CN105258920B - Detection method for loss of transmission optical fiber joint of Raman optical fiber amplifier - Google Patents

Abstract

The present invention provides a method for detecting the loss of a Raman fiber amplifier transmission optical fiber joint. a detector, the power detector is connected to the power coupler through WDM; the out-of-band ASE detection unit includes an ASE band detector, and the ASE band detector is connected to the central control processor, and the steps include: the first step: setting an initial pump The pump optical power is P1; the second step: detect the out-of-band ASE power value Pase1; the third step: set the pump optical power to P2; the fourth step: detect the out-of-band ASE power value Pase2; the fifth step: the program automatically converges The joint loss of the Raman fiber amplifier and the transmission fiber is calculated; in practical work, the measured joint loss of the Raman fiber amplifier and the transmission fiber has nothing to do with the signal optical power within the working bandwidth; moreover, the optical fiber joint loss and The attenuation coefficient of the transmission fiber is irrelevant, and the consistency is good.

Description

A method for detecting the loss of a Raman fiber amplifier transmission fiber splice

technical field

The invention relates to a Raman fiber amplifier, in particular to a method for detecting the loss of a Raman fiber amplifier transmission fiber joint.

Background technique

Stimulated Raman Scattering (SRS) is a nonlinear phenomenon in optical fibers that transfers a small fraction of the incident optical power to a Stokes wave with a lower frequency; if a weak signal is simultaneous with a strong pump wave The weak signal light can be amplified by transmitting it in the fiber and placing the weak signal wavelength within the Raman gain bandwidth of the pump light. This kind of optical amplifier based on the stimulated Raman scattering mechanism is called a fiber Raman amplifier ( FRA).

For distributed Raman fiber amplifiers, the gain is generally controlled by scaling the gain and the amplified optical power of spontaneous emission within a certain wavelength outside the working bandwidth of the signal. If there is a large joint loss between the transmission fiber and the Raman fiber amplifier, it will affect the scaling relationship between the spontaneous emission optical power and the gain, resulting in a large gain error. Accurate measurement of splice loss between transmission fibers.

Patent CN102749783 describes a mathematical relationship between the amplified optical power of the out-of-band spontaneous emission and the pump optical power, and the mathematical relationship between the joint loss and the out-of-band spontaneous emission amplified optical power to determine the joint loss value. However, the limitation of this method is that the calculated fiber splice loss is related to the loss of the transmission fiber, rather than a certain loss difference between fibers in the same batch, which leads to the existence of the calculated fiber splice loss. certain error.

SUMMARY OF THE INVENTION

In order to avoid optical fiber splice loss errors caused by differences in optical fiber loss, the present invention provides a method for detecting the loss of a Raman optical fiber amplifier transmission optical fiber splice.

In order to achieve the above-mentioned purpose of the invention, the technical scheme provided by the present invention is as follows: a method for detecting the loss of a Raman fiber amplifier transmission optical fiber joint, the structure of which includes a pump power monitoring unit and an out-of-band ASE detection unit; wherein, the pump power monitoring unit Connected to the central control processor, and includes a power detector, the power detector is connected to the power coupler through WDM; the out-of-band ASE detection unit includes an ASE band detector, and the ASE band detector is connected to the central control processor, which is Steps include:

Step 1: Set the initial pump light power as P1;

The second step: detect the out-of-band ASE power value Pase1;

Step 3: Set the pump optical power to P2;

Step 4: Detect the out-of-band ASE power value Pase2;

Step 5: The program automatically converges to calculate the splice loss between the Raman fiber amplifier and the transmission fiber.

Wherein, the preferred embodiment is: for a multi-pump Raman fiber amplifier, the pump optical power is set to the short-wavelength pump power or the sum of the powers of multiple pump lights, and the power detector of the pump power monitoring unit detects the power The power value of part of the pump light separated by the coupler is sent to the central control processor.

