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CN-122000774-A - Thulium-doped optical fiber with high spectral purity and preparation method thereof

CN122000774ACN 122000774 ACN122000774 ACN 122000774ACN-122000774-A

Abstract

The invention provides a thulium-doped optical fiber with high spectral purity and a preparation method thereof, wherein the thulium-doped optical fiber with high spectral purity adopts a section design that the refractive index of a main gain layer follows linear gradual change distribution of a primary function and the refractive index of a secondary gain layer is constant, so that the mode distribution of a fiber fundamental mode is accurately overlapped with the main gain layer, and the secondary gain layer is positioned at the lowest point of the refractive index of a waveguide. In addition, on the premise of not sacrificing the gain efficiency of the optical fiber, the invention can realize the effective separation of the emission wavelength of the main gain layer and the secondary gain layer through bending regulation and control by depending on the bending loss difference of the main gain layer and the secondary gain layer, retain the target wavelength of the main gain layer and filter the non-target wavelength of the secondary gain layer, and finally improve the spectral purity of the thulium-doped optical fiber.

Inventors

  • ZHOU JIAN
  • Lu Fanyong
  • WANG YIBO

Assignees

  • 武汉长进光子技术股份有限公司

Dates

Publication Date
20260508
Application Date
20260128

Claims (10)

  1. 1. The thulium-doped optical fiber with high spectral purity is characterized by comprising a fiber core and a cladding which are sequentially arranged from inside to outside along the radial direction, wherein a main gain layer and a secondary gain layer are arranged outside the fiber core from inside to outside along the radial direction, and thulium elements are doped in the main gain layer and the secondary gain layer; The refractive index of the main gain layer is kxr1+b, the refractive index of the main gain layer is linearly reduced outwards along the radial direction, r1 is a radial coordinate taking the central axis of the fiber core as an origin in the main gain layer, the value range of r1 is-20 mu m less than or equal to 20 mu m, k and b are constants, k is not equal to 0, b is not equal to 0, the refractive index of the secondary gain layer is constant and c is not equal to 0, and the value range of a radial coordinate r2 taking the central axis of the fiber core as the origin in the secondary gain layer meets the following relational expression that the value range of r2 is not more than 20 mu m less than 30 mu m.
  2. 2. The high spectral purity thulium doped fiber according to claim 1 wherein the refractive index of any point of said primary gain layer is greater than the refractive index of said secondary gain layer and the refractive index of said secondary gain layer is greater than the refractive index of said cladding layer.
  3. 3. The high spectral purity thulium doped fiber according to claim 1, wherein when the diameter of the primary gain layer is 10-20 μm, the deviation between the outer diameter of the secondary gain layer and the diameter of the primary gain layer is ±10 μm.
  4. 4. The high-spectral purity thulium-doped optical fiber according to claim 1, wherein the bending radius of the thulium-doped optical fiber is 5-50 cm, and when the minimum bending radius of the thulium-doped optical fiber is 6.5cm, the output laser spectrum of the thulium-doped optical fiber shows a single peak, and the side mode suppression ratio is not less than 40db.
  5. 5. A method of preparing a high spectral purity thulium doped optical fiber according to any one of claims 1 to 4, comprising: S10, placing a clean quartz tube on a lathe, introducing a first mixed gas into the quartz tube, and depositing a fluorine-containing barrier layer on the inner wall of the reaction tube to obtain a first reaction tube, wherein the first mixed gas comprises oxygen, silicon tetrachloride and sulfur hexafluoride; s20, introducing a second mixed gas into the first reaction tube, and depositing a loose layer on the tube wall of the first reaction tube to obtain a second reaction tube, wherein the second mixed gas comprises oxygen, helium, silicon tetrachloride and germanium tetrachloride; s30, soaking the second reaction tube with the loose layer attached to the inner wall in an ion solution containing Tm 3+ ; S40, baking the soaked second reaction tube in a third mixed gas atmosphere to obtain a third reaction tube, wherein the third mixed gas comprises silicon tetrachloride, oxygen, helium, nitrogen and chlorine; s50, sequentially performing vitrification shrinkage treatment and wiredrawing treatment on the third reaction tube to obtain the thulium-doped optical fiber with high spectral purity.
  6. 6. The method for preparing the thulium-doped optical fiber with high spectral purity according to claim 5, wherein in the step S10, an oxyhydrogen lamp is used for baking the quartz tube, the baking temperature is 1400-2100 ℃, the moving direction of the oxyhydrogen lamp is the same as the flowing direction of the first mixed gas in the quartz tube, the flow rate of sulfur hexafluoride in the first mixed gas is more than 0 and less than or equal to 50sccm, and the flow rate of silicon tetrachloride is more than 100sccm and less than 300sccm.
  7. 7. The method for preparing the thulium doped optical fiber with high spectral purity according to claim 5, wherein in the step S20, an oxyhydrogen lamp is used for baking the first reaction tube, the baking temperature is 1400-2100 ℃, the moving direction of the oxyhydrogen lamp is the same as the flowing direction of the second mixed gas in the first reaction tube, the flow rate of silicon tetrachloride in the second mixed gas is more than 150sccm and less than or equal to 300sccm, and the flow rate of germanium tetrachloride is more than 5sccm and less than or equal to 30sccm.
  8. 8. The method for preparing a high-spectral-purity thulium-doped optical fiber according to claim 5, wherein in the step S30, the solvent of the ionic solution is pure water or absolute ethyl alcohol, the concentration of Tm 3+ is 0.03-0.2 mol/l, and the soaking time is 0.5-2 h.
  9. 9. The method according to claim 5, wherein in the step S40, the flow rate of silicon tetrachloride in the third mixed gas is greater than 180sccm and less than or equal to 300sccm, and the flow rate of chlorine is greater than 100sccm and less than or equal to 200sccm.
  10. 10. The method for preparing the thulium doped optical fiber with high spectral purity according to claim 9, wherein the second reaction tube is baked by using an oxyhydrogen lamp, the baking temperature is 800-1400 ℃ or 800-1300 ℃, and the moving direction of the oxyhydrogen lamp is the same as the flowing direction of the third mixed gas in the second reaction tube.

