Device and method for measuring gosnr (generalized optical signal to noise ratio)

Abstract

To enable GOSNR obtained by adding nonlinear noise power to be measured from signal light.SOLUTION: According to the present disclosure, there is provided a GOSNR measuring device comprising a calculation processing unit (14) that: using Stokes parameters acquired by propagating signal light through an optical fiber transmission path (93), calculates a total noise power (Ptotal-noise) obtained by adding together a nonlinear noise power (Pnl) and an ASE noise power (Pase) in the optical fiber transmission path; and measures a GOSNR using the total noise power.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an apparatus and method for measuring GOSNR in an optical fiber. [Background technology]

[0002] When high-power light propagates through an optical fiber, nonlinear polarization occurs in the glass, resulting in various nonlinear optical phenomena. For example, in optical fiber, the refractive index of the optical fiber changes in proportion to the optical power of the incident light due to the Kerr effect. This causes self-phase modulation (SPM) and cross-phase modulation (XPM). SPM is a phenomenon in which the refractive index changes due to the Kerr effect caused by the optical power of the signal light itself, resulting in phase modulation. XPM is a phenomenon in which the refractive index changes due to the Kerr effect caused by the optical power of other optical signals, resulting in phase modulation. Another major nonlinear optical phenomenon that occurs in optical fiber is four-wave mixing (FWM), in which when signal light of two or more wavelengths is input, a new wavelength of light is generated by the beat between the signal light.

[0003] When such nonlinear optical phenomena occur in optical fibers, waveform degradation occurs due to loss of linearity in the optical response, and crosstalk worsens due to the generation of wavelengths other than the incident light. These nonlinear noises degrade the quality of signals propagating through the optical fiber. For this reason, it is necessary to measure the generalized optical signal-to-noise ratio (GOSNR) after the signal propagates through the optical fiber using the total noise, which is the sum of the amplified spontaneous emission (ASE) noise and the nonlinear noise.

[0004] GOSNR is the OSNR due to ASE noise. ASE , and OSNR due to nonlinear noise NL Taking this into consideration, it can be expressed as follows: 1 / GOSNR=1 / OSNR ASE +1 / OSNR NL = (ASE noise power + nonlinear noise power) / signal optical power

[0005] An optical spectrum analyzer has been proposed that is equipped with a Stokes parameter measurement unit and can measure the optical spectrum and polarization state of signal light (see, for example, Patent Document 1). However, Patent Document 1 is capable of measuring the ASE noise power from signal light, but is unable to measure the GOSNR that includes nonlinear noise power. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-002190 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present disclosure is to make it possible to measure the GOSNR including nonlinear noise power from signal light. [Means for solving the problem]

[0008] Nonlinear polarization is expressed as the sum of terms proportional to the square and cube of the optical field of incident light. The coefficient of the second-order nonlinear optical term is called the second-order nonlinear optical susceptibility, and the coefficient of the third-order nonlinear optical term is called the third-order nonlinear optical susceptibility. Nonlinear optical phenomena in optical fibers are mainly caused by the third-order nonlinear optical susceptibility, since optical fibers have a point-symmetric structure centered on the central axis of the core. Therefore, in this disclosure, nonlinear noise power is measured using the third-order nonlinear optical term.

[0009] The GOSNR measurement device of the present disclosure uses the Stokes parameters obtained by propagating signal light through an optical fiber transmission line (93) to measure the nonlinear noise power (P nl) and ASE noise power (P ase ) and the total noise power (P total-noise ) and measures a generalized optical signal to noise ratio (GOSNR) using the total noise power.

[0010] The arithmetic processing unit The signal light power (P sig ) using the third-order nonlinear optical term for The nonlinear noise power (P nl ) coefficient of polarization component (k PL ) and the coefficient of the unpolarized component (k NPL ) to the third-order nonlinear optical term, the nonlinear noise power (P nl ) may be calculated.

[0011] The arithmetic processing unit The Stokes parameters are used to calculate the unpolarized noise power (P NPLnoise ) is calculated, The above k PL and the above P sig Using the polarization noise power (P PLnoise ) is calculated, The total noise power (P total-noise ) may be obtained.

[0012] The arithmetic processing unit A first measured power P is calculated using the Stokes parameters obtained by propagating the first signal light through the optical fiber transmission line. total (L1) and the first unpolarized noise power P NPLnoise (L1), and a second measured power P is calculated using the Stokes parameters obtained by propagating a second signal light having a different signal light power from that of the first signal light through the optical fiber transmission line. total (L2) and the second unpolarized noise power P NPLnoise Calculate (L2) The first measured power Ptotal (L1), the first non-polarization noise power P NPLnoise (L1), the second measurement power P total (L2) and the second non-polarization noise power P NPLnoise (L2), the signal light power P sig (L1) or the signal light power P sig (L2) may be calculated.

