CN104062012A - Method and device for carrying out frequency domain staring pumping detection on Brillouin signals based on detection light flat top spectrum modulation method - Google Patents

Abstract

The invention discloses a method and device for carrying out frequency domain staring pumping detection on Brillouin signals based on the detection light flat top spectrum modulation method, and belongs to the field of optics. By means of the method for carrying out frequency domain staring pumping detection on the Brillouin signals based on the detection light flat top spectrum modulation method, staring detection of the Brillouin gain/loss signals transmitted in media can be carried out in a spectral space. The method comprises the frequency domain staring pumping detection technology and the detection light flat top spectrum modulation technology. According to the frequency domain staring pumping detection technology, staring detection of the Brillouin signal is achieved in a frequency domain based on the principle of selective SBS between staring detection light and pumping light. According to the detection light flat top spectrum modulation technology, internal modulation of a small-line-width DFB laser device is achieved through an arbitrary waveform generator, and the flat-topped glaring detection light with the frequency domain view field and the frequency spectrum power density capable of being flexibly adjusted is obtained.

Description

Based on surveying light flat-top spectrum modulation method, realize method and the device that Brillouin's signal frequency domain is stared pump probe

Technical field

The information extracting method that the present invention relates to a kind of Brillouin's signal, belongs to optical field.

Background technology

Brillouin's signal (being brillouin gain/loss spectra) comprises the important informations such as Brillouin shift, live width and gain envelope, at aspects such as the filter and amplification of distributing optical fiber sensing, feeble signal and Brillouin laser radar detections, is widely used.In order to obtain Brillouin's signal of high s/n ratio, conventionally adopt pumping-detection method to amplify to Brillouin's signal extractions, by being excited the stimulated Brillouin scattering (SBS) of sound field and pump light and detection light in nonlinear medium, act on the power transfer (comprising brillouin gain and Brillouin's loss) realizing between pump light and detection light.Due to the accurate coupling of above-mentioned SBS process need frequency, the frequency sweeping time that traditional pumping-probe method needs is longer, quick information in the time of cannot effectively extracting, and frequency sweep process can cause gain spectral distortion simultaneously.

In order to address the above problem, the people such as the Gao Wei of Harbin University of Science and Technology once proposed three kinds of solutions:

1, Chinese patent < < pumping-detection method non-scanning type is measured the device and method > > of brillouin gain spectrum, publication number is CN102967371A, and publication date is on March 13rd, 2013; This patent discloses a kind of method, and the mode that the ASE light source of usining is stared detection light as frequency domain has realized non-scanning type pumping-detection method measurement brillouin gain spectrum.

2, Chinese patent < < seed injects BOTDR distributed optical fiber sensing system > >, and publication number is CN103604450A, and publication date is on February 26th, 2014; This patent discloses the remote distributed optical fiber sensing system of high-performance based on above-mentioned principle, has brillouin gain/loss signal of high s/n ratio and without lay optical fiber circuit for double-end measurement.But as frequency domain, stare the ASE light source of surveying light, its frequency domain visual field (frequency range) and spectral power density modulation underaction, and seed light modular structure is complicated, and not ideal enough for sensor-based system.

3, Chinese patent < < adopts rectangle spectrum to survey the device and method > > of photo measure optical fiber Brillouin gain spectral, publication number is CN103308171A, publication date is on September 18th, 2013, the frequency domain that this patent adopts microwave signal generator and intensity modulator to obtain Stokes frequency displacement is stared detection light, and carry out shaping to surveying light spectrum, make it be applicable to being applied in remote distributed sensing, yet microwave signal generator is expensive, intensity modulator is subject to the stability influence of bias direct current power supply larger.

Summary of the invention

The object of the present invention is to provide a kind of technology that realization is stared pump probe to Brillouin's signal enforcement frequency domain based on detection light flat-top spectrum modulation method, can in spectral space, stare detection to the brillouin gain/loss signal transmitting in medium.Compared to the inventor's disclosed technology in patent documentation 1,3, this system has more performance and cost advantage under some application scenarios.Structure is relatively simple, cost is lower, for providing a kind of new Scheme Choice such as application scenarioss such as brillouin distributed optical fiber sensing systems.

