Multi-cladding erbium-ytterbium co-doped polarization maintaining optical fiber

Abstract

The utility model relates to a multi-cladding erbium-ytterbium co-doped polarization maintaining optical fiber. The cross section of the optical fiber comprises a fiber core, a step layer, a stress area, a circular inner cladding, a circular outer cladding and a circular organic polymer coating layer from inside to outside. Compared with the traditional erbium-ytterbium co-doped polarization maintaining optical fiber, the erbium-ytterbium co-doped polarization maintaining optical fiber adopts a plurality of different end face structure areas, and is additionally provided with a low-refraction glass inner cladding, so that the interaction of an organic coating on pump light can be effectively reduced, the aging of the organic coating during high-power output is inhibited, the high-temperature tolerance of the optical fiber is improved, and the service life of the optical fiber is prolonged. And the optical fiber burning risk is reduced. Meanwhile, the step layer is added to the outer ring of the fiber core, the effective numerical aperture of the fiber core and the cladding is reduced, good light beam quality can be guaranteed under the condition that the size of the fiber core is improved, and the output power of the optical fiber is effectively improved. According to the utility model, the erbium-ytterbium co-doped polarization maintaining optical fiber is more suitable for long-term stable use under high-power and high-temperature conditions.

Description

Technical Field

[0001] This utility model relates to the field of fiber laser technology, specifically to a multi-clad ytterbium-erbium co-doped polarization-maintaining fiber. Background Technology

[0002] 1.5-micron band erbium-ytterbium co-doped polarization-maintaining fiber has wide applications in the field of wind lidar. The optical signal in this band has significant advantages in terms of eye safety and relatively low loss during atmospheric transmission, making wind lidar based on 1.5-micron band erbium-ytterbium co-doped polarization-maintaining fiber show great application potential in many fields such as meteorological monitoring, aerospace, and wind power generation.

[0003] To effectively extend the detection range of wind-measuring lidar and thus enhance its ability to accurately acquire wind field information from distant targets, increasing the output power of the optical fiber has become a crucial technical requirement. Higher output power means that the lidar can emit stronger signal light, thereby receiving sufficiently strong echo signals at greater distances to achieve accurate measurement of wind field parameters. However, under high-power output operating conditions, the long-term reliability of erbium-ytterbium optical fiber becomes a core factor restricting the quality and performance stability of wind-measuring lidar products.

[0004] Traditional erbium-ytterbium co-doped optical fibers have a relatively simple structural design, typically consisting of an organic resin material directly coated onto the outer surface of a pure silica cladding as a protective layer. While this design may meet basic requirements in low-power operating environments, its limitations become apparent in high-power output scenarios. Because organic resin materials have a high absorption coefficient for 1.5-micron wavelength signals, when leaked 1.5-micron wavelength signals are directly absorbed by the organic resin, they are rapidly converted into heat, causing a sharp increase in the local temperature of the fiber coating.

[0005] Under the long-term combined effects of light and heat, the chemical structure and physical properties of organic coatings undergo a series of complex changes, gradually leading to aging. The mechanical and optical properties of aged organic coatings significantly decline, weakening their protective effect on optical fibers. As aging intensifies, in severe cases, light leakage and bright spots may appear on the fiber surface. These light leaks and bright spots not only represent energy loss within the fiber but also directly indicate excessively high local temperatures. Once the local temperature exceeds the fiber material's tolerance limit, it can easily lead to fiber burnout. Fiber burnout not only prevents the lidar system from functioning properly but also threatens the safety of surrounding equipment and personnel, severely impacting the long-term reliability of fiber lasers in high-power applications such as wind-measuring lidar.

[0006] Therefore, how to effectively solve the long-term reliability problem of traditional erbium-ytterbium co-doped optical fibers under high power output has become a key technical challenge that urgently needs to be overcome in the field of fiber lasers. This is of great significance for promoting the further development and widespread application of wind lidar technology. Utility Model Content

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a multi-clad erbium-ytterbium co-doped polarization-maintaining fiber that can significantly reduce the absorption of signal light in the 1.5-micron band by the organic coating, thereby solving the reliability problem mentioned in the background.

