Fiber-optic sensing system based on stimulated Raman amplification to achieve full-range sensitivity balance

Abstract

The present invention provides an optical fiber sensing system for achieving full-distance sensitivity balance based on stimulated Raman amplification, comprising: a light source module, which is suitable for generating detection light and intrinsic light; a gain amplification module, which comprises: an optical fiber, the first end of which is connected to the light source module, which is suitable for receiving the detection light and generating signal light in the opposite direction of the detection light by Rayleigh scattering in the optical fiber; a stimulated Raman optical fiber amplifier, which is connected to the second end of the optical fiber, which is opposite to the first end, so as to inject Raman pump light in the opposite direction of the detection light transmission into the optical fiber, and is suitable for amplifying the detection light and the signal light by utilizing the stimulated Raman scattering effect; and a heterodyne coherent detection module, which is suitable for receiving the intrinsic light and the signal light, and heterodyne coherence of the intrinsic light and the signal light to obtain an original beat frequency signal.

Description

Technical Field

[0001] The present invention relates to the field of distributed optical fiber sensing and laser signal amplification, and in particular to an optical fiber sensing system for achieving full-distance sensitivity balance based on stimulated Raman amplification. Background Art

[0002] Distributed fiber optic acoustic sensing technology can realize real-time monitoring of spatial disturbances. Using optical fiber as a sensing unit can be applied to harsh working environments. It has been applied to oil and gas, electricity, transportation, geological exploration and other fields. The basic principle of distributed fiber optic sensing technology is that the light emitted by the light source is coupled into the sensing fiber. When the external measured physical quantity acts on the sensing fiber, the properties of the light in the fiber will change, including intensity, phase, etc. The properties of the measured physical quantity are measured by detecting the property changes of the light.

[0003] However, since the detection light intensity decays exponentially in the optical fiber, the Rayleigh scattered light intensity decays exponentially accordingly, so the Rayleigh scattered light intensity received by the detector becomes weaker as the detection distance increases. This makes the signal intensity at the front end of the optical fiber and the intensity at the back end of the sensing optical fiber very different when the sensing optical fiber is tens of kilometers long. The detection sensitivity is related to the light intensity, which means that the detection sensitivity of the part with a strong light signal at the front end is high, and the detection sensitivity becomes lower and lower as the distance increases, and the signal-to-noise ratio of the signal becomes worse and worse. For the entire section of optical fiber, it is difficult to obtain a uniform vibration monitoring threshold. When the sensing distance is longer, this problem becomes more significant. Summary of the invention

[0004] In view of this, the present invention provides a fiber optic sensing system that realizes full-distance sensitivity balance based on stimulated Raman amplification.

[0005] The optical fiber sensing system based on stimulated Raman amplification to achieve full-distance sensitivity balance provided by the present invention includes: a light source module, which is suitable for generating detection light and intrinsic light; a gain amplification module, which includes: an optical fiber, the first end of which is connected to the light source module, which is suitable for receiving the detection light and generating signal light in the opposite direction of the detection light by Rayleigh scattering in the optical fiber; a stimulated Raman fiber amplifier, which is connected to the second end of the optical fiber opposite to the first end to inject Raman pump light in the opposite direction of the detection light transmission into the optical fiber, which is suitable for amplifying the detection light and the signal light by utilizing the stimulated Raman scattering effect; and a heterodyne coherent detection module, which is suitable for receiving the intrinsic light and the signal light, and heterodyne coherence of the intrinsic light and the signal light to obtain the original beat frequency signal.

[0006] According to an embodiment of the present invention, the gain amplification module includes a plurality of optical fibers and stimulated Raman fiber amplifiers connected in sequence.

[0007] According to an embodiment of the present invention, the light source module includes: a narrow linewidth laser, which is suitable for emitting an initial laser; a coupler, which is arranged downstream of the optical path of the narrow linewidth laser, and is suitable for receiving the initial laser and splitting the initial laser to form a detection light and an intrinsic light respectively; a circulator, which is arranged downstream of the optical path of the coupler, and is suitable for receiving the detection light and transmitting the detection light to the optical fiber, and receiving the signal light transmitted back from the optical fiber and transmitting the signal light to the heterodyne coherent detection module.

