CN107329205B - Rare earth doped optical fiber - Google Patents

Abstract

The invention discloses a rare earth doped optical fiber. The optical fiber comprises a doped fiber core, a first quartz cladding, a second quartz cladding and an organic coating cladding from inside to outside; the numerical aperture of the second quartz cladding relative to the first quartz cladding is between 0.1 and 0.24; the numerical aperture of the organic coating cladding relative to the first quartz cladding is greater than or equal to 0.35. The optical fiber greatly reduces light leakage of the organic coating layer, improves long-term working reliability and prolongs service life.

Description

A rare earth doped fiber

technical field

The invention belongs to the technical field of optical fiber lasers, and more particularly relates to a rare earth doped optical fiber for lasers.

Background technique

Fiber laser is a kind of laser that uses fiber as laser gain medium. By doping different rare earth ions in fiber quartz matrix, laser output in different wavelength bands is obtained. Fiber lasers have been widely used in industrial processing, medical, military and communication fields due to their high beam quality, large specific surface area, good heat dissipation, high conversion efficiency, small size, compact structure, and easy maintenance.

In the early days, single-clad rare-earth doped fibers were used, and the pump light was required to be injected directly into the fiber core. When the pump power gradually increased, it was difficult to further improve the pump light injection efficiency with only a few tens of μm cores. and power, coating a certain thickness of low-refractive index coating on the outside of the traditional fiber pure silica cladding, the refractive index is from 1.3 to 1.4, more multi-mode pump light can be injected. Layered optical fibers, especially ytterbium-doped double-clad optical fibers, have a cladding diameter of more than 400 μm, and larger ones can reach 600 μm or even 800 μm, which can achieve a single-fiber laser output of several kilowatts or even 10,000 watts. And other rare earth doped fibers, such as thulium-doped, erbium and other double-clad fibers can also achieve several kilowatts of laser output.

At the same time, this double-clad fiber can be converted into a mode with better mode and higher power in a low-NA and small-sized rare-earth-doped core (usually the core size is 10 μm or 20 μm) by injecting multi-mode pump light into the cladding. Laser of a specific wavelength. In order to obtain higher laser conversion efficiency, the quartz cladding often adopts a non-circular cross-section, which breaks the symmetry shape, so that more pump light is injected into the fiber core, which is absorbed by the fiber core and converted into the required laser output. In the double cladding light, pure quartz glass is used as the inner cladding, and fluorine-doped acrylic resin paint is used as the outer cladding. Since the fluorine-doped acrylic resin coating has an ultra-low refractive index (the refractive index is about 1.3), the pump light injected into the inner cladding is totally reflected at the interface between the inner cladding and the outer cladding. However, the interface is not a complete mirror surface, and some pump light will propagate in the fluorine-doped acrylic resin in the form of evanescent waves. After a long time of laser radiation, excessive temperature, laser radiation and water vapor intrusion All will cause the aging of low-refractive index coatings, especially in high-power lasers, the aging rate will be accelerated. When the low-refractive index coating ages, its absolute index of refraction will increase, the adhesion to the glass cladding will decrease, and at the same time, peeling off and micro-cracks will occur, which will affect the gain performance of the fiber. Light leakage will burn the fiber, and even damage other components of the fiber laser, including beam combiners, pump elements, isolators, etc.

At the same time, it is difficult to draw an asymmetric optical fiber preform into an optical fiber that meets the requirements. Under the existing technical conditions, the geometric control of the optical fiber is difficult to control, especially the control of the wire diameter and the measurement of the drawing tension are unstable. The fluctuation of the wire diameter brings about the loss of fiber fusion, and the fluctuation of the tension will cause the strength of the fiber to deteriorate and the loss to increase.

SUMMARY OF THE INVENTION

In view of the above defects or improvement needs of the prior art, the present invention provides a rare-earth doped optical fiber for lasers, the purpose of which is to add silica with a lower refractive index between the silica cladding and the low-refractive-index organic coating cladding cladding, which solves the problem of short laser life due to the easy aging of rare earth-doped optical fiber coatings for lasers, and also solves the technical problem of large differences in fiber parameters caused by non-circular preform drawing wire diameter and tension fluctuations.

