JP2006078543A - Low bending loss trench type multimode fiber - Google Patents

Low bending loss trench type multimode fiber Download PDF

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JP2006078543A
JP2006078543A JP2004259501A JP2004259501A JP2006078543A JP 2006078543 A JP2006078543 A JP 2006078543A JP 2004259501 A JP2004259501 A JP 2004259501A JP 2004259501 A JP2004259501 A JP 2004259501A JP 2006078543 A JP2006078543 A JP 2006078543A
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refractive index
core
trench
bending loss
loss
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Yasushi Kan
寧 官
Katsuhiro Takenaga
勝宏 竹永
Kazuhiko Aikawa
和彦 愛川
Kuniharu Himeno
邦治 姫野
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Fujikura Ltd
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a low bending loss trench type multimode fiber which is bent with a small radius. <P>SOLUTION: The low bending loss trench type multimode fiber has a core part 1 having a refractive index higher than that of a clad part 2 a clad part around thereof and a trench layer 3 provided to enclose the core part and having a refractive index lower than that of the clad part. The core part is composed of a central first core 4 made of a material having a refractive index higher than that of the clad part and a second core 5 surrounding the first core and composed of a material having a refractive index different from that of the first core and higher than that of the clad part. The low bending loss trench type multimode fiber has the following characteristics: (a) two or more transmission modes exist between wavelengths 1.2 and 1.6 μm (where degeneration mode is not redundantly counted as the number of transmission modes), the absolute value of a group refractive index difference Δn<SB>g</SB>between LP<SB>01</SB>mode and LP<SB>11</SB>mode is smaller than 1×10<SP>-3</SP>, and (b) the bending loss at a bending diameter of ϕ=10 mm is 0.1 dB/m or smaller at the wavelength 1.55 μm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

本発明は、極小な曲げ径に対しても低い曲げ損失特性が得られる低曲げ損失トレンチ型マルチモードファイバに関する。本発明のマルチモードファイバは、従来の光ファイバよりも曲げ損失が小さく、接続損失が小さいので、屋内（宅内）の配線などに適している。   The present invention relates to a low bending loss trench type multimode fiber that can obtain a low bending loss characteristic even with a minimum bending diameter. Since the multimode fiber of the present invention has a smaller bending loss and lower connection loss than conventional optical fibers, it is suitable for indoor (home) wiring and the like.

ＦＴＴＨ（Fiber to the home）技術に用いられる屋内配線光ファイバは、配線の柔軟性や施工性を考慮すると、曲げ損失特性に優れることが望ましい。曲げ損失特性を向上させるためには、コア−クラッド間の比屈折率差を大きくすればよいが、比屈折率差が大きいと、高次モードの閉じ込みも強くなってしまい、高次モードのカットオフ波長が長くなってしまう恐れがある。   An indoor wiring optical fiber used for FTTH (Fiber to the home) technology is preferably excellent in bending loss characteristics in consideration of wiring flexibility and workability. In order to improve the bending loss characteristics, the relative refractive index difference between the core and the clad may be increased. However, if the relative refractive index difference is large, higher-order mode confinement becomes stronger. There is a possibility that the cut-off wavelength becomes long.

トレンチ型光ファイバは、ステップ状屈折率分布を有し、クラッド部より高屈折率のコア部と、その周囲のクラッド部と、コア部を囲むように設けられクラッド部より低屈折率のトレンチ層とを有し、このトレンチ層を設けることで低曲げ損失を実現している。
S.Matsuo, et al.,“Bend-insensitive and low-splice-loss optical fiber for indoor wiring in FTTH”,OFC2004, ThI3, 2004 米国特許第４８７７３０４号明細書 The trench type optical fiber has a step-shaped refractive index distribution, a core part having a higher refractive index than the cladding part, a surrounding cladding part, and a trench layer having a lower refractive index than the cladding part so as to surround the core part. By providing this trench layer, low bending loss is realized.
S. Matsuo, et al., “Bend-insensitive and low-splice-loss optical fiber for indoor wiring in FTTH”, OFC2004, ThI3, 2004 US Pat. No. 4,877,304

しかしながら、従来のトレンチ型光ファイバでは、低曲げ損失を実現できるものの、曲げ損失を小さくすれば、カットオフ波長が長くなるというトレードオフを完全に克服することはできない（非特許文献１参照。）。   However, although the conventional trench optical fiber can realize a low bending loss, the trade-off that the cut-off wavelength becomes long cannot be completely overcome if the bending loss is reduced (see Non-Patent Document 1). .

このことは、特に極めて小さな曲げ径（例えば、曲げ直径φ＝１０ｍｍ程度）で曲げた際にも小さな曲げ損失が要求される場合、光伝送路に使用される通常のシングルモードファイバ（以下、ＳＭＦと記す。）との接続において接続損失が大きくなることを犠牲にしなければ達成できないことを意味する。   This means that when a small bending loss is required even when bending with a very small bending diameter (for example, a bending diameter φ = about 10 mm), a normal single mode fiber (hereinafter referred to as SMF) used in an optical transmission line is required. This means that it cannot be achieved without sacrificing an increase in connection loss.

本発明は前記事情に鑑みてなされ、小さい曲率での曲げが想定される屋内配線光ファイバとして好適な低曲げ損失トレンチ型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 of the present invention is to provide a low bending loss trench type multimode fiber suitable as an indoor wiring optical fiber which is expected to be bent with a small curvature.

前記目的を達成するため、本発明は、クラッド部より高屈折率のコア部と、その周囲のクラッド部と、コア部を囲むように設けられクラッド部より低屈折率のトレンチ層とを有し、コア部は、クラッド部より高屈折率の材料からなる中央の第１コアと、該第１コアの周りに、屈折率が第１コアと異なり、かつクラッド部より高屈折率の材料からなる第２コアとからなり、次の特性、
（ａ）波長１．２〜１．６μｍの間で２つ以上の伝搬モード（ただし、この伝搬モード数は縮退モードを重複カウントしない数である。）を有し、ＬＰ０１モードとＬＰ１１モードの群屈折率差Δｎｇの絶対値が１×１０−３より小さく、かつ
（ｂ）φ＝１０ｍｍの曲げ直径に対して、曲げ損失が波長１．５５μｍで０．１ｄＢ／ｍ以下である、
を有することを特徴とする低曲げ損失トレンチ型マルチモードファイバを提供する。 In order to achieve the above object, the present invention includes a core portion having a higher refractive index than the cladding portion, a surrounding cladding portion, and a trench layer provided to surround the core portion and having a lower refractive index than the cladding portion. The core portion is made of a central first core made of a material having a higher refractive index than that of the cladding portion, and is made of a material having a refractive index different from that of the first core and having a higher refractive index than the cladding portion around the first core. The second core consists of the following characteristics:
(A) It has two or more propagation modes between wavelengths 1.2 to 1.6 μm (however, this number of propagation modes is a number that does not repeatedly count degenerate modes), and LP 01 mode and LP 11 mode the absolute value of the group refractive index difference [Delta] n g of less than 1 × 10 -3, and to bending diameter (b) φ = 10mm, the bending loss is less than 0.1 dB / m at a wavelength of 1.55 .mu.m,
A low bending loss trench type multimode fiber is provided.

