JP4358127B2 - Mode dispersion compensation method and optical waveguide - Google Patents

Description

  The present invention relates to a multimode dispersion compensating fiber (hereinafter referred to as MM-DCF) for compensating the modal dispersion of a multimode fiber (hereinafter referred to as MMF), and a target using the same. The present invention relates to a compensation method for modal dispersion of a compensation fiber, an optical waveguide formed by connecting an MMF and a compensated fiber, an optical transmission line using the optical waveguide, and an optical communication system. By using the MM-DCF of the present invention, the transmission bandwidth can be increased in a wavelength band other than the optimized wavelength band. Further, the MM-DCF of the present invention has a very wide wavelength region that is a high transmission bandwidth compared to the conventional dispersion compensating fiber, and is suitable for wavelength multiplexing.

  A graded index (hereinafter referred to as GI) type MMF is widely used as an optical transmission line of an optical local area network (hereinafter referred to as LAN). The accuracy of profile control of GI-type MMF has been improved in accordance with the demand for high-speed LAN, and has almost reached the performance limit at present. In order to further increase the bandwidth of the GI-type MMF, wavelength division multiplexing (hereinafter referred to as WDM) must be performed.

  However, MMFs made by adding germanium (Ge) as a dopant to quartz glass have an optimum shape that greatly depends on the wavelength. Therefore, MMFs optimized for a specific wavelength have different wavelengths. Then, the transmission bandwidth is considerably deteriorated and is not suitable for WDM.

  The present inventors have invented MM-DCF having a high transmission bandwidth at a desired wavelength and have already filed patent applications (Japanese Patent Application Nos. 2003-83790 and 2003-83791).

In addition, as a prior art relevant to this invention, it is disclosed by the nonpatent literatures 1-4, for example.
R. Olshansky and DB Keck, “Pulse broadening in graded-index optical fibers,” Appl. Opt., Vol. 15, pp. 483-491, 1976 N. Shibata and T. Edahiro, “Refractive-index dispersion for GeO2-, P2O5-, and B2O3-doped silica glasses in optical fibers,” Trans. IECE Japan, vol. E65, pp. 166-172, 1982 JW Fleming, “Material dispersion in lightguide glasses,” Electron Lett., Vol. 14, pp. 326-328, 1978 Mode Scrambler Requirements for Overfilled Launching Conditions to Multimode Fibers, TIA / EIA Fiber Optic Test Procedure (FOTP) -54, Dec. 2001

  However, the MM-DCF proposed by the present inventors in Japanese Patent Application Nos. 2003-83790 and 2003-83791 is prepared by adding germanium (Ge) as a dopant to quartz glass, as in the conventional MMF. Therefore, it is possible to increase the transmission bandwidth of the desired wavelength, but there is still a problem that the transmission bandwidth rapidly deteriorates in a wavelength region slightly deviated from the wavelength.

  The present invention has been made in view of the above circumstances, and has a very wide wavelength region with a high transmission bandwidth, and is suitable for WDM. An MM-DCF compensation method using the same, an optical waveguide, an optical transmission line, and an optical communication system The purpose is to provide.

In order to achieve the above object, the present invention connects a multimode dispersion compensating fiber to a compensated fiber made of a multimode fiber prepared by adding germanium as a dopant to quartz glass, and optimizing the compensated fiber. A method for compensating the mode dispersion of the compensated fiber so that a transmission bandwidth in a wavelength or wavelength band other than the selected wavelength is higher than a transmission bandwidth in the optimized wavelength,
The multi-mode dispersion compensating fiber is made of a fluorine-added fiber prepared by adding fluorine as a dopant to quartz glass, the α value is 2.030 ≦ α ≦ 2.045, and the core radius a is 15 μm ≦ a ≦. The maximum relative refractive index difference Δ is 0.005 ≦ Δ ≦ 0.025, and the length thereof is the ratio R of the length of the compensated fiber to the total fiber length connected to the compensated fiber. A mode dispersion compensation method is provided, wherein 0.15 ≦ R ≦ 0.35 .

The present invention also provides a multimode dispersion compensating fiber connected to a compensated fiber made of a multimode fiber manufactured by adding germanium as a dopant to quartz glass, and a wavelength other than the optimized wavelength of the compensated fiber. Or a method of compensating the mode dispersion of the compensated fiber so that the transmission bandwidth in the wavelength band is higher than the transmission bandwidth in the optimized wavelength,
The multimode dispersion compensating fiber is made of a fluorine-added fiber prepared by adding fluorine to quartz glass as a dopant, α value is 1.9 ≦ α ≦ 2.1, and core radius a is 15 μm ≦ a ≦. The maximum relative refractive index difference Δ is 0.005 ≦ Δ ≦ 0.025, and the length thereof is the ratio R of the length of the compensated fiber to the total fiber length connected to the compensated fiber. A mode dispersion compensation method is provided, wherein 0.25 ≦ R ≦ 0.45.

The present invention also provides a multimode dispersion compensating fiber connected to a compensated fiber made of a multimode fiber manufactured by adding germanium as a dopant to quartz glass, and a wavelength other than the optimized wavelength of the compensated fiber. Or a method of compensating the mode dispersion of the compensated fiber so that the transmission bandwidth in the wavelength band is higher than the transmission bandwidth in the optimized wavelength,
The multi-mode dispersion compensating fiber is made of a fluorine-added fiber prepared by adding fluorine as a dopant to quartz glass, the α value is 1.8 ≦ α ≦ 2.0, and the core radius a is 15 μm ≦ a ≦. The maximum relative refractive index difference Δ is 0.005 ≦ Δ ≦ 0.025, and the length thereof is the ratio R of the length of the compensated fiber to the total fiber length connected to the compensated fiber. A mode dispersion compensation method is provided, wherein 0.47 ≦ R ≦ 0.67.

