JP3584619B2 - Optical cable and method for manufacturing the same - Google Patents

Description

同様に、ｉ心目の光ファイバ素線の線路長をｌ_ｉ とすると、

となる。したがって、光ケーブルの１ｍ当たりで発生する線長差Δｌは、

となる。
【００２７】
光速をｃ、光ファイバのコア部の屈折率をｎとすると、光ケーブル１ｍ当たりのスキューは、

となる。石英系光ファイバの屈折率をｎ＝１．４５とすると、

となる。ｉ心目の光ファイバ素線のスキューをＹｉとして上式を書き換えると、
Ｙｉ［ｐｓｅｃ／ｍ］＝α（Ｘｉ／Ｌ）²
となる。αは、定数で、上式の場合は、１×１０⁵ ［ｐｓｅｃ／ｍ］である。
【００２８】
上述したスキューの式は、光ケーブル中心からテープ状光ファイバ心線２の収納位置までの距離Ｒに依存しない。また、螺旋状態が一方向の撚りの場合でも、撚りが反転する場合でも、同様である。光ファイバ素線４の心数が偶数、例えば、図示のような１２心の場合には、６心目と７心目の光ファイバ素線４の境界がテープ状光ファイバ心線２の中心になるため、６心目，７心目の光ファイバ素線４が伝達時間の最も短かい光ファイバ素線になるが、これらの光ファイバ素線４も光ファイバ心線２の中心にある仮想の光ファイバ素線に対して伝達時間の差を有するため、６心目，７心目の光ファイバ素線４の伝達時間を基準にすると、この分だけ実際の伝達時間の差は少なくなる。
【００２９】
複数本の光ファイバ素線４をテープ化してテープ状光ファイバ心線２を得る際に、螺旋半径の差による延びに応じた光路長の差を、あらかじめ逆方向に与えておく。テープ状光ファイバ心線２の中央の光ファイバ素線４、上述した例では、６心目，７心目の光ファイバ素線４から両端部寄りの光ファイバ素線４、上述した例では、１心目，１２心目に近づくにつれ、光ファイバ素線４の光路長が短かくなるようにし、時間を早くする方向を正として、１×１０^５ ×（Ｘｉ／Ｌ）^２ ［ｐｓｅｃ／ｍ］の伝達時間の差が生じるようにする。
【００３０】
ただし、実際には、テープ状光ファイバ心線２内の各光ファイバ素線４の屈折率管理と物理長管理を合わせたスキュー管理の能力には限度があるから、上述した式の通りの伝達時間の差を完全に補償することは困難である。
【００３１】
しかし、テープ状光ファイバ心線を光ケーブルに収容する前の状態において、ｉ心目の光ファイバ素線のテープ状光ファイバ心線の中心からの距離Ｘｉの値と、ｉ心目の光ファイバ素線のスキュー量の測定値とから、スキュー量Ｙを（Ｘｉ／Ｌ）をパラメータとして２次曲線近似をすると、
Ｙ［ｐｓｅｃ／ｍ］＝α（Ｘｉ／Ｌ）²
で近似できる（１次項と定数項は省略した）。この近似を最小自乗法で近似したときの前記αは、理論値としては、上述したように、１×１０⁵ ［ｐｓｅｃ／ｍ］である。この近似を最小自乗法で近似したときの前記αは、理論値に対して、好ましい範囲で幅を持たせることができる。すなわち、理論値１×１０⁵ を中心として、±５０％の範囲であり、０．５×１０⁵ ［ｐｓｅｃ／ｍ］以上、１．５×１０⁵ ［ｐｓｅｃ／ｍ］以下の範囲である。αが、０．５×１０⁵ ［ｐｓｅｃ／ｍ］を下回るとスキュー補償の効果が薄く、１．５×１０⁵ ［ｐｓｅｃ／ｍ］を超えると補償の方が過剰になり、かえって逆効果となるから、この範囲が好ましい。
【００３２】
螺旋半径の差による伸びに応じた光路長の差を補償する具体的な方法の１は、テープ化時のバックテンションの張力に差を持たせることである。バックテンションの張力が小さいときには、光ファイバ素線４がテープ状光ファイバ心線２内で僅かながら蛇行した状態で収容されてテープ状光ファイバ心線２が作製されるが、バックテンションの張力が大きいときには、光ファイバ素線４がテープ状光ファイバ心線２内で長手方向に直線的な配列状態で収容されてテープ状光ファイバ心線２が作製され、光ファイバ素線４の物理長が蛇行状態よりも短かくなる。テープ状光ファイバ心線２の中央の光ファイバ素線４からの距離が大きい光ファイバ素線４ほど、テープ化時に加えるバックテンションを大きくして物理長を短かくし、上述した２次の係数が理論値の１×１０^５ に近づくようにする。
【００３３】
別の具体的な方法は、光ファイバ素線４の屈折率に差を持たせることである。テープ状光ファイバ心線２の中央の光ファイバ素線４からの距離が大きい光ファイバ素線４ほど光ファイバコア部の屈折率の小さなものを用い、上述した２次の係数が理論値の１×１０^５ に近づくようにする。あるいは、テープ化時の張力差と屈折率の差の両者の組み合わせにより上述した２次の係数が理論値の１×１０^５ に近づくようにしてもよい。
【００３４】
具体的な数値を用いて説明する。０．２５ｍｍピッチで外径０．２５ｍｍの光ファイバ素線４が配列された１２心の石英系テープ状光ファイバ心線２を、螺旋ピッチ０．５ｍの光ケーブルに収容した場合では、ケーブル化によって、１，１２心目の光ファイバ素線では、Ｘ_ｉ が１．３７５ｍｍ、６，７心目の光ファイバ素線ではＸ_ｉ が０．１２５ｍｍであるから、上述した近似式を用いると、６，７心目の光ファイバ素線の伝達時間を基準にとると、０．７５［ｐｓｅｃ／ｍ］のテープ内スキューが発生する。したがって、あらかじめ、テープ状光ファイバ心線２の両端の光ファイバ素線４と中央の光ファイバ素線４との間にスキューとして０．７５［ｐｓｅｃ／ｍ］の光路長差を逆に与えたテープ状光ファイバ心線２を用いれば、ケーブル化によってスキューは理論的には０になる。