本発明の低曲げ損失トレンチ型マルチモードファイバにおいて、第１コアのクラッド部に対する比屈折率差Δ１、第１コアの半径ｒ１、第２コアのクラッド部に対する比屈折率差Δ２、第２コアの半径ｒ２が、それぞれ、０．３％≦Δ１≦１％、０．１％≦Δ２≦０．６％、２μｍ≦ｒ１≦５μｍ、３μｍ≦ｒ２≦８μｍの範囲内であることが好ましい。 In the low bending loss trench type multimode fiber of the present invention, the relative refractive index difference Δ 1 with respect to the cladding portion of the first core, the radius r 1 of the first core, the relative refractive index difference Δ 2 with respect to the cladding portion of the second core, The radius r 2 of the two cores is in the range of 0.3% ≦ Δ 1 ≦ 1%, 0.1% ≦ Δ 2 ≦ 0.6%, 2 μm ≦ r 1 ≦ 5 μm, 3 μm ≦ r 2 ≦ 8 μm, respectively. It is preferable that

本発明の低曲げ損失トレンチ型マルチモードファイバにおいて、コア部中心からトレンチ層の内側エッジまでの距離ｒ３、コア部中心からトレンチ層の外側エッジまでの距離ｒ４、トレンチ層のクラッド部に対する比屈折率差Δ３が、５μｍ≦ｒ３≦１０μｍ、７μｍ≦ｒ４≦２０μｍ、−１．２％≦Δ３≦−０．２％の範囲内であることが好ましい。 In the low bending loss trench type multimode fiber of the present invention, the distance r 3 from the core part center to the inner edge of the trench layer, the distance r 4 from the core part center to the outer edge of the trench layer, the ratio of the trench layer to the cladding part The refractive index difference Δ 3 is preferably in the range of 5 μm ≦ r 3 ≦ 10 μm, 7 μm ≦ r 4 ≦ 20 μm, −1.2% ≦ Δ 3 ≦ −0.2%.

本発明の低曲げ損失トレンチ型マルチモードファイバにおいて、コア部とトレンチ層との間の領域の、トレンチ層よりも外側のクラッド部に対する比屈折率差Δ´が−０．２％≦Δ´≦０．２％の範囲内であることが好ましい。   In the low bending loss trench multimode fiber of the present invention, the relative refractive index difference Δ ′ of the region between the core portion and the trench layer with respect to the cladding portion outside the trench layer is −0.2% ≦ Δ ′ ≦. It is preferable to be within the range of 0.2%.

本発明の低曲げ損失トレンチ型マルチモードファイバにおいて、ＳＭＦと接続した時、モード分散が波長１．２〜１．６μｍの間で０．５ｎｓ／ｋｍ以下であることが好ましい。   In the low bending loss trench type multimode fiber of the present invention, when connected to the SMF, the mode dispersion is preferably 0.5 ns / km or less between wavelengths of 1.2 to 1.6 μm.

本発明の低曲げ損失トレンチ型マルチモードファイバにおいて、ＳＭＦと接続し、光源のＲＭＳスペクトル幅５ｎｍ以下の時、波長分散とモード分散からなる全分散によるパルス幅の劣化が波長１．２〜１．６μｍの間で１ｎｓ／ｋｍ以下であることが好ましい。   In the low bending loss trench type multimode fiber of the present invention, when connected to the SMF and the RMS spectral width of the light source is 5 nm or less, the pulse width deterioration due to the total dispersion composed of the chromatic dispersion and the mode dispersion is 1.2 to 1. It is preferable that it is 1 ns / km or less between 6 micrometers.

本発明の低曲げ損失トレンチ型マルチモードファイバにおいて、ステップ状屈折率分布を持つＳＭＦとの融着接続損失が波長１．５５μｍで０．２ｄＢ以下、メカニカル接続損失が０．４ｄＢ以下となり、かつ反射減衰量が４０ｄＢ以上となることが好ましい。   In the low bending loss trench type multimode fiber of the present invention, the fusion splice loss with an SMF having a stepped refractive index profile is 0.2 dB or less at a wavelength of 1.55 μm, the mechanical splice loss is 0.4 dB or less, and the reflection The attenuation is preferably 40 dB or more.

本発明の低曲げ損失トレンチ型マルチモードファイバにおいて、同じファイバを接続した時、融着接続損失が波長１．５５μｍで０．２ｄＢ以下、メカニカル接続損失が０．４ｄＢ以下となり、かつ反射減衰量が４０ｄＢ以上となることが好ましい。   In the low bending loss trench type multimode fiber of the present invention, when the same fiber is connected, the fusion splicing loss is 0.2 dB or less at the wavelength of 1.55 μm, the mechanical splicing loss is 0.4 dB or less, and the return loss is It is preferable to be 40 dB or more.

本発明の低曲げ損失トレンチ型マルチモードファイバは、シンプルな構成で非常に低い曲げ損失を有し、かつ光伝送路に使用される通常のＳＭＦと非常に低い接続損失で接続できることから、配線の柔軟性や施工性が要求される屋内配線に適用し、光通信性能を向上させることができる。   The low bending loss trench type multimode fiber of the present invention has a very low bending loss with a simple configuration and can be connected to a normal SMF used for an optical transmission line with a very low connection loss. It can be applied to indoor wiring that requires flexibility and workability, and optical communication performance can be improved.

