JP2005181911A - Photonic crystal fiber, dispersion compensation fiber module and optical fiber transmission line - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photonic crystal fiber for improving residual dispersion in a wide wavelength range without degrading the RDS of a dispersion compensation fiber having large RDS and a dispersion compensation fiber module and an optical fiber transmission line. <P>SOLUTION: In a photonic crystal fiber in which grid holes which are provided in a clad part surrounding a core part and having the same diameter are arranged in a hexagonal closest structure, this photonic crystal fiber is characterized in that three grid hole formation parts which do not adjoin each other in six grid hole formation parts arranged around the core part are not vacant holes and an interval Λ between the grid holes is within the range of 1.0 to 1.5μm and the diameter (d) of the grid hole is within the range of 0.6 to 0.8μm. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a photonic crystal fiber and a dispersion-compensating fiber module used for compensating the cumulative chromatic dispersion of a transmission optical fiber having positive chromatic dispersion in a used wavelength range, and in particular, a fourth-order after dispersion compensation. The present invention relates to a photonic crystal fiber, a dispersion compensating fiber module, and an optical fiber transmission line that can reduce dispersion and suppress residual dispersion in a wide wavelength range.

  With the practical use of erbium-doped optical fiber amplifiers, systems using optical amplifiers such as ultra-long distance non-regenerative repeaters have already been commercialized at wavelengths of 1.53 μm to 1.63 μm. In addition, with the increase in communication capacity, development of wavelength multiplexing transmission has been rapidly advanced, and some transmission paths have already been commercialized. In the future, it is expected that the widening of the wavelength band and the increase in the number of wavelength multiplexing will proceed rapidly.

  Assuming high-speed transmission, these transmission lines are desirably optical fiber transmission lines that have as little chromatic dispersion as possible in the transmission band and that do not become zero in order to suppress nonlinear effects.

  In order to increase the transmission capacity in the wavelength division multiplexing transmission system, it is effective to widen the used wavelength region and increase the transmission rate per channel. In order to increase the transmission speed, it is necessary to reduce the cumulative dispersion of the transmission path. As the transmission speed increases, the allowable residual dispersion decreases. Therefore, dispersion compensation for each span becomes indispensable when the transmission distance becomes long and the transmission speed is increased. Since this is required over the entire wavelength band to be used, it is necessary to simultaneously compensate for the accumulated dispersion slope of the transmission line.

  Wavelength 1.3 μm band single-mode optical fiber networks have been widely used since early and are inexpensive and have been laid and used extensively. Also, a dispersion-shifted optical fiber in which the value of chromatic dispersion is almost zero in the 1.55 μm wavelength band, or a dispersion of around several ps / nm / km in the used wavelength band by slightly shifting the zero dispersion wavelength from the used wavelength band Various non-zero dispersion shifted optical fibers (NZ-DSF) are also used. These optical fibers are several ps in C-band (wavelength 1.525 μm to 1.565 μm), L-band (wavelength 1.565 μm to 1.625 μm), U-band (1.625 μm to 1.675 μm). It has a wavelength dispersion of about 10 nm / km / km to 10 ps / nm / km. When these fibers are used, chromatic dispersion is accumulated. By compensating the accumulated chromatic dispersion with a dispersion compensating fiber module, it becomes possible to transmit 10 Gb / s or 40 Gb / s.

Examples of the dispersion compensating fiber for compensating the chromatic dispersion and dispersion slope of the non-zero dispersion shifted optical fiber (hereinafter referred to as NZ-DSF) include, for example, dispersion compensating fibers disclosed in Patent Documents 1 and 2 and Non-Patent Document 1. There is. By using the dispersion compensating fiber disclosed in these documents, it is possible to compensate the accumulated chromatic dispersion in the wavelength range from 1.525 μm to 1.625 μm of the NZ-DSF.
JP 2000-162462 A JP 2000-47048 A Kazuhiko Aikawa et al., “High-performance, broadband dispersion compensating fiber module for NZ-DSF”, IEICE Technical Report, OCS 2002-7, April 2002, p35-p40 Yamamoto et al., "Hybrid dispersion compensating fiber module considering fourth-order dispersion characteristics", Electronics Society Conference of IEICE, C-3-49, September 2003 A. Ferrando, et al “Nearly zero ultraflattened dispersion in photonic crystal fibers,” Optics Letters. Vol. 25, No. 11, 2000

Here, the dispersion slope compensation will be briefly described. A value used when obtaining the performance of dispersion slope compensation is a ratio of dispersion slope to chromatic dispersion (RDS: Relative Dispersion Slope). If the chromatic dispersion is D and the dispersion slope is S, RDS can be expressed as the following equation (1).
RDS = S / D (1)

