JP5660627B2 - Multi-core single-mode optical fiber and optical cable - Google Patents

Description

  The present invention relates to a single mode optical fiber and an optical cable for single mode optical communication.

  With the rapid spread of data communication, the demand for further expansion of transmission capacity is increasing year by year. For this reason, studies are being made to increase the transmission capacity per optical fiber by using various multiplexing techniques. For example, Non-Patent Document 1 and Non-Patent Document 2 disclose multi-core optical fiber technology that improves the spatial multiplexing efficiency per optical fiber core by arranging a plurality of cores in the same cladding cross section. .

  However, in the multi-core optical fiber technology disclosed in Non-Patent Document 1 and Non-Patent Document 2, the outer diameter of the cladding is expanded to 125 μm or more, and is used in the conventional single-core single-mode optical fiber technology. The input / output technology that has been used has a problem that it cannot be applied due to structural mismatch. In addition, as the outer diameter of the clad is increased to 125 μm or more, there is a problem that the probability of breakage of the optical fiber generated by bending, pulling, twisting, or the like increases.

  Furthermore, in the multi-core optical fiber technology disclosed in Non-Patent Document 1, the characteristics of the cutoff wavelength, the zero dispersion wavelength, and the mode field diameter are zero. Since the characteristics of the dispersion wavelength and the mode field diameter are different from the transmission characteristics of the general-purpose single-core single-mode optical fiber disclosed in Non-Patent Document 3, respectively, the combined use with the above-described general-purpose single-core single-mode optical fiber There has been a problem that it becomes difficult to construct an optical transmission line by means of the above.

  The present invention has been made in view of the background as described above, and its object is to maintain a cladding outer diameter and transmission characteristics equivalent to those of a conventional general-purpose single-core single-mode optical fiber while maintaining space. An object of the present invention is to provide a multi-core single mode optical fiber and an optical cable that can improve the multiplexing efficiency.

  In the multi-core single mode optical fiber of the present invention, two or three higher refractive indexes than those of the cladding part are provided in the cladding part having a diameter of 125 μm ± 1 μm, which is equivalent to the conventional single core single mode optical fiber. Or the four core parts are arranged at equal distances Λ, and the distance from the center of the core part to the outer periphery of the cladding part is not less than r, and the distances Λ and r and the standard of the core part By controlling the relationship with the conversion frequency V so as to be suitable, the above-described problem is solved.

  According to the multi-core single mode optical fiber of the present invention, the clad outer diameter equivalent to that of the conventional general-purpose single-core single-mode optical fiber is maintained, and the same as that of the conventional general-purpose single-core single-mode optical fiber. While realizing the effective cutoff wavelength, zero dispersion wavelength, and bending loss characteristics, the space utilization efficiency can be increased by 2 to 4 times.

  In addition, according to the multi-core single mode optical fiber of the present invention, since the clad outer diameter equivalent to that of the conventional general single core single mode optical fiber is maintained, the conventional general single core single mode optical fiber is provided. There is also an effect that the input / output technology used in the technology can be applied.

  In addition, according to the multi-core single mode optical fiber of the present invention, an effective cutoff wavelength, a zero dispersion wavelength, and a bending loss characteristic equivalent to those of a conventional general-purpose single core single mode optical fiber are realized. The optical transmission line mixed with the general-purpose single core single mode optical fiber can also be easily designed.

  Furthermore, according to the multi-core single mode optical fiber of the present invention, it has a mode field diameter characteristic that falls within the range of the conventional general single core single mode optical fiber. The effects of reducing the connection loss with the one-mode optical fiber and facilitating the construction of the optical transmission line by mixing the multicore and single core optical fibers are also achieved.

  In addition, according to the multi-core single-mode optical fiber of the present invention, the cladding outer diameter equivalent to that of the conventional general-purpose single-core single-mode optical fiber and the same as that of the conventional general-purpose single-core single-mode optical fiber The structural conditions of the inter-core distance Λ and the minimum distance r from the center of the core part to the outer periphery of the clad part to realize the effective cutoff wavelength, the zero dispersion wavelength, and the bending loss characteristics, the mode field diameter and the normalized frequency V of the core part By deriving from this relationship, there is also an effect that it can be applied to a multi-core single mode optical fiber using a core having an arbitrary refractive index distribution.

