CN116774346B - Method and system for designing optical fiber cladding for inhibiting mode instability in optical fiber amplifier - Google Patents
Method and system for designing optical fiber cladding for inhibiting mode instability in optical fiber amplifier Download PDFInfo
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- 238000005253 cladding Methods 0.000 title claims abstract description 108
- 239000013307 optical fiber Substances 0.000 title claims abstract description 96
- 238000000034 method Methods 0.000 title claims abstract description 27
- 230000002401 inhibitory effect Effects 0.000 title claims abstract description 11
- 239000000835 fiber Substances 0.000 claims abstract description 93
- 238000009826 distribution Methods 0.000 claims abstract description 57
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- 238000006243 chemical reaction Methods 0.000 claims description 8
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- 230000007423 decrease Effects 0.000 claims description 2
- 239000011159 matrix material Substances 0.000 description 14
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- BTBUEUYNUDRHOZ-UHFFFAOYSA-N Borate Chemical compound [O-]B([O-])[O-] BTBUEUYNUDRHOZ-UHFFFAOYSA-N 0.000 description 2
- 229910019142 PO4 Inorganic materials 0.000 description 2
- 239000000919 ceramic Substances 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 230000009022 nonlinear effect Effects 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 2
- 239000010452 phosphate Substances 0.000 description 2
- 239000010453 quartz Substances 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
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Abstract
The invention discloses a special optical fiber structure design method and system capable of inhibiting mode instability in an optical fiber amplifier. S100, a mode field distribution model is built, wherein the mode field distribution model comprises a basic mode and a high-order mode; s200, respectively calculating the powers of a fundamental mode and a high-order mode in the fiber core and the cladding according to the mode field distribution model; s300, introducing a grating with the same period as the interference light field into the optical fiber cladding, and setting the grating at a corresponding position through calculation and placing the grating; s400, after passing through the grating, all the energy of the fundamental mode and the high-order mode in the fiber cladding are converted mutually, the component duty ratio and the power of the high-order mode and the fundamental mode are changed, and the flow of the energy from the high-order mode to the fundamental mode is realized; s500, based on the energy flow, according to the energy distribution rule of the modes, the energy of the fundamental mode in the cladding enters the fiber core, the energy of the fundamental mode in the fiber core is increased, and the flow of the energy in the fiber core from the high-order mode to the fundamental mode is realized.
Description
Technical Field
The invention belongs to the field of optical fiber cladding design, and particularly relates to an optical fiber cladding design method and system for inhibiting mode instability in an optical fiber amplifier.
Background
The high-power fiber laser has the advantages of high power, good beam quality, small volume, easy heat dissipation and the like, is valued and developed rapidly by the industry, and has great effect in the fields of high-end manufacturing, national defense safety, information detection and the like. However, as performance indexes of the fiber laser are continuously improved, the ultra-high power density causes adverse phenomena such as nonlinear effect, mode instability effect and the like in the high-power fiber laser. The mode instability effect means that in some cases, the fundamental mode energy is suddenly exchanged with the high-order mode energy continuously, and the exchange is disordered, so that the laser output cannot be utilized, thereby preventing the improvement of the optical fiber transmission power and limiting the further development of the high-power optical fiber laser.
In order to suppress the Mode Instability (MI) effect, a bending mode selection method is adopted to set the optical fiber into a bending shape, and the purpose of filtering out the higher-order mode after the optical fiber is transmitted for a sufficient distance can be achieved by designing a proper bending radius because the bending loss of the higher-order mode is larger than that of the fundamental mode. In addition, the patent with the application number of CN115566518B proposes a method of placing a magnetostrictive material wrapped optical fiber in a strong magnetic field, and determining the intensity and direction of the strong magnetic field according to the optical fiber structural parameters, the power of signal light and pump light, the optical field distribution, and the like, so that the refractive index variation of the wrapped optical fiber caused by the magnetostrictive material is weakened or counteracted with the thermally induced refractive index variation, and the mode instability in the optical fiber laser is suppressed.
