CN101567725A - Method and device for inhibiting stimulated Brillouin scattering based on multiple frequency phase modulation - Google Patents

Abstract

The invention relates to a method and a device for inhibiting stimulated Brillouin scattering based on multiple frequency phase modulation, in particular to a method and a device for inhibiting stimulated Brillouin scattering through a multiple frequency phase modulation method in an optical fiber system, aiming at solving the problems of smaller inhibition degree, lower efficiency and poorer stability of the prior method for inhibiting the stimulated Brillouin scattering. Pumping light is split after being modulated, the spectrum of a first output beam is measured, a second light beam is split, and the centripetal fiber power P of the split first light beam is measured; and the second light beam enters a single mode optical fiber through an optical circulator and the power P SBS is measured. A multiple frequency phase modulator, an optical isolator and a first coupler are all arranged on an emission light path of a single mode laser, an F-P interferometer and a second coupler are respectively arranged on two emergence light paths of the first coupler, a first detector and the optical circulator are respectively arranged on two emergence light paths of a second coupler, a second detector is arranged on a reverse emergence light path of the light circulator, and the single mode optical fiber is arranged on an emergence light path of the light circulator.

Description

Stimulated Brillouin scattering (SBS) suppression method and device based on the multifrequency phase modulation

Technical field

The present invention relates to the optical communication field, be specifically related to a kind of method and device that in fibre system, suppresses stimulated Brillouin scattering by the method for multifrequency phase modulation.

Background technology

Many nonlinear effects are arranged, as stimulated Brillouin scattering (SBS), stimulated Raman scattering (SRS), four wave mixing, from phase modulated, cross-phase modulation etc. in the optical fiber.Wherein stimulated Brillouin scattering is the nonlinear effect that a kind of luminous power with the fl transmission light signal is transferred to rear orientation light and phonon fields, several nonlinear effects of in stimulated Brillouin scattering effect and the optical fiber other relatively, have minimum threshold power, thereby be easy to most take place.The stimulated Brillouin scattering effect causes the loss of flashlight, causes the receiving terminal Optical Signal To Noise Ratio to descend, and seriously influences the performance of optical transmission system.For fear of the generation of stimulated Brillouin scattering effect, the launched power of system can only be limited in below the stimulated Brillouin scattering threshold value, and this has influenced the raising of the performance of optical transmission system.Usually adopt the method that improves the threshold value of stimulated Brillouin scattering effect in the optical fiber to suppress the stimulated Brillouin scattering effect.

The inhibition method of stimulated Brillouin scattering mainly contains laser high-frequency dithering, dispersion compensation method, elongation strain method and and single-frequency phase modulated method in the optical fiber.But the shortcoming of these four kinds of methods is limited for the degree of the inhibition of stimulated Brillouin scattering effect, and efficient is lower, and stability is also lower, therefore needs a kind of method that can suppress the stimulated Brillouin scattering effect effectively.

Summary of the invention

The existing inhibition degree that the method for inhibition stimulated Brillouin scattering exists in optical fiber is less, efficient is lower and the problem of less stable, and a kind of stimulated Brillouin scattering (SBS) suppression method and device based on the multifrequency phase modulation is provided in order to solve in the present invention.Method of the present invention is realized by following steps:

Step 1, the pumping light that fiber laser is produced are input in the multifrequency phase modulator and modulate, and obtain light modulated;

Step 2, with this light modulated by the optical isolator beam split, by first coupler output, two bundle light modulated, first bundle is by its spectrum of F-P interferometer measurement again;

Another bundle light modulated of step 3, the output of first coupler is divided into two bundles through second coupler, and wherein a branch of light modulated is input to first detector, records the launched power P of this light modulated;

Another bundle light modulated of step 4, the output of second coupler enters monomode fiber through optical circulator, and is surveyed the power P of scattered light by second detector on the optical transmission opposite direction that is arranged on monomode fiber _SBS

Device of the present invention is by fiber laser, the multifrequency phase modulator, optical isolator, first coupler, the F-P interferometer, second coupler, first detector, second detector, optical circulator and monomode fiber are formed, the multifrequency phase modulator, the optical isolator and first coupler all are successively set on the fiber laser emission light path, the F-P interferometer is arranged on first emitting light path of first coupler, second coupler is arranged on second emitting light path of first coupler, first detector is arranged on first emitting light path of second coupler, optical circulator is arranged on second emitting light path of second coupler, second detector is arranged on the reverse emitting light path of optical circulator, and monomode fiber is arranged on the emitting light path of optical circulator.

