Optical fiber amplifier with double-sideband resonance and in-band ASE suppression method

Abstract

The invention discloses a double-sideband resonance optical fiber amplifier and an in-band ASE suppression method. The optical fiber amplifier comprises a narrow-linewidth seed light source, a narrow-linewidth laser pre-amplification system, a main amplification system, a seventh single-mode optical fiber, a mode field adapter, a first large-mode-field optical fiber, a laser collimating lens and a transmission type diffraction grating. Final pre-amplified signal light output in the narrow linewidth laser pre-amplification system passes through an FBG of a first LWS resonant cavity, an FBG of a second LWS resonant cavity, an FBG of a first SWS resonant cavity and an FBG of a second SWS resonant cavity in the main amplification system, long-wave sideband laser and short-wave sideband laser are obtained respectively, a gain optical fiber of the main amplifier absorbs pump light, and the pump light is transmitted to the main amplification system. The pump light and the sideband laser are processed by the laser output end cap to obtain divergent laser beams; amplified signal laser is obtained through processing of the laser collimating lens and the transmission-type diffraction grating. According to the invention, the influence on signal laser gain is reduced to the greatest extent, and the method can be applied to a main amplification stage with higher power.

Description

Technical Field

[0001] The invention relates to the field of laser technology, and in particular to a double-sideband resonant optical fiber amplifier and a same-band ASE suppression method. Background Art

[0002] In the amplification process of narrow linewidth lasers, ASE (Amplified Spontaneous Emission), especially co-band ASE, is a major factor that seriously restricts the increase of amplifier power. Specifically, co-band ASE causes the laser spectrum contrast of the fiber amplifier to quickly reach saturation as the power increases. Further increasing the pump intensity may also lead to parasitic self-oscillation in the time domain, which will not only further reduce the spectral contrast, making the spectral profile more complex and unstable, but also easily cause damage to the gain fiber itself.

[0003] At present, the suppression of ASE in the same band mainly adopts spectral filtering technology. Apart from this, there are almost no other practical technologies used for its effective suppression. However, traditional spectral filtering devices of all-fiber can generally only be used in the pre-amplification stage of lower power, and there is still a lack of relevant technologies in the main amplification stage of higher power of hundreds of watts or even kilowatts. Summary of the invention

[0004] The technical problem to be solved by the present invention is: in order to solve the adverse effects of same-band ASE in the current high-power narrow-linewidth fiber amplifier, a double-sideband resonant fiber amplifier and a same-band ASE suppression method are provided to achieve laser amplification with high spectral contrast and low ASE level.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A double-sideband resonant optical fiber amplifier, comprising:

[0007] Narrow linewidth seed light source, narrow linewidth laser pre-amplification system, main amplification system, seventh single-mode optical fiber, mode field adapter, first large mode field optical fiber, laser collimating lens and transmission diffraction grating.

[0008] The output end of the narrow linewidth laser pre-amplification system is connected to one end of the mode field adapter through the seventh single-mode optical fiber, and the other end of the mode field adapter is connected to the input end of the main amplification system through the first large mode field optical fiber.

[0009] The input narrow linewidth seed light source is processed by the narrow linewidth laser pre-amplification system, the main amplification system and the mode field adapter to output a divergent laser beam, which is transmitted to the laser collimation lens for collimation to obtain a collimated beam. The collimated beam is separated by a transmission diffraction grating to obtain an amplified signal laser.

[0010] Furthermore, the narrow linewidth seed light source is an all-fiber structure narrow linewidth seed light source or a single-frequency semiconductor laser dual laser seed light source.

[0011] Furthermore, a narrow-linewidth laser pre-amplification system is used to provide narrow-linewidth optical power, and the system includes a first single-mode optical fiber, a second single-mode optical fiber, a third single-mode optical fiber, a fourth single-mode optical fiber, a fifth single-mode optical fiber, a sixth single-mode optical fiber, a first-stage pre-amplifier, a second-stage pre-amplifier, a third-stage pre-amplifier, a first bandpass filter, a second bandpass filter, and a third bandpass filter.

