JP4322630B2 - Evaluation method of cut-off wavelength characteristics of single-mode optical fiber - Google Patents

Evaluation method of cut-off wavelength characteristics of single-mode optical fiber Download PDF

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JP4322630B2
JP4322630B2 JP2003376519A JP2003376519A JP4322630B2 JP 4322630 B2 JP4322630 B2 JP 4322630B2 JP 2003376519 A JP2003376519 A JP 2003376519A JP 2003376519 A JP2003376519 A JP 2003376519A JP 4322630 B2 JP4322630 B2 JP 4322630B2
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和秀 中島
健 周
克介 田嶋
泉 三川
千里 深井
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Description

本発明は、単一モード光ファイバの実効的な遮断波長特性を評価する評価方法に関するものである。 The present invention relates to an evaluation method for evaluating an effective cut-off wavelength characteristics of single-mode optical fiber.

単一モード光ファイバの遮断波長特性は、単一モード光通信において必要不可欠な特性の１つであり、これまでに様々な遮断波長特性の評価方法が提案されている。   The cutoff wavelength characteristic of a single mode optical fiber is one of the indispensable characteristics in single mode optical communication, and various evaluation methods for cutoff wavelength characteristics have been proposed so far.

例えば特許文献１では、伝搬する２モード間の群遅延特性の測定結果から、特許文献４及び特許文献７では、被測定単一モード光ファイバ中の後方散乱光強度の測定結果から、特許文献６では被測定単一モード光ファイバの屈折率分布の測定結果から、更に、非特許文献１では遠方出射パターンの測定結果から、それぞれ該単一モード光ファイバの遮断波長特性を数値解析により導出する手法が提案されている。   For example, in Patent Document 1, from the measurement result of the group delay characteristic between the two modes to propagate, and in Patent Document 4 and Patent Document 7, from the measurement result of the backscattered light intensity in the single-mode optical fiber to be measured, Patent Document 6 A method for deriving the cutoff wavelength characteristics of a single-mode optical fiber by numerical analysis from the measurement result of the refractive index distribution of the single-mode optical fiber to be measured, Has been proposed.

また、非特許文献３及び非特許文献４では、それぞれ２直交偏波の光強度、並びに反射光強度の測定結果から、単一モード光ファイバの理論遮断波長を直接評価する手法も提案されている。   Non-Patent Document 3 and Non-Patent Document 4 also propose a method for directly evaluating the theoretical cutoff wavelength of a single-mode optical fiber from the measurement results of the light intensity of two orthogonal polarizations and the reflected light intensity, respectively. .

更に、特許文献２，３，５並びに非特許文献２では、被測定光ファイバへの曲げ付与に伴う光強度の変化を測定する事により、該被測定光ファイバの実効的な遮断波長特性を直接評価する手法も提案されている。   Further, in Patent Documents 2, 3, and 5 and Non-Patent Document 2, an effective cutoff wavelength characteristic of the optical fiber to be measured is directly measured by measuring a change in light intensity accompanying the bending of the optical fiber to be measured. An evaluation method has also been proposed.

特開昭５７−１７８３４号公報JP-A-57-17834 特開昭６３−２１８８３８号公報JP 63-218838 A 特開平１−２３２２２９号公報JP-A-1-232229 特開平６−２１３７７０号公報JP-A-6-213770 特開平９−２２９８１６号公報JP-A-9-229816 特開２００１−２８１０９４号公報Japanese Patent Laid-Open No. 2001-281094 特開２００２−３６５１６１号公報JP 2002-365161 A W.A.Gambling,et al.,"Determination of core diameter and refractive-index difference of single-mode fibers by observation of the far-field pattern",IEEJ.Microwaves,opt.＆ Accoust .,vol.1,pp.13-17,1976.WAGambling, et al., “Determination of core diameter and refractive-index difference of single-mode fibers by observation of the far-field pattern”, IEEJ. Microwaves, opt. & Accoust., Vol.1, pp.13- 17,1976. Y.Katsuyama,et al.,"New method for measuring V-valueof a single-mode optical fibre",Electron.Lett.,vol.12,No.25,pp.669-670,1976Y. Katsuyama, et al., "New method for measuring V-valueof a single-mode optical fiber", Electron.Lett., Vol.12, No.25, pp.669-670,1976 Y.kato, et al.,"Novel method for measuring cutoff wavelength of HE21-,TE01-and TM01-modes",Electron.Lett.,vol.15,No.14,pp.410-411,1979.Y.kato, et al., "Novel method for measuring cutoff wavelength of HE21-, TE01-and TM01-modes", Electron.Lett., Vol.15, No.14, pp.410-411, 1979. W.A.Bhagavatula,et al.,"Refracted power technique for cutoff wavelength measurement in single-mode waveguides",Electron.Lett.,vol.16,No.18,pp.695-696,1980W.A.Bhagavatula, et al., "Refracted power technique for cutoff wavelength measurement in single-mode waveguides", Electron.Lett., Vol.16, No.18, pp.695-696,1980 D.Marcuse,"Loss analysis of single-mode fiber spiece",Bell Syst.Tech.J.,vl.56,No.5,pp.703-718,1977.D. Marcuse, "Loss analysis of single-mode fiber spiece", Bell Syst. Tech. J., vl. 56, No. 5, pp. 703-718, 1977.

