CN107425406B - Pump source of third-order Raman amplifier - Google Patents
Pump source of third-order Raman amplifier Download PDFInfo
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- CN107425406B CN107425406B CN201710589518.7A CN201710589518A CN107425406B CN 107425406 B CN107425406 B CN 107425406B CN 201710589518 A CN201710589518 A CN 201710589518A CN 107425406 B CN107425406 B CN 107425406B
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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
- H01S3/09—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
- H01S3/094042—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a fibre laser
- H01S3/094046—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a fibre laser of a Raman fibre laser
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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
- H01S3/30—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range using scattering effects, e.g. stimulated Brillouin or Raman effects
- H01S3/302—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range using scattering effects, e.g. stimulated Brillouin or Raman effects in an optical fibre
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Abstract
The invention provides a pumping source of a third-order Raman amplifier, which has simple and reasonable structure, convenient application and low cost, can obtain the optimal Raman gain effect or the optimal system transmission effect, and comprises a high-power Raman laser, wherein an adjustable power distributor divides the output power of the high-power Raman laser into two parts, the first part keeps the wavelength unchanged, the first part is used as a 3-stage pumping source of a 3-stage pumping laser in the total output, and the second part forms two cascaded Raman resonant cavities by adding a frequency selecting device: the first cascade Raman laser resonant cavity and the second cascade Raman laser resonant cavity sequentially generate 2-level pump light and 1-level pump light, and the power of each level of pump light in the gain fiber changes along with the distance.
Description
Technical Field
The invention relates to the technical field of optical fiber communication, in particular to a pumping source of a third-order Raman amplifier.
Background
Raman amplifiers are commonly used in optical communication technology as pump sources, which are optical amplifiers using stimulated raman scattering phenomena, where the transfer of light is achieved by raman shift, i.e. a high power pump signal λp and a low power pump signal λs are introduced into the same transmission fiber, and the energy from the high power pump light is transferred into the low power optical signal, thus completing the amplification of the signal, typically with λp smaller than λs, and with the difference between λp and λs being designed to be approximately equal to the stokes transfer of the transmission medium.
The raman shift can be used for a high-order raman effect, which is also called multiple raman scattering, i.e. the energy of a high-power photon at high frequency can be subjected to stokes shift several times to pump a low-frequency photon step by step. The communication optical fiber is mostly a germanium-silicon optical fiber, the Raman frequency shift of the germanium-silicon optical fiber is 440cm < -1 >, and the communication optical fiber can be calculated according to a calculation formula of the ith-order output wavelength of the Raman optical fiber:the calculation is as follows: the power of 1389.5nm light is shifted to 1480nm wavelength after raman shift, and the power of 1480nm light is shifted to 1550nm band after raman shift.
Raman amplification technology has become increasingly widely used in recent years: such as cascaded raman pump lasers, a high-order raman amplifier applied in the unrepeatered transmission technique, is specifically applied as follows:
(1) Cascaded raman pump laser
The patent "cascaded raman fiber laser system based on filter fibers" (application number 201080010155.3) proposes a light generation and amplification system comprising a length of laser activated filter fiber having a refractive index profile that suppresses unwanted stokes orders at wavelengths longer than the target wavelength and having normal dispersion at its operating wavelength. A series of nested reflective devices are provided at the input and output ends of the optical fiber and configured to provide a series of nested raman cavities separated in wavelength by approximately corresponding stokes shifts.
The patent 'single pump multi-wavelength lasing semiconductor Raman pump laser and pump wave combining device' (application number 201210047801.4) provides a single pump multi-wavelength lasing semiconductor Raman pump laser and pump wave combining device which can enable gain to be flat and correspond to multiple wavelength lasing by using at least two or more than two different center wavelengths on an output tail fiber of the pump laser.
