an optical fiber having a helical core, which is end-polished and / or or The object of the present invention is to realize an optical fiber in which the change in the position of the core at the end face, which may occur when excess length processing is performed, is suppressed. [Means for solving the problem]

[0006] An optical fiber according to one embodiment of the present invention is an optical fiber having at least one core, and includes a helical section in which the core is helical, and a first non-helical section in which the core is straight, the first non-helical section including a first end of the optical fiber, or a first loose helical section in which the number of helices per unit length of the core is fewer than the helical section, the first loose helical section including the first end of the optical fiber.

[0007] A method for manufacturing an optical device according to one aspect of the present invention includes a cutting step of cutting an optical fiber having at least one core, the optical fiber including a spiral section in which the core is spirally shaped, and a gentle spiral section in which the number of spirals per unit length of the core is fewer than that of the spiral section, at the gentle spiral section. [Effects of the Invention]

[0008] According to one aspect of the present invention, an optical fiber having a spiral core can be realized in which changes in the position of the core at the end face, which may occur when polishing the end face and / or performing excess length processing, are suppressed. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a perspective view showing the configuration of an optical fiber according to a first embodiment of the present invention. [Figure 2]2 is a perspective view showing an example of a method for manufacturing the optical fiber shown in FIG. [Figure 3] FIG. 4 is a perspective view showing the configuration of an optical fiber according to a second embodiment of the present invention. [Figure 4] 4 is a perspective view showing an example of a method for manufacturing the optical fiber shown in FIG. 3. FIG. [Figure 5] 2 is a perspective view showing the configuration of a connectorized optical fiber including the optical fiber shown in FIG. 1. FIG. [Figure 6] 2 is a perspective view showing the configuration of an optical device including the optical fiber shown in FIG. 1. FIG. [Figure 7] FIG. 4 is a cross-sectional view showing a modified example of the optical fiber shown in FIG. 1 or 3. DETAILED DESCRIPTION OF THE INVENTION

[0010] [First embodiment] (Optical fiber configuration) An optical fiber 1 according to a first embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a perspective view showing the configuration of the optical fiber 1.

[0011] The optical fiber 1 includes a central core 11, a non-central core 12 (an example of "at least one core" in the claims), and a cladding 13. The optical fiber 1 also includes a helical section I0, a first non-helical section I1, and a second non-helical section I2.

[0012] The central core 11 is a columnar (cylindrical in the illustrated example) structure formed on the central axis of the optical fiber 1 and having a higher refractive index than the cladding. The central core 11 is made of, for example, silica glass doped with an up-dopant such as germanium (Ge). Note that if the cladding 13 is doped with a down-dopant, the central core 11 may be made of pure silica glass. In the helical section I0, the first non-helical section I1, and the second non-helical section I2, the central core 11 is linear and includes the central axis of the optical fiber 1. The central core 11 forms a linear optical path inside the optical fiber 1 that includes the central axis of the optical fiber 1.

[0013] The diameter of the central core 11 is, for example, 5 μm or more and 15 μm or less. However, the diameter of the central core 11 is arbitrary and is not limited to 5 μm or more and 15 μm or less. Furthermore, an FBG (Fiber Bragg Grating) may be formed in the central core 11. This makes it possible to realize an optical fiber 1 that can be suitably used for fiber sensing. Of course, the optical fiber 1 can also be suitably used for communications, in which case there is no need to form an FBG in the central core 11.

[0014] The non-center core 12 is a columnar (e.g., cylindrical) structure formed at a position other than the central axis of the optical fiber 1 and having a higher refractive index than the cladding. FIG. 1 illustrates two non-center cores 12a and 12b as examples of the non-center core 12. Like the central core 11, the non-center core 12 is made of silica glass doped with an up-dopant such as germanium (Ge). Note that when the cladding 13 is doped with a down-dopant, the non-center core 12 may be made of pure silica glass. In the helical section I0, the non-center core 12 has a helical shape that revolves around the central axis of the optical fiber 1. On the other hand, in the first non-helical section I1 and the second non-helical section I2, the non-center core 12 has a linear shape that is parallel to the central axis of the optical fiber 1. The non-center core 12 forms two helical optical paths inside the optical fiber 1 that revolve around the central axis of the optical fiber 1. The polarization mode dispersion of the spiral section I0 tends to be smaller than the polarization mode dispersion of the non-spiral sections I1 and I2, and the polarization mode dispersion of the non-spiral sections I1 and I2 tends to be larger than the polarization mode dispersion of the spiral section I0.

[0015] The diameter of the non-central core 12 is, for example, 5 μm or more and 15 μm or less. However, the diameter of the non-central core 12 is arbitrary and is not limited to 5 μm or more and 15 μm or less. The non-central core 12 may have the same diameter as the central core 11 or a different diameter from the central core 11. The distance d between the central axis of the cladding 13 and the central axis of the non-central core 12 in the helical section I0 (hereinafter also referred to as the center-to-center distance d) is, for example, 35 μm. However, the center-to-center distance d is arbitrary and is not limited to 35 μm. For example, the center-to-center distance d is preferably (1) greater than 0 μm (the center of the non-central core 12 is spaced from the center of the cladding 13), more preferably (2) 0.5 μm or more, and even more preferably (3) 1 / 2 or more of the core diameter (the diameter of the central core 11 or the diameter of the non-central core 12). The center-to-center distance d is, for example, preferably 35 μm or less.

[0016] The center-to-center distance d may be determined appropriately taking into consideration, for example, crosstalk between the cores, the difference in optical path length between the central core 11 and the non-central cores 12, and the difference in the amount of strain between the central core 11 and the non-central cores 12 when the optical fiber 1 is bent. Furthermore, an FBG (Fiber Bragg Grating) may be formed in the non-central cores 12. This makes it possible to realize an optical fiber 1 that is suitable for use in fiber sensing. Of course, the optical fiber 1 can also be suitable for use in communications, in which case there is no need to form an FBG in the non-central cores 12.

[0017] Furthermore, when the optical fiber 1 includes a plurality of non-center cores 12, these non-center cores 12 are, for example, arranged at equal intervals on the circumference of a circle of radius d in each cross section perpendicular to the central axis of the optical fiber 1. The optical fiber 1 shown in the figure includes two non-center cores 12a and 12b. However, the number of non-center cores 12 is arbitrary and is not limited to two. Furthermore, the number of spirals of the non-center core 12 per unit length in the spiral section I0 is, for example, 50 turns / m. In other words, the period of the non-center core 12 in the spiral section I0 (the length in the longitudinal direction of the optical fiber 1 per turn) is, for example, 20 mm. However, the number of spirals of the non-center core 12 per unit length is arbitrary and is not limited to 50 turns / m. Furthermore, the number of spirals of the non-center core 12a per unit length and the number of spirals of the non-center core 12b per unit length may or may not be the same.

