JP2005070552A - Dispersion compensator, optical transmission line and optical communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dispersion compensator capable of compensating the wavelength dispersion of a transmission optical fiber sufficiently over a broad wavelength band. <P>SOLUTION: A dispersion compensator 10 can compensate the wavelength dispersion of the transmission optical fiber by a dispersion compensator which is characterized in that it is constituted by cascading N lines (N is an integer of two or more) of optical fibers 11<SB>1</SB>to 11<SB>N</SB>and when the length of an n-th optical fiber among these N lines of optical fibers is defined as L<SB>n</SB>[Km] and in the predetermined wavelength in a wavelength region of a band width of 30nm or more, the dispersion value of the n-th optical fiber and the fourth dispersion value of the n-the optical fiber are defined respectively as D<SB>n</SB>[ps/nm<SP>3</SP>/km], C<SB>n</SB>[ps/nm<SP>3</SP>/km], the absolute value of RDC is ≤10<SP>-4</SP>/nm<SP>2</SP>. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a dispersion compensator that compensates for chromatic dispersion of an optical fiber for transmission, an optical transmission line including the optical fiber for transmission and the dispersion compensator, and an optical communication system that transmits signal light through the optical transmission line. It is.

  2. Description of the Related Art A wavelength division multiplexing (WDM) optical communication system multiplexes multi-wavelength signal light and transmits it through an optical transmission line, and can transmit and receive a large amount of information at high speed. In order to perform high-quality signal light transmission in such a WDM optical communication system, the absolute value of the accumulated chromatic dispersion of the signal light transmission path from the optical transmitter to the optical receiver is set to the entire signal light wavelength band. It is required to be small throughout.

Incidentally, since a transmission optical fiber generally used as an optical transmission line has chromatic dispersion, a dispersion compensator for compensating the chromatic dispersion of the transmission optical fiber is inserted into the signal light transmission path. That is, since the chromatic dispersion of a general transmission optical fiber is positive, a dispersion compensator having a negative chromatic dispersion can be used, and a dispersion compensating optical fiber can be used as the dispersion compensator. Furthermore, in order to compensate for dispersion in a wide wavelength range, not only chromatic dispersion is compensated, but also dispersion slope is compensated. In addition, as an entire optical transmission line including a transmission optical fiber and a dispersion compensator (dispersion compensation optical fiber), the absolute value of cumulative chromatic dispersion over the entire signal light wavelength band is reduced (for example, Patent Documents). 1).
US Pat. No. 6,393,188

  However, even if both chromatic dispersion and dispersion slope can be completely compensated for at a certain wavelength in the signal light wavelength band, the optical transmission line is used at other wavelengths (for example, wavelengths at both ends of the signal light wavelength band). Reduction of the absolute value of the total accumulated chromatic dispersion is not sufficient.

  The present invention has been made to solve the above-described problems, and a dispersion compensator capable of sufficiently compensating the chromatic dispersion of a transmission optical fiber over a wide wavelength range, and accumulating over a wide wavelength range. It is an object of the present invention to provide an optical transmission line in which the absolute value of chromatic dispersion can be sufficiently reduced, and an optical communication system capable of performing higher-quality multi-wavelength signal light transmission.

In the dispersion compensator according to the present invention, N optical fibers (N is an integer of 2 or more) are cascade-connected, and the length of the nth optical fiber among these N optical fibers is L _n [km]. , The dispersion value of the n-th optical fiber is D _n [ps / nm / km] at a predetermined wavelength in the wavelength band of 30 nm or more, and the fourth-order dispersion value of the n-th optical fiber is C _{When n} [ps / nm ³ / km], the absolute value of the RDC value represented by the following formula (1) is 10 ⁻⁴ / nm ² or less. More preferably, the absolute value of the RDC value is 10 ⁻⁵ / nm ² or less.

このようにＲＤＣ値の絶対値が小さい分散補償器は、一般にＲＤＣ値の絶対値が小さい伝送用光ファイバの波長分散を、広い波長域に亘って充分に補償することができる。なお、波長域は、その分散補償器が用いられる光通信システムにおける信号光波長帯域であり、例えばＣバンドである。また、上記の要件（および、以降の要件）は、波長域内の少なくとも１波長で満たされればよいが、或る波長範囲で満たされるのがより好適である。

In this way, the dispersion compensator having a small absolute value of the RDC value can sufficiently compensate for the chromatic dispersion of the transmission optical fiber generally having a small absolute value of the RDC value over a wide wavelength range. The wavelength band is a signal light wavelength band in an optical communication system in which the dispersion compensator is used, and is, for example, a C band. In addition, the above requirement (and subsequent requirements) may be satisfied with at least one wavelength within the wavelength range, but it is more preferable that the above requirement is satisfied within a certain wavelength range.

  The dispersion compensator according to the present invention preferably includes, as N optical fibers, one having a positive fourth-order dispersion value and one having a negative fourth-order dispersion value. This is convenient for reducing the absolute value of the RDC value.

  In the dispersion compensator according to the present invention, as a first aspect, it is preferable that the RDS value is 0.0043 / nm or more and 0.0043 / nm or less. In this case, the international standard ITU-T G When the single mode optical fiber defined by .652 is used as a transmission optical fiber, the chromatic dispersion of the transmission optical fiber can be sufficiently compensated over a wide wavelength range.