しかしながら、特許文献１，４，６，７並びに非特許文献１に記載の手法は、数値解析に基づく遮断特性の評価手法であるため、その適用対象は屈折率分布が既知の単一モード光ファイバに限定される、あるいは実効的な遮断波長特性の評価が困難であるといった問題点があった。   However, since the methods described in Patent Documents 1, 4, 6, and 7 and Non-Patent Document 1 are evaluation methods of cutoff characteristics based on numerical analysis, the application target is a single-mode optical fiber with a known refractive index distribution. However, it is difficult to evaluate effective cutoff wavelength characteristics.

また、非特許文献３，４に記載の評価方法では、測定精度が被測定光ファイバのファイバ長に依存し、実際の光通信で使用される実用的なファイバ長に対する実効的な遮断波長の評価には不向きであるといった問題点があった。   In the evaluation methods described in Non-Patent Documents 3 and 4, the measurement accuracy depends on the fiber length of the optical fiber to be measured, and the effective cutoff wavelength is evaluated with respect to the practical fiber length used in actual optical communication. There was a problem that it was unsuitable.

また更に、特許文献２，３，５並びに非特許文献２に記載の評価方法では、極めて簡便な測定系で実効的な遮断波長特性が評価できる反面、曲げ損失特性が飛躍的に改善された光ファイバ等、曲げ付与による光強度変化の観測が困難である場合には適用不可能となるといった問題点があった。   Furthermore, in the evaluation methods described in Patent Documents 2, 3 and 5 and Non-Patent Document 2, an effective cutoff wavelength characteristic can be evaluated with a very simple measurement system, but a light whose bending loss characteristic is dramatically improved. There is a problem that it becomes impossible to observe when the change in light intensity due to bending is difficult to observe such as a fiber.

本発明はこのような問題に鑑み、異なる２種類以上の励振条件で測定した遠方出射パターンの測定波長に対する変化を測定することにより、曲げ損失特性が改善された単一モード光ファイバに対しても適用可能な、実効的な遮断波長特性の評価方法を提供することを目的とする。 In view of such a problem, the present invention is also applicable to a single mode optical fiber having improved bending loss characteristics by measuring a change in the far-emitted pattern with respect to the measurement wavelength measured under two or more different excitation conditions. An object of the present invention is to provide an effective evaluation method of cutoff wavelength characteristics that can be applied.

本発明の評価方法は、
測定光が入射される被測定単一モード光ファイバの励振条件を異なる２種類の励振条件とし、
各励振条件において、被測定単一モード光ファイバの出射端面から出射される測定光の光強度を、前記出射端面を中心とする円弧上の予め決めた角度範囲の各受光角度において測定することにより、前記出射端面を中心とする円弧上の各受光角度における測定光の光強度の特性を示す遠方出射パターン（Ｆ（λ、θ））を、前記測定光の所望の波長範囲について求め、
更に、各励振条件において、前記波長範囲の各波長における遠方出射パターン（Ｆ（λ、θ））を式（１）に適用することにより各波長におけるモードフィールド径（２Ｗ（λ））を求めて、各励振条件毎にモードフィールド径と波長との関係特性を求め、
２種類の励振条件のうちの一方の励振条件でのモードフィールド径と波長との関係特性を示す特性曲線と、２種類の励振条件のうちの他方の励振条件でのモードフィールド径と波長との関係特性を示す特性曲線とが交差する波長（λｃ０）を求め、
この交差した波長（λｃ０）と、遠方出射パターンの受光角度範囲に依存して予め定められた定数（λｃ（θ））とを加算して、被測定単一モード光ファイバの遮断波長λｃ（ＦＦＰ）を求めることを特徴とする単一モード光ファイバの遮断波長特性の評価方法。

