JP4205455B2 - Optical fiber and optical transmission system using the same - Google Patents

Description

【００７２】
表１から明らかなように、実施例１〜６の光ファイバは、いずれも、１５００ｎｍ帯と１３００ｎｍ帯で使用可能な特性を備えているが、比較例１〜３の光ファイバは実施例に比べて劣る点を持っている。
【００７３】
以下、比較例と実施例の特徴的な点について述べる。
実施例２、６は実施例１に対してΔ１が大きくなっており、このため分散が小さくなっている。特に実施例２は、１３００ｎｍでの分散の値が請求範囲の下限であり、Δ１がこれ以上大きくなると、範囲を満たさなくなる。
【００７４】
逆に、実施例3は実施例1に対してΔ₁が小さくなっており、このため分散が大きくなっている。特に1550nmでの分散は請求範囲の上限であり、Δ₁がこれ以上小さくなると、範囲を満たさなくなることは明かである。
【００７５】
また、実施例２と実施例３を比較すると、実施例３では１５５０ｎｍの分散が９．９ｐｓ／ｎｍ／ｋｍ、コア有効断面積が６５．４μｍ²であるのに対して、実施例２では５．５ｐｓ／ｎｍ／ｋｍ、コア有効断面積が５０．０μｍ²となっている。これから、コア有効断面積を大きくして非線形効果を抑制しようとしても、分散が大きくなることで信号歪みが大きくなってしまうことがわかる。それ故、分散とコア有効断面積をうまくバランスさせることが重要である。
【００７６】
参考例１は実施例１に対してΔ２が小さくなっているため、分散の傾きが小さくなっている。
【００７７】
実施例４は実施例１に対してΔ３が大きくなっており、このためカットオフ波長が大きくなっている。この例ではカットオフ波長は請求範囲の中にあるものの、実施例１の値との比較から、これ以上Δ３が大きくなると、範囲を満たさなくなることは明かである。
【００７８】
さらに、実施例５は実施例１に対してΔ２が大きくなっており、このため分散の傾きとカットオフ波長が大きくなっている。カットオフ波長と１５５０ｎｍでの分散の傾きは請求範囲の中にあるものの、実施例１の値との比較から、更にΔ２が大きくなると、範囲を満たさなくなることは明かである。
【００７９】
屈折率分布パラメータα値が小さい比較例１は、カットオフ波長が１５７０nmと大きいため、１３００ｎｍ帯でシングルモード動作をしないと考えられ、この波長帯での伝送には適さない。
【００８０】
比較例２は実施例５よりΔ１とΔ２を大きくしたものである。この例では、実施例５に比べてΔ１を大きくすることでΔ２が大きくなったことによるカットオフ波長の増大は抑えることができているが、分散の傾きが大きくなり、請求範囲から外れている。このため、１５５０ｎｍでの分散値は所望の値にもかかわらず、１３００ｎｍの分散は所望の範囲から外れている。このことから、１５５０ｎｍの分散の傾きを、０．０６５ｐｓ／ｎｍ／ｋｍ以下にしなければ、１５５０ｎｍと１３００ｎｍで所望の分散値を取ることは難しいことが理解できる。
【００８１】
比較例３は、コア有効断面積を大きくすることを目的としてａを小さくしたものである。２ｒ₃を小さくすることで、コア有効断面積を７７．１μｍ²と大きくすることができるが、分散の傾きと曲げ損失が大きくなり、所望の範囲を外れている。このため、コア有効断面積は、他の特性とのバランスを考慮して大きくても７５μｍ²以下に制限される必要がある。
【００８２】
実施例６
実施例１の光ファイバと、図６で示した分散特性を有する分散補償光ファイバを接続した。後者の長さは、前者の長さの約１／１５とした。
【００８３】
そしてこの接続線路の分散特性を図７に示した。図７から明らかなように、１５３０〜１６２５nmの波長帯域で、残留する分散は−１．０〜１．０ps／nm／kmになっていて、形成された接続線路では分散が良好に補償されている。
【００８４】
【発明の効果】
以上の説明で明らかなように、本発明の光ファイバは、１３００ｎｍ帯と１５５０ｎｍ帯での伝送が可能な特性を備えている。
【００８５】
本発明の光ファイバを用いることにより、伝送容量の大きな伝送システムの構築が可能となるので、その工業的価値は大である。
【図面の簡単な説明】
【図１】本発明の光ファイバ屈折率分布プロファイルの一実施例を示す概略図である。
【図２】本発明の光ファイバ屈折率分布プロファイルの他の実施例を示す概略図である。
【図３】本発明の光ファイバ屈折率分布プロファイルの更に他の実施例を示す概略図である。
【図４】本発明の光ファイバのカットオフ波長の測定条長依存性を示す特性図である。
【図５】本発明の光ファイバのコア有効断面積の第１サイドコアの断面積依存性を示す特性図である。
【図６】負の分散の傾きをもつ分散補償ファイバの分散特性図である。
【図７】本発明の光ファイバと図５の分散補償ファイバを接続した線路の分散特性図である。
【符号の説明】
１ 中心のコア領域
２ 第１サイドコア領域
３ 第２サイドコア領域
４ トレンチ領域
５ クラッド領域[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber used for construction of an optical communication system and an optical transmission system using the same, and more particularly to an optical fiber suitable for use in construction of an optical transmission system of a wavelength division multiplexing (WDM) transmission system.
