阅读说明：本技术 一种高精度保偏光纤及其制备方法 (High-precision polarization maintaining optical fiber and preparation method thereof ) 是由 肖敏 杨思美 柳涛 蔡钊 于 2020-05-24 设计创作，主要内容包括：本发明公开了一种高精度保偏光纤及其制备方法。所述保偏光纤由内而外依次设置有芯层和石英包层,所述石英包层内设有两个沿所述芯层呈中心对称的应力区；光纤横截面应力区中心连线为慢轴,光纤横截面与慢轴方向相垂直的直径方向为快轴。在室温下光纤芯层快轴方向具有压应力,光纤芯层区域在快轴方向上的压应力绝对值最大值大于17MPa,芯层慢轴方向具有张应力,且光纤芯层区域在慢轴方向上的张应力绝对值最大值大于12MPa。其制备方法包括步骤：将石英玻璃基质的光纤预制棒加热至粘弹态甚至熔融态,拉丝冷却定形成为光纤。本发明设计了一种新的保偏光纤的组成结构,通过拉丝过程中的张力和强制冷却速率控制,将拉丝过程中的残余应力的一部分留存于光纤中,合理调节保偏光纤快轴、慢轴方向的压、张应力值,从而优化双折射效应,改善了保偏光纤的精度。(The invention discloses a high-precision polarization maintaining optical fiber and a preparation method thereof. The polarization maintaining optical fiber is sequentially provided with a core layer and a quartz cladding layer from inside to outside, and two stress regions which are centrosymmetric along the core layer are arranged in the quartz cladding layer; the central connecting line of the stress area of the cross section of the optical fiber is a slow axis, and the diameter direction of the cross section of the optical fiber, which is vertical to the slow axis direction, is a fast axis. The optical fiber core layer has compressive stress in the fast axis direction at room temperature, the maximum value of the absolute value of the compressive stress of the optical fiber core layer region in the fast axis direction is larger than 17MPa, the tensile stress of the core layer region in the slow axis direction is larger than 12MPa, and the maximum value of the absolute value of the tensile stress of the optical fiber core layer region in the slow axis direction is larger than 12 MPa. The preparation method comprises the following steps: heating the optical fiber prefabricated rod with the quartz glass substrate to a viscoelastic state or even a molten state, and drawing, cooling and shaping to obtain the optical fiber. The invention designs a novel composition structure of the polarization maintaining optical fiber, and retains part of residual stress in the drawing process in the optical fiber through tension and forced cooling rate control in the drawing process, and reasonably adjusts the pressure and tension stress values in the directions of a fast axis and a slow axis of the polarization maintaining optical fiber, thereby optimizing the birefringence effect and improving the precision of the polarization maintaining optical fiber.)

1. A high-precision polarization maintaining optical fiber is characterized in that a panda type polarization maintaining optical fiber is sequentially provided with a core layer and a quartz cladding layer from inside to outside, and two stress regions which are centrosymmetric along the core layer are arranged in the quartz cladding layer; the central connecting line of the stress area of the cross section of the optical fiber is a slow axis, and the diameter direction of the cross section of the optical fiber, which is vertical to the direction of the slow axis, is a fast axis; the optical fiber core layer has compressive stress in the fast axis direction at room temperature, the maximum value of the absolute value of the compressive stress of the optical fiber core layer region in the fast axis direction is larger than 17MPa, the tensile stress of the core layer region in the slow axis direction is larger than 12MPa, and the maximum value of the absolute value of the tensile stress of the optical fiber core layer region in the slow axis direction is larger than 12 MPa.

2. The high precision polarization maintaining optical fiber of claim 1, wherein the optical fiber core layer region has an absolute value maximum of compressive stress in the fast axis direction of greater than 30MPa, preferably 30MPa to 50 MPa; the maximum value of the tensile stress absolute value of the optical fiber core layer region in the slow axis direction is more than 19MPa, preferably 19MPa to 35MPa, and more preferably the maximum value of the tensile stress absolute value of the polarization maintaining optical fiber stress region in the slow axis direction is 25MPa to 35 MPa.

