CN116015462B - EDFA optical gain setting method applied to optical fiber time transmission - Google Patents

EDFA optical gain setting method applied to optical fiber time transmission Download PDF

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CN116015462B
CN116015462B CN202310169995.3A CN202310169995A CN116015462B CN 116015462 B CN116015462 B CN 116015462B CN 202310169995 A CN202310169995 A CN 202310169995A CN 116015462 B CN116015462 B CN 116015462B
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CN116015462A (en
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刘博�
刘涛
张首刚
董瑞芳
郭新兴
孔维成
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National Time Service Center of CAS
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Abstract

The invention discloses an EDFA optical gain setting method applied to optical fiber time transmission, which is applied to an optical fiber time transmission system, wherein the optical fiber time transmission system comprises an optical fiber link, a local end and a remote end which are in communication connection through the optical fiber link, and the optical fiber link comprisesNEach section of optical fiber is provided with a bidirectional erbium-doped optical fiber amplifier respectively; the method comprises the following steps: the local end and the remote end respectively send time-frequency signals; measuring a first signal-to-noise ratio of a local end and a second signal-to-noise ratio of a remote end; constructing an objective function based on the first signal-to-noise ratio and the second signal-to-noise ratio, and determining constraint conditions of the objective function; and calculating an optimal solution of the objective function under the constraint condition by using a genetic algorithm to obtain gain coefficients of the bidirectional erbium-doped fiber amplifiers. The invention establishes the objective function with the aim of maximizing the bidirectional receiving signal-to-noise ratio, and obtains the optical gain coefficient of each bidirectional erbium-doped fiber amplifier by solving through a genetic algorithm, thereby greatly improving the optimization speed and the optimization precision.

Description

EDFA optical gain setting method applied to optical fiber time transmission
Technical Field
The invention belongs to the technical field of optical fiber time transmission, and particularly relates to an EDFA (ErbiumDoped Fiber Amplifier, erbium-doped fiber amplifier) optical gain setting method applied to optical fiber time transmission.
Background
Compared with the traditional cable, the optical fiber has the advantages of low loss, high bandwidth, strong electromagnetic interference resistance and the like, and has better stability than a free space channel, so that the optical fiber link is utilized for high-precision long-distance time-frequency transmission and draws a great deal of attention.
To compensate for optical losses of 0.2-0.3 dB/km caused by fiber links, bi-directional erbium-doped fiber amplifiers are used for long-distance fiber time synchronization. However, there are various kinds of noise in the fiber-optic time transfer link, such as rayleigh scattering noise, ASE (spontaneous emission) noise of the amplifier, laser phase noise-to-intensity noise, and the like. The EDFA inevitably amplifies the noise signals together with the main signal, which together with the main signal reach the receivers at the local and remote ends of the link, resulting in a degradation of the quality of the desired signal, i.e. the signal-to-noise ratio.
Therefore, the reasonable optimization of the number of EDFAs on the optical fiber link and their gain coefficients is a problem to be solved by those skilled in the art.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides an EDFA optical gain setting method applied to optical fiber time transmission. The technical problems to be solved by the invention are realized by the following technical scheme:
the invention provides an EDFA optical gain setting method applied to optical fiber time transmission, which is applied to an optical fiber time transmission system, wherein the optical fiber time transmission system comprises the following components: an optical fiber link and local and remote ends communicatively connected by the optical fiber link, the optical fiber link comprisingNEach section of optical fiber is provided with a bidirectional erbium-doped optical fiber amplifier respectively;
the EDFA optical gain setting method comprises the following steps:
the local end and the remote end respectively send time-frequency signals;
measuring a first signal-to-noise ratio of the local end and a second signal-to-noise ratio of the remote end;
constructing an objective function based on the first signal-to-noise ratio and the second signal-to-noise ratio, and determining constraint conditions of the objective function;
and calculating the optimal solution of the objective function under the constraint condition by using a genetic algorithm to obtain the gain coefficients of each bidirectional erbium-doped fiber amplifier in the fiber time transfer system.
