JP2006170976A - Device and method for setting incidence light power ratio, program, and recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure wavelength dispersion in a measured optical fiber while keeping a ratio of P1 to P2 in a prescribed value. <P>SOLUTION: A measuring system 1 is provided with a multiplier 33 for multiplying the first incident light having λ1 of wavelength and the second incident light having λ2 of wavelength, and capable of making variable the power ratio that is a ratio of the power P1 of the first incident to the power P2 of the second incident light, a circulator 52 for making a multiplied light output from the multiplier 33 get incident into the measured optical fiber 4 to acquire rear scattered light from an incident end 4a of the measured optical fiber 4, a multiplied light acquisition unit 60 for acquiring the multiplied light from the multiplier 33, and a personal computer 2 for measuring the power ratio based on an output from the multiplied light acquisition unit 60, and for finding setting of the multiplier 33 to bring the power ratio into the prescribed value, and the circulator 52 is connected to the multiplier 33 via the multiplied light acquisition unit 60. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to measurement of chromatic dispersion distribution of an optical fiber.

  Conventionally, the chromatic dispersion distribution of an optical fiber has been measured. As a method for measuring the chromatic dispersion distribution, a method using four-wave mixing is known (for example, see Patent Document 1).

An outline of the four-wave mixing method will be described. First, two pulse lights having different wavelengths (wavelengths λ1, λ2: λ1 <λ2) are amplified by an optical amplifier such as an EDFA (Erbium Doped Fiber Amplifier), and then incident on a test fiber. In the test fiber, four light waves are mixed. The Rayleigh backscattered light of Stokes light or anti-Stokes light generated in the test fiber by mixing the four light waves is extracted from the incident end in the test fiber and detected. Based on the detected Rayleigh backscattered light, the chromatic dispersion distribution of the test fiber can be obtained.
Here, the measurement error of chromatic dispersion caused by self-phase modulation and cross-phase modulation is proportional to 2P1-P2 for Stokes light and proportional to 2P2-P1 for anti-Stokes light (for example, [0031 of Patent Document 1] ] And [0032]). However, P1 is the power of the incident light of wavelength λ1, and P2 is the power of the incident light of wavelength λ2.

  Therefore, in the case of P2 = 2P1, the chromatic dispersion measurement error can be set to zero for Stokes light. In the case of P1 = 2P2, the measurement error of chromatic dispersion can be made zero for anti-Stokes light. Therefore, it is conceivable to reduce the measurement error of chromatic dispersion by adjusting the power ratio of incident light in this way.

Japanese Patent Laid-Open No. 10-83006

  However, by using an optical amplifier such as EDFA, the ratio of P1 and P2 varies due to factors such as wavelengths λ1, λ2, measurement distance range, EDFA gain, etc., and P2 = 2P1 or P1 = 2P2 is difficult to keep.

  Accordingly, an object of the present invention is to enable measurement of chromatic dispersion in an optical fiber to be measured while maintaining a ratio between P1 and P2 at a predetermined value.

  An incident light power ratio setting device according to the present invention combines first incident light having a first wavelength and second incident light having a second wavelength, and the power of the first incident light and the power of the second incident light. A combining means having a variable power ratio, an incident means for causing the combined light output from the combining means to enter the optical fiber to be measured, and backscattered light from the incident end of the optical fiber to be measured. Backscattered light acquiring means for acquiring the combined light acquiring means for acquiring the combined light from the combining means, power ratio measuring means for measuring the power ratio from the output of the combined light acquiring means, and the power Based on the measurement result of the ratio measuring means, there is provided a set value deriving means for obtaining the setting of the multiplexing means so that the power ratio becomes a predetermined value.

  According to the incident light power ratio setting apparatus configured as described above, the multiplexing unit combines the first incident light having the first wavelength and the second incident light having the second wavelength, and the first incident light is combined. The power ratio, which is the ratio between the power of the second incident light and the power of the second incident light, is variable. The incident means causes the combined light output from the combining means to enter the optical fiber to be measured. The backscattered light acquisition means acquires backscattered light from the incident end of the measured optical fiber. The combined light acquisition unit acquires the combined light from the combining unit. The power ratio measuring means measures the power ratio from the output of the combined light acquisition means. The setting value deriving means obtains the setting of the multiplexing means so that the power ratio becomes a predetermined value based on the measurement result of the power ratio measuring means.

  In the incident light power ratio setting device according to the present invention, the incident means may be connected to the multiplexing means via the combined light acquisition means.

  Further, the incident light power ratio setting device according to the present invention may include chromatic dispersion measuring means for measuring chromatic dispersion of the measured optical fiber from the backscattered light.

  Further, in the incident light power ratio setting device according to the present invention, the chromatic dispersion measuring means measures chromatic dispersion of the optical fiber to be measured based on Stokes light of the backscattered light, and the first wavelength May be shorter than the second wavelength and the predetermined value may be 1: 2.

  In the incident light power ratio setting device according to the present invention, the chromatic dispersion measuring unit measures chromatic dispersion of the optical fiber to be measured based on the anti-Stokes light of the backscattered light. The wavelength may be shorter than the second wavelength, and the predetermined value may be 2: 1.

  In the incident light power ratio setting device according to the present invention, the combined light acquisition unit includes an optical branching unit that branches the acquired combined light into two branched lights, and the optical branching unit includes the branching unit. One of the lights may be given to the incident means.

  In the incident light power ratio setting device according to the present invention, the combined light acquisition unit outputs the acquired combined light to a first output terminal or a second output terminal connected to the incident unit. You may make it have.

  Moreover, the incident light power ratio setting device according to the present invention may include an output of the combined light acquisition unit or a light switching unit that outputs the backscattered light.

