Double pump wide band optical fiber parameter amplifier
Technical field
The present invention relates to a kind of double pump wide band optical fiber parameter amplifier (FOPA), relate in particular to a kind of double pump wide band optical fiber parameter amplifier of three grades of highly nonlinear optical fiber cascades, be applicable to optical fiber telecommunications system and network.
Background technology
Present optical fiber telecommunications system is extensive use of wavelength-division multiplex technique (WDM), and it can effectively utilize bandwidth of an optical fiber and realize high capacity, long-distance optical fiber communication, can increase number of services in user allocation system.In the application of these wavelength-division multiplex techniques, need the loss of each channel of a plurality of amplifier cascade peer-levels ground compensation of bigger bandwidth, thereby realized the transmission of multi-wavelength extra long distance.Yet traditional Erbium-Doped Fiber Amplifier (EDFA) (EDFA) only can provide the amplification of 1530-1625nm wavelength coverage light signal, can not satisfy the further requirement of dilatation of DWDM (dense wave division multipurpose).Adopt the fiber Raman amplifier of multi wavelength pumping can provide the broadband about 100nm to amplify, although analyze theoretically, adopt and divide the band pumping configuration, can cover the whole low loss window (from 1250nm to 1650nm) of all-wave fiber on the smooth bandwidth theory of raman amplifier, but need to adopt full wave multiplexer and demodulation multiplexer, this has increased the insertion loss greatly, causes that the system power cost raises, and has reduced the transmission performance of system.Therefore, to cover the fiber amplifier of whole all-wave fiber low loss window be the research theme of wavelength division multiplexing communications systems to research Wideband fiber amplifier, particularly gain bandwidth (GB).Optical fiber parameter amplifier utilizes the four-wave mixing effect amplifying optical signals, can provide a broadband to amplify at any wave band, its noise figure is lower than the quantum limit of 3dB in addition, can be used as wide-band optical amplifier, wavelength shifter, return-to-zero code pulse producer, Optical Time Division Multiplexing switch and full light signal sampling thief etc.Single pumping single-stage optical fiber parameter amplifier has obtained the gain bandwidth (GB) of 200nm in the laboratory, but flat gain is very poor, makes it be difficult to be applied in the wavelength-division multiplex system.Application number is to propose to use the highly nonlinear optical fiber of level Four cascade to constitute single pumping multi-stage fiber parameter amplifier in 200410025214.0 the Chinese invention patent, this amplifier can provide the bandwidth of 320nm in theory, but its bandwidth can't cover the low loss window (1250-1650nm) of all-wave fiber, simultaneously, the employed highly nonlinear optical fiber progression of this amplifier is more, has increased splice loss, splice attenuation.
Therefore, research band optical fiber parameter amplifier, the particularly gain bandwidth (GB) fiber amplifier that covers whole all-wave fiber low loss window is the research theme of WDM communication system.
Summary of the invention
The objective of the invention is at the deficiencies in the prior art, propose a kind of double pump wide band optical fiber parameter amplifier, reduce highly nonlinear optical fiber progression, and make the smooth bandwidth of optical fiber parameter amplifier can cover the low loss window of all-wave fiber.
In order to realize such purpose, in technical scheme of the present invention, double pump wide band optical fiber parameter amplifier by two pump lasers, pumping coupler, signal laser, signal coupler, wavelength division multiplexer and successively three grades of highly nonlinear optical fibers of cascade constitute.The output of two pump lasers connects wavelength division multiplexer through pumping coupler, and the output of signal laser connects wavelength division multiplexer through signal coupler, and the output of wavelength division multiplexer is connected to three grades of highly nonlinear optical fibers of cascade successively.
Two pumping light wave (λ that pump laser is launched
P1, λ
P2) be coupled into Transmission Fibers through pumping coupler, the flashlight (λ that same signal laser is launched
s) also be coupled into Transmission Fibers through signal coupler, and then by wave division multiplex coupler two pump lights and flashlight are multiplexed in three grades of highly nonlinear optical fibers of cascade successively the four-wave mixing effect takes place, thereby realized the effect that parameter amplifies.Wherein, the zero-dispersion wavelength (λ of first order optical fiber
0) and two pump light centre wavelength (λ
c=(λ
P1+ λ
P2)/2) approaching, second level optical fiber the 2nd order chromatic dispersion of pump light central wavelength be on the occasion of, and third level optical fiber is negative value in the 2nd order chromatic dispersion of pump light central wavelength.
Two pump lights and flashlight through pumping coupler and signal coupler coupling, after wavelength division multiplexer is multiplexing, enter the first order, the second level, third level highly nonlinear optical fiber respectively more successively.Input signal light and two pump lights will produce idle light after entering first order optical fiber, and the gain spectral of its output terminal becomes near symmetrical to distribute about pump light centre wavelength, but uneven.Then flashlight, pump light and idle light through second level optical fiber after, the sunk part in the middle of the gain spectral has reduced, the uneven degree of gain spectral curve (maximum gain and least gain poor) reduction.Behind third level optical fiber, gain spectral obtains revising, and its flatness reaches in the 0.2dB.
