JP2014006374A - Optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-mode optical fiber that is an optical fiber for transmission, using a mode multiplex transmission technique, the optical fiber being able to hold propagation mode numbers 2, 4, and 6 in a broad band.SOLUTION: An optical fiber according to the invention is an optical fiber that has a plurality of holes in a cross-section of the fiber. If a hollow diameter is d and a hole interval is Λ: Λ<13.6 μm, 0.57<d/Λ<0.70, and a propagation mode number is 2; Λ<13.9 μm, 0.73<d/Λ<0.80, and the propagation mode number is 4; or Λ<13.8 μm, 0.82<d/Λ<0.88, and the propagation mode number is 6.

Description

  The present invention relates to an optical fiber using a higher-order mode by a communication multimode optical fiber.

  In optical fiber communication systems, nonlinear effects and fiber fuses that occur in optical fibers become a problem, and transmission capacity and long distance are limited. In order to alleviate these restrictions, it is necessary to reduce the density of light guided to the optical fiber. As shown in Non-Patent Documents 1 and 2, a large core fiber has been studied.

  However, bending loss reduction, single mode operation area expansion, and effective area expansion are in a trade-off relationship with each other, and there is a problem that the amount of effective area expansion under certain conditions is limited. In order to overcome these limitations, a mode multiplexing technique using a higher-order mode that has been a signal deterioration factor has been studied (for example, see Non-Patent Documents 3 and 4).

  The mode multiplexing technology uses a multimode optical fiber as a transmission medium and can increase the transmission capacity and eliminate the need for the single-mode operating conditions that were the limiting factors of the large core optical fiber described above. It is also a feature that is possible.

  In a mode multiplex transmission system, each transmitted signal propagates through a different propagation mode, so all modes must achieve the desired bending loss. For example, ITU-T G.I. The recommended bending loss at 652 is 0.1 dB / 100 turn or less at a bending radius of 30 mm. Further, in order to realize mode multiplexing transmission using N signals, the optical fiber needs to have at least N or more propagation modes. Further, the effective area of each mode is preferably large in order to reduce the nonlinear effect generated in the optical fiber. So far, the use of optical fibers with a limited number of modes has been proposed (for example, Non-Patent Documents 5 and 6).

T.A. Matsui, et al. , "Applicability of Photonic Crystal Fiber With Uniform Air-Hole Structure to High-Speed, Wide-Band Transmission OverTownConversion. Lightwave Technol. 27, 5410-5416, 2009. K. Mukasa, et al. , "Comparisons of merits on wide-band transmission systems between using extremely improved solid SMFs with Aeff of 160μm2 and loss of 0.175dB / km and using large-Aeff holey fibers enabling transmission over 600 nm bandwidth," the Proceedings of OFC2008, OthR1 , Feb. 2008. N. Hanzawa, et al. , “Demonstration of mode-division multiplexing transmission 10 km two-mode fiber with mode coupler,” the Proceedings of OFC 4, 2011. 2011. R. Ryf, et al. “Mode-Division Multiplexing Over 96 km of Few-Mode Fiber Using Coherent 6 × 6 MIMO Processing,” J. Lightwave Technol. 30, 521-531, 2012. P. Sillard, et al. "Few-Mode Fiber for Uncoupled Mode-Division Multiplexing Transmissions," the Proceedings of ECOC2011, Tu. 5. LeCervin. 7, Sep. 2011. L. G. -Nielsen, et al. “Few Mode Transmission Fiber with low DGD, low Mode Coupling and Low Loss,” the Processing of OFC2012, PDP5A. 1, Mar. 2012. K. Mukasa, et al. , “Optimizing 2 mode fibers with Aeff of 170 μm2 for LP01 mode and studying a possible of rearing endlessly 2 mode of operation.” 16, Mar. 2012. K. Saitoh, et al. , “Empirical relations for simple design of photonic crystal fibers,” Opt. Express 13, 267-274, 2005. D. Marcuse, “Field deformation and lost caused by civil of optical fibers,” J. Am. Opt. Soc. Am 66, 311-320, 1976.

  However, since the conventional multimode optical fiber has applicable conditions for the number of modes and the used wavelength band, there is a limit to applicable mode multiplex transmission.

