JP4413823B2 - Dispersion compensating fiber and optical transmission line - Google Patents

Description

  The present invention relates to a dispersion compensating fiber and an optical transmission line, and more particularly to a dispersion compensating fiber and an optical transmission line suitable for high-speed and large-capacity optical communication using a wavelength of 1310 nm band.

  In high-speed optical transmission systems, it is essential to compensate for the accumulated dispersion during optical transmission. For this reason, various dispersion compensating fibers have been proposed for the purpose of compensating the chromatic dispersion characteristics of various optical fibers. For example, Patent Document 1 aims at improving transmission characteristics in a wavelength band of 1.5 μm or 1.6 μm using a dispersion-shifted fiber (DSF) optical transmission line. An optical fiber that compensates the chromatic dispersion of a path has been proposed. In Patent Document 1, a dispersion compensating fiber that compensates the accumulated dispersion in a dispersion-shifted fiber optical transmission path to ± 200 ps / nm · km or less, and the optical transmission path The technology regarding is disclosed.

Republished patent (A1) WO00 / 17685

  However, the conventional dispersion compensating fiber is mainly intended for compensation of dispersion characteristics in the 1400 nm band to 1600 nm band, and the dispersion compensating fiber applicable to the wavelength 1310 nm band has not been sufficiently clarified. In general, when performing dispersion compensation of an optical fiber having negative chromatic dispersion characteristics at a wavelength of 1310 nm, a dispersion compensating fiber having sufficiently large positive chromatic dispersion in the wavelength band is required. However, when the refractive index distribution is formed by the additive material and the chromatic dispersion characteristic of the optical fiber is controlled as in the conventional case, the influence of the material dispersion on the chromatic dispersion characteristic of the optical fiber is shorter than the wavelength 1400 nm band. Since it becomes dominant, there is a problem that it becomes difficult to realize sufficiently large positive wavelength dispersion in the wavelength 1310 nm band.

  Therefore, the present invention has been proposed in view of the above-described problems. In addition to the conventional control of chromatic dispersion characteristics by the refractive index distribution, the hole structure is appropriately arranged so that the chromatic dispersion is sufficient in the wavelength 1310 nm band. An object of the present invention is to provide a dispersion compensating fiber and an optical transmission line having a large positive value, specifically, +30 ps / nm · km or more.

The dispersion compensating fiber according to the first invention for solving the above-described problem is
A core portion a radius of the relative refractive index difference a is delta, and a cladding portion covering the core portion, a predetermined distance Λ from the center of the core portion, at least four diameters d which are formed at equal intervals And a hole portion of
A normalized hole position Λ / a in which the predetermined distance Λ is normalized by the core radius a, and a normalized hole diameter d / 2a in which the hole diameter d is normalized by the core diameter 2a of the core portion. The core radius a and the relative refractive index difference Δ of the core part are (0.4 ≦ Λ / a ≦ 0.5), (0.2 ≦ d / 2a ≦ 0.3), and (4, respectively). 0.0 μm ≦ a ≦ 6.5 μm) and (0.7% ≦ Δ ≦ 1.5%), or (1.0 ≦ Λ / a ≦ 1.4) and (0.4 ≦ d / 2a ≦). 1.2), and (1.5 μm ≦ a ≦ 2.5 μm) and (0.7% ≦ Δ ≦ 1.5%), and the chromatic dispersion at a wavelength of 1310 nm is set to +30 ps / nm · km or more. It is characterized by that.

The optical transmission line according to the second invention for solving the above-described problem is as follows.
And 1310nm band negative dispersion fiber having a negative chromatic dispersion at 1310nm band, front of the 1310nm band negative dispersion fiber, to have a dispersion compensating fiber according to the first invention, which is disposed downstream, or both, Features.

  According to the dispersion compensating fiber according to the present invention, the normalized hole position Λ / a, the normalized hole diameter d / 2a, the core radius a, and the relative refractive index difference Δ of the core part with respect to the cladding part are each in a predetermined range. By doing so, the chromatic dispersion becomes a positive value sufficiently large in the 1310 nm band, specifically, +30 ps / nm · km or more.

  According to the optical transmission line according to the present invention, the cumulative dispersion in the wavelength 1310 nm band can be reduced, and the high-speed optical transmission characteristic and the transmission distance limitation can be improved.

  The best mode for carrying out the dispersion compensating fiber according to the present invention will be specifically described below with reference to the drawings.

