A high-power Raman fiber amplifier based on cladding pumping

Abstract

The invention belongs to the technical field of optical fiber lasers and provides a high-power Raman optical fiber amplifier based on cladding pumping, comprising a seed source (1), a high-power optical fiber laser pump source array (2), a pump signal combiner (3), a Raman optical fiber (4) and an end cap (5); the seed source (1) is a laser source of a signal light wavelength and is connected to a central signal arm of the pump signal combiner (3); the output arms of the high-power optical fiber laser pump source array (3) are respectively connected to the pump input arms of the pump signal combiner (3); the output end of the pump signal combiner (3) is connected to the Raman optical fiber (4), the other end of the Raman optical fiber (4) is connected to the end cap (5), and the Raman laser is output through the end cap (5); the Raman optical fiber (4) is a double-clad passive optical fiber; the output optical fiber of the pump signal combiner (3) and the pigtail of the end cap (5) are both double-clad passive optical fibers that are the same as the Raman optical fiber (4).

Description

Technical Field

[0001] The present invention generally belongs to the technical field of optical fiber lasers, and in particular relates to a high-power Raman optical fiber amplifier based on cladding pumping. Background Art

[0002] Most laser applications have strict requirements not only on laser power and wavelength, but also on brightness. Brightness is defined as the laser power emitted per unit area and per unit solid angle, and represents the ability of the beam to be focused. Generally speaking, for lasers with the same power, the higher the brightness, the better the beam quality and the better the effect. 2 The factor evaluates the quality of the laser beam. Its ideal value is 1, which corresponds to the fundamental mode in the optical fiber. The larger the value, the worse the beam quality.

[0003] Beam purification in cladding-pumped Raman fiber lasers refers to the generation of laser gain through stimulated Raman scattering in a double-cladding passive fiber, and the use of laser feedback or seed source in the core to make the Raman gain in the core dominant, thereby converting the low-brightness pump light transmitted in the cladding into a high-brightness signal light output transmitted in the core. Cladding-pumped Raman fiber lasers allow the use of higher-power but lower-brightness pump light, and can simultaneously achieve high-power, high-beam-quality laser output, with good beam purification effects.

[0004] At present, the all-fiber Raman fiber oscillator based on cladding pumping has achieved a 7-fold brightness improvement, with an output power of 1200W. However, the fiber oscillator requires special customization of fiber Bragg gratings based on double-clad fiber, which is expensive. The beam purification at high power is affected by temperature, and further brightness improvement is difficult. On the other hand, Raman fiber amplifiers that do not require fiber Bragg gratings have the potential for power amplification. However, the injection of seeds and pumps is based on a power combiner, and there is a lack of consideration for maintaining the brightness of the seed laser. After passing through the power combiner, the brightness of the seed drops severely, resulting in low brightness of the amplified laser and an unobvious beam purification effect. Summary of the invention

[0005] The purpose of the present invention is to maintain the seed brightness of the Raman fiber amplifier input and maximize the beam purification effect based on cladding pumping. Its main feature is that at the input end of the Raman fiber amplifier, a pump signal combiner is used to combine the pump laser and the seed laser, and the seed laser is connected to the central signal arm of the combiner, and the output fiber and the end cap pigtail of the pump signal combiner are both double-clad passive fibers that are the same as the Raman fiber. Since the output fiber and the end cap pigtail of the pump signal combiner are both double-clad passive fibers that are the same as the Raman fiber, there is no mode field mismatch at the fusion point, which is also conducive to maintaining the input laser brightness.

[0006] The technical solution of the present invention is a high-power Raman fiber amplifier based on cladding pumping, which includes a seed source, a high-power fiber laser pump source array, a pump signal combiner, a Raman fiber and an end cap; the seed source is a laser source of a signal light wavelength, which is connected to the central signal arm of the pump signal combiner; the output arms of the high-power fiber laser pump source array are respectively connected to the pump input arms of the pump signal combiner; the output end of the pump signal combiner is connected to the Raman fiber, the other end of the Raman fiber is connected to the end cap, and the Raman laser is output through the end cap, and the Raman fiber is a double-clad passive fiber; the output fiber of the pump signal combiner and the end cap pigtail are both double-clad passive fibers that are the same as the Raman fiber.

