JP4750678B2 - Negative dispersion optical fiber, broadband optical transmission line and optical transmission system - Google Patents

Description

  The present invention relates to large-capacity optical communication using a single-mode optical fiber, and in particular, a negative dispersion optical fiber that enables high-speed optical communication using two wavelength bands of a wavelength 1310 nm band and a wavelength 1550 nm band simultaneously, and the negative dispersion The present invention relates to a configuration method of a broadband optical transmission line using an optical fiber and an optical communication system using the broadband optical transmission line.

  With the widespread use of broadband data communication services, the transmission capacity required for optical communication systems has increased dramatically. For this reason, wavelength division multiplexing (WDM) technology for propagating light of a plurality of wavelengths in the same optical fiber has been widely used for the purpose of increasing the transmission capacity per single-mode optical fiber. Yes. High-speed optical communication technology with a transmission speed of 10 Gbit / s or more is also used for the purpose of expanding the transmission capacity per wavelength. In general, in such high-speed WDM transmission, degradation of transmission characteristics due to cumulative dispersion in an optical fiber becomes a problem. For this reason, for the purpose of reducing the accumulated dispersion in the optical transmission line, a dispersion compensating fiber (DCF) having a chromatic dispersion characteristic opposite in sign to that of the optical fiber used in the optical transmission line has been developed.

On the other hand, in recent years, a hole fiber having a structure (hole structure) in which a plurality of holes are opened in the optical fiber propagation axis direction at a uniform size and interval in the cross section of the optical fiber has been developed. In addition, it has attracted attention from the viewpoint of flexible controllability of chromatic dispersion characteristics. In general, a holey fiber having a hole structure with a uniform size and interval in the cross section of the optical fiber has a larger positive wavelength dispersion than an optical fiber without a conventional hole structure, and its zero dispersion wavelength is 1300 nm. It is known to shift to the following (for example, Non-Patent Document 1). Therefore, even in high-speed optical transmission using holey fibers, it is essential to reduce the accumulated dispersion in the signal light wavelength band. In Non-Patent Document 2, the possibility of reducing the accumulated dispersion in the wavelength 1550 nm band using the conventional DCF is required. Is disclosed.
However, the conventional DCF is intended for use in the wavelength band of 1550 nm, and at the maximum, the wavelength band of 1460 to 1625 nm. The conventional DCF is used, and in particular, the holes 1310 and 1550 nm of the holey fiber having the positive wavelength dispersion are used. There is a problem that it is difficult to simultaneously reduce the cumulative dispersion of bands.

J.C.Knight, et al., “Anomalous dispersion in photonic crystal fiber,” Photon. Technol. Lett., Vol.12, no.7, pp.807-809, 2000. Nakajima et al., “PCF 1550nm Band 40Gbit / s × 8 Wave DWDM Transmission Characteristics,” Shinso Univ., B-13-17, p.501, 2006.

  In view of the above background, in the present invention, an optical fiber having positive chromatic dispersion characteristics in the wavelength 1310 and 1550 nm bands, a negative dispersion optical fiber that simultaneously reduces cumulative dispersion in the wavelength band, and the negative dispersion optical fiber are provided. It is an object of the present invention to provide a broadband optical transmission line used and an optical transmission system using the broadband optical transmission line.

The negative dispersion optical fiber of the first invention that achieves the above object has negative chromatic dispersion characteristics in the wavelength 1310 nm band and the wavelength 1550 nm band, and has positive chromatic dispersion characteristics in the wavelength 1310 nm band and the wavelength 1550 nm band. A negative dispersion optical fiber that simultaneously reduces cumulative dispersion in two wavelength bands including at least the wavelength 1310 nm band and the wavelength 1550 nm band,
Ratio D ₁₆₂₅ / D ₁₅₅₀ of the chromatic dispersion D ₁₅₅₀ at a wavelength dispersion D ₁₆₂₅ and the wavelength 1550nm in wavelength 1625nm is 1.1 to 1.2, the ratio of the chromatic dispersion D ₁₅₅₀ and the wavelength dispersion D ₁₃₁₀ at a wavelength of 1310nm D ₁₃₁₀ / D ₁₅₅₀ is 0.3 to 0.6,
A clad part having a uniform refractive index, a first core part having a higher refractive index than the clad part, and a second core part having a lower refractive index than the clad part,
The ratio Ra = a1 / a of the radius a1 of the first core portion to the radius a of the second core portion is in the range of 0.24 to 0.70, and the relative refractive index of the second core portion to the cladding portion. The ratio RΔ = Δ1 / Δ between the difference Δ1 and the relative refractive index difference Δ of the first core portion with respect to the cladding portion is in the range of −0.13 to −1.73, and the radius of the second core portion The relative refractive index difference Δ between a and the first core part is in the range of 2.3 to 6.0 μm and 0.3 to 1.5%, respectively.

