A high-birefringence solid-core polarization-maintaining microstructure optical fiber and its preparation method

Abstract

The present invention belongs to the field of microstructured optical fiber technology, and discloses a high-birefringence solid-core polarization-maintaining microstructured optical fiber and its preparation method. The cross-section of the optical fiber provided by the present invention is circular, and the optical fiber includes, from the outside to the inside, a quartz cladding, a first air hole cladding, a second air hole cladding, and a core; the number of layers of the first air hole cladding is at least one; the multiple first air holes in each layer of the first air hole cladding are arranged in a hexagonal shape with the cross-section center of the optical fiber as the center; the second air hole cladding is composed of four second air holes and two third air holes, and are symmetrically distributed with the line connecting the centers of the third air holes as the axis; the diameter of the third air hole is larger than the diameter of the first air hole, and the diameter of the first air hole is larger than the diameter of the second air hole. The solid-core polarization-maintaining microstructured optical fiber provided by the present invention has high birefringence performance, good resistance to environmental changes, simple structure, and is easy to implement in process and mass production.

Description

Technical Field

[0001] The present invention belongs to the technical field of microstructure optical fibers, and more specifically, relates to a high-birefringence solid-core polarization-maintaining microstructure optical fiber and a preparation method thereof. Background Art

[0002] The concept of microstructured fiber was first proposed by Russell et al. in 1992, who introduced this theory into optical fiber applications. By incorporating a two-dimensional photonic crystal structure into the cladding, light is confined to the fiber core. In 1996, J.C. Night of the University of Southampton in the UK designed and fabricated the world's first total internal reflection solid-core microstructured fiber. The advent of microstructured fiber greatly increased the flexibility in fiber structural design, and also brought flexibility to the design of polarization-maintaining microstructured fibers. By manipulating the size and arrangement of the pores in the microstructured fiber cladding, the symmetry of the fiber structure is disrupted, thereby increasing birefringence during light transmission. In 2000, Blanch et al. successfully drew the world's first high-birefringence photonic crystal fiber, utilizing an asymmetric internal structure to generate birefringence. This broadened the application scenarios of microstructured fibers. In practical applications, due to the flexible structure and continued research, high-birefringence microstructured polarization-maintaining fibers have been widely used in sensors, polarization-maintaining devices, and lasers.

[0003] In recent years, researchers have leveraged this wide range of design freedom to design various types of polarization-maintaining photonic crystal fibers (PMCFs), which outperform traditional PMCFs in birefringence and resistance to environmental fluctuations. Improving birefringence, improving resistance to environmental fluctuations, and reducing manufacturing complexity are key challenges in designing PMCFs. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-birefringence solid-core polarization-maintaining microstructure optical fiber, so that the solid-core polarization-maintaining microstructure optical fiber has higher birefringence performance and better ability to resist environmental changes.

[0005] The present invention provides a high-birefringence solid-core polarization-maintaining microstructure optical fiber. The cross-section of the optical fiber is circular. The optical fiber comprises, from the outside to the inside, a quartz cladding, a first air-hole cladding, a second air-hole cladding, and a core. The first air-hole cladding has at least one layer. The multiple first air holes in each layer of the first air-hole cladding are arranged in a hexagonal pattern with the cross-section center of the optical fiber as the center. The second air-hole cladding consists of four second air holes and two third air holes, and is symmetrically distributed about a line connecting the centers of the third air holes. The diameter of the third air holes is larger than that of the first air holes, and the diameter of the first air holes is larger than that of the second air holes.

[0006] Preferably, the first pore cladding layer has one layer, and the layer consists of 12 first pores.

[0007] Preferably, the first pore cladding has two layers, consisting of 12 and 18 first pores respectively.

[0008] Preferably, the first pore cladding has three layers, consisting of 12 first pores, 18 first pores, and 24 first pores respectively.

[0009] Preferably, the diameter d1 of the first pores is 2.00-8.00 μm, the diameter d2 of the second pores is 0.50-7.50 μm, and the diameter D of the third pores is 3.00-12.00 μm.

[0010] Preferably, the distance Λ between two adjacent pores is 3.00-12.00 μm, the duty ratio d1 / Λ of the first pore is 0.17-0.90, the duty ratio d2 / Λ of the second pore is 0.05-0.83, and the duty ratio D / Λ of the third pore is 0.25-1.30.

