CN107516811A - Fiber amplifier and multi-stage fiber amplifier system - Google Patents
Fiber amplifier and multi-stage fiber amplifier system Download PDFInfo
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- CN107516811A CN107516811A CN201710919175.6A CN201710919175A CN107516811A CN 107516811 A CN107516811 A CN 107516811A CN 201710919175 A CN201710919175 A CN 201710919175A CN 107516811 A CN107516811 A CN 107516811A
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- 239000000835 fiber Substances 0.000 title claims abstract description 167
- 239000013307 optical fiber Substances 0.000 claims abstract description 149
- 238000005086 pumping Methods 0.000 claims abstract description 51
- 230000008878 coupling Effects 0.000 claims abstract description 4
- 238000010168 coupling process Methods 0.000 claims abstract description 4
- 238000005859 coupling reaction Methods 0.000 claims abstract description 4
- 238000000605 extraction Methods 0.000 claims description 5
- 230000009022 nonlinear effect Effects 0.000 abstract description 10
- 230000009103 reabsorption Effects 0.000 abstract description 7
- 238000000926 separation method Methods 0.000 abstract 1
- 230000003321 amplification Effects 0.000 description 19
- 238000003199 nucleic acid amplification method Methods 0.000 description 19
- 238000010521 absorption reaction Methods 0.000 description 10
- 238000010586 diagram Methods 0.000 description 10
- 230000009102 absorption Effects 0.000 description 9
- 238000005253 cladding Methods 0.000 description 7
- 230000005281 excited state Effects 0.000 description 6
- -1 rare earth ion Chemical class 0.000 description 5
- 150000002500 ions Chemical class 0.000 description 4
- 239000002245 particle Substances 0.000 description 4
- 238000004064 recycling Methods 0.000 description 4
- 230000007704 transition Effects 0.000 description 4
- 238000001069 Raman spectroscopy Methods 0.000 description 3
- 230000005855 radiation Effects 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- 229910052769 Ytterbium Inorganic materials 0.000 description 2
- 230000009471 action Effects 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 239000002019 doping agent Substances 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 230000010287 polarization Effects 0.000 description 2
- 229910052691 Erbium Inorganic materials 0.000 description 1
- 229910052689 Holmium Inorganic materials 0.000 description 1
- 229910052775 Thulium Inorganic materials 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000004927 fusion Effects 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- QEFYFXOXNSNQGX-UHFFFAOYSA-N neodymium atom Chemical compound [Nd] QEFYFXOXNSNQGX-UHFFFAOYSA-N 0.000 description 1
- 230000010355 oscillation Effects 0.000 description 1
- 229910052761 rare earth metal Inorganic materials 0.000 description 1
- 238000004904 shortening Methods 0.000 description 1
- NAWDYIZEMPQZHO-UHFFFAOYSA-N ytterbium Chemical compound [Yb] NAWDYIZEMPQZHO-UHFFFAOYSA-N 0.000 description 1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/06—Construction or shape of active medium
- H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
- H01S3/067—Fibre lasers
- H01S3/06754—Fibre amplifiers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/06—Construction or shape of active medium
- H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
- H01S3/067—Fibre lasers
- H01S3/06754—Fibre amplifiers
- H01S3/06758—Tandem amplifiers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/09—Processes or apparatus for excitation, e.g. pumping
- H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
- H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
- H01S3/094003—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light the pumped medium being a fibre
- H01S3/094015—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light the pumped medium being a fibre with pump light recycling, i.e. with reinjection of the unused pump light back into the fiber, e.g. by reflectors or circulators
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- Electromagnetism (AREA)
- Engineering & Computer Science (AREA)
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- Sustainable Development (AREA)
- Lasers (AREA)
Abstract
The invention provides a kind of fiber amplifier, including：Pumping coupler, gain fibre and pumping feedback device；Wherein, the pumping coupler is used for coupling pump light to the gain fibre；The length of the gain fibre is less than preset length, wherein, the preset length is the length that the fiber amplifier reaches corresponding gain fibre during maximum extracted efficiency；The pumping feedback device is used to be back to the pumping coupler by the remnant pump light and separation by laser in the gain fibre, and by the remnant pump light.In the present invention, by the way that the length of gain fibre is set smaller than into preset length, effectively suppress the generation of nonlinear effect, reduce reabsorption of the gain fibre to seed optical fiber.Meanwhile the remnant pump light obtained after the length of gain fibre is shortened using pumping feedback device is back in pumping coupler, improves the pumping efficiency of fiber amplifier, and then realize the high-power output of fiber amplifier.
