阅读说明：本技术 一种椭圆芯保偏光纤的制造方法 (Method for manufacturing elliptical core polarization maintaining optical fiber ) 是由 朱婷婷 汪杰 赵霞 徐丹 吴浩 姜恺铭 史连凤 张慧 张冬梅 于 2020-04-22 设计创作，主要内容包括：本发明涉及一种椭圆芯保偏光纤的制造方法,包括以下步骤：步骤一、选择合适芯棒的基管,进行预处理；步骤二、制造芯棒,芯棒包括内包层与芯层；步骤三、在芯棒的芯层沉积结束后,先进行芯层内壁一侧的定向刻蚀,刻出月牙型；然后对相对侧刻出相同弧度的月牙型,最终基管内空心圆由最初的圆形刻蚀为椭圆形；步骤四、芯棒沉积、刻蚀结束后,对基管进行正向和反向塌缩,制成一根实心椭圆芯光棒；步骤五、将芯棒放置在沉积后的石英套管中,组合构成椭圆芯保偏光棒；步骤六、光棒进行拉丝,拉制成细径裸光纤,并在裸光纤外表面涂覆光纤涂料,得到最终椭圆芯保偏光纤。本发明通过定向刻蚀,一次成型,减少工艺的程序,稳定性、可靠性提高。(The invention relates to a method for manufacturing an elliptical core polarization maintaining optical fiber, which comprises the following steps: firstly, selecting a base pipe with a proper mandrel for pretreatment; manufacturing a core rod, wherein the core rod comprises an inner cladding and a core layer; step three, after the core layer deposition of the core rod is finished, firstly, performing directional etching on one side of the inner wall of the core layer to etch a crescent shape; then, the opposite sides are engraved with crescent shapes with the same radian, and finally, the hollow circle in the base tube is etched into an ellipse from the initial circle; after the deposition and the etching of the core rod are finished, collapsing the base tube in the forward direction and the reverse direction to manufacture a solid elliptical core rod; placing the core rod in the deposited quartz sleeve, and combining to form an elliptical core polarization maintaining rod; and sixthly, drawing the optical rod into a thin-diameter bare optical fiber, and coating an optical fiber coating on the outer surface of the bare optical fiber to obtain the final elliptic core polarization maintaining optical fiber. The invention reduces the process procedures and improves the stability and the reliability through directional etching and one-step molding.)

1. A method for manufacturing an elliptical core polarization maintaining optical fiber is characterized in that: the method comprises the following steps:

selecting a base pipe with a proper mandrel, and pretreating the base pipe;

manufacturing a core rod by using a chemical vapor deposition method, wherein the core rod comprises an inner cladding layer and a core layer;

step three, after the core layer deposition of the core rod is finished, firstly, performing directional etching on one side of the inner wall of the core layer to etch a crescent shape; then, the opposite sides are engraved with crescent shapes with the same radian, and finally, the hollow circle in the base tube is etched into an ellipse from the initial circle;

after the deposition and the etching of the core rod are finished, collapsing the base tube in the forward direction and the reverse direction to manufacture a solid elliptical core rod;

placing the core rod in the deposited quartz sleeve, and combining to form an elliptical core polarization maintaining rod;

and sixthly, drawing the optical rod after the step is finished, drawing the optical rod into a thin-diameter bare optical fiber, and coating optical fiber coating on the outer surface of the bare optical fiber to obtain the final elliptic core polarization maintaining optical fiber.

2. The method of claim 1, wherein the method comprises: the size of the core layer is 1-3 mm, the doping elements are germanium and phosphorus, and the relative refractive index difference is 0.8% -1.6%; the ratio of the diameter of the inner cladding to the diameter of the core layer is 3: 1-6: 1, wherein the doping element of the inner cladding is fluorine, and the refractive index difference is-0.5% -0.1%.

3. The method of claim 2, wherein the method comprises: when the three steps of directional etching are carried out, fluorine-containing corrosive gas is introduced into the base tube, the base tube is externally etched by using a fire head to move back and forth along the axial direction of the base tube, finally, a crescent is carved on one side of the core layer, and then after the base tube is rotated for 180 degrees, a crescent with the same radian is carved according to the same previous steps.

4. The method of claim 1, wherein the method comprises: ellipse core ovality e after completion of collapseWherein L is the thickness of the core layer, r is the radius of the hollow circle in the base tube, n is the number of times of back-and-forth erosion of the fire head, and Delta L₁Is the average thickness per etch.

5. The method of claim 4, wherein the method comprises: by controlling the etching thickness, the ellipticity of the elliptical core is accurately controlled, and finally the range of the ratio e of the long axis to the short axis of the elliptical core is 2: 1-5: 1.

Technical Field

The invention relates to the technical field of optical fiber sensing, in particular to a method for manufacturing an elliptical core polarization maintaining optical fiber.

Background

The polarization maintaining fiber is a special single-mode fiber, and the difference between two orthogonal propagation constants is larger by introducing double refraction into the single-mode fiber, so that the coupling probability of two modes is reduced, and the polarization state of light can be kept unchanged after being transmitted for a distance when linearly polarized light is injected along one main shaft of the fiber. In principle, stress-induced birefringence and geometric-induced birefringence are commonly used for birefringence generation.

At present, panda type polarization maintaining optical fibers are most widely used in stress-induced birefringence in China. It has the characteristics of easy coupling and simple manufacture. The polarization performance of the fiber is generally improved by increasing the stress region diameter, and the boron doping concentration. But its temperature stability over the full temperature range is poor due to its large stress zone size.

