JP3983597B2 - Optical fiber manufacturing method - Google Patents

Description

【００１６】
ここで、Ｖ₀はこの振動モードにおける伝搬速度であり、これは、下記式（２）により求められる。また、ｎ＝１，２，３，…である。
【００１７】
【数２】

【００１８】
式（２）中、Ｔは光ファイバ素線３に働く張力［Ｎ］であり、ρは光ファイバ素線３の線密度［ｋｇ／ｍ］である。
【００１９】
式（１）と式（２）から、固有振動数ν_0,nは下記式（３）により求めることができる。
【００２０】
【数３】

【００２１】
次に、光ファイバ素線３の移動速度（紡糸線速）の影響を有する振動モードについて考察する。ねじり装置１６から発せられた振動のうち、線引き方向に対して反対方向に進行するものは、第２の被覆装置１４において反射し、再びねじり装置１６の方向に伝搬する。
従って、光ファイバ素線３の紡糸線速をＶ_f［ｍ／ｓ］とすると、ねじり装置１６から第２の被覆装置１４に至る方向に伝搬する振動の伝搬速度Ｖ₁は、Ｖ₁＝Ｖ₀−Ｖ_fで表され、また、第２の被覆装置１４からねじり装置１６に至る方向に伝搬する振動の伝搬速度Ｖ₂は、Ｖ₂＝Ｖ₀＋Ｖ_fで表される。
【００２２】
これらの振動の固有振動数ν_1,nおよびν_2,nは、それぞれ、下記式（４）および式（５）により表現される。
【００２３】
【数４】

【００２４】
【数５】

【００２５】
従って、本実施の形態においては、上述のようにして求められた３種類の振動モードに対応する固有振動数ν_0,n、ν_1,nおよびν_2,nを、これらのｎ倍振動を含めて考慮し、これらのいずれに対しても、ねじり装置１６の振動数と、光ファイバ素線が共振しないだけの差を生じさせる。
ねじり装置１６の振動数と光ファイバ素線３の固有振動数の差としては、０．２Ｈｚ以上とすることが好ましい。
【００２６】
ねじり装置１６が発生する振動数と光ファイバ素線３の固有振動数を一致させないための方法としては、例えば、ねじり装置１６の振動数を可能な範囲で変更してずらす方法が可能である。
ここで、ねじり装置１６の振動数について、ねじり装置１６の具体的な構成例を参照しながら説明する。
【００２７】
図２に、ねじり装置１６の第１例の概略構成を示す。同図に示す装置は、鉛直方向に線引きされている光ファイバ素線３を側方から押圧する押圧ローラ１０１と、この押圧ローラ１０１の上流側に位置する上流ローラ１０２、および、下流側に位置する下流ローラ１０３とを有している。
【００２８】
押圧ローラ１０１の円周面は、光ファイバ素線３の経路を、鉛直方向に垂直かつ押圧ローラ１０１の軸方向に垂直な方向に、所定の変位にて撓ませるようになっている。また、押圧ローラ１０１は、ベアリング１０４、１０４に支持されたシャフト１０５を軸として回転可能なヨーク１０６に取り付けられており、これにより、押圧ローラ１０１は、シャフト１０５を軸として揺動するようになっている。
【００２９】
また、押圧ローラ１０１を揺動させる動力として、モータ１０７が設けられており、このモータ１０７の動力は、クランク１０８および接続ロッド１０９を介してヨーク１０６に伝達され、これにより、押圧ローラ１０１は、クランク１０８の回転に同期して揺動するようになっている。
【００３０】
上流ローラ１０２および下流ローラ１０３は、製造装置の壁面１１０に固定されており、かつその位置は、上流ローラ１０２の上流および下流ローラ１０３の下流で、光ファイバ素線３の経路が鉛直になるような位置とされており、これにより、光ファイバ素線３が押圧ローラ１０１により押圧されても円滑に線引きされるように、光ファイバ素線３の経路を規制している。
このようなねじり装置１６においては、その転動の振動数は、クランク１０８の回転数に等しい。
【００３１】
図３は、ねじり装置１６の第２例を示す斜視図である。同図に示す装置は、一対の第１のローラ２０１ａと第２のローラ２０１ｂとを備えている。これらのローラ２０１ａ、２０１ｂは、光ファイバ素線３が該ローラ２０１ａ、２０１ｂの周曲面に接するように走行し、かつこれらの間で押圧されるように構成されている。
【００３２】
第１のローラ２０１ａは、第１の要素キャリッジ２０２ａの上に取り付けられており、そしてこの第１の要素キャリッジ２０２ａは、第１の取り付け台２０３ａの上に配置されている。
同様に、第２のローラ２０１ｂは、第２の要素キャリッジ２０２ｂの上に取り付けられており、そしてこの第２の要素キャリッジ２０２ｂは、第２の取り付け台２０３ｂの上に配置されている。
【００３３】
第１および第２の要素キャリッジ２０２ａ、２０２ｂは、それぞれ第１および第２の取り付け台２０３ａ、２０３ｂの上をスライド可能とされている。
第１の要素キャリッジ２０２ａは、バネ２０４により光ファイバ素線３を押圧する方向に付勢されており、かつ、止め具２０５により、光ファイバ素線３を押圧する変位量が所定の量を超えないように、移動を制限されている。
また、第２の要素キャリッジ２０２ｂは、マイクロ調整装置２０６により、第２の取り付け台２０３ｂ上における位置を調整可能である。これらの機構を用いることにより、この例のねじり装置では、第１および第２のローラ２０１ａ、２０１ｂの間隔を調整することができるようになっている。
【００３４】
さらに、このねじり装置には、線形アクチュエータ等の揺動駆動装置２１０が取り付けられている。これにより、光ファイバ素線３が線引される方向に対して垂直かつ第１の取り付け台２０３ａが光ファイバ素線３を押圧する方向に対して垂直に、第１の取り付け台２０３ａを揺動することができるようになっている。
第１の取り付け台２０３ａは、第１のピンジョイント接続ロッド２１１ａを介してピボットリンク２１２の一端に接続されており、また、第２の取り付け台２０３ｂは、第２のピンジョイント接続ロッド２１１ｂを介して前記ピボットリンク２１２の他端に接続されている。このピボットリンク２１２は、ねじり装置の壁面２１３に固定されたピボット２１４を中心にして回動可能となっている。
これにより、第２の取り付け台２０３ｂは、第１の取り付け台２０３ａの揺揺方向に対して反対の方向に揺動されられるようになっている。