[0008] According to an embodiment of the present invention, the central wavelength of the initial laser light matches the gain wavelength range of the Raman pump light.

[0009] According to an embodiment of the present invention, the light source module further includes: an acousto-optic modulation module, which is arranged between the coupler and the circulator and is suitable for modulating the detection light.

[0010] According to an embodiment of the present invention, the light source module further includes an erbium-doped fiber amplifier, which is disposed between the acousto-optic modulation module and the circulator and is suitable for amplifying the power of the detection light.

[0011] According to an embodiment of the present invention, the light source module further includes a first filter, which is disposed between the erbium-doped fiber amplifier and the circulator and is suitable for filtering noise signals generated after the detection light is amplified by the erbium-doped fiber amplifier.

[0012] According to an embodiment of the present invention, a second filter is further included, which is arranged between the circulator and the heterodyne coherent detection module and is suitable for filtering the Raman pump light in the signal light returned via the optical fiber.

[0013] According to an embodiment of the present invention, it further includes an acquisition module adapted to receive an original beat frequency signal and convert the original beat frequency signal into phase information.

[0014] According to an embodiment of the present invention, it also includes an arbitrary waveform generator, which is connected to the acquisition module and is suitable for sending a pulse trigger signal to the acquisition module to trigger the acquisition module to start acquiring the original beat frequency signal, and is also suitable for sending a timing control signal to the acquisition module to control the acquisition timing of the original beat frequency signal.

[0015] According to the optical fiber sensing system for realizing full-distance sensitivity balance based on stimulated Raman amplification provided by the present invention, by connecting the first end of the optical fiber to the light source module, and connecting the stimulated Raman optical fiber amplifier to the second end opposite to the first end of the optical fiber, the transmission directions of the detection light and the Raman pump light in the optical fiber are opposite, and the Raman pump light can amplify the detection light and the signal light based on the stimulated Raman scattering effect. Further, since the light intensity of the detection light and the signal light generated by Rayleigh scattering in the optical fiber decays exponentially with the increase of distance, the closer the detection light and the signal light are to the second end of the optical fiber, the weaker the light intensity; and the light intensity of the Raman pump light also decays exponentially with the increase of the propagation distance, and the closer the Raman pump light is to the first end of the optical fiber, the weaker the light intensity. Therefore, the weak detection light and weak signal light near the second end of the optical fiber will receive a stronger amplification gain when encountering the strong pump light, while the strong detection light and strong signal light near the first end of the optical fiber will encounter the attenuated pump light and thus receive a weaker amplification gain, so that the signal light intensity of the entire section of the optical fiber detected is approximately consistent, and the detection of distributed optical fiber full-distance sensitivity balance can be realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0017] Figure 1 A schematic diagram of a structure of an optical fiber sensing system for achieving full-distance sensitivity balance based on stimulated Raman amplification according to an embodiment of the present invention is shown;

[0018] Figure 2 Schematically showing a principle diagram of sequentially connecting a plurality of optical fibers and stimulated Raman fiber amplifiers according to an embodiment of the present invention;

[0019] Figure 3a A schematic diagram showing the result of the original beat frequency signal when the stimulated Raman fiber amplifier is turned off according to an embodiment of the present invention;

[0020] Figure 3b A schematic diagram showing the result of the original beat frequency signal when the stimulated Raman fiber amplifier is turned on according to an embodiment of the present invention

[0021] Figure 4a A schematic diagram schematically shows the result of the original beat frequency signal when the stimulated Raman fiber amplifier is turned off according to another embodiment of the present invention;

[0022] Figure 4b The result schematic diagram of the original beat frequency signal when the stimulated Raman fiber amplifier is turned on according to another embodiment of the present invention is schematically shown.

[0023] Reference numerals

[0024] 100. Light source module;

[0025] 110. Narrow linewidth laser;

[0026] 120. Coupler;

[0027] 130. Acousto-optic modulation module;

[0028] 131. Acousto-optic modulator;

[0029] 132. RF driver;

[0030] 140. Erbium-doped fiber amplifier;

[0031] 150. A first filter;

[0032] 160, Circulator;

[0033] 200, gain amplifier module;

[0034] 210. Optical fiber;

[0035] 220. Stimulated Raman fiber amplifier;

[0036] 221. Pump laser;

[0037] 222. Isolator;

[0038] 223. Wavelength division multiplexer;

[0039] 300. heterodyne coherent detection module;

[0040] 400, acquisition module;

[0041] 410, acquisition card;

[0042] 420, PC;

[0043] 500, second filter;

[0044] 600. Arbitrary waveform generator. DETAILED DESCRIPTION

[0045] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0046] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The terms "comprise", "include", etc. used herein indicate the existence of features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0047] All terms used herein, including technical and scientific terms, have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification, and should not be interpreted in an idealized or overly rigid manner.