In one embodiment of the invention, the objective function and the constraint are expressed as:
Figure SMS_1
；
Figure SMS_2
；
wherein ,
Figure SMS_5
representing maximization, ++>
Figure SMS_8
Representing constraint conditions, bi-directional received signal-to-noise ratio
Figure SMS_10
，/>
Figure SMS_4
A first signal-to-noise ratio indicative of said local side,>
Figure SMS_7
a second signal-to-noise ratio indicative of said remote side, ">
Figure SMS_11
Representing the +.>
Figure SMS_13
Attenuation coefficient of the segment fiber, ">
Figure SMS_3
Representing the +.>
Figure SMS_9
Length of optical fiber length->
Figure SMS_12
Indicate->
Figure SMS_14
Gain factor of bidirectional erbium-doped fiber amplifier corresponding to section fiber, < ->
Figure SMS_6
Representing the initial fiber in the fiber optic link.
In one embodiment of the present invention,
Figure SMS_15
；
wherein ,
Figure SMS_16
representing the responsivity of the photodiode in the local side receiver, < >>
Figure SMS_19
Indicating the optical power of the time-frequency signal received by the local side,/-for the local side>
Figure SMS_21
，/>
Figure SMS_17
Representing the average transmit power of the local side, +.>
Figure SMS_20
Representing the optical power loss of said initial fiber, < >>
Figure SMS_23
Representing the first of the optical fiber linksiOptical power loss of a segment of optical fiber, < >>
Figure SMS_25
，/>
Figure SMS_18
A primary rayleigh scattering noise current signal representing the local reception,>
Figure SMS_22
indicating local terminationReceived self-radiating noise current signal, +.>
Figure SMS_24
Representing the received secondary Rayleigh scattering noise current signal at the local side, < >>
Figure SMS_26
Representing the received thermal noise current signal at the local side.
In one embodiment of the present invention,
Figure SMS_27
；
wherein ,
Figure SMS_29
indicating the responsivity of the photodiode in the remote receiver,/->
Figure SMS_31
Indicating the optical power of the time-frequency signal received by the remote terminal, < >>
Figure SMS_33
，/>
Figure SMS_30
Representing the average transmit power of the remote side, +.>
Figure SMS_32
Representing the received primary Rayleigh scattering noise current signal at the remote end,>
Figure SMS_34
representing the self-radiated noise current signal received by the remote terminal,
Figure SMS_35
representing the received secondary Rayleigh scattering noise current signal at the remote end,>
Figure SMS_28
representing the thermal noise current signal received at the remote end.
In one embodiment of the present invention, the step of calculating an optimal solution of the objective function under the constraint condition by using a genetic algorithm to obtain gain coefficients of each bidirectional erbium-doped fiber amplifier in the fiber time transfer system includes:
determining an initialization population
Figure SMS_36
，/>
Figure SMS_37
Representing the first of the initialized populationsdThe number of individuals who are to be treated,xrepresenting population size;
calculating the fitness value of each individual and the total fitness value of all individuals according to the objective function, and determining the firstdA selection probability of the individual;
based on the selection probability, determining a parent population from the initialized population by utilizing a Monte Carlo selection algorithm, and then intersecting and mutating the parent population to generate a new individual;
judging whether the current iteration number is smaller than or equal to the preset iteration number or not; if yes, returning to the step of calculating the fitness value of each individual and the total fitness value of all the individuals according to the objective function; if not, determining the individual with the minimum fitness in all the individuals after the round of iteration as the optimal solution of the objective function.
In one embodiment of the invention, the individuals in the initial population are determined according to the following formula:
Figure SMS_38
；
wherein ,
Figure SMS_39
indicating the optimal received signal-to-noise ratio of the remote receiver and the local receiver, < >>
Figure SMS_40
Represent the firstdAttenuation coefficient of individual corresponding fiber, +.>
Figure SMS_41
Represent the firstd-1 attenuation coefficient of the individual corresponding fiber, < ->
Figure SMS_42
Represent the firstdIndividual corresponds to the length of the optical fiber, < >>
Figure SMS_43
Represent the firstd-1 individual corresponds to the length of the optical fiber.