【００３５】
このねじり装置においては、上述のように、第１の取り付け台２０３ａと第２の取り付け台２０３ｂとが振動すると、それらの上に配設されている第１および第２のローラ２０１ａ、２０１ｂも振動するようになっており、これにより、光ファイバ素線３にねじれを付与することができる。
このようなねじり装置においては、その振動数は、揺動駆動装置２１０の振動数に等しい。
【００３６】
図４は、ねじり装置１６の第３例を示す斜視図である。同図に示す装置は、一対の第１のローラ３０１ａと第２のローラ３０１ｂとを備えている。第１のローラ３０１ａは、第１のヨーク３０２ａに取り付けられており、第２のローラ３０１ｂは、第２のヨーク３０２ｂに取り付けられている。これらのローラ３０１ａ、３０１ｂは、それぞれ、第１または第２のヨーク３０２ａ、３０２ｂに対して相対的に決められる所定の回転軸を中心に回転可能であり、これにより、該ローラ３０１ａ、３０１ｂの間を走行する光ファイバ素線３を押圧することができるようになっている。
【００３７】
これらのヨーク３０２ａ、３０２ｂは、紙面に垂直な揺動軸３０３を中心として揺動できるように、ねじり装置の壁面（図示せず）上に取り付けられている。また、第１のヨーク３０２ａは、第１のピンジョイント接続ロッド３０４ａを介してリンク３０５の一端に接続されており、また、第２のヨーク３０２ｂは、第２のピンジョイント接続ロッド３０４を介して前記リンク３０５の他端に接続されている。このリンク３０５は、駆動装置３０６により、上下に往復運動しうるように構成されている。
【００３８】
駆動装置３０６により、リンク３０５が往復運動すると、第１および第２のヨーク３０２ａ、３０２ｂは、揺動軸３０３を中心として揺動し、これにより、第１および第２のローラ３０１ａ、３０１ｂを介して光ファイバ素線３にねじれを付与することができるようになっている。
このようなねじり装置においては、その振動数は、駆動装置３０６の振動数に等しい。
【００３９】
本発明に用いられるねじり装置１６の構成は上述の例のものに制限されるものではないが、一般に、ねじり装置１６には、往復運動、揺動運動等、周期的な動力を与える動力源が設けられている。このため、この運動の振動数を、ねじり装置１６が発生する振動の振動数とみなすことができる。
従って、この運動の振動数を適宜変更することにより、光ファイバ素線３の共振を抑制することができる。
【００４０】
しかし、一般に、ねじり装置１６の振動数を変更する際には、以下の２点に注意する必要がある。
（１） 光ファイバのＰＭＤを低減させるためには、光ファイバを所定の長さごとに一回ねじる必要がある。また、一般に、紡糸線速が速いほど、所要のねじり装置１６の振動数（下限値）は大きくなる。ねじり装置１６の振動数が上記下限値より小さいと、光ファイバのＰＭＤを十分に低減させることができない。
（２） ねじり装置１６の振動数を過度に大きくすると、被覆装置１２、１４において光ファイバと被覆用の樹脂との界面が乱されやすくなり、被覆不良が発生しやすくなる。
【００４１】
従って、ねじり装置１６の振動数を変更しにくい事情がある場合には、光ファイバ素線３の紡糸線速や紡糸張力、ねじり装置１６と第２の被覆装置１４との間隔などの条件を変更し、光ファイバ素線３の固有振動数を変化させることにより、両振動数に十分な差が付くようにしてもよい。
例えば、ねじり装置１６と第２の被覆装置１４のいずれか一方もしくは両方を、光ファイバ素線３の走行方向に沿って移動可能とし、ねじり装置１６と第２の被覆装置１４との間隔を変更できるようにした装置を用いることにより、第２の被覆装置１４とねじり装置１６との間で走行する光ファイバ素線３の固有振動数を容易に変更することができる。
もちろん、ねじり装置１６の振動数と、光ファイバ素線３の固有振動数の両方を適切に変更することによっても、共振現象を抑制することができる。
【００４２】
【実施例】
（実施例１）
図１に示す装置を用い、第１の被覆装置１２および第２の被覆装置１４にウレタンアクリレート系紫外線硬化型樹脂を供給しながら、光ファイバ母材１を紡糸炉１０中加熱して、外径１２５ミクロンの光ファイバ裸線２を線引きし、さらにこの外周上に一次被覆および二次被覆を順次形成して被覆径２５０μｍの光ファイバ裸線２を製造した。この光ファイバ裸線２の線密度ρは約０．００７ｋｇ／ｍである。また、紡糸線速Ｖ_fは３００ｍ／分とし、紡糸張力Ｔは１００ｇｆとした。
【００４３】
光ファイバ裸線２を線引きする際、ねじり装置１６として、図２に示す装置を用いて所定の条件でねじれを付与した。この条件では、ＰＭＤを十分に低減させるためには、１２０回／分以上の振動とする必要がある。ねじり装置１６と第２の被覆装置１４との間隔は３ｍであるので、ねじり装置１６と第２の被覆装置１４の間に張られている光ファイバ素線３の固有振動数は、基底振動（ｎ＝１）に対して求めると、それぞれν_0,1＝２.０Ｈｚ、ν_1,1＝１.１Ｈｚ、ν_2,1＝２.８Ｈｚであり、毎分に換算するとそれぞれ１１８、６８、１６８回／分である。同様に、２倍振動（ｎ＝２）の振動数を算出すると、それぞれ２３７、１３７、３３７回／分である。
【００４４】
ねじり装置１６の振動数を１３０回／分、１５０回／分、または１９０回／分等とした場合、目立った振動は発生しなかった。これに対して、ねじり装置１６の振動数を１２０、１４０、１７０回／分の場合、光ファイバ素線３と共振し、光ファイバ素線３の振動が極めて大きくなった。
以上の結果を基に、また、ねじり装置１６の振動数を不必要に高くすると被覆不良が発生しやすくなることを踏まえ、ねじり装置１６の振動数を１３０回／分として光ファイバを製造したところ、品質の優れた光ファイバを問題なく製造することができた。
【００４５】
（実施例２）
紡糸線速Ｖ_fを６００ｍ／分とし、紡糸張力Ｔを１５０ｇｆとし、ねじり装置１６として、図３に示す装置を用いることを除いて、実施例１と同様の紡糸条件を用いて、光ファイバを製造した。