[0048] When using expressions such as "at least one of A, B, and C, etc.", it should generally be interpreted as the meaning of the expression generally understood by those skilled in the art. For example, "a system having at least one of A, B, and C" should include but not be limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc. When using expressions such as "at least one of A, B, or C, etc.", it should generally be interpreted as the meaning of the expression generally understood by those skilled in the art. For example, "a system having at least one of A, B, or C" should include but not be limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.

[0049] It should also be noted that the directional terms mentioned in the embodiments, such as "upper", "lower", "front", "back", "left", "right", etc., are only reference directions of the drawings and are not intended to limit the scope of protection of the present invention. Throughout the drawings, the same elements are represented by the same or similar reference numerals. Conventional structures or configurations will be omitted when they may cause confusion in the understanding of the present invention.

[0050] Figure 1 The structure block diagram of the optical fiber sensing system for achieving full-distance sensitivity balance based on stimulated Raman amplification according to an embodiment of the present invention is schematically shown.

[0051] According to the optical fiber sensing system based on stimulated Raman amplification to achieve full-distance sensitivity balance provided by the present invention, Figure 1 As shown, it includes a light source module 100, a gain amplifier module 200 and a heterodyne coherent detection module 300. The light source module 100 is suitable for generating detection light and intrinsic light. The gain amplifier module 200 includes an optical fiber 210 and a stimulated Raman fiber amplifier 220. The first end of the optical fiber 210 is connected to the light source module 100, which is suitable for receiving the detection light, and Rayleigh scattering occurs in the optical fiber 210 to generate a signal light in the opposite direction of the detection light. The stimulated Raman fiber amplifier 220 is connected to the second end of the optical fiber 210 opposite to the first end, so as to inject Raman pump light in the opposite direction of the detection light transmission into the optical fiber 210, and is suitable for amplifying the detection light and the signal light by using the stimulated Raman scattering effect. The heterodyne coherent detection module 300 is suitable for receiving the intrinsic light and the signal light, and heterodyne coherence is performed on the intrinsic light and the signal light to obtain the original beat signal.

[0052] In such an embodiment, by connecting the first end of the optical fiber 210 to the light source module 100 and connecting the stimulated Raman fiber amplifier 220 to the second end of the optical fiber 210 opposite to the first end, the detection light and the Raman pump light are transmitted in opposite directions in the optical fiber 210, and the Raman pump light can amplify the detection light and the signal light based on the stimulated Raman scattering effect. Further, since the light intensity of the detection light and the signal light generated by Rayleigh scattering in the optical fiber 210 decays exponentially with the increase of distance, the closer the detection light is to the second end of the optical fiber 210, the weaker the light intensity of the generated signal light is; and the light intensity of the Raman pump light also decays exponentially with the increase of the propagation distance, and the closer the Raman pump light is to the first end of the optical fiber 210, the weaker the light intensity is. Therefore, the weak detection light and weak signal light near the second end of the optical fiber 210 will receive a stronger amplification gain when encountering the strong pump light, while the strong detection light and strong signal light near the first end of the optical fiber 210 will encounter the attenuated Raman pump light and thus receive a weaker amplification gain, so that the signal light intensity detected in the entire section of the optical fiber is approximately consistent, and distributed optical fiber full-distance balanced sensitivity detection can be achieved.

[0053] According to an embodiment of the present invention, Figure 1 As shown, the light source module 100 includes a narrow linewidth laser 110, a coupler 120 and a circulator 160. The narrow linewidth laser 110 is suitable for emitting an initial laser. The coupler 120 is arranged downstream of the optical path of the narrow linewidth laser 110, and is suitable for receiving the initial laser and splitting the initial laser to form a detection light and an intrinsic light respectively. The circulator 160 is arranged downstream of the optical path of the coupler 120, and is suitable for receiving the detection light and transmitting the detection light to the optical fiber 210, and receiving the signal light transmitted back from the optical fiber 210 and transmitting the signal light to the heterodyne coherent detection module 300.