Description

Thulium-doped optical fiber with high spectral purity and preparation method thereof Technical Field The invention relates to the technical field of gain optical fibers, in particular to a thulium-doped optical fiber with high spectral purity and a preparation method thereof. Background The research and development and application of thulium fiber lasers are hot, and the core is derived from the fact that the unique output characteristics of the thulium fiber lasers are highly matched with the front application requirements. The laser can realize the output of the wave band approximately equal to 2 mu m, has the advantages of high peak power, narrow pulse width and the like, can be precisely matched with three key application scenes, namely meeting the cold processing requirements of the precision processing and biomedical fields, adapting to the ideal pumping source requirements required by the infrared ultrafast laser generation in the middle, and adapting to the adaptation requirements of the laser radar and photoelectric countermeasure fields to the human eye safety and the atmospheric transmission window. Among them, the narrow linewidth thulium doped laser occupies an irreplaceable core position in basic scientific research and leading edge technology application by virtue of extremely high spectral purity, extremely long coherence length and extremely low phase noise. The core of the thulium fiber laser with high spectral purity depends on a special thulium-doped fiber, but the inherent ion property of the fiber brings about significant technical challenges. The thulium-doped optical fiber has an ultra-wide emission spectrum, provides convenience for partial application, but also leads to different dominant emission wavelengths in different doping concentration areas, and in an oscillation structure, the wavelength difference is extremely easy to cause a multi-wavelength oscillation phenomenon, so that the popularization of a high-purity spectrum laser in various precise applications is directly hindered, and the method becomes a key bottleneck for restricting the technology to fall to the ground. The main scheme for realizing high-power and high-purity spectrum thulium-doped lasers in the current market is MOPA (Master Oscillator Power Amplifier, main oscillation power amplification) structure, and the spectrum purity is ensured by a seed source. However, the scheme has obvious limitations that on one hand, the complexity of an optical system of the MOPA structure is high, the equipment debugging difficulty and the stability control cost are increased, and on the other hand, the high price of the high-purity 2-micrometer seed source greatly improves the research and development and mass production cost of the whole machine, and the dual factors limit the large-scale development and popularization application of the high-purity and high-power thulium fiber laser. Disclosure of Invention The invention aims to provide a thulium-doped optical fiber with high spectral purity and a preparation method thereof, which are used for improving the technical problem that the existing thulium-doped optical fiber is easy to have spectral multiple peaks. In order to solve the technical problems, the thulium-doped optical fiber with high spectral purity comprises a fiber core and a cladding which are sequentially arranged from inside to outside along the radial direction, wherein a main gain layer and a secondary gain layer are arranged outside the fiber core from inside to outside along the radial direction, and thulium elements are doped in the main gain layer and the secondary gain layer; The refractive index of the main gain layer is kxr1+b, the refractive index of the main gain layer is linearly reduced outwards along the radial direction, r1 is a radial coordinate taking the central axis of the fiber core as an origin in the main gain layer, the value range of r1 is-20 mu m less than or equal to r1 less than or equal to 20 mu m, k and b are constants, k is not equal to 0, b is not equal to 0, the refractive index of the secondary gain layer is constant c and is not equal to 0, and the value range of a radial coordinate r2 taking the central axis of the fiber core as the origin in the secondary gain layer meets the following relational expression that the value range of r2 is less than or equal to 30 mu m and is 20 mu m < |r2|. Specifically, the refractive index of the main gain layer is linearly reduced along the radial direction, the refractive index of the secondary gain layer is constant, so that the optical fiber fundamental mode distribution is precisely overlapped with the main gain layer, and meanwhile, on the basis of ensuring the gain efficiency, the non-target emission wavelength of the secondary gain layer caused by different doping concentrations is effectively filtered out by virtue of the bending loss difference of the main gain layer and the secondary gain layer, the problem of spectrum multimod