  The incident light power ratio setting device according to the present invention extracts the light of the first wavelength or the light of the second wavelength when the light switching unit outputs the output of the combined light acquisition unit, When the light switching means outputs the backscattered light, a light extraction means for extracting Stokes light or anti-Stokes light of the backscattered light may be provided.

  Further, in the incident light power ratio setting device according to the present invention, when the light switching means outputs the output of the combined light acquisition means, the light extraction means is the light of the first wavelength or the light of the second wavelength. Light extraction may be performed continuously with calculation of the setting of the multiplexing means by the setting value deriving means.

  In the incident light power ratio setting device according to the present invention, the multiplexing unit may attenuate one or both of the first incident light and the second incident light.

  In the incident light power ratio setting device according to the present invention, the multiplexing unit may change the branching ratio of the first incident light and the second incident light.

  In the incident light power ratio setting method according to the present invention, the combining means combines the first incident light of the first wavelength and the second incident light of the second wavelength, and the power of the first incident light and the first A combining step in which the power ratio, which is a ratio to the power of the two incident lights, is variable; an incident step in which the incident means causes the combined light output from the combining means to enter the measured optical fiber; and backscattered light An acquisition unit acquires a backscattered light from the incident end of the optical fiber to be measured, a backscattered light acquisition step, a combined light acquisition unit acquires the combined light from the combining unit, and a power A power ratio measuring step in which the ratio measuring means measures the power ratio from the output of the combined light acquisition means, and a set value deriving means has a predetermined value based on the measurement result of the power ratio measuring means. Setting value for determining the setting of the multiplexing means such that Configured with a step out.

  The present invention combines the first incident light of the first wavelength and the second incident light of the second wavelength, and the power ratio that is the ratio of the power of the first incident light and the power of the second incident light is Variable combining means, incident means for allowing the combined light output from the combining means to enter the optical fiber to be measured, and backscattered light acquisition means for acquiring backscattered light from the incident end of the optical fiber to be measured A program for causing a computer to execute an incident light power ratio setting process in an incident light power ratio setting device comprising: a combined light acquisition unit that acquires the combined light from the combining unit; Based on the output of the means, a power ratio measurement process for measuring the power ratio, and a setting value derivation for determining the setting of the multiplexing means so that the power ratio becomes a predetermined value based on the measurement result of the power ratio measurement process Processing and the computer Is a program for executing the.

  The present invention combines the first incident light of the first wavelength and the second incident light of the second wavelength, and the power ratio that is the ratio of the power of the first incident light and the power of the second incident light is Variable combining means, incident means for allowing the combined light output from the combining means to enter the optical fiber to be measured, and backscattered light acquisition means for acquiring backscattered light from the incident end of the optical fiber to be measured And a computer that records a program for causing a computer to execute an incident light power ratio setting process in an incident light power ratio setting device including a combined light acquisition unit that acquires the combined light from the combining unit. A recording medium comprising: a power ratio measurement process for measuring the power ratio from an output of the combined light acquisition means; and a measurement result of the power ratio measurement process before the power ratio becomes a predetermined value. A recording medium readable by the recording a computer program for executing the setting value derivation to the computer to determine the setting of the multiplexing means.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of a measurement system 1 according to an embodiment of the present invention. The measurement system 1 is connected to the optical fiber 4 to be measured. The measurement system 1 is for measuring the chromatic dispersion distribution of the optical fiber 4 to be measured.

  The measurement system 1 includes a personal computer 2, a first incident light source 32a, a second incident light source 32b, a multiplexer 33, an optical switch 34, an EDFA 36, a circulator 38, an EDFA 52, an adjustable optical filter 54, a photoelectric converter 55, and an amplifier 56. , A low-pass filter 58, a combined light acquisition unit 60, and an optical switching unit 70.

  The personal computer 2 includes a CPU, a hard disk, and a medium (floppy (registered trademark) disk, CD-ROM, etc.) reading device. Furthermore, the personal computer 2 includes a dispersion measuring device 2a, an A / D converter 2b, and a pulse generator 2c.

  The dispersion measuring device 2a obtains the chromatic dispersion distribution of the measured optical fiber 4 based on the digital signal output from the A / D converter 2b. The dispersion measuring device 2a can be mounted by causing the media reading device of the personal computer 2 to read the medium on which the program for realizing the function of the dispersion measuring device 2a is recorded and installing it on the hard disk.

  The dispersion measuring device 2a obtains the setting of the multiplexer 33 (for example, the attenuation factor of the output of the first incident light source 32a) before measuring the chromatic dispersion distribution.

  The A / D converter 2b converts the analog signal output from the low-pass filter 58 into a digital signal. The pulse generator 2c generates a pulse.

  The first incident light source 32a generates first incident light having a wavelength λ1 (first wavelength). The second incident light source 32b generates second incident light having a wavelength λ2 (second wavelength). Note that λ1 <λ2.

  The multiplexer 33 multiplexes the first incident light and the second incident light. The multiplexer 33 can control the ratio (referred to as “power ratio”) between the power P1 of the first incident light and the power P2 of the second incident light. For example, control can be performed such that P1: P2 = 1: 2, 2: 1.

  The configuration of the multiplexer 33 is shown in FIG. For example, as shown in FIG. 3A, the multiplexer 33 includes a variable attenuator 33a that attenuates the first incident light generated by the first incident light source 32a and has a variable attenuation factor. The first incident light attenuated by the variable attenuator 33a and the second incident light are combined.