【００３５】
実際には、テープ状光ファイバ心線２のスキュー管理制御の実力は、屈折率管理と物理長管理を合わせて、０．５［ｐｓｅｃ／ｍ］程度である。したがって、テープ状光ファイバ心線２のスキューの目標特性を０．３［ｐｓｅｃ／ｍ］とした。１本のテープ状光ファイバ心線２の両端の光ファイバ素線４の中心間隔をＷ、螺旋ピッチをＬとしたとき、テープ状光ファイバ心線２の両端に位置する光ファイバ素線の中心からの距離Ｘｉ＝（Ｗ／２）であるから、テープ状光ファイバ心線２の中央に位置する光ファイバ素線４を基準にした伝達時間の差は、１×１０⁵ ×（Ｗ／２Ｌ）² ［ｐｓｅｃ／ｍ］となる。ここでは、中央に位置する光ファイバ素線４のテープ状光ファイバ心線２の中心からの距離Ｘｉを０として近似している。
【００３６】
上述したようにテープ状光ファイバ心線２のスキューの目標特性を０．３［ｐｓｅｃ／ｍ］としたとき、
１×１０⁵ ×（Ｗ／２Ｌ）² ［ｐｓｅｃ／ｍ］≧０．３［ｐｓｅｃ／ｍ］
となる光ケーブルでは、スキュー補償を行なわないと、スキューが目標特性を超えてしまう。この式からＷ／Ｌの範囲を求めると、
（Ｗ／２Ｌ）² ≧０．３×１０^-5
（Ｗ／Ｌ）² ≧１．２×１０^-5
（Ｗ／Ｌ）≧３．５×１０^-3
となる。したがって、（Ｗ／Ｌ）≧３．５×１０^-3となる光ケーブルにおいては、スキュー補償を行なうことによって、０．３［ｐｓｅｃ／ｍ］とした目標特性を達成できるのである。Ｗ／Ｌの値は、光ファイバ素線４の径が大きいほど、また、テープ状光ファイバ心線２の心数が多いほど大きくなり、また、螺旋半径が小さいほど大きくなり、（Ｗ／Ｌ）≧３．５×１０^-3となる光ケーブルにおいては、スキュー補償の効果が大きい。
【００３７】
スキューを補償する具体的な方法として、テープ化時に光ファイバ素線４のバックテンションに差を持たせる場合、所定範囲内において張力差と伝達時間差はほぼ比例し、基準とする光ファイバ素線４に対し、２０ｇだけ大きな張力が加えられた光ファイバ素線４は、線長が約０．０２％短かくなり、これは約１ｐｓｅｃ／ｍだけ伝達時間を短かくする。また、光ファイバ素線４の屈折率に差を持たせる場合、屈折率の差と伝達時間差は比例し、基準となる光ファイバ素線４に対し、比屈折率差Δｎで０．０２％だけ大きな屈折率の光ファイバ素線４は、約１ｐｓｅｃ／ｍだけ伝達時間を短かくする。
【００３８】
【実施例】
図４に示した断面構造の光ケーブルにおいて、外径０．２５ｍｍの石英系単一モードの光ファイバ素線４を０．２５ｍｍピッチで１２心有するテープ状光ファイバ心線２を用い、螺旋ピッチ０．５ｍの光ケーブルを試作した。テープ化時に張力制御を施して、あらかじめ予想されるスキュー変化を補償するテープ内スキューを持つようにした第１のテープ状光ファイバ心線、および、テープ状光ファイバ心線単体で低スキューを狙って作製した第２のテープ状光ファイバ心線、の２通りのテープ状光ファイバ心線２を光ケーブルに収容してスキュー測定を行なった。
【００３９】
図２は、本発明に用いる第１のテープ状光ファイバ心線のスキューを表わす線図であり、図２（Ａ）は第１のテープ状光ファイバ心線２の単体でのスキューを表わす線図、図２（Ｂ）はケーブル化後のスキューを表わす線図である。図中、横軸は、光ファイバ素線の心線番号、縦軸はスキュー（ｐｓｅｃ／ｍ）であり、スキューは、１心目を基準とし、伝達時間が早くなる方向を正の符号で表わしている。
【００４０】
第１のテープ状光ファイバ心線は、本発明に用いるテープ状光ファイバ心線の一具体例である。図２（Ａ）に示されるように、ケーブル化前では、光ファイバ素線の心線番号５，６が最も伝達時間が遅く、かつ、上述した１×１０^５ ×（Ｘｉ／Ｌ）^２ ［ｐｓｅｃ／ｍ］の螺旋半径の差に基づくスキューをほぼ補償できるように設計されている。ケーブル化前ではスキューは、心線番号５の光ファイバ素線と心線番号２，１２の光ファイバ素線の間が最も大きく、０．９４［ｐｓｅｃ／ｍ］であった。図２（Ｂ）に示されるように、ケーブル化によって、スキューは、心線番号５，１０と心線番号２の光ファイバ素線との間が最も大きいが、そのスキュー量は、０．５４［ｐｓｅｃ／ｍ］に改善された。
【００４１】
図３は、従来から用いられている第２ののテープ状光ファイバ心線のスキューを表わす線図であり、図３（Ａ）は第２のテープ状光ファイバ心線２の単体でのスキュー量を表わす線図、図３（Ｂ）はケーブル化後のスキュー量を表わす線図である。横軸及び縦軸は図２と同様であり説明を省略する。
【００４２】
第２のテープ状光ファイバ心線は、従来のテープ状光ファイバ心線の具体例である。図３（Ａ）に示すように、ケーブル化前では、光ファイバ素線４の伝達時間差がほぼ補償されるように設計されており、スキュー量は、心線番号９と心線番号３，５の間が最も大きく、０．４７［ｐｓｅｃ／ｍ］であった。図３（Ｂ）に示すように、ケーブル化によって、中心側の光ファイバ素線の伝達時間が早くなり、心線番号１と心線番号５との間のスキュー量は、０．８９［ｐｓｅｃ／ｍ］にまで悪化した。
【００４３】
【発明の効果】