[0018] The cladding 13 is a columnar (e.g., cylindrical) structure in which the central core 11 and the non-central cores 12 are embedded. The cladding 13 is made of, for example, pure silica glass. Note that if the central core 11 and the non-central cores 12 are made of pure silica glass, the cladding 13 may be made of silica glass doped with a down dopant. The outer surface of the cladding 13 may be covered with a coating (not shown).

[0019] A connector may be attached to the end of the optical fiber 1 to facilitate connection with other optical fibers. The connector is attached by (1) inserting the optical fiber 1 into a ferrule and positioning the non-center core 12 in the rotational direction, or (2) positioning the non-center core 12 in the rotational direction, inserting the optical fiber 1 into the ferrule, and then fixing the optical fiber to the ferrule using an adhesive or the like. Thus, the optical fiber 1 is attached to the connector so that it is non-rotatable or difficult to rotate. After that, excess length processing and / or end face polishing are performed. In excess length processing, for example, the portion of the optical fiber 1 protruding from the ferrule is cut off. In end face polishing, the end faces of the optical fiber 1 and the ferrule are processed into a shape suitable for connection. The end faces of the optical fiber 1 and the ferrule may be re-polished to remove foreign matter or scratches on the end faces of the optical fiber 1. If such excess length processing and / or end face polishing were performed in a state where the non-helical sections I1 and I2 were not present and a connector was attached to the helical section I0, the position of the non-center core 12 would change circumferentially relative to the connector.

[0020] In contrast, the optical fiber 1 according to this embodiment includes non-helical sections I1 and I2 at the end portion, in which the non-center core 12 is linear. Therefore, the connector is attached to the non-helical sections I1 and I2, not the helical section I0, in a manner that makes it impossible or difficult to rotate. This prevents the position of the non-center core 12 at the end face relative to the connector from changing, which may occur due to excess length processing and / or end face polishing. Furthermore, the optical fiber 1 includes a helical section I0 in the center, in which the non-center core 12 is helical. This prevents polarization mode dispersion.

[0021] The length of the helical section I0 is preferably longer than the lengths of the first non-helical section I1 and the second non-helical section I2. This further enhances the effect of suppressing polarization mode dispersion. Furthermore, ITU-T standards such as G.654.A and G.657.B specify the upper limit of polarization mode dispersion as 0.50 ps / sqrt (km). Furthermore, ITU-T standards such as G.652.B, G.652.D, G.654.B, G.654.C, G.654.D, G.654.E, and G.657.B specify the upper limit of polarization mode dispersion as 0.20 ps / sqrt (km). Therefore, polarization mode dispersion is preferably 0.50 ps / sqrt (km) or less, more preferably 0.20 ps / sqrt (km) or less, and even more preferably 0.10 ps / sqrt (km) or less. The spiral section I0 has a polarization mode dispersion of 0.50ps / sqrt(km). below The non-helical sections I1 and I2 can also be defined as sections in which the polarization mode dispersion is greater than 0.50 ps / sqrt(km).

[0022] In the present embodiment, the optical fiber 1 has been described as including a helical section I0, a first non-helical section I1, and a second non-helical section I2. However, the present invention is not limited to this. For example, one of the first non-helical section I1 and the second non-helical section I2 can be omitted. That is, the scope of the present invention also includes an optical fiber 1 including only the helical section I0 and the first non-helical section I1, and an optical fiber 1 including only the helical section I0 and the second non-helical section I2. The scope of the present invention also includes an optical fiber 1 in which the first non-helical section I1 is replaced with a first loose helical section I3 (described below), or in which the second non-helical section I2 is replaced with a second loose helical section I4 (described below). Furthermore, it is preferable that the core arrangement, core shape, MFD (Mode Field Diameter), cladding shape, and cladding diameter of the first non-helical section I1 and the second non-helical section I2 are identical or substantially identical. This is because splice loss can be reduced.

[0023] Furthermore, in this embodiment, the optical fiber 1 including the central core 11 and the non-central cores 12 has been described, but the present invention is not limited to this. For example, the central core 11 can be omitted. That is, an optical fiber 1 including only a non-central core 12 also falls within the scope of the present invention. Furthermore, in this embodiment, the optical fiber 1 including multiple non-central cores 12 has been described, but the present invention is not limited to this. That is, an optical fiber 1 including a single non-central core 12 also falls within the scope of the present invention.

[0024] In other words, (1) a single-core fiber including a single non-central core 12, (2) a multi-core fiber including multiple non-central cores 12, (3) a multi-core fiber including a single non-central core 12 and a single central core 11, and (4) a multi-core fiber including multiple non-central cores 12 and a single central core 11 are all included in the scope of the present invention. In the optical fibers of (1) to (4), each core may be a single-mode core designed to transmit only a single mode (fundamental mode), or a multi-mode core designed to transmit multiple modes (fundamental mode and higher-order modes). In addition, the multi-core fibers of (2) to (4) may be coupled multi-core fibers designed to optically couple the cores to each other, or may be uncoupled multi-core fibers designed to prevent the cores from optically coupling to each other. All of these optical fibers have at least one helical core, and are therefore included in the scope of the present invention.

[0025] (Two forms of optical fiber) The optical fiber 1 can take at least the following forms:

[0026] The first form is a form that is constituted by an optical fiber 1A including a helical section 10, a second optical fiber 1B including a first non-helical section 11, and an optical fiber 1C including a second non-helical section 12. In this case, the optical fiber 1 includes a splice point between the optical fiber 1A and the optical fiber 1B, and a splice point between the optical fiber 1A and the optical fiber 1C.

[0027] The second form is a form constituted by a single optical fiber 1D including a helical section I0, a first non-helical section I1, and a second non-helical section I2. In this case, the optical fiber 1 does not include a connection point between the helical section I0 and the first non-helical section I1, or a connection point between the helical section I0 and the second non-helical section I2.

[0028] Fig. 2 is a perspective view showing an example of a manufacturing method of the optical fiber 1 according to the first embodiment. In the manufacturing method shown in Fig. 2, an optical fiber 1A including a helical section I0, a second optical fiber 1B including a first non-helical section I1, and an optical fiber 1C including a second non-helical section I2 are used as materials.