If the RDS of the dispersion compensating fiber is equal to the RDS of the transmission optical fiber, the dispersion slope can be completely compensated when the chromatic dispersion is compensated.
The dispersion slope compensation rate can be expressed as the following equation (2), where RDS of the transmission optical fiber is RDS _TMF and RDS of the dispersion compensation fiber is RDS _SC-DCF .
Dispersion slope compensation ratio = RDS _SC-DCF / RDS _TMF × 100 (2)

When the RDS of the dispersion compensating fiber is equal to the RDS of the transmission optical fiber, if the chromatic dispersion is completely compensated, the dispersion slope can be completely compensated at that wavelength. This is schematically shown in FIG. However, this is a case where the dispersion slope of the transmission optical fiber and the dispersion slope of the dispersion compensation fiber are constant with respect to the wavelength. In actual transmission optical fibers and dispersion compensating fibers, the dispersion slope has wavelength dependency. That is, the dispersion characteristic is not a straight line but a curved curve. Although the wavelength dependence of the dispersion slope of the transmission optical fiber is smaller than that of the dispersion compensating fiber, the dispersion compensating fiber is relatively large. In particular, the dispersion compensation fiber having a larger RDS has a greater wavelength dependency of the dispersion slope. A dispersion curve of the dispersion compensating fiber for NZ-DSF is shown in FIG. Looking at the dispersion curve of the dispersion compensating fiber having a large RDS, it can be seen that the dispersion curve is convex upward. If an attempt is made to reduce the residual dispersion at the center wavelength using such a dispersion compensating fiber, dispersion overcompensation occurs on the short wavelength and long wavelength sides as shown in FIG. 3, resulting in deterioration of transmission characteristics. Normally, adjustment is made so that the residual dispersion becomes as small as possible within the band. Therefore, as shown in FIGS. 4 and 5, the residual dispersion is set to the plus side near the center wavelength, and the absolute value of the residual dispersion is obtained over the entire wavelength used. The value is adjusted to be smaller.
4 and 5 show the residual dispersion when each transmission optical fiber 80 km is connected to a dispersion compensating fiber module whose length is adjusted so that the absolute value of the residual dispersion becomes small in the band.

The dispersion compensating fiber has a refractive index profile as shown in FIG. 6, for example. The delta of the refractive index distribution can adjust various optical characteristics including RDS by adjusting the ratio of the radius of each layer. This RDS can be designed and manufactured relatively easily in the range where the RDS is small, and the dispersion compensation fiber having a small dispersion curve but a RDS exceeding 0.01 nm ⁻¹ has a wavelength of If an attempt is made to produce while increasing the absolute value of the dispersion, this dispersion curve tends to bend.
For this reason, if the chromatic dispersion of the NZ-DSF is compensated using the dispersion compensating fiber as shown in FIG. 2, an upward convex residual dispersion is generated as shown in FIGS.

  As a method for improving the characteristics of a dispersion compensating fiber having a small RDS, a technique such as Non-Patent Document 2 is disclosed. However, this is applied to the dispersion compensating fiber for SMF, and the absolute value of dispersion of the dispersion compensating fiber (concave dispersion curve) for connection for improving the fourth order dispersion is improved by being connected. Since it has a dispersion value of about three times that of the dispersion compensating fiber (convex dispersion curve) on the side, it is not desirable because it causes a large RDS degradation.

  Further, Non-Patent Document 3 reports a fiber having a downwardly convex dispersion curve in L-band or U-band in a fiber using a photonic crystal structure. However, this is a method for obtaining a dispersion flat fiber, and is not optimized in terms of compensating for the residual dispersion after compensation by the dispersion compensation fiber module.

  The present invention is made in view of the above circumstances, and is connected to a dispersion compensating fiber having a large RDS to improve fourth-order dispersion. In particular, the photonic crystal can be improved without degrading the RDS of the dispersion compensating fiber having a large RDS. An object of the present invention is to provide a fiber, a dispersion compensating fiber module using the fiber, and an optical fiber transmission line using the module.