[0012] The narrow linewidth seed light source is connected to one end of the first-stage pre-amplifier through the first single-mode optical fiber, the other end of the first-stage pre-amplifier is connected to one end of the first band-pass filter through the second single-mode optical fiber, the other end of the first band-pass filter is connected to one end of the second-stage pre-amplifier through the third single-mode optical fiber, the other end of the second-stage pre-amplifier is connected to one end of the second band-pass filter through the fourth single-mode optical fiber, the other end of the second band-pass filter is connected to one end of the third-stage pre-amplifier through the fifth single-mode optical fiber, and the other end of the third-stage pre-amplifier is connected to one end of the third band-pass filter through the sixth single-mode optical fiber.

[0013] Furthermore, the main amplification system is used to achieve high-power laser output, and the system includes a second large mode field fiber, a third large mode field fiber, a fourth large mode field fiber, a fifth large mode field fiber, a sixth large mode field fiber, a seventh large mode field fiber, an eighth large mode field fiber, an FBG (Fiber Bragg Grating) of a first LWS (Long-wave Sideband) resonant cavity, an FBG of a second LWS resonant cavity, an FBG of a first SWS (Short-wave Sideband) resonant cavity, an FBG of a second SWS resonant cavity, a forward pump LD (Laser Diode), a reverse pump LD, a forward pump / signal combiner, a reverse pump / signal combiner, a main amplifier gain fiber and a laser output end cap.

[0014] The other end of the mode field adapter is connected to one end of the FBG of the first LWS resonant cavity through the first large mode field fiber, the other end of the FBG of the first LWS resonant cavity is connected to one end of the FBG of the first SWS resonant cavity through the second large mode field fiber, the other end of the FBG of the first SWS resonant cavity is connected to one end of the forward pump / signal combiner through the third large mode field fiber, one end of the forward pump / signal combiner is connected to one end of the forward pump LD through the multimode pigtail, and the other end of the forward pump / signal combiner is connected to one end of the main amplifier gain fiber through the fourth large mode field fiber , the other end of the main amplifier gain fiber is connected to one end of the reverse pump / signal combiner through the fifth large mode field fiber, one end of the reverse pump / signal combiner is connected to the reverse pump LD through the multimode pigtail, the other end of the reverse pump / signal combiner is connected to one end of the FBG of the second SWS resonant cavity through the sixth large mode field fiber, the other end of the FBG of the second SWS resonant cavity is connected to one end of the FBG of the second LWS resonant cavity through the seventh large mode field fiber, and the other end of the FBG of the second LWS resonant cavity is connected to one end of the laser output end cap through the eighth large mode field fiber.

[0015] Further, the FBG of the first LWS resonant cavity, the FBG of the second LWS resonant cavity, the FBG of the first SWS resonant cavity, and the FBG of the second SWS resonant cavity are all FBGs with a reflectivity greater than 99%.

[0016] Further, the FBG of the first LWS resonant cavity and the FBG of the first SWS resonant cavity are both FBGs with a reflectivity greater than 99%, and the FBG of the second LWS resonant cavity and the FBG of the second SWS resonant cavity are both FBGs with a reflectivity greater than 10%.

[0017] Furthermore, the single-mode optical fiber and the large-mode-area optical fiber are connected by fusion splicing.

[0018] Furthermore, the present invention also proposes a method for suppressing the same-band ASE of a double-sideband resonant optical fiber amplifier, comprising:

[0019] S1. Input a narrow linewidth seed light source into a narrow linewidth laser pre-amplification system, in which the signal light is transmitted in a single-mode form through a single-mode optical fiber, and sequentially passes through a first-stage pre-amplifier, a second-stage pre-amplifier, and a third-stage pre-amplifier, and performs primary, secondary, and tertiary pre-amplification, respectively. The first bandpass filter performs same-band ASE filtering on the signal light after the primary pre-amplification, the second bandpass filter performs same-band ASE filtering on the signal light after the secondary pre-amplification, and the third bandpass filter performs same-band ASE filtering on the signal light after the tertiary pre-amplification, to obtain the final pre-amplified signal light.

[0020] S2. The mode field adapter transitions the final pre-amplified signal light from the single-mode fiber to the large-mode field fiber with low loss. At this time, the final pre-amplified signal light enters the main amplification system. In this system, the final pre-amplified signal light is transmitted through the large-mode field fiber in the form of nearly single-mode and larger mode field. When the final pre-amplified signal light passes through the FBG of the first LWS resonant cavity and the FBG of the second LWS resonant cavity, a long-wave sideband laser is formed at the long-wave sideband. When the final pre-amplified signal light passes through the FBG of the first SWS resonant cavity and the FBG of the second SWS resonant cavity, a short-wave sideband laser is formed at the short-wave sideband, namely, LWS and SWS.

