Low-noise Brillouin sensing device and method based on injection-locked chaotic laser

Abstract

The invention belongs to the technical field of distributed optical fiber sensing, and discloses a low-noise Brillouin sensing device and method based on injection-locked chaotic laser. The device comprises a broadband chaotic laser source, an adjustable attenuator, a polarization controller, a first circulator, a semiconductor laser, a beam splitter, an optical delay generator, an optical isolator, a sensing optical fiber, a single-sideband modulator, a semiconductor optical amplifier, a low-noise amplifier, a second circulator, an optical filter, a photodetector, a phase-locked amplifier, and a computer. The invention utilizes injection-locked chaotic laser to excite a narrowband correlation peak, suppresses the intensity noise introduced by the broadband chaotic laser source, improves the measurement signal-to-noise ratio, and can realize distributed temperature and strain monitoring with long distance, high spatial resolution, and high measurement accuracy.

Description

Technical Field

[0001] The invention belongs to the technical field of distributed optical fiber sensing, and in particular relates to a low-noise Brillouin sensing device and method based on injection-locked chaotic laser. Background Art

[0002] Distributed optical fiber sensors have the advantages of small and light size, high sensitivity, strong resistance to electromagnetic interference, and integrated sensing and transmission. They are widely used in large-scale structural health monitoring, oil and gas pipeline transportation safety, geological disaster detection, and medical testing. Distributed optical fiber sensing technology based on Brillouin scattering can not only achieve simultaneous measurement of multiple external parameters such as temperature, strain, and vibration, but also has high measurement accuracy and long sensing distance, and is favored by many researchers.

[0003] Traditional Brillouin sensing devices have the problem that they cannot have long sensing distance, high resolution, and high precision at the same time. For the optical time domain solution (BOTDA), the stimulated Brillouin gain of the entire optical fiber can be measured with only one scan through pulse flight time positioning; theoretically, the spatial resolution is half of the pulse width. As the spatial resolution increases, the broadened Brillouin gain spectrum (BGS) will seriously affect the measurement accuracy of the system; as the sensing distance increases, the pulse spectrum and BGS are broadened due to nonlinear effects such as self-phase modulation caused by pulse distortion during the propagation of the pump pulse light, and the frequency accuracy corresponding to the wide-linewidth gain spectrum is low. At present, 150km temperature or strain sensing has been achieved in the Brillouin optical time domain analysis system; however, due to the limitation of phonon lifetime, the spatial resolution of the Brillouin optical time domain solution is difficult to exceed 1m in theory. For the optical correlation domain scheme (BOCDA), high spatial resolution sensing at the millimeter level can be achieved by using narrowband correlation peaks. Theoretically, the spatial resolution is half the width of the autocorrelation curve. As the correlation peak becomes narrower, the beat spectrum of the pump light and the detection light is broadened, resulting in the broadening of the gain spectrum. The weak Brillouin gain in the short correlation peak is easily submerged by noise. As the sensing distance increases, the weak stimulated Brillouin amplification at non-correlated positions gradually accumulates, severely limiting the performance of the system. However, in order to avoid gain crosstalk between different correlation peaks, the system sensing distance is limited to the interval between adjacent correlation peaks in principle. At the same time, the bandwidth limitation of the modulation device also hinders the further improvement of spatial resolution.

[0004] Based on chaotic lasers, amplified spontaneous emission (ASE) and other intrinsic low-coherence, noise-like broadband lasers as light sources, there is only one correlation peak in the optical fiber to be tested, which can solve the contradiction between sensing distance and spatial resolution, and there is no need to perform high-speed external modulation of the laser, which can eliminate the restrictions on RF signals and modulation bandwidth, and it is easier to achieve millimeter-level spatial resolution. However, the power spectrum density of the ASE light source is very low, resulting in a poor system signal-to-noise ratio and a sensing distance of only tens of centimeters. In the Brillouin light correlation domain measurement technology based on broadband chaotic lasers (Chinese invention patent ZL201310045097.3, distributed optical fiber sensing device based on chaotic laser coherence method and its measurement method), the chaotic laser power time series shows large-amplitude, irregular oscillations, and the peak-to-peak value is about 7 times that of ordinary single-frequency lasers. When the optical power demodulates the Brillouin gain spectrum, a large amount of intensity noise will be introduced, resulting in the weak stimulated Brillouin gain being almost submerged by the noise, and the system signal-to-noise ratio is severely limited.

[0005] The performance of a distributed Brillouin optical fiber sensor is determined by the sensing distance, spatial resolution, and Brillouin frequency shift uncertainty, and ultimately depends on the signal-to-noise ratio of the measurement. Therefore, it is necessary to improve the Brillouin optical sensor in the prior art to improve the system signal-to-noise ratio, thereby achieving distributed optical fiber sensing with long distance, high spatial resolution, and high measurement accuracy. Summary of the invention

