CN118198839A - Double-ended dual-wavelength fiber laser - Google Patents

Abstract

The invention provides a double-end output dual-wavelength fiber laser, which comprises a high reflection fiber grating, a gain fiber, a low reflection fiber grating, a backward pumping beam combiner, a pumping source, a Raman high reflection fiber grating, a forward output end and a backward output end, wherein the pumping fiber of the backward pumping beam combiner is connected with the pumping source, and the high reflection fiber grating, the gain fiber and the low reflection fiber grating are sequentially connected to form a fiber laser resonant cavity; the Raman high-reflection fiber grating is positioned outside the fiber laser resonant cavity; the Raman high-reflection fiber grating is connected between the low-reflection fiber grating and the backward pumping beam combiner or between the backward pumping beam combiner and the forward output end. The invention utilizes the Raman high-reflection fiber grating to output Stokes light from the backward output end, and the signal light output by the fiber laser resonant cavity is output from the forward output end, thereby realizing double-end output of dual-wavelength laser.

Description

Double-ended dual-wavelength fiber laser

Technical Field

The invention mainly relates to the technical field of optical fiber laser, in particular to a double-end output dual-wavelength optical fiber laser.

Background technique

Fiber lasers have the advantages of high efficiency, compact structure, flexible operation, and low maintenance cost. They have gradually become the main light source in the fields of industrial manufacturing, energy environment, biomedicine, national defense and security. Fiber lasers have been widely used in various fields. How to reduce the cost, volume and weight of fiber lasers is a research focus of fiber lasers. Conventional near-single-mode fiber lasers generally use a resonant cavity, using high-reflection gratings and low-reflection gratings to form a resonant cavity, and using low-reflection fiber gratings to output lasers.

For all-fiber lasers with double-ended output, the basic idea of a current solution is to use low-reflection fiber Bragg gratings to replace high-reflection fiber Bragg gratings in ordinary resonant cavities, and achieve laser output at both ends of the laser. In this way, only one water-cooling structure, one resonant cavity, and one gain fiber are needed to realize the functions of two lasers, which greatly reduces the cost of the laser under the condition of equal output power and beam quality. However, the center wavelengths of the two gratings in the oscillator of this solution must be consistent, and the wavelengths of the laser output at both ends must be the same.

On the other hand, when the fiber laser oscillator is running at high power, nonlinear effects will occur through the action of the long optical fiber. Once the stimulated Raman scattering threshold is reached, the signal laser will undergo energy transfer and produce stimulated Raman laser, which will affect the spectral purity and beam quality of the strong output laser. At present, the common method to suppress the stimulated Raman scattering effect is to filter out the Raman laser through filtering devices such as chirped tilted fiber gratings. The disadvantage of this method is that it increases the cost and reduces the efficiency of the laser. At the same time, the power tolerance of the filtering device also limits the further increase of power.

Summary of the invention

In view of the cost control demand of fiber lasers and the stimulated Raman scattering problem faced by existing high-power fiber oscillators, the present invention proposes a dual-end output dual-wavelength fiber laser, which aims to remove the influence of stimulated Raman scattering effect, purify the spectrum of forward output laser, and at the same time output the Stokes light generated by stimulated Raman scattering effect from the backward direction, so that the fiber oscillator can achieve dual-end output of dual-wavelength laser.

To achieve the above purpose, the technical solution adopted by the present invention is as follows:

On the one hand, the present invention provides a double-end output dual-wavelength fiber laser, comprising a high-reflection fiber Bragg grating, a gain fiber, a low-reflection fiber Bragg grating, a backward pumping combiner, a pump source, a Raman high-reflection fiber Bragg grating, a forward output end and a backward output end, wherein the pump fiber of the backward pumping combiner is connected to the pump source, and the high-reflection fiber Bragg grating, the gain fiber, and the low-reflection fiber Bragg grating are connected in sequence to form a fiber laser resonant cavity; the Raman high-reflection fiber Bragg grating is located outside the fiber laser resonant cavity; the Raman high-reflection fiber Bragg grating is connected between the low-reflection fiber Bragg grating and the backward pumping combiner or the Raman high-reflection fiber Bragg grating is connected between the backward pumping combiner and the forward output end, wherein the central wavelength of the Raman high-reflection fiber Bragg grating is shifted down by 13.2 THz compared with the central wavelength of the low-reflection fiber Bragg grating, the bandwidth of the Raman high-reflection fiber Bragg grating is in the range of 10 nm to 40 nm, and the bandwidth of the Raman high-reflection fiber Bragg grating has no overlapping area with the bandwidth of the high-reflection fiber Bragg grating.