[0002]
[Prior art]
With the development of the information society, the amount of communication information tends to increase dramatically, and in accordance with this, research is being conducted to increase the transmission capacity in the optical transmission system.
[0003]
In that case, the optical fiber that is the optical transmission path is required to be able to transmit the optical signal in a single mode at the used wavelength. This is because when a plurality of modes propagates in the optical fiber, mode dispersion is unavoidably caused by a difference in group velocity for each propagation mode, resulting in signal waveform deterioration.
[0004]
For this reason, first, a single mode fiber (SMF) having an atmospheric dispersion wavelength around 1300 nm was used as an optical transmission line. When this SMF is used, the transmission distance can be increased to 100 km or more near the wavelength of 1300 nm, and optical transmission with a transmission capacity of several hundred Mbps is also possible.
[0005]
On the other hand, the transmission loss of the optical fiber is the smallest near the wavelength of 1550 nm. Therefore, in terms of loss, it is preferable to perform optical transmission in the 1550 nm band.
[0006]
As an optical fiber that meets such requirements, a dispersion shifted fiber (DSF) having an atmospheric dispersion wavelength near 1550 nm has been developed. In this DSF, the profile of the refractive index distribution in its cross section is a step type. With the development of this DSF, optical transmission with a transmission capacity of several Gbps is now possible near the wavelength of 1550 nm.
[0007]
Recently, for the purpose of further increasing the transmission capacity, research on a wavelength division multiplexing (WDM) transmission system that transmits optical signals of a plurality of wavelengths using a single optical fiber has been advanced.
[0008]
The optical fiber used in this WDM transmission system is required to have the following characteristics.
First, in order to prevent the occurrence of, for example, four-wave mixing (FWM), which is one of nonlinear phenomena, there is a characteristic that no atmospheric dispersion wavelength exists in the used wavelength band.
[0009]
As an optical fiber that meets such requirements, a non-zero dispersion shifted fiber (NZDSF) has been developed that does not have an atmospheric dispersion wavelength in the used wavelength band. When this NZDSF is used, FWM hardly occurs, and is currently evaluated as an optimum optical fiber in the WDM transmission system.
[0010]
Further, since the signal waveform deteriorates when the dispersion is large, the small dispersion is also an important characteristic for the optical fiber used in the WDM transmission system.
[0011]
Furthermore, when high power is introduced, other nonlinear phenomena such as self-phase modulation and cross-phase modulation are likely to occur in optical fibers, so that the core effective cross-sectional area is required to be large in order to suppress them. .
[0012]
In recent years, for the purpose of increasing the transmission capacity, a fiber considering the use of both the 1550 nm band and the 1300 nm band has also been proposed. (For example, Patent Literature 1 to Patent Literature 4)
[0013]
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-221352
[Patent Document 2]
JP 2001-264568 A
[Patent Document 3]
US Pat. No. 6,396,987
[Patent Document 4]
US Patent No. 5,905,838
[0014]
In Patent Document 1, the zero dispersion wavelength is 1370 nm to 1500 nm, and the absolute value of the slope of dispersion at the zero dispersion wavelength is 0.10 ps / nm.²A fiber that is less than / km is disclosed. According to this, in order to prevent the occurrence of four-wave mixing in the 1300 nm band and the 1550 nm band, the zero dispersion wavelength is positioned in the middle of the long wavelength band.
[0015]
Patent Document 2 discloses a fiber having a dispersion at 1550 nm of 5 to 11 ps / nm / km and a value obtained by dividing the dispersion by the dispersion slope (DPS) of 250 to 370 nm.