Figure 0004322630
The evaluation method of the present invention is:
The excitation conditions of the single-mode optical fiber to be measured that are incident on the measurement light are two different excitation conditions,
Under each excitation condition , by measuring the light intensity of the measurement light emitted from the exit end face of the single-mode optical fiber to be measured at each light receiving angle in a predetermined angle range on an arc centered on the exit end face , A far emission pattern (F (λ, θ)) indicating the characteristics of the light intensity of the measurement light at each light receiving angle on the arc centered on the emission end face is obtained for a desired wavelength range of the measurement light,
Further, in each excitation condition, the mode field diameter (2W (λ)) at each wavelength is obtained by applying the far emission pattern (F (λ, θ)) at each wavelength in the wavelength range to Equation (1). , Find the relationship between the mode field diameter and wavelength for each excitation condition ,
The characteristic curve showing the relationship between the mode field diameter and the wavelength under one of the two excitation conditions, and the mode field diameter and the wavelength under the other of the two excitation conditions. Find the wavelength (λc0) at which the characteristic curve indicating the relationship characteristic intersects,
The crossed wavelength (λc0) and a constant (λc (θ)) determined in advance depending on the light receiving angle range of the far emission pattern are added to obtain the cutoff wavelength λc (FFP ) of the single-mode optical fiber to be measured. ) For determining the cutoff wavelength characteristic of a single-mode optical fiber.
Figure 0004322630

また本発明の評価方法は、前記被測定単一モード光ファイバの端面に入射する前記測定光の入射位置を制御することにより、被測定単一モード光ファイバの励振条件を変化させることを特徴とする。   The evaluation method of the present invention is characterized in that the excitation condition of the single-mode optical fiber to be measured is changed by controlling the incident position of the measurement light incident on the end face of the single-mode optical fiber to be measured. To do.

本発明による実効的な遮断波長の評価方法によれば、異なる２種類以上の励振条件における遠方出射パターンを測定し、モードフィールド径の測定光波長に対する変化を評価することにより、被測定光ファイバの実効的な遮断波長特性を高精度に評価できるといった特徴を有する。 According to the effective cutoff wavelength evaluation method of the present invention, the far-field emission pattern under two or more different excitation conditions is measured, and the change of the mode field diameter with respect to the measurement light wavelength is evaluated. The effective cutoff wavelength characteristic can be evaluated with high accuracy.

また、本発明による実効的な遮断波長の評価方法は、任意の屈折率分布を有する任意の長さの光ファイバに対して適用可能であると同時に、従来の曲げ付与法では測定が困難であった、曲げ損失特性が向上された光ファイバに対しても適用可能であるといった効果も奏する。 Further, the effective cutoff wavelength evaluation method according to the present invention can be applied to an optical fiber having an arbitrary refractive index distribution and an arbitrary length, and at the same time, measurement is difficult by the conventional bending method. In addition, there is an effect that it can be applied to an optical fiber having improved bending loss characteristics.

以下では図面に基づき、本発明の実施の形態について説明する。   Hereinafter, embodiments of the present invention will be described with reference to the drawings.

図１は本発明の評価方法に用いる、実効的な遮断波長特性の評価装置の１構成例を示す概念図である。 FIG. 1 is a conceptual diagram showing one configuration example of an effective cutoff wavelength characteristic evaluation apparatus used in the evaluation method of the present invention.

同図に示すように、単一モード光源１１から発生した測定光は、励振用光ファイバ１２の入射端面１２ａに入射されて、この励振用光ファイバ１２を伝搬し、励振用光ファイバ１２の出射端面１２ｂから出射される。つまり単一モード光源１１から発生した測定光は、励振用光ファイバ１２により導出されて出射端面１２ｂから出射される。なお、単一モード光源１１から発生する測定光は、その波長を可変にすることができる。   As shown in the figure, the measurement light generated from the single mode light source 11 is incident on the incident end surface 12 a of the excitation optical fiber 12, propagates through the excitation optical fiber 12, and exits from the excitation optical fiber 12. The light is emitted from the end face 12b. That is, the measurement light generated from the single mode light source 11 is led out by the excitation optical fiber 12 and emitted from the emission end face 12b. Note that the wavelength of the measurement light generated from the single mode light source 11 can be made variable.