As a further improvement of the above technical solution:

Furthermore, the type of the pump source is not limited, and it can be a semiconductor laser, a fiber laser or other types of lasers. The wavelength of the pump source is not limited, and a semiconductor laser with a wavelength of 976nm, 915nm, 940nm or 981nm can be used, or the pump source can be a fiber laser with a wavelength of 1018nm.

Furthermore, the backward pump signal combiner is a (N+1)×1 pump signal combiner.

Furthermore, it also includes a forward pump combiner, which adopts a bidirectional pumping structure, and the forward pump combiner is a (N+1)×1 pump signal combiner.

Furthermore, the central wavelengths of the high-reflection fiber Bragg grating and the low-reflection fiber Bragg grating are the same, or the central wavelengths of the high-reflection fiber Bragg grating and the low-reflection fiber Bragg grating differ within a range of 0.4 nm.

Furthermore, the length of the gain fiber is determined according to the pump absorption, and generally ranges from a few meters to tens of meters.

Furthermore, the type of gain fiber is not limited to step-index distribution fiber, and may be other refractive index distribution fibers, such as graded-index fiber, partially doped fiber, W-type fiber, and the like.

Compared with the prior art, the present invention can produce the following technical effects:

The double-ended output dual-wavelength fiber laser provided by the present invention does not need to overcome the stimulated Raman scattering effect in the high-power fiber oscillator, but instead utilizes it so that the signal laser and the Stokes wavelength laser are output from the two ends of the laser respectively. When the fiber laser oscillator is running at high power, when the stimulated Raman scattering threshold is reached, bidirectionally transmitted Stokes light will be generated, and the wavelength frequency shift is about 13.2THz. The central wavelength of the Raman high-reflection grating is the Stokes wavelength, and the central wavelength of the Raman high-reflection fiber grating is shifted down by 13.2THz compared with the central wavelength of the low-reflection fiber grating. The Raman high-reflection fiber grating has no area that overlaps with the high-reflection fiber grating bandwidth. Therefore, the signal wavelength output by the laser oscillator can be output from the forward output end through the Raman high-reflection fiber grating without loss, and at the same time, the Raman high-reflection fiber grating can reflect the forward-transmitted Stokes light to the backward direction, and the Stokes light can also be output from the backward output end through the fiber laser resonant cavity without loss, thus realizing the double-ended output dual-wavelength laser.

The double-ended dual-wavelength fiber laser provided by the present invention can generate two wavelengths of laser light at the same time without additional design, thereby reducing the number of pump sources. The dual-wavelength laser light can utilize the existing incoherent synthesis technology/spectral synthesis to synthesize a higher brightness laser light, thereby increasing the laser output power. This method can improve the laser conversion efficiency and greatly reduce the cost of high-power fiber lasers.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

FIG1 is a schematic diagram of the structure of a double-end output dual-wavelength fiber laser provided in one embodiment of the present invention;

FIG2 is a schematic diagram of the structure of a double-end output dual-wavelength fiber laser provided in one embodiment of the present invention;

FIG3 is a schematic diagram of the structure of a double-end output dual-wavelength fiber laser provided in one embodiment of the present invention;

FIG4 is a schematic diagram of the structure of a double-end output dual-wavelength fiber laser provided in one embodiment of the present invention;

FIG5 is a schematic diagram of the structure of a double-end output dual-wavelength fiber laser provided in one embodiment of the present invention;

Numbers in the figure:

1. High-reflection fiber Bragg grating; 2. Gain fiber; 3. Low-reflection fiber Bragg grating; 4. Backward pump combiner; 5. Pump source; 6. Raman high-reflection fiber Bragg grating; 7. Forward output end; 8. Backward output end; 9. Forward pump combiner; 10. Amplifier stage optical path.