  Therefore, the present invention has been made in view of the above problems, and is an optical fiber for transmission using mode multiplexing transmission technology, in which the number of modes is 2, 4, and 6, and the number of propagation modes is maintained in a wide band. The present invention provides a multimode optical fiber that can be used.

  The present invention solves this problem by designing the hole structure of a multimode optical fiber having a plurality of holes in mode multiplexing transmission to the proposed parameters.

  An optical fiber according to the present invention is an optical fiber in which a step-type refractive index profile is equivalently formed by having a plurality of holes in the cross section of the fiber, and for an operating wavelength band of 1530 nm to 1625 nm. The diameter d of the holes and the interval Λ of the holes are Λ <13.6 μm, 0.57 <d / Λ <0.70, and the number of propagation modes is 2.

  An optical fiber according to the present invention is an optical fiber in which a step-type refractive index profile is equivalently formed by having a plurality of holes in the cross section of the fiber, and is used for a wavelength range of 1460 nm to 1625 nm. The diameter d of the holes and the interval Λ of the holes are Λ <13.0 μm, 0.57 <d / Λ <0.70, and the number of propagation modes is 2.

  An optical fiber according to the present invention is an optical fiber in which a step-type refractive index profile is equivalently formed by having a plurality of holes in the cross section of the fiber, and for an operating wavelength band of 1260 nm to 1625 nm. The diameter d of the holes and the interval Λ of the holes are Λ <11.8 μm, 0.57 <d / Λ <0.69, and the number of propagation modes is 2.

  An optical fiber according to the present invention is an optical fiber in which a step-type refractive index distribution is equivalently formed by having a plurality of holes in the cross section of the fiber, and for an operating wavelength band of 980 nm to 1625 nm. The diameter d of the holes and the interval Λ of the holes are Λ <10.0 μm, 0.57 <d / Λ <0.68, and the number of propagation modes is 2.

  An optical fiber according to the present invention is an optical fiber in which a step-type refractive index profile is equivalently formed by having a plurality of holes in the cross section of the fiber, and for an operating wavelength band of 1530 nm to 1625 nm. The diameter d of the holes and the interval Λ of the holes are Λ <13.9 μm, 0.73 <d / Λ <0.80, and the number of propagation modes is 4.

  An optical fiber according to the present invention is an optical fiber in which a step-type refractive index profile is equivalently formed by having a plurality of holes in the cross section of the fiber, and is used for a wavelength range of 1460 nm to 1625 nm. The diameter d of the holes and the interval Λ of the holes are Λ <13.5 μm, 0.73 <d / Λ <0.80, and the number of propagation modes is 4.

  An optical fiber according to the present invention is an optical fiber in which a step-type refractive index profile is equivalently formed by having a plurality of holes in the cross section of the fiber, and for an operating wavelength band of 1260 nm to 1625 nm. The diameter d of the holes and the interval Λ of the holes are Λ <12.3 μm, 0.73 <d / Λ <0.80, and the number of propagation modes is four.

  An optical fiber according to the present invention is an optical fiber in which a step-type refractive index distribution is equivalently formed by having a plurality of holes in the cross section of the fiber, and for an operating wavelength band of 980 nm to 1625 nm. The diameter d of the holes and the interval Λ of the holes are Λ <10.5 μm, 0.73 <d / Λ <0.78, and the number of propagation modes is four.

  An optical fiber according to the present invention is an optical fiber in which a step-type refractive index profile is equivalently formed by having a plurality of holes in the cross section of the fiber, and for an operating wavelength band of 1530 nm to 1625 nm. The hole diameter d and the gap interval Λ are Λ <13.8 μm, 0.82 <d / Λ <0.88, and the number of propagation modes is six.

  An optical fiber according to the present invention is an optical fiber in which a step-type refractive index profile is equivalently formed by having a plurality of holes in the cross section of the fiber, and is used for a wavelength range of 1460 nm to 1625 nm. The diameter d of the holes and the interval Λ of the holes are Λ <13.3 μm, 0.82 <d / Λ <0.88, and the number of propagation modes is 6.

  An optical fiber according to the present invention is an optical fiber in which a step-type refractive index profile is equivalently formed by having a plurality of holes in the cross section of the fiber, and for an operating wavelength band of 1260 nm to 1625 nm. The diameter d of the holes and the interval Λ of the holes are Λ <12.1 μm, 0.82 <d / Λ <0.87, and the number of propagation modes is 6.