The negative dispersion optical fiber of the second invention is the negative dispersion optical fiber of the first invention.
The clad portion has at least six holes having a diameter d, which are arranged so as to circumscribe a circumference of a distance Λ from the center of the first core portion,
The ratio Λ / a between the distance Λ and the radius a of the second core part is 2.0 or more, and the ratio d / 2a between the hole diameter d and the diameter 2a of the second core part is 0. It is 5 or more.

Further, the broadband optical transmission line of the third invention includes the negative dispersion optical fiber of the first or second invention,
An optical fiber having positive wavelength dispersion characteristics in a wavelength 1310 nm band and a wavelength 1550 nm band is used.

The broadband optical transmission line of the fourth invention is the broadband optical transmission line of the third invention.
The optical fiber having positive wavelength dispersion characteristics in the wavelength 1310 nm band and the wavelength 1550 nm band is a hole fiber having a structure in which a plurality of holes are opened in the axial direction.

An optical transmission system according to a fifth aspect of the invention uses the broadband optical transmission line of the third or fourth aspect of the invention, and uses at least two wavelength bands including a wavelength band of 1310 nm and a wavelength of 1550 nm as a signal transmission band. .

As described above, according to the negative dispersion optical fiber of the present invention, it is possible to simultaneously reduce the accumulated dispersion in the wavelength band of the optical fiber having positive wavelength dispersion characteristics in the wavelength 1310 and 1550 nm bands. As compared with the conventional DCF, there is an effect that the reduction band of the cumulative dispersion can be dramatically expanded.
Further, according to the broadband optical transmission line and the optical transmission system of the present invention, it is possible to realize broadband and high-speed optical transmission using at least two wavelength bands of the wavelength 1310 and 1550 nm bands at the same time. There is also an effect that the capacity can be dramatically increased.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a conceptual diagram showing one configuration example of a broadband optical transmission line and an optical transmission system according to an embodiment of the present invention. As shown in FIG. 1, the optical transmission system according to the present embodiment includes a transmission unit 11, a reception unit 14, and a broadband optical transmission line 15, and the transmission unit 11 and the reception unit 14 include a broadband optical transmission line. 15 is connected.

  The transmission unit 11 has a function of generating an optical signal in a wavelength band including at least two wavelength bands of the wavelength 1310 and the 1550 nm band and sending it to the broadband optical transmission line 15. Similarly, the receiving unit 14 has a function of receiving an optical signal in the wavelength band transmitted from the transmitting unit 11 via the broadband optical transmission line 15.

  The broadband optical transmission line 15 includes an optical fiber 12 having positive chromatic dispersion characteristics in the wavelengths 1310 and 1550 nm, and a negative dispersion optical fiber 13 having negative chromatic dispersion characteristics in the wavelength bands. Here, the optical fiber 12 is constituted by, for example, a hole fiber having a structure (hole structure) in which a plurality of holes are opened in the propagation axis direction of the optical fiber at a uniform size and interval in the cross section of the optical fiber. be able to. In addition, by appropriately adjusting the length of the optical fiber 12 and the negative dispersion optical fiber 13 or one of them, the cumulative dispersion over the entire length of the broadband optical transmission line 15 in the wavelength 1310 and 1550 nm bands can be simultaneously reduced. It becomes possible.