[0006] In order to solve the problem in the prior art that it is difficult to achieve long sensing distance, high spatial resolution and high precision at the same time, the present invention provides a low-noise Brillouin sensing device and method based on injection-locked chaotic laser by improving the signal-to-noise ratio of the Brillouin sensing system.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: a low-noise Brillouin sensing device based on injection-locked chaotic laser, comprising: a broadband chaotic laser source, an adjustable attenuator, a polarization controller, a first circulator, a semiconductor laser, a beam splitter, an optical delay generator, an optical isolator, a sensing optical fiber, a single-sideband modulator, a semiconductor optical amplifier, a low-noise amplifier, a second circulator, an optical filter, a photodetector, a phase-locked amplifier, and a computer;

[0008] The broadband chaotic laser output by the broadband chaotic laser source is injected into the semiconductor laser after passing through the adjustable attenuator, the polarization controller and the first circulator in sequence, so that it outputs broadband chaotic laser. The broadband chaotic laser output by the semiconductor laser is divided into two beams after passing through the first circulator by the optical splitter, one of which is used as the detection light and passes through the optical delay generator and the optical isolator in sequence to enter one end of the sensing optical fiber, and the other is used as the pump light and passes through the single-sideband modulator, the semiconductor optical amplifier, the low-noise amplifier and the second circulator in sequence to enter the other end of the sensing optical fiber to cause Brillouin scattering of the detection light.

[0009] The optical delay generator is used to adjust the optical path of the detection light, and the optical isolator is used to isolate the pump light output from the sensing optical fiber; the single sideband modulator is used to perform single sideband modulation on the pump light to shift the frequency of the pump light up by v B The semiconductor optical amplifier is used to modulate the pump light into a pulse light with a pulse width less than the feedback delay time, and the low noise amplifier is used to amplify the single sideband pump light;

[0010] The detection light output from the other end of the sensing optical fiber is detected by the photodetector after passing through the second circulator and the optical filter in turn, and is converted into an electrical signal and sent to the phase-locked amplifier. The phase-locked amplifier phase-locks the signal and amplifies it, and then sends it to the computer for data processing to obtain the Brillouin gain spectrum.

[0011] The low-noise Brillouin sensing device based on injection-locked chaotic laser also includes a broadband microwave signal source and a pulse signal generator. The broadband microwave signal source is used to output a broadband microwave signal to drive the single-sideband modulator, and the pulse signal generator is used to output a pulse signal to drive the semiconductor optical amplifier.

[0012] The broadband microwave signal source and the pulse signal generator are connected to the phase-locked amplifier and are respectively used to synchronously input broadband microwave signals and pulse signals to the phase-locked amplifier.

[0013] The up-shift frequency v of the pump light B Approximately equal to the Brillouin frequency shift, the sweep bandwidth is greater than the bandwidth of the Brillouin spectrum line Δv B .

[0014] The low-noise Brillouin sensing device based on injection-locked chaotic laser also includes an optical polarization scrambler, which is arranged between the delay generator and the optical isolator and is used to randomly perturb the polarization state of the detection light.

[0015] The optical splitter is a fiber coupler, and the broadband chaotic laser source, adjustable attenuator, polarization controller, first circulator, semiconductor laser, optical splitter, optical delay generator, optical isolator, sensing fiber, single sideband modulator, semiconductor optical amplifier, low noise amplifier, second circulator, optical filter, and photodetector are connected through single-mode fiber jumpers.

[0016] The sensing optical fiber adopts G652 single-mode optical fiber or G655 single-mode optical fiber, the semiconductor optical amplifier is an OAM-SOA-PL type high extinction ratio semiconductor optical amplifier, the low-noise amplifier includes a first-stage optical amplifier, a filter and a second-stage optical amplifier connected in sequence, the optical delay generator is a programmable optical delay generator, and the optical filter is a tunable optical filter.

[0017] In addition, the present invention also provides a low-noise Brillouin sensing method based on injection-locked chaotic laser, which is implemented according to the low-noise Brillouin sensing device based on injection-locked chaotic laser, comprising the following steps:

[0018] S1, adjusting the power and polarization state of the injected light through an adjustable attenuator and a polarization controller to make the semiconductor laser output a low-noise broadband chaotic laser;

[0019] S2, adjusting the frequency up-shift frequency and frequency sweep bandwidth of the pump light through a single sideband modulator;

[0020] S3, performing correlation amplification on the detection signal of the photodetector through a lock-in amplifier to obtain a Brillouin gain spectrum;

[0021] S4, adjusting the optical path of the detection light by means of an optical delay generator, so that the pump light and the detection light meet at various positions along the sensing optical fiber and then stimulated Brillouin amplification occurs, and the Brillouin gain spectrum along the sensing optical fiber is obtained;

[0022] S5. Calculate the dynamic temperature and strain information along the entire sensing optical fiber using the Brillouin gain spectrum along the sensing optical fiber.

[0023] In step S2, the up-shift frequency v of the pump light B Approximately equal to the Brillouin frequency shift, the sweep bandwidth is greater than the bandwidth of the Brillouin spectrum line Δv B .

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The present invention provides a low-noise Brillouin sensing device and method based on injection-locked chaotic laser. Through the injection-locking method, a weak broadband intensity chaotic laser is used to control the spectral characteristics, mode phase characteristics and spatial characteristics of a strong laser output light. That is, by changing the frequency detuning amount between the broadband chaotic laser and the semiconductor laser, adjusting the injected optical power and polarization state of the broadband chaos, the semiconductor laser outputs low-noise broadband chaotic light. The output optical power maintains the characteristics of the semiconductor laser itself, which not only maintains the broadband spectrum characteristics of the chaotic light, but also suppresses the power fluctuation of the chaotic light output by the broadband chaotic light source, thereby outputting a low-noise broadband chaotic laser with a wide spectrum, low coherence and extremely small peak-to-peak oscillation.

