Method for designing polarization maintaining optical fiber with stress-induced heating and cooling
By using a simulated stress zone heating and cooling method for polarization-maintaining fiber design, the problem of unclear relationship between fiber geometry parameters and optical properties was solved, enabling precise design and improved consistency of polarization-maintaining fiber, and shortening design time and cost.
Patent Information
- Application Number
- CN202310291455.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-03-23
- Publication Date
- 2026-02-27
- Estimated Expiration
- 2043-03-23
AI Technical Summary
The relationship between optical fiber geometric parameters and optical fiber properties is unclear in existing technologies, which leads to problems such as long exploration cycle of polarization-maintaining fiber technology, poor fiber consistency, and lack of theory for tracing property degradation.
A comprehensive design method for polarization-maintaining optical fibers using simulated stress zone heating and cooling is adopted. The stress distribution is generated through the finite element algorithm, the stress birefringence and fiber loss are calculated, the influence analysis curve is generated, the target parameters are set, and the geometric parameters of the panda-type polarization-maintaining fiber are selected.
It has achieved accurate simulation and calculation of stress distribution in stress zones, and realized comprehensive analysis of four parameters of optical fiber: structural parameters, stress distribution, birefringence, and loss. This has shortened the design time and cost of optical fiber and improved the consistency and performance of optical fiber.
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Figure CN116243481B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of polarization maintaining optical fiber, in particular to a polarization maintaining optical fiber comprehensive design method simulating stress zone heating and cooling. BACKGROUND
[0002] As a kind of full solid state inertial angular velocity sensor, after decades of development, with its unique technology and performance advantages, such as full solid state structure, high reliability, long service life, fast start speed, short response time, large measurement range, wide dynamic range, impact, vibration resistance, chemical corrosion resistance, small size, light weight, low cost and suitable for mass production, etc., in civil and military fields, it has become an important navigation control sensor, and is widely used in various fields. Fiber optic gyroscope is to use Sagnac effect, that is, the phase difference between two main waves in the same light path, clockwise (CW) and counterclockwise (CCW) propagation, is related to the rotation speed of the light path, and the phase shift caused by the rotation of the carrier is calculated by correlation detection to obtain the angular velocity of the carrier.
[0003] With the continuous expansion of the application field of fiber optic gyroscope, the contradiction between its volume, weight and precision is increasingly prominent. With the existing technology, it is difficult to further improve the precision of fiber optic gyroscope while maintaining a certain size and volume. And the traditional optical fiber is sensitive to irradiation and magnetic field, so the magnetic shielding and irradiation protection cannot be removed, which directly increases the volume and weight of the fiber optic gyroscope.
[0004] Therefore, it is very important to develop panda type polarization maintaining optical fiber with low loss, high birefringence and radiation resistance for improving the performance of fiber optic gyroscope. SUMMARY
[0005] The purpose of the present application is to solve the problems in the prior art that the relationship between fiber geometric parameters and fiber optical characteristics is not clear, the design parameters of the fiber are numerous and complex, there is no unified design model, the process groping period of the polarization maintaining optical fiber is long, the consistency of the fiber is poor, and the characteristic degradation tracing theory is lacking. A polarization maintaining optical fiber comprehensive design method simulating stress zone heating and cooling is proposed.
[0006] To achieve the above purpose, the present application provides a polarization maintaining optical fiber comprehensive design method simulating stress zone heating and cooling, comprising:
[0007] Select panda type polarization maintaining optical fiber;
[0008] Establish the finite element model and finite element unit grid of panda type polarization maintaining optical fiber, generate the stress distribution of polarization maintaining optical fiber stress zone by finite element algorithm; According to the stress-optical relationship, calculate the stress birefringence of polarization maintaining optical fiber and fiber loss; Generate stress birefringence, fiber loss and influence analysis curve of core and stress zone boundary distance;
[0009] By scanning the fiber geometry parameters and curve fitting, a relationship curve chart or a fitting function between the fiber loss, birefringence and the core and stress region boundary distance of the polarization maintaining fiber under different stress region diameters is obtained.
[0010] The maximum value of the target fiber loss and the minimum value of the stress birefringence are set, and according to the relationship curve chart or the fitting function, the geometry parameters of the panda type polarization maintaining fiber, i.e. the core and stress region boundary distance and the stress region diameter, are selected.