  FIG. 1 is a cross-sectional view of a dispersion compensating fiber according to the best mode of the present invention. FIG. 1 (a) shows a cross section when a hole is formed in the core region, and FIG. The cross section when a void | hole part is formed in the area | region of a clad part is shown.

The dispersion compensating fiber according to the best mode of the present invention includes a clad portion having a uniform refractive index, a core portion having a predetermined relative refractive index difference with respect to the clad portion, and a predetermined distance from the center of the core portion. And at least four holes formed at equal intervals. That is, such a dispersion compensating fiber, as shown in FIG. 1 (a), a core portion 1 of the core radius a ₁ is the refractive index n1, covering the core portion 1, and clad portion 2 is the refractive index n2 FIG. 1B shows a dispersion compensating fiber 10 having six hole portions 3 formed at equal intervals from the center C ₁ of the core portion 1 in the region of the core portion 1 at a predetermined distance Λ ₁ . as shown, the refractive index n1 and the core portion 11 of the core radius a _2, covering the core portion 11, and the cladding portion 12 is a refractive index n2, predetermined from the center C ₂ of the core portion 11 in the region of the cladding portion 12 And a dispersion compensating fiber 20 having six holes 13 formed at equal intervals at a distance [Lambda] ₂ .

The relative refractive index difference Δ is defined by the following equation (1) using the refractive index n1 of the core portions 1 and 11 and the refractive index n2 of the cladding portions 2 and 12.
Δ = (n1 ² −n2 ² ) / (2n1 ² ) (1)

  Here, a value obtained by normalizing the distance Λ from the center of the core part to the hole part by the core radius a is defined as a normalized hole position Λ / a, and the hole diameter d of the hole part is defined by the core diameter 2a. The normalized value is defined as the normalized hole diameter d / 2a.

  FIG. 2 shows the relationship between the normalized hole position Λ / a and the normalized hole diameter d / 2a where the chromatic dispersion at a wavelength of 1310 nm is +30 ps / nm · km or more in the dispersion compensating fiber according to the best mode of the present invention. FIG.

  As shown in FIG. 2, the normalized hole position Λ / a and the normalized hole diameter d / 2a at which the dispersion compensating fiber is +30 ps / nm · km or more in the 1310 nm band are shaded regions, that is, (0 .4 ≦ Λ / a ≦ 0.5) and (0.2 ≦ d / 2a ≦ 0.3), or (1.0 ≦ Λ / a ≦ 1.4) and (0.4 ≦ d / 2a ≦ 1.2).

  FIG. 3 shows a dispersion compensating fiber according to the best mode of the present invention, specifically, a dispersion compensating fiber satisfying the relationship between the normalized hole position Λ / a and the normalized hole diameter d / 2a in FIG. It is a figure which shows the relationship between the core radius a and the relative refractive index difference (DELTA) of a core part. FIG. 3A shows the relationship between the core radius a and the relative refractive index difference Δ when the hole is formed in the core region, and FIG. 3B shows the hole in the cladding region. The relationship between the core radius a and the relative refractive index difference Δ of the core portion when formed is shown. However, the shaded region in FIG. 3 shows the relationship between the core radius a and the relative refractive index Λ of the core portion that satisfies the relationship between the normalized hole position Λ / a and the normalized hole diameter Λ / 2a. Show.

  Here, in order to increase the refractive index in the optical fiber, germanium is generally added to the glass material, but from the viewpoint of an increase in loss accompanying an increase in the addition amount, a specific refraction of 1.4 to 1.5% or more. It is difficult to realize the rate difference Δ. Further, when the core radius a is smaller than 1.5 μm, the effect of confining light inside the core is lowered, and there is a possibility that fundamental mode propagation cannot be realized.

  Therefore, as shown in FIGS. 2 and 3, in the dispersion compensating fiber, the normalized hole position Λ / a and the normalized hole diameter d / 2a, in which the chromatic dispersion at a wavelength of 1310 nm is +30 ps / nm · km or more, The relative refractive index difference Δ between the core radius a and the core portion is (0.4 ≦ Λ / a ≦ 0.5), (0.2 ≦ d / 2a ≦ 0.3), and (4.0 μm ≦), respectively. a ≦ 6.5 μm) and (0.7% ≦ Δ ≦ 1.5%), or (1.0 ≦ Λ / a ≦ 1.4) and (0.4 ≦ d / 2a ≦ 1). .2), and (1.5 μm ≦ a ≦ 2.5 μm) and (0.7% ≦ Δ ≦ 1.5%).