  An optical fiber according to the present invention is an optical fiber in which a step-type refractive index distribution is equivalently formed by having a plurality of holes in the cross section of the fiber, and for an operating wavelength band of 980 nm to 1625 nm. The diameter d of the holes and the interval Λ of the holes are Λ <10.2 μm, 0.82 <d / Λ <0.86, and the number of propagation modes is 6.

  According to the present invention, a transmission optical fiber using a mode multiplexing transmission technique can maintain the number of modes in 2, 4 and 6 and the number of propagation modes in a wide band. Thereby, the optical fiber of the present invention can expand the transmission capacity and the wavelength band.

The schematic which shows the cross-section of the photonic crystal fiber which concerns on this embodiment is shown. In the use wavelength band 1530 to 1625 nm according to the first embodiment, the number of propagation modes is set to 2, and regions of d and d / Λ for satisfying a desired bending loss are shown. In the use wavelength band of 1460 to 1625 nm according to the second embodiment, the number of propagation modes is set to 2, and regions of d and d / Λ for satisfying a desired bending loss are shown. In the use wavelength band of 1260 to 1625 nm according to the third embodiment, the number of propagation modes is set to 2, and regions of d and d / Λ for satisfying a desired bending loss are shown. In the use wavelength band of 980 to 1625 nm according to the fourth embodiment, the number of propagation modes is set to 2, and regions of d and d / Λ for satisfying a desired bending loss are shown. In the use wavelength band 1530 to 1625 nm according to the fifth embodiment, the number of propagation modes is set to 4, and regions of d and d / Λ for satisfying a desired bending loss are shown. In the use wavelength band of 1460 to 1625 nm according to the sixth embodiment, the number of propagation modes is set to 4, and regions of d and d / Λ for satisfying a desired bending loss are shown. In the use wavelength band of 1260 to 1625 nm according to the seventh embodiment, the number of propagation modes is set to 4, and regions of d and d / Λ for satisfying a desired bending loss are shown. In the use wavelength band of 980 to 1625 nm according to the eighth embodiment, the number of propagation modes is set to 4, and regions of d and d / Λ for satisfying a desired bending loss are shown. In the use wavelength band 1530-1625nm which concerns on Embodiment 9, the number of propagation modes is set to 6, and the area | region of d and d / Λ for satisfying a desired bending loss is shown. In the use wavelength band of 1460 to 1625 nm according to the tenth embodiment, the number of propagation modes is set to 6, and regions of d and d / Λ for satisfying a desired bending loss are shown. In the use wavelength band of 1260 to 1625 nm according to the eleventh embodiment, the number of propagation modes is 6, and regions of d and d / Λ for satisfying a desired bending loss are shown. In the wavelength band 980 to 1625 nm according to the twelfth embodiment, the number of propagation modes is set to 6, and regions of d and d / Λ for satisfying a desired bending loss are shown.

  Embodiments of the present invention will be described with reference to the drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments.

  FIG. 1 is an example of a cross-sectional view of an optical fiber according to the present embodiment. The optical fiber according to the present embodiment is a photonic crystal fiber having a plurality of holes 12 in a fiber formed of a uniform material such as quartz glass 11. Here, the diameter of the holes 12 formed in a cross section perpendicular to the major axis direction is d, and the interval between the holes 12 is Λ. As described in Non-Patent Document 8, the refractive index distribution that can be regarded as equivalent to a photonic crystal fiber having a uniform hole structure, that is, an effective refractive index distribution is a step type as shown in the lower part of FIG.

  In the present embodiment, the diameters d of the air holes 12 are equal and arranged at equal intervals. For example, the first layer closest to the central axis of the optical fiber is provided with six holes 12 with a spacing Λ, and the second layer has a spacing of Λ with the first layer of holes 12. Twelve holes 12 are provided so that the distance between the holes 12 in the second layer is Λ, and the hole in the second layer is connected to the holes 12 in the second layer. Eighteen holes 12 are provided so that the distance is Λ and the distance between the holes 12 in the third layer is Λ.