Description
Technical Field
The present invention relates to the field of laser technology, and more particularly, to an optical fiber amplifier and a multi-stage optical fiber amplifier system.
Background
Fiber lasers are receiving increasing attention for their superior characteristics, such as excellent beam quality, high power and power density, ease of cooling, high stability and reliability, etc., and are widely used in a variety of fields.
At present, when the output of a high-power laser is realized, a high-power optical fiber amplifier structure is generally adopted. In fiber amplifiers, it is often desirable to have sufficient pump absorption to achieve maximum pump utilization, and sufficient pump absorption means that a longer gain fiber is required. The existing optical fiber amplifier mainly comprises a pumping source, a pumping coupler and a gain optical fiber, wherein the length of the gain optical fiber is usually obtained by theoretical calculation, and is usually the length of the corresponding gain optical fiber when the optical fiber amplifier reaches the maximum extraction efficiency, which is also called as a preset length. The adoption of the gain fiber with the preset length can ensure that the fiber amplifier realizes the maximum pumping utilization rate, but the adopted gain fiber has longer length, which can bring about extremely serious nonlinear effect, especially in the high-power fiber amplificationIn the device. Therefore, in the development of high power optical fiber amplifiers, the nonlinear effect becomes an important bottleneck to the development. Specifically, the formula of the stimulated Raman scattering threshold value in the optical fiber is as followsWherein, Pth1Is a stimulated Raman scattering threshold, AeffIs the effective cross-sectional area of the core of the optical fiber, LeffIs the effective length of the optical fiber, gRIs the raman gain constant. The formula of the threshold value of the stimulated Brillouin scattering in the optical fiber isWherein, Pth2Is the stimulated Brillouin scattering threshold, K is the polarization factor, AeffIs the effective cross-sectional area, g, of the core of the optical fiberBIs the Brillouin gain constant, LeffIs the effective length of the optical fiber. The above two formulas can intuitively show that each nonlinear effect threshold is inversely proportional to the effective length of the optical fiber, so if the length of the gain optical fiber is increased in order to ensure high output power and high pumping efficiency of the amplification stage, the nonlinear effect is inevitably serious, and the quality and the output power of the output beam of the laser are influenced.
In order to solve the above problems, in the prior art, an optical fiber amplifier is provided, in which a length of a gain fiber in the optical fiber amplifier is set to be smaller than a preset length, so that although a nonlinear effect caused by the gain fiber can be reduced, a pump cannot be sufficiently absorbed at the same time, a maximum pump utilization rate cannot be realized, and further, an output power of the optical fiber amplifier can be affected.
Disclosure of Invention
To overcome or at least partially solve the above problems, the present invention provides an optical fiber amplifier and a multistage optical fiber amplifier system.
In one aspect, the present invention provides an optical fiber amplifier comprising: a pump coupler, a gain fiber and a pump feedback device; wherein the pump coupler is configured to couple pump light to the gain fiber; the length of the gain optical fiber is smaller than a preset length, wherein the preset length is the length of the gain optical fiber corresponding to the optical fiber amplifier when the optical fiber amplifier reaches the maximum extraction efficiency; the pump feedback device is used for separating residual pump light in the gain fiber from laser and returning the residual pump light to the pump coupler.
Preferably, the pump coupler is further used for inputting seed light into the optical fiber amplifier;
correspondingly, the pumping feedback device is also used for outputting laser.
Preferably, the pump feedback device specifically includes: having an input and M outputs, where M is an integer greater than 1; the input end of the beam splitter is connected with one end of the gain fiber, and each output end of the M-1 output ends of the beam splitter is connected with one input end of the pump coupler.
Preferably, when M >2, the pump feedback device further comprises: n beam combiners having N input terminals and one output terminal, where N is an integer not less than 1, and N x N is M-1; each input end of the n beam combiners is connected with one output end of the beam splitter, and each output end of the n beam combiners is connected with one input end of the pump coupler.
Preferably, a tapered adapter is further arranged between the input end of the beam splitter and one end of the gain fiber; the optical fiber cross-sectional area of the first end of the tapered adapter is smaller than that of the second end of the tapered adapter, the first end of the tapered adapter is connected with one end of the gain optical fiber, and the second end of the tapered adapter is connected with the input end of the beam splitter.
Preferably, the pump feedback device is further used for inputting seed light into the optical fiber amplifier; correspondingly, the pump coupler is also used for outputting laser light.
