A high-reliability multi-core optical fiber excess length control method based on submarine optical cable

Abstract

The application discloses a high-reliability multi-core optical fiber excess length control method based on a submarine optical cable, and comprises the following steps: defining an upper boundary of the excess length of the multi-core optical fiber based on transmission performance and defining a lower boundary of the excess length of the multi-core optical fiber based on mechanical performance; and according to the structural characteristics of the multi-core optical fiber, the excess length boundary model of the multi-core optical fiber of the submarine optical cable is established from the two aspects of transmission performance and mechanical performance, so as to provide a theoretical calculation method for the design of the excess length of the multi-core optical fiber.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of submarine optical cable, in particular to a high-reliability multi-core fiber excess length control method based on submarine optical cable. BACKGROUND

[0002] Submarine optical cable can be applied to short-distance communication between land and island, island and island, and long-distance communication across the ocean, and plays an important role in international communication domain with its excellent characteristics such as large communication capacity, high transmission quality and strong anti-interference ability, and is an important part of modern global communication network.

[0003] At present, with the rapid development of IoT, cloud computing, 5G / 6G technology, the global demand for data transmission capacity is showing explosive growth, and the communication capacity of submarine optical cable is facing severe challenges. The new generation of space division multiplexing (SDM) technology based on multi-core fiber can transmit multiple optical signals simultaneously by using parallel space channels, breaking through the single-core fiber nonlinear Shannon limit, and providing an important solution to the "capacity crisis".

[0004] The traditional single-core fiber cladding structure only contains one middle core, while the multi-core fiber is different from the single-core fiber, and its internal structure is more complex. The cladding structure contains multiple parallel cores (≥2), to realize the transmission of multiple independent optical signals. This complex structure directly affects the reliability of multi-core fiber in submarine optical cable, and is more prone to additional attenuation, therefore, it is necessary to reasonably design the excess length of multi-core fiber in submarine optical cable to achieve the balance control of low cabling additional attenuation and high reliability life.

[0005] In the prior art, the excess length control boundary of the optical fiber is relatively single, and the multi-core fiber needs to consider many factors, therefore, a more perfect multi-core fiber excess length control method is needed to guide the application of multi-core fiber in the field of marine communication. SUMMARY

[0006] The technical problem solved by the present application is to provide a high-reliability multi-core fiber excess length control method based on submarine optical cable, to provide a theoretical calculation method for the design of multi-core fiber excess length, and to define the upper and lower boundaries of multi-core fiber excess length.

[0007] To solve the above technical problems, one technical solution adopted by the present application is to provide a high-reliability multi-core fiber excess length control method based on submarine optical cable, comprising the following steps:

[0008] Defining the upper boundary of the multi-core fiber excess length based on transmission performance:

[0009] The transmission performance of the optical fiber mainly refers to the fiber loss (attenuation), and the fiber loss includes intrinsic transmission loss and additional transmission loss. The intrinsic transmission loss of the optical fiber is inherent loss of the optical fiber, which is determined by the material itself. The additional transmission loss mainly refers to the bending loss, which is closely related to the excess length design of the optical fiber of the submarine cable;

[0010] Therefore, for the transmission performance of the multi-core optical fiber, an upper boundary of the excess length of the multi-core optical fiber of the submarine cable can be established;

[0011] A fiber bending loss model is established:

[0012]

[0013] wherein, represents the fiber bending loss, is a fiber bending loss coefficient, is a fiber length; is a normalized phase constant, is an axial normalized constant, is a normalized frequency, which can be calculated by formula (2), is an axial propagation constant when not disturbed; is a Bessel function; is a core radius; is a conjugate variable of Fourier transform; is an Airy function, is a process parameter of the cladding, is a process parameter of the coating layer, is a cladding position in a horizontal coordinate of a Cartesian coordinate system, is a coating layer position in a horizontal coordinate of a Cartesian coordinate system;

[0014]

[0015] In the formula, is a wave number in vacuum, is a wavelength, and are refractive indexes of the core and the cladding, respectively;