[0021] S3, the forward pump LD provides forward pump light, the reverse pump LD provides reverse pump light, the forward pump / signal combiner combines the forward pump light into the subsequent large mode area fiber, the reverse pump / signal combiner combines the reverse pump light into the previous large mode area fiber, the main amplifier gain fiber absorbs the pump light, the pump light and the sideband laser are processed by the laser output end cap to obtain a divergent laser beam.

[0022] S4. The divergent laser beam is collimated by a laser collimating lens to obtain a collimated beam. The collimated beam is separated by a transmission diffraction grating, and the LWS and SWS are filtered out to obtain the amplified SL (Signal Laser), thus completing the same-band ASE suppression.

[0023] Furthermore, the process of laser output end cap treatment is as follows: the sideband laser is transmitted in the quartz column for about 3-5 mm, the beam gradually diverges, and when it reaches the quartz / air interface, the beam diameter changes from 20-30 microns to more than 1 mm. The quartz / air interface is cut at an angle of 8° and coated with an anti-reflection film.

[0024] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0025] The sideband resonance of the present invention can effectively reduce the ASE ratio and improve the spectral contrast of SL, and the smaller gain of the sideband resonance can minimize the impact on the SL gain. In addition, the present invention can be applied to the main amplification stage with higher power, and is particularly suitable for ASE suppression in high-power amplifiers, and the present invention can be extended to various different wavelengths and different rare earth doped fiber amplifiers, including erbium-doped, ytterbium-doped, thulium-doped, holmium-doped and other fiber amplifiers. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is the overall structure diagram of the optical fiber amplifier of the present invention.

[0027] Figure 2 This is a typical position distribution diagram of SWS, SL and LWS on the erbium-doped fiber ASE spectrum according to an embodiment of the present invention.

[0028] Figure 3 Spectral distribution and shape characteristic diagram of SWS, SL and LWS according to an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0030] To achieve the above object, the present invention proposes a double-sideband resonant optical fiber amplifier, such as Figure 1 As shown, including:

[0031] Narrow linewidth seed light source, narrow linewidth laser pre-amplification system, main amplification system, seventh single-mode optical fiber 2g, mode field adapter 5, first large mode field optical fiber 6a, laser collimating lens 14 and transmission diffraction grating 16.

[0032] The output end of the narrow linewidth laser pre-amplification system is connected to one end of the mode field adapter 5 through the seventh single-mode optical fiber 2g, and the other end of the mode field adapter 5 is connected to the input end of the main amplification system through the first large mode field optical fiber 6a.

[0033] The input narrow linewidth seed light source is processed by the narrow linewidth laser pre-amplification system, the main amplification system and the mode field adapter 5, and a divergent laser beam 13 is output. The divergent laser beam 13 is transmitted to the laser collimating lens 14 for collimation to obtain a collimated light beam 15. The collimated light beam 15 is separated by a transmission diffraction grating 16, and the LWS (Long-wave Sideband) 17 and SWS (Short-wave Sideband) 19 are filtered out to obtain an amplified SL (Signal Laser) 18.

[0034] The narrow linewidth seed light source is an all-fiber structure narrow linewidth seed light source 1a or a single-frequency semiconductor laser dual laser seed light source 1b.

[0035] The narrow-linewidth laser pre-amplification system includes a first single-mode optical fiber 2a, a second single-mode optical fiber 2b, a third single-mode optical fiber 2c, a fourth single-mode optical fiber 2d, a fifth single-mode optical fiber 2e, a sixth single-mode optical fiber 2f, a first-stage pre-amplifier 3a, a second-stage pre-amplifier 3b, a third-stage pre-amplifier 3c, a first bandpass filter 4a, a second bandpass filter 4b and a third bandpass filter 4c, which are used to provide sufficient narrow-linewidth optical power for the main amplifier.