3. A high-precision polarization maintaining optical fiber is characterized in that a core layer and a quartz cladding layer are sequentially arranged from inside to outside, and two stress regions which are centrosymmetric along the core layer are arranged in the quartz cladding layer; the central connecting line of the stress area of the cross section of the optical fiber is a slow axis, and the diameter direction of the cross section of the optical fiber, which is vertical to the direction of the slow axis, is a fast axis; the distribution of tensile stress of the polarization maintaining optical fiber in the slow axis direction meets the following relation:

tensile stress f at a distance x from the center of the fiber on the slow axis, and core radius r₁Radius of cladding layer is r₀The slow axis tensile stress value F represented by the following formula is 1 MPa. mu.m^-1Above and 40 MPa.mu.m^-1The following;

the preferred F value is 3 MPa.mu.m^-1Above 35 MPa.mu.m^-1The following

More preferably, the F value is 10 MPa-. mu.m^-1Above and 30 MPa.mu.m^-1The following.

4. The high precision polarization maintaining optical fiber of any one of claims 1 to 3, wherein the silica cladding has a refractive index n₀Refractive index of core layer n₁Relative refractive index difference Delta between core layer and quartz cladding layer₁₀The value range of (A) is 0.3% -1.5%, preferably delta₁₀At 0.35% to 0.6%, wherein:

5. a high precision polarization maintaining fiber according to any of claims 1 to 3, wherein the core layer is doped with germanium in a molar content of 2 to 15 mol%, preferably 3 to 6 mol%; preferably, the core layer is doped with fluorine, and the content of fluorine is less than 10% of the content of germanium; preferably its stress regionDoped with boron, with B₂O₃The content percentage of the compound is 1 to 35 mol%, preferably 3 to 25%, more preferably 10 to 23%, and still more preferably 15 to 21%.

6. A high precision polarization maintaining fiber according to any of claims 1 to 3, wherein the cut-off wavelength is less than 1530nm, or less than 1295nm, or less than 830 nm.

7. The high precision polarization maintaining optical fiber according to any of claims 1 to 3, wherein the diameter of the silica cladding of the polarization maintaining optical fiber is d₀；

When d is more than or equal to 124.0 mu m₀When the diameter is less than or equal to 126.0 mu m, the polarization maintaining optical fiber has an inner and outer double-coating structure, wherein the diameter of the inner coating is d₄And the diameter of the outer coating is d₅Respectively satisfy: d is not less than 170.0 mu m₄≤205.0μm，235.0μm≤d₅Less than or equal to 250.0 mu m; the Young modulus of the inner coating is smaller than that of the outer coating, preferably the Young modulus of the inner coating is 0.5 MPa-2.5 MPa and the Young modulus of the outer coating is 450 MPa-1550 MPa;

when d is not less than 79.0 mu m₀Less than or equal to 81.0 mu m and the polarization maintaining optical fiber has an inner and outer double-coating structure, wherein the inner coating has a diameter d₄And the diameter of the outer coating is d₅Respectively satisfy: d is not less than 115.0 mu m₄≤135.0μm，150.0μm≤d₅Less than or equal to 170.0 mu m; the Young modulus of the inner coating is smaller than that of the outer coating, preferably the Young modulus of the inner coating is 0.5 MPa-2.5 MPa and the Young modulus of the outer coating is 450 MPa-1550 MPa;

when d is not less than 79.0 mu m₀When the polarization maintaining optical fiber has a single coating structure and is less than or equal to 81.0 mu m, the diameter d of the coating satisfies: d is more than or equal to 134.0 mu m and less than or equal to 180.0 mu m; the Young modulus of the coating is 80-750 Mpa, preferably 80-350 Mpa, more preferably 80-230 Mpa;

when d is less than or equal to 58.0 mu m₀Less than or equal to 62.0 μm and the polarization maintaining fiber has an inner and outer double-coating structure, wherein the inner coating has a diameter d₄And the diameter of the outer coating isd₅Respectively satisfy: d is not less than 70.0 mu m₄≤90.0μm，90.0μm≤d₅Less than or equal to 120.0 mu m; the Young modulus of the inner coating is smaller than that of the outer coating, preferably the Young modulus of the inner coating is 0.5 MPa-2.5 MPa and the Young modulus of the outer coating is 450 MPa-1550 MPa;

when d is less than or equal to 58.0 mu m₀62.0 μm or less and the polarization maintaining optical fiber has a single-coating structure, the diameter d of the coating satisfies: d is more than or equal to 90.0 mu m and less than or equal to 120.0 mu m; the Young modulus of the coating is 80-750 Mpa, preferably 80-350 Mpa, more preferably 80-230 Mpa;

when d is more than or equal to 38.0 mu m₀42.0 μm or less, the polarization maintaining optical fiber has a single coating structure, and the diameter d of the coating satisfies: d is more than or equal to 70.0 mu m and less than or equal to 100.0 mu m; the Young modulus of the coating is 80-750 MPa, preferably 80-350 MPa, and more preferably 80-230 MPa.