It is a conceptual diagram which shows the cross-section of the multi-core single mode optical fiber of this invention. It is a conceptual diagram which shows the cross-section of the multi-core single mode optical fiber of this invention. It is a conceptual diagram which shows the cross-section of the multi-core single mode optical fiber of this invention. In the multi-core single-mode optical fiber of the present invention, the minimum inter-core distance Λ for which the crosstalk between adjacent cores after transmission of 10 km at a wavelength of 1550 nm is −30 dB or less is standardized with a mode field diameter of 1310 nm and a wavelength of 1310 nm 3 is a diagram showing a function of frequency V. In the multi-core single mode optical fiber of the present invention, the distance r from the center of the core part to the confinement loss at a wavelength of 1625 nm of 0.01 dB / km or less to the outer periphery of the cladding part is set to a mode field diameter of 1310 nm and a wavelength of 1310 nm. 3 is a diagram showing the normalized frequency V as a function. 6 is a diagram showing the relationship between the minimum inter-core distance Λ and the maximum distance r-max from the center of the core part to the outer periphery of the cladding part as a function of the number of cores in the multicore single-mode optical fiber of the present invention.

  Hereinafter, embodiments of the multi-core single mode optical fiber and the optical cable of the present invention will be described with reference to the drawings.

  1 to 3 are conceptual views showing a cross-sectional structure of a multi-core single mode optical fiber according to the present invention. The multi-core single mode optical fiber of the present invention has a clad part 1 having a uniform refractive index and a diameter D of 125 μm ± 1 μm, and two (FIG. 1) or three having a higher refractive index than the clad part 1 (FIG. 2) or four core parts 2 (FIG. 3).

  Here, each core part 2 is arranged such that the distance Λ between the centers of the core part 2 and the adjacent core part 2 in the cross section of the clad part 1 is equal, and from the center of the core part 2 to the outer periphery of the clad part 1. It arrange | positions so that the minimum distance to may become r.

The normalized frequency V of the core part 2 at the wavelength λ is 2a as the diameter of the core part 2, n ₁ as the refractive index, and n ₂ as the refractive index of the cladding part 1.
V≡ (2πa / λ) ・ (n ₁ ² −n ₂ ² ) ^1/2 (1)
Defined by

  FIG. 4 shows a multicore single-mode optical fiber according to the present invention, in which the minimum inter-core distance Λ for which the crosstalk between adjacent cores after transmission of 10 km at a wavelength of 1550 nm is −30 dB or less is set to a mode field diameter of 1310 nm and a wavelength of 1310 nm. It is drawing shown as a function of the normalized frequency V. Here, the solid line in the figure indicates the minimum inter-core distance Λ. A dotted line, a broken line, and an alternate long and short dash line indicate an effective cutoff wavelength, a bending loss, and a zero dispersion wavelength condition, respectively.

  According to Non-Patent Document 3, the conventional general-purpose single-core single-mode optical fiber has an effective cutoff wavelength of 1260 nm or less, a bending loss of 1625 nm, a bending radius of 30 mm, a winding number of 100 turns, 0.1 dB or less, and zero dispersion wavelength characteristics. Is recommended as 1300 to 1324 nm, and it is possible to satisfy the above-described cutoff wavelength, bending loss, and zero dispersion wavelength characteristics in the region surrounded by the dashed line on the left side of FIG. . In other words, in the region surrounded by all of the dotted line, broken line, and alternate long and short dash line in FIG. 4, it is possible to realize the effective cutoff wavelength, bending loss, and zero dispersion wavelength characteristics equivalent to those of the conventional single core single mode optical fiber. It becomes.

  According to Non-Patent Document 3, it is recommended that the mode field diameter of a conventional general-purpose single-core single-mode optical fiber at a wavelength of 1310 nm is 8.6 to 9.5 μm ± 0.6 μm. It is known that the deviation in diameter leads to an increase in connection loss at the connection point.

  Therefore, as shown in FIG. 4, when the normalized frequency V is in the range of 2.32 to 2.67, the diameter of the core portion 2 and the relative refractive index difference are controlled so that the mode field diameter is in the range of 8.0 to 10.1 μm, and the minimum core By setting the distance Λ to be in the range of 40 to 50 μm, the effective cut-off wavelength, bending loss, and zero dispersion wavelength characteristics equivalent to those of general-purpose single-core single-mode optical fibers are achieved, and crosstalk between adjacent cores is reduced. It becomes possible to reduce to -30 dB or less.