The present invention also provides a multimode dispersion compensating fiber connected to a compensated fiber made of a multimode fiber manufactured by adding germanium as a dopant to quartz glass, and a wavelength other than the optimized wavelength of the compensated fiber. Or a method of compensating the mode dispersion of the compensated fiber so that the transmission bandwidth in the wavelength band is higher than the transmission bandwidth in the optimized wavelength,
The multi-mode dispersion compensating fiber is made of a fluorine-added fiber prepared by adding fluorine as a dopant to quartz glass, α value is 1.7 ≦ α ≦ 1.9, and core radius a is 15 μm ≦ a ≦. The maximum relative refractive index difference Δ is 0.005 ≦ Δ ≦ 0.025, and the length thereof is the ratio R of the length of the compensated fiber to the total fiber length connected to the compensated fiber. A mode dispersion compensation method is provided, wherein 0.57 ≦ R ≦ 0.77.

The present invention also provides a multimode dispersion compensating fiber connected to a compensated fiber made of a multimode fiber manufactured by adding germanium as a dopant to quartz glass, and a wavelength other than the optimized wavelength of the compensated fiber. Or a method of compensating the mode dispersion of the compensated fiber so that the transmission bandwidth in the wavelength band is higher than the transmission bandwidth in the optimized wavelength,
The multimode dispersion compensating fiber is made of a fluorine-added fiber prepared by adding fluorine as a dopant to quartz glass, α value is 1.5 ≦ α ≦ 1.7, and core radius a is 15 μm ≦ a ≦. The maximum relative refractive index difference Δ is 0.005 ≦ Δ ≦ 0.025, and the length thereof is the ratio R of the length of the compensated fiber to the total fiber length connected to the compensated fiber. A mode dispersion compensation method is provided, wherein 0.69 ≦ R ≦ 0.89.

In the mode dispersion compensation method of the present invention, it is preferable that the compensated fiber has a maximum transmission bandwidth at a wavelength of 0.85 μm.
In the mode dispersion compensation method of the present invention, it is preferable that the compensated fiber has a maximum relative refractive index Δ of 0.01, a core radius a of 25 μm, and an α value of 2.086.

Further, the present invention provides a compensated fiber comprising a multimode fiber manufactured by adding germanium as a dopant to quartz glass,
A multimode dispersion compensating fiber connected to the compensated fiber;
An optical waveguide comprising:
  The multi-mode dispersion compensating fiber is made of a fluorine-added fiber prepared by adding fluorine as a dopant to quartz glass, the α value is 2.030 ≦ α ≦ 2.045, and the core radius a is 15 μm ≦ a ≦. The maximum relative refractive index difference Δ is 0.005 ≦ Δ ≦ 0.025, and the length thereof is the ratio R of the length of the compensated fiber to the total fiber length connected to the compensated fiber. 0.15 ≦ R ≦ 0.35,
There is provided an optical waveguide characterized in that a transmission bandwidth in a wavelength or wavelength band other than the optimized wavelength of the compensated fiber is higher than a transmission bandwidth in the optimized wavelength.

Further, the present invention provides a compensated fiber comprising a multimode fiber manufactured by adding germanium as a dopant to quartz glass,
A multimode dispersion compensating fiber connected to the compensated fiber;
An optical waveguide comprising:
The multimode dispersion compensating fiber is made of a fluorine-added fiber prepared by adding fluorine to quartz glass as a dopant, α value is 1.9 ≦ α ≦ 2.1, and core radius a is 15 μm ≦ a ≦. The maximum relative refractive index difference Δ is 0.005 ≦ Δ ≦ 0.025, and the length thereof is the ratio R of the length of the compensated fiber to the total fiber length connected to the compensated fiber. 0.25 ≦ R ≦ 0.45,
There is provided an optical waveguide characterized in that a transmission bandwidth in a wavelength or wavelength band other than the optimized wavelength of the compensated fiber is higher than a transmission bandwidth in the optimized wavelength.

Further, the present invention provides a compensated fiber comprising a multimode fiber manufactured by adding germanium as a dopant to quartz glass,
A multimode dispersion compensating fiber connected to the compensated fiber;
An optical waveguide comprising:
The multi-mode dispersion compensating fiber is made of a fluorine-added fiber prepared by adding fluorine as a dopant to quartz glass, the α value is 1.8 ≦ α ≦ 2.0, and the core radius a is 15 μm ≦ a ≦. The maximum relative refractive index difference Δ is 0.005 ≦ Δ ≦ 0.025, and the length thereof is the ratio R of the length of the compensated fiber to the total fiber length connected to the compensated fiber. 0.47 ≦ R ≦ 0.67,
  There is provided an optical waveguide characterized in that a transmission bandwidth in a wavelength or wavelength band other than the optimized wavelength of the compensated fiber is higher than a transmission bandwidth in the optimized wavelength.

