JP2007041426A - Photonic crystal fiber and optical transmission system using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photonic crystal fiber capable of chromatic dispersion compensating, even if an optical fiber has a zero chromatic dispersion on the side of the wavelength that is longer than 1,310 nm, and to provide an optical transmission system that uses the same. <P>SOLUTION: The photonic crystal fiber 10 is arranged at least on either the front or rear stage of an optical waveguide, having a negative chromatic dispersion in the wavelength band of 1,310 nm, to perform dispersion compensation in the wavelength band of 1,310 nm. The fiber 10 is provided with a core 11 and a clad 12 surrounding the core 11, wherein the core 11 and the clad 12 rises a medium having a uniform refractive index. With a plurality of uniform holes 12a formed longitudinally along the clad 12, the fiber 10 has chromatic dispersion of 30 ps/nm-km or higher in the wavelength band, wherein the inclination of the chromatic dispersion is negative. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a photonic crystal fiber and an optical transmission system using the photonic crystal fiber.

  In high-speed optical transmission systems, waveform distortion due to accumulation of chromatic dispersion becomes a problem, and various dispersion compensating fibers have been proposed so far for the purpose of compensating for chromatic dispersion. For example, in Patent Document 1 below, a dispersion-compensating fiber for improving transmission characteristics at a wavelength of 1500 nm or 1600 nm with a dispersion-shifted fiber having a zero-dispersion wavelength at a wavelength of 1.5 μm and a configuration of an optical transmission line using the same. is suggesting.

  Further, in order to improve transmission characteristics in the wavelength 1550 nm band with a non-zero dispersion shifted fiber, a dispersion compensating fiber that can realize a chromatic dispersion of −40 ps / nm · km or less and a negative dispersion slope (dispersion slope) in the wavelength band. Has also been proposed.

International Publication No. 00/017685 Pamphlet

  Incidentally, an optical fiber having a zero dispersion wavelength on the longer wavelength side than the wavelength 1310 nm generally has a negative chromatic dispersion at a wavelength of 1310 nm and a positive dispersion slope. For this reason, in order to compensate the chromatic dispersion of the optical fiber having the zero dispersion wavelength on the longer wavelength side than the wavelength 1310 nm, the wavelength dispersion in the wavelength 1310 nm band has a positive characteristic and a negative dispersion slope. A dispersion compensating fiber is required.

  However, in the vicinity of the wavelength of 1310 nm, the influence of material dispersion is generally large, and it is difficult to obtain a large positive wavelength dispersion or negative dispersion slope. For this reason, the conventional dispersion compensation fiber proposed in Patent Document 1 and the like as described above can only perform chromatic dispersion compensation at wavelengths of 1460 to 1625 nm.

  For this reason, the present invention uses a photonic crystal fiber that can compensate for chromatic dispersion even in an optical fiber having a zero dispersion wavelength on the longer wavelength side than the wavelength of 1310 nm, and the same. An object is to provide an optical transmission system.

  A photonic crystal fiber according to a first invention for solving the above-described problem is disposed at least one of a front stage and a rear stage of an optical transmission line having negative chromatic dispersion in a wavelength 1310 nm band, and has a wavelength of 1310 nm. A photonic crystal fiber that performs dispersion compensation in a band, and includes a core part and a clad part surrounding the core part, and the core part and the clad part are made of a medium having a uniform optical refractive index. In addition, a plurality of uniform holes are formed in the cladding along the longitudinal direction, the wavelength band has a wavelength dispersion of 30 ps / nm · km or more, and the slope of the wavelength dispersion is negative in the wavelength band. It is characterized by that.

  A photonic crystal fiber according to a second invention is the photonic crystal fiber according to the first invention, wherein an interval between the centers of the adjacent holes of the cladding part is 1.2 to 2.05 μm, and the cladding parts are adjacent to each other. The ratio of the diameter of the hole to the distance between the centers of the holes is 0.37 or more.

  A photonic crystal fiber according to a third aspect of the present invention is a photonic crystal fiber that is disposed in at least one of a front stage and a rear stage of an optical transmission line having negative wavelength dispersion in a wavelength 1310 nm band and performs dispersion compensation in a wavelength 1310 nm band. A crystal fiber, a first core part, a first cladding part surrounding the first core part, a second core part surrounding the first cladding part, and the second core A second clad portion surrounding the portion, and the first and second core portions and the first and second clad portions are made of a medium having a uniform optical refractive index, and the first and second clads A plurality of uniform vacancies are formed in the cladding along the longitudinal direction, the chromatic dispersion is 30 ps / nm · km or more in the wavelength band, and the slope of the chromatic dispersion is negative in the wavelength band. Features.