[0026] 2. The present invention provides a low-noise Brillouin sensing device and method based on injection-locked chaotic laser, which performs single-sideband modulation on the pump light. By applying pulse modulation with a pulse duration less than the feedback delay time τ to the pump light, the noise caused by the sideband modulation is limited to the pulse duration and the deterioration of the system signal-to-noise ratio caused by the non-zero noise floor along the optical fiber is effectively suppressed. The effective power of the pump light is increased by a low-noise amplifier and the spontaneous scattering noise generated during the amplification process is reduced; in this way, the influence of the low-intensity noise transfer from the pump light to the detection light on the measurement is negligible, and long-distance sensing can be achieved; at the same time, the detection light path experimental device is less, which greatly reduces the complexity of the experimental device and fully improves the signal-to-noise ratio of the system. The amplified detection light enters the photodetector and is converted into an electrical signal. Due to the high spatial resolution and short distance of the Brillouin action of the BOCDA system, the signal is very weak. The electrical signal is correlated and amplified by a phase-locked amplifier to remove noise interference and improve the efficiency of measurement.

[0027] 3. Compared with the Brillouin sensing technology of broadband intensity chaotic laser, the timing of broadband intensity chaotic laser shows large amplitude and irregular oscillation, which will introduce a large amount of intensity noise when demodulating the Brillouin gain spectrum with optical power, causing the weak stimulated Brillouin gain to be almost submerged by noise, and the system signal-to-noise ratio is severely limited. The Brillouin distributed optical fiber sensing method based on injection-locked chaotic laser of the present invention improves the characteristics of broadband chaotic laser by adjusting the detuning frequency of the master and slave lasers, changing the injected optical power and polarization state, etc. while maintaining the wide spectrum characteristics of chaotic laser, suppressing the peak-to-peak oscillation of chaotic laser timing to 1 / 6 of the peak-to-peak value of the original broadband intensity chaotic laser, avoiding power fluctuations in traditional systems, reducing the intensity noise introduced by the broadband chaotic laser source, and theoretically increasing the system signal-to-noise ratio to the original 7.7dB, further broadening the effective sensing distance.

[0028] 4. Compared with the traditional Brillouin light correlation domain measurement technology based on sinusoidal modulation and phase encoding, the Brillouin light correlation domain distributed optical fiber sensing device based on injection-locked chaotic laser described in the present invention has the following advantages: (1) The light source has noise-like characteristics. There is only one correlation peak in the sensing optical fiber, which avoids the crosstalk of adjacent correlation peaks. The pulse modulation and low-noise amplifier suppress the influence of the non-zero noise floor along the optical fiber on the system signal-to-noise ratio, thereby achieving a longer sensing distance; (2) The light source has wide spectrum and low coherence characteristics, which fundamentally reduces the intensity noise of the laser, making the weak Brillouin gain in the short correlation peak less likely to be submerged by noise. The spatial resolution of the system is determined by the half-height full width of the correlation peak, which can reach the millimeter level; (3) The incomplete modulation of the light source in the traditional Brillouin sensing technology leads to the non-peak Brillouin interaction, which will introduce additional noise, and the noise will accumulate with the increase of the optical fiber length, thereby deteriorating the sensing performance of the system. The present light source is not limited by the bandwidth of the modulation signal and eliminates the expensive microwave signal source. It has a simple structure and low cost. (4) By adjusting the programmable optical delay generator to change the optical path difference between the detection light and the pump light to achieve the position scanning of the correlation peak, the line width of the light source will not be changed, and the phase delay of the output light source amplitude and frequency will not be caused by changing the light source modulation frequency, causing system errors and reducing measurement accuracy. Therefore, in the distributed measurement process, the system has no position scanning error and can achieve accurate positioning of the sensor point. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic structural diagram of a low-noise Brillouin sensing device of an injection-locked chaotic laser provided in Embodiment 1 of the present invention;

[0030] Figure 2 A schematic diagram of the structure of a low noise amplifier according to an embodiment of the present invention;

[0031] Figure 3 The spectrum diagram of chaotic light output by broadband chaotic laser source and injection-locked semiconductor laser;

[0032] Figure 4 The timing diagram of chaotic light output by broadband chaotic laser source and injection-locked semiconductor laser;

[0033] Figure 5 The Brillouin gain spectra obtained when the broadband chaotic laser and the injection-locked chaotic laser are used as signal sources respectively in the embodiment of the present invention;

[0034] Figure 6 A schematic diagram of the structure of a low-noise Brillouin sensing device of injection-locked chaotic laser provided in the second embodiment of the present invention;

