CN111948751B - Design method of optical fiber current transformer optical fiber sensing ring based on 650nm wave band - Google Patents

Abstract

The invention is a design method of the optical fiber sensing ring of the optical fiber current transformer based on the 650nm band. The invention belongs to the technical field of all-fiber current sensing design. In the method, the cross-sectional structure of the optical fiber is provided with multi-layer air holes; Chiral parameter; determine the value range of the air filling ratio of the optical fiber, and take any value that meets the requirements as the final air filling ratio of the optical fiber; determine the lattice constant of the optical fiber according to the obtained chirality parameter and air filling ratio of the optical fiber The value range of , and any value that meets the requirements is taken as the final lattice constant of the fiber. The ratio difference of the optical fiber current transformer system using the chiral photonic crystal optical fiber sensing ring scheme of the present invention is 0.235%, which proves the rationality of the designed chiral photonic crystal optical fiber parameter design, and shows that the current measurement of the optical fiber current transformer system is accurate. degree of improvement.

Description

A Design Method of Optical Fiber Sensing Ring of Optical Fiber Current Transformer Based on 650nm Band

technical field

The invention relates to the technical field of all-fiber current sensing design, and relates to a design method for an optical fiber sensing ring of an optical fiber current transformer based on a 650 nm waveband.

Background technique

Optical fiber current transformer is a kind of optical fiber sensor based on Faraday rotation effect. It is widely used in power transmission industry and electrolytic aluminum industry due to its advantages of good insulation, high reliability, wide frequency range and good transient characteristics. These industries all put forward high-precision requirements for the current measurement of fiber-optic current transformers. One of the main factors limiting the accuracy of the system is the imperfection originating from the system's fiber optic sensing loop. Polarized light is transmitted in the form of circularly polarized light in an ideal optical fiber sensing ring, but the optical fiber will have residual linear birefringence due to its unsatisfactory manufacturing process, which will cause a rotation of the polarization plane of the polarized light, resulting in a The indistinguishable error signal caused by the Faraday effect causes polarization errors in the system transmission of light, which in turn reduces the accuracy of the current measured by the system.

Therefore, in order to improve the accuracy of the current measurement of the system, it is necessary to consider increasing the circular birefringence of the fiber sensing ring or reducing its residual linear birefringence. The current mainstream solution is to use a rotating panda-type silicon-based polarization-maintaining fiber as the optical fiber sensing ring of the system. In this fiber, the two stress filaments of the panda-type silicon baseline polarization-maintaining fiber are stretched around the core in a molten state and rotated at a uniform speed. Due to the averaging effect, the effective circular birefringence caused by the off-axis rotation of the stress filaments is enhanced. However, there are still some problems with this fiber. First, the rotational rate of the fiber stress filament is non-uniform, which means that its pitch is also non-uniform, which results in residual linear birefringence in the fiber. Second, there is a great stress in the fiber drawing process. This stress will cause the photoelastic properties of the fiber core to change over time, which will gradually weaken its linear birefringence suppression effect. These problems in the fiber limit the further improvement of the system accuracy. Therefore, it is necessary to find a new type of highly circular-maintaining polarization fiber to improve the current measurement accuracy of the fiber-optic current transformer system.

SUMMARY OF THE INVENTION

In order to reduce the polarization error introduced by the residual linear birefringence of the optical fiber sensing ring in the optical fiber current transformer system, and further improve the current measurement accuracy of the optical fiber current transformer system, the invention provides an optical fiber based on the 650nm band. The present invention provides the following technical solutions:

A method for designing an optical fiber sensing ring of an optical fiber current transformer based on a 650nm band, comprising the following steps:

Step 1: Use a refractive index-guided chiral photonic crystal fiber, and set the cross-sectional structure of the fiber to have multiple air holes;

Step 2: According to the concentration of griseofulvin in PMMA in the refractive index-guided chiral photonic crystal fiber, determine the chiral parameter of the fiber;

Step 3: According to the obtained chirality parameters of the optical fiber and the determined lattice constant, determine the value range of the air filling ratio of the optical fiber, and take any value as the final air filling ratio of the optical fiber;

Step 4: Determine the value range of the lattice constant of the fiber according to the obtained chirality parameter and air filling ratio, and take any value as the final lattice constant of the fiber.