The above-mentioned series of methods proposed by researchers all have certain drawbacks. The bending mode selection technology is close to the bottleneck at present and is difficult to continuously lift; schemes that increase the media size can result in enhanced nonlinear effects; the method of using low NA fibers is limited by the state of the art and cannot be fully implemented. These methods can only suppress the mode-unstable effect to some extent to increase the output laser power. In order to promote the development of high-power solid-state lasers, a new and efficient method for inhibiting MI is needed to realize the conversion of energy from a high-order mode to a fundamental mode, so as to achieve the effect of ensuring the energy of an enhanced light beam.
Disclosure of Invention
Aiming at the defects or improvement demands of the prior art, the invention provides a method and a system for designing an optical fiber cladding for inhibiting mode instability in an optical fiber amplifier, which lead a high-order mode in the cladding to be converted into a fundamental mode by introducing a specific grating structure into the optical fiber cladding, lead the converted fundamental mode to enter an optical fiber core, achieve the effect of reducing the content of the high-order mode in the optical fiber and realize the aim of inhibiting the mode instability in the optical fiber.
In order to achieve the above object, according to a first aspect of the present invention, there is provided an optical fiber cladding design method for suppressing mode instability in an optical fiber amplifier, comprising the steps of:
s100, a mode field distribution model is built, wherein the mode field distribution model comprises a basic mode and a high-order mode;
s200, respectively calculating the powers of a fundamental mode and a high-order mode in the fiber core and the cladding according to the mode field distribution model;
s300, introducing a grating with the same period as the interference light field into the optical fiber cladding, and setting the grating at a corresponding position through calculation and placing the grating;
s400, after passing through the grating, all the energy of the fundamental mode and the high-order mode in the fiber cladding are converted mutually, the component duty ratio and the power of the high-order mode and the fundamental mode are changed, and the flow of the energy from the high-order mode to the fundamental mode is realized;
s500, based on the energy flow, according to the energy distribution rule of the modes, the energy of the fundamental mode in the cladding enters the fiber core, the energy of the fundamental mode in the fiber core is increased, and the flow of the energy in the fiber core from the high-order mode to the fundamental mode is realized.
Further, in step S100, a mode field distribution model of the fundamental mode and the higher-order mode is constructed according to the bessel function:
the mode field distribution model of the fundamental mode is as follows:
；
the mode field distribution model of the high-order mode is as follows:
；
wherein J is 0 Represents Bessel functions of the first kind, J 1 Representing the Bessel function of the second type, U is a normalized transverse phase parameter, r is the radial direction of the fiber, a is the core diameter, ϕ is the radial angle of the fiber, N 01 Represents the normalization factor, N, of the fundamental mode LP01 mode field distribution 11 Represents the normalization factor of the high-order mode LP11 mode field distribution, n is the refractive index of the fiber core, c is the speed of light, and ε is the dielectric constant.
Further, in step S200,
according to the mode field distribution model, the powers of a fundamental mode and a high-order mode in the fiber core and the cladding are calculated respectively, and the method is as follows:
power of fundamental mode in the core:
，
the power of the fundamental mode in the cladding is as follows:
。
further, in step S200, the power of the higher-order modes in the fiber core:
，
the power of the higher-order mode in the cladding is as follows:
。
further, in step S300,
the method comprises the steps that a grating with the same period as an interference light field is introduced into an optical fiber cladding, the grating presents a sectional structure, the distribution positions are designed to meet the requirement of axial positions with less fundamental mode content and more high-order mode content distributed in the cladding through calculation, so that all or most of high-order mode energy is converted into a fundamental mode, and then the formula of the positions of the cladding grating with the same period is set as follows:
，
wherein,is refractive in natureChange value of rate>Is the propagation constant difference between the fundamental mode and the higher order mode, z and x represent the axial and radial positions of the fiber, respectively;
obtaining an energy flow period S in the optical fiber; when the grating length is half of the flow period or the integer multiple of the flow period is half of the flow period, the exchange of the duty ratio of the high-order mode component and the fundamental mode component is realized through the grating, and the grating length L is set as follows according to the energy flow period in the optical fiber:
，
wherein n is a positive integer.