  In addition, the structure of the multiplexer 33 is not restricted to what is shown to Fig.3 (a). For example, as shown in FIG. 3B, the multiplexer 33 has a variable attenuator 33b that attenuates the second incident light generated by the second incident light source 32b and has a variable attenuation factor. Good. The second incident light attenuated by the variable attenuator 33b and the first incident light are combined.

  Further, as shown in FIG. 3C, the multiplexer 33 may include a variable attenuator 33a and a variable attenuator 33b. The first incident light and the second incident light attenuated by the variable attenuator 33b are combined by the variable attenuator 33a.

  Furthermore, as shown in FIG. 3D, the multiplexer 33 may include a variable branching device 33c that can change a branching ratio between the first incident light and the second incident light. The variable branching device 33c can be realized by using, for example, a coupler.

  The optical switch 34 receives a pulse from the pulse generator 2c. Based on the received pulse, the light output from the multiplexer 33 is pulsed.

EDFA (Erbium Doped Fiber
The amplifier 36 amplifies the pulsed light output from the optical switch 34.

  The multiplexed light acquisition unit 60 acquires the combined light output from the multiplexer 33 from the EDFA 36. The acquired combined light is given to the circulator 38 and the optical switch 70.

  The combined light acquisition unit 60 includes an optical branching unit 62 and an attenuator 64. The optical branching device 62 branches the combined light into two. One of the branched lights is given to the circulator 38. The other one of the branched lights is supplied to the attenuator 64. The attenuator 64 attenuates the applied light and outputs it. The output of the attenuator 64 is the output of the combined light acquisition unit 60.

  A modification of the combined light acquisition unit 60 is shown in FIG. Referring to FIG. 4, the combined light acquisition unit 60 includes an optical selector 66 instead of the optical branching unit 62. The optical selector 66 has a first output terminal 66a and a second output terminal 66b. The first output terminal 66 a is connected to the attenuator 64. The second output terminal 66 b is connected to the circulator 38. The light selector 66 outputs the combined light to the first output terminal 66a or the second output terminal 66b. You can select which to output.

  The circulator 38 receives the combined light output from the multiplexer 33 via the optical switch 34, the EDFA 36 and the combined light acquisition device 60, and enters the measured optical fiber 4.

  In the optical fiber 4 to be measured, two photons having a wavelength λ1 are combined with one photon having a wavelength λ2 to form a Stokes photon having a wavelength λs. The two photons having the wavelength λ2 are combined with one photon having the wavelength λ1 to form an anti-Stokes photon having the wavelength λa. Note that λ2−λ1 = λ1−λs = λa−λ2. Thus, in the optical fiber 4 to be measured, four light waves having wavelengths λ1, λ2, λs, and λa are mixed.

  When the light output from the multiplexer 33 is incident on the measured optical fiber 4, backscattered light is output from the incident end 4 a of the measured optical fiber 4. The backscattered light includes Stokes light and anti-Stokes light.

  The circulator 38 acquires backscattered light and gives it to the EDFA 52.

EDFA (Erbium Doped Fiber
Amplifier) 52 amplifies the backscattered light.

  The optical switch 70 receives the amplified backscattered light that is the output of the EDFA 52 and the output of the combined light acquisition unit 60, and outputs either one. You can select which one to output.

  When the combined light acquisition unit 60 includes the light selector 66 (see FIG. 4), the optical switching unit 70 uses the amplified backscattered light that is the output of the EDFA 52 and the output of the combined light acquisition unit 60. Just output what you actually received. When the optical selector 66 outputs the combined light to the first output terminal 66a, the optical switch 70 receives the output of the combined light acquirer 60 and does not receive the amplified backscattered light. Therefore, the output of the optical switch 70 is the output of the combined light acquisition unit 60. When the optical selector 66 outputs the combined light to the second output terminal 66b, the optical switch 70 receives the amplified backscattered light and does not receive the output of the combined light acquisition unit 60. Therefore, the output of the optical switch 70 is amplified backscattered light.

  The adjustable optical filter 54 receives the output of the optical switch 70. If the output of the optical switch 70 is amplified backscattered light, the adjustable optical filter 54 extracts Stokes light or anti-Stokes light from the amplified backscattered light. The adjustable optical filter 54 can adjust the wavelength of transmitted light. Therefore, the Stokes light or the anti-Stokes light is extracted by adjusting so as to transmit the wavelength of the Stokes light or the anti-Stokes light. Note that which of the Stokes light and the anti-Stokes light is extracted is also given to the dispersion measuring device 2a.

  If the output of the optical switch 70 is the output of the combined light acquirer 60, the adjustable optical filter 54 determines whether the light having the wavelength λ1 (first incident light) or the light having the wavelength λ2 (second incident light) from the combined light. To extract. Note that which of the light with the wavelength λ1 and the light with the wavelength λ2 is extracted is also given to the dispersion measuring device 2a.

  The photoelectric converter 55 photoelectrically converts the extracted Stokes light, anti-Stokes light, etc., and outputs an electrical signal.

  The amplifier 56 amplifies the electric signal.

  The low pass filter 58 removes noise from the amplified electrical signal.

  FIG. 2 is a functional block diagram showing the configuration of the dispersion measuring instrument 2a according to the embodiment of the present invention. The dispersion measuring device 2a includes a power calculation unit 21, a first power recording unit 22a, a second power recording unit 22b, a power ratio calculation unit 23, a power ratio determination unit 25, an attenuation factor calculation unit (setting value deriving unit) 27, a wavelength. A dispersion measuring unit 29 is provided.

  The chromatic dispersion measuring unit 29 calculates the chromatic dispersion distribution of the optical fiber 4 to be measured based on the digital signal provided from the A / D converter 2b. However, it operates when the output of the optical switch 70 is amplified backscattered light. The chromatic dispersion measuring unit 29 calculates the chromatic dispersion distribution based on the Stokes light, or calculates the chromatic dispersion distribution based on the anti-Stokes light.

