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JP4684593B2 - Low bending loss multimode fiber - Google Patents

Low bending loss multimode fiber Download PDF

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JP4684593B2
JP4684593B2 JP2004229003A JP2004229003A JP4684593B2 JP 4684593 B2 JP4684593 B2 JP 4684593B2 JP 2004229003 A JP2004229003 A JP 2004229003A JP 2004229003 A JP2004229003 A JP 2004229003A JP 4684593 B2 JP4684593 B2 JP 4684593B2
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refractive index
bending loss
band
core
multimode fiber
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JP2006047719A (en
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寧 官
勝宏 竹永
邦治 姫野
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/028—Optical fibres with cladding with or without a coating with core or cladding having graded refractive index
    • G02B6/0288—Multimode fibre, e.g. graded index core for compensating modal dispersion
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
    • G02B6/03616—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference
    • G02B6/03638—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 3 layers only
    • G02B6/0365—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 3 layers only arranged - - +
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
    • G02B6/03616—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference
    • G02B6/03688—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 5 or more layers

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Description

本発明は、従来のグレーテッドインデックス型（以下、ＧＩ型と記す。）マルチモードファイバを改良し、極小な曲げ径に対しても損失が低いマルチモードファイバに関するものである。従来のＧＩ型マルチモードファイバ（以下、ＧＩファイバと記す。）は、クラッドに対するコアの屈折率差が高いので、元々曲げに強いが、ＦＴＴＦ（Fiber to the home）に用いられる屋内配線に用いる場合、極小な曲げ径に対しても、低い曲げ損失特性が要求される。   The present invention relates to a multimode fiber that improves a conventional graded index type (hereinafter referred to as GI type) multimode fiber and has a low loss even for a minimum bending diameter. Conventional GI type multimode fiber (hereinafter referred to as GI fiber) has a high refractive index difference between the core and the clad, so it is inherently resistant to bending, but is used for indoor wiring used in FTTF (Fiber to the home). Even for extremely small bending diameters, low bending loss characteristics are required.

従来のＧＩファイバは通常、次式（１）に示すα乗屈折率分布をもつコアを有する。   A conventional GI fiber usually has a core having an α-th power refractive index distribution represented by the following equation (1).

Figure 0004684593
Figure 0004684593

（式中、ａはコア半径、ｎ１はコア中心屈折率、Δは比屈折率差を表し、αは所望の波長帯で帯域が最大になるように設定されるパラメータである。）
従来のＧＩファイバは、そのままでは極小な曲げ径に対する曲げ損失が大きくなり、宅内配線の要求を満たすことができない。
一方、帯域が最大になるように、ファイバの屈折率分布を合成する方法が提案されている（例えば、非特許文献１参照。）。
この従来技術で得られる屈折率分布は、α乗屈折率分布に近い分布の外側に屈折率がクラッドよりも小さくなる領域（デプレスド領域）が存在するのが特徴であり、この構造では曲げ損失特性の良いファイバが得られることが予想される。
K. Okamoto and T. Okoshi,“Computer-aided synthesis of the optimum refractive index profile for a multimode fiber,”IEEE Trans. Microwave Theory Tech., vol. MTT-25, pp.213-221, 1976 (In the formula, a is a core radius, n 1 is a core center refractive index, Δ is a relative refractive index difference, and α is a parameter set so that the band is maximized in a desired wavelength band.)
The conventional GI fiber has a large bending loss with respect to a minimum bending diameter as it is, and cannot satisfy the demand for home wiring.
On the other hand, a method of synthesizing the refractive index distribution of the fiber so as to maximize the band has been proposed (see, for example, Non-Patent Document 1).
The refractive index distribution obtained by this conventional technique is characterized by the fact that there is a region where the refractive index is smaller than the cladding (depressed region) outside the distribution close to the α power refractive index distribution. It is expected that a good fiber will be obtained.
K. Okamoto and T. Okoshi, “Computer-aided synthesis of the optimum refractive index profile for a multimode fiber,” IEEE Trans. Microwave Theory Tech., Vol. MTT-25, pp.213-221, 1976

しかしながら、非特許文献１において提案された屈折率分布は、簡単な式で表すことができず、ファイバ製造上屈折率分布を精密に制御しなければならないため、製造するのが困難である。   However, the refractive index distribution proposed in Non-Patent Document 1 cannot be expressed by a simple formula and is difficult to manufacture because the refractive index distribution must be precisely controlled for fiber manufacture.