(2) High-order Raman amplifier applied to relay-free transmission technology
With the development of the unrepeatered transmission technology, transmission paragraphs requiring more than 400km are more and more, and the raman amplification technology and the remote pump amplification technology are gradually adopted, but with the further increase of the transmission distance, the higher-order raman amplifier is gradually favored due to higher gain and lower noise. But the pump source structure of the 3-stage raman amplifier is very complex and very costly. As shown in fig. 1, a pump source of a commercial 3-stage raman amplifier is formed by two independent control frames (1U frames x 2), and two frames are selected because the types of pump lasers adopted are completely different, and optical path design and circuit software control cannot be completed in one frame. One of the machine frames comprises a plurality of semiconductor lasers, at least comprising 3 semiconductor lasers: at least one semiconductor laser having a wavelength of about 1370nm, typically within 100mW, and at least 3 semiconductor lasers having a wavelength of 1425-1465 nm and an output power of 100-300 mW. The other frame is composed of three-stage lasers with shorter wavelength, the power is usually several watts, and semiconductor lasers with high power are not yet developed, so that a high-power fiber Raman laser needs to be selected. The laser is formed by a plurality of Raman cascade resonant cavities and gain fibers. The output power is more than 5W. The drive control of a 1+ two-stage Raman pump source circuit formed by a plurality of semiconductor lasers is very complex [ patent application number of a second-order Raman amplifier and a control method thereof is CN201510863985.5]. The practical implementation of laser safety and pump-off-free functions becomes very troublesome because two single plates are involved. Meanwhile, each frame needs remote control, and the raman pump sources of different frames (mechanisms) need to realize non-optical pump or gain/power mode linkage control, which is very difficult.
In the commercial 3-stage raman pump source shown in fig. 1, a three-stage pump source of 3.5-5W is generally required, and the wavelength is 1270-1280 nm; a two-stage raman laser is usually required as a seed source, the wavelength is 1370-1380 nm, and the power is tens of milliwatts; at least 3 primary pump light is also required, each having a wavelength of 1425nm,1445nm,1465nm. The power is 100-200 mW. By the arrangement, a relatively flat gain and a relatively low noise figure can be obtained, and certain occasions where only 1-order and 2-order Raman amplifiers cannot be qualified are realized. Such as where the ultra-long span unrepeatered transmission distance exceeds 400 km. The above 3-order raman pump source composed of several semiconductor lasers and high-order raman lasers is very costly.
From the above examples, it can be seen that the raman laser output power is high, typically up to 10W or more, and the shorter the wavelength (the higher the frequency), the easier it is to obtain high power output, and the principle of fabrication is generally that of a cascaded raman laser. As is well known, raman lasers generally have a final goal in terms of light-to-light conversion efficiency during production. The optical-optical conversion efficiency is designed as a target, and as a result, the cascade raman lasers all transfer high-frequency raman power to the low-frequency pump light. In the laser output power, there is only a small amount of residual high-frequency Raman laser power (and the finished laser filters out the high-order laser to obtain good laser output spectrum characteristics), and most of the high-order laser power is transferred to the low-order (low-frequency) light by Stokes' shift effectAnd go away. The power transfer process of a three-stage raman cascade laser as shown in fig. 2, the ordinate indicates the power of the laser, and in this process, λ3 rd The power (of the high frequency tertiary) is first transferred to its stokes wavelength λ2 rd On the other hand, when the second-order lasing threshold is reached, λ2 rd The power on is transferred to the next Stokes shift, i.e. λ1 rd Is a kind of medium. The primary stokes light is finally transferred to the optical signal to be amplified. The output characteristic of the cascaded raman laser is that all the pump power is converted to the last stage (the lowest frequency stage).
In summary, in the research and use process of the practical raman amplifier, the pumping configuration of each stage of the high-order raman amplifier has unique characteristics, taking the 3-order raman amplifier as an example, the characteristics of the pumping source configuration of the high-order raman amplifier: the three-stage is largest, 3.5W-5W, the two-stage is smallest, only tens of milliwatts are needed, the first-stage power is centered to be 100 mW-200 mW, the power configuration mode generally requires that the pump source of the third-order Raman amplifier is composed of a plurality of semiconductor lasers and a plurality of high-power lasers, and the cost is quite high.
Disclosure of Invention
Aiming at the problems of complex structure, inconvenient application, high cost and the like of a Raman amplifier in the prior art, the invention provides a pumping source of a third-order Raman amplifier, which has the advantages of simple and reasonable structure, convenient application and low cost, and can obtain the optimal Raman gain effect or the optimal system transmission effect.