  When the output of the optical switch 70 is amplified backscattered light, the waveform captured by the personal computer 2 is Stokes light (or anti-Stokes light) newly generated by mixing four light waves. And an interference waveform of Stokes light (or anti-Stokes light) that has already been generated. The relationship between the vibration frequency fsig of the interference waveform and the chromatic dispersion distribution D (λ1, z) is shown in the following equation (for details, see Patent Document 1). The chromatic dispersion distribution is chromatic dispersion associated with the distance z from the incident end 4a of the optical fiber 4 to be measured.

ただし、ｎ：屈折率、ｃ：真空中での光速、δλ＝｜λ２−λ１｜である。
波長分散測定部２９は、Ａ／Ｄ変換器２ｂから与えられたデジタル信号をＦＦＴ(fast Fourier tranform)して、振動周波数fsigを求める。求められたfsigを上記の式に代入すると波長分散分布D(λ1,z)を算出することができる。波長分散分布D(λ2,z)も同様に算出できる。

Here, n: refractive index, c: speed of light in vacuum, δλ = | λ2-λ1 |.
The chromatic dispersion measuring unit 29 obtains a vibration frequency fsig by performing FFT (fast Fourier tranform) on the digital signal given from the A / D converter 2b. By substituting the obtained fsig into the above equation, the chromatic dispersion distribution D (λ1, z) can be calculated. The chromatic dispersion distribution D (λ2, z) can be calculated in the same manner.

  The measurement error of chromatic dispersion caused by self phase modulation and cross phase modulation is shown in the following equation. This is the case for Stokes light. In the case of anti-Stokes light, 2P1-P2 becomes 2P2-P1.

ただし、測定波長λは、λ１である。
光は減衰しながら被測定光ファイバ４内を進む（詳しくは、特許文献１を参照）。よって、自己位相変調および相互位相変調によって生じる波長分散の測定誤差を、下記の式のように修正する。

However, the measurement wavelength λ is λ1.
The light travels through the optical fiber 4 to be measured while being attenuated (refer to Patent Document 1 for details). Therefore, the measurement error of chromatic dispersion caused by self phase modulation and cross phase modulation is corrected as in the following equation.

よって、ストークス光の場合は、Ｐ１：Ｐ２＝１：２のときに測定誤差が０となる。アンチストークス光の場合は、Ｐ１：Ｐ２＝２：１のときに測定誤差が０となる。

Therefore, in the case of Stokes light, the measurement error becomes 0 when P1: P2 = 1: 2. In the case of anti-Stokes light, the measurement error is 0 when P1: P2 = 2: 1.

  The power calculator 21 calculates the power of light output from the optical switch 70 based on the digital signal given from the A / D converter 2b. However, it operates when the output of the optical switching device 70 is the output of the combined light acquisition device 60.

  The power calculator 21 is also given the type of light (the light of wavelength λ1 or the wavelength λ2) extracted by the adjustable optical filter 54. Depending on the type of light, the portion where the output of the power calculation unit 21 is recorded (the first power recording unit 22a and the second power recording unit 22b) differs.

  That is, the power of the light of wavelength λ1 (first incident light) is recorded in the first power recording unit 22a, and the power of the light of wavelength λ2 (second incident light) is recorded in the second power recording unit 22b.

  The power ratio calculation unit 23 calculates a power ratio (P1: P2) that is a ratio between the power P1 of the first incident light and the power P2 of the second incident light. However, when the first incident light and the second incident light pass through the combined light acquisition unit 60, the optical switching unit 70, and the adjustable optical filter 54, a wavelength dependent loss occurs. Therefore, the power P1 of the first incident light is obtained by multiplying the power P1 'recorded in the first power recording unit 22a by the correction coefficient K1 for correcting the wavelength dependent loss. Further, the power P2 'of the second incident light is obtained by multiplying the power P2' recorded in the second power recording unit 22b by a correction coefficient K2 for correcting the wavelength dependent loss. Therefore, the power ratio P2 / P1 = (K2 · P2 ′) / (K1 · P1 ′). The correction coefficients K1 and K2 are acquired for each measurement system 1.

  When the chromatic dispersion measuring unit 29 calculates the chromatic dispersion distribution based on the Stokes light, the power ratio determining unit 25 determines whether or not the power ratio P2 / P1 satisfies 2-δ1 <P2 / P1 <2 + δ1. judge. Further, when the chromatic dispersion measuring unit 29 calculates the chromatic dispersion distribution based on the anti-Stokes light, it is determined whether or not the power ratio P2 / P1 satisfies 1 / 2−δ2 <P2 / P1 <1/2 + δ2. judge. Note that δ1 and δ2 are arbitrary positive numbers, but are considerably smaller than 2, 1/2, respectively.

  If the above conditions are met, the output of the light switch 70 is switched from the output of the combined light acquisition device 60 to amplified backscattered light.

  If the above condition is not met, the power ratio P2 / P1 is given to the attenuation rate calculation unit 27.

  The attenuation factor calculation unit (setting value deriving unit) 27 has a power ratio (P1: P2) of 1: 2 (when calculating the chromatic dispersion distribution based on Stokes light) based on the measurement result of the power ratio determination unit 25 or The setting of the multiplexer 33 is determined so as to be 2: 1 (when the chromatic dispersion distribution is calculated based on the anti-Stokes light).