微動台１３の上には、励振用光ファイバ１２の出射端面１２ｂと、被測定光ファイバ１４の入射端面１４ａとが相対向する状態となるように、両光ファイバ１２，１４が設置されている。即ち、励振用光ファイバ１２の出射端面１２ｂから出射された測定光が、被測定光ファイバ１４の入射端面１４ａに入射できるように、両光ファイバ１２，１４が対向配置されている。   On the fine movement base 13, both optical fibers 12 and 14 are installed so that the emission end face 12b of the excitation optical fiber 12 and the incident end face 14a of the optical fiber 14 to be measured are opposed to each other. . That is, the two optical fibers 12 and 14 are arranged to face each other so that the measurement light emitted from the emission end face 12 b of the excitation optical fiber 12 can enter the incidence end face 14 a of the optical fiber 14 to be measured.

しかも、微動台１３は、励振用光ファイバ１２の出射端面１２ｂの位置に対する、被測定光ファイバ１４の入射端面１４ａの位置を調整・制御することができるようになっている。即ち、光ファイバ１２，１４の光の伝搬方向をＺ軸とし、これに直交する方向をＸ軸，Ｙ軸とした場合に、励振用光ファイバ１２の出射端面１２ｂの位置に対する、被測定光ファイバ１４の入射端面１４ａの位置をＸ軸方向及びＹ軸方向に沿い微小量だけ移動させる調整・制御ができるようになっている。   In addition, the fine movement table 13 can adjust and control the position of the incident end face 14 a of the optical fiber 14 to be measured with respect to the position of the exit end face 12 b of the excitation optical fiber 12. That is, when the light propagation direction of the optical fibers 12 and 14 is the Z axis and the directions orthogonal to the Z axis are the X axis and the Y axis, the measured optical fiber with respect to the position of the exit end face 12b of the excitation optical fiber 12 The adjustment and control of moving the position of the 14 incident end faces 14a by a minute amount along the X-axis direction and the Y-axis direction can be performed.

このような微動台１３の調整・制御により、被測定光ファイバ１４の入射端面１４ａへの、測定光の入射位置を制御することができる。このように、入射端面１４ａへの入射位置を制御することにより、被測定光ファイバ１４の励振条件を変化させることができる。   By adjusting and controlling the fine movement table 13 as described above, the incident position of the measurement light on the incident end face 14a of the measured optical fiber 14 can be controlled. In this way, by controlling the incident position on the incident end face 14a, the excitation condition of the measured optical fiber 14 can be changed.

被測定ファイバ１４の出射端面１４ｂ側には、遠方出射パターン受光素子１５が配置されている。この遠方出射パターン受光素子１５は、被測定光ファイバ１４を伝搬してきて出射端面１４ｂから出射された測定光の光強度を、出射端面１４ｂを中心とする円弧上の任意の受光角度θにおいて測定するものである。   A far-end outgoing pattern light receiving element 15 is disposed on the outgoing end face 14 b side of the measured fiber 14. The far-end outgoing pattern light receiving element 15 measures the light intensity of the measurement light that has propagated through the optical fiber 14 to be measured and is emitted from the outgoing end face 14b at an arbitrary light receiving angle θ on an arc centered on the outgoing end face 14b. Is.

このような構成となっている、遮断波長特性の評価装置では、単一モード光源１１から出射された波長λの測定光は、測定波長よりも短い遮断波長を有する励振用光ファイバ１２を介して、被測定光ファイバ（単一モード光ファイバ）１４に入射されて被測定光ファイバ１４が励振される。ここで、励振用光ファイバ１２と被測定光ファイバ１４の位置を微動台１３により制御することにより、被測定光ファイバ１４への励振条件を変化させることが可能となる。   In the cutoff wavelength characteristic evaluation apparatus having such a configuration, the measurement light having the wavelength λ emitted from the single mode light source 11 passes through the excitation optical fiber 12 having a cutoff wavelength shorter than the measurement wavelength. Then, it enters a measured optical fiber (single mode optical fiber) 14 and the measured optical fiber 14 is excited. Here, by controlling the positions of the excitation optical fiber 12 and the optical fiber 14 to be measured by the fine movement table 13, the excitation conditions for the optical fiber 14 to be measured can be changed.

