CN104062012B - Method and the device that Brillouin signal frequency domain stares pump probe is realized based on detection light flat-top spectrum modulation method - Google Patents

Abstract

Method and the device that Brillouin signal frequency domain stares pump probe is realized based on detection light flat-top spectrum modulation method, belong to optical field, the present invention realizes implementing to Brillouin signal the technology that frequency domain stares pump probe based on detection light flat-top spectrum modulation method for providing a kind of, can stare detection to the brillouin gain transmitted in medium/loss signal in spectral space.The inventive method comprises: frequency domain stares pump probe technology, utilizes the selectivity SBS principle of staring between detection light and pump light, realizes staring detection in a frequency domain to Brillouin signal; With detection light flat-top spectrum modulation technique, utilize the internal modulation that arbitrary waveform signal generator realizes narrow linewidth Distributed Feedback Laser, obtain flat-top and frequency domain visual field and spectral power density are adjustable flexibly stares detection light.

Description

Method and the device that Brillouin signal frequency domain stares pump probe is realized based on detection light flat-top spectrum modulation method

Technical field

The present invention relates to a kind of information extracting method of Brillouin signal, belong to optical field.

Background technology

Brillouin signal (i.e. brillouin gain/loss spectra) comprises the important informations such as Brillouin shift, live width and gain envelope, is widely used in the filter and amplification and Brillouin laser radar detection etc. of distributing optical fiber sensing, feeble signal.In order to obtain the Brillouin signal of high s/n ratio, usual employing pumping-detection method is carried out amplification to Brillouin signal and is extracted, and namely acts on by being excited sound field and pump light and the stimulated Brillouin scattering (SBS) that detects light in nonlinear medium the power transfer (comprising brillouin gain and Brillouin's loss) realizing pump light and detect between light.Due to the accurate match of above-mentioned SBS process need frequency, the frequency scan time that traditional pumping-probe method needs is longer, quick information when cannot effectively extract, and frequency sweep process can cause gain spectral to be out of shape simultaneously.

In order to solve the 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 measures the device and method of brillouin gain spectrum ", publication number is CN102967371A, and publication date is on March 13rd, 2013; Which disclose a kind of method, the mode of staring detection light using ASE light source as frequency domain achieves non-scanning type pumping-detection method and measures brillouin gain spectrum.

2, Chinese patent " injection seeded BOTDR distributed optical fiber sensing system ", publication number is CN103604450A, and publication date is on February 26th, 2014; Which disclose the remote distributed optical fiber sensing system of high-performance based on above-mentioned principle, have high s/n ratio brillouin gain/loss signal and without the need to laying optical fiber circuit in order to double-end measurement.But stare the ASE light source of detection light as frequency domain, its frequency domain visual field (frequency range) and spectral power density modulation underaction, and seed light modular structure is complicated, not ideal enough for sensor-based system.

3, Chinese patent " adopting the device and method of rectangle spectrum detection 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 stares detection light, and shaping is carried out to detection light spectrum, make it be applicable to being applied in remote distributed sensing, but microwave signal generator is expensive, intensity modulator is larger by the stability influence of bias direct current power supply.

Summary of the invention

The object of the present invention is to provide a kind of technology realizing staring Brillouin signal enforcement frequency domain pump probe based on detection light flat-top spectrum modulation method, detection can be stared to the brillouin gain transmitted in medium/loss signal in spectral space.Compared to the present inventor's technology disclosed 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 the application scenarioss such as such as brillouin distributed optical fiber sensing system provide a kind of new Scheme Choice.

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

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

With

Detection light flat-top spectrum modulation technique, utilizes the internal modulation that arbitrary waveform signal generator realizes narrow linewidth Distributed Feedback Laser, obtains flat-top and frequency domain visual field and spectral power density are adjustable flexibly stares detection light.

Above-described frequency domain is stared pump probe technology and is interpreted as further, as shown in Figure 1, when frequency domain visual field completely or partially cover pump light Brillouin shift scope stare detection light and medium in transmit pump light generation spectral selectivity SBS effect time, pump light detects light and in media as well frequency-selecting power transfer will occur with staring, and finally reaches to stare Effect on Detecting to Brillouin signal.