In one embodiment of the present invention, before the step of calculating the fitness value of each individual and the total fitness value of all the individuals according to the objective function, the method further includes:
and coding the individuals in the initialized population in a binary coding mode.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides an EDFA optical gain setting method applied to optical fiber time transfer, which aims to establish an objective function for maximizing a bidirectional receiving signal-to-noise ratio, and solves and obtains optical gain coefficients of each bidirectional erbium-doped optical fiber amplifier by utilizing a genetic algorithm.
The present invention will be described in further detail with reference to the accompanying drawings and examples.
Drawings
FIG. 1 is a flow chart of an EDFA optical gain setting method applied to optical fiber time transfer according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a fiber optic time transfer system according to an embodiment of the present invention;
FIG. 3 is a flow chart of a genetic algorithm provided by an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to specific examples, but embodiments of the present invention are not limited thereto.
Fig. 1 is a flowchart of an EDFA optical gain setting method applied to optical fiber time transfer according to an embodiment of the present invention, and fig. 2 is a schematic diagram of an optical fiber time transfer system according to an embodiment of the present invention. As shown in fig. 1-2, an embodiment of the present invention provides an EDFA optical gain setting method applied to optical fiber time transfer, applied to an optical fiber time transfer system, where the optical fiber time transfer system includes: an optical fiber link and local and remote ends communicatively connected by an optical fiber link, the optical fiber link comprisingNEach section of optical fiber is provided with a bidirectional erbium-doped optical fiber amplifier respectively;
the EDFA optical gain setting method comprises the following steps:
s1, a local end and a remote end respectively send time-frequency signals;
s2, measuring a first signal-to-noise ratio of the local end and a second signal-to-noise ratio of the remote end;
s3, constructing an objective function based on the first signal-to-noise ratio and the second signal-to-noise ratio, and determining constraint conditions of the objective function;
and S4, calculating an optimal solution of the objective function under the constraint condition by utilizing a genetic algorithm to obtain gain coefficients of each bidirectional erbium-doped fiber amplifier in the fiber time transfer system.
In this embodiment, the optical fiber time transfer system includes: the system comprises a local end, a remote end, an optical fiber link and a plurality of bidirectional erbium-doped optical fiber amplifiers, wherein the local end comprises a local end receiver and a local end transmitter, and the remote end comprises a remote end receiver and a remote end transmitter. Specifically, in the step S1, the local end transmitter and the remote end transmitter respectively transmit time-frequency signals, the time-frequency signals transmitted by the local end reach the remote end receiver through the optical fiber link, and the time-frequency signals transmitted by the remote end reach the local end receiver through the optical fiber link; since various noise is included in the time-frequency signal when the time-frequency signal is transmitted in the optical fiber, the optical power of the signals received by the remote end and the local end can be expressed as:
Figure SMS_44
；
Figure SMS_45
；
in the formula ,
Figure SMS_46
representing the optical power of the signal received by the remote terminal, < >>
Figure SMS_47
Indicating the optical power of the time-frequency signal received by the remote terminal, < >>
Figure SMS_48
Indicating the optical power of the noise signal received at the remote end, < >>
Figure SMS_49
Representing the optical power of the signal received by the local side,
Figure SMS_50
indicating the optical power of the time-frequency signal received by the local side,/-for the local side>
Figure SMS_51
Representing the noise signal optical power received by the local side.
Further, in step S2-S3, after measuring the first signal-to-noise ratio of the local end and the second signal-to-noise ratio of the remote end, taking the product of the first signal-to-noise ratio and the second signal-to-noise ratio as an objective function, and solving an optimal solution of the objective function under the constraint condition by using a genetic algorithm to obtain gain coefficients of each bidirectional erbium-doped fiber amplifier in the fiber time transfer system.
It should be noted that, the EDFA optical gain setting method provided by the invention is suitable for long distance optical fiber time transmission such as thousands kilometers; also, although only two EDFAs are shown in fig. 2, the number of EDFAs may be plural in practice, and the number of EDFAs is not limited in the present application.