この条件では、ＰＭＤを十分に低減させるためには、２５０回／分以上の振動とする必要がある。ねじり装置１６と第２の被覆装置１４との間隔を３ｍとすると、ねじり装置１６と第２の被覆装置１４の間に張られている光ファイバ素線３の固有振動数は、基底振動（ｎ＝１）に対して、それぞれν_0,1＝２．４Ｈｚ、ν_1,1＝０．７Ｈｚ、ν_2,1＝４．１Ｈｚであり、毎分に換算するとそれぞれ１４５、４５、２４５回／分である。同様に、２倍振動（ｎ＝２）の振動数を算出すると、それぞれ２９０、９０、４９０回／分である。
【００４６】
ねじり装置１６の振動数を２５０回／分と決めてあるため、この条件では、ねじり装置１６の振動が光ファイバと共振してしまう。そこで、ねじり装置１６と第２の被覆装置１４との間隔を３．２ｍとすると、ねじり装置１６と第２の被覆装置１４の間に張られている光ファイバ素線３の固有振動数は、基底振動に対して、それぞれν_0,1＝２．３Ｈｚ、ν_1,1＝０．７Ｈｚ、ν_2,1＝３．８Ｈｚであり、毎分に換算するとそれぞれ１３６、４２、２３０回／分である。同様に、２倍振動の振動数を算出すると、それぞれ２７２、８４、４５９回／分である。これにより、ねじり装置１６の振動数を２５０回／分としても、光ファイバ素線との共振を防止でき、線引き中の光ファイバ素線３が線ぶれすることなく、品質の優れた光ファイバを問題なく製造することができた。
【００４７】
（実施例３）
紡糸線速Ｖ_fを１０００ｍ／分とし、紡糸張力Ｔを１９０ｇｆとし、ねじり装置１６として、図４に示す装置を用いること以外は、実施例１と同様の紡糸条件を用いて、光ファイバを製造した。
この条件では、ＰＭＤを十分に低減させるためには、３５０回／分以上の振動とする必要がある。ねじり装置１６と第２の被覆装置１４との間隔を３ｍとすると、ねじり装置１６と第２の被覆装置１４の間に張られている光ファイバ素線３の固有振動数は、基底振動（ｎ＝１）に対して、それぞれν_0,1＝２．７Ｈｚ、ν_1,1＝０．０Ｈｚ、ν_2,1＝５．５Ｈｚである。
【００４８】
ねじり装置１６から第２の被覆装置１４へ向かう振動の振動数ν_1,0がほぼ０であるので、この振動の速度と紡糸線速とがほとんど拮抗し、波動として伝搬していかない。このため、第２の被覆装置１４からねじり装置１６に向かう反射波もなくなる。従って、この条件で観測される振動は、ν_0,1の振動（固有振動数は２．７Ｈｚ、すなわち１６３回／分）およびそのｎ倍振動（ν_0,n）のみであるので、ねじり装置１６の振動数を３５０回／分として製造したところ、光ファイバ素線３との共振を防止でき、線引き中の光ファイバ素線３が線ぶれすることなく、品質の優れた光ファイバを問題なく製造することができた。
【００４９】
【発明の効果】
以上説明したように、本発明の光ファイバの製造方法によれば、光ファイバ素線にねじれを付与しても、ねじり装置の振動に光ファイバ素線が共振することを効果的に防止することができる。従って、光ファイバ素線が線ぶれしにくくなり、その外径を正確に測定することができ、生産管理を容易にする。また、光ファイバ素線の被覆厚が不均一になることを抑制し、歩留まりを向上することができる。
【図面の簡単な説明】
【図１】 光ファイバの製造装置の一例を示す概略図である。
【図２】 本発明の光ファイバの製造方法において用いられるねじり装置の第１例の概略構成を示す斜視図である。
【図３】 本発明の光ファイバの製造方法において用いられるねじり装置の第２例の概略構成を示す斜視図である。
【図４】 本発明の光ファイバの製造方法において用いられるねじり装置の第３例の概略構成を示す側面図である。
【符号の説明】
１…光ファイバ母材、２…光ファイバ裸線、３…光ファイバ素線、１０…紡糸炉、１２…第１の被覆装置、１４…第２の被覆装置、１６…ねじり装置。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a twisted optical fiber in order to suppress polarization mode dispersion.
[0002]
[Prior art]
Conventionally, in order to reduce the polarization mode dispersion (PMD) of an optical fiber such as a single mode optical fiber, a method of imparting twist to the optical fiber when manufacturing the optical fiber is known.
As a method for imparting twist to an optical fiber, for example, after cooling an optical fiber bare wire melt-spun from an optical fiber base material, coating it to form an optical fiber strand, and then using a roller or the like, A method of rolling a line so that the movement in the horizontal direction is periodically reversed is known (for example, refer to Japanese Patent Publication No. 10-507438 and Japanese Patent No. 3224235).
[0003]
Conventionally, a manufacturing apparatus and a manufacturing method for imparting twist to an optical fiber will be described with reference to FIG.