本発明の低曲げ損失トレンチ型マルチモードファイバ（以下、ＭＭＦと略記する。）は、主に短距離の信号伝送に用いることを想定し、極小数のマルチモード伝搬を許容するように構成されている。ただし、極力マルチモード伝搬によるモード分散を小さくし、実質的に信号伝送に影響を与えないようにする。また、その代わりに非常に低い曲げ損失が達成でき、かつ通常のＳＭＦと接続する際に非常に低い接続損失を達成できるようになっている。少数のモードが伝搬する光ファイバは既に提案されているが（特許文献１参照。）、極小の曲げ径でも低曲げ損失を有するように設計されていない。   The low-bending loss trench type multimode fiber (hereinafter abbreviated as MMF) of the present invention is mainly configured to be used for short-distance signal transmission and is configured to allow multimode propagation of a minimal number. Yes. However, mode dispersion due to multi-mode propagation is reduced as much as possible so that signal transmission is not substantially affected. Instead, a very low bending loss can be achieved, and a very low connection loss can be achieved when connecting to a normal SMF. An optical fiber in which a small number of modes propagate has already been proposed (see Patent Document 1), but it is not designed to have a low bending loss even with a very small bending diameter.

本発明のＭＭＦは、従来のトレンチ型光ファイバに対して、コア部を単純なステップ状屈折率分布ではなく、図１に示すように２段ステップ状屈折率分布としている。
図１は本発明のＭＭＦの屈折率分布の一例を示す図であり、図中符号１はコア部、２はクラッド部、３はトレンチ層、４は第１コア、５は第２コア、６はクラッド部のトレンチ内側領域である。 In the MMF of the present invention, the core portion is not a simple step-shaped refractive index distribution but a two-step step-shaped refractive index distribution as shown in FIG.
FIG. 1 is a diagram showing an example of the refractive index distribution of the MMF of the present invention. In the figure, reference numeral 1 denotes a core part, 2 denotes a cladding part, 3 denotes a trench layer, 4 denotes a first core, 5 denotes a second core, 6 Is the trench inner region of the cladding.

このＭＭＦは、石英系ガラスからなり、クラッド部２より高屈折率のコア部１と、その周囲のクラッド部２と、コア部１を囲むように設けられクラッド部２より低屈折率のトレンチ層３とからなり、コア部１は、屈折率が最も高い中央の第１コア４と、該第１コアの周りに設けられ、屈折率が第１コアより低くクラッド部２より高い第２コア５とからなり、次の特性、
（ａ）波長１．２〜１．６μｍの間で２つ以上の伝搬モード（ただし、この伝搬モード数は縮退モードを重複カウントしない数である。）を有し、ＬＰ０１モードとＬＰ１１モードの群屈折率差Δｎｇの絶対値が１×１０−３より小さく、かつ
（ｂ）φ＝１０ｍｍの曲げ直径に対して、曲げ損失が波長１．５５μｍで０．１ｄＢ／ｍ以下である、
を有することを特徴としている。 This MMF is made of silica glass, and has a core part 1 having a higher refractive index than that of the cladding part 2, a surrounding cladding part 2, and a trench layer provided so as to surround the core part 1 and having a lower refractive index than the cladding part 2. The core portion 1 includes a central first core 4 having the highest refractive index and a second core 5 provided around the first core and having a refractive index lower than that of the first core and higher than that of the cladding portion 2. With the following characteristics:
(A) It has two or more propagation modes between wavelengths 1.2 to 1.6 μm (however, this number of propagation modes is a number that does not repeatedly count degenerate modes), and LP 01 mode and LP 11 mode the absolute value of the group refractive index difference [Delta] n g of less than 1 × 10 -3, and to bending diameter (b) φ = 10mm, the bending loss is less than 0.1 dB / m at a wavelength of 1.55 .mu.m,
It is characterized by having.

前記群屈折率差Δｎｇの絶対値が１×１０−３よりも大きいと、マルチモード伝搬によるモード分散が大きくなり、信号伝送に影響が生じて信号の品質を劣化させるおそれがある。
またφ＝１０ｍｍの曲げ直径に対して、曲げ損失が波長１．５５μｍで０．１ｄＢ／ｍを超えると、屋内（宅内）配線光ファイバのような小さな曲げ径で小さな曲げ損失が要求される用途に適用し難くなる。 If the absolute value of the group refractive index difference Δng is greater than 1 × 10 −3, mode dispersion due to multimode propagation increases, which may affect signal transmission and degrade signal quality.
In addition, when the bending loss exceeds 0.1 dB / m at a wavelength of 1.55 μm with respect to the bending diameter of φ = 10 mm, an application that requires a small bending loss with a small bending diameter such as an indoor (home) wiring optical fiber. It becomes difficult to apply to.

このＭＭＦにおいて、２段ステップ状屈折率分布を持つコア部１は、第１コア４のクラッド部２に対する比屈折率差Δ１、第１コア４の半径ｒ１、第２コア５のクラッド部２に対する比屈折率差Δ２、第２コア５の半径ｒ２が、それぞれ、０．３％≦Δ１≦１％、０．１％≦Δ２≦０．６％、２μｍ≦ｒ１≦５μｍ、３μｍ≦ｒ２≦８μｍ（ただし、ｒ１＜ｒ２）の範囲内であることが好ましい。
また、トレンチ層３は、コア部１中心からトレンチ層３の内側エッジまでの距離ｒ３、コア部１中心からトレンチ層３の外側エッジまでの距離ｒ４、トレンチ層３のクラッド部２に対する比屈折率差Δ３が、５μｍ≦ｒ３≦１０μｍ、７μｍ≦ｒ４≦２０μｍ（ただし、ｒ３＜ｒ４）、−１．２％≦Δ３≦−０．２％の範囲内とすることが好ましい。 In this MMF, the core portion 1 having a two-step step-shaped refractive index distribution includes a relative refractive index difference Δ 1 with respect to the cladding portion 2 of the first core 4, a radius r 1 of the first core 4, and a cladding portion of the second core 5. The relative refractive index difference Δ 2 with respect to 2 and the radius r 2 of the second core 5 are 0.3% ≦ Δ 1 ≦ 1%, 0.1% ≦ Δ 2 ≦ 0.6%, 2 μm ≦ r 1 ≦, respectively. It is preferable to be in the range of 5 μm, 3 μm ≦ r 2 ≦ 8 μm (where r 1 <r 2 ).
Further, the trench layer 3 has a distance r 3 from the center of the core portion 1 to the inner edge of the trench layer 3, a distance r 4 from the center of the core portion 1 to the outer edge of the trench layer 3, and a ratio of the trench layer 3 to the cladding portion 2. The refractive index difference Δ 3 is within the range of 5 μm ≦ r 3 ≦ 10 μm, 7 μm ≦ r 4 ≦ 20 μm (where r 3 <r 4 ), −1.2% ≦ Δ 3 ≦ −0.2%. Is preferred.

