JP5481735B2 - Optical fiber - Google Patents

Description

The present invention relates to a fiber optic.

In optical fiber communication systems, chromatic dispersion and nonlinear effects of optical fibers limit transmission characteristics. Therefore, various optical fiber structures have been developed and widely used in order to reduce chromatic dispersion and nonlinear effects of optical fibers. Recently, a hole-structured optical fiber having holes in an optical fiber has various characteristics that cannot be realized by a conventional solid-state optical fiber, and thus has attracted high interest as a new optical transmission medium.
For example, in the following Non-Patent Documents 1 and 2, an optical fiber having an expanded effective cross-sectional area, which is an area in which a light wave propagates, is reported in order to realize a low nonlinear optical transmission line using a hole structure optical fiber. .

Takashi Matsui, 4 others, “Examination of effective cross-sectional area expansion of photonic crystal fiber”, 2008 IEICE Communication Society Conference, Communication Lecture 2, September 2008, p. 275 Kazunori Mukasa, and three others, "Comparisons of merits on wide-band transmission systems between Using extremely improved solid SMFs with Aeff of 160mm2 and loss of 0.175dB / km and Using large-Aeff holey fibers enabling transmission over 600nm bandwidth", The Proceedings of OFC2008, February 2008, OthR1 Masanori Koshiba, Kunimasa Saitoh, “Simple evaluation of confinement in holey fibers”, Optics Communications Volume 253, Issues 1-3, May 1-3. 95-98

  However, in the study of the effective area expansion using the above photonic crystal fiber, the hole diameter and the space between holes are optimized, but the optimization including the number of holes is not possible. It has not been studied so far, and the structure that maximizes the effective area has not been clarified.

  In view of the above, an object of the present invention is to provide an optical fiber that can realize the maximization of the effective area of the photonic crystal fiber and can reduce the nonlinear effect generated in the fiber.

An optical fiber according to a first invention for solving the above-described problem is
Having a plurality of uniform holes in the longitudinal direction in the optical fiber;
The holes are arranged in a polygonal shape around the core region,
The number of layers of the holes arranged is 3 layers,
The distance between the centers of the adjacent holes is 13.3 μm,
The diameter of the holes is 0.517 times the distance between the centers of the holes.

An optical fiber according to a second invention for solving the above-described problem is
Having a plurality of uniform holes in the longitudinal direction in the optical fiber;
The holes are arranged in a polygonal shape around the core region,
The number of layers of the holes arranged is 5 layers,
The interval between the centers of the adjacent holes is 13.0 μm,
The diameter of the holes is 0.517 times the distance between the centers of the holes.
An optical fiber according to a third invention for solving the above-described problem is
In the optical fiber according to the first or second invention,
The cutoff wavelength is 1450 nm or less,
The bending loss at a wavelength of 1450 to 1625 nm and a bending radius of 30 mm is 0.5 dB or less per 100 turns.

  According to the present invention, it is possible to provide an optical fiber capable of maximizing the effective cross-sectional area of the photonic crystal fiber and reducing the nonlinear effect generated in the fiber.

It is the schematic diagram which showed an example of the structure of the optical fiber which concerns on this invention. It is a characteristic view showing the structure in which the low bending loss and single mode operation | movement are obtained in the photonic crystal fiber at the time of making a void | hole layer number into five layers. It is a characteristic view showing the structure where the low bending loss and single mode operation | movement are obtained in the photonic crystal fiber at the time of making a void | hole layer number into four layers. It is a characteristic view showing the structure where the low bending loss and single mode operation | movement in a photonic crystal fiber in case the number of hole layers is 3 layers are obtained. It is the schematic diagram which showed an example of the structure of the conventional photonic crystal fiber.

Hereinafter, embodiments for implementing an optical fiber according to the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view showing an example of the structure of an optical fiber according to the present invention. FIG. 5 is a schematic view showing an example of the structure of a conventional photonic crystal fiber.
As shown in FIG. 5, in a conventional photonic crystal fiber, a background 1 having a refractive index n1 and holes 2 having a diameter d are arranged in a regular hexagonal shape with a hole interval Λ.

  A region in which a plurality of holes 2 are arranged corresponds to the cladding region, and a region without the central hole 2 corresponds to the core region. Since the effective refractive index in the cladding region is lower than that in the core region, the light wave incident on the core region propagates through the optical fiber by total reflection. In addition, although the arrangement | positioning of the hole 2 was made into the regular hexagon shape, another regular polygon shape may be sufficient.