[0035] In the figure: 1- broadband chaotic laser source, 2- adjustable attenuator, 3- polarization controller, 4- first circulator, 5- semiconductor laser, 6- optical splitter, 7- optical delay generator, 8- optical scrambler, 9- optical isolator, 10- sensing fiber, 11- single sideband modulator, 12- broadband microwave signal source, 13- semiconductor optical amplifier, 14- pulse signal generator, 15- low noise amplifier, 16- second circulator, 17- optical filter, 18- photodetector, 19- phase-locked amplifier, 20- computer. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0037] Embodiment 1

[0038] like Figure 1 As shown, an embodiment of the present invention provides a low-noise Brillouin sensing device based on injection-locked chaotic laser, including: a broadband chaotic laser source 1, an adjustable attenuator 2, a polarization controller 3, a first circulator 4, a semiconductor laser 5, a beam splitter 6, an optical delay generator 7, an optical isolator 9, a sensing optical fiber 10, a single-sideband modulator 11, a semiconductor optical amplifier 13, a low-noise amplifier 15, a second circulator 16, an optical filter 17, a photodetector 18, a phase-locked amplifier 19, and a computer 20.

[0039] The broadband chaotic laser output by the broadband chaotic laser source 1 is injected into the semiconductor laser 5 after passing through the adjustable attenuator 2, the polarization controller 3, and the first circulator 4 in sequence, so that it outputs broadband chaotic laser. The broadband chaotic laser output by the semiconductor laser 5 passes through the first circulator 4 and is divided into two beams by the optical splitter 6. One beam is used as a detection light and passes through the optical delay generator 7 and the optical isolator 9 in sequence to enter one end of the sensing optical fiber 10. The other beam is used as a pump light and passes through the single-sideband modulator 11, the semiconductor optical amplifier 13, the low-noise amplifier 15, and the second circulator 16 in sequence to enter the other end of the sensing optical fiber 10.

[0040] The optical delay generator 7 is used to adjust the optical path of the detection light, the optical isolator 9 is used to isolate the pump light output from the sensing optical fiber 10; the single sideband modulator 11 is used to perform single sideband modulation on the pump light to shift the frequency of the pump light upward and sweep the frequency, the semiconductor optical amplifier 13 is used to modulate the pump light into a pulse light with a pulse width less than the feedback delay time of the broadband chaotic laser output by the semiconductor laser 5, and the low noise amplifier 15 is used to amplify the single sideband pump light. Among them, the feedback delay time of the broadband chaotic laser output by the semiconductor laser 5 is the external cavity delay of the broadband chaotic laser output by the semiconductor laser 5.

[0041] The detection light output from the other end of the sensing optical fiber 10 is detected by the photodetector 18 after passing through the second circulator 16 and the optical filter 17, and is converted into an electrical signal and sent to the phase-locked amplifier 19. The phase-locked amplifier 19 performs phase-locked amplification on the signal and sends it to the computer 20 for data processing to obtain the Brillouin gain spectrum.

[0042] Specifically, in this embodiment, the up-shift frequency v of the pump light is B Approximately equal to the Brillouin frequency shift, the sweep bandwidth is greater than the bandwidth of the Brillouin spectrum line Δv B Assuming that the frequency of the broadband chaotic laser emitted by the semiconductor laser 5 is v0, after the single-sideband modulator modulates the pump light, the frequency of the pump light with an upward frequency shift is v0+v B For ordinary single-mode optical fiber, the value of the Brillouin frequency shift is about 10.8 GHz, so v BThe value of is 10.6-11 GHz, and the sweep bandwidth is 200-400 MHz. Specifically, in this embodiment, the optical splitter 6 is a 1×2 fiber coupler, and the broadband chaotic laser source 1, the adjustable attenuator 2, the polarization controller 3, the first circulator 4, the semiconductor laser 5, the optical splitter 6, the optical delay generator 7, the optical isolator 9, the sensing fiber 10, the single sideband modulator 11, the semiconductor optical amplifier 13, the low noise amplifier 15, the second circulator 16, the optical filter 17, and the photodetector 18 are connected by a single-mode optical fiber jumper. Specifically, the broadband chaotic laser source 1 is connected to the adjustable attenuator 2, the polarization controller 3 and the first port of the first circulator 4 in sequence through a single-mode optical fiber jumper; the second port of the first circulator 4 is connected to the optical output end of the semiconductor laser 5 through the single-mode optical fiber jumper; the second port of the first circulator 4 is connected to the input end of the 1×2 optical fiber coupler through the single-mode optical fiber jumper; the first output end of the 1×2 optical fiber coupler 6 is connected to the input end of the optical delay generator 7 through the single-mode optical fiber jumper, and the output end of the programmable optical delay generator 7 is connected to the input end of the optical isolator 9 through the single-mode optical fiber jumper; the output end of the optical isolator 9 is connected to one end of the sensing optical fiber 10; the first output end of the 1×2 optical fiber coupler 6 is connected to the input end of the optical delay generator 7 through the single-mode optical fiber jumper; the output end of the optical isolator 9 is connected to one end of the sensing optical fiber 10; The two output ends are connected to the input end of the single sideband modulator 11 through a single mode fiber jumper, the output end of the single sideband modulator 11 is connected to the input end of the semiconductor optical amplifier 13 through a single mode fiber jumper, and the output end of the semiconductor optical amplifier 13 is connected to the input end of the low noise optical amplifier 15 through a single mode fiber jumper; the output end of the low noise optical amplifier 15 is connected to the first port end of the second optical circulator 16 through a single mode fiber jumper; the second port of the second optical circulator 16 is connected to the other end of the sensing optical fiber 10, and the third port is connected to the input end of the optical filter 17 through a single mode fiber jumper; the output end of the optical filter is connected to the input end of the photodetector 18 through a single mode fiber jumper. The output end of the photodetector 18 is input into the phase lock amplifier 19 through a high frequency coaxial cable, and finally processed by the computer 20 to obtain the gain spectrum.