In the figure, reference numeral 1 denotes an optical fiber preform. The optical fiber preform 1 is heated in the spinning furnace 10 and drawn to become a bare optical fiber 2. The drawn optical fiber bare wire 2 is sent to the cooling cylinder 11 and cooled, and then the primary coating resin is applied by the first coating device 12, and then the inside of the first bridging cylinder 13. The primary coating can be provided by curing the primary coating resin. Further, after the secondary coating resin is applied by the second coating device 14, the secondary coating resin is cured by curing the secondary coating resin in the second cross-linking cylinder 15, and the optical fiber strand is provided. 3
[0004]
The optical fiber 3 is twisted by the twisting device 16. The twisting device 16 generally includes a roller, a wheel, and the like. While the optical fiber 3 is pressed by the roller or the like, the rotation direction of the roller or the like is periodically reversed, and the like. This is a device that applies a clockwise or counterclockwise torque to the line 3 with respect to the longitudinal direction periodically.
[0005]
Thus, the torque applied to the optical fiber 3 propagates back to the bare optical fiber 2 before being cooled by the cooling cylinder 11, and the bare optical fiber 2 is still soft and is not twisted. Is granted. The bare optical fiber 2 to which the twist is applied in this way is cooled while being twisted, and then coated to form the optical fiber 3. The optical fiber 3 is taken up by a take-up machine 18 through a turn pulley 17, screened by a dancer 19, and then taken up by a winder 20.
[0006]
[Problems to be solved by the invention]
However, in the conventional manufacturing method, when the optical fiber strand 3 is twisted, the optical fiber strand 3 may vibrate greatly (straight line). In this case, in order to inspect the outer diameter of the optical fiber 3 being manufactured, when measuring the outer diameter of the optical fiber 3 using a non-contact type outer diameter measuring device, the measured value is inaccurate. This is a problem in production management. Further, if the vibration of the optical fiber 3 becomes too large, the coating thickness of the resin applied by the first coating device 12 or the second coating device 14 is adversely affected, and the coating thickness becomes non-uniform, There is a possibility that the coating is eccentric (uneven thickness).
[0007]
Therefore, the object of the present invention is to accurately measure the outer diameter of the optical fiber even when twisting the optical fiber in the manufacturing process of the optical fiber, and to make the coating uniform. An object of the present invention is to provide a method of manufacturing an optical fiber that can be provided.