[0036] The main amplification system includes a second large mode field fiber 6b, a third large mode field fiber 6c, a fourth large mode field fiber 6d, a fifth large mode field fiber 6e, a sixth large mode field fiber 6f, a seventh large mode field fiber 6g, an eighth large mode field fiber 6h, an FBG (Fiber Bragg Grating) 7a of the first LWS resonant cavity, an FBG7b of the second LWS resonant cavity, an FBG8a of the first SWS resonant cavity, an FBG8b of the second SWS resonant cavity, a forward pump LDD (Laser Diode) 9a, a reverse pump LD9b, a forward pump / signal combiner 10a, a reverse pump / signal combiner 10b, a main amplifier gain fiber 11 and a laser output end cap 12, for achieving high-power laser output.

[0037] The all-fiber structure narrow linewidth seed light source 1a or the single-frequency semiconductor laser second laser seed light source 1b is connected to one end of the first stage preamplifier 3a through the first single-mode optical fiber 2a, the other end of the first stage preamplifier 3a is connected to one end of the first bandpass filter 4a through the second single-mode optical fiber 2b, the other end of the first bandpass filter 4a is connected to one end of the second stage preamplifier 3b through the third single-mode optical fiber 2c, the other end of the second stage preamplifier 3b is connected to one end of the second bandpass filter 4b through the fourth single-mode optical fiber 2d, and the other end of the second bandpass filter 4b is connected to one end of the second bandpass filter 4b through the fourth single-mode optical fiber 2d. The fifth single-mode optical fiber 2e is connected to one end of the third stage preamplifier 3c, the other end of the third stage preamplifier 3c is connected to one end of the third bandpass filter 4c through the sixth single-mode optical fiber 2f, the other end of the third bandpass filter 4c is connected to one end of the mode field adapter 5 through the seventh single-mode optical fiber 2g, the other end of the mode field adapter 5 is connected to one end of the FBG7a of the first LWS resonant cavity through the first large mode field optical fiber 6a, and the other end of the FBG7a of the first LWS resonant cavity is connected to one end of the FBG8a of the first SWS resonant cavity through the second large mode field optical fiber 6b The other end of FBG8a of the first SWS resonant cavity is connected to one end of the forward pump / signal combiner 10a through the third large mode field fiber 6c, one end of the forward pump / signal combiner 10a is connected to one end of the forward pump LD9a through the multimode pigtail, the other end of the forward pump / signal combiner 10a is connected to one end of the main amplifier gain fiber 11 through the fourth large mode field fiber 6d, the other end of the main amplifier gain fiber 11 is connected to one end of the reverse pump / signal combiner 10b through the fifth large mode field fiber 6e, and the reverse pump / signal combiner 10b One end of the reverse pump LD9b is connected to the reverse pump LD9b through a multimode pigtail, the other end of the reverse pump / signal combiner 10b is connected to one end of the FBG8b of the second SWS resonant cavity through the sixth large mode field fiber 6f, the other end of the FBG8b of the second SWS resonant cavity is connected to one end of the FBG7b of the second LWS resonant cavity through the seventh large mode field fiber 6g, the other end of the FBG7b of the second LWS resonant cavity is connected to one end of the laser output end cap 12 through the eighth large mode field fiber 6h, and the laser collimating lens 14 and the transmission diffraction grating 16 process the light beam.

[0038] The first single-mode optical fiber 2a, the second single-mode optical fiber 2b, the third single-mode optical fiber 2c, the fourth single-mode optical fiber 2d, the fifth single-mode optical fiber 2e and the sixth single-mode optical fiber 2f are generally the pigtails of the device, and they can be polarization-maintaining or non-polarization-maintaining, depending on the specific optical fiber system used.

[0039] FBG7a of the first LWS resonant cavity and FBG8a of the first SWS resonant cavity are both FBGs with a reflectivity greater than 99%, and FBG7b of the second LWS resonant cavity and FBG8b of the second SWS resonant cavity are both FBGs with a reflectivity greater than 10%.

[0040] Both single-mode optical fiber and large-mode-area optical fiber are connected by fusion splicing.

[0041] The sideband resonance is realized by the resonant cavity formed by the FBG pair whose central wavelength is at the gain edge. The sideband includes LWS and SWS, which are respectively at the long-wave edge and short-wave edge of the active fiber gain spectrum.