  FIG. 4 shows a dispersion compensation fiber according to the best mode of the present invention, specifically, a dispersion compensation fiber satisfying the conditions shown in FIGS. 2 and 3, and a normalized hole position Λ / a and a normalized hole. It is a figure which shows the wavelength dispersion characteristic when the diameter d / 2a, the core radius a, and relative refractive index difference (DELTA) of a core part are each made into the predetermined value. In this figure, the solid line indicates a dispersion compensating fiber in which the hole portion is formed in the region of the core portion, that is, the normalized hole position Λ / a, the normalized hole diameter d / 2a, the core radius a, and the relative refractive index. The chromatic dispersion characteristics of the dispersion compensating fiber are shown with a difference Δ of 0.4, 0.2, 5.5 μm, and 1.3%, respectively. The broken line indicates the dispersion compensating fiber in which the hole portion is formed in the region of the cladding portion, that is, the normalized hole position Λ / a, the normalized hole diameter d / 2a, the core radius a, and the relative refractive index difference Δ, The chromatic dispersion characteristics of the dispersion compensating fibers are 1.2, 0.8, 2 μm, and 1.3%, respectively.

  As shown in this figure, in the dispersion compensation fiber in which the hole portion is formed in the core region and the dispersion compensation fiber in which the hole portion is formed in the cladding region, the wavelength is from 1.3 μm to 1.4 μm. , The chromatic dispersion is +30 ps / nm · km or more, specifically, +30 ps / nm · km to +40 ps / nm · km.

  Here, as shown in FIG. 5, the optical communication system 30 includes a transmitter 31 that converts an electrical signal from a signal source (not shown) and transmits the optical signal, and a reception that receives the optical signal and converts it into an electrical signal. 13, a 1310 nm band negative dispersion fiber 34 having a negative chromatic dispersion in the 1310 nm band, and a 1310 nm band negative dispersion fiber, as an optical transmission line 33 connected to the transmitter 32, the transmitter 31, and the receiver 32 and transmitting an optical signal. The dispersion compensating fibers 10 and 20 according to the best mode of the present invention are arranged in both the front stage and the rear stage of 34, and optical signal transmission / reception (transmission) is performed between the transmitter 31 and the receiver 32. Done. The dispersion compensating fibers 10 and 20 may be incorporated in the transmitter 31 or the receiver 32.

  6 shows a dispersion compensating fiber according to the best mode of the present invention, specifically, the dispersion compensating fiber shown in FIG. 4 and a 1310 nm band negative dispersion fiber (dispersion shifted fiber) having negative chromatic dispersion in the 1310 nm band. The chromatic dispersion characteristics in the optical transmission line connecting the In this figure, the solid line indicates a dispersion compensating fiber in which the hole portion is formed in the region of the core portion, that is, the normalized hole position Λ / a, the normalized hole diameter d / 2a, the core radius a, and the relative refractive index. The chromatic dispersion characteristics of an optical transmission line having a dispersion compensating fiber having a difference Δ of 0.4, 0.2, 5.5 μm, and 1.3% and the 1310 nm band negative dispersion fiber 34 are shown. The broken line indicates the dispersion compensating fiber in which the hole portion is formed in the region of the cladding portion, that is, the normalized hole position Λ / a, the normalized hole diameter d / 2a, the core radius a, and the relative refractive index difference Δ, The chromatic dispersion characteristics of an optical transmission line having a dispersion compensating fiber of 1.2, 0.8, 2 μm, and 1.3% and the 1310 nm band negative dispersion fiber are shown. A one-dot chain line indicates a wavelength dispersion characteristic in an optical transmission line having only the 1310 nm band negative dispersion fiber.

  As shown in FIG. 6, by using an optical transmission line having the 1310 nm band negative dispersion fiber and the dispersion compensating fiber according to the best mode of the present invention, an optical transmission line consisting only of the 1310 nm band negative dispersion fiber is obtained. In comparison, it can be seen that the absolute value of chromatic dispersion in the wavelength 1310 nm band is reduced. In particular, the absolute value of chromatic dispersion after dispersion compensation at wavelengths from 1300 nm to 1320 nm is reduced to about 1/10 of the value before dispersion compensation. Therefore, it can be seen that by using the dispersion compensating fiber, the limitation of the transmission distance due to chromatic dispersion in the wavelength range can be improved by 10 times or more. Accordingly, by appropriately combining the dispersion compensating fiber according to the best mode of the present invention and the 1310 nm band negative dispersion fiber to be compensated, the cumulative dispersion in the wavelength 1310 nm band can be reduced and the high-speed optical transmission characteristics can be improved. it can.