In this embodiment, the objective function and the constraint condition are expressed as:
Figure SMS_52
；
Figure SMS_53
；
wherein ,
Figure SMS_55
representing maximization, ++>
Figure SMS_59
Representing constraint conditions, bi-directional received signal-to-noise ratio
Figure SMS_61
，/>
Figure SMS_57
A first signal-to-noise ratio indicative of the local side, < >>
Figure SMS_60
Representing a second signal-to-noise ratio at the remote end,
Figure SMS_63
indicating the%>
Figure SMS_65
Attenuation coefficient of the segment fiber, ">
Figure SMS_54
Indicating the%>
Figure SMS_58
Length of optical fiber length->
Figure SMS_62
Indicate->
Figure SMS_64
Gain factor of bidirectional erbium-doped fiber amplifier corresponding to section fiber, < ->
Figure SMS_56
Representing the initial fiber in the fiber optic link.
Specifically, there are three constraints on the objective function in this application, the first constraint is the firstiAttenuation coefficient of a segment of optical fiber
Figure SMS_66
0.2 to 0.3dB/km, the second constraint is +.>
Figure SMS_67
Length of section of optical fiber->
Figure SMS_68
For 50-100 km, further, the gain factor of EDFAs should not exceed about 25dB as a rule of thumb to have a certain safety margin, so a third constraint is that the gain factor of each EDFA is +.>
Figure SMS_69
10-25 db.
Further, in the present embodiment
Figure SMS_70
；
wherein ,
Figure SMS_72
representing the responsivity of the photodiode in the local side receiver, < >>
Figure SMS_76
Indicating the optical power of the time-frequency signal received by the local side,/-for the local side>
Figure SMS_79
，/>
Figure SMS_74
Representing the average transmit power of the local side, +.>
Figure SMS_77
Representing the optical power loss of said initial optical fiber link, < >>
Figure SMS_80
Representation houseThe optical fiber link is->
Figure SMS_82
Optical power loss of a segment of optical fiber, < >>
Figure SMS_71
，
Figure SMS_75
A primary rayleigh scattering noise current signal representing the local reception,>
Figure SMS_78
a self-radiated noise current signal representing the local reception,/->
Figure SMS_81
Representing the received secondary Rayleigh scattering noise current signal at the local side, < >>
Figure SMS_73
Representing the received thermal noise current signal at the local side.
Further, in the present embodiment
Figure SMS_83
；
wherein ,
Figure SMS_84
indicating the responsivity of the photodiode in the remote receiver,/->
Figure SMS_87
Indicating the optical power of the time-frequency signal received by the remote terminal, < >>
Figure SMS_89
，/>
Figure SMS_85
Representing the average transmit power of the remote side, +.>
Figure SMS_88
Primary Rayleigh scattering noise current signal representing remote end receivedNumber (1)/(2)>
Figure SMS_90
Indicating the self-radiated noise current signal received at the remote end, < >>
Figure SMS_91
Representing the received secondary Rayleigh scattering noise current signal at the remote end,>
Figure SMS_86
representing the thermal noise current signal received at the remote end.
It should be understood that the optical power of the noise signal in the signal received by the remote end is composed of three parts, namely:
Figure SMS_92
；
similarly, the optical power of the noise signal in the signal received by the local terminal is also composed of three parts:
Figure SMS_93
；
wherein ,
Figure SMS_95
representing the optical power of the noise signal in the signal received by the remote terminal,/->
Figure SMS_97
Optical power representing the primary Rayleigh scattering noise received at the remote end,/for the remote end>
Figure SMS_99
Representing the optical power of the secondary rayleigh scattering noise received at the remote end,
Figure SMS_96
optical power representing self-radiated noise received at the remote end, < >>
Figure SMS_98
Representing noise in signals received at the local endSignal light power,/->
Figure SMS_100
Optical power representing primary Rayleigh scattering noise received at the local side, < >>
Figure SMS_101
Optical power representing the received secondary Rayleigh scattering noise at the local side,/for the local side>
Figure SMS_94
Representing the optical power of the self-radiated noise received by the local side.
