JP5605630B2 - Optical fiber - Google Patents

Description

  The present invention relates to an optical fiber, and is particularly effective when used for a transmission medium of an optical transmission system.

  In an optical fiber communication system, transmission characteristics are limited by chromatic dispersion and nonlinear effects of optical fibers. Therefore, optical fibers having various structures have been developed and started to be widely used so as to reduce chromatic dispersion and nonlinear effects of the optical fiber. In recent years, an optical fiber having a hole in an optical fiber has been attracting high interest as a new optical transmission medium because it can exhibit various characteristics that cannot be achieved with conventional solid optical fibers.

  For example, the following Non-Patent Documents 1 and 2 report an optical fiber with an expanded effective cross-sectional area, which is an area in which a light wave propagates, in order to realize a low nonlinear optical transmission line using an optical fiber having a hole structure. ing.

Matsui et al., “Examination of effective area expansion of photonic crystal fiber”, Society of Electronics, Information and Communication Engineers Society Conference 2008, p. 275, Sep. 2008. K. Mukasa et al, "Comparisons of merits on wide-band transmission systems between using extremely improved solid SMFs with Aeff of 160 μm2 and loss of 0.175 dB / km and using large-Aeff holey fibers enabling transmission over 600 nm bandwidth", the Proceedings of OFC2008, OthR1, Feb. 2008.

  However, the conventional hole structure type optical fiber as described above has the following problems.

(1) Even in a hole-structured optical fiber, characteristics such as bending loss reduction, single mode operation area expansion, effective cross-sectional area expansion, and the like have a trade-off relationship with each other. There was a limit to the amount of expansion of the effective area.
(2) Since a hole structure type optical fiber requires a technique for controlling the hole structure in manufacturing, the manufacturing yield is lowered and the manufacturing cost is increased.
(3) Since the hole structure type optical fiber requires a special process such as hole sealing at the end face or adjustment of discharge conditions at the time of fusion, the connection cost becomes high. .
(4) Since the hole structure type optical fiber has a strong tendency to have a positive waveguide dispersion due to the hole structure, the wavelength dispersion in the communication wavelength band is larger than that of a conventional solid type optical fiber. turn into.

An optical fiber according to the present invention for solving the above-described problem is made of a solid material having a refractive index n2 smaller than that of a fiber body made of a solid material having a refractive index n1, and has a diameter smaller than the diameter D of the fiber body. a plurality of low-refractive-index bodies forming d surround the central portion of the fiber main body so as to surround the central portion, so that the central portion of the fiber main body constitutes a core region, and the fiber An optical fiber in which the peripheral portion of the main body constitutes a cladding region, and a relative refractive index difference Δ of a refractive index n2 of the low refractive index body with respect to a refractive index n1 of the fiber main body is −0.8% or less. There, the center distance (pitch) of the adjacent low refractive index member lambda, and, the low refractive index member the diameter d normalized rod diameter d / lambda normalized with the pitch lambda of, the cutoff wavelength is 12 0nm less and bending loss wavelength 1260~1625nm at radius 30mm bend is characterized in that 0.1dB / 100turns following conditions are satisfied.

The optical fiber according to the present invention is a low refractive index body made of a solid material having a refractive index n2 smaller than that of a fiber body made of a solid material having a refractive index n1 and having a diameter d smaller than the diameter D of the fiber body. Are embedded in a peripheral portion surrounding the central portion of the fiber body so as to surround the central portion, so that the central portion of the fiber main body constitutes a core region, and the peripheral portion of the fiber main body is clad. An optical fiber constituting a region, wherein a relative refractive index difference Δ of a refractive index n2 of the low refractive index body with respect to a refractive index n1 of the fiber body is −0.7% or less, and the adjacent low refractive index the distance between the centers of Ritsutai (pitch) lambda, and, the low refractive index member the diameter d normalized rod diameter d / lambda normalized by the pitch lambda of, the cutoff wavelength is 1260nm or less, and bending Bending loss wavelength 1260~1625nm in diameter 30mm is characterized in that it satisfies the following conditions shall 0.5dB / 100turns.