本発明は前記事情に鑑みてなされ、容易に製造でき、優れた曲げ損失特性をもったマルチモードファイバの提供を目的とする。   The present invention has been made in view of the above circumstances, and an object thereof is to provide a multimode fiber that can be easily manufactured and has excellent bending loss characteristics.

前記目的を達成するため、本発明は、次式（１）   In order to achieve the above object, the present invention provides the following formula (1):

Figure 0004684593
Figure 0004684593

（式中、ａはコア半径、ｎ１はコア中心屈折率、Δは比屈折率差を表し、αは所望の波長帯で帯域が最大になるように設定されるパラメータである。）で表されるα乗屈折率分布をもつコアと、その外側のクラッドとを有するマルチモードファイバであって、コアの外側に、クラッドよりも低屈折率でそれぞれ屈折率の異なる複数のデプレスド領域が設けられ、これらのデプレスド領域が４層階段状の屈折率分布をなし、ａ＝２５μｍ、α＝２．０４であり、Δ＝０．０１、ｒ≦２５μｍでα乗屈折率分布をもち、前記デプレスド領域の４層の内側境界までの半径が、最も内側の層から順に、２５．５μｍ、２６．８μｍ、２８μｍ及び２９μｍであり、最も外側の境界までの半径が３０．１μｍであり、前記デプレスド領域の４層の比屈折率差Δ ０ が、最も内側の層から順に、−０．００１、−０．００２、−０．００４及び−０．００３であり、０．８５μｍ波長帯でＯＦＬ帯域が１．５ＧＨｚ・ｋｍ以上、定常モード励振時、φ１０の曲げに対する曲げ損失が５ｄＢ／ｍ以下であることを特徴とする低曲げ損失マルチモードファイバを提供する。 (Wherein, a is a core radius, n 1 is a core center refractive index, Δ is a relative refractive index difference, and α is a parameter set to maximize the band in a desired wavelength band). A multimode fiber having a core having an α power refractive index profile and an outer cladding, and a plurality of depressed regions each having a lower refractive index and a different refractive index than the cladding are provided outside the core. these Depuresudo region forms the refractive index distribution of a four-layer stepped, a = 25 [mu] m, an α = 2.04, Δ = 0.01, has alpha-ride refractive index distribution r ≦ 25 [mu] m, the Depuresudo region The radius to the inner boundary of the four layers is 25.5 μm, 26.8 μm, 28 μm, and 29 μm in order from the innermost layer, and the radius to the outermost boundary is 30.1 μm. 4 layers of relative refractive index difference Δ 0 is -0.001, -0.002, -0.004, and -0.003 in order from the innermost layer, and the OFL band is 1.5 GHz · km or more in the 0.85 μm wavelength band. Provided is a low bending loss multimode fiber characterized by having a bending loss of 5 dB / m or less with respect to the bending of φ10 during excitation.

本発明によれば、極小な曲げ径に対しても低い曲げ損失を有する低曲げ損失マルチモードファイバを提供することができる。
また、本発明の低曲げ損失マルチモードファイバは、コアの外側にクラッドよりも低屈折率で均一な屈折率分布をもつデプレスド領域を設けた簡単な構造であるため、製造が容易であり、低コストで提供することができる。
また、本発明の低曲げ損失マルチモードファイバは、極小な曲げ径に対しても低い曲げ損失を有することから、配線の柔軟性や施工性が要求される宅内配線に好適に用いることができる。
また、０．８５μｍ波長帯用のＶＣＳＥＬレーザが安価であり、ＧＩファイバの接続の容易さから、０．８５μｍ波長帯で高い帯域と低い曲げ損失を有する本発明の低曲げ損失マルチモードファイバは、ユーザ自身が配線を行い、光ＬＡＮを構築するためのファイバとして最適である。 ADVANTAGE OF THE INVENTION According to this invention, the low bending loss multimode fiber which has a low bending loss with respect to an extremely small bending diameter can be provided.
The low bending loss multimode fiber of the present invention has a simple structure in which a depressed region having a uniform refractive index distribution with a lower refractive index than the cladding is provided on the outer side of the core. Can be provided at a cost.
Moreover, since the low bending loss multimode fiber of the present invention has a low bending loss even with respect to an extremely small bending diameter, it can be suitably used for home wiring that requires wiring flexibility and workability.
In addition, the VCSEL laser for the 0.85 μm wavelength band is inexpensive, and the low bending loss multimode fiber of the present invention having a high band and a low bending loss in the 0.85 μm wavelength band is obtained from the ease of connection of the GI fiber. It is optimal as a fiber for the user to perform wiring and construct an optical LAN.

