An embedded polygon inner cladding active optical fiber and a preparation method thereof

Abstract

This invention provides an active optical fiber with an embedded polygonal inner cladding and its fabrication method. The active optical fiber includes an active core, an inner cladding, a buffer layer, and a coating layer arranged sequentially from the inside out. The outer contour of the inner cladding is polygonal, and the outer contour of the buffer layer is circular. The diameter ratio of the inner cladding to the active core is CCDR2, and the diameter ratio of the buffer layer to the active core is CCDR1, wherein CCDR2 is between 2 and 80, and CCDR2 is 20% to 90% of CCDR1. The fabrication method includes drawing a preform containing the active core, the circularly contoured inner cladding, and the buffer layer with an arbitrary polygonal outer contour. The drawing temperature and the flow direction of the protective gas in the drawing furnace are controlled to make the outer contour of the buffer layer rounded and the outer contour of the inner cladding polygonal. The active optical fiber obtained by this invention has high quality, a simple fabrication method, and a high yield rate.

Description

Technical Field

[0001] This invention relates to the field of optical fibers, and more particularly to an active optical fiber with an embedded polygonal inner cladding and its fabrication method. Background Technology

[0002] Active optical fibers use rare-earth ions doped in their core as a gain medium to convert pump light into high-beam-quality laser light, thereby increasing the output power of the laser. To meet the ever-increasing high-power demands of fiber lasers, current methods primarily focus on increasing the geometric dimensions of the active optical fiber to improve output power. With the increase in fiber pump absorption efficiency, higher demands are placed on the reliability of coating materials. However, low-refractive-index acrylic resin remains the most mainstream material. This system's coating has poor heat resistance, increasing the risk of coating failure. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides an active optical fiber with an embedded polygonal inner cladding and its fabrication method.

[0004] This invention provides an active optical fiber with an embedded polygonal inner cladding, comprising an active core layer, an inner cladding layer, a buffer layer, and a coating layer arranged sequentially from the inside out. The outer contour of the inner cladding layer is polygonal, the outer contour of the buffer layer is circular, the diameter ratio of the inner cladding layer to the active core layer is CCDR2, and the diameter ratio of the buffer layer to the active core layer is CCDR1, wherein CCDR2 is between 2 and 80, and CCDR2 is 20% to 90% of CCDR1.

[0005] The embedded polygonal inner cladding active optical fiber provided by the present invention has an inner cladding of pure silica glass and a buffer layer of low refractive index doped silica glass, preferably with the doping element being F and / or B.

[0006] The embedded polygonal cladding active optical fiber provided by the present invention has a buffer layer with a numerical aperture between 0 and 0.30 relative to the silica glass.

[0007] The embedded polygonal inner cladding active optical fiber provided by the present invention has one or more layers of coating.

[0008] Preferably, the coating is a two-layer coating, wherein the layer closest to the buffer layer is a low-refractive-index coating with a numerical pore size ≥0.30 relative to the silica glass, and the other layer is a protective layer.

[0009] The present invention also provides a method for fabricating the above-mentioned embedded polygonal inner cladding active optical fiber, comprising:

[0010] The preform containing an active core layer, an inner cladding layer with a circular outer contour, and a buffer layer with an arbitrary polygonal outer contour is drawn into wire. The drawing temperature and the flow direction of the protective gas in the drawing furnace are adjusted to make the outer contour of the buffer layer rounded and the outer contour of the inner cladding layer polygonal.

[0011] According to the preparation method provided by the present invention, the drawing temperature is increased by 50 to 300°C compared with the drawing temperature of the outer circle and inner square preform of the same geometric size.

[0012] According to the preparation method provided by the present invention, the flow direction of the protective gas in the drawing furnace is controlled to be symmetrical about the center and directly opposite the corner of the outer contour of the polygonal buffer layer.

[0013] According to the preparation method provided by the present invention, the preparation of the preform includes: firstly preparing a first preform comprising an active core layer, an inner cladding layer with a circular outer contour, and a buffer layer with a circular outer contour; and then polishing the buffer layer of the first preform to obtain the preform.

[0014] According to the preparation method provided by the present invention, a coating is applied during the wire drawing process.

[0015] This invention provides an embedded polygonal inner cladding active optical fiber and its fabrication method. The design of the buffer layer reduces the risk of coating failure and improves the reliability of the optical fiber. By adjusting the area of ​​the buffer layer, the cladding pump absorption coefficient can be flexibly adjusted. In addition, the improvement of the fabrication method can reduce the production difficulty, improve production efficiency, and increase the product qualification rate and concentricity. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the structure of the embedded polygonal inner cladding active optical fiber provided in an embodiment of the present invention;

[0018] Figure 2 This is a schematic diagram of the fabrication method of the embedded polygonal inner cladding active optical fiber provided in the embodiment of the present invention;

[0019] Figure 3 This is a schematic diagram illustrating the specific process of fabricating an active optical fiber with an embedded polygonal inner cladding provided in an embodiment of the present invention;

[0020] Figure 4 This is a schematic diagram illustrating the specific process of fabricating the active optical fiber with an embedded polygonal inner cladding in Comparative Example 1.