Detailed ways

The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Referring to Fig. 1, an embodiment provides a double-end output dual-wavelength fiber laser, including a high-reflection fiber Bragg grating 1, a gain fiber 2, a low-reflection fiber Bragg grating 3, a backward pumping combiner 4, a pump source 5, a Raman high-reflection fiber Bragg grating 6, a forward output end 7 and a backward output end 8, wherein the pump fiber of the backward pumping combiner 4 is connected to the pump source 5, the high-reflection fiber Bragg grating 1, the gain fiber 2, and the low-reflection fiber Bragg grating 3 are sequentially connected to form a fiber laser resonant cavity; the Raman high-reflection fiber Bragg grating 6 is located outside the fiber laser resonant cavity; the Raman high-reflection fiber Bragg grating 6 is connected between the backward pumping combiner 4 and the forward output end 7, and the high-reflection fiber Bragg grating 1 is connected to the backward output end 8. The forward output end 7 and the backward output end 8 both use fiber end caps. The central wavelength of the Raman high-reflection fiber Bragg grating 6 is shifted down by 13.2 THz compared with the central wavelength of the low-reflection fiber Bragg grating 3, the bandwidth of the Raman high-reflection fiber Bragg grating 3 is in the range of 10nm to 40nm, and the bandwidth of the Raman high-reflection fiber Bragg grating 6 has no overlapping area with the bandwidth of the high-reflection fiber Bragg grating 1.

2, an embodiment provides a double-end output dual-wavelength fiber laser, including a high-reflection fiber Bragg grating 1, a gain fiber 2, a low-reflection fiber Bragg grating 3, a backward pumping combiner 4, a pump source 5, a Raman high-reflection fiber Bragg grating 6, a forward output end 7 and a backward output end 8, wherein the pump fiber of the backward pumping combiner 4 is connected to the pump source 5, the high-reflection fiber Bragg grating 1, the gain fiber 2, and the low-reflection fiber Bragg grating 3 are sequentially connected to form a fiber laser resonant cavity; the Raman high-reflection fiber Bragg grating 6 is located outside the fiber laser resonant cavity; the Raman high-reflection fiber Bragg grating 6 is connected between the low-reflection fiber Bragg grating 3 and the backward pumping combiner 4, and the high-reflection fiber Bragg grating 1 is connected to the backward output end 8. The forward output end 7 and the backward output end 8 both use fiber end caps. Among them, the Raman high-reflection fiber Bragg grating 6 adopts a chirped Bragg grating. According to the Raman gain spectrum of the quartz fiber, the central wavelength of the Raman high-reflection fiber Bragg grating 6 should be shifted down by 13.2 THz compared with the central wavelength of the low-reflection fiber Bragg grating 3. According to the power and spectral characteristics of the laser output, the bandwidth of the Raman high-reflection fiber Bragg grating 3 can be in the range of 10nm to 40nm, and the bandwidth of the Raman high-reflection fiber Bragg grating 6 has no overlapping area with the bandwidth of the high-reflection fiber Bragg grating 1.

3, an embodiment provides a double-end output dual-wavelength fiber laser, including a forward pump combiner 9, a high-reflection fiber Bragg grating 1, a gain fiber 2, a low-reflection fiber Bragg grating 3, a backward pump combiner 4, a pump source 5, a Raman high-reflection fiber Bragg grating 6, a forward output end 7 and a backward output end 8. The pump fiber of the backward pump combiner 4 is connected to the pump source 5, the high-reflection fiber Bragg grating 1, the gain fiber 2, and the low-reflection fiber Bragg grating 3 are connected in sequence to form a fiber laser resonant cavity; the Raman high-reflection fiber Bragg grating 6 is located outside the fiber laser resonant cavity; the Raman high-reflection fiber Bragg grating 6 is connected between the backward pump combiner 4 and the forward output end 7. The pump fiber of the forward pump combiner 9 is connected to the pump source 5, the signal fiber on one side of the forward pump combiner 9 is connected to the high-reflection fiber Bragg grating 1, and the signal fiber on the other side of the forward pump combiner 9 is connected to the backward output end 8. The forward output end 7 and the backward output end 8 both use fiber end caps. The central wavelength of the Raman high-reflection fiber grating 6 is shifted down by 13.2 THz compared with the central wavelength of the low-reflection fiber grating 3, the bandwidth of the Raman high-reflection fiber grating 3 is in the range of 10nm to 40nm, and the bandwidth of the Raman high-reflection fiber grating 6 has no overlapping area with the bandwidth of the high-reflection fiber grating 1.