In order to reach this object, provided by the present inventionly based on surveying light flat-top spectrum modulation method, realize the method that Brillouin's signal frequency domain is stared pump probe, it is characterized in that, the method comprises:

Frequency domain is stared pump probe technology, utilizes and stares the selectivity SBS principle of surveying between light and pump light, realizes the detection of staring to Brillouin's signal in frequency domain;

With

Survey light flat-top spectrum modulation technique, utilize arbitrary waveform signal generator to realize the internal modulation to narrow linewidth Distributed Feedback Laser, obtain flat-top and frequency domain visual field and the spectral power density adjustable detection light of staring flexibly.

Above-described frequency domain is stared pump probe technology and is further interpreted as, as shown in Figure 1, when frequency domain visual field completely or partially covers staring of pump light Brillouin shift scope and surveys the pump light generation spectral selectivity SBS effect of transmitting in light and medium, pump light is surveyed light, in medium, frequency-selecting power transfer will be occurred with staring, and finally reaches the Effect on Detecting of staring to Brillouin's signal.

Therefore technology of the present invention can be made frequency domain to Brillouin's signal fast flexibly according to demand and stares detection, now the present invention is summarized as follows: the present invention is based on SBS principle, the radiofrequency signal of utilizing arbitrary waveform signal generator to produce, narrow linewidth Distributed Feedback Laser is carried out to internal modulation formation frequency domain and stare detection light, its frequency domain visual field covers the Brillouin shift spectral limit that pump light forms in medium, and the bandwidth width that frequency domain visual field can be realized according to actual needs within the scope of flat-top error 1dB is adjustable arbitrarily.Whole measurement mechanism is simple in structure, easy to operate, and cost is lower, has substantially contained the advantage of the apparatus and method of previous all detection brillouin gain spectrums.With take the device that ASE surveys light pumping-detection method non-scanning type as staring measures brillouin gain spectrum and compare, stare and survey light and more stablize and there is fabulous flat-top effect and signal to noise ratio (S/N ratio), frequency domain visual field and spectral power density can be modulated flexibly, and device is simple, strong operability; Utilize the method, can greatly improve the signal to noise ratio (S/N ratio) of measuring brillouin gain spectrum at low-power incident pump light, more than signal to noise ratio (S/N ratio) is improved to 35dB.

Accompanying drawing explanation

Fig. 1 is that frequency domain is stared pump probe technology and Brillouin's signal implemented to stare the schematic diagram of detection at frequency domain;

Fig. 2 realizes of the present inventionly based on surveying light flat-top spectrum modulation method, realizing the light channel structure schematic diagram that Brillouin's signal frequency domain is stared the device of pumping detecting method in optical fiber;

Fig. 3 (a), (b) stare to survey light spectral pattern figure;

Fig. 4 (a), (b) stare the amplification effect performance plot of surveying light brillouin gain signal.

Embodiment

Embodiment one: present embodiment is described in conjunction with Fig. 2, the present embodiment is in optical fiber, to demonstrate based on surveying light flat-top spectrum modulation method, to realize the practical measuring examples that Brillouin's signal frequency domain is stared pump probe technology described in the present invention, this example is based on brillouin scattering signal in optical fiber and stare detection light selecting performance SBS principle, and adopting heterodyne detection method to demonstrate amplification effect, it is by narrow band fiber laser instrument 1, fiber coupler 2,4,12; Polarization Controller 3,9,11; Photoswitch 7; Optical fiber circulator 5; Medium optical fiber 6; Fibre optic isolater 8; Stare and survey light generation module 10; Photodetector 13; Signal processor 14 forms.