[0054] According to the embodiment of the present invention, the spectral linewidth of the narrow linewidth laser 110 is very narrow, so that its spectral stability is very good, it is not affected by external interference, has good anti-interference performance, and can provide a stable output signal in a complex environment.

[0055] According to an embodiment of the present invention, the coupler 120 includes an input end, a first output end, and a second output end. The output end of the narrow linewidth laser 110 is connected to the input end of the coupler 120, and the coupler 120 can divide the initial laser into two beams of light, one of which is output from the first output end as a detection light and transmitted to the optical fiber 210 for detection and sensing; the second output end of the coupler 120 is connected to the heterodyne coherent detection module 300, and the other beam is input from the second output end to the heterodyne coherent detection module 300 as an intrinsic light.

[0056] According to an embodiment of the present invention, the circulator 160 also has a first input end, a first output end, and a second output end. The detection light is input from the first input end of the circulator 160 and transmitted from the first output end to the optical fiber 210. The detection light generates back Rayleigh scattered light (i.e., signal light) in the optical fiber 210, which is input from the first output end of the circulator 160 and output from the second output end of the circulator 160.

[0057] According to an embodiment of the present invention, the light source module 100 further includes an acousto-optic modulation module 130 , which is disposed between the coupler 120 and the circulator 160 and is suitable for modulating the detection light.

[0058] In an illustrative embodiment, Figure 1 As shown, the acousto-optic modulation module 130 includes an acousto-optic modulator 131 and a radio frequency driver 132. The first input end of the acousto-optic modulator 131 is connected to the first output end of the coupler 120, and the second input end of the acousto-optic modulator 131 is connected to the input end of the radio frequency driver 132. The acousto-optic modulator 131 can utilize the acousto-optic effect to modulate the intensity, direction and frequency of the laser beam by detecting the refractive index grating generated by the light in the acousto-optic modulator 131. The radio frequency driver 132 can provide a radio frequency signal. When the radio frequency signal acts on the acousto-optic modulator 131, the internal crystal will generate periodic elastic strain and generate an acousto-optic effect, thereby realizing the modulation of the optical signal.

[0059] In an exemplary embodiment, the RF driver 132 may be connected to an arbitrary waveform generator 600, and the arbitrary waveform generator 600 provides a sinusoidal pulse train signal to the RF driver 132. The RF driver 132 converts the sinusoidal pulse train signal into a driving signal required by the acousto-optic modulator 131, thereby achieving precise modulation of the detection light.

[0060] According to an embodiment of the present invention, Figure 1 As shown, the light source module 100 further includes an erbium-doped fiber amplifier 140 disposed between the acousto-optic modulation module 130 and the circulator 160 and adapted to amplify the power of the detection light.

[0061] In such an embodiment, after the detection light is amplified by the gain medium in the erbium-doped fiber amplifier 140, the intensity of the detection light input to the optical fiber 210 can be preliminarily amplified to meet the requirements of long-distance optical fiber detection.

[0062] According to an embodiment of the present invention, Figure 1 As shown, the light source module 100 further includes a first filter 150 , which is disposed between the erbium-doped fiber amplifier 140 and the circulator 160 and is adapted to filter the noise signal generated after the detection light is amplified by the erbium-doped fiber amplifier 140 .

[0063] According to an embodiment of the present invention, Figure 1 As shown, the input end of the erbium-doped fiber amplifier 140 is connected to the output end of the acousto-optic modulator 131, the output end of the erbium-doped fiber amplifier 140 is connected to the input end of the filter, and the output end of the first filter 150 is connected to the first input end of the circulator 160. After the detection light is modulated by the acousto-optic modulator 131, the frequency-shifted pulse detection light is obtained, and then the power of the detection light is amplified by the erbium-doped fiber amplifier 140, and then the optical noise caused by the erbium-doped fiber amplifier 140 is removed by filtering by the filter, and the filtered detection light enters the sensing fiber 210 through the circulator 160 for transmission.