Further, the present invention provides a compensated fiber comprising a multimode fiber manufactured by adding germanium as a dopant to quartz glass,
A multimode dispersion compensating fiber connected to the compensated fiber;
An optical waveguide comprising:
The multi-mode dispersion compensating fiber is made of a fluorine-added fiber prepared by adding fluorine as a dopant to quartz glass, α value is 1.7 ≦ α ≦ 1.9, and core radius a is 15 μm ≦ a ≦. The maximum relative refractive index difference Δ is 0.005 ≦ Δ ≦ 0.025, and the length thereof is the ratio R of the length of the compensated fiber to the total fiber length connected to the compensated fiber. 0.57 ≦ R ≦ 0.77,
There is provided an optical waveguide characterized in that a transmission bandwidth in a wavelength or wavelength band other than the optimized wavelength of the compensated fiber is higher than a transmission bandwidth in the optimized wavelength.

Further, the present invention provides a compensated fiber comprising a multimode fiber manufactured by adding germanium as a dopant to quartz glass,
A multimode dispersion compensating fiber connected to the compensated fiber;
An optical waveguide comprising:
The multimode dispersion compensating fiber is made of a fluorine-added fiber prepared by adding fluorine as a dopant to quartz glass, α value is 1.5 ≦ α ≦ 1.7, and core radius a is 15 μm ≦ a ≦. The maximum relative refractive index difference Δ is 0.005 ≦ Δ ≦ 0.025, and the length thereof is the ratio R of the length of the compensated fiber to the total fiber length connected to the compensated fiber. 0.69 ≦ R ≦ 0.89,
There is provided an optical waveguide characterized in that a transmission bandwidth in a wavelength or wavelength band other than the optimized wavelength of the compensated fiber is higher than a transmission bandwidth in the optimized wavelength.

In the optical waveguide of the present invention, it is preferable that the compensated fiber has a maximum transmission bandwidth at a wavelength of 0.85 μm.
In the optical waveguide of the present invention, it is preferable that the compensated fiber has a maximum relative refractive index Δ of 0.01, a core radius a of 25 μm, and an α value of 2.086.

By using the MM-DCF of the present invention, a compensated fiber made of Ge-added MMF can have a high transmission bandwidth in a wide wavelength region. If WDM is performed taking advantage of these characteristics, the transmission bandwidth of the MMF can be significantly increased at low cost.
Since the target of compensation using the MM-DCF of the present invention includes an existing fiber transmission line, it can be used over a very wide range, and an optical transmission line capable of WDM by increasing the transmission bandwidth of the existing fiber line is configured. can do.

  The present invention provides an MM-DCF for compensating the mode dispersion of a compensated fiber made of Ge-added MMF made by adding Ge as a dopant to quartz glass. In a preferred embodiment of the present invention, this MM-DCF includes F-added MM-DCF produced by adding fluorine (F) as a dopant to quartz glass.

  This F-added MM-DCF is composed of a core in which F is added to quartz glass as a dopant, and the amount of F added gradually increases from the center toward the radially outer side, and a fluorine-added quartz glass surrounding the core. An MMF configured with a cladding is preferably used. The core of this F-added MM-DCF has a GI type refractive index profile, and the maximum refractive index at the center of the core is almost equal to the refractive index of quartz glass.

  Further, the compensated fiber made of Ge-added MMF includes a core made of Ge-added quartz glass in which the Ge addition amount is gradually increased from the outer periphery toward the center, and a clad made of quartz glass (for example, pure quartz glass) surrounding the core. A Ge-added GI type MMF comprising the above is preferably used. In the present invention, the compensated fiber made of Ge-added MMF is preferably optimized at a wavelength of 0.85 μm and has a maximum transmission bandwidth at the wavelength.

  When one end of the F-added MM-DCF is connected to one end of the compensated fiber, the connection method is not limited, and a fusion connection method, a connection method using an optical connector or a mechanical splice, or the like can be employed. When one end of the F-added MM-DCF and one end of the compensated fiber are connected, reflection occurs at the connection point because the refractive indexes of both cores are different, but the reflection is minus tens of dB or less. As expected, there is no practical problem.

  When the F-added MM-DCF is connected to a Ge-added compensated fiber, the transmission bandwidth of a desired wavelength other than the design wavelength of the compensated fiber (OFL band, see Non-Patent Document 4) can be significantly increased. Further, since the F-added MMF differs from the Ge-added MMF in the dispersion characteristics of the additive, it can have a high transmission bandwidth not only at a desired wavelength but also in a wide wavelength region around it. If this configuration is used, WDM by MMF becomes possible, and transmission capacity in short-distance optical communication, for example, FTTH (Fiber To The Home), LAN, and SAN (Storage Area Network) can be dramatically increased. .

  MMF uses a GI fiber profile to minimize the difference in transmission speed between multimodes and achieve a high transmission bandwidth. This type of fiber has a high numerical aperture (NA) and is expected as a short-distance optical communication path.

  The refractive index of the GI fiber is usually manufactured so as to have an α power refractive index distribution represented by the following formula (1).

In equation (1), a represents the core radius, r represents the radial coordinate, n ₁ represents the core center refractive index, and Δ represents the maximum relative refractive index difference. α is controlled so that the band is maximized in a desired wavelength band.

The optimum value α _opt of α is calculated by the WKB method as in the following equation (2) (see Non-Patent Document 1).

  However, y is following Formula (3).

Olshansky parameter given by. Here, λ represents a wavelength, and N ₁ = n ₁ −λ (dn ₁ / dλ) represents a group refractive index at the core center.