[0016]
In Patent Document 3, the dispersion is 6 ps / nm / km to 10 ps / nm / km at 1550 nm, and the absolute value of the dispersion slope is 0.07 ps / nm.²/ Km or less and core effective area is 60μm²The above optical fiber is disclosed.
[0017]
In Patent Document 4, the absolute value of dispersion at 1310 nm and 1550 nm is 1.0 ps / nm / km or more and 8.0 ps / nm / km or less, and the dispersion slope is 0.06 ps / nm.²An optical fiber that is less than / km is disclosed.
[0018]
[Problems to be solved by the invention]
However, in Patent Document 1, when a possible range of dispersion of 1300 nm and 1550 nm is estimated from this disclosed value, it is −25 ps / nm / km or more at 1300 nm and 15 ps / nm / km or less at 1550 nm. When SMF is used in the 1550 nm band, DCF is necessary to compensate for dispersion of about 17 ps / nm / km. Considering this, it cannot be said that the above dispersion range has good characteristics in both wavelength bands.
[0019]
Further, in Patent Document 2, it is estimated from the disclosed value that the zero dispersion wavelength is in the vicinity of 1300 nm. This is because the zero-dispersion wavelength is on the short-wave side compared to SMF. For this reason, the dispersion in the 1300 nm band is almost zero, and when performing WDM transmission in this wavelength band, there is a high possibility of causing four-wave mixing.
[0020]
Therefore, it is difficult to say that these optical fibers are suitable for WDM transmission in both the 1300 nm band and the 1550 nm band.
[0021]
In Patent Document 3, there is no description of the characteristics in the 1300 nm band in the claims, and it is considered that the use in the 1550 nm band is assumed.
[0022]
On the other hand, in Patent Document 4, the core effective area of 1550 nm described in the drawing is 50 μm.²It is as follows.
Thus, when the core effective area is small, there is a high possibility that a nonlinear phenomenon will occur. In particular, the dispersion and the core effective area are in a trade-off relationship with WDM transmission. For example, if the dispersion is reduced, deterioration of the signal waveform is suppressed, but on the other hand, the core effective area is reduced and nonlinear phenomena occur. It tends to occur.
[0023]
Conversely, if the core effective cross-sectional area is enlarged to suppress the occurrence of nonlinear phenomena, the dispersion of the optical fiber increases and the signal waveform deteriorates. Also, the bending loss of the optical fiber increases, so that it becomes difficult to assemble a gable using the optical fiber.
[0024]
Such a trade-off relationship between the dispersion of the optical fiber and the core effective area is such that the dispersion at the SMF wavelength of 1550 nm is about 17 ps / nm / km and the core effective area is about 75 μm.²On the other hand, in DSF, they are about 0ps / nm / km, about 50μm²As an example, it can be mentioned that this is the case. Therefore, how to balance dispersion and effective core area is an important point in designing the refractive index profile of an optical fiber. Furthermore, in an optical fiber for WDM transmission, a refractive index profile that can expand the core effective cross-sectional area in order to suppress the occurrence of nonlinear phenomena while maintaining other characteristics such as dispersion slope in addition to dispersion at a desired value. Development becomes very important.
[0025]
An object of the present invention is to solve the above-described problems, provide an optimal balance between dispersion and core effective area, and provide an optical fiber suitable for use in a WDM transmission system in both the 1300 nm band and the 1550 nm band. To do.
[0026]
[Means for Solving the Problems]
  In order to achieve the above object, in the present invention, the refractive index n₀And a refractive index n along the central axis of the cladding layer.₁Radius r₁Center core, and its outer periphery has a refractive index n₂Radius r₂And a refractive index n on the outer periphery of the first side core.₃Radius r₃The center core has a refractive index distribution parameter α of 3 or more and less than infinity, and each refractive index is n.₁> N₃> N₀> N₂In the optical fiber in the relationship of
Regarding the refractive index profile in the cross section, r corresponding to the cross-sectional area of the first side core region.₁To r₂The absolute value of the value obtained by integrating the relative refractive index difference of the first side core region up to is 0.60% · μm or less,
The dispersion at a wavelength of 1300 nm is -10.0 ps / nm / km or more and -2.5 ps / nm / km or less,
Core effective area at a wavelength of 1550 nm is 50 μm²75 μm or more²And
The cutoff wavelength at a length of 2 m is 1450 nm or less,
The dispersion at a wavelength of 1550 nm is 5.0 ps / nm / km or more and 10.0 ps / nm / km or less,
The slope of dispersion at a wavelength of 1550 nm is 0.065 ps / nm.²/ Km or less 0.055ps / nm²/ Km or more,
The bending loss when bent at a diameter of 20 mm at a wavelength of 1550 nm is 10 dB / m or less,
The dispersion at a wavelength of 1620 nm is 7.5 ps / nm / km or more and 20.0 ps / nm / km or less.,
Center core relative refractive index difference Δ₁0.45% or more and 0.6% or less, relative refractive index difference Δ of the first side core₂Is -0.15% or more and -0.10% or less, relative refractive index difference Δ of the second side core₃Is 0.45% or less and 0.3% or more, and the diameter of the second side core is 2r.₃Is 14.3 μm or more and 17.6 μm or less, and an optical fiber is provided.