[0007] Furthermore, the high-power Raman fiber amplifier based on cladding pumping of the present invention includes a fiber Bragg grating, one end of which is connected to the fusion point between the output fiber of the pump signal combiner and the Raman fiber, and the other end is connected to the fusion point between the Raman fiber and the end cap, so that the fiber Bragg grating and the Raman fiber are connected in parallel between the pump signal combiner and the end cap.

[0008] Furthermore, the high-power Raman fiber amplifier based on cladding pumping of the present invention also includes a next-stage amplifier, which includes an isolator, a second high-power fiber laser pump source array, a second pump signal combiner and a second Raman fiber, wherein the output end of the Raman fiber is connected to the isolator input arm, the isolator output arm is connected to the second high-power fiber laser pump source array, the second pump signal combiner and the second Raman fiber in sequence, the output end of the second Raman fiber is connected to the end cap, and the function of the isolator is to prevent the backward return light of the next-stage amplifier from being damaged.

[0009] Furthermore, the seed source is one of a semiconductor laser, an ytterbium-doped fiber laser, and a Raman fiber laser, and the signal light wavelength thereof is located within the Raman gain spectrum corresponding to the wavelength of the high-power fiber laser pump source array, for example, the frequency shift is 13.2 THz, corresponding to the maximum Raman gain coefficient of the quartz fiber; the signal light beam quality factor M 2 Less than the laser beam quality factor M of high power fiber laser pump source array 2 , for example, M 2 Less than or equal to 3.

[0010] Furthermore, the high-power fiber laser pump source array is composed of one or more lasers, which are semiconductor lasers and / or ytterbium-doped fiber lasers; the wavelength range of the high-power fiber laser pump source array is between 0.9 microns and 1.1 microns.

[0011] Furthermore, the pump signal combiner is an end-pump combiner or a side-pump combiner, and its output optical fiber is the same as the Raman optical fiber, which is a double-clad passive optical fiber.

[0012] Furthermore, when the above-mentioned pump signal combiner is an end-pump pump signal combiner, the number of its input optical fibers is 7 or 19, one of which is a signal input arm, and the rest are pump input arms.

[0013] Furthermore, the signal input arm is located at the central arm of the tapered fiber bundle, the seed source is connected to the signal input arm, and the signal is output through the pump signal combiner, the seed source power loss is less than or equal to 90%, and the beam quality factor M 2 The degradation ratio is less than or equal to 50%.

[0014] Furthermore, when the pump signal combiner is a side pump signal combiner, the number of input optical fibers is 3, one of which is a signal input arm, and the other two are pump input arms. The seed source is connected to the signal input arm and output through the pump signal combiner. The power loss of the seed source is less than or equal to 90%, and the beam quality factor M 2 The degradation ratio is less than or equal to 50%.

[0015] Furthermore, the above-mentioned Raman optical fiber, pump signal combiner output optical fiber and end cap pigtail are all double-clad passive optical fibers, and the refractive index distribution of their cores is a step type or a gradient type with a square rate distribution, and their core-clad area ratio is less than or equal to 20, and the optimal value range is less than or equal to 8.

[0016] Furthermore, the above-mentioned double-clad passive optical fiber is a large mode field optical fiber with long-wave filtering function, and there is a low refractive index groove in the junction area between the core and the cladding, such as one or more of W-type optical fiber, single groove, and multiple groove type optical fiber.

[0017] The advantages of the present invention compared to the prior art are:

[0018] 1) By using double-clad passive fiber as Raman fiber and utilizing the stimulated Raman scattering effect therein, Raman gain can be generated and amplified, converting low-brightness pump light into high-brightness Raman laser output.