[0029] 2 includes (1) a connecting step S1 of connecting the optical fiber 1B to a first end of the optical fiber 1A, and (2) a connecting step S2 of connecting the optical fiber 1C to a second end of the optical fiber 1A. The connections in the connecting steps S1 and S2 may be made using a connector, an adhesive, or fusion splicing.

[0030] The optical fiber 1 according to the first embodiment has the advantage that it is easy to make the refractive index profile in the helical section I0 different from the refractive index profile in the non-helical sections I1 and I2, thereby realizing an optical fiber 1 with a high degree of freedom in the refractive index profile.

[0031] In the non-helical sections I1 and I2, where the non-center core 12 is linear, crosstalk tends to occur more easily when bending occurs, compared to the helical section I0, where the non-center core 12 is helical. Therefore, it is preferable to adopt a configuration in which the effective refractive index of the non-center core 12 in the non-helical sections I1 and I2 is higher than the effective refractive index of the non-center core 12 in the helical section I0, thereby suppressing deterioration of crosstalk. Such a configuration can be easily realized in the optical fiber 1 according to the first embodiment. For example, an optical fiber with a step-index refractive index profile may be used as the optical fiber 1A constituting the helical section I0, and optical fibers 1B and 1C constituting the non-helical sections I1 and I2 may be used, in which a trench layer and / or a depressed layer is formed around the non-center core 12, and the effective refractive index of the non-center core 12 is higher than that of the optical fiber 1A. Furthermore, generally, the more complex the refractive index profile, the higher the manufacturing cost. By using the above configuration, the cost of the optical fiber connector can be reduced compared to using optical fibers in which a trench layer and / or a depressed layer is formed even in the helical sections. The same applies to a second embodiment described below, with the non-helical sections I1 and I2 replaced with gentle helical sections I3 and I4.

[0032] On the other hand, the fiber 1 according to the second embodiment has the advantage that the number of splicing points can be reduced, and therefore it is easy to suppress loss occurring at the splicing points.

[0033] The optical fiber 1 may or may not have a structure attached to its end. Here, the structure may be the connector described above, or may be a structure other than a connector. Examples of structures other than connectors include a V-groove array or a fiber holder. In particular, when a connector is attached to the end of the optical fiber 1, the task of connecting the optical fiber 1 to another optical fiber becomes easier. On the other hand, when a connector is not attached to the end of the optical fiber 1, space saving becomes easier.

[0034] Second Embodiment (Optical fiber configuration) An optical fiber 2 according to a second embodiment of the present invention will be described with reference to Fig. 3. Fig. 3 is a perspective view showing the configuration of the optical fiber 2.

[0035] The optical fiber 2 includes a central core 21, a non-central core 22 (an example of "at least one core" in the claims), and a cladding 23. The optical fiber 2 also includes a spiral section I0, a first loose spiral section I3, and a second loose spiral section I4.

[0036] The central core 21 is a columnar (cylindrical in the illustrated example) structure formed on the central axis of the optical fiber 2 and having a higher refractive index than the cladding. The central core 21 is made of, for example, silica glass doped with an up-dopant such as germanium (Ge). Note that if a down-dopant is doped in the cladding 23, the central core 21 may be made of pure silica glass. In the helical section I0, the first slow helical section I3, and the second slow helical section I4, the central core 21 is linear and includes the central axis of the optical fiber 2. The central core 21 forms a linear optical path inside the optical fiber 2 that includes the central axis of the optical fiber 2.

[0037] The diameter of the central core 21 is, for example, 5 μm or more and 15 μm or less. However, the diameter of the central core 21 is arbitrary and is not limited to 5 μm or more and 15 μm or less. Furthermore, an FBG (Fiber Bragg Grating) may be formed in the central core 21. This makes it possible to realize an optical fiber 2 that can be suitably used for fiber sensing. Of course, the optical fiber 2 can also be suitably used for communications, in which case there is no need to form an FBG in the central core 21.

[0038] The non-center core 22 is a columnar (e.g., cylindrical) structure formed at a position other than the central axis of the optical fiber 2 and having a higher refractive index than the cladding. FIG. 3 illustrates two non-center cores 22a and 22b as examples of the non-center core 22. Like the central core 21, the non-center core 22 is made of silica glass doped with an up-dopant such as germanium (Ge). Note that when a down-dopant is doped in the cladding 23, the non-center core 22 may be made of pure silica glass. In the helical section I0, the first slow helical section I3, and the second slow helical section I4, the non-center core 22 has a helical shape that winds around the central axis of the optical fiber 2. However, the number of helical turns per unit length of the non-center core 22 in the first slow helical section I3 and the second slow helical section I4 is smaller than the number of helical turns per unit length of the non-center core 22 in the helical section I0. The non-central core 22 forms, inside the optical fiber 2, two helical optical paths that revolve around the central axis of the optical fiber 2. The polarization mode dispersion in the helical section I0 tends to be smaller than the polarization mode dispersion in the slow helical sections I3 and I4, and the polarization mode dispersion in the slow helical sections I3 and I4 tends to be larger than the polarization mode dispersion in the helical section I0.

[0039] The diameter of the non-central core 22 is, for example, 5 μm or more and 7 μm or less. However, the diameter of the non-central core 22 is arbitrary and is not limited to 5 μm or more and 7 μm or less. The non-central core 22 may have the same diameter as the central core 21 or a different diameter from the central core 21. The distance d between the central axis of the cladding 23 and the central axis of the non-central core 22 in the helical section I0 (hereinafter also referred to as the center-to-center distance d) is, for example, 35 μm. However, the center-to-center distance d is arbitrary and is not limited to 35 μm. For example, the center-to-center distance d is preferably (1) greater than 0 μm (the center of the non-central core 22 is spaced from the center of the cladding 23), more preferably (2) 0.5 μm or more, and more preferably (3) ½ or more of the core diameter (the diameter of the central core 21 or the diameter of the non-central core 22). The center-to-center distance d is, for example, preferably 35 μm or less.

[0040] The center-to-center distance d may be determined appropriately taking into consideration, for example, crosstalk between the cores, the difference in optical path length between the central core 21 and the non-central cores 22, and the difference in the amount of strain between the central core 21 and the non-central cores 22 when the optical fiber 2 is bent. Furthermore, an FBG (Fiber Bragg Grating) may be formed in the non-central core 22. This makes it possible to realize an optical fiber 2 that can be suitably used for fiber sensing. Of course, the optical fiber 2 can also be suitably used for communications, in which case there is no need to form an FBG in the non-central core 22.