一方、遠方出射パターン測定受光素子１５では、被測定光ファイバ１４の出射端面１４ｂを中心とする同心円状の任意の受光角度θでの光強度を測定することにより被測定光ファイバ１４の波長λでの遠方出射パターンを測定する。   On the other hand, the far-field emission pattern measurement light receiving element 15 measures the light intensity at an arbitrary light receiving angle θ concentrically centered on the emission end face 14b of the optical fiber 14 to be measured, thereby measuring the wavelength λ of the optical fiber 14 to be measured. Measure the far emission pattern.

図２は本発明の実施の形態における、実効的な遮断波長特性評価方法の評価手順を示すフローチャートである。初めに、被測定光ファイバ１４の出射端での光出力が最大となるよう、微動台１３により励振用光ファイバ１２と被測定光ファイバ１４の位置を制御する（ステップ１）。   FIG. 2 is a flowchart showing an evaluation procedure of an effective cutoff wavelength characteristic evaluation method according to the embodiment of the present invention. First, the positions of the excitation optical fiber 12 and the measured optical fiber 14 are controlled by the fine movement base 13 so that the light output at the output end of the measured optical fiber 14 is maximized (step 1).

本励振条件において所望の波長範囲（例えば１２７０ｎｍから１６５０ｎｍ）における遠方出射パターンＦ０（λ、θ）を、遠方出射パターン受光素子１５により測定し、次式（１）により波長λにおけるモードフィールド径（以下、Mode Field Diameter:MFDとする）、２Ｗ０（λ）を算出する（ステップ２）。

Figure 0004322630
The far emission pattern F0 (λ, θ) in a desired wavelength range (for example, 1270 nm to 1650 nm) is measured by the far emission pattern light receiving element 15 under the main excitation conditions, and the mode field diameter at the wavelength λ (hereinafter referred to as the following equation (1)). , Mode Field Diameter: MFD), 2W0 (λ) is calculated (step 2).
Figure 0004322630

次に微動台１３をＸ軸、もしくはＹ軸方向に微小量移動させ被測定光ファイバ１４の励振条件を変化させる（ステップ３）。   Next, the fine movement base 13 is moved by a minute amount in the X-axis or Y-axis direction to change the excitation condition of the optical fiber 14 to be measured (step 3).

本励振条件において前記、ステップ２と同様の所望の波長範囲（例えば１２７０ｎｍから１６５０ｎｍ）における遠方出射パターンＦ１（λ、θ）を、遠方出射パターン受光素子１５により測定し、前記、式（１）により波長λにおけるＭＦＤ、２Ｗ１（λ）を算出する（ステップ４）。   Under the main excitation conditions, the far-emitted pattern F1 (λ, θ) in the desired wavelength range (for example, 1270 nm to 1650 nm) similar to that in step 2 is measured by the far-emitted pattern receiving element 15, and the above equation (1) is used. MFD and 2W1 (λ) at the wavelength λ are calculated (step 4).

次に、ステップ２及びステップ４で得られたＭＦＤの波長特性を、適当な関数を用いて近似し、ステップ２及びステップ４の特性が交差する波長λｃ０を算出する（ステップ５）。   Next, the wavelength characteristics of the MFD obtained in Step 2 and Step 4 are approximated using an appropriate function, and a wavelength λc0 where the characteristics of Step 2 and Step 4 intersect is calculated (Step 5).

更にステップ５で得られたλｃ０と次式（２）を用いて、被測定光ファイバの実効的な遮断波長λｃ（ＦＦＰ）を評価する（ステップ６）。
λｃ（ＦＦＰ）＝λｃ０＋λｃ（θ） （２） Further, the effective cutoff wavelength λc (FFP) of the optical fiber to be measured is evaluated using λc0 obtained in step 5 and the following equation (2) (step 6).
λc (FFP) = λc0 + λc (θ) (2)

ここで、λｃ（θ）は前記、ステップ２及びステップ４におけるＭＦＤの算出で使用した遠方出射パタンーの受光角度範囲θ、即ち、前記、式（１）におけるθの積分範囲に依存した定数を表す。   Here, λc (θ) represents a light receiving angle range θ of the far emission pattern used in the calculation of the MFD in Step 2 and Step 4, that is, a constant depending on the integration range of θ in the formula (1). .

以下では前記、本発明の実施の形態に基づき、カットオフ・シフト・ファイバ（以下、Cutoff Shifted Fiber :ＣＳＦとする）の実効遮断波長の評価を行った結果について、図面を用いて説明する。   In the following, based on the embodiment of the present invention, the results of evaluation of the effective cutoff wavelength of a cut-off shifted fiber (hereinafter referred to as “Cutoff Shifted Fiber”) will be described with reference to the drawings.

