A single-crystal optical fiber with tunable doped ion distribution and its growth method

Abstract

This invention relates to a method for growing a single-crystal optical fiber with a tunable distribution of doped ions, comprising: (1) selecting a crystal or ceramic with a uniform doped ion concentration of n at% and cutting a homogeneous crystal or ceramic without doped ions into square rods, and then cutting, polishing and splicing them according to the tangent designed on the side to obtain a first source rod; (2) using a crystal or ceramic without doped ions as a seed crystal, fixing the obtained source rod in a laser-heated base single-crystal optical fiber growth furnace, and performing a first forward growth of the single-crystal optical fiber using the laser-heated base method; (3) using the single-crystal optical fiber grown in the first forward growth as a second source rod for a first reverse growth; (4) using the single-crystal optical fiber grown in the first reverse growth as a third source rod for a second forward growth; (5) using the single-crystal optical fiber grown in the second forward growth as a fourth source rod for a second reverse growth to obtain the single-crystal optical fiber with a tunable distribution of doped ions.

Description

Technical Field

[0001] This invention relates to a single-crystal optical fiber with tunable doped ion distribution and its growth method, belonging to the field of crystal growth and device technology. Background Technology

[0002] Laser diode-pumped solid-state lasers generate significant heat during operation due to quantum defect, the energy difference between the lower and ground states, and laser quenching. In traditional uniformly doped laser crystals, the pump light exhibits exponential decay during pumping from one end due to absorption by gain ions, resulting in a much higher temperature near the pump source end compared to the side further away. Consequently, during high-power laser generation, the accumulation and uneven distribution of heat can easily lead to laser damage, thermal lensing, and thermal birefringence, severely limiting the laser's output power and beam quality.

[0003] Current methods for developing slab lasers, disk lasers, single-crystal fibers, and bonded crystals primarily mitigate the thermal effects during laser generation by increasing heat dissipation. However, these methods still fail to address the issue of different absorption rates of pump light at different locations in the gain medium during laser pumping. Therefore, leveraging the containerless growth characteristic of laser-heated substrate methods, the distribution of doped ions can be controlled through the design of the source rod, thus managing the heat generated during pumping at its source. This further reduces the maximum temperature in the gain medium during laser generation, improving pump light absorption efficiency and laser performance. Summary of the Invention

[0004] To address the problem of uneven heat distribution during laser generation due to uneven absorption of pump light energy in existing homogeneous doping methods, this invention provides a single-crystal optical fiber with tunable dopant ion distribution and its growth method. This technology allows for the controllability of the dopant ion distribution within the single-crystal optical fiber.

[0005] On one hand, the present invention provides a method for growing a single-crystal optical fiber with tunable doped ion distribution, comprising:

[0006] (1) Select crystals or ceramics with at least a uniform doped ion concentration of n at% and cut undoped homogeneous crystals or ceramics into square rods, then cut, polish and splice them according to the side design tangent to obtain the first source rod.

[0007] (2) Using undoped crystals or ceramics as seed crystals, the obtained source rod is fixed in a laser-heated base single-crystal fiber growth furnace, and the single-crystal fiber is grown in the first forward direction using the laser-heated base method.

[0008] (3) Use the single crystal fiber grown in the first forward direction as the second source rod to perform a reverse growth;

[0009] (4) Use the single crystal fiber after the first reverse growth as the third source rod for the second forward growth.

[0010] (5) The single-crystal fiber after the second forward growth is used as the fourth source rod for the second reverse growth to obtain the single-crystal fiber with adjustable distribution of doped ions.

[0011] This invention allows for the controllable distribution of doped ions in the grown single-crystal fiber by designing the source rod during the growth process. This distribution enables uniform absorption of pump light along the pump direction during laser pumping, thereby reducing the large temperature gradient in the laser gain medium caused by the exponential decay of pump light intensity in traditional solid-state lasers. This also reduces the severe thermal lensing and thermally induced birefringence effects caused by the temperature gradient on laser output power and beam quality. This growth method simplifies the process by allowing the desired ion distribution to be achieved through source rod design.