[0008] To achieve the above objectives, the present invention proposes the following technical solution:

[0009] A multi-clad ytterbium-erbium co-doped polarization-maintaining fiber, characterized in that it comprises, from the inside out, the following components arranged sequentially:

[0010] Erbium-ytterbium doped fiber core (1) is used to conduct 1.5-micron band signal light;

[0011] A stepped layer (2) is wrapped around the outer periphery of the fiber core (1), and its refractive index is lower than that of the erbium-ytterbium doped fiber core (1) to form a first optical confinement structure;

[0012] A pure quartz glass cladding (3) covers the stepped layer (2) and has two stress zones (4) symmetrically embedded inside to provide polarization maintenance and suppress cladding spiral light;

[0013] A fluorine-doped quartz glass cladding (5) covers the outer surface of the pure quartz glass cladding (3) and has a lower refractive index than the pure quartz glass cladding (3) to form a second light confinement structure.

[0014] An organic polymer coating layer (6) covers the outer surface of the fluorine-doped quartz glass cladding layer (5);

[0015] The stepped layer (2) and the fluorine-doped quartz glass cladding (5) work together to confine the signal light within the erbium-ytterbium doped fiber core (1) and the pure quartz glass cladding (3), reducing the light absorption of the organic polymer coating layer (6) and thus solving the problem of coating aging under high power.

[0016] Furthermore, the pure quartz glass cladding (3) has a circular structure and is concentrically set with the circular structure of the fluorine-doped quartz glass cladding (5). The interface between the two is seamlessly fused to eliminate bubbles and bright spots during high-temperature rod assembly.

[0017] Furthermore, the stress region (4) is circular and symmetrically distributed on both sides of the fiber core (1), and its diameter is greater than 3 times the diameter of the fiber core (1), which is used to enhance stress birefringence and improve pump light absorption efficiency.

[0018] Furthermore, the ratio of the diameter of the stepped layer (2) to the diameter of the erbium-ytterbium doped fiber core (1) is 1.8 to 3. By reducing the effective numerical aperture of the fiber core, the beam quality can be guaranteed while increasing the size of the fiber core.

[0019] Furthermore, the diameter ratio of the fluorine-doped quartz glass cladding (5) to the diameter of the pure quartz glass cladding (3) is 1.05~1.3, ensuring that the cladding light is effectively confined and the fusion interface is free of defects.

[0020] Furthermore, the refractive indices of each layer strictly satisfy the following: the refractive index of the erbium-ytterbium doped fiber core (1) > the refractive index of the stepped layer (2) > the refractive index of the pure quartz cladding (3) > the refractive index of the stress zone (4) > the refractive index of the fluorine-doped quartz cladding (5), forming a stepped refractive index distribution to optimize the optical field constraint.

[0021] Furthermore, the organic polymer coating (6) and the fluorine-doped quartz glass cladding (5) achieve thermal isolation through physical contact, and its diameter is larger than that of the fluorine-doped quartz glass cladding (5) to provide mechanical protection.

[0022] Furthermore, when the optical fiber is used in a 1.5-micron band lidar system, it has an output power of ≥50W and a continuous working life of over 10,000 hours.

[0023] Compared with the prior art, the beneficial effects of this utility model are:

[0024] 1) By using a double-layer optical confinement (stepped layer + fluorine-doped cladding), the light absorption of the organic coating is reduced, thus lowering the risk of heat generation and aging. The symmetrical stress zone design simultaneously achieves high birefringence and efficient pump absorption, shortening the fiber length and reducing costs.

[0025] 2) The signal light can be confined in a pure quartz glass layer, reducing the contact between the signal light and the organic coating interface, reducing the heat generated by the organic coating, improving the high temperature resistance of the optical fiber, and reducing the risk of optical fiber burnout.

[0026] 3) Both the pure silica cladding and the fluorine-doped silica cladding of this optical fiber are circular, which can reduce the generation of bubbles and bright spots at the interface between the two glass types during high-temperature cladding, reduce scattering points, and improve the reliability and stability of the optical fiber.