Preferably, the pump feedback device specifically includes: a beam splitter having 2 inputs and M outputs, where M is an integer greater than or equal to 1; one input end of the beam splitter is used for inputting seed light, the other input end of the beam splitter is connected with one end of the gain fiber, and the other input end of the beam splitter is used for outputting the seed light to the gain fiber and receiving residual pump light in the gain fiber; each of the M output terminals of the beam splitter is connected to one input terminal of the pump coupler.
Preferably, when M >1, the pump feedback device further includes: n beam combiners, each beam combiner having N input ends and an output end, wherein N is an integer not less than 1, and N x N is M; each input end of the n beam combiners is connected with one output end of the beam splitter, and each output end of the n beam combiners is connected with one input end of the pump coupler.
Preferably, a tapered adapter is further arranged between the other input end of the beam splitter and one end of the gain fiber; the optical fiber cross-sectional area of the first end of the tapered adapter is smaller than that of the second end of the tapered adapter, the first end of the tapered adapter is connected with one end of the gain optical fiber, and the second end of the tapered adapter is connected with the input end of the pumping feedback device.
In another aspect, the present invention provides a multi-stage fiber amplifier system comprising at least two sequentially arranged fiber amplifiers as described above.
According to the optical fiber amplifier provided by the invention, the length of the gain optical fiber is set to be smaller than the preset length, so that the reabsorption of the seed optical fiber by the gain optical fiber is reduced. Meanwhile, residual pump light obtained after the length of the gain optical fiber is shortened is returned to the pump coupler by using the pump feedback device, so that the pumping efficiency of the optical fiber amplifier is improved, and the high-power output of the optical fiber amplifier is realized.
Drawings
Fig. 1 is a schematic structural diagram of an optical fiber amplifier according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of an optical fiber amplifier according to another embodiment of the present invention;
fig. 3 is a schematic structural diagram of an optical fiber amplifier according to another embodiment of the present invention;
fig. 4 is a schematic structural diagram of an optical fiber amplifier according to another embodiment of the present invention;
fig. 5 is a schematic structural diagram of an optical fiber amplifier according to another embodiment of the present invention;
FIG. 6 is a schematic diagram of a multi-stage fiber amplifier system according to another embodiment of the present invention;
fig. 7 is a schematic structural diagram of an optical fiber amplifier according to another embodiment of the present invention;
fig. 8 is a schematic structural diagram of an optical fiber amplifier according to another embodiment of the present invention;
fig. 9 is a schematic structural diagram of an optical fiber amplifier according to another embodiment of the present invention;
fig. 10 is a schematic structural diagram of a multi-stage fiber amplifier system according to yet another embodiment of the present invention.
Detailed Description
The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
As shown in fig. 1, in one embodiment of the present invention, there is provided an optical fiber amplifier including: a pump coupler 11, a gain fiber 12 and a pump feedback device 13.
Wherein the pump coupler 11 is used for coupling pump light to the gain fiber 12; the length of the gain fiber 12 is less than a preset length. Here, the preset length is the length of the gain fiber 12 corresponding to the maximum extraction efficiency of the fiber amplifier;
the pump feedback device 13 is configured to separate the residual pump light in the gain fiber 12 from the laser light and return the residual pump light to the pump coupler 11.
Specifically, in order to ensure that the optical fiber amplifier can achieve the maximum pumping utilization rate in the prior art, the length of the gain fiber in the optical fiber amplifier is set to be the length of the corresponding gain fiber when the optical fiber amplifier achieves the maximum extraction efficiency, that is, the preset length. This results in a tendency to make nonlinear effects more likely, especially in multi-stage amplifier configurations, which severely affect the output beam quality and output power of the fiber amplifier. In addition, the long gain fiber causes a re-absorption problem of the output laser, which is determined by an absorption curve of the dopant ions, and even if the absorption cross section of the gain fiber is small, the laser generated in the gain fiber is re-absorbed by the long gain fiber, thereby reducing the efficiency of the fiber amplifier.
On the other hand, in some fiber lasers operating at specific wavelengths (e.g., 975nm to 1030nm band of ytterbium-doped fiber lasers), if the gain fiber is longer than a certain value, the laser of the desired wavelength cannot be oscillated. This is because the ytterbium doped fiber has a large absorption cross section near 975nm to 1030nm, which is much higher than the absorption cross section near zero at a wavelength above 1050nm, and therefore, the reabsorption is severe. The reabsorption increases the oscillation output threshold of 1010 nm-1030 nm laser, so that the laser is difficult to excite.