8. The method of making a polarization maintaining optical fiber of any one of claims 1 to 7, comprising the steps of: heating the optical fiber preform with the quartz glass substrate to a viscoelastic state or even a molten state, and drawing, cooling and shaping to obtain an optical fiber; the wire drawing speed is more than 100 m/min; the optical fiber is forced to cool from the drawing furnace to the take-up device at a cooling rate of 1550 ℃/s to 5800 ℃/s, preferably 1550 ℃/s to 4000 ℃/s, more preferably 1550 ℃/s to 3000 ℃/s.

9. The method of making a polarization maintaining optical fiber of any one of claims 1 to 7, comprising the steps of: heating the optical fiber preform with the quartz glass substrate to a viscoelastic state or even a molten state, and drawing, cooling and shaping to obtain an optical fiber; the uncoated bare optical fiber is subjected to a tension in the direction of motion of the optical fiber in the viscoelastic state during drawing of 11 to 75MPa, preferably 15 to 45MPa, more preferably 20 to 35 MPa.

10. The method of making a polarization maintaining optical fiber of any one of claims 1 to 7, comprising the steps of: heating the optical fiber preform with the quartz glass substrate to a viscoelastic state or even a molten state, and drawing, cooling and shaping to obtain an optical fiber; in the cooling process, the stress area and the cladding of the optical fiber are converted into solid state from viscoelastic state, and the residual stress of the cladding in the fast axis direction caused by the drawing tension is more than 5 MPa.

Technical Field

The invention belongs to the field of sensing optical fibers, and particularly relates to a high-precision polarization maintaining optical fiber.

Background

In the field of sensing and control, physical quantities such as magnetic field, temperature, stress, inertia and the like need to be measured and controlled, and therefore, various optical fiber sensors are developed. The most deep application of the optical fiber gyroscope is that the optical fiber gyroscope has the advantages of short starting time, simple structure, light weight, no movable element and strong environment adaptability, overcomes the locking phenomenon of the annular laser gyroscope, does not need a mechanical jitter prevention measure, and becomes a core device for realizing the key technology of controlling the posture and the track of a carrier. In addition, the optical fiber hydrophone is used for inertial navigation and sonar, and has extremely high application value in military affairs. The sensing elements in the fiber-optic gyroscope and the hydrophone are polarization-maintaining fiber devices, so that the characteristics of the polarization-maintaining fiber determine the performance of the sensor.

Polarization Maintaining Optical Fiber (Polarization Maintaining Optical Fiber, Polarization Maintaining Optical Fiber for short) is a special Optical Fiber that maintains its linear Polarization state while realizing the single-mode transmission characteristic of light. The artificial introduction of double refraction in single-mode fiber by the polarization maintaining fiber causes effective refractive index difference in different directions of fiber core of the single-mode fiber, and increases HE₁₁ ^xAnd HE₁₁ ^yThe propagation constants of the modes are different, and therefore the polarization maintaining characteristic of the optical fiber is achieved.

The commonly used polarization maintaining fiber is a stress type polarization maintaining fiber, and has the advantages of high enough birefringence coefficient and easy temperature disturbance, thereby influencing the precision of the polarization maintaining fiber. The development of the sensing device is towards high sensitivity and high precision, and the device is required to have sensitivity and stability and improve the precision. In order to solve the problem that the prior art cannot take the performances into consideration, the invention provides a high-precision polarization maintaining optical fiber product and a manufacturing method thereof.

Disclosure of Invention

Aiming at the defects or the improvement requirements of the prior art, the invention provides a high-precision polarization maintaining optical fiber and a preparation method thereof, aiming at precisely controlling the stress distribution of the panda type polarization maintaining optical fiber in the directions of a fast axis and a slow axis, so that the polarization maintaining optical fiber has good attenuation and excellent extinction ratio performance under the wavelengths of 400-680 nm, 850nm, 1310nm and 1550nm, and a sensing device gives consideration to the sensitivity and stability of the polarization maintaining optical fiber and improves the precision thereof, thereby solving the technical problems that the sensitivity or the stability of the sensing device is lower and the precision of the sensor is not high due to the overlarge attenuation or poor extinction ratio performance of the existing polarization maintaining optical fiber.