[0064] According to an embodiment of the present invention, the central wavelength of the initial laser matches the gain wavelength range of the Raman pump light. For example, the high-power Raman pump laser with a wavelength of 1450nm-1460nm generated by the stimulated Raman fiber amplifier 220 can amplify the detection light with a central wavelength of 1550.12nm and the backscattered Rayleigh light.

[0065] Figure 2 The schematic diagram shows a principle diagram of sequentially connecting a plurality of optical fibers 210 and stimulated Raman fiber amplifiers 220 according to an embodiment of the present invention.

[0066] According to an embodiment of the present invention, Figure 2 As shown, the gain amplification module 200 includes a plurality of optical fibers 210 and stimulated Raman fiber amplifiers 220 connected in sequence.

[0067] For details, see Figure 2 The stimulated Raman fiber amplifier 220 includes a pump laser 221, an isolator 222, and a wavelength division multiplexer 223. After the detection light enters the stimulated Raman fiber amplifier 220 from the first section of optical fiber 210, it enters the second section of optical fiber 210 and the stimulated Raman fiber amplifier 220 through the wavelength division multiplexer 223 in the stimulated Raman fiber amplifier 220. The Raman pump light emitted by the pump laser 221 passes through the isolator 222 and is incident on the wavelength division multiplexer 223, and then is incident on the first section of optical fiber 210, so as to amplify the detection light and signal light of the first section of optical fiber 210.

[0068] In such an embodiment, since the light intensities of the signal light and the detection light of the entire section of optical fiber 210 are approximately the same, the problem of the attenuation of the optical fiber 210 sensing signal intensity as the detection distance increases is solved. Through multiple sequentially connected optical fibers 210 and stimulated Raman fiber amplifiers 220, the optical fiber 210 sensing system can perform detection over a longer distance.

[0069] According to an embodiment of the present invention, a second filter 500 is further included, which is disposed between the circulator 160 and the heterodyne coherent detection module 300 and is suitable for filtering the Raman pump light in the signal light returned via the optical fiber 210 .

[0070] According to an embodiment of the present invention, the input end of the second filter 500 is connected to the second output end of the circulator 160, and the output end of the second filter 500 is connected to the input end of the heterodyne coherent detection module 300. After the Raman pump light is removed by the second filter 500, the signal light is incident on the heterodyne coherent detection module 300, and heterodyne coherence is performed with the intrinsic light from the second output end of the coupler 120 to obtain the original beat frequency signal.

[0071] According to an embodiment of the present invention, a collection module 400 is further included, which is adapted to receive an original beat frequency signal and convert the original beat frequency signal into phase information.

[0072] According to an embodiment of the present invention, the acquisition module 400 includes an acquisition card 410 and a PC (i.e., computer) 420. The acquisition card 410 is connected to the heterodyne coherent detection module 300 to convert the original beat frequency signal into phase information, thereby realizing quantitative measurement of the acoustic signal. The PC (i.e., computer) 420 is used to edit and store data.

[0073] According to an embodiment of the present invention, the arbitrary waveform generator 600 is connected to the acquisition module 400, and is suitable for sending a pulse trigger signal to the acquisition module 400 to trigger the acquisition module 400 to start acquiring the original beat frequency signal, and is also suitable for sending a timing control signal to the acquisition module 400 to control the acquisition timing of the original beat frequency signal.

[0074] In such an implementation, the arbitrary waveform generator 600 is connected to the acquisition module 400, and the signal emitted by the arbitrary waveform generator 600 is used to control the timing of the entire distributed acoustic sensing system, thereby ensuring the continuity and accuracy of signal acquisition.

[0075] In an exemplary embodiment, the narrow linewidth laser 110 emits continuous light with a central wavelength of 1550.12 nm. After being split by the coupler 120, modulated by the acousto-optic modulation module 130, amplified by the erbium-doped fiber amplifier 140, and filtered by the first filter 150, the detection light enters from the first end of the optical fiber 210 through the circulator 160. According to the Beer-Lambert law, the intensity of the detection light in the optical fiber 210 is shown in formula (1):

[0076] (1)

[0077] in, is the light intensity of the probe light injected into the first end of the optical fiber 210, z is the propagation distance of the light, is the intensity of light when the detection light transmission distance is z, e represents a natural constant, is the attenuation coefficient of the detection light.