The geometry is birefringence type, and the asymmetry of the material geometry is utilized, so that the refractive index of the optical fiber has difference in different directions, and birefringence is caused. The ellipticity of the fiber core of the elliptical core polarization maintaining fiber is calculated by the major axis and the minor axis of the elliptical core, wherein e is alpha/b, alpha is the length of the major axis of the elliptical core, and b is the length of the minor axis of the elliptical core. The elliptical core polarization maintaining fiber generates double refraction based on the asymmetry of the geometric structure, is compared with stress type polarization, has good temperature stability, and can be used in the fields of optical fiber type current transformers and high-precision gyroscopes. By designing the ellipticity of the fiber core of the elliptical core polarization-maintaining optical fiber, higher birefringence can be realized, so that the polarization performance of the optical fiber is maintained.

Currently, elliptical core polarization maintaining optical fibers are prepared by forming shaped articles mainly by machining processes. For example, chinese patent document CN106199827 Α discloses "an elliptical-core panda-type polarization maintaining optical fiber and a method for manufacturing the same", which comprises processing a preform having a circular core to flatten the outer surface thereof to form a preform, and preprocessing the preform into an elliptical-core polarization maintaining optical fiber by heating and stretching. However, the method has great difficulty in accurately controlling the ovality of the elliptical core, and in addition, the prefabricated rod needs to be mechanically treated for many times, so that the processing difficulty is great; further, chinese patent CN105985015 a discloses "an elliptical core polarization maintaining optical fiber and a method for manufacturing the same", which comprises using a target rod with a diamond structure, depositing a quartz glass sleeve by using an external spraying process, and removing the target rod to form a pure quartz glass diamond inner hole sleeve. And machining the core rod to make it tangent to the inner surface of the diamond inner hole casing to form the prefabricated rod. It has extremely high requirements on the processing technology and complex technology.

In summary, the elliptical core polarization maintaining optical fiber manufacturing method in the conventional art has a complicated mechanical processing procedure, which results in high processing difficulty and poor stability.

Disclosure of Invention

The invention aims to solve the technical problem of providing a method for manufacturing a polarization maintaining optical fiber which is formed in one step, has stable temperature performance and can freely control the ellipticity of an elliptical core in the prior art.

The technical scheme adopted by the invention for solving the problems is as follows: a method of making an elliptical core polarization maintaining fiber, the method comprising the steps of:

step one, selecting a base pipe with a proper mandrel, and pretreating the base pipe, so that on one hand, the purpose of preheating is realized, and on the other hand, attachments such as impurities on the inner wall of the base pipe are removed.

And step two, manufacturing a core rod by using a chemical vapor deposition method, wherein the core rod comprises an inner cladding layer and a core layer. Depositing an inner cladding layer by the core rod deposition, and then depositing a germanium-phosphorus co-doped core layer, wherein the deposition thickness is L. The size of the core layer is 1-3 mm, the doping elements are germanium and phosphorus, and the relative refractive index difference is 0.8% -1.6%; the ratio of the diameter of the inner cladding to the diameter of the core layer is 3: 1-6: 1, wherein the doping element of the inner cladding is fluorine, and the refractive index difference is-0.5% -0.1%. The substrate layer is made of pure silicon and has a relative refractive index difference of 0.

And step three, after the deposition of the germanium-phosphorus co-doped layer of the core rod is finished, the radius of a hollow circle in the base tube is r. At the moment, the directional etching of the germanium-phosphorus co-doped layer on one side is firstly carried out, the fluorine-containing corrosive gas is introduced into the base tube, and the base tube is etched by using a fire head to move back and forth along the axial direction of the base tube. Finally, a crescent shape is carved on one side of the core layer. And then, after the liner tube is rotated by 180 degrees, the same radian is carved according to the same steps, and finally, the hollow circle in the base tube is etched into an oval shape from the initial circle. The etching thickness Delta L is controlled by the reciprocating times of the moving of the fire head.

Fourthly, after the deposition and the etching of the core rod are finished, the base tube is collapsed in the forward direction and the reverse direction to manufacture a solid elliptical core rod, the Cross Sectional Area (CSA) formula before and after the collapse can be obtained, and the ovality e of the elliptical core after the collapse is finished meets the requirementWherein L is the thickness of the core layer deposition, and r is the half of the hollow circle in the base tubeDiameter, n is the number of round-trip erosion times of the fire head, Δ L₁Is the average thickness per etch. By controlling the etching thickness, the ellipticity of the elliptical core can be accurately controlled, and the range of the ratio e of the long axis to the short axis of the elliptical core is finally 2: 1-5: 1.

And step five, placing the core rod in the deposited quartz sleeve, and combining to form the elliptical core polarization maintaining rod.

And sixthly, drawing the optical rod after the step is finished, drawing the optical rod into a small-diameter bare optical fiber, and coating two layers of acrylic resin optical fiber coatings on the outer surface of the bare optical fiber to obtain the final elliptic core polarization maintaining optical fiber.

Compared with the prior art, the invention has the advantages that:

1. within the working temperature range, stable temperature performance is realized, and the external interference resistance is strong.

2. The ellipticity of the elliptical core polarization maintaining optical fiber can be accurately controlled through the size of the etched area, so that the polarization degree of the optical fiber is controlled.

3. Through directional etching and one-step forming, the process procedures are reduced, and the stability and the reliability are improved.

Drawings

FIG. 1 is a schematic cross-sectional view of a mandrel after deposition is completed in an example of the present invention.

FIG. 2 is a schematic cross-sectional view of a mandrel after etching is completed in an embodiment of the present invention.

Fig. 3 is a schematic cross-sectional view of a collapsed core rod in an example of the invention.

FIG. 4 is a cross-sectional view of an elliptical mandrel thimble completed in accordance with an embodiment of the present invention.

FIG. 5 is a cross-sectional view of an elliptical core polarization maintaining fiber in an embodiment of the present invention.

Detailed Description

The invention is described in further detail below with reference to the accompanying examples.