[0041] Furthermore, when the optical fiber 2 includes a plurality of non-center cores 22, these multiple non-center cores 22 are, for example, arranged at equal intervals on the circumference of a circle of radius d in each cross section perpendicular to the central axis of the optical fiber 2. The illustrated optical fiber 2 includes two non-center cores 22a and 22b. However, the number of non-center cores 22 is arbitrary and is not limited to two. Furthermore, the number of spirals of the non-center core 22 per unit length in the spiral section I0 is, for example, 50 turns / m. In other words, the period of the non-center core 22 in the spiral section I0 (the length in the longitudinal direction of the optical fiber 2 per turn) is, for example, 20 mm. However, the number of spirals of the non-center core 22 per unit length is arbitrary and is not limited to 50 turns / m. Furthermore, the number of spirals of the non-center core 22a per unit length and the number of spirals of the non-center core 22b per unit length may or may not be the same.

[0042] The cladding 23 is a columnar (e.g., cylindrical) structure in which the central core 21 and the non-central cores 22 are embedded. The cladding 23 is made of, for example, silica glass. The outer surface of the cladding 23 may be covered with a coating (not shown).

[0043] As described above, the optical fiber 2 according to this embodiment includes loose spiral sections I3 and I4 at the end, where the number of spiral turns per unit length of the non-center core 22 is less than the number of spiral turns per unit length in the spiral section I0. Therefore, the connector is attached to the loose spiral sections I3 and I4, not to the spiral section I0, so that it is not possible or difficult to rotate. This makes it possible to prevent the position of the non-center core 22 on the end face from changing relative to the connector, which may occur due to excess length processing and / or end face polishing. Furthermore, the optical fiber 2 includes the spiral section I0 in the center, where the non-center core 22 is spiral. Therefore, it is possible to suppress polarization mode dispersion. In particular, in the optical fiber 2 according to this embodiment, the spiral section I0 Since the non-center core 22 is spiral in sections other than the spiral sections (i.e., the gentle spiral sections I3 and I4), polarization mode dispersion can be suppressed more effectively than in the optical fiber 1 of the first embodiment, in which the non-center core 12 is linear in sections other than the spiral sections (i.e., the non-spiral sections I1 and I2).

[0044] If the center-to-center distance is d [m], the number of turns (synonymous with the number of spirals) per unit length of non-center core 22 in loose spiral sections I3 and I4 is s [turns / m], and the amount of change in fiber length due to excess length treatment and / or end face polishing is Δl [m], the displacement Δr [m] of non-center core 22 at the end face due to excess length treatment and / or end face polishing is given by the following equation (1) using the cosine theorem. Solving the following equation (1) for the number of turns s gives the following equation (2).

[0045]

number

number

[0046] In order to sufficiently suppress an increase in splice loss, it is preferable that the displacement Δr of the non-center core 22 at the end face is 0.1 μm or less. That is, it is preferable that the number of turns s satisfies the following inequality (3).

[0047]

number

[0048] Here, consider optical fiber 2 in which non-center cores 22 are arranged at the vertices of a square with sides of 40 μm in each cross section. In this case, the center-to-center distance d is approximately 28.3 μm. By setting the fiber length change Δl to 30 μm, 50 μm, 100 μm, 200 μm, 1000 μm, 3000 μm, 5000 μm, and 10000 μm, the right-hand side of inequality (3) above, i.e., the upper limit smax of the number of turns s at which the displacement Δr of non-center core 22 at the end face is 0.1 μm or less, is calculated, and Table 1 below is obtained.

[0049] [Table 1]

[0050] For example, when only end face polishing is performed, the fiber length change Δl is approximately 30 μm to 200 μm. When the fiber length change Δl is 30 μm, the displacement Δr of the non-center core 22 at the end face can be reduced to 0.1 μm or less by setting the amount of twist (synonymous with the number of twists) s to 18.76 turns or less. When the fiber length change Δl is 50 μm, the displacement Δr of the non-center core 22 at the end face can be reduced to 0.1 μm or less by setting the amount of twist s to 11.25 turns or less. When the fiber length change Δl is 100 μm, the displacement Δr of the non-center core 22 at the end face can be reduced to 0.1 μm or less by setting the amount of twist s to 5.63 turns or less. When the fiber length change Δl is 200 μm, the displacement Δr of the non-center core 22 at the end face can be reduced to 0.1 μm or less by setting the amount of twist s to 2.81 turns or less.

[0051] Furthermore, when excess length processing is performed, the fiber length change amount Δl is approximately 1 mm to 10 mm. When the fiber length change amount Δl is 1 mm, the displacement amount Δr of the non-center cores 22 at the end face can be made 0.1 μm or less by setting the amount of twist s to 0.56 turns or less. When the fiber length change amount Δl is 3 mm, the displacement amount Δr of the non-center cores 22 at the end face can be made 0.1 μm or less by setting the amount of twist s to 0.19 turns or less. When the fiber length change amount Δl is 5 mm, the displacement amount Δr of the non-center cores 22 at the end face can be made 0.1 μm or less by setting the amount of twist s to 0.11 turns or less. When the fiber length change amount Δl is 10 mm, the displacement amount Δr of the non-center cores 22 at the end face can be made 0.1 μm or less by setting the amount of twist s to 0.06 turns or less. In addition, taking into consideration that the fiber length change Δl due to excess length processing is often less than 10 mm, it is preferable that the lengths of the loose spiral sections I3 and I4 are each 10 mm or more. This is because it reduces the possibility that the loose spiral sections I3 and I4 will disappear during excess length processing. The same can be said for the non-spiral sections I1 and I2 in the first embodiment.

[0052] Furthermore, the length of the spiral section I0 is preferably longer than the lengths of the first and second slow spiral sections I3 and I4. This further enhances the effect of suppressing polarization mode dispersion. Furthermore, ITU-T standards such as G.654.A and G.657.B specify the upper limit of polarization mode dispersion as 0.50 ps / sqrt (km). Furthermore, ITU-T standards such as G.652.B, G.652.D, G.654.B, G.654.C, G.654.D, G.654.E, and G.657.B specify the upper limit of polarization mode dispersion as 0.20 ps / sqrt (km). Therefore, the length of the spiral section I0 is preferably set so that polarization mode dispersion is 0.50 ps / sqrt (km) or less, and more preferably so that polarization mode dispersion is 0.20 ps / sqrt (km) or less.

[0053] In this embodiment, the optical fiber 2 including the helical section I0, the first slow helical section I3, and the second slow helical section I4 has been described, but the present invention is not limited to this. For example, one of the first slow helical section I3 and the second slow helical section I4 can be omitted. That is, an optical fiber 2 including only the helical section I0 and the first slow helical section I3, and an optical fiber 2 including only the helical section I0 and the second slow helical section I4 are also included in the scope of the present invention. Furthermore, it is preferable that the core arrangement, core shape, MFD (Mode Field Diameter), cladding shape, and cladding diameter of the first slow helical section I3 and the second slow helical section I4 are the same or approximately the same. This is because splice loss can be reduced.