The optical fiber according to the present invention is a low refractive index body made of a solid material having a refractive index n2 smaller than that of a fiber body made of a solid material having a refractive index n1 and having a diameter d smaller than the diameter D of the fiber body. Are embedded in a peripheral portion surrounding the central portion of the fiber body so as to surround the central portion, so that the central portion of the fiber main body constitutes a core region, and the peripheral portion of the fiber main body is clad. An optical fiber constituting a region, wherein a relative refractive index difference Δ of a refractive index n2 of the low refractive index body with respect to a refractive index n1 of the fiber body is −0.7% or less, and the adjacent low refractive index the distance between the centers of Ritsutai (pitch) lambda, and, the low refractive index member the diameter d normalized rod diameter d / lambda normalized by the pitch lambda of, the cutoff wavelength is 1450nm or less, and bending Bending loss wavelength 1450~1625nm in diameter 30mm is characterized in that it satisfies the following conditions shall 0.1dB / 100turns.

The optical fiber according to the present invention is a low refractive index body made of a solid material having a refractive index n2 smaller than that of a fiber body made of a solid material having a refractive index n1 and having a diameter d smaller than the diameter D of the fiber body. Are embedded in a peripheral portion surrounding the central portion of the fiber body so as to surround the central portion, so that the central portion of the fiber main body constitutes a core region, and the peripheral portion of the fiber main body is clad. An optical fiber constituting a region, wherein a relative refractive index difference Δ of a refractive index n2 of the low refractive index body with respect to a refractive index n1 of the fiber body is −0.8% or less, and the adjacent low refractive index the distance between the centers of Ritsutai (pitch) lambda, and, the low refractive index member the diameter d normalized rod diameter d / lambda normalized by the pitch lambda of, the cutoff wavelength is 1450nm or less, and bending Bending loss wavelength 1450~1625nm in diameter 30mm is characterized in that it satisfies the following conditions shall 0.5dB / 100turns.

  Further, the optical fiber according to the present invention is the above-described optical fiber, in which the plurality of low refractive index bodies are disposed in the peripheral portion of the fiber body so as to surround the center portion of the fiber body in a regular polygonal shape or an annular shape. It is arranged.

  In the optical fiber according to the present invention, in the above-described optical fiber, a plurality of the low-refractive-index members are arranged in the peripheral portion of the fiber body so as to surround the central portion of the fiber body with three layers in the radial direction. It is characterized by being.

  Further, in the optical fiber according to the present invention, in the optical fiber described above, a plurality of the low-refractive-index bodies are arranged at the peripheral portion of the fiber main body so as to surround the central portion of the fiber main body in a regular hexagonal shape. It is characterized by being.

  The optical fiber according to the present invention is characterized in that, in the above-described optical fiber, the fiber main body is made of pure quartz, and the low refractive index body is made of quartz to which an impurity for reducing the refractive index is added. To do.

  The optical fiber according to the present invention is characterized in that, in the optical fiber described above, the fiber main body is made of quartz to which an impurity for increasing a refractive index is added, and the low refractive index body is made of pure quartz. To do.

  The optical fiber according to the present invention is the above-described optical fiber, wherein the fiber body is made of quartz to which an impurity for increasing a refractive index is added, and the low refractive index body is added with an impurity for reducing a refractive index. It is characterized by being made of quartz.

  According to the optical fiber according to the present invention, since a plurality of low refractive index bodies made of a solid material are discretely arranged in a fiber body made of a solid material, the optical fiber is equivalent to or better than a conventional optical fiber having a hole structure. The optical characteristics can be realized, and the hole control and special connection process at the time of manufacturing are not required, so that the yield can be improved and the cost can be reduced.

