Core-defocused rare-earth-doped optical fibers, their applications, fiber lasers, and fiber amplifiers

Abstract

The present invention discloses an eccentric rare earth doped optical fiber and its application, an optical fiber laser, and an optical fiber amplifier. The glass part of the optical fiber includes a rare earth doped core with a decreasing refractive index from the inside to the outside, and an eccentric inner cladding; the outer contour of the cross section of the core is a rectangle or a regular polygon; the outer contour of the cross section of the eccentric inner cladding is a circle, and its center coincides with the geometric center of the cross section of the eccentric rare earth doped optical fiber; there is a distance D between the geometric center of the cross section outer contour of the core and the center of the outer contour of the eccentric inner cladding, and D>0. The eccentric rare earth doped optical fiber provided by the present invention adopts a rectangular or regular polygonal core, which, on the one hand, improves the absorption efficiency of the core, and on the other hand, reduces the energy loss of the cladding evanescent wave overflow, thereby comprehensively improving the pumping efficiency. The present invention is used as an optical gain medium for lasers and optical fiber amplifiers, and has the advantages of device miniaturization, high absorption efficiency, and low fusion loss.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber lasers, and more specifically, relates to an off-core rare earth doped optical fiber, its application, an optical fiber laser, and an optical fiber amplifier. Background Art

[0002] The laser phenomenon of rare earth ions was first reported in the 1960s, and laser output at 1.06μm was achieved. Subsequently, the laser phenomenon was observed in ytterbium-doped glass. However, the development of ytterbium-doped fiber lasers has been slow for more than 20 years, and the output power has not improved much. It was not until 1988 that a double-clad fiber structure was proposed, combined with the development of cladding pumping technology, that the transmission of pump light in the optical fiber was enhanced. Since then, the output power of fiber lasers has increased rapidly.

[0003] The key element of cladding pumping technology is double-clad gain fiber. The core doping of double-clad gain fiber can achieve single-mode transmission for the corresponding wavelength. The inner cladding is a quartz material with a lower refractive index and a size and numerical aperture that matches the output of the corresponding light source. The outer cladding is made of quartz or polymer materials with a lower refractive index than the inner cladding. In communication applications, cladding pumped fiber can concentrate the energy of multiple multi-mode laser diodes to make it a single-mode high-energy signal beam. In energy applications, in order to increase the output power, rare earth-doped optical fibers used as gain media for high-power fiber lasers also use double-clad design, that is, the pump light is coupled into the inner cladding of the optical fiber, and passes through the core multiple times during the total reflection process in the double-clad optical fiber, so that the pump light is absorbed by the doped medium, forming a population inversion and generating a laser wavelength output.

[0004] The earliest inner cladding structure was circular. Since the circular inner cladding is completely symmetrical, a large amount of pump light forms spiral light, which cannot pass through the fiber core with a large amount of rare earth elements during transmission, thus greatly reducing the absorption efficiency of the pump light. In response to this problem, researchers have conducted a lot of research on inner claddings of different shapes. When the inner cladding is circular, the pump light is likely to form spiral light when it is transmitted in it, which is not conducive to the absorption of the fiber core. Therefore, the inner cladding is generally made into different non-circular shapes, such as rectangular, D-shaped, octagonal, etc., which can greatly improve the absorption efficiency of the pump light. Usually, an octagonal inner cladding with a simpler process is used.

[0005] Another solution to break the spiral light formed by pumping light is to use an off-center core, that is, the currently used offset core double-clad fiber. The diameter of the offset core fiber can be smaller than that of the double-clad fiber with a non-circular cladding, which is in line with the trend of device miniaturization and the growing application demand. However, the current offset core fiber pump efficiency is low, and improving the pump efficiency of the offset core fiber has become an urgent problem to be solved. Summary of the invention

[0006] In view of the above defects or improvement requirements of the prior art, the present invention provides an eccentric rare-earth doped fiber, its application, a fiber laser, and a fiber amplifier. The purpose is to adopt a rectangular or regular polygonal core and optimize the eccentricity degree and attitude of the core, so that the eccentric rare-earth doped fiber has a high pumping efficiency under the condition of a small fiber diameter, and an eccentric rare-earth doped fiber with a diameter equivalent to that of a communication fiber is fabricated, thereby solving the technical problem of low absorption efficiency of the existing eccentric fiber.

[0007] To achieve the above object, according to one aspect of the present invention, an eccentric rare-earth doped fiber is provided. Its glass part includes, from the inside out, a rare-earth doped core with a gradually decreasing refractive index, and an eccentric inner cladding.

[0008] The outer contour of the cross-section of the core is rectangular or regular polygonal.

[0009] The outer contour of the cross-section of the eccentric inner cladding is circular, and its center coincides with the geometric center of the cross-section of the eccentric rare-earth doped fiber.

[0010] There is a distance D between the geometric center of the outer contour of the cross-section of the core and the center of the outer contour of the eccentric inner cladding, and D > 0.

[0011] Preferably, for the eccentric rare-earth doped fiber, the circumradius R0 of the outer contour of the cross-section of the core is between 2 - 7.5 μm.