Further, in step S400,
after the light beam passes through the grating, the energy of the fundamental mode and the high-order mode in the fiber cladding are all converted mutually, so that the flow of the energy from the high-order mode to the fundamental mode is realized;
the power of the fundamental mode in the cladding is at this time，
Total power of fundamental mode in the optical fiberThe calculation formula is as follows:
。
further, the power of the higher-order mode in the cladding is，
High order mode total power in the fiberThe calculation formula is as follows:
。
further, in step S500,
after the mode energy flows from the high-order mode to the fundamental mode, the fundamental mode energy in the cladding enters the fiber core according to the energy distribution rule of the mode, so that the fundamental mode energy in the fiber core is increased, the high-order mode energy in the fiber core enters the cladding, and the high-order mode energy is reduced;
the energy of the fundamental mode in the cladding enters the fiber core, the energy of the fundamental mode in the fiber core is increased, and the specific calculation formula is as follows:
；
further, in step S500, the energy of the higher-order mode in the fiber core enters the cladding, and the energy of the higher-order mode in the fiber core is reduced, and the specific calculation formula is as follows:
。
according to a second aspect of the present invention, there is provided an optical fiber cladding design system for suppressing mode instability in an optical fiber amplifier, comprising:
the model building module is used for building a model field distribution model, and comprises a basic mode and a model field distribution model of a high-order mode;
the power calculation module is used for calculating the powers of a fundamental mode and a high-order mode in the fiber core and the cladding respectively according to the mode field distribution model;
the grating introducing module is used for introducing a grating with the same period as the interference light field into the optical fiber cladding, and setting the grating at a corresponding position through calculation and placing the grating;
the energy conversion module is used for realizing the mutual conversion of all the energy of the fundamental mode and the high-order mode in the fiber cladding after passing through the grating, and the high-order mode and the fundamental mode have the components of changing the ratio and the power so as to realize the flow of the energy from the high-order mode to the fundamental mode;
and the energy flow module is used for enabling the energy of the fundamental mode in the cladding to enter the fiber core according to the energy distribution rule of the modes based on the energy flow, increasing the energy of the fundamental mode in the fiber core and realizing the flow of the energy in the fiber core from the high-order mode to the fundamental mode.
In general, the above technical solutions conceived by the present invention, compared with the prior art, enable the following beneficial effects to be obtained:
1. according to the invention, a specific grating structure is introduced into the optical fiber cladding, so that a medium-high order mode in the cladding is converted into a fundamental mode, and the converted fundamental mode enters the optical fiber core, thereby achieving the effect of reducing the content of the medium-high order mode in the optical fiber and achieving the purpose of inhibiting unstable modes in the optical fiber;
2. the optical fiber for realizing the mode instability suppression effect can be applied to gain optical fibers and transmission optical fibers, the optical fiber capable of realizing the mode instability effect has wide selection of materials, and can be matrix optical fibers such as quartz matrix, phosphate matrix, borate matrix and the like, and also can be glass matrix, ceramic matrix or crystal matrix optical fibers;
3. the grating structure introduced by the invention is designed according to the optical fiber parameters and the optical field condition calculation, so that all or most of high-order modes passing through the grating are converted into the fundamental mode, and the fundamental mode in the cladding enters the fiber core, thereby achieving the effect of inhibiting mode instability.
Drawings
FIG. 1 is a flow chart of a method for designing an optical fiber cladding to suppress mode instability in an optical fiber amplifier according to the present invention;
FIG. 2 is a schematic illustration of the fiber structure of the present invention after a grating structure is introduced into the cladding layer;
FIG. 3 shows the conversion of higher order modes in the cladding layer to fundamental modes under the action of cladding layer gratings according to the present invention.
Like reference numerals denote like technical features throughout the drawings, in particular: 1-is the optical fiber cladding, 2-is the optical fiber core, 3-is the higher order modes in the cladding, and 4-is the fundamental modes in the cladding.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
The optical fiber cladding design method and system for inhibiting the mode instability in the optical fiber amplifier can be applied to the gain optical fiber and the transmission optical fiber, the optical fiber which can realize the effect by using the method has wide selection range, and can be a matrix optical fiber such as quartz matrix, phosphate matrix, borate matrix and the like, and can also be a glass matrix, ceramic matrix or crystal matrix optical fiber.
