A distributed optical fiber detection light source system based on pulse dense comb frequency modulation

Abstract

The application relates to the technical field of optical fiber sensing, and provides a distributed optical fiber detection light source system based on pulse dense comb frequency modulation, which comprises the following components: an optical source assembly for generating detection light; a modulation device connected with the optical source assembly and forming a frequency shift ring cavity; the modulation device comprises a first optical fiber coupler, a delay optical fiber assembly, a double-parallel Mach-Zehnder modulator and an erbium-doped optical fiber assembly arranged in sequence; the modulation device is configured to modulate the frequency of the detection light in the frequency shift ring cavity; an output optical fiber is connected with the output end of the first optical fiber coupler, and the output optical fiber is used for outputting the detection light after frequency shift. The distributed optical fiber detection light source system based on pulse dense comb frequency modulation has a relatively simple structure, can effectively reduce the speed of the detection light circulating frequency shift in the frequency shift ring, and further accelerates the output of the detection light after frequency shift, so that the detection efficiency of the detection light used for detection is improved, and the detection time is shortened.

Description

Technical Field

[0001] This application relates to the field of fiber optic sensing technology, and in particular to a distributed fiber optic detection optical source system based on pulsed close comb frequency modulation. Background Technology

[0002] Distributed fiber optic sensing technology enables continuous spatial measurement of external signals by modulating light waves in optical fibers, and is widely used in many fields such as pipeline leak detection, seismic exploration, and ranging.

[0003] Optical time-domain reflectometry (OTDR) and optical frequency-domain reflectometry (OFDR) are commonly used for measurements. However, OTD requires wide pulse widths to achieve long detection distances, leading to prolonged measurement times and difficulty in quickly responding to dynamic signals. OFDR, on the other hand, requires a wide wavelength tuning range to achieve high spatial resolution, but its long light source sweep period significantly increases detection time, failing to meet real-time monitoring requirements.

[0004] Therefore, there is an urgent need for a detection technology that can effectively reduce detection time and improve detection efficiency. Summary of the Invention

[0005] This application provides a distributed optical fiber detection light source system based on pulsed close comb frequency modulation to solve the technical problems of long detection time and low efficiency in existing systems.

[0006] The distributed optical fiber detection light source system based on pulsed close-comb frequency modulation provided in this application includes: a light source component configured to generate detection light; a modulation device connected to the light source and forming a frequency-shifting cavity; the modulation device includes a first optical fiber coupler, a delay optical fiber component, a dual parallel Mach-Zehnder modulator, and an erbium-doped optical fiber component arranged sequentially; the modulation device is configured to modulate the frequency of the detection light in the frequency-shifting cavity; wherein, the input end of the first optical fiber coupler is connected to the light source component and the erbium-doped optical fiber component respectively, and the output end of the first optical fiber coupler is connected to the delay optical fiber component; the delay optical fiber component is configured to delay the detection light; the dual parallel Mach-Zehnder modulator is configured to modulate the frequency of the detection light; the erbium-doped optical fiber component is configured to receive the detection light and compensate for the detection light loss; and an output optical fiber connected to the output end of the first optical fiber coupler, the output optical fiber being configured to output the frequency-shifted detection light.

[0007] In some feasible implementations, the increase in the frequency of the detection light provided in this application is positively correlated with the number of cycles of the detection light in the frequency shifting cavity, and the time for the detection light to cycle once in the frequency shifting cavity is less than or equal to the pulse width of the detection light.

[0008] In some feasible implementations, the delay fiber assembly includes an optical switch, a first delay fiber, and a second delay fiber; the input end of the optical switch is connected to a first fiber coupler; the output end of the optical switch is connected to the first delay fiber and the second delay fiber, respectively; the optical switch is configured to conduct the first delay fiber or the second delay fiber to control the detection optical delay.

[0009] In some feasible implementations, the first delay fiber and the second delay fiber have different lengths.

[0010] In some feasible implementations, the erbium-doped fiber assembly includes an erbium-doped fiber and an erbium-doped fiber amplifier; the distributed fiber detection optical source system based on pulsed close-comb frequency modulation also includes a first wavelength division multiplexer; the two input ends of the erbium-doped fiber are connected to the input ends of the first wavelength division multiplexer, and detection light of the same frequency interferes within the erbium-doped fiber to form a refractive index grating; the erbium-doped fiber amplifier is connected to the output end of the first wavelength division multiplexer, and the erbium-doped fiber amplifier is configured to compensate for detection light loss.