[0027]
  The above invention has an effective core area of 33 μm at a wavelength of 1300 nm.²65 μm or more²Less thanBottom, 2The cut-off wavelength measured using an optical fiber of length m is 1450 nm or lessBecause there isIt can be used for optical transmission in the 1300 nm band, especially for WDM transmission systems.
[0028]
  The above inventionThe dispersion at a wavelength of 1550 nm is 5.0 ps / nm / km or more and 10.0 ps / nm / km or less, and the dispersion slope is 0.065 ps / nm.²/ Km or less,MoreZero dispersion wavelength is 1450nm or less0.051ps / nm ² / Km or more, wavelengthFeatures suitable for WDM transmission at 1550 nm.
[0029]
  The above inventionSince the bending loss at a wavelength of 1550 nm when bent at a diameter of 20 mm is 10 dB or less, the optical fiber can prevent an increase in loss due to a side pressure during cable formation.
[0030]
  The above inventionHas a dispersion at a wavelength of 1620 nm of 7.5 ps / nm / km or more and 20.0 ps / nm / km or less.SoSince dispersion is smaller than that of the conventional SMF, optical transmission in the L band is possible.
[0031]
  Also,The above inventionLoss in the wavelength band of 1375 to 1395 nm is 0.5 dB / km or lessSoTransmission in the S band (1460-1530 nm) using Raman amplification is also possible.
[0033]
  Furthermore, in the present invention, an optical transmission line including any of the optical fibers described above,1550An optical transmission system is provided in which a dispersion compensating fiber having a negative dispersion slope in a wavelength band of ˜1650 nm is connected.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
The optical fiber of the present invention has been developed for use in a WDM transmission system. As described above, the optical fiber used in the WDM transmission system has a large core effective cross-sectional area to prevent the occurrence of nonlinear phenomena, and chromatic dispersion is small to prevent signal waveform deterioration. Moreover, since the dispersion slope is not large and the optical fiber is laid in a cable, characteristics such as an increase in optical loss hardly occur at the time of cable laying and laying are required.
[0035]
In order to satisfy the above requirements, the present inventors set the following characteristic targets for the development target optical fiber.
[0036]
(1) First, in order to realize the WDM transmission system, the core effective area at a wavelength of 1550 nm is at least 50 μm as generally considered.²Above, preferably 60μm²This is necessary for the optical fiber used.
[0037]
However, if the core effective area is too large, the bending loss of the optical fiber increases, so the core effective area at the wavelength of 1550 nm is 75 μm at the maximum.²Should be regulated.
[0038]
(2) Next, regarding the dispersion, since the waveform distortion is accumulated according to the dispersion while the optical signal is transmitted through the optical fiber, the dispersion is reduced as the optical fiber is used for long-distance transmission. It will be necessary. However, when such an optical fiber is used for short distance transmission, it may exhibit excessive performance.
[0039]
In addition, as shown in the case of using SMF used in the 1300 nm band in the 1550 nm band, even if the optical fiber has a large dispersion, a dispersion compensator should be installed in the transmission line as necessary. Long-distance transmission is also possible.
[0040]
For this reason, it can be said that the dispersion constraint on the optical fiber is not large compared to the constraint due to the core effective area described above. However, it is said that the dispersion of the optical fiber used in the WDM transmission system is preferably smaller than that of the SMF used in the 1300 nm band (about 17 ps / nm / km). Not too long. Also, the smaller the dispersion slope, the smaller the difference in waveform distortion due to the signal wavelength, which is preferable.
[0041]
(3) Considering WDM transmission in the 1300 nm band, it is necessary to have dispersion that is small and not 0 even in the 1300 nm band. For this reason, it is necessary to determine the dispersion and the dispersion slope so that WDM transmission can be performed in both the 1550 nm band and the 1300 nm band.