Therefore, based on the above, the present invention provides an optical fiber amplifier, in which the length of the adopted gain fiber can be much smaller than the preset length, which will effectively suppress the generation of the nonlinear effect, and at the same time effectively avoid the reabsorption of the laser generated inside by the gain fiber. Meanwhile, a gain fiber smaller than a predetermined length may cause a decrease in pump absorption, resulting in unutilized pump light, i.e., residual pump light. The pumping efficiency of the optical fiber amplifier is improved by recycling the residual pumping light, and thus triple guarantees of the output power, the laser efficiency and the beam quality of the high-power optical fiber amplifier are achieved.
The content of the residual pump light in the gain fiber is related to the absorption coefficient of the gain fiber, for example, when the absorption coefficient of the gain fiber is 1.2dB/m, the content of the residual pump light in a predetermined length of the gain fiber is usually less than 10% of all the pump light in the gain fiber. When the length of the gain fiber is less than the preset length, the content of the residual pump light is more than 10% of all the pump light. Preferably, the length of the gain fiber can be shortened to 30% -50% of the preset length, so that the content of the residual pump light in the gain fiber can reach about 30%.
The pump coupler is an optical device for coupling pump light into a gain fiber, the input end of the pump coupler is used for inputting the pump light into the fiber amplifier, the pump light is coupled into the gain fiber through the pump coupler, a gain medium in the gain fiber, namely doped ions in a fiber core of the gain fiber, absorb the pump light and are excited to a high energy state, particles in the high energy state are quickly relaxed to an excited state with lower energy, after the seed light enters the gain fiber, the particles on the excited state generate stimulated radiation and jump to a low energy state to release stored energy, so that the seed light is amplified to form laser. Because the laser is mixed with residual pump light, the residual pump light in the gain fiber is separated from the laser through the pump feedback device, the obtained residual pump light is returned to the input end of the pump coupler, and the high-efficiency and high-power laser output is obtained after the pump light is recycled.
The optical fiber amplifier provided in this embodiment may be a forward pumping optical fiber amplifier, and may also be a backward pumping optical fiber amplifier.
In this embodiment, the length of the gain fiber is set to be smaller than the preset length, so that the generation of the nonlinear effect is effectively suppressed, and the reabsorption of the laser generated inside by the gain fiber is reduced. Meanwhile, residual pump light obtained after the length of the gain optical fiber is shortened is returned to the pump coupler by using the pump feedback device, so that the pumping efficiency of the optical fiber amplifier is improved, and the high-power output of the optical fiber amplifier is realized.
On the basis of the above embodiment, the pump coupler is further configured to input seed light into the optical fiber amplifier;
correspondingly, the pumping feedback device is also used for outputting laser.
Specifically, in this embodiment, one input end of the pump coupler can also be used as the input end of the whole optical fiber amplifier for inputting the seed light. After the pump coupler, the gain optical fiber and the pump feedback device are sequentially connected, pump light and seed light are respectively input into the gain optical fiber through the input end of the pump coupler, doping substances in the gain optical fiber are subjected to transition and relaxation to an excited state with lower energy under the action of the pump light, and the seed light enables particles on the excited state to generate stimulated radiation and transition to a low energy state to release energy, so that the seed light is amplified to generate laser.
In this embodiment, a forward pump fiber amplifier is provided, which couples pump light and seed light into a gain fiber through a pump coupler. The optical fiber amplifier feeds back the residual pump light to the input end of the pump coupler through the pump feedback device, so that the residual pump light is recycled, and the power of the optical fiber amplifier can be fully improved.
As shown in fig. 2, on the basis of the above embodiment, the optical fiber amplifier may include: a seed device 14 and a pumping device 15. The seed device 14 and the pump device 15 are each connected to an input of the pump coupler 11. The seed device 14 can be used as a seed source of the optical fiber amplifier to provide seed light for the optical fiber amplifier. The seed light emitted from the seed device 14 is injected into the gain fiber 12 through the pump coupler 11 for pump pumping amplification. The pumping device 15 can be used as a pumping source of the optical fiber amplifier to provide pumping light for the optical fiber amplifier. The pump light emitted by the pump device 15 is also coupled to the gain fiber 12 through the pump coupler, exciting the dopant ions in the gain fiber 12.
In this embodiment, the seed device and the pumping device are provided, so that the optical fiber amplifier can continuously operate to continuously generate high-power laser.