Among them, the preferred embodiment is: the out-of-band ASE detection unit uses a power coupler and a filter to extract the ASE light outside part of the signal bandwidth, and transmits the extracted ASE light to the ASE-band detector, and the ASE-band detector will The power value is sent to the central control processor to calculate the ASE power value within the range of the actual system.

Compared with the prior art, the method for detecting the splice loss of the Raman fiber amplifier transmission fiber of the present invention has the following advantages and positive effects: in actual work, the splice loss and working bandwidth of the Raman fiber amplifier and the transmission fiber are measured. The optical power of the signal inside is irrelevant; moreover, the fiber splice loss calculated by this method has nothing to do with the attenuation coefficient of the transmission fiber, and the consistency is good.

Description of drawings

FIG. 1 is a schematic diagram of a pumped RFA applied to a communication system.

FIG. 2 is a schematic structural diagram of a functional module of the Raman fiber amplifier of the present invention.

FIG. 3 is a schematic flowchart of a method for detecting the loss of a Raman fiber amplifier transmission fiber splice according to the present invention.

Detailed ways

In order to have a further understanding of the purpose, structural features and functions of the present invention, the following detailed description is provided in conjunction with the accompanying drawings. It should be understood that the specific embodiments described in this section are only used to explain the present invention, but not to limit the present invention.

As shown in Figure 1, taking the distributed Raman fiber amplifier (RFA) using the backward pumping method as an example, the initial power of the pump 10 light of the RFA in the figure is set to P1; the forward transmission is the signal light S1; The signal light S1 is emitted from the remote end, transmitted to the RFA input end I1 through the long-distance transmission fiber 110, and output through the RFA output end O1. Among them, the input end I1 of the RFA is not only the input end of the signal light S1, but also the output end of the RFA pump light P1.

Please refer to FIG. 2 at the same time. FIG. 2 is a laser functional module 500 in the Raman fiber amplifier of the present invention. The functional module 500 includes a pump power monitoring unit 510 and an out-of-band ASE detection unit 530 . The pump power monitoring unit 510 is connected to the central control processor, and includes a power detector, and the power detector is connected to the power coupler of the RFA through the WDM of the RFA100. The out-of-band ASE detection unit 530 includes an ASE band detector, and the ASE band detector is connected to the central control processor.

Please refer to Fig. 3, the detection method of the Raman fiber amplifier transmission fiber connector loss (Connector Loss) of the present invention, comprises the following steps:

First, set the initial pump 10 optical power as P1, in mW; for multi-pump Raman fiber amplifiers, set P1 as the short-wavelength pump power or the sum of the powers of multiple pump lights, and the pump power is monitored. The power detector of the unit 510 detects the power value of the partial pump light separated by the power coupler of the RFA and transmits it to the central control processor;

Secondly, detect the out-of-band ASE power value Pase1, the unit is dBm; the out-of-band ASE detection unit 530 uses a power coupler and a filter to extract the ASE light outside part of the signal bandwidth, and transmits the extracted ASE light to the ASE band The detector, the ASE band detector detects the out-of-band ASE power value Pase1 and transmits it to the central control processor;

Again, set the pump 10 optical power as P2, in mW; for multi-pump Raman fiber amplifiers, set P2 as the short-wavelength pump power, or the sum of the powers of multiple pump lights, the pump power monitoring unit The power detector of 510 detects the power value of part of the pump light separated by the power coupler of the RFA and transmits it to the central control processor;

Then, detect the out-of-band ASE power value Pase2, the unit is dBm; the out-of-band ASE detection unit 530 uses a power coupler and a filter to extract the ASE light outside part of the signal bandwidth, and transmits the extracted ASE light to the ASE band The detector, the ASE band detector detects the out-of-band ASE power value Pase1 and transmits it to the central control processor;

Finally, the joint loss LossCon of the Raman fiber amplifier and the transmission fiber is obtained by calculation; the calculation method is explained in detail as follows:

The spontaneous emission ASE term of the Raman fiber amplifier in the main optical path is 2h*ν*Δν*gR*Pp, where h is Planck's constant, ν is the frequency of the spontaneous emission, and Δν is the Raman of the spontaneous emission relative to the pump light frequency shift, gR is the Raman gain coefficient, and Pp is the pump light power.