  FIG. 5 is a diagram for explaining the operation of the attenuation rate calculation unit 27. However, it is assumed that the multiplexer 33 has a configuration as shown in FIG. Here, a method in which the attenuation factor calculation unit 27 calculates the attenuation factor A of the variable attenuator 33a will be described. FIG. 5 is a graph showing the relationship between the attenuation factor of the variable attenuator 33a and the power ratio, and shows the true characteristics and the linear approximation that approximates it with a straight line.

  Here, n is a positive integer. It is assumed that when the attenuation factor of the variable attenuator 33a is An-1, the power ratio P2 / P1 (described as PB) is PBn-1. Further, it is assumed that when the attenuation factor of the variable attenuator 33a is An, the power ratio is PBn. Here, the true characteristics are approximated by straight lines passing through (An-1, PBn-1) and (An, PBn), and an attenuation factor An + 1 where PB = 2 is obtained. It is assumed that the chromatic dispersion distribution is calculated based on Stokes light.

  Here, the slope αn of the straight line passing through (An-1, PBn-1) and (An, PBn) is (PBn-PBn-1) / (An-An-1). In addition, αn (An + 1−An) = 2−Pbn. Therefore, An + 1 = An + (2-Pbn) / αn. The power ratio Pbn + 1 at the attenuation rate An + 1 is closer to 2 than the power ratio Pbn. In this way, attenuation rates An + 1, An + 2, An + 3,... Are obtained until the power ratio Pb is within a predetermined range from 2 (exceeding 2-δ1 and less than 2 + δ1).

  That is, the attenuation rate An + 1 is obtained, the variable attenuator 33a of the multiplexer 33 is set to the attenuation rate An + 1, and the power ratio Pbn + 1 is obtained. Then, the attenuation rate An + 2 is obtained. Then, the variable attenuator 33a of the multiplexer 33 is set to the attenuation factor An + 2, and the power ratio Pbn + 2 is obtained. Repeat this.

  Α1 and A1 are arbitrary values. After arbitrarily setting the attenuation factor A1, the combined light is obtained by the multiplexer 33, and the power ratio Pb1 is measured. Then, arbitrarily set α1 is substituted into A2 = A1 + (2−Pb1) / α1 to obtain an attenuation factor A2.

  In addition, although the method of calculating | requiring the attenuation factor A of the variable attenuator 33a was demonstrated, even if the multiplexer 33 has taken the structure as shown to FIG.3 (b)-(d), it can obtain | require similarly. If the multiplexer 33 has the configuration shown in FIG. 3B, the attenuation factor of the variable attenuator 33b can be obtained in the same manner by taking the attenuation factor of the variable attenuator 33b on the horizontal axis in FIG. . If the multiplexer 33 has the configuration shown in FIG. 3C, the ratio of the attenuation factor of the variable attenuator 33a and the attenuation factor of the variable attenuator 33b in FIG. The ratio of attenuation rate can be obtained. When the multiplexer 33 has the configuration shown in FIG. 3D, the branching ratio can be obtained in the same manner by taking the branching ratio on the horizontal axis in FIG.

  Next, the operation of the embodiment of the present invention will be described.

  FIG. 6 is a flowchart showing the operation of the measurement system 1 according to the embodiment of the present invention. First, the power ratio is set (S10). The output of the optical switch 70 is set to be the output of the combined light acquisition unit 60. When the chromatic dispersion measuring unit 29 calculates the chromatic dispersion distribution based on the Stokes light, the power ratio P2 / P1 is set to 2. When the chromatic dispersion measuring unit 29 calculates the chromatic dispersion distribution based on the anti-Stokes light, the power ratio P2 / P1 is set to ½. However, even if the power ratio is not exactly 2 or 1/2, if the power ratio exceeds 2-δ1 and less than 2 + δ1 or exceeds 1 / 2−δ2 and less than 1/2 + δ2, the power ratio is exactly 2 or 1 / It is assumed that the value has become 2, and the setting is completed.

  FIG. 7 is a flowchart showing a detailed operation of the measurement system 1 in setting the power ratio.

  First, the adjustable optical filter 54 is adjusted to extract light having a wavelength λ2 (second incident light).

  The first incident light having the wavelength λ 1 generated by the first incident light source 32 a and the second incident light having the wavelength λ 2 generated by the second incident light source 32 b are combined by the multiplexer 33. The combined light output from the multiplexer 33 is given to the combined light acquisition device 60 via the optical switch 34 and the EDFA 36.

  The combined light supplied to the combined light acquisition unit 60 is branched by the optical branching unit 62 and supplied to the optical switching unit 70 via the attenuator 64.

  The light branched by the optical branching device 62 is also given to the circulator 38, and backscattered light is output from the incident end 4 a of the measured optical fiber 4. The backscattered light is given to the optical switch 70 via the circulator 38 and the EDFA 52.

  Since the output of the optical switch 70 is the output of the combined light acquisition unit 60, the combined light is given to the adjustable optical filter 54. The adjustable optical filter 54 extracts light having the wavelength λ2 (second incident light) (S102). The light having the wavelength λ <b> 2 (second incident light) is converted into an electric signal by the photoelectric converter 55. The electric signal is given to the A / D converter 2b via the amplifier 56 and the low-pass filter 58. The A / D converter 2b converts the electrical signal into a digital signal and gives it to the dispersion measuring device 2a.

  Based on the digital signal given from the A / D converter 2b, the power calculation unit 21 of the dispersion measuring device 2a calculates the power of the light of wavelength λ2 (second incident light) and records it in the second power recording unit 22b. . The power P2 ′ recorded in the second power recording unit 22b is a wavelength-dependent loss when passing through the multiplexed light acquisition unit 60, the optical switching unit 70, and the adjustable optical filter 54, and thus the power P2 of the second incident light. Is smaller than Here, P2 = K2 · P2 ′. The correction coefficient K2 is acquired for each measurement system 1.