Preferably, the step 1 is specifically:

There are 5 layers of air holes in the cross-sectional structure of the optical fiber. Each layer of air holes in the optical fiber cross-section is arranged in a regular hexagon. The innermost air hole in the center of the fiber is the first layer of air holes, and the outermost air hole in the center of the fiber is The fifth layer of air holes, the number of layers from the innermost layer to the outermost layer increases layer by layer;

For the first layer of air holes, the distance from all 6 air holes to the center of the fiber is Λ, and the distances for the air holes on the entire optical fiber cross-section are the same, which is Λ, and all air holes are round holes And the diameters are all equal to d, the ratio of the diameter of the fiber air hole to its lattice constant and the air filling ratio of the defined fiber is d/Λ.

Preferably, the step 2 is specifically:

When the concentration of griseofulvin in PMMA is 0.067g/cm, the corresponding optical rotation δ ₀ is expressed by the Boltzmann formula, and the corresponding optical rotation δ ₀ is expressed by the following formula:

Wherein, B ₁ and B ₂ are both constants, B ₁ =1.46×10 ^4° ·nm ² /mm, B ₂ =1.82×10 ^10° ·nm ⁴ /mm;

The chiral parameter is determined according to the optical rotation δ ₀ , and the chiral parameter ξ ₀ is determined by the following formula:

k ₀ =2π/λ

Among them, k ₀ is the light wave vector, and λ is the light wavelength of the light source.

Preferably, the step 3 is specifically:

Under the determined chirality parameters and the distance from the air hole to the center of the fiber, the effective refractive index of the guided mode and space-filling mode of the chiral photonic crystal fiber with different air filling ratios is calculated by the two-dimensional chiral plane wave expansion method. When the effective refractive index of the optical fiber is greater than the effective refractive index of the space-filling mode and the effective refractive index of the high-order mode of the fiber is smaller than the effective refractive index of the space-filling mode, the single-mode transmission of light in the fiber is guaranteed, and the air-filling ratio is designed to satisfy all air-filling ratios value of .

Preferably, the step 4 is specifically:

Under the determined chirality parameters and air filling ratio, the effective refractive index of the guided mode and space-filling mode of the chiral photonic crystal fiber with different lattice constants is calculated by the two-dimensional chiral plane wave expansion method. When the effective refractive index of the fundamental mode of the fiber is When the effective refractive index is greater than the effective refractive index of the space-filling mode and the effective refractive index of the high-order mode of the fiber is smaller than that of the space-filling mode, the single-mode transmission of light in the fiber can be ensured, and the lattice constant is designed to satisfy all lattice constants.

The present invention has the following beneficial effects:

The scheme of the present invention replaces the original silicon-based torsional circular-maintaining optical fiber sensing ring scheme, not only has the advantages of low cost, but also improves the optical fiber current transformer system by optimizing the design of the structural parameters of the chiral photonic crystal optical fiber sensing ring The accuracy of the current measurement reduces the ratio difference of the system from 4.5% to 0.235%.

The ratio difference of the fiber optic current transformer system using the silicon-based twisted panda-type circular polarization fiber sensing ring scheme is 4.5%, while the ratio difference of the fiber optic current transformer system using the photonic crystal fiber sensing ring scheme is 0.235%. This result strongly proves the rationality of the parameter design of the chiral photonic crystal fiber designed in this patent, and shows the degree of improvement of the current measurement accuracy of the fiber optic current transformer system.

Description of drawings

Figure 1 is a schematic diagram of a cross-sectional structure of an optical fiber;

Figure 2 is a graph showing the relationship between the effective refractive index of the guided mode and the space-filling mode of the crystal fiber and the air filling ratio of the fiber;

Fig. 3 is a graph showing the variation of the effective refractive index of the guided mode and the space-filling mode of the crystal fiber with the lattice constant of the fiber;

Figure 4 shows the relationship between the ratio difference and the measured current between the fiber optic current transformer system of the chiral photonic crystal fiber sensing ring and the fiber optic current transformer system using the silicon-based twisted circularly polarized fiber sensing ring.