The optimum value of α varies depending on the material added to quartz. FIG. 1 shows the wavelength dependence of α _opt when Δ = 0.01 and Ge and F are added. As shown in the figure, it can be seen that in either case, the value of α _opt changes greatly with changes in wavelength. This means, for example, that any MMF optimized in the wavelength band of 0.85 μm deviates from the optimum α value in other wavelengths, for example, wavelength of 1.3 μm, and a high transmission bandwidth cannot be obtained there. In this calculation and all the following calculations, the material distribution coefficients of pure quartz and Ge-added quartz use the values described in Non-Patent Document 2, and F-added quartz is described in Non-Patent Document 3. Is used.

In Figure 1, if Ge is added MMF, F added MMF is assumed both shall optimized at a wavelength of 0.85μm band, alpha took optimum value α _Ge0.85, α _F0.85 at that wavelength To do. As can be seen from Figure 1, the long wavelength, for example, in the 1.3μm, α _Ge0.85 is greater than the optimum value, alpha _F0.85 is smaller than the optimum value. That is, a signal having a wavelength of 1.3 μm is transmitted in the higher-order mode later than the lower-order mode in the Ge-added MMF transmission, and conversely, in the F-added MMF transmission, the higher-order mode is transmitted faster than the lower-order mode. When these two types of MMFs are connected and used, the mode dispersion of the 1.3 μm band signal is canceled and compensated without degrading the transmission bandwidth of the 0.85 μm band signal. As a result, if the configurations of both MMFs are optimized, a high transmission bandwidth can be realized in a very wide wavelength region.

  Further, when a mechanism in which the Ge-doped MMF and the F-doped MMF cancel each other's mode dispersion is positively used, an F-doped MMF is used as a fiber that compensates the mode dispersion of the Ge-doped MMF that has been used conventionally. Thus, a high transmission bandwidth can be realized in a wide wavelength region.

  This F-added MM-DCF is optimized in the wavelength 0.85 μm band, and when connected to the compensated fiber 12 made of Ge-added MMF having the maximum transmission bandwidth at the wavelength, the wavelength 0. It has a characteristic of compensating the mode dispersion of the compensated fiber 12 so that the transmission bandwidth becomes high at a wavelength or wavelength band other than 85 μm.

In a preferred embodiment of the present invention, the F-doped MM-DCF has at least one of the following (a) to (e), more preferably two or more when connected to the compensated fiber. It is preferable.
(A) It has a characteristic of compensating the mode dispersion so that the transmission bandwidth is higher than that of the compensated fiber 12 in the wavelength region of 0.7 μm to 1.65 μm.
(B) The transmission bandwidth of the wavelength region of 1.2 μm to 1.6 μm is 3 GHz · km or more without reducing the transmission bandwidth of the compensated fiber 12 in the wavelength region of 0.8 μm to 0.9 μm. It has a characteristic to compensate modal dispersion.
(C) Without reducing the transmission bandwidth of the compensated fiber 12 in the wavelength region of 0.8 μm to 0.9 μm, the transmission bandwidth of the wavelength region of 1.3 μm to 1.6 μm is 5 GHz · km or more. It has a characteristic to compensate modal dispersion.
(D) It has a characteristic to compensate the mode dispersion so that the transmission bandwidth in the wavelength region of 1.2 μm to 1.6 μm is 4 GHz · km or more.
(E) It has a characteristic to compensate the mode dispersion so that the transmission bandwidth in the wavelength region of 1.3 μm to 1.6 μm is 5 GHz · km or more.

  FIG. 2 is a configuration diagram illustrating an example of an optical waveguide configured using the MM-DCF according to the present invention. The optical waveguide 10 includes a compensated fiber 12 including an F-doped MM-DCF 11 and a Ge-doped MMF. (Target) is connected at the connection point 13.

In this optical waveguide 10, when the compensated fiber 12 is a compensated fiber 12 made of Ge-doped MMF that is optimized in the wavelength of 0.85 μm band and has the maximum transmission bandwidth at the wavelength, The characteristics and length of the F-added MM-DCF 11 connected to the terminal are selected so as to be at least one of the following (1) to (5), preferably two or more, more preferably three or more Is preferred. The length of the F-containing MM-DCF 11 is the length of the compensating fiber 12 the lengths of _L 1, F added MM-DCF 11 when the _{L 2,} R = _L 1 _/ a _(L 1 + _{L 2)} It shall be represented by the ratio R calculated by the calculation formula.
(1) The F-added MM-DCF 11 has an α value of 2.030 ≦ α ≦ 2.045, a core radius a of 15 μm ≦ a ≦ 35 μm, and a maximum relative refractive index difference Δ of 0.005 ≦ Δ ≦. The length is 0.025, and the ratio R is 0.15 ≦ R ≦ 0.35.
(2) The F-added MM-DCF 11 has an α value of 1.9 ≦ α ≦ 2.1, a core radius a of 15 μm ≦ a ≦ 35 μm, and a maximum relative refractive index difference Δ of 0.005 ≦ Δ ≦. The length R is 0.025, and the ratio R is 0.25 ≦ R ≦ 0.45.
(3) The F-added MM-DCF 11 has an α value of 1.8 ≦ α ≦ 2.0, a core radius a of 15 μm ≦ a ≦ 35 μm, and a maximum relative refractive index difference Δ of 0.005 ≦ Δ ≦. The length is 0.025, and the ratio R is 0.47 ≦ R ≦ 0.67.
(4) The F-added MM-DCF 11 has an α value of 1.7 ≦ α ≦ 1.9, a core radius a of 15 μm ≦ a ≦ 35 μm, and a maximum relative refractive index difference Δ of 0.005 ≦ Δ ≦. The length is 0.025, and the ratio R is 0.57 ≦ R ≦ 0.77.
(5) The F-added MM-DCF 11 has an α value of 1.5 ≦ α ≦ 1.7, a core radius a of 15 μm ≦ a ≦ 35 μm, and a maximum relative refractive index difference Δ of 0.005 ≦ Δ ≦. The length is 0.025, and the ratio R is 0.69 ≦ R ≦ 0.89.