図３は波長１３７５ｎｍにおいて測定した２種類の励振条件におけるＣＳＦの遠方出射パターンの測定例を示す。図中の実線はステップ２の励振条件における波形を、また点線はステップ４の励振条件において、微動台１３をＸ軸方向に５μｍ移動させた時の波形を示す。   FIG. 3 shows an example of measurement of the CSF far emission pattern under two excitation conditions measured at a wavelength of 1375 nm. The solid line in the figure shows the waveform under the excitation condition of Step 2, and the dotted line shows the waveform when the fine movement base 13 is moved by 5 μm in the X-axis direction under the excitation condition of Step 4.

図３から微動台１３による励振位置の変化により被測定光ファイバ１４の励振条件が変化し、遠方出射パターンに変化が現れることが確認できる。   From FIG. 3, it can be confirmed that the excitation condition of the optical fiber 14 to be measured changes due to the change of the excitation position by the fine movement table 13 and the change appears in the far emission pattern.

図４は波長１３７５ｎｍにおいて測定した、微動台１３のＸ軸方向の移動量とＭＦＤの相対変化量の関係を表す図面である。尚、図４において前記、式（１）におけるθの積分範囲は±１０度とした。図４から微動台１３による励振位置の可変により、ＭＦＤの値が減少することが確認できる。   FIG. 4 is a diagram showing the relationship between the amount of movement of the fine movement table 13 in the X-axis direction and the relative change amount of MFD measured at a wavelength of 1375 nm. In FIG. 4, the integration range of θ in the equation (1) is ± 10 degrees. It can be confirmed from FIG. 4 that the value of MFD decreases by changing the excitation position by the fine movement table 13.

図５は波長１２７０ｎｍから１６５０ｎｍの範囲で測定した遠方出射パターンを用い、ＭＦＤの測定波長に対する変化を表す。図中の黒丸はステップ２の励振条件における測定結果を、白丸はステップ４の励振条件において、微動台１３のＸ軸方向の移動量を５μｍとした時の測定結果を表す。尚、ＭＦＤの計算は±１０度の受光範囲のデータを用いて行った。また、図中の実線は最小２乗法による近似曲線を表し、本実施例では単一モード光ファイバにおけるＭＦＤ波長特性の近似式として、次式（３）を用いた（非特許文献５）。
２Ｗ＝ｇ０＋ｇ１λ1.5＋ｇ２λ6 （３）
図５よりステップ５のλｃ０は約１４７７ｎｍであることが分かる。 FIG. 5 shows the change of the MFD with respect to the measured wavelength, using the far emission pattern measured in the wavelength range of 1270 nm to 1650 nm. The black circles in the figure represent the measurement results under the excitation conditions in Step 2, and the white circles represent the measurement results when the amount of movement of the fine movement table 13 in the X-axis direction is 5 μm under the excitation conditions in Step 4. The MFD calculation was performed using data of the light receiving range of ± 10 degrees. In addition, the solid line in the figure represents an approximate curve by the least square method, and in this example, the following expression (3) was used as an approximate expression of the MFD wavelength characteristic in a single mode optical fiber (Non-patent Document 5).
2W = g0 + g1λ 1.5 + g2λ 6 (3)
FIG. 5 shows that λc0 in step 5 is about 1477 nm.

図６は前記、式（２）中の定数λｃ（θ）と受光角度範囲θの関係を表す。図６より±１０度の受光範囲に対するλｃ（θ）は７６ｎｍであり、以上の結果から被測定ＣＳＦの実効遮断波長λｃ（ＦＦＰ）は式（２）を用いて（１４７７＋７４＝１５５１ｎｍ）と評価される。ここで、従来の曲げ付与法による遮断波長の評価結果は１５４９ｎｍであり、本手法による評価結果と良く一致していることが分かる。   FIG. 6 shows the relationship between the constant λc (θ) in the equation (2) and the light receiving angle range θ. From FIG. 6, λc (θ) for the light reception range of ± 10 degrees is 76 nm, and the effective cutoff wavelength λc (FFP) of the CSF to be measured is evaluated as (1477 + 74 = 1551 nm) using the equation (2) from the above results. The Here, the evaluation result of the cutoff wavelength by the conventional bending method is 1549 nm, and it can be seen that the evaluation result by this method is in good agreement.