Let G(ratio) be the linear switching gain of the Raman amplifier, when G(ratio)>>1, after a series of approximations to the ASE power, we can get:

Pase(dBm)=10*log10(G(ratio)-1)+a(1)

Among them, Pase (dBm) is the ASE power in dBm; a is a parameter related to the effective length of the fiber and the Raman gain coefficient, which is independent of the pump power and the fiber attenuation coefficient;

And there is the following formula for G(ratio):

G(ratio)=exp(gR*Pp*Leff/Aeff) (2)

Where gR is the Raman gain coefficient, Pp is the pump light power, in mW; Leff is the effective length of the fiber, and Aeff is the effective area of the fiber. If the unit of G(ratio) is dB, then there is a linear relationship between G(ratio) and the pump power Pp,

Set Pase(mW)=10^(Pase(dBm)/10), the unit is mW, according to the formula (1), the calibration can be

Get G(ratio)=ga1*Pase(mW)+ga2+1 (3)

Among them, ga1 and ga2 are scaling coefficients independent of fiber loss.

First, set the pump power to P1, measure the out-of-band ASE power Pase1 (dBm), and the corresponding linear switch gain is G1 (ratio); then set the pump power to P2, if P2>P1, take P2 as P1 twice, record the out-of-band ASE power Pase2 (dBm) at this time, and the corresponding linear switch gain is G2 (ratio).

It can be obtained from formula (2)

10*log(G1(ratio))*P2/P1-10*log(G2(ratio))=0 (4)

Suppose the joint loss between the Raman fiber amplifier and the transmission fiber is LossCon, the unit is dB, and the Pase (mW) before the fiber joint loss can be converted as follows

Pase(mW)=10^((Pase(dBm)+LossCon)/10) (5)

Substitute formula (5) into formula (3) to get

G(ratio)=ga1*10^((Pase(dBm)+LossCon)/10)+ga2+1 (6)

Substitute formula (6) into formula (4) to get

10*log(ga1*10^((Pase1(dBm)+LossCon)/10)+ga2+1)*P2/P1

-10*log(ga1*10^((Pase2(dBm)+LossCon)/10)+ga2+1)=Error (7)

Error is the error, use the iterative method to find LossCon so that Error=0

Set the convergence factor ke so that

LossCon=LossCon+Error*ke;

The program will automatically converge to calculate the joint loss LossCon of the Raman fiber amplifier and the transmission fiber.

Compared with the prior art, the method for detecting the splice loss of the Raman fiber amplifier transmission fiber of the present invention has the following advantages and positive effects: in actual work, the splice loss and working bandwidth of the Raman fiber amplifier and the transmission fiber are measured. The optical power of the signal inside is irrelevant; moreover, the fiber splice loss calculated by this method has nothing to do with the attenuation coefficient of the transmission fiber, and the consistency is good.

The above descriptions are only the best embodiments of the present invention, and are not intended to limit the scope of the present invention. Any equivalent changes or modifications made according to the scope of the patent application of the present invention are all covered by the present invention.