In order to achieve the above object, the present invention provides a photonic crystal fiber in which lattice holes of the same diameter provided in a cladding portion surrounding a core portion are arranged in a hexagonal close-packed structure, and arranged around the core portion. Among the six lattice hole forming portions that are not adjacent to each other, three lattice hole forming portions that are not adjacent to each other are not holes, and the lattice hole interval Λ is in the range of 1.0 to 1.5 μm. A photonic crystal fiber having a diameter d in the range of 0.6 to 0.8 μm is provided.
The photonic crystal fiber of the present invention has a wavelength at which the dispersion slope becomes zero in the wavelength range of 1.525 μm to 1.565 μm, the dispersion slope is negative at a wavelength shorter than that wavelength, and the dispersion slope is It is preferable that the dispersion slope is positive at a wavelength longer than the wavelength at which it becomes zero. This photonic crystal fiber preferably has a transmission loss of 1.0 dB / km or less in a wavelength range of 1.525 μm to 1.565 μm.
The photonic crystal fiber of the present invention has a wavelength at which the dispersion slope becomes zero in a wavelength range of 1.565 μm to 1.625 μm, and the dispersion slope is negative at a wavelength shorter than that wavelength. The dispersion slope may be positive at a wavelength longer than the wavelength at which becomes zero. This photonic crystal fiber preferably has a transmission loss of 1.0 dB / km or less in a wavelength range of 1.565 μm to 1.625 μm.
The photonic crystal fiber of the present invention has a wavelength at which the dispersion slope becomes zero in a wavelength range of 1.625 μm to 1.675 μm, and the dispersion slope is negative at a wavelength shorter than the wavelength, and the dispersion slope The dispersion slope may be positive at a wavelength longer than the wavelength at which becomes zero. This photonic crystal fiber preferably has a transmission loss of 1.0 dB / km or less in a wavelength range of 1.625 μm to 1.675 μm.

Further, the present invention provides a fiber formed by connecting a dispersion compensating fiber having negative chromatic dispersion and dispersion slope over the entire wavelength range of 1.525 μm to 1.675 μm and the above-described photonic crystal fiber of the present invention. A dispersion compensating fiber module is provided.
In this dispersion compensating fiber module, the value obtained by dividing the value of the dispersion slope by the value of chromatic dispersion is preferably in the range of 0.003 nm ^{−1 to} 0.03 nm ⁻¹ .

  The present invention also provides an optical fiber transmission line formed by connecting the above-described dispersion compensating fiber module of the present invention to a transmission optical fiber.

The photonic crystal fiber of the present invention is a photonic crystal fiber in which lattice holes of the same diameter provided in a cladding portion surrounding a core portion are arranged in a hexagonal close-packed structure, and is arranged around the core portion. Of the six lattice hole forming portions, three lattice hole forming portions that are not adjacent to each other are not holes, and the lattice hole interval Λ is in the range of 1.0 to 1.5 μm, and the diameter d of the lattice holes is Has a wavelength in which the dispersion slope is zero in the wavelength range of 1.525 μm to 1.675 μm, and is dispersed at wavelengths shorter than that wavelength. The slope is negative and the dispersion slope is positive at wavelengths longer than the wavelength at which the dispersion slope is zero. By using a photonic crystal fiber having a downward convex dispersion curve, the upward convex dispersion characteristic can be flatly compensated.
The dispersion compensating fiber module of the present invention connects a dispersion compensating fiber having negative chromatic dispersion and dispersion slope over the entire wavelength range of 1.525 μm to 1.675 μm and the photonic crystal fiber of the present invention. Therefore, the residual dispersion can be kept low over a wide band, and an optical fiber transmission line capable of high-speed transmission can be constructed.
Further, since the optical fiber transmission line of the present invention is formed by connecting the dispersion compensating fiber module to a transmission optical fiber, the residual dispersion can be kept low in a wide band, and high-speed transmission is possible.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 8 is a diagram showing an example of a cross-sectional structure of the photonic crystal fiber of the present invention. In the photonic crystal fiber of the present invention, lattice holes of the same diameter provided in the clad portion surrounding the core portion are arranged in a hexagonal close-packed structure, and six lattice hole forming portions arranged around the core portion. Among them, the three lattice hole forming portions that are not adjacent to each other are not vacant holes but have cladding portions, the lattice hole interval Λ is in the range of 1.0 to 1.5 μm, and the diameter d of the lattice holes is 0. It is characterized by being in the range of 6 to 0.8 μm. If the gap Λ of the lattice holes is less than 1.0 μm, the curve of the dispersion curve becomes large and the residual dispersion becomes large. Further, if the lattice hole interval Λ exceeds 1.5 μm, the curve of the dispersion curve becomes small, and the residual dispersion cannot be reduced in a wide band, which is not preferable. If the diameter d of the grating holes is less than 0.6 μm, the bottom of the curve of the dispersion curve shifts to a short wavelength, which is not suitable for the fourth-order dispersion compensation in the wavelength band of the present invention. If the diameter d of the grating hole exceeds 0.8 μm, the bottom of the curve of the dispersion curve shifts to a long wavelength, which is not preferable for the fourth-order dispersion compensation in the wavelength band of the present invention.