On the basis of the above embodiment, the pump feedback device 13 specifically includes: a beam splitter 131 having one input and M outputs, where M is an integer greater than 1;
the input end of the beam splitter 131 is connected to one end of the gain fiber, and each of the M-1 output ends of the beam splitter 131 is connected to one input end of the pump coupler 11.
Specifically, as shown in fig. 3, for example, one seed device and six pump devices are connected to the input end of the pump coupler 11. The six pumping devices are used to ensure that sufficient pumping light is provided to the gain fiber, but the number of pumping devices is not particularly limited in the present invention. In fig. 3, M is 2, one output end of the beam splitter 131 is connected to one input end of the pump coupler 11, and the other output end is used for outputting laser light obtained by amplifying the seed light. Since the residual pump light is mostly located in the cladding region of the gain fiber, the beam splitter 131 can distinguish the residual pump light from the laser light by the difference in numerical aperture.
In this embodiment, a plurality of pumping devices are provided to provide sufficient pumping light for the fiber amplifier. Meanwhile, one output end of the beam splitter is connected with the input end of the pump coupler, so that residual pump light generated in the gain fiber can enter the gain fiber again through the input end of the pump coupler, the aim of recycling is fulfilled, resources are saved, and the efficiency of the optical fiber amplifier is improved.
On the basis of the above embodiment, when M >2, the pump feedback device further includes: n beam combiners, each beam combiner having N input ends and an output end, wherein N is an integer not less than 1, and N x N is M-1;
each input end of the n beam combiners is connected with one output end of the beam splitter, and each output end of the n beam combiners is connected with one input end of the pump coupler.
Specifically, as shown in fig. 4, fig. 4 is different from fig. 3 only in that a beam splitter 131 having one input end and 7 output ends is adopted as the pump feedback device 13 in fig. 4, and there are 2 beam combiners in fig. 4, each beam combiner having 3 input ends and one output end, that is, M is 7, N is 2, and N is 3. The 6 output ends of the beam splitter 131 are 3 upper and lower, each of the upper 3 output ends is connected to one input end of the beam combiner 132, and the output end of the beam combiner 132 is connected to the input end of the pump coupler 11. Each of the lower 3 outputs is connected to one input of a combiner 133, the output of which combiner 133 is also connected to the input of the pump coupler 11.
It should be noted that the number of input ends or output ends of the beam splitter or the beam combiner is not limited in particular. But the use of more output splitters allows the residual pump light in the gain fiber to be more fully separated and utilized.
On the basis of the above embodiment, a tapered adapter may be further disposed between the input end of the beam splitter and one end of the gain fiber;
the optical fiber cross-sectional area of the first end of the tapered adapter is smaller than that of the second end of the tapered adapter, the first end of the tapered adapter is connected with one end of the gain optical fiber, and the second end of the tapered adapter is connected with the input end of the beam splitter.
Specifically, as shown in fig. 5, fig. 5 differs from fig. 4 only in that a tapered adapter 17 is further provided between the input end of the beam splitter 131 and one end of the gain fiber 12. The tapered adapter 17 has a first end connected to one end of the gain fiber 12 and a second end connected to the input end of the beam splitter 131. Because most of the residual pump light is positioned in the cladding region of the gain fiber, the proportion of the cladding region in the whole fiber end face is increased, the feedback efficiency of the residual pump light can be improved, and the efficiency of the fiber amplifier is improved. Therefore, in this embodiment, the tapered adapter 17 is added to keep the size of the fiber core of the gain fiber unchanged, increase the area of the end face of the gain fiber as a whole, convert the small-diameter gain fiber into a large-diameter fiber, increase the proportion of the cladding region in the end face, and connect the large-diameter fiber with the input end of the beam splitter 131.
Another embodiment of the present invention provides a multi-stage fiber amplifier system, comprising at least two forward-pumped fiber amplifiers as described in the previous embodiments, arranged in series.
Preferably, for every two adjacent optical fiber amplifiers in the multi-stage optical fiber amplifier system, the laser output by the previous optical fiber amplifier is the seed light of the next optical fiber amplifier.
