JPS60217309A - Double core optical fiber - Google Patents

Abstract

PURPOSE:To form an optical line which is excellent in its crosstalk characteristic by limiting a crosstalk, by containing a double core optical fiber having plural cores, in a double layer clad, and marking a refractive index of the clad of the inside larger than a refractive index of the clad of the outside. CONSTITUTION:When a double core optical fiber having plural cores 1 is contained in double layer clads 3, 4, and a refractive index of the clad 3 of the inside and a refractive index of the clad 4 of the outside are denoted as n1 and n2, respectively, and set as n1>n2, a light whose incident angle theta satisfies a condition of an inequality I is totally reflected, and not made incident on the adjacent core. Also, as for a part where the optical fiber has been bent by a radius of curvature (r), when a thickness of the clad 3 is denoted as t1 so as to satisfy a condition of an inequality II, a light 5 as indicated with an arrow is totally reflected at a point A, and not made incident on the adjacent core. In this way, a crosstalk is prevented, and an optical circuit whose characteristic is excellent is formed.

Description

【発明の詳細な説明】 （技術分野） 本発明はコア内を伝搬する光信号の隣接コアへの漏話を
減少させる複心光ファイバに関するものである０ （従来技術） 従来の複心光ファイバの構造例として第１図に示す５心
平形パンチフアイバがあげられる０この構造は図示する
ように、各コア１が共通のクラッド２の中にほぼ等間隔
に配列されたものである。DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a multi-core optical fiber that reduces crosstalk of optical signals propagating within the core to adjacent cores. An example of this structure is the five-core flat punched fiber shown in FIG. 1. As shown in the figure, each core 1 is arranged in a common cladding 2 at approximately equal intervals.

光線路の経済化に資するためにく第１図に示すｂ心事形
パンチファイバ金高密度にした方が有利であることは言
うまでもないが、この場合、隣りあうコア間の距離が短
くなり、光伝送網においては漏話量増大の不都合が生じ
、該５心平形パンチフアイバの高密度化が制限される〇 さらに光損失等の光伝送特性面から複心平形パンチファ
イバのコア径および比屈折率差等のファイバパラメー・
夕を最適化する場合にも、漏話特性により光フアイバパ
ラメータの選定範囲が制限される。It goes without saying that it is advantageous to use a high-density punched fiber in the b-core type shown in Figure 1 to contribute to the economicalization of optical lines, but in this case, the distance between adjacent cores is shortened, and the optical In the transmission network, the inconvenience of increased crosstalk occurs, which limits the increase in density of the five-core flat punched fiber.Furthermore, from the viewpoint of optical transmission characteristics such as optical loss, the core diameter and relative refractive index difference of the double-core flat punched fiber are Fiber parameters such as
When optimizing optical fiber parameters, crosstalk characteristics also limit the selection range of optical fiber parameters.

（発明の目的） 本発明はこれらの問題を解決するため、複心光７アイハ
における各コアを囲む第１クラツドの屈折率に対し、該
第１クラツドを囲む第２クラツドの屈折率を小さくして
、他コアへの漏話を減少させるものであシ、その目的は
漏話特性の優れた光線路を形成することを可能にするこ
とにある０以下図面によυ本発明の詳細な説明する０ （発明の構成および作用） 第２図は本発明の複心光ファイ、バの一実施例の断面図
、第８図は第２図における複心光ファイバの屈折率分布
を示す図である０第２図の複心光ファイバの断面図にお
いて、コア１を囲む屈折率ｎ０の第１クラツド８に対し
１該第１クラツドを囲む屈折率ｎの第２クラット番の屈
折率を小さくすることに本発明の特徴がある。(Objective of the Invention) In order to solve these problems, the present invention makes the refractive index of the second cladding surrounding the first cladding smaller than the refractive index of the first cladding surrounding each core in the compound-centered optical 7A. The purpose of this is to reduce crosstalk to other cores, and its purpose is to make it possible to form an optical path with excellent crosstalk characteristics. (Structure and operation of the invention) FIG. 2 is a cross-sectional view of an embodiment of the multi-core optical fiber of the present invention, and FIG. 8 is a diagram showing the refractive index distribution of the multi-core optical fiber in FIG. 2. In the cross-sectional view of the double-core optical fiber shown in FIG. 2, the refractive index of the second clad 8 with a refractive index n surrounding the first clad is made smaller than the first clad 8 with a refractive index n0 surrounding the core 1. There are features of the present invention.