[0008]
[Means for Solving the Problems]
As a result of intensive studies by the present inventors, the vibration of the optical fiber is generated along with the rolling that imparts torsion to the optical fiber, and the frequency of the rolling is applied to the manufacturing apparatus. The present inventors have found that the above-mentioned problem has occurred because a resonance phenomenon has occurred when the natural frequency of the optical fiber is equal to or very close to the natural frequency.
[0009]
That is, the optical fiber manufacturing method of the present invention for solving the above-described problems is such that the first coating apparatus applies the primary coating resin to the running optical fiber bare wire obtained by melt spinning the optical fiber preform. After providing the primary coating, the secondary coating resin is applied by the second coating device to provide the secondary coating to obtain an optical fiber strand, and this optical fiber strand is periodically rotated by the twisting device. A method of manufacturing an optical fiber that is twisted by being moved , wherein after calculating the natural frequency of the optical fiber, the frequency of the twisting device or the distance between the twisting device and the second coating device by changing the a frequency of the rolling of imparting the twist, between the natural frequency of the optical fiber, the optical fiber with the rolling was shown to occur a difference in not only resonate manufacturing in the state And it is characterized in and.
[0010]
In the above-described optical fiber manufacturing method, the natural frequency of the optical fiber is L [m] between the twisting device and the second coating device, and T [N] is the tension acting on the optical fiber. ], The linear density of the optical fiber is ρ [kg / m], the spinning speed of the optical fiber is V _f [m / s], and V ₀ = √ (T / ρ), V ₁ = V ₀ When −V _f , V ₂ = V ₀ + V _f , the natural frequency of the n-fold vibration (where n = 1, 2, 3,...)
ν _{o, n} = (n / 2L) V ₀ ,
ν _{1, n} = (n / 2L) V ₁ ,
ν _{2, n} = (n / 2L) V ₂ ,
As
The difference between each of these ν _{o, n} , ν _{1, n} and ν _{2, n so} that the optical fiber does not resonate with the rolling with the frequency of the rolling imparting the torsion. It is preferable to manufacture in the state which produced.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on embodiments.
For example, when an optical fiber is manufactured using the apparatus shown in FIG. 1, the optical fiber 3 is prevented from moving in the direction perpendicular to the longitudinal direction at various points in the manufacturing apparatus. It may vibrate as a string with both ends of the position fixed. Among the positions that become the fixed ends, the location that causes the fiber shake of the optical fiber 3 is a location where the lateral vibration of the optical fiber 3 is suppressed immediately above the twisting device 16. In the case of the apparatus shown in FIG. 1, it is the position of the second coating apparatus 14.
[0012]
Therefore, whether the natural frequency of the optical fiber 3 stretched between the twisting device 16 and the second coating device 14 matches the rolling frequency of the twisting device 16 or is very close to it. Then, the optical fiber 3 may resonate with the rolling of the twisting device 16. Then, the vibration amplitude of the optical fiber 3 becomes extremely large, and there is a possibility that an error in measuring the outer diameter increases or a coating defect occurs.
[0013]
Therefore, if a difference is generated between the rolling frequency imparting the twist and the natural frequency of the optical fiber 3 so that the optical fiber does not resonate with the rolling, the resonance will occur. Since the phenomenon can be effectively prevented, the outer diameter of the optical fiber can be accurately measured, and the coating can be provided uniformly.
[0014]
Next, a method for obtaining the natural frequency of the optical fiber 3 will be described.
First, considering a vibration mode that is not affected by the moving speed (spinning speed) of the optical fiber 3, this vibration can be considered as a vibration of a string of length L [m] with both ends fixed. . As this length L, it can be set as the space | interval of the twist apparatus 16 and the 2nd coating | coated apparatus 14, for example. In this case, the natural frequency ν _{0, n} of this vibration mode is expressed by the following equation (1).
[0015]
[Expression 1]

[0016]
Here, V ₀ is a propagation speed in this vibration mode, and this is obtained by the following equation (2). In addition, n = 1, 2, 3,.
[0017]
[Expression 2]

[0018]
In formula (2), T is the tension [N] acting on the optical fiber 3, and ρ is the linear density [kg / m] of the optical fiber 3.
[0019]
From the equations (1) and (2), the natural frequency ν _{0, n} can be obtained by the following equation (3).
[0020]
[Equation 3]

[0021]
Next, the vibration mode having the influence of the moving speed (spinning speed) of the optical fiber 3 will be considered. Of the vibrations emitted from the twisting device 16, those that travel in the direction opposite to the drawing direction are reflected by the second coating device 14 and propagate again in the direction of the twisting device 16.
Accordingly, if the spinning speed of the optical fiber 3 is V _f [m / s], the propagation speed V ₁ of the vibration propagating in the direction from the twisting device 16 to the second coating device 14 is V ₁ = V. ₀ is represented by -V _f, also the propagation velocity V ₂ of the vibration propagating in a direction leading to the second coating device 14 from the twisting device 16 is represented by _{V 2 = V 0 + V f} .
[0022]
The natural frequencies ν _{1, n} and ν _{2, n} of these vibrations are expressed by the following equations (4) and (5), respectively.