  In the configuration example of FIG. 1, a configuration in which the negative dispersion optical fiber 13 is connected to the subsequent stage of the optical fiber 12 is illustrated, but the optical fiber 12 is connected to the subsequent stage of the negative dispersion optical fiber 13. It doesn't matter. The optical fiber 12 and the negative dispersion optical fiber 13 may be divided into a plurality of sections having an arbitrary length and connected in an arbitrary order. Further, the entire length of the negative dispersion optical fiber 13 or a part thereof may be incorporated in the transmission unit 11 and the reception unit 14 or one of them.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Example 1]
In Example 1 of the present invention, in the embodiment shown in FIG. 1, a plurality of holes are formed in an optical fiber having positive chromatic dispersion in the wavelength 1310 and 1550 nm bands, with a uniform size and spacing in the cross section of the optical fiber. A negative dispersion optical fiber and a broadband optical transmission line for a case where a hole fiber having a structure (hole structure) opened in the propagation axis direction of the optical fiber will be described with reference to the drawings.

2A and 2B are a conceptual diagram and a cross-sectional view showing the refractive index distribution of the negative dispersion optical fiber used in the example of the present invention. As shown in FIG. 2, the negative dispersion optical fiber of the present invention includes a clad part 21 having a uniform refractive index, a first core part 22 having a relative refractive index difference Δ and a radius a1 with respect to the clad part, and the clad And a second core portion 23 having a relative refractive index difference Δ1 and a radius a. The relative refractive index differences Δ and Δ1 (unit%) are described by the relationship of the following equation (1) using the refractive index n0 of the cladding part and the refractive index n of the first core part or the second core part. Is done.

Further, here, the radii of the first core part and the second core part and the ratio of the relative refractive index difference are defined by the following expressions (2) and (3) as Ra and RΔ, respectively.

  3A, 3B, and 3C are a diagram, a side view, and a cross-sectional view showing wavelength dispersion characteristics of the holey fiber used in the embodiment of the present invention. The solid line and the broken line in FIG. 3A show the measurement results for two types of hole fibers 1 and 2 having different hole structures (standardized hole diameter d0 / Λ0 and hole interval Λ0). In the hole fibers shown in FIGS. 3B and 3C, 31 is a cladding part, and 32 is a plurality of holes. As shown in FIGS. 3B and 3C, d0 and Λ0 are the diameter and interval of the hole 32, and the hole 32 has a uniform size (diameter d0) and interval Λ0 in the hole fiber cross section. And open in the propagation axis direction of the holey fiber. In the illustrated example, 60 holes are arranged in a hexagonal shape, but the number of holes is arbitrary (generally several tens to several hundreds), and the hole arrangement pattern is also an arbitrary shape to be rotated (4 (A rectangular shape, an octagonal shape, a concentric circular shape, etc.) are possible. In FIG. 3A, the hole fiber 1 has a hole structure of d0 / Λ0 = 0.5 and Λ0 = 7.5 μm, and the hole fiber 2 has a hole structure of d0 / Λ0 = 0.6 and Λ0 = 5.5 μm. Have As shown in FIG. 3A, the holey fibers 1 and 2 both have positive chromatic dispersion characteristics in the wavelength 1310 and 1550 nm bands, and the optical fiber (15) in the broadband optical transmission line (15) shown in FIG. It can be seen that it is applicable as 12).

Table 1 shows the chromatic dispersion at the wavelengths 1310, 1625 and 1460 nm of the hole fibers 1 and 2 shown in FIG. 3A from the measurement results of the hole fibers 1 and 2 shown in FIG. It is the list which computed the ratio of chromatic dispersion in wavelength 1550nm, _D1310 / _D1550 , _D1625 / _D1550 , and _D1460 / _D1550 , respectively.

From Table 1, the chromatic dispersion ratio D ₁₃₁₀ / D _{1550 at} wavelengths 1310 and 1550 nm and the chromatic dispersion ratio D ₁₆₂₅ / D _{1550 at} wavelengths 1625 and 1550 nm are about 0.4 to 0.5 and 1.15, respectively. It can be confirmed that there is a relationship.