  In the present embodiment, the first layer closest to the central axis of the optical fiber is disposed on a concentric circle whose distance from the long axis of the optical fiber is equal to the interval Λ. In this embodiment, as an example, six holes 12 are provided in the first layer closest to the long axis of the optical fiber, and twelve holes 12 are provided in the second layer next to the long axis of the optical fiber. In the example, 18 holes 12 are provided in the third layer farthest from the long axis of the optical fiber. However, the present invention is not limited to this as long as a refractive index distribution that can approximate a step type can be formed.

A step approximation according to Non-Patent Document 8 obtains the v-value of the photonic crystal fiber from the diameter d of the holes 12 and the interval between the holes 12 Λ, and satisfies the wavelength λ _c that satisfies the following cut-off condition v _c The diameter d and the hole interval Λ were searched by the following formula.
(Equation 1)
v _c = j _{1, l−1} ... LP _0l mode (l ≧ 2)
v _c = j _{m−1, l} ... LP _ml mode where j _{n, l} is the l-th zero of the _n- th order Bessel function J _n (x).

ここで、ａ＝Λ／√３、ｎ_１は石英ガラス１１の屈折率である。

Here, a = Λ / √3, n ₁ is the refractive index of the quartz glass 11.

  Hereinafter, in the first to fourth embodiments, a design region of a photonic crystal fiber having a propagation mode number of two modes will be described.

(Embodiment 1)
FIG. 2 shows a design range in which the used wavelength band is 1530 to 1625 nm (CL band), the bending loss is 0.1 dB / 100 turn or less, and the number of propagation modes is 2. The void interval Λ was calculated from 5 μm to 20 μm.

  Note that the LP11 mode, which is the second mode of propagation in the used wavelength band, and the LP21 mode, which is the third mode of propagation, do not propagate, and the LP11 mode cutoff condition at 1625 nm and the LP21 mode at wavelength 1530 nm. The region was surrounded by the mode cutoff conditions. Furthermore, a condition in which the bending loss at the bending radius of 30 mm in the LP11 mode is 0.1 dB / m or less at a wavelength of 1530 nm where the bending loss becomes the largest in the wavelength band used was calculated by the formula described in Non-Patent Document 9.

From FIG. 2, the combination of Λ and d / Λ in which the number of modes is limited to 2 in the used wavelength band and the propagation modes can all satisfy the desired bending loss is Λ <13.6 μm surrounded by a solid line and a dotted line, This can be realized by setting the region 0.57 <d / Λ <0.70. From FIG. 2, the maximum effective cross-sectional area of the LP01 mode obtained is 145 μm ² at a wavelength of 1530 nm when Λ = 13.6 μm and d / Λ = 0.66.

(Embodiment 2)
As in the first embodiment, FIG. 3 shows a design range in which the used wavelength band is 1460 to 1625 nm (SL band), the bending loss is 0.1 dB / 100 turn or less, and the number of propagation modes is two. The filled part becomes the design area.

  Note that the LP11 mode, which is the second mode of propagation in the used wavelength band, and the LP21 mode, which is the third mode of propagation, do not propagate, and the LP11 mode cutoff condition at 1625 nm and the LP21 mode at 1460 nm. The region was surrounded by the mode cutoff conditions. Furthermore, the condition that the bending loss at the bending radius of 30 mm in the LP11 mode is 0.1 dB / m or less at a wavelength of 1460 nm where the bending loss becomes the largest in the used wavelength band was calculated according to the formula described in Non-Patent Document 9.

From FIG. 3, the combination of Λ and d / Λ in which the number of modes is limited to 2 in the used wavelength band and the propagation modes can satisfy all desired bending losses is Λ <13.0 μm surrounded by a solid line and a dotted line, This can be realized by setting the region 0.57 <d / Λ <0.70. From FIG. 3, the effective area of the maximum LP01 mode obtained is 133 μm ² at a wavelength of 1460 nm when Λ = 13.0 μm and d / Λ = 0.66.

(Embodiment 3)
As in the first embodiment, FIG. 4 shows a design range in which the used wavelength band is 1260 to 1625 nm (OL band), the bending loss is 0.1 dB / 100 turn or less, and the number of propagation modes is 2. The filled part becomes the design area.

  Note that the LP11 mode, which is the second mode of propagation in the used wavelength band, and the LP21 mode, which is the third mode of propagation, do not propagate, and the LP11 mode cutoff condition at 1625 nm and the LP21 mode at 1260 nm. The region was surrounded by the mode cutoff conditions. Furthermore, the condition that the bending loss at a bending radius of 30 mm in the LP11 mode is 0.1 dB / m or less at a wavelength of 1260 nm at which the bending loss becomes the largest in the used wavelength band was calculated by the equation described in Non-Patent Document 9.