[0023]
[Expression 4]

[0024]
[Equation 5]

[0025]
Therefore, in the present embodiment, the natural frequencies ν _{0, n} , ν _{1, n} and ν _{2, n} corresponding to the three types of vibration modes obtained as described above are represented by these n-fold vibrations. In consideration of all of these, the frequency of the twisting device 16 and a difference that does not cause the optical fiber to resonate are caused for any of these.
The difference between the frequency of the twisting device 16 and the natural frequency of the optical fiber 3 is preferably 0.2 Hz or more.
[0026]
As a method for making the frequency generated by the twisting device 16 and the natural frequency of the optical fiber 3 not coincide with each other, for example, a method of changing and shifting the frequency of the twisting device 16 within a possible range is possible.
Here, the frequency of the twisting device 16 will be described with reference to a specific configuration example of the twisting device 16.
[0027]
FIG. 2 shows a schematic configuration of a first example of the twisting device 16. The apparatus shown in the figure includes a pressing roller 101 that presses the optical fiber 3 drawn in the vertical direction from the side, an upstream roller 102 that is positioned upstream of the pressing roller 101, and a position that is positioned downstream. And a downstream roller 103.
[0028]
The circumferential surface of the pressure roller 101 bends the path of the optical fiber 3 with a predetermined displacement in a direction perpendicular to the vertical direction and perpendicular to the axial direction of the pressure roller 101. Further, the pressing roller 101 is attached to a yoke 106 that can rotate about a shaft 105 supported by bearings 104 and 104, whereby the pressing roller 101 swings about the shaft 105. ing.
[0029]
Further, a motor 107 is provided as a power for swinging the pressing roller 101, and the power of the motor 107 is transmitted to the yoke 106 via the crank 108 and the connecting rod 109, whereby the pressing roller 101 is It swings in synchronization with the rotation of the crank 108.
[0030]
The upstream roller 102 and the downstream roller 103 are fixed to the wall surface 110 of the manufacturing apparatus, and the positions thereof are upstream of the upstream roller 102 and downstream of the downstream roller 103 so that the path of the optical fiber strand 3 is vertical. Accordingly, the path of the optical fiber 3 is regulated so that the optical fiber 3 is smoothly drawn even if the optical fiber 3 is pressed by the pressing roller 101.
In such a twisting device 16, the rolling vibration frequency is equal to the rotation speed of the crank 108.
[0031]
FIG. 3 is a perspective view showing a second example of the twisting device 16. The apparatus shown in the figure includes a pair of first roller 201a and second roller 201b. These rollers 201a and 201b are configured so that the optical fiber 3 travels in contact with the peripheral curved surfaces of the rollers 201a and 201b and is pressed between them.
[0032]
The first roller 201a is mounted on the first element carriage 202a, and the first element carriage 202a is disposed on the first mounting base 203a.
Similarly, the second roller 201b is mounted on the second element carriage 202b, and the second element carriage 202b is disposed on the second mounting base 203b.
[0033]
The first and second element carriages 202a and 202b are slidable on the first and second mounting bases 203a and 203b, respectively.
The first element carriage 202a is biased in the direction of pressing the optical fiber 3 by the spring 204, and the displacement amount of pressing the optical fiber 3 by the stopper 205 exceeds a predetermined amount. The movement is restricted so that there is no.
Further, the position of the second element carriage 202b on the second mounting base 203b can be adjusted by the micro adjustment device 206. By using these mechanisms, the twisting device of this example can adjust the distance between the first and second rollers 201a and 201b.
[0034]
Further, a swing drive device 210 such as a linear actuator is attached to the twisting device. As a result, the first mounting base 203a is swung perpendicularly to the direction in which the optical fiber strand 3 is drawn and perpendicular to the direction in which the first mounting base 203a presses the optical fiber strand 3. Can be done.
The first mounting base 203a is connected to one end of the pivot link 212 via the first pin joint connecting rod 211a, and the second mounting base 203b is connected via the second pin joint connecting rod 211b. And connected to the other end of the pivot link 212. The pivot link 212 is rotatable about a pivot 214 fixed to the wall surface 213 of the twisting device.
As a result, the second mounting base 203b is swung in a direction opposite to the swinging direction of the first mounting base 203a.
[0035]
In this twisting device, as described above, when the first mounting base 203a and the second mounting base 203b vibrate, the first and second rollers 201a and 201b disposed on them also vibrate. As a result, the optical fiber strand 3 can be twisted.
In such a twisting device, the frequency is equal to the frequency of the swing drive device 210.
[0036]
FIG. 4 is a perspective view showing a third example of the twisting device 16. The apparatus shown in the figure includes a pair of a first roller 301a and a second roller 301b. The first roller 301a is attached to the first yoke 302a, and the second roller 301b is attached to the second yoke 302b. These rollers 301a and 301b can rotate around a predetermined rotation axis determined relative to the first or second yoke 302a and 302b, respectively, and thereby, between the rollers 301a and 301b. It is possible to press the optical fiber 3 that travels along the line.