以上の説明から明らかなように、請求項１に記載の発明によれば、複数心の光ファイバ素線を有するテープ状光ファイバ心線が螺旋状に収容されている光ケーブルにおいて、テープ状光ファイバ心線は、その光ファイバ素線のそれぞれが、テープ状光ファイバ心線が光ケーブルに収容されていない状態で、それぞれの光ファイバ素線の螺旋半径の相違による光路長の差をほぼ補償する伝達時間差を持たせたものであることから、光ケーブルに螺旋状に収容されたテープ状光ファイバ心線内の光ファイバ素線のスキューを低減することができるという効果がある。また、テープ状光ファイバ心線は、その光ファイバ素線が石英系の光ファイバ素線であり、テープ状光ファイバ心線の螺旋ピッチをＬ、ｉ心目の光ファイバ素線のテープ状光ファイバ心線の中心からの距離をＸｉとしたとき、前記テープ状光ファイバ心線が前記光ケーブルに収容されていない状態での前記複数心の光ファイバ素線の前記伝達時間差Ｙを（Ｘｉ／Ｌ）をパラメータとして表せば、
Ｙ［ｐｓｅｃ／ｍ］＝α（Ｘｉ／Ｌ）²
で近似され、この近似を最小自乗法で近似したときのαが、０．５×１０⁵ ［ｐｓｅｃ／ｍ］以上、１．５×１０⁵ ［ｐｓｅｃ／ｍ⁵ ］以下の範囲である。係数αの値が、０．５×１０⁵ ［ｐｓｅｃ／ｍ］を下回るとスキュー補償の効果が薄く、１．５×１０⁵ ［ｐｓｅｃ／ｍ］を超えると過剰補償となるため、係数の値が上述した範囲であれば、実用上、十分なスキュー補償の効果を有するという効果がある。
【００４４】
請求項２に記載の発明によれば、テープ状光ファイバ心線の両端に位置する光ファイバ素線の中心間の距離をＷ、テープ状光ファイバ心線の螺旋ピッチをＬとしたとき、テープ状光ファイバ心線のＷ／Ｌの値が３．５×１０^-3以上であることから、ケーブル化に起因するスキューが０．３［ｐｓｅｃ／ｍ］以上に達し、実用上無視できないスキュー量であるため、スキュー補償が有効に働くという効果がある。
【００４５】
請求項３に記載の発明によれば、複数心の光ファイバ素線を有するテープ状光ファイバ心線を螺旋状に収容する光ケーブルの製造方法において、テープ状光ファイバ心線として、その光ファイバ素線のそれぞれが、テープ状光ファイバ心線が光ケーブルに収容されていない状態で、それぞれの光ファイバ素線の螺旋半径の相違による光路長の差をほぼ補償する伝達時間差を持たせて、テープ状光ファイバ心線を光ケーブルに収容することから、光ケーブル内に螺旋状に収容された状態のテープ状光ファイバ心線内のスキューを低減する光ケーブルを得ることができるという効果がある。また、テープ状光ファイバ心線は、その光ファイバ素線が石英系の光ファイバ素線であり、テープ状光ファイバ心線の螺旋ピッチをＬ、ｉ心目の光ファイバ素線のテープ状光ファイバ心線の中心からの距離をＸｉとしたとき、前記テープ状光ファイバ心線が前記光ケーブルに収容されていない状態での前記複数心の光ファイバ素線の前記伝達時間差Ｙを（Ｘｉ／Ｌ）をパラメータとして表せば、
Ｙ［ｐｓｅｃ／ｍ］＝α（Ｘｉ／Ｌ）²
で近似され、この近似を最小自乗法で近似したときのαが、０．５×１０⁵ ［ｐｓｅｃ／ｍ］以上、１．５×１０⁵ ［ｐｓｅｃ／ｍ⁵ ］以下の範囲になるものを用いるため、実用上のスキュー補償の効果を有する光ケーブルを得ることができるという効果がある。
【００４６】
請求項４に記載の発明によれば、光ファイバ素線をテープ化する際に、光ファイバ素線に加える張力に差を持たせることから、テープ状光ファイバ心線が光ケーブルに収容される前に、光ファイバ素線に光路長差を容易に持たせることができるという効果がある。
【００４７】
請求項５に記載の発明によれば、複数の光ファイバ素線として、光ファイバコアの屈折率に差を有する光ファイバ素線を用いることから、テープ状光ファイバ心線が光ケーブルに収容される前に、光ファイバ素線に光路長差を容易に持たせることができるという効果がある。
【図面の簡単な説明】
【図１】本発明の光ケーブルに収容するテープ状光ファイバ心線内のスキューの説明図である。
【図２】本発明に用いる第１のテープ状光ファイバ心線のスキューを表わす線図であり、図２（Ａ）は第１のテープ状光ファイバ心線２の単体でのスキューを表わす線図、図２（Ｂ）はケーブル化後のスキューを表わす線図である。
【図３】従来から用いられている第２のテープ状光ファイバ心線のスキューを表わす線図であり、図３（Ａ）は第２のテープ状光ファイバ心線２の単体でのスキュー量を表わす線図、図３（Ｂ）はケーブル化後のスキュー量を表わす線図である。
【図４】テープ状光ファイバ心線を収容したスロット構造の光ケーブルの説明図であり、図４（Ａ）は、光ケーブルの模式断面図、図４（Ｂ）はテープ状光ファイバ心線の模式断面図である。
【図５】図４に示したスロットロッドの斜視図であり、図５（Ａ）はＳ撚りのスロットロッドの例、図５（Ｂ）はＳＺ撚りスロットロッドの例を表わす。
【図６】テープ状光ファイバ心線を収容したルースチューブ構造の光ケーブルの模式断面図である。
【符号の説明】
１…スロットロッド、１ａ…中心抗張力体、２…テープ状光ファイバ心線、３…シース，４…光ファイバ素線、１１…チューブ、１２…シース。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical cable for optical parallel transmission and a method for manufacturing the same.