[0011] Further, the cross section of the panda type polarization maintaining fiber is circular, and the structure from outside to inside is a high polymer material coating layer, a quartz cladding layer composed of high purity silica glass, a stress region composed of boron-doped quartz glass rod and a high refractive index core doped with low concentration germanium; the geometry parameters of the panda type polarization maintaining fiber include the core and stress region boundary distance, the stress region diameter, the cladding diameter and the fiber diameter.
[0012] Further, the stress distribution function in the finite element algorithm is divided into two parts according to whether it is related to the propagation constant β, and when performing finite element calculation, the entire fiber geometry is divided into triangular meshes, wherein the minimum interval of the meshes around the core is half of the wavelength, each element contains three node components (Φ z1 ,Φ z2 ,Φ z3 ) and three edge components (Φ t1 ,Φ t2 ,Φ t3 ); the node components adopt traditional linear interpolation, and the edge components adopt vector basis function interpolation.
[0013] The polarization maintaining fiber comprehensive design method for simulating stress region heating and cooling of the application realizes the following technical effects:
[0014] (1) The stress distribution of the stress region can be accurately simulated and calculated.
[0015] (2) The four parameter comprehensive analysis of fiber "structure parameter-stress distribution-birefringence-loss" can be realized, and the polarization maintaining fiber comprehensive design is realized.
[0016] (3) It can be applied to the structure design of ultra-thin diameter polarization maintaining fiber, and the limit optical properties of the polarization maintaining fiber are explored.
[0017] (4) It provides a comprehensive theoretical basis for fiber preparation, and greatly shortens the fiber design time and cost. BRIEF DESCRIPTION OF DRAWINGS
[0018] Figure 1 is a structural model schematic diagram of a panda type polarization maintaining fiber;
[0019] Figure 2is the analysis curve of the influence of the boundary distance between the core and the stress region of the polarization maintaining optical fiber on the fast and slow axis transmission loss of the optical fiber;
[0020] Figure 3 is the analysis curve of the influence of the boundary distance between the core and the stress region of the polarization maintaining optical fiber on the stress birefringence;
[0021] Figure 4 is the analysis curve of the influence of the boundary distance between the core and the stress region of the polarization maintaining optical fiber on the fiber loss and stress birefringence under the condition of different stress region diameters;
[0022] Figure 5 is the calculation result diagram of the mode field of the polarization maintaining optical fiber;
[0023] Figure 6 is the calculation result diagram of the stress distribution of the cross section of the polarization maintaining optical fiber. DETAILED DESCRIPTION
[0024] To further illustrate the embodiments, the present application provides accompanying drawings. These accompanying drawings are part of the disclosure of the present application, which mainly serve to illustrate the embodiments, and can be used to explain the operating principle of the embodiments in conjunction with the related description of the specification. Those of ordinary skill in the art should be able to understand other possible implementations and advantages of the present application in conjunction with these.
[0025] The present application will be further described in conjunction with the accompanying drawings and specific embodiments.
[0026] The panda polarization maintaining optical fiber is an optical fiber that realizes polarization maintaining capability by using stress birefringence. Its typical feature is that two larger diameter stress regions are symmetrically arranged on both sides of the core, similar to two “cat eyes”. The anti-radiation capability of the optical fiber can be improved by stress region doping. Compared with the elliptical core and the bow-tie polarization maintaining optical fiber, the panda optical fiber has the following advantages:
[0027] 1) The internal structure of the optical fiber is circular, the shape is well maintained during the fiber drawing process, the fiber diameter is more uniform, and the preparation process is simplified.
[0028] 2) The optical fiber can realize high mode birefringence through stress region design, thereby ensuring better polarization maintaining capability of the optical fiber, and the uniform structure makes the internal scattered light of the optical fiber small, which will not become the main optical path noise of the high-precision fiber-optic gyroscope.
[0029] 3) The mode field of the optical fiber is circularly symmetric Gaussian mode field, and the fusion loss with traditional optical fibers and devices is low, which will not introduce special large optical path loss.