[0019] 2) Using a pump signal combiner, the seed source is connected to the central signal arm of the pump signal combiner so that the seed brightness is maintained.

[0020] 3) The output fiber of the pump signal combiner and the end cap pigtail are both double-clad passive fibers that are the same as the Raman fibers in the amplifier. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] These and / or other aspects and advantages of the present invention will become more clear and easier to understand from the following detailed description of the embodiments of the present invention in conjunction with the accompanying drawings, in which:

[0022] Figure 1A schematic diagram of the structure of a high-power Raman fiber amplifier based on cladding pumping according to the present invention;

[0023] Figure 2 It is a structural schematic diagram of the input optical fiber when the pump signal combiner of the high-power Raman optical fiber amplifier based on cladding pumping of the present invention is an end-pump pump signal combiner;

[0024] Figure 3 It is a schematic structural diagram of the input optical fiber when the pump signal combiner of the high-power Raman optical fiber amplifier based on cladding pumping of the present invention is a side pump pump signal combiner;

[0025] Figure 4 A schematic diagram of a single trench optical fiber in a high-power Raman optical fiber amplifier based on cladding pumping of the present invention;

[0026] Figure 5 It is a schematic structural diagram of the high-power Raman fiber amplifier based on cladding pumping of the present invention when it includes a fiber Bragg grating 8 connected in parallel with the Raman fiber;

[0027] Figure 6 The present invention is a schematic diagram of the structure of a Raman fiber amplifier including a next-stage amplifier structure in a high-power Raman fiber amplifier based on cladding pumping. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0029] Example 1

[0030] A high-power Raman fiber amplifier based on cladding pumping, the structure of which is as follows Figure 1 As shown, it includes a seed source 1, a high-power fiber laser pump source array 2, a pump signal combiner 3, a Raman fiber 4 and an end cap 5; the seed source 1 is a laser source of a signal light wavelength, which is connected to the central signal arm of the pump signal combiner 3; the output arms of the high-power fiber laser pump source array 2 are respectively connected to the pump input arms of the pump signal combiner 3; the output end of the pump signal combiner 3 is connected to the Raman fiber 4, the other end of the Raman fiber 4 is connected to the end cap 5, and the Raman laser is output through the end cap 5, and the Raman fiber 4 is a double-clad passive fiber; the output fiber of the pump signal combiner 3 and the pigtail of the end cap 5 are both double-clad passive fibers; the specific structure and characteristics of each part are as follows:

[0031] The seed source 1 is one of a semiconductor laser, an ytterbium-doped fiber laser, and a Raman fiber laser, and the wavelength of its signal light is within the Raman gain spectrum corresponding to the wavelength of the high-power fiber laser pump source array 2; the signal light beam quality factor M 2Less than the laser beam quality factor M of high power fiber laser pump source array 2 2 .

[0032] The high-power fiber laser pump source array 2 is composed of one or more lasers, which are semiconductor lasers and / or ytterbium-doped fiber lasers; the wavelength range of the high-power fiber laser pump source array 2 is between 0.9 microns and 1.1 microns.

[0033] The pump signal combiner 3 is an end-pump combiner or a side-pump combiner: When the pump signal combiner 3 is an end-pump combiner, its input optical fiber (such as Figure 2 The number of the optical fibers is 7 or 19, one of which is a signal input arm 6, and the rest are pump input arms. Preferably, the signal input arm 6 is located at the center arm of the tapered optical fiber bundle, the seed source 1 is connected to the signal input arm 6, and is output through the pump signal combiner 3. The power loss of the seed source 1 is less than or equal to 90%, and the beam quality factor M 2 The degradation ratio is less than or equal to 50%, and the optimal degradation ratio is less than or equal to 10%; when the pump signal combiner 3 is a side pump pump signal combiner, the number of input optical fibers (such as Figure 3 As shown in FIG. 3 , one of which is a signal input arm 6 and the other two are pump input arms. The seed source 1 is connected to the signal input arm 6 and outputted through the pump signal combiner 3. The power loss of the seed source is less than or equal to 90%. The beam quality factor M 2 The degradation ratio is less than or equal to 50%, and the optimal degradation ratio is less than or equal to 10%.