  Since the photonic crystal fiber of the present invention has the above-described structure, C-band (wavelength 1.525 μm to 1.565 μm), L-band (wavelength 1.565 μm to 1.625 μm), U-band (1 .625 μm to 1.675 μm) and the like, the dispersion slope has a wavelength that becomes zero, the dispersion slope is negative at a wavelength shorter than that wavelength, and the wavelength at which the dispersion slope becomes zero. It has a dispersion characteristic that the dispersion slope becomes positive at a long wavelength.

Thus, by using a photonic crystal fiber whose dispersion curve is convex downward (see FIGS. 11, 16, and 22), it is possible to compensate for the residual dispersion that is convex upward.
The photonic crystal fiber of the present invention desirably has a transmission loss of 1.0 dB / km or less in a wavelength region of 1.525 μm to 1.675 μm. If the transmission loss is 1.0 dB / km or less, the residual dispersion characteristics can be improved without greatly degrading the loss of the module even when connected to the dispersion compensating fiber module.

9 and 10 are diagrams for explaining an example of a method for producing a photonic crystal fiber according to the present invention.
In this method, first, a large number of quartz rods 7 and quartz tubes 8 are prepared. It is desirable that these have substantially the same outer diameter. Next, three quartz rods 7 and three quartz tubes 8 are alternately arranged around the quartz rod 7 to form a hexagonal close-packed structure, and 12 quartz tubes 8 are arranged around the hexagonal close-packed structure. Arranged to form an assembly 9 having the structure shown in FIG.

  Separately, a quartz tube 10 having a hole for inserting the assembly 9 is prepared, and the assembly 9 is inserted into the hole of the quartz tube 10 as shown in FIG. Next, this composite is used as a preform, mounted in an optical fiber drawing furnace, and drawn in the same manner as a normal optical fiber to produce a photonic crystal fiber having a desired outer diameter.

  The dispersion compensating fiber module of the present invention has a dispersion compensating fiber having a negative chromatic dispersion and dispersion slope over the entire wavelength range from 1.525 μm to 1.675 μm, and a dispersion characteristic that is convex downward in the wavelength band to be used. It is characterized by having a fiber formed by connecting the photonic crystal fiber of the present invention. For example, as shown in FIG. 6, the dispersion compensating fiber used in the dispersion compensating fiber module of the present invention comprises a core 1 and a clad 2, and the core 1 has a high refractive index central core portion 3 and its core An intermediate core portion 4 provided at the outer periphery and having a lower refractive index than the clad 2; a ring core portion 5 provided at the outer periphery of the intermediate core portion 4 and having a refractive index higher than the clad 2 and lower than the central core portion 3; A dispersion compensating fiber having a structure including a depressed core portion 6 provided on the outer periphery of the ring core portion 5 and having a refractive index between the intermediate core portion 4 and the clad 2, or a depressed core portion 6 as shown in FIG. A dispersion compensation fiber having the same structure as the dispersion compensation fiber of FIG.

  By using the dispersion compensating fiber module of the present invention, the wavelength characteristics of residual dispersion can be flattened, and the residual dispersion can be kept small over the entire wavelength range to be used. A transmission path capable of high-speed transmission such as 10 Gbit / s or 40 Gbit / s can be provided.

The dispersion compensating fiber module of the present invention is characterized in that a value (RDS) obtained by dividing the dispersion slope value by the chromatic dispersion value is 0.003 nm ^{−1 to} 0.03 nm ⁻¹ . If this RDS is less than 0.003 nm ⁻¹ , dispersion slope compensation is insufficient, and if RDS exceeds 0.03 nm ⁻¹ , the dispersion slope is overcompensated, which is not preferable.

  This RDS value can be obtained by combining the photonic crystal fiber of the present invention with a known dispersion compensating fiber. When combining the photonic crystal fiber and the dispersion compensating fiber with a convex dispersion curve below the target RDS, adjust the RDS and chromatic dispersion values, and set the fiber length to be used for each. It is necessary to adjust appropriately.

  The optical fiber transmission line of the present invention is formed by connecting the dispersion compensating fiber modules. By using these modules as an optical fiber transmission line, since the residual dispersion is small over the entire wavelength range to be used, high-speed transmission such as 10 Gbit / s and 40 Gbit / s becomes possible.