FIG. 1 is a cross-sectional view illustrating a schematic structure of a main embodiment of an optical fiber according to the present invention. FIG. 2 is a graph showing the relationship between the normalized rod diameter d / Λ and the normalized cutoff wavelength λc / Λ of the optical fiber according to the present invention and the conventional optical fiber having a hole structure. FIG. 3A is a graph showing a range of a structure in which low bending loss and single mode operation of an optical fiber according to the present invention with a relative refractive index difference Δ of −1.5% can be obtained, and FIG. It is a graph showing the range of the structure from which the low bending loss and single mode operation | movement of an optical fiber of a hole structure are obtained. FIG. 4 is a graph showing the range of the structure in which the low bending loss and single mode operation of the optical fiber according to the present invention can be obtained, and FIG. 4A shows the case where the relative refractive index difference Δ is −0.6%. 4B shows the case where the relative refractive index difference Δ is −0.7%, FIG. 4C shows the case where the relative refractive index difference Δ is −0.8%, and FIG. 4D shows the relative refractive index difference Δ. 4E is a case where the relative refractive index difference Δ is −1.5%, and FIG. 4F is a case where the relative refractive index difference Δ is −2.0%. is there. FIG. 5 is a graph showing the range of the structure in which the low bending loss and single mode operation of the optical fiber according to the present invention can be obtained, and FIG. 5A shows the case where the relative refractive index difference Δ is −0.6%. 5B shows the case where the relative refractive index difference Δ is −0.7%, FIG. 5C shows the case where the relative refractive index difference Δ is −0.8%, and FIG. 5D shows the relative refractive index difference Δ. Is a case where the relative refractive index difference Δ is −1.5%, and FIG. 5F is a case where the relative refractive index difference Δ is −2.0%. is there. FIG. 6 is a graph showing the range of the structure in which the low bending loss and single mode operation of the optical fiber according to the present invention can be obtained, and FIG. 6A shows the case where the relative refractive index difference Δ is −0.6%. 6B shows the case where the relative refractive index difference Δ is −0.7%, FIG. 6C shows the case where the relative refractive index difference Δ is −0.8%, and FIG. 6D shows the relative refractive index difference Δ. 6E is a case where the relative refractive index difference Δ is −1.5%, and FIG. 6F is a case where the relative refractive index difference Δ is −2.0%. is there. FIG. 7 is a graph showing the range of the structure in which the low bending loss and single mode operation of the optical fiber according to the present invention can be obtained, and FIG. 7A shows the case where the relative refractive index difference Δ is −0.6%. 7B shows a case where the relative refractive index difference Δ is −0.7%, FIG. 7C shows a case where the relative refractive index difference Δ is −0.8%, and FIG. 7D shows a relative refractive index difference Δ. Is −0.9%, FIG. 7E shows a case where the relative refractive index difference Δ is −1.5%, and FIG. 7F shows a case where the relative refractive index difference Δ is −2.0%. is there. FIG. 8 is a graph showing the relationship between the maximum effective area and the relative refractive index difference Δ under the low bending loss and single mode operation conditions of the optical fiber according to the present invention. FIG. 9 is a graph showing the range of the structure in which the low bending loss and single mode operation of the optical fiber according to the present invention in which the number of layers of the low refractive index body is 3 can be obtained. FIG. 10 is a graph showing the wavelength dispersion characteristics of the optical fiber according to the present invention.

  Embodiments of an optical fiber according to the present invention will be described below with reference to FIGS. 1 to 5, but the present invention is not limited to only the following embodiments described with reference to the drawings.

[Main embodiments]
As shown in FIG. 1, the optical fiber 10 according to the present embodiment is made of a solid material having a refractive index n2 (n1> n2) smaller than the fiber body (background) 11 made of a solid material having a refractive index n1. A low-refractive index body (rod) 12 having a diameter d (D> d) smaller than the diameter D of the fiber main body 11 is a center portion Ec of the fiber main body 11 (inside the inner dotted line in FIG. 1). A plurality of layers (steps) in the radial direction (in this embodiment, five layers (steps)) in the peripheral portion Ea (in FIG. 1, the range between the inside of the outer dotted line and the outer side of the inner dotted line) By embedding a plurality of regular polygonal shapes (regular hexagonal shapes in this embodiment) so as to surround the central portion Ec, the central portion Ec of the fiber main body 11 constitutes a core region, and Peripheral part Ea is Constitute the area. In FIG. 1, Λ is the distance (pitch) between the centers of the adjacent low refractive index bodies (rods) 12.

  Here, when the fiber body 11 is made of pure quartz, the solid material is added with impurities (for example, fluorine (F), boron (B), etc.) that reduce the refractive index of the low refractive index body 12. When the low refractive index body 12 is pure quartz, the fiber body 11 is made of quartz to which an impurity that increases the refractive index (for example, germanium (Ge), aluminum (Al), etc.) is added. The fiber body 11 may be made of quartz added with the refractive index increasing impurity, and the low refractive index body 12 may be made of quartz added with the refractive index reducing impurity.