This optical waveguide 10 has a configuration in which an F-added MM-DCF 11 and a compensated fiber 12 (target) made of Ge-added MMF are connected at a connection point 13, and the configuration of each fiber is the above (1) to (5). By optimizing as illustrated in (1), a high transmission bandwidth can be realized in a very wide wavelength region, and WDM becomes possible.
In addition, the F-added MM-DCF 11 to be used can be easily manufactured because it can be manufactured by adding one kind of dopant alone.
Further, by applying the optical waveguide structure to the optical transmission line or the like by using an optical fiber such as an optical transmission line already laid as the corrected fiber 12, the transmission bandwidth of the optical transmission line or the like is improved. Can be easily done.
Further, a wide transmission bandwidth can be obtained by adjusting the length of the F-added MM-DCF 11 to be connected without strictly controlling the shape of the refractive index profile of the F-added MM-DCF 11 to be used. Therefore, the demand for manufacturing tolerance of MM-DCF can be lowered.
In addition, since the wavelength characteristics of the optical waveguide 10 or the entire optical transmission line can be adjusted by changing the length of the F-added MM-DCF 11 to be connected, it is possible to select a wavelength region that requires a wide transmission bandwidth. it can.

  Further, in the present invention, the above-described F-doped MM-DCF 11 is connected to the compensated fiber 12 made of Ge-doped MMF, and the transmission bandwidth in the wavelength or wavelength band other than the optimized wavelength of the compensated fiber 12 is A mode dispersion compensation method is provided that compensates the mode dispersion of the compensated fiber 12 so as to be higher than the transmission bandwidth at the optimized wavelength. According to the method of the present invention, by connecting the F-added MM-DCF 11 to the compensated fiber 12 made of Ge-added MMF installed in an existing optical transmission line, a high transmission bandwidth in a very wide wavelength region is obtained. It is possible to provide an optical waveguide capable of WDM, an optical transmission line including the optical waveguide, and an optical communication system such as FTTH, LAN, or SAN configured using the optical transmission line. it can.

[Example 1]
Consider a case where a compensated fiber 12 (target) made of Ge-added MMF and an F-added MM-DCF 11 are connected as shown in FIG. The length of the compensated fiber 12 is L ₁ , the length of the F-added MM-DCF 11 is L _2, and R = L ₁ / (L ₁ + L ₂ ).

The compensated fiber 12 is assumed to be optimized to have a wavelength of 0.85 μm with Δ = 0.01, a = 25 μm, an α value of α _Ge = 2.086. The F-added MM-DCF11 is also set to Δ = 0.01, a = 25 μm, and the α value is α _F = 2.037. This F-added MM-DCF 11 alone has the maximum transmission bandwidth in the vicinity of a wavelength of 0.85 μm.

FIG. 3 is a graph showing the wavelength characteristics of the transmission bandwidth (OFL band, see Non-Patent Document 4) when 0.2 ≦ R ≦ 0.3. However, the calculation of the transmission bandwidth (OFL band) is as follows: Full width at half-maximum (FWHM) Δτ _FWHM = 1 ns of the incident pulse, Root Mean Square (RMS) width Δλ _RMS = 0 .5 nm, beam FWHM width Δω _FWHM = 50 μm. FIG. 4 shows a case where R = 0.28 and dispersion compensation is performed by the F-added MM-DCF 11, only the compensated fiber 12, and a case where the compensated fiber 12 is compensated by the Ge-added MM-DCF (Ge MMDCF). It is the graph which compared the wavelength characteristic of each transmission bandwidth. The transmission bandwidth when the compensated fiber 12 is optimized on the long wavelength side is substantially the same as the transmission bandwidth when compensated with the Ge-added MM-DCF.

  As shown in FIG. 3 and FIG. 4, when the compensation fiber 12 is dispersion-compensated by connecting the F-added MM-DCF 11 with 0.2 ≦ R ≦ 0.3, the transmission bandwidth on the short wavelength side of 0.85 μm The transmission bandwidth on the long wavelength side can be significantly increased without lowering the frequency. In particular, when R = 0.28, the transmission bandwidth in the wavelength region from 1.3 μm to 1.55 μm can be greatly increased. This wavelength characteristic has a high transmission bandwidth in a very wide wavelength region as compared with a case where dispersion compensation is performed with a Ge-added MM-DCF or when a Ge-added MMF is optimized on the long wavelength side.

[Example 2]
The compensated fiber 12 is a Ge-added MMF optimized for a wavelength of 0.85 μm as in the first embodiment. In the F-added MM-DCF 11, Δ = 0.01, a = 25 μm, and the α value is α _F = 2.0.