Specifically, as shown in fig. 6, the forward-pumped multistage fiber amplifier system shown in fig. 6 includes three sequentially arranged fiber amplifiers as described in the above embodiments, wherein the first fiber amplifier serves as a primary amplification, the second fiber amplifier serves as a secondary amplification, and the third fiber amplifier serves as a tertiary amplification. One input end of the first optical fiber amplifier is connected with a seed device and used for providing seed light for the multistage optical fiber amplifier system, the output end of the first optical fiber amplifier used for outputting laser is connected with the input end of the second optical fiber amplifier used for inputting the seed light, namely, the laser obtained by the first-stage amplification is input into the second optical fiber amplifier as the seed light to be subjected to second-stage amplification, similarly, the output end of the second optical fiber amplifier used for outputting the laser is connected with the input end of the third optical fiber amplifier used for inputting the seed light, namely, the laser obtained by the second-stage amplification is input into the third optical fiber amplifier as the seed light to be subjected to third-stage amplification, and finally, the laser subjected to third-stage amplification is output through.
The multistage optical fiber amplifier system provided by the embodiment can multiply the power of the output laser. Thereby realizing high-power laser output.
On the basis of the above embodiment, the pump feedback device is further configured to input seed light into the optical fiber amplifier;
correspondingly, the pump coupler is also used for outputting laser light.
Specifically, in this embodiment, one input end of the pump feedback device is used as the input end of the whole optical fiber amplifier for inputting the seed light. After the pump coupler, the gain optical fiber and the pump feedback device are sequentially connected, pump light is input into the gain optical fiber through the input end of the pump coupler, doping substances in the gain optical fiber are subjected to transition and relaxation to an excited state with lower energy under the action of the pump light, seed light is input through the input end of the pump feedback device, and the seed light enables particles on the excited state to generate stimulated radiation and transition to a low energy state to release energy, so that the seed light is amplified to generate laser.
In this embodiment, a backward pump fiber amplifier is provided, so that the pump light and the seed light are coupled into the gain fiber respectively. The optical fiber amplifier feeds back the residual pump light to the input end of the pump coupler through the pump feedback device, so that the residual pump light is recycled, and the power of the optical fiber amplifier can be fully improved.
As shown in fig. 7, on the basis of the above embodiment, the optical fiber amplifier may include: a seed device 24 and a pumping device 25. The seed device 24 is connected to the input of the pump feedback device 23 and the pump device 25 is connected to the input of the pump coupler 21. The pumping device 25 can be used as a pumping source of the optical fiber amplifier to provide pumping light for the optical fiber amplifier. The pump light emitted by the pump device 25 is coupled to the gain fiber 22 through the pump coupler 21, and excites the doped ions in the gain fiber 22. The seed device 24 serves as a seed source for the optical fiber amplifier and provides seed light for the optical fiber amplifier. The seed light emitted by the seed device 24 is injected into the gain fiber 22 through the pump feedback device 23 for pump pumping amplification. And the amplified laser is output through the output end of the pump coupler.
In this embodiment, the seed device and the pumping device are provided, so that the optical fiber amplifier can continuously operate to continuously generate high-power laser.
On the basis of the above embodiments, the pump feedback device specifically includes: a beam splitter having 2 inputs and M outputs, where M is an integer greater than or equal to 1;
one input end of the beam splitter is used for inputting seed light, the other input end of the beam splitter is connected with one end of the gain fiber, and the other input end of the beam splitter is used for outputting the seed light to the gain fiber and receiving residual pump light in the gain fiber;
each of the M output terminals of the beam splitter is connected to one input terminal of the pump coupler.
Specifically, as shown in fig. 8, six pumping devices are connected to the input end of the pump coupler 21 in fig. 8 as an example. The six pumping devices are used to ensure that sufficient pumping light is provided to the gain fiber, but the number of pumping devices is not particularly limited in the present invention. In fig. 8, M is equal to 1, and the beam splitter 231 has two input ends, one of which is connected to the seed device for inputting the seed light, and the other of which is connected to one end of the gain fiber. The beam splitter 231 has 1 output, and the output of the beam splitter 231 is connected to the input of the pump coupler 21. One output end of the pump coupler 21 is connected to one end of the gain fiber 22, and the other output end is used for outputting laser light.
In this embodiment, a plurality of pumping devices are provided to provide sufficient pumping light for the fiber amplifier. Meanwhile, the output end of the beam splitter is connected with the input end of the pump coupler, so that residual pump light generated in the gain fiber can enter the gain fiber again through the input end of the pump coupler, the aim of recycling is fulfilled, and resources are saved.
On the basis of the above embodiment, when M >1, the pump feedback device further includes: n beam combiners, each beam combiner having N input ends and an output end, wherein N is an integer not less than 1, and N x N is M;
each input end of the n beam combiners is connected with one output end of the beam splitter, and each output end of the n beam combiners is connected with one input end of the pump coupler.