Physical parameter such as zero-dispersion wavelength, 2nd order chromatic dispersion and fourth-order dispersion, fiber lengths and the two pump light wavelength and the pumping light powers of first order optical fiber are depended in the smooth bandwidth of optical fiber parameter amplifier of the present invention and gain, and the effect of second, third grade optical fiber is that the gain spectral that first order optical fiber is produced becomes smooth.
The length of the first order optical fiber of optical fiber parameter amplifier of the present invention, second level optical fiber, third level optical fiber is between 0.1-300 rice, and the nonlinear factor of optical fiber is at 1-300W
-1.Km
-1Between, the fourth-order dispersion absolute value is less than 1.0 * 10
-4Ps
4Km
-1The mean wavelength of the zero-dispersion wavelength of first order optical fiber and two pump lights is approaching, and the selection of pump light wavelength is positioned at the 1250-1650nm scope, promptly covers the low loss window of all-wave fiber.Second level optical fiber the 2nd order chromatic dispersion of pump light central wavelength be on the occasion of, and third level optical fiber is negative value in the 2nd order chromatic dispersion of pump light central wavelength.
Double pumping action optical fiber parameter amplifier of the present invention not only can provide a gain spectral that the broadband is smooth, and can overcome because the idle spectrum line that pump light shake causes is widened, and can also use the pump light of pairwise orthogonal polarization and obtains independently characteristic of polarization.The double pumping action optical fiber parameter amplifier of three grades of highly nonlinear optical fiber cascade structures of use can provide the gain bandwidth (GB) above 400nm, with respect to the level Four cascade structure, not only reduced highly nonlinear optical fiber progression, and suitably choosing by parameter, make the smooth bandwidth of optical fiber parameter amplifier can cover the low loss window (from 1250nm to 1650nm) of all-wave fiber, increased the wavelength coverage applicatory of WDM to a great extent, thereby can make full use of the bandwidth of all-wave fiber, promote the development of WDM optical fiber telecommunications system.
Description of drawings
Fig. 1 is the structural representation of band optical fiber parameter amplifier of the present invention.
Fig. 2 is the gain spectrogram of the band optical fiber parameter amplifier of 405nm for bandwidth.
Among Fig. 2, G
1, G
2, G
3Be respectively through the first, two, the gain spectral behind three grades of high non-linearities.
Embodiment
Below in conjunction with drawings and Examples technical scheme of the present invention is further described.
The structure of double pump wide band optical fiber parameter amplifier of the present invention as shown in Figure 1, by two pump lasers, pumping coupler, signal laser, signal coupler, wavelength division multiplexer, first order highly nonlinear optical fiber, second level highly nonlinear optical fiber and third level highly nonlinear optical fiber constitute.The output of two pump lasers connects wavelength division multiplexer through pumping coupler, and the output of signal laser connects wavelength division multiplexer through signal coupler, and the output of wavelength division multiplexer is connected to three grades of highly nonlinear optical fibers of cascade successively.
Two pumping light wave (λ that the pump light laser instrument is launched
P1, λ
P2) be coupled into Transmission Fibers through the pump light coupling mechanism, the flashlight (λ that same flashlight laser instrument is launched
s) also be coupled into Transmission Fibers through the flashlight coupling mechanism, and then by wavelength division multiplexer two pump lights and flashlight are multiplexed in three grades of highly nonlinear optical fibers of cascade successively non-linear four-wave mixing effect takes place, thereby realized the effect that parameter amplifies.Wherein, the zero-dispersion wavelength (λ of first order optical fiber
0) and pump light centre wavelength (λ
c=(λ
P1+ λ
P2)/2) approaching, second level optical fiber the 2nd order chromatic dispersion of pump light central wavelength be on the occasion of, and third level optical fiber is negative value in the 2nd order chromatic dispersion of pump light central wavelength.
Two pump lights and flashlight through pumping coupler and signal coupler coupling, after wavelength division multiplexer is multiplexing, enter the first order respectively more successively, the second level, third level highly nonlinear optical fiber, three grades of highly nonlinear optical fibers use the joints of optical fibre to couple together, and general interface loss is about 0.6dB.Input signal light and two pump lights will produce idle light after entering first order optical fiber, and the gain spectral of its output terminal is approximated to symmetrical distribution about pump light centre wavelength, but uneven.Then flashlight, pump light and idle light through second level optical fiber after, the sunk part in the middle of the gain spectral reduces, thereby has reduced the gain shake that first order optical fiber is produced.Behind third level optical fiber, gain spectral is further revised, and its flatness reaches in the 0.2dB.