以下、図面を参照して本発明の実施形態を説明する。
図１は本発明に係る低曲げ損失マルチモードファイバの屈折率分布の一例を示す図である。図中、符号１はコア、２はクラッド、３はデプレスド領域を表し、また符号ａはコア半径、ｒは半径、Δはクラッドに対する比屈折率差、ｒ１はデプレスド領域内側境界までの半径、ｒ２はデプレスド領域外側境界までの半径、Δ０はデプレスド領域の比屈折率差を表している。 Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing an example of a refractive index distribution of a low bending loss multimode fiber according to the present invention. In the figure, reference numeral 1 is a core, 2 is a cladding, 3 is a depressed area, a is a core radius, r is a radius, Δ is a relative refractive index difference with respect to the cladding, r 1 is a radius to the inner boundary of the depressed area, r 2 represents the radius to the outer boundary of the depressed region, and Δ 0 represents the relative refractive index difference of the depressed region.

この低曲げ損失マルチモードファイバは、前述した式（１）で表されるα乗屈折率分布をもつコア１と、その外側のクラッド２と、コア１の外側近傍に設けられ、クラッド２よりも低屈折率で均一な屈折率分布をもつデプレスド領域３とから構成されている。図１に示す低曲げ損失マルチモードファイバの屈折率分布は、半径ｒがａより小さい領域ではα乗屈折率分布に従い、ｒ≧ａの領域にはコア１を囲むリング状のデプレスド領域３を有する。好ましい例示において、コア１はＧｅドープ石英ガラス、クラッド２は石英ガラス、デプレスド領域３はＦドープ石英ガラスからなっているが、これに限定されない。   This low-bending loss multimode fiber is provided in the core 1 having the α power refractive index distribution represented by the above-described formula (1), the outer cladding 2 thereof, and the outer vicinity of the core 1, which is more than the cladding 2. And a depressed region 3 having a low refractive index and a uniform refractive index distribution. The refractive index profile of the low bending loss multimode fiber shown in FIG. 1 follows the α power refractive index profile in a region where the radius r is smaller than a, and has a ring-shaped depressed region 3 surrounding the core 1 in a region where r ≧ a. . In a preferred example, the core 1 is made of Ge-doped quartz glass, the cladding 2 is made of quartz glass, and the depressed region 3 is made of F-doped quartz glass, but is not limited thereto.

図１の例示においてこのデプレスド領域３は、ｒ１からｒ２までの領域に形成され、クラッド２よりも低く均一な屈折率分布、すなわち単純な凹状の屈折率分布になっている。
この低曲げ損失マルチモードファイバは、従来公知のＧＩファイバ用母材製造プロセスにおいて、コアとなる母材の外側にクラッド層を形成する際に、Ｆドープ石英ガラスなどの低屈折率材料からなる層を介在させ、得られた母材を従来公知の方法で線引きすることにより製造することができる。 In the illustration of FIG. 1, the depressed region 3 is formed in the region from r 1 to r 2 and has a uniform refractive index distribution lower than that of the cladding 2, that is, a simple concave refractive index distribution.
This low bending loss multimode fiber is a layer made of a low refractive index material such as F-doped quartz glass when a cladding layer is formed on the outer side of the core base material in a conventionally known GI fiber base material manufacturing process. Can be produced by drawing the obtained base material by a conventionally known method.