The output port of narrow band fiber laser instrument 1 is connected to the input port of the first fiber coupler 2, the first output port 2-1 of the first fiber coupler 2 is communicated with the input port of the first Polarization Controller 3, the second output port 2-2 of the first fiber coupler 2 and the input port of the 3rd Polarization Controller 11 join

Optical fiber circulator 5 comprises the first port 5-1, the second port 5-2 and the 3rd port 5-3,

The output terminal port of the first Polarization Controller 3 joins with the first port 5-1 of optical fiber circulator 5 through the second fiber coupler 4, one end of the second port 5-2 connecting media optical fiber 6 of optical fiber circulator 5, output port and the second Polarization Controller 9 of staring detection light generation module 10 join, the output port of the second Polarization Controller 9 connects photoswitch 7 through fibre optic isolater 8, the other end of the direct access medium optical fiber 6 of photoswitch 7 first output terminal 7-1, the second output terminal 7-2 meets the second coupling mechanism 4 first input end 4-1, optical fiber circulator 5 the 3rd port 5-3 is as measured signal output port,

Optical fiber circulator 5 the 3rd port 5-3 connects the first input end mouth 12-1 of the 3rd fiber coupler 12, the output terminal of the 3rd Polarization Controller 11 connects the second input port 12-2 of the 3rd fiber coupler 12, the output port 12-3 of the 3rd fiber coupler 12 connects the input port of photodetector 13, and the input port of the output port of photodetector 13 and signal processor 14 joins.

Embodiment two: present embodiment is that the concrete behavior of photoswitch 7 in embodiment one is described further is that both-end frequency domain is stared pump probe method when staring detection light from optoisolator 8 output terminal outputs when the first output terminal of photoswitch 7 enters medium optical fiber 6; When staring from optoisolator 8 output terminals, survey light and for utilizing, stare the single-ended frequency domain of surveying light reflection and stare pump probe method when the second output terminal of photoswitch 7 accesses the first input end 4-1 of the second fiber coupler 4.

Embodiment three: present embodiment is to stare further illustrating of pump probe technology to realizing Brillouin's signal frequency domain based on seed light flat-top spectrum modulation method described in embodiment one, the output port of arbitrarily signal generating device 10-2 is communicated with the radio-frequency (RF) signal input end mouth of C-band Distributed Feedback Laser 10-1, the light signal output end mouth of C-band Distributed Feedback Laser 10-1 is to stare the light signal output end mouth of surveying light generation module 10, and the light signal output end mouth of C-band Distributed Feedback Laser 10-1 is connected with the second Polarization Controller 9.

Embodiment four: present embodiment is to realize the further restriction of the technology of Brillouin's signal-selectivity amplification described in embodiment one based on seed light flat-top spectrum modulation method, described narrow band fiber laser instrument 1 is C-band Distributed Feedback Laser, and live width scope is 1KHz～10MHz; Narrow linewidth DFB module 10 is C-band Distributed Feedback Laser, and live width scope is 1KHz～50MHz.

Embodiment five: present embodiment is the further restriction of surveying light generation module 10 to staring described in embodiment three, the radio frequency output signal of described arbitrarily signal generating device 10-2 is that 2.8MHz, symmetry are 37.6%, amplitude is the periodicity triangular signal that 28mVpp, drift rate are 0mVpp.

Embodiment six: present embodiment is to being described further based on seed light flat-top spectrum modulation method described in the present invention: DFB (Distributed Feedback Laser), be distributed feedback laser, the Bragg grating that has been built-in and belong to the semiconductor laser of side-emitted.Distributed Feedback Laser has spectrum widening effect under the effect of current-modulation, relates to three kinds of main mechanisms here:

1. instantaneous chirp, it is directly proportional to the interconversion rate of electric current (light intensity); The typical time constant of Distributed Feedback Laser is 100ps, and for the direct modulation of MHz magnitude, the instantaneous frequency displacement producing of warbling can be ignored.