FIG. 4 is a calculation result showing a relationship between the chromatic dispersion ratios D ₁₃₁₀ / D ₁₅₅₀ , D ₁₆₂₅ / D ₁₅₅₀ , and D ₁₄₆₀ / D ₁₅₅₀ in the hole fiber and the hole interval Λ0. The solid and broken lines in the figure show the results when the normalized hole diameter d0 / Λ0 is 0.2 and 0.5, respectively. As shown in FIG. 4, the chromatic dispersion ratios D ₁₃₁₀ / D ₁₅₅₀ and D ₁₆₂₅ / D ₁₅₅₀ of the holey fiber having a uniform hole structure are in the range of 0.3 to 0.6 and 1.1 to 1.2, respectively. Thus, it can be seen that the measurement results for the actual holey fiber shown in FIG. It can also be seen that the chromatic dispersion ratio D ₁₄₆₀ / D ₁₅₅₀ is about 0.8.

Table 2 is a list that summarizes the chromatic dispersion ratios D ₁₃₁₀ / D ₁₅₅₀ , D ₁₆₂₅ / D ₁₅₅₀ , and D ₁₄₆₀ / D ₁₅₅₀ in the holey fiber having the uniform hole structure shown in FIG.

Therefore, in the configuration example shown in FIG. 1 of the embodiment of the present invention, in the negative dispersion optical fiber (13), by realizing chromatic dispersion characteristics satisfying the relations of the following expressions (4) and (5), It is possible to simultaneously reduce the accumulated dispersion in the wavelength 1310, 1550 nm, and 1625 nm bands of the hole fiber. More preferably, by setting the ratio of chromatic dispersion D ₁₄₆₀ / D ₁₅₅₀ at wavelengths 1460 and 1550 nm to be close to 0.8, it is possible to realize a reduction in cumulative dispersion in a wider band including the wavelength 1460 nm band.

  FIG. 5 shows a radius ratio Ra and a relative refractive index satisfying the relations of the expressions (4) and (5) at the same time in the negative dispersion optical fiber having the refractive index distribution shown in FIG. 2 of the embodiment of the present invention. It is a drawing showing a region of a difference ratio RΔ. In the region surrounded by the two curves in the figure, a negative dispersion optical fiber having a wavelength dispersion characteristic that simultaneously satisfies the relations of the expressions (4) and (5) can be realized.

  FIG. 6 is a diagram showing the relationship between the maximum value (including the sign) of the relative refractive index difference Δ1 of the second core portion and the radius ratio Ra, which satisfies the design area of Ra and RΔ shown in FIG. is there. From FIG. 6, it can be seen that the maximum value of Δ1 tends to decrease as Ra increases. In general, when the cladding is made of pure silica glass, a technique of adding fluorine to the pure silica glass is used to obtain a lower refractive index than that of the cladding. From the viewpoint of difficulty, the range of change in the relative refractive index difference due to fluorine is limited to about -0.5%. That is, it is considered difficult to actually realize a negative dispersion optical fiber in a region where Ra exceeds 0.7.

Therefore, from FIGS. 5 and 6, in the negative dispersion optical fiber having the refractive index distribution shown in FIG. 2 of the embodiment of the present invention, the radius ratio Ra and the relative refractive index difference ratio RΔ are respectively expressed by the following equations (6). And it can be seen that by controlling in the region of (7), chromatic dispersion characteristics satisfying the relations of the equations (4) and (5) can be realized. The first and second cores of the negative dispersion optical fiber having the refractive index distribution shown in FIG. 2 of the present embodiment can be formed by adding germanium and fluorine to pure silica glass to change the refractive index. it can.

FIG. 7 is a diagram showing the relationship between the maximum value of the chromatic dispersion ratio D ₁₄₆₀ / D _{1550 at} the wavelengths 1460 and 1550 nm and the radius ratio Ra that can be realized in the design region of Ra and RΔ shown in FIG. is there. It can be seen from FIG. 7 that D ₁₄₆₀ / D ₁₅₅₀ tends to increase with Ra. In the relationship shown in the above formulas (6) and (7), it is more preferable that Ra is in the range of 0.35 to 0.51, so that D ₁₄₆₀ / D ₁₅₅₀ is 0.78 near 0.8. It can be seen that a more preferable characteristic of ˜0.82 can be set.