このデプレスト領域３を有する低曲げ損失マルチモードファイバは、次の（ａ）〜（ｆ）に示す条件のいずれかを満たすことが好ましい。
（ａ）０．８５μｍ波長帯でＯＦＬ帯域が１．５ＧＨｚ・ｋｍ以上、定常モード励振時、φ１０の曲げに対する曲げ損失が５ｄＢ／ｍ以下であり、比屈折率差Δが０．０１１以下であること。
（ｂ）０．８５μｍ波長帯でＯＦＬ帯域が０．８ＧＨｚ・ｋｍ以上、定常モード励振時、φ１０の曲げに対する曲げ損失が３ｄＢ／ｍ以下であり、比屈折率差Δが０．０２２以下であること。
（ｃ）Δ≦０．０１１、ｒ≦２５μｍでα乗屈折率分布をもち、２５μｍ≦ｒ１≦２８μｍ、２６μｍ≦ｒ２≦３２μｍ、−０．００６≦Δ０≦−０．００１で表される凹状屈折率分布をもつデプレスド領域３を有すること。
（ｄ）Δ≦０．０２２、ｒ≦３２．５μｍでα乗屈折率分布をもち、３２．５μｍ≦ｒ１≦３５．５μｍ、３３．５μｍ≦ｒ２≦４０．５μｍ、−０．００５≦Δ０≦−０．００１で表される凹状屈折率分布をもつデプレスド領域を有すること。
（ｅ）０．８５μｍ波長帯でＯＦＬ帯域が０．４ＧＨｚ・ｋｍ以上、１．３０ｍｍ波長帯でＯＦＬ帯域が０．４ＧＨｚ・ｋｍ以上、０．８５μｍ及び１．３０μｍのいずれの波長帯に対しても、定常モード励振時、φ１０の曲げに対する曲げ損失が５ｄＢ／ｍ以下であり、比屈折率差Δが０．０１１以下であること。
（ｆ）０．８５μｍ波長帯でＯＦＬ帯域が０．３ＧＨｚ・ｋｍ以上、１．３０ｍｍ波長帯でＯＦＬ帯域が０．３ＧＨｚ・ｋｍ以上、０．８５μｍ及び１．３０μｍのいずれの波長帯に対しても、定常モード励振時、φ１０の曲げに対する曲げ損失が３ｄＢ／ｍ以下であり、比屈折率差Δが０．０２２以下であること。 The low bending loss multimode fiber having the depressed region 3 preferably satisfies any of the following conditions (a) to (f).
(A) In the 0.85 μm wavelength band, the OFL band is 1.5 GHz · km or more, the bending loss with respect to the bending of φ10 is 5 dB / m or less and the relative refractive index difference Δ is 0.011 or less at the time of steady mode excitation. thing.
(B) In the 0.85 μm wavelength band, the OFL band is 0.8 GHz · km or more, the bending loss with respect to the bending of φ10 is 3 dB / m or less and the relative refractive index difference Δ is 0.022 or less at the time of steady mode excitation. thing.
(C) Δ ≦ 0.011, r ≦ 25 μm, α power refractive index distribution, 25 μm ≦ r 1 ≦ 28 μm, 26 μm ≦ r 2 ≦ 32 μm, −0.006 ≦ Δ 0 ≦ −0.001 A depressed region 3 having a concave refractive index profile.
(D) Δ ≦ 0.022, r ≦ 32.5 μm, α power refractive index distribution, 32.5 μm ≦ r 1 ≦ 35.5 μm, 33.5 μm ≦ r 2 ≦ 40.5 μm, −0.005 ≦ It has a depressed region having a concave refractive index profile represented by Δ 0 ≦ −0.001.
(E) With respect to any wavelength band of 0.85 μm and 1.30 μm, the OFL band is 0.4 GHz · km or more in the 0.85 μm wavelength band, and the OFL band is 0.4 GHz · km or more in the 1.30 mm wavelength band. In the steady mode excitation, the bending loss with respect to the bending of φ10 is 5 dB / m or less, and the relative refractive index difference Δ is 0.011 or less.
(F) In the 0.85 μm wavelength band, the OFL band is 0.3 GHz · km or more, and in the 1.30 mm wavelength band, the OFL band is 0.3 GHz · km or more, for any of the wavelength bands of 0.85 μm and 1.30 μm. In the steady mode excitation, the bending loss with respect to the bending of φ10 is 3 dB / m or less, and the relative refractive index difference Δ is 0.022 or less.

この低曲げ損失マルチモードファイバは、α乗屈折率分布をもつコア２の外側に、単純な屈折率分布形状をしたデプレスド領域３を設けることにより、帯域を落とすことなく、曲げ損失特性を向上させることができ、極小な曲げ径に対しても低い曲げ損失を有するものとなる。
また、この低曲げ損失マルチモードファイバは、コアの外側にクラッドよりも低屈折率で均一な屈折率分布をもつデプレスド領域を設けた簡単な構造であるため、製造が容易であり、低コストで提供することができる。
また、この低曲げ損失マルチモードファイバは、極小な曲げ径に対しても低い曲げ損失を有することから、配線の柔軟性や施工性が要求される宅内配線に好適に用いることができる。
また、０．８５μｍ波長帯用のＶＣＳＥＬレーザが安価であり、ＧＩファイバの接続の容易さから、０．８５μｍ波長帯で高い帯域と低い曲げ損失を有する本発明の低曲げ損失マルチモードファイバは、ユーザ自身が配線を行い、光ＬＡＮを構築するためのファイバとして最適である。 This low bending loss multimode fiber improves the bending loss characteristics without dropping the band by providing a depressed region 3 having a simple refractive index distribution shape outside the core 2 having an α power refractive index distribution. It is possible to have a low bending loss even for a very small bending diameter.
In addition, this low bending loss multimode fiber has a simple structure in which a depressed region having a uniform refractive index distribution with a lower refractive index than that of the cladding is provided outside the core. Can be provided.
Moreover, since this low bending loss multimode fiber has a low bending loss with respect to an extremely small bending diameter, it can be suitably used for home wiring that requires wiring flexibility and workability.
In addition, the VCSEL laser for the 0.85 μm wavelength band is inexpensive, and the low bending loss multimode fiber of the present invention having a high band and a low bending loss in the 0.85 μm wavelength band is obtained from the ease of connection of the GI fiber. It is optimal as a fiber for the user to perform wiring and construct an optical LAN.