[0011] In some feasible implementations, the following are also included: a second fiber coupler, a first polarization controller, and a second polarization controller; the input end of the second fiber coupler is connected to one end of the first delay fiber and the second delay fiber away from the optical switch; the first polarization controller is disposed between the second fiber coupler and the dual parallel Mach-Zehnder modulator, and the first polarization controller is configured to control the polarization-maintaining state of the detection light input to the dual parallel Mach-Zehnder modulator; the second polarization controller is disposed between the erbium-doped fiber amplifier and the first fiber coupler, and the second polarization controller is configured to control the polarization-maintaining state of the detection light output from the dual parallel Mach-Zehnder modulator.

[0012] In some feasible implementations, the light source assembly includes a light source, a second wavelength division multiplexer, and an active phase-shifting fiber grating; the light source is configured to generate pump light of a first wavelength; the second wavelength division multiplexer is connected between the light source and the active phase-shifting fiber grating; the second wavelength division multiplexer is configured to transmit the pump light of the first wavelength to the active phase-shifting fiber grating and output laser light of a second wavelength; wherein the second wavelength is greater than the first wavelength.

[0013] Some feasible implementations also include: an isolator and a filter; the isolator is positioned between the first fiber coupler and the optical switch, and is configured to isolate the return light; the filter is positioned between the dual parallel Mach-Zehnder modulator and the first wavelength division multiplexer, and is configured to filter noise.

[0014] In some feasible implementations, a third fiber coupler and an electro-optic modulator are also included; the third fiber coupler is disposed between the second wavelength division multiplexer and the electro-optic modulator; the electro-optic modulator is connected to the input of the first fiber coupler and is configured to modulate the detection light.

[0015] Some feasible implementations also include: a first signal generator and a second signal generator; the first signal generator is connected to the electro-optic modulator and is used to control the electro-optic modulator; the second signal generator is connected to a dual parallel Mach-Zehnder modulator and is used to control the dual parallel Mach-Zehnder modulator.

[0016] The distributed optical fiber detection light source system based on pulsed close comb frequency modulation in this application has a relatively simple structure. It can effectively reduce the speed of the detection light cyclically changing frequency in the frequency shifting loop, thereby accelerating the output of the detection light after frequency conversion. This improves the detection efficiency when the detection light is used for detection and shortens the detection time. Moreover, the light source system can simultaneously take into account the three major parameters of spatial resolution, detection distance, and bandwidth, effectively ensuring the performance of the system. Attached Figure Description

[0017] To more clearly illustrate the technical solution of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of a distributed optical fiber detection optical source system based on pulsed close comb frequency modulation provided in an embodiment of this application;

[0019] Figure 2 This is a schematic diagram of a dual parallel Mach-Zehnder modulator provided in an embodiment of this application.

[0020] 100- A distributed optical fiber detection optical source system based on pulsed close-comb frequency modulation;

[0021] 10-Light source assembly; 11-Light source; 12-Second wavelength division multiplexer; 13-Active phase-shift fiber Bragg grating;

[0022] 20-Modulation device; 20a-Frequency shifting ring cavity; 21-First fiber coupler; 22-Delay fiber assembly; 221-Optical switch; 222-First delay fiber; 223-Second delay fiber; 23-Dual parallel Mach-Zehnder modulator; 24-Erbium-doped fiber assembly; 241-Erbium-doped fiber; 242-Erbium-doped fiber amplifier; 25-Second fiber coupler; 26-First polarization controller; 27-Second polarization controller; 28-Isolator; 29-Filter;

[0023] 30 - Output fiber;

[0024] 40 - First wavelength division multiplexer; 50 - Third fiber optic coupler; 60 - Electro-optic modulator; 70 - First signal generator; 80 - Second signal generator. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are all within the protection scope of this application.

[0026] In the following description, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0027] Furthermore, in this application, directional terms such as "upper," "lower," "inner," and "outer" are defined relative to the indicated placement of the components in the accompanying drawings. It should be understood that these directional terms are relative concepts, used for relative description and clarification, and can change accordingly depending on the placement of the components in the accompanying drawings.

[0028] To address the technical problems of long detection time and low efficiency in existing technologies, this application proposes a novel distributed optical fiber sensing technology that optimizes the frequency shifting speed, frequency shifting range, pulse width, instantaneous linewidth, optical power, and signal-to-noise ratio of the light source.