  In the optical fiber 10 according to this embodiment, since the effective refractive index in the peripheral portion (cladding region) Ea is lower than that in the central portion (core region) Ec, the light wave incident on the central portion (core region) Ec. Will be totally reflected and propagate inside.

  For this reason, in the optical fiber 10 according to the present embodiment, since the waveguide is formed with a solid structure without forming a hole structure, a process such as hole control is not required at the time of manufacture, and the connection is made. No special connection process is required.

  FIG. 2 is a graph showing the relationship between the normalized rod diameter d / Λ and the normalized cutoff wavelength λc / Λ of the optical fiber according to the present invention and the conventional optical fiber having a hole structure. In FIG. 2, the horizontal axis represents the normalized rod diameter d / Λ obtained by normalizing the diameter d of the rod 12 with the pitch Λ, and the vertical axis represents the normalized cutoff wavelength λc obtained by normalizing the cutoff wavelength λc with the pitch Λ. / Λ. Δ is the relative refractive index difference of the rod 12 with respect to the fiber body 11.

  As can be seen from FIG. 2, the optical fiber according to the present invention has a single wide wavelength region as in the case of a conventional optical fiber having a hole structure, regardless of the value of the relative refractive index difference Δ. It was recognized that mode operation could be realized. Further, it was found that the cutoff wavelength λc of the optical fiber according to the present invention becomes shorter even in the same structure as the relative refractive index difference Δ is decreased. Therefore, the optical fiber according to the present invention can obtain optical characteristics equivalent to or better than those of conventional optical fibers having a hole structure in a wider design range by setting the relative refractive index difference Δ to an appropriate value. Admitted.

FIG. 3 is a graph representing the range of structures where low bending loss and single mode operation of the optical fiber can be obtained. FIG. 3A shows a case of an optical fiber according to the present invention in which the relative refractive index difference Δ is −1.5%, and FIG. 3B shows a case of a conventional optical fiber having a hole structure. In FIG. 3, the bending loss condition is set to be 0.1 dB or less per 100 turns when the bending loss BL _FM of the fundamental mode is 1260 to 1625 nm and the bending radius is 30 mm. The evaluation conditions for the single mode operation were set to 1 dB / m or more when the bending loss BL _HOM in the first higher-order mode was 1260 to 1625 nm and the bending radius was 140 mm.

First, in an optical fiber having a conventional hole structure, as can be seen from FIG. 3B, the center-to-center distance (pitch) Λ of adjacent holes (diameter d) is 10.7 μm or less, and the normalized hole diameter d / Λ It was confirmed that the above-described conditions can be satisfied when the structure is smaller than 0.5. From the non-patent document 1, the maximum effective area obtained under these conditions is about 130 μm ² at a wavelength of 1550 nm.

On the other hand, in the optical fiber according to the present invention, as can be seen from FIG. 3A, when the pitch Λ is 11.8 μm or less and the normalized rod diameter d / Λ is 0.64 or less, the above-described conditions can be satisfied. Was recognized. The effective area obtained under these conditions is about 150 μm ² at a wavelength of 1550 nm.

  Therefore, the optical fiber according to the present invention can increase the pitch Λ that satisfies the above-described conditions, compared with the conventional optical fiber having a hole structure, and thus can increase the core area and the effective area. It was.

FIG. 4 is a graph representing the range of structures where low bending loss and single mode operation of the optical fiber can be obtained. FIG. 4A shows the case of the optical fiber according to the present invention in which the relative refractive index difference Δ is −0.6%, and FIG. 4B shows the light according to the present invention in which the relative refractive index difference Δ is −0.7%. FIG. 4C shows the case of the optical fiber according to the present invention in which the relative refractive index difference Δ is −0.8%, and FIG. 4D shows the relative refractive index difference Δ of −0.9%. 4E shows the case of the optical fiber according to the present invention in which the relative refractive index difference Δ is −1.5%, and FIG. 4F shows the relative refractive index difference Δ. This is the case of the optical fiber according to the present invention with -2.0%. In FIG. 4, the bending loss conditions are as follows. The bending loss BL _{FM in} the basic mode is 1260 to 1625 nm in wavelength and the bending radius is 30 mm. It was set to 0.1 dB or less per 100 turns satisfying 652. The evaluation conditions for the single mode operation were set to 1 dB / m or more when the bending loss BL _HOM in the first higher-order mode was 1260 to 1625 nm and the bending radius was 140 mm.