A pump source for a third order raman amplifier comprising a high power raman laser characterized in that: the adjustable power distributor divides the output power of the high-power Raman laser into two parts, the first part keeps the wavelength unchanged, the first part is used as a 3-stage pump source of a 3-stage pump laser in the total output, and 3-stage pump light generated by the adjustable power distributor directly enters one input end of the broadband combiner; the second part forms two cascaded Raman laser resonant cavities by adding a frequency selecting device: the system comprises a first cascade Raman laser resonant cavity and a second cascade Raman laser resonant cavity, wherein 3-level pump light separated by an adjustable power distributor is used as input pump light, high-frequency 3-level pump light is converted into low-frequency 2-level pump light in the first cascade Raman laser resonant cavity, 2-level pump light generated by the first cascade Raman laser resonant cavity is converted into 1-level pump light in the second cascade Raman laser resonant cavity, the first cascade Raman laser resonant cavity and the second cascade Raman laser resonant cavity sequentially generate 2-level pump light and 1-level pump light, the power of each level pump light in a gain fiber changes along with the distance, and the feedback and transmission processes of the 3-level pump light, the 2-level pump light and the 1-level pump light in the resonant cavity are described by the following equations:
f and B respectively represent the front and rear transmission directions; p represents power, P p3 ,P p2 ,P p1 Respectively representing 3-level pump power, 2-level pump light power and 1-level pump light power; alpha is Raman fiber loss; g is the Raman gain coefficient of the Raman fiber. In the case of strong pumping, the spontaneous raman scattering effect (ASE) in raman fibers is usually very weak, so ASE is ignored in the above equation.
The boundary conditions at z=0, z=l are respectively:
P p3 (0)＝P IN
it is further characterized by:
the first cascade Raman laser resonant cavity comprises a frequency-selecting device 2-level Bragg high-reflection grating (FBG 2), a gain fiber and a 2-level adjustable Bragg grating (FBG 3);
the second cascaded Raman laser resonant cavity comprises a frequency-selective device 1-level Bragg high-reflection grating (FBG 1) and a 1-level adjustable Bragg broadband grating (FBG 4);
the reflectivity of the frequency selective device is adjustable, and the power and the proportion of the output light of the 1-level pump light and the 2-level pump light are realized by adjusting the reflectivity of the fiber bragg grating of the frequency selective device. Furthermore, the distribution proportion of the adjustable power distributor is also adjustable, so that the pump power of the 1-level pump light, the 2-level pump light and the 3-level pump light and the respective proportion thereof can be balanced;
further, the method comprises the steps of,
the optimal Raman gain effect or the optimal system transmission effect can be obtained on site by adjusting the proportion of the adjustable power distributor and the reflectivity of the adjustable Bragg grating;
the output power of the high-power Raman laser is more than 5W, and the wavelength is 1260-1280 nm. The high power raman laser type may be a fiber raman laser or other type of high power laser;
the adjustable power distributor can divide the output power of the high-power laser into two parts, and the power distribution proportion of each part can be adjusted within the adjustment range of 10-90%. The tuning proportion can be realized on site through an upper computer; the power ratio of the 3-level pump light to the 1-level pump light and the 2-level pump light can be adjusted by adjusting the distribution proportion;
the 2-level Bragg high reflection grating is positioned at the signal input end, the reflection wavelength is 1360-1380 nm, the reflection bandwidth is 5-10 nm, and the reflectivity is more than 95%; the 2-level adjustable Bragg grating is positioned at the signal output end, the reflection wavelength is 1360-1380 nm, the reflection bandwidth is 5-10 nm, the reflectivity is adjustable, and the adjustment range is 5-90%; the 1-level Bragg high reflection grating is positioned at the signal input end, the reflection wavelength is 1420-1480 nm, the reflection bandwidth is 20-40 nm, and the reflectivity is more than 95%; the 1-level Bragg adjustable grating positioned at the signal output end is also a broadband grating, the reflection wavelength is 1420-1480 nm, and the reflection bandwidth is 20-40 nm; the reflectivity is adjustable, and the adjustment range is between 5 and 90 percent
The gain fiber is germanium-silicon fiber and has the characteristic of high Raman gain coefficient. Stokes' shift was 440cm-1.
The invention is applied to an optical fiber signal transmission system, and a high-power laser is divided into two parts by an adjustable power distributor: the first part is used as the pumping light of the three-stage pumping laser to directly enter the first input end of the broadband combiner, the second part forms a resonant cavity of a two-stage cascade Raman pumping laser, and the two cascade Raman pumping resonant cavities sequentially generate a one-stage pumping laser, the one-stage pumping light of the 2-stage pumping laser and a two-stage pump Pu Guang; the power of the primary pump light and the power of the secondary pump Pu Guang and the proportion thereof which are actually required by the amplifier are realized by adjusting the reflectivity FBG4 of the primary adjustable Bragg grating and the reflectivity of the secondary adjustable Bragg grating FBG3, the tuning proportion of the adjustable power distributor is realized on site by an upper computer, and the power proportion of the tertiary pump light and the primary light and the secondary light is adjusted by adjusting the distribution proportion, so that the optimal Raman gain effect or the optimal system transmission effect is obtained; the invention can replace the traditional third-order Raman pump laser pumping combination by only one Raman laser, not only simplifies the pumping source structure of the amplifier, but also greatly reduces the cost of the laser, and simultaneously meets the requirements of wide and flat gain bandwidth of the Raman amplifier by designing the resonant cavity of the first-order pumping light.