[0029] Figure 1 This is a schematic diagram of a distributed optical fiber detection optical source system based on pulsed close comb frequency modulation provided in an embodiment of this application.

[0030] See Figure 1 The distributed optical fiber detection light source system 100 based on pulsed close comb frequency modulation includes a light source component 10, a modulation device 20, and an output optical fiber 30.

[0031] The light source assembly 10 is used to generate detection light. The detection light can be an infrared laser with a wavelength of 1550nm to match the transmission of long-distance, high-capacity optical signals.

[0032] The modulation device 20 is connected to the light source assembly 10 and has a frequency-shifting ring cavity 20a formed inside it. The modulation device 20 is used to receive the detection light emitted by the light source assembly 10 and modulate the frequency of the detection light in the frequency-shifting ring cavity 20a to produce a frequency change.

[0033] Specifically, the modulation device 20 includes a first fiber coupler 21, a delay fiber assembly 22, a dual parallel Mach-Zehnder modulator 23, and an erbium-doped fiber assembly 24 arranged sequentially.

[0034] The first fiber optic coupler 21 is located at the entrance of the frequency-shifting cavity 20a. The detection light emitted by the light source assembly 10 directly enters the frequency-shifting cavity 20a through the first fiber optic coupler 21. The first fiber optic coupler 21 is used for both receiving and outputting the detection light. The input end of the first fiber optic coupler 21 is connected to both the light source assembly 10 and the erbium-doped fiber assembly 24. In this way, the detection light emitted by the light source assembly 10 can enter the frequency-shifting cavity 20a through the input end of the first fiber optic coupler 21, and finally return to the first fiber optic coupler 21 through the erbium-doped fiber assembly 24, thus achieving a complete cycle of the detection light within the frequency-shifting cavity 20a.

[0035] The delay fiber assembly 22 is used to receive and control the delay of the detection light during propagation. This facilitates the control of different pulse widths of the detection light, enabling modulation of different pulse widths and frequencies.

[0036] A dual parallel Mach-Zehnder modulator 23 is disposed between the delay fiber assembly 22 and the erbium-doped fiber assembly 24 to receive the detection light transmitted by the delay fiber assembly 22 and modulate the frequency of the detection light.

[0037] Erbium-doped fiber assembly 24 is used to receive the detection light transmitted by dual parallel Mach-Zehnder modulator 23 and to compensate for the loss of the detection light propagating in the frequency shifting cavity 20a.

[0038] The output optical fiber 30 is located outside the frequency-shifting ring cavity 20a. The output optical fiber 30 is connected to the output end of the first optical fiber coupler 21 and is used to output the frequency-shifted detection light to perform specific functions, such as pipeline leak detection, seismic exploration, and ranging, to meet the needs of various fields.

[0039] In one specific implementation, the dual parallel Mach-Zehnder modulator 23 can frequency shift the detection light within the frequency-shifting ring cavity 20a, with an initial frequency of... f 0 The continuous single-frequency light is modulated to form a pulse width τ. Part of the pulse is directly output after passing through the first fiber coupler 21 and connected to the output fiber 30, while the other part enters the frequency-shifting ring cavity 20a. After being modulated by the dual parallel Mach-Zehnder modulator 23, the frequency of the pulse light becomes... f 0 +Ω, after optical amplification by the first fiber coupler 21 to compensate for optical loss, part of the detection light is output through the output fiber 30, and the other part of the detection light re-enters the frequency shifting loop cavity 20a, where the frequency changes to... f 0 +2Ω. By repeating this cycle, frequency-shift detection light output can be continuously obtained.

[0040] The distributed optical fiber detection optical source system 100 based on pulse close-comb frequency modulation provided in this application embodiment, by setting a frequency-shifting ring cavity 20a, allows the detection light after passing through the dual parallel Mach-Zehnder modulators 23 to continuously cycle and modulate its frequency within the frequency-shifting ring cavity 20a, thereby achieving dense frequency-changing pulse width of the detection light within the pulse. Furthermore, the structure of the distributed optical fiber detection optical source system 100 based on pulse close-comb frequency modulation in this application is relatively simple, effectively reducing the speed of frequency-changing of the detection light within the frequency-shifting ring cavity 20a, thereby accelerating the output of the frequency-changed detection light, improving the detection efficiency when the detection light is used for detection, and shortening the detection time.