Therefore technology of the present invention can making frequency domain to Brillouin signal fast stares detection flexibly according to demand, now the present invention is summarized as follows: the present invention is based on SBS principle, utilize the radiofrequency signal that arbitrary waveform signal generator produces, internal modulation formation frequency domain is carried out to narrow linewidth Distributed Feedback Laser and stares detection light, its frequency domain visual field covers the Brillouin shift spectral limit that pump light is formed in media as well, and the bandwidth width that frequency domain visual field can realize according to actual needs within the scope of flat-top error 1dB is adjustable arbitrarily.Whole measurement mechanism structure is simple, and easy to operate, cost is lower, substantially covers the advantage of the apparatus and method of previous all detection brillouin gain spectrum.Be stare the pumping-detection method non-scanning type detecting light to measure compared with the device of brillouin gain spectrum with ASE, stare detection light 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 flexible modulation, and device is simple, strong operability; Utilize the method, greatly can improve the signal to noise ratio (S/N ratio) in low-power incident pump photo measure brillouin gain spectrum, signal to noise ratio (S/N ratio) is improved more than 35dB.

Accompanying drawing explanation

Fig. 1 is the schematic diagram that frequency domain stares that pump probe technology implements to stare detection at frequency domain to Brillouin signal;

Fig. 2 realizes of the present inventionly realizing based on detection light flat-top spectrum modulation method the light channel structure schematic diagram that Brillouin signal frequency domain stares the device of pumping detecting method in a fiber;

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

Fig. 4 (a), (b) are the amplification effect performance plots staring detection light brillouin gain signal.

Embodiment

Embodiment one: composition graphs 2 illustrates present embodiment, the present embodiment demonstrates in a fiber to realize based on detection light flat-top spectrum modulation method the practical measuring examples that Brillouin signal frequency domain stares pump probe technology described in the present invention, this example detects light selectivity SBS principle based on brillouin scattering signal in optical fiber with staring, 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 detection 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, first output port 2-1 of the first fiber coupler 2 is communicated with the input port of the first Polarization Controller 3, second output port 2-2 of the first fiber coupler 2 connects with the input port of the 3rd Polarization Controller 11

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 connects with the first port 5-1 of optical fiber circulator 5 through the second fiber coupler 4, one end of second port 5-2 connecting media optical fiber 6 of optical fiber circulator 5, the output port staring detection light generation module 10 connects with the second Polarization Controller 9, 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, 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 output port of photodetector 13 connects with the input port of signal processor 14.

Embodiment two: present embodiment is described further the concrete behavior of photoswitch 7 in embodiment one is that both-end frequency domain stares pump and probe method when staring when detection light enters medium optical fiber 6 through the first output terminal of photoswitch 7 from the output of optoisolator 8 output terminal; Be utilize the single-ended frequency domain staring the reflection of detection light to stare pump and probe method when staring detection light from optoisolator 8 output terminal and accessing the first input end 4-1 of the second fiber coupler 4 through the second output terminal of photoswitch 7.

Embodiment three: present embodiment stares further illustrating of pump probe technology to realizing Brillouin 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 for staring the light signal output end mouth of detection 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 the further restriction to realizing the technology that Brillouin signal selectivity is amplified 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 to staring detection light generation module 10 described in embodiment three, the periodic triangular ripple signal that the radio frequency output signal of described arbitrarily signal generating device 10-2 is 2.8MHz, symmetry is 37.6%, amplitude is 28mVpp, drift rate is 0mVpp.

Embodiment six: present embodiment is described further based on seed light flat-top spectrum modulation method described in the present invention: DFB (DistributedFeedbackLaser), i.e. distributed feedback laser has been built-in Bragg grating 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 directly modulation of MHz magnitude, the instantaneous frequency displacement produced 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) caused can be expressed as

△υ _a(t)＝C _a·△i(t)(1)

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

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

Suddenly the Injection Current increased along with, continuing to increase of active area temperature result in the change of an optical frequency along with similar exponential damping, until the appearance of thermal equilibrium state.That warbles to heat in research before establishes a simplified model about convolution, can represent the unit impulse response of hot chirp with the e index of a series of N number of different weight.