  The effect of the number of layers has not been taken into consideration in the study of the effective area expansion of the photonic crystal fiber that has been studied so far. Therefore, it will be described with reference to FIGS. 2 to 4 that the effective cross-sectional area can be enlarged by changing the number of layers of holes to form a three-layer hole structure photonic crystal fiber as shown in FIG.

  As shown in Non-Patent Document 3 (particularly FIG. 4), if the number of hole layers is smaller than 3, the confinement in the fundamental mode becomes weak and the confinement loss increases rapidly, which is not preferable. Further, when the number of pore layers is larger than 5, the same result as that of 5 layers is obtained, so it is not considered. Further, since the outer diameter of the fiber is increased due to the large number of layers, compatibility with an existing optical fiber system is deteriorated, and problems are caused in terms of handleability and connection with existing equipment, which is not preferable.

FIG. 2 is a characteristic diagram showing a structure capable of obtaining a low bending loss and a single mode operation in a photonic crystal fiber when the number of hole layers is five.
In FIG. 2, the condition of the bending loss BL _{FM in} the basic mode is set to 0.5 dB or less per 100 turns at a bending radius of 30 mm satisfying ITU-T G.655 or G.656, and evaluation of single mode operation is performed. As a method, the bending loss BL _HOM in the first higher-order mode was set to 1 dB / m or more at a bending radius of 140 mm.

In the photonic crystal fiber, the bending loss increases toward the shorter wavelength side. Therefore, in FIG. 2, assuming the communication wavelength band S to L band, the bending loss in the fundamental mode shows a value at 1450 nm which is the shortest wavelength. For the higher-order mode, the longest wavelength of 1625 nm is shown. It can be seen that the photonic crystal fiber having a five-layer hole structure assumed in Non-Patent Document 1 can expand the hole interval to 13.0 μm and realize an effective area of 185 μm ^{2 at} the maximum.

  FIG. 3 is a characteristic diagram showing a structure capable of obtaining low bending loss and single mode operation in a photonic crystal fiber when the number of hole layers is four. FIG. 4 is a characteristic diagram showing a structure capable of obtaining a low bending loss and a single mode operation in a photonic crystal fiber when the number of hole layers is three. 3 and 4, the bending loss and higher-order mode loss conditions are the same as those in FIG.

As shown in FIG. 3, by using a four-layer hole structure, the maximum value of the hole interval is 13 μm or less, and the effective cross-sectional area obtained is small.
On the other hand, as shown in FIG. 4, when the number of hole layers is three, the hole interval can be expanded to a maximum of 13.3 μm, and the communication wavelength band S can be reduced by setting d / Λ to 0.517 or less. Single mode operation in ~L band, and 193.5Myuemu ² can achieve effective area at most.

  Therefore, in the present invention, by using the three-layer hole structure optical fiber, the effective cross-sectional area can be increased by about 5% compared with the conventional five-layer hole structure photonic crystal fiber, and the optical transmission line It is possible to reduce the characteristic deterioration due to the non-linear effect in the case.

Table 1 is a table showing the optimum structure in the number of layers 3 to 5 and the pore region diameter (2Λ × number of layers + d).

  In production, the outer diameter of the cladding must be several tens of μm larger than the hole area diameter. Since the outer diameter of the existing optical fiber is 125 μm, it can be seen that five layers cannot be manufactured with the same outer diameter as the existing optical fiber. In the case of three layers, it is about 90 μm, so that it can be manufactured with the same outer diameter as a conventional optical fiber from the viewpoint of manufacturing.

  In the structure of FIGS. 1 and 5, the background material has a refractive index such as pure quartz, fluorine (F) or boron (B) to which an impurity for reducing the refractive index is added, germanium (Ge) or aluminum (Al). Quartz doped with increasing impurities can be used.

  The present invention can be used, for example, as a transmission medium in an optical transmission system.

1 Background 2 Hole

Claims (3)

Having a plurality of uniform holes in the longitudinal direction in the optical fiber;
The holes are arranged in a polygonal shape around the core region,
The number of layers of the holes arranged is 3 layers,
The distance between the centers of the adjacent holes is 13.3 μm,
The diameter of the hole is 0.517 times the distance between the centers of the holes. Having a plurality of uniform holes in the longitudinal direction in the optical fiber;
The holes are arranged in a polygonal shape around the core region,
The number of layers of the holes arranged is 5 layers,
The interval between the centers of the adjacent holes is 13.0 μm,
The diameter of the hole is 0.517 times the distance between the centers of the holes. The cutoff wavelength is 1450 nm or less,
The optical fiber according to claim 1 or 2 , wherein a bending loss at a wavelength of 1450 to 1625 nm and a bending radius of 30 mm is 0.5 dB or less per 100 turns.

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