  In the dispersion compensator according to the present invention, as a second aspect, it is preferable that the RDS value is 0.000068 / nm or more and 0.0008 / nm or less. In this case, the dispersion compensator is defined by ITU-T G.655. Among these non-zero dispersion shifted optical fibers, when PureGuide (registered trademark) is used as a transmission optical fiber, the chromatic dispersion of the transmission optical fiber can be sufficiently compensated over a wide wavelength range.

  In the dispersion compensator according to the present invention, as a third aspect, it is preferable that the RDS value is 0.0009 / nm or more and 0.011 / nm or less. In this case, the dispersion compensator is defined by ITU-T G.655. Among the non-zero dispersion shifted optical fibers, when TrueWave-RS (registered trademark) is used as a transmission optical fiber, the chromatic dispersion of the transmission optical fiber can be sufficiently compensated over a wide wavelength range. .

  The dispersion compensator according to the present invention preferably has an insertion loss α [dB] of “−0.005 × (total chromatic dispersion [ps / nm]) + 1.1” or less.

  An optical transmission line according to a first aspect of the present invention includes a transmission optical fiber that transmits signal light, and the dispersion compensator according to the first aspect that compensates the chromatic dispersion of the transmission optical fiber. And the difference in RDS value between the dispersion compensators is 0.0003 / nm or less. It is preferable that the absolute value of the total chromatic dispersion is 0.01 ps / nm / km or less at all wavelengths in the wavelength range.

  An optical transmission line according to a second invention includes a transmission optical fiber that transmits signal light, and the dispersion compensator according to the second aspect that compensates the chromatic dispersion of the transmission optical fiber, and the transmission optical fiber. And the difference in RDS value between the dispersion compensators is 0.0007 / nm or less. It is preferable that the absolute value of the total chromatic dispersion is 0.05 ps / nm / km or less at all wavelengths in the wavelength range.

  An optical transmission line according to a third aspect of the present invention includes a transmission optical fiber that transmits signal light, and the dispersion compensator according to the third aspect that compensates the chromatic dispersion of the transmission optical fiber, and the transmission optical fiber. The difference between the RDS values of the dispersion compensator and the dispersion compensator is 0.001 / nm or less. It is preferable that the absolute value of the overall chromatic dispersion is 0.02 ps / nm / km or less at all wavelengths in the wavelength range.

  An optical transmission line according to a fourth aspect of the present invention includes an optical fiber for transmission having an RDS value of 0.0032 / nm or more and 0.0043 / nm or less at any predetermined wavelength in a wavelength band having a bandwidth of 30 nm or more. A dispersion compensator that compensates for the chromatic dispersion of the transmission optical fiber, and the difference between the RDS values of the transmission optical fiber and the dispersion compensator at a predetermined wavelength is 0.0003 / nm or less, The absolute value of chromatic dispersion is 0.01 ps / nm / km or less.

  An optical transmission line according to a fifth invention includes a transmission optical fiber having an RDS value of 0.0065 / nm or more and 0.0008 / nm or less at any predetermined wavelength in a wavelength band having a bandwidth of 30 nm or more. A dispersion compensator that compensates for the chromatic dispersion of the transmission optical fiber, and the difference between the RDS values of the transmission optical fiber and the dispersion compensator at a predetermined wavelength is 0.0007 / nm or less, The absolute value of chromatic dispersion is 0.05 ps / nm / km or less.

  An optical transmission line according to a sixth invention includes a transmission optical fiber having an RDS value of 0.0009 / nm or more and 0.011 / nm or less at any predetermined wavelength in a wavelength band having a bandwidth of 30 nm or more. A dispersion compensator that compensates for the chromatic dispersion of the transmission optical fiber, and the difference between the RDS values of the transmission optical fiber and the dispersion compensator at a predetermined wavelength is 0.001 / nm or less. The absolute value of chromatic dispersion is 0.019 ps / nm / km or less.

  The optical transmission lines according to the fourth to sixth inventions preferably include a wavelength band of 1535 nm to 1565 nm.

  In any of the optical transmission lines according to the first to sixth inventions, the absolute value of the entire chromatic dispersion can be sufficiently reduced over a wide wavelength range. The optical transmission lines according to the first and fourth inventions include a single mode optical fiber defined by ITU-T G.652 as a transmission optical fiber. The optical transmission lines according to the second and fifth inventions include PureGuide (registered trademark) as a transmission optical fiber among non-zero dispersion shifted optical fibers defined by ITU-T G.655. The optical transmission lines according to the third and sixth inventions include TrueWave-RS (registered trademark) as a transmission optical fiber among non-zero dispersion shifted optical fibers defined by ITU-T G.655. .

  An optical communication system according to the present invention is characterized in that multi-wavelength signal light is transmitted by any one of the optical transmission lines according to the first to sixth inventions. Since this optical communication system transmits signal light through the above-described optical transmission line with a sufficiently small absolute value of chromatic dispersion over a wide wavelength range, it is possible to transmit multi-wavelength signal light with high quality. it can.