  The photonic crystal fiber according to a fourth aspect of the present invention is the photonic crystal fiber according to the third aspect, wherein an interval between the centers of the adjacent holes of the first cladding portion is 1.2 to 2.05 μm. The ratio of the diameter of the hole with respect to the distance between the centers of the adjacent holes of the clad portion is 0.37 or more.

  A photonic crystal fiber according to a fifth invention is the photonic crystal fiber according to the third or fourth invention, wherein the width of the second core portion is equal to that of the holes adjacent to the first cladding portion. The diameter of the hole of the second clad portion is larger than the distance between the holes, and the diameter of the hole of the first clad portion is larger.

  A photonic crystal fiber according to a sixth invention is characterized in that, in any one of the first to fifth inventions, the holes are arranged in an annular shape or a polygonal shape.

  A photonic crystal fiber according to a seventh aspect of the present invention is the photonic crystal fiber according to any one of the first to sixth aspects, wherein the optical refractive index is lower than the optical refractive index of the medium constituting the core portion and the cladding portion. The medium is filled in the pores.

  In addition, an optical transmission system according to an eighth aspect of the invention for solving the above-described problem is the first to seventh in at least one of a front stage and a rear stage of an optical transmission line having negative wavelength dispersion in a wavelength of 1310 nm band. The photonic crystal fiber according to any of the second inventions is used as a dispersion compensating fiber.

  According to the photonic crystal fiber and the optical transmission system using the same according to the present invention, it is possible to compensate for chromatic dispersion even in an optical fiber having a zero-dispersion wavelength longer than the wavelength of 1310 nm. And high-speed transmission in the wavelength band is possible.

  Embodiments of a photonic crystal fiber and an optical transmission system using the same according to the present invention will be described below with reference to the drawings. However, the present invention is not limited to the following embodiments.

[Photonic crystal fiber]
<First embodiment>
A first embodiment of a photonic crystal fiber according to the present invention will be described with reference to FIGS. 1 is a schematic configuration diagram of a photonic crystal fiber, FIG. 2 is a graph showing the characteristics of the photonic crystal fiber of FIG. 1, and FIG. 3 is a graph showing the relationship between the wavelength and chromatic dispersion of the photonic crystal fiber of FIG. It is a graph to represent.

  As shown in FIG. 1, a photonic crystal fiber 10 according to this embodiment has a core portion 11 and a cladding portion 12 in a medium having a uniform optical refractive index, and a hole having a diameter d in the cladding portion 12. A plurality of 12a are uniformly formed along the longitudinal direction so that they are arranged at the center-to-center spacing Λ. In such a photonic crystal fiber 10, since the refractive index is effectively lower than that of the core portion 11 due to the presence of the plurality of holes 12 a in the cladding portion 12, A waveguide structure is formed between them.

  In such a photonic crystal fiber 10 according to this embodiment, as shown in FIG. 2, the center-to-center spacing Λ of the adjacent holes 12a is 1.2 to 2.05 μm, and the holes 12a When the ratio (d / Λ) of the diameter d to the center-to-center spacing Λ is 0.37 or more, chromatic dispersion of 30 ps / nm · km or more and a negative dispersion slope can be realized simultaneously at a wavelength of 1310 nm.

  Specifically, for example, when Λ is 1.5 μm and d / Λ is 0.6, as shown in FIG. 3, at the wavelength 1310 nm, the wavelength dispersion is 30 ps / nm · km or more. Negative dispersion slope can be realized.

  Therefore, according to the photonic crystal fiber 10 according to the present embodiment, chromatic dispersion can be compensated even for an optical fiber having a zero dispersion wavelength on the longer wavelength side than the wavelength 1310 nm.

<Second Embodiment>
A second embodiment of the photonic crystal fiber according to the present invention will be described with reference to FIGS. 4 is a schematic configuration diagram of the photonic crystal fiber, FIG. 5 is a graph showing the characteristics of the photonic crystal fiber of FIG. 4, and FIG. 6 shows the relationship between the wavelength and chromatic dispersion of the photonic crystal fiber of FIG. It is a graph to represent. In addition, about the part similar to 1st embodiment mentioned above, by using the code | symbol similar to the code | symbol used in description of 1st embodiment mentioned above, in 1st embodiment mentioned above, A description overlapping with the description is omitted.

  As shown in FIG. 4, the photonic crystal fiber 20 according to the present embodiment includes a first core portion 21A and a first core portion 21A surrounding a first core portion 21A in a medium having a uniform optical refractive index. The first clad portion 22A has a clad portion 22A, a second core portion 21B surrounding the first clad portion 22A, and a second clad portion 22B surrounding the second core portion 21B. A plurality of holes 22a of d1 are uniformly formed along the longitudinal direction so as to be arranged at the center-to-center interval Λ1, and the holes 22b of diameter d2 are arranged to be arranged at the center-to-center interval Λ2 in the second cladding portion 22B. A plurality are formed uniformly along the direction.