[0016] The process parameter in formula (1) can be calculated by the following formula:

[0017]

[0018] In the formula, is a horizontal coordinate of a Cartesian coordinate system of a fiber cross section, is a relative curvature, is a curvature radius, is a zone refractive index, is a cladding radius;

[0019] According to the structural characteristics of the multi-core fiber, a correction factor is introduced to correct the cladding radius, and the correction factor is The calculation is as follows:

[0020]

[0021] In the formula, is the minimum distance from the core to the cladding edge in the multi-core fiber;

[0022] The correction factor is brought into formula (3) to obtain the solution method of the process parameter of the multi-core fiber, that is:

[0023]

[0024] The formula of formula (5) is brought into formula (1) to obtain the bending loss model of the multi-core fiber;

[0025] The multi-core fiber structure parameters are brought into the above formula to obtain the relationship between the bending loss of the multi-core fiber and the radius of curvature; in order to ensure the transmission characteristics of the multi-core fiber submarine cable during the service period, the fiber loss caused by bending needs to be controlled to be less than 10 -4 dB / km, and the minimum radius of curvature allowed by the multi-core fiber is obtained ;

[0026] Due to the existence of fiber excess length, the fiber in the submarine cable is usually distributed in a curved state along the radial direction, and the relationship between the minimum radius of curvature of the multi-core fiber and the excess length is calculated as follows:

[0027]

[0028] In the formula, is the equivalent radius in the optical unit, is the equivalent pitch ratio, is the fiber pitch, is the fiber excess length, is the radius in the optical unit, and the minimum radius of curvature of the fiber The upper bound of the excess length of the multi-core fiber can be obtained, that is, ;

[0029] The lower bound of the excess length of the multi-core fiber is defined based on the mechanical performance:

[0030] The crack growth theory of brittle materials is as follows:

[0031]

[0032] In the formula, is the initial strength, is the residual strength, ​In order to apply pressure, For time, To maintain crack strength parameters, This is a parameter related to crack stress corrosion sensitivity.

[0033] The mechanical life model of optical fiber can be derived from the above formula, as shown below:

[0034]

[0035] In the formula and These represent the design lifetime of a multi-core optical fiber and the maximum allowable stress within that lifetime, respectively. and These are the screening time and screening stress for multi-core optical fibers, respectively. Probability of survival; This refers to the length of the optical fiber. The slope is the Weibull slope. The characteristic parameter value of the Weibull distribution can be calculated using the following formula:

[0036]

[0037] In the formula, To screen for fiber breakage rate;

[0038]

[0039] Using formula (10) Converted to the maximum allowable strain In the formula, The fiber modulus;

[0040] By substituting the multi-core fiber screening parameters and test parameters into equation (8), the design life of the multi-core fiber is obtained. Maximum allowable strain of multi-core optical fiber The relationship between them;

[0041] Lower boundary of excess length in multi-core optical fiber =Strain of multi-core fiber optic submarine cable - Maximum allowable strain of multi-core optical fiber .

[0042] In a preferred embodiment of the present invention, the strain of a multi-core fiber optic submarine cable can be calculated using the following formula:

[0043]

[0044] In the formula, This refers to the tensile force experienced during the construction of submarine optical cables. This refers to the stiffness of the submarine optical cable.

[0045] In a preferred embodiment of the present application, according to the state experienced by the multi-core fiber submarine cable, it can be divided into: laying (usually working tensile load, lasting for 48 hours), operation (usually permanent tensile load, lasting for 25 years) and recovery (usually short-term tensile load, lasting for 1 hour), the lower boundary of the multi-core fiber excess length becomes:

[0046] The lower boundary of the multi-core fiber excess length =max[laying state( ), operation state( ), recovery state( )].

[0047] In a preferred embodiment of the present application, the is 2 or 3, representing the fiber cladding and coating, respectively.