[0042]
(4) From the conditions regarding dispersion shown in (2) to (3), the absolute value of dispersion at 1550 nm and 1300 nm is limited to 10 ps / nm / km or less. If it is larger than this, the waveform distortion due to dispersion increases. On the other hand, when the dispersion at 1550 nm decreases, the dispersion at 1300 nm decreases accordingly. Since the dispersion at 1300 nm is negative, that is, the absolute value becomes large, making it unsuitable for transmission at 1300 nm. For this reason, it is necessary to provide a lower limit for the dispersion value at 1550 nm, and 5 ps / nm / km is appropriate. The upper limit of dispersion at 1300 nm is limited to -2.5 ps / nm / km due to the WDM transmission conditions described in (3). Due to these restrictions, the zero dispersion wavelength is 1450 nm or less.
[0043]
(6) The core effective area at 1300 nm is 50 μm or more and 75 μm at 1550 nm.²Since it was determined as follows, the wavelength dependence of the core effective area is 33 μm.²65 μm or more²The following can be determined. However, if the core effective cross-sectional area is small, there is a problem that loss at the time of fiber connection tends to increase, and it is preferably 38 μm or more.
[0044]
(7) Further, regarding an optical fiber used in the WDM transmission system, when it is bent at a diameter of 20 mm, its bending loss needs to be 10 dB / m or less. The bending loss is preferably 5 dB / m or less, more preferably 2 dB / m or less. This is an important standard for preventing an increase in loss due to a side pressure applied during or after laying the fiber, or an increase in loss when the fiber is routed in a device with a small radius.
[0045]
(8) The cutoff wavelength decreases as the length of the measurement fiber increases. FIG. 4 shows the relationship between the measured values of the cutoff wavelength at 2 m and a length of 22 m corresponding to the cable state for the fiber of the present invention. As shown in this figure, the 22 m fiber tends to be 200 nm smaller than the 2 m fiber. Since the actual line transmits longer distances, the actual fiber cut-off wavelength should be much smaller. However, since the actual length of the line varies, it is represented by the value at 22 m. In the present invention, considering use in the 1300 nm band, the cutoff at 22 m needs to be 1250 nm or less. For this reason, here, the upper limit of the cutoff wavelength measured at 2 m is set to 1450 nm.
[0046]
In order to satisfy the above-described target characteristics from the above viewpoint, the present inventors consider other characteristics, and then search for a refractive index profile. A refractive index profile as shown in FIG. 1 is preferable. I found out.
[0047]
The refractive index profile shown in FIG. 1 includes a center core region 1, a first side core region 2 arranged in an annular shape outside the center core region 1, a second side core region 3 arranged in an annular shape outside the center core region 1, and It has the clad area | region 4 arrange | positioned on the outer side at the annular | circular shape. The relative refractive index difference of the center core region 1 relative to the cladding region 4, the relative refractive index difference of the first side core region 2 relative to the cladding region 4, and the relative refractive index difference of the second side core region 3 relative to the cladding region 4 are respectively Δ₁(%), Δ₂(%), Δ_Three(%), Radius is r₁(Μm), r₂(Μm), r_Three(Μm).
[0048]
Where Δ₁(%), Δ₂(%), Δ_Three(%) Is defined as shown in FIG. 1 for the portion where the absolute value of the refractive index of each region is the largest.
[0049]
R₁, R₂Is defined by the position of the point where the line connecting the center core and the first side core of the refractive index profile and the line connecting the first side core and the second side core are equal to the refractive index of the cladding. R_ThreeIs defined by the position of the point where the tangent S of the portion where the gradient of the refractive index profile is the largest in the portion outside the maximum value of the second side core becomes equal to the refractive index of the cladding. However, when a trench layer having a refractive index lower than that of the cladding exists in a portion adjacent to the second side core as shown in FIG.₁The point where the line connecting the second side core and the trench layer is equal to the refractive index of the cladding is_ThreeTo
[0050]
In these refractive index profiles, Δ₁The value is preferably set to 0.45% or more and 0.6% or less. A more preferable range is 0.45% or more and 0.55% or less. In general, this Δ₁Increasing the value decreases the variance and also reduces the core effective area, and vice versa.₁When the value is decreased, the core effective area is increased, but the dispersion is increased and the bending loss is also increased. In order to meet the above design goals for core effective area and dispersion simultaneously, Δ₁The value is preferably within the above range.
[0051]
Since the dispersion value at 1550 nm is smaller than that of the SMF having a zero dispersion wavelength in the 1300 nm band, the optical fiber of the present invention can transmit longer distance than the case of using the 1300 nm zero dispersion SMF. enable. Of course, if necessary, the optical fiber of the present invention can be used for long-distance transmission by using a dispersion compensator.