コア部１における比屈折率差Δ１、Δ２、半径ｒ１、ｒ２を前記範囲内とするとともに、トレンチ層の位置ｒ３と幅（ｒ４−ｒ３）及び比屈折率差Δ３を前記範囲とすることにより、このＭＭＦは前述した特性（ａ）、（ｂ）を満たすことができるとともに、光伝送路に使用される通常のＳＭＦと非常に低い接続損失で接続できる。このＭＭＦは、ステップ状屈折率分布を持つ通常のＳＭＦと接続した場合、融着接続損失が波長１．５５μｍで０．２ｄＢ以下、それぞれのファイバ端に光コネクタを成端して突き合わせ接続した場合のメカニカル接続損失が０．４ｄＢ以下となり、かつ反射減衰量が４０ｄＢ以上となる。また、このＭＭＦ同士を接続した場合には、融着接続損失が波長１．５５μｍで０．２ｄＢ以下、メカニカル接続損失が０．４ｄＢ以下となる。 The relative refractive index differences Δ 1 and Δ 2 , the radii r 1 and r 2 in the core portion 1 are within the above range, and the position r 3 and width (r 4 −r 3 ) of the trench layer and the relative refractive index difference Δ 3. By setting the above to the above range, this MMF can satisfy the characteristics (a) and (b) described above, and can be connected to a normal SMF used for an optical transmission line with a very low connection loss. When this MMF is connected to a normal SMF having a stepped refractive index profile, the fusion splice loss is 0.2 dB or less at a wavelength of 1.55 μm, and an optical connector is terminated at each fiber end to make a butt connection. The mechanical connection loss becomes 0.4 dB or less and the return loss becomes 40 dB or more. Further, when the MMFs are connected to each other, the fusion splicing loss is 0.2 dB or less and the mechanical splicing loss is 0.4 dB or less at a wavelength of 1.55 μm.

また、このＭＭＦを通常のＳＭＦと接続した時、モード分散が波長１．２〜１．６μｍの間で０．５ｎｓ／ｋｍ以下となり、かつ光源のＲＭＳ（Root mean aquared）スペクトル幅５ｎｍ以下の時、波長分散とモード分散からなる全分散によるパルス幅の劣化が波長１．２〜１．６μｍの間で１ｎｓ／ｋｍ以下となる。   When this MMF is connected to a normal SMF, the mode dispersion is 0.5 ns / km or less between wavelengths of 1.2 to 1.6 μm and the RMS (Root mean aquared) spectrum width of the light source is 5 nm or less. The deterioration of the pulse width due to the total dispersion composed of chromatic dispersion and mode dispersion is 1 ns / km or less between wavelengths 1.2 to 1.6 μm.

本発明のＭＭＦにおいて、コア部１とトレンチ層３との間のトレンチ内側領域６は、図１に示すように、トレンチ層３の外側のクラッド部２と同じ屈折率として構成してもよいし、このトレンチ内側領域６をクラッド部２と異なる屈折率で構成してもよい。後者の場合、トレンチ内側領域６のクラッド部２に対する比屈折率差Δ´を、−０．２％≦Δ´≦０．２％の範囲内とすることが好ましい。   In the MMF of the present invention, the trench inner region 6 between the core portion 1 and the trench layer 3 may be configured to have the same refractive index as that of the outer cladding portion 2 of the trench layer 3 as shown in FIG. The trench inner region 6 may be configured with a refractive index different from that of the cladding portion 2. In the latter case, it is preferable that the relative refractive index difference Δ ′ of the trench inner region 6 with respect to the cladding portion 2 is in a range of −0.2% ≦ Δ ′ ≦ 0.2%.

このＭＭＦは、シンプルな構成で非常に低い曲げ損失を有し、かつ光伝送路に使用される通常のＳＭＦと非常に低い接続損失で接続できることから、配線の柔軟性や施工性が要求される屋内配線に適用し、光通信性能を向上させることができる。   This MMF has a very low bending loss with a simple configuration, and can be connected to a normal SMF used for an optical transmission line with a very low connection loss. Therefore, flexibility and workability of wiring are required. It can be applied to indoor wiring to improve optical communication performance.

［実施例１］
図１に示す屈折率分布を有し、ｒ１＝３μｍ、ｒ２＝６μｍ、Δ１＝０．５％、Δ２＝０．３％のコア部を有し、トレンチ層の位置と幅は一定とし（ｒ３＝８μｍ、ｒ４＝１４μｍ）、トレンチ層の比屈折率差Δ３を０〜−０．８％の間で変え、得られるＭＭＦの特性を計算した。波長１．５５μｍにおける光学特性を表１に示す。 [Example 1]
1 having a refractive index profile, r 1 = 3 μm, r 2 = 6 μm, Δ 1 = 0.5%, Δ 2 = 0.3%, and the position and width of the trench layer are The characteristics of the obtained MMF were calculated by keeping constant (r 3 = 8 μm, r 4 = 14 μm) and changing the relative refractive index difference Δ 3 of the trench layer between 0 and −0.8%. Table 1 shows the optical characteristics at a wavelength of 1.55 μm.

Figure 2006078543
Figure 2006078543

表１からわかるように、トレンチ層の比屈折率差Δ３を変えても、Δｎｇ（Δｎｇ＝ｎｇｆ−ｎｇｈ）を除く各特性はほとんど変わらない。ただし、ｎｇｆとｎｇｈはファイバの基本モード（ＬＰ０１）と高次モード（ＬＰ１１）の等価群屈折率を表す。また、トレンチ層の比屈折率差Δ３が−０．７％〜−０．２％の範囲では、｜Δｎｇ｜≦５×１０−４となる。
マルチモード伝搬のモード分散によるパルス信号のパルス増加の上限は、次式（１） As can be seen from Table 1, changing the relative refractive index difference delta 3 of the trench layer, each characteristic except Δn g (Δn g = n gf -n gh) hardly changes. Here, n gf and n gh represent the equivalent group refractive indexes of the fundamental mode (LP 01 ) and the higher order mode (LP 11 ) of the fiber. In the range where the relative refractive index difference Δ 3 of the trench layer is −0.7% to −0.2%, | Δn g | ≦ 5 × 10 −4 .
The upper limit of the pulse increase of the pulse signal due to mode dispersion of multimode propagation is expressed by the following equation (1)

Figure 2006078543
Figure 2006078543

（式中、Ｌは伝搬距離、ｃは光速を表す。）で評価できる。｜Δｎｇ｜≦５×１０−４である場合、モード分散による信号の劣化は最大１．７ｎｓ／ｋｍになるが、実際のファイバはＳＭＦと接続して使用するので、その際に高次モードがほとんど励振されず、実際のモード分散による信号の劣化は０．３ｎｓ／ｋｍ以下である。 (In the formula, L represents the propagation distance, and c represents the speed of light.) When | Δn g | ≦ 5 × 10 −4 , the maximum signal degradation due to mode dispersion is 1.7 ns / km. However, since the actual fiber is used in connection with the SMF, the higher-order mode is used at that time. Are hardly excited, and signal degradation due to actual mode dispersion is 0.3 ns / km or less.