なお、本発明の低曲げ損失マルチモードファイバは、前述した例示に限定されるものではなく、種々の変更が可能である。
例えば、デプレスド領域３は一層に限らず、図５に示すようにコア１の外側に、それぞれ屈折率の異なる複数のデプレスド領域３Ａ，３Ｂ，３Ｃ，３Ｄを設け、これらのデプレスド領域３Ａ，３Ｂ，３Ｃ，３Ｄが多層階段状の屈折率分布をなしている構成としてもよい。 In addition, the low bending loss multimode fiber of this invention is not limited to the illustration mentioned above, A various change is possible.
For example, the depressed region 3 is not limited to one layer, and a plurality of depressed regions 3A, 3B, 3C, and 3D having different refractive indexes are provided outside the core 1 as shown in FIG. 5, and these depressed regions 3A, 3B, 3C and 3D may have a multilayer stepwise refractive index distribution.

［実施例１］
波長０．８５μｍで最適化される低曲げ損失マルチモードファイバとして、図２に示すように、従来のα乗屈折率分布（α＝２．０４、ａ＝２５μｍ、Δ＝０．０１）をもつコアの外側に、ｒ１＝２６μｍ、ｒ２＝３０μｍとなる凹状の屈折率分布をもつデプレスド領域を設ける。デプレスド領域の比屈折率差Δ０を変えた場合、有限要素法（K. Okamoto,“Comparison of calculated and measured impulse responses of optical fibers,”Appl. Opt., vol.18, pp.2199-2206, 1979参照。）に基づいて計算した帯域の変化を図３に示す。
図３に示すように、デプレスド領域の比屈折率差Δ０を０〜−０．００４に設定した構造は、デプレスド領域がない構造に比べて高い帯域をもつ。すなわち、｜Δ０｜を０．００４程度に大きくすることにより、帯域を劣化させることなく、曲げ損失を低減することが可能である。
従来のＧＩファイバ製造用のコア母材（ｒ≦ａに相当する部分の母材）を用い、外付け法によりファイバ母材を作製する際、デプレスド領域を設けない従来のファイバおよびデプレスド領域を設けたファイバを作製し、特性を比較した。デプレスド領域を設けていないＧＩファイバは、ＯＦＬ（Overfilled-launched）帯域（規格ＩＥＣ６０７９３−１−４９参照。）が２．３ＧＨｚ・ｋｍ、１０ｍｍの曲げ直径（φ１０）に対して定常モード励振時（規格ＩＥＣ６０７９３−１−４０参照。）の曲げ損失が１０ｄＢ／ｍであったが、ｒ１＝２６μｍ、ｒ２＝３０μｍ、Δ０＝−０．００４のデプレスド領域を設けると、ＯＦＬ帯域が２．２ＧＨｚ・ｋｍで、φ１０に対して定常モード励振時の曲げ損失が２．５ｄＢ／ｍに改善された。 [Example 1]
As a low bending loss multimode fiber optimized at a wavelength of 0.85 μm, as shown in FIG. 2, it has a conventional α power refractive index profile (α = 2.04, a = 25 μm, Δ = 0.01). A depressed region having a concave refractive index distribution with r 1 = 26 μm and r 2 = 30 μm is provided outside the core. When the relative refractive index difference Δ 0 in the depressed region is changed, the finite element method (K. Okamoto, “Comparison of calculated and measured impulse responses of optical fibers,” Appl. Opt., Vol.18, pp.2199-2206, FIG. 3 shows the change of the bandwidth calculated based on 1979.
As shown in FIG. 3, the structure in which the relative refractive index difference Δ 0 in the depressed region is set to 0 to −0.004 has a higher band than the structure without the depressed region. That is, by increasing | Δ 0 | to about 0.004, it is possible to reduce bending loss without degrading the band.
When using a conventional GI fiber manufacturing core preform (a portion corresponding to r ≦ a) to produce a fiber preform by an external method, a conventional fiber and a depressed region are provided without a depressed region. Fibers were fabricated and the characteristics were compared. The GI fiber without a depressed region has an OFL (Overfilled-launched) band (see standard IEC 60793-1-49) at 2.3 GHz · km and a bending diameter (φ10) of 10 mm (standard) The bending loss of IEC 60793-1-40 was 10 dB / m. However, when a depressed region of r 1 = 26 μm, r 2 = 30 μm, Δ 0 = −0.004 is provided, the OFL band is 2.2 GHz. -At km, the bending loss during steady mode excitation with respect to φ10 was improved to 2.5 dB / m.