In order to achieve the above object, according to one aspect of the present invention, a high-precision polarization maintaining fiber is provided, which is a panda-type polarization maintaining fiber, and is sequentially provided with a core layer and a quartz cladding layer from inside to outside, wherein two stress regions which are centrosymmetric along the core layer are arranged in the quartz cladding layer; the central connecting line of the stress area of the cross section of the optical fiber is a slow axis, and the diameter direction of the cross section of the optical fiber, which is vertical to the slow axis direction, is a fast axis. The optical fiber core layer has compressive stress in the fast axis direction at room temperature, the maximum value of the absolute value of the compressive stress of the optical fiber core layer region in the fast axis direction is larger than 17MPa, the tensile stress of the core layer region in the slow axis direction is larger than 12MPa, and the maximum value of the absolute value of the tensile stress of the optical fiber core layer region in the slow axis direction is larger than 12 MPa.

Preferably, the high-precision polarization maintaining optical fiber has a maximum value of the absolute value of the compressive stress of the optical fiber core layer region in the fast axis direction of more than 30MPa, preferably 30MPa to 50 MPa; the maximum value of the tensile stress absolute value of the optical fiber core layer region in the slow axis direction is more than 19MPa, preferably 19MPa to 35MPa, and more preferably the maximum value of the tensile stress absolute value of the polarization maintaining optical fiber stress region in the slow axis direction is 25MPa to 35 MPa.

According to another aspect of the invention, a high-precision polarization maintaining optical fiber is provided, which is sequentially provided with a core layer and a quartz cladding layer from inside to outside, wherein two stress regions which are centrosymmetric along the core layer are arranged in the quartz cladding layer; the central connecting line of the stress area of the cross section of the optical fiber is a slow axis, and the diameter direction of the cross section of the optical fiber, which is vertical to the direction of the slow axis, is a fast axis; the distribution of tensile stress of the polarization maintaining optical fiber in the slow axis direction meets the following relation:

tensile stress f at a distance x from the center of the fiber on the slow axis, and core radius r₁Radius of cladding layer is r₀The slow axis tensile stress value F represented by the following formula is 1 MPa. mu.m^-1Above and 40 MPa.mu.m^-1The following;

the preferred F value is 3 MPa.mu.m^-1Above 35 MPa.mu.m^-1The following

More preferably, the F value is 10 MPa-. mu.m^-1Above and 30 MPa.mu.m^-1The following.

Preferably, the high-precision polarization maintaining optical fiber has a refractive index n of the quartz cladding₀Refractive index of core layer n₁Relative refractive index difference Delta between core layer and quartz cladding layer₁₀The value range of (A) is 0.3% -1.5%, preferably delta₁₀At 0.35% to 0.6%, wherein:

preferably, the high-precision polarization maintaining optical fiber is doped with germanium in the core layer, and the molar content percentage of the germanium is 2 to 15 mol%, preferably 3 to 6 mol%; preferably, the core layer is doped with fluorine, and the content of fluorine is less than 10% of the content of germanium; the stress region is doped with boron and with B₂O₃The content percentage of the compound is 1 to 35 mol%, preferably 3 to 25%, more preferably 10 to 23%, and still more preferably 15 to 21%.

Preferably, the high-precision polarization maintaining optical fiber has a cutoff wavelength of less than 1530nm, or less than 1295nm, or less than 830 nm.

Preferably, the high-precision polarization maintaining optical fiber has a quartz cladding diameter d₀；