[0041] In some feasible implementations, the transmittance of the detection light through the first fiber coupler 21 can be T. That is, after passing through the first fiber coupler 21, the detection light of 1-T enters the frequency shifting loop cavity 20a for frequency shifting and amplification. The detection light of T is output through the output fiber 30.

[0042] In some feasible implementations, the increase in the frequency of the detection light is positively correlated with the number of cycles the detection light undergoes within the frequency-shifting cavity 20a. For example, the initial frequency of the detection light is... f 0 After one cycle within the frequency-shifting cavity 20a, the frequency increases to f 0 +Ω. It can be seen that the increase in frequency of the detection light after one cycle within the frequency shift loop is Ω. That is, as the number of cycles increases, the frequency increase also increases. For example, if the number of cycles is *a*, then the frequency increase of the detection light is *a* times Ω. Thus, the desired frequency can be achieved by controlling the number of cycles of the detection light within the frequency shift loop cavity 20a.

[0043] In some feasible implementations, the time it takes for the detection light to circulate once within the frequency-shifting cavity 20a is less than or equal to the pulse width of the detection light. This effectively avoids overlap of the detection light within the frequency-shifting cavity 20a, thereby ensuring the normal operation of the distributed fiber optic detection light source system 100 based on pulse close-comb frequency modulation.

[0044] In a specific implementation, see [link to relevant documentation]. Figure 1 As shown, the delay fiber assembly 22 may include an optical switch 221, a first delay fiber 222, and a second delay fiber 223; wherein the first delay fiber 222 and the second delay fiber 223 have different lengths.

[0045] The input end of the optical switch 221 is connected to the first optical fiber coupler 21; the output end of the optical switch 221 is connected to the first delay fiber 222 and the second delay fiber 223 respectively; the optical switch 221 is configured to conduct the first delay fiber 222 or the second delay fiber 223 to control the detection optical delay.

[0046] In other words, the optical path of the detection light can be selected by controlling the state of the optical switch 221. That is, the first delay fiber 222 or the second delay fiber 223 can be selected as the optical path of the detection light.

[0047] See also the following for some feasible implementation methods. Figure 1 The erbium-doped fiber assembly 24 includes an erbium-doped fiber 241 and an erbium-doped fiber amplifier 242; the distributed optical fiber detection light source system 100 based on pulsed close comb frequency modulation also includes a first wavelength division multiplexer 40.

[0048] The first wavelength division multiplexer 40 is used to receive the frequency-shifted detection light transmitted by the dual parallel Mach-Zehnder modulator 23, and input the detection light into the erbium-doped fiber 241 through the two input ends of the erbium-doped fiber 241 for interference.

[0049] Specifically, the two input ends of the erbium-doped fiber 241 are connected to the input ends of the first wavelength division multiplexer 40. Detection light of the same frequency interferes within the erbium-doped fiber 241 to form a refractive index grating, which is then output through the first wavelength division multiplexer 40.

[0050] The detection light enters the erbium-doped fiber 241 simultaneously in two separate paths. The detection light of the same frequency will form two waves that mix and interfere in the erbium-doped fiber 241, forming a refractive index grating with the same wavelength interval. The refractive index grating has a filtering effect on the light passing through, which can effectively reduce the spectral signal-to-noise ratio and spectral linewidth broadening of the detection light, and better obtain a pulse detection light with high signal-to-noise ratio and narrow linewidth, thereby ensuring the detection accuracy.

[0051] The intensity relationship of two-beam interference in optical interference phenomena is as follows:

[0052] ;

[0053] The instantaneous total light intensity of the two coherent beams superimposed at a certain point in space; The intensity of one of the beams of light; The intensity of another beam of light; The phase of one of the beams of light; This represents the phase of another beam of light.

[0054] Since the two beams have the same frequency and a constant phase difference, interference fringes, or refractive index gratings, are formed inside the erbium-doped fiber 241. The spacing of the refractive index gratings is the wavelength of the pulse detection light.

[0055] The erbium-doped fiber amplifier 242 is connected to the output of the first wavelength division multiplexer 40. During operation, the erbium-doped fiber amplifier 242 receives the detection light output from the first wavelength division multiplexer 40 and outputs the detection light to the first fiber coupler 21. Through the output of the first fiber coupler 21, a portion of the detection light re-enters the frequency-shifting cavity 20a, while the remaining portion is output for detection. The erbium-doped fiber amplifier 242 is used to compensate for the loss of the detection light by various optical devices within the frequency-shifting cavity 20a.