[0011] Preferably, the optical fiber further comprises a coating layer coated outside the quartz cladding, and the diameter d of the quartz cladding is cl is 40 to 100 μm, and the diameter d of the coating layer is co It is 100~165μm.

[0012] Preferably, the transmission attenuation of the optical fiber at a wavelength of 1550 nm is less than or equal to 4.00 dB / km, and the transmission attenuation at a wavelength of 1310 nm is less than or equal to 5.50 dB / km; the beat length of the optical fiber at a wavelength of 1550 nm is less than or equal to 5.00 mm, and the beat length at a wavelength of 1310 nm is less than or equal to 4.23 mm; the mode field diameter of the optical fiber at a wavelength of 1550 nm is less than or equal to 9.00 μm, and the mode field diameter at a wavelength of 1310 nm is less than or equal to 10.00 μm; the polarization extinction ratio of the optical fiber at a wavelength of 1550 nm is greater than or equal to 20 dB / 100 m, and the polarization extinction ratio at a wavelength of 1550 nm is greater than or equal to 15 dB / 1000 m.

[0013] Preferably, the quartz cladding, the first air-hole cladding, the second air-hole cladding and the core are all made of pure quartz glass material.

[0014] In another aspect, the present invention provides a method for preparing the above-mentioned high-birefringence solid-core polarization-maintaining microstructure optical fiber, comprising the following steps:

[0015] Stacking the capillaries to form a preform;

[0016] The preform rod is subjected to optical fiber drawing, and the pressure in each capillary is independently controlled in a partitioned manner to obtain the high-birefringence solid-core polarization-maintaining microstructure optical fiber.

[0017] One or more technical solutions provided in the present invention have at least the following technical effects or advantages:

[0018] The optical fiber provided by the present invention comprises, from the outside inward, a quartz cladding, a first air-hole cladding, a second air-hole cladding, and a core. The first air-hole cladding comprises at least one layer, and the multiple first air holes in each layer of the first air-hole cladding are arranged in a hexagonal pattern centered on the cross-sectional center of the optical fiber. The second air-hole cladding comprises four second air holes and two third air holes, symmetrically distributed about the line connecting the centers of the third air holes. The diameter of the third air holes is larger than that of the first air holes, and the diameter of the first air holes is larger than that of the second air holes. By introducing two large air holes (i.e., the third air holes) and four small air holes (i.e., the second air holes) into the second air-hole cladding, the present invention disrupts the symmetry of the optical fiber structure, resulting in different propagation constants in the two fundamental modes of the optical fiber, and different refractive indices of light in the x-axis and y-axis directions, thereby enhancing the birefringence performance of the optical fiber. In addition, compared to the design of the second pore cladding with four large holes and two small holes, the design of the second pore cladding of the present invention with two large holes and four small holes can increase the area of ​​the glass part around the fiber core, so that it can enhance the ability to resist environmental changes (such as changes in temperature and stress) while ensuring greater birefringence performance. The pore cladding of the present invention is composed of three pores of different diameters (i.e., first pores, second pores, and third pores) arranged according to a certain rule. The diameter of the first pore is larger than the diameter of the second pore. This not only helps to enhance the birefringence effect of the optical fiber and the ability to resist environmental changes, but also takes into account the balance between optical fiber attenuation and birefringence. Through the above design, the present invention enables the solid core polarization-maintaining microstructure optical fiber to have higher birefringence performance and better ability to resist environmental changes. In addition, the optical fiber has a simple structure and is easy to implement in process and actual production. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the end face of a high-birefringence solid-core polarization-maintaining microstructure optical fiber provided in Example 1 of the present invention;

[0020] Figure 2 The fundamental mode of the x-polarization state of the high-birefringence solid-core polarization-maintaining microstructure optical fiber provided in Example 1 of the present invention;

[0021] Figure 3 This is the fundamental mode of the y-polarization state of a high-birefringence solid-core polarization-maintaining microstructure optical fiber provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0022] In order to better understand the above technical solution, the above technical solution will be described in detail below with reference to the accompanying drawings and specific implementation methods.

[0023] Example 1:

[0024] Example 1 provides a high birefringence solid core polarization maintaining microstructure optical fiber, see Figure 1 The cross-section of the optical fiber is circular, and the optical fiber includes, from the outside to the inside, a quartz cladding 5, a first air-hole cladding, a second air-hole cladding, and a core 1; the first air-hole cladding has at least one layer; the multiple first air holes 4 in each layer of the first air-hole cladding are arranged in a hexagonal pattern with the cross-section center of the optical fiber as the center; the second air-hole cladding consists of four second air holes 3 and two third air holes 2, and are symmetrically distributed with the line connecting the centers of the third air holes as the axis; the diameter of the third air hole 2 is larger than the diameter of the first air hole 4, and the diameter of the first air hole 4 is larger than the diameter of the second air hole 3.