  FIG. 5 shows the distance r to the minimum cladding outer periphery where the confinement loss at a wavelength of 1625 nm is 0.01 dB / km or less, the mode field diameter of the wavelength of 1310 nm, and the normalized frequency of the wavelength of 1310 nm in the multi-core single mode optical fiber of the present invention. FIG. Dotted lines, broken lines, and alternate long and short dash lines in the figure indicate the same effective cutoff wavelength, bending loss, and zero dispersion wavelength conditions as in FIG.

  From FIG. 5, the diameter and relative refractive index difference of the core part 2 are controlled so that the mode field diameter is in the range of 8.0 to 10.1 μm in the range of the normalization frequency V from 2.32 to 2.67, and to the minimum cladding outer periphery. By setting the distance r in the range of 33 to 38 μm, an effective cut-off wavelength, bending loss, and zero dispersion wavelength characteristics equivalent to those of a general-purpose single-core single mode optical fiber are realized, and a confinement loss at a wavelength of 1625 nm is 0.01. It becomes possible to reduce to dB / km or less.

Here, according to Non-Patent Document 4, the normalized frequency V and mode field diameter 2W of a step-type core having a core diameter of 2a and a core refractive index of n ₁ are:
W / a = 0.62 + 1.619V ^-1.5 + 2.879V ^-6 (2)
It is disclosed that it can be described by.

Further, according to Non-Patent Document 5, the standardized frequency V in the above-described step-type refractive index distribution is the extended standardized frequency T for an arbitrary refractive index distribution,
T ² = 2 (2π / λ) ² ∫ {n ² (r) −n ² (∞)} rdr (3)
It is disclosed that it can be rewritten.

  Here, n (r) represents the refractive index at the point of radius r, and n (∞) represents the refractive index of the cladding. Therefore, the relationship between the mode field diameter and the minimum inter-core distance Λ with respect to the normalized frequency V and the relationship between the mode field diameter and the normalized frequency V with respect to the distance r to the minimum cladding outer circumference disclosed in FIGS. The present invention can also be applied to the core portion 2 having a refractive index distribution of

  FIG. 6 shows the relationship between the minimum inter-core distance Λ and the maximum distance r-max from the center of the core part to the outer periphery of the clad part when the diameter D of the clad part is 125 μm in the multi-core single mode optical fiber of the present invention. FIG. 2 is a drawing showing the number of cores as a function. In the figure, the solid line, the broken line, and the alternate long and short dash line indicate cases where there are two, three, and four core parts, respectively.

  From FIG. 6, when two core parts are arranged in the same clad part, if the minimum inter-core distance Λ is set to 50 μm, the r-max needs to be about 37 μm, and all those shown in FIG. 4 and FIG. It becomes difficult to satisfy these conditions simultaneously. Therefore, the minimum inter-core distance Λ is in the range of 40 to 49 μm ± 1 μm, the distance r to the outer circumference of the cladding is in the range of 33 to 37 μm ± 1 μm, the normalized frequency V of the core is in the range of 2.32 to 2.67, and the mode field diameter is 8.0. By setting each in the range of ˜10.1 μm, it has the same cutoff wavelength, bending loss, and zero dispersion wavelength characteristics as a general-purpose single-core single-mode optical fiber, and the outer diameter of the cladding is 125 μm ± 1 μm A two-core single mode optical fiber can be realized.

  Similarly, when three core parts are arranged, the minimum inter-core distance Λ is in the range of 40 to 42 μm ± 1 μm, the distance r to the cladding outer periphery is in the range of 33 to 37 μm ± 1 μm, and the normalized frequency V of the core part Has a cutoff wavelength, bending loss, and zero dispersion wavelength characteristics equivalent to a general-purpose single-core single-mode optical fiber by setting the mode field to 2.48 to 2.59 and the mode field diameter to 8.0 to 8.5 μm. In addition, it is possible to realize a three-core single mode optical fiber having an outer diameter of the cladding of 125 μm ± 1 μm.

  Similarly, when four core parts are arranged, the minimum inter-core distance Λ is in the range of 40 to 41.5 μm ± 1 μm, the distance r to the outer periphery of the cladding is in the range of 33 μm ± 1 μm, and the normalized frequency of the core part By setting V in the range of 2.50 to 2.58 and the mode field diameter in the range of 8.0 to 8.3 μm, it has the same cutoff wavelength, bending loss, and zero dispersion wavelength characteristics as a general-purpose single-core single-mode optical fiber. In addition, it is possible to realize a four-core single mode optical fiber having a cladding outer diameter of 125 μm ± 1 μm.