  The dispersion compensator according to the present invention can sufficiently compensate for the chromatic dispersion of the transmission optical fiber over a wide wavelength range.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In the following, the embodiment will be described assuming the C band (1530 nm to 1565 nm) as the signal light wavelength band, but the present invention is not limited to the C band.

  FIG. 1 is a configuration diagram of an optical communication system 1 according to the present embodiment. The optical communication system 1 shown in this figure includes an optical transmission line 2 including a dispersion compensator 10 and a transmission optical fiber 20, an optical transmitter 30, and an optical receiver 40. The transmission optical fiber 20 is laid between the optical transmitter 30 and the optical receiver 40. The dispersion compensator 10 may be laid between the optical transmitter 30 and the optical receiver 40, or may be modularized and provided at a certain position. In this optical communication system 1, the multi-wavelength signal light multiplexed and transmitted from the optical transmitter 30 is transmitted through the optical transmission path 2 to reach the optical receiver 40, and in this optical receiver 40, for each wavelength. Received.

  The optical transmission path 2 in the signal light transmission path from the optical transmitter 30 to the optical receiver 40 includes the transmission optical fiber 20 and the dispersion compensator 10 in the subsequent stage. The transmission optical fiber 20 is, for example, a single mode optical fiber defined by the international standard ITU-T G.652, a dispersion shifted optical fiber defined by ITU-T G.653, or an ITU -T Non-zero dispersion shifted optical fiber defined by G.655. The dispersion compensator 10 compensates the chromatic dispersion of the transmission optical fiber 20 and is formed by connecting N optical fibers in cascade. However, N is an integer of 2 or more.

FIG. 2 is a configuration diagram of the dispersion compensator 10 according to the present embodiment. The dispersion compensator 10 according to the present embodiment is formed by connecting _N optical fibers 11 _{1 to} 11 _N in cascade. Here, the length of the n-th optical fiber 11 _n is L _n [km], the dispersion value (Dispersion) of the n-th optical fiber 11 _n is D _n [ps / nm / km], and the n-th light The dispersion slope of the fiber 11 _n is S _n [ps / nm ² / km], and the fourth-order dispersion value (Dispersion Curvature) of the nth optical fiber 11 _n is C _n [ps / nm ³ / km]. And However, n is each integer of 1 or more and N or less. At this time, there is a relationship expressed by the following equation (2) among the chromatic dispersion D _n , the dispersion slope S _{n, the} fourth-order dispersion value C _n, and the wavelength λ [nm] of each optical fiber 11 _n .

一般に、光ファイバのＲＤＳ（Relative Dispersion Slope）値［１／ｎｍ］は、分散スロープＳと波長分散Ｄとの比（Ｓ／Ｄ）で定義され、分散スロープの補償率を表す指標として用いられる。また、一般に、光ファイバのＲＤＣ（Relative Dispersion Curvature）値［１／ｎｍ^２］は、四次分散値Ｃと波長分散Ｄとの比（Ｃ／Ｄ）で定義され、四次分散の補償率を表す指標として用いられる。

In general, an RDS (Relative Dispersion Slope) value [1 / nm] of an optical fiber is defined by a ratio (S / D) between a dispersion slope S and a chromatic dispersion D, and is used as an index representing a dispersion slope compensation rate. In general, the RDC (Relative Dispersion Curvature) value [1 / nm ² ] of an optical fiber is defined by the ratio (C / D) between the fourth-order dispersion value C and the chromatic dispersion D, and the compensation rate of the fourth-order dispersion is expressed as follows. Used as an index to represent.

  The fourth-order dispersion value C of an optical fiber generally installed and used as a transmission optical fiber is very small in the signal light wavelength band, whereas the fourth-order dispersion value C as a single unit of a conventional dispersion-compensating optical fiber is absolutely The value is a large negative number. Therefore, even if the conventional dispersion compensator can completely compensate both the chromatic dispersion and the dispersion slope of the transmission optical fiber at a certain wavelength within the signal light wavelength band, For example, compensation is insufficient at the wavelengths at both ends of the signal light wavelength band.

Therefore, the dispersion compensator 10 according to the present embodiment is configured by cascade-connecting N optical fibers, and the absolute value of the entire RDC value of the dispersion compensator 10 expressed by the following equation (3) is 10 ^{−. 4} / nm ² or less. More preferably, the absolute value of the entire RDC value of the dispersion compensator 10 is 10 ⁻⁵ / nm ² or less.

Ｎ本の光ファイバ１１_１〜１１_Ｎのうち、いずれかの光ファイバの四次分散値が正であり。他のいずれかの光ファイバの四次分散値が負であるのが好適であり、このようにすることにより、分散補償器１０の全体のＲＤＣ値の絶対値は１０^−４／ｎｍ^２以下（または１０^−５／ｎｍ^２以下）となり得る。

Of the _N optical fibers 11 _{1 to} 11 _N , the fourth-order dispersion value of any one of the optical fibers is positive. It is preferable that the fourth-order dispersion value of any other optical fiber is negative. By doing so, the absolute value of the total RDC value of the dispersion compensator 10 is 10 ⁻⁴ / nm ² or less ( Or 10 ⁻⁵ / nm ² or less).

  Further, the entire RDS value of the dispersion compensator 10 is expressed by the following equation (4).