[0027] 4) Introducing two stress zones inside the circular pure quartz cladding not only provides polarization-maintaining performance but also increases the pump light absorption coefficient and shortens the fiber length. Attached Figure Description

[0028] Figure 1 This is a cross-sectional schematic diagram of the present invention;

[0029] Figure 2 This is a schematic diagram of the refractive index difference distribution on the cross section of this utility model;

[0030] In the figure: 1. Erbium-ytterbium doped fiber core; 2. Stepped layer; 3. Pure quartz glass cladding; 4. Stress zone; 5. Fluorine-doped glass cladding; 6. Organic coating. The refractive indices of the erbium-ytterbium doped fiber core, the stepped layer, the pure quartz glass cladding, the stress zone, the fluorine-doped glass cladding, and the pure quartz glass cladding are Δn1, Δn2, Δn3, Δn4, and Δn5, respectively. Detailed Implementation

[0031] The technical solutions of the present utility model will be fully described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present utility model, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present utility model without creative effort are within the scope of protection of the present utility model.

[0032] Please see Figure 1 and Figure 2 This utility model provides a multi-clad erbium-ytterbium co-doped optical fiber, including an erbium-ytterbium doped fiber core (1), in which rare earth elements erbium and ytterbium are doped, and its refractive index is the highest. There is a step layer (2) outside the fiber core (1), and the refractive index of the step layer is lower than that of the fiber core. The fiber core (1) and the step layer (2) constitute the first cladding structure, which is a 1.5-micron band signal light transmission channel.

[0033] Specifically, the optimal ratio of the step layer diameter to the fiber core diameter is 1.8 to 3. This ratio can ensure effective confinement of the signal light and reduce the effective numerical aperture of the fiber core, while avoiding excessively large step layer sizes that would require more step layer deposition times and thus increase the fabrication difficulty.

[0034] The stepped layer (2) is covered with a pure quartz glass cladding (3), and there are two stress zones (4) inside the pure quartz glass cladding (3), Δn3=0.

[0035] Specifically, the pure quartz cladding is circular in shape, unlike conventional double-clad and triple-clad optical fibers. Compared to the conventional octagonal pure quartz inner cladding, the circular pure quartz cladding is easier to grind and polish using rotary machinery, saving production time and improving production efficiency. Furthermore, the circular pure quartz cladding has better compatibility with circular fluorine-doped quartz tubes, making it easier to achieve a tighter bond during high-temperature melting and shrinking, reducing the probability of bubble and bright spot formation, and improving the reliability and stability of subsequent fiber drawing.

[0036] Specifically, the two stress zones (4) inside the pure quartz glass cladding (3) are symmetrically distributed on both sides of the fiber core. The refractive index of the two stress zones is lower than that of the pure quartz cladding, i.e., Δn4 < 0. The area of ​​the stress zones should not be too small, and the ratio of the diameter of the stress zone to the diameter of the fiber core is generally greater than 3. By introducing two circular stress zones (4) inside the circular pure quartz cladding (3), stress birefringence can be provided, and the generation of cladding spiral light can be effectively suppressed, thereby increasing the cladding absorption coefficient. This is beneficial for reducing the length of the optical fiber and saving laser product costs.

[0037] The pure quartz glass cladding (3) is covered with a fluorine-doped quartz glass cladding (5), and the fluorine-doped quartz glass cladding (5) is covered with an organic polymer coating (6).

[0038] Specifically, the fluorine-doped quartz glass cladding (5) is circular in shape, and its refractive index is lower than that of the pure quartz cladding (3), i.e., Δn5 < 0. The lower refractive index of the fluorine-doped quartz glass cladding confines the cladding light within the high-damage-threshold pure quartz cladding, significantly reducing the interaction between the cladding light and the organic polymer coating. This helps reduce fiber heating and improve long-term reliability. The ratio of the diameter of the fluorine-doped quartz glass cladding (5) to that of the pure quartz glass cladding (3) is 1.05 to 1.3. A smaller ratio will cause the cladding light to leak from the pure quartz cladding, while a larger ratio can easily lead to bubbles and bright spots during high-temperature melting and shrinkage.

[0039] The table below shows the dimensional parameters of a representative optical fiber actually manufactured in accordance with this invention, used to illustrate the size and proportion of the above-mentioned optical fiber structure.