Detailed ways

The present invention is described in detail below with reference to specific embodiments.

Specific embodiment one:

The invention provides a design method of an optical fiber current transformer optical fiber sensing ring based on a 650nm band, specifically:

A method for designing an optical fiber sensing ring of an optical fiber current transformer based on a 650nm band, comprising the following steps:

Step 1: Use a refractive index-guided chiral photonic crystal fiber, set the cross-sectional structure of the fiber to have multiple air holes, and determine the distance from the air hole to the center of the fiber;

The step 1 is specifically:

There are 5 layers of air holes in the cross-sectional structure of the optical fiber. Each layer of air holes in the optical fiber cross-section is arranged in a regular hexagon. The innermost air hole in the center of the fiber is the first layer of air holes, and the outermost air hole in the center of the fiber is The fifth layer of air holes, the number of layers increases from the innermost layer to the outermost layer. Air holes A1, A2, ..., A6 are the first layer of air holes, and air holes B1, B2, ..., B12 are the second layer. Air holes, air holes C1, C2, ..., C18 are the third layer air holes, air holes D1, D2, ..., D24 are the fourth layer air holes, air holes E1, E2, ..., E30 are the fifth layer air holes ;

For the first layer of air holes, the distance from all six air holes A1, A2, ..., A6 to the center of the fiber is Λ, and the distances for the air holes on the entire fiber cross-section are equal, which is Λ, All air holes are round holes with equal diameters and are d. The ratio of the diameter of the air holes of the fiber to its lattice constant and the air filling ratio of the defined fiber is d/Λ.

Preferably, the distance Λ from the air hole to the center of the optical fiber is taken as 4 μm.

Step 2: According to the concentration of griseofulvin in PMMA in the refractive index-guided chiral photonic crystal fiber, determine the chiral parameter of the fiber;

The step 2 is specifically:

When the concentration of griseofulvin in PMMA is 0.067g/cm, the corresponding optical rotation δ ₀ is expressed by the Boltzmann formula, and the corresponding optical rotation δ ₀ is expressed by the following formula:

Wherein, B ₁ and B ₂ are both constants, B ₁ =1.46×10 ^4° ·nm ² /mm, B ₂ =1.82×10 ^10° ·nm ⁴ /mm;

The chiral parameter is determined according to the optical rotation δ ₀ , and the chiral parameter ξ ₀ is determined by the following formula:

k ₀ =2π/λ

Among them, k ₀ is the light wave vector, and λ is the light wavelength of the light source.

Step 3: Determine the air filling ratio of the fiber according to the obtained chirality parameter of the fiber and the distance from the air hole to the center of the fiber;

The step 3 is specifically:

Under the determined chirality parameters and the distance from the air hole to the center of the fiber, the effective refractive index of the guided mode and space-filling mode of the chiral photonic crystal fiber with different air filling ratios is calculated by the two-dimensional chiral plane wave expansion method. When the effective refractive index of the optical fiber is greater than the effective refractive index of the space-filling mode and the effective refractive index of the high-order mode of the fiber is smaller than the effective refractive index of the space-filling mode, the single-mode transmission of light in the fiber is guaranteed, and the air-filling ratio is designed to satisfy all air-filling ratios value of .

Step 4: Determine the lattice constant of the fiber according to the obtained chirality parameter and air filling ratio.

The step 4 is specifically:

Under the determined chirality parameters and air filling ratio, the effective refractive index of the guided mode and space-filling mode of the chiral photonic crystal fiber with different lattice constants is calculated by the two-dimensional chiral plane wave expansion method. When the effective refractive index of the fundamental mode of the fiber is When the effective refractive index is greater than the effective refractive index of the space-filling mode and the effective refractive index of the high-order mode of the fiber is smaller than that of the space-filling mode, the single-mode transmission of light in the fiber can be ensured, and the lattice constant is designed to satisfy all lattice constants.

The ratio difference of the fiber optic current transformer system can be expressed as:

in

Among them, N is the number of turns of the coil, and its size is N=10; V is the Verdet constant of the fiber, I is the measured current, Δβ is the residual linear birefringence in the fiber, and T is the inherent circular birefringence of the fiber.