  Here, Table 1 shown below shows an optimum structure under the conditions of FIG. HF in Table 1 assumes a conventional optical fiber having a hole structure. In the optical fiber according to the present invention, as can be seen from Table 1, the relative refractive index difference Δ is -0.6%, -0.7%, -0.8%, -0.9%, -1.5. % And -2.0%, the distance between rods of 9.5 μm or more can be realized, and the relative refractive index difference Δ is set to −0.8% or less, so that light with a conventional hole structure can be realized. It was found that a large effective area can be realized compared with the fiber.

FIG. 5 is a graph showing the range of structures where low bending loss and single mode operation of the optical fiber can be obtained. FIG. 5A shows the case of the optical fiber according to the present invention in which the relative refractive index difference Δ is −0.6%, and FIG. 5B shows the light according to the present invention in which the relative refractive index difference Δ is −0.7%. FIG. 5C shows the case of the optical fiber according to the present invention in which the relative refractive index difference Δ is −0.8%, and FIG. 5D shows the relative refractive index difference Δ of −0.9%. 5E shows the case of the optical fiber according to the present invention in which the relative refractive index difference Δ is −1.5%, and FIG. 5F shows the relative refractive index difference Δ. This is the case of the optical fiber according to the present invention with -2.0%. In FIG. 5, the bending loss condition is that the fundamental mode bending loss BL _FM is ITU-T Recommendation G.3 when the wavelength is 1260 to 1625 nm and the bending radius is 30 mm. 0.5 dB or less per 100 turns satisfying 655 and 656. The conditions for evaluating the single mode operation were the same as those in FIG.

  Here, Table 2 shown below shows the optimum structure under the conditions shown in FIG. HF in Table 2 assumes a conventional hole-structured optical fiber. In the optical fiber according to the present invention, as can be seen from Table 2, the relative refractive index difference Δ is -0.6%, -0.7%, -0.8%, -0.9%, -1. In both cases of 5% and -2.0%, a distance between rods of 10 μm or more can be realized, and a relative refractive index difference Δ is set to −0.7% or less, so that an optical fiber having a conventional hole structure is used. It was confirmed that a large effective area can be realized as compared with.

FIG. 6 is a graph representing the range of structures that provide low bending loss and single mode operation of the optical fiber. FIG. 6A shows the case of the optical fiber according to the present invention in which the relative refractive index difference Δ is −0.6%, and FIG. 6B shows the light according to the present invention in which the relative refractive index difference Δ is −0.7%. FIG. 6C shows the case of the optical fiber according to the present invention in which the relative refractive index difference Δ is −0.8%, and FIG. 6D shows the relative refractive index difference Δ of −0.9%. 6E shows the case of the optical fiber according to the present invention in which the relative refractive index difference Δ is −1.5%, and FIG. 6F shows the relative refractive index difference Δ. This is the case of the optical fiber according to the present invention with -2.0%. In FIG. 6, the bending loss condition is set to 0.1 dB or less per 100 turns when the bending loss BL _FM of the fundamental mode is 1450 to 1625 nm and the bending radius is 30 mm. The evaluation conditions for the single mode operation were 1 dB / m or more when the bending loss BL _HOM in the first higher-order mode was 1450 to 1625 nm and the bending radius was 140 mm.

  Here, Table 3 shown below shows the optimum structure under the conditions of FIG. HF in Table 3 assumes a conventional optical fiber having a hole structure. In the optical fiber according to the present invention, as can be seen from Table 3, the relative refractive index difference Δ is -0.6%, -0.7%, -0.8%, -0.9%, -1.5. % And −2.0%, the distance between rods of 11 μm or more can be realized, and the relative refractive index difference Δ is −0.7% or less. In comparison, it was found that a large effective area can be realized.