4, an embodiment provides a double-end output dual-wavelength fiber laser, including a forward pump combiner 9, a high-reflection fiber Bragg grating 1, a gain fiber 2, a low-reflection fiber Bragg grating 3, a backward pump combiner 4, a pump source 5, a Raman high-reflection fiber Bragg grating 6, a forward output end 7 and a backward output end 8. The pump fiber of the backward pump combiner 4 is connected to the pump source 5, the high-reflection fiber Bragg grating 1, the gain fiber 2, and the low-reflection fiber Bragg grating 3 are connected in sequence to form a fiber laser resonant cavity; the Raman high-reflection fiber Bragg grating 6 is located outside the fiber laser resonant cavity; the Raman high-reflection fiber Bragg grating 6 is connected between the low-reflection fiber Bragg grating 3 and the backward pump combiner 4. The pump fiber of the forward pump combiner 9 is connected to the pump source 5, the signal fiber on one side of the forward pump combiner 9 is connected to the high-reflection fiber Bragg grating 1, and the signal fiber on the other side of the forward pump combiner 9 is connected to the backward output end 8. The forward output end 7 and the backward output end 8 both use fiber end caps. Among them, the Raman high-reflection fiber Bragg grating 6 adopts a chirped Bragg grating. According to the Raman gain spectrum of the quartz fiber, the central wavelength of the Raman high-reflection fiber Bragg grating 6 should be shifted down by 13.2 THz compared with the central wavelength of the low-reflection fiber Bragg grating 3. According to the power and spectral characteristics of the laser output, the bandwidth of the Raman high-reflection fiber Bragg grating 3 can be in the range of 10nm to 40nm, and the bandwidth of the Raman high-reflection fiber Bragg grating 6 has no overlapping area with the bandwidth of the high-reflection fiber Bragg grating 1.

5, an embodiment provides a double-end output dual-wavelength fiber laser, including a backward output end 8, an amplifying stage optical path 10, a forward pumping combiner 9, a high-reflection fiber grating 1, a gain fiber 2, a low-reflection fiber grating 3, a backward pumping combiner 4, a Raman high-reflection fiber grating 6, and a forward output end 7 connected in sequence. The pump fiber of the backward pumping combiner 4 is connected to a pump source 5, and the high-reflection fiber grating 1, the gain fiber 2, and the low-reflection fiber grating 3 are connected in sequence to form a fiber laser resonant cavity; the Raman high-reflection fiber grating 6 is located outside the fiber laser resonant cavity. The Raman high-reflection fiber grating 6 is connected between the backward pumping combiner 4 and the forward output end 7. The pump fiber of the forward pump combiner 9 is connected to the pump source 5, the signal fiber on one side of the forward pump combiner 9 is connected to the high-reflection fiber grating 1, and the signal fiber on the other side of the forward pump combiner 9 is connected to one end of the amplifier stage optical path 10, and the amplifier stage optical path 10 includes more than one amplifier stage, and each amplifier stage includes a gain fiber for realizing power amplification. The other end of the amplifier stage optical path 10 is connected to the backward output end 8. The forward output end 7 and the backward output end 8 both use fiber end caps. The gain fiber of the amplifier stage optical path 10 can use quartz fiber or doped fiber. Among them, the Raman high-reflection fiber grating 6 uses a chirped Bragg grating. According to the Raman gain spectrum of the quartz fiber, the central wavelength of the Raman high-reflection fiber grating 6 should be shifted down by 13.2 THz compared with the central wavelength of the low-reflection fiber grating 3. According to the power and spectral characteristics of the laser output, the bandwidth of the Raman high-reflection fiber Bragg grating 3 may be in the range of 10 nm to 40 nm, and the bandwidth of the Raman high-reflection fiber Bragg grating 6 has no overlap with the bandwidth of the high-reflection fiber Bragg grating 1 .