[0012] Preferably, in step (1), the matrix of the crystal or ceramic having uniform doped ion concentrations is YAG, LuAG or YAP, and the doped ion is at least one of Nd, Yb, Tm or Er, with a doping concentration of n at%, n = 0 to 20% at.

[0013] Preferably, in step (1), the side length of the square rod is 1-3 mm and the length is 10-100 mm; more preferably, the square rod is placed in alcohol and ultrasonically cleaned at 60-120 W for 10-20 min.

[0014] Preferably, in step (1), the side length of the square base of the rod is set to a, and the height to b. A coordinate axis is established using the rectangle on the side of the rod, with a as the X-axis and b as the Y-axis, and the angle θ between the tangent and the X-axis is in the range of 10° to 90°. Crystals or ceramics with uniformly doped ions and undoped ions are cut with the same tangent to ensure that they can fit together fully during subsequent assembly and to reduce air bubbles on the assembly surface.

[0015] Preferably, in step (1), a portion of a uniformly doped crystal or ceramic rod cut along the tangent is selected, and another portion is replaced with an undoped crystal or ceramic rod of the same size. After polishing the cut surface, the two portions are pieced together to reconstruct the rod and fixed with the clamps of the laser-heated single-crystal fiber furnace. At this point along the tangent, Y = X * tanθ, the ion concentration distribution at this point after melt growth is nX / a; therefore, the ion distribution in the single-crystal fiber can be controlled according to the angle between the tangent and the X-axis.

[0016] Preferably, in step (2), the side length of the seed crystal is 0.5 to 1 mm.

[0017] Preferably, in step (2), the seed crystal and the source rod are respectively fixed to the pulling device and the feeding device of the laser-heated base single-crystal fiber furnace. The laser power is set to 30-60W to heat the top of the square rod until it melts. Then, the seed crystal is placed into the melting zone, so that the pulling device and the feeding device are facing upwards to perform the first forward growth of the single-crystal fiber. The parameters of the first forward growth include: the pulling speed V of the pulling device of the laser-heated base single-crystal fiber furnace. f The upward feeding speed Vs of the feeding device with the fixed first source bar is 5-20 mm / h, which is 20-80 mm / h.

[0018] The diameter r1 of the single-crystal fiber grown in the first forward direction ranges from 0.5 to 1.5 mm.

[0019] Preferably, in step (3), after increasing the laser power by 2-10W, the lifting device and the feeding device are lowered to perform a first reverse growth of the single-crystal fiber; the parameters of the first reverse growth include: the descent speed V of the feeding device of the laser-heated base single-crystal fiber furnace is 5-20mm / h, and the descent feeding speed of the lifting device with the second source rod fixed is 20-80mm / h; the diameter R1 of the single-crystal fiber after reverse growth should satisfy πR1 2 =a 2 This ensures that the cross-sectional area of ​​the optical fiber is the same as that of the square rod, thereby ensuring that the doped ions in the grown single-crystal optical fiber are distributed along the tangent.

[0020] The diameter R1 of the single-crystal optical fiber after the first reverse growth ranges from 1 to 3 mm.

[0021] Preferably, in step (4), the diameter r2 of the single-crystal fiber after the secondary forward growth is the same as the diameter r1 of the single-crystal fiber after the primary forward growth; the parameters of the secondary forward growth include: the pulling speed V of the pulling device of the laser-heated substrate single-crystal fiber furnace. f The upward feed speed Vs of the feeding device with a fixed third source rod is 5–20 mm / h, and the radius R1 and the radius r2 of the forward-grown fiber satisfy Vs / V f =[R1 / r2] 2 The diameter r2 of the single-crystal fiber grown in the secondary forward direction ranges from 0.5 to 1.5 mm.