2. adiabatic chirp effect, it is directly proportional to the instantaneous value of electric current (light intensity), affects the refractive index of medium and the concentration of charge carrier; Its frequency shift (FS) causing can be expressed as

△υ _a(t)＝C _a·△i(t) (1)

C wherein _atypical value is 0.1-1GHz/mA.

3. hot chirp, it is a kind of cumulative effect slowly, the meeting of Injection Current causes active area in Distributed Feedback Laser PN junction (gain region) temperature variation, and then affects refractive index and the effective length of medium, and outgoing light frequency is changed.

Along with an Injection Current increasing suddenly, the continuing to increase of active area temperature caused an optical frequency along with the variation of similar exponential damping, until the appearance of thermal equilibrium state.The foundation of in research before, heat being warbled the simplified model of a relevant convolution, can represent with the e index of a series of N different weights the unit impulse response of hot chirp.

The frequency displacement that hot chirp causes is changed to

$\mathrm{\&Delta;}{\mathrm{\&upsi;}}_{\mathrm{th}}\left(t\right)=\mathrm{\&Delta;i}\left(t\right)\&CircleTimes;h_{\mathrm{th}}\left(t\right)---\left(2\right)$

The frequency displacement that unit impulse response causes is changed to

$h_{\mathrm{th}}\left(t\right)=-\underset{n=1}{\overset{N}{\mathrm{\&Sigma;}}}{C}_{n,\mathrm{th}}\&CenterDot;\exp (-\frac{t}{{\mathrm{\&tau;}}_n}),{\mathrm{\&tau;}}_1<{\mathrm{\&tau;}}_2<\&CenterDot;\&CenterDot;\&CenterDot;{\mathrm{\&tau;}}_n---\left(3\right)$

By a series of time constant, can describe the optical frequency of Distributed Feedback Laser and other narrow linewidth transmitter warbles.Here the Distributed Feedback Laser of testing, the shortest time constant is 11ns, due to the thermal response of active area in non-radiative heating process, the complete dynamic behaviour of Distributed Feedback Laser can be simulated with impulse response, and the e index summation that impulse response has different time constant by some represents.The value of these time constants, from tens nanoseconds to millisecond magnitude, depends on the precision architecture of laser instrument.When some application, the quantity of time constant is determined by time range and Measurement Resolution, generally for modulation bit length, from several nanoseconds, to the direct modulating frequency of millisecond magnitude Distributed Feedback Laser, become degree measurement, the theoretical model that comprises four time constants just can well realistic result.When the magnitude of bit length is limited in 1 μ s, only need two time constants to carry out simulation calculation.

For the implementation case, be used for modulating all MHz magnitude periodic signals of 1550nmDFB laser instrument, τ ₁magnitude at 10-20ns, τ ₂magnitude at 100-200ns;

Corresponding scale-up factor is C _{i, th}=0.1-0.5GHz/mA, wherein i gets 1,2.

Heat warble and adiabatic chirp acting in conjunction under, DFB total frequency displacement that directly modulation produces is

△υ(t)＝△υ _a(t)+△υ _th(t) (3)

Can obtain the time dependent frequency values of Distributed Feedback Laser is

υ(t)＝υ ₀+△υ(t) (4)

Wherein, υ ₀the original frequency of Distributed Feedback Laser when unmodulated.

The expression formula of output light field after Distributed Feedback Laser modulation,

Wherein, I ₀(t) represent Distributed Feedback Laser amplitude modulation(PAM) part, numerical value is relevant with modulation signal; represent Distributed Feedback Laser output light phase, derive from the integration of instantaneous light frequency υ (t).

Now provide I ₀(t) be proportional to signal i (t) expression formula of modulation

I ₀(t)＝k·i(t)+k ₀(5)

Wherein, k and k ₀for amplitude modulation(PAM) coefficient.