[0002]
[Prior art]
Matsuoka et al., "B-634, 80-core array flat cable", using a tape-shaped optical fiber core as an optical cable for optical parallel transmission, Proc. Of the IEICE Autumn Conference, (1992), 4th volume p. 27, or Nasuno et al., "B-941, Small Skew of Tape Fiber," Proc. Of the IEICE Spring Conference, (1994), Vol. 7 and so on.
[0003]
In optical parallel transmission, digital data expressed in units of several bits (often about 8 to 12 bits) is transmitted to each optical fiber in order to be transmitted simultaneously by being divided into a plurality of optical fibers. It is necessary to synchronize the bits.
[0004]
Usually, one parallel transmission unit is transmitted by one tape-shaped optical fiber core. For this reason, the tape-shaped optical fiber core wire used for the optical parallel transmission needs to be manufactured so as to reduce the difference in transmission time (hereinafter, referred to as “skew”). The skew is an important factor that limits a transmission speed (bit rate) and a transmittable distance. The skew in the tape-shaped optical fiber core is caused by the difference in the optical path length of each built-in optical fiber, and the optical path length is represented by the product of the refractive index and the physical length (fiber length) of each optical fiber.
[0005]
Therefore, by strictly controlling the refractive index and physical length of each optical fiber, the skew between the optical fibers in the tape-shaped optical fiber is suppressed. At the time of manufacturing a tape-shaped optical fiber core, the physical length and the refractive index of the optical fiber are made uniform by equalizing the back tension at the time of forming the tape.
[0006]
4A and 4B are explanatory diagrams of an optical cable having a slot structure accommodating a tape-shaped optical fiber core. FIG. 4A is a schematic cross-sectional view of the optical cable, and FIG. It is sectional drawing. In the figure, 1 is a slot rod, 1a is a central tensile member, 2 is a tape-shaped optical fiber core, 3 is a sheath, and 4 is an optical fiber.
[0007]
First, the tape-shaped optical fiber core wire 2 will be described with reference to FIG. The tape-shaped optical fiber core 2 is a flat multi-core optical fiber coated with a plurality of coated optical fiber wires 4, in the illustrated example, eight cores covered with a tape coating. It is.
[0008]
As shown in FIG. 4A, this optical cable is an optical cable having a slot structure. One or more grooves, in the illustrated example, four grooves are engraved on the outer periphery of the slot rod 1 having a substantially circular cross section, and are covered with the sheath 3. Before the sheath is covered with the sheath 3, the retainer may be wound, but is not shown. The tape-shaped optical fiber core wire 2 is accommodated in the groove as a single layer or a laminated body. The cross section of this groove is substantially rectangular. When the optical cable is bent, each tape-shaped optical fiber core 2 is extended along the length of the optical cable so that an unreasonable tensile force or compressive force is not applied to the tape-shaped optical fiber core 2 housed in the groove of the slot rod 1. It is accommodated in a spiral state with respect to the direction. Therefore, the groove of the slot rod 1 is spirally formed in the longitudinal direction of the optical cable.
[0009]
FIG. 5 is a perspective view of the slot rod shown in FIG. 4, in which FIG. 5A shows an example of an S-twisted slot rod, and FIG. 5B shows an example of an SZ-twisted slot rod. In FIG. 5A, each groove of the slot rod 1 is formed in a spiral shape in which the twist direction is constant (in the example shown, S twist) with respect to the longitudinal direction of the optical cable. In FIG. 5B, each groove of the slot rod 1 is spirally carved by so-called SZ twist in which the twist direction is reversed with respect to the longitudinal direction of the optical cable.
[0010]
The reason for accommodating the tape-shaped optical fiber core 2 in the S-twisted or Z-twisted spiral state in which the twist direction is constant in the optical cable, or the SZ-twisted spiral state in which the twist direction is reversed is that when the optical cable is drum-wound, Alternatively, when the optical cable is bent when the optical cable is laid, a difference between the plurality of tape-shaped optical fiber cores 2 caused by a difference in the lamination position of the plurality of tape-shaped optical fiber cores 2 housed in a stack. The helical pitch in a normal optical cable having a diameter of about 20 mmφ is generally set to about 50 cm in terms of both characteristics and manufacturability.
[0011]
FIG. 6 is a schematic sectional view of an optical cable having a loose tube structure accommodating a tape-shaped optical fiber core. In the figure, the same parts as those in FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted. 11 is a tube and 12 is a sheath. The seven tape-shaped optical fiber cores 2 are accommodated in a tube 11 in a so-called loose state having a gap, and the tube 11 is covered with a sheath 12. In some cases, a tensile strength member is embedded inside each coating of the tube 11 and the sheath 12. Even in such an optical cable having a loose tube structure, the tape-shaped optical fiber core wire 2 may be twisted in the tube 11 and housed in a spiral state.
[0012]
When the tape-shaped optical fiber cores 2 are used in a spiral state as shown in FIGS. 4 and 6, the optical fiber wires 4 near both ends in each tape-shaped optical fiber core 2 are located at the center. Passes through a path having a larger helical radius from the helical center as compared with the optical fiber wire 4 of FIG. Accordingly, the physical length is longer than that of the optical fiber 4 at the center, thereby increasing the physical length. As a result, there is a problem that skew occurs.
[0013]
[Problems to be solved by the invention]
The present invention has been made in view of the above-described circumstances, and accommodates a tape-shaped optical fiber core wire 2 in a spiral state and reduces skew between optical fiber strands in the tape-shaped optical fiber core wire. It is an object of the present invention to provide an optical cable and a method for manufacturing the same.