  Next, the adjustable optical filter 54 is adjusted so as to extract light having the wavelength λ1 (first incident light).

  Then, the combined light is given to the adjustable optical filter 54 as in the above operation. The adjustable optical filter 54 extracts light having the wavelength λ1 (first incident light) (S106). The light having the wavelength λ1 (first incident light) is converted into an electric signal by the photoelectric converter 55. The electric signal is given to the A / D converter 2b via the amplifier 56 and the low-pass filter 58. The A / D converter 2b converts the electrical signal into a digital signal and gives it to the dispersion measuring device 2a.

  Based on the digital signal given from the A / D converter 2b, the power calculation unit 21 of the dispersion measuring device 2a calculates the power of the light having the wavelength λ1 (first incident light) and records it in the first power recording unit 22a. . The power P1 ′ recorded in the first power recording unit 22a is a wavelength-dependent loss when passing through the multiplexed light acquisition unit 60, the optical switching unit 70, and the adjustable optical filter 54, and thus the power P1 of the first incident light. Is smaller than Here, P1 = K1 · P1 ′. The correction coefficient K1 is acquired for each measurement system 1.

  The power ratio calculation unit 23 calculates a power ratio (P1: P2) that is a ratio between the power P1 of the first incident light and the power P2 of the second incident light (S110). The power ratio P2 / P1 = (K2 · P2 ′) / (K1 · P1 ′).

  Here, the power ratio determination unit 25 has a power ratio P2 / P1 of a predetermined value (2 when calculating the chromatic dispersion distribution based on Stokes light, and 1 when calculating the chromatic dispersion distribution based on anti-Stokes light. / 2) is determined (S112).

  That is, if the power ratio exceeds 2-δ1 and is less than 2 + δ1, the power ratio can be regarded as 2. If the power ratio exceeds 1 / 2−δ2 and is less than 1/2 + δ2, the power ratio can be regarded as 1/2.

  If the power ratio P2 / P1 can be regarded as a predetermined value (S112, Yes), the setting of the power ratio (S10) is terminated.

  If the power ratio P2 / P1 cannot be regarded as a predetermined value (S112, No), the attenuation rate calculation unit 27 calculates the attenuation rate of the variable attenuator 33a (S114). The attenuation rate of the variable attenuator 33a is matched with the obtained attenuation rate.

  Then, the combined light is given to the adjustable optical filter 54 in the same manner as the above operation. The tunable optical filter 54 remains set to extract light of wavelength λ1 (first incident light). Therefore, the adjustable optical filter 54 extracts light having the wavelength λ1 (first incident light) (S116).

  As described above, the extraction of the light of the wavelength λ1 (first incident light) is continuously performed with the calculation of the attenuation rate (S114) (S106, S116). “Continuous” means that the step of extracting light of wavelength λ2 does not enter between the steps of extracting light of wavelength λ1. Thereby, it is not necessary to change the setting of the adjustable optical filter 54 immediately after the calculation of the attenuation rate (S114).

  The light having the wavelength λ1 (first incident light) is converted into an electric signal by the photoelectric converter 55. The electric signal is given to the A / D converter 2b via the amplifier 56 and the low-pass filter 58. The A / D converter 2b converts the electrical signal into a digital signal and gives it to the dispersion measuring device 2a.

  Based on the digital signal given from the A / D converter 2b, the power calculation unit 21 of the dispersion measuring device 2a calculates the power of the light having the wavelength λ1 (first incident light) and records it in the first power recording unit 22a. .

  Next, the adjustable optical filter 54 is adjusted so as to extract light having the wavelength λ2 (second incident light).

  Then, the combined light is given to the adjustable optical filter 54 as in the above operation. The adjustable optical filter 54 extracts light having the wavelength λ2 (second incident light) (S120). The light having the wavelength λ <b> 2 (second incident light) is converted into an electric signal by the photoelectric converter 55. The electric signal is given to the A / D converter 2b via the amplifier 56 and the low-pass filter 58. The A / D converter 2b converts the electrical signal into a digital signal and gives it to the dispersion measuring device 2a.

  Based on the digital signal given from the A / D converter 2b, the power calculation unit 21 of the dispersion measuring device 2a calculates the power of the light of wavelength λ2 (second incident light) and records it in the second power recording unit 22b. .

  The power ratio calculation unit 23 calculates a power ratio (P1: P2) that is a ratio between the power P1 of the first incident light and the power P2 of the second incident light (S123). This is the same as S110.

  Here, the power ratio determination unit 25 has a power ratio P2 / P1 of a predetermined value (2 when calculating the chromatic dispersion distribution based on Stokes light, and 1 when calculating the chromatic dispersion distribution based on anti-Stokes light. / 2) is determined (S124). This is the same as S112.

  If the power ratio P2 / P1 can be regarded as a predetermined value (S124, Yes), the power ratio setting (S10) is terminated.

  If the power ratio P2 / P1 cannot be regarded as a predetermined value (S124, No), the attenuation rate calculation unit 27 calculates the attenuation rate of the variable attenuator 33a (S126). The attenuation rate of the variable attenuator 33a is matched with the obtained attenuation rate.

  And it returns to extraction (S102) of the light (2nd incident light) of wavelength (lambda) 2.

  As described above, the extraction of the light with the wavelength λ2 (second incident light) is continuously performed with the calculation of the attenuation rate (S126) (S120, S102). “Continuous” means that the step of extracting light of wavelength λ1 does not enter between the steps of extracting light of wavelength λ2. Thereby, it is not necessary to change the setting of the adjustable optical filter 54 immediately after the calculation of the attenuation rate (S126).