[0048] The present application has the beneficial effect that the high-reliability multi-core fiber excess length control method based on submarine cable provided by the present application establishes the excess length boundary model of the multi-core fiber of the submarine cable from the transmission performance and mechanical performance two aspects according to the structural characteristics of the multi-core fiber, provides a theoretical calculation method for the design of the multi-core fiber excess length, and is beneficial to the application of the multi-core fiber in the field of marine communication. BRIEF DESCRIPTION OF DRAWINGS

[0049] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0050] Figure 1 is a flowchart of a preferred embodiment of the high-reliability multi-core fiber excess length control method based on submarine cable of the present application;

[0051] Figure 2 is a schematic diagram of the minimum distance from the core to the cladding edge in the multi-core fiber;

[0052] Figure 3 is a schematic diagram of the relationship between the loss of the multi-core fiber and the curvature radius;

[0053] Figure 4 is a schematic diagram of the relationship between the fiber excess length and the bending radius. DETAILED DESCRIPTION

[0054] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work belong to the protection scope of the present application.

[0055] Please refer to Figures 1-4 The embodiments of the present application include:

[0056] A high-reliability multi-core optical fiber excess length control method based on a submarine optical cable, comprising the following steps:

[0057] The excess length design in the multi-core optical fiber submarine optical cable is mainly based on the transmission performance to define the upper boundary of the excess length of the multi-core optical fiber and based on the mechanical performance to define the lower boundary of the excess length of the multi-core optical fiber, the former is used to realize low additional attenuation, and the latter is used to ensure the high-reliability life of the submarine optical cable fiber;

[0058] The upper boundary of the excess length of the multi-core optical fiber based on the transmission performance is defined as follows:

[0059] The fiber bending loss model is established as follows:

[0060]

[0061] Wherein, represents the fiber bending loss, is the fiber bending loss coefficient, is the fiber length; is the normalized phase constant, is the axial normalized constant, is the normalized frequency, which can be calculated by formula (2), is the axial propagation constant when not disturbed; is the Bessel function; is the core radius; is the conjugate variable of Fourier transform; and is the Airy function, is the process parameter of the cladding, is the process parameter of the coating layer, is the cladding position in the horizontal coordinate of the Cartesian coordinate system, is the coating layer position in the horizontal coordinate of the Cartesian coordinate system;

[0062]

[0063] In the formula, is the wave number in vacuum, is the wavelength, and are the refractive indexes of the core and the cladding respectively;

[0064] Process parameter in formula (1) It can be calculated by the following formula:

[0065]

[0066] In the formula, is the horizontal coordinate of the Cartesian coordinate system of the fiber cross section, is the relative curvature, is the radius of curvature, is the zone refractive index, is 2 or 3, representing the fiber cladding and the coating layer respectively, is the cladding radius;

[0067] For the structural characteristics of multi-core fiber itself, a correction factor is introduced to correct the cladding radius, and the correction factor is calculated as follows:

[0068]

[0069] As Figure 2 shown, in the formula, is the small distance from the core to the cladding edge in the multi-core fiber;

[0070] The correction factor is brought into formula (3) to obtain the solution method of the process parameter of the multi-core fiber, that is:

[0071]

[0072] The formula of formula (5) is brought into formula (1) to obtain the bending loss model of the multi-core fiber;

[0073] The multi-core fiber structure parameters are brought into the above formula to obtain the relationship between the bending loss of the multi-core fiber and the radius of curvature; in order to ensure the transmission characteristics of the submarine optical cable during the service period, the fiber loss caused by bending needs to be controlled to be less than 10 -4 dB / km, and the minimum radius of curvature allowed by the multi-core fiber is ;

[0074] Due to the existence of fiber excess length, the fiber in the submarine optical cable is usually distributed in a curved state along the radial direction, and the relationship between the minimum radius of curvature of the multi-core fiber and the excess length is calculated as follows:

[0075]

[0076] In the formula, is the equivalent radius in the optical unit, is the equivalent pitch ratio, is the fiber pitch, is the fiber excess length, The inner radius of the optical unit is given by the minimum radius of curvature of the optical fiber. It is possible to obtain the excess length of multi-core optical fibers. The upper boundary, i.e. ;