The fiber core and the cladding of the optical fiber are distributed with the fundamental mode and the high-order mode, the fundamental mode in the fiber core is more than the high-order mode, and the high-order mode in the cladding is more than the fundamental mode. As shown in fig. 1, by introducing a grating structure into a cladding layer, energy interconversion between a fundamental mode and a high-order mode can be achieved, and by increasing conversion from the high-order mode to the fundamental mode, conversion from the fundamental mode to the high-order mode is reduced, so that the high-order mode has a small duty ratio, and the fundamental mode has a large duty ratio, thus ensuring better beam quality, and the specific steps include:
s100, a mode field distribution model is built, wherein the mode field distribution model comprises a basic mode and a high-order mode;
specifically, in step S100, a mode field distribution model of the fundamental mode and the higher-order mode is constructed according to the bessel function, and the specific model is as follows:
further, the mode field distribution model of the fundamental mode LP01 is:
，
further, the mode field distribution model of the higher-order mode LP11 is:
，
wherein J is 0 Represents Bessel functions of the first kind, J 1 Representing Bessel functions of the second kindU is normalized transverse phase parameter, r is fiber radius direction, a is fiber core diameter, ϕ is fiber radial angle, N 01 Represents the normalization factor, N, of the fundamental mode LP01 mode field distribution 11 Represents the normalization factor of the high-order mode LP11 mode field distribution, n is the refractive index of the fiber core, c is the speed of light, and ε is the dielectric constant.
S200, respectively calculating the powers of a fundamental mode and a high-order mode in the fiber core and the cladding according to the mode field distribution model;
specifically, in step S200, the powers of the fundamental mode and the higher-order mode in the fiber core and the cladding are calculated according to the mode field distribution model, which is specifically as follows:
specifically, the power of the LP01 mode in the core:
，
further, since the total power of the LP01 mode in the fiber is approximately equal to the sum of the power in the cladding and the core, the power of the LP01 mode in the cladding can be calculated as:
；
specifically, the power of the LP11 mode in the core is:
，
further, since the total power of the LP11 mode in the fiber is approximately equal to the sum of the power in the cladding and the core, the power of the LP11 mode in the cladding can be calculated as:
。
s300, introducing a grating with the same period as the interference light field into the optical fiber cladding;
specifically, in step S300, by introducing a grating with the period consistent with the period of the interference light field into the fiber cladding, as shown in fig. 2, the grating has a segmented structure, and the distribution positions are calculated to satisfy the axial positions with less fundamental mode content and more high-order mode content distributed in the cladding, so that all or most of the high-order mode energy can be converted into the fundamental mode, and then the formula of the positions of the cladding gratings with the same period is set as follows:
，
wherein,is the value of the change in refractive index, +.>Is the propagation constant difference between the fundamental mode and the higher order mode, z and x represent the axial and radial positions of the fiber, respectively;
further, obtaining an energy flow period S in the optical fiber; when the grating length is half the flow period or integer multiple of the flow period is half the period, the components of the higher order mode and the fundamental mode are exchanged through the grating, the mutual energy flows as shown in the following figure 3, and specific placement positions are set according to the grating length L:
，
wherein n is a positive integer.
S400, after passing through the grating, the component duty ratio and the power of the high-order mode and the fundamental mode are changed, so that the flow of energy from the high-order mode to the fundamental mode is realized;
specifically, in step S400, after passing through the grating, the energy of the fundamental mode LP01 mode and the high-order mode LP11 mode in the fiber cladding are all converted;
further, at this time, the power of the LP01 mode in the cladding is，
LP01 mode Total Power in optical fiberThe calculation formula is as follows:
；
further, at this point the power of the LP11 mode in the cladding is，
LP11 mode Total Power in optical fiberThe calculation formula is as follows:
；
thereby enabling the flow of energy from the higher order modes to the fundamental mode.
S500, based on the energy flow, according to the energy distribution rule of the modes, the flow of energy in the fiber core from the high-order mode to the fundamental mode is realized.