The frequency displacement that hot chirp causes is changed to

$\mathrm{\Δ}{\mathrm{\υ}}_{\mathrm{th}}\left(t\right)=\mathrm{\Δi}\left(t\right)\⊗h_{\mathrm{th}}\left(t\right)---\left(2\right)$

The frequency displacement that unit impulse response causes is changed to

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

The optical frequency that can be described Distributed Feedback Laser and other narrow linewidth transmitter by a series of time constant is warbled.Here the Distributed Feedback Laser tested, 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 that impulse response has a different time constant by some is sued for peace and represented.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 become degree measurement from a few nanosecond to millisecond magnitude Distributed Feedback Laser directly modulation frequency for modulation bit length, the theoretical model comprising four time constants just can well realistic result.When the magnitude of bit length is limited in 1 μ s, two time constants are only needed to carry out simulation calculation.

For the implementation case 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, and 2.

Warble with under adiabatic chirp acting in conjunction in heat, total frequency displacement that DFB 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 ₀for the original frequency of Distributed Feedback Laser time unmodulated.

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

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

Now provide I ₀t () is 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.

Just can obtain Output of laser spread spectrum scenarios by carrying out Fourier transform to output light field, the optical electric field distribution after modulation is expressed as

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

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

More than analyze and Distributed Feedback Laser is exported light be considered to single-frequency situation.In fact laser has certain bandwidth, therefore unmodulated for Distributed Feedback Laser front optical electric field 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, removed by the item containing high frequency light wave component, the modulation signal namely obtaining not containing carrier information is

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

Electric Field Distribution after deriving 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 then 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 that the bandwidth range described in the present invention is dynamically adjustable stares detection light.Modulation signal adopt triangular signal and when choosing relevant parameter effect relatively good, other waveform signals also can reach this effect.Fig. 3 is for staring the spectral characteristic of detection light described in the present invention, Fig. 4 carries out to Brillouin signal the amplification effect that frequency domain stares pump probe based on device shown in Fig. 2 for principle of the present invention, demonstrates principle of the present invention correct and possess exploitativeness.

Claims (6)

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

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

With

Detection light flat-top spectrum modulation technique, utilizes the internal modulation that arbitrary waveform signal generator realizes narrow linewidth Distributed Feedback Laser, obtains flat-top and frequency domain visual field and spectral power density are adjustable flexibly stares detection light;

Concrete operations are:

Step one: utilize the radiofrequency signal that arbitrary waveform signal generator produces, internal modulation formation frequency domain is carried out to narrow linewidth Distributed Feedback Laser and stares detection light, its frequency domain visual field covers the Brillouin shift spectral limit that pump light is formed in media as well, and the bandwidth width that frequency domain visual field realizes according to actual needs within the scope of flat-top error 1dB is adjustable arbitrarily;

Step 2: frequency domain stares the pump light generation spectral selectivity SBS effect transmitted in detection light and medium, pump light and stare and detect light and in media as well frequency-selecting power transfer will occur, reaches and stares Effect on Detecting to Brillouin signal.

2. realize based on detection light flat-top spectrum modulation method the method that Brillouin signal frequency domain stares pump probe according to claim 1, it is characterized in that: described frequency domain stares pump probe technology, utilize pump light detect light and frequency-selecting SBS effect will occur in nonlinear medium power transfer occurs with staring, realization stares detection in a frequency domain to Brillouin signal.

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

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

5. realize realizing based on detection light flat-top spectrum modulation method the method that Brillouin signal frequency domain stares pump probe described in claim 1, 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 stares detection light.

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

The laser beam that narrow band fiber laser instrument (1) exports is incident to the input end of the first fiber coupler (2), two-way light beam is exported after the first fiber coupler (2) coupling, first via light beam is for the formation of 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), this light beam exports after the second fiber coupler (4) coupling, re-shoot the port (5-1) to 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) exports after the modulation of arbitrarily signal generating device (10-2) stares detection light, described staring detects the input end that light is incident to fibre optic isolater (8) under the control of the second Polarization Controller (9), stare the output terminal outgoing of detection light from 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 detects light and meets in medium optical fiber (6) with staring, there is spectral selectivity SBS effect, carry out frequency-selecting power transfer, stare detection light to be amplified by selectivity, the detection light of staring be enlarged is incident to the port (5-2) of optical fiber circulator (5) after medium optical fiber (6) outgoing, and from port (5-3) outgoing of optical fiber circulator (5); The input end of the 3rd fiber coupler 13 is incident to together with staring of the being enlarged reference light that detection light and the first fiber coupler (2) export, the photosurface that light beam after coupling is incident to photodetector (13) carries out heterodyne detection, and this light signal converts to after electric signal in the upper display of signal processor (14) by photodetector (13).