  As described above, according to the multi-core single mode optical fiber of the present invention, the cladding outer diameter of 125 μm ± 1 μm equivalent to the conventional general-purpose single core single mode optical fiber and the effective cutoff wavelength of 1260 nm or less And a zero dispersion wavelength of 1300 to 1324 nm, a bending loss characteristic of a wavelength of 1625 nm, a bending radius of 30 mm and 0.1 dB / 100 turns or less, and the spatial multiplexing efficiency can be expanded to 2 to 4 times. Become.

  1: Clad part, 2: Core part.

"Effective Space Division Multiplexing by Multi-Core Fibers", K. Imamura, et al., In Proc. ECOC'10, P1.09 (2010). "Multi-core holey fibers for the long-distance (> 100 km) ultra large capacity transmission", K. Imamura, et al., In Proc. OFC'09, OTuC3 (2009). "Characteristics of a single-mode optical fiber and cable", ITU-T, Recommendation G.652. "Loss analysis of single-mode fiber splices", D. Marcuse, Bell Sys. Tech. J, vol. 56, no. 5, p. 703 (1976). "Optical fibers and fiber-type devices", Kawakami, et al., Baifukan, (1996).

Claims (4)

A clad part having a uniform refractive index and a diameter of 125 μm ± 1 μm, and two core parts having a refractive index higher than that of the clad part;
The core parts are arranged such that the distance between the centers is Λ,
Center distance Λ the range of 40~49μm ± 1μm of the core portion, the closest distance r the range of 33~37μm ± 1μm position to on outer periphery of the center from the cladding portion of the core portion, the core portion The normalization frequency V is set in the range of 2.32 to 2.67, and the mode field diameter of the core portion at the wavelength of 1310 nm is set in the range of 8.0 to 0.1 μm.
It has a bending loss property of 0.1 dB / 100 or less at a wavelength of 1625 nm, a bending radius of 30 mm, an effective cutoff wavelength property of 1260 nm or less, and a zero dispersion wavelength property of 1300 to 1324 nm.
A multi-core single mode optical fiber characterized in that the crosstalk between the two core portions after 10 km transmission at a wavelength of 1550 nm is -30 dB or less. A clad part having a uniform refractive index and a diameter of 125 μm ± 1 μm, and three core parts having a refractive index higher than that of the clad part;
The core parts are arranged so that the distances Λ between the centers of the core parts adjacent to each other in the cross section of the clad part are equal.
Center distance Λ the range of 40~42μm ± 1μm of the core portion, the closest distance r the range of 33~37μm ± 1μm position to on outer periphery of the center from the cladding portion of the core portion, the core portion The normalization frequency V is set in the range of 2.48 to 2.59, and the mode field diameter of the core portion at the wavelength of 1310 nm is set in the range of 8.0 to 8.5 μm.
It has a bending loss property of 0.1 dB / 100 or less at a wavelength of 1625 nm, a bending radius of 30 mm, an effective cutoff wavelength property of 1260 nm or less, and a zero dispersion wavelength property of 1300 to 1324 nm.
A multi-core single mode optical fiber characterized in that the crosstalk between the three core portions after 10 km transmission at a wavelength of 1550 nm is -30 dB or less. A clad part having a uniform refractive index and a diameter of 125 μm ± 1 μm, and four core parts having a refractive index higher than that of the clad part;
The core parts are arranged so that the distances Λ between the centers of the core parts adjacent to each other in the cross section of the clad part are equal.
Range 40~41.5μm ± 1μm distance between the centers Λ of the core portion, from the center of the core portion range of distance r of 33μm ± 1μm to the nearest position on the outer periphery of the cladding portion, the core portion The normalized frequency V is set in a range of 2.50 to 2.58, and the mode field diameter of the core portion at a wavelength of 1310 nm is set in a range of 8.0 to 8.3 μm.
It has a bending loss property of 0.1 dB / 100 or less at a wavelength of 1625 nm, a bending radius of 30 mm, an effective cutoff wavelength property of 1260 nm or less, and a zero dispersion wavelength property of 1300 to 1324 nm.
A multi-core single mode optical fiber characterized in that crosstalk between the four core portions after 10 km transmission at a wavelength of 1550 nm is -30 dB or less.   An optical cable using at least one multi-core single-mode optical fiber according to any one of claims 1 to 3.

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