From FIG. 4, the combination of Λ and d / Λ in which the number of modes is limited to 2 in the used wavelength band and the propagation modes can all satisfy the desired bending loss is Λ <11.8 μm surrounded by a solid line and a dotted line, This can be realized by setting the region 0.57 <d / Λ <0.69. From FIG. 4, the maximum effective cross-sectional area of the LP01 mode obtained is 111 μm ² at a wavelength of 1260 nm when Λ = 11.8 μm and d / Λ = 0.66.

(Embodiment 4)
As in the first embodiment, FIG. 5 shows a design range in which the used wavelength band is 980 to 1625 nm, the bending loss is 0.1 dB / 100 turn or less, and the number of propagation modes is 2. The filled part becomes the design area.

  Note that the LP11 mode, which is the second propagation mode, propagates in the used wavelength band, and the LP21 mode, which is the third propagation mode, does not propagate. The LP11 mode cutoff condition at a wavelength of 1625 nm and the LP21 mode at a wavelength of 980 nm. The region was surrounded by the mode cutoff conditions. Furthermore, a condition in which the bending loss at a bending radius of 30 mm in the LP11 mode is 0.1 dB / m or less at a wavelength of 980 nm where the bending loss becomes the largest in the used wavelength band was calculated according to the formula described in Non-Patent Document 9.

From FIG. 5, the combination of Λ and d / Λ in which the number of modes is limited to 2 in the used wavelength band and the propagation modes can satisfy all desired bending losses is Λ <10.0 μm surrounded by a solid line and a dotted line, This can be realized by setting the region 0.57 <d / Λ <0.68. From FIG. 5, the effective area of the maximum LP01 mode obtained is 77 μm ² at a wavelength of 980 nm when Λ = 10.0 μm and d / Λ = 0.65.

  Next, in Embodiments 5 to 8, a design region of a photonic crystal fiber having a propagation mode number of 4 modes will be described.

(Embodiment 5)
FIG. 6 shows a design range in which the used wavelength band is 1530 to 1625 nm (CL band), the bending loss is 0.1 dB / 100 turn or less, and the number of propagation modes is 4. The filled part becomes the design area.

  Note that the LP02 mode, which is the fourth mode of propagation, propagates in the wavelength band used, and the LP31 mode, which is the fifth mode of propagation, does not propagate. The LP02 mode cut-off condition at a wavelength of 1625 nm and the LP31 mode at a wavelength of 1530 nm. The region was surrounded by the mode cutoff conditions. Furthermore, the condition that the bending loss at a bending radius of 30 mm in the LP02 mode is 0.1 dB / m or less at a wavelength of 1530 nm at which the bending loss becomes the largest in the used wavelength band was calculated by the equation described in Non-Patent Document 9.

From FIG. 6, the combination of Λ and d / Λ in which the number of modes in the used wavelength band is limited to 4 and the propagation modes can all satisfy the desired bending loss is Λ <13.9 μm surrounded by a solid line and a dotted line, This can be realized by setting the region 0.73 <d / Λ <0.80. From FIG. 6, the effective area of the maximum LP01 mode obtained is 126 μm ² at a wavelength of 1530 nm when Λ = 13.9 μm and d / Λ = 0.76.

(Embodiment 6)
As in the fifth embodiment, FIG. 7 shows a design range in which the used wavelength band is 1460 to 1625 nm (SL band), the bending loss is 0.1 dB / 100 turn or less, and the number of propagation modes is four. The filled part becomes the design area.

  Note that the LP02 mode, which is the fourth mode of propagation, propagates in the wavelength band used, and the LP31 mode, which is the fifth mode of propagation, does not propagate. The LP02 mode cutoff condition at 1625 nm and the LP31 mode at 1460 nm are used as conditions. The region was surrounded by the mode cutoff conditions. Furthermore, the condition that the bending loss at a bending radius of 30 mm in the LP02 mode is 0.1 dB / m or less at a wavelength of 1460 nm where the bending loss becomes the largest in the used wavelength band was calculated according to the formula described in Non-Patent Document 9.