Specifically, as shown in fig. 9, a beam splitter having 2 inputs and 6 outputs is used as the pump feedback device 23, and fig. 9 has 2 combiners, each combiner having 3 inputs and one output, i.e., M ═ 6, N ═ 2, and N ═ 3. The 6 output ends of the beam splitter 231 are 3 upper and lower, each of the upper 3 output ends is connected to one input end of a beam combiner 232, and the output end of the beam combiner 232 is connected to one input end of the pump coupler 21. Each of the lower 3 output terminals is connected to one input terminal of a combiner 233, and the output terminal of the combiner 233 is also connected to one input terminal of the pump coupler 21.
It should be noted that the number of input ends or output ends of the beam splitter or the beam combiner is not limited in particular. But the use of more output splitters allows the residual pump light in the gain fiber to be more fully separated and utilized.
On the basis of the above embodiment, a tapered adapter may be further disposed between the input end of the beam splitter and one end of the gain fiber;
the optical fiber cross-sectional area of the first end of the tapered adapter is smaller than that of the second end of the tapered adapter, the first end of the tapered adapter is connected with one end of the gain optical fiber, and the second end of the tapered adapter is connected with the input end of the beam splitter.
Specifically, since most of the residual pump light is located in the cladding region of the gain fiber, the proportion of the cladding region to the entire fiber end face is increased, which can improve the feedback efficiency of the residual pump light, thereby improving the efficiency of the fiber amplifier. Therefore, in this embodiment, the tapered adapter is added to keep the size of the fiber core of the gain fiber unchanged, increase the area of the end face of the gain fiber as a whole, convert the small-diameter gain fiber into the large-diameter fiber, increase the proportion of the cladding region in the end face, and connect the large-diameter fiber with the input end of the beam splitter.
Another embodiment of the present invention provides a multi-stage fiber amplifier system comprising at least two sequentially arranged backward-pumped fiber amplifiers as described in the previous embodiments.
Preferably, for every two adjacent optical fiber amplifiers in the multi-stage optical fiber amplifier system, the laser output by the previous optical fiber amplifier is the seed light of the next optical fiber amplifier.
Specifically, as shown in fig. 10, the backward-pumped multi-stage fiber amplifier system shown in fig. 10 includes three backward-pumped fiber amplifiers as described in the above embodiments, which are arranged in sequence, wherein the first fiber amplifier serves as a first-stage amplification, the second fiber amplifier serves as a second-stage amplification, and the third fiber amplifier serves as a third-stage amplification. One input end of the first optical fiber amplifier is connected with a seed device and used for providing seed light for the multistage optical fiber amplifier system, the output end of the first optical fiber amplifier used for outputting laser is connected with the input end of the second optical fiber amplifier used for inputting the seed light, namely, the laser obtained by the first-stage amplification is input into the second optical fiber amplifier as the seed light to be subjected to second-stage amplification, similarly, the output end of the second optical fiber amplifier used for outputting the laser is connected with the input end of the third optical fiber amplifier used for inputting the seed light, namely, the laser obtained by the second-stage amplification is input into the third optical fiber amplifier as the seed light to be subjected to third-stage amplification, and finally, the laser subjected to third-stage amplification is output through.
The multistage optical fiber amplifier system provided by the embodiment can multiply the power of the output laser. Thereby realizing high-power laser output.
On the basis of the above embodiments, since the optical fiber amplifier is all-fiber, the connections between the optical devices in the optical fiber amplifier can be made by fiber fusion, and can also be made by using an optical fiber adapter, which is not limited specifically herein.
Based on the above embodiments, the pump feedback device used in the fiber amplifier can be implemented by using a combination of a 45-degree beam splitter and a lens.
Specifically, taking a forward pump fiber amplifier as an example, the output through the gain fiber is a mixed light, specifically including the residual pump light and the laser light. The residual pump light and the laser can be separated after passing through the 45-degree beam splitter, the obtained laser is directly output, and the obtained residual pump light is converged to the input end of the pump coupler through the lens.
In order to reduce the length of the whole light path, a plane mirror can be added into the light path.
In the embodiment, the combination of the 45-degree beam splitter and the lens is adopted to realize the recycling of residual pump light, so that a new structure is provided for the pump feedback device.
On the basis of the above embodiment, the gain fiber may include: multi-clad optical fibers, multi-core optical fibers, polarization maintaining optical fibers, and the like.