  In such a photonic crystal fiber 20 according to the present embodiment, the wavelength dispersion characteristic is largely governed by the diameter d1 of the air holes 22a of the first clad portion 22A and the center-to-center spacing Λ1, so FIG. As shown, the center-to-center spacing Λ1 of the holes 22a is 1.2 to 2.05 μm, and the ratio of the diameter d1 to the center-to-center spacing Λ1 of the holes 22a (d1 / Λ1) is 0.37 or more. If so, it is possible to simultaneously realize chromatic dispersion of 30 ps / nm · km or more and a negative dispersion slope at a wavelength of 1310 nm.

  Moreover, by having the 2nd core part 21B, the area | region which propagates light can be expanded and an effective cross-sectional area can be expanded. Here, the width of the second core portion 21B is such that the distance a1 between the center of the first core portion 21A and the outer periphery of the hole 22a layer of the first cladding portion 22A, The difference (a2−a1) between the center of the core portion 21A and the inner circumference of the layer of the hole 22b of the second cladding portion 22B is adjacent to the first cladding portion 22A. It needs to be larger than the distance (Λ1-d1) between the matching holes 22a.

  Furthermore, by having the second clad portion 22B, a greater confinement effect can be obtained than in the case of the first embodiment (FIG. 1) described above, and leakage loss can be reduced. Here, it is preferable that the diameter d2 of the hole 22b of the second cladding part 22B is larger than the diameter d1 of the hole 22a of the first cladding part 22A (d2> d1) because the confinement effect can be further enhanced. .

  In the photonic crystal fiber 20 according to this embodiment, for example, the Λ1 is 1.42 μm, the d1 / Λ1 is 0.66, the Λ2 is 2.89 μm, and the d2 / Λ2 = 0. As shown in FIG. 6, at a wavelength of 1310 nm, a negative dispersion slope can be realized at the same time as having a wavelength dispersion of 30 ps / nm · km or more, as shown in FIG.

  Therefore, the photonic crystal fiber 20 according to the present embodiment is an optical fiber having a zero dispersion wavelength on the longer wavelength side than the wavelength 1310 nm, as in the case of the first embodiment described above. However, not only can chromatic dispersion be compensated, but also a greater confinement effect can be obtained than in the case of the first embodiment described above, and leakage loss can be reduced.

<Other embodiments>
In the photonic crystal fiber 10 according to the first embodiment described above, the number of layers of the holes 12a of the cladding portion 12 is six as shown in FIG. For example, it is possible to have one, 2 to 5 or 7 or more.

  Further, in the photonic crystal fiber 20 according to the second embodiment described above, the number of layers of the holes 22a in the first cladding portion 22A is two as shown in FIG. As an embodiment, for example, it is possible to use one, or three or more. Furthermore, although the number of the holes 22b of the second clad portion 22B is five, as another embodiment, it may be one, 2 to 4, or 6 or more.

  Moreover, in the photonic crystal fibers 10 and 20 according to the first and second embodiments described above, as shown in FIGS. 1 and 4, the holes 12a, 221a, Although 22b was arranged in the shape of a regular hexagon, as another embodiment, for example, it is also possible to arrange it in an annular shape, another regular polygon shape, or a polygon shape other than a regular shape.

  Further, in the photonic crystal fibers 10 and 20 according to the first and second embodiments described above, by making the inside of the holes 12a, 221a, and 22b of the cladding portions 12, 22A, and 22B hollow, The effective refractive index of the cladding parts 12, 22A, 22B is made lower than the refractive index of the core parts 11, 21A, 21B. However, as another embodiment, for example, the core part and the core part, By filling the pores with a medium having a light refractive index lower than that of the material constituting the cladding part, the effective light refractive index of the cladding part is made higher than the light refractive index of the core part. Can also be lowered.

[Optical transmission system]
An embodiment of an optical transmission system using a photonic crystal fiber according to the present invention will be described with reference to FIG. FIG. 7 is a schematic configuration diagram of an optical transmission system. In addition, about the part similar to embodiment of the photonic crystal fiber mentioned above, by using the code | symbol similar to the code | symbol used in description of embodiment of the photonic crystal fiber mentioned above, implementation of the photonic crystal fiber mentioned above is carried out. The description overlapping with the description in the form is omitted.

  As shown in FIG. 7, the optical transmission system according to the present embodiment uses the photonic crystal fibers 10 and 20 according to the above-described embodiment for the 1310 nm band with respect to the optical transmission line 111 having a negative dispersion at a wavelength of 1310 nm. The dispersion compensating fiber 112 is disposed only in the rear stage (see FIG. 7A), only in the front stage (see FIG. 7B), and in both the front stage and the rear stage (see FIG. 7C). In FIG. 7, 113 is a transmitter and 114 is a receiver.