[0054] Furthermore, in this embodiment, the optical fiber 2 including the central core 21 and the non-central cores 22 has been described, but the present invention is not limited to this. For example, the central core 21 can be omitted. That is, an optical fiber 2 including only a non-central core 22 also falls within the scope of the present invention. Furthermore, in this embodiment, the optical fiber 2 including multiple non-central cores 22 has been described, but the present invention is not limited to this. That is, an optical fiber 2 including a single non-central core 22 also falls within the scope of the present invention.

[0055] In other words, (1) a single-core fiber including a single non-central core 22, (2) a multi-core fiber including multiple non-central cores 22, (3) a multi-core fiber including a single non-central core 22 and a single central core 21, and (4) a multi-core fiber including multiple non-central cores 22 and a single central core 21 are all included in the scope of the present invention.

[0056] The optical fiber 2 may have a structural connector attached to its end, or may not have a structural connector attached to its end. Here, the structural connector may be the connector described above, or may be a structural component other than a connector. Examples of structural components other than a connector include a V-groove array or a fiber holder. In particular, when a connector is attached to the end of the optical fiber 2, the task of connecting the optical fiber 2 to another optical fiber becomes easier. On the other hand, when a connector is not attached to the end of the optical fiber 2, space saving becomes easier.

[0057] (Supplementary information on the definitions of the spiral section I0 and the slow spiral sections I3 and I4) The definitions of the spiral section I0 and the loose spiral sections I3 and I4 for cases where the number of spirals per unit length of the non-center core 22 is not uniform are further explained below. In this case, for example, the average or median of the number of spirals per unit length of the non-center core 22 throughout the entire optical fiber 2 is determined and used as the representative value. Alternatively, if the number of spirals per unit length of the non-center core 22 changes periodically, the average or median of the number of spirals per unit length of the non-center core 22 over one period is determined and used as the representative value. Then, for example, the spiral section I0 is defined as the section where the number of spirals per unit length of the non-center core 22 is greater than the representative value. Furthermore, for example, the loose spiral section I3 is defined as the section including one end of the optical fiber 2 among sections where the number of spirals per unit length of the non-center core 22 is less than the representative value. Alternatively, the loose spiral section I3 is defined as the section including one end of the optical fiber 2 among sections where the number of spirals per unit length of the non-center core 22 is less than α times the representative value. Here, α is a real number greater than 0 and less than 1, for example, 0.1. The slow spiral section I4 can be defined in the same way as the slow spiral section I3.

[0058] (Two forms of optical fiber) The optical fiber 2 can take at least the following forms:

[0059] The first form is a form configured by an optical fiber 2A including a spiral section 10, a second optical fiber 2B including a first gentle spiral section 13, and an optical fiber 2C including a second gentle spiral section 14. In this case, the optical fiber 2 includes a splice point between the optical fiber 2A and the optical fiber 2B, and a splice point between the optical fiber 2A and the optical fiber 2C.

[0060] The second form is a form constituted by a single optical fiber 2D including a spiral section I0, a first gentle spiral section I3, and a second gentle spiral section I4. In this case, the optical fiber 2 does not include a connection point between the spiral section I0 and the first gentle spiral section I3, or a connection point between the spiral section I0 and the second gentle spiral section I4.

[0061] Fig. 4 is a perspective view showing an example of a method for manufacturing the optical fiber 2 according to the second embodiment. In the manufacturing method shown in Fig. 4, an optical fiber 2D' including points P1 and P2 at which the winding direction of the non-center core 22' is reversed is used as a material.

[0062] The manufacturing method shown in FIG. 4 includes (1) a cutting step S3 of cutting the optical fiber 2D' at point P1 where the winding direction of the non-center core 22' reverses, and (2) a cutting step S4 of cutting the optical fiber 2D' at point P2 where the winding direction of the non-center core 22' reverses. Around points P1 and P2 where the winding direction of the non-center core 22' reverses, the number of spirals per unit length of the non-center core 22' becomes relatively small. Therefore, the manufacturing method shown in FIG. 4 can manufacture an optical fiber 2 including a spiral section I0, a first gentle spiral section I3, and a second gentle spiral section I4. When this manufacturing method is employed, it is preferable that the cross-sectional shape of the cladding of the optical fiber 2D' is non-circular (for example, elliptical). If the cross-sectional shape of the cladding of the optical fiber 2D' is non-circular, point P2 where the winding direction of the non-center core 22' reverses can be set to the point P1 or P2 where the winding direction of the non-center core 22' reverses. 2D’ This is because it is easy to identify the loose spiral sections I3 and I4 from the appearance of the optical fiber 2. When such an optical fiber 2D' is used as a material, the cross-sectional shape of the cladding of the optical fiber 2 also becomes non-circular. Therefore, the loose spiral sections I3 and I4 in the manufactured optical fiber 2 can also be easily identified from the appearance of the optical fiber 2.

[0063] The optical fiber 2D' may include a helical section in which the non-central core 22' is helical, and a loose helical section in which the non-central core 22' has fewer spiral turns per unit length than the helical section. Furthermore, the location at which the optical fiber 2D' is cut in the above-described cutting step S4 may be any point within the loose helical section. Note that, while the loose helical sections I3 and I4 described above are required to include an end of the optical fiber 2, the loose helical section referred to here is not required to include an end of the optical fiber 2. Furthermore, if the cross-sectional shape of the cladding of the optical fiber 2D' is non-circular, the number of spiral turns in each portion of the optical fiber 2D' can be determined from the appearance of the optical fiber 2D', making it easy to identify the position of the loose helical section in the optical fiber 2D'.

[0064] For example, in the optical fiber 2D', if sections in which the non-center core 22' turns clockwise and sections in which the non-center core 22' turns counterclockwise alternately appear, the area around point P1 where the turning direction of the non-center core 22' reverses will be the gentle spiral section. Alternatively, in the optical fiber 2D', if the turning direction of the non-center core 22' is constant and the number of helical turns per unit length of the non-center core 22' varies periodically, the area around the point where the number of helical turns per unit length of the non-center core 22' takes a minimum value will be the gentle spiral section. Alternatively, in the optical fiber 2D', if sections in which the non-center core 22 is linear are intermittently included, the sections in which the non-center core 22 is linear will be the gentle spiral section. In this case, the turning direction of the non-center core 22 in the sections in which the non-center core 22 is spiral may be exclusively clockwise, exclusively counterclockwise, or a mixture of clockwise and counterclockwise turns.