When d is more than or equal to 124.0 mu m₀When the thickness is less than or equal to 126.0 mu m, the polarization maintaining optical fiber has an inner and outer double-coating structure, whereinInner coating diameter d₄And the diameter of the outer coating is d₅Respectively satisfy: d is not less than 170.0 mu m₄≤205.0μm，235.0μm≤d₅Less than or equal to 250.0 mu m; the Young modulus of the inner coating is smaller than that of the outer coating, preferably the Young modulus of the inner coating is 0.5 MPa-2.5 MPa and the Young modulus of the outer coating is 450 MPa-1550 MPa;

when d is not less than 79.0 mu m₀Less than or equal to 81.0 mu m and the polarization maintaining optical fiber has an inner and outer double-coating structure, wherein the inner coating has a diameter d₄And the diameter of the outer coating is d₅Respectively satisfy: d is not less than 115.0 mu m₄≤135.0μm，150.0μm≤d₅Less than or equal to 170.0 mu m; the Young modulus of the inner coating is smaller than that of the outer coating, preferably the Young modulus of the inner coating is 0.5 MPa-2.5 MPa and the Young modulus of the outer coating is 450 MPa-1550 MPa;

when d is not less than 79.0 mu m₀When the polarization maintaining optical fiber has a single coating structure and is less than or equal to 81.0 mu m, the diameter d of the coating satisfies: d is more than or equal to 134.0 mu m and less than or equal to 180.0 mu m; the Young modulus of the coating is 80-750 Mpa, preferably 80-350 Mpa, more preferably 80-230 Mpa;

when d is less than or equal to 58.0 mu m₀Less than or equal to 62.0 μm and the polarization maintaining fiber has an inner and outer double-coating structure, wherein the inner coating has a diameter d₄And the diameter of the outer coating is d₅Respectively satisfy: d is not less than 70.0 mu m₄≤90.0μm，90.0μm≤d₅Less than or equal to 120.0 mu m; the Young modulus of the inner coating is smaller than that of the outer coating, preferably the Young modulus of the inner coating is 0.5 MPa-2.5 MPa and the Young modulus of the outer coating is 450 MPa-1550 MPa;

when d is less than or equal to 58.0 mu m₀62.0 μm or less and the polarization maintaining optical fiber has a single-coating structure, the diameter d of the coating satisfies: d is more than or equal to 90.0 mu m and less than or equal to 120.0 mu m; the Young modulus of the coating is 80-750 Mpa, preferably 80-350 Mpa, more preferably 80-230 Mpa;

when d is more than or equal to 38.0 mu m₀42.0 μm or less, the polarization maintaining optical fiber has a single coating structure, and the diameter d of the coating satisfies: d is more than or equal to 70.0 mu m and less than or equal to 100.0 mu m; the coating layerThe Young's modulus is 80 to 750MPa, preferably 80 to 350MPa, more preferably 80 to 230 MPa. According to another aspect of the present invention, there is provided a method for preparing the polarization maintaining optical fiber, comprising the steps of: heating the optical fiber preform with the quartz glass substrate to a viscoelastic state or even a molten state, and drawing, cooling and shaping to obtain an optical fiber; the wire drawing speed is more than 100 m/min; the optical fiber is forced to cool from the drawing furnace to the take-up device at a cooling rate of 1550 ℃/s to 5800 ℃/s, preferably 1550 ℃/s to 4000 ℃/s, more preferably 1550 ℃/s to 3000 ℃/s.

According to another aspect of the present invention, there is provided a method for preparing the polarization maintaining optical fiber, comprising the steps of: heating the optical fiber preform with the quartz glass substrate to a viscoelastic state or even a molten state, and drawing, cooling and shaping to obtain an optical fiber; the uncoated bare optical fiber is subjected to a tension in the direction of motion of the optical fiber in the viscoelastic state during drawing of 11 to 75MPa, preferably 15 to 45MPa, more preferably 20 to 35 MPa.

According to another aspect of the present invention, there is provided a method for preparing the polarization maintaining optical fiber, comprising the steps of: heating the optical fiber preform with the quartz glass substrate to a viscoelastic state or even a molten state, and drawing, cooling and shaping to obtain an optical fiber; in the cooling process, the stress area and the cladding of the optical fiber are converted into solid state from viscoelastic state, and the residual stress of the cladding in the fast axis direction caused by the drawing tension is more than 5 MPa.

In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:

the invention designs a novel composition structure of the polarization maintaining optical fiber, and retains part of residual stress in the drawing process in the optical fiber through tension and forced cooling rate control in the drawing process, and reasonably adjusts the pressure and tension stress values in the directions of a fast axis and a slow axis of the polarization maintaining optical fiber, thereby optimizing the birefringence effect and improving the precision of the polarization maintaining optical fiber. The stress structure of the fast axis and the slow axis of the optical fiber is accurately controlled, so that the polarization maintaining optical fiber can meet the winding requirements of multi-type optical fiber gyroscopes with the diameters of 850nm, 1310nm and 1550 nm.