  Hereinafter, the effects of the present invention will be demonstrated by examples, but the present invention is not limited to the following examples. Of the comparative examples and examples, [Comparative Example 1] is an example when Aeff (effective cross-sectional area) expansion type NZ-DSF and low dispersion slope type NZ-DSF are compensated with a conventional dispersion compensating fiber module ( [Comparative Example 2] is an example (L-band) when Aeff expansion type NZ-DSF, low dispersion slope type NZ-DSF, and DSF are compensated by a conventional dispersion compensating fiber module. [Comparative Example 3] is an example (U-band) when DSF is compensated by a conventional dispersion compensating fiber module. [Embodiment 1] is an example (C-band) when Aeff expansion type NZ-DSF and low dispersion slope type NZ-DSF are compensated by the dispersion compensating fiber module of the present invention, and [Embodiment 2] is Aeff. The expanded NZ-DSF, the low dispersion slope type NZ-DSF, and the DSF are compensated by the dispersion compensating fiber module of the present invention (L-band), and [Example 3] is the DSF of the dispersion compensation of the present invention. It is an example (U-band) when compensating with a fiber module.

[Comparative Example 1]
Dispersion compensating fibers A and B (hereinafter referred to as fibers A and B) having a refractive index profile as shown in FIG. 6 were produced by a known method such as VAD method or MCVD method. At this time, Δ1, Δ2, Δ3, Δ4, b / a, c / b, d / c, and depressed core radius d were manufactured so as to have the values shown in Table 1.
Table 2 shows the optical characteristics of these fibers A and B. The chromatic dispersion characteristics of the fibers A and B are as shown by the curves A and B in FIG.
Using the dispersion compensating fiber module using these fibers A and B, the residual dispersion characteristics when the accumulated chromatic dispersion of 80 km of NZ-DSF is compensated are as shown by thick lines in FIGS. became.
The residual dispersion within each band is 5 ps / nm or less when the module using the fiber A is connected to the low dispersion slope type NZ-DSF, and the fiber B is used for the large Aeff type NZ-DSF. When the module was connected, the maximum residual dispersion was 20 ps / nm or less.
Assuming that the allowable residual dispersion limit of 10 Gbit / s transmission is 1040 ps / nm, when a module using fiber A is connected to a low slope NZ-DSF, further dispersion compensation is required at 208 km, and a large Aeff type When a module using the fiber B is connected to the NZ-DSF, further dispersion compensation is required at 52 km, which increases the number of dispersion compensations and complicates the overall configuration of the optical fiber transmission line, which is not desirable.

[Example 1]
9 and 10 show a method for manufacturing an optical fiber according to the present invention. First, the quartz tube is selected so that the interval between the lattice holes and the diameter of the lattice hole become predetermined values, and the quartz tube and the quartz rod are arranged as shown in FIG. As shown in FIG. 10, the photonic crystal fiber (fiber C) of the present invention is obtained by inserting and setting it in a larger quartz tube, melting it and spinning it. As shown in FIG. 8, the core portion is a photonic crystal structure fiber in which the same lattice holes (holes of lattice structure) provided in the cladding portion surrounding the core portion are arranged in a hexagonal close-packed structure. The spacing (lattice spacing) Λ was 1.2 μm, and the diameter d of the lattice holes was 0.66 μm.
FIG. 11 shows the chromatic dispersion characteristics of the fiber C of the present invention. The transmission loss was 0.32 dB / km (1.55 μm).
A dispersion compensating fiber having a refractive index profile as shown in FIG. 6 was manufactured by a known method such as VAD method or MCVD method. At this time, Δ1, Δ2, Δ3, Δ4, b / a, c / b, d / c, and depressed core radius d were manufactured so as to have the values shown in Table 3.
Table 4 shows optical characteristics of the dispersion compensating fibers D and E (hereinafter referred to as fibers D and E).
The fibers C of the present invention were connected to the fibers D and E, respectively, to obtain dispersion compensating fiber modules D and E (hereinafter referred to as modules D and E). The fiber length used in module D was 7.2 km for fiber C, 10.3 km for fiber D, 8.3 km for fiber C and 9.0 km for fiber E in module E.
When these dispersion compensating fiber modules were used to compensate the accumulated chromatic dispersion of 80 km of NZ-DSF, the residual dispersion characteristics were as shown in FIGS.
The residual dispersion in each band is a maximum residual dispersion of 3.5 ps / nm or less when the module D is used for the low slope NZ-DSF, and the residual dispersion characteristic using the conventional module (5 ps / nm). On the other hand, it could be reduced to 70%. In addition, when module E is used for a large Aeff type NZ-DSF, the maximum residual dispersion is 10 ps / nm or less, and the residual dispersion characteristic (20 ps / nm or less) using a conventional module is reduced to 1/2. We were able to.
Assuming that the allowable residual dispersion limit of 10 Gbit / s transmission is 1040 ps / nm, when a module using fiber D is connected to a low-slope NZ-DSF, transmission up to 297 km is possible. The distance that can be transmitted by compensation can be increased up to 1.4 times.
In addition, when a module using fiber E is connected to a large Aeff type NZ-DSF, transmission up to 104 km is possible, and the transmission distance can be increased up to twice as long as one dispersion compensation. .