[0012] Preferably, for the eccentric rare-earth doped fiber, the maximum value of the distance from the points on the outer contour of the cross-section of the core to the center of the outer contour of the eccentric inner cladding, that is, the eccentricity distance is p, and 18 μm < p ≤ 54 μm.

[0013] Preferably, for the eccentric rare-earth doped fiber, the eccentricity degree p / R1 of the core satisfies: 0.3 < p / R1 < 0.90, where R1 is the radius of the outer contour of the cross-section of the eccentric inner cladding.

[0014] Preferably, for the eccentric rare-earth doped fiber, 0.45 < p / R1 ≤ 0.9 and 27 μm < p ≤ 54 μm; preferably, 0.6 < p / R1 ≤ 0.9 and 36 μm < p ≤ 54 μm.

[0015] Preferably, for the eccentric rare-earth doped fiber, the thickness of the thinnest part of the eccentric inner cladding, that is, the wall thickness d = R1 - p, and 6 μm < d < 42 μm.

[0016] Preferably, for the eccentric rare-earth doped fiber, the radius R1 of the eccentric inner cladding is between 62 - 62.5 μm.

[0017] Preferably, in the eccentric rare earth doped optical fiber, the ratio of the cross-sectional area of ​​the core to the eccentric cladding is between (1-64):1000.

[0018] Preferably, the core of the eccentric rare earth doped optical fiber contains rare earth ion oxide, aluminum oxide, and / or phosphorus pentoxide; wherein the content of rare earth ions is 0.1%-3%, the content of phosphorus pentoxide is 0.3-1.5%, and the content of aluminum oxide is 0.8%-6%. Preferably, the content of rare earth ions is 0.7%-1.8%; the rare earth ions are selected from one or more of samarium, praseodymium, rubidium, gadolinium, cerium, thulium, erbium, and ytterbium; the relative refractive index difference Δ1 of the core is between 0.6% and 2.0%.

[0019] Preferably, the eccentric rare earth-doped optical fiber has two points on the outer contour of the cross section of the core, which satisfy the following conditions:

[0020] A. The distance between the two points is the maximum value of the distance between any two points on the outer contour of the cross section of the fiber core;

[0021] B. The two points are collinear with the center of the outer contour of the eccentric inner cladding.

[0022] Preferably, the cross-section of the core of the eccentric rare earth-doped optical fiber is a regular polygon with an odd number of sides, the axis of symmetry of the core cross-section is on the diameter of the outer contour of the eccentric inner cladding, and the vertex of the axis of symmetry is the point on the outer contour of the linear cross-section that is farthest from the center of the outer contour of the eccentric inner cladding.

[0023] Preferably, the core of the eccentric rare-earth-doped optical fiber is a regular polygon, and the number of sides of the regular polygon is between 4 and 8.

[0024] Preferably, the glass portion of the eccentric rare earth doped optical fiber has an outer cladding, and the outer cladding is coated on the outside of the eccentric inner cladding; the refractive index of the outer cladding is lower than the refractive index of the eccentric inner cladding; the eccentric inner cladding is preferably made of pure quartz, and the outer cladding is preferably made of fluorine-doped quartz.

[0025] Preferably, for the eccentric rare-earth-doped optical fiber, the geometric center of the outer contour of the cross-section of the outer cladding coincides with the center of the outer contour of the eccentric inner cladding.

[0026] Preferably, the radius R2 of the outer contour of the outer cladding of the eccentric rare-earth-doped optical fiber is between 61-75 μm.

[0027] According to another aspect of the present invention, there is provided an application of the off-core rare-earth doped optical fiber, which is used to prepare an optical gain medium of an optical fiber laser or a cladding pumped optical gain medium of an optical fiber amplifier.

[0028] Preferably, the eccentric rare-earth doped optical fiber is used to prepare a cladding pump light gain medium of an optical fiber amplifier; the outer contour of the cross section of the core is a rectangle.

[0029] According to another aspect of the present invention, there is provided an optical fiber laser which adopts a cladding pumping structure, wherein the cladding pumping light gain medium is the eccentric rare-earth doped optical fiber provided by the present invention.

[0030] According to another aspect of the present invention, there is provided an optical fiber amplifier which adopts a cladding pumping structure, wherein the cladding pumping optical gain medium is the eccentric rare-earth doped optical fiber provided by the present invention.

[0031] Preferably, the cross-sectional outer contour of the core of the optical fiber amplifier is rectangular.

[0032] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0033] The eccentric rare earth doped optical fiber provided by the present invention adopts a rectangular or regular polygonal core, breaking through the limitation of the circular core, improving the core absorption efficiency on the one hand, and reducing the energy loss of the cladding evanescent wave overflow on the other hand, thereby comprehensively improving the pumping efficiency. The present invention improves the pumping efficiency of the eccentric fiber while maintaining the advantage of the small diameter of the eccentric pump fiber, and produces an eccentric rare earth doped optical fiber with a diameter equivalent to that of a communication optical fiber, which is used as an optical gain medium for lasers and optical fiber amplifiers, and has the advantages of device miniaturization, high absorption efficiency, and low fusion loss.