[0014]
[Means for Solving the Problems]
The invention according to claim 1 is an optical cable in which a tape-shaped optical fiber having a plurality of optical fibers is spirally accommodated, wherein the tape-shaped optical fiber is an optical fiber. Each of the wires has a transmission time difference that almost compensates for a difference in optical path length due to a difference in a helical radius of each of the optical fiber wires in a state where the tape-shaped optical fiber core wire is not accommodated in the optical cable. In the optical cable, the tape-shaped optical fiber core wire is a silica-based optical fiber wire, and the helical pitch of the tape-shaped optical fiber core wire is L, and the i-th optical fiber strand is When the distance from the center of the tape-shaped optical fiber core is Xi, the plurality of optical fibers in a state where the tape-shaped optical fiber core is not housed in the optical cable Expressed said transmission time difference Y line of (Xi / L) as a parameter,
Y [psec / m] = α (Xi / L)^Two
Α when this approximation is approximated by the least squares method is 0.5 × 10^Five[Psec / m] or more, 1.5 × 10^Five[Psec / m^Five] It is characterized by the following range.
[0015]
According to a second aspect of the present invention, in the optical cable according to the first aspect, a distance between centers of optical fiber strands located at both ends of the tape-shaped optical fiber core is W, and the distance between the centers of the tape-shaped optical fiber core is W. When the helical pitch is L, the value of W / L of the optical fiber ribbon is 3.5 × 10^-3The above is the feature.
[0016]
The invention according to claim 3 is a method for manufacturing an optical cable in which a tape-shaped optical fiber having a plurality of optical fibers is spirally accommodated, wherein the tape-shaped optical fiber is an optical fiber. Each of the fiber strands has a transmission time difference that almost compensates for a difference in optical path length due to a difference in the helical radius of each of the optical fiber strands in a state where the tape-shaped optical fiber core is not housed in the optical cable. In the method for manufacturing an optical cable housed in the optical cable using the tape-shaped optical fiber core wire, the tape-shaped optical fiber core wire is a silica-based optical fiber strand, and the tape Assuming that the helical pitch of the optical fiber ribbon is L and the distance of the i-th optical fiber from the center of the optical fiber ribbon is Xi, Expressed said transmission time difference Y of the plurality center of the optical fiber in a state where Aiba cord is not received in the light cable (Xi / L) as a parameter,
Y [psec / m] = α (Xi / L)^Two
Α when this approximation is approximated by the least squares method is 0.5 × 10^Five[Psec / m] or more, 1.5 × 10^Five[Psec / m^Five] It is characterized by the following range.
[0017]
According to a fourth aspect of the present invention, in the method of manufacturing an optical cable according to the third aspect, when the optical fiber is formed into a tape, a difference is provided in tension applied to the optical fiber. Is what you do.
[0018]
According to a fifth aspect of the present invention, in the method for manufacturing an optical cable according to the third or fourth aspect, an optical fiber having a difference in refractive index of an optical fiber core is used as the plurality of optical fibers. It is a feature.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
In one embodiment of the optical cable according to the present invention, an optical cable for spirally housing a tape-shaped optical fiber core 2 as shown in FIGS. 4 and 6, wherein the tape-shaped optical fiber core 2 is an optical cable. In the state where it is not accommodated in the optical fiber core wire 2, the optical path length of the optical fiber strand 4 housed outside the tape-shaped optical fiber core 2 is made longer than the optical path length of the optical fiber strand 4 housed in the center side in advance. An optical cable designed to be short.
[0022]
When the tape-shaped optical fiber core wire 2 is spirally accommodated in the optical cable, the outer optical fiber wire 4 near both ends has a longer helical radius, so that the optical fiber wire 4 extends and the optical path length becomes longer. However, since the optical path length of the optical fiber 4 accommodated outside is shortened in advance, the elongation causes the total optical path length of each optical fiber 4 in the tape-shaped optical fiber core 2. It will be uniform.
[0023]
As described later, since there is a limit in the management of the optical path length of the optical fiber 4, the difference in the optical path length due to the difference in the helical radius of all the optical fibers in the tape-shaped optical fiber 2 is completely eliminated. Is difficult to compensate for, but it is sufficient that at least one optical fiber 4 can be compensated almost. That is, at least one core of the optical fiber 4 has a transmission time difference that almost compensates for a difference in optical path length due to a difference in the helical radius of the optical fiber 4, and the tape-shaped optical fiber 2 is not accommodated in the optical cable. What is necessary is just to have it in a state.
[0024]
FIG. 1 is an explanatory diagram of a skew in a tape-shaped optical fiber core housed in an optical cable of the present invention. In the figure, the same parts as those in FIG. Assuming that a normal quartz optical fiber 4 is used, the helical pitch of the tape-shaped optical fiber 2 accommodated in the above-mentioned optical cable is L, and the i-th optical fiber in the tape-shaped optical fiber 2 is Assuming that the distance of the strand 4 from the center of the tape-shaped optical fiber core 2 is Xi, the optical fiber strand 4 at the i-th center and the optical fiber strand 4 at the center have a line length due to the difference in the spiral radius. The difference causes a difference in the optical path length. Based on the optical path length of the optical fiber 4 located at the center of the tape-shaped optical fiber core 2, 1 × 10⁵× (Xi / L)²A difference in transmission time of [psec / m], that is, skew occurs.
[0025]
In the case where the number of optical fibers 4 is an even number, for example, 12 fibers as shown, the central optical fiber 4 is not located at the center, but the virtual optical fiber is located at the center. It will be described as if it exists.
[0026]
The basis of the above equation will be described below. In one pitch length of the spiral, the line length of the central optical fiber is l_o, Where the spiral radius of the central optical fiber is R,

Similarly, let the line length of the i-th optical fiber strand be l_iThen

It becomes. Therefore, the line length difference Δl generated per meter of the optical cable is

It becomes.
[0027]
Assuming that the speed of light is c and the refractive index of the core of the optical fiber is n, the skew per meter of the optical cable is

It becomes. Assuming that the refractive index of the silica-based optical fiber is n = 1.45,

It becomes. Rewriting the above equation with the skew of the i-th optical fiber strand as Yi,
Yi [psec / m] = α (Xi / L)^Two
It becomes. α is a constant, and in the above equation, 1 × 10^Five[Psec / m].