When the working wavelength is 850nm, the attenuation of the polarization maintaining optical fiber is less than 4.0dB/km, and the extinction ratio is higher than 20 dB/km;

when the working wavelength is 1310nm, the attenuation of the polarization maintaining optical fiber is less than 0.6dB/km, and the extinction ratio is higher than 26 dB/km;

when the working wavelength is 1550nm, the attenuation of the polarization maintaining optical fiber is less than 0.8dB/km, and the extinction ratio is higher than 24 dB/km;

in the preferable scheme, by matching with the structural design of the optical fiber, when the diameter of the optical fiber cladding evolves from 125 micrometers to 80 micrometers, even 60 micrometers or 40 micrometers, experiments show that the performance of the optical fiber is more sensitive to the tensile stress in the slow axis direction, the extinction ratio is not high enough when the tensile stress is small, and the precision is reduced and the attenuation is increased when the tensile stress is large; the invention solves the problems of large attenuation and low precision by limiting the doping of the core layer and the stress region. The invention not only has good attenuation and excellent extinction ratio, but also has the attenuation variation per kilometer of the polarization maintaining optical fiber of less than 0.2dB and the full-temperature extinction ratio variation of less than 3dB at the temperature of-55-85 ℃.

Drawings

FIG. 1 is a schematic cross-sectional view of a polarization maintaining optical fiber according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of stress distribution in the fast axis direction of a polarization maintaining optical fiber according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of stress distribution in the slow axis direction of a polarization maintaining optical fiber according to an embodiment of the present invention;

in the figure: 1 is a core layer; 2 is a quartz cladding; and 3 is a stress area.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

The high-precision polarization maintaining optical fiber provided by the invention is a panda type polarization maintaining optical fiber, as shown in figure 1, a core layer and a quartz cladding are sequentially arranged from inside to outside and are of a single-coating structure or a double-coating structure, and the quartz cladding is externally provided with the core layer and the quartz claddingThe side is provided with an inner coating and an outer coating in sequence from inside to outside; having a cladding diameter d₀

Two stress regions which are centrosymmetric along the core layer are arranged in the quartz cladding layer; the axis of the symmetry axis in the cross section of the optical fiber is a fast axis, the central connection line of the stress area is a slow axis, the optical fiber core layer has compressive stress in the fast axis direction at room temperature, the maximum value of the absolute value of the compressive stress of the optical fiber core layer area in the fast axis direction is larger than 17MPa, the core layer has tensile stress in the slow axis direction, and the maximum value of the absolute value of the tensile stress of the optical fiber core layer area in the slow axis direction is larger than 12 MPa. Preferably, the maximum value of the absolute value of the compressive stress of the optical fiber core layer region in the direction of the fast axis is more than 30MPa and not more than 50 MPa; the maximum value of the tensile stress absolute value of the optical fiber core layer region in the slow axis direction is more than 19MPa and not more than 35MPa, and preferably, the maximum value of the tensile stress absolute value of the polarization maintaining optical fiber stress region in the slow axis direction is more than 25 MPa.

The distribution of tensile stress of the polarization maintaining optical fiber in the slow axis direction meets the following relation:

tensile stress f at a distance x from the center of the fiber on the slow axis, and core radius r₁Radius of cladding layer is r₀The slow axis tensile stress value F represented by the following formula is 1 MPa. mu.m^-1Above and 40 MPa.mu.m^-1The following;

the preferred F value is 3 MPa.mu.m^-1Above 35 MPa.mu.m^-1The following

More preferably, the F value is 10 MPa-. mu.m^-1Above and 30 MPa.mu.m^-1The following.

The refractive index of the quartz cladding is n₀Refractive index of core layer n₁Relative refractive index difference Delta between core layer and quartz cladding layer₁₀The value range of (A) is 0.3% -1.5%, preferably delta₁₀At 0.35% to 0.6%, wherein:

the core layer is doped with germanium, and the molar content percentage of the germanium is 2 to 15 mol%, preferably 3 to 6 mol%; preferably, the core layer is doped with fluorine, and the content of fluorine is less than 10% of the content of germanium; the stress region is doped with boron and with B₂O₃The content percentage of the compound is 1 to 35 mol%, preferably 3 to 25%, more preferably 10 to 23%, and still more preferably 15 to 21%.