[0021] Figure 5 This is a schematic diagram of the protective gas flow direction during the preparation process of this invention.

[0022] Figure label:

[0023] 101: Active core layer; 102: Inner cladding layer; 103: Buffer layer; 104: Coating layer. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0025] like Figure 1 As shown, this embodiment of the invention provides an active optical fiber with an embedded polygonal inner cladding, comprising an active core layer 101, an inner cladding layer 102, a buffer layer 103, and a coating layer 104 arranged sequentially from the inside out. The outer contour of the inner cladding layer 102 is polygonal, the outer contour of the buffer layer 103 is circular, the diameter ratio of the inner cladding layer 102 to the active core layer 101 is CCDR2, and the diameter ratio of the buffer layer 103 to the active core layer 101 is CCDR1. CCDR2 is between 2 and 80, and CCDR2 is 20% to 90% of CCDR1.

[0026] The active optical fiber of the present invention has a buffer layer 103, which can reduce the light transmission requirements of the coating 104, thereby reducing the failure risk of the coating 104 and improving the reliability of the optical fiber.

[0027] Furthermore, by controlling the diameter ratio of the active core layer 101, inner cladding layer 102, and buffer layer 103 within the aforementioned range, i.e., adjusting CCDR1 and CCDR2, the cladding pump absorption coefficient can be adjusted within a reasonable range. During the fabrication process, under the existing double-clad active fiber rod fabrication process, only the area of ​​the buffer layer 103 needs to be adjusted to flexibly adjust the cladding pump absorption coefficient. The specific principle is as follows: the pump light undergoes total internal reflection in the inner cladding of the active fiber, thus repeatedly passing through the fiber core and being absorbed by the core. The cladding pump absorption coefficient α... Clad satisfy:

[0028]

[0029] Where, α Core S is the core pump absorption coefficient. Core S is the core area. Clad This represents the area of ​​the optical guide cladding.

[0030] In this embodiment of the invention, it is assumed that the pump absorption coefficient of the inner cladding is α. Clad2 The actual cladding pump absorption coefficient α of the active optical fiber in this invention is... Clad1 :

[0031]

[0032] The following formulas ①, ②, and ③ are used to derive the results.

[0033]

[0034]

[0035]

[0036] As shown in the formula, without changing the original double-clad active fiber rod fabrication process, the cladding pump absorption coefficient can be adjusted by adjusting the diameter of the buffer layer 103, i.e., adjusting the ratio of CCDR1 to CCDR2, so as to cope with different application scenarios.

[0037] The active fiber buffer layer 103 of the present invention has a circular outer contour, which has a high fusion splicing matching degree with conventional circular passive optical fibers. This can improve the fusion splicing quality with circular passive optical fibers, thereby reducing fiber loss and improving beam quality.

[0038] According to some embodiments of the present invention, the inner cladding 102 is pure silica glass, and the buffer layer 103 is low-refractive-index doped silica glass, wherein the doping element is F and / or B. Fluorine has a low refractive index, and the use of a fluorine-doped buffer layer makes the refractive index of the inner cladding 102 exhibit a step distribution, thereby preventing some cladding light from being reflected at the coating interface, significantly reducing the heat resistance requirements of the coating, and thus improving the reliability of the optical fiber.

[0039] According to some embodiments of the present invention, the numerical pore size of the buffer layer 103 relative to the silica glass is between 0 and 0.30.

[0040] According to some embodiments of the present invention, the coating 104 is one or more layers.

[0041] Preferably, the coating 104 consists of two layers, one of which is a low-refractive-index coating with a numerical pore size ≥0.30 relative to the silica glass, and the other is a protective layer.

[0042] This invention also provides a method for fabricating the above-mentioned embedded polygonal inner cladding active optical fiber, such as... Figure 2As shown, the process includes: drawing a preform containing an active core layer 101, an inner cladding layer 102 with a circular outer contour, and a buffer layer 103 with an arbitrary polygonal outer contour; adjusting the drawing temperature and the flow direction of the protective gas in the drawing furnace to make the outer contour of the buffer layer 103 rounded and the outer contour of the inner cladding layer 102 polygonal. Further, a coating 104 is applied during the drawing process.