[0043] Specifically, in this embodiment, the sensing optical fiber 10 uses a G652 single-mode optical fiber or a G655 single-mode optical fiber, the semiconductor optical amplifier 13 is an OAM-SOA-PL type high extinction ratio semiconductor optical amplifier, and the optical delay generator 7 is a programmable optical delay generator, through which the optical delay generator 7 can adjust the optical path of the detection light to control the position of the correlation peak, thereby realizing the distributed measurement of the entire optical fiber to be measured; the optical filter 17 is a tunable optical filter, such as an XTM-50 broadband wavelength tunable filter; the optical filter can filter out stray light in the detection light output from the other end of the sensing optical fiber. The single-sideband modulator 11 can specifically be a Mach-Zehnder modulator.

[0044] Specifically, Figure 2As shown, in this embodiment, the low noise amplifier 15 includes a first-stage optical amplifier EDFA1, a filter and a second-stage optical amplifier EDFA2 connected in sequence. The low noise amplifier 15 is a two-stage amplification module. The first-stage optical amplifier pre-amplifies the pump light and amplifies the lower-power pump light. The filter is then connected to remove part of the spontaneous radiation noise. The output of the filter is connected to the second-stage optical amplifier. The second-stage optical amplifier amplifies the power of the pump light again, and the effective power of the pump light is increased by the low noise amplifier.

[0045] Since the BOCDA system has high spatial resolution, the distance of the Brillouin effect is short, and the signal is very weak, in this embodiment, the electrical signal obtained by the photodetector 18 is correlated and amplified by a phase-locked amplifier 19 to remove noise interference and improve the system signal-to-noise ratio.

[0046] The working principle of the embodiment of the present invention is as follows:

[0047] 1. The broadband chaotic laser source 1 is a bandwidth-enhanced chaotic laser with an output central wavelength of 1550nm, a central frequency of v0, and a -3dB spectral linewidth of about 10GHz. Its theoretical spatial resolution is in the millimeter range, and the power sequence shows large-amplitude, irregular oscillations, and the peak-to-peak value of the fluctuation is about 7 times that of an ordinary single-frequency laser. The broadband chaotic laser source 1, the adjustable attenuator 2, the polarization controller 3, the first circulator 4, and the semiconductor laser 5 together constitute the injection system. Relaxation oscillation is an inherent characteristic of semiconductor lasers. When the bias current of the semiconductor laser 5 is small, there is a relaxation oscillation peak in the frequency response curve of the laser. With the increase of the bias current, the number of photons in the laser resonant cavity increases, so that the relaxation oscillation frequency moves toward the high frequency direction. At the same time, the increase in the photon number density means that the feedback of the relaxation oscillation in the cavity is accelerated, so that the relaxation oscillation peak value decreases. When the power of the semiconductor laser 5 is increased, with the increase of the bias current, the power and wavelength of the output light of the semiconductor laser 5 are also gradually increasing, the relaxation oscillation frequency is gradually increasing, the peak value is gradually decreasing, and the frequency response curve is gradually flattened. Optical injection locking is the use of a weak laser beam to control the spectral characteristics, mode phase characteristics and spatial characteristics of a strong laser output light. That is, by adjusting the injected optical power, frequency detuning and polarization state of the broadband chaotic light, the semiconductor laser can output a wide-spectrum chaotic light. The output optical power maintains the characteristics of the semiconductor laser itself, which not only maintains the wide-spectrum characteristics of the chaotic light, but also suppresses the power fluctuation of the chaotic light output by the broadband chaotic light source, thereby outputting a low-noise broadband chaotic laser. The spectrum of the chaotic light output by the broadband chaotic laser source 1 and the injection-locked semiconductor laser 5 is shown in Figure 1. Figure 3 As shown in the timing diagram, Figure 4 As shown, Figure 4(a) corresponds to the chaotic laser output by the broadband chaotic laser source 1, and (b) corresponds to the chaotic light output by the semiconductor laser 5. It can be observed from the figure that the chaotic light output by the semiconductor laser 5 after injection locking still maintains a wide spectrum of 6.5 GHz, but the spectrum tends to be flat and the peak-to-peak value of the timing oscillation decreases from 27.57 mV to 3.97 mV.