分散補償器１０が伝送用光ファイバ２０の波長分散および分散スロープの双方を補償するには、分散補償器１０のＲＤＳ値が伝送用光ファイバ２０のＲＤＳ値と略等しいことが好ましい。さらに、分散補償器１０が伝送用光ファイバ２０の四次分散をも補償するには、分散補償器１０のＲＤＣ値が伝送用光ファイバ２０のＲＤＣ値と略等しいことが好ましい。そこで、伝送用光ファイバとして一般に敷設されて用いられる光ファイバの四次分散値Ｃの絶対値が信号光波長帯域において非常に小さいことに対応して、本実施形態に係る分散補償器１０のＲＤＣ値の絶対値も小さいことが好ましい。

In order for the dispersion compensator 10 to compensate for both chromatic dispersion and dispersion slope of the transmission optical fiber 20, it is preferable that the RDS value of the dispersion compensator 10 is substantially equal to the RDS value of the transmission optical fiber 20. Further, in order for the dispersion compensator 10 to compensate for the fourth-order dispersion of the transmission optical fiber 20, it is preferable that the RDC value of the dispersion compensator 10 is substantially equal to the RDC value of the transmission optical fiber 20. Accordingly, in response to the fact that the absolute value of the fourth-order dispersion value C of an optical fiber generally installed and used as a transmission optical fiber is very small in the signal light wavelength band, the RDC of the dispersion compensator 10 according to the present embodiment. It is preferable that the absolute value of the value is also small.

  It is preferable that the RDS value of the dispersion compensator 10 as a whole is 0.0034 / nm or more and 0.0043 / nm or less. In this case, when a single mode optical fiber defined by ITU-T G.652 is used as the transmission optical fiber 20, the dispersion compensator 10 increases the wavelength dispersion of the transmission optical fiber 20 with a wide signal light wavelength. It is possible to sufficiently compensate over the band. Further, it is preferable that the difference between the RDS values of the transmission optical fiber 20 and the dispersion compensator 10 is 0.0003 / nm or less. Furthermore, it is preferable that the absolute value of the chromatic dispersion of the entire optical transmission line 2 is 0.01 ps / nm / km or less.

  The overall RDS value of the dispersion compensator 10 is preferably 0.000068 / nm or more and 0.0008 / nm or less. In this case, when the PureGuide (registered trademark) is used as the transmission optical fiber 20 among the non-zero dispersion-shifted optical fibers defined by ITU-T G.655, the dispersion compensator 10 is used as the transmission optical fiber. The chromatic dispersion of 20 can be sufficiently compensated over a wide signal light wavelength band. Further, it is preferable that the difference between the RDS values of the transmission optical fiber 20 and the dispersion compensator 10 is 0.0007 / nm or less. Further, it is preferable that the absolute value of the chromatic dispersion of the entire optical transmission line 2 is 0.05 ps / nm / km or less.

  The overall RDS value of the dispersion compensator 10 is preferably 0.009 / nm or more and 0.011 / nm or less. In this case, when TrueWave-RS (registered trademark) is used as the transmission optical fiber 20 among the non-zero dispersion shifted optical fibers defined by ITU-T G.655, the dispersion compensator 10 is used for the transmission. The chromatic dispersion of the optical fiber 20 can be sufficiently compensated over a wide signal light wavelength band. Further, it is preferable that the difference between the RDS values of the transmission optical fiber 20 and the dispersion compensator 10 is 0.001 / nm or less. Furthermore, it is preferable that the absolute value of the chromatic dispersion of the entire optical transmission line 2 is 0.02 ps / nm / km or less.

  Further, the insertion loss α [dB] of the dispersion compensator 10 preferably satisfies the following formula (5).

帯域幅が３０ｎｍ以上の波長帯の中のいずれかの所定波長において伝送用光ファイバ２０のＲＤＳ値が０.００３２／ｎｍ以上０.００３８／ｎｍ以下であり、所定波長において伝送用光ファイバ２０および分散補償器１０それぞれのＲＤＳ値の差が０.０００３／ｎｍ以下であり、上記波長帯において光伝送路２の全体の波長分散の絶対値が０.０１ｐｓ／ｎｍ／ｋｍ以下であるのが好適である。なお、上記波長帯は１５３５ｎｍ〜１５６５ｎｍの波長帯を含むのが好適であり、上記の特性を有する伝送用光ファイバ２０として、ＩＴＵ-Ｔ Ｇ.６５２で規定されるシングルモード光ファイバが挙げられる。

The RDS value of the transmission optical fiber 20 is 0.0034 / nm or more and 0.0043 / nm or less at any one of the predetermined wavelengths in the wavelength band of 30 nm or more, and the transmission optical fiber 20 at the predetermined wavelength and It is preferable that the difference between the RDS values of the dispersion compensators 10 is 0.0003 / nm or less, and that the absolute value of the overall chromatic dispersion of the optical transmission line 2 in the wavelength band is 0.01 ps / nm / km or less. It is. The wavelength band preferably includes a wavelength band of 1535 nm to 1565 nm, and the transmission optical fiber 20 having the above characteristics includes a single mode optical fiber defined by ITU-T G.652.