[0042] The working principle of the same-band ASE suppression method of the double-sideband resonant fiber amplifier is:

[0043] S1. Input the narrow linewidth seed light source into the narrow linewidth laser pre-amplification system, in which the signal light is transmitted in single-mode form through a single-mode optical fiber, and passes through the first-stage pre-amplifier 3a, the second-stage pre-amplifier 3b and the third-stage pre-amplifier 3c in sequence, and performs primary, secondary and tertiary pre-amplification respectively. The first bandpass filter 4a performs same-band ASE filtering on the signal light after the primary pre-amplification, the second bandpass filter 4b performs same-band ASE filtering on the signal light after the secondary pre-amplification, and the third bandpass filter 4c performs same-band ASE filtering on the signal light after the tertiary pre-amplification, to obtain the final pre-amplified signal light.

[0044] S2, the mode field adapter 5 transitions the final pre-amplified signal light from the single-mode optical fiber to the large-mode-field optical fiber with low loss. At this time, the final pre-amplified signal light enters the main amplification system, in which the final pre-amplified signal light is transmitted through the large-mode-field optical fiber in the form of nearly single-mode and larger mode field. When the final pre-amplified signal light passes through the FBG7a of the first LWS resonant cavity, it provides a high reflectivity (>99%) for the light at the long-wave sideband, and when it passes through the FBG7b of the second LWS resonant cavity, it provides a partial reflectivity (>10%) for the light at the long-wave sideband, forming a long-wave sideband laser, i.e., LWS, at the long-wave sideband. When it passes through the FBG8a of the first SWS resonant cavity, it provides a high reflectivity (>99%) for the light at the short-wave sideband, and when it passes through the FBG8b of the second SWS resonant cavity, it provides a partial reflectivity (>10%) for the light at the short-wave sideband, forming a short-wave sideband laser, i.e., SWS, at the short-wave sideband.

[0045] S3, forward pump LD9a provides forward pump light, reverse pump LD9b provides reverse pump light, forward pump / signal combiner 10a combines the forward pump light into the subsequent large mode area optical fiber, and reverse pump / signal combiner 10b combines the reverse pump light into the previous large mode area optical fiber. The pump light provides sufficient optical power and is further converted into signal light through the stimulated radiation process in the active optical fiber, thereby increasing the power of the signal light; the main amplifier gain fiber 11 absorbs the pump light to provide gain for LWS, SWS and SL. The pump light and sideband laser are processed by the laser output end cap 12 to reduce the power density at the quartz / air interface and avoid light reflection back into the amplifier to obtain a divergent laser beam 13.

[0046] S4. The divergent laser beam 13 is collimated by a laser collimating lens 14 to obtain a collimated beam 15. The collimated beam 15 is separated by a transmission diffraction grating 16, and the LWS 17 and SWS 19 are filtered out to obtain an amplified SL 18, thereby completing the same-band ASE suppression.

[0047] The processing process of the laser output end cap 12 is as follows: the sideband laser is transmitted in the quartz column for about 3-5 mm, and the light beam gradually diverges. When it reaches the quartz / air interface, the beam diameter can be changed from 20-30 microns to more than 1 mm. The quartz / air interface is generally cut at an angle of 8° and coated with an anti-reflection film to avoid backward reflection of light.

[0048] Figure 2 and Figure 3 The results of an implementation example based on an EDF (Erbium-doped Fiber) amplifier are given. Figure 2 The ASE spectrum of EDF is given. The EDF used is a polarization-maintaining single-mode fiber, specifically EDF50-PM EC, produced by OFS Fitel LLC. The center wavelength of the single-mode pump LD used in the measurement is 976nm, and the pump power is 100mW. The spectrometer model used for the spectrum measurement is AQ6374, produced by Yokogawa Electric Corporation. SL is at the center wavelength with a larger gain, while LWS and SWS are at the edge of ASE with a smaller gain.

[0049] Figure 3The seed light source used is a single-frequency semiconductor LD with a linewidth of <100kHz. The amplifier uses a 3m long polarization-maintaining erbium-ytterbium co-doped fiber as the gain fiber, and a 910nm multimode semiconductor LD as the pump source. The specific model of the gain fiber is DCF-EY-10 / 128-PM, produced by CorActive. The spectrometer model used for spectral measurement is AQ6374, produced by Yokogawa Electric Corporation. The central wavelengths of LWS, SL and SWS are at 1520.21, 1550.49 and 1580.92nm, respectively. The wavelength position and linewidth of LWS and SWS are determined by the inscribed FBG pair. Compared with the case where sideband resonance is not adopted, the spectral contrast of the center wavelength to ASE is increased from 37.643dB to 42.826dB.