FIG. 7 is a graph showing the range of structures where low bending loss and single mode operation of the optical fiber can be obtained. FIG. 7A shows the case of the optical fiber according to the present invention in which the relative refractive index difference Δ is −0.6%, and FIG. 7B shows the light according to the present invention in which the relative refractive index difference Δ is −0.7%. FIG. 7C shows a case of an optical fiber according to the present invention in which the relative refractive index difference Δ is −0.8%, and FIG. 7D shows a relative refractive index difference Δ of −0.9%. FIG. 7E shows the case of the optical fiber according to the present invention in which the relative refractive index difference Δ is −1.5%, and FIG. 7F shows the relative refractive index difference Δ. This is the case of the optical fiber according to the present invention with -2.0%. In FIG. 7, the bending loss condition was set to 0.5 dB or less per 100 turns when the bending loss BL _FM of the fundamental mode was 1450 to 1625 nm and the bending radius was 30 mm. The conditions for single mode operation evaluation were the same as those in FIG.

  Here, Table 4 shown below shows the optimum structure under the conditions of FIG. HF in Table 4 assumes a conventional optical fiber having a hole structure. In the optical fiber according to the present invention, as can be seen from Table 4, the relative refractive index difference Δ is -0.6%, -0.7%, -0.8%, -0.9%, -1.5. % And -2.0%, the distance between the rods of 10 μm or more can be realized, and the relative refractive index difference Δ is set to −0.8% or less. In comparison, it was found that a large effective area can be realized.

  From Tables 3 and 4, it is preferable that the relative refractive index difference Δ is −0.8% or less because an effective area larger than that of the conventional hole-structured optical fiber can be obtained and the nonlinear effect can be further suppressed. On the other hand, when the relative refractive index difference Δ is -0.6 to -0.8%, the amount of impurities added can be suppressed, so that an effective area equivalent to that of a conventional hole-structured optical fiber can be obtained and stable. Therefore, it is preferable to realize the manufacturability and connectivity.

FIG. 8 is a graph showing the relationship between the maximum effective area and the relative refractive index difference Δ under the low bending loss and single mode operation conditions of the optical fiber according to the present invention. In FIG. 8, the horizontal axis represents the relative refractive index difference Δ, and the vertical axis represents the maximum effective area obtained under the conditions of low bending loss and single mode operation (for example, in the case of FIG. 3A, the pitch Λ = 11.8 μm, normalized rod diameter d / Λ = 0.64, and effective area is about 150 μm ² ). The target wavelength bands were 1260 to 1625 nm and 1450 to 1625 nm, and the bending loss and single mode operation conditions were the same as those shown in FIG.

As can be seen from FIG. 8, when the relative refractive index difference Δ is −0.7% or less, the optical fiber according to the present invention can realize an effective area of 130 μm ² or more while satisfying the above conditions at wavelengths of 1260 to 1625 nm. When the relative refractive index difference Δ is −0.5% or less, it was confirmed that an effective area of 150 μm ² or more can be realized while satisfying the above conditions at a wavelength of 1450 to 1625 nm. Therefore, it was confirmed that the optical fiber according to the present invention can obtain optical characteristics equal to or higher than those of the conventional optical fiber having a hole structure.

  So far, the description has been given using the optical fiber in which the plurality of low refractive index bodies 12 surround the central portion of the fiber main body 11 in a regular hexagonal shape with five layers in the radial direction, but the plurality of low refractive index bodies 12 include the fiber main body 11. An optical fiber that surrounds the central portion of the optical fiber in a radial direction with three layers in a regular hexagonal shape is more preferable because an outer diameter equivalent to that of a conventional optical fiber can be realized and compatibility with existing products and systems can be obtained.

FIG. 9 shows a structure in which a low bending loss and a single mode operation of an optical fiber according to the present invention are obtained in which a plurality of low-refractive-index bodies 12 surround a central portion of the fiber body 11 in a regular hexagonal shape with three layers in the radial direction It is a graph showing the range of. The relative refractive index difference Δ was set to −0.6%, and the bending loss conditions were set to 0.5 dB or less per 100 turns when the bending loss BL _FM of the fundamental mode was 1450 to 1625 nm and the bending radius was 30 mm. The evaluation conditions for the single mode operation were 1 dB / m or more when the bending loss BL _HOM in the first higher-order mode was 1450 to 1625 nm and the bending radius was 140 mm.

  As can be seen from FIG. 9, the distance between the rods can be set to 13 μm or more, and it was recognized that the value exceeding 12.7 μm shown in Table 4 can be realized. In the case of five layers, the width to the outermost low refractive index body (2Λ × number of layers + d) is 136.6 μm, and the outer diameter of the existing optical fiber is 125 μm. It was found that it cannot be manufactured with the same outer diameter as the optical fiber. In the case of three layers, since it is about 87.6 μm, it was confirmed that it can be manufactured with the same outer diameter as that of a conventional optical fiber from the viewpoint of manufacturing.