From FIG. 7, the number of modes is limited to 4 in the wavelength band to be used, and the combination of Λ and d / Λ in which all propagation modes can satisfy the desired bending loss is Λ <13.5 μm surrounded by a solid line and a dotted line, This can be realized by setting the region 0.73 <d / Λ <0.80. From FIG. 7, the effective area of the maximum LP01 mode obtained is 119 μm ² at a wavelength of 1460 nm when Λ = 13.5 μm and d / Λ = 0.76.

(Embodiment 7)
Similarly to the fifth embodiment, FIG. 8 shows a design range in which the used wavelength band is 1260 to 1625 nm (OL band), the bending loss is 0.1 dB / 100 turn or less, and the number of propagation modes is 4. The filled part becomes the design area.

  Note that the LP02 mode, which is the fourth mode of propagation, propagates in the used wavelength band, and the LP31 mode, which is the fifth mode of propagation, does not propagate, and the LP02 mode cutoff condition at 1625 nm and the LP31 mode at 1260 nm. The region was surrounded by the mode cutoff conditions. Furthermore, the condition that the bending loss at a bending radius of 30 mm in the LP02 mode is 0.1 dB / m or less at a wavelength of 1260 nm at which the bending loss becomes the largest in the used wavelength band was calculated according to the formula described in Non-Patent Document 9.

From FIG. 8, the number of modes is limited to 4 in the wavelength band used, and the combination of Λ and d / Λ that can satisfy all the desired bending loss in the propagation modes is Λ <12.3 μm surrounded by a solid line and a dotted line, This can be realized by setting the region 0.73 <d / Λ <0.80. From FIG. 8, the effective area of the maximum LP01 mode obtained is 99 μm ² at a wavelength of 1260 nm when Λ = 12.3 μm and d / Λ = 0.76.

(Embodiment 8)
Similarly to the fifth embodiment, FIG. 9 shows a design range in which the used wavelength band is 980 to 1625 nm, the bending loss is 0.1 dB / 100 turn or less, and the number of propagation modes is 4. The filled part becomes the design area.

  Note that the LP02 mode, which is the fourth mode of propagation, propagates in the wavelength band used and the LP31 mode, which is the fifth mode of propagation, does not propagate. The LP02 mode cutoff condition at a wavelength of 1625 nm and the LP31 mode at a wavelength of 980 nm. The region was surrounded by the mode cutoff conditions. Furthermore, the condition that the bending loss at the bending radius of 30 mm in the LP02 mode is 0.1 dB / m or less at a wavelength of 980 nm where the bending loss becomes the largest in the used wavelength band was calculated by the formula described in Non-Patent Document 9.

From FIG. 9, the number of modes is limited to 4 in the wavelength band used, and the combination of Λ and d / Λ in which all propagation modes can satisfy the desired bending loss is Λ <10.5 μm surrounded by a solid line and a dotted line, This can be realized by setting the region 0.73 <d / Λ <0.78. From FIG. 9, the effective area of the maximum LP01 mode obtained is 72 μm ² at a wavelength of 980 nm when Λ = 10.5 μm and d / Λ = 0.76.

  Next, in the ninth to twelfth embodiments, a design region of a photonic crystal fiber having a propagation mode number of six modes will be described.

(Embodiment 9)
FIG. 10 shows a design range in which the used wavelength band is 1530 to 1625 nm (CL band), the bending loss is 0.1 dB / 100 turn or less, and the number of propagation modes is 6. The filled part becomes the design area.

  Note that the LP12 mode, which is the sixth mode of propagation, propagates in the used wavelength band, and the LP41 mode, which is the seventh mode of propagation, does not propagate. The LP12 mode cut-off condition at the wavelength 1625 nm and the LP41 mode at the wavelength 1530 nm. The region was surrounded by the mode cutoff conditions. Furthermore, the condition in which the bending loss at the bending radius of 30 mm in the LP12 mode is 0.1 dB / m or less at a wavelength of 1530 nm where the bending loss becomes the largest in the used wavelength band was calculated by the equation described in Non-Patent Document 9.