[0065] The definitions of the spiral section and the loose spiral section in the optical fiber 2D' when the number of spirals per unit length of the non-central core 22' is not uniform are similar to the definitions of the loose spiral sections I3 and I4 in the optical fiber 2 when the number of spirals per unit length of the non-central core 22 is not uniform. However, the only difference between the two definitions is that the loose spiral sections I3 and I4 of the optical fiber 2 must include the end of the optical fiber 2, whereas the loose spiral section of the optical fiber 2D does not need to include the end of the optical fiber 2D.

[0066] The optical fiber 2 according to the first embodiment has the advantage that it is easy to make the refractive index profile in the spiral section I0 different from the refractive index profile in the loose spiral sections I3 and I4. On the other hand, the fiber 1 according to the second embodiment has the advantage that it is easy to reduce the loss occurring at the splices because the number of splices can be reduced.

[0067] The spiral section I0 of the optical fiber 2 may alternately include sections in which the non-center core 12 turns clockwise and sections in which it turns counterclockwise. In this case, by cutting the optical fiber 2 at a point where the direction of the non-center core 22 turns reverses, the number of spiral turns per unit length of the non-center core 22 can be kept small around the new end face created by the cutting. Therefore, it is possible to keep small the change in the position of the non-center core 22 at the end face created by the cutting, which may occur due to excess length processing and / or end face polishing.

[0068] [Usage example] (optical fiber with connector) A connectorized optical fiber 3 including the optical fiber 1 (see FIG. 1) will be described with reference to Fig. 5. Fig. 5 is a perspective view showing the configuration of the connectorized optical fiber 3 including the optical fiber 1.

[0069] The connectorized optical fiber 3 includes an optical fiber 1 and a connector 30. The connector 30 may be provided at one end of the optical fiber 1 or at both ends of the optical fiber 1, but Fig. 5 illustrates the latter configuration.

[0070] The connector 30 includes a ferrule 31 and a housing 32. The ferrule 31 is an annular member having a fiber hole formed therein, into which the end of the optical fiber 1 is inserted. The housing 32 is a rectangular parallelepiped member that accommodates the ferrule 31. A key 32a is formed on the side of the housing 32. The key 32a is a rectangular parallelepiped protrusion that prevents incorrect connection to another optical fiber to be connected and that serves to align the optical fiber to the other optical fiber to be connected. The positions of the non-central cores 12a to 12b on the end face of the optical fiber 1 are aligned based on the key 32a formed on the housing 32. Note that, in this example, the key 32a is a protrusion, assuming that the adapter has a recess that fits with the key 32a, but this is not limiting. If the adapter has a protrusion that fits with the key 32a, the key 32a may be a recess.

[0071] Here, the ferrule 31 is fixed (integrated) to the end of the optical fiber 1 so that one end face is flush with the end face of the optical fiber 1. The ferrule 31 is housed in the housing 32 so that rotation around the axis does not occur or is unlikely to occur. Because rotation around the axis of the ferrule 31 does not occur or is unlikely to occur, rotation around the axis of the optical fiber 1, which is integrated with the ferrule 31, also does not occur or is unlikely to occur.

[0072] The length of the non-helical sections I1, I2 of the optical fiber 1 may be such that the entire non-helical sections I1, I2 are accommodated inside the connector 30, or such that only a portion of the non-helical sections I1, I2 are accommodated inside the connector 30. In the former case, the connection points between the non-helical sections I1, I2 and the helical section I0 are accommodated inside the connector 30, which is advantageous in terms of strength.

[0073] In the connectorized optical fiber 3, if foreign matter that is impossible or difficult to remove is attached to the end face of the optical fiber 1, or if the core of the optical fiber 1 is damaged, the problem of increased connection loss during connector mating can occur. In such cases, the problem can sometimes be solved by re-polishing the end face of the optical fiber 1 together with the ferrule 31. In this case, if the end of the optical fiber 1 has non-helical sections I1 and I2, it is possible to suppress changes in the positions of the non-center cores 12a and 12b relative to the key 32a that can occur when the end face of the optical fiber 1 is re-polished. This reduces the possibility of the problem of increased connection loss during connector mating due to re-polishing occurring.

[0074] While the connectorized optical fiber 3 including the optical fiber 1 has been described here, the same can be achieved for a connectorized optical fiber including the optical fiber 2. However, the slack processing and / or end face polishing of the optical fiber 1 described above may be performed after the connector 30 is assembled. In this case, a change in the position of the non-center core 12 at the end face of the optical fiber 1, which may occur due to the slack processing and / or end face polishing, results in a misalignment between the position of the non-center core 12 and the position of the key 32a. Therefore, it is preferable to use an optical fiber 1 in which the position of the non-center core 12 is less likely to change due to end face polishing. Although a single-core connector is shown in this application example, a multi-core connector such as an MPO connector may also be used. The optical fibers 1 and 2 may be used in all cores of the multi-core connector, or the optical fibers 1 and 2 may be used in some cores of the multi-core connector.

[0075] (Optical Devices) An optical device 4 including the optical fiber 1 (see FIG. 1) will be described with reference to FIG. 6. FIG. 6 is a block diagram showing the configuration of the optical device 4.

[0076] The optical device 4 includes an optical fiber 1, a fan-in / fan-out device 41, and single-core fibers 42a to 42c. The fan-in / fan-out device 41 and the single-core fibers 42a to 42c may be provided at one end of the optical fiber 1 or at both ends of the optical fiber 1, but Fig. 6 illustrates the latter configuration.

[0077] The fan-in-fan-out device 41 is a device for connecting multiple cores of a multicore fiber to multiple single-core fibers. In the configuration shown in Fig. 6, the fan-in-fan-out device 41, for example, (1) connects the central core 11 of the optical fiber 1 to the single-core fiber 42a, (2) connects the non-central core 12a of the optical fiber 1 to the single-core fiber 42b, and (3) connects the non-central core 12b of the optical fiber 1 to the single-core fiber 42c.

[0078] While the optical device 4 including the optical fiber 1 has been described here, the same can be realized for an optical device including the optical fiber 2 and an optical device including the connectorized optical fiber 3. In an optical device including the optical fibers 1 and 2, the optical fibers 1 and 2 are fusion-spliced ​​or adhesively connected to the fan-in-fan-out device 41. On the other hand, in an optical device including the connectorized optical fiber 3, the optical fibers 1 and 2 are connector-connected to the fan-in-fan-out device 41. Therefore, in the latter case, a connector complementary to the connector 30 is also provided on the fan-in-fan-out device 41 side. In either case, the position of the non-center core 12 at the end face of the optical fiber 1 is unlikely to change due to end face polishing, making it easy to connect the optical fibers 1 and 2 to the fan-in-fan-out device 41.