[0043] In the above preparation method, the wire drawing temperature is increased by 50 to 300°C compared to the wire drawing temperature of a preform with an outer circle and inner square of the same geometric dimensions.

[0044] It should be noted that the preformed rod with an outer circle and inner square in the present invention refers to a preformed rod containing an active core layer, an inner cladding layer with a polygonal outer contour, and a buffer layer with a circular outer contour, i.e., the preformed rod 46 in Comparative Example 1 of the present invention.

[0045] In addition, the specific increase in drawing temperature should be adjusted within the range of 50 to 300°C according to the diameter of the buffer layer 103. For example, for active optical fibers with embedded polygonal inner cladding and a buffer layer 103 with a diameter of about 500 μm, the drawing temperature should be increased by 80 to 180°C.

[0046] Furthermore, the flow direction of the protective gas inside the drawing furnace is controlled to be symmetrical around the center and directly opposite the corner of the outer contour of the polygonal buffer layer 103, such as... Figure 5 As shown. The protective gas used is typically argon or helium. To ensure the flow direction of the protective gas is as follows... Figure 5 As shown, the heating element can be customized to meet the protective gas flow direction requirements. Furthermore, the flow rate of the protective gas can be adjusted according to the size of the preform.

[0047] In some embodiments of the present invention, the preparation of the preform includes: firstly preparing a first preform comprising an active core layer 101, an inner cladding layer 102 with a circular outer contour, and a buffer layer 103 with a circular outer contour; and then polishing the buffer layer 103 of the first preform to obtain a preform comprising an active core layer 101, an inner cladding layer 102 with a circular outer contour, and a buffer layer 103 with an arbitrary polygonal outer contour.

[0048] The arbitrary polygon is preferably a polygon with any number of sides between 8 and 20. For example, octagons, decagons, dodecagons, hexagons, etc.

[0049] In one specific embodiment of the present invention, a specific process for fabricating an active optical fiber with an embedded polygonal inner cladding is provided, such as... Figure 3 As shown, it includes:

[0050] Step 1: An active core rod 30 is prepared using the MCVD method, comprising a core rod and a partial inner cladding layer; the active core rod 30 is embedded in a pure silica quartz sleeve 31 and melted to obtain a basic preform 32, comprising a core rod and an inner cladding layer; the basic preform 32 is embedded in a fluorine-doped silica glass sleeve 33 and melted to obtain a first preform 34, comprising a core rod, an inner cladding layer, a fluorine-doped buffer layer, and a silica glass layer outside the fluorine-doped buffer layer;

[0051] Step 2: Grind the buffer layer of the first preform 34 into an arbitrary polygonal structure to obtain the preform 35;

[0052] Step 3, the preform 35 is processed as follows Figure 2 The drawing process shown in the diagram rounds the buffer layer, making the inner cladding a polygonal structure, and then sequentially applies a low-refractive-index inner coating and a protective layer to obtain an active optical fiber 36 with an embedded polygonal inner cladding.

[0053] The concentricity of the active optical fiber with a buffer layer diameter of about 500 μm obtained by the above method is between 1 and 3 μm.

[0054] Comparative Example 1

[0055] This comparative example is based on existing manufacturing processes, specifically as follows: Figure 4 As shown, it includes:

[0056] Step 1: Prepare an active core rod 40 using the MCVD method, including a core rod and a partial inner cladding; embed the above active core rod 40 into a pure silica quartz sleeve 41 and melt it to obtain a basic preform 42, including a core rod and an inner cladding.

[0057] Step 2: Grind the above-mentioned basic preform 42 into an arbitrary polygonal structure to obtain preform 43, including a core rod and a polygonal inner cladding;

[0058] Step 3: The above-mentioned preform 43 is embedded in the fluorine-doped silica glass sleeve 44 and melted to obtain preform 45, which includes a core rod, a polygonal inner cladding, a fluorine-doped buffer layer and a silica glass layer outside the fluorine-doped buffer layer.

[0059] Step 4: Grind off the silica glass layer outside the fluorine-doped buffer layer of the preform 2 45 to obtain the preform 3 46.

[0060] Step 5: The preform 46 undergoes a wire drawing process, followed by the sequential application of a low-refractive-index inner coating and a protective layer to obtain an embedded polygonal active optical fiber 47. The wire drawing process parameters are conventional techniques in the field, generally controlling the wire drawing temperature between 1900 and 2100°C, with upper and lower air seals and no airflow purging the preform.

[0061] The optical fiber with a buffer layer diameter of approximately 500 μm prepared using this comparative method has a concentricity between 5 and 10 μm.