Drawings
FIG. 1 is a schematic diagram of pump source configuration for a commercial third-order Raman amplifier;
FIG. 2 is a schematic diagram of pump energy transfer of a cascaded Raman laser;
FIG. 3 is a schematic diagram of the construction of the present invention;
FIG. 4 is a schematic diagram of the structure of a 1+2 stage Raman laser of the third-stage Raman pump of the present invention;
FIG. 5 is a graph showing the power of pump light power at each stage in a theoretical simulation as a function of distance in a laser cavity;
FIG. 6 is a graph of pump conversion and tuning principles at each stage in a cascaded Raman laser;
FIG. 7 is a flow chart of a pump power adjustment method and steps for each stage;
FIG. 8 is a gain spectrum of a Raman amplifier implemented using the present invention;
FIG. 9 is a schematic diagram of an embodiment of a forward pumping structure of the present invention applied to a Raman amplifier;
FIG. 10 is a schematic diagram of an embodiment of a reverse pump structure of the present invention applied to a Raman amplifier;
FIG. 11 is a schematic diagram of a two-way pump structure embodiment of the present invention applied to a Raman amplifier;
fig. 12 is a schematic diagram of an embodiment of the present invention applied to a remote pump amplifier.
Detailed Description
As shown in fig. 3 to 12, a pump source of a third-order raman amplifier includes a high-power raman laser 1, an adjustable power divider 2, and an output power of the high-power raman laser 1 is above 5W, and a wavelength is between 1260 nm and 1280nm, and the type of the pump source may be a fiber raman laser or other types of high-power lasers; the distribution ratio of the adjustable power distributor 2 is also adjustable, the output power of the high-power laser can be divided into two parts, the power distribution ratio of each part can be adjusted, the adjustment range is between 10 and 90 percent, the tuning ratio can be realized on site through an upper computer, the adjustable power distributor 2 divides the output power of the high-power Raman laser 1 into two parts, the first part keeps the wavelength unchanged, the first part is used as a pump source of the 3-stage pump laser 4 in the total output, 3-stage pump light is generated, and the second part forms two cascaded Raman laser resonant cavities by adding a frequency selective device: the first cascade Raman laser resonant cavity and the second cascade Raman laser resonant cavity, the first cascade Raman laser resonant cavity comprises a frequency-selecting device 2-level Bragg high-reflection grating (FBG 2), a gain fiber 6 and a 2-level adjustable Bragg grating (FBG 3), the 2-level Bragg high-reflection grating (FBG 2) is positioned at a signal input end, the reflection wavelength is 1360-1380 nm, the reflection bandwidth is 5-10 nm,
the reflectivity is more than 95 percent; the 2-level adjustable Bragg grating (FBG 3) is positioned at the signal output end, the reflection wavelength is 1360-1380 nm, the reflection bandwidth is 5-10 nm, the reflectivity is adjustable, and the adjustment range is 5-90%; the gain fiber 6 is a germanium-silicon fiber and has the characteristic of high Raman gain coefficient, and Stokes frequency shift is 440cm < -1 >.
The second cascade Raman laser resonant cavity comprises a frequency-selecting device 1-level Bragg high-reflection grating (FBG 1) and a 1-level adjustable Bragg broadband grating (FBG 4), wherein the 1-level Bragg high-reflection grating (FBG 1) is positioned at the signal input end, the reflection bandwidth is 20-40 nm, and the reflectivity is more than 95%; the 1-level Bragg adjustable grating (FBG 4) positioned at the signal output end is also a broadband grating, and the reflection bandwidth is 20-40 nm;
the 3-stage pump light of the 3-stage pump laser 4 split by the adjustable power distributor 2 is taken as input pump light, the input pump light directly enters one input end of the broadband combiner 5, the high-frequency 3-stage pump light is converted into the low-frequency 2-stage pump light in the first cascade Raman laser resonant cavity, the 2-stage pump light generated by the first cascade Raman laser resonant cavity is converted into the 1-stage pump light in the second cascade Raman laser resonant cavity, the first cascade Raman laser resonant cavity and the second cascade Raman laser resonant cavity sequentially generate the 2-stage pump light and the 1-stage pump light, the 3-stage pump light, the pump power of the 2-stage pump light and the pump power of the 1-stage pump light and the respective proportion of the pump power are balanced by the adjustable power distributor 2, and the power of each stage pump light changes along with the distance in the gain optical fiber 6.