  The RDS value of the transmission optical fiber 20 is 0.000068 / nm or more and 0.0008 / nm or less at any predetermined wavelength in the wavelength band of 30 nm or more, and the transmission optical fiber 20 is used at the predetermined wavelength. And the difference between the RDS values of the dispersion compensators 10 is 0.0007 / nm or less, and the absolute value of the overall chromatic dispersion of the optical transmission line 2 in the wavelength band is 0.05 ps / nm / km or less. Is preferred. The wavelength band preferably includes a wavelength band of 1535 nm to 1565 nm, and the transmission optical fiber 20 having the above characteristics is a non-zero dispersion shifted optical fiber defined by ITU-T G.655. PureGuide (registered trademark).

  The RDS value of the transmission optical fiber 20 is 0.0009 / nm or more and 0.011 / nm or less at any given wavelength in the wavelength band of 30 nm or more, and the transmission optical fiber 20 is used at the predetermined wavelength. The difference between the RDS values of the dispersion compensator 10 and the dispersion compensator 10 is 0.001 / nm or less, and the absolute value of the overall chromatic dispersion of the optical transmission line 2 in the wavelength band is 0.019 ps / nm / km or less. Is preferred. The wavelength band preferably includes a wavelength band of 1535 nm to 1565 nm, and the transmission optical fiber 20 having the above characteristics is a non-zero dispersion shifted optical fiber defined by ITU-T G.655. Examples include TrueWave-RS (registered trademark).

Hereinafter, a case where N is a value of 2, that is, a case where the dispersion compensator 10 includes two optical fibers 11 ₁ and 11 ₂ will be described.

The first optical fiber 11 ₁ value and RDC ₁ value ₁ of RDS is expressed by the following equation (6). The second optical fiber 11 _{and second} RDS ₂ values and RDC ₂ value is expressed by the following equation (7).

分散補償器１０のＲＤＳ_０値およびＲＤＣ_０値は下記(8)式で表される。また、分散補償器１０のＲＤＣ_０値は、第１の光ファイバ１１_１のＲＤＳ_１値およびＲＤＣ_１値、第２の光ファイバ１１_２のＲＤＳ_２値およびＲＤＣ_２値、ならびに、分散補償器１０のＲＤＳ_０値を用いて、下記(9)式で表される。

The RDS ₀ value and RDC ₀ value of the dispersion compensator 10 are expressed by the following equation (8). The RDC ₀ value of the dispersion compensator 10 includes the RDS ₁ value and RDC ₁ value of the _first optical fiber 11 ₁ , the RDS ₂ value and RDC ₂ value of the second optical fiber 11 ₂ , and the dispersion compensator 10. This is expressed by the following formula (9) using the RDS ₀ value.

  Next, examples of the optical transmission line 2 and the dispersion compensator 10 according to the present embodiment will be described. In each of the following embodiments, it is assumed that the dispersion compensator is composed of two optical fibers.

  FIG. 3 is a table summarizing the specifications of the optical fibers F2 to F13 that can constitute the dispersion compensator of the embodiment and the optical fibers F14 to F16 that can be used as transmission optical fibers.

Each of the optical fibers F2 to F7 and F9 to F13 has a refractive index profile as shown in FIG. This refractive index profile is of a triple clad type, and in order from the center is a core region (maximum refractive index n ₁ , outer diameter 2a), first cladding region (refractive index n ₂ , outer diameter 2b), second cladding. It has a region (refractive index n ₃ , outer diameter 2c) and an outermost cladding region (refractive index n ₀ ).

The optical fiber F8 has a refractive index profile as shown in FIG. This refractive index profile is of a quadruple clad type, and in order from the center is a core region (maximum refractive index n ₁ , outer diameter 2a), first cladding region (refractive index n ₂ , outer diameter 2b), second cladding. It has a region (refractive index n ₃ , outer diameter 2c), a third cladding region (refractive index n ₄ , outer diameter 2d) and an outermost cladding region (refractive index n ₀ ).

  In the refractive index profiles shown in FIG. 4 and FIG. 5 respectively, the relative refractive index difference of the core region is Δn1 and the relative refractive index difference of the first cladding region is Δn2 with reference to the refractive index of the outermost cladding region. The relative refractive index difference of the second cladding region is Δn3, and the relative refractive index difference of the third cladding region is Δn4.

  FIG. 3 shows the relative refractive index difference Δn1 of the core region, the relative refractive index difference Δn2 of the first cladding region, the relative refractive index difference Δn3 of the second cladding region, and the relative refractive index difference of the third cladding region. Δn4, the outer diameter 2a of the core region, the outer diameter 2b of the first cladding region, the outer diameter 2c of the second cladding region, and the outer diameter 2d of the third cladding region are shown. Subsequently, chromatic dispersion D, dispersion slope S, fourth-order dispersion value C, RDS value, and RDC value at a wavelength of 1550 nm are shown. Subsequently, the effective cutoff wavelength and the bending loss at the bending diameter of 40 mmφ and the bending diameter of 60 mmφ at the wavelength of 1550 nm are shown.