In order to achieve the above object, according to one aspect of the present invention, a rare earth doped optical fiber is provided, the optical fiber includes a doped fiber core, a first silica cladding, a second silica cladding, and an organic coating package from the inside to the outside. Floor;

The numerical aperture of the second quartz cladding relative to the first quartz cladding is between 0.1 and 0.24;

The numerical aperture of the organic paint cladding layer relative to the first quartz cladding layer is greater than or equal to 0.35.

Preferably, in the rare earth doped optical fiber, the cross-sectional area ratio of the doped core and the first silica cladding is between 1:6-1600.

Preferably, in the rare earth doped optical fiber, the ratio of the cross-sectional area of the first silica cladding to the second silica cladding is between 3-50:1.

Preferably, in the rare earth-doped optical fiber, the second silica cladding layer is a fluorine-doped silica layer.

Preferably, in the rare-earth doped optical fiber, the cross-sectional shape of the second quartz cladding layer is circular and geometrically concentric with the doped fiber core.

Preferably, in the rare earth doped optical fiber, the first silica cladding is a pure silica cladding.

Preferably, in the rare earth doped optical fiber, the cross-sectional shape of the first silica cladding is non-circular.

Preferably, in the rare earth doped optical fiber, the cross-sectional shape of the first quartz cladding layer is 4D, D-shaped, octagonal, hexagonal, quincunx, square, or rectangular.

Preferably, in the rare earth doped optical fiber, the numerical aperture of the doped core relative to the first silica cladding is between 0.06 and 0.25, and the radius of the doped core is between 2.5 μm and 200 μm.

Preferably, the thickness of the organic coating cladding layer of the rare earth doped optical fiber is between 20 μm and 40 μm.

In general, compared with the prior art, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

The invention provides a rare-earth doped optical fiber for laser. On the basis of the original rare-earth doped optical fiber, a layer of low-refractive-index quartz cladding layer, such as a fluorine-doped quartz layer, is added between the pure quartz cladding layer and the organic paint cladding layer. The refractive index and geometric parameters were explored, so that the core, the first silica cladding and the second silica cladding formed a refractive index "trap", thereby ensuring the injection of more pump light, which has the advantages of the current double cladding fiber. Application characteristics, can be directly applied to existing lasers; at the same time, the refractive index gradient of the first quartz cladding, the second adaptive cladding and the organic coating cladding decreases, which greatly reduces the light leakage of the organic coating cladding. When the laser works at high power, The pump light is limited inside the fiber, the life of the organic coating is greatly increased, and other components of the laser can be prevented from burning, thereby improving the laser power of the fiber, improving the reliability of long-term operation, prolonging the service life, and avoiding accidental losses.

In a preferred solution, the rare earth doped optical fiber of the present invention provides the second quartz cladding with a circular cross-sectional shape, which can improve the consistency of fusion splicing. Since the existing optical fiber fusion splicers are designed for the circular optical fiber of communication, especially the V-groove where the optical fiber is placed, the angle of the non-circular symmetric optical fiber placed in the V-groove is different, and the angle of the core and cladding of the optical fiber is different. The height and position of the core after placement are inconsistent, and it is difficult to ensure the consistency of each fusion. The outer layer of the three-clad optical fiber glass of the present invention is circular, which can be used for a fusion splicer of communication optical fibers, significantly improves the consistency of fusion splicing, and reduces the requirements for operators and fusion splicers.

At the same time, it can improve the success rate of fiber end face cutting, especially for large diameter fibers, reduce the number of cutting times and improve efficiency. Since the glass cladding of the double-clad fiber is generally non-circular, and the existing fiber cleavers are designed for circular fibers, the edges and faces of the non-circularly symmetric fibers are subjected to different forces during cutting, and the edges are formed when cutting the edges. The probability of edge chipping and chipping is higher; the outer layer of the three-clad optical fiber glass of the present invention is circular, and the force is uniform during cutting, especially for large-diameter fibers, the optimized chipping and chipping during cutting are significantly optimized.

The cross-sectional shape of the second quartz cladding layer of the optical fiber provided by the present invention is circular, which is easy to be drawn into shape, and can improve the fluctuation of the drawing wire diameter of the optical fiber. The twisting of the optical fiber in the middle will increase the difficulty in controlling the wire diameter. The glass outer layer of the optical fiber of the present invention is circular, and the wire diameter control of the circular drawn optical fiber is equivalent to the conventional communication optical fiber, which is easier to control, reduces the fluctuation of the wire diameter, and improves the performance of the optical fiber. Batch consistency.