[0034] The preferred solution is to optimize the design of the rectangular or regular polygonal core posture, which further improves the pump absorption efficiency and reduces the cladding evanescent wave overflow under the condition that other core cladding designs are equivalent. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The invention relates to a method for preparing an eccentric core preform;

[0036] Figure 2A is a schematic diagram of the cross-sectional structure of an eccentric core optical fiber with a square core in posture 1 provided in Example 1;

[0037] Figure 2B is a schematic diagram of the cross-sectional structure of an eccentric core optical fiber with a square core in posture 2 provided in Example 1;

[0038] Figure 3A is a schematic diagram of the cross-sectional structure of an eccentric-core optical fiber with a rectangular core in posture 1 provided in Example 2;

[0039] Figure 3B is a schematic diagram of the cross-sectional structure of an eccentric-core optical fiber with a rectangular core in posture 2 provided in Example 2;

[0040] Figure 4 is a schematic diagram of the cross-sectional structure of an eccentric-core optical fiber with a regular pentagonal core provided in Example 3;

[0041] Figure 5 is a schematic diagram of the cross-sectional structure of an eccentric-core optical fiber with a regular pentagonal core provided in Example 4;

[0042] Fig. 6A is a schematic diagram of the cross-sectional structure of an eccentric core optical fiber with a regular hexagonal core in posture 1 provided in Example 5;

[0043] Figure 6B This is a schematic diagram of the cross-sectional structure of an eccentric-core optical fiber with a regular hexagonal core in posture 2 provided in Example 5. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended 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.

[0045] Unless otherwise specified, the relative refractive index difference of each layer of the optical fiber is Δ i It is defined by the following equation, Where n i is the refractive index of the glass at each position of the optical fiber, and n c is the refractive index of pure silicon dioxide.

[0046] The eccentric rare earth doped optical fiber provided by the present invention comprises a glass part and a low refractive index coating, wherein the glass part comprises, from the inside to the outside, a rare earth doped core, an eccentric inner cladding, and a possible outer cladding, the refractive index of which decreases successively; the outer cladding is coated on the outside of the eccentric inner cladding; and the refractive index of the outer cladding is lower than the refractive index of the eccentric inner cladding.

[0047] The fiber core contains rare earth ions, preferably aluminum oxide, and / or phosphorus pentoxide; wherein the content of rare earth ions is 0.1%-3%, the content of phosphorus pentoxide is 0.3-1.5%, and the content of aluminum oxide is 0.8%-6%. Preferably, the content of rare earth ions is 0.7%-1.8%, and it is not limited to doping with one rare earth element, but can also be a composite doping of multiple rare earth elements. The rare earth ions are selected from one or more of samarium, praseodymium, rubidium, gadolinium, cerium, thulium, erbium, and ytterbium. The relative refractive index difference Δ1 of the fiber core is between 0.6% and 2.0%.

[0048] The outer contour of the cross-section of the core is rectangular or regular polygon; the number of sides of the regular polygon is between 4 and 8. If the number of sides of the regular polygon is too small, the glass processing performance is worse, manufacturing is difficult, and the cross-sectional area is relatively small; if the number of sides of the regular polygon is too large, it is closer to a circle, and the pump absorption performance decreases relatively. The rectangular or regular polygon core has a higher absorption efficiency than a circular core with a comparable cross-sectional area. The radius R0 of the circumscribed circle of the outer contour of the core cross-section is between 2 - 7.5 μm.

[0049] In a preferred embodiment, to further improve the absorption efficiency: when the outer contour of the cross-section of the core is rectangular, its diagonal is above the outer contour diameter of the eccentric inner cladding; when the outer contour of the cross-section of the core is a regular polygon with an even number of sides, the connection line of its vertices is above the outer contour diameter of the eccentric inner cladding; when the outer contour of the cross-section of the core is a regular polygon with an odd number of sides, the connection line of its vertices closest to the center is above the outer contour diameter of the eccentric inner cladding.

[0050] The outer contour of the eccentric inner cladding is circular; the radius R1 of the outer contour of the cross-section of the eccentric inner cladding is between 55 - 60 μm. It is preferably made of pure quartz material; the refractive index is 1.44402, and the relative refractive index difference Δ2 is 0.

[0051] There is a distance D between the geometric center of the outer contour of the cross-section of the core and the center of the circle of the outer contour of the eccentric inner cladding, D > 0. The maximum value of the distance from the points on the outer contour of the cross-section of the core to the center of the circle of the outer contour of the eccentric inner cladding is p, 18 μm < p ≤ 54 μm; the eccentricity degree p / R1 of the core satisfies: 0.3 < p / R1 < 0.90, where R1 is the radius of the eccentric inner cladding.

[0052] The radius R1 of the outer contour of the cross-section of the eccentric inner cladding is between 55 - 60 μm, preferably 60 μm. As the eccentric distance increases, the pump absorption efficiency gradually increases.