For the silicon-based twisted panda-type circularly-maintaining polarized fiber, its Verdet constant is V ₁ =4.37μrad/A, the residual linear birefringence Δβ ₁ =1571rad/m, and the circular birefringence is T ₁ =38080rad/m. For a chiral photonic crystal fiber, its Verdet constant is V ₂ =3.13 μrad/A, the residual linear birefringence Δβ ₂ =0.468rad/m, and the circular birefringence T ₂ =4.7617rad/m. When the measured current value I increases from 0A to 1000A, a comparison chart of the system ratio difference between the silicon-based twisted panda-type circularly-maintaining polarization fiber sensing ring and the chiral photonic crystal fiber sensing ring can be obtained, as shown in Figure 4. Show. The simulation results show that the ratio difference of the fiber optic current transformer system using the silicon-based twisted panda-type circular polarization fiber sensing ring scheme is 4.5%, while the ratio difference of the fiber optic current transformer system using the photonic crystal fiber sensing ring scheme It is 0.235%. This result strongly proves the rationality of the parameter design of the chiral photonic crystal fiber designed by this patent, and shows the degree of improvement of the current measurement accuracy of the fiber current transformer system.

Specific embodiment two:

A method for designing an optical fiber sensing ring of an optical fiber current transformer based on a 650nm band, comprising the following steps:

Step 1. Use a refractive index-guided chiral photonic crystal fiber to replace the original rotating panda-type silicon-based circularly-maintaining fiber. The base material of this optical fiber is polymethyl methacrylate (PMMA) doped with the chiral molecule griseofulvin. The cross-sectional structure of its optical fiber has a total of 5 layers of air holes, as shown in Figure 1. Wherein (1) is the base material composition of the optical fiber, and each layer of air holes in the optical fiber cross-section is arranged in a regular hexagon. The layer of air holes closest to the center of the fiber is defined as the first layer of air holes, and the layer of air holes farthest from the center of the fiber is defined as the fifth layer of air holes. The number of layers increases from the innermost layer to the outermost layer. In Figure 1, there is no air hole in the center of the designed chiral photonic crystal fiber. Air holes A1, A2, ..., A6 are the first layer of air holes, and air holes B1, B2, ..., B12 are the second layer of air holes. The holes C1, C2, ..., C18 are the third layer air holes, the air holes D1, D2, ..., D24 are the fourth layer air holes, and the air holes E1, E2, ..., E30 are the fifth layer air holes. For the first layer of air holes, the distances of all 6 air holes A1, A2,..., A6 from the center of the fiber are Λ, and the distances for the air holes on the entire fiber cross-section are equal, which is Λ , defining this distance as the lattice constant of the fiber. All air holes are round holes and have the same diameter, d. The ratio of the diameter of the fiber air hole to its lattice constant and the air filling ratio of the defined fiber is d/Λ.

Step 2. After designing the cross-sectional structure of the optical fiber, it is first necessary to determine the chiral parameters of the optical fiber. The chirality parameter of the fiber is a function related to the wavelength of light, and the specific calculation process is as follows:

When the concentration of griseofulvin in PMMA is 0.067g/cm, the corresponding optical rotation δ ₀ can be expressed as:

Wherein, B ₁ and B ₂ are both constants, and their values are B ₁ =1.46×10 ^4° ·nm ² /mm, and B ₂ =1.82×10 ^10° ·nm ⁴ /mm, respectively. Then the chiral parameter ξ ₀ can be calculated by the following formula:

Wherein, k ₀ is the light wave vector, and its value is k ₀ =2π/λ, and λ is the light wavelength of the light source, and its value is λ=650nm. The calculated chirality parameter ξ ₀ =-1.1482×10 ^-8 rad·μm.