［実施例２］
実施例１では、デプレスド領域の比屈折率差Δ０を最適化して、低曲げ損失ＧＩファイバを実現しているが、Δ０を固定して、デプレスド領域の幅を変えても同様な結果が得られる。図４は、ｒ１＝２６μｍ、Δ０＝−０．００３と固定し、ｒ２を変えた場合の帯域の変化を示す。
実施例１と同じコア母材を用いて、外付け時にｒ１＝２６μｍ、ｒ２＝２８μｍ、Δ０＝−０．００３のデプレスド領域を設けると、ＯＦＬ帯域が２．３ＧＨｚ・ｋｍで、φ１０に対して定常モード励振時の曲げ損失が３．５ｄＢ／ｍに改善された。 [Example 2]
In Example 1, the relative refractive index difference Δ 0 in the depressed region is optimized to realize a low bending loss GI fiber. However, the same result can be obtained even when Δ 0 is fixed and the width of the depressed region is changed. can get. FIG. 4 shows changes in the band when r 1 = 26 μm and Δ 0 = −0.003 and r 2 is changed.
Using the same core base material as in Example 1 and providing a depressed region of r 1 = 26 μm, r 2 = 28 μm, and Δ 0 = −0.003 at the time of external attachment, the OFL band is 2.3 GHz · km, φ10 In contrast, the bending loss during steady mode excitation was improved to 3.5 dB / m.

［実施例３］
実施例１，２は、最も簡単な凹状屈折率分布をもつデプレスド領域を有する構造であるが、デプレスド領域の屈折率分布を単純な凹状に限定する必要はなく、多層構造でも同様な効果がある。α乗屈折率分布（α＝２．０４、ａ＝２５μｍ、Δ＝０．０１）の外側に、図５に示すような４層構造を有し、ｒ１＝２５．５μｍ、ｒ２＝２６．８μｍ、ｒ３＝２８μｍ、ｒ４＝２９μｍ、ｒ５＝３０．１μｍ、Δ０＝−０．００１、Δ１＝−０．００２、Δ２＝−０．００４、Δ３＝−０．００３となる４層のデプレスド領域を設けた場合、計算したＯＦＬ帯域は２．６８ＧＨｚ・ｋｍであった。
実施例１で使用したコア母材の外側に同じデプレスド領域を設けてファイバを作製すると、ＯＦＬ帯域が２．３ＧＨｚ・ｋｍで、φ１０に対して定常モード励振時の曲げ損失が２．８ｄＢ／ｍに改善された。 [Example 3]
Examples 1 and 2 are structures having a depressed region having the simplest concave refractive index distribution, but it is not necessary to limit the refractive index distribution of the depressed region to a simple concave shape, and the same effect can be obtained even in a multilayer structure. . 5 has a four-layer structure outside the α power refractive index distribution (α = 2.04, a = 25 μm, Δ = 0.01), r 1 = 25.5 μm, r 2 = 26. .8 μm, r 3 = 28 μm, r 4 = 29 μm, r 5 = 30.1 μm, Δ 0 = −0.001, Δ 1 = −0.002, Δ 2 = −0.004, Δ 3 = −0. When a four-layer depressed region having 003 was provided, the calculated OFL band was 2.68 GHz · km.
When a fiber is manufactured by providing the same depressed region outside the core base material used in Example 1, the OFL band is 2.3 GHz · km, and the bending loss during steady mode excitation with respect to φ10 is 2.8 dB / m. Improved.