[0013] For example, the first signal light and the second signal light have a known signal light power ratio α, The calculation processing unit calculates the signal light power P sig (L1) may be calculated.

[0014] The GOSNR measurement method of the present disclosure includes: a first measurement procedure for measuring a first Stokes parameter by propagating a first signal light through an optical fiber transmission line (93); a second measurement procedure for measuring a first Stokes parameter by propagating a second signal light having a signal light power different from that of the first signal light through an optical fiber transmission line; Equipped with A calculation processing unit (14) calculates a nonlinear noise power (P nl ) and ASE noise power (P ase ) and the total noise power (P total-noise ) is calculated, and the GOSNR is calculated using the total noise power.

[0015] The above disclosures can be combined as much as possible. [Effects of the Invention]

[0016] According to the present disclosure, it is possible to measure the GOSNR including the nonlinear noise power from the signal light. [Brief explanation of the drawings]

[0017] [Figure 1] 1 shows an example of the configuration of a GOSNR measurement device according to the present disclosure. [Figure 2] 1 shows an example of the configuration of a GOSNR measurement method according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These implementation examples are merely illustrative, and the present disclosure can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. Note that components with the same reference numerals in this specification and drawings indicate the same components.

[0019] (First embodiment) 1 shows an example of a system configuration according to the present disclosure. The system according to the present disclosure executes the GOSNR measurement method according to the present disclosure. Specifically, signal light is input from a signal light output unit 92 to an optical fiber transmission line 93, and the polarization characteristics of the signal light after propagation through the optical fiber transmission line 93 are measured by a GOSNR measurement device 91. The signal light output unit 92 sequentially outputs two or more signal lights with a known signal light power ratio to the optical fiber transmission line 93. The signal light is, for example, WDM signal light.

[0020] The GOSNR measurement device 91 of this embodiment includes a spectroscopic unit 11, a Stokes parameter measurement unit 12, an arithmetic processing unit 14, an optical input unit 15, and a spectral wavelength control unit 16. The optical input unit 15 inputs signal light that has propagated through an optical fiber transmission line 93. The spectroscopic unit 11 spectroscopically separates the signal light input from the optical input unit 15 according to wavelength. This allows the spectroscopic unit 11 to extract light of any wavelength component. The present disclosure may also include a spectral wavelength control unit 16 that controls the sweep of the wavelengths spectroscopically separated by the spectroscopic unit 11.

[0021] The Stokes parameter measurement unit 12 measures each polarization component required for measuring the Stokes parameters (S0, S1, S2, S3) for each wavelength split by the spectroscopic unit 11. Various modes can be adopted for these polarization components, but in this embodiment, as an example, the optical power I0 of the 0-degree linear polarization component and the optical power I of the 90-degree linear polarization component are used. 90 , the optical power of the 45-degree linearly polarized component I 45 , the optical power of the circularly polarized component I q45 An example of measuring is shown below.

[0022] The calculation processing unit 14 calculates the Stokes parameters using the polarization components obtained by the Stokes parameter measurement unit 12. For example, the calculation processing unit 14 calculates the Stokes parameters (S0, S1, S2, S3) using the following equations. (Number 1) S0=I0+I 90 (1) S1=2×I0-S0(2) S2=2×I 45 -S0(3) S3=2×I q45 -S0(4) Here, S0 is the total amount of light, S1 is the difference between the amount of x-polarized light and the amount of y-polarized light, S2 is the difference between the amount of 45-degree polarized light and the amount of 135-degree polarized light, and S3 is the difference between the amount of right-handed circularly polarized light and the amount of left-handed circularly polarized light. Completely polarized light is displayed as a polarization state on the Poincaré sphere with S1, S2, and S3 as the coordinate axes.

[0023] Let the signal optical power be P sig , the nonlinear noise power is P nl , ASE noise power is P ase Then, the measured power (P total =S0) is expressed by the following equation: (Number 5) P total =P sig +P nl +P ase (5)

[0024] In the case of a glass medium, the atomic arrangement inside the glass is random and effectively isotropic, and there is no second-order nonlinear optical term. Therefore, when an optical fiber made of a glass medium is used for the optical fiber transmission line 93, the nonlinear noise power P nl can be expressed as a third-order nonlinear optical term as follows: (Number 6) P nl =k P sig 3 (6) where k is a proportionality constant.