  FIG. 5 is a graph showing the wavelength characteristics of the transmission bandwidth when 0.3 ≦ R ≦ 0.4. FIG. 6 shows a case where R = 0.37 and dispersion compensation is performed by the F-doped MM-DCF 11, a case where only the compensated fiber 12 is used, and a case where the compensated fiber 12 is compensated by the Ge-doped MM-DCF (Ge MMDCF). It is the graph which compared the wavelength characteristic of the transmission bandwidth of.

  As shown in FIGS. 5 and 6, when the compensated fiber 12 is dispersion-compensated by the F-added MM-DCF 11 with 0.3 ≦ R ≦ 0.4, the transmission bandwidth on the long wavelength side can be significantly increased. it can. In particular, when R = 0.37, the transmission bandwidth in the wavelength region from the wavelength 1.3 μm to the wavelength 1.55 μm can be significantly increased. This wavelength characteristic has a high transmission bandwidth in a very wide wavelength region as compared with the case where dispersion compensation is performed with Ge-added MM-DCF or the case where the compensated fiber 12 is optimized on the long wavelength side.

[Example 3]
The compensated fiber 12 is a Ge-added MMF optimized for a wavelength of 0.85 μm as in the first embodiment. In the F-added MM-DCF11, Δ = 0.01, a = 25 μm, and the α value is α _F = 1.9.

  FIG. 7 is a graph showing the wavelength characteristics of the transmission bandwidth when 0.52 ≦ R ≦ 0.62. FIG. 8 shows a case where R = 0.54 and dispersion compensation is performed by the F-added MM-DCF 11, a case where only the compensated fiber 12 is used, and a case where the compensated fiber 12 is compensated by the Ge-added MM-DCF (Ge MMDCF). It is the graph which compared the wavelength characteristic of the transmission bandwidth of.

  As shown in FIGS. 7 and 8, when the compensated fiber 12 is compensated for dispersion by the F-added MM-DCF 11 with 0.52 ≦ R ≦ 0.62, the transmission bandwidth on the long wavelength side can be significantly increased. it can. In particular, when R = 0.54, the transmission bandwidth in the wavelength region from the wavelength 1.3 μm to the wavelength 1.55 μm can be significantly increased. This wavelength characteristic has a high transmission bandwidth in a very wide wavelength region as compared with the case where dispersion compensation is performed with Ge-added MM-DCF or the case where the compensated fiber 12 is optimized on the long wavelength side.

[Example 4]
The compensated fiber 12 is a Ge-added MMF optimized for a wavelength of 0.85 μm as in the first embodiment. In the F-added MM-DCF 11, Δ = 0.01, a = 25 μm, and the α value is α _F = 1.8.

  FIG. 9 is a graph showing the wavelength characteristics of the transmission bandwidth when 0.62 ≦ R ≦ 0.72. FIG. 10 shows a case where R = 0.64 and dispersion compensation is performed with the F-added MM-DCF 11, a case where only the compensated fiber 12 is used, and a case where the compensated fiber 12 is compensated using the Ge-added MM-DCF (Ge MMDCF). It is the graph which compared the wavelength characteristic of the transmission bandwidth of.

  As shown in FIGS. 9 and 10, when the compensated fiber is dispersion-compensated with F-added MM-DCF 11 with 0.62 ≦ R ≦ 0.72, the transmission bandwidth on the long wavelength side can be significantly increased. . In particular, when R = 0.64, the transmission bandwidth in the wavelength region from the wavelength 1.3 μm to the wavelength 1.55 μm can be significantly increased. This wavelength characteristic has a high transmission bandwidth in a very wide wavelength region as compared with the case where dispersion compensation is performed with Ge-added MM-DCF or the case where the compensated fiber 12 is optimized on the long wavelength side.

[Example 5]
The compensated fiber 12 is a Ge-added MMF optimized for a wavelength of 0.85 μm as in the first embodiment. In the F-added MM-DCF 11, Δ = 0.01, a = 25 μm, and the α value is α _F = 1.6.

  FIG. 11 is a graph showing the wavelength characteristics of the transmission bandwidth when 0.74 ≦ R ≦ 0.84. FIG. 12 shows a case where R = 0.76 and dispersion compensation is performed with the F-added MM-DCF 11, a case where only the compensated fiber 12 is used, and a case where the compensated fiber 12 is compensated using the Ge-added MM-DCF (Ge MMDCF). It is the graph which compared the wavelength characteristic of the transmission bandwidth of.

  As shown in FIGS. 11 and 12, when the compensated fiber 12 is compensated for dispersion by the F-added MM-DCF 11 with 0.74 ≦ R ≦ 0.84, the transmission bandwidth on the long wavelength side can be significantly increased. it can. In particular, when R = 0.76, the transmission bandwidth in the wavelength region from the wavelength 1.3 μm to the wavelength 1.55 μm can be significantly increased. This wavelength characteristic has a high transmission bandwidth in a very wide wavelength region as compared with the case where dispersion compensation is performed with Ge-added MM-DCF or the case where the compensated fiber 12 is optimized on the long wavelength side.