図７及び図８は曲げ損失特性が向上された光ファイバにおいて、それぞれ波長１３１０ｎｍ、及び８５０ｎｍにおける遠方出射パターンを評価した結果を表す。図中の実線は前記、ステップ２の励振条件における測定結果を、点線はステップ４においてＸ軸方向に５μｍの移動量を設定した場合の測定結果を表す。測定に用いた光ファイバの数値計算による理論遮断波長は約１３８６ｎｍであり、該光ファイバの実効遮断波長は１３８６ｎｍ以下の領域で得られるものと考えられる。しかし、該光ファイバの波長８００ｎｍから１７００ｎｍにおける、曲げ半径１０ｍｍでの曲げ損失は０．０１ｄＢ未満であり、従来の曲げ付与による実効遮断波長の評価が適用できない。   FIG. 7 and FIG. 8 show the results of evaluating the far emission pattern at wavelengths of 1310 nm and 850 nm, respectively, in an optical fiber with improved bending loss characteristics. The solid line in the figure represents the measurement result under the excitation condition in Step 2, and the dotted line represents the measurement result when a movement amount of 5 μm is set in the X-axis direction in Step 4. The theoretical cutoff wavelength by numerical calculation of the optical fiber used for the measurement is about 1386 nm, and the effective cutoff wavelength of the optical fiber is considered to be obtained in the region of 1386 nm or less. However, the bending loss at a bending radius of 10 mm in the wavelength range of 800 nm to 1700 nm of the optical fiber is less than 0.01 dB, and the conventional evaluation of the effective cutoff wavelength by applying bending is not applicable.

一方、本発明の手法に基づく遠方出射パターンの測定結果によれば、図７の測定波長では２種類の励振条件における遠方出射パターンがほぼ一致しているのに対して、図８の測定波長では励振条件の変化に伴い、前記、図３のＣＳＦにおける測定結果と類似の、遠方出射パターンの変化が観測されていることが確認できる。従って、該光ファイバの実効遮断波長が波長１３１０ｎｍから波長８５０ｎｍの領域に存在することが確認できる。以上の結果から、本発明による評価方法が、曲げ損失特性が向上された単一モード光ファイバに対しても適用可能であることが確認できる。   On the other hand, according to the measurement result of the far emission pattern based on the method of the present invention, the far emission patterns under the two types of excitation conditions are almost the same at the measurement wavelength of FIG. 7, whereas at the measurement wavelength of FIG. It can be confirmed that a change in the far emission pattern similar to the measurement result in the CSF of FIG. 3 is observed with the change in the excitation condition. Therefore, it can be confirmed that the effective cutoff wavelength of the optical fiber exists in the wavelength region from 1310 nm to 850 nm. From the above results, it can be confirmed that the evaluation method according to the present invention is applicable to a single mode optical fiber with improved bending loss characteristics.

本発明の評価方法に用いる評価装置を示す構成図である。It is a block diagram which shows the evaluation apparatus used for the evaluation method of this invention. 本発明の実施の形態による遮断波長特性の評価手順を示すフローチャートである。It is a flowchart which shows the evaluation procedure of the cut-off wavelength characteristic by embodiment of this invention. 本発明の実施の形態における、カットオフ・シフト・ファイバの波長１３７５ｎｍにおける遠方出射パターンの測定例を示す特性図である。It is a characteristic view which shows the example of a measurement of the distant emission pattern in wavelength 1375nm of cut-off shift fiber in embodiment of this invention. 本発明の実施の形態において、微動台のＸ軸方向の移動量とＭＦＤの相対変化量の関係を示す特性図である。In the embodiment of the present invention, it is a characteristic diagram showing the relationship between the amount of movement of the fine movement table in the X-axis direction and the relative change amount of MFD. 本発明の実施の形態において、カットオフ・シフト・ファイバにおけるＭＦＤの測定波長に対する変化を評価した結果を示す特性図である。In embodiment of this invention, it is a characteristic view which shows the result of having evaluated the change with respect to the measurement wavelength of MFD in a cutoff shift fiber. 本発明の実施の形態において、遠方出射パターンの受光角度と、式（２）の定数λｃ（θ）の関係を示す特性図である。In the embodiment of the present invention, it is a characteristic diagram showing the relationship between the light receiving angle of the far-out emission pattern and the constant λc (θ) of Equation (2). 本発明の実施の形態において、波長１３１０ｎｍで測定した曲げ損失特性向上型光ファイバの遠方出射パターンを示す特性図である。In embodiment of this invention, it is a characteristic view which shows the far emission pattern of the bending loss characteristic improvement type | mold optical fiber measured with wavelength 1310nm. 本発明の実施の形態において、波長８５０ｎｍで測定した曲げ損失特性向上型光ファイバの遠方出射パターンを示す特性図である。In embodiment of this invention, it is a characteristic view which shows the far emission pattern of the bending loss characteristic improvement type | mold optical fiber measured with wavelength 850nm.