[0028]
The skew equation described above does not depend on the distance R from the center of the optical cable to the storage position of the tape-shaped optical fiber core 2. The same applies to the case where the spiral state is a one-way twist and the case where the twist is reversed. In the case where the number of optical fibers 4 is an even number, for example, 12 as shown, the boundary between the sixth and seventh optical fibers 4 becomes the center of the tape-shaped optical fiber 2. , The sixth and seventh optical fiber strands 4 are the optical fiber strands having the shortest transmission time, and these optical fiber strands 4 are also virtual optical fiber strands at the center of the optical fiber core strand 2. , There is a difference in the transmission time, so that the difference in the actual transmission time is reduced by that much, based on the transmission time of the sixth and seventh optical fiber strands 4.
[0029]
When a plurality of optical fiber wires 4 are taped to obtain a tape-shaped optical fiber core wire 2, a difference in optical path length according to the elongation due to a difference in helical radius is given in the opposite direction in advance. The optical fiber wire 4 at the center of the tape-shaped optical fiber core wire 2, in the above-described example, the optical fiber wire 4 near both ends from the sixth and seventh optical fiber wires 4, and in the above-mentioned example, the first optical fiber wire 4 , As approaching the 12th fiber, the optical path length of the optical fiber 4 is shortened, and the direction in which the time is shortened is defined as 1 × 10⁵× (Xi / L)²A transmission time difference of [psec / m] is set.
[0030]
However, in practice, there is a limit in the ability of skew management combining the refractive index management and the physical length management of each optical fiber 4 in the tape-shaped optical fiber core wire 2, and therefore, the transmission according to the above-described formula is performed. It is difficult to completely compensate for time differences.
[0031]
However, before the tape-shaped optical fiber is accommodated in the optical cable, the value of the distance Xi of the i-th optical fiber from the center of the tape-shaped optical fiber and the value of the i-th optical fiber are determined. When the skew amount Y is approximated by a quadratic curve using (Xi / L) as a parameter from the measured value of the skew amount,
Y [psec / m] = α (Xi / L)^Two
(The first-order and constant terms have been omitted). When the approximation is approximated by the method of least squares, the theoretical value is, as described above, 1 × 10^Five[Psec / m]. The value of α when this approximation is approximated by the least square method can have a range within a preferable range with respect to a theoretical value. That is, the theoretical value is 1 × 10^Five± 50% around 0.5 × 10^Five[Psec / m] or more, 1.5 × 10^Five[Psec / m] or less. α is 0.5 × 10^FiveIf it is less than [psec / m], the effect of skew compensation is weak, and 1.5 × 10^FiveIf the ratio exceeds [psec / m], the compensation becomes excessive, and the effect is rather adverse. Therefore, this range is preferable.
[0032]
One specific method of compensating for the difference in the optical path length according to the elongation due to the difference in the helical radius is to provide a difference in the tension of the back tension when the tape is formed. When the tension of the back tension is small, the optical fiber 4 is accommodated in a slightly meandering state in the tape-shaped optical fiber 2 to produce the tape-shaped optical fiber 2, but the tension of the back tension is reduced. When it is large, the optical fiber 4 is accommodated in the tape-shaped optical fiber 2 in a linearly arrayed state in the longitudinal direction to produce the tape-shaped optical fiber 2, and the physical length of the optical fiber 4 is reduced. Shorter than in a meandering state. The larger the distance from the center optical fiber 4 of the tape-shaped optical fiber core 2 to the larger optical fiber 4, the larger the back tension applied at the time of tape-making to shorten the physical length, and the above-described second-order coefficient is reduced. 1 × 10 of theoretical value⁵To approach.
[0033]
Another specific method is to provide a difference in the refractive index of the optical fiber 4. The larger the distance from the center optical fiber 4 of the tape-shaped optical fiber core 2 to the larger the optical fiber 4, the smaller the refractive index of the optical fiber core is used. × 10⁵To approach. Alternatively, the above-mentioned second order coefficient is 1 × 10 of the theoretical value by a combination of both the difference in tension and the difference in refractive index at the time of tape formation.⁵May be approached.
[0034]
This will be described using specific numerical values. In the case where a 12-core quartz-based tape-shaped optical fiber core wire 2 in which optical fiber wires 4 having an outer diameter of 0.25 mm are arranged at a pitch of 0.25 mm is accommodated in an optical cable having a helical pitch of 0.5 m, a cable is formed. , The 1st and 12th optical fibers are X_iIs 1.375 mm, X is_iIs 0.125 mm, the skew in the tape of 0.75 [psec / m] occurs based on the transmission time of the sixth and seventh optical fiber strands using the above-described approximate expression. Therefore, an optical path length difference of 0.75 [psec / m] was previously given as a skew between the optical fiber 4 at both ends of the tape-shaped optical fiber 2 and the central optical fiber 4. If the tape-shaped optical fiber core wire 2 is used, the skew is theoretically zero due to the use of a cable.
[0035]
Actually, the ability of the skew management control of the tape-shaped optical fiber core 2 is about 0.5 [psec / m] including the management of the refractive index and the management of the physical length. Therefore, the target characteristic of the skew of the tape-shaped optical fiber core wire 2 is set to 0.3 [psec / m]. When the center distance between the optical fiber wires 4 at both ends of one tape-shaped optical fiber core wire 2 is W and the helical pitch is L, the center of the optical fiber wires located at both ends of the tape-shaped optical fiber core wire 2 , The difference in transmission time with respect to the optical fiber 4 located at the center of the tape-shaped optical fiber core 2 is 1 × 10^Five× (W / 2L)^Two[Psec / m]. Here, the distance Xi of the optical fiber 4 located at the center from the center of the tape-shaped optical fiber 2 is approximated as 0.