[0053] Preferably, 0.3 < p / R1 ≤ 0.9, 18 μm < p ≤ 54 μm;

[0054] More preferably, 0.45 < p / R1 ≤ 0.9, 27 μm < p ≤ 54 μm;

[0055] Most preferably, 0.6 < p / R1 ≤ 0.9, 36 μm < p ≤ 54 μm;

[0056] The thickness at the thinnest part of the wall thickness is d = R1 - p.

[0057] The eccentric distance is the maximum value p = 54 μm, and at this time the wall thickness is the minimum value of 6 μm.

[0058] The eccentric distance is the minimum value p = 18 μm, and at this time the wall thickness is the maximum value of 42 μm.

[0059] Therefore, the wall thickness range meets 6μm <d<42μm

[0060] The ratio of the cross-sectional area of ​​the core and the eccentric cladding is between (1-64):1400.

[0061] Generally speaking, for the same size of eccentric inner cladding, when the eccentric distance p is larger and the core radius R0 is larger, the absorption efficiency is higher in theory. However, the increase of eccentric distance p and core diameter R0 will lead to a decrease in the sleeve wall thickness d. Too low wall thickness will cause the pump light to leak, thereby reducing the absorption efficiency, so the wall thickness d should not be too small.

[0062] For the eccentric inner cladding of the same size, when the eccentric distance p increases and the core radius decreases, the wall thickness d is increased and the core radius gradually decreases, resulting in a reduction in the gain medium of the core. At the same time, it will also cause the internal power density of the core to be too high, causing the generation of nonlinear behavior and increasing the core loss. Therefore, the wall thickness d should not be too large.

[0063] The degree of eccentricity p / R1 needs to be coordinated with the eccentricity distance and wall thickness so that they are within the appropriate range.

[0064] The theoretical fiber pumping efficiency when the eccentric cross section is rectangular or polygonal can be estimated by the area of ​​the shaded part, as follows:

[0065]

[0066] Among them, μ is the pump absorption efficiency; R1 is the inner cladding radius; s is the area of ​​the effective absorption part; when the cylindrical coordinate system is established with the geometric center axis of the eccentric rare-earth-doped optical fiber as the Z axis, the polar diameter of any point on the eccentric inner cladding of the eccentric rare-earth-doped optical fiber in the polar coordinate system of its cross section is r, and the polar angle is θ; f(r, θ) is the power distribution function on the incident plane.

[0067] The effective absorption area of ​​the offset core fiber with a rectangular or regular polygonal core is equivalent to that of the circular core with its circumscribed circle, and under the same core cross-sectional area, the effective absorption area of ​​the rectangular or regular polygonal core is larger than that of the circular core. At the same time, compared with the offset core fiber with its circumscribed circle as a circular core, the regular polygonal core effectively increases the thickness of the offset core cladding and reduces the energy loss of the cladding evanescent wave overflow. This effect is more obvious when the degree of eccentricity is high and the wall thickness is small. Combining the above two aspects, the rectangular or regular polygonal core effectively improves the pumping efficiency of the offset core fiber.

[0068] The maximum value of the estimated pump efficiency is obtained in different situations, and the conditions satisfied by the cross-section design of the eccentric rare-earth-doped optical fiber when the pump absorption efficiency is at the maximum are determined, showing:

[0069] When the cross-sectional outer contour of the fiber core is a rectangle, the area s of the effective absorption part is estimated as follows:

[0070]

[0071] Wherein, a and b are the length and width of the rectangle respectively; R1 is the radius of the inner cladding; s is the symmetry axis perpendicular to the long side, and the geometric line connecting the geometric center of the fiber core and the center of the eccentric inner cladding circle, between which there is an angle α; the polar diameter of any point within the eccentric distance on the eccentric inner cladding of the eccentric rare earth doped optical fiber in the polar coordinate system of the cross section where it is located is r; f(r, θ) is the power distribution function on the incident plane.

[0072] By finding the maximum value of the pump efficiency μ, we know that when its diagonal is above the outer contour diameter of the eccentric inner cladding, the eccentric fiber has the best absorption efficiency in theory when other conditions remain unchanged; at this time:

[0073]

[0074] When the cross-sectional outer contour of the fiber core is a regular polygon with an even number of sides, the area s of the effective absorption part is estimated as follows:

[0075]

[0076] Among them, a is the side length of the regular polygon; R1 is the inner cladding radius; n is the number of sides; draw a symmetry axis perpendicular to any side, and a geometric line connecting the center of the fiber core and the center of the eccentric inner cladding, and there is an angle α between the two.

[0077] By finding the maximum value of the pump efficiency μ, we know that when the line connecting its vertices is used as the symmetry axis and the symmetry axis is above the outer contour diameter of the eccentric inner cladding, the eccentric fiber has the best absorption efficiency in theory when other conditions remain unchanged; at this time:

[0078]

[0079] When the cross-sectional outer contour of the fiber core is a regular polygon with an odd number of sides, the area s of the effective absorption part is estimated as follows:

[0080]

[0081] Among them, a is the side length of the regular polygon; n is the number of sides; draw a symmetry axis perpendicular to any side, and a geometric line connecting the center of the fiber core and the center of the eccentric inner cladding, and there is an angle α between the two.