[0022] Preferably, in step (5), the diameter R2 of the single-crystal fiber with tunable distribution of doped ions is the same as the diameter R1 of the single-crystal fiber after the first reverse growth; the parameters of the second reverse growth include: the descent speed V of the laser-heated base single-crystal fiber furnace is 5-20 mm / h, and the descent feed speed of the fourth source rod is 20-80 mm / h.

[0023] In another aspect, the present invention provides a single-crystal optical fiber with tunable distribution of doped ions prepared according to the above-described growth method.

[0024] Beneficial effects:

[0025] Unlike traditional uniformly doped single-crystal fibers, this invention provides a method for growing single-crystal fibers with tunable dopant ion distribution. By designing the source rod, the distribution of dopant ions in the grown single-crystal fiber can be controlled as needed, resulting in similar or identical absorption along the pump direction during laser pumping. This prevents localized overheating of the gain medium during laser generation, effectively reducing adverse factors such as thermal lensing and thermal damage caused by high temperatures during high-power laser processes. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the source rod splicing;

[0027] Figure 2 The results of elemental analysis of the cross-section of a single-crystal optical fiber are shown in Example 1, representing a single-crystal optical fiber undergoing reverse growth.

[0028] Figure 3 The elemental test results for the cross-section of the single-crystal fiber during the two reverse growth processes in Example 1 are shown.

[0029] Figure 4 The radial elemental distribution of the single-crystal fiber after two reverse growths in Example 1. Detailed Implementation

[0030] The present invention will be further illustrated by the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0031] This disclosure discloses a method for growing single-crystal optical fibers with tunable distribution of doped ions using a laser-heated substrate.

[0032] The selected crystals or ceramics are either crystals or ceramics with a uniform dopant ion concentration of n at% (0 < n ≤ 20) or homogeneous crystals or ceramics without dopant ions. The selected crystals or ceramics are primarily oxides such as YAG, LuAG, and YAP, and the dopant ions are laser gain ions such as Nd, Yb, Tm, and Er.

[0033] After uniformly doped and undoped crystals or ceramics are cut into square rods, they are cut along a tangent designed on the side, and the cut surfaces are polished. The uniformly doped and undoped crystals or ceramics are then cut into square rods of the same size using an internal circular cutter or wire cutter. The side length of the cut square rods is 1–3 mm, and the length is 10 mm–100 mm. After cutting, the square rods are ultrasonically cleaned in alcohol for 10–20 minutes. The tangent is designed along the rectangular side of the square rod according to the desired ion distribution, and both uniformly doped and undoped crystals or ceramics are cut along the same tangent. A portion of the uniformly doped crystal or ceramic square rod cut along the tangent is selected, and another portion is replaced with an undoped crystal or ceramic of the same size. The polished cut surfaces are then pieced together to reconstruct the square rod and fixed with the clamps of a laser-heated single-crystal fiber furnace. At this point along the tangent, Y = X * tanθ, the ion concentration distribution at this point after melt growth is nX / a; therefore, the ion distribution in the single-crystal fiber can be controlled according to the angle between the tangent and the X-axis. In this invention, ensuring the same slope on the inclined planes is to better bond the doped and undoped crystals. This assembly reduces gaps at the contact surface. The slope has no specific range and can be adjusted according to the required ion distribution; therefore, it is a method for growing single-crystal optical fibers with controllable doped ion distribution.

[0034] Uniformly doped and undoped crystals or ceramics, after being cut, are spliced ​​together along the cut surfaces to form a new square rod, which serves as the first source rod. A single-crystal fiber is then grown forward using a laser-heated substrate method. The equipment includes a built-in fixing device to bond the doped and undoped crystals together and secure them with clamps. An undoped square rod is selected as the seed crystal, and the spliced ​​square rod serves as the source rod. Both are fixed to the lifting and feeding devices of the laser-heated substrate single-crystal fiber furnace, with the lifting device facing upwards and the feeding device facing upwards, for forward growth of the single-crystal fiber. The side length L of the square rod and the lifting speed V of the laser-heated substrate single-crystal fiber furnace are specified. f The feed rate Vs and the fiber radius r satisfy 4Vs / πV f =[r / L] 2 This allows for the selection of the diameter of the optical fiber grown in a single forward direction, with a diameter range of 0.5–1.5 mm.