By output light field being carried out to Fourier transform, just can obtain Output of laser frequency spectrum situation, the optical electric field distribution table after modulation is shown

$E\left(t\right)=\sqrt{\mathrm{ki}\left(t\right)+k_0}\mathrm{aexp}\left[j2\mathrm{\&pi;}({\mathrm{\&upsi;}}_{0}t+{\&Integral;}_{-\&infin;}^t\mathrm{\&Delta;\&upsi;}\left(t^{\&prime;}\right){\mathrm{dt}}^{\&prime;})\right]---\left(6\right)$

Wherein, a is unmodulated Distributed Feedback Laser output light light field range coefficient.

More than analyze and Distributed Feedback Laser is exported to light be considered to single-frequency situation.In fact laser is to have certain bandwidth, therefore the unmodulated front optical electric field of Distributed Feedback Laser can be expressed as

$E_0\left(t\right)=\underset{i}{\mathrm{\&Sigma;}}{a}_i\cos \left[{\mathrm{\&upsi;}}_{0\left(i\right)}\right]i=\mathrm{1,2,3},......---\left(7\right)$

Adopt the mode of variables separation, will contain removing of high frequency light wave component, obtain not containing the modulation signal of carrier information be

$f_c\left(t\right)=\sqrt{\mathrm{ki}\left(t\right)+k_0}\cos \left[j2\mathrm{\&pi;}{\&Integral;}_{-\&infin;}^t\mathrm{\&Delta;\&upsi;}\left(t^{\&prime;}\right){\mathrm{dt}}^{\&prime;}\right]---\left(8\right)$

The Electric Field Distribution of being derived after final modulation by formula (6) and (7) is

$\begin{array}{c}E\left(t\right)=\underset{i}{\mathrm{\&Sigma;}}\sqrt{\mathrm{ki}\left(t\right)+k_0}{a}_i\exp \left[j2\mathrm{\&pi;}({\mathrm{\&upsi;}}_{0\left(i\right)}t+{\&Integral;}_{-\&infin;}^t\mathrm{\&Delta;\&upsi;}\left(t^{\&prime;}\right){\mathrm{dt}}^{\&prime;})\right]\\ =\sqrt{\mathrm{ki}\left(t\right)+k_0}\exp \left[j2\mathrm{\&pi;}{\&Integral;}_{-\&infin;}^t\mathrm{\&Delta;\&upsi;}\left(t^{\&prime;}\right){\mathrm{dt}}^{\&prime;}\right]\&CenterDot;\underset{i}{\mathrm{\&Sigma;}}{a}_i\exp \left(j2\mathrm{\&pi;}{\mathrm{\&upsi;}}_{0\left(i\right)}t\right)\\ =f_c\left(t\right)\&CenterDot;E_0\left(t\right)\end{array}---\left(9\right)$

To formula (9), Fourier transform is got at two ends has

$F\left(w\right)=F_c\left(w\right)\&CircleTimes;F_0\left(w\right)---\left(10\right)$

Therefore, suitably select modulating current parameter (amplitude, frequency and dutycycle) etc., can realize the dynamically adjustable detection light of staring of the bandwidth range described in the present invention.When modulation signal adopts triangular signal and chooses relevant parameter, effect is relatively good, and other waveform signals also can reach this effect.Fig. 3 stares the spectral characteristic of surveying light described in the present invention, Fig. 4 is that principle of the present invention carries out to Brillouin's signal the amplification effect that frequency domain is stared pump probe based on device shown in Fig. 2, has proved that principle of the present invention is correct and has possessed exploitativeness.

Claims (6)

1. based on surveying light flat-top spectrum modulation method, realize the method that Brillouin's signal frequency domain is stared pump probe, it is characterized in that, the method comprises:

Frequency domain is stared pump probe technology, utilizes and stares the selectivity SBS principle of surveying between light and pump light, realizes the detection of staring to Brillouin's signal in frequency domain;

With

Survey light flat-top spectrum modulation technique, utilize arbitrary waveform signal generator to realize the internal modulation to narrow linewidth Distributed Feedback Laser, obtain flat-top and frequency domain visual field and the spectral power density adjustable detection light of staring flexibly.