[0082] By finding the maximum value of the pump efficiency μ, we know that when the vertex is used as a symmetry axis and the symmetry axis is above the outer contour diameter of the eccentric inner cladding, the eccentric fiber has the best absorption efficiency in theory when other conditions remain unchanged. At this time:

[0083]

[0084] Based on the above situation with optimal absorption efficiency, the relationship between the cross-sectional attitude of the core and the attitude of the eccentric cladding is summarized as follows:

[0085] There are two points on the cross-sectional outer contour of the core that satisfy the following conditions:

[0086] A. The distance between the two points is the maximum value of the distance between any two points on the outer contour of the cross section of the fiber core;

[0087] B. The two points are collinear with the center of the outer contour of the eccentric inner cladding.

[0088] When the above conditions A and B are met at the same time, the core has the highest absorption efficiency in theory. More importantly, compared with the circular eccentric core optical fiber, since the point with the larger distance from the center of the outer contour of the eccentric inner cladding among the two points of the core is the vertex of the outer contour of the cross section of the core, the cladding thickness on both sides increases rapidly at the thinnest part of the core and the eccentric cladding, reducing the optical power of the evanescent wave overflowing the cladding of the eccentric core optical fiber.

[0089] However, when the outer contour of the cross section of the core is a regular polygon and the number of sides is an odd number, the core is asymmetric. The optical power of the evanescent wave of this asymmetric core design is larger than that of the symmetrical design. Under the condition of high and equal degree of eccentricity, for example, 0.6<p / R1≤0.9, the symmetrically designed eccentric rare earth doped optical fiber has better pumping efficiency and manufacturing performance. This design is preferably: the symmetry axis of the core cross section is on the diameter of the outer contour of the eccentric inner cladding, and the vertex of the symmetry axis is the point on the outer contour of the linear cross section that is farthest from the center of the outer contour of the eccentric inner cladding.

[0090] The geometric center of the outer contour of the cross section of the outer cladding coincides with the center of the outer contour of the eccentric inner cladding. The radius R2 of the outer contour of the outer cladding is between 61-75 μm; the relative refractive index difference Δ3 of the outer cladding is between -0.2% and -0.8%, and is preferably a fluorine-doped quartz layer. The low-refractive-index quartz cladding can further reduce the power of the evanescent wave, improve the pump efficiency, and extend the service life of the low-refractive-index coating.

[0091] The radius R3 of the low refractive index coating is between 120-130 μm, and the relative refractive index difference of the coating layer is between -3.0% and -5.0%.

[0092] The eccentric optical fiber preparation process provided by the present invention comprises the following steps: doping a core rod and putting an eccentric sleeve around the rod and then drawing the wire. Figure 1 As shown, the specific steps include:

[0093] (1) An eccentric hole is drilled on a pure quartz sleeve. The eccentric sleeve needs to be drilled so that the hole diameter and shape match the rare earth-doped core rod used to form the rare earth-doped fiber core; the inner hole of the eccentric sleeve is a rectangle or a regular polygon; the eccentric sleeve preferably uses a pure quartz matrix with a refractive index of 1.44402.

[0094] (2) inserting the rare earth doped core rod into the eccentric hole formed in step (1), and melting and sintering to form a semi-finished solid rod;

[0095] (3) The semi-finished solid rod obtained in step (2) is combined with the outer cladding sleeve to form a preform rod, and the small core diameter eccentric active optical fiber is obtained after drawing.

[0096] Compared with the rare-earth-doped optical fiber with a special-shaped cladding, the eccentric rare-earth-doped optical fiber provided by the present invention has a circular outer contour of the eccentric cladding, and isotropic bending performance. At the same time, due to the reduction in the cladding area, it has a smaller diameter at a comparable absorption efficiency. Combining the above two aspects, the eccentric rare-earth-doped optical fiber provided by the present invention has good bending performance. When used as an optical gain medium, it has better bending performance and a thinner core diameter, which makes the device have obvious miniaturization advantages. In addition, since the core diameter is relatively small, when the device volume is comparable, the eccentric optical fiber provided by the present invention can use a longer length, thereby improving the absorption efficiency of the pump light.

[0097] In summary, the eccentric rare-earth doped optical fiber provided by the present invention is used as an optical gain medium, such as an optical gain medium of a laser and an optical fiber amplifier, and has the advantages of device miniaturization and high pumping light absorption efficiency.

[0098] The application of the eccentric rare earth doped optical fiber provided by the present invention is applied to the preparation of the optical gain medium of the optical fiber laser or the cladding pump optical gain medium of the optical fiber amplifier.

[0099] When used for preparing the cladding pump light gain medium of the optical fiber amplifier, the outer contour of the cross section of the fiber core is a rectangle.

[0100] The optical fiber laser provided by the present invention adopts a cladding pumping structure, and the cladding pumping light gain medium thereof is the eccentric rare-earth doped optical fiber provided by the present invention.