Description of drawings

1 to 3 are schematic diagrams of the structure and refractive index cross-section of rare earth doped optical fibers according to Embodiments 1 to 3 of the present invention, respectively;

4 is a schematic diagram of the structure of a rare earth doped optical fiber with a first quartz cladding in a non-circular symmetrical shape according to the present invention; FIG. 4A is a 4D first quartz cladding; FIG. 4B is a D-type first quartz cladding; A quartz cladding layer; Fig. 4D is a rectangular first quartz cladding layer; Fig. 4E is a plum-shaped first quartz cladding layer; The outer boundary of the cladding section is matched.

In all the drawings, the same reference numerals are used to denote the same structure, wherein: 1 is the fiber core, 2 is the first silica cladding, 3 is the second silica cladding, 4 is the organic paint cladding, and 5 is the outer layer.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

The rare earth doped optical fiber for laser provided by the present invention, as shown in FIG. 1 , includes a doped fiber core, a first quartz cladding layer, a second quartz cladding layer, an organic paint cladding layer, and an outer layer from the inside to the outside;

The numerical aperture of the doped fiber core relative to the first quartz cladding is between 0.06 and 0.25. Its cross section is preferably circular, and its radius is between 2.5 μm and 200 μm. The core can be doped with dopants such as germanium, aluminum, phosphorus, and fluorine; and can also be doped with rare earth ions including one or a combination of ytterbium, erbium, thulium, holmium, and cerium.

The first silica cladding layer is preferably a pure silica layer, and the cross-sectional area ratio of the doped fiber core and the first silica cladding layer is between 1:3 and 1600. Its cross-sectional shape and the core layer cross-sectional shape are non-concentric, that is, when the first quartz cladding cross-sectional shape is circular, the first quartz cladding cross-sectional shape is not concentric with the core layer cross-sectional shape, or the first quartz cladding layer is not concentric. The cross-sectional shape is non-circular. The cross-sectional shape of the first quartz cladding is preferably non-circular, including symmetrical shapes, such as: 4D shape, octagon, hexagon, quincunx, square, or rectangle; asymmetrical shapes, such as D shape. The first quartz cladding adopts a non-circular symmetrical shape, and the geometric size is much larger than that of the doped fiber core, which is used to constrain the pumping light of the cladding, so that the pumping light is fully absorbed by the core layer.

The numerical aperture of the second quartz cladding layer relative to the first quartz cladding layer is between 0.1 and 0.24; the second quartz cladding layer is a fluorine-doped quartz layer. The fluorine-doped quartz can meet the requirements of the present invention for the numerical aperture of the second quartz cladding layer, while ensuring the transmission efficiency of pump light, which is more convenient for industrial mass production. The cross-sectional inner shape of the second quartz cladding is a non-circular symmetrical shape that matches the first quartz cladding, such as 4D, D, octagon, hexagon, quincunx, square, or rectangle (as shown in Figure 4). 9); its outer shape is in a shape that is easy to draw and process, such as square, round. The cross-sectional area ratio of the first quartz cladding layer and the second quartz cladding layer is between 3-50:1. The second quartz cladding is used to prevent the pumping light from leaking into the organic coating cladding, and to increase the heat resistance of the optical fiber to improve the pumping power. Considering the processing difficulty, absorption effect, transmission performance and cost, the above numerical aperture is selected. and geometric dimensions. If the relative numerical aperture is small, the geometric size will increase accordingly, and the cost will increase. At the same time, the pump absorption effect and transmission performance will not be significantly improved. If the geometric size is too small, the relative numerical aperture cannot be further improved, and the absorption effect and transmission performance cannot be guaranteed. At the same time, the processing difficulty is sharp. rise.

The numerical aperture of the organic paint cladding layer relative to the first quartz cladding layer is greater than or equal to 0.35, and the thickness thereof is between 20 μm and 40 μm.

The outer layer is a resin coating.