It should be noted that, the detectors at the local end and the remote end can convert the received signals from optical signals to current signals, and at this time, the current signals at the local end and the remote end not only include time-frequency current signals but also include noise current signals. In general, if the noise current signal differs from the time-frequency current signal by more than four orders of magnitude, then the portion of the noise current signal may be ignored, and therefore only considered within the EDFA gain range
Figure SMS_102
、/>
Figure SMS_103
、/>
Figure SMS_104
、/>
Figure SMS_105
Four noise current signals affect the time-frequency current signal.
Specifically, take the remote end as an example:
Figure SMS_106
；
Figure SMS_107
；
Figure SMS_108
；
Figure SMS_109
；
in the formula ,
Figure SMS_110
representing the Boltzmann constant,/->
Figure SMS_111
Indicating the fixed temperature of the remote receiver, +.>
Figure SMS_112
Representing remote-side electromechanical bandwidth,/->
Figure SMS_113
Representing remote receiver load->
Figure SMS_114
Representing the filter bandwidth.
FIG. 3 is a flow chart of a genetic algorithm provided by an embodiment of the present invention. As shown in fig. 3, the step of calculating an optimal solution of the objective function under the constraint condition by using a genetic algorithm to obtain gain coefficients of each bidirectional erbium-doped fiber amplifier in the fiber time transfer system includes:
determining an initialization population
Figure SMS_115
，/>
Figure SMS_116
Representing the first of the initialized populationdAn individual may be presented with a set of information,xrepresenting population size;
calculating fitness value of each individual and total fitness value of all individuals according to the objective function, and determining the firstdA selection probability of the individual;
based on the selection probability, after determining the parent population from the initialized population by utilizing a Monte Carlo selection algorithm, intersecting and mutating the parent population to generate a new individual;
judging whether the current iteration number is smaller than or equal to the preset iteration number or not; if yes, returning to the step of calculating the fitness value of each individual and the total fitness value of all the individuals according to the objective function; if not, determining the individual with the minimum fitness in all the individuals after the round of iteration as the optimal solution of the objective function.
The genetic algorithm simulates the evolution process of organisms, is a heuristic algorithm based on natural selection and genetic mechanism, and is used for solving an objective function
Figure SMS_117
Is a solution to the optimization of (3).
Specifically, the initialization population is first determined, and in this embodiment, the initialization population can be calculated according to the following formula, unlike the random initialization method in the prior art
Figure SMS_118
Is a subject of (1):
Figure SMS_119
；
in the formula ,
Figure SMS_120
indicating the optimal received signal-to-noise ratio of the remote receiver and the local receiver, < >>
Figure SMS_121
Represent the firstdAttenuation coefficient of individual corresponding fiber, +.>
Figure SMS_122
Represent the firstd-1 attenuation coefficient of the individual corresponding fiber, < ->
Figure SMS_123
Represent the firstdIndividual corresponds to the length of the optical fiber, < >>
Figure SMS_124
Represent the firstd-1 individual corresponds to the length of the optical fiber, the population size is usually between 10 and 200, optionally +.in this embodiment>
Figure SMS_125
。
Next, after the generation of the initialized population, two bases are represented by 0 and 1 in a binary coding manner, and the generated gene has a length of n, so that all individuals in the initialized population are subjected to
Figure SMS_126
Coding is carried out to obtain the gene of the initialized population. In the genetic algorithm, the purpose of the selection operation is to prevent the better genes from being eliminated excessively, so that individuals with larger fitness values have larger genetic possibilities, and the convergence capacity and the efficiency of the genetic algorithm are enhanced. In the embodiment, the Monte Carlo selection method is used for selection operation, the selected probability of the individual is in direct proportion to the fitness value, then the following isdSelection probability of individuals->
Figure SMS_127
The method comprises the following steps:
Figure SMS_128
；
in the formula ,
Figure SMS_129
represent the firstdFitness value of individual->
Figure SMS_130
Representing the total fitness value of all individuals, it is apparent that the higher the fitness value, the easier it is for individuals to replicate.