[0030] The sensitivity of the fiber-optic gyroscope can be expressed by the following formula:
[0031]
[0032] From formula (1), in order to improve the precision of the gyroscope, the length L of the fiber ring should be increased, the diameter D of the fiber ring should be increased, and the wavelength λ of the light source should be reduced. In general, the diameter D is determined by the user and cannot be changed. For light fiber gyroscopes, especially for low-precision fiber gyroscopes (> 0.1° / h), the length of the fiber is most effective.
[0033] In the field of fiber gyroscopes, in order to improve the precision of the fiber gyroscope as much as possible within the volume and mass required by the user, a short-wavelength light source (such as an 850nm light source) and a long-distance high-performance fiber ring are required. In order to ensure that the fiber ring has high polarization maintenance, radiation resistance, and magnetic field resistance, and to ensure low-loss transmission of light waves, the relationship between the geometric parameters and optical properties of the fiber needs to be determined, and the fiber design model needs to be unified to shorten the panda polarization maintaining fiber process groping period and improve the consistency of the fiber. Therefore, the present application proposes a comprehensive design method for simulating stress zone heating and cooling of polarization maintaining fiber, which realizes the comprehensive design of four types of parameters including "structure-stress-loss-birefringence". The method comprises the following steps:
[0034] 1. Select the geometric parameters of the polarization maintaining fiber model:
[0035] In the present method, a panda polarization maintaining fiber is selected, and the structure of the panda polarization maintaining fiber is simple. The structure model of the panda polarization maintaining fiber is as shown in Figure 1 The specific structure is as follows: the cross section of the polarization maintaining fiber is circular, and the structure from the outside to the inside is a high polymer material coating layer 4, a quartz cladding layer 3 composed of high-purity silica glass, a stress zone 2 composed of boron-doped quartz glass rod, and a high refractive index core 1 doped with low-concentration germanium. In the calculation of the present method, the following technical parameters of the panda fiber are used, including: the core and stress zone boundary distance t, the stress zone diameter D dress , the cladding diameter D cladding , the fiber diameter D coating , etc.
[0036] The polarization maintaining fiber is due to the difference in thermal expansion coefficient between the stress zone and the cladding caused by doping in the stress zone, and stress birefringence is generated after high-temperature annealing. The relationship can be approximately linear stress-optical relationship, and the refractive index change Δn can be expressed by "stress-optical" tensor (B) and "stress" tensor (S) as
[0037] Δn=-B·S
[0038] The matrix expansion expression is
[0039]
[0040] The above calculation can obtain the distribution of the real part of the refractive index of the optical fiber under stress conditions, set the imaginary part of the material refractive index as m, and simulate the fixed wavelength in the method. Therefore, the absorption and scattering of the material to light are represented by the imaginary part of the refractive index m, so as to estimate the optical fiber loss. The derivation of the theoretical calculation for solving Maxwell's equation is as follows:
[0041]
[0042] wherein ε r =(n-im) 2 , n=N+Δn, N is the real part of the refractive index of the material at room temperature, and k0 is the light wave number in vacuum.
[0043] The electric field vector is as follows:
[0044] β=n eff ·k0
[0045] According to the effective refractive index n eff of the transmission mode in the optical fiber, the stress birefringence generated by the optical fiber can be calculated, and then the simulation result of the loss of the optical fiber is obtained. In the simulation of the loss of the optical fiber, the Rayleigh scattering loss is fitted by using the core absorption loss, the absorption loss in the stress region is increased to realize the simulation of the transmission loss of the polarization maintaining optical fiber. The calculation relationship between the optical fiber loss and the imaginary part of the refractive index is as follows:
[0046]
[0047] wherein λ is the wavelength.
[0048] 2. The stress distribution of the stress region of the polarization maintaining optical fiber is generated by the finite element algorithm.