符号の説明Explanation of symbols

１１ 単一モード光源
１２ 励振用光ファイバ
１２ａ 入射端面
１２ｂ 出射端面
１３ 微動台
１４ 被測定光ファイバ（単一モード光ファイバ）
１４ａ 入射端面
１４ｂ 出射端面
１５ 遠方出射パターン受光素子
DESCRIPTION OF SYMBOLS 11 Single mode light source 12 Excitation optical fiber 12a Incident end surface 12b Outgoing end surface 13 Fine movement table 14 Optical fiber to be measured (single mode optical fiber)
14a Incident end face 14b Outgoing end face 15 Far exit pattern light receiving element

Claims (2)

測定光が入射される被測定単一モード光ファイバの励振条件を異なる２種類の励振条件とし、
各励振条件において、被測定単一モード光ファイバの出射端面から出射される測定光の光強度を、前記出射端面を中心とする円弧上の予め決めた角度範囲の各受光角度において測定することにより、前記出射端面を中心とする円弧上の各受光角度における測定光の光強度の特性を示す遠方出射パターン（Ｆ（λ、θ））を、前記測定光の所望の波長範囲について求め、
更に、各励振条件において、前記波長範囲の各波長における遠方出射パターン（Ｆ（λ、θ））を式（１）に適用することにより各波長におけるモードフィールド径（２Ｗ（λ））を求めて、各励振条件毎にモードフィールド径と波長との関係特性を求め、
２種類の励振条件のうちの一方の励振条件でのモードフィールド径と波長との関係特性を示す特性曲線と、２種類の励振条件のうちの他方の励振条件でのモードフィールド径と波長との関係特性を示す特性曲線とが交差する波長（λｃ０）を求め、
この交差した波長（λｃ０）と、遠方出射パターンの受光角度範囲に依存して予め定められた定数（λｃ（θ））とを加算して、被測定単一モード光ファイバの遮断波長λｃ（ＦＦＰ）を求めることを特徴とする単一モード光ファイバの遮断波長特性の評価方法。
Figure 0004322630
 The excitation conditions of the single-mode optical fiber to be measured that are incident on the measurement light are two different excitation conditions,
Under each excitation condition , by measuring the light intensity of the measurement light emitted from the exit end face of the single-mode optical fiber to be measured at each light receiving angle in a predetermined angle range on an arc centered on the exit end face , A far emission pattern (F (λ, θ)) indicating the characteristics of the light intensity of the measurement light at each light receiving angle on the arc centered on the emission end face is obtained for a desired wavelength range of the measurement light,
Further, in each excitation condition, the mode field diameter (2W (λ)) at each wavelength is obtained by applying the far emission pattern (F (λ, θ)) at each wavelength in the wavelength range to Equation (1). , Find the relationship between the mode field diameter and wavelength for each excitation condition ,
The characteristic curve showing the relationship between the mode field diameter and the wavelength under one of the two excitation conditions, and the mode field diameter and the wavelength under the other of the two excitation conditions. Find the wavelength (λc0) at which the characteristic curve indicating the relationship characteristic intersects,
The crossed wavelength (λc0) and a constant (λc (θ)) determined in advance depending on the light receiving angle range of the far emission pattern are added to obtain the cutoff wavelength λc (FFP ) of the single-mode optical fiber to be measured. ) For determining the cutoff wavelength characteristic of a single-mode optical fiber.
Figure 0004322630
 前記被測定単一モード光ファイバの端面に入射する前記測定光の入射位置を制御することにより、被測定単一モード光ファイバの励振条件を変化させることを特徴とする請求項１に記載の単一モード光ファイバの遮断波長特性の評価方法。   2. The single-mode optical fiber according to claim 1, wherein the excitation condition of the single-mode optical fiber to be measured is changed by controlling an incident position of the measurement light incident on an end face of the single-mode optical fiber to be measured. Evaluation method of cut-off wavelength characteristics of single-mode optical fiber.
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