[0078] The high-power Raman pump light output by the stimulated Raman fiber amplifier 220 has a wavelength of 1450nm-1460nm and enters from the second end of the optical fiber 210. Due to the stimulated Raman scattering effect, it can be roughly understood that the energy of the Raman pump light is transferred to the 1550.12nm signal light, thereby achieving the amplification of the signal light. The light intensity of the pump light in the optical fiber 210 can be expressed by referring to formula (2):

[0079] (2)

[0080] in, is the intensity of the Raman pump light injected into the stimulated Raman fiber amplifier 220 at the second end of the optical fiber 210, L is the total length of the optical fiber 210, represents the intensity of the Raman pump light at the optical fiber position z, is the attenuation coefficient of the Raman pump light.

[0081] The signal light emitted from the second output end of the circulator 160 passes through the second filter 500 to remove the Raman pump light, and the obtained signal light enters the heterodyne coherent detection system. The light intensity of the signal light obtained after passing through the gain amplification system can be referred to in formula (3):

[0082] (3)

[0083] in, is the Rayleigh backscattering coefficient, is the light intensity of the probe light injected into the first end of the optical fiber 210, e represents a natural constant, is the Raman gain coefficient, is the intensity of the Raman pump light injected into the stimulated Raman fiber amplifier 220 at the second end of the optical fiber 210, is the attenuation coefficient of the Raman pump light, is the attenuation coefficient of the detection light, It is the intensity of the signal light returned to the detector after passing through the gain amplification system at the optical fiber position z.

[0084] Therefore, by adjusting and The intensity of the signal light can be approximately balanced throughout the sensing optical fiber 210 .

[0085] Figure 3a A schematic diagram showing the result of the original beat frequency signal when the stimulated Raman fiber amplifier is turned off according to an embodiment of the present invention; Figure 3bThe result schematic diagram of the original beat frequency signal when the stimulated Raman fiber amplifier is turned on according to an embodiment of the present invention is schematically shown.

[0086] The total length of the optical fiber 210 is 30 km. When the stimulated Raman fiber amplifier 220 is turned off, the obtained signal light and intrinsic light are detected by a heterodyne coherent detection system to obtain the original beat frequency signal as shown in FIG. Figure 3a As shown in FIG. 1 , the signal strength of the original beat frequency signal gradually decays with the increase of distance. When the stimulated Raman fiber amplifier 220 is turned on, the current of the stimulated Raman fiber amplifier 220 is adjusted to match the pump light energy with the distance, and the obtained signal light and intrinsic light are obtained through the heterodyne coherent detection system to obtain the original beat frequency signal as shown in FIG. Figure 3b As shown, it can be seen that the signal light intensity of the entire section of optical fiber 210 is approximately equal, and the detection sensitivity will not decrease with the increase of the sensing distance. Since the greater the signal light intensity received by the detector, the higher the detection sensitivity of the system, the measurement accuracy and sensitivity of the entire system can be improved.

[0087] Figure 4a A schematic diagram schematically shows the result of the original beat frequency signal when the stimulated Raman fiber amplifier is turned off according to another embodiment of the present invention; Figure 4b The result schematic diagram of the original beat frequency signal when the stimulated Raman fiber amplifier is turned on according to another embodiment of the present invention is schematically shown.

[0088] The total length of the optical fiber 210 is 50 km. When the stimulated Raman fiber amplifier 220 is turned off, the obtained signal light and intrinsic light are detected by a heterodyne coherent detection system to obtain the original beat frequency signal as shown in FIG. Figure 4a When the stimulated Raman fiber amplifier 220 is turned on, the obtained signal light and intrinsic light are detected by the heterodyne coherent detection system to obtain the original beat frequency signal as shown in FIG. Figure 4b As shown, it can be seen that when the total length of the optical fiber 210 reaches 50 km, by adjusting the current of the stimulated Raman fiber amplifier 220 to match the pump light energy with the distance, the signal light intensity of the entire section of the optical fiber 210 can still be approximately equal, and the detection sensitivity will not decrease with the increase of the sensing distance.