In the prior art, the crossover probability and the mutation probability are set to be fixed values, and the natural index e is introduced in crossover and mutation operations in the embodiment, so that the crossover probability and the mutation probability can be reasonably set according to parameters such as the current iteration times and fitness values. By way of example only, and in an illustrative,
Figure SMS_131
；
Figure SMS_132
；
in the formula ,
Figure SMS_134
represents a preset maximum value of cross probability +.>
Figure SMS_136
Representing a preset cross probability minimum, +.>
Figure SMS_140
Represents the maximum value of variation probability, < >>
Figure SMS_135
Respectively represent the minimum value of mutation probability, +.>
Figure SMS_137
For the optimal fitness value of the population individuals, +.>
Figure SMS_139
For the average fitness value of the population of individuals, +.>
Figure SMS_142
For the current fitness value of the individual, +.>
Figure SMS_133
For the two population individuals, the individual with larger fitness value when the crossing operation is carried out, the +.>
Figure SMS_138
Representing a preset attenuation coefficient, t being the current iteration number, < ->
Figure SMS_141
Is the preset iteration number.
To avoid population trapping in the locally optimal solution, the embodiment can further introduce a catastrophe machineAnd (5) preparing. Specifically, at each iteration of the genetic algorithm
Figure SMS_143
After that, sorting fitness values of the population from high to low, arranging the first 10% of chromosomes belonging to optimal fitness, and reserving; chromosomes with higher fitness values are arranged in 10% -60%, and deleted; the bars of 60% -100% represent chromosomes with lower fitness values after selection, which remain. New individuals are randomly generated to fill the gaps, so that the total number of the individuals in the population is not changed. Cross probability of the catastrophe mechanism introduced at this time +.>
Figure SMS_144
And mutation probability->
Figure SMS_145
The method comprises the following steps:
Figure SMS_146
；
Figure SMS_147
；
in the formula ,
Figure SMS_148
representing a preset catastrophe factor, ">
Figure SMS_149
Every>
Figure SMS_150
Multiple iterations with one catastrophe>
Figure SMS_151
Indicating the number of times that the current has been catastrophic.
The genetic algorithm is a cyclic reciprocating and continuous calculation solving process, and solutions with high fitness are continuously searched in the cyclic calculation process, so that the output result approaches to the optimal solution infinitely. However, it is easy to get trapped in endless form in repeated calculationsDead-loop, therefore, a termination condition should be set to prevent the genetic algorithm from proceeding without termination of the loop process. In the actual operation process, the iteration number of the genetic algorithm is generally set, the operation is limited by the set maximum iteration number, when the iteration number reaches the set value, the operation is immediately finished, the result is output, and the output result is the objective function
Figure SMS_152
Is a solution to the optimization of (3). Optionally, the maximum number of iterations is set to 2000 in this embodiment.
According to the above embodiments, the beneficial effects of the invention are as follows:
the invention provides an EDFA optical gain setting method applied to optical fiber time transfer, which aims to establish an objective function for maximizing a bidirectional receiving signal-to-noise ratio, and solves and obtains optical gain coefficients of each bidirectional erbium-doped optical fiber amplifier by utilizing a genetic algorithm.
In the description of the present invention, the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present invention, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.
In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Further, one skilled in the art can engage and combine the different embodiments or examples described in this specification.
The foregoing is a further detailed description of the invention in connection with the preferred embodiments, and it is not intended that the invention be limited to the specific embodiments described. It will be apparent to those skilled in the art that several simple deductions or substitutions may be made without departing from the spirit of the invention, and these should be considered to be within the scope of the invention.