複心光ファイバにおける漏話の原因として・光信号が光
フアイバ中を伝搬することにより生じるもの、接続部で
の軸ずれにより生じるもの・および光ファイバに側圧ま
たは曲げが加わり、コア中を伝搬する光信号が放射によ
り他のコアへ漏話するものに大別できる。前記のいずれ
の場合でも、漏話は伝搬される光信号の一部がクラッド
を介して他のコアへ伝わる現象であるので、クラッド部
を屈折率ｎ□の第１クラツドおよび屈折率ｎ、の第２ク
ラツドの２層構造にし、第２クラツドの屈折率ｎ２’（
Ｈ第１クラッドの屈折率ｎ□よシ小さくすることにより
、第１クラツドと第２クラツドの境界層で該境界層に対
して、ある角度θを有する光線のうち１ なる関係ケ有するものは全反射され、他のコアの第１ク
ラツドには入射しない０その結果、漏話現象が制限され
、光信号が伝搬しているコアから他のコアへの漏話量は
減少する。Causes of crosstalk in double-core optical fibers include: ・Crosstalk caused by optical signals propagating through the optical fiber; ・Crosstalk caused by axial misalignment at the connection; and lateral pressure or bending applied to the optical fiber, resulting in light propagating through the core. It can be broadly classified into those in which the signal crosstalks to other cores by radiation. In any of the above cases, crosstalk is a phenomenon in which a part of the propagated optical signal is transmitted to another core via the cladding, so the cladding part is divided into a first cladding with a refractive index n□ and a second cladding with a refractive index n, A two-layer structure with two clads is used, and the refractive index of the second clad is n2' (
By making the refractive index n□ of the H first cladding smaller, all of the rays having a certain angle θ with respect to the boundary layer between the first cladding and the second cladding have a relationship of 1. As a result, the crosstalk phenomenon is limited and the amount of crosstalk from the core through which the optical signal is propagating to the other cores is reduced.

光線路において、余長処理等で光ファイバの曲げ部は必
要不可欠である。曲げ時に生じる光信号の放射による漏
話現象に対して漏話現象を制限する第１クラツドの屈折
率および厚み、第２クラツ（８） ドの屈折率の範囲を定める〇 第４図は複心光ファイバに曲げを加えた時のモデル図を
示したものであり、１はコア、８は第１クラツド、４は
第８クラツドである０複心光フアイバに曲率半径ｒの曲
げを加えた場合、曲げによりコアから放射される光信号
はコアの接線方向成分が主である０該接線方向成分の第
１クラツドにおける光線５が第２クラツドと第１クラツ
ドの境界層と交わる点をＡとする０漏話を制限する条件
、すなわち隣接クラッドに放射光が入らない条件は一点
ムで光線５が全反射する条件であるので１第１クラツド
の屈折率をｎｏ、第２クラツドの屈折重金ｎ、とすると
、全反射条件として、 となる。In optical lines, bends in optical fibers are indispensable for processing excess length and the like. The refractive index and thickness of the first cladding and the range of the refractive index of the second cladding are defined to limit the crosstalk phenomenon due to the radiation of optical signals that occur during bending. Figure 4 shows a compound optical fiber. 1 is the core, 8 is the first cladding, and 4 is the eighth cladding. When bending a 0-complex optical fiber with a radius of curvature r, the bending The optical signal emitted from the core is mainly composed of the tangential component of the core.0Crosstalk where A is the point where the ray 5 in the first clad of the tangential component intersects the boundary layer between the second clad and the first clad. The condition that limits the number of claddings, that is, the condition that synchrotron radiation does not enter the adjacent cladding, is the condition that the ray 5 is totally reflected at one point, so if the refractive index of the first cladding is no, and the refractive index of the second cladding is n, then The total internal reflection condition is as follows.

一方、θ、は複心光ファイバの曲げ半径ヲｒ１第１クラ
ッドの厚みをｔｏとすると− （４） となる■ よって式（１）、式（２）より全反射する条件として、
がまる。On the other hand, θ is - (4) where the bending radius of the multi-core optical fiber is r1 and the thickness of the first cladding is to. Therefore, from equations (1) and (2), as a condition for total reflection,
Gamaru.