[0035] A single-crystal fiber grown in the first forward direction is used as a second source rod for a first reverse growth. The radius R of the fiber grown in the first reverse direction is related to the radius r of the fiber grown in the first forward direction by Vs / V. f =[R / r] 2 At the same time, πR should be satisfied. 2 =a 2This ensures that the doped ions in the grown single-crystal fiber are distributed along the tangent. Specifically, after increasing the laser power by 2–10W, the pulling device and the feeding device are positioned downwards to perform reverse growth of the single-crystal fiber. The diameter of the reverse-grown single-crystal fiber ranges from 1 to 3 mm.

[0036] The single-crystal fiber grown in the first inverse growth is used as the third source rod for a second forward growth. The second forward growth does not change the diameter of the single-crystal fiber. After the first inverse growth, the cross-sectional ion distribution is uneven.

[0037] The single-crystal fiber, after a secondary forward growth, is then subjected to a secondary reverse growth to obtain a single-crystal fiber with a controllable distribution of doped ions. The secondary reverse growth does not change the diameter of the single-crystal fiber. Both the secondary forward and reverse growth processes fully utilize the convection present during zone melting to ensure a uniform distribution of doped ions across the cross-section of the single-crystal fiber.

[0038] As a detailed example of a method for growing single-crystal optical fibers with tunable dopant distribution using a laser-heated substrate, it includes:

[0039] (1) Select YAG, LuAG, YAP crystals or ceramics with uniform doped ion concentration and no doped ions, cut them into square bars with the same side length and length, with a side length of 1-3 mm and a length of 10-100 mm. After cutting, put the square bars into alcohol and ultrasonically clean them for 10-20 minutes.

[0040] (2) Cut the crystal or ceramic rod with uniform doped ion concentration and undoped ions along the tangent designed according to the requirements, and polish the cut surface. Select a part of the uniformly doped crystal or ceramic rod after cutting along the tangent, and replace the other part with an undoped crystal or ceramic rod with the same size as this part, and assemble them according to the polished cut surface;

[0041] (3) Select a square rod without doped ions as a seed crystal and fix it on the laser heating base single crystal fiber furnace pulling device. Fix the assembled square rod as a source rod on the laser heating base single crystal fiber furnace feeding device and adjust it to a suitable position. Slowly increase the laser power to form a hemispherical melting zone at the top of the source rod. After slowly placing the seed crystal into the melting zone, raise the pulling device and the feeding device to perform a first forward growth of the single crystal fiber with a diameter range of 0.5 to 1.5 mm.

[0042] (4) Once the forward-grown fiber has reached the required length, growth is stopped, and the laser power is increased by 2–10 W. After the fusion zone stabilizes, the pulling device and the feeding device are moved downwards to perform the first reverse-grown single-crystal fiber. The diameter of the single-crystal fiber to be reverse-grown is calculated according to the ratio Vs / Vf = [R / r].2 Set the lifting and feeding speeds, while also satisfying πR. 2 =a 2 Its diameter ranges from 1 to 2 mm;

[0043] (5) After the first reverse growth is completed, stop the growth, reduce the laser power by 2-10W, so that the lifting device moves upward and the feeding device moves upward, and perform the second forward growth of the single crystal fiber again.

[0044] (6) After the second forward growth is completed, the second reverse growth is performed again according to the process in step (4). This is to make full use of the convection present during the zone melting to make the doped ions uniformly distributed in the cross section of the single crystal fiber.