[0077] In this embodiment, the core radius Take 4.15 μm, cladding radius The core diameter is set to 62.5 μm, and the minimum distance from the core to the cladding edge in a multi-core fiber is set to 16.60 μm. The refractive indices of the core, cladding, and coating are also set. The core parameter, wavelength, is provided by the fiber optic supplier. Using 1550nm, the relationship between loss and radius of curvature of multi-core optical fiber is obtained, as follows: Figure 3 As shown;

[0078] By controlling the fiber loss caused by bending to below 10 -4 dB / km corresponds to the minimum allowable radius of curvature for multi-core optical fibers. It is 59mm;

[0079] In this embodiment, the relationship between the fiber excess length and the bending radius is as follows: Figure 4 As shown, the excess length of the multi-core fiber is obtained. The upper boundary, i.e. It is 0.161%.

[0080] The lower boundary of excess length in multi-core optical fibers is defined based on mechanical properties:

[0081] The theory of crack growth in brittle materials is as follows:

[0082]

[0083] In the formula, For initial strength, For residual strength, In order to apply pressure, For time, To maintain crack strength parameters, This is a parameter related to crack stress corrosion sensitivity.

[0084] The mechanical life model of optical fiber can be derived from the above formula, as shown below:

[0085]

[0086] In the formula, These represent the design lifetime of a multi-core optical fiber and the maximum allowable stress within that lifetime, respectively. and These are the screening time and screening stress for multi-core optical fibers, respectively. Probability of survival; is the fiber length; is the Weibull slope; is the Weibull distribution characteristic value, which can be calculated by the following formula:

[0087]

[0088] In the formula, is the screening fiber breakage rate;

[0089]

[0090] Using formula (10) to convert to the maximum allowable strain of the multi-core fiber, in which, is the fiber modulus;

[0091] By bringing the multi-core fiber screening parameters and test parameters into formula (8), the multi-core fiber design life is obtained, which is related to the maximum allowable strain of the multi-core fiber;

[0092] The lower limit of the multi-core fiber excess length = the submarine cable strain of the multi-core fiber - the maximum allowable strain of the multi-core fiber ;

[0093] The submarine cable strain of the multi-core fiber can be calculated by the following formula:

[0094]

[0095] In the formula, is the tension received during the submarine cable construction process, is the submarine cable stiffness;

[0096] In addition, according to the state experienced by the multi-core fiber submarine cable, it is divided into laying, running and recovery, and the lower limit of the multi-core fiber excess length becomes:

[0097] The lower limit of the multi-core fiber excess length = max [laying state ( ), running state ( ), recovery state ( )].

[0098] In this embodiment, the multi-core fiber screening strain is 1.38 GPa, the multi-core fiber screening time is 1 s, the survival probability is 1-10 -9 , and the multi-core fiber length is 360km, the screening fracture rate is 10 -4 , the weibull slope is 3, the stress corrosion sensitivity parameter is 27.

[0099] The maximum strain allowed by the multicore optical fiber in the three states is obtained as: 0.563% (working tensile load, 48 hours), 0.412% (permanent tensile load, 25 years), and 0.649% (temporary tensile load, 1 hour). Combined with the stiffness 6.20MN of the multicore submarine optical cable, the lower boundary of the excess length of the multicore optical fiber is 0.064%.

[0100] In summary, the high-reliability multicore optical fiber excess length control method based on a submarine optical cable provided by the application can obtain the upper boundary and the lower boundary of the excess length of the multicore optical fiber, and provides a more reliable theoretical calculation method for the design of the excess length of the multicore optical fiber.

[0101] The above description is merely an embodiment of the application, and does not limit the patent scope of the application, and any equivalent structure or equivalent process transformation using the content of the specification of the application, or direct or indirect application in other related technical fields, is also included in the patent protection scope of the application.