[0034] For seed source 1 power loss less than or equal to 90%, the beam quality factor M 2 The degradation ratio is less than or equal to 10%. According to the brightness calculation formula, the brightness is equal to the power divided by the beam quality factor M. 2 The square of the seed brightness degradation ratio is estimated to be less than or equal to 72.9%. For Raman fiber amplifiers, the conventional gain can reach 10-13dB, so the brightness of the seed output by the amplifier can be increased by 7.29-14.58 times compared with the seed source. Compared with the existing technology, it has a significant beam purification effect and has obvious technical progress.

[0035] The Raman fiber 4, the output fiber of the pump signal combiner 3 and the pigtail of the end cap 5 are all double-clad passive fibers, whose core-clad area ratio is less than or equal to 20, and whose core refractive index distribution is a step-type or a gradient type with a square rate distribution; the double-clad passive fiber can be a large mode field fiber with a long-wave filtering function, and there is a low refractive index groove in the interface area between the core and the cladding, such as W-type fiber, single groove, multiple groove type fiber (such as Figure 4 As shown, r is the fiber radius, n(r) is the fiber refractive index), etc.

[0036] Example 2

[0037] A high-power Raman fiber amplifier based on cladding pumping, the structure of which is as follows Figure 5 As shown, in addition to the components in the above-mentioned embodiment 1, it also includes a fiber grating 8, one end of which is connected to the fusion point between the output fiber of the pump signal combiner 3 and the Raman fiber 4, and the other end is connected to the fusion point between the Raman fiber 4 and the end cap 5, so that the fiber grating 8 and the Raman fiber 4 are connected in parallel between the pump signal combiner 3 and the end cap 5.

[0038] Example 3

[0039] A high-power Raman fiber amplifier based on cladding pumping, the structure of which is as follows Figure 6 As shown, in addition to the components in the above-mentioned embodiment 1 or 2, it includes a next-stage amplifier, which includes an isolator 9, a second high-power fiber laser pump source array 10, a second pump signal combiner 11 and a second Raman fiber 12. When the amplifier in embodiment 1 is used as a seed source, the output end of the Raman fiber 4 is connected to the input arm of the isolator 9, the output arm of the isolator 9 is connected to the central signal arm of the second pump signal combiner 11, the remaining pump arms of the second pump signal combiner 11 are connected to the second high-power fiber laser pump source array 10, and the output fiber of the second pump signal combiner 11 is sequentially connected to the second Raman fiber 12 and the end cap 5. The output fiber of the second pump signal combiner 11, the second Raman fiber 12 and the pigtail of the end cap 5 are all double-clad passive fibers of the same type. The function of the isolator 9 is to prevent the backward return light of the next stage amplifier from being damaged so as to perform cascade amplification; the high-power Raman fiber amplifier based on cladding pumping in Example 1 can be used as the seed source of the next stage amplifier for cascade amplification; when the amplifier based on Example 2 is used as the seed source, the input end of the isolator 9 is connected to the output end of the grating fiber 8, and the output end of the isolator 9 is connected to the central signal arm of the second pump signal combiner 11, and the connection method of the remaining components is the same.

[0040] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. Therefore, the scope of protection of the present invention should be subject to the scope of protection of the claims.