FIG. 8 is a view showing the relationship between the radius a of the second core portion and the relative refractive index difference Δ of the first core portion, which satisfies the design area of Ra and RΔ shown in FIG. The six curves in the figure show the relationship between a and Δ under the conditions where Ra is 0.24, 0.3, 0.4, 0.5, 0.6 and 0.7, respectively. It can be seen from FIG. 8 that when the relative refractive index difference Δ is constant, the core radius a tends to decrease as Ra increases. On the other hand, when the core radius a is constant, it can be seen that the relative refractive index difference Δ tends to decrease as Ra increases. Therefore, in the refractive index profile shown in FIG. 2 of the embodiment of the present invention, the core radius a of the second core part and the relative refractive index difference Δ of the first core part are indicated by a region surrounded by a solid line and a broken line in FIG. That is, it can be seen that a negative dispersion optical fiber satisfying the relational expressions (4) and (5) can be realized by designing in a region satisfying the following relational expressions (8) and (9).

  FIG. 9 is a diagram showing the configuration of the negative dispersion optical fiber satisfying the relationship between the core radius a and the relative refractive index difference Δ shown in FIG. 8 and the hole fiber 1 shown in FIG. It is drawing which shows the effective chromatic dispersion characteristic in the full length of the broadband optical transmission line of invention. In the figure, the solid line, the broken line, and the alternate long and short dash line indicate that (Ra, RΔ, a, Δ) in the refractive index distribution of FIG. 2 is (0.40, −0.34, 3.4 μm, 1.35%), respectively. , (0.50, -0.56, 3.8 μm, 0.80%) and (0.60, −0.90, 3.6 μm, 0.70%) designed results for negative dispersion optical fibers Indicates. A dotted line (thin broken line) shows a result when a conventional DCF, that is, a DCF that does not satisfy the relational expressions (4) and (5) is used. From FIG. 9, it can be seen that in the conventional DCF, the chromatic dispersion in the wavelength band other than the wavelength 1550 nm band tends to increase toward the negative sign side. On the other hand, when the negative dispersion optical fiber of the present invention is used, it can be seen that the absolute value of chromatic dispersion in the wavelengths 1310, 1550 and 1625 nm bands is reduced. Therefore, using the refractive index distribution shown in FIG. 2, a negative dispersion optical fiber satisfying the relational expressions (4) to (7), (8) and (9) is realized, and shown in FIG. 3 of the embodiment. By combining a plurality of holes with a hole fiber having a structure opened in the propagation axis direction of the cross section of the optical fiber at a uniform size and interval in the cross section of the optical fiber, accumulation in at least two wavelengths of wavelengths 1310 and 1550 nm is achieved. It can be seen that the broadband optical transmission line of the present invention that simultaneously reduces dispersion can be realized.

  In the embodiment of the present invention, as shown in FIG. 2, a clad portion having a uniform refractive index, a first core portion having a higher refractive index than the clad portion, and a second refractive index lower than that of the clad portion. Although a negative dispersion optical fiber having a core portion has been described, a negative dispersion optical fiber having an arbitrary refractive index distribution, for example, a third having a higher refractive index than the cladding portion outside the second core portion. A refractive index distribution having a core part and a fourth core part (outside the third core part) having a lower refractive index than the cladding part may be used. In the optical fiber having the refractive index distribution, By satisfying the relational expressions (4) and (5), it is possible to achieve the same operation and effect as the embodiment of the present invention.

[Example 2]
In the second embodiment of the present invention, a case where a hole structure is used in a negative dispersion optical fiber will be described with reference to the drawings.

  FIG. 10 is a conceptual diagram showing a cross-sectional structure of a negative dispersion optical fiber using a hole structure. As shown in FIG. 10, the negative dispersion optical fiber having a hole structure according to the present invention circumscribes the circumference at a distance Λ from the center of the core portion 81, and is evenly spaced (circumferential direction) in the cladding portion 82 having a uniform refractive index. And a structure (hole structure) having at least six holes 83 with a diameter d arranged at equal intervals. Here, the core part 81 in FIG. 10 corresponds to the core region including the first core part and the second core part shown in FIG. 2 of Example 1, and the core radius a in FIG. It is equal to the radius a of the second core part inside.