The stimulated Raman scattering effect in the fiber laser is undesirable. When the bandwidth of the low-reflection fiber Bragg grating 3 is narrow, the stimulated Raman scattering threshold will be greatly reduced. When the threshold of stimulated Raman scattering is reached, the energy of the signal light will be transferred to the Raman Stokes light. When the laser is output, the forward-transmitted Raman Stokes light is transformed into backward transmission through the reflection of the Raman high-reflection grating. Only the signal light is output forward. The fiber Bragg grating of the resonant cavity has no loss to the Raman wavelength, and the Stokes light is output backward. When the Stokes light power is weak, the structure provided in the embodiment of Figure 5 can be adopted. After one-stage amplification or multiple-stage amplification, the gain fiber can be a quartz fiber or a doped fiber. This method can regulate the output power at both ends of the laser and increase the efficiency of spectral synthesis.

In any of the above embodiments, the backward pump combiner 4 is an N+1×1 pump signal combiner, including N pump fibers, and each pump fiber of the backward pump combiner 4 is connected to a pump source 5 .

In the above embodiment, if bidirectional pumping is adopted, that is, in the embodiment including the forward pump combiner 9, the forward pump combiner 9 is an N+1×1 pump signal combiner, including N pump fibers, and each pump fiber of the forward pump combiner 9 is respectively connected to a pump source 5.

In any of the above embodiments, the type of the pump source is not limited, and may be a semiconductor laser or a fiber laser.

In any of the above embodiments, the length of the gain fiber in the fiber laser resonant cavity is determined according to pump absorption, and generally ranges from several meters to tens of meters.

In any of the above embodiments, the wavelength of the pump source is not limited. If the pump source uses a semiconductor laser with a wavelength of 976nm, 915nm, 940nm or 981nm, the gain fiber in the fiber laser resonant cavity is tens of meters of ytterbium-doped fiber. Or if the pump source uses a fiber laser with a wavelength of 1018nm, the gain fiber in the fiber laser resonant cavity is tens of meters of ytterbium-doped fiber.

Furthermore, the type of gain fiber in the fiber laser resonant cavity is not limited to step-index distribution fiber, but may be other refractive index distribution fibers, such as graded-index fiber, partially doped fiber, W-type fiber, and the like.

In any of the above embodiments, the central wavelengths of the high-reflection fiber Bragg grating and the low-reflection fiber Bragg grating are the same, or the central wavelengths of the high-reflection fiber Bragg grating and the low-reflection fiber Bragg grating differ within a range of 0.4 nm.

In any of the above embodiments, the gain fiber in the fiber laser resonant cavity is an ytterbium-doped fiber or other types of doped fibers.

The key to any of the above embodiments of the present invention is to introduce a Raman high-reflection grating in the fiber laser oscillator, and output the forward-transmitted Stokes light in the fiber laser resonant cavity from the backward output of the oscillator. During the backward transmission process, the Raman Stokes light will not affect the resonant cavity. The central wavelength of the grating pair of the resonant cavity determines the central wavelength of the forward signal laser. According to the Raman gain spectrum of the quartz fiber, the frequency shift when the gain coefficient is maximum is about 13.2THz. For example, in an ytterbium-doped fiber laser with a signal laser wavelength of 1080nm, the Raman wavelength is about 1133nm, and the grating bandwidth of the resonant cavity is usually below 4nm. Therefore, the resonant cavity will not cause loss or other effects on the transmission of Raman Stokes light. On the other hand, when the fiber oscillator generates stimulated Raman scattering, the Raman Stokes light is transmitted bidirectionally, which means that the backward-transmitted Raman Stokes light will not affect the operation of the resonant cavity itself.

The embodiment shown in FIG. 1 or FIG. 2 is used to provide a double-end output dual-wavelength fiber laser, and a backward pumping structure is adopted. The backward Raman light power carried by the high-reflection fiber grating 1 is relatively high, and the preparation process of the femtosecond laser writing grating can be used to improve the grating power carrying capacity.