[0056] See also the following for some feasible implementation methods. Figure 1 The modulation device 20 also includes a second fiber coupler 25, a first polarization controller 26, and a second polarization controller 27.

[0057] The input end of the second fiber optic coupler 25 is connected to one end of the first delay fiber 222 and the second delay fiber 223 away from the optical switch 221. That is, the second fiber optic coupler 25 is connected to the output ends of the first delay fiber 222 and the second delay fiber 223.

[0058] A first polarization controller 26 is disposed between the second fiber coupler 25 and the dual parallel Mach-Zehnder modulator 23. The first polarization controller 26 is used to control the polarization-maintaining configuration of the detection light input to the dual parallel Mach-Zehnder modulator 23. In this way, it can be ensured that the detection light entering the dual parallel Mach-Zehnder modulator 23 is polarization-maintaining light.

[0059] The second polarization controller 27 is disposed between the erbium-doped fiber amplifier 242 and the first fiber coupler 21. The second polarization controller 27 is configured to control the polarization-maintaining mode of the detection light output by the dual parallel Mach-Zehnder modulator 23.

[0060] By setting the first polarization controller 26 and the second polarization controller 27, the detection light within the frequency-shifting ring cavity 20a can be effectively guaranteed to be in a polarized state. This avoids problems such as signal distortion and power fluctuations caused by polarization effects.

[0061] See also the following for some feasible implementation methods. Figure 1The light source assembly 10 may include a light source 11, a second wavelength division multiplexer 12, and an active phase-shifting fiber grating 13. The light source 11 is used to generate pump light of a first wavelength. The second wavelength division multiplexer 12 is connected between the light source 11 and the active phase-shifting fiber grating 13. The second wavelength division multiplexer 12 is used to transmit the pump light of the first wavelength to the active phase-shifting fiber grating 13 and output laser light of a second wavelength. The second wavelength is greater than the first wavelength. That is to say, the detection light mentioned in this application is laser light of the second wavelength.

[0062] Specifically, the light source 11 can use pump light of the first wavelength. After passing through the second wavelength division multiplexer 12, the pump light enters the active phase-shifting fiber grating 13 of the second wavelength. In the example, the first wavelength can be 980 nm and the second wavelength can be 1550 nm. The active phase-shifting fiber grating 13 can be a single-frequency fiber optic detector based on the active phase-shifting fiber grating 13. By combining the distributed feedback detection light polarization line with the slow axis-to-axis coupling technology of polarization-maintaining fiber, a narrow linewidth detection light polarization-maintaining laser output with a polarization extinction ratio greater than 30 dB is achieved. Its center wavelength is 1550.12 nm, the linewidth is less than 3 kHz, and the phase noise is less than 110 dB rad² / Hz after noise suppression.

[0063] In one specific implementation, the frequency interval of the light source 11 is determined by the frequency shift of the dual parallel Mach-Zehnder modulator 23, and the frequency shift range of the output detection light is determined by the number of cycles. The more cycles, the larger the frequency shift range. With each cycle, the spontaneous emission light is amplified. As the number of cycles increases, noise accumulation in the spontaneous emission light reduces the spectral signal-to-noise ratio and spectral linewidth broadening of the detection light, thereby shortening the system's detection distance. The dual parallel Mach-Zehnder modulator 23 in the frequency-shifting ring cavity 20a can determine important parameters such as the scanning detection light frequency shift speed, frequency shift range, pulse width, and instantaneous linewidth through control parameter optimization and noise suppression.

[0064] See also the following for some feasible implementation methods. Figure 1 The modulation device 20 may also include an isolator 28 and a filter 29.

[0065] Isolator 28 is disposed between the first fiber coupler 21 and the optical switch 221. The input end of isolator 28 is connected to the output end of the first fiber coupler 21, and the output end of isolator 28 is connected to the optical switch 221. Isolator 28 is used to isolate the return light, thereby ensuring the unidirectional output of the detection light within the frequency shifting cavity 20a.