It is a graph which shows the wavelength dependence of the optimal alpha value of Ge addition fiber and F addition fiber. It is a block diagram which shows an example of the optical waveguide of this invention. 6 is a graph showing wavelength characteristics of a transmission bandwidth when a compensated fiber is compensated with the F-added MM-DCF used in Example 1. When the compensated fiber is compensated with the F-doped MM-DCF used in Example 1, the wavelength characteristics of the respective transmission bandwidths when the compensated fiber is compensated only with the Ge-doped MM-DCF are shown. It is a graph to show. 10 is a graph showing wavelength characteristics of a transmission bandwidth when a compensated fiber is compensated with the F-added MM-DCF used in Example 2. When the compensated fiber is compensated with the F-doped MM-DCF used in Example 2, the wavelength characteristics of the respective transmission bandwidths when the compensated fiber is compensated only with the Ge-doped MM-DCF are shown. It is a graph to show. 10 is a graph showing wavelength characteristics of a transmission bandwidth when a compensated fiber is compensated with the F-added MM-DCF used in Example 3. When the compensated fiber is compensated with the F-doped MM-DCF used in Example 3, the wavelength characteristics of the respective transmission bandwidths when the compensated fiber is compensated with the Ge-doped MM-DCF are shown. It is a graph to show. 10 is a graph showing wavelength characteristics of a transmission bandwidth when a compensated fiber is compensated with the F-added MM-DCF used in Example 4. When the compensated fiber is compensated with the F-doped MM-DCF used in Example 4, the wavelength characteristics of the respective transmission bandwidths when the compensated fiber is compensated with the Ge-doped MM-DCF are shown. It is a graph to show. 10 is a graph showing wavelength characteristics of a transmission bandwidth when a compensated fiber is compensated with the F-added MM-DCF used in Example 5. When the compensated fiber is compensated with the F-doped MM-DCF used in Example 5, the wavelength characteristics of the respective transmission bandwidths when the compensated fiber is compensated with the Ge-doped MM-DCF are shown. It is a graph to show.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Optical waveguide, 11 ... F addition MM-DCF, 12 ... Compensated fiber, 13 ... Connection point.

Claims (14)