[0050] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A double-sideband resonant optical fiber amplifier, characterized in that: include: A narrow linewidth seed light source, a narrow linewidth laser pre-amplification system, a main amplification system, a seventh single-mode optical fiber (2g), a mode field adapter (5), a first large mode field optical fiber (6a), a laser collimating lens (14) and a transmission diffraction grating (16); The main amplification system is used to realize high-power laser output, and the system includes a second large mode field fiber (6b), a third large mode field fiber (6c), a fourth large mode field fiber (6d), a fifth large mode field fiber (6e), a sixth large mode field fiber (6f), a seventh large mode field fiber (6g), an eighth large mode field fiber (6h), an FBG (7a) of a first LWS resonant cavity, an FBG (7b) of a second LWS resonant cavity, an FBG (8a) of a first SWS resonant cavity, an FBG (8b) of a second SWS resonant cavity, a forward pump LD (9a), a reverse pump LD (9b), a forward pump / signal combiner (10a), a reverse pump / signal combiner (10b), a main amplifier gain fiber (11), and a laser output end cap (12); The output end of the narrow line width laser pre-amplification system is connected to one end of the mode field adapter (5) through a seventh single-mode optical fiber (2g), and the other end of the mode field adapter (5) is connected to the input end of the main amplification system through a first large mode field optical fiber (6a); The input narrow line width seed light source is processed by a narrow line width laser pre-amplification system, a main amplification system and a mode field adapter (5) to output a divergent laser beam (13). The divergent laser beam (13) is transmitted to a laser collimating lens (14) for collimation to obtain a collimated light beam (15). The collimated light beam (15) is separated by a transmission diffraction grating (16) to obtain an amplified signal laser (18).

2. The double-sideband resonant optical fiber amplifier according to claim 1, characterized in that: The narrow line width seed light source is a narrow line width seed light source (1a) with an all-fiber structure or a single-frequency semiconductor laser dual laser seed light source (1b).

3. The double-sideband resonant optical fiber amplifier according to claim 1, characterized in that: The narrow linewidth laser pre-amplification system is used for providing narrow linewidth optical power, the system comprising a first single-mode optical fiber (2a), a second single-mode optical fiber (2b), a third single-mode optical fiber (2c), a fourth single-mode optical fiber (2d), a fifth single-mode optical fiber (2e), a sixth single-mode optical fiber (2f), a first-stage pre-amplifier (3a), a second-stage pre-amplifier (3b), a third-stage pre-amplifier (3c), a first band-pass filter (4a), a second band-pass filter (4b) and a third band-pass filter (4c); The narrow linewidth seed light source is connected to one end of a first-stage preamplifier (3a) through a first single-mode optical fiber (2a); the other end of the first-stage preamplifier (3a) is connected to one end of a first band-pass filter (4a) through a second single-mode optical fiber (2b); the other end of the first band-pass filter (4a) is connected to one end of a second-stage preamplifier (3b) through a third single-mode optical fiber (2c); the other end of the second-stage preamplifier (3b) is connected to one end of a second band-pass filter (4b) through a fourth single-mode optical fiber (2d); the other end of the second band-pass filter (4b) is connected to one end of a third-stage preamplifier (3c) through a fifth single-mode optical fiber (2e); and the other end of the third-stage preamplifier (3c) is connected to one end of a third band-pass filter (4c) through a sixth single-mode optical fiber (2f).