[0066] Filter 29 is positioned between the dual parallel Mach-Zehnder modulator 23 and the first wavelength division multiplexer 40. Filter 29 is used to filter out amplifier spontaneous emission noise, thereby improving signal quality. The parameters of filter 29 can be selected to filter out the portion of the detection light with increasing frequency or the portion with decreasing frequency, allowing for the generation of pulses with different frequency intervals to meet various needs. For example, the detection light passing through the dual parallel Mach-Zehnder modulator 23 can generate two frequencies, including a frequency increase of [missing information - likely a specific frequency range]. f 0 The detection light and frequency of +Ω decreased to f 0 -Ω detection light, filter 29 can filter out f 0 -Ω part.

[0067] See also the following for some feasible implementation methods. Figure 1 The distributed optical fiber detection optical source system 100 based on pulsed close comb frequency modulation may further include: a third optical fiber coupler 50 and an electro-optic modulator 60.

[0068] The third fiber optic coupler 50 is positioned between the second wavelength division multiplexer 12 and the electro-optic modulator 60.

[0069] Specifically, the input of the third fiber coupler 50 is connected to the output of the second wavelength division multiplexer 12, and the output of the third fiber coupler 50 is connected to the input of the electro-optic modulator 60.

[0070] The electro-optic modulator 60 is connected to the input end of the first fiber optic coupler 21. The electro-optic modulator 60 is used to receive and modulate the on-time and repetition frequency of the detection light.

[0071] The distributed optical fiber detection light source system 100 based on pulsed close comb frequency modulation may further include: a first signal generator 70 and a second signal generator 80.

[0072] The first signal generator 70 is connected to the electro-optic modulator 60 and is used to control the electro-optic modulator 60. The first signal generator 70 can be used to control the on-time and repetition frequency of the modulation detection light by the electro-optic modulator 60.

[0073] The second signal generator 80 is connected to the dual parallel Mach-Zehnder modulator 23 and is used to control the dual parallel Mach-Zehnder modulator 23. The second signal generator 80 can be used to control the frequency shift of the detection light by the dual parallel Mach-Zehnder modulator 23.

[0074] Specifically, the first signal generator 70 can control the electro-optic modulator 60 to achieve frequency modulation of the detection light in different pulses, and obtain pulse detection light with equal interval step size or a certain proportional relationship of frequency increase or decrease; the dual parallel Mach-Zehnder modulator 23 can perform single-sideband frequency shift on the pulse detection light to obtain an output spectrum with equal interval frequency shift or a certain regularity.

[0075] In this application, the pulse width and detection distance It is positively correlated with the detection frequency band. f H It is inversely correlated with spatial resolution. A z They show an inverse correlation.

[0076] Among them, the detection range of the distributed fiber optic sensing system, under the condition that other parameters are constant, is... From the detection pulse width and light source linewidth The specific relationship is determined by the following formula.

[0077] ;

[0078] The attenuation coefficient; The Brillouin scattering power; The speed at which pulsed light travels through the medium; Rayleigh scattering coefficient; This is the scattering loss coefficient; Wave number; To reduce Planck's constant; The frequency of light; This refers to the coherent bandwidth.

[0079] Detection frequency band f H and detection distance L Inversely proportional to the detection pulse width They are inversely proportional, and the specific relationship is shown by the following formula.

[0080] ;

[0081] in, The pulse frequency; It is the speed of light in a vacuum; The refractive index of the optical fiber; This refers to the input optical power.

[0082] Spatial resolution refers to the minimum distance between two disturbance events that a system can effectively distinguish, and it is related to the positioning accuracy of the sensing system. When the distance is less than the spatial resolution, the two disturbance events cannot be distinguished. The system monitors the interference result of backscattered light within the pulse time. Theoretically, spatial resolution is mainly related to the pulse width of the probe pulse light. Relevant. Ideally, spatial resolution. Az The expression is:

[0083] .

[0084] In other words, spatial resolution Az From pulse width Decide.

[0085] Single-frequency pulse sources, continuous scanning sources, and intra-pulse continuous scanning sources in distributed system detection optical sources are single or continuous frequency sweep modulations within a pulse. They can achieve high spatial resolution measurements, but are difficult to achieve long-distance and high-frequency synchronous measurements. Multi-frequency pulse sources are single modulations of multiple frequency pulses at equal time intervals within a scanning period. They can achieve higher frequency band measurements, but are difficult to achieve high spatial resolution and high-frequency synchronous measurements. The above sources are single modulations within a pulse (single or continuous) and between pulse sequences (multi-frequency). They do not involve research on intra-pulse (equal-interval continuous multi-frequency) and inter-pulse joint modulation. Therefore, they cannot fundamentally solve the problem of the constraints between long detection distance, wide detection bandwidth, and high spatial resolution in traditional distributed fiber optic sensing technology.