  As shown in FIG. 3, the fourth-order dispersion value C of each of the optical fibers F2 to F5, F9 to F11 is positive, and the fourth-order dispersion value C of each of the optical fibers F6 to F8, F12, and F13 is negative. The transmission optical fiber F14 corresponds to a single mode optical fiber defined by ITU-T G.652. The transmission optical fiber F15 corresponds to PureGuide (registered trademark) among non-zero dispersion shifted optical fibers defined by ITU-T G.655. Further, the transmission optical fiber F16 corresponds to TrueWave-RS (registered trademark) among non-zero dispersion-shifted optical fibers defined by ITU-T G.655.

  FIG. 6 is a table summarizing specifications of the dispersion compensators M9 to M12 of the example. In this figure, for each dispersion compensator, the type of optical fiber (shown in FIG. 3), length, glass diameter, and coating diameter are shown. Subsequently, the total chromatic dispersion, total dispersion slope, total fourth-order dispersion value, RDS, RDC, insertion loss, polarization mode dispersion (PMD), and nonlinear phase shift amount of the dispersion compensator at the wavelength of 1550 nm are shown. . Further, the storage form and coil diameter of each optical fiber are shown.

The nonlinear phase shift amount φ is expressed by the following equation (10). Here, λ is the wavelength [nm], n ₂ is the nonlinear refractive index [m ² / W], A _eff is the effective core area [μm ² ], and L is the length [km]. , Α is transmission loss [1 / km], and P ₀ is input optical power [W]. The input light power P ₀ was determined so that the power of the output light from the dispersion compensator was −28 dBm.

実施例の分散補償器Ｍ９〜Ｍ１２それぞれは、構成する各光ファイバがコイル状に巻かれて樹脂保持され、サイズ２２０ｍｍ×２３０ｍｍ×４０ｍｍの筐体の中に収納された。

In each of the dispersion compensators M9 to M12 of the example, each optical fiber constituting the coil was wound in a coil shape and held in a resin, and housed in a housing having a size of 220 mm × 230 mm × 40 mm.

As shown in this figure, at the wavelength of 1550 nm, the absolute values of the RDC values of the dispersion compensators M9 to M11 of the example are 10 ⁻⁵ / nm ² or less, and the RDC values of the dispersion compensator M12 of the example are The absolute value is 10 ⁻⁴ / nm ² or less.

  FIG. 7 is a diagram illustrating the chromatic dispersion characteristics of the dispersion compensator M9 of the embodiment and the two optical fibers F2 and F6 constituting the dispersion compensator M9. FIG. 8 is a diagram illustrating the overall chromatic dispersion characteristics of the optical transmission line of the example including the dispersion compensator M9 of the example and the transmission optical fiber F14 having a length of 100 km. At the wavelength of 1550 nm, the RDS value of the dispersion compensator M9 is 0.0033 / nm, the RDS value of the transmission optical fiber F14 is 0.0033 / nm, and the difference between them is substantially zero.

  FIG. 9 is a diagram illustrating the chromatic dispersion characteristics of the dispersion compensator M10 of the embodiment and the two optical fibers F4 and F7 constituting the dispersion compensator M10. FIG. 10 is a diagram illustrating the overall chromatic dispersion characteristics of the optical transmission line of the example including the dispersion compensator M10 of the example and the transmission optical fiber F14 having a length of 80 km. At the wavelength of 1550 nm, the RDS value of the dispersion compensator M10 is 0.0033 / nm, the RDS value of the transmission optical fiber F14 is 0.0033 / nm, and the difference between them is substantially zero.

  FIG. 11 is a diagram illustrating the chromatic dispersion characteristics of the dispersion compensators M11 and M12 of the embodiment and the two optical fibers F5 and F8 constituting them. FIG. 12 is a diagram illustrating the overall chromatic dispersion characteristics of the optical transmission line of the example including the dispersion compensator M11 of the example and the transmission optical fiber F15 having a length of 100 km. FIG. 13 is a diagram illustrating the overall chromatic dispersion characteristics of the optical transmission line of the example including the dispersion compensator M12 of the example and the transmission optical fiber F16 having a length of 100 km. At the wavelength of 1550 nm, the RDS value of the dispersion compensator M11 is 0.0075 / nm, the RDS value of the transmission optical fiber F15 is 0.0075 / nm, and the difference between them is substantially zero. At a wavelength of 1550 nm, the RDS value of the dispersion compensator M12 is 0.0100 / nm, the RDS value of the transmission optical fiber F16 is 0.00098 / nm, and the difference between these is 0.0002 / nm.

  As can be seen from FIG. 7, FIG. 9, and FIG. 11, each of the dispersion compensators M9 to M12 of the example has almost linear relationship with respect to the wavelength in the C band, and the absolute value of the fourth-order dispersion value. The value is very small. As can be seen from FIGS. 8, 10, 12, and 13, the optical transmission line of each example has an extremely small chromatic dispersion value of 0.02 ps / nm / km or less in the C band. .

  In particular, the optical transmission line of the embodiment shown in FIG. 8 has an absolute value of chromatic dispersion of 0.009 ps / nm / km or less in the C band. The optical transmission line of the embodiment shown in FIG. 10 has an absolute value of chromatic dispersion of 0.006 ps / nm / km or less in the C band. In the optical transmission line of the embodiment shown in FIG. 12, the absolute value of chromatic dispersion in the C band is 0.005 ps / nm / km or less.