図１に示す屈折率分布を有し、ｒ１＝３μｍ、ｒ２＝６μｍ、Δ１＝０．５％、Δ２＝０．３％のコア部を有し、トレンチ層の幅と比屈折率差Δ３は一定とし（ｒ４−ｒ３＝６μｍ、Δ３＝−０．４％）、トレンチ層の位置、すなわちコア部中心からトレンチ層の内側エッジまでの距離ｒ３を６μｍ〜１０μｍの間で変え、得られるＭＭＦの特性を計算した。波長１．５５μｍにおける光学特性を表２に示す。 1 having a refractive index distribution, r 1 = 3 μm, r 2 = 6 μm, Δ 1 = 0.5%, Δ 2 = 0.3%, and the width and relative refraction of the trench layer The rate difference Δ 3 is constant (r 4 −r 3 = 6 μm, Δ 3 = −0.4%), and the position of the trench layer, that is, the distance r 3 from the center of the core portion to the inner edge of the trench layer is 6 μm to 10 μm. And obtained MMF characteristics were calculated. Table 2 shows the optical characteristics at a wavelength of 1.55 μm.

Figure 2006078543
Figure 2006078543

表２からわかるように、トレンチ層の位置を変えても、Δｎｇを除く各特性はほとんど変わらない。また、ｒ３が６．５μｍ〜９．５μｍの範囲では、｜Δｎｇ｜≦５×１０−４となる。 As can be seen from Table 2, also by changing the position of the trench layer, each characteristic with the exception of Δn g is almost unchanged. Further, when r 3 is in the range of 6.5 μm to 9.5 μm, | Δn g | ≦ 5 × 10 −4 .

図１に示す屈折率分布を有し、ｒ１＝３μｍ、ｒ２＝６μｍ、Δ１＝０．５％、Δ２＝０．３％のコア部を有し、トレンチ層の位置と比屈折率差Δ３は一定とし（ｒ３＝８μｍ、Δ３＝−０．４％）、トレンチ層の幅（ｒ４−ｒ３）を２μｍ〜１０μｍの間で変え、得られるＭＭＦの特性を計算した。波長１．５５μｍにおける光学特性を表３に示す。 1 having a refractive index profile, r 1 = 3 μm, r 2 = 6 μm, Δ 1 = 0.5%, Δ 2 = 0.3%, and the position and relative refraction of the trench layer The rate difference Δ 3 is constant (r 3 = 8 μm, Δ 3 = −0.4%), the width of the trench layer (r 4 −r 3 ) is changed between 2 μm and 10 μm, and the characteristics of the obtained MMF are calculated. did. Table 3 shows the optical characteristics at a wavelength of 1.55 μm.

Figure 2006078543
Figure 2006078543

表３からわかるように、トレンチ層の幅を変えても、Δｎｇを除く各特性はほとんど変わらない。また、トレンチ層の幅（ｒ４−ｒ３）が４．０μｍ〜１０．０μｍの範囲では、｜Δｎｇ｜≦１×１０−４となる。 As can be seen from Table 3, also by changing the width of the trench layer, each characteristic with the exception of Δn g is almost unchanged. In the range where the width (r 4 -r 3 ) of the trench layer is 4.0 μm to 10.0 μm, | Δn g | ≦ 1 × 10 −4 .

以上の結果より、ｒ１＝３μｍ、ｒ２＝６μｍ、Δ１＝０．５％、Δ２＝０．３％のコア部に対して、トレンチ層の位置、幅又は比屈折率差を変えることにより、ＭＭＦの光学特性を大幅に変えることなく、モード分散を支配する｜Δｎｇ｜及び曲げ損失を調整することができる。 From the above results, the position, width or relative refractive index difference of the trench layer is changed with respect to the core portion of r 1 = 3 μm, r 2 = 6 μm, Δ 1 = 0.5%, Δ 2 = 0.3%. Thus, it is possible to adjust | Δn g | that governs mode dispersion and bending loss without significantly changing the optical characteristics of the MMF.

実際に、図１に示す屈折率分布を有し、ｒ１＝３μｍ、ｒ２＝６μｍ、Δ１＝０．５％、Δ２＝０．３％のコア部と、ｒ３＝８μｍ、ｒ４＝１４μｍ、Δ３＝−０．４％のトレンチ層をもつＭＭＦを作製した。このＭＭＦの基本モード（ＬＰ０１）と高次モード（ＬＰ１１）の等価群屈折率を測定した結果を図２に示す。図示のように、両モード間の群屈折率差｜Δｎｇ｜は波長１．２〜１．６μｍで２×１０−４以下である。 Actually, it has the refractive index distribution shown in FIG. 1, and has a core portion of r 1 = 3 μm, r 2 = 6 μm, Δ 1 = 0.5%, Δ 2 = 0.3%, r 3 = 8 μm, r An MMF having a trench layer of 4 = 14 μm and Δ 3 = −0.4% was produced. FIG. 2 shows the results of measuring the equivalent group refractive index of the fundamental mode (LP 01 ) and higher-order mode (LP 11 ) of this MMF. As shown, the group refractive index difference | Δn g | between the two modes is 2 × 10 −4 or less at a wavelength of 1.2 to 1.6 μm.

また、このＭＭＦの基本モード（ＬＰ０１）のモードフィールド径（Mode-field diameter；ＭＦＤ）と波長との関係を図３に示す。このＭＭＦのＭＦＤは、光伝送路に使用される通常のＳＭＦのそれとほぼ同じであることから、通常のＳＭＦと低い接続損失で接続できる。 FIG. 3 shows the relationship between the mode-field diameter (MFD) of the basic mode (LP 01 ) of the MMF and the wavelength. Since the MFD of this MMF is almost the same as that of a normal SMF used for an optical transmission line, it can be connected to a normal SMF with low connection loss.