[0086] The distributed optical fiber detection light source system 100 based on pulse dense comb frequency modulation provided in this application can simultaneously perform joint modulation of intra-pulse signals and inter-pulse signals. According to the relationship between detection distance, detection bandwidth and spatial resolution, the distributed detection light source that meets the requirements of long detection distance, wide detection bandwidth and high spatial resolution can be realized by sparse and dense modulation of pulse light.

[0087] Multi-frequency detection optical pulse sequence expression:

[0088] ;

[0089] in, It is a time-varying function, representing the laser electric field in t The instantaneous value, i Indicates the first i One pulse sequence period, T Indicates the period of the pulse sequence. M Indicates the number of pulse sequences. r Indicates the first r One light pulse, Indicates the negative exponential phase term. A rIndicates the first r Each light pulse amplitude value t Indicates the time of light emission detected. f 0 This represents the fundamental frequency of the multi-frequency detection optical pulse sequence. N This indicates the number of multi-frequency detection optical pulse sequences, and Ω represents the frequency increment step size of the multi-frequency detection optical pulse sequence. u r Indicates the first r The time of occurrence of each pulse W r Indicates the first r The pulse width of a light pulse.

[0090] To better understand the distributed optical fiber detection optical source system 100 based on pulsed dense comb frequency modulation provided in this application, the following will be combined with... Figure 1 A brief introduction to the work process.

[0091] After the pump light source 11 is turned on, it generates 980nm pump light, which is input to the active phase-shifting fiber grating 13 through the second wavelength division multiplexer 12 to generate 1550nm laser light. Then, it enters the electro-optic modulator 60 after passing through the third fiber coupler 50. The first signal generator 70 controls the electro-optic modulator 60, thereby adjusting the on-time and repetition frequency of the detection light. After the detection light is modulated, it enters the frequency-shifting cavity 20a through the first fiber coupler 21, and then passes sequentially through the isolator 28, optical switch 221, first delay fiber 222, second delay fiber 223, second fiber coupler 25, first polarization controller 26, dual parallel Mach-Zehnder modulator 23, filter 29, first wavelength division multiplexer 40, erbium-doped fiber 241, erbium-doped fiber amplifier 242, and finally flows back to the first fiber coupler 21 through the second polarization controller 27 to complete one cycle of the detection light in the frequency-shifting cavity 20a. After one cycle, the frequency of the detection light increases. Part of it can be directly output through the output fiber 30, while the other part of the detection light enters the frequency shifting cavity 20a again through the isolator 28 for a second cycle. By repeating this cycle, the required frequency of the detection light can be obtained.

[0092] Figure 2 This is a schematic diagram of a dual parallel Mach-Zehnder modulator provided in an embodiment of this application.

[0093] See Figure 2 As shown, the dual parallel Mach-Zehnder modulator 23 can be an IQ modulator, a key device for realizing single-sideband modulation modes. It primarily uses a Ti-diffused LiNbO3 (lithium niobate) waveguide to form the master Mach-Zehnder interferometer (MZI) structure, as shown below. Figure 2As shown, the input light is split into four paths, forming two sub-MZI structures. These two sub-MZIs serve as two arms, forming a main MZI structure. Each arm of the MZI1 and MZI2 structures has an LN modulator, designated as LN1, LN2, LN3, and LN4 respectively, and each is controlled by an external RF drive signal. The RF drive signal applied to MZI2 is phase-delayed by 90° with the RF drive signal on MZI1 through a 90° phase shifter. Each of the sub-arms of MZI1, MZI2, and the main MZI structure has a phase shifter, biased by a DC voltage. V 1 , V 2 and V 3 Control, can be achieved between the two arms respectively. Δφ 1 , Δφ 2 and Δφ 3 The phase difference is tuned. The interference relationship satisfies the following formula.

[0094] ;

[0095] Total light intensity; , The light intensity of two independently detected beams; This is the initial phase difference; Phase modulation depth; The modulation angular frequency; It is a time variable; This represents the DC component of the total light intensity. The amplitude of the interference term.