Step 3. Next, the air filling ratio of the fiber needs to be determined. Here, the lattice constant of the fiber is Λ=4μm, and the chirality parameter ξ ₀ =-1.1482×10 ^-8 rad·μm. The value of the air filling ratio d/Λ of the optical fiber is from 0.04 to 0.6 with a step size of 0.02. At this time, the relationship between the effective refractive index n _eff of the guided mode and the space-filling mode of the chiral photonic crystal fiber with the air filling ratio d/Λ of the fiber can be obtained, as shown in Figure 2. When the effective refractive index of the guided mode of the fiber is greater than the effective refractive index of the space-filling mode, the guided mode light can be stably transmitted in the fiber. When the air-filling ratio of the fiber is less than 0.08, the effective refractive index of the fiber fundamental mode and the effective refractive index of the higher-order mode are both smaller than the effective refractive index of the space-filling mode; when the air-filling ratio of the fiber is greater than 0.46, the effective refractive index of the fiber fundamental mode The effective refractive index of the high-order mode and the high-order mode are both greater than the effective refractive index of the space-filling mode; since it is necessary to ensure that there is only one mode of light in the fiber for transmission, that is, the transmission of the fundamental mode light in the fiber, the effective refractive index of the fundamental mode is required. It is greater than the effective refractive index of the space-filling mode and the effective refractive index of the higher-order mode is less than the effective refractive index of the space-filling mode. Therefore, it is necessary to ensure that the air filling ratio d/Λ of the optical fiber is between 0.08 and 0.46.

Step 4. Finally, the lattice constant of the fiber needs to be determined. According to the value range of the air filling ratio determined in Content 3, one of the values is arbitrarily selected here. The air filling ratio of the optical fiber is taken as 0.42, and the chirality parameter ξ ₀ =-1.1482×10 ^{- 8} rad·μm. The value of the lattice constant Λ of the fiber ranges from 0.4 μm to 7 μm with a step size of 0.2 μm. At this time, the relationship between the effective refractive index n _eff of the guided mode and the space-filling mode of the chiral photonic crystal fiber with the lattice constant Λ of the fiber can be obtained, as shown in Figure 3. When the lattice constant of the fiber is less than 1.2 μm, the effective refractive index of the fundamental mode and the higher-order mode of the fiber are both smaller than the effective refractive index of the space-filling mode; when the lattice constant of the fiber is greater than 4.4 μm, the effective refractive index of the fundamental mode and the higher-order mode of the fiber are greater than the effective refractive index of the space-filling mode; since it is necessary to ensure that there is only one mode of light in the fiber for transmission, that is, the transmission of the fundamental mode light in the fiber, the effective refractive index of the fundamental mode needs to be greater than the effective refractive index of the space-filling mode. The effective index of refraction for higher order modes is less than the effective index of refraction for space-filling modes. Therefore, it is necessary to ensure that the lattice constant Λ of the optical fiber is between 1.2 μm and 4.4 μm. Here, Λ=4 μm is taken.

The ratio difference of the fiber optic current transformer system can be expressed as:

in

Among them, N is the number of turns of the coil, and its size is N=10; V is the Verdet constant of the fiber, I is the measured current, Δβ is the residual linear birefringence in the fiber, and T is the inherent circular birefringence of the fiber.

For the silicon-based twisted panda-type circularly-maintaining polarized fiber, its Verdet constant is V ₁ =4.37μrad/A, the residual linear birefringence Δβ ₁ =1571rad/m, and the circular birefringence is T ₁ =38080rad/m. For a chiral photonic crystal fiber, its Verdet constant is V ₂ =3.13 μrad/A, the residual linear birefringence Δβ ₂ =0.468rad/m, and the circular birefringence T ₂ =4.7617rad/m. When the measured current value I increases from 0A to 1000A, a comparison chart of the system ratio difference between the silicon-based twisted panda-type circularly-maintaining polarization fiber sensing ring and the chiral photonic crystal fiber sensing ring can be obtained, as shown in Figure 4. Show. The simulation results show that the ratio difference of the fiber optic current transformer system using the silicon-based twisted panda-type circular polarization fiber sensing ring scheme is 4.5%, while the ratio difference of the fiber optic current transformer system using the photonic crystal fiber sensing ring scheme It is 0.235%. This result strongly proves the rationality of the parameter design of the chiral photonic crystal fiber designed by this patent, and shows the degree of improvement of the current measurement accuracy of the fiber current transformer system.