Specifically, in step S500, after the mode energy flows from the higher-order mode to the fundamental mode, according to the energy distribution rule of the mode, the fundamental mode energy in the cladding enters the fiber core, and the fundamental mode energy in the fiber core increases, and the specific calculation formula is as follows:
，
further, the energy of the higher-order mode in the fiber core enters the cladding, the energy of the higher-order mode in the fiber core is reduced, and the specific calculation formula is as follows:
，
the energy of the fundamental mode in the cladding enters the fiber core, so that the energy of the fundamental mode in the fiber core is increased; the higher order mode energy in the core enters the cladding and the higher order mode energy decreases.
Examples
Taking a 20/400 double-clad straight optical fiber with NA=0.05 as an example, optical fiber transmissionTransmitting 100W signal light, wherein 50% is the fundamental mode LP01 mode and 50% is the high-order mode LP11 mode, the total power of the LP01 mode and the LP11 mode in the optical fiber respectively accounts for 50% of the transmission signal light power, namely the total power of the fundamental mode LP01=50w, total power of higher order modes LP11 +.>=50W。
Specifically, in step S100, a mode field distribution model of the fundamental mode and the higher-order mode is constructed according to the bessel function, and the specific model is as follows:
further, the mode field distribution model of the fundamental mode LP01 is:
，
further, the mode field distribution model of the higher-order mode LP11 is:
，
wherein J is 0 Represents Bessel functions of the first kind, J 1 Representing the Bessel function of the second type, U is a normalized transverse phase parameter, r is the radial direction of the fiber, a is the core diameter, ϕ is the radial angle of the fiber, N 01 Represents the normalization factor, N, of the fundamental mode LP01 mode field distribution 11 Represents the normalization factor of the high-order mode LP11 mode field distribution, n is the refractive index of the fiber core, c is the speed of light, and ε is the dielectric constant.
In step S200, according to the mode field distribution model, the powers of the fundamental mode and the higher-order mode in the fiber core and the cladding are calculated respectively, which is specifically as follows:
specifically, the power of the LP01 mode in the core:
，
further, since in the 20/400, na=0.05 double-clad straight fiber, the fiber propagatesOutputting 50W signal light, wherein 50% of the signal light is a fundamental mode LP01 mode, and the total power of the LP01 mode is=50w, the power of the LP01 mode in the cladding is:
，
specifically, the power of the LP11 mode in the core:
，
further, since the optical fiber transmits 100W signal light in the 20/400, na=0.05 double-clad straight optical fiber, 50% of which is the fundamental mode LP11 mode, the total power of the LP11 mode is known to be=50w, the power of the LP11 mode in the cladding is:
，
it can also be seen that the fundamental mode is more in the core and the higher order mode is more in the cladding.
In step S300, by introducing a grating with the period consistent with the interference light field into the fiber cladding, the grating presents a sectional structure, and the distribution positions are calculated to satisfy the axial positions with less fundamental mode content and more high-order mode content distributed in the cladding, so that all or most of the high-order mode energy can be converted into the fundamental mode, and then the formula of the positions of the cladding gratings with the same period is set as follows:
，
wherein,is the value of the change in refractive index, +.>Is the difference in propagation constants of the fundamental mode and the higher order modes, here equal to 2445.5m -1 Z and x represent the axial and radial positions of the fiber, respectively;
further, the flow period to obtain 20/400 na=0.05 double clad straight fiber energy is s=0.0026 m; when the grating length is half of the flow period or an integer multiple of the flow period is half of the flow period, the components of the high-order mode and the fundamental mode are exchanged in proportion and energy flows mutually through the grating, so the grating length L is set as follows:
，
specifically, it is known that in this type of optical fiber, the energy flow period s=0.0026m, the grating length L is obtained as:
，
wherein n is a positive integer.
In step S400, after passing through the grating, the energy of the fundamental mode LP01 mode and the high-order mode LP11 mode in the fiber cladding are all converted;
further, at this time, the power of the LP01 mode in the cladding:
；
LP01 mode Total Power in optical fiberThe calculation formula is as follows:
，
further, at this point the power of the LP11 mode in the cladding:
；
LP11 mode Total Power in optical fiberThe calculation formula is as follows:
，
thereby enabling the flow of energy from the higher order modes to the fundamental mode.