［実施例４］
波長０．８５μｍでΔが０．０２の低曲げ損失マルチモードファイバとして、従来のα乗屈折率分布（α＝２．０４、ａ＝２５μｍ、Δ＝０．０２）をもつコアの外側に、ｒ１＝３４．５μｍ、ｒ２＝３８．５μｍと固定した凹状屈折率分布をもつデプレスド領域を設ける。デプレスド領域の比屈折率差Δ０を変えた場合、有限要素法に基づいて計算した帯域の変化を図６に示す。
図６に示すように、デプレスド領域の比屈折率差Δ０を０〜−０．００２５に設定した構造は、デプレスド領域がない構造に比べて高い帯域をもつ。すなわち、｜Δ０｜を０．００２５程度に大きくすることにより、帯域を劣化させることなく、曲げ損失を低減することが可能である。
従来のＧＩファイバのコア母材を用いて外付けする際、デプレスド領域を設けない従来のファイバおよびデプレスド領域を設けたファイバを作製し、特性を比較した。デプレスド領域を設けていないＧＩファイバは、ＯＦＬ帯域が１．５ＧＨｚ・ｋｍ、φ１０に対して定常モード励振時の曲げ損失が４．５ｄＢ／ｍであったが、ｒ１＝３４．５μｍ、ｒ２＝３８．５μｍ、Δ０＝−０．００２５のデプレスド領域を設けると、ＯＦＬ帯域が１．５ＧＨｚ・ｋｍで、φ１０に対して定常モード励振時の曲げ損失が２．０ｄＢ／ｍに改善された。 [Example 4]
As a low-bending loss multimode fiber with a wavelength of 0.85 μm and Δ of 0.02, outside the core having a conventional α power refractive index profile (α = 2.04, a = 25 μm, Δ = 0.02), A depressed region having a concave refractive index distribution fixed at r 1 = 34.5 μm and r 2 = 38.5 μm is provided. FIG. 6 shows a change in the band calculated based on the finite element method when the relative refractive index difference Δ 0 in the depressed region is changed.
As shown in FIG. 6, the structure in which the relative refractive index difference Δ0 in the depressed region is set to 0 to −0.0025 has a higher band than the structure without the depressed region. That is, by increasing | Δ 0 | to about 0.0025, it is possible to reduce the bending loss without degrading the band.
When externally attached using a core base material of a conventional GI fiber, a conventional fiber without a depressed region and a fiber with a depressed region were manufactured, and the characteristics were compared. The GI fiber not provided with the depressed region had an OFL band of 1.5 GHz · km and a bending loss of 4.5 dB / m during steady mode excitation with respect to φ10, but r 1 = 34.5 μm, r 2 = 38.5 μm, Δ 0 = -0.0025, when the depressed region is provided, the OFL band is 1.5 GHz · km, and the bending loss during steady mode excitation is improved to 2.0 dB / m for φ10 .

［実施例５］
実施例４では、デプレスド領域の比屈折率差Δ０を最適化して、低曲げ損失ＧＩファイバを実現しているが、Δ０を固定して、デプレスド領域の幅を変えても同様な結果が得られる。図７は、ｒ１＝３４．５μｍ、Δ０＝−０．００３と固定し、ｒ２を変えた場合の帯域の変化を示す。
実施例４と同じコア母材を用いて、外付け時にｒ１＝３４．５μｍ、ｒ２＝３６．０μｍ、Δ０＝−０．００３のデプレスド領域を設けると、ＯＦＬ帯域が１．４ＧＨｚ・ｋｍで、φ１０に対して定常モード励振時の曲げ損失が３．２ｄＢ／ｍに改善された。 [Example 5]
In Example 4, the relative refractive index difference Δ 0 in the depressed region is optimized to realize a low bending loss GI fiber, but the same result is obtained even when Δ 0 is fixed and the width of the depressed region is changed. can get. FIG. 7 shows changes in the band when r 1 = 34.5 μm and Δ 0 = −0.003 and r 2 is changed.
Using the same core base material as in Example 4 and providing a depressed region of r 1 = 34.5 μm, r 2 = 36.0 μm, and Δ 0 = −0.003 when externally attached, the OFL band is 1.4 GHz · At km, the bending loss during steady mode excitation was improved to 3.2 dB / m for φ10.