On the basis of the above embodiments, the doping substance in the core of the gain optical fiber may be a rare earth ion, specifically, an ytterbium ion, a thulium ion, an erbium ion, a holmium ion, or a neodymium ion.
The optical fiber amplifier provided by the invention effectively inhibits the generation of nonlinear effect by shortening the length of the gain optical fiber in the optical fiber amplifier, and meanwhile, the short gain optical fiber effectively inhibits the reabsorption of the gain optical fiber to signal light. Meanwhile, the pumping feedback device provided by the invention has the advantage of improving the pumping efficiency. In addition, the multistage optical fiber amplifier system provided by the invention comprises more optical fiber amplifiers, the advantage of improving the pumping efficiency is more obvious, and the power of the output laser is higher. The optical fiber amplifier provided by the invention is suitable for a continuous optical fiber amplifier and also suitable for a pulse optical fiber amplifier. In addition, the structure is simple and reliable, the operation is convenient, and the fiber laser can be widely applied to various doped fiber lasers and is suitable for forward and backward pumping multistage fiber amplifier systems.
Finally, the method of the present invention is only a preferred embodiment and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. An optical fiber amplifier, comprising: a pump coupler, a gain fiber and a pump feedback device; wherein,
the pump coupler is used for coupling pump light to the gain fiber; the length of the gain optical fiber is smaller than a preset length, wherein the preset length is the length of the gain optical fiber corresponding to the optical fiber amplifier when the optical fiber amplifier reaches the maximum extraction efficiency;
the pump feedback device is used for separating residual pump light in the gain fiber from laser and returning the residual pump light to the pump coupler.
2. The fiber amplifier of claim 1, wherein the pump coupler is further configured to input seed light into the fiber amplifier;
correspondingly, the pumping feedback device is also used for outputting laser.
3. The fiber amplifier according to claim 2, wherein the pump feedback means comprises in particular: a beam splitter having one input and M outputs, where M is an integer greater than 1;
the input end of the beam splitter is connected with one end of the gain fiber, and each output end of the M-1 output ends of the beam splitter is connected with one input end of the pump coupler.
4. The fiber amplifier of claim 3, wherein when M >2, the pump feedback arrangement further comprises: n beam combiners, each beam combiner having N input ends and an output end, wherein N is an integer not less than 1, and N x N is M-1;
each input end of the n beam combiners is connected with one output end of the beam splitter, and each output end of the n beam combiners is connected with one input end of the pump coupler.
5. The fiber amplifier of claim 4, wherein a tapered adapter is further disposed between the input end of the beam splitter and the one end of the gain fiber;
the optical fiber cross-sectional area of the first end of the tapered adapter is smaller than that of the second end of the tapered adapter, the first end of the tapered adapter is connected with one end of the gain optical fiber, and the second end of the tapered adapter is connected with the input end of the beam splitter.
6. The fiber amplifier of claim 1, wherein the pump feedback device is further configured to input seed light into the fiber amplifier;
correspondingly, the pump coupler is also used for outputting laser light.
7. The fiber amplifier according to claim 6, wherein said pump feedback means comprises in particular: a beam splitter having 2 inputs and M outputs, where M is an integer greater than or equal to 1;
one input end of the beam splitter is used for inputting seed light, the other input end of the beam splitter is connected with one end of the gain fiber, and the other input end of the beam splitter is used for outputting the seed light to the gain fiber and receiving residual pump light in the gain fiber;
each of the M output terminals of the beam splitter is connected to one input terminal of the pump coupler.
8. The fiber amplifier of claim 7, wherein when M >1, the pump feedback arrangement further comprises: n beam combiners having N input terminals and one output terminal, where N is an integer not less than 1, and N x N is M;
each input end of the n beam combiners is connected with one output end of the beam splitter, and each output end of the n beam combiners is connected with one input end of the pump coupler.
9. The fiber amplifier of claim 8, wherein a tapered adapter is further disposed between the other input end of the beam splitter and the one end of the gain fiber;
the optical fiber cross-sectional area of the first end of the tapered adapter is smaller than that of the second end of the tapered adapter, the first end of the tapered adapter is connected with one end of the gain optical fiber, and the second end of the tapered adapter is connected with the input end of the pumping feedback device.
10. A multi-stage fiber amplifier system, comprising: at least two sequentially arranged optical fiber amplifiers according to any of claims 2-5; or,
at least two sequentially arranged optical fiber amplifiers according to any of claims 6-9.
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