[0040] Site Shape Diameter Erbium / ytterbium-doped core Cylindrical 25 microns Base layer Cylindrical 50 microns Pure silica glass cladding Cylindrical 300 microns Stress region Cylindrical 80 microns Fluorine-doped glass cladding Cylindrical 350 microns Organic polymer coating Cylindrical 475 microns

[0041] The above description is only a preferred embodiment of the present utility model, but the protection scope of the present utility model is not limited thereto. Any equivalent substitutions or changes made by those skilled in the art within the technical scope disclosed in the present utility model, based on the technical solution and inventive concept of the present utility model, should be included within the protection scope of the present utility model.

Claims

1. A multi-clad erbium-ytterbium co-doped polarization-maintaining optical fiber, characterized in that, Including the following, arranged sequentially from the inside out: Erbium-ytterbium doped fiber core (1) is used to conduct 1.5-micron band signal light; A stepped layer (2) is wrapped around the outer periphery of the fiber core (1), and its refractive index is lower than that of the erbium-ytterbium doped fiber core (1) to form a first optical confinement structure; A pure quartz glass cladding (3) covers the stepped layer (2) and has two stress zones (4) symmetrically embedded inside to provide polarization maintenance and suppress cladding spiral light; A fluorine-doped quartz glass cladding (5) covers the outer surface of the pure quartz glass cladding (3) and has a lower refractive index than the pure quartz glass cladding (3) to form a second light confinement structure. An organic polymer coating layer (6) covers the outer surface of the fluorine-doped quartz glass cladding layer (5); The stepped layer (2) and the fluorine-doped quartz glass cladding (5) work together to confine the signal light within the erbium-ytterbium doped fiber core (1) and the pure quartz glass cladding (3), reducing the light absorption of the organic polymer coating layer (6) and thus solving the problem of coating aging under high power.

2. The multi-clad erbium-ytterbium co-doped polarization-maintaining optical fiber as described in claim 1, characterized in that: The pure quartz glass cladding (3) has a circular structure and is concentrically set with the circular structure of the fluorine-doped quartz glass cladding (5). The interface of the two is seamlessly fused to eliminate bubbles and bright spots when the rod is clad at high temperature.

3. The multi-clad erbium-ytterbium co-doped polarization-maintaining optical fiber as described in claim 1, characterized in that: The stress zone (4) is circular and symmetrically distributed on both sides of the fiber core (1). Its diameter is greater than 3 times the diameter of the fiber core (1), which is used to enhance stress birefringence and improve pump light absorption efficiency.

4. The multi-clad erbium-ytterbium co-doped polarization-maintaining optical fiber as described in claim 1, characterized in that: The ratio of the diameter of the stepped layer (2) to the diameter of the erbium-ytterbium doped fiber core (1) is 1.8 to 3. By reducing the effective numerical aperture of the fiber core, the beam quality can be guaranteed while increasing the size of the fiber core.

5. The multi-clad erbium-ytterbium co-doped polarization-maintaining optical fiber as described in claim 1, characterized in that: The diameter ratio of the fluorine-doped quartz glass cladding (5) to the diameter of the pure quartz glass cladding (3) is 1.05~1.3, ensuring that the cladding light is effectively confined and the fusion interface is free of defects.

6. The multi-clad erbium-ytterbium co-doped polarization-maintaining optical fiber as described in claim 1, characterized in that: The refractive indices of each layer strictly satisfy the following: the refractive index of the erbium-ytterbium doped fiber core (1) > the refractive index of the step layer (2) > the refractive index of the pure quartz glass cladding (3) > the refractive index of the stress zone (4) > the refractive index of the fluorine-doped quartz glass cladding (5), forming a stepped refractive index distribution to optimize the optical field constraint.

7. The multi-clad erbium-ytterbium co-doped polarization-maintaining optical fiber as described in claim 1, characterized in that: The organic polymer coating (6) and the fluorine-doped quartz glass cladding (5) achieve thermal insulation through physical contact, and the diameter of the organic polymer coating (6) is larger than that of the fluorine-doped quartz glass cladding (5) to provide mechanical protection.

8. A multi-clad erbium-ytterbium co-doped polarization-maintaining optical fiber as described in any one of claims 1-7, characterized in that: When the optical fiber is used in a 1.5-micron band lidar system, it has an output power of ≥50W and a continuous working life of over 10,000 hours.

Images