  FIG. 14 is a table summarizing the specifications of the dispersion compensator and the optical transmission line of another embodiment. This figure shows the types of the first optical fiber and the second optical fiber constituting the dispersion compensator, the RDS value and the RDC value, the RDS value and RDC value of the dispersion compensator, the type of optical fiber for transmission, and the optical The residual dispersion of the transmission line is shown. The residual dispersion of the optical transmission line is the maximum absolute value of chromatic dispersion in the C band. This figure also shows what has already been shown in FIGS.

As shown in this figure, the dispersion compensator of each example has an absolute value of the RDC value of 10 ⁻⁴ / nm ² or less at a wavelength of 1550 nm. In particular, each of the dispersion compensators M9 to M11, M13, and M14 has an absolute value of an RDC value of 10 ⁻⁵ / nm ² or less at a wavelength of 1550 nm. Among them, the dispersion compensator M14 including the optical fibers F9 and F12 has an absolute value of the RDC value of 10 ⁻⁶ / nm ² or less at a wavelength of 1550 nm.

  In the optical transmission line of each example, the absolute value of chromatic dispersion in the C band is 0.05 ps / nm / km or less. In particular, an optical transmission path composed of the dispersion compensator M9 and the transmission optical fiber F14, an optical transmission path composed of the dispersion compensator M10 and the transmission optical fiber F14, an optical transmission path composed of the dispersion compensator M11 and the transmission optical fiber F14, The optical transmission line composed of the dispersion compensator M13 and the transmission optical fiber F14 and the optical transmission line composed of the dispersion compensator M14 and the transmission optical fiber F15 each have an absolute value of chromatic dispersion of 0.01 ps / cm in the C band. It is below nm / km and very small.

FIG. 15 is a graph showing the relationship between the insertion loss α and the total chromatic dispersion of the dispersion compensator of the example. FIG. 16 is a graph showing the relationship between the nonlinear phase shift amount φ and the total chromatic dispersion of the dispersion compensator of the example. FIG. 17 is a graph showing the relationship between the polarization mode dispersion (PMD) and the total chromatic dispersion of the dispersion compensator of the example. FIG. 18 is a graph showing the relationship between γL _eff and the total chromatic dispersion of the dispersion compensator of the example. Here, γ is a nonlinear coefficient.

  15 to 18 show Examples A to C and Comparative Examples a to c, respectively. The dispersion compensator of Example A is suitably used when a single mode optical fiber defined by ITU-T G.652 is used as a transmission optical fiber. The dispersion compensator of Example B is preferably used when PureGuide (registered trademark) is used as a transmission optical fiber among non-zero dispersion shifted optical fibers defined by ITU-T G.655. Further, the dispersion compensator of Example C is suitably used when TrueWave-RS (registered trademark) is used as a transmission optical fiber among non-zero dispersion shifted optical fibers defined by ITU-T G.655. Is.

  The straight line shown in FIG. 15 indicates the boundary of the range represented by the above-described equation (5). Each of the dispersion compensators in Examples A to C satisfies the condition of the above formula (5). Further, as can be seen from FIGS. 15 to 18, the dispersion compensators of Examples A to C have no problem with respect to insertion loss, nonlinear phase shift amount, polarization mode dispersion, and nonlinearity.

1 is a configuration diagram of an optical communication system 1 according to the present embodiment. It is a lineblock diagram of dispersion compensator 10 concerning this embodiment. It is the table | surface which summarized each item of the optical fibers F2-F13 which can comprise the dispersion compensator of an Example, and the optical fibers F14-F16 which can be used as an optical fiber for transmission. It is a figure which shows the refractive index profile of the optical fiber which can comprise the dispersion compensator of an Example. It is a figure which shows the refractive index profile of the optical fiber which can comprise the dispersion compensator of an Example. It is the table | surface which summarized the item of each dispersion compensator M9-M12 of an Example. It is a figure which shows the wavelength dispersion characteristic of the dispersion compensator M9 of an Example, and two optical fiber F2, F6 which comprises this. It is a figure which shows the whole chromatic dispersion characteristic of the optical transmission line of an Example containing the dispersion compensator M9 of an Example, and the optical fiber F14 for transmission of length 100km. It is a figure which shows the wavelength dispersion characteristic of the dispersion compensator M10 of an Example, and the two optical fibers F4 and F7 which comprise this. It is a figure which shows the whole chromatic dispersion characteristic of the optical transmission line of an Example containing the dispersion | distribution compensator M10 of an Example, and the optical fiber F14 for 80 km in length. It is a figure which shows the wavelength dispersion characteristic of dispersion compensator M11, M12 of an Example, and the two optical fibers F5 and F8 which comprise these. It is a figure which shows the chromatic dispersion characteristic of the whole optical transmission line of an Example containing the dispersion | distribution compensator M11 of an Example, and the optical fiber F15 for transmission of length 100km. It is a figure which shows the chromatic dispersion characteristic of the whole optical transmission line of an Example containing the dispersion | distribution compensator M12 of an Example, and the optical fiber F16 for transmission of length 100km. It is the table | surface which summarized the item of the dispersion compensator and optical transmission line of another Example. It is a graph which shows the relationship between the insertion loss (alpha) and the total chromatic dispersion of the dispersion compensator of an Example. It is a graph which shows the relationship between the nonlinear phase shift amount (phi) of the dispersion compensator of an Example, and total chromatic dispersion. It is a graph which shows the relationship between the polarization mode dispersion (PMD: Polarization Mode Dispersion) of the dispersion compensator of an Example, and total chromatic dispersion. Is a graph showing the relationship between GanmaL _eff and the total chromatic dispersion of the dispersion compensator embodiment.