[Comparative Example 2]
Dispersion compensating fibers F, G, and H (hereinafter referred to as fibers F, G, and H) having a refractive index profile as shown in FIG. 6 were manufactured by a known method such as the VAD method and the MCVD method. At this time, Δ1, Δ2, Δ3, Δ4, b / a, c / b, d / c, and depressed core radius d were manufactured so as to have the values shown in Table 5.
Table 6 shows the optical characteristics of these fibers F, G, and H. The chromatic dispersion characteristics of the fibers F, G, and H are as shown by the curves F and G in FIG. 2 and FIG.
Using the dispersion compensating fiber module using these fibers F, G, and H, the residual dispersion characteristics when compensating the accumulated chromatic dispersion of the low dispersion slope type NZ-DSF of 80 km and DSF are shown in FIGS. Among them, the characteristics shown in FIG.
The residual dispersion in each band is 7 ps / nm or less when the module using the fiber F is connected to the low dispersion slope type NZ-DSF, and the fiber G is used for the large Aeff type NZ-DSF. When the module was connected, the maximum residual dispersion was 20 ps / nm or less. Further, when a module using the fiber H was connected to the DSF, the maximum residual dispersion was 40 ps / nm or less.
Assuming that the allowable residual dispersion limit of 10 Gbit / s transmission is 1040 ps / nm, when a module using fiber F is connected to a low slope NZ-DSF, further dispersion compensation is required at 149 km, and a large Aeff type When a module using the fiber G is connected to the NZ-DSF, further dispersion compensation is required at 52 km, and when a module using the fiber H is connected to the DSF, further dispersion compensation is required at 26 km. The number of times of dispersion compensation increases, and the entire configuration of the optical fiber transmission line becomes complicated, which is not desirable.

[Example 2]
A photonic crystal fiber I was produced in the same manner as in Example 1. As shown in FIG. 8, the core part is a photonic crystal structure fiber in which lattice holes of the same diameter (holes of the lattice structure) provided in the cladding part surrounding the core part are arranged in a hexagonal close-packed structure. The hole interval (lattice interval) Λ was 1.2 μm, and the diameter d of the lattice hole was 0.68 μm.
The chromatic dispersion characteristics of this fiber I are shown in FIG. The transmission loss was 0.33 dB / km (1.55 μm).
A dispersion compensating fiber having a refractive index profile as shown in FIG. 6 was manufactured by a known method such as VAD method or MCVD method. At this time, Δ1, Δ2, Δ3, Δ4, b / a, c / b, d / c, and depressed core radius d were manufactured so as to have the values shown in Table 7.
Table 8 shows optical characteristics of the dispersion compensating fibers J, K, and L (hereinafter, referred to as fibers J, K, and L).
The fibers I of the present invention were connected to the fibers J, K, and L, respectively, to obtain dispersion compensating fiber modules J, K, and L (hereinafter referred to as modules J, K, and L). The fiber length used for module J is 6.7 km for fiber I, 7.5 km for fiber J, 7.8 km for fiber I for module K, 11.0 km for fiber K, and 7. I for module L. It was 4 km and the fiber L was 6.7 km.
Using these modules J, K, and L, the residual dispersion characteristics when the accumulated chromatic dispersion of the 80 km NZ-DSF was compensated were as shown in FIGS. Further, the residual dispersion characteristic when the accumulated chromatic dispersion of the 80 km DSF is compensated is as shown in FIG.
The residual dispersion within each band is a maximum residual dispersion of 3.5 ps / nm or less when the module J is used for the low slope NZ-DSF, and the residual dispersion characteristic using the conventional module (7 ps / nm). On the other hand, it was possible to reduce to 1/2. Further, when the module K is used for the large Aeff type NZ-DSF, the maximum residual dispersion is 11 ps / nm or less, which is about 1/2 of the residual dispersion characteristics (20 ps / nm or less) using the conventional module. It was possible to reduce it. Furthermore, when module L is used for DSF, the maximum residual dispersion is 15 ps / nm or less, which can be reduced to about 38% of the residual dispersion characteristics (40 ps / nm or less) using conventional modules. It was.
Assuming that the allowable residual dispersion limit of 10 Gbit / s transmission is 1040 ps / nm, when module J is connected to a low slope NZ-DSF, transmission is possible up to 297 km, and transmission is possible with one dispersion compensation. Long distances can be increased up to about twice.
Further, when the module K is connected to the large Aeff type NZ-DSF, it is possible to transmit up to 95 km, and the distance that can be transmitted by one dispersion compensation can be increased to about 1.8 times.
Further, when the module L is connected to the DSF, transmission up to 69 km is possible, and the distance that can be transmitted by one dispersion compensation can be increased up to about 2.7 times.