Claims

1. A high-reliability multicore fiber excess length control method based on a submarine optical cable, characterized by, The method comprises the following steps: Defining the upper boundary of the excess length of the multicore optical fiber based on transmission performance: Establishing a fiber bending loss model: ； wherein represents the fiber bend loss, is the fiber bend loss coefficient, is the fiber length; is the normalized phase constant, is the axial normalized constant, is the normalized frequency, which can be calculated by equation (2), is the axial propagation constant without perturbation; is the Bessel function; is the core radius; is the conjugate variable of the Fourier transform; and is the Airy function, is the process parameter of the cladding, is the transverse coordinate of the cladding position in the Cartesian coordinate system, is the transverse coordinate of the coating position in the Cartesian coordinate system; wherein is the wave number in vacuum, is the wavelength, and are the refractive indices of the core and cladding, respectively; Process variable may be calculated by the formula: ； wherein is the Cartesian x-coordinate of the fiber cross-section, is the relative curvature, is the radius of curvature, is the is the relative refractive index, is the cladding radius; For the structural characteristics of the multicore optical fiber, a correction factor is introduced to correct the cladding radius, and the correction factor The calculation is as follows: In the formula, is the minimum distance from the core to the cladding edge in the multicore optical fiber; The correction factor is brought into formula (3) to obtain a solution method of the process parameter of the multicore optical fiber, that is: ； The formula of formula (5) is brought into formula (1) to obtain a bending loss model of the multicore optical fiber; The multi-core fiber structure parameters are brought into the above formula to obtain the relationship between the multi-core fiber bending loss and the curvature radius; to ensure the transmission characteristics of the multi-core fiber submarine cable during the service period, the fiber loss caused by the bending needs to be controlled to be lower than 10 -4 dB / km, and the minimum curvature radius allowed by the multi-core fiber is correspondingly obtained ; Due to the existence of the excess length of the optical fiber, the optical fiber in the submarine cable is usually distributed in a curved state along the radial direction, and the relationship between the minimum curvature radius of the multicore optical fiber and the excess length is calculated as follows: wherein is the equivalent radius within the optical unit, is the equivalent pitch ratio, is the fiber pitch, is the fiber excess length, is the radius within the optical unit, by the fiber minimum curvature radius The upper bound of the multi-core fiber excess length can be obtained, i.e. ; Defining the lower boundary of the excess length of the multicore optical fiber based on mechanical performance: The crack growth theory of brittle materials is as follows: wherein is the initial strength, is the residual strength, is the applied stress, is the time, is the crack strength retention parameter, is the crack stress corrosion susceptibility parameter; Through the above formula, a fiber mechanical life model can be derived, as shown in the following formula: wherein and are the design lifetime of the multicore optical fiber and the maximum stress allowed under this lifetime, respectively, and are the screening time and the screening stress of the multicore optical fiber, respectively; is the survival probability; is the fiber length; is the Weibull slope; is the Weibull distribution characteristic parameter value, which can be calculated by the following equation: In the formula, to screen the broken fiber rate; Using equation (10) to convert to the allowable maximum strain where is the fiber modulus; The design lifetime of the multi-core optical fiber is obtained by bringing the multi-core optical fiber screening parameter and the test parameter into formula (8) and the relationship between the maximum allowable strain of the multi-core optical fiber ​ Lower bound on excess fiber length for multi-core fiber Strain on multi-core fiber submarine cable Maximum strain allowed for multi-core fiber .

2. The high-reliability multi-core fiber slack storage control method based on a submarine optical cable according to claim 1, characterized by, The strain of the multicore optical fiber submarine cable can be calculated by the following formula: wherein is the tension experienced by the submarine cable during installation, is the stiffness of the submarine cable. 3.The high-reliability multi-core fiber slack storage control method based on a submarine optical cable according to claim 1, wherein, According to the state of the multi-core fiber submarine cable, it is divided into laying, running and recovery, and the lower boundary of the multi-core fiber excess length becomes: becomes: Lower boundary of excess length of multicore optical fiber = max [installation state ( ), operation state ( ), recovery state ( ) ].​​​ 4.The high-reliability multi-core fiber slack storage control method based on a submarine optical cable according to claim 1, wherein, The 2 or 3, representing the fiber cladding and coating, respectively.

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