The rare earth doped optical fiber for laser provided by the present invention is prepared as follows:

(1) Wrap the doped fiber core with the first quartz cladding material, and process its cross-section into a predetermined shape to obtain a semi-finished preform; one of the following operations can be used:

A. Outer vapor deposition;

B. Vapor axial deposition;

C, chemical vapor deposition;

D. Plasma chemical vapor deposition;

E. The melting tube is burnt and wrapped.

(2) The semi-finished preform obtained in step (1) is wrapped with a second quartz cladding material, and its cross section is processed into a predetermined shape to obtain the rare earth-doped optical fiber preform. Also take one of the following actions:

A. Outer vapor deposition;

B. Vapor axial deposition;

C, chemical vapor deposition;

D. Plasma chemical vapor deposition;

E. The melting tube is burnt and wrapped.

Preferably, a melting tube is used for burning and wrapping, specifically:

The doped fiber core to be wrapped is fixed in the melting tube of the first quartz cladding material or the semi-finished preform is fixed in the melting tube of the second quartz layer material, and the melting and sintering is performed.

(3) The optical fiber preform obtained in the step (2) is drawn into a shape, that is, the rare earth doped optical fiber is produced.

The following are examples:

Example 1

A rare earth doped optical fiber for laser, as shown in FIG. 1 , includes a doped fiber core, a first quartz cladding layer, a second quartz cladding layer, an organic paint cladding layer, and an outer layer from the inside to the outside;

The numerical aperture of the doped fiber core relative to the first quartz cladding layer is 0.06. Its cross section is circular, and its radius is between 25 μm. The core doping components are 1.2%wt Yb ₂ O ₃ , 3.5%wt P ₂ O ₅ and 3.0%wt Al ₂ O ₃ .

The first quartz cladding layer is a pure quartz layer, the cross-sectional shape is a regular octagon, and the radius is 182.5 μm, and the radius of the first quartz cladding layer refers to half the distance between two parallel opposite sides of the octagon.

The numerical aperture of the second quartz cladding layer relative to the first quartz cladding layer is 0.22; the second quartz cladding layer is a fluorine-doped quartz layer, and the mass percentage of fluorine-doped is 5%. The cross-section of the second quartz cladding layer is matched with the first quartz cladding layer; its outer shape is circular. The radius of the second quartz cladding layer is 200 μm.

The numerical aperture of the organic paint cladding layer relative to the first quartz cladding layer is 0.47, and the thickness thereof is 35 μm.

The outer layer is an acrylic resin coating, round, with a radius of 275 μm and a numerical aperture of 0.25 relative to pure quartz.

The rare-earth-doped fiber for the laser provided in this embodiment is prepared according to the following method:

(1) wrap the doped fiber core with the first quartz cladding material, and process its cross section into a regular octagon to obtain a semi-finished preform; prepare by chemical vapor deposition;

(2) wrap the semi-finished preform obtained in step (1) with a second quartz cladding material, and process its cross-section into a predetermined shape to obtain the rare earth-doped optical fiber preform, which is sintered and wrapped with a melting tube preparation.

(3) Drawing the rare-earth-doped optical fiber preform obtained in step (2) to form a rare-earth-doped optical fiber.

Example 2

A rare earth doped optical fiber for laser, as shown in FIG. 2 , includes a doped fiber core, a first quartz cladding, a second quartz cladding, an organic paint cladding, and an outer layer from the inside to the outside;

The doped fiber core has a numerical aperture of 0.2 relative to the first quartz cladding. Its cross section is circular, and its radius is between 5 μm. The core doping components are 1.0%wt Yb ₂ O ₃ , 3.5%wt P ₂ O ₅ and 6.2%wt Al ₂ O ₃ .

The first quartz cladding layer is a pure quartz layer, and the cross-sectional shape is a regular hexagon; the radius is 65 μm, and the radius of the first quartz cladding layer is half of the distance between two parallel opposite sides of the hexagon.

The numerical aperture of the second quartz cladding layer relative to the first quartz cladding layer is 0.12; the second quartz cladding layer is a fluorine-doped quartz layer, and the mass percentage of fluorine-doped is 1.18%. The cross-section of the second quartz cladding layer is matched with the first quartz cladding layer; its outer shape is circular. The radius of the second quartz cladding layer is 75 μm.

The numerical aperture of the organic paint cladding layer relative to the first quartz cladding layer is 0.47, and the thickness thereof is 35 μm.

The outer layer is an acrylic resin coating and is round.