[Comparative Example 3]
A dispersion compensating fiber M (hereinafter referred to as a fiber M) having a refractive index profile as shown in FIG. 7 for compensating DSF with U-band was prepared by a known method such as VAD method or MCVD method. At this time, Δ1, Δ2, Δ3, b / a, c / b, and core radius c were manufactured so as to have the values shown in Table 9.
Table 10 shows the optical characteristics of the fiber M. Further, the wavelength dispersion characteristic is as shown in FIG. Also. Using the dispersion compensating fiber module using the fiber M, the residual dispersion characteristics when the accumulated chromatic dispersion of the 80 km DSF is compensated in the U-band are as shown in FIG.
The residual dispersion within the band was a maximum residual dispersion of 20 ps / nm or less.
If the allowable residual dispersion limit for 10 Gbit / s transmission is 1040 ps / nm, further dispersion compensation is required at 52 km, which increases the number of dispersion compensations and complicates the configuration of the optical fiber transmission line, which is not desirable.

[Example 3]
A photonic crystal fiber N was produced in the same manner as in Examples 1 and 2. As shown in FIG. 8, the core part is a photonic crystal structure fiber in which lattice holes of the same diameter (holes of the lattice structure) provided in the cladding part surrounding the core part are arranged in a hexagonal close-packed structure. The hole interval (lattice interval) Λ was 1.2 μm, and the diameter d of the lattice hole was 0.70 μm.
The chromatic dispersion characteristics of the fiber N are shown in FIG. The transmission loss was 0.34 dB / km (1.55 μm).
A dispersion compensating fiber having a refractive index profile as shown in FIG. 7 was manufactured by a known method such as VAD method or MCVD method. At this time, Δ1, Δ2, Δ3, b / a, c / b, and core radius c were manufactured so as to have values shown in Table 11.
Table 12 shows the optical characteristics of the dispersion compensating fiber P (hereinafter referred to as fiber P).
The fiber N of the present invention was connected to the fiber P to obtain a dispersion compensating fiber module P (hereinafter referred to as module P). The fiber length used was 9.0 km for fiber P and 8.3 km for fiber N.
Using these modules P, the residual dispersion characteristics when compensating for the accumulated chromatic dispersion of the 80 km DSF were as shown in FIG.
The residual dispersion within the band is a maximum residual dispersion of 3.5 ps / nm or less, and can be reduced to 70% with respect to the residual dispersion characteristic (5 ps / nm) using the conventional module.
Assuming that the allowable residual dispersion limit of 10 Gbit / s transmission is 1040 ps / nm, when module P is connected to a low slope NZ-DSF, transmission is possible up to 297 km, and transmission is possible with one dispersion compensation. Long distances can be increased up to about 1.4 times.

  As described above, the photonic crystal fibers according to the first to third embodiments of the present invention show downward chromatic dispersion in a specific wavelength region (C-band, L-band, U-band), and this is compensated for dispersion. The dispersion-compensating fiber module obtained by connecting to the fiber can flatten the accumulated chromatic dispersion of the transmission optical fiber having convex chromatic dispersion upward in a specific wavelength range, and can increase the distance that can be transmitted by one dispersion compensation. It was possible to extend.