The working principle is as follows: the invention is applied to an optical fiber signal transmission system, and the high-power Raman laser 1 is divided into two parts by the adjustable power distributor 2: the first part is used as the pump light of the three-stage pump laser 4 to directly enter the first input end of the broadband combiner 5, the second part forms a resonant cavity of the two-stage cascade Raman pump laser 3, and the resonant cavities of the two cascade Raman pump lasers 3 sequentially generate a secondary pump Pu Guang and a primary pump light; the actual required primary pump light power and secondary pump Pu Guang power of the amplifier and the proportion thereof are realized by adjusting the reflectivity of the primary adjustable Bragg grating FBG4 and the reflectivity of the secondary adjustable Bragg grating FBG3, the tuning proportion of the adjustable power distributor 2 is realized on site by an upper computer, and the power proportion of the tertiary pump light, the secondary pump Pu Guang and the primary pump light is adjusted by adjusting the distribution proportion.
In the invention, a 2-stage Bragg high-reflection grating FBG2, a gain fiber and a 2-stage adjustable Bragg grating FBG3 form a first laser resonant cavity, three-stage pump light separated by an adjustable power distributor 2 is used as input pump light in the resonant cavity, and high-frequency three-stage optical pump is converted into low-frequency two-stage pump light in the first resonant cavity;
the level 1 bragg high reflection grating FBG1 and the level 1 tunable bragg broadband grating FBG4 constitute a second laser resonator. The fiber grating is used as a frequency selecting device, and the secondary pumping light generated by the first resonant cavity is converted into primary pumping light.
In the two cascade resonators described above, the feedback and transmission process of the three-stage pump light, the two-stage pump Pu Guang and the one-stage pump light in the resonators can be described by the following equations:
f and B respectively represent the front and rear transmission directions; p represents power, P p3 ,P p2 ,P p1 Representing three-stage pump power, two-stage pump Pu Guang power and one-stage pump light power respectively; alpha is Raman fiber loss; g is the Raman gain coefficient of the Raman fiber. In the case of strong pumping, the spontaneous raman scattering effect ASE in raman fibers is usually very weak, and thus ASE is ignored in the above equation.
The boundary conditions at z=0, z=l are respectively:
P p3 (0)＝P IN
the simulation result of the transmission process of the pump light of each stage can be obtained through the above formula and boundary conditions, and is shown in fig. 5. The power of each stage of pump light (including both forward and reverse) in the gain fiber (transmission fiber) as a function of distance can be seen in fig. 5.
Meanwhile, a corresponding experiment is carried out, and in an early experiment, the cascade Raman resonant cavity is found that pump light of each stage does not suddenly appear or disappear in the resonant cavity. For example, fig. 6 shows a three-stage pump injection to gradual enhancement, three-stage pump to one-stage pump power transfer process. The pump light is third-stage pump light, the power of the injected pump light increases to be near the second-stage Raman threshold value 3W, the second-stage pump light starts to appear, the power of the third-stage pump light gradually decreases, and the power of the second-stage pump Pu Guang gradually increases as the second-stage pump Pu Guang appears. When the pump light power injected from the outside is further enhanced, the second-stage pump light power is increased to a certain value, and is near 2.9W, the threshold value of the first-stage pump light is reached, the first-stage pump light starts to generate, the second-stage pump light is gradually weakened along with the continuous increase of the injected pump light power after the first-stage pump light is generated, the first-stage pump light is gradually enhanced, the second-stage pump Pu Guang almost disappears after reaching 10W, the first-stage pump light is continuously enhanced, and if the pump light power is continuously injected, the stokes shift light of the next stage with lower frequency (longer wavelength) is also generated when the first-stage pump light increases to reach a certain value to reach the Raman threshold value of the next stage.