  Returning to FIG. 6, next, chromatic dispersion is measured (S20). The output of the optical switch 70 is set to be amplified backscattered light.

  The first incident light having the wavelength λ 1 generated by the first incident light source 32 a and the second incident light having the wavelength λ 2 generated by the second incident light source 32 b are combined by the multiplexer 33. Here, P1: P2 = 1: 2 (or 2: 1) and the type of light is Stokes light (or anti-Stokes light). The light output from the multiplexer 33 is incident on the optical fiber 4 to be measured via the optical switch 34, the EDFA 36, the multiplexed light acquisition device 60, and the circulator 38.

  In the optical fiber 4 to be measured, four light waves having wavelengths λ1, λ2, λs, and λa are mixed. Back scattered light is output from the incident end 4 a of the optical fiber 4 to be measured. The backscattered light includes Stokes light and anti-Stokes light.

  The backscattered light is given to the adjustable optical filter 54 via the circulator 38, the EDFA 52 and the optical switch 70. The adjustable optical filter 54 extracts Stokes light (or anti-Stokes light). Stokes light (or anti-Stokes light) is converted into an electrical signal by the photoelectric converter 55. The electric signal is given to the A / D converter 2b via the amplifier 56 and the low-pass filter 58. The A / D converter 2b converts the electrical signal into a digital signal and gives it to the dispersion measuring device 2a.

  The chromatic dispersion measuring unit 29 of the dispersion measuring device 2a calculates the chromatic dispersion distribution of the measured optical fiber 4 based on the digital signal given from the A / D converter 2b. When the measurement is based on Stokes light, the measurement error becomes 0 when P1: P2 = 1: 2, but the measurement error becomes 0 because P1: P2 = 1: 2. In the case of measurement based on anti-Stokes light, the measurement error becomes 0 when P1: P2 = 2: 1. However, the measurement error becomes 0 because P1: P2 = 2: 1. .

  According to the embodiment of the present invention, the power ratio (P1: P2) is 1: 2 (when the chromatic dispersion distribution is calculated based on Stokes light) or 2: 1 (the chromatic dispersion distribution is calculated based on anti-Stokes light). The attenuation rate calculation unit 27 calculates the attenuation rate of the variable attenuator 33a and sets the variable attenuator 33a.

  Therefore, the chromatic dispersion distribution can be measured while reducing the measurement error of the chromatic dispersion distribution of the optical fiber 4 to be measured.

  Note that the optical switch 70 can be omitted. FIG. 8 is a diagram illustrating a configuration of the measurement system 1 according to a modification in which the optical switch 70 is omitted.

  The measurement system 1 according to the modification includes a personal computer 2, a first incident light source 32a, a second incident light source 32b, a multiplexer 33, an optical switch 34, an EDFA 36, a circulator 38, an EDFA 52, an adjustable optical filter 54a, and a photoelectric converter. 55a, an amplifier 56a, a low-pass filter 58a, an adjustable optical filter 54b, a photoelectric converter 55b, an amplifier 56b, a low-pass filter 58b, a combined light acquisition device 60, and an optical switch 70.

  The adjustable optical filter 54 a receives the output of the combined light acquirer 60. The adjustable optical filter 54a extracts light having a wavelength λ1 (first incident light) or light having a wavelength λ2 (second incident light) from the combined light. Note that which of the light with the wavelength λ1 and the light with the wavelength λ2 is extracted is also given to the dispersion measuring device 2a.

  The photoelectric converter 55a photoelectrically converts the extracted light of wavelength λ1 or light of wavelength λ2 and outputs an electrical signal.

  The amplifier 56a amplifies the electric signal.

  The low-pass filter 58a removes the noise of the amplified electrical signal and gives it to the A / D converter 2b.

  The adjustable optical filter 54b receives the amplified backscattered light. The adjustable optical filter 54b extracts Stokes light or anti-Stokes light from the amplified backscattered light. Note that which of the Stokes light and the anti-Stokes light is extracted is also given to the dispersion measuring device 2b.

  The photoelectric converter 55b photoelectrically converts the extracted Stokes light or anti-Stokes light and outputs an electrical signal.

  The amplifier 56b amplifies the electric signal.

  The low-pass filter 58b removes noise from the amplified electrical signal and supplies it to the A / D converter 2b.

  Even in such a modification, the power ratio (P1: P2) is 1: 2 (when the chromatic dispersion distribution is calculated based on Stokes light) or 2: 1 (the chromatic dispersion distribution is calculated based on anti-Stokes light). Case).

  However, since the optical switch 70 is omitted, two sets of the adjustable optical filter 54, the photoelectric converter 55, the amplifier 56, and the low-pass filter 58 are necessary.

It is a figure which shows the structure of the measurement system 1 concerning embodiment of this invention. It is a functional block diagram which shows the structure of the dispersion | distribution measuring device 2a concerning embodiment of this invention. 3 is a diagram illustrating a configuration of a multiplexer 33. FIG. It is a figure which shows the modification of the multiplexed light acquisition device. FIG. 6 is a diagram for explaining the operation of an attenuation rate calculation unit 27. It is a flowchart which shows operation | movement of the measurement system 1 concerning embodiment of this invention. It is a flowchart which shows the detailed operation | movement of the measurement system 1 in the setting of power ratio. It is a figure which shows the structure of the measurement system 1 concerning the modification which abbreviate | omitted the optical switch.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Measurement system 2 Personal computer 21 Power calculation part 22a 1st power recording part 22b 2nd power recording part 23 Power ratio calculation part 25 Power ratio determination part 27 Attenuation rate calculation part (setting value deriving means)
29 chromatic dispersion measuring unit 32a first incident light source 32b second incident light source 33 multiplexer 38 circulator 54 tunable optical filter 60 multiplexed light acquisition device 62 optical splitter 66 optical selector 70 optical switch