From FIG. 10, the number of modes in the used wavelength band is limited to 6, and the combination of Λ and d / Λ that can satisfy all the desired bending loss is Λ <13.8 μm surrounded by a solid line and a dotted line, This can be realized by setting the region 0.82 <d / Λ <0.88. From FIG. 10, the maximum effective cross-sectional area of the LP01 mode obtained is 112 μm ² at a wavelength of 1530 nm when Λ = 13.8 μm and d / Λ = 0.183.

(Embodiment 10)
As in the ninth embodiment, FIG. 11 shows a design range in which the used wavelength band is 1460 to 1625 nm (SL band), the bending loss is 0.1 dB / 100 turn or less, and the number of propagation modes is six. The filled part becomes the design area.

  Note that the LP12 mode, which is the sixth mode of propagation, propagates in the wavelength band used, and the LP41 mode, which is the seventh mode of propagation, does not propagate. The LP12 mode cutoff condition at 1625 nm and the LP41 mode at wavelength 1460 nm The region was surrounded by the mode cutoff conditions. Furthermore, the condition in which the bending loss at the bending radius of 30 mm in the LP12 mode is 0.1 dB / m or less at the wavelength of 1460 nm where the bending loss becomes the largest in the used wavelength band was calculated by the formula described in Non-Patent Document 9.

From FIG. 11, the number of modes is limited to 6 in the wavelength band used, and the combination of Λ and d / Λ that can satisfy all the desired bending loss is Λ <13.3 μm surrounded by a solid line and a dotted line, This can be realized by setting the region 0.82 <d / Λ <0.88. From FIG. 11, the effective area of the maximum LP01 mode obtained is 104 μm ² at a wavelength of 1460 nm when Λ = 13.3 μm and d / Λ = 0.83.

(Embodiment 11)
As in the ninth embodiment, FIG. 12 shows a design range in which the used wavelength band is 1260 to 1625 nm (OL band), the bending loss is 0.1 dB / 100 turn or less, and the number of propagation modes is 6. The filled part becomes the design area.

  Note that the LP12 mode, which is the sixth mode of propagation, propagates in the wavelength band used, and the LP41 mode, which is the seventh mode of propagation, does not propagate. The LP12 mode cutoff condition at the wavelength 1625 nm and the LP41 mode at the wavelength 1260 nm. The region was surrounded by the mode cutoff conditions. Furthermore, the condition that the bending loss at a bending radius of 30 mm in the LP12 mode is 0.1 dB / m or less at a wavelength of 1260 nm at which the bending loss becomes the largest in the used wavelength band was calculated according to the formula described in Non-Patent Document 9.

From FIG. 12, the number of modes in the used wavelength band is limited to 6, and the combination of Λ and d / Λ that can satisfy all the desired bending losses in the propagation modes is Λ <12.1 μm surrounded by a solid line and a dotted line, This can be realized by setting the region 0.82 <d / Λ <0.87. From FIG. 12, the maximum effective area of the LP01 mode obtained is 86 μm ² at a wavelength of 1260 nm when Λ = 12.1 μm and d / Λ = 0.83.

Embodiment 12
Similarly to the ninth embodiment, FIG. 13 shows a design range in which the used wavelength band is 980 to 1625 nm, the bending loss is 0.1 dB / 100 turn or less, and the number of propagation modes is six. The filled part becomes the design area.

  Note that the LP12 mode, which is the sixth mode of propagation, propagates in the wavelength band used and the LP41 mode, which is the seventh mode of propagation, does not propagate. The LP12 mode cutoff condition at a wavelength of 1625 nm and the LP41 mode at a wavelength of 980 nm The region was surrounded by the mode cutoff conditions. Furthermore, the condition in which the bending loss at the bending radius of 30 mm in the LP12 mode is 0.1 dB / m or less at a wavelength of 980 nm where the bending loss becomes the largest in the used wavelength band was calculated by the formula described in Non-Patent Document 9.

From FIG. 13, the number of modes is limited to 6 in the wavelength band used, and the combination of d and d / Λ that can satisfy all the desired bending loss is Λ <10.2 μm surrounded by the solid line and the dotted line. This can be realized by setting the region 0.82 <d / Λ <0.86. From FIG. 13, the effective area of the maximum LP01 mode obtained is 61 μm ² at a wavelength of 980 nm when Λ = 10.2 μm and d / Λ = 0.82.

  The present invention can realize a large capacity and long distance of optical fiber transmission by utilizing a higher-order mode in the fiber.