[0025] The proportionality k is the proportionality coefficient of the nonlinear noise power of the polarization component (k PL ) and the proportionality coefficient of the nonlinear noise power of the unpolarized component (k NPL ) can be expressed as the following equation: (Number 7) P nl =(k PL +k NPL )·P sig 3 (7)

[0026] Furthermore, the following equation is obtained from equations (5) and (7). (Number 8) P total =P sig +(k PL +k NPL )·P sig 3 +P ase =P sig +k PL P sig 3 +(k NPL P sig 3 +P ase ) =P sig +k PL P sig 3 +P NPLnoise (8)

[0027] The first term in equation (8) represents the signal light power, the second term represents the nonlinear noise power of the polarization component, and the third term represents the nonlinear noise power of the nonpolarization component. Here, the nonpolarization noise power P NPLnoise is the nonlinear noise power of the unpolarized component k NPL P sig 3 and ASE noise power P ase The noise power of the unpolarized component consisting of

[0028] Also, the unpolarized noise power P NPLnoise can be expressed as follows using the Stokes parameters (S0, S1, S2, S3):

number

[0029] In this disclosure, a plurality of signal lights with different signal light powers are input from a signal light output unit 92 to an optical fiber transmission line 93 at different timings, and the Stokes parameters (S0, S1, S2, S3) are measured in a GOSNR measurement device 91, and the measured power P total and unpolarized noise power P NPLnoise In this embodiment, when the signal light power is P sig (L1) and P sig An example is shown in which two signal lights (L2) are input from a signal light output unit 92 to an optical fiber transmission line 93 at different timings.

[0030] The signal optical power is P sig (L1) and P sig In the case of (L2), equation (8) becomes equations (9) and (10). (Number 10) P total (L1)=P sig (L1)+k PL P sig (L1) 3 +P NPLnoise (L1) (10) (Number 11) P total (L2)=P sig (L2)+k PL P sig(L2) 3 +P NPLnoise (L2) (11)

[0031] In this embodiment, the signal light power P sig (L1) and P sig The following equation holds between (L2): P sig (L2)=α×P sig (L1)

[0032] Therefore, equations (12) and (13) are obtained from equations (10) and (11). (Number 12) P total (L1)=P sig (L1)+k PL P sig (L1) 3 +P NPLnoise (L1) (12) (Number 13) P total (L2)=α·P sig (L1)+k PL α 3 P sig (L1) 3 +P NPLnoise (L2) (13)

[0033] From equation (12), the following equation is obtained: (Number 14) k PL P sig (L1) 3 =P total (L1)-P NPLnoise (L1)-P sig (L1) (14)

[0034] Substituting equation (14) into equation (13) gives equation (15), which in turn gives equation (16). (Number 15) P total (L2)-P NPLnoise (L2) =α P sig (L1)+α3 ·{P total (L1)-P NPLnoise (L1)-P sig (L1)} (15)

number

[0035] P total is the total amount of light S0 expressed by equation (1). total (L2) is the signal light power P sig I0 and I1 measured when the signal light (L2) is propagated through the optical fiber transmission line 93 90 It can be calculated using P total For (L1), the signal light power P sig I0 and I1 measured when the signal light (L1) is propagated through the optical fiber transmission line 93 90 It can be calculated using:

[0036] The desired P sig Substituting (L1) into equation (12) gives k PL For example, the calculation processing unit 14 can determine k (proportionality constant) using the following equation: PL Calculate (proportionality constant). (Number 17) k PL ={P total (L1)-P NPLnoise (L1)-P sig (L1)} / P sig (L1) 3 (17)

[0037] The calculation processing unit 14 also calculates the polarization noise power P PLnoise (L1) can be found. (Number 18) P PLnoise (L1)=k PL P sig (L1) 3 (18)

[0038] Furthermore, the polarization noise power P PLnoise (L1) and the unpolarized noise power P NPLnoise By adding (L1), the nonlinear noise power P nl (L1) and ASE noise power P ase (L1) and the total noise power P total-noise (L1) can be found. (Number 19) P total-noise (L1)=P nl (L1)+P ase (L1) =P PLnoise (L1)+P NPLnoise (L1) (19)

[0039] Signal light power P sig (L1) and the total noise power P total-noise From (L1), the GOSNR can be calculated using equation (20). (Number 20) GOSNR(L1)=10·LOG 10 {P sig (L1) / P total-noise (L1)}+10·LOG 10 (B m / B ref ) (20) where B m : Measurement optical bandwidth, B ref : Reference optical bandwidth (typically 0.1 nm)