  In such an optical transmission system 110, since the dispersion compensating fiber 112 has a wavelength dispersion of 30 ps / nm · km or more at a wavelength of 1310 nm, by appropriately setting the length of the dispersion compensating fiber 112, the wavelength band In addition, the negative accumulated dispersion in the optical transmission line 111 can be canceled out, and the negative dispersion slope that is opposite to the dispersion slope of the optical transmission line 111 at a wavelength of 1310 nm is provided, so that the compensation band can be expanded. .

  Note that the photonic crystal fibers 10 and 20 according to the above-described embodiments are applied to the constituent members of the transmitter 113 and the receiver 114 as dispersion compensating fibers for the 1310 nm band, and are applied to the constituent members such as a repeater. It is also possible.

  The photonic crystal fiber according to the present invention and the optical transmission system using the same can compensate for chromatic dispersion even in an optical fiber having a zero dispersion wavelength on the longer wavelength side than the wavelength of 1310 nm. Since high-speed transmission in the wavelength band is possible, it can be used extremely beneficially in the communication industry.

It is a schematic block diagram of 1st embodiment of the photonic crystal fiber which concerns on this invention. It is a graph showing the characteristic of the photonic crystal fiber of FIG. It is a graph showing the relationship between the wavelength of the photonic crystal fiber of FIG. 1, and wavelength dispersion. It is a schematic block diagram of 2nd embodiment of the photonic crystal fiber which concerns on this invention. It is a graph showing the characteristic of the photonic crystal fiber of FIG. It is a graph showing the relationship between the wavelength of the photonic crystal fiber of FIG. 4, and wavelength dispersion. 1 is a schematic configuration diagram of an embodiment of an optical transmission system using a photonic crystal fiber according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Photonic crystal fiber 11 Core part 12 Cladding part 12a Hole 20 Photonic crystal fiber 21A First core part 21B Second core part 22A First clad part 22a Hole 22B Second clad part 22b Hole 110 Optical transmission system 111 Optical transmission line 112 Dispersion compensation fiber 113 Transmitter 114 Receiver a1 Distance between the center of the first core part and the outer periphery of the hole layer of the first cladding part a2 of the first core part Distance between the center and the inner circumference of the hole layer of the second cladding part d, d1, d2 Hole diameter Λ, Λ1, Λ2 Hole center distance

Claims (8)

A photonic crystal fiber disposed in at least one of a front stage and a rear stage of an optical transmission line having negative chromatic dispersion in a wavelength 1310 nm band and performing dispersion compensation in a wavelength 1310 nm band,
The core,
A clad portion surrounding the core portion,
The core part and the clad part are made of a medium having a uniform optical refractive index,
A plurality of uniform holes are formed in the cladding along the longitudinal direction,
A photonic crystal fiber having a chromatic dispersion of 30 ps / nm · km or more in the wavelength band and a negative slope of chromatic dispersion in the wavelength band. In claim 1,
The center-to-center spacing of the adjacent holes in the cladding is 1.2 to 2.05 μm;
The ratio of the diameter of the hole to the distance between the centers of the adjacent holes in the clad portion is 0.37 or more. A photonic crystal fiber disposed in at least one of a front stage and a rear stage of an optical transmission line having negative chromatic dispersion in a wavelength 1310 nm band and performing dispersion compensation in a wavelength 1310 nm band,
The first core,
A first cladding part surrounding the first core part;
A second core portion surrounding the first cladding portion;
A second clad portion surrounding the second core portion,
The first and second core portions and the first and second cladding portions are made of a medium having a uniform optical refractive index,
A plurality of uniform holes are formed in the first and second cladding portions along the longitudinal direction,
A photonic crystal fiber having a chromatic dispersion of 30 ps / nm · km or more in the wavelength band and a negative slope of chromatic dispersion in the wavelength band. In claim 3,
An interval between the centers of the adjacent holes of the first cladding portion is 1.2 to 2.05 μm;
The ratio of the diameter of the said hole with respect to the space | interval between the centers of the said adjacent holes of said 1st clad part is 0.37 or more. The photonic crystal fiber characterized by the above-mentioned. In claim 3 or claim 4,
The width of the second core portion is larger than the distance between the adjacent holes of the first cladding portion;
The photonic crystal fiber, wherein a diameter of the hole in the second cladding portion is larger than a diameter of the hole in the first cladding portion. In any one of Claims 1-5,
The photonic crystal fiber, wherein the holes are arranged in an annular shape or a polygonal shape. In any one of Claims 1-6,
The photonic crystal fiber is characterized in that a medium having a light refractive index lower than that of the medium constituting the core part and the clad part is filled in the holes. An optical transmission characterized in that the photonic crystal fiber according to any one of claims 1 to 7 is used as a dispersion compensating fiber in at least one of a front stage and a rear stage of an optical transmission line having negative wavelength dispersion in a wavelength 1310 nm band. system.

Images