In step S500, after the mode energy flows from the higher-order mode to the fundamental mode, according to the energy distribution rule of the mode, the fundamental mode energy in the cladding enters the fiber core, and the fundamental mode energy in the fiber core increases, and the specific calculation formula is as follows:
，
the energy of the medium-high order mode in the fiber core enters the cladding, the energy of the medium-high order mode in the fiber core is reduced, and the specific calculation formula is as follows:
，
therefore, the purposes of increasing the energy of the fundamental mode in the fiber core and reducing the energy of the high-order mode are achieved, and the mode instability effect in the fiber can be further restrained.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (10)
1. The method for designing the optical fiber cladding for inhibiting the mode instability in the optical fiber amplifier is characterized by comprising the following steps:
s100, a mode field distribution model is built, wherein the mode field distribution model comprises a basic mode and a high-order mode;
s200, respectively calculating the powers of a fundamental mode and a high-order mode in the fiber core and the cladding according to the mode field distribution model;
s300, introducing a grating with the same period as the interference light field into the optical fiber cladding, and setting the grating at a corresponding position through calculation and placing the grating;
s400, after passing through the grating, all the energy of the fundamental mode and the high-order mode in the fiber cladding are converted mutually, the component duty ratio and the power of the high-order mode and the fundamental mode are changed, and the flow of the energy from the high-order mode to the fundamental mode is realized;
s500, based on the energy flow, according to the energy distribution rule of the modes, the energy of the fundamental mode in the cladding enters the fiber core, the energy of the fundamental mode in the fiber core is increased, and the flow of the energy in the fiber core from the high-order mode to the fundamental mode is realized.
2. The method for designing an optical fiber cladding for suppressing mode instability in an optical fiber amplifier according to claim 1, wherein in step S100, a mode field distribution model of a fundamental mode and a higher-order mode is constructed from a bessel function:
the mode field distribution model of the fundamental mode is as follows:
；
the mode field distribution model of the high-order mode is as follows:
，
wherein J is 0 Represents Bessel functions of the first kind, J 1 Representing a second class of bessel functions, U is the normalized transverse phase parameter, r is the fiber radius direction, a is the core diameter,refers to the radial angle of the optical fiber, N 01 Represents the normalization factor, N, of the fundamental mode LP01 mode field distribution 11 Represents the normalization factor of the distribution of the mode field of the high-order mode LP11, n is the refractive index of the fiber core, c is the speed of light, +.>Is the dielectric constant.
3. The method for designing an optical fiber cladding for suppressing mode instability in an optical fiber amplifier according to claim 1, wherein in step S200,
according to the mode field distribution model, the powers of a fundamental mode and a high-order mode in the fiber core and the cladding are calculated respectively, and the method is as follows:
power of fundamental mode in the core:
，
the power of the fundamental mode in the cladding is as follows:
。
4. the method for designing an optical fiber cladding for suppressing mode instability in an optical fiber amplifier according to claim 3, wherein in step S200, the power of the higher order modes in the core:
，
the power of the higher-order mode in the cladding is as follows:
。
5. the method for designing an optical fiber cladding for suppressing mode instability in an optical fiber amplifier according to claim 1, wherein in step S300,
the method comprises the steps that a grating with the same period as an interference light field is introduced into an optical fiber cladding, the grating presents a sectional structure, the distribution positions are designed to meet the requirement of axial positions with less fundamental mode content and more high-order mode content distributed in the cladding through calculation, so that all or most of high-order mode energy is converted into a fundamental mode, and then the formula of the positions of the cladding grating with the same period is set as follows:
，
wherein,is the value of the change in refractive index, +.>Is the propagation constant difference between the fundamental mode and the higher order mode, z and x represent the axial and radial positions of the fiber, respectively;
obtaining an energy flow period S in the optical fiber; therefore, when the grating length is half of the flow period or the integer multiple of the flow period is half of the flow period, the exchange of the duty ratio of the high-order mode component and the fundamental mode component is realized through the grating, and the grating length L is set as follows according to the energy flow period in the optical fiber:
，
wherein n is a positive integer.