[0025] The high-birefringence, solid-core, polarization-maintaining microstructured optical fiber provided by the present invention consists solely of pure silica and pores arranged in a regular pattern. By introducing two large pores (i.e., third pores 2) and four small pores (i.e., second pores 3) into the second pore cladding surrounding the fiber core 1, the present invention disrupts the symmetry of the optical fiber structure. By adjusting the size parameters of the three pores (i.e., first pores 4, second pores 3, and third pores 2), the present invention not only enhances the optical fiber's birefringence effect but also strengthens the optical fiber's resistance to environmental changes.

[0026] The number of layers of the first porous cladding in the present invention can be adjusted according to application requirements, for example:

[0027] (1) The number of layers of the first pore cladding is one, and the layer is composed of twelve first pores 4.

[0028] (2) The first pore cladding has two layers, consisting of twelve first pores 4 and eighteen first pores 4, respectively. Figure 1 shown.

[0029] (3) The number of layers of the first pore cladding is three, consisting of twelve first pores 4, eighteen first pores 4, and twenty-four first pores 4, respectively.

[0030] That is, the first porous cladding in the present invention has a symmetrical structure, and the pores in each layer are arranged in a hexagonal shape. The number of layers of the first porous cladding can be one, two, three or other numbers.

[0031] Taking the number of the first air hole cladding layers as two as an example, the fundamental mode of the x polarization state of the high birefringence solid core polarization maintaining microstructure optical fiber provided by the present invention is as follows: Figure 2As shown, the fundamental mode of the y polarization state is Figure 3 shown.

[0032] In the present invention, the diameter d1 of the first pore 4 is 2.00-8.00 μm, the diameter d2 of the second pore 3 is 0.50-7.50 μm, and the diameter D of the third pore 2 is 3.0-12.00 μm.

[0033] The distance Λ between two adjacent pores is 3.00-12.00 μm, the duty ratio d1 / Λ of the first pore 4 is 0.17-0.90, the duty ratio d2 / Λ of the second pore 3 is 0.05-0.83, and the duty ratio D / Λ of the third pore 2 is 0.25-1.30.

[0034] In addition, the optical fiber further includes a coating layer coated outside the quartz cladding 5, and the diameter d of the quartz cladding 5 is cl is 40 to 100 μm, and the diameter d of the coating layer is co It is 100~165μm.

[0035] The quartz cladding 5 , the first air hole cladding, the second air hole cladding and the core 1 are all made of pure quartz glass material.

[0036] The structural parameters and performance of the high-birefringence solid-core polarization-maintaining microstructured optical fiber provided by the present invention are described below with reference to specific numerical values. Table 1 lists the optical fiber structural cross-sectional parameters of a preferred embodiment of the present invention. Table 2 lists the optical transmission characteristics corresponding to the optical fiber in Table 1.

[0037] Table 1 Fiber structure end face parameters

[0038]

[0039]

[0040] Table 2 Fiber performance parameters

[0041]

[0042] As can be seen from Tables 1 and 2, the transmission attenuation of the optical fiber at a wavelength of 1550 nm is less than or equal to 4.00 dB / km, and the transmission attenuation at a wavelength of 1310 nm is less than or equal to 5.50 dB / km; the beat length of the optical fiber at a wavelength of 1550 nm is less than or equal to 5.00 mm, and the beat length at a wavelength of 1310 nm is less than or equal to 4.23 mm; the mode field diameter of the optical fiber at a wavelength of 1550 nm is less than or equal to 9.00 μm, and the mode field diameter at a wavelength of 1310 nm is less than or equal to 10.00 μm; the polarization extinction ratio of the optical fiber at a wavelength of 1550 nm is greater than or equal to 20 dB / 100 m, and the polarization extinction ratio at a wavelength of 1550 nm is greater than or equal to 15 dB / 1000 m.

[0043] In summary, the present invention obtains a high-birefringence solid-core polarization-maintaining microstructured optical fiber that can meet practical application requirements through specific designs of multiple aspects including aperture, hole spacing, hole arrangement, etc.