Careful study found that: the conversion from three-stage pumping to two-stage pumping is completed in the first cascaded Raman laser resonant cavity, and the first-stage and second-stage pumping powers have a superposition area in the conversion process, but the superposition area cannot be utilized because the third-stage pumping power requirement is the largest in a 3-stage Raman amplifier.
The power conversion from the secondary pump to the primary pump is accomplished in the second laser resonator. In the conversion from the secondary pump to the primary pump, there is a coincidence zone II which we can use to change the ratio of the powers of the secondary pump and the primary pump. In order to obtain proper pump light power of each stage and proper proportion of the first-stage pump and the second-stage pump Pu Guang, the invention is realized by selecting the Bragg grating with adjustable reflectivity, and the proportion of the first-stage pump and the second-stage pump Pu Guang can be controlled by adjusting the reflectivity of the first-stage Bragg grating, and the purpose of controlling the respective power can be achieved.
And meanwhile, the adjustable power distributor can be adjusted to adjust the power and the proportion of the three-stage pump and the one-stage pump. If the ratio is not up to the target, the reflectivity of the second-stage tunable Bragg grating can be further adjusted.
Specific operation as shown in fig. 7, the individual conditioning steps may follow the following sequence and procedure:
(1) Setting the output power of the high-power laser to be 2 times of the given target three-stage pump power, wherein the initial splitting ratio of the adjustable power distributor is 50:50;
(2) The output end adopts a power meter, a spectrometer and other means to monitor the power of the primary pump light, the secondary pump light and the tertiary pump light;
(3) And if the proportion of the primary pumping and the secondary pumping is not in accordance with the requirement, the reflectivity of the primary Bragg output grating is regulated. The power distribution ratio of the primary and secondary output light of the overlapping region II is changed.
(4) When the distribution ratio of the first-level light and the second-level light basically meets the requirement, observing whether the ratio of the first-level pump light to the second-level pump light to the third-level pump light meets the requirement or not; if the ratio of the first-stage pump light to the second-stage pump light does not meet the requirement, the ratio of the second-stage pump light to the third-stage pump light is finely adjusted to meet the requirement;
(5) The reflectivity of the second-stage Bragg output grating is finely adjusted, so that the first-stage pump light, the second-stage pump light and the third-stage pump light meet the requirements;
(6) The above adjustment can be carried out on the site of the amplifier or the site of the system, and the adjustable power distributor is adjusted by combining the system parameters, the first-stage Bragg output grating reflectivity and the second-stage Bragg output grating reflectivity, so that the first-stage, second-stage and third-stage pumping light distribution rates finally meet the amplification requirements of the 3-stage Raman amplifier.
The invention is applied to forward pumping structure, backward pumping structure, bidirectional pumping structure and remote pumping amplifier in Raman amplifier, and the specific embodiments are shown in figures 9-12.
Claims (9)
1. A pump source for a third order raman amplifier comprising a high power raman laser characterized in that: the adjustable power distributor divides the output power of the high-power Raman laser into two parts, the first part keeps the wavelength unchanged, the first part is used as a 3-stage pumping source of a 3-stage pumping laser in the total output, 3-stage pumping light generated by the first part directly enters one input end of the broadband combiner, and the second part forms two cascaded Raman laser resonant cavities by adding a frequency selecting device: the system comprises a first cascade Raman laser resonant cavity and a second cascade Raman laser resonant cavity, wherein 3-level pump light separated by an adjustable power distributor is used as input pump light, high-frequency 3-level pump light is converted into low-frequency 2-level pump light in the first cascade Raman laser resonant cavity, 2-level pump light generated by the first cascade Raman laser resonant cavity is converted into 1-level pump light in the second cascade Raman laser resonant cavity, the first cascade Raman laser resonant cavity and the second cascade Raman laser resonant cavity sequentially generate 2-level pump light and 1-level pump light, the power of each level pump light in a gain fiber changes along with the distance, and the feedback and transmission processes of the 3-level pump light, the 2-level pump light and the 1-level pump light in the resonant cavity are described by the following equations:
f and B respectively represent the front and rear transmission directions; p represents power, P p3 ,P p2 ,P p1 Respectively representing 3-level pump power, 2-level pump light power and 1-level pump light power; alpha is Raman fiber loss; g is the Raman gain coefficient of the Raman fiber; in the case of strong pumping, the spontaneous raman scattering effect ASE in raman fibers is usually very weak, so ASE is ignored in the above equation;
the boundary conditions at z=0, z=l are respectively:
P p3 (0)＝P IN
2. the pump source of a third order raman amplifier according to claim 1, wherein: the first cascade Raman laser resonant cavity comprises a frequency-selecting device 2-level Bragg high-reflection grating (FBG 2), a gain fiber and a 2-level adjustable Bragg grating (FBG 3); the second cascaded Raman laser resonant cavity comprises a 1-level Bragg high-reflection grating (FBG 1) and a 1-level tunable Bragg broadband grating (FBG 4) of the frequency selective device.