The coating structure is as follows:

when d is more than or equal to 124.0 mu m₀When the diameter is less than or equal to 126.0 mu m, the polarization maintaining optical fiber has an inner and outer double-coating structure, wherein the diameter of the inner coating is d₄And the diameter of the outer coating is d₅Respectively satisfy: d is not less than 170.0 mu m₄≤205.0μm，235.0μm≤d₅Less than or equal to 250.0 mu m; the Young modulus of the inner coating is smaller than that of the outer coating, preferably the Young modulus of the inner coating is 0.5 MPa-2.5 MPa and the Young modulus of the outer coating is 450 MPa-1550 MPa;

when d is not less than 79.0 mu m₀Less than or equal to 81.0 mu m and the polarization maintaining optical fiber has an inner and outer double-coating structure, wherein the inner coating has a diameter d₄And the diameter of the outer coating is d₅Respectively satisfy: d is not less than 115.0 mu m₄≤135.0μm，150.0μm≤d₅Less than or equal to 170.0 mu m; the Young modulus of the inner coating is smaller than that of the outer coating, preferably the Young modulus of the inner coating is 0.5 MPa-2.5 MPa and the Young modulus of the outer coating is 450 MPa-1550 MPa;

when d is not less than 79.0 mu m₀When the polarization maintaining optical fiber has a single coating structure and is less than or equal to 81.0 mu m, the diameter d of the coating satisfies: d is more than or equal to 134.0 mu m and less than or equal to 160.0 mu m; the Young modulus of the coating is 80-750 Mpa, preferably 80-350 Mpa, more preferably 80-230 Mpa;

when d is less than or equal to 58.0 mu m₀Less than or equal to 62.0 μm and the polarization maintaining fiber has an inner and outer double-coating structure, wherein the inner coating has a diameter d₄And the diameter of the outer coating is d₅Respectively satisfy: d is not less than 70.0 mu m₄≤90.0μm，90.0μm≤d₅≤120.0Mu m; the Young modulus of the inner coating is smaller than that of the outer coating, preferably the Young modulus of the inner coating is 0.5 MPa-2.5 MPa and the Young modulus of the outer coating is 450 MPa-1550 MPa;

when d is less than or equal to 58.0 mu m₀62.0 μm or less and the polarization maintaining optical fiber has a single-coating structure, the diameter d of the coating satisfies: d is more than or equal to 95.0 mu m and less than or equal to 120.0 mu m; the Young modulus of the coating is 80-750 Mpa, preferably 80-350 Mpa, more preferably 80-230 Mpa;

when d is more than or equal to 38.0 mu m₀42.0 μm or less, the polarization maintaining optical fiber has a single coating structure, and the diameter d of the coating satisfies: d is more than or equal to 73.0 mu m and less than or equal to 87.0 mu m; the Young modulus of the coating is 80-750 MPa, preferably 80-350 MPa, and more preferably 80-230 MPa.

The cut-off wavelength of the polarization maintaining optical fiber is less than 1530nm, or less than 1295nm, or less than 830 nm.

The invention provides a preparation method of a high-precision polarization maintaining optical fiber, which comprises the following steps: heating the optical fiber preform with the quartz glass substrate to a viscoelastic state or even a molten state, and drawing, cooling and shaping to obtain an optical fiber; wherein:

a wire drawing step: the wire drawing speed is more than 100 m/min; the optical fiber is subjected to a tension in the direction of motion of the optical fiber in the viscoelastic state during drawing of the fiber of 11MPa to 75MPa, preferably 15MPa to 45MPa, more preferably 20MPa to 35 MPa.

And (3) cooling: the optical fiber is forced to cool from the drawing furnace to the take-up device at a cooling rate of 1550 ℃/s to 5800 ℃/s, preferably 1550 ℃/s to 4000 ℃/s, more preferably 1550 ℃/s to 3000 ℃/s.