A multimode dispersion compensating fiber is connected to a compensated fiber made of a multimode fiber made by adding germanium as a dopant to quartz glass, and transmitted in a wavelength or wavelength band other than the optimized wavelength of the compensated fiber. Compensating the mode dispersion of the compensated fiber such that the bandwidth is higher than the transmission bandwidth at the optimized wavelength,
The multi-mode dispersion compensating fiber is made of a fluorine-added fiber prepared by adding fluorine as a dopant to quartz glass, the α value is 2.030 ≦ α ≦ 2.045, and the core radius a is 15 μm ≦ a ≦. The maximum relative refractive index difference Δ is 0.005 ≦ Δ ≦ 0.025, and the length thereof is the ratio R of the length of the compensated fiber to the total fiber length connected to the compensated fiber. A mode dispersion compensation method, wherein 0.15 ≦ R ≦ 0.35. A multimode dispersion compensating fiber is connected to a compensated fiber made of a multimode fiber made by adding germanium as a dopant to quartz glass, and transmitted in a wavelength or wavelength band other than the optimized wavelength of the compensated fiber. Compensating the mode dispersion of the compensated fiber such that the bandwidth is higher than the transmission bandwidth at the optimized wavelength,
The multimode dispersion compensating fiber is made of a fluorine-added fiber prepared by adding fluorine to quartz glass as a dopant, α value is 1.9 ≦ α ≦ 2.1, and core radius a is 15 μm ≦ a ≦. The maximum relative refractive index difference Δ is 0.005 ≦ Δ ≦ 0.025, and the length thereof is the ratio R of the length of the compensated fiber to the total fiber length connected to the compensated fiber. A mode dispersion compensation method, wherein 0.25 ≦ R ≦ 0.45. A multimode dispersion compensating fiber is connected to a compensated fiber made of a multimode fiber made by adding germanium as a dopant to quartz glass, and transmitted in a wavelength or wavelength band other than the optimized wavelength of the compensated fiber. Compensating the mode dispersion of the compensated fiber such that the bandwidth is higher than the transmission bandwidth at the optimized wavelength,
The multi-mode dispersion compensating fiber is made of a fluorine-added fiber prepared by adding fluorine as a dopant to quartz glass, the α value is 1.8 ≦ α ≦ 2.0, and the core radius a is 15 μm ≦ a ≦. The maximum relative refractive index difference Δ is 0.005 ≦ Δ ≦ 0.025, and the length thereof is the ratio R of the length of the compensated fiber to the total fiber length connected to the compensated fiber. A mode dispersion compensation method, wherein 0.47 ≦ R ≦ 0.67. A multimode dispersion compensating fiber is connected to a compensated fiber made of a multimode fiber made by adding germanium as a dopant to quartz glass, and transmitted in a wavelength or wavelength band other than the optimized wavelength of the compensated fiber. Compensating the mode dispersion of the compensated fiber such that the bandwidth is higher than the transmission bandwidth at the optimized wavelength,
The multi-mode dispersion compensating fiber is made of a fluorine-added fiber prepared by adding fluorine as a dopant to quartz glass, α value is 1.7 ≦ α ≦ 1.9, and core radius a is 15 μm ≦ a ≦. The maximum relative refractive index difference Δ is 0.005 ≦ Δ ≦ 0.025, and the length thereof is the ratio R of the length of the compensated fiber to the total fiber length connected to the compensated fiber. A mode dispersion compensation method, wherein 0.57 ≦ R ≦ 0.77. A multimode dispersion compensating fiber is connected to a compensated fiber made of a multimode fiber made by adding germanium as a dopant to quartz glass, and transmitted in a wavelength or wavelength band other than the optimized wavelength of the compensated fiber. Compensating the mode dispersion of the compensated fiber such that the bandwidth is higher than the transmission bandwidth at the optimized wavelength,
The multimode dispersion compensating fiber is made of a fluorine-added fiber prepared by adding fluorine as a dopant to quartz glass, α value is 1.5 ≦ α ≦ 1.7, and core radius a is 15 μm ≦ a ≦. The maximum relative refractive index difference Δ is 0.005 ≦ Δ ≦ 0.025, and the length thereof is the ratio R of the length of the compensated fiber to the total fiber length connected to the compensated fiber. A mode dispersion compensation method, wherein 0.69 ≦ R ≦ 0.89. 6. The mode dispersion compensation method according to claim 1, wherein the compensated fiber has a maximum transmission bandwidth in a wavelength band of 0.85 [mu] m. The mode dispersion compensation according to claim 1, wherein the compensated fiber has a maximum relative refractive index Δ of 0.01, a core radius a of 25 μm, and an α value of 2.086. Method. A compensated fiber composed of a multimode fiber made by adding germanium as a dopant to quartz glass;
A multimode dispersion compensating fiber connected to the compensated fiber;
An optical waveguide comprising:
  The multi-mode dispersion compensating fiber is made of a fluorine-added fiber prepared by adding fluorine as a dopant to quartz glass, the α value is 2.030 ≦ α ≦ 2.045, and the core radius a is 15 μm ≦ a ≦. The maximum relative refractive index difference Δ is 0.005 ≦ Δ ≦ 0.025, and the length thereof is the ratio R of the length of the compensated fiber to the total fiber length connected to the compensated fiber. 0.15 ≦ R ≦ 0.35,
An optical waveguide, wherein a transmission bandwidth in a wavelength or wavelength band other than the optimized wavelength of the compensated fiber is higher than a transmission bandwidth in the optimized wavelength. A compensated fiber composed of a multimode fiber made by adding germanium as a dopant to quartz glass;
A multimode dispersion compensating fiber connected to the compensated fiber;
An optical waveguide comprising:
The multi-mode dispersion compensating fiber is made of a fluorine-added fiber prepared by adding fluorine to quartz glass as a dopant, α value is 1.9 ≦ α ≦ 2.1, and core radius a is 15 μm ≦ a ≦. 35 μm, the maximum relative refractive index difference Δ is 0.005 ≦ Δ ≦ 0.025, and the length thereof is the ratio R of the length of the compensated fiber to the total fiber length connected to the compensated fiber. 0.25 ≦ R ≦ 0.45,
An optical waveguide, wherein a transmission bandwidth in a wavelength or wavelength band other than the optimized wavelength of the compensated fiber is higher than a transmission bandwidth in the optimized wavelength. A compensated fiber composed of a multimode fiber made by adding germanium as a dopant to quartz glass;
A multimode dispersion compensating fiber connected to the compensated fiber;
An optical waveguide comprising:
The multi-mode dispersion compensating fiber is made of a fluorine-added fiber prepared by adding fluorine as a dopant to quartz glass, the α value is 1.8 ≦ α ≦ 2.0, and the core radius a is 15 μm ≦ a ≦. 35 μm, the maximum relative refractive index difference Δ is 0.005 ≦ Δ ≦ 0.025, and the length thereof is the ratio R of the length of the compensated fiber to the total fiber length connected to the compensated fiber. 0.47 ≦ R ≦ 0.67,
  An optical waveguide, wherein a transmission bandwidth in a wavelength or wavelength band other than the optimized wavelength of the compensated fiber is higher than a transmission bandwidth in the optimized wavelength. A compensated fiber composed of a multimode fiber made by adding germanium as a dopant to quartz glass;
A multimode dispersion compensating fiber connected to the compensated fiber;
An optical waveguide comprising:
The multimode dispersion compensating fiber is made of a fluorine-added fiber prepared by adding fluorine as a dopant to quartz glass, the α value is 1.7 ≦ α ≦ 1.9, and the core radius a is 15 μm ≦ a ≦. 35 μm, the maximum relative refractive index difference Δ is 0.005 ≦ Δ ≦ 0.025, and the length thereof is the ratio R of the length of the compensated fiber to the total fiber length connected to the compensated fiber. 0.57 ≦ R ≦ 0.77,
An optical waveguide, wherein a transmission bandwidth in a wavelength or wavelength band other than the optimized wavelength of the compensated fiber is higher than a transmission bandwidth in the optimized wavelength. A compensated fiber composed of a multimode fiber made by adding germanium as a dopant to quartz glass;
A multimode dispersion compensating fiber connected to the compensated fiber;
An optical waveguide comprising:
The multimode dispersion compensating fiber is made of a fluorine-added fiber prepared by adding fluorine as a dopant to quartz glass, α value is 1.5 ≦ α ≦ 1.7, and core radius a is 15 μm ≦ a ≦. The maximum relative refractive index difference Δ is 0.005 ≦ Δ ≦ 0.025, and the length thereof is the ratio R of the length of the compensated fiber to the total fiber length connected to the compensated fiber. 0.69 ≦ R ≦ 0.89,
An optical waveguide, wherein a transmission bandwidth in a wavelength or wavelength band other than the optimized wavelength of the compensated fiber is higher than a transmission bandwidth in the optimized wavelength. The optical waveguide according to claim 8, wherein the compensated fiber has a maximum transmission bandwidth at a wavelength of 0.85 μm. The optical waveguide according to claim 8, wherein the compensated fiber has a maximum relative refractive index Δ of 0.01, a core radius a of 25 μm, and an α value of 2.086.

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