[0036]
As described above, when the target characteristic of the skew of the tape-shaped optical fiber core 2 is 0.3 [psec / m],
1 × 10^Five× (W / 2L)^Two[Psec / m] ≧ 0.3 [psec / m]
In such an optical cable, if skew compensation is not performed, the skew exceeds the target characteristic. When the range of W / L is obtained from this equation,
(W / 2L)^Two≧ 0.3 × 10^-Five
(W / L)^Two≧ 1.2 × 10^-Five
(W / L) ≧ 3.5 × 10^-3
It becomes. Therefore, (W / L) ≧ 3.5 × 10^-3By performing skew compensation, the target characteristic of 0.3 [psec / m] can be achieved. The value of W / L increases as the diameter of the optical fiber 4 increases, as the number of cores of the tape-shaped optical fiber core 2 increases, and as the spiral radius decreases, the value of W / L increases. ) ≧ 3.5 × 10^-3In the optical cable, the effect of skew compensation is great.
[0037]
As a specific method for compensating for skew, when a difference is made in the back tension of the optical fiber 4 during tape formation, the difference in tension and the difference in transmission time are approximately proportional within a predetermined range. On the other hand, the optical fiber 4 to which a large tension is applied by 20 g has a wire length shortened by about 0.02%, which shortens the transmission time by about 1 psec / m. When the refractive index of the optical fiber 4 is made different, the difference between the refractive index and the transmission time is proportional, and the relative refractive index difference Δn is 0.02% relative to the reference optical fiber 4. The optical fiber 4 having a large refractive index shortens the transmission time by about 1 psec / m.
[0038]
【Example】
In the optical cable having the cross-sectional structure shown in FIG. 4, a tape-shaped optical fiber core 2 having 12 cores of quartz single-mode optical fiber 4 having an outer diameter of 0.25 mm at a pitch of 0.25 mm is used. A prototype of a 0.5 m optical cable was manufactured. A first tape-shaped optical fiber core with a skew in the tape that compensates for a skew expected in advance by applying tension control at the time of tape formation, and a low skew is aimed at with the tape-shaped optical fiber core alone. The two tape-shaped optical fiber cores 2 prepared as described above were accommodated in an optical cable, and skew measurement was performed.
[0039]
FIG. 2 is a diagram showing the skew of the first optical fiber ribbon used in the present invention, and FIG. 2 (A) is a line showing the skew of the first optical fiber ribbon 2 alone. FIG. 2 (B) is a diagram showing the skew after conversion into a cable. In the figure, the abscissa indicates the core number of the optical fiber, and the ordinate indicates the skew (psec / m). I have.
[0040]
The first tape-shaped optical fiber is a specific example of the tape-shaped optical fiber used in the present invention. As shown in FIG. 2 (A), before conversion into a cable, the core numbers 5 and 6 of the optical fiber wires have the slowest transmission time and the above-mentioned 1 × 10⁵× (Xi / L)²It is designed so that skew based on the difference of the spiral radius of [psec / m] can be almost compensated. Before the cable conversion, the skew was the largest between the optical fiber strand of core number 5 and the optical fiber strands of core numbers 2 and 12, being 0.94 [psec / m]. As shown in FIG. 2 (B), the skew is the largest between the core numbers 5 and 10 and the optical fiber of the core number 2 due to the use of the cable, but the skew amount is 0.54. [Psec / m].
[0041]
FIG. 3 is a diagram showing the skew of a second conventionally used optical fiber ribbon, and FIG. 3 (A) shows the skew of the second optical fiber ribbon 2 alone. FIG. 3B is a diagram illustrating the amount of skew after cable conversion. The horizontal axis and the vertical axis are the same as in FIG.
[0042]
The second optical fiber ribbon is a specific example of the conventional optical fiber ribbon. As shown in FIG. 3A, before the cable is formed, the transmission time difference of the optical fiber 4 is designed to be substantially compensated, and the skew amount is determined by the core numbers 9 and 3,5. The largest value was 0.47 [psec / m]. As shown in FIG. 3B, the transmission time of the optical fiber at the center is shortened by the use of the cable, and the skew amount between the core number 1 and the core number 5 is 0.89 [psec]. / M].
[0043]
【The invention's effect】
As is apparent from the above description, according to the first aspect of the present invention, in an optical cable in which a tape-shaped optical fiber having a plurality of optical fibers is spirally accommodated, In the state where the optical fibers are not accommodated in the optical cable, each of the optical fibers barely compensates for a difference in optical path length due to a difference in the helical radius of each optical fiber. Since there is a time difference, there is an effect that the skew of the optical fiber in the tape-shaped optical fiber core spirally housed in the optical cable can be reduced. In addition, the tape-shaped optical fiber is a silica-based optical fiber, and the helical pitch of the tape-shaped optical fiber is L, and the i-th optical fiber is a tape-shaped optical fiber. When the distance from the center of the core wire is Xi, the transmission time difference Y of the plurality of optical fiber strands when the tape-shaped optical fiber core wire is not accommodated in the optical cable is (Xi / L). By expressing as a parameter,
Y [psec / m] = α (Xi / L)^Two
Α when this approximation is approximated by the least squares method is 0.5 × 10^Five[Psec / m] or more, 1.5 × 10^Five[Psec / m^Five] The range is as follows. The value of the coefficient α is 0.5 × 10^FiveIf it is less than [psec / m], the effect of skew compensation is weak, and 1.5 × 10^FiveIf the coefficient exceeds [psec / m], excessive compensation will occur. Therefore, if the value of the coefficient is in the above-mentioned range, there is an effect that practically sufficient skew compensation effect is obtained.
[0044]
According to the invention described in claim 2, when the distance between the centers of the optical fiber strands located at both ends of the tape-shaped optical fiber is W, and the helical pitch of the tape-shaped optical fiber is L, the tape The value of W / L of the optical fiber ribbon is 3.5 × 10^-3As described above, the skew due to the cable connection reaches 0.3 [psec / m] or more, and the skew amount is not negligible in practical use. Therefore, there is an effect that the skew compensation works effectively.