[0101] The optical fiber amplifier provided by the present invention adopts a cladding pump structure, and its cladding pump light gain medium is the eccentric rare earth doped optical fiber provided by the present invention. The cross-sectional outer contour of the core is a rectangle.

[0102] Compared with circular core fibers, the core structure of offset square core fiber is asymmetric, which makes it have polarization-maintaining fiber characteristics. The modes it supports cannot be rotated at any angle like circular core fibers. At the same time, each listed mode has two polarization modes with perpendicular polarization directions, which can be completely independent and not rotated in square core fiber. Therefore, the total number of supported modes must be multiplied by 2, which can increase the number of modes used for communication and increase the transmission capacity of the communication system. Therefore, the offset rectangular fiber designed in this solution can support more modes, increase the transmission capacity of the communication system, and also has polarization-maintaining characteristics, which is a good solution for polarization-maintaining fiber amplifiers.

[0103] The following are examples:

[0104] Example 1

[0105] The cross-sectional structure of the eccentric rare earth doped optical fiber provided in this embodiment is as follows: Figure 2A As shown, the eccentric distance satisfies 33μm<p≤49.5μm, the radius R0 of the core circumscribed circle is 3μm, and the relative refractive index difference Δ1 is 0.6%; the radius R1 of the eccentric inner cladding is 55μm, and the relative refractive index difference Δ2 is 0; the outer cladding is a fluorine-doped quartz layer, the radius R2 is 62.5μm, and the relative refractive index difference Δ3 is -0.2%; the radius R3 of the coating layer is 125μm, and the relative refractive index difference of the coating layer is -5%. The ratio of the cross-sectional area of ​​the doped core and the eccentric cladding is 10:1400, and the wall thickness is 5.5μm<d≤38.5μm. The diagonal of the square cross section of the core is above the outer contour diameter of the eccentric inner cladding (posture 1).

[0106] The fiber core contains rare earth ion oxide, aluminum oxide, and phosphorus pentoxide; wherein the content of rare earth ions is 0.9%, the content of phosphorus pentoxide is 0.3%, and the content of aluminum oxide is 0.8%.

[0107] The preparation method is as follows: a eccentric hole is drilled on a pure quartz sleeve, the inner hole of the eccentric sleeve is processed into a square, the eccentric sleeve adopts a pure quartz matrix, and the refractive index is 1.44402. A rare earth doped core rod is inserted into the eccentric hole, and then inserted into the fluorine doped sleeve, melted, sintered and drawn to make a coating layer.

[0108] It is estimated that the pump absorption efficiency μ of the eccentric rare earth doped optical fiber provided in this embodiment is between 40% and 93%, which is lower than that of the solution of attitude 2 (such as Figure 2B As shown, the symmetry axis of the core cross section is perpendicular to the edge and passes through the geometric center of the offset rare earth doped optical fiber), and the pump absorption efficiency μ is increased by 5%-10%.

[0109] Example 2

[0110] The cross-sectional structure of the eccentric rare earth doped optical fiber provided in this embodiment is as follows: Figure 3AAs shown, the eccentric distance satisfies 36μm<p≤54μm, the radius R0 of the circumscribed circle of the core is 4μm, and the side lengths are 2 and The relative refractive index difference Δ1 is 0.8%; the radius R1 of the eccentric inner cladding is 60μm, and the relative refractive index difference Δ2 is 0; the outer cladding is a fluorine-doped quartz layer, the radius R2 is 62.5μm, and the relative refractive index difference Δ3 is between -0.4%; the radius R3 of the coating layer is 125μm, and the relative refractive index difference of the coating layer is -3.0%. The ratio of the cross-sectional area of ​​the doped core and the eccentric cladding is 2:1400, and the wall thickness is 42μm<d≤33μm. The diagonal of the core cross-sectional rectangle is above the outer contour diameter of the eccentric inner cladding (posture 1).

[0111] The fiber core contains rare earth ion oxide, aluminum oxide, and phosphorus pentoxide; wherein the content of rare earth ions accounts for 2.2%, the content of phosphorus pentoxide is 0.8%, and the content of aluminum oxide is 1.5%.

[0112] The preparation method is as follows: a core hole is drilled on a pure quartz sleeve, the inner hole of the core hole is processed into a rectangular shape, the core hole adopts a pure quartz matrix, and the refractive index is 1.44402. A rare earth doped core rod is inserted into the core hole, and then inserted into the fluorine doped sleeve, melted, sintered, and drawn to make a coating layer.

[0113] It is estimated that the pump absorption efficiency μ of the eccentric rare earth doped optical fiber provided in this embodiment is between 38% and 91%, which is lower than that of the solution of attitude 2 (such as Figure 2B As shown, the symmetry axis of the core cross section is perpendicular to the long side and passes through the geometric center of the offset rare earth doped optical fiber), and the pump absorption efficiency μ is increased by 7%-12%.