[0062] In Comparative Example 1, embedding the octagonal inner cladding into the preform during the rod fabrication process requires two grinding operations, increasing processing time and undoubtedly reducing product quality, especially significantly impacting the concentricity of the optical fiber. This invention, however, only requires one grinding operation. Specifically, in Comparative Example 1, a polygonal preform 43 is embedded into a circular fluorine-doped silica glass sleeve 44. Due to the mismatch between the octagonal and circular structures, the resulting preform 45 has concentricity issues. Furthermore, the ground polygonal preform 43 has numerous defects such as burrs and pores on its surface, which are difficult to compensate for during the melting process. This can lead to defects at the fusion interface between the polygonal preform 43 and the fluorine-doped silica glass sleeve 44, resulting in bright spots and other defects in the drawn optical fiber, thus reducing the fiber drawing yield. More seriously, current methods cannot detect these fusion interface defects, making it impossible to assess the preform drawing process in advance. Furthermore, in Comparative Example 1, the silica glass layer outside the fluorine-doped buffer layer of preform 2 (45) was ground off, which places high demands on the grinding process. If the grinding is insufficient, the silica glass layer will remain, which will cause the optical fiber to become elliptical during the drawing process, and the optical fiber will not meet the design requirements and will be scrapped. If the grinding is excessive, it will not only cause the produced optical fiber to not meet the optical fiber geometric design requirements, but also waste the fluorine-doped layer and increase production costs.

[0063] Compared to Comparative Example 1, the preparation method of the present invention not only reduces the number of process steps and the difficulty of the process, but also improves the product quality, including fiber concentricity and pass rate. For example, the circular first preform 34 is ground into an arbitrary polygon, especially an octagonal structure. The process is mature, and defects such as surface burrs and pores can be compensated during the wire drawing process. The pass rate is high, the waste of raw materials is reduced, and it is more suitable for mass production.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for manufacturing an embedded polygon inner-cladding active optical fiber, the embedded polygon inner-cladding active optical fiber comprising, in order from the inside out, an active core layer, an inner cladding layer, a buffer layer, and a coating layer, wherein the outer profile of the inner cladding layer is polygonal, the outer profile of the buffer layer is circular, the inner cladding layer is pure silica glass, and the buffer layer is low refractive index doped silica glass, characterized in that, The preparation method comprises: The preform rod comprising the active core layer, the inner cladding layer with a circular outer contour and the buffer layer with an arbitrary polygonal outer contour is drawn, the drawing temperature and the flow direction of the protective gas in the drawing furnace are regulated so that the outer contour of the buffer layer is circularized and the outer contour of the inner cladding layer becomes polygonal; The drawing temperature is increased by 50-300 DEG C than that of the preform rod with the same geometric size and the outer circle and the inner square. The flow direction of the protective gas in the drawing furnace is circularly symmetrical and directly opposite to the angle of the polygonal outer contour of the buffer layer.

2. The method of claim 1, wherein the method further comprises: The diameter ratio of the inner cladding layer to the active core layer is CCR2, and the diameter ratio of the buffer layer to the active core layer is CCR1, wherein CCR2 is between 2 and 80, and CCR2 is 20-90% of CCR1.

3. The method of claim 1, wherein the step of forming the inner cladding comprises the steps of: forming a first layer of glass on the core; and forming a second layer of glass on the first layer of glass, the second layer of glass having a lower index of refraction than the first layer of glass. The doping element is F and / or B.

4. The method of claim 1, wherein the inner cladding is a polygonal shape. The numerical aperture of the buffer layer relative to silica glass is between 0 and 0.

30.

5. The method of claim 1, wherein the step of forming the inner cladding comprises the steps of: forming a first layer of glass on the core; and forming a second layer of glass on the first layer of glass, the second layer of glass having a lower index of refraction than the first layer of glass. The coating layer is one or more layers.

6. The method of claim 4, wherein the step of forming the inner cladding comprises the steps of: forming a first layer of glass on the core; and forming a second layer of glass on the first layer of glass, the second layer of glass having a lower index of refraction than the first layer of glass. The coating layer is two layers, wherein one layer close to the buffer layer is a low refractive index coating layer, and the numerical aperture relative to silica glass is greater than or equal to 0.30, and the other layer is a protective layer.

7. The method of claim 1, wherein the step of forming the inner cladding comprises the steps of: forming a first layer of glass on the core; and forming a second layer of glass on the first layer of glass, the second layer of glass having a lower index of refraction than the first layer of glass. The preparation of the preform rod comprises: first, a first preform rod comprising an active core layer, an inner cladding layer with a circular outer contour and a buffer layer with a circular outer contour is prepared, and then the buffer layer of the first preform rod is polished to obtain the preform rod.

8. The method of claim 1 or 2, wherein the method further comprises: In the drawing process, the coating layer is coated.

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