[0040] An example of the GOSNR measurement method of the present disclosure is shown in Figure 2. The GOSNR measurement method of the present disclosure includes a first measurement procedure S11, a second measurement procedure S12, and a calculation procedure S13. In the first measurement procedure S11, the first Stokes parameter is measured by propagating the first signal light through the optical fiber transmission line 93. As a result, the calculation processing unit 14 calculates P total (L1) and P NPLnoise (L1) can be calculated. In the second measurement procedure S12, the second Stokes parameter is measured by propagating the second signal light through the optical fiber transmission line 93. As a result, the calculation processing unit 14 calculates P total (L2) and P NPLnoise (L2) can be calculated. In the calculation step S13, the calculation processing unit 14 calculates the polarization noise power P PLnoise (L1) can be calculated.

[0041] In this way, by inputting signal light with a known signal power ratio α and detecting each Stokes parameter, the signal light power P sig (L1), the polarization noise power P PLnoise (L1), the non-polarized noise power P consisting of the non-linear noise power of the non-polarized component and the ASE noise power NPLnoise (L1) can be obtained. In this embodiment, the polarization noise power P PLnoise (L1) and the unpolarized noise power P NPLnoise (L1) is shown as an example, but the polarization noise power P PLnoise (L2) and the unpolarized noise power P NPLnoise (L2) may be calculated. This also applies to the following embodiments.

[0042] (Second embodiment) This method can also be applied to cases with second-order and third-order nonlinear optical terms. For example, the measured power P obtained from the Stokes parameters total =S0 can be calculated using the following formula: (Number 21) P total =P sig +P nl +P ase (twenty one) where P sig is the signal light power, P nl is the nonlinear noise power, P ase is the ASE noise power.

[0043] Nonlinear noise power P nl can be calculated using the following formula: (Number 22) P nl =k2·P sig 2 +k3·P sig 3 (twenty two) Here, k2 is the proportionality constant of the second-order nonlinear optical term, and k3 is the proportionality constant of the third-order nonlinear optical term.

[0044] The proportionality k2 and k3 are the proportionality coefficients of the nonlinear noise power of the polarization components (k PL2 and k PL3 ) and the proportionality coefficient of the nonlinear noise power of the unpolarized component (k NPL2 and k NPL3 ), equation (22) can be expressed as equation (23). (Number 23) P nl =(k PL2 +k NPL2 )·P sig 2 +(k PL3 +k NPL3 )·P sig 3 (twenty three) where k PL2 is the proportionality coefficient of the second-order nonlinear noise of the polarization component, k NPL2 is the proportionality coefficient of the second-order nonlinear noise of the unpolarized component, k PL3 is the proportionality coefficient of the third-order nonlinear noise of the polarization components, k NPL3 is the proportionality coefficient of the third-order nonlinear noise of the unpolarized light component.

[0045] Therefore, equation (21) can be expressed as equation (24). (Number 24) P total =P sig +(k PL2 +k NPL2 )·P sig 2 +(k PL3 +k NPL3 )·P sig 3+P ase =P sig +(k PL2 P sig 2 +k PL3 P sig 3 ) +(k NPL2 P sig 2 +k NPL3 P sig 3 +P ase ) (twenty four) The first term in equation (24) represents the signal light power, the second term represents the nonlinear noise power of the polarized component, and the third term represents the nonpolarized noise power (P NPLnoise =k NPL2 P sig 2 +k NPL3 P sig 3 +P ase ) is shown.

[0046] In this embodiment, three signal lights with known signal light power ratios (α, β) are used. sig (L1), P sig (L2) and P sig (L3) is expressed by the following equation. P sig (L1), P sig (L2)=α×P sig (L1) P sig (L3)=β×P sig (L1)

[0047] From these relationships, the following equation holds: (Number 25) P total (L1)=P sig (L1)+k PL2 P sig (L1) 2 +k PL3 P sig (L1) 3 +P NPLnoise (L1) (25) (Number 26) P total (L2)=P sig (L2)+k PL2 P sig (L2) 2 +k PL3 P sig (L2) 3 +P NPLnoise (L2) =P sig (L1)+k PL2 α 2 P sig (L1) 2 +k PL3 α 3 P sig (L1) 3 +P NPLnoise (L2) (26) (Number 27) P total (L3)=P sig (L3)+k PL2 P sig (L3) 2 +k PL3 P sig (L3) 3 +P NPLnoise (L3) =P sig (L1)+k PL2 β 2 P sig (L1) 2 +k PL3 β 3 P sig (L1) 3 +P NPLnoise (L2) (27)