[0114] Example 3

[0115] The cross-sectional structure of the eccentric rare earth doped optical fiber provided in this embodiment is as follows: Figure 4 As shown, the eccentric distance satisfies 36μm<p≤54μm, the radius R0 of the circumscribed circle of the core is 6μm, and the relative refractive index difference Δ1 is 1.0%; the radius R1 of the eccentric inner cladding is 60μm, and the relative refractive index difference Δ2 is 0; the outer cladding is a fluorine-doped quartz layer, the radius R2 is 62.5μm, and the relative refractive index difference Δ3 is between -0.8%; the radius R3 of the coating layer is 130μm, and the relative refractive index difference of the coating layer is -3.0%. The ratio of the cross-sectional area of ​​the doped core and the eccentric cladding is 28:1400, and the wall thickness is 6μm<d≤24μm. The symmetry axis of the core cross section is on the diameter of the outer contour of the eccentric inner cladding, and the vertex of the symmetry axis is the point on the outer contour of the core cross section that is farthest from the center of the outer contour of the eccentric inner cladding.

[0116] The core contains rare earth ion oxides, alumina, and phosphorus pentoxide; among them, the content ratio of rare earth ions is 1.5%, the content of phosphorus pentoxide is 6%, and the content of alumina is 1.8%.

[0117] The preparation method is as follows: Drill an eccentric hole on a pure quartz sleeve, process the inner hole of the eccentric sleeve into a regular pentagon, and one vertex is collinear with the center of the eccentric inner cladding and the center of the core. The eccentric sleeve uses a pure quartz matrix with a refractive index of 1.44402. Insert the rare earth doped core rod into the eccentric hole, then insert it into the fluorine-doped sleeve, melt and shrink it, sinter it solid, and draw it to make a coating layer.

[0118] It is estimated that the pump absorption efficiency μ of the eccentric rare earth doped fiber provided in this embodiment is between 51% and 95%.

[0119] Example 4

[0120] For the eccentric rare earth doped fiber provided in this embodiment, its cross-sectional structure is as Figure 5 shown. The eccentric distance satisfies 18μm < p ≤ 54μm, the radius R0 of the circumscribed circle of the core is 7.5μm, and the relative refractive index difference Δ1 is 0.6%; the radius R1 of the eccentric inner cladding is 60μm, and the relative refractive index difference Δ2 is 0; the outer cladding is a fluorine-doped quartz layer with a radius R2 of 62.5μm, and the relative refractive index difference Δ3 is between -0.4%; the radius R3 of the coating layer is 125μm, and the relative refractive index difference of the coating layer is -4.0%. The cross-sectional area ratio of the doped core to the eccentric cladding is 64:1400, and the wall thickness 6μm < d < 52μm. As Figure 5 shown, the longest vertex connection line is above the outer contour diameter of the eccentric inner cladding.

[0121] The core contains rare earth ion oxides, alumina, and phosphorus pentoxide; among them, the content ratio of rare earth ions is 3%, the content of phosphorus pentoxide is 0.3%, and the content of alumina is 1.8%.

[0122] Drill an eccentric hole on a pure quartz sleeve, process the inner hole of the eccentric sleeve into a regular pentagon, and two non-adjacent vertices are collinear with the center of the circle. The eccentric sleeve uses a pure quartz matrix with a refractive index of 1.44402. Insert the rare earth doped core rod into the eccentric hole, then insert it into the fluorine-doped sleeve, melt and shrink it, sinter it solid, and draw it to make a coating layer.

[0123] It is estimated that the pump absorption efficiency μ of the eccentric rare earth doped fiber provided in this embodiment is between 48% and 95%.

[0124] Example 5

[0125] For the eccentric rare earth doped fiber provided in this embodiment, its cross-sectional structure is as Fig. 6AAs shown, the eccentricity distance satisfies 18μm < p ≤ 54μm, the radius R0 of the circumscribed circle of the core is 7.5μm, and the relative refractive index difference Δ1 is 2.0%; the radius R1 of the eccentric inner cladding is 60μm, and the relative refractive index difference Δ2 is 0; the outer cladding is a fluorine-doped silica layer with a radius R2 of 62.5μm, and the relative refractive index difference Δ3 is between -0.8%; the radius R3 of the coating layer is 125μm, and the relative refractive index difference of the coating layer is -4.0%. The cross-sectional area ratio of the doped core to the eccentric cladding is 64:1400, and the wall thickness is 6μm < d < 24μm. The line connecting its vertices is used as the axis of symmetry, and this axis of symmetry is above the outer contour diameter of the eccentric inner cladding (as Fig. 6A shown, attitude 1).

[0126] The core contains rare earth ion oxides, alumina, and phosphorus pentoxide; among them, the content ratio of rare earth ions is 2.5%, the content of phosphorus pentoxide is 4%, and the content of alumina is 1.8%.

[0127] An eccentric hole is drilled in the pure silica sleeve, and the inner hole of the eccentric sleeve is processed into a regular hexagon. The eccentric sleeve uses a pure silica matrix with a refractive index of 1.44402. The rare earth-doped core rod is inserted into the eccentric hole, and then inserted into the fluorine-doped sleeve, and fused, sintered, and drawn to make the coating layer.