  Here, Table 5 shown below shows the optimum structure for the relative refractive index difference Δ and the maximum effective area that can be realized. In the optical fiber according to the present invention, as can be seen from Table 5, it is recognized that a large effective area can be realized by setting the relative refractive index difference Δ to −0.8% or less as compared with the case of five layers. Therefore, the nonlinear effect can be further suppressed, which is preferable.

  If the number of layers of the low refractive index is smaller than 3, it is not preferable because the confinement in the fundamental mode becomes weak and the confinement loss increases rapidly.

  FIG. 10 is a graph showing the wavelength dispersion characteristics of the optical fiber according to the present invention. The optical fiber at this time has a pitch Λ = 11.6 μm, a normalized rod diameter d / Λ = 0.64, and a relative refractive index difference Δ = −1.5%.

  As can be seen from FIG. 10, in the optical fiber according to the present invention, when the wavelength was 1550 nm, the chromatic dispersion was 21 ps / nm / km, and the wavelength characteristics had the same tendency as the material dispersion. On the other hand, according to Non-Patent Document 1, the conventional optical fiber having a hole structure has a chromatic dispersion of 27 ps / nm / km. From this, it can be said that the optical fiber according to the present invention can obtain smaller wavelength dispersion than the conventional optical fiber having a hole structure. The reason for this is considered that the optical fiber of the hole structure gives positive waveguide dispersion, whereas the optical fiber according to the present invention has no hole, so that the waveguide dispersion is reduced. .

  Therefore, the optical fiber according to the present invention can obtain a large effective area with a smaller chromatic dispersion than a conventional optical fiber having a hole structure, and can reduce characteristic deterioration due to chromatic dispersion and nonlinear effects in an optical transmission line. Admitted.

  In addition, as described above, the optical fiber according to the present invention can be composed of only a silica-based material without using holes, so that it is special in connection with an optical fiber having a conventional hole structure. A process is unnecessary, and a hole control technique at the time of manufacture is also unnecessary.

  Therefore, according to the optical fiber according to the present invention, it is possible to realize optical characteristics equivalent to or better than those of the conventional optical fiber having a hole structure, and it becomes unnecessary to control the hole at the time of manufacturing and a special connection process, thereby improving the yield. Cost can be reduced.

[Other Embodiments]
In the above-described embodiment, a plurality of low-refractive-index bodies (rods) 12 are formed in the periphery Ea of the fiber body 11 so as to surround the center Ec in a regular hexagonal shape with five layers (steps) in the radial direction. The case of the embedded optical fiber 10 has been described. However, the present invention is not limited to this, and the low refractive index body 12 is formed in an equilateral triangular shape with one layer (step) or more in the radial direction in the peripheral portion Ea of the fiber body 11. If the optical fiber 10 is embedded in a plurality so as to surround the central portion Ec in the above-described regular polygon or annular shape, the same operational effects as those of the above-described embodiment can be obtained.

  The optical fiber according to the present invention can realize optical characteristics equivalent to or better than those of conventional optical fibers having a hole structure, and can improve yield and reduce costs. Can be used extremely beneficially.

10 Optical fiber 11 Fiber body (background)
12 Low refractive index body (rod)
Ec center (core region)
Ea peripheral part (cladding region)

Claims (10)