[0048] P total (L3), P NPLnoise (L3), P total (L2), P NPLnoise (L2), P total (L1), P NPLnoise (L1) is found from the Stokes parameters. Also, since α and β are known values, Psig (L1), k PL2 , k PL3 Therefore, the calculation processing unit 14 uses the equation (28) to obtain the nonlinear noise power P PLnoise (L1) can be found. (Number 28) P PLnoise (L1)=k PL2 P sig (L1) 2 +k PL3 P sig (L1) 3 (28)

[0049] Furthermore, the polarization noise power P PLnoise (L1) and the unpolarized noise power P NPLnoise By adding (L1), the nonlinear noise power P nl (L1) and ASE noise power P ase (L1) and the total noise power P total-noise (L1) can be found. (Number 29) P total-noise (L1)=P nl (L1)+P ase (L1) =P PLnoise (L1)+P NPLnoise (L1) (29)

[0050] Signal light power P sig (L1) and the total noise power P total-noise From (L1), the GOSNR can be calculated using equation (30). (Number 30) GOSNR(L1)=10·LOG 10 {P sig (L1) / P total-noise (L1)}+10·LOG 10 (B m / B ref ) (30) where B m : Measurement optical bandwidth, B ref : Reference optical bandwidth (typically 0.1 nm)

[0051] (Other embodiments) The GOSNR measurement device of the present invention can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided via a network. [Explanation of symbols]

[0052] 11: Spectroscopic section 12: Stokes parameter measurement unit 14: Processing unit 15: Optical input section 16: Spectral wavelength control section 91: GOSNR measurement device 92: Signal light output section 93: Optical fiber transmission line

Claims

1. The nonlinear noise power (P ｎｌ ) and ASE noise power (P ａｓｅ ) and the total noise power (P ｔｏｔａｌ－ｎｏｉｓｅ and a calculation processing unit (14) that calculates a total noise power and measures a generalized optical signal to noise ratio (GOSNR), GOSNR measurement device.

2. The arithmetic processing unit The signal light power (P ｓｉｇ ) using the third-order nonlinear optical term for The nonlinear noise power (P ｎｌ ) the coefficient (k ＰＬ ) and the coefficient of the unpolarized component (k ＮＰＬ ) to the third-order nonlinear optical term, the nonlinear noise power (P ｎｌ ) to calculate The GOSNR measurement device according to claim 1 .

3. The arithmetic processing unit The Stokes parameters are used to calculate the unpolarized noise power (P ＮＰＬｎｏｉｓｅ ) is calculated, The k ＰＬ and the P ｓｉｇ Using the polarization noise power (P ＰＬｎｏｉｓｅ ) is calculated, The total noise power (P ｔｏｔａｌ－ｎｏｉｓｅ ) The GOSNR measurement device according to claim 2 .

4. The arithmetic processing unit A first measured power P is calculated using the Stokes parameters obtained by propagating the first signal light through the optical fiber transmission line. ｔｏｔａｌ (L １ ) and the first non-polarization noise power P ＮＰＬｎｏｉｓｅ (L １ ) is calculated, and a second measured power P is calculated using the Stokes parameters obtained by propagating a second signal light having a signal light power different from that of the first signal light through the optical fiber transmission line. ｔｏｔａｌ (L ２ ) and the second non-polarized noise power P ＮＰＬｎｏｉｓｅ (L ２ ) is calculated, The first measured power P ｔｏｔａｌ (L １ ), the first non-polarization noise power P ＮＰＬｎｏｉｓｅ (L １ ), the second measured power P ｔｏｔａｌ (L ２ ) and the second non-polarization noise power P ＮＰＬｎｏｉｓｅ (L ２ ) to obtain the signal light power P ｓｉｇ (L １ ) or the signal light power P ｓｉｇ (L ２ ) to calculate The GOSNR measurement device according to claim 2 .

5. a signal light power ratio α between the first signal light and the second signal light is known; The calculation processing unit calculates the signal light power P of the first signal light using the following equation: ｓｉｇ (L １ ) to calculate The GOSNR measurement device according to claim 4 . [Math C1]

6. a first measurement procedure for measuring a first Stokes parameter by propagating a first signal light through an optical fiber transmission line (93); a second measurement procedure for measuring a second Stokes parameter by propagating a second signal light having a signal light power different from that of the first signal light through an optical fiber transmission line; Equipped with A calculation processing unit (14) calculates a nonlinear noise power (P ｎｌ ) and ASE noise power (P ａｓｅ ) and the total noise power (P ｔｏｔａｌ－ｎｏｉｓｅ ) and calculate a generalized optical signal to noise ratio (GOSNR) using the total noise power. GOSNR measurement method.

Images