Explanation of symbols

1 ... optical communication system, 2 ... optical transmission line, 10 ... dispersion compensator, ₁₁ 1 to 11 N _... optical fiber, 20 ... transmission optical fiber, 30 ... optical transmitter, 40 ... optical receiver.

Claims (18)

N optical fibers (N is an integer of 2 or more) are connected in cascade, and the length of the n-th optical fiber among these N optical fibers is L _n [km], and has a bandwidth of 30 nm or more. The dispersion value of the n-th optical fiber is D _n [ps / nm / km] and the fourth-order dispersion value of the n-th optical fiber is C _n [ps / nm ³ / km]. And when

A dispersion compensator, wherein an absolute value of an RDC value represented by the following formula is 10 ⁻⁴ / nm ² or less. The dispersion compensator according to claim 1, wherein an absolute value of the RDC value is 10 ⁻⁵ / nm ² or less.   The dispersion compensator according to claim 1, wherein the N optical fibers include those having a positive fourth-order dispersion value and those having a negative fourth-order dispersion value.   2. The dispersion compensator according to claim 1, wherein the RDS value is 0.0034 / nm or more and 0.0043 / nm or less.   2. The dispersion compensator according to claim 1, wherein the RDS value is 0.000068 / nm or more and 0.0008 / nm or less.   The dispersion compensator according to claim 1, wherein the RDS value is 0.0009 / nm or more and 0.011 / nm or less.   The dispersion compensator according to claim 1, wherein the insertion loss α [dB] is equal to or less than “−0.005 × (total chromatic dispersion [ps / nm]) + 1.1”. A transmission optical fiber for transmitting signal light; and the dispersion compensator according to claim 4 for compensating chromatic dispersion of the transmission optical fiber,
The difference in RDS values between the transmission optical fiber and the dispersion compensator is 0.0003 / nm or less,
An optical transmission line characterized by that.   9. The optical transmission line according to claim 8, wherein the absolute value of the total chromatic dispersion is 0.01 ps / nm / km or less at all wavelengths in the wavelength band. A transmission optical fiber for transmitting signal light, and a dispersion compensator according to claim 5 for compensating the chromatic dispersion of the transmission optical fiber,
The difference between the RDS values of the transmission optical fiber and the dispersion compensator is 0.0007 / nm or less,
An optical transmission line characterized by that.   11. The optical transmission line according to claim 10, wherein the absolute value of the entire chromatic dispersion is 0.05 ps / nm / km or less at all wavelengths in the wavelength band. A transmission optical fiber for transmitting signal light; and the dispersion compensator according to claim 6 for compensating the chromatic dispersion of the transmission optical fiber,
The difference between the RDS values of the transmission optical fiber and the dispersion compensator is 0.001 / nm or less,
An optical transmission line characterized by that.   13. The optical transmission line according to claim 12, wherein the absolute value of the total chromatic dispersion is 0.02 ps / nm / km or less at all wavelengths in the wavelength band. A transmission optical fiber having an RDS value of 0.0034 / nm or more and 0.0043 / nm or less at any given wavelength in a wavelength band of 30 nm or more, and chromatic dispersion of the transmission optical fiber are compensated. A dispersion compensator,
A difference in RDS values between the transmission optical fiber and the dispersion compensator at the predetermined wavelength is 0.0003 / nm or less;
The absolute value of the overall chromatic dispersion in the wavelength band is 0.01 ps / nm / km or less,
An optical transmission line characterized by that. A transmission optical fiber having an RDS value of 0.0065 / nm or more and 0.0008 / nm or less at any given wavelength in a wavelength band of 30 nm or more, and chromatic dispersion of the transmission optical fiber are compensated A dispersion compensator,
A difference in RDS values between the transmission optical fiber and the dispersion compensator at the predetermined wavelength is 0.0007 / nm or less;
The absolute value of the overall chromatic dispersion in the wavelength band is 0.05 ps / nm / km or less.
An optical transmission line characterized by that. A transmission optical fiber whose RDS value is 0.009 / nm or more and 0.011 / nm or less at any given wavelength in a wavelength band of 30 nm or more, and chromatic dispersion of the transmission optical fiber is compensated A dispersion compensator,
A difference between RDS values of the transmission optical fiber and the dispersion compensator at the predetermined wavelength is 0.001 / nm or less;
The absolute value of the total chromatic dispersion in the wavelength band is 0.019 ps / nm / km or less,
An optical transmission line characterized by that.   The optical transmission line according to claim 14, wherein the wavelength band includes a wavelength band of 1535 nm to 1565 nm. An optical communication system, wherein multi-wavelength signal light is transmitted by the optical transmission line according to any one of claims 8 to 17.

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