4. The double-sideband resonant optical fiber amplifier according to claim 1, characterized in that: The other end of the mode field adapter (5) is connected to one end of the FBG (7a) of the first LWS resonant cavity through the first large mode field optical fiber (6a), the other end of the FBG (7a) of the first LWS resonant cavity is connected to one end of the FBG (8a) of the first SWS resonant cavity through the second large mode field optical fiber (6b), the other end of the FBG (8a) of the first SWS resonant cavity is connected to one end of the forward pump / signal combiner (10a) through the third large mode field optical fiber (6c), one end of the forward pump / signal combiner (10a) is connected to one end of the forward pump LD (9a) through the multimode pigtail, and the other end of the forward pump / signal combiner (10a) is connected to one end of the main amplifier gain optical fiber (11) through the fourth large mode field optical fiber (6d). The other end of the main amplifier gain fiber (11) is connected to one end of the reverse pump / signal combiner (10b) through a fifth large mode field fiber (6e), one end of the reverse pump / signal combiner (10b) is connected to the reverse pump LD (9b) through a multimode pigtail, the other end of the reverse pump / signal combiner (10b) is connected to one end of the FBG (8b) of the second SWS resonant cavity through a sixth large mode field fiber (6f), the other end of the FBG (8b) of the second SWS resonant cavity is connected to one end of the FBG (7b) of the second LWS resonant cavity through a seventh large mode field fiber (6g), and the other end of the FBG (7b) of the second LWS resonant cavity is connected to one end of the laser output end cap (12) through an eighth large mode field fiber (6h).

5. The double-sideband resonant optical fiber amplifier according to claim 1, characterized in that: The FBG (7a) of the first LWS resonant cavity, the FBG (7b) of the second LWS resonant cavity, the FBG (8a) of the first SWS resonant cavity and the FBG (8b) of the second SWS resonant cavity are all FBGs with a reflectivity greater than 99%.

6. The double-sideband resonant optical fiber amplifier according to claim 1, characterized in that: The FBG (7a) of the first LWS resonant cavity and the FBG (8a) of the first SWS resonant cavity are FBGs with a reflectivity greater than 99%, and the FBG (7b) of the second LWS resonant cavity and the FBG (8b) of the second SWS resonant cavity are FBGs with a reflectivity greater than 10%.

7. The double-sideband resonant optical fiber amplifier according to claim 1, characterized in that: Both single-mode optical fiber and large-mode-area optical fiber are connected by fusion splicing.

8. The same-band ASE suppression method applied to the double-sideband resonant optical fiber amplifier of claim 1, characterized in that: include: S1. Input a narrow linewidth seed light source into a narrow linewidth laser pre-amplification system, in which the signal light is transmitted in a single-mode form through a single-mode optical fiber, and sequentially passes through a first-stage pre-amplifier, a second-stage pre-amplifier, and a third-stage pre-amplifier, and performs primary, secondary, and tertiary pre-amplification, respectively. The first bandpass filter performs same-band ASE filtering on the signal light after the primary pre-amplification, the second bandpass filter performs same-band ASE filtering on the signal light after the secondary pre-amplification, and the third bandpass filter performs same-band ASE filtering on the signal light after the tertiary pre-amplification, to obtain the final pre-amplified signal light; S2, the mode field adapter transitions the final pre-amplified signal light from the single-mode fiber to the large-mode field fiber with low loss. At this time, the final pre-amplified signal light enters the main amplification system, in which the final pre-amplified signal light is transmitted through the large-mode field fiber in the form of nearly single-mode and larger mode field. When the final pre-amplified signal light passes through the FBG of the first LWS resonant cavity and the FBG of the second LWS resonant cavity, a long-wave sideband laser is formed at the long-wave sideband. When the final pre-amplified signal light passes through the FBG of the first SWS resonant cavity and the FBG of the second SWS resonant cavity, a short-wave sideband laser is formed at the short-wave sideband. S3, the forward pump LD provides forward pump light, the reverse pump LD provides reverse pump light, the forward pump / signal combiner combines the forward pump light into the subsequent large mode area fiber, the reverse pump / signal combiner combines the reverse pump light into the preceding large mode area fiber, the main amplifier gain fiber absorbs the pump light, the pump light and the sideband laser are processed by the laser output end cap to obtain a divergent laser beam; S4. The divergent laser beam is collimated by a laser collimating lens to obtain a collimated beam. The collimated beam is separated by a transmission diffraction grating, and the long-wave sideband and the short-wave sideband are filtered out to obtain an amplified signal laser, thereby completing the same-band ASE suppression.

9. The method for suppressing same-band ASE in a double-sideband resonant optical fiber amplifier according to claim 8, characterized in that: The process of laser output end cap processing is as follows: the sideband laser is transmitted in the quartz column for about 3-5 mm, the beam gradually diverges, and when it reaches the quartz / air interface, the beam diameter changes from 20-30 microns to more than 1 mm. The quartz / air interface is cut at an 8° angle and coated with an anti-reflection film.

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