[0048] 2. The broadband chaotic light output by the semiconductor laser 5 is divided into two paths by a 10:90 1×2 fiber coupler, one path is used as the detection light (90%), and the other path is used as the pump light (10%). The detection light enters the optical delay generator 7, and the position of the correlation peak in the sensing optical fiber is changed by adjusting the distance of the optical delay generator 7, thereby realizing the distributed scanning of the entire optical fiber. The single-sideband modulator 11 modulates the pump light (10%) to generate a frequency-upshifted pump light with a frequency of v0+v B , where v B The frequency shift of the frequency upshift is equal to the Brillouin frequency shift (the Brillouin frequency shift of ordinary single-mode optical fiber is about 10.8GHz). The semiconductor optical amplifier 13 applies pulse modulation with a pulse duration less than the feedback delay time to the pump light, which can limit the noise caused by the sideband modulation to the pulse duration and effectively suppress the deterioration of the system signal-to-noise ratio caused by the non-zero noise floor along the optical fiber; the pump pulse light is incident on the low-noise optical amplifier 15 to compensate for the optical power loss caused by the single-sideband modulation.

[0049] 3. The frequency-detuned chaotic pump light and the detection light are incident from both ends of the optical fiber and meet in the optical fiber. When the frequency detuning amount meets the SBS phase matching condition, the coherent beat frequency position in the optical fiber will excite a stable SBS acoustic wave field, and its position and intensity obey the chaotic laser autocorrelation function curve. Therefore, due to the quasi-δ function characteristics of the chaotic laser, the SBS acoustic wave field of the chaotic BOCDA system is confined to the central peak of the autocorrelation function, which is called the correlation peak. The half-height full width of the correlation peak determines the spatial range of the excited acoustic wave field, that is, the spatial resolution. The broadband and autocorrelation characteristics of the chaotic laser ensure that there is a unique, narrow-band correlation peak in any length of optical fiber, which in principle solves the contradiction between the sensing distance and the spatial resolution.

[0050] 4. Due to the fluctuation of the light source amplitude, the output pump light and the detection light |As(z=0,t)| 2 The power of the probe light is essentially random and has nothing to do with stimulated Brillouin scattering, while the relative power gain of the probe light at the ultrashort resolution point is very weak. This noise mechanism has a fundamental limitation on the measurement signal-to-noise ratio and cannot be overcome by simply increasing the average signal power. The signal-to-noise ratio (SNR) of the signal power gain measurement can be estimated as:

[0051]

[0052] g0 is the SBS gain coefficient in single-mode fiber, v g is the group velocity of light propagating in the optical fiber, |A p0 | 2 is the average power of the pump light, Δτ is the half-height full width of the chaotic laser center peak, that is, the theoretical spatial resolution of the system, T PD is the detector integration time, τ c In contrast, in the Brillouin light correlation domain distributed measurement of injection-locked chaotic light, the power of the signal wave can be considered deterministic, reducing the intensity noise introduced by the broadband chaotic laser source.

[0053] Compared with broadband chaotic lasers, injection-locked chaotic lasers have small power fluctuations, very low peak-to-peak intensity oscillations, and significantly reduced intrinsic intensity noise, thus improving the system signal-to-noise ratio. Figure 5 As shown, with broadband chaotic laser as the signal source, its Brillouin gain spectrum noise peak reaches 0.378, and the system signal-to-noise ratio is about 4.23dB; with the same bandwidth injection-locked chaotic laser as the signal source, its Brillouin gain spectrum noise peak reaches 0.087, and the system signal-to-noise ratio can reach 10.65dB, which is an increase of 6.42dB, and the noise floor fluctuation is very weak, further widening the effective sensing distance. In addition, the stimulated Brillouin scattering gain spectrum excited by the broadband chaotic laser is further broadened and accompanied by strong noise; the injection-locked chaotic laser can excite a narrower and stronger stimulated Brillouin scattering gain spectrum. Therefore, the injection-locked chaotic laser used in the present invention can suppress intensity noise, improve the system signal-to-noise ratio, obtain a Brillouin gain spectrum with a larger signal intensity, and widen the effective sensing distance.

[0054] 5. Use XTM-50 broadband wavelength tunable filter to filter the detection light and filter out the required Stokes light. The filtered light signal is converted into an electrical signal by the photodetector and input into the phase-locked amplifier 19 through a high-frequency coaxial cable. Then, the gain spectrum is calculated by the computer 20 to obtain the temperature and pressure sensing information.

[0055] Embodiment 2

[0056] like Figure 6 As shown, the second embodiment of the present invention provides a low-noise Brillouin sensing device based on injection-locked chaotic laser. Similar to the embodiment, it includes a broadband chaotic laser source 1, an adjustable attenuator 2, a polarization controller 3, a first circulator 4, a semiconductor laser 5, a spectrometer 6, an optical delay generator 7, an optical isolator 9, a sensing fiber 10, a single-sideband modulator 11, a semiconductor optical amplifier 13, a low-noise amplifier 15, a second circulator 16, an optical filter 17, a photodetector 18, a phase-locked amplifier 19, and a computer 20.

[0057] Different from the first embodiment, this embodiment further includes a broadband microwave signal source 12 and a pulse signal generator 14. The broadband microwave signal source 12 is used to output a broadband microwave signal to drive the single-sideband modulator 11, and the pulse signal generator 14 is used to output a pulse signal to drive the semiconductor optical amplifier 13.

[0058] Furthermore, in this embodiment, the broadband microwave signal source 12 and the pulse signal generator 14 are connected to the phase-locked amplifier, and are used to synchronously input a broadband microwave trigger signal and a pulse reference signal to the phase-locked amplifier, respectively.