[0045] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0046] Example 1

[0047] (1) Select undoped YAG crystals and Nd:YAG crystals with a doping concentration of 1 at%, cut them into 1.5×1.5×50mm square rods using an internal circular cutter, ultrasonically clean them for 15 minutes, and then arrange the undoped YAG crystals and Nd:YAG crystals with a doping concentration of 1 at% according to... Figure 1 The line is cut to make the angle between the line and 'a' 60°. After cutting, the cut surface is polished with diamond polishing paste. Then, according to... Figure 1 As shown, undoped YAG and doped Nd:YAG are assembled and fixed in the feeding device of a laser-heated base single-crystal fiber growth furnace. Simultaneously, an undoped YAG square rod is used as a seed crystal and fixed in the pulling device of the laser-heated base single-crystal fiber growth furnace.

[0048] (2) Adjust the position of the feeding device so that the top of the assembled square rod is located at the laser focusing and heating position. Slowly increase the power to melt the top of the assembled square rod, and after forming a hemispherical melting zone, slowly put the seed crystal into the melting zone. After the melting zone stabilizes, start pulling the seed crystal upward at 28.6 mm / h and feeding the square rod upward at 10 mm / h to perform the first forward growth of the single crystal fiber. The fiber diameter is about 1 mm and the length of the grown single crystal fiber is 57.2 mm.

[0049] (3) When the desired length is reached, growth is stopped, and the laser power is increased by 5W. The lifting device moves downward at a speed of 28.6 mm / h, and the feeding device moves downward at a speed of 10 mm / h, thus initiating a reverse growth cycle. The ion distribution of the grown single-crystal fiber is measured using a coordinate system established with the center of the circular cross-section as the origin, in a cross-shaped configuration. Figure 2 As shown, the ions in the cross section are not yet evenly mixed, so another growth process is required.

[0050] (4) After the 57.2mm long and 1mm diameter optical fiber is consumed, the lifting device is raised at a speed of 28.6mm / h and the feeding device is raised at a speed of 10mm / h to start the second positive growth.

[0051] (5) After growing a 1mm single-crystal fiber to a length of 57.2mm, the pulling device is lowered again at a speed of 28.6mm / h, and the feeding device is lowered at a speed of 10mm / h to begin the second reverse growth. Finally, a single-crystal fiber with a linear distribution of doped ions is obtained. EPMA testing shows that the cross-sectional ion distribution of the grown single-crystal fiber is as follows: Figure 4 As shown in the figure, the doped ions are evenly distributed across the cross-section of the single-crystal fiber, indicating uniform mixing. Simultaneously, the radial elemental distribution of the single-crystal fiber is shown in the attached figure. Figure 4 As shown, the distribution is approximately linear, therefore the doped ions along the radial direction can be controlled according to the angle of the tangent.

Claims

1. A method of growing a single crystal fiber with a controllable distribution of dopant ions, comprising: The method comprises the following steps: (1) selecting a crystal or ceramic with a uniform doping ion concentration of n at%, and a homogenous crystal or ceramic without doping ions, cutting, polishing and splicing the crystal or ceramic into a square rod according to the design of the side surface cutting line to obtain a first source rod; (2) using the crystal or ceramic without doping ions as a seed crystal, fixing the obtained first source rod in a laser heating pedestal single crystal fiber growth furnace, and performing a first forward growth of the single crystal fiber by using the laser heating pedestal method; (3) taking the first forward growth single crystal fiber as a second source rod to perform a first reverse growth; (4) taking the first reverse growth single crystal fiber as a third source rod to perform a second forward growth; (5) taking the second forward growth single crystal fiber as a fourth source rod to perform a second reverse growth, and obtaining the single crystal fiber with a controllable distribution of doping ions.

2. The growing method of claim 1, wherein, In step (1), the substrate of the crystal or ceramic with a uniform doping ion concentration of n at% is YAG, LuAG or YAP, the doping ion is at least one of Nd, Yb, Tm and Er, and n = 0-20% at.

3. The growth method of claim 1, wherein, In step (1), the square rod has a side length of 1-3 mm and a length of 10-100 mm; the square rod is placed in alcohol and ultrasonically cleaned at 60-120 W for 10-20 min.