Beneficial effect: this method splits into many spectral lines by the spectrum of multifrequency phase being modulated pumping light, energy just according to the mould of fundamental frequency and each rank side frequency complex amplitude square ratio be assigned on each bar spectral line, the threshold power of stimulated Brillouin scattering is significantly improved under the constant amplitude situation, simultaneously as can be known the threshold power of stimulated Brillouin scattering except outside the Pass having with modulation depth, phase angle, also relation is arranged with the modulation fundamental frequency, this method can suppress the stimulated Brillouin scattering effect effectively, has the advantages that modulation electric is forced down, efficient high and stability is high.

Description of drawings

Fig. 1 is an apparatus structure schematic diagram of the present invention; Fig. 2 is not for there being the modulation reflectance curve; Fig. 3 is three constant amplitude reflectance curves; Fig. 4 is five constant amplitude reflectance curves.

Embodiment

Embodiment one: referring to Fig. 1～Fig. 4, the method for present embodiment is made up of following steps:

Step 1, the pumping light that operation wavelength is produced at the distribution type fiber-optic laser 1 of the narrow linewidth of 1550.12nm are input in the multifrequency phase modulator 2 and modulate, and obtain the light modulated of three constant amplitudes or five constant amplitudes;

Step 2, this light modulated be by optical isolator 3 beam split, 1% of first coupler, 4 these light modulated of output by 1: 99 measures its spectrum by cofocus scanning F-P interferometer 5 again;

Another bundle light modulated of step 3,4 outputs of first coupler is divided into two bundles through 1: 1 second coupler 6, and wherein a branch of light modulated is input to first detector 7, records the launched power P of this light modulated;

Another bundle light modulated of step 4,6 outputs of second coupler enters monomode fiber 10 through optical circulator 9, and is surveyed the power P of scattered lights by second detector 8 on the optical transmission opposite direction that is arranged on monomode fiber 10 _SBS

Spectrum through multifrequency phase modulation pumping light splits into many spectral lines, and formula (1) has provided the complex amplitude of the fundamental frequency after the modulation and each rank side frequency:

$\left\{\begin{array}{c}{\mathrm{<figure-callout\; id="0"\; label="A"\; filenames="A20081006434800081.png,A20081006434800082.png"\; state="\{\{state\}\}">A</figure-callout>}}_0=\underset{{\mathrm{\&Sigma;}}_{k=1}^{+\&infin;}k\&CenterDot;n_k=0}{\mathrm{\&Sigma;}}{\mathrm{\&Pi;}}_{k=1}^{+\&infin;}{J}_{n_k}({\mathrm{\&gamma;}}_k,{\mathrm{\&phi;}}_k)\\ A_i=\underset{{\mathrm{\&Sigma;}}_{k=1}^{+\&infin;}k\&CenterDot;n_k=i}{\mathrm{\&Sigma;}}{\mathrm{\&Pi;}}_{k=1}^{+\&infin;}{J}_{n_k}({\mathrm{\&gamma;}}_k,{\mathrm{\&phi;}}_k)i=\mathrm{1,2,3}\&CenterDot;\&CenterDot;\&CenterDot;\\ A_{-i}=\underset{{\mathrm{\&Sigma;}}_{k=1}^{+\&infin;}k\&CenterDot;n_k=-i}{\mathrm{\&Sigma;}}{\mathrm{\&Pi;}}_{k=1}^{+\&infin;}{J}_{n_k}({\mathrm{\&gamma;}}_k,{\mathrm{\&phi;}}_k)\end{array}\right.---\left(1\right)$

Wherein, A ₀Be the fundamental frequency amplitude, A _iAnd A _-iBe respectively the amplitude of lower side frequency on the i rank, Be modulation index, φ _kIt is the initial phase of harmonic wave.Because the right of formula (1) all is unlimited combination, can not carry out numerical simulation, and the voltage that experimentally is carried on the modulator can be very not big, therefore when numerical simulation the choice of modulation number less than 4.The value of the high-order distortion Bessel function on formula (1) the right is very little in addition, therefore can ignore, and can carry out numerical simulation.Spectrum through multifrequency phase modulation pumping light splits into many spectral lines, energy just according to the mould of fundamental frequency and each rank side frequency complex amplitude square ratio be assigned on each bar spectral line, formula (1) has provided the complex magnitude of fundamental frequency and each rank side frequency.If the threshold power of stimulated Brillouin scattering is P during no modulation system ₀Then the threshold power after ovennodulation is:

$P={\mathrm{<figure-callout\; id="0"\; label="P"\; filenames="A20081006434800081.png,A20081006434800082.png"\; state="\{\{state\}\}">P</figure-callout>}}_0\&CenterDot;\frac{1}{\max {\left|A_i\right|}^2}---\left(2\right)$