[0059] The phase-locked amplifier 19 is an amplifier that can separate a specific carrier frequency signal from a strong noise environment, and it can measure weak continuous periodic signals. For example, the pulse reference signal input by the pulse signal generator 14 is represented by V s sin(w r t+θ s ), where V s is the signal strength, w r is the signal frequency, θ s At the same time, the phase-locked amplifier generates an internal local oscillation signal V according to the signal input by the photodetector 18. loc sin(w L t+θ loc ). loc is the signal strength, w L is the signal frequency, θ loc The multiplier in the phase-locked amplifier 19 multiplies the two signals to obtain two frequencies (w r +w L ) and (w r -w L ) of the AC signal:

[0060]

[0061] After this signal passes through the low-pass filter in the phase-locked amplifier 19, only the signal with a frequency close to the reference signal is retained. That is, the output V output for:

[0062]

[0063] The signal measured by the lock-in amplifier 19 is actually the accumulation of stimulated Brillouin gain with the same frequency and phase as the reference signal and other noise. The frequency of the pulse signal generator 14 is used as a reference signal to extract the stimulated Brillouin gain with the same frequency and phase as the reference signal from the measured signal, which can greatly reduce the influence of noise. The detection sensitivity of the lock-in amplifier is very high, which can highly suppress noise and improve the received signal-to-noise ratio.

[0064] The frequency sweep output signal of the broadband microwave signal source 12 is used as a trigger signal of the phase-locked amplifier 19, thereby realizing synchronization of frequency sweep and signal acquisition.

[0065] Furthermore, a low-noise Brillouin sensing device based on injection-locked chaotic laser in this embodiment also includes an optical polarization scrambler 8, which is arranged between the optical delay generator 7 and the optical isolator 9, and is used to randomly perturb the polarization state of the detection light to avoid the influence of Brillouin gain polarization sensitivity.

[0066] Embodiment 3

[0067] Embodiment 3 of the present invention provides a low-noise Brillouin sensing method based on injection-locked chaotic laser, which is implemented based on a low-noise Brillouin sensing device based on injection-locked chaotic laser described in embodiment 1 or 2, and includes the following steps:

[0068] S1, adjusting the power and polarization state of the injected light through the adjustable attenuator 2 and the polarization controller 3 so that the semiconductor laser 5 outputs low-noise broadband chaotic laser;

[0069] S2, adjusting the frequency up-shift frequency and the frequency sweep bandwidth of the pump light through the single sideband modulator 11;

[0070] S3, performing correlation amplification on the detection signal of the photodetector 18 through the lock-in amplifier 19 to obtain a Brillouin gain spectrum;

[0071] S4, adjusting the optical path of the detection light by the optical delay generator 7, so that the pump light and the detection light meet at various positions along the sensing optical fiber 10 and then stimulated Brillouin amplification occurs, and the Brillouin gain spectrum along the sensing optical fiber 10 is obtained;

[0072] S5. Calculate the dynamic temperature and strain information along the entire sensing optical fiber using the Brillouin gain spectrum along the sensing optical fiber 10.

[0073] In step S2, the frequency shift frequency v of the pump light B Approximately equal to the Brillouin frequency shift, the sweep bandwidth is greater than the bandwidth of the Brillouin spectrum line Δv B .

[0074] In summary, the present invention provides a low-noise Brillouin sensing device and method based on injection-locked chaotic laser, which uses injection-locked chaotic laser to excite narrowband correlation peaks, suppresses the intensity noise introduced by broadband chaotic laser sources, and improves the measurement signal-to-noise ratio. Single-sideband modulation and pulse modulation are located in the pump path, which not only suppresses the noise caused by time delay, but also limits the intensity noise caused by single-sideband modulation to the pulse duration; in this way, the influence of low-intensity noise transmission from pump light to detection wave on measurement can be ignored. In order to optimize the signal-to-noise ratio, part of the spontaneous radiation noise is removed by a low-noise amplifier to increase the effective power of the pump light; in addition, the detection light after stimulated Brillouin scattering is correlated and amplified by a phase-locked amplifier to remove noise interference and fully improve the system signal-to-noise ratio. At the same time, the spatial resolution of the present invention is only determined by the bandwidth of the injection-locked chaotic laser, and does not change with the positioning distance. It can realize all-fiber equal precision and blind-spot-free sensing measurement, and finally realize distributed temperature and strain sensing that takes into account long distance and high spatial resolution.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low-noise Brillouin sensing device based on injection-locked chaotic laser, characterized in that: include: Broadband chaotic laser source (1), adjustable attenuator (2), polarization controller (3), first circulator (4), semiconductor laser (5), optical splitter (6), optical delay generator (7), optical isolator (9), sensing fiber (10), single sideband modulator (11), semiconductor optical amplifier (13), low noise amplifier (15), second circulator (16), optical filter (17), photodetector (18), phase-locked amplifier (19), computer (20); The broadband chaotic laser light outputted by the broadband chaotic laser source (1) passes through an adjustable attenuator (2), a polarization controller (3), and a first circulator (4) in sequence, and is then injected into a semiconductor laser (5) to make it output broadband chaotic laser light. The broadband chaotic laser light outputted by the semiconductor laser (5) passes through the first circulator (4) and is then split into two beams by a beam splitter (6). One beam is used as a detection light and passes through an optical delay generator (7) and an optical isolator (9) in sequence, and then enters one end of a sensing optical fiber (10). The other beam is used as a pump light and passes through a single-sideband modulator (11), a semiconductor optical amplifier (13), a low-noise amplifier (15), and a second circulator (16) in sequence, and then enters the other end of the sensing optical fiber (10) to cause Brillouin scattering of the detection light. The optical delay generator (7) is used to adjust the optical path of the detection light, and the optical isolator (9) is used to isolate the pump light output from the sensing optical fiber (10); the single sideband modulator (11) is used to perform single sideband modulation on the pump light to shift the frequency of the pump light upward. v B The semiconductor optical amplifier (13) is used to modulate the pump light into a pulse light with a pulse width less than the feedback delay time, and the low noise amplifier (15) is used to amplify the single sideband pump light; The detection light output from the other end of the sensing optical fiber (10) passes through the second circulator (16) and the optical filter (17) in sequence, is detected by the photodetector (18), converted into an electrical signal, and then sent to the phase-locked amplifier (19). The phase-locked amplifier (19) performs phase-locked amplification on the signal and then sends it to the computer (20) for data processing to obtain the Brillouin gain spectrum.