[0089] According to the fiber optic sensing system based on stimulated Raman scattering provided by the present invention, a Raman pump laser with a transmission direction opposite to that of the incident detection light is used to achieve balanced gain of the optical signal of the entire fiber optic. Thus, the signal detected by the fiber optic sensor remains constant or fluctuates within a very small range, so that the signal intensity is in almost the same dynamic range, and the detection sensitivity does not decrease with the increase of the sensing distance, thereby improving the measurement accuracy and sensitivity of the equipment and reducing the difficulty of data demodulation.

[0090] The gain amplification module according to the present invention includes, but is not limited to, fiber optic acoustic sensing, fiber optic vibration sensing, and fiber optic strain sensing, etc., which are applicable to the field of fiber optic sensing.

[0091] The embodiments of the present invention are described above. However, these embodiments are only for the purpose of illustration, and are not intended to limit the scope of the present invention. Although each embodiment is described above, it does not mean that the measures in each embodiment cannot be used in combination. The scope of the present invention is defined by the attached claims and their equivalents. Without departing from the scope of the present invention, those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present invention.

Claims

1. A fiber optic sensing system based on stimulated Raman amplification to achieve full-range sensitivity balance, characterized in that: include: A light source module (100) is adapted to generate detection light and intrinsic light; The gain amplification module (200) comprises: An optical fiber (210), wherein a first end of the optical fiber (210) is connected to the light source module (100), and is adapted to receive the detection light and generate signal light in a direction opposite to the detection light by Rayleigh scattering in the optical fiber (210); a stimulated Raman fiber amplifier (220), connected to a second end of the optical fiber (210) opposite to the first end, to inject Raman pump light in a direction opposite to the transmission direction of the detection light into the optical fiber (210), and adapted to amplify the detection light and the signal light by utilizing a stimulated Raman scattering effect; and A heterodyne coherent detection module (300), adapted to receive the intrinsic light and the signal light, and perform heterodyne coherence on the intrinsic light and the signal light to obtain an original beat frequency signal; The gain amplification module (200) comprises a plurality of optical fibers (210) connected in sequence, and the stimulated Raman fiber amplifier (220) is arranged downstream of the optical path of each optical fiber (210).

2. The optical fiber sensing system according to claim 1, characterized in that: The light source module (100) comprises: A narrow linewidth laser (110) suitable for emitting an initial laser; A coupler (120), arranged downstream of the optical path of the narrow linewidth laser, adapted to receive the initial laser and split the initial laser to form the detection light and the intrinsic light respectively; The circulator (160) is arranged downstream of the optical path of the coupler (120), and is adapted to receive the detection light and transmit the detection light to the optical fiber (210), and to receive the signal light transmitted back from the optical fiber (210) and transmit the signal light to the heterodyne coherent detection module (300).

3. The optical fiber sensing system according to claim 2, characterized in that: The central wavelength of the initial laser matches the gain wavelength range of the Raman pump light.

4. The optical fiber sensing system according to claim 2, characterized in that: The light source module (100) further comprises: The acousto-optic modulation module (130) is arranged between the coupler (120) and the circulator (160) and is suitable for modulating the detection light.

5. The optical fiber sensing system according to claim 4, characterized in that: The light source module (100) further comprises an erbium-doped fiber amplifier (140), which is arranged between the acousto-optic modulation module (130) and the circulator (160) and is suitable for amplifying the power of the detection light.

6. The optical fiber sensing system according to claim 5, characterized in that: The light source module (100) further comprises a first filter (150), which is arranged between the erbium-doped fiber amplifier (140) and the circulator (160) and is suitable for filtering the noise signal generated after the detection light is amplified by the erbium-doped fiber amplifier (140).

7. The optical fiber sensing system according to claim 2, characterized in that: It also includes a second filter (500), which is arranged between the circulator (160) and the heterodyne coherent detection module (300) and is suitable for filtering the Raman pump light in the signal light returned via the optical fiber (210).

8. The optical fiber sensing system according to any one of claims 1 to 7, characterized in that: It also includes a collection module (400) adapted to receive the original beat frequency signal and convert the original beat frequency signal into phase information.

9. The optical fiber sensing system according to claim 8, characterized in that: It also includes an arbitrary waveform generator (600), which is connected to the acquisition module (400) and is suitable for sending a pulse trigger signal to the acquisition module (400) to trigger the acquisition module (400) to start acquiring the original beat frequency signal, and is also suitable for sending a timing control signal to the acquisition module (400) to control the acquisition timing of the original beat frequency signal.

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