FIG. 11 shows the relationship between the amount of change in the chromatic dispersion ratio and the normalized hole position Λ / a in which the distance Λ to the hole is normalized by the radius a of the core in a negative dispersion optical fiber having a hole structure. It is a drawing. Here, the vertical axis indicates the amount of change in the chromatic dispersion ratio, D ₁₃₁₀ / D ₁₅₅₀ , D ₁₄₆₀ / D _1550, and D ₁₆₂₅ / D ₁₅₅₀ after the hole structure is imparted before the pore structure is imparted. The solid line, the broken line, and the alternate long and short dash line in the figure indicate that the normalized hole diameter d / 2a obtained by normalizing the hole diameter d with the core diameter 2a is 0.2, 0.6, and 1.0, respectively. The calculation result is shown. From FIG. 11, it can be seen that the amount of change in the chromatic dispersion ratios D ₁₃₁₀ / D ₁₅₅₀ and D ₁₄₆₀ / D ₁₅₅₀ tends to increase as the normalized hole position Λ / a decreases. On the other hand, it can be seen that the amount of change of D ₁₆₂₅ / D ₁₅₅₀ tends to decrease with Λ / a. It can also be seen that if the normalized hole position Λ / a is 2.0 or more, the amount of change in the chromatic dispersion ratio can be reduced to 0.1 or less. More preferably, by setting the normalized hole position Λ / a to 2.3 or more, the amount of change in the chromatic dispersion ratios D ₁₄₆₀ / D ₁₅₅₀ and D ₁₆₂₅ / D ₁₅₅₀ accompanying the addition of the holes is made substantially zero. It becomes possible.

FIG. 12 is a drawing showing the relationship between the amount of change in the chromatic dispersion ratio and the normalized hole diameter d / 2a in a negative dispersion optical fiber having a hole structure with a normalized hole position Λ / a of 2.0. . The solid line, broken line, and alternate long and short dash line in the figure indicate the results for the chromatic dispersion ratios D ₁₃₁₀ / D ₁₅₅₀ , D ₁₄₆₀ / D ₁₅₅₀ and D ₁₆₂₅ / D ₁₅₅₀ , respectively. As shown in FIG. 12, the dependence of the change amount of the chromatic dispersion ratio on the normalized hole diameter d / 2a is relatively smaller than the dependence on the normalized hole position Λ / a shown in FIG. It can be seen that in the region of 0.5 or more, there is a tendency to converge to a substantially constant change amount.

Therefore, from the results shown in FIGS. 11 and 12, in the refractive index distribution suitable for the procedure described in Example 1, by providing holes at positions where the normalized hole position Λ / a is 2.0 or more. Thus, it is possible to reduce the amount of change in the chromatic dispersion ratio and to maintain the preferred chromatic dispersion ratio conditions shown in the relational expressions (4) and (5) of the first embodiment. More preferably, in the procedure shown in Example 1, the following equation (10) is used as the condition of the chromatic dispersion ratio D ₁₃₁₀ / D ₁₅₅₀ , so that the suitable chromatic dispersion shown in Example 1 can be obtained even after the formation of holes. It becomes possible to satisfy the relational expressions (4) and (5) of the ratio.

  FIG. 13 is a diagram showing the relationship between the reduction amount of bending loss and the normalized hole diameter d / 2a in a negative dispersion optical fiber having a hole structure. Here, the vertical axis represents the amount of reduction in bending loss accompanying the provision of holes. The solid line, broken line, and alternate long and short dash line in the figure represent the results when the normalized hole positions Λ / a are 2.0, 2.2, and 2.4, respectively. From FIG. 13, it can be seen that the bending loss of the negative dispersion optical fiber is improved with the provision of the holes, and the effect increases exponentially with respect to the normalized hole diameter d / 2a. Also, the bending loss reduction effect increases as the normalized hole position Λ / a decreases, but the dependency of the bending loss reduction effect on Λ / a is relatively small compared to the dependency on d / 2a. As can be seen, in the negative dispersion optical fiber having a refractive index profile suitable for the procedure shown in Example 1, by providing a hole structure in which the normalized hole diameter d / 2a is 0.5 or more. It can be seen that the bending loss can be improved by an order of magnitude or more compared to before the formation of holes. More preferably, when the normalized hole position Λ / a is in the range of 2.0 to 2.4 and the normalized hole diameter d / 2a is 1.1 or more, the bending loss due to the provision of the hole structure is reduced. The reduction effect can be made two digits or more.