2. A low-noise Brillouin sensor device based on injection-locked chaotic laser according to claim 1, characterized in that: It also includes a broadband microwave signal source (12) and a pulse signal generator (14), wherein the broadband microwave signal source (12) is used to output a broadband microwave signal to drive the single-sideband modulator (11), and the pulse signal generator (14) is used to output a pulse signal to drive the semiconductor optical amplifier (13).

3. A low-noise Brillouin sensor device based on injection-locked chaotic laser according to claim 2, characterized in that: The broadband microwave signal source (12) and the pulse signal generator (14) are connected to the phase-locked amplifier and are used to synchronously input broadband microwave signals and pulse signals to the phase-locked amplifier, respectively.

4. A low-noise Brillouin sensing device based on injection-locked chaotic laser according to claim 1, characterized in that: The up-shift frequency v of the pump light B Approximately equal to the Brillouin frequency shift, the sweep bandwidth is greater than the bandwidth of the Brillouin spectrum Δ v B .

5. A low-noise Brillouin sensor device based on injection-locked chaotic laser according to claim 1, characterized in that: It also includes a light scrambler (8), which is arranged between the delay generator (7) and the optical isolator (9) and is used to randomly perturb the polarization state of the detection light.

6. A low-noise Brillouin sensing device based on injection-locked chaotic laser according to claim 1, characterized in that: The optical splitter (6) is an optical fiber coupler, and the broadband chaotic laser source (1), the adjustable attenuator (2), the polarization controller (3), the first circulator (4), the semiconductor laser (5), the optical splitter (6), the optical delay generator (7), the optical isolator (9), the sensing optical fiber (10), the single-sideband modulator (11), the semiconductor optical amplifier (13), the low-noise amplifier (15), the second circulator (16), the optical filter (17), and the photodetector (18) are connected via single-mode optical fiber jumpers.

7. A low-noise Brillouin sensor device based on injection-locked chaotic laser according to claim 1, characterized in that: The sensing optical fiber (10) adopts a G652 single-mode optical fiber or a G655 single-mode optical fiber, the semiconductor optical amplifier (13) is an OAM-SOA-PL type high extinction ratio semiconductor optical amplifier, the low noise amplifier (15) comprises a first-stage optical amplifier, a filter and a second-stage optical amplifier connected in sequence, the optical delay generator (7) is a programmable optical delay generator, and the optical filter (17) is a tunable optical filter.

8. A low-noise Brillouin sensing method based on injection-locked chaotic laser, implemented according to the low-noise Brillouin sensing device based on injection-locked chaotic laser according to claim 1, characterized in that: The following steps are involved: S1, adjusting the power and polarization state of the injected light through an adjustable attenuator (2) and a polarization controller (3) so that the semiconductor laser (5) outputs a low-noise broadband chaotic laser; S2, adjusting the frequency up-shift frequency and the frequency sweep bandwidth of the pump light by means of a single sideband modulator (11); S3, performing correlation amplification on the detection signal of the photodetector (18) through a phase-locked amplifier (19) to obtain a Brillouin gain spectrum; S4, adjusting the optical path of the detection light by means of the optical delay generator (7), so that the pump light and the detection light meet at various positions along the sensing optical fiber (10) and thus stimulated Brillouin amplification occurs, thereby obtaining a Brillouin gain spectrum along the sensing optical fiber (10); S5. Calculate the dynamic temperature and strain information along the entire sensing optical fiber using the Brillouin gain spectrum along the sensing optical fiber (10).

9. A low-noise Brillouin sensing method based on injection-locked chaotic laser according to claim 8, characterized in that: In step S2, the up-shift frequency of the pump light v B Approximately equal to the Brillouin frequency shift, the sweep bandwidth is greater than the bandwidth of the Brillouin spectrum Δ v B .

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