Claims (5)

1. An EDFA optical gain setting method applied to a fiber time transfer, characterized in that it is applied to a fiber time transfer system, the fiber time transfer system comprising: the optical fiber link comprises N sections of optical fibers, and each section of optical fiber is provided with a bidirectional erbium-doped optical fiber amplifier respectively;
the EDFA optical gain setting method comprises the following steps:
the local end and the remote end respectively send time-frequency signals;
measuring a first signal-to-noise ratio of the local end and a second signal-to-noise ratio of the remote end;
constructing an objective function based on the first signal-to-noise ratio and the second signal-to-noise ratio, and determining constraint conditions of the objective function;
calculating an optimal solution of the objective function under the constraint condition by utilizing a genetic algorithm to obtain gain coefficients of each bidirectional erbium-doped fiber amplifier in the fiber time transfer system;
wherein the objective function and the constraint are expressed as:
MAXmizeSNR；
Figure FDA0004219144560000011
wherein MAXsize represents maximization, sT. represents constraint, bidirectional received signal-to-noise ratio snr=snr L ×SNR R ，SNR L Representing the first signal-to-noise ratio, SNR, of the local side R Representing a second signal-to-noise ratio, alpha, of said remote end i Represents the attenuation coefficient, l, of the ith section of optical fiber in the optical fiber link i Representing the length of the ith section of optical fiber in the optical fiber link, G i Representing the gain coefficient of a bidirectional erbium-doped fiber amplifier corresponding to the ith section of fiber, wherein i=0 represents the initial fiber in the fiber link;
Figure FDA0004219144560000012
wherein ,
Figure FDA0004219144560000021
representing the responsivity, P, of a photodiode in a local side receiver R→L Indicating the optical power of the time-frequency signal received by the local side,/-for the local side>
Figure FDA0004219144560000022
P R Representing the average transmit power of the local side, L 0 Representing the optical power loss of the initial fiber, L i Representing the optical power loss of the ith section of optical fiber in the optical fiber link, < >>
Figure FDA0004219144560000023
i SRB-L Representing a primary Rayleigh scattering noise current signal, i, received at the local end S-ASE-L Representing a self-radiated noise current signal i received at the local terminal S-DRB-L Representing a received secondary Rayleigh scattering noise current signal i Themral-L Representing the received thermal noise current signal at the local side.
2. The EDFA optical gain setting method applied to optical fiber time transfer as claimed in claim 1,
Figure FDA0004219144560000024
wherein ,
Figure FDA0004219144560000025
representing the responsivity of the photodiode in the remote receiver, P L→R Indicating the optical power of the time-frequency signal received by the remote terminal, < >>
Figure FDA0004219144560000026
P L Representing the average transmit power of the remote end, i SRB-R Representing a primary Rayleigh scattering noise current signal, i, received at a remote location S-ASE-R Indicating the self-radiated noise current signal i received at the remote end S-DRB-R Representing a secondary Rayleigh scattering noise current signal, i, received at a remote location Themral-R Representing the thermal noise current signal received at the remote end.
3. The EDFA optical gain setting method applied to optical fiber time transfer according to claim 1, wherein the step of calculating an optimal solution of the objective function under the constraint condition by using a genetic algorithm to obtain gain coefficients of each bidirectional erbium-doped fiber amplifier in the optical fiber time transfer system comprises:
determining an initialization population
Figure FDA0004219144560000031
Figure FDA0004219144560000032
Representing the d-th individual in the initialized population, x representing the population size;
calculating the fitness value of each individual and the total fitness value of all the individuals according to the objective function, and determining the selection probability of the d-th individual;
based on the selection probability, determining a parent population from the initialized population by utilizing a Monte Carlo selection algorithm, and then intersecting and mutating the parent population to generate a new individual;
judging whether the current iteration number is smaller than or equal to the preset iteration number or not; if yes, returning to the step of calculating the fitness value of each individual and the total fitness value of all the individuals according to the objective function; if not, determining the individual with the minimum fitness in all the individuals after the round of iteration as the optimal solution of the objective function.
4. A method of setting the optical gain of an EDFA for optical fiber time transfer according to claim 3, wherein the individuals in said initialisation population are determined according to the following formula:
Figure FDA0004219144560000033
where ε represents the optimal received signal-to-noise ratio, α, for the remote receiver and the local receiver d Represents the attenuation coefficient, alpha, of the d-th individual corresponding optical fiber d-1 Represents the attenuation coefficient, l, of the d-1 th individual corresponding optical fiber d Represents the length of the corresponding optical fiber of the d-th individual, l d-1 Indicating the length of the d-1 th individual corresponding fiber.
5. A method of setting an optical gain of an EDFA for optical fiber time transfer according to claim 3, further comprising, before the step of calculating the fitness value of each individual and the total fitness value of all individuals according to said objective function:
and coding the individuals in the initialized population in a binary coding mode.
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