  As described above, in the negative dispersion optical fiber having the refractive index distribution suitable for the procedure shown in Example 1, the normalized hole position Λ / a is 2.0 or more and the normalized hole diameter d / 2a is By providing the hole structure shown in FIG. 10 of Example 2 under the condition of 0.5 or more, the condition of the chromatic dispersion ratio suitable for the negative dispersion optical fiber of the present invention is satisfied, and the bending loss is remarkably increased. It is possible to realize a negative dispersion optical fiber that is reduced to a very low level.

  Note that the change in the chromatic dispersion ratio associated with the provision of holes is caused by the holes changing the electric field distribution in the cross section of the optical fiber, and generally the electric field distribution in the optical fiber decreases in the radial direction. It has the characteristic to do. Therefore, as shown in FIGS. 11 and 12, the change in the chromatic dispersion ratio can be controlled mainly by the distance to the hole, and hardly depends on the number of holes. In addition, the effect of improving the bending loss associated with the provision of the holes is obtained by blocking the leaching of the electric field distribution accompanying the provision of the bending into the cladding part. When holes are provided, a stronger bending loss reduction effect can be realized by increasing the region where the hole interface blocks the electric field distribution. Therefore, in the second embodiment of the present invention, the case where the number of holes is six has been described. However, even when a hole structure having more than six holes is provided, the normalized hole position Λ / a and the normalized holes are also described. By setting the hole diameter d / 2a to 2.0 or more and 0.5 or more, respectively, the effect of maintaining the chromatic dispersion ratio and the effect of reducing the bending loss equal to or more than the case of 6 holes are obtained. It can be realized.

  In particular, the present invention provides a negative dispersion optical fiber, a broadband optical transmission line using the negative dispersion optical fiber, and the broadband, which enable high-speed optical communication using two wavelength bands of a wavelength 1310 nm band and a wavelength 1550 nm band simultaneously. The present invention is useful when applied to an optical communication system using an optical transmission line.

It is a conceptual diagram which shows the structural example of the broadband optical transmission line and optical transmission system which concern on the embodiment of this invention. It is the conceptual diagram and sectional drawing which show the refractive index distribution of the negative dispersion optical fiber used in the Example of this invention. It is a figure which shows the wavelength dispersion characteristic of the holey fiber used in the Example of this invention, a side view, and sectional drawing. 6 is a diagram illustrating a relationship between a wavelength dispersion ratio and a hole interval Λ0 in a holey fiber having a uniform hole structure, which is considered in an example of the present invention. 5 is a diagram showing a region of a radius ratio Ra and a relative refractive index difference ratio RΔ that satisfies the requirements of the chromatic dispersion ratios D ₁₃₁₀ / D ₁₅₅₀ and D ₁₆₂₅ / D ₁₅₅₀ in the negative dispersion optical fiber of the present invention. 6 is a diagram illustrating the relationship between the maximum value of the relative refractive index difference Δ1 of the second core portion and the radius ratio Ra that can be realized using the relationship between Ra and RΔ shown in FIG. 5 according to the embodiment of the present invention. Achievable using embodiments Figure 5 the relationship Ra and RΔ shown in the of the present invention, is a view showing a relationship between the wavelength dispersion ratio D ₁₄₆₀ / D ₁₅₅₀ and the radius ratio Ra at the wavelength 1460 and 1550 nm. 6 is a diagram illustrating a relationship between a radius a of the second core portion and a relative refractive index difference Δ of the first core portion satisfying the relationship between Ra and RΔ illustrated in FIG. 5 according to the embodiment of the present invention. The broadband optical transmission line of the present invention constructed using the negative dispersion optical fiber satisfying the relationship between a and Δ shown in FIG. 8 of the embodiment of the present invention and the holey fiber 1 shown in FIG. 3 of the embodiment. It is drawing which shows an effective wavelength dispersion characteristic. It is a conceptual diagram which shows the cross-section of the negative dispersion optical fiber using a void structure. 6 is a drawing showing the relationship between the amount of change in wavelength dispersion ratio and the normalized hole position Λ / a in a negative dispersion optical fiber having a hole structure. 6 is a drawing showing the relationship between the amount of change in wavelength dispersion ratio and the normalized hole diameter d / 2a in a negative dispersion optical fiber having a hole structure with a normalized hole position Λ / a of 2.0. It is drawing which shows the relationship between the reduction amount of a bending loss and the normalized hole diameter in the negative dispersion optical fiber which has a hole structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Transmission part 12 Optical fiber which has positive wavelength dispersion characteristic in wavelength 1310 and 1550 nm band 13 Negative dispersion optical fiber 14 Reception part 15 Broadband optical transmission line 21 Cladding part 22 1st core part 23 2nd core part 31 Cladding part 32 Sky Hole 81 Core part 82 Clad part 83 Hole