Embodiment:
The double pump wide band optical fiber parameter amplifier of 405nm bandwidth.Two pumping light power P wherein
1=P
2=1W, two pump light wavelength X
P1=1440nm, λ
P1=1460nm, optical fiber fourth-order dispersion factor beta
4=-2 * 10
-6Ps
4Km
-1, nonlinear fiber coefficient gamma=60km
-1W
-1First order highly nonlinear optical fiber length L
1=25m, the 2nd order chromatic dispersion factor beta
21=0ps
2Km
-1Second level highly nonlinear optical fiber length L
2=2.6m, the 2nd order chromatic dispersion factor beta
22=2.91 * 10
-2Ps
2Km
-1Third level highly nonlinear optical fiber length L
3=2.3m, the 2nd order chromatic dispersion factor beta
23=-11.29 * 10
-2Ps
2Km
-1The present invention at first by finding the solution non-linear Schrodinger equation, obtains the gain function of double pump wide band optical fiber parameter amplifier, utilizes genetic algorithm to obtain the optimal value of three grades of highly nonlinear optical fiber parameters then.The zero-dispersion wavelength of first order optical fiber and pump light centre wavelength are approaching, promptly in the pump light central wavelength lambda
0=1450nm place 2nd order chromatic dispersion β
21=0; First order optical fiber has determined band optical fiber parameter amplifier gain level and gain bandwidth (GB), and therefore in order to produce a big gain, getting first order fiber lengths is 25m; In order to satisfy phase-matching condition, need make the fourth-order dispersion β of 3-stage optical fiber
4Be negative value, get β
41=β
42=β
43-2 * 10
-6Ps
4Km
-1Input signal light and pump light will produce idle light after wave division multiplex coupler is coupled into first order optical fiber, the gain spectral of its output terminal becomes near symmetrical to distribute about pump light centre wavelength, but uneven, as the gain spectrum G among Fig. 2
1Shown in.Second level optical fiber is on the occasion of, β in the 2nd order chromatic dispersion of pump light central wavelength
22=2.91 * 10
-2Ps
2Km
-1, it does not utilize when not satisfying phase-matching condition and produces parametric gain in the normal dispersion district, and the result of cross modulation can produce the gain that a secondary increases, and this grade fiber lengths is 2.6m.Flashlight, pump light and idle light through second level optical fiber after, the sunk part in the middle of the gain spectral reduces, the uneven degree of gain spectral curve (maximum gain and least gain poor) reduction is as the gain spectrum G among Fig. 2
2Shown in.The 2nd order chromatic dispersion of third level optical fiber is a negative value, β
23=-11.29 * 10
-2Ps
2Km
-1, it is used for providing the gain of a squarish at an abnormal dispersion fiber, thereby reduces the gain shake that first order optical fiber is produced.This grade fiber lengths is 2.3m.So behind the second level and third level optical fiber, the gain spectral of double pump wide band optical fiber parameter amplifier is further revised, its flatness reaches in the 0.2dB, as the gain spectrum G among Fig. 2
3Shown in.In addition, the loss of optical fiber at different levels junction also is to need to consider that the interface loss of general highly nonlinear optical fiber that is to say power with loss 13% about 0.6dB, so k section optical fiber porch pump power should be adjusted into P when calculating
k=P
0α
(k-1), α=0.87, wherein P
0=P
1+ P
2=2W.In a word, first order optical fiber is used to produce a big gain, and back two-stage optical fiber is used to even up gain spectral.By to the 3-stage optical fiber optimum Design of Parameters, finally obtained the band optical fiber parameter amplifier of gain bandwidth (GB) 405nm, its gain flatness is less than 0.2dB.
Physical parameter such as zero-dispersion wavelength, 2nd order chromatic dispersion and fourth-order dispersion, fiber lengths and the pump light wavelength and the pumping light power of first order optical fiber depended in the smooth bandwidth of double pump wide band optical fiber parameter amplifier of the present invention and gain, and the effect of second, third grade optical fiber is that the gain spectral that first order optical fiber is produced becomes smooth.Suitable these parameters of choosing can obtain the optical fiber parameter amplifier that smooth bandwidth covers the all-wave fiber low loss window, thereby can make full use of the bandwidth of all-wave fiber, promote the development of WDM optical fiber telecommunications system.
Table 1 is the most optimized parameter of the double pump wide band optical fiber parameter amplifier of bandwidth 405nm, and L is the length of optical fiber in the table, β
2Be 2nd order chromatic dispersion coefficient, β
4Be fourth-order dispersion coefficient, P
1, P
2Be two pumping light powers, γ is the nonlinear fiber coefficient, λ
P1, λ
P2Be two pump light wavelength, λ
0Be the zero-dispersion wavelength of optical fiber, bandwidth is the gain bandwidth (GB) of the band optical fiber parameter amplifier that obtains.
Optical fiber | The 1st grade | The 2nd grade | 3rd level |
L(m) | 25 | 2.6 | 2.3 |
β
2(×10
-2ps
2km
-1)
| 0 | 2.91 | -11.29 |
P
1=P
2=1W,β
4=-2×10
-6ps
4km
-1,γ=60km
-1W
-1,λ
p1=1440nm, λ
p2=1460nm,λ
0=1450nm,bandwidth=405nm.
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