Claims (15)

The first incident light having the first wavelength and the second incident light having the second wavelength are combined, and a power ratio that is a ratio of the power of the first incident light and the power of the second incident light is variable. Wave means,
Incident means for allowing the combined light output from the combining means to enter the optical fiber to be measured;
Backscattered light acquisition means for acquiring backscattered light from the incident end of the measured optical fiber;
Combined light acquisition means for acquiring the combined light from the combining means;
Power ratio measuring means for measuring the power ratio from the output of the combined light acquisition means;
Based on the measurement result of the power ratio measuring means, a setting value deriving means for obtaining the setting of the multiplexing means so that the power ratio becomes a predetermined value;
An incident light power ratio setting device. The incident light power ratio setting device according to claim 1,
The incident means is connected to the multiplexing means via the combined light acquisition means,
Incident light power ratio setting device. The incident light power ratio setting device according to claim 1 or 2,
Chromatic dispersion measuring means for measuring chromatic dispersion of the optical fiber to be measured from the backscattered light,
An incident light power ratio setting device. An incident light power ratio setting device according to claim 3,
The chromatic dispersion measuring means measures chromatic dispersion of the optical fiber to be measured based on Stokes light of the backscattered light,
The first wavelength is shorter than the second wavelength,
The predetermined value is 1: 2.
Incident light power ratio setting device. An incident light power ratio setting device according to claim 3,
The chromatic dispersion measuring means measures the chromatic dispersion of the optical fiber to be measured based on the anti-Stokes light of the backscattered light,
The first wavelength is shorter than the second wavelength,
The predetermined value is 2: 1;
Incident light power ratio setting device. An incident light power ratio setting device according to any one of claims 1 to 5,
The combined light acquisition means includes:
A light branching means for branching the obtained combined light into two branched lights;
The light branching means provides one of the branched lights to the incident means;
Incident light power ratio setting device. An incident light power ratio setting device according to any one of claims 1 to 5,
The combined light acquisition means includes:
A light selecting means for outputting the acquired combined light to a first output terminal or a second output terminal connected to the incident means;
Incident light power ratio setting device. An incident light power ratio setting device according to any one of claims 1 to 5,
Light switching means for outputting the combined light acquisition means or the backscattered light;
An incident light power ratio setting device. The incident light power ratio setting device according to claim 8,
When the light switching means outputs the output of the combined light acquisition means, the light of the first wavelength or the light of the second wavelength is extracted, and when the light switching means outputs the backscattered light, Light extraction means for extracting Stokes light or anti-Stokes light of the backscattered light,
An incident light power ratio setting device. The incident light power ratio setting device according to claim 9,
When the light switching means outputs the output of the combined light acquisition means, the light extraction means extracts the light of the first wavelength or the light of the second wavelength by the setting value deriving means. Continuously across the calculation of means settings,
Incident light power ratio setting device. An incident light power ratio setting device according to any one of claims 1 to 5,
The multiplexing means attenuates one or both of the first incident light and the second incident light;
Incident light power ratio setting device. An incident light power ratio setting device according to any one of claims 1 to 5,
The multiplexing means changes the branching ratio of the first incident light and the second incident light.
Incident light power ratio setting device. The multiplexing means combines the first incident light having the first wavelength and the second incident light having the second wavelength, and a power ratio that is a ratio between the power of the first incident light and the power of the second incident light. A combining process in which is variable,
An incident step in which the incident means makes the combined light output from the combining means incident on the optical fiber to be measured;
Backscattered light acquisition means, a backscattered light acquisition step of acquiring backscattered light from the incident end of the measured optical fiber;
A combined light acquisition means for acquiring the combined light from the combining means;
A power ratio measuring means for measuring the power ratio from the output of the combined light acquisition means; and
A setting value deriving step for obtaining a setting of the multiplexing unit such that the power ratio becomes a predetermined value based on the measurement result of the power ratio measuring unit;
An incident light power ratio setting method comprising: The first incident light having the first wavelength and the second incident light having the second wavelength are combined, and a power ratio that is a ratio of the power of the first incident light and the power of the second incident light is variable. A wave means; an incident means for causing the combined light output from the combining means to enter the optical fiber to be measured; a backscattered light acquiring means for acquiring backscattered light from an incident end of the optical fiber to be measured; A program for causing a computer to execute an incident light power ratio setting process in an incident light power ratio setting device provided with a combined light acquisition means for acquiring wave light from the multiplexing means,
From the output of the combined light acquisition means, a power ratio measurement process for measuring the power ratio,
Based on the measurement result of the power ratio measurement process, a set value derivation process for obtaining the setting of the multiplexing means such that the power ratio becomes a predetermined value;
A program that causes a computer to execute. The first incident light having the first wavelength and the second incident light having the second wavelength are combined, and a power ratio that is a ratio of the power of the first incident light and the power of the second incident light is variable. A wave means; an incident means for causing the combined light output from the combining means to enter the optical fiber to be measured; a backscattered light acquiring means for acquiring backscattered light from an incident end of the optical fiber to be measured; A computer-readable recording medium storing a program for causing a computer to execute an incident light power ratio setting process in an incident light power ratio setting device including a combined light acquisition unit that acquires wave light from the combining unit. And
From the output of the combined light acquisition means, a power ratio measurement process for measuring the power ratio,
Based on the measurement result of the power ratio measurement process, a set value derivation process for obtaining the setting of the multiplexing means such that the power ratio becomes a predetermined value;
A computer-readable recording medium on which a program for causing a computer to execute is stored.

Images