[0079] 〔summary〕 The optical fiber according to aspect 1 of the present invention is an optical fiber having at least one core, and includes a helical section in which the core is helical, and a first non-helical section in which the core is linear, the first non-helical section including a first end of the optical fiber, or a first loose helical section in which the number of helices per unit length of the core is fewer than the helical section, the first loose helical section including the first end of the optical fiber.

[0080] In the optical fiber according to aspect 2 of the present invention, in addition to the configuration of aspect 1, a configuration is adopted in which the optical fiber comprises a first optical fiber including the spiral section, and a second optical fiber including the first non-spiral section or the first loose spiral section, and includes a connection point between the first optical fiber and the second optical fiber.

[0081] In the optical fiber of aspect 3 of the present invention, in addition to the configuration of aspect 1, an optical fiber is provided that includes the spiral section and the first non-spiral section or the first gentle spiral section, and does not include a connection point between the spiral section and the first non-spiral section or the first gentle spiral section.

[0082] In the optical fiber according to aspect 4 of the present invention, in addition to the configuration of any one of aspects 1 to 3, a configuration is adopted in which the core is a second non-helical section that includes a second end of the optical fiber, or a second loose-helical section that has fewer spirals per unit length of the core than the spiral section, and the second non-helical section includes the second end of the optical fiber.

[0083] In the optical fiber according to aspect 5 of the present invention, in addition to the configuration of aspect 4, a configuration is adopted in which the optical fiber comprises a first optical fiber including the spiral section, and a third optical fiber including the second non-spiral section or the second loose spiral section, and includes a connection point between the first optical fiber and the third optical fiber.

[0084] In the optical fiber of aspect 6 of the present invention, in addition to the configuration of aspect 4, an optical fiber is provided that includes the spiral section and the second non-spiral section or the second gentle spiral section, and does not include a connection point between the spiral section and the second non-spiral section or the second gentle spiral section.

[0085] In the optical fiber according to aspect 7 of the present invention, in addition to the configuration of any one of aspects 1 to 6, a configuration is adopted in which the length of the spiral section is longer than the length of the first non-spiral section or the first loose spiral section.

[0086] In the optical fiber according to aspect 8 of the present invention, in addition to the configuration of any one of aspects 1 to 6, a configuration is adopted in which the length of the spiral section is shorter than the length of the first non-spiral section or the first loose spiral section.

[0087] In the optical fiber according to aspect 9 of the present invention, in addition to the configuration of any one of aspects 1 to 8, a configuration is adopted in which the spiral section alternately includes sections in which the core turns clockwise and sections in which the core turns counterclockwise.

[0088] In the optical fiber according to aspect 10 of the present invention, in addition to the configuration of any one of aspects 1 to 9, a cladding is further provided surrounding the core, and in the spiral section, the center of the core is spaced apart from the center of the cladding.

[0089] An optical fiber according to an eleventh aspect of the present invention employs, in addition to the configuration of any one of aspects 1 to 10, a configuration in which the optical fiber is a multi-core fiber having a plurality of cores, and the core is any one of the plurality of cores.

[0090] In the optical fiber according to aspect 12 of the present invention, in addition to the configuration of aspect 11, the effective refractive index of the core in the first non-helical section or the first gentle helical section is higher than the effective refractive index of the core in the helical section.

[0091] In the optical fiber according to aspect 13 of the present invention, in addition to the configuration of any one of aspects 1 to 12, a configuration is adopted in which the end of the optical fiber is attached to the structure in a manner that makes it impossible or difficult to rotate.

[0092] An optical device according to a fourteenth aspect of the present invention comprises the optical fiber of any one of the eleventh to thirteenth aspects, and one or a pair of fan-in / fan-out devices connected to one or both ends of the optical fiber.

[0093] A method for manufacturing an optical device according to aspect 15 of the present invention includes a cutting step of cutting an optical fiber having at least one core, the optical fiber including a spiral section in which the core is spirally shaped and a gentle spiral section in which the number of spirals per unit length of the core is fewer than that of the spiral section, at the gentle spiral section.

[0094] An optical fiber according to a sixteenth aspect of the present invention has the same structure as that of the tenth aspect, but further has a structure in which the distance between the center of the core and the center of the cladding is 0.5 μm or more.

[0095] [Additional Notes] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in the above-described embodiments are also included in the technical scope of the present application.

[0096] For example, in this embodiment, the length of the non-helical sections I1 and I2 or the slow helical sections I3 and I4 is longer than the length of the helical section I0. shortAlthough the above configuration has been described, the technical scope of the present application is not limited thereto. That is, a configuration in which the length of the non-helical sections I1, I2 or the loose helical sections I3, I4 is longer than the length of the helical section I0 is also included in the technical scope of the present application. When cutting the optical fibers I1, I2 and connecting the cut surface to another optical component (such as an optical fiber, a connector, or a fan-in / fan-out device), it is preferable to find the non-helical sections I1, I2 or the loose helical sections I3, I4 and cut the found sections. In this case, the above configuration makes it easy to find the non-helical sections I1, I2 or the loose helical sections I3, I4.

[0097] The technical scope of the present application also includes a method for manufacturing an optical device, including a cutting step of cutting an optical fiber 2D having a helical core and including a point where the core's rotation direction reverses, at or near that point. Here, the optical device manufactured by this manufacturing method may be an optical device including an optical fiber 2D' and another optical component (such as another optical fiber, a connector, or a fan-in / fan-out device) connected to the cut surface of the optical fiber 2D'. In this case, an optical device can be manufactured in which the optical fiber 2D' and another optical component are connected, and the optical device has low loss at the connection point. Alternatively, the optical device may be an optical fiber 2D' itself, which has a cut surface formed in preparation for connection with another optical component, manufactured by this manufacturing method. In this case, an optical device can be manufactured in which the connection point with the other optical component has low loss when connected to the other optical component.