[0049] In the method, the accurate calculation is realized by the finite element algorithm. According to the variational principle, the functional expression of the derivation of Maxwell's equation can be written as:
[0050]
[0051] wherein F(Φ) represents the stress distribution function; Φ represents the field vector; and Ω represents the cross-sectional area of the optical fiber surrounded by the boundary. If the light propagates along the z direction (the direction perpendicular to the cross section Ω of the optical fiber), and the optical fiber is uniform along the z direction, the field vector Φ can be represented as the vector sum of the transverse component and the longitudinal component, that is,
[0052]
[0053] wherein and are the transverse and longitudinal components of the vector field, is the unit vector in the z direction. Substituting the formula into the formula can obtain:
[0054]
[0055] in As the transverse gradient operator, the [p] and [q] tensors are decomposed into
[0056]
[0057] Introducing transformation Then the expression can be transformed into
[0058]
[0059] In the formula, F(Φ) is divided into two parts depending on whether it is related to the propagation constant β. * indicates conjugate. When performing finite element calculations, the entire optical fiber geometry is divided into triangular meshes, where the minimum mesh spacing around the fiber core is half the wavelength. Each element contains three nodal components (Φ). z1 ,Φ z2 ,Φ z3 ) and the three edge components (Φ t1 ,Φ t2 ,Φ t3 Traditional linear interpolation is used for nodal components, while vector basis functions are used for edge components. This method can eliminate spurious solutions that have no physical meaning and improve the accuracy of the calculation.
[0060] 3. Based on the theoretical equations and algorithms in step 2, simulation calculations are performed using the finite element method and node-based methods to generate an analysis curve of the influence of the distance t between the fiber core and the stress zone boundary of the polarization-maintaining fiber on the transmission loss of the fast and slow axes of the fiber, such as... Figure 2 As shown. The distance *t* between the core and the stress region boundary of the polarization-maintaining fiber was varied, and the fiber loss was simulated and calculated. The loss difference between the fast-axis and slow-axis propagating fundamental modes was compared. From... Figure 2 It can be seen that the fiber loss decreases rapidly with the increase of the distance t between the fiber core and the stress zone boundary, and then tends to stabilize. This shows that the distance between the fiber core and the stress zone boundary has a significant impact on fiber loss. In the rapidly decreasing region, the fundamental mode loss of the slow axis is slightly lower than that of the fast axis, while in the stable region, the fiber loss is almost equal. To ensure that the fiber loss is <0.5dB / km, the distance t between the fiber core and the stress zone boundary should be >3.8μm.
[0061] 4. Based on the theoretical equations and algorithms in step 2, generate an analysis curve of the influence of the distance t between the core and the stress zone boundary of the polarization-maintaining fiber on the stress birefringence Δn, as shown in the figure. Figure 3 As shown, the stress birefringence characteristics were simulated by changing the distance between the fiber core and the boundary of the stress region. The stress birefringence decreases approximately linearly with increasing distance *t* between the fiber core and the stress region boundary. To ensure the stress birefringence value is higher than 5 × 10⁻⁶... -4 The distance t between the core of the polarization-maintaining fiber and the boundary of the stress zone should be less than 6.3 μm.
[0062] 5. Based on the influence analysis curves from steps 3 and 4, obtain the diameter d in different stress zones. stress Under the given conditions, the influence of the distance t between the core and the stress region boundary of the polarization-maintaining fiber on fiber loss and stress birefringence is analyzed using the following curves: Figure 4 As shown. Analysis reveals that: with the diameter d of the stress zone... stress As the fiber density increases, both the fiber loss and stress birefringence results shift upwards overall.
[0063] 6. By scanning the optical fiber geometry parameters, the distance t between the fiber core and the stress region boundary, and the diameter d of the stress region, can be obtained. stress The true value is obtained, and then the diameter d in different stress zones is obtained. stress The graph shows the relationship between fiber loss, birefringence, and the distance *t* between the fiber core and the stress region boundary. The analytical expression for the optical properties of this polarization-maintaining fiber can be obtained through curve fitting. In the example, the analytical expressions for the optical properties of this polarization-maintaining fiber are as follows:
[0064]
[0065]
[0066] In the formula, the diameter d of the stress zone stress The unit is μm; the unit of the distance t between the fiber core and the stress zone boundary is μm.
[0067] Therefore, the appropriate stress zone diameter d can be selected based on actual application requirements, taking into account both fiber loss and stress birefringence. stress And the distance t between the fiber core and the boundary of the stress zone.
[0068] The results of the polarization-maintaining fiber mode field calculation are as follows: Figure 5 As shown, its mode field exhibits a Gaussian mode field distribution.
[0069] The stress distribution across the cross section of the polarization-maintaining fiber was calculated, and the results are as follows: Figure 6 As shown. Analysis of its stress distribution reveals that the stress is greater near the boundary sides of the stress zone; therefore, the diameter d of the stress zone is... stress It cannot grow indefinitely.