また、このＭＭＦの基本モード（ＬＰ０１）の波長分散特性を図４に示す。波長分散によるパルス信号のパルス幅増加は、次式（２） FIG. 4 shows the chromatic dispersion characteristics of the fundamental mode (LP 01 ) of this MMF. The pulse width increase of the pulse signal due to chromatic dispersion is expressed by the following equation (2)

Figure 2006078543
Figure 2006078543

（式中、Ｌは伝搬距離、Ｄは波長分散、δλは光源のスペクトル幅を表す。）で評価できる。ここで波長１．５５μｍの光源はδλ＝５ｎｍとすると、波長分散による信号の劣化は約０．１ｎｓ／ｋｍとなる。 (In the formula, L represents the propagation distance, D represents the chromatic dispersion, and δλ represents the spectral width of the light source). Here, assuming that δλ = 5 nm for a light source having a wavelength of 1.55 μm, signal degradation due to chromatic dispersion is about 0.1 ns / km.

試作したＭＭＦは、波長１．５５μｍで曲げ直径φ＝１０ｍｍにおける曲げ損失が０．０２ｄＢ／ｍ、モード分散による信号の劣化は０．１ｎｓ／ｋｍ以下であり、波長分散による信号の劣化と同程度となる。また、このＭＭＦは、光伝送路に使用される通常のＳＭＦと接続した場合、波長１．５５μｍにおいて、融着接続損失が０．０２ｄＢ、それぞれのファイバ端に光コネクタを成端して突き合わせ接続した場合のメカニカル接続損失が０．０５ｄＢと低損失で接続できた。   The prototype MMF has a bending loss of 0.02 dB / m at a wavelength of 1.55 μm and a bending diameter of φ = 10 mm, and the signal degradation due to mode dispersion is 0.1 ns / km or less, which is similar to the signal degradation due to wavelength dispersion. It becomes. In addition, when this MMF is connected to a normal SMF used in an optical transmission line, the splicing loss is 0.02 dB at a wavelength of 1.55 μm, and an optical connector is terminated at each fiber end to make a butt connection. In this case, the mechanical connection loss was as low as 0.05 dB and the connection could be made.

［実施例２］
図１に示す屈折率分布を有し、ｒ１＝２．７μｍ、ｒ２＝５．４μｍ、Δ１＝０．６％、Δ２＝０．４％のコア部を有し、トレンチ層の位置と幅は一定とし（ｒ３＝８μｍ、ｒ４＝１６μｍ）、トレンチ層の比屈折率差Δ３を０〜−１．０％の間で変え、得られるＭＭＦの特性を計算した。波長１．５５μｍにおける光学特性を表４に示す。 [Example 2]
1 having a refractive index profile, r 1 = 2.7 μm, r 2 = 5.4 μm, Δ 1 = 0.6%, Δ 2 = 0.4%, and a trench layer The position and width were constant (r 3 = 8 μm, r 4 = 16 μm), and the relative refractive index difference Δ 3 of the trench layer was changed between 0 and −1.0%, and the characteristics of the obtained MMF were calculated. Table 4 shows the optical characteristics at a wavelength of 1.55 μm.

Figure 2006078543
Figure 2006078543

表４からわかるように、トレンチ層の比屈折率差Δ３を変えても、Δｎｇを除く各特性はほとんど変わらない。また、トレンチ層の比屈折率差Δ３が−１．０％〜−０．２％の範囲では、｜Δｎｇ｜≦５×１０−４となる。 As can be seen from Table 4, changing the relative refractive index difference delta 3 of the trench layer, each characteristic except for the [Delta] n g hardly changes. Further, in a range the relative refractive index difference delta 3 of the trench layer is -1.0% ~-0.2%, | a ≦ 5 × 10 -4 | Δn g .

図１に示す屈折率分布を有し、ｒ１＝２．７μｍ、ｒ２＝５．４μｍ、Δ１＝０．６％、Δ２＝０．４％のコア部を有し、トレンチ層の幅と比屈折率差Δ３は一定とし（ｒ４−ｒ３＝８μｍ、Δ３＝−０．５％）、トレンチ層の位置、すなわちコア部中心からトレンチ層の内側エッジまでの距離ｒ３を６μｍ〜１０μｍの間で変え、得られるＭＭＦの特性を計算した。波長１．５５μｍにおける光学特性を表５に示す。 1 having a refractive index profile, r 1 = 2.7 μm, r 2 = 5.4 μm, Δ 1 = 0.6%, Δ 2 = 0.4%, and a trench layer The width and relative refractive index difference Δ 3 are constant (r 4 −r 3 = 8 μm, Δ 3 = −0.5%), and the distance r 3 from the position of the trench layer, that is, the center of the core portion to the inner edge of the trench layer. Was varied between 6 μm and 10 μm, and the properties of the obtained MMF were calculated. Table 5 shows the optical characteristics at a wavelength of 1.55 μm.

Figure 2006078543
Figure 2006078543

表５からわかるように、トレンチ層の位置を変えても、Δｎｇを除く各特性はほとんど変わらない。また、ｒ３が７．０μｍ〜９．５μｍの範囲では、｜Δｎｇ｜≦５×１０−４となる。 As can be seen from Table 5, also by changing the position of the trench layer, each characteristic with the exception of Δn g is almost unchanged. Further, when r 3 is in the range of 7.0 μm to 9.5 μm, | Δn g | ≦ 5 × 10 −4 .

図１に示す屈折率分布を有し、ｒ１＝２．７μｍ、ｒ２＝５．４μｍ、Δ１＝０．６％、Δ２＝０．４％のコア部を有し、トレンチ層の位置と比屈折率差Δ３は一定とし（ｒ３＝８μｍ、Δ３＝−０．５％）、トレンチ層の幅（ｒ４−ｒ３）を２μｍ〜１０μｍの間で変え、得られるＭＭＦの特性を計算した。波長１．５５μｍにおける光学特性を表６に示す。 1 having a refractive index profile, r 1 = 2.7 μm, r 2 = 5.4 μm, Δ 1 = 0.6%, Δ 2 = 0.4%, and a trench layer Position and relative refractive index difference Δ 3 are constant (r 3 = 8 μm, Δ 3 = −0.5%), and the width of the trench layer (r 4 −r 3 ) is changed between 2 μm and 10 μm to obtain the MMF The characteristics of were calculated. Table 6 shows the optical characteristics at a wavelength of 1.55 μm.