[0044] Example 2:

[0045] Example 2 provides a method for preparing a high-birefringence solid-core polarization-maintaining microstructure optical fiber to obtain the high-birefringence solid-core polarization-maintaining microstructure optical fiber as described in Example 1. Example 2 adopts the "stacked rod drawing" method, which includes the following steps: stacking capillaries to form a preform rod; drawing the preform rod into an optical fiber, and independently controlling the pressure in each capillary by partitioning to obtain the high-birefringence solid-core polarization-maintaining microstructure optical fiber. That is, first, based on the specific structure of Example 1, the required capillaries are stacked to form a preform rod using a stacking tool, and then the pressure in the capillary is controlled by a pressure device, and a drawing device is used to draw the high-birefringence solid-core polarization-maintaining microstructure optical fiber. Since Example 2 is a preparation method corresponding to Example 1, it can be implemented by referring to the description of Example 1 and will not be repeated here.

[0046] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A high birefringence solid core polarization-maintaining microstructure optical fiber, characterized in that: The optical fiber has a circular cross-section and comprises, from the outside to the inside, a quartz cladding, a first air-hole cladding, a second air-hole cladding, and a core. The first air-hole cladding has at least one layer. The multiple first air holes in each layer of the first air-hole cladding are arranged in a hexagonal pattern with the center of the optical fiber cross-section as the center. The second air-hole cladding consists of four second air holes and two third air holes, and is symmetrically distributed about a line connecting the centers of the third air holes. The diameter of the third air holes is larger than the diameter of the first air holes, and the diameter of the first air holes is larger than the diameter of the second air holes. The diameter d1 of the first pore is 2.00 to 8.00 μm, the diameter d2 of the second pore is 0.50 to 7.50 μm, and the diameter D of the third pore is 3.00 to 12.00 μm; When the number of layers of the first pore cladding is three, it consists of 12 first pores, 18 first pores, and 24 first pores respectively.

2. The high birefringence solid core polarization-maintaining microstructure optical fiber according to claim 1, characterized in that: When the number of layers of the first pore cladding is one, the layer consists of 12 first pores.

3. The high birefringence solid core polarization-maintaining microstructure optical fiber according to claim 1, characterized in that: When the number of layers of the first pore cladding is two, it is composed of 12 first pores and 18 first pores respectively.

4. The high birefringence solid core polarization-maintaining microstructure optical fiber according to claim 1, characterized in that: The distance Λ between two adjacent pores is 3.00-12.00 μm, the duty ratio d1 / Λ of the first pore is 0.17-0.90, the duty ratio d2 / Λ of the second pore is 0.05-0.83, and the duty ratio D / Λ of the third pore is 0.25-1.

30.

5. The high birefringence solid core polarization-maintaining microstructure optical fiber according to claim 1, characterized in that: The optical fiber further includes a coating layer coated outside the quartz cladding, and the diameter d of the quartz cladding is cl is 40 to 100 μm, and the diameter d of the coating layer is co 100~165 μm.

6. The high birefringence solid core polarization-maintaining microstructure optical fiber according to claim 1, characterized in that: The transmission attenuation of the optical fiber at a wavelength of 1550 nm is less than or equal to 4.00 dB / km, and the transmission attenuation at a wavelength of 1310 nm is less than or equal to 5.50 dB / km; the beat length of the optical fiber at a wavelength of 1550 nm is less than or equal to 5.00 mm, and the beat length at a wavelength of 1310 nm is less than or equal to 4.23 mm; the mode field diameter of the optical fiber at a wavelength of 1550 nm is less than or equal to 9.00 µm, and the mode field diameter at a wavelength of 1310 nm is less than or equal to 10.00 µm; the polarization extinction ratio of the optical fiber at a wavelength of 1550 nm is greater than or equal to 20 dB / 100 m, and the polarization extinction ratio at a wavelength of 1550 nm is greater than or equal to 15 dB / 1000 m.

7. The high birefringence solid core polarization-maintaining microstructure optical fiber according to claim 1, characterized in that: The quartz cladding, the first air hole cladding, the second air hole cladding and the fiber core are all made of pure quartz glass material.

8. A method for preparing a high-birefringence solid-core polarization-maintaining microstructure optical fiber according to any one of claims 1 to 7, characterized in that: The following steps are involved: Stacking the capillaries to form a preform; The preform rod is subjected to optical fiber drawing, and the pressure in each capillary is independently controlled in a partitioned manner to obtain the high-birefringence solid-core polarization-maintaining microstructure optical fiber.

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