Claims

1. A high-power Raman fiber amplifier based on cladding pumping, characterized in that: It includes a seed source (1), a high-power fiber laser pump source array (2), a pump signal combiner (3), a Raman fiber (4) and an end cap (5); The seed source (1) is a laser source of the signal light wavelength, which is connected to the central signal arm of the pump signal combiner (3); The output arms of the high-power fiber laser pump source array (2) are respectively connected to the pump input arms of the pump signal combiner (3); The output end of the pump signal combiner (3) is connected to the Raman optical fiber (4), the other end of the Raman optical fiber (4) is connected to the end cap (5), and the Raman laser is output through the end cap (5), and the Raman optical fiber (4) is a double-clad passive optical fiber; The output optical fiber of the pump signal combiner (3) and the pigtail of the end cap (5) are both double-clad passive optical fibers that are the same as the Raman optical fiber (4); It also includes a fiber Bragg grating (8), one end of which is connected to the fusion point between the output fiber of the pump signal combiner (3) and the Raman fiber (4), and the other end of which is connected to the fusion point between the Raman fiber (4) and the end cap (5), so that the fiber Bragg grating (8) and the Raman fiber (4) are connected in parallel between the pump signal combiner (3) and the end cap (5); It also includes a next-stage amplifier, which includes an isolator (9), a second high-power fiber laser pump source array (10), a second pump signal combiner (11) and a second Raman fiber (12), wherein the output end of the Raman fiber (4) is connected to the input arm of the isolator (9), the output arm of the isolator (9) is connected to the second high-power fiber laser pump source array (10), the second pump signal combiner (11) and the second Raman fiber (12) in sequence, and the output end of the second Raman fiber (12) is connected to the end cap (5), and the function of the isolator (9) is to prevent the backward return light of the next-stage amplifier from being damaged; The pump signal combiner (3) is an end-pump combiner or a side-pump combiner, and its output optical fiber and the Raman optical fiber (4) are double-clad passive optical fibers of the same type.

2. The high-power Raman fiber amplifier based on cladding pumping according to claim 1, characterized in that: The seed source (1) is one of a semiconductor laser, an ytterbium-doped fiber laser, and a Raman fiber laser, and the wavelength of its signal light is within the Raman gain spectrum corresponding to the wavelength of the high-power fiber laser pump source array (2); the signal light beam quality factor M 2 Less than the laser beam quality factor M of the high power fiber laser pump source array (2) 2 .

3. The high-power Raman fiber amplifier based on cladding pumping according to claim 1, characterized in that: The high-power fiber laser pump source array (2) is composed of one or more lasers, wherein the lasers are semiconductor lasers and / or ytterbium-doped fiber lasers; the wavelength range of the high-power fiber laser pump source array (2) is between 0.9 microns and 1.1 microns.

4. The high-power Raman fiber amplifier based on cladding pumping according to claim 3, characterized in that: When the pump signal combiner (3) is an end-pump pump signal combiner, the number of its input optical fibers is 7 or 19, wherein the central fiber of the optical fiber bundle is the signal input arm (6), and the remaining optical fibers surrounding the central fiber are the pump input arms.

5. The high-power Raman fiber amplifier based on cladding pumping according to claim 4, characterized in that: The signal input arm (6) is located at the central arm of the tapered optical fiber bundle, the seed source (1) is connected to the signal input arm (6), and is output through the pump signal combiner (3). The beam quality factor M 2 The degradation ratio is less than or equal to 50%.

6. The high-power Raman fiber amplifier based on cladding pumping according to claim 3, characterized in that: When the pump signal combiner (3) is a side pump pump signal combiner, the number of its input optical fibers is 3, one of which is a signal input arm (6), and the other two are pump input arms. The seed source (1) is connected to the signal input arm (6) and is output through the pump signal combiner (3). The beam quality factor M 2 The degradation ratio is less than or equal to 50%.

7. The high-power Raman fiber amplifier based on cladding pumping according to claim 1, characterized in that: The Raman optical fiber (4), the output optical fiber of the pump signal combiner (3) and the pigtail of the end cap (5) are all double-clad passive optical fibers, the refractive index distribution of their cores is a step-type or a gradient type with a square rate distribution, and the core-clad area ratio is less than or equal to 20.

8. The high-power Raman fiber amplifier based on cladding pumping according to claim 1, characterized in that: The double-clad passive optical fiber is a large mode field optical fiber with long-wave filtering function. There is a low refractive index groove in the interface area between the core and the cladding. The low refractive index groove is one or more of W-type optical fiber, single groove, and multiple groove optical fiber.

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