[0128] It is estimated that the pump absorption efficiency μ of the eccentric rare earth-doped fiber provided in this embodiment is between 55% and 95%. Compared with the solution of attitude 2 (as Figure 6B shown, the straight line where the axis of symmetry perpendicular to the side passes through the geometric center of the inner cladding of the eccentric rare earth-doped fiber), the pump absorption efficiency μ is increased by 2% - 5%.

[0129] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A core-biased rare earth-doped optical fiber, It is characterized in that The glass part includes a rare earth doped core with decreasing refractive index from the inside to the outside, and an off-core inner cladding; The outer contour of the cross section of the fiber core is a rectangle or a regular polygon; The outer contour of the cross section of the eccentric inner cladding is a circle, and the center of the circle coincides with the geometric center of the cross section of the eccentric rare-earth-doped optical fiber; There is a distance D between the geometric center of the outer contour of the cross section of the core and the center of the outer contour of the eccentric inner cladding, where D>0.

2. The eccentric rare earth doped optical fiber according to claim 1, It is characterized in that The radius R of the circumscribed circle of the outer contour of the core cross section 0 Between 2-7.5μm; the relative refractive index difference of the fiber core Δ 1 Between 0.6-2.0%.

3. The eccentric rare earth doped optical fiber according to claim 1, It is characterized in that The maximum value of the distance between a point on the outer contour of the cross section of the core and the center of the outer contour of the eccentric inner cladding is p, 18 μm<p≤54 μm.

4. The eccentric rare earth doped optical fiber according to claim 3, It is characterized in that The degree of eccentricity of the core p / R 1 Satisfied: 0.3 <p / R 1 <0.90, where R 1 is the radius of the outer contour of the cross section of the eccentric inner cladding.

5. The eccentric rare earth doped optical fiber according to claim 4, It is characterized in that 0.45<p / R 1 ≤0.9 and 27μm<p≤54μm.

6. The eccentric rare earth doped optical fiber according to claim 5, It is characterized in that 0.6<p / R 1 ≤0.9 and 36μm <p≤54μm。 7. The eccentric rare earth doped optical fiber according to claim 3, It is characterized in that The thinnest thickness of the eccentric inner cladding is d = R 1 -p, 6μm<d<42μm.

8. The eccentric rare earth doped optical fiber according to claim 1, It is characterized in that The radius R of the eccentric inner cladding 1 Between 55-60μm.

9. The eccentric rare earth doped optical fiber according to claim 1, It is characterized in that The ratio of the cross-sectional area of ​​the core to the eccentric inner cladding is between (1-64):1000.

10. The eccentric rare earth doped optical fiber according to claim 1, It is characterized in that There are two points on the cross-sectional outer contour of the core that satisfy the following conditions: A. The distance between the two points is the maximum value of the distance between any two points on the outer contour of the cross section of the fiber core; B. The two points are collinear with the center of the outer contour of the eccentric inner cladding.

11. The eccentric rare earth doped optical fiber according to claim 1, It is characterized in that The cross section of the fiber core is a regular polygon with an odd number of sides. The axis of symmetry of the fiber core cross section is on the diameter of the outer contour of the eccentric inner cladding, and the point on the outer contour of the fiber core cross section that is farthest from the center of the outer contour of the eccentric inner cladding is on the axis of symmetry.

12. The eccentric rare earth doped optical fiber according to claim 1, It is characterized in that The fiber core is a regular polygon, and the number of sides of the regular polygon is between 4 and 8.

13. The eccentric rare earth doped optical fiber according to any one of claims 1 to 11, It is characterized in that The glass part has an outer cladding, which covers the outer side of the eccentric inner cladding; the refractive index of the outer cladding is lower than the refractive index of the eccentric inner cladding; the eccentric inner cladding is made of pure quartz, and the outer cladding is fluorine-doped quartz.

14. The eccentric rare earth doped optical fiber according to claim 13, It is characterized in that The geometric center of the outer contour of the cross section of the outer cladding coincides with the center of the outer contour of the eccentric inner cladding.

15. The eccentric rare earth doped optical fiber according to claim 13, It is characterized in that The radius R of the outer contour of the outer cladding 2 Between 61-75μm.

16. A use of the eccentric rare earth doped optical fiber according to any one of claims 1 to 15, It is characterized in that The eccentric rare earth doped optical fiber is used for preparing optical gain medium of optical fiber laser or optical fiber amplifier.

17. Use of the eccentric rare earth doped optical fiber as claimed in claim 16, It is characterized in that The eccentric rare earth doped optical fiber is used for preparing the cladding pump light gain medium of the optical fiber amplifier.

18. Use of the eccentric rare earth doped optical fiber according to claim 16 or 17, It is characterized in that The cross-sectional outer contour of the fiber core is a rectangle.

19. A fiber laser, It is characterized in that A cladding pump structure is adopted, and its cladding pump light gain medium is the eccentric rare-earth doped optical fiber as claimed in any one of claims 1 to 15.

20. An optical fiber amplifier, It is characterized in that A cladding pump structure is adopted, wherein the cladding pump light gain medium is the eccentric rare earth doped optical fiber as claimed in any one of claims 1 to 15, and the cross-sectional outer contour of the eccentric rare earth doped core is a rectangle.

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