[0037]
These yokes 302a and 302b are mounted on a wall surface (not shown) of the twisting device so that the yokes 302a and 302b can swing around a swing shaft 303 perpendicular to the paper surface. The first yoke 302a is connected to one end of the link 305 via the first pin joint connecting rod 304a, and the second yoke 302b is connected via the second pin joint connecting rod 304. The other end of the link 305 is connected. The link 305 is configured to reciprocate up and down by a driving device 306.
[0038]
When the link 305 is reciprocated by the driving device 306, the first and second yokes 302a and 302b are swung around the swinging shaft 303, whereby the first and second rollers 301a and 301b are interposed. Thus, the optical fiber 3 can be twisted.
In such a twisting device, the frequency is equal to the frequency of the driving device 306.
[0039]
The configuration of the torsion device 16 used in the present invention is not limited to the above-described example, but in general, the torsion device 16 has a power source that applies periodic power such as reciprocating motion and swing motion. Is provided. For this reason, the frequency of this motion can be regarded as the frequency of the vibration generated by the twisting device 16.
Therefore, resonance of the optical fiber 3 can be suppressed by appropriately changing the frequency of the motion.
[0040]
However, generally, when changing the frequency of the twisting device 16, it is necessary to pay attention to the following two points.
(1) In order to reduce PMD of an optical fiber, it is necessary to twist the optical fiber once every predetermined length. In general, the higher the spinning line speed, the greater the required frequency (lower limit) of the twisting device 16. If the frequency of the twisting device 16 is smaller than the lower limit value, the PMD of the optical fiber cannot be sufficiently reduced.
(2) When the frequency of the twisting device 16 is excessively increased, the interface between the optical fiber and the coating resin is likely to be disturbed in the coating devices 12 and 14, and defective coating is likely to occur.
[0041]
Therefore, when there is a situation where it is difficult to change the frequency of the twisting device 16, the conditions such as the spinning speed and spinning tension of the optical fiber 3 and the interval between the twisting device 16 and the second coating device 14 are changed. Then, by changing the natural frequency of the optical fiber 3, a sufficient difference may be provided between the two frequencies.
For example, one or both of the twisting device 16 and the second coating device 14 can be moved along the traveling direction of the optical fiber 3, and the distance between the twisting device 16 and the second coating device 14 is changed. By using the device that can be used, the natural frequency of the optical fiber 3 traveling between the second coating device 14 and the twisting device 16 can be easily changed.
Of course, the resonance phenomenon can also be suppressed by appropriately changing both the frequency of the twisting device 16 and the natural frequency of the optical fiber 3.
[0042]
【Example】
Example 1
The optical fiber preform 1 is heated in the spinning furnace 10 while supplying the urethane acrylate ultraviolet curable resin to the first coating device 12 and the second coating device 14 using the apparatus shown in FIG. A bare optical fiber 2 of 125 microns was drawn, and a primary coating and a secondary coating were sequentially formed on the outer periphery to produce a bare optical fiber 2 having a coating diameter of 250 μm. The linear density ρ of the bare optical fiber 2 is about 0.007 kg / m. The spinning linear velocity _Vf was 300 m / min, and the spinning tension T was 100 gf.
[0043]
When the bare optical fiber 2 was drawn, the twisting device 16 was twisted under predetermined conditions using the device shown in FIG. Under this condition, in order to sufficiently reduce PMD, vibrations of 120 times / minute or more are required. Since the distance between the twisting device 16 and the second coating device 14 is 3 m, the natural frequency of the optical fiber 3 stretched between the twisting device 16 and the second coating device 14 is the base vibration ( n = 1), ν _0,1 = 2.0 Hz, ν _1,1 = 1.1 Hz, ν _2,1 = 2.8 Hz, respectively, 118, 68, 168 times / min. Similarly, the frequency of double vibration (n = 2) is calculated to be 237, 137, and 337 times / minute, respectively.
[0044]
When the frequency of the twisting device 16 was 130 times / minute, 150 times / minute, 190 times / minute, or the like, no noticeable vibration was generated. On the other hand, when the vibration frequency of the twisting device 16 is 120, 140, and 170 times / minute, it resonates with the optical fiber 3 and the vibration of the optical fiber 3 becomes extremely large.
On the basis of the above results, an optical fiber was manufactured by setting the frequency of the twisting device 16 to 130 times / minute in view of the fact that a coating defect is likely to occur if the frequency of the twisting device 16 is unnecessarily increased. We were able to produce an optical fiber with excellent quality without any problems.
[0045]
(Example 2)
The optical fiber was spun using the same spinning conditions as in Example 1 except that the spinning linear velocity _Vf was 600 m / min, the spinning tension T was 150 gf, and the twisting device 16 used was the device shown in FIG. Manufactured.
Under this condition, in order to sufficiently reduce PMD, vibrations of 250 times / minute or more are required. If the distance between the twisting device 16 and the second coating device 14 is 3 m, the natural frequency of the optical fiber 3 stretched between the twisting device 16 and the second coating device 14 is the base vibration (n = 1), ν _0,1 = 2.4 Hz, ν _1,1 = 0.7 Hz, and ν _2,1 = 4.1 Hz, respectively, converted to 145, 45, 245 times / minute respectively. Minutes. Similarly, the frequency of double vibration (n = 2) is calculated to be 290, 90, and 490 times / minute, respectively.