Therefore, according to the dispersion compensating fibers 10 and 20 according to the best mode of the present invention, the normalized hole position Λ / a, the normalized hole diameter d / 2a, the core radius a, and the ratio of the core part to the cladding part. By setting the refractive index difference Δ to a predetermined range, the chromatic dispersion in the 1310 nm band is a positive value with a sufficiently large value, specifically, +30 ps / nm · km or more.
Moreover, according to the optical transmission line 33 according to the present invention, the cumulative dispersion in the wavelength 1310 nm band can be reduced, and the high-speed optical transmission characteristic and the transmission distance limitation can be improved.

  In the above description, the optical transmission line 33 having the 1310 nm band negative dispersion fiber 34 and the dispersion compensating fibers 10 and 20 arranged at both the front stage and the rear stage of the 1310 nm band negative dispersion fiber 34 has been described. An optical transmission line in which the dispersion compensating fiber is disposed only in the front stage or the rear stage of the dispersion fiber 34 and the 1310 nm-band negative dispersion fiber 34 may be used, and the same effect as the optical transmission path 33 is achieved.

  The present invention relates to a dispersion compensating fiber and an optical transmission line, and in particular, can be used for a dispersion compensating fiber and an optical transmission line suitable for high-speed and large-capacity optical communication using a wavelength of 1310 nm band.

It is sectional drawing of the dispersion compensation fiber which concerns on the best form of this invention. The figure which shows the relationship between the normalized hole position (LAMBDA) / a and the normalized hole diameter d / 2a in which the wavelength dispersion in wavelength 1310nm becomes + 30ps / nm * km or more in the dispersion compensation fiber which concerns on the best form of this invention It is. It is a figure which shows the relationship between the core radius a and the relative refractive index difference (DELTA) of a core part in the dispersion compensation fiber which concerns on the best form of this invention. In the dispersion compensating fiber according to the best mode of the present invention, the normalized hole position Λ / a, the normalized hole diameter d / 2a, the core radius a, and the relative refractive index difference Δ of the core part are set to predetermined values, respectively. It is a figure which shows the wavelength dispersion characteristic at the time of doing. 1 is a schematic diagram of an optical communication system using a dispersion compensating fiber according to the best mode of the present invention. It is a figure which shows the chromatic dispersion characteristic in the optical transmission line which connected the dispersion compensation fiber which concerns on the best form of this invention, and the 1310 nm band negative dispersion fiber which has a negative chromatic dispersion in a 1310 nm band.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,11 Core part 2,12 Clad part 3,13 Hole part 10,20 Dispersion compensation fiber 30 Optical communication system 31 Transmitter 32 Receiver 33 Optical transmission line 34 1310 nm band negative dispersion fiber

Claims (2)

A core portion a radius of the relative refractive index difference a is delta, and a cladding portion covering the core portion, a predetermined distance Λ from the center of the core portion, at least four diameters d which are formed at equal intervals And a hole portion of
A normalized hole position Λ / a in which the predetermined distance Λ is normalized by the core radius a, and a normalized hole diameter d / 2a in which the hole diameter d is normalized by the core diameter 2a of the core portion. The core radius a and the relative refractive index difference Δ of the core portion are (0.4 ≦ Λ / a ≦ 0.5), (0.2 ≦ d / 2a ≦ 0.3), and (4, respectively). 0.0 μm ≦ a ≦ 6.5 μm) and (0.7% ≦ Δ ≦ 1.5%), or (1.0 ≦ Λ / a ≦ 1.4) and (0.4 ≦ d / 2a ≦). 1.2), and (1.5 μm ≦ a ≦ 2.5 μm) and (0.7% ≦ Δ ≦ 1.5%), and the chromatic dispersion at a wavelength of 1310 nm is set to +30 ps / nm · km or more. A dispersion compensating fiber characterized by that. A 1310 nm-band negative dispersion fiber having negative chromatic dispersion in the 1310 nm band, and the dispersion-compensating fiber according to claim 1 disposed at a front stage, a rear stage, or both of the 1310 nm-band negative dispersion fiber. An optical transmission line.

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