[0052]
Δ_ThreeAs the value increases, the cut-off wavelength increases to keep the bending loss within the standard range, and there is a tendency that the single-mode is not substantially achieved in the used wavelength band. For this reason, Δ_ThreeIs limited to 0.45% or less.
[0053]
  Furthermore, Δ2 is negative, preferably-0.15% or more-0.10% Or less. If it is more than this, the slope of dispersion tends to increase, the cutoff wavelength increases, and single mode operation may not occur in the used wavelength band.
[0054]
Regarding the slope of dispersion and the size of the core effective area, it corresponds to the width of the first side core (r₂−r₁)₂A result similar to that obtained when adjusting may be obtained. In particular, Δ₂When the width of the first side core is reduced, the dispersion slope and the size of the core effective cross-sectional area can be maintained at a substantially constant value by increasing the width of the first side core. Focusing on this point, r₁To r₂The absolute value of the value obtained by integrating the relative refractive index differences up to is introduced as “the cross-sectional area of the first side core”. The unit is% · μm (hereinafter,% · μm is simply referred to as% μm).
[0055]
  FIG. 5 shows an example.5The relationship between the cross-sectional area of the first side core and the core effective cross-sectional area was investigated by changing Δ2 and (r2-r1) in various ways based on the profile of. From these figures, the effective core area is 50 μm.²To achieve the above, the cross-sectional area of the first side core needs to be 0.75% μm or less. Further, when the same investigation was performed on the refractive index profiles of various parameters, it was found that the characteristics were satisfied if the refractive index profile was 0.60% μm or less.
[0056]
Incidentally, when the cross-sectional area of the first side core is estimated from the diagram described in Patent Document 4, all are 0.61% μm or more, and the core effective cross-sectional area specified in the diagram is 50 μm.²It is as follows.
[0057]
When the refractive index distribution parameter α is decreased, the cutoff wavelength increases when the bending loss is kept within the standard range. In particular, when the refractive index distribution parameter α is smaller than 2, the cut-off wavelength tends not to be substantially single mode. is there. For this reason, the refractive index distribution parameter α needs to be 3 or more. Further, when the refractive index distribution parameter α is small, the characteristics greatly vary due to the variation of the refractive index distribution parameter α. Therefore, the refractive index distribution parameter α is preferably 4 or more.
[0058]
However, when the refractive index distribution parameter α is infinite, that is, a perfect rectangle, since the relative refractive index difference between the first side core is negative, the refractive index change at the interface between the center core and the first side core becomes large. For this reason, the difference in viscosity at the interface becomes large and distortion occurs, which may induce structural defects in the glass and increase transmission loss. For this reason, infinity of the refractive index distribution parameter α should be avoided.
[0059]
In the fiber of the present invention, the effective core area at 1550 nm is 50 μm.²75 μm or more²Since it is set as follows, the bending loss is small and the occurrence of a nonlinear phenomenon can be suppressed. Since the dispersion in the 1550 nm band is 5.0 ps / nm / km or more and 10.0 ps / nm / km or less, FWM can be suppressed and a fiber suitable for DWM transmission can be provided.
[0060]
The slope of dispersion at 1550 nm is 0.065 ps / nm.²Since it is set to / km or less, not only a wide wavelength band in the 1550 nm band can be taken, but also the absolute value of dispersion at 1300 nm can be reduced.
[0061]
For this reason, the optical fiber of the present invention has a dispersion at a wavelength of 1300 nm of -10.0 ps / nm / km or more. Since this value is smaller than that of the above-described fiber, the optical fiber of the present invention can be used as a transmission line for signal light in the 1300 nm band. In that case, the core effective area of the optical fiber of the present invention is 33 μm at a wavelength of 1300 nm.²65 μm or more²Set to:
[0062]
In the optical fiber of the present invention, dispersion at a wavelength of 1620 nm is 7.5 ps / nm / km or more and 20.0 ps / nm / km or less. This value is smaller than the above-mentioned 1300 nm zero dispersion SMF and can be used for L-band transmission.
[0063]
The above characteristics are basically obtained from the profile of the refractive index distribution shown in FIG. 1, and the shapes of the central core region 1, the first side core region 2, and the second side core region 3 and the outer diameters of these three regions. 2r_ThreeIt is stipulated in.
[0064]
Therefore, the profile of the refractive index distribution in the optical fiber of the present invention is not limited to that shown in FIG. 1, and any profile that exhibits the above-described characteristics, for example, as shown in FIGS. 1 may be a profile in which a trench layer is provided outside the structure of FIG.