The rare-earth-doped fiber for the laser provided in this embodiment is prepared according to the following method:

(1) wrap the doped fiber core with the first quartz cladding material, and process its cross section into a regular octagon to obtain a semi-finished preform; prepare by chemical vapor deposition;

(2) wrap the semi-finished preform obtained in step (1) with a second quartz cladding material, and process its cross-section into a predetermined shape to obtain the rare earth-doped optical fiber preform, which is sintered and wrapped with a melting tube preparation.

(3) Drawing the rare-earth-doped optical fiber preform obtained in step (2) to form a rare-earth-doped optical fiber.

Example 3

A rare earth doped optical fiber for laser, as shown in FIG. 3 , includes a doped fiber core, a first quartz cladding, a second quartz cladding, an organic coating cladding, and an outer layer from the inside to the outside;

The doped fiber core has a numerical aperture of 0.1 relative to the first quartz cladding. Its cross section is circular, and its radius is between 100 μm. The core doping components are 1.0%wt Yb ₂ O ₃ , 3.5%wt P ₂ O ₅ , and 4.1%wt Al ₂ O ₃ .

The first quartz cladding layer is a pure quartz layer, and the cross-sectional shape is a regular octagon; the radius is 200 μm, and the radius of the first quartz cladding layer refers to half of the distance between two parallel opposite sides of the octagon.

The numerical aperture of the second quartz cladding layer relative to the first quartz cladding layer is 0.20; the second quartz cladding layer is a fluorine-doped quartz layer, and the mass percentage of fluorine-doped is 3.96%. The cross-section of the second quartz cladding layer is matched with the first quartz cladding layer; its outer shape is circular. The radius of the second quartz cladding layer is 1400 μm.

The numerical aperture of the organic paint cladding layer relative to the first quartz cladding layer is 0.47, and the thickness thereof is 35 μm.

The outer layer is an acrylic resin coating and is round.

The rare-earth-doped fiber for the laser provided in this embodiment is prepared according to the following method:

(1) wrap the doped fiber core with the first quartz cladding material, and process its cross section into a regular octagon to obtain a semi-finished preform; prepare by chemical vapor deposition;

(2) wrap the semi-finished preform obtained in step (1) with a second quartz cladding material, and process its cross-section into a predetermined shape to obtain the rare earth-doped optical fiber preform, which is sintered and wrapped with a melting tube preparation.

(3) Drawing the rare-earth-doped optical fiber preform obtained in step (2) to form a rare-earth-doped optical fiber.

The doped optical fiber structure provided by the present invention is suitable for a variety of asymmetrical first quartz cladding layers, as shown in FIG. 4 .

Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, etc., All should be included within the protection scope of the present invention.

Claims (5)

1. A three-clad rare earth-doped optical fiber, characterized in that, the optical fiber comprises a doped fiber core, a first quartz cladding, a second quartz cladding, and an organic coating cladding from inside to outside; The numerical aperture of the second quartz cladding relative to the first quartz cladding is between 0.1 and 0.24; The numerical aperture of the organic paint cladding relative to the first quartz cladding is greater than or equal to 0.35; The cross-sectional shape of the first quartz cladding is non-circular, and the cross-sectional shape of the second quartz cladding is circular and geometrically concentric with the doped fiber core; The cross-sectional area ratio of the doped fiber core and the first quartz cladding is between 1:3-1600; The cross-sectional area ratio of the first quartz cladding layer and the second quartz cladding layer is between 3-50:1; The second quartz cladding layer is a fluorine-doped quartz layer. 2 . The rare earth doped optical fiber according to claim 1 , wherein the first silica cladding layer is a pure silica cladding layer. 3 . 3 . The rare earth doped optical fiber according to claim 1 , wherein the cross-sectional shape of the first silica cladding is 4D, D-shaped, octagonal, hexagonal, quincunx, square, or rectangular. 4 . 4 . The rare earth doped optical fiber according to claim 1 , wherein the numerical aperture of the doped core relative to the first silica cladding is between 0.06 and 0.25, and the radius of the doped core is between 2.5 μm and 2.5 μm. 5 . between 200μm. 5 . The rare earth doped optical fiber according to claim 1 , wherein the thickness of the organic coating layer is between 20 μm and 40 μm. 6 .

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