次に具体的な数値によシ複心光７アイパの設計例を示す
。Next, a design example of a multi-core optical 7-eyeper will be shown based on specific numerical values.

表１は曲率半径３　Ｑ　ｒｎｔｎ　、第１クラツドの屈
折率１．４６のとき、種々の第１クラツド厚に対する最
大の第２クラツドの屈折率ｎ、ヲ示したものでらり１該
屈折率ｎ、以下の第２クラツドの屈醇に対しては全反射
条件を満足し、漏話を制限できる０表２は曲率半径１　
ｏ　ｍｍ、第１クラツドの屈折　。Table 1 shows the maximum refractive index n of the second cladding for various first cladding thicknesses when the radius of curvature is 3 Qrntn and the refractive index of the first cladding is 1.46. , for the following curvature of the second cladding, it satisfies the total internal reflection condition and can limit crosstalk.Table 2 shows the radius of curvature 1
o mm, refraction of the first cladding.

率１．４６のとき、種々の第１クラツド厚に対する最大
の第２クラツドの屈折率ｎ、を示したものであり、該屈
折率ｎ２以下の第２クラツドの屈折率に対しては全反射
条件を満足し、漏話を制限できる〇表１　（ｒ＝８（ｌ
Ｌｆｉの場合） 表２　（ｒ＝　１０ＷｗＬ（７）場合〕（発明の効果） 以上説明したように本発明の複心光ファイバは１コアを
囲むクラッドの屈折率を制御することによシ１漏話金制
限できるＯこの几め不発Ｆ！Ａを用いた複心光ファイバ
により、漏話特性の優れた光線路を形成することが可能
であり、光通信の発展に寄与するところは大きい〇 （７）When the refractive index is 1.46, it shows the maximum refractive index n of the second cladding for various first cladding thicknesses, and for the refractive index of the second cladding less than or equal to the refractive index n2, the total reflection condition is Table 1 (r=8(l
Lfi) Table 2 (r = 10WwL(7)) (Effects of the Invention) As explained above, the compound optical fiber of the present invention can reduce crosstalk by controlling the refractive index of the cladding surrounding one core. It is possible to form an optical path with excellent crosstalk characteristics by using a multi-core optical fiber using this method, which can limit the amount of money.It will greatly contribute to the development of optical communications〇(7)

【図面の簡単な説明】[Brief explanation of the drawing]

第１図は従来のら６平形パンチファイバの構造を示す断
面図、第２図は本発明の複心光ファイバの一実施例の断
面図、第８図は複心光ファイバの屈折率分布を示す模式
図、第４図は複心光ファイバに曲げを加えた時のモデル
図である０１・・・コア　２・・・クラッド ８・・・第１クラツド　４・・・第２クラツド５・・・
光線。 特許出願人　日本電信電話公社 （８）Fig. 1 is a cross-sectional view showing the structure of a conventional hexagonal punched fiber, Fig. 2 is a cross-sectional view of an embodiment of the multi-core optical fiber of the present invention, and Fig. 8 is a cross-sectional view showing the refractive index distribution of the multi-core optical fiber. The schematic diagram shown in Fig. 4 is a model diagram when bending is applied to a multi-core optical fiber.01... Core 2... Clad 8... First clad 4... Second clad 5...・
Ray of light. Patent applicant: Nippon Telegraph and Telephone Public Corporation (8)

Claims (1)

【特許請求の範囲】 １　クラッドの内側に複数のコアを有する複心光ファイ
バにおいて、該クラッドは２層から成シ各コアを囲む第
１クラツドの屈折率をｎ１該第１クラツドを囲む第２ク
ラ）ドの屈折率をｎ　とし、ｎ□）　ｎｇなる関係を満
たすことを特徴とする複心光ファイバ◇ 龜　第１クラツドの厚み’２ｔ　複心光ファイ１　、 バの最小許容曲げ半径’６ｒとし、 なる関係を満たすことを特徴とする特許請求の範囲第１
項記載の複心光ファイバ。[Claims] 1. In a multi-core optical fiber having a plurality of cores inside the cladding, the cladding is made up of two layers. A multi-core optical fiber characterized by satisfying the relationship n□) ng, where the refractive index of the cladding is n, the thickness of the first cladding is 2t, the minimum allowable bending radius of the multi-core optical fiber 1 is 6r. The first claim characterized in that the following relationship is satisfied:
Compound optical fiber as described in Section 1.