Figure 2006078543
Figure 2006078543

表６からわかるように、トレンチ層の幅を変えても、Δｎｇを除く各特性はほとんど変わらない。また、トレンチ層の幅（ｒ４−ｒ３）が３．０μｍ〜１０．０μｍの範囲では、Δｎｇ｜≦１×１０−４となる。 As can be seen from Table 6, also by changing the width of the trench layer, each characteristic with the exception of Δn g is almost unchanged. Further, Δn g | ≦ 1 × 10 −4 when the width (r 4 −r 3 ) of the trench layer is in the range of 3.0 μm to 10.0 μm.

以上の結果より、ｒ１＝２．７μｍ、ｒ２＝５．４μｍ、Δ１＝０．６％、Δ２＝０．４％のコア部に対して、トレンチ層の位置、幅又は比屈折率差を変えることにより、ＭＭＦの光学特性を大幅に変えることなく、モード分散を支配する｜Δｎｇ｜及び曲げ損失を調整することができる。 From the above results, the position, width, or relative refraction of the trench layer with respect to the core portion of r 1 = 2.7 μm, r 2 = 5.4 μm, Δ 1 = 0.6%, Δ 2 = 0.4% By changing the rate difference, it is possible to adjust | Δn g | that governs the mode dispersion and bending loss without significantly changing the optical characteristics of the MMF.

実際に、図１に示す屈折率分布を有し、ｒ１＝２．７μｍ、ｒ２＝５．４μｍ、Δ１＝０．６％、Δ２＝０．４％のコア部と、ｒ３＝８μｍ、ｒ４＝１６μｍ、Δ３＝−０．５％のトレンチ層をもつＭＭＦを作製した。このＭＭＦの基本モード（ＬＰ０１）と高次モード（ＬＰ１１）の等価群屈折率を測定した結果を図５に示す。図示のように、両モード間の群屈折率差｜Δｎｇ｜は波長１．２〜１．６μｍで１×１０−４以下である。 Actually, it has the refractive index distribution shown in FIG. 1 and has a core portion of r 1 = 2.7 μm, r 2 = 5.4 μm, Δ 1 = 0.6%, Δ 2 = 0.4%, and r 3 An MMF having a trench layer of = 8 μm, r 4 = 16 μm, and Δ 3 = −0.5% was manufactured. FIG. 5 shows the results of measuring the equivalent group refractive index of the fundamental mode (LP 01 ) and higher-order mode (LP 11 ) of this MMF. As shown, the group refractive index difference | Δn g | between the two modes is 1 × 10 −4 or less at a wavelength of 1.2 to 1.6 μm.

また、このＭＭＦの基本モードのＭＦＤと波長との関係を図６に示す。このＭＭＦのＭＦＤは、光伝送路に使用される通常のＳＭＦのそれよりもやや小さくなっているが、通常のＳＭＦと低い接続損失で接続できる。   FIG. 6 shows the relationship between the MFD and the wavelength of the basic mode of the MMF. The MFD of this MMF is slightly smaller than that of a normal SMF used for an optical transmission line, but can be connected to a normal SMF with a low connection loss.

また、このＭＭＦの基本モード（ＬＰ０１）の波長分散特性を図７に示す。波長分散によるパルス信号（波長１．５５μｍの光源はδλ＝５ｎｍとする）の劣化は、約０．１ｎｓ／ｋｍとなる。 Further, FIG. 7 shows the chromatic dispersion characteristics of the fundamental mode (LP 01 ) of this MMF. Degradation of the pulse signal due to chromatic dispersion (δλ = 5 nm for a light source with a wavelength of 1.55 μm) is about 0.1 ns / km.

試作したＭＭＦは、波長１．５５μｍで曲げ直径φ＝１０ｍｍにおける曲げ損失が０．００６ｄＢ／ｍ、モード分散による信号の劣化は０．１ｎｓ／ｋｍ以下であった。また、このＭＭＦは、光伝送路に使用される通常のＳＭＦと接続した場合、波長１．５５μｍにおいて、融着接続損失が０．０５ｄＢ、それぞれのファイバ端に光コネクタを成端して突き合わせ接続した場合のメカニカル接続損失が０．０７ｄＢと低損失で接続できた。   The prototype MMF had a bending loss of 0.006 dB / m at a wavelength of 1.55 μm and a bending diameter φ = 10 mm, and signal degradation due to mode dispersion was 0.1 ns / km or less. In addition, when this MMF is connected to a normal SMF used in an optical transmission line, the splicing loss is 0.05 dB at a wavelength of 1.55 μm, and an optical connector is terminated at each fiber end to make a butt connection. In this case, the mechanical connection loss was as low as 0.07 dB, and connection was possible.

本発明に係るＭＭＦの屈折率分布を例示するグラフである。It is a graph which illustrates the refractive index distribution of MMF concerning the present invention. 本発明に係る実施例１で試作したＭＭＦの波長と等価群屈折率の関係を示すグラフである。It is a graph which shows the relationship between the wavelength of MMF made as an experiment in Example 1 which concerns on this invention, and an equivalent group refractive index. 本発明に係る実施例１で試作したＭＭＦの波長とＭＦＤの関係を示すグラフである。It is a graph which shows the relationship between the wavelength of MMF made as an experiment in Example 1 which concerns on this invention, and MFD. 本発明に係る実施例１で試作したＭＭＦの波長と分散の関係を示すグラフである。It is a graph which shows the relationship between the wavelength and dispersion | distribution of MMF made as an experiment in Example 1 which concerns on this invention. 本発明に係る実施例２で試作したＭＭＦの波長と等価群屈折率の関係を示すグラフである。It is a graph which shows the relationship between the wavelength of MMF made as an experiment in Example 2 which concerns on this invention, and an equivalent group refractive index. 本発明に係る実施例２で試作したＭＭＦの波長とＭＦＤの関係を示すグラフである。It is a graph which shows the relationship between the wavelength of MMF made as an experiment in Example 2 which concerns on this invention, and MFD. 本発明に係る実施例２で試作したＭＭＦの波長と分散の関係を示すグラフである。It is a graph which shows the relationship between the wavelength and dispersion | distribution of MMF made as an experiment in Example 2 which concerns on this invention.

符号の説明Explanation of symbols

１…コア部、２…クラッド部、３…トレンチ層、４…第１コア、５…第２コア、６…トレンチ内側領域。
DESCRIPTION OF SYMBOLS 1 ... Core part, 2 ... Cladding part, 3 ... Trench layer, 4 ... 1st core, 5 ... 2nd core, 6 ... Trench inner side area | region.