Claims (3)

1. A detection method of Raman fiber amplifier transmission fiber joint loss comprises a pumping power monitoring unit and an out-of-band ASE detection unit; the pumping power monitoring unit is connected with the central control processor and comprises a power detector, and the power detector is connected with the power coupler through WDM; the out-of-band ASE detection unit comprises an ASE band detector, and the ASE band detector is connected to the central control processor, and the steps of the ASE band detector comprise:

the first step is as follows: setting the initial pump light power as P1;

the second step is that: detecting an out-of-band ASE power value Pase 1;

the third step: setting the power of the pump light to be P2;

the fourth step: detecting an out-of-band ASE power value Pase 2;

the fifth step: the program automatically converges and calculates to obtain the joint loss of the Raman fiber amplifier and the transmission fiber;

the calculation method of the loss LossCon of the connector of the Raman fiber amplifier and the transmission fiber is as follows:

the spontaneous radiation ASE term of the Raman fiber amplifier in a main optical path is 2h v Δ v gR Pp, wherein h is a Planck constant, v is spontaneous radiation optical frequency, Δ v is Raman frequency shift of spontaneous radiation relative to pump light, gR is a Raman gain coefficient, and Pp is pump light power;

setting G (ratio) as the linear switch gain of the Raman amplifier, and when G (ratio) > >1, obtaining the ASE power after a series of approximations:

Pase(dBm)＝10*log10(G(ratio)-1)+a (1)

wherein Pase (dBm) is ASE power, and the unit is dBm; a is a parameter related to the effective length of the optical fiber and the Raman gain coefficient, and is independent of the pumping power and the optical fiber attenuation coefficient;

and for G (ratio) there is the following formula:

G(ratio)＝exp(gR*Pp*Leff/Aeff) (2)

wherein gR is a Raman gain coefficient, Pp is pump light power, and the unit is mW; leff is the effective length of the optical fiber, and Aeff is the effective area of the optical fiber; if G (ratio) is in dB, then G (ratio) is linear with the pump power Pp,

let Pase (mW) ^ 10 (Pase (dBm)/10), unit mW, according to (1), through the scaling, can obtain G (ratio) ═ ga1 ^ Pase (mW) + ga2+1 (3)

Wherein ga1, ga2 are scaling coefficients independent of fiber loss;

firstly, setting the pump power as P1, measuring out-of-band ASE power Pase1(dBm) at the time, and measuring the corresponding linear switch gain as G1 (ratio); then setting the pump power to P2, P2> P1, taking P2 as twice as much as P1, recording the out-of-band ASE power Pase2(dBm) at the moment, and the corresponding linear switch gain is G2 (ratio);

from the formula (2)

10*log(G1(ratio))*P2/P1-10*log(G2(ratio))＝0 (4)

Let the loss at the splice between the Raman fiber amplifier and the transmission fiber be LossCon in dB, and can be calculated as follows for Pase (mW) before the loss at the splice

Pase(mW)＝10^((Pase(dBm)+LossCon)/10) (5)

Substituting formula (5) into formula (3) can obtain

G(ratio)＝ga1*10^((Pase(dBm)+LossCon)/10)+ga2+1 (6)

Substituting the formula (6) into the formula (4) can obtain

10*log(ga1*10^((Pase1(dBm)+LossCon)/10)+ga2+1)*P2/P1

-10*log(ga1*10^((Pase2(dBm)+LossCon)/10)+ga2+1)＝Error (7)

Error is Error, and LossCon is solved by iteration method to make Error equal to 0

Setting a convergence factor ke so that LossCon + Error ke;

and (4) automatically converging and calculating by a program to obtain the loss LossCon of the connector of the Raman fiber amplifier and the transmission fiber.

2. A method of detecting loss in a transmission fiber splice of a raman fiber amplifier according to claim 1, wherein: for the multi-pump Raman fiber amplifier, the pump light power is set to be short-wavelength pump power or the sum of the powers of a plurality of pump lights, and a power detector of the pump power monitoring unit detects the power value of part of the pump lights separated by the power coupler and transmits the power value to the central control processor.

3. A method of detecting loss in a transmission fiber splice of a raman fiber amplifier according to claim 1, wherein: the out-of-band ASE detection unit uses a power coupler and a filter to extract ASE light outside a partial signal bandwidth and transmits the extracted ASE light to an ASE band detector, which detects an out-of-band ASE power value Pase1 and transmits it to the central control processor.

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