[0065]
However, the refractive index profile shown in FIG. 1 is preferable in that the refractive index profile structure is simple, and therefore the manufacturing thereof is easy and the manufacturing yield is high.
[0066]
The optical fiber of the present invention can be manufactured by, for example, manufacturing an optical fiber preform by VAD method or MCVD method, drawing it into transparent glass, and then drawing.
[0067]
In particular, when an optical fiber preform is manufactured by the VAD method and made transparent glass in a halogen-containing gas atmosphere, the obtained optical fiber has a small OH absorption peak at a wavelength of 1390 nm, specifically, at a wavelength of 1390 nm. The optical fiber has a loss of 0.5 dB / km or less. Such an optical fiber can be used in a system that uses Raman amplification in the S-band.
[0068]
Furthermore, when the height of the OH absorption peak is 0.1 dB / km or less, a wavelength band near 1390 nm can be used for transmission, which is more preferable.
[0069]
The optical fiber of the present invention has a positive chromatic dispersion slope in the wavelength band of 1400 to 1650 nm. A dispersion compensator having a negative dispersion slope is provided in an optical transmission line constructed with this optical fiber. By connecting, a dispersion compensating line can be configured.
[0070]
【Example】
  Examples 1 to6. Reference Example 1And Comparative Examples 1-3 are described.
  Various optical fibers having the refractive index profile shown in FIG. 1 were manufactured, and their characteristics were investigated. The structural parameters and characteristics of the refractive index profile are collectively shown in Table 1. The cutoff wavelength is measured with a 2 m fiber.
[0071]
[Table 1]

[0072]
  As is clear from Table 1, Examples 1 to6Each of the optical fibers has characteristics that can be used in the 1500 nm band and the 1300 nm band, but the optical fibers of Comparative Examples 1 to 3 are inferior to the examples.
[0073]
  The characteristic points of the comparative example and the example will be described below.
  Example 2, 6Has a larger Δ1 than that of the first embodiment, and thus the dispersion is small. Particularly, in Example 2, the dispersion value at 1300 nm is the lower limit of the claims, and when Δ1 becomes larger than this, the range is not satisfied.
[0074]
Conversely, Example 3 is Δ₁Is small, and thus the dispersion is large. In particular, dispersion at 1550 nm is the upper limit of the claim, and Δ₁Obviously, if becomes smaller, the range will not be met.
[0075]
Further, when Example 2 and Example 3 are compared, in Example 3, the dispersion at 1550 nm is 9.9 ps / nm / km, and the effective core area is 65.4 μm.²In contrast, in Example 2, 5.5 ps / nm / km and the effective core area is 50.0 μm.²It has become. From this, it can be seen that even if an attempt is made to suppress the nonlinear effect by increasing the core effective area, the signal distortion increases as the dispersion increases. It is therefore important to balance the dispersion and the core effective area.
[0076]
  Reference example 1Since Δ2 is smaller than that in Example 1, the slope of dispersion is small.
[0077]
  Example4Δ3 is larger than that of the first embodiment, and therefore the cutoff wavelength is larger. In this example, although the cutoff wavelength is within the claimed range, it is clear from the comparison with the value of Example 1 that the range is not satisfied when Δ3 is further increased.
[0078]
  Further examples5[Delta] 2 is larger than that of Example 1, and therefore, the dispersion slope and the cutoff wavelength are large. Although the cutoff wavelength and the slope of dispersion at 1550 nm are within the claimed range, it is clear from the comparison with the value of Example 1 that the range is not satisfied when Δ2 is further increased.
[0079]
Since Comparative Example 1 having a small refractive index distribution parameter α value has a large cutoff wavelength of 1570 nm, it is considered that single mode operation is not performed in the 1300 nm band, and is not suitable for transmission in this wavelength band.
[0080]
  Comparative Example 2 is an example5Further, Δ1 and Δ2 are made larger. In this example, the example5By increasing Δ1, the increase in cut-off wavelength due to an increase in Δ2 can be suppressed, but the slope of dispersion increases and deviates from the claims. For this reason, although the dispersion value at 1550 nm is a desired value, the dispersion at 1300 nm is out of the desired range. From this, it can be understood that it is difficult to obtain desired dispersion values at 1550 nm and 1300 nm unless the slope of dispersion at 1550 nm is 0.065 ps / nm / km or less.