[0045]
According to the third aspect of the present invention, in the method for manufacturing an optical cable in which a tape-shaped optical fiber having a plurality of optical fibers is spirally accommodated, the optical fiber is used as the tape-shaped optical fiber. Each of the wires has a transmission time difference that almost compensates for the difference in the optical path length due to the difference in the helical radius of each optical fiber in a state where the tape-shaped optical fiber core is not accommodated in the optical cable. Since the optical fiber is accommodated in the optical cable, there is an effect that it is possible to obtain an optical cable that reduces skew in the tape-shaped optical fiber in a state of being spirally accommodated in the optical cable. In addition, the tape-shaped optical fiber is a silica-based optical fiber, and the helical pitch of the tape-shaped optical fiber is L, and the i-th optical fiber is a tape-shaped optical fiber. When the distance from the center of the core wire is Xi, the transmission time difference Y of the plurality of optical fiber strands when the tape-shaped optical fiber core wire is not accommodated in the optical cable is (Xi / L). By expressing as a parameter,
Y [psec / m] = α (Xi / L)^Two
Α when this approximation is approximated by the least squares method is 0.5 × 10^Five[Psec / m] or more, 1.5 × 10^Five[Psec / m^FiveSince the following range is used, an optical cable having a practical skew compensation effect can be obtained.
[0046]
According to the fourth aspect of the present invention, when the optical fiber is made into a tape, the tension applied to the optical fiber is made different, so that the tape-shaped optical fiber is not accommodated in the optical cable. In addition, there is an effect that the optical fiber strand can easily have an optical path length difference.
[0047]
According to the fifth aspect of the present invention, since the plurality of optical fibers are optical fibers having a difference in the refractive index of the optical fiber core, the tape-shaped optical fiber is accommodated in the optical cable. First, there is an effect that the optical fiber strand can easily have an optical path length difference.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a skew in a tape-shaped optical fiber core housed in an optical cable of the present invention.
FIG. 2 is a diagram showing a skew of a first tape-shaped optical fiber core wire used in the present invention, and FIG. 2 (A) is a line showing a skew of the first tape-shaped optical fiber core wire 2 alone; FIG. 2 (B) is a diagram showing the skew after conversion into a cable.
FIG. 3 is a diagram showing a skew of a conventionally used second tape-shaped optical fiber core, and FIG. 3 (A) is a skew amount of the second tape-shaped optical fiber core 2 alone; FIG. 3B is a diagram illustrating a skew amount after the cable is formed.
4A and 4B are explanatory views of an optical cable having a slot structure accommodating a tape-shaped optical fiber core. FIG. 4A is a schematic cross-sectional view of the optical cable, and FIG. It is sectional drawing.
5 is a perspective view of the slot rod shown in FIG. 4, wherein FIG. 5 (A) shows an example of an S-twisted slot rod, and FIG. 5 (B) shows an example of an SZ-twisted slot rod.
FIG. 6 is a schematic sectional view of an optical cable having a loose tube structure accommodating a tape-shaped optical fiber core.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Slot rod, 1a ... Center tensile strength member, 2 ... Tape-shaped optical fiber core wire, 3 ... Sheath, 4 ... Optical fiber wire, 11 ... Tube, 12 ... Sheath.

Claims (5)

An optical cable in which a tape-shaped optical fiber having a plurality of optical fiber strands is spirally accommodated, wherein each of the tape-shaped optical fiber strands is the tape-shaped optical fiber. In an optical cable having a transmission time difference substantially compensating for a difference in optical path length due to a difference in a helical radius of each optical fiber in a state where a fiber core is not accommodated in the optical cable, the tape-shaped optical fiber core In the line, the optical fiber is a silica-based optical fiber, the helical pitch of the tape-shaped optical fiber is L, the center of the tape-shaped optical fiber of the i-th optical fiber. When the distance from Xi is Xi, the transmission time difference Y of the plurality of optical fiber strands in a state where the tape-shaped optical fiber core is not accommodated in the optical cable is Expressed xi / L) as parameters,
Y [psec / m] = α (Xi / L) ²
And the α when the approximation is approximated by the least squares method is in a range of 0.5 × 10 ⁵ [psec / m ⁵ ] or more and 1.5 × 10 ⁵ [psec / m ⁵ ] or less. Optical cable characterized by the following. When the distance between the centers of the optical fiber strands located at both ends of the tape-shaped optical fiber core is W and the spiral pitch of the tape-shaped optical fiber core is L, W / 2. The optical cable according to claim 1, wherein the value of L is 3.5 × 10 ⁻³ or more. A method for manufacturing an optical cable that spirally accommodates a tape-shaped optical fiber having a plurality of optical fiber strands, wherein each of the optical fiber strands is the tape-shaped optical fiber strand. In a state in which the optical fibers are not accommodated in the optical cable, a tape-shaped optical fiber having a transmission time difference that substantially compensates for the difference in the optical path length due to the difference in the helical radius of each optical fiber is used. In the method for manufacturing an optical cable housed in the optical cable, the tape-shaped optical fiber core wire is a silica-based optical fiber wire, and the helical pitch of the tape-shaped optical fiber core wire is When the distance from the center of the tape-shaped optical fiber core to the optical fiber strand at the L-th and i-th cores is Xi, the tape-shaped optical fiber core is the optical cable. Expressed said transmission time difference Y of the plurality center of the optical fiber in a state that is not accommodated in Le a (Xi / L) as a parameter,
Y [psec / m] = α (Xi / L) ²
And the α when the approximation is approximated by the least squares method is in a range of 0.5 × 10 ⁵ [psec / m ⁵ ] or more and 1.5 × 10 ⁵ [psec / m ⁵ ] or less. A method for manufacturing an optical cable, comprising: The method for manufacturing an optical cable according to claim 3, wherein when the optical fiber is formed into a tape, a difference is provided in tension applied to the optical fiber. The method according to claim 3, wherein an optical fiber having a difference in refractive index of an optical fiber core is used as the plurality of optical fibers.

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