6. The method for designing an optical fiber cladding for suppressing mode instability in an optical fiber amplifier according to any one of claims 1 to 5, wherein in step S400,
after the light beam passes through the grating, the energy of the fundamental mode and the high-order mode in the fiber cladding are all converted mutually, so that the flow of the energy from the high-order mode to the fundamental mode is realized;
the power of the fundamental mode in the cladding is at this time，
Total power of fundamental mode in the optical fiberThe calculation formula is as follows:
。
7. the method for designing a cladding for an optical fiber for suppressing mode instability in an optical fiber amplifier according to claim 6, wherein the power of the higher order modes in the cladding is，
High order mode total power in the fiberThe calculation formula is as follows:
。
8. the method for designing an optical fiber cladding for suppressing mode instability in an optical fiber amplifier according to any one of claims 1 to 5, wherein in step S500,
after the mode energy flows from the high-order mode to the fundamental mode, the fundamental mode energy in the cladding enters the fiber core according to the energy distribution rule of the mode, so that the fundamental mode energy in the fiber core is increased, the high-order mode energy in the fiber core enters the cladding, and the high-order mode energy is reduced;
the energy of the fundamental mode in the cladding enters the fiber core, the energy of the fundamental mode in the fiber core is increased, and the specific calculation formula is as follows:
。
9. the method for designing a cladding for an optical fiber for suppressing mode instability in an optical fiber amplifier according to claim 8, wherein in step S500, the energy of the higher order modes in the core enters the cladding, and the energy of the higher order modes in the core decreases as follows:
。
10. an optical fiber cladding design system for suppressing mode instability in an optical fiber amplifier, comprising:
the model building module is used for building a model field distribution model, and comprises a basic mode and a model field distribution model of a high-order mode;
the power calculation module is used for calculating the powers of a fundamental mode and a high-order mode in the fiber core and the cladding respectively according to the mode field distribution model;
the grating introducing module is used for introducing a grating with the same period as the interference light field into the optical fiber cladding, and setting the grating at a corresponding position through calculation and placing the grating;
the energy conversion module is used for realizing the mutual conversion of all the energy of the fundamental mode and the high-order mode in the fiber cladding after passing through the grating, and the high-order mode and the fundamental mode have the components of changing the ratio and the power so as to realize the flow of the energy from the high-order mode to the fundamental mode;
and the energy flow module is used for enabling the energy of the fundamental mode in the cladding to enter the fiber core according to the energy distribution rule of the modes based on the energy flow, increasing the energy of the fundamental mode in the fiber core and realizing the flow of the energy in the fiber core from the high-order mode to the fundamental mode.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH10111421A (en) * | 1996-10-08 | 1998-04-28 | Sumitomo Electric Ind Ltd | Optical waveguide device |
| CN115566518A (en) * | 2022-11-07 | 2023-01-03 | 中国航天三江集团有限公司 | Method and device for inhibiting MI (Mimi) effect in optical fiber laser by using magnetostrictive material |
| CN115663576A (en) * | 2022-10-24 | 2023-01-31 | 中国航天三江集团有限公司 | Optical fiber mode purification method and system |
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| JP2003057469A (en) * | 2001-04-11 | 2003-02-26 | Makoto Fujimaki | Optical waveguide grating and its forming method, and mask for formation thereof |
| FR2860598B1 (en) * | 2003-10-03 | 2005-12-16 | Cit Alcatel | SUPRESSION OF MODE (S) FOR PROPAGATION OF UNDESIRABLE SIGNALS BEFORE A MODE CONVERTER |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH10111421A (en) * | 1996-10-08 | 1998-04-28 | Sumitomo Electric Ind Ltd | Optical waveguide device |
| CN115663576A (en) * | 2022-10-24 | 2023-01-31 | 中国航天三江集团有限公司 | Optical fiber mode purification method and system |
| CN115566518A (en) * | 2022-11-07 | 2023-01-03 | 中国航天三江集团有限公司 | Method and device for inhibiting MI (Mimi) effect in optical fiber laser by using magnetostrictive material |
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