11: Quartz glass 12: Hole

Claims (12)

An optical fiber in which a step-type refractive index profile is equivalently formed by having a plurality of holes in the cross section of the fiber,
For the wavelength range of 1530 nm to 1625 nm,
An optical fiber characterized in that Λ <13.6 μm, 0.57 <d / Λ <0.70 with respect to the diameter d of the holes and the interval Λ of the holes, and the number of propagation modes is two. An optical fiber in which a step type refractive index profile is equivalently formed by having a plurality of holes in a cross section of the fiber,
For the wavelength range of 1460 nm to 1625 nm,
An optical fiber characterized in that Λ <13.0 μm, 0.57 <d / Λ <0.70 with respect to the diameter d of the holes and the interval Λ of the holes, and the number of propagation modes is two. An optical fiber in which a step-type refractive index profile is equivalently formed by having a plurality of holes in the cross section of the fiber,
For the wavelength range of 1260 nm to 1625 nm,
An optical fiber characterized in that Λ <11.8 μm, 0.57 <d / Λ <0.69, and the number of propagation modes is 2 for the diameter d of the holes and the interval Λ of the holes. An optical fiber in which a step-type refractive index profile is equivalently formed by having a plurality of holes in the cross section of the fiber,
For the operating wavelength band of 980 nm to 1625 nm,
An optical fiber, wherein the hole diameter d and the hole interval Λ are Λ <10.0 μm, 0.57 <d / Λ <0.68, and the number of propagation modes is two. An optical fiber in which a step-type refractive index profile is equivalently formed by having a plurality of holes in the cross section of the fiber,
For the wavelength range of 1530 nm to 1625 nm,
An optical fiber characterized in that Λ <13.9 μm, 0.73 <d / Λ <0.80 with respect to the diameter d of the holes and the interval Λ of the holes, and the number of propagation modes is four. An optical fiber in which a step-type refractive index profile is equivalently formed by having a plurality of holes in the cross section of the fiber,
For the wavelength range of 1460 nm to 1625 nm,
An optical fiber characterized in that Λ <13.5 μm, 0.73 <d / Λ <0.80, and the number of propagation modes is 4 for the diameter d of the holes and the interval Λ of the holes. An optical fiber in which a step type refractive index profile is equivalently formed by having a plurality of holes in a cross section of the fiber,
For the wavelength range of 1260 nm to 1625 nm,
An optical fiber characterized in that Λ <12.3 μm, 0.73 <d / Λ <0.80, and the number of propagation modes is 4 for the diameter d of the holes and the interval Λ of the holes. An optical fiber in which a step-type refractive index profile is equivalently formed by having a plurality of holes in the cross section of the fiber,
For the operating wavelength band of 980 nm to 1625 nm,
An optical fiber characterized in that Λ <10.5 μm, 0.73 <d / Λ <0.78 with respect to the diameter d of the holes and the interval Λ of the holes, and the number of propagation modes is four. An optical fiber in which a step-type refractive index profile is equivalently formed by having a plurality of holes in the cross section of the fiber,
For the wavelength range of 1530 nm to 1625 nm,
An optical fiber characterized in that Λ <13.8 μm, 0.82 <d / Λ <0.88, and the number of propagation modes is 6 for the diameter d of the holes and the interval Λ of the holes. An optical fiber in which a step-type refractive index profile is equivalently formed by having a plurality of holes in the cross section of the fiber,
For the wavelength range of 1460 nm to 1625 nm,
An optical fiber characterized in that Λ <13.3 μm, 0.82 <d / Λ <0.88, and the number of propagation modes is 6 for the diameter d of the holes and the interval Λ of the holes. An optical fiber in which a step-type refractive index profile is equivalently formed by having a plurality of holes in the cross section of the fiber,
For the wavelength range of 1260 nm to 1625 nm,
An optical fiber, wherein the hole diameter d and the hole interval Λ are Λ <12.1 μm, 0.82 <d / Λ <0.87, and the number of propagation modes is six. An optical fiber in which a step-type refractive index profile is equivalently formed by having a plurality of holes in the cross section of the fiber,
For the operating wavelength band of 980 nm to 1625 nm,
An optical fiber characterized in that Λ <10.2 μm, 0.82 <d / Λ <0.86, and the number of propagation modes is 6 for the diameter d of the holes and the interval Λ of the holes.

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