It is a schematic diagram for demonstrating the basic concept of the compensation of chromatic dispersion in an optical fiber transmission line. It is a graph which illustrates the wavelength dispersion of the dispersion compensation fiber for NS-DSF. It is a graph which illustrates residual dispersion at the time of using the conventional dispersion compensation fiber. It is a graph which illustrates residual dispersion at the time of using the conventional dispersion compensation fiber. It is a graph which illustrates residual dispersion at the time of using the conventional dispersion compensation fiber. It is a schematic diagram which illustrates the cross-sectional refractive index distribution of a dispersion compensation fiber. It is a schematic diagram which illustrates the cross-sectional refractive index distribution of another dispersion compensation fiber. It is a principal part expanded sectional view which shows an example of the photonic crystal fiber of this invention. It is a figure explaining the manufacturing method of the photonic crystal fiber of this invention, and is sectional drawing which shows the arrangement | positioning state of a quartz tube and a quartz rod. It is a figure explaining the manufacturing method of the photonic crystal fiber of this invention, and is a perspective view which shows the state which accommodates the aggregate | assembly of a quartz tube and a quartz rod in a quartz tube. It is a graph which shows the wavelength dispersion characteristic of the photonic crystal fiber of this invention. It is a graph which shows a residual dispersion characteristic when it compensates with the dispersion compensation fiber module of this invention. It is a graph which shows a residual dispersion characteristic when it compensates with the dispersion compensation fiber module of this invention. It is a graph which shows the dispersion characteristic of the dispersion compensation fiber for DSF. It is a graph which shows a residual dispersion characteristic when it compensates with the dispersion compensation fiber for DSF. It is a graph which shows the wavelength dispersion characteristic of the photonic crystal fiber of this invention. It is a graph which shows a residual dispersion characteristic when it compensates with the dispersion compensation fiber module of this invention. It is a graph which shows a residual dispersion characteristic when it compensates with the dispersion compensation fiber module of this invention. It is a graph which shows a residual dispersion characteristic when it compensates with the dispersion compensation fiber module of this invention. It is a graph which shows the wavelength dispersion of the module for compensating DSF by U-band. It is a graph which shows a residual dispersion characteristic when it compensates with the conventional dispersion compensation fiber module. It is a graph which shows the wavelength dispersion characteristic of the photonic crystal fiber of this invention. It is a graph which shows a residual dispersion characteristic when it compensates with the dispersion compensation fiber module of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Core, 2 ... Cladding, 3 ... Center core part, 4 ... Intermediate core part, 5 ... Ring core part, 6 ... Depressed core part, 7 ... Quartz rod, 8 ... Quartz tube, 9 ... Aggregate, 10 ... Quartz tube.

Claims (10)

  A photonic crystal fiber in which lattice holes of the same diameter provided in a clad portion surrounding a core portion are arranged in a hexagonal close-packed structure, out of six lattice hole forming portions arranged around the core portion The three lattice hole forming portions that are not adjacent to each other are not holes, the lattice hole interval Λ is in the range of 1.0 to 1.5 μm, and the diameter d of the lattice holes is 0.6 to 0.8 μm. A photonic crystal fiber characterized by a range.   In the wavelength range of 1.525 μm to 1.565 μm, it has a wavelength at which the dispersion slope becomes zero, the dispersion slope is negative at a wavelength shorter than that wavelength, and at a wavelength longer than the wavelength at which the dispersion slope becomes zero The photonic crystal fiber according to claim 1, wherein the dispersion slope is positive.   The photonic crystal fiber according to claim 2, wherein a transmission loss is 1.0 dB / km or less in a wavelength range of 1.525 µm to 1.565 µm.   In the wavelength range of 1.565 μm to 1.625 μm, it has a wavelength at which the dispersion slope becomes zero, the dispersion slope is negative at a wavelength shorter than that wavelength, and at a wavelength longer than the wavelength at which the dispersion slope becomes zero The photonic crystal fiber according to claim 1, wherein the dispersion slope is positive.   5. The photonic crystal fiber according to claim 4, wherein a transmission loss is 1.0 dB / km or less in a wavelength range of 1.565 μm to 1.625 μm.   In the wavelength range of 1.625 μm to 1.675 μm, the dispersion slope has a wavelength that becomes zero, the dispersion slope is negative at a wavelength shorter than that wavelength, and the wavelength that is longer than the wavelength at which the dispersion slope becomes zero The photonic crystal fiber according to claim 1, wherein the dispersion slope is positive.   The photonic crystal fiber according to claim 6, wherein a transmission loss is 1.0 dB / km or less in a wavelength range of 1.625 μm to 1.675 μm.   A fiber formed by connecting a dispersion compensating fiber having negative chromatic dispersion and dispersion slope over the entire wavelength range of 1.525 μm to 1.675 μm and the photonic crystal fiber according to claim 1. A dispersion compensating fiber module comprising: 9. The dispersion compensating fiber module according to claim 8, wherein a value obtained by dividing the value of the dispersion slope by the value of chromatic dispersion is in the range of 0.003 nm ^{−1 to} 0.03 nm ⁻¹ . An optical fiber transmission line formed by connecting the dispersion compensating fiber module according to claim 8 or 9 to a transmission optical fiber.

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