This scheme proposes a new type of polymer material photonic crystal fiber sensing ring scheme. This scheme replaces the original silicon-based twisted circular polarization fiber sensing ring scheme. It not only has the advantages of low cost, but also uses chiral photons. The optimized design of the structural parameters of the crystal fiber sensing ring improves the accuracy of the current measurement of the fiber optic current transformer system, which reduces the ratio difference of the system from 4.5% to 0.235%.

The above is only a preferred embodiment of a design method for an optical fiber current transformer optical fiber sensing ring based on a 650 nm wavelength band, and the protection scope of a design method for an optical fiber current transformer optical fiber sensing ring based on a 650 nm wavelength band is not limited to In the above-mentioned embodiments, all technical solutions under this idea belong to the protection scope of the present invention. It should be pointed out that for those skilled in the art, some improvements and changes without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims (2)

1. a design method based on the optical fiber current transformer optical fiber sensing ring of 650nm wave band, it is characterized in that: comprise the following steps: Step 1: Use a refractive index-guided chiral photonic crystal fiber, and set the cross-sectional structure of the fiber to have multiple air holes; The step 1 is specifically: There are 5 layers of air holes in the cross-sectional structure of the optical fiber. Each layer of air holes in the optical fiber cross-section is arranged in a regular hexagon. The innermost air hole in the center of the fiber is the first layer of air holes, and the outermost air hole in the center of the fiber is The fifth layer of air holes, the number of layers from the innermost layer to the outermost layer increases layer by layer; For the first layer of air holes, the distance from all 6 air holes to the center of the fiber is Λ, and the distances for the air holes on the entire optical fiber cross-section are the same, which is Λ, and all air holes are round holes And the diameters are all equal to d, the ratio of the diameter of the fiber air hole to its lattice constant and the air filling ratio of the defined fiber is d/Λ; Step 2: According to the concentration of griseofulvin in PMMA in the refractive index-guided chiral photonic crystal fiber, determine the chiral parameter of the fiber; The step 2 is specifically: When the concentration of griseofulvin in PMMA is 0.067g/cm, the corresponding optical rotation δ ₀ is expressed by the Boltzmann formula, and the corresponding optical rotation δ ₀ is expressed by the following formula:

Wherein, B ₁ and B ₂ are both constants, B ₁ =1.46×10 ^4° ·nm ² /mm, B ₂ =1.82×10 ^10° ·nm ⁴ /mm; The chiral parameter is determined according to the optical rotation δ ₀ , and the chiral parameter ξ ₀ is determined by the following formula:

k ₀ =2π/λ Among them, k ₀ is the light wave vector, and λ is the light wavelength of the light source; Step 3: According to the obtained chirality parameter of the optical fiber and the determined lattice constant, determine the value range of the air filling ratio of the optical fiber, and take any value as the final air filling ratio of the optical fiber; The step 3 is specifically: Under the determined chirality parameters and the distance from the air hole to the center of the fiber, the effective refractive index of the guided mode and space-filling mode of the chiral photonic crystal fiber with different air filling ratios is calculated by the two-dimensional chiral plane wave expansion method. When the effective refractive index of the optical fiber is greater than the effective refractive index of the space-filling mode and the effective refractive index of the high-order mode of the fiber is smaller than the effective refractive index of the space-filling mode, the single-mode transmission of light in the fiber is guaranteed, and the air-filling ratio is designed to satisfy all air-filling ratios the value of ; Step 4: Determine the value range of the lattice constant of the fiber according to the obtained chirality parameter and air filling ratio, and take any value as the final lattice constant of the fiber. 2. a kind of design method based on the optical fiber current transformer optical fiber sensing ring of 650nm wave band according to claim 1, is characterized in that: described step 4 is specifically: Under the determined chirality parameters and air filling ratio, the effective refractive index of the guided mode and space-filling mode of the chiral photonic crystal fiber with different lattice constants is calculated by the two-dimensional chiral plane wave expansion method. When the effective refractive index of the fundamental mode of the fiber is When the effective refractive index is greater than the effective refractive index of the space-filling mode and the effective refractive index of the high-order mode of the fiber is smaller than that of the space-filling mode, the single-mode transmission of light in the fiber can be ensured, and the lattice constant is designed to satisfy all lattice constants.

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