[0070] Through simulation analysis, the distance t between the fiber core and the boundary of the stress region and the diameter d of the stress region were analyzed. stress Identify geometric parameters to clarify the relationship between fiber geometry and optical properties.
[0071] In practical applications, it is necessary to obtain polarization-maintaining fibers with low loss and high birefringence. The technical parameters required are: fast-axis and slow-axis losses of the fundamental mode below 0.5 dB / km, and fiber birefringence greater than 5 × 10⁻⁶. -4The stress region diameter d of the panda polarization maintaining optical fiber can be set by the influence analysis curve or formula and in combination with the technical parameter requirements stress and the distance t between the core and the stress region boundary.
[0072] The comprehensive design method of the polarization maintaining optical fiber simulating stress region heating and cooling has the following technical effects:
[0073] (1) The stress distribution of the stress region can be accurately simulated and calculated.
[0074] (2) The comprehensive analysis of the four parameters of "structural parameters-stress distribution-birefringence-loss" of the optical fiber can be realized, and the comprehensive design of the polarization maintaining optical fiber can be realized.
[0075] (3) The method can be applied to the structural design of the ultra-thin diameter polarization maintaining optical fiber, and the limit optical characteristics of the polarization maintaining optical fiber can be explored.
[0076] (4) A comprehensive theoretical basis is provided for the optical fiber preparation, and the optical fiber design time and cost are greatly shortened.
[0077] Although the present application is specifically demonstrated and introduced in combination with the preferred embodiments, those skilled in the art should understand that various changes can be made to the present application in form and details without departing from the spirit and scope of the present application defined by the appended claims, and all such changes are within the protection scope of the present application.
Claims
1. A method of comprehensive design of a polarization maintaining optical fiber simulating heating and cooling of a stress region, characterized by, The method comprises the following steps: Step S1, selecting a panda polarization maintaining optical fiber; Step S2, establishing a finite element model and a finite element unit grid of the panda polarization maintaining optical fiber, simulating thermal stress generated in the stress region in the heating and cooling process through a finite element algorithm, and generating stress distribution of the stress region of the polarization maintaining optical fiber; According to the stress-optical relationship, the stress birefringence of the polarization maintaining optical fiber and the fiber loss caused by the stress distribution are calculated; The influence analysis curves of the stress birefringence, the fiber loss and the distance between the fiber core and the stress region boundary are generated; Step S3, by scanning the distance between the fiber core and the stress region boundary and the diameter of the stress region, and performing curve fitting, the coupling relationship curves or fitting functions of the fiber loss, the birefringence and the distance between the fiber core and the stress region boundary of the polarization maintaining optical fiber under different diameters of the stress region are obtained; Step S4, setting the maximum value of the target fiber loss and the minimum value of the stress birefringence, according to the coupling relationship curves or fitting functions obtained in step S3, in the parameter space composed of the distance between the fiber core and the stress region boundary and the diameter of the stress region, a geometric parameter combination satisfying the target fiber loss and the target stress birefringence is determined, so as to select the distance between the fiber core and the stress region boundary and the diameter of the stress region of the panda polarization maintaining optical fiber.
2. The method of comprehensive design of analog stress region heated-cooled polarization maintaining optical fiber according to claim 1, characterized in that, The cross section of the panda polarization maintaining optical fiber is circular, and the structure from outside to inside is a high polymer material coating layer, a quartz cladding layer composed of high-purity silica glass, a stress region composed of boron-doped quartz glass rod and a low-concentration germanium-doped high refractive index core. The geometric parameters of the panda polarization maintaining optical fiber include the distance between the fiber core and the stress region boundary, the diameter of the stress region, the diameter of the cladding layer and the diameter of the optical fiber.
3. The method of comprehensive design of a simulated stress region heated-cooled polarization maintaining optical fiber according to claim 2, wherein, The stress distribution function in finite element algorithm is divided into two parts according to whether it is related to the propagation constant β. In the finite element calculation, the whole fiber geometry is divided into triangular meshes, in which the minimum interval around the core is half of the wavelength. Each element contains three node components (Φ z1 ,Φ z2 ,Φ z3 ) and three edge components (Φ t1 ,Φ t2 ,Φ t3 ). The node components are interpolated by traditional linear interpolation, and the edge components are interpolated by vector basis functions.