[0081]
In Comparative Example 3, a is decreased for the purpose of increasing the core effective area. 2r_ThreeBy reducing the effective cross-sectional area of the core by 77.1 μm²However, the dispersion slope and the bending loss are large, which is out of the desired range. For this reason, the core effective cross-sectional area is 75 μm at the maximum considering the balance with other characteristics.²Must be limited to:
[0082]
Example6
  The optical fiber of Example 1 was connected to the dispersion compensating optical fiber having the dispersion characteristics shown in FIG. The length of the latter was about 1/15 of the length of the former.
[0083]
The dispersion characteristics of this connection line are shown in FIG. As is apparent from FIG. 7, the remaining dispersion is -1.0 to 1.0 ps / nm / km in the wavelength band of 1530 to 1625 nm, and the dispersion is well compensated in the formed connection line. Yes.
[0084]
【The invention's effect】
As is apparent from the above description, the optical fiber of the present invention has characteristics that allow transmission in the 1300 nm band and the 1550 nm band.
[0085]
By using the optical fiber of the present invention, it is possible to construct a transmission system having a large transmission capacity, and its industrial value is great.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an embodiment of an optical fiber refractive index profile according to the present invention.
FIG. 2 is a schematic view showing another embodiment of the optical fiber refractive index profile of the present invention.
FIG. 3 is a schematic view showing still another embodiment of the optical fiber refractive index profile of the present invention.
FIG. 4 is a characteristic diagram showing the measurement length dependency of the cutoff wavelength of the optical fiber of the present invention.
FIG. 5 is a characteristic diagram showing the cross-sectional area dependence of the first side core of the core effective cross-sectional area of the optical fiber of the present invention.
FIG. 6 is a dispersion characteristic diagram of a dispersion compensating fiber having a negative dispersion slope.
7 is a dispersion characteristic diagram of a line connecting the optical fiber of the present invention and the dispersion compensating fiber of FIG. 5;
[Explanation of symbols]
1 Core area in the center
2 First side core region
3 Second side core region
4 Trench region
5 Clad region

Claims (5)

A clad layer having a refractive index n ₀ , a center core having a refractive index n ₁ radius r ₁ along the central axis of the clad layer, a first side core having a refractive index n ₂ radius r ₂ on the outer periphery thereof; having a second side core refractive index n ₃ a radius r ₃ in its periphery, has a structure having at least three layers of which the inner cladding layer, the center core is less than infinite refractive index distribution parameter α is 3 or more In the optical fiber in which each refractive index has a relationship of n ₁ > n ₃ > n ₀ > n ₂ ,
Regarding the refractive index profile in the cross section, the absolute value of the integrated value of the relative refractive index difference of the first side core region from r ₁ to r ₂ corresponding to the cross sectional area of the first side core region is 0.60% · μm or less. Yes,
The dispersion at a wavelength of 1300 nm is -10.0 ps / nm / km or more and -2.5 ps / nm / km or less,
Core effective cross-sectional area at the wavelength 1550nm is at 50 [mu] m ² or more 75 [mu] m ² or less,
The cutoff wavelength at a length of 2 m is 1450 nm or less ,
The dispersion at a wavelength of 1550 nm is 5.0 ps / nm / km or more and 10.0 ps / nm / km or less,
The slope of dispersion at a wavelength of 1550 nm is 0.065 ps / nm ² / km or less and 0.055 ps / nm ² / km or more,
The bending loss when bent at a diameter of 20 mm at a wavelength of 1550 nm is 10 dB / m or less,
The dispersion at a wavelength of 1620 nm is 7.5 ps / nm / km or more and 20.0 ps / nm / km or less ,
0.6% the relative refractive index difference delta ₁ 0.45% or more of the center core below, the relative refractive index difference delta ₂ of the first side core is -0.10% inclusive -0.15%, the ratio of the second side core An optical fiber, wherein the refractive index difference Δ ₃ is 0.45% or less and 0.3% or more, and the diameter 2r ₃ of the second side core is 14.3 μm or more and 17.6 μm or less. ^2. The optical fiber according to claim 1, wherein an effective core area at a wavelength of 1300 nm is 33 μm ² or more and 65 μm ² or less . The optical fiber according to claim 1 or 2, wherein a zero dispersion wavelength is 1450 nm or less. The optical fiber according to any one of claims 1 to 3, wherein a loss in a wavelength band of 1375 to 1395 nm is 0.5 dB / km or less. An optical transmission line including the optical fiber according to claim 1, wherein a dispersion compensating fiber having negative dispersion and a slope of negative dispersion in a wavelength band of 1550 to 1650 nm is connected to the optical transmission line. system.

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