A low refractive index body made of a solid material having a refractive index n2 smaller than that of the fiber body made of a solid material having a refractive index n1 and having a diameter d smaller than the diameter D of the fiber body surrounds the central portion of the fiber body. A plurality of optical fibers are embedded in the peripheral portion so as to surround the central portion, so that the central portion of the fiber body constitutes a core region, and the peripheral portion of the fiber body constitutes a cladding region. And
The relative refractive index difference Δ of the refractive index n2 of the low refractive index body with respect to the refractive index n1 of the fiber body is −0.8% or less,
A distance (pitch) Λ between adjacent low-refractive index bodies and a normalized rod diameter d / Λ obtained by normalizing the diameter d of the low-refractive index bodies by the pitch Λ have a cutoff wavelength of 1260 nm or less , In addition , an optical fiber characterized in that a bending loss at a wavelength of 1260 to 1625 nm at a bending radius of 30 mm satisfies a condition of 0.1 dB / 100 turn or less. A low refractive index body made of a solid material having a refractive index n2 smaller than that of the fiber body made of a solid material having a refractive index n1 and having a diameter d smaller than the diameter D of the fiber body surrounds the central portion of the fiber body. A plurality of optical fibers are embedded in the peripheral portion so as to surround the central portion, so that the central portion of the fiber body constitutes a core region, and the peripheral portion of the fiber body constitutes a cladding region. And
The relative refractive index difference Δ of the refractive index n2 of the low refractive index body with respect to the refractive index n1 of the fiber body is −0.7% or less,
A distance (pitch) Λ between adjacent low-refractive index bodies and a normalized rod diameter d / Λ obtained by normalizing the diameter d of the low-refractive index bodies by the pitch Λ have a cutoff wavelength of 1260 nm or less , and, bending the optical fiber, wherein a bending loss wavelength 1260~1625nm at radius 30mm is of 0.5dB / 100turns following conditions are satisfied. A low refractive index body made of a solid material having a refractive index n2 smaller than that of the fiber body made of a solid material having a refractive index n1 and having a diameter d smaller than the diameter D of the fiber body surrounds the central portion of the fiber body. A plurality of optical fibers are embedded in the peripheral portion so as to surround the central portion, so that the central portion of the fiber body constitutes a core region, and the peripheral portion of the fiber body constitutes a cladding region. And
The relative refractive index difference Δ of the refractive index n2 of the low refractive index body with respect to the refractive index n1 of the fiber body is −0.7% or less,
A distance (pitch) Λ between adjacent low-refractive index bodies and a normalized rod diameter d / Λ obtained by normalizing the diameter d of the low-refractive index bodies by the pitch Λ have a cutoff wavelength of 1450 nm or less , and, bending the optical fiber, wherein a bending loss wavelength 1450~1625nm at radius 30mm is of 0.1dB / 100turns following conditions are satisfied. A low refractive index body made of a solid material having a refractive index n2 smaller than that of the fiber body made of a solid material having a refractive index n1 and having a diameter d smaller than the diameter D of the fiber body surrounds the central portion of the fiber body. A plurality of optical fibers are embedded in the peripheral portion so as to surround the central portion, so that the central portion of the fiber body constitutes a core region, and the peripheral portion of the fiber body constitutes a cladding region. And
The relative refractive index difference Δ of the refractive index n2 of the low refractive index body with respect to the refractive index n1 of the fiber body is −0.8% or less,
A distance (pitch) Λ between adjacent low-refractive index bodies and a normalized rod diameter d / Λ obtained by normalizing the diameter d of the low-refractive index bodies by the pitch Λ have a cutoff wavelength of 1450 nm or less , and, bending the optical fiber, wherein a bending loss wavelength 1450~1625nm at radius 30mm is of 0.5dB / 100turns following conditions are satisfied. In the optical fiber according to any one of claims 1 to 4 ,
The optical fiber, wherein the plurality of low-refractive-index members are arranged at the peripheral portion of the fiber body so as to surround the center of the fiber body in a regular polygonal shape or an annular shape. In the optical fiber according to any one of claims 1 to 5 ,
A plurality of the low-refractive-index members are arranged at the peripheral portion of the fiber body so as to surround the center of the fiber body with three layers in the radial direction. The optical fiber according to claim 6 , wherein
A plurality of the low refractive index bodies are arranged at the peripheral portion of the fiber body so as to surround the center portion of the fiber body in a regular hexagonal shape. The optical fiber according to any one of claims 1 to 7 ,
The fiber body is made of pure quartz,
The optical fiber, wherein the low refractive index body is made of quartz to which an impurity for reducing the refractive index is added. The optical fiber according to any one of claims 1 to 7 ,
The fiber body is made of quartz doped with impurities that increase the refractive index;
The optical fiber, wherein the low refractive index body is made of pure quartz. The optical fiber according to any one of claims 1 to 7 ,
The fiber body is made of quartz doped with impurities that increase the refractive index;
The optical fiber, wherein the low refractive index body is made of quartz to which an impurity for reducing the refractive index is added.

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