[0046]
Since the frequency of the twisting device 16 is determined to be 250 times / minute, the vibration of the twisting device 16 resonates with the optical fiber under this condition. Therefore, when the distance between the twisting device 16 and the second coating device 14 is 3.2 m, the natural frequency of the optical fiber 3 stretched between the twisting device 16 and the second coating device 14 is Ν _0,1 = 2.3 Hz, ν _1,1 = 0.7 Hz, and ν _2,1 = 3.8 Hz with respect to the base vibration, respectively, 136, 42, and 230 times / minute when converted to each minute It is. Similarly, the frequency of double vibration is calculated to be 272, 84, and 459 times / minute, respectively. As a result, even if the frequency of the twisting device 16 is 250 times / minute, resonance with the optical fiber strand can be prevented , and an optical fiber having excellent quality can be obtained without causing the optical fiber strand 3 being drawn to be shaken. It was possible to manufacture without problems.
[0047]
(Example 3)
An optical fiber is manufactured under the same spinning conditions as in Example 1, except that the spinning linear velocity V _f is 1000 m / min, the spinning tension T is 190 gf, and the twisting device 16 uses the device shown in FIG. did.
Under this condition, in order to sufficiently reduce PMD, vibrations of 350 times / minute or more are required. If the distance between the twisting device 16 and the second coating device 14 is 3 m, the natural frequency of the optical fiber 3 stretched between the twisting device 16 and the second coating device 14 is the base vibration (n = 1), ν _0,1 = 2.7 Hz, ν _1,1 = 0.0 Hz, and ν _2,1 = 5.5 Hz, respectively.
[0048]
Since the vibration frequency ν _1,0 from the twisting device 16 toward the second coating device 14 is substantially 0, the speed of this vibration and the spinning line speed almost antagonize and do not propagate as waves. For this reason, there is no reflected wave from the second coating device 14 toward the twisting device 16. Therefore, the vibrations observed under this condition are only the vibration of ν _0,1 (the natural frequency is 2.7 Hz, that is, 163 times / min) and its n-fold vibration (ν _{0, n} ). When the frequency of 16 was manufactured at 350 times / min, resonance with the optical fiber 3 could be prevented , and the optical fiber 3 being drawn was not shaken, and an excellent quality optical fiber could be obtained without problems. Could be manufactured.
[0049]
【The invention's effect】
As described above , according to the optical fiber manufacturing method of the present invention , even if a twist is applied to the optical fiber, the optical fiber is effectively prevented from resonating with the vibration of the twisting device. Can do. Therefore, the optical fiber strands are less likely to be shaken, and the outer diameter can be accurately measured, facilitating production management. Moreover, it is possible to suppress the coating thickness of the optical fiber strands from becoming non-uniform and improve the yield.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of an optical fiber manufacturing apparatus.
FIG. 2 is a perspective view showing a schematic configuration of a first example of a twisting apparatus used in the optical fiber manufacturing method of the present invention.
FIG. 3 is a perspective view showing a schematic configuration of a second example of the twisting apparatus used in the method for producing an optical fiber of the present invention.
FIG. 4 is a side view showing a schematic configuration of a third example of the twisting apparatus used in the method for producing an optical fiber of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Optical fiber preform, 2 ... Bare optical fiber, 3 ... Optical fiber strand, 10 ... Spinning furnace, 12 ... 1st coating apparatus, 14 ... 2nd coating apparatus, 16 ... Twist apparatus

Claims (2)

The primary coating resin is applied to the bare bare optical fiber obtained by melt spinning the optical fiber preform by the first coating apparatus to provide the primary coating, and then the secondary coating is performed by the second coating apparatus. An optical fiber manufacturing method in which a resin coating is applied to provide an optical fiber strand by providing a secondary coating, and the optical fiber strand is periodically rolled by a twisting device to impart twist.
After calculating the natural frequency of the optical fiber, by changing the frequency of the twisting device or the interval between the twisting device and the second coating device, the frequency of rolling imparting the twist If, between the natural frequency of the optical fiber, optical fiber manufacturing method which is characterized in that optical fiber in accordance with the rolling to manufacture while being caused a difference in not only resonate. The natural frequency of the optical fiber is defined as L [m] between the twisting device and the second coating device, T [N] as the tension acting on the optical fiber, and the linear density of the optical fiber. Ρ [kg / m], the spinning speed of the optical fiber is V _f [M / s] and V ₀ = √ (T / ρ), V ₁ = V ₀ -V _f , V ₂ = V ₀ + V _f The natural frequency of the n-fold vibration (where n = 1, 2, 3,...)
ν _{o, n} = (N / 2L) V ₀ ,
ν _{1, n} = (N / 2L) V ₁ ,
ν _{2, n} = (N / 2L) V ₂ ,
As
These ν _{o, n} , Ν _{1, n} And ν _{2, n} Any of the above is manufactured in a state in which a difference that does not resonate with the rolling is generated between the rolling frequency imparting the twist and the frequency of rolling. 2. A method for producing an optical fiber according to 1.

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