3. The pump source of a third order raman amplifier according to claim 1, wherein: the reflectivity of the frequency selective device is adjustable, and the power and the proportion of the output light of the 1-level pump light and the 2-level pump light are realized by adjusting the reflectivity of the fiber bragg grating of the frequency selective device.
4. The pump source of a third order raman amplifier according to claim 1, wherein: the distribution proportion of the adjustable power distributor is adjustable, and the pump power of the 1-level pump light, the 2-level pump light and the 3-level pump light and the respective proportion thereof can be balanced.
5. The pump source of a third order raman amplifier according to claim 1, wherein: the optimal Raman gain effect or the optimal system transmission effect can be obtained on site by adjusting the proportion of the adjustable power distributor and the reflectivity of the adjustable Bragg grating.
6. The pump source of a third order raman amplifier according to claim 1, wherein: the output power of the high-power Raman laser is more than 5W, the wavelength is 1260-1280 nm, and the high-power Raman laser can be an optical fiber Raman laser or other types of high-power lasers.
7. A pump source for a third order raman amplifier according to claim 1 or 4, wherein: the adjustable power distributor can divide the output power of the high-power laser into two parts, the power distribution proportion of each part can be adjusted, the adjusting range is between 10 and 90 percent, the tuning proportion can be realized on site through an upper computer, and the power proportion of 3-level pump light and 1-level pump light and 2-level pump light can be adjusted through adjusting the distribution proportion.
8. A pump source for a third order raman amplifier according to claim 2, wherein: the 2-level Bragg high reflection grating is positioned at the signal input end, the reflection wavelength is 1360-1380 nm, the reflection bandwidth is 5-10 nm, and the reflectivity is more than 95%; the 2-level adjustable Bragg grating is positioned at the signal output end, the reflection wavelength is 1360-1380 nm, the reflection bandwidth is 5-10 nm, the reflectivity is adjustable, and the adjustment range is 5-90%; the 1-level Bragg high reflection grating is positioned at the signal input end, the reflection wavelength is 1420-1480 nm, the reflection bandwidth is 20-40 nm, and the reflectivity is more than 95%; the 1-stage Bragg adjustable grating at the signal output end is also a broadband grating, the reflection wavelength is 1420-1480 nm, the reflection bandwidth is 20-40 nm, the reflectivity is adjustable, and the adjustment range is 5-90%.
9. A pump source for a third order raman amplifier according to claim 2, wherein: the gain fiber is germanium-silicon fiber and has the characteristic of high Raman gain coefficient, and Stokes frequency shift is 440cm < -1 >.
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| WO2001065647A2 (en) * | 2000-02-28 | 2001-09-07 | Jds Uniphase Corporation | Cascaded raman resonator with seed source |
| CN1477739A (en) * | 2003-06-04 | 2004-02-25 | 清华大学 | All optical fibre adjustable width continuous spectrum laser pump source for superflat wide-band Raman amplification |
| CN102231476A (en) * | 2011-05-20 | 2011-11-02 | 北京化工大学 | Random fiber laser of semiconductor laser cascaded pump |
| CN102437500A (en) * | 2011-12-02 | 2012-05-02 | 北京化工大学 | Random fiber laser with tunable wavelength |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2001065647A2 (en) * | 2000-02-28 | 2001-09-07 | Jds Uniphase Corporation | Cascaded raman resonator with seed source |
| CN1477739A (en) * | 2003-06-04 | 2004-02-25 | 清华大学 | All optical fibre adjustable width continuous spectrum laser pump source for superflat wide-band Raman amplification |
| CN102231476A (en) * | 2011-05-20 | 2011-11-02 | 北京化工大学 | Random fiber laser of semiconductor laser cascaded pump |
| CN102437500A (en) * | 2011-12-02 | 2012-05-02 | 北京化工大学 | Random fiber laser with tunable wavelength |
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