In the drawing and cooling process, the stress area and the cladding of the optical fiber are converted from a viscoelastic state to a solid state, and the residual stress of the cladding in the fast axis direction caused by the drawing tension is more than 5 MPa. These residual stresses increase the birefringence coefficient of the optical fiber, which is beneficial to the polarization maintaining performance of the polarization maintaining optical fiber, thereby improving the precision of the polarization maintaining optical fiber. The residual stress was measured by sampling the same batch of optical fibers and heat treating the samples. One of the heat treatment procedures is to slowly raise the temperature of the optical fiber from normal temperature to 1100 ℃ at a temperature raising rate of less than 10 ℃ per minute, maintain the temperature for 30 minutes, and then slowly lower the temperature to normal temperature at a temperature lowering rate of less than 10 ℃ per minute, more preferably, less than 10 ℃ per minute. The difference in residual stress can be determined by measuring and comparing the stress of the heat-treated and non-heat-treated fibers using an FSA-100 thermal stress analyzer.

Through tests, the high-precision polarization maintaining optical fiber provided by the invention has the following characteristics:

when the working wavelength is 850nm, the attenuation of the polarization maintaining optical fiber is less than 4.0dB/km, the extinction ratio is higher than 20dB/km, and the cut-off wavelength of the polarization maintaining optical fiber is less than 830 nm;

when the working wavelength is 1310nm, the attenuation of the polarization maintaining optical fiber is less than 0.6dB/km, the extinction ratio is higher than 26dB/km, and the cut-off wavelength of the polarization maintaining optical fiber is less than 1295 nm;

when the working wavelength is 1550nm, the attenuation of the polarization maintaining optical fiber is less than 0.8dB/km, the extinction ratio is higher than 24dB/km, and the cut-off wavelength of the polarization maintaining optical fiber is less than 1530 nm;

under the temperature of minus 55 ℃ to 85 ℃, the variation of the total temperature attenuation of the polarization maintaining optical fiber 1550nm per kilometer is less than 0.2dB, and the variation of the total temperature extinction ratio is less than 3 dB.

The following are examples:

referring to fig. 1, one embodiment of the present invention provides a polarization maintaining fiber in a panda type structure. The optical fiber is provided with a slow axis and a fast axis, and along the diameter direction of the slow axis of the optical fiber, the polarization maintaining optical fiber comprises a core layer 1 doped with germanium and a cladding layer 2 which is basically pure quartz which are sequentially arranged from inside to outside, and two stress regions 3 doped with boron are also arranged in the quartz cladding layer in the slow axis direction; the centers of the two stress areas 3 are positioned on the slow axis and are symmetrically distributed on two sides of the optical fiber layer 1; there is a space between the stress region 3 and the core 1, which is part of the silica cladding.

Referring to FIG. 1, the quartz cladding 2 has a diameter d₀The diameters of the inner coating and the outer coating are respectively d₄And d₅；

When the quartz cladding 2 has a typical diameter of 125 μm, d₀D is not less than 124.0 mu m₀Less than or equal to 126.0 mu m, and d is less than or equal to 170.0 mu m₄≤205.0μm，235.0μm≤d₅≤250.0μm。

When the quartz cladding 2 has a typical diameter of 80 μm, d₀D is within the range of 79.0 mu m or less₀Less than or equal to 81.0 mu m. In the single-coating structure, d is more than or equal to 134.0 mu m and less than or equal to 140.0 mu m, and the Young modulus of the single-layer outer coating is 80 Mpa-750 Mpa. In the double-coating structure, d is more than or equal to 115.0 mu m₄≤135.0μm，162.0μm≤d₅≤170.0μm。

When the quartz cladding 2 has a typical diameter of 60 μm, d₀D is within a range of 58.0 mu m or less₀Less than or equal to 62.0 μm, and the optical fiber can adopt a double-coating structure or a single-coating structure. In the double-coating structure, d is more than or equal to 70.0 mu m₄≤90.0μm，98.0μm≤d₅Less than or equal to 110.0 mu m; in the single coating structure, only one coating layer, namely the outer coating layer, is coated, the diameter of the coating layer is d, and d is more than or equal to 90.0 mu m₅Less than or equal to 110.0 microns, and the Young modulus of the single-layer outer coating is 80-750 MPa.

When the typical diameter of the quartz cladding 2 is 40 μm, d₀D is within the range of 38.0 mu m or less₀Less than or equal to 42.0 mu m and d less than or equal to 77.0 mu m and less than or equal to 83.0 mu m, wherein the optical fiber adopts a single-layer coating structure, namely only one coating is coated, the diameter of the coating is d, and d less than or equal to 70.0 mu m₅Less than or equal to 100.0 microns, and the Young modulus of the single-layer outer coating is 80-350 MPa.

The present invention will be described in further detail with reference to specific embodiments and drawings.