4. The growth method of claim 1, wherein, In step (1), the bottom square of the square rod has a side length of a and a height of b; the long rectangle of the side surface of the square rod is used to establish a coordinate axis, a is the X axis and b is the Y axis, the angle θ between the cutting line and the X axis is 10-90°; the crystal or ceramic with uniform doping ions and the crystal or ceramic without doping ions are cut by the same cutting line to ensure that they can be fully fitted when spliced and the air bubbles existing in the spliced surface are reduced.

5. The growth method of claim 1, wherein, In step (1), a part of the square rod of the crystal or ceramic with uniform doping after cutting by the cutting line is selected, another part is replaced by the crystal or ceramic without doping which has the same size as the part, the cutting surface is polished, and then the two parts are spliced together to form a square rod again and fixed by the clamp of the laser heating pedestal single crystal fiber furnace; at this time, Y = X*tanθ at any point on the cutting line, and the ion concentration distribution of the point after melting growth is nX / a; the ion distribution in the single crystal fiber is adjusted according to the angle between the cutting line and the X axis.

6. The growth method of claim 1, wherein, In step (2), the seed crystal has a side length of 0.5-1 mm.

7. The growth method of claim 1, wherein, In step (2), the seed crystal and the first source rod are fixed to the pulling device and the feeding device of the laser-heated base single-crystal fiber furnace, respectively. The laser power is set to 30-60W to heat the top of the square rod until it melts. Then, the seed crystal is placed into the melting zone, and the pulling device and the feeding device are raised to perform the first forward growth of the single-crystal fiber. The parameters of the first forward growth include: the pulling speed V of the pulling device of the laser-heated base single-crystal fiber furnace. f The upward feeding speed Vs of the feeding device that fixes the first source rod is 5-20 mm / h, which is 20-80 mm / h; the diameter r1 of the single crystal fiber grown in the first forward direction is in the range of 0.5-1.5 mm.

8. The growth method of claim 1, wherein, In step (3), the laser power is increased to 2-10 W, then the pulling device is lowered, the feeding device is lowered, and the single crystal fiber is grown in a reverse direction; the parameters of the reverse growth include: the feeding device of the laser heating base single crystal fiber furnace is lowered at a speed V=5-20 mm / h, the pulling device with the second source rod is lowered at a speed of 20-80 mm / h, and the diameter R1 of the single crystal fiber after the reverse growth should satisfy πR1 2 =a 2 , i.e. the cross-sectional area of the fiber is the same as that of the square rod, so that the grown single crystal fiber is distributed according to a tangent line; the diameter R1 of the single crystal fiber after the reverse growth ranges from 1 mm to 3 mm.

9. The growth method of claim 1, wherein, In step (4), the diameter r2 of the single crystal optical fiber after the secondary forward growth is the same as the diameter r1 of the single crystal optical fiber after the primary forward growth; the parameters of the secondary forward growth include: the pulling speed V of the pulling device of the laser heating base single crystal optical fiber furnace f is 20-80 mm / h, the upward feeding speed Vs of the feeding device for fixing the third source rod is 5-20 mm / h; the relationship between the radius R1 and the radius r2 of the second forward growth optical fiber satisfies Vs / V f =[R1 / r2] 2 , and the diameter r2 of the single crystal optical fiber after the secondary forward growth ranges from 0.5 mm to 1.5 mm.

10. The growth method of claim 1, wherein, In step (5), the single crystal fiber with a controllable distribution of doping ions has the same diameter R2 as the single crystal fiber after the first reverse growth, and the parameters of the second reverse growth include a lowering speed V of the laser heating pedestal single crystal fiber furnace of 5-20 mm / h and a lowering feeding speed of the fourth source rod of 20-80 mm / h.

11. A single crystal fiber with a controllable distribution of doping ions prepared by the growth method according to any one of claims 1-10.

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