When the double-end output dual-wavelength fiber laser provided by the embodiment shown in FIG. 3 or FIG. 4 is used and a bidirectional pumping structure is adopted, the forward pump signal combiner will carry a higher Raman optical power. In order to prevent the Raman light of the combiner signal fiber from leaking into the pump fiber and affecting the pump source, the anti-back reflection capability of the pump source should be considered.

By using the double-end output dual-wavelength fiber laser provided by the embodiment shown in FIG5 , even if the stimulated Raman effect of the original oscillator is very weak or the power of the reflected backward Raman light is very low, the power of the backward Raman light can be increased by amplification. In this process, the Raman light output backward by the fiber oscillator is equivalent to the seed signal and will not affect the resonant cavity, thereby greatly enhancing the stability and reliability of the system.

Matters not covered by the present invention are known technologies.

The technical features of the above embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims (10)

1. A double-end output dual-wavelength fiber laser, characterized in that it comprises a high-reflection fiber Bragg grating (1), a gain fiber (2), a low-reflection fiber Bragg grating (3), a backward pumping combiner (4), a pump source (5), a Raman high-reflection fiber Bragg grating (6), a forward output end (7) and a backward output end (8), wherein the pump fiber of the backward pumping combiner (4) is connected to the pump source (5), the high-reflection fiber Bragg grating (1), the gain fiber (2) and the low-reflection fiber Bragg grating (3) are connected in sequence to form a fiber laser resonant cavity; the Raman high-reflection fiber Bragg grating (6) Located outside the fiber laser resonant cavity; the Raman high-reflection fiber grating (6) is connected between the low-reflection fiber grating (3) and the backward pumping combiner (4) or the Raman high-reflection fiber grating (6) is connected between the backward pumping combiner (4) and the forward output end (7), wherein the central wavelength of the Raman high-reflection fiber grating is shifted down by 13.2 THz compared with the central wavelength of the low-reflection fiber grating, the bandwidth of the Raman high-reflection fiber grating is in the range of 10 nm to 40 nm, and the bandwidth of the Raman high-reflection fiber grating does not overlap with the bandwidth of the high-reflection fiber grating. 2. The double-end output dual-wavelength fiber laser according to claim 1, characterized in that the high-reflection fiber grating (1) is connected to the backward output end (8). 3. The double-end output dual-wavelength fiber laser according to claim 1 or 2, characterized in that it also includes a forward pump combiner (9), the pump fiber of the forward pump combiner (9) is connected to a pump source (5), the signal fiber on one side of the forward pump combiner (9) is connected to the high-reflection fiber grating (1), and the signal fiber on the other side of the forward pump combiner (9) is connected to the backward output end (8). 4. The double-end output dual-wavelength fiber laser according to claim 3, characterized in that the forward pump combiner (9) is a (N+1)×1 pump signal combiner, comprising N pump fibers, and each pump fiber of the forward pump combiner (9) is respectively connected to a pump source (5). 5. The double-end output dual-wavelength fiber laser according to claim 2, characterized in that the backward pumping combiner (4) is a (N+1)×1 pump signal combiner, comprising N pump fibers, and each pump fiber of the backward pumping combiner (4) is respectively connected to a pump source (5). 6. The double-end output dual-wavelength fiber laser according to claim 1, 2, 4 or 5, characterized in that the pump source is a semiconductor laser or a fiber laser. 7. The double-end output dual-wavelength fiber laser according to claim 6, characterized in that the central wavelengths of the high-reflection fiber Bragg grating and the low-reflection fiber Bragg grating are the same, or the central wavelengths of the high-reflection fiber Bragg grating and the low-reflection fiber Bragg grating differ within a range of 0.4 nm. 8 . The double-end output dual-wavelength fiber laser according to claim 1 , wherein the gain fiber is an ytterbium-doped fiber. 9. The double-end output dual-wavelength fiber laser according to claim 1, characterized in that the pump source adopts a semiconductor laser with a wavelength of 976nm, 915nm, 940nm or 981nm, or the pump source adopts a fiber laser with a wavelength of 1018nm. 10 . The double-end output dual-wavelength fiber laser according to claim 1 , wherein the backward output end is connected to an amplifier stage optical path.