[0098] The scope of the present application also includes a fiber bundle comprising a plurality of optical fibers. In this case, it is preferable that at least one optical fiber is the optical fiber 1 or optical fiber 2 described above, i.e., that at least one optical fiber has a non-spiral section I1 or a loose spiral section I3 at one end of the fiber bundle. This facilitates low-loss connection of a multifiber connector to one end of the fiber bundle. If at least one optical fiber also has a non-spiral section I2 or a loose spiral section I4 at the other end of the fiber bundle, it also facilitates low-loss connection of a multifiber connector to the other end of the fiber bundle. Furthermore, in this case, it is even more preferable that all optical fibers are the optical fiber 1 or optical fiber 2 described above, i.e., that all optical fibers have a non-spiral section I1 or a loose spiral section I3 at one end of the fiber bundle. This further facilitates low-loss connection of a multifiber connector to one end of the fiber bundle. For all optical fibers, if a non-helical section I2 or a loose helical section I4 is also arranged at the other end of the fiber bundle, it becomes even easier to connect a multi-core connector to the other end of the fiber bundle with low loss.

[0099] Finally, the number, arrangement, and design of the non-central cores 12, 22 in the cross section of the optical fibers 1, 2 are arbitrary. For example, a configuration in which four cores are arranged on the vertices of a square in the cross section of the optical fibers 1, 2 (see FIG. 7(a)) and a configuration in which eight cores are arranged on the vertices of a regular octagon in the cross section of the optical fibers 1, 2 (see FIG. 7(b)) are also included in the technical scope of the present application. Note that, although FIG. 7 illustrates an example of a configuration in which the central core 11, 21 does not exist, a configuration in which the central core 11, 21 exists is also included in the technical scope of the present application. [Explanation of symbols]

[0100] 1. Optical fiber 11 Central Core 12 Non-central core 13 Clad I0 Spiral section I1 First non-helical section I2 Second non-helical section 2. Optical Fiber 21 Central Core 22 Non-central core 23 Clad I3 First gentle spiral section I4 Second slow spiral section 3 Connectorized optical fiber 4. Optical Devices 41 Fan-in / fan-out devices

Claims

1. An optical fiber comprising at least one core and a cylindrical cladding surrounding the core, a helical section in which the core is helical; a first non-helical section in which the core is linear, the first non-helical section including a first end of the optical fiber, or a first loose helical section in which the number of helices per unit length of the core is fewer than that of the helical section, the first loose helical section including the first end of the optical fiber; In the spiral section, the center of the core is spaced apart from the center of the cladding, In the first non-helical section or the first loose helical section, a center of the core is spaced apart from a center of the cladding, The spiral section alternately includes a section in which the core turns clockwise and a section in which the core turns counterclockwise.

1. An optical fiber characterized by:

2. An optical fiber comprising at least one core and a cylindrical cladding surrounding the core, a helical section in which the core is helical; a first non-helical section in which the core is linear, the first non-helical section including a first end of the optical fiber, or a first loose helical section in which the number of helices per unit length of the core is fewer than that of the helical section, the first loose helical section including the first end of the optical fiber; In the spiral section, the center of the core is spaced apart from the center of the cladding, In the first non-helical section or the first loose helical section, a center of the core is spaced apart from a center of the cladding, An optical fiber, wherein the core is a single-mode core designed to transmit only a fundamental mode.

3. An optical fiber comprising at least one core and a cylindrical cladding surrounding the core, a helical section in which the core is helical; a first non-helical section in which the core is linear, the first non-helical section including a first end of the optical fiber, or a first loose helical section in which the number of helices per unit length of the core is fewer than that of the helical section, the first loose helical section including the first end of the optical fiber; In the spiral section, the center of the core is spaced apart from the center of the cladding, In the first non-helical section or the first loose helical section, a center of the core is spaced apart from a center of the cladding, does not include a connection point between the spiral section and the first non-spiral section or the first gentle spiral section, 1. An optical fiber characterized by:

4. An optical fiber comprising at least one core and a cylindrical cladding surrounding the core, a helical section in which the core is helical; a first non-helical section in which the core is linear, the first non-helical section including a first end of the optical fiber, or a first loose helical section in which the number of helices per unit length of the core is less than that of the helical section, the first loose helical section including the first end of the optical fiber; a second non-helical section in which the core is linear, the second non-helical section including a second end of the optical fiber, or a second loose-helical section in which the number of helices per unit length of the core is fewer than that of the helical section, the second non-helical section including the second end of the optical fiber; In the spiral section, the center of the core is spaced apart from the center of the cladding, In the first non-helical section or the first loose helical section, a center of the core is spaced apart from a center of the cladding, does not include a connection point between the spiral section and the second non-spiral section or the second gentle spiral section, 1. An optical fiber characterized by:

5. a first optical fiber including the helical section, and a second optical fiber including the first non-helical section or the first gentle helical section; a connection point between the first optical fiber and the second optical fiber; 3. The optical fiber according to claim 1 or 2.

6. the core further includes a second non-helical section in which the core is linear, the second non-helical section including the second end of the optical fiber, or a second loose-helical section in which the number of helices per unit length of the core is fewer than that of the helical section, the second non-helical section including the second end of the optical fiber; 3. The optical fiber according to claim 1 or 2.

7. a first optical fiber including the helical section, and a third optical fiber including the second non-helical section or the second gentle helical section; a connection point between the first optical fiber and the third optical fiber; 7. The optical fiber according to claim 6.

8. The length of the spiral section is longer than the length of the first non-helical section or the first gentle spiral section. The optical fiber according to any one of claims 1 to 4.

9. The length of the spiral section is shorter than the length of the first non-helical section or the first gentle spiral section. The optical fiber according to any one of claims 1 to 4.

10. the optical fiber is a multicore fiber having a plurality of cores, The core is any one of the plurality of cores. The optical fiber according to any one of claims 1 to 4.

11. An optical fiber having at least one core, a helical section in which the core is helical; a first non-helical section in which the core is linear, the first non-helical section including a first end of the optical fiber, or a first loose helical section in which the number of helices per unit length of the core is fewer than that of the helical section, the first loose helical section including the first end of the optical fiber; the optical fiber is a multicore fiber having a plurality of cores, the core is any one of the plurality of cores, an effective refractive index of the core in the first non-helical section or the first gentle helical section is higher than an effective refractive index of the core in the helical section; 1. An optical fiber characterized by:

12. The end of the optical fiber is attached to the structure in a non-rotatable or difficult to rotate manner. The optical fiber according to any one of claims 1 to 4.

13. The optical fiber according to claim 10; one or a pair of fan-in / fan-out devices connected to one or both ends of the optical fiber, An optical device characterized by:

14. A method for manufacturing an optical device, comprising a cutting step of cutting an optical fiber having at least one core, the optical fiber including a spiral section in which the core is spirally shaped, and a gentle spiral section in which the number of spirals per unit length of the core is fewer than that of the spiral section, at the gentle spiral section.

Images