2. based on surveying light flat-top spectrum modulation method, realize the method that Brillouin's signal frequency domain is stared pump probe according to claim 1, it is characterized in that: described frequency domain is stared pump probe technology, utilize pump light and stare detection light frequency-selecting SBS effect generation power transfer will occur in nonlinear medium, realize the detection of staring to Brillouin's signal in frequency domain.

3. based on surveying light flat-top spectrum modulation method, realize the method that Brillouin's signal frequency domain is stared pump probe according to claim 2, it is characterized in that, the frequency domain visual field that staring detection light that frequency domain is stared in pump probe technology should cover the Brillouin shift spectral limit of pump light in medium, surveys signal to noise ratio (S/N ratio) and is proportional to the spectral power density of staring detection light.

4. according to claim 3ly based on surveying light flat-top spectrum modulation method, realize the method that Brillouin's signal frequency domain is stared pump probe, it is characterized in that, frequency domain visual field is to stare the frequency domain bandwidth of surveying light.

5. realize described in claim 1 and realize based on surveying light flat-top spectrum modulation method the method that Brillouin's signal frequency domain is stared pump probe, it is characterized in that: described detection light flat-top spectrum modulation technique, utilize the spectrum widening effect of Distributed Feedback Laser under the effect of current-modulation, obtain frequency domain visual field and the adjustable flat-top of spectral power density and stare detection light.

6. realize described in claim 1 and realize based on surveying light flat-top spectrum modulation method the device that Brillouin's signal frequency domain is stared the method for pump probe, it is characterized in that: it comprises narrow band fiber laser instrument (1), the first fiber coupler (2), the first Polarization Controller (3), the second fiber coupler (4), optical fiber circulator (5), medium optical fiber (6), photoswitch (7), fibre optic isolater (8), the second Polarization Controller (9), stare and survey light generation module (10), the 3rd Polarization Controller (11), the 3rd fiber coupler (12), photodetector (13) and signal processor (14),

The input end of laser beam incident to the first fiber coupler (2) of narrow band fiber laser instrument (1) output, output two-way light beam after the first fiber coupler (2) coupling, first via light beam is used to form pump light, and the second road light beam is as local reference light;

First via light beam is incident to the input end of the second fiber coupler (4) under the control of the first Polarization Controller (3), the output after the second fiber coupler (4) coupling of this light beam, reenter the port (5-1) that is incident upon optical fiber circulator (5), this light beam forms pump light from port (5-2) outgoing of optical fiber circulator (5), and described pump light is incident to one end of medium optical fiber (6);

Stare detection light generation module (10) and comprise C-band Distributed Feedback Laser (10-1) and arbitrarily signal generating device (10-2); C-band Distributed Feedback Laser (10-1) is exported and is stared detection light after the modulation of arbitrarily signal generating device (10-2), the described detection light of staring is incident to the input end of fibre optic isolater (8) under the control of the second Polarization Controller (9), stare and survey light from the output terminal outgoing of fibre optic isolater (8), and be incident to the input end of photoswitch (7), under the control of photoswitch (7), stare detection light and be incident to the other end of medium optical fiber (6) or the input end of the second fiber coupler (4);

Pump light is surveyed light and is met in medium optical fiber (6) with staring, there is spectral selectivity SBS effect, carry out frequency-selecting power transfer, staring detection light is amplified by selectivity, staring of being enlarged surveyed light and from medium optical fiber (6) outgoing, is incident to the port (5-2) of optical fiber circulator (5), and from port (5-3) outgoing of optical fiber circulator (5); Staring of being enlarged surveyed the input end that is incident to the 3rd fiber coupler 13 together with the reference light that light exports with the first fiber coupler (2), light beam after coupling is incident on the photosurface of photodetector (13) and carries out heterodyne detection, and photodetector (13) converts this light signal after electric signal to and shows signal processor (14) is upper.