By formula (2) as can be known, the threshold power after the modulation is with square the being inversely proportional to relation of the mould of fundamental frequency and each rank side frequency complex amplitude, and according to optimization method as if obtaining high as far as possible threshold power, spectrum line must be a constant amplitude.By the selection of modulation index, get γ ₁,, can know max|A at=1.435 o'clock through numerical simulation ₃| ²=0.300; Get γ ₁=1.240, γ ₂=1.531, φ ₂During=0.5 π, through numerical simulation, max|A ₅| ²=0.138.In this execution mode, the modulation signal fundamental frequency of three constant amplitudes, five constant amplitudes is 60MHz, and this is because the roomy about 30MHz of Brillouin zone in the monomode fiber, and fundamental frequency to be its two times make light comb opening very much of dividing between each bar spectral line, avoided mutual influence.And the stimulated Brillouin scattering threshold value of not having when modulating is known, so substitution max|A ₃| ²=0.300 and max|A ₅| ²=0.138 just can obtain the stimulated Brillouin scattering threshold value under three constant amplitudes and the five constant amplitude situations.

The definition reflectivity is that 1% o'clock launched power is the threshold power of stimulated Brillouin scattering, then can obtain not having modulation from curve, the experiment value of three constant amplitudes, five constant amplitude stimulated Brillouin scattering threshold powers.Threshold power substitution formula (2) during with the nothing modulation obtains the theoretical value of each constant amplitude stimulated Brillouin scattering threshold power, the threshold power of stimulated Brillouin scattering is not 6.53mW when having modulation, the threshold power of the stimulated Brillouin scattering the during modulation of three constant amplitudes is 21.69mW, and the threshold power of the stimulated Brillouin scattering the during modulation of three constant amplitudes is 44.82mW.

The theoretical improvement value of three constant amplitudes and five constant amplitudes modulation lower threshold value is respectively 5.23dB and 8.60dB, and the improvement value of experiment is 5.21dB and 8.36dB, and in the scope that error allows, the multifrequency phase modulation method can well suppress the stimulated Brillouin scattering effect.

Embodiment two: referring to Fig. 1, the device of present embodiment is by fiber laser 1, multifrequency phase modulator 2, optical isolator 3, first coupler 4, F-P interferometer 5, second coupler 6, first detector 7, second detector 8, optical circulator 9 and monomode fiber 10 are formed, multifrequency phase modulator 2, the optical isolator 3 and first coupler 4 all are successively set on the fiber laser 1 emission light path, F-P interferometer 5 is arranged on first emitting light path of first coupler 4, second coupler 6 is arranged on second emitting light path of first coupler 4, first detector 7 is arranged on first emitting light path of second coupler 6, optical circulator 9 is arranged on second emitting light path of second coupler 6, second detector 8 is arranged on the reverse emitting light path of optical circulator 9, and monomode fiber 10 is arranged on the emitting light path of optical circulator 9.

Claims (2)

1,, it is characterized in that it is realized by following steps based on the stimulated Brillouin scattering (SBS) suppression method of multifrequency phase modulation:

Step 1, the pumping light that fiber laser (1) is produced are input in the multifrequency phase modulator (2) and modulate, and obtain light modulated;

Step 2, with this light modulated by optical isolator (3) beam split, by first coupler (4) output, two bundle light modulated, first bundle is measured its spectrum by F-P interferometer (5) again;

Another bundle light modulated of step 3, first coupler (4) output is divided into two bundles through second coupler (6), and wherein a branch of light modulated is input to first detector (7), records the launched power P of this light modulated;

Another bundle light modulated of step 4, second coupler (6) output enters monomode fiber (10) through optical circulator (9), and is surveyed the power P of scattered light by second detector (8) on the optical transmission opposite direction that is arranged on monomode fiber (10) _SBS

2, stimulated Brillouin scattering restraining device based on the multifrequency phase modulation, it is characterized in that it is by fiber laser (1), multifrequency phase modulator (2), optical isolator (3), first coupler (4), F-P interferometer (5), second coupler (6), first detector (7), second detector (8), optical circulator (9) and monomode fiber (10) are formed, multifrequency phase modulator (2), optical isolator (3) and first coupler (4) all are successively set on fiber laser (1) the emission light path, F-P interferometer (5) is arranged on first emitting light path of first coupler (4), second coupler (6) is arranged on second emitting light path of first coupler (4), first detector (7) is arranged on first emitting light path of second coupler (6), optical circulator (9) is arranged on second emitting light path of second coupler (6), second detector (8) is arranged on the reverse emitting light path of optical circulator (9), and monomode fiber (10) is arranged on the emitting light path of optical circulator (9).

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