Claims (8)

クラッド部より高屈折率のコア部と、その周囲のクラッド部と、コア部を囲むように設けられクラッド部より低屈折率のトレンチ層とを有し、コア部は、クラッド部より高屈折率の材料からなる中央の第１コアと、該第１コアの周りに、屈折率が第１コアと異なり、かつクラッド部より高屈折率の材料からなる第２コアとからなり、次の特性、
（ａ）波長１．２〜１．６μｍの間で２つ以上の伝搬モード（ただし、この伝搬モード数は縮退モードを重複カウントしない数である。）を有し、ＬＰ０１モードとＬＰ１１モードの群屈折率差Δｎｇの絶対値が１×１０−３より小さく、かつ
（ｂ）φ＝１０ｍｍの曲げ直径に対して、曲げ損失が波長１．５５μｍで０．１ｄＢ／ｍ以下である、
を有することを特徴とする低曲げ損失トレンチ型マルチモードファイバ。 It has a core part having a higher refractive index than the cladding part, a surrounding cladding part, and a trench layer provided to surround the core part and having a lower refractive index than the cladding part. The core part has a higher refractive index than the cladding part. And a second core made of a material having a refractive index different from that of the first core and having a refractive index higher than that of the cladding portion, and having the following characteristics:
(A) It has two or more propagation modes between wavelengths 1.2 to 1.6 μm (however, this number of propagation modes is a number that does not repeatedly count degenerate modes), and LP 01 mode and LP 11 mode the absolute value of the group refractive index difference [Delta] n g of less than 1 × 10 -3, and to bending diameter (b) φ = 10mm, the bending loss is less than 0.1 dB / m at a wavelength of 1.55 .mu.m,
A low bending loss trench type multimode fiber characterized by comprising: 第１コアのクラッド部に対する比屈折率差Δ１、第１コアの半径ｒ１、第２コアのクラッド部に対する比屈折率差Δ２、第２コアの半径ｒ２が、それぞれ、０．３％≦Δ１≦１％、０．１％≦Δ２≦０．６％、２μｍ≦ｒ１≦５μｍ、３μｍ≦ｒ２≦８μｍの範囲内であることを特徴とする請求項１に記載の低曲げ損失トレンチ型マルチモードファイバ。 The relative refractive index difference Δ 1 with respect to the cladding portion of the first core, the radius r 1 of the first core, the relative refractive index difference Δ 2 with respect to the cladding portion of the second core, and the radius r 2 of the second core are each 0.3. 2 ≦ Δ 1 ≦ 1%, 0.1% ≦ Δ 2 ≦ 0.6%, 2 μm ≦ r 1 ≦ 5 μm, 3 μm ≦ r 2 ≦ 8 μm Low bending loss trench type multimode fiber. コア部中心からトレンチ層の内側エッジまでの距離ｒ３、コア部中心からトレンチ層の外側エッジまでの距離ｒ４、トレンチ層のクラッド部に対する比屈折率差Δ３が、５μｍ≦ｒ３≦１０μｍ、７μｍ≦ｒ４≦２０μｍ、−１．２％≦Δ３≦−０．２％の範囲内であることを特徴とする請求項１又は２に記載の低曲げ損失トレンチ型マルチモードファイバ。 The distance r 3 from the core part center to the inner edge of the trench layer, the distance r 4 from the core part center to the outer edge of the trench layer, and the relative refractive index difference Δ 3 with respect to the cladding part of the trench layer are 5 μm ≦ r 3 ≦ 10 μm , 7μm ≦ r 4 ≦ 20μm, -1.2% ≦ Δ 3 ≦ -0.2% low bending loss trench multimode fiber according to claim 1 or 2, characterized in that in the range. コア部とトレンチ層との間の領域の、トレンチ層よりも外側のクラッド部に対する比屈折率差Δ´が−０．２％≦Δ´≦０．２％の範囲内であることを特徴とする請求項１〜３のいずれかに記載の低曲げ損失トレンチ型マルチモードファイバ。   The relative refractive index difference Δ ′ of the region between the core portion and the trench layer with respect to the cladding portion outside the trench layer is in the range of −0.2% ≦ Δ ′ ≦ 0.2%. The low bending loss trench type multimode fiber according to claim 1. シングルモードファイバと接続した時、モード分散が波長１．２〜１．６μｍの間で０．５ｎｓ／ｋｍ以下であることを特徴とする請求項１〜４のいずれかに記載の低曲げ損失トレンチ型マルチモードファイバ。   The low bending loss trench according to any one of claims 1 to 4, wherein mode dispersion is 0.5 ns / km or less between wavelengths of 1.2 to 1.6 µm when connected to a single mode fiber. Type multimode fiber. シングルモードファイバと接続し、光源のＲＭＳスペクトル幅５ｎｍ以下の時、波長分散とモード分散からなる全分散によるパルス幅の劣化が波長１．２〜１．６μｍの間で１ｎｓ／ｋｍ以下であることを特徴とする請求項１〜５のいずれかに記載の低曲げ損失トレンチ型マルチモードファイバ。   When connected to a single mode fiber and the RMS spectral width of the light source is 5 nm or less, the degradation of the pulse width due to the total dispersion consisting of chromatic dispersion and mode dispersion is 1 ns / km or less between wavelengths 1.2 to 1.6 μm. The low bending loss trench type multimode fiber according to any one of claims 1 to 5. ステップ状屈折率分布を持つシングルモードファイバとの融着接続損失が波長１．５５μｍで０．２ｄＢ以下、メカニカル接続損失が０．４ｄＢ以下となり、かつ反射減衰量が４０ｄＢ以上となることを特徴とする請求項１〜６のいずれかに記載の低曲げ損失トレンチ型マルチモードファイバ。   The splicing loss with a single mode fiber having a stepped refractive index profile is 0.2 dB or less at a wavelength of 1.55 μm, the mechanical splicing loss is 0.4 dB or less, and the return loss is 40 dB or more. The low bending loss trench type multimode fiber according to claim 1. 同じファイバを接続した時、融着接続損失が波長１．５５μｍで０．２ｄＢ以下、メカニカル接続損失が０．４ｄＢ以下となり、かつ反射減衰量が４０ｄＢ以上となることを特徴とする請求項１〜７のいずれかに記載の低曲げ損失トレンチ型マルチモードファイバ。

The splicing loss is 0.2 dB or less at a wavelength of 1.55 μm, the mechanical splicing loss is 0.4 dB or less, and the return loss is 40 dB or more when the same fiber is connected. 8. The low bending loss trench type multimode fiber according to any one of 7 above.

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