本発明による低曲げ損失マルチモードファイバの屈折率分布の一例を示すグラフである。It is a graph which shows an example of the refractive index distribution of the low bending loss multimode fiber by this invention. 本発明に係る実施例１で作製した低曲げ損失マルチモードファイバの屈折率分布を示すグラフである。It is a graph which shows the refractive index distribution of the low bending loss multimode fiber produced in Example 1 which concerns on this invention. 実施例１で作製した低曲げ損失マルチモードファイバのデプレスド領域の屈折率と帯域の関係を示すグラフである。4 is a graph showing a relationship between a refractive index and a band of a depressed region of a low bending loss multimode fiber manufactured in Example 1. 本発明に係る実施例２で作製した低曲げ損失マルチモードファイバのデプレスド領域の幅と帯域の関係を示すグラフである。It is a graph which shows the relationship between the width | variety of a depressed area | region of a low bending loss multimode fiber produced in Example 2 which concerns on this invention, and a zone | band. 本発明に係る実施例３で作製した低曲げ損失マルチモードファイバの屈折率分布を示すグラフである。It is a graph which shows the refractive index distribution of the low bending loss multimode fiber produced in Example 3 which concerns on this invention. 本発明に係る実施例４で作製した低曲げ損失マルチモードファイバのデプレスド領域の屈折率と帯域の関係を示すグラフである。It is a graph which shows the relationship between the refractive index and the zone | band of the depressed area | region of the low bending loss multimode fiber produced in Example 4 which concerns on this invention. 本発明に係る実施例５で作製した低曲げ損失マルチモードファイバのデプレスド領域の幅と帯域の関係を示すグラフである。It is a graph which shows the relationship between the width | variety of a depressed area | region of a low bending loss multimode fiber produced in Example 5 which concerns on this invention, and a zone | band.

符号の説明Explanation of symbols

１…コア、２…クラッド、３，３Ａ，３Ｂ，３Ｃ，３Ｄ…デプレスド領域。
DESCRIPTION OF SYMBOLS 1 ... Core, 2 ... Cladding, 3, 3A, 3B, 3C, 3D ... Depressed area | region.

Claims (1)

次式（１）
Figure 0004684593
 （式中、ａはコア半径、ｎ１はコア中心屈折率、Δは比屈折率差を表し、αは所望の波長帯で帯域が最大になるように設定されるパラメータである。）で表されるα乗屈折率分布をもつコアと、その外側のクラッドとを有するマルチモードファイバであって、コアの外側に、クラッドよりも低屈折率でそれぞれ屈折率の異なる複数のデプレスド領域が設けられ、これらのデプレスド領域が４層階段状の屈折率分布をなし、
ａ＝２５μｍ、α＝２．０４であり、
Δ＝０．０１、ｒ≦２５μｍでα乗屈折率分布をもち、
前記デプレスド領域の４層の内側境界までの半径が、最も内側の層から順に、２５．５μｍ、２６．８μｍ、２８μｍ及び２９μｍであり、最も外側の境界までの半径が３０．１μｍであり、
前記デプレスド領域の４層の比屈折率差Δ ０ が、最も内側の層から順に、−０．００１、−０．００２、−０．００４及び−０．００３であり、
０．８５μｍ波長帯でＯＦＬ帯域が１．５ＧＨｚ・ｋｍ以上、定常モード励振時、φ１０の曲げに対する曲げ損失が５ｄＢ／ｍ以下であることを特徴とする低曲げ損失マルチモードファイバ。 The following formula (1)
Figure 0004684593
 (Wherein, a is a core radius, n 1 is a core center refractive index, Δ is a relative refractive index difference, and α is a parameter set to maximize the band in a desired wavelength band). A multimode fiber having a core having an α power refractive index profile and an outer cladding, and a plurality of depressed regions each having a lower refractive index and a different refractive index than the cladding are provided outside the core. These depressed regions have a four- layered stepped refractive index profile,
a = 25 μm, α = 2.04,
Δ = 0.01 , r ≦ 25 μm and α power refractive index distribution,
The radius to the inner boundary of the four layers of the depressed area is 25.5 μm, 26.8 μm, 28 μm and 29 μm in order from the innermost layer, and the radius to the outermost boundary is 30.1 μm,
Wherein the relative refractive index difference delta 0 of 4 layers of Depuresudo region, in order from the innermost layer, -0.001, -0.002, was -0.004 and -0.003,
A low-bending loss multimode fiber characterized by having an OFL band of 1.5 GHz · km or more in a 0.85 μm wavelength band and a bending loss of 5 dB / m or less with respect to φ10 bending during steady mode excitation.
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