Claims (5)

Two wavelengths including at least the wavelength 1310 nm band and the wavelength 1550 nm band of an optical fiber having negative wavelength dispersion characteristics in the wavelength 1310 nm band and the wavelength 1550 nm band and having positive wavelength dispersion characteristics in the wavelength 1310 nm band and the wavelength 1550 nm band A negative dispersion optical fiber that simultaneously reduces the cumulative dispersion in the band,
Ratio D ₁₆₂₅ / D ₁₅₅₀ of the chromatic dispersion D ₁₅₅₀ at a wavelength dispersion D ₁₆₂₅ and the wavelength 1550nm in wavelength 1625nm is 1.1 to 1.2, the ratio of the chromatic dispersion D ₁₅₅₀ and the wavelength dispersion D ₁₃₁₀ at a wavelength of 1310nm D ₁₃₁₀ / D ₁₅₅₀ is 0.3 to 0.6,
A clad part having a uniform refractive index, a first core part having a higher refractive index than the clad part, and a second core part having a lower refractive index than the clad part,
The ratio Ra = a1 / a of the radius a1 of the first core portion to the radius a of the second core portion is in the range of 0.24 to 0.70, and the relative refractive index of the second core portion to the cladding portion. The ratio RΔ = Δ1 / Δ between the difference Δ1 and the relative refractive index difference Δ of the first core portion with respect to the cladding portion is in the range of −0.13 to −1.73, and the radius of the second core portion A negative dispersion optical fiber, wherein the relative refractive index difference Δ between a and the first core portion is in the range of 2.3 to 6.0 μm and 0.3 to 1.5%, respectively. The negative dispersion optical fiber according to claim 1 ,
The clad portion has at least six holes having a diameter d, which are arranged so as to circumscribe a circumference of a distance Λ from the center of the first core portion,
The ratio Λ / a between the distance Λ and the radius a of the second core part is 2.0 or more, and the ratio d / 2a between the hole diameter d and the diameter 2a of the second core part is 0. A negative dispersion optical fiber characterized by being 5 or more. The negative dispersion optical fiber according to claim 1 or 2 ,
A broadband optical transmission line comprising an optical fiber having positive chromatic dispersion characteristics in a wavelength 1310 nm band and a wavelength 1550 nm band. In the broadband optical transmission line according to claim 3 ,
A broadband optical transmission line, wherein the optical fiber having positive chromatic dispersion characteristics in the wavelength 1310 nm band and the wavelength 1550 nm band is a hole fiber having a structure in which a plurality of holes are opened in the axial direction. 5. An optical transmission system using the broadband optical transmission line according to claim 3 or 4 , wherein at least two wavelength bands including a wavelength 1310 nm band and a wavelength 1550 nm band are used as a signal transmission band.

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