[0096] After expansion using Bessel functions, it becomes:

[0097] ;

[0098] It is a Bessel function of the first kind with order k, where k can be 0, 2n, or 2n+1 in the above formula.

[0099] The carrier angular frequency; For output signal; The amplitude factor is a constant. The carrier angular frequency; This is the initial phase.

[0100] To minimize the magnitude of the third-order component and increase the value of the first-order component, the modulation coefficient can be adjusted appropriately. m The size of makes J 1 (m) >> J 3 (m) At the same time, it also needs to meet the following requirements. A larger value is needed to achieve a better frequency shift effect. Modulation coefficient m It is related to the energy of the radio frequency signal loaded on the dual parallel Mach-Zehnder modulator 23.

[0101] The distributed optical fiber detection light source system 100 based on pulse dense-comb frequency modulation provided in this application simultaneously satisfies the relationship between detection distance, detection bandwidth, and spatial resolution and pulse width and pulse bandwidth. Modulation can be achieved using an electro-optic modulator 60 and a dual parallel Mach-Zehnder modulator 23, with the pulses capable of both intra-pulse and inter-pulse modulation. Intra-pulse frequency modulation can be performed using the dual parallel Mach-Zehnder modulator 23, while inter-pulse modulation can be achieved using a first signal generator 70 and the electro-optic modulator 60. By establishing a mechanism for equalizing parameters such as the number of intra-pulse dense frequency conversion pulse widths, inter-pulse sparse frequency conversions, pulse width, and equal interval time, long detection distance, high detection bandwidth, and high spatial resolution are achieved. This enables both intra-pulse dense frequency modulation and inter-pulse sparse frequency modulation, resulting in tunable pulse output detection light with multi-frequency variation patterns within and between pulses. Furthermore, the distributed optical fiber detection light source system 100 based on pulse dense-comb frequency modulation provided in this application has a relatively simple structure and can effectively shorten detection time and improve detection accuracy while meeting detection accuracy requirements.

[0102] It should be noted that, upon considering the specification and practicing the application disclosed herein, those skilled in the art will readily conceive of other embodiments of this application. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein.

[0103] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The true scope is indicated by this application.

Claims

1. A distributed optical fiber detection optical source system based on pulsed close-comb frequency modulation, characterized in that, include: The light source assembly is configured to generate detection light; A modulation device is connected to the light source assembly, and the modulation device forms a frequency-shifting ring cavity; The modulation device includes a first fiber coupler, a delay fiber assembly, a dual parallel Mach-Zehnder modulator, and an erbium-doped fiber assembly arranged sequentially; the modulation device is configured to modulate the frequency of the detection light within the frequency-shifting cavity; Wherein, the input end of the first fiber coupler is connected to the light source assembly and the erbium-doped fiber assembly respectively, and the output end of the first fiber coupler is connected to the delay fiber assembly; the delay fiber assembly is configured to delay the detection light; the dual parallel Mach-Zehnder modulator is configured to modulate the frequency of the detection light; the erbium-doped fiber assembly is configured to receive the detection light and compensate for the loss of the detection light; An output optical fiber is connected to the output end of the first optical fiber coupler, and the output optical fiber is configured to output the frequency-shifted detection light. The delay fiber assembly includes an optical switch, a first delay fiber, and a second delay fiber; the first delay fiber and the second delay fiber have different lengths; the input end of the optical switch is connected to the first fiber coupler; the output end of the optical switch is connected to both the first delay fiber and the second delay fiber; the optical switch is configured to turn on either the first delay fiber or the second delay fiber to control the delay of the detection light. The erbium-doped fiber assembly includes an erbium-doped fiber and an erbium-doped fiber amplifier; the distributed optical fiber detection light source system based on pulsed close-comb frequency modulation further includes a first wavelength division multiplexer; the two input ends of the erbium-doped fiber are connected to the input ends of the first wavelength division multiplexer, and the detection light of the same frequency interferes within the erbium-doped fiber to form a refractive index grating; the erbium-doped fiber amplifier is connected to the output end of the first wavelength division multiplexer, and the erbium-doped fiber amplifier is configured to compensate for the detection light loss; The modulation device further includes: a second fiber coupler, a first polarization controller, and a second polarization controller; the input end of the second fiber coupler is connected to the first delay fiber and the end of the second delay fiber away from the optical switch; the first polarization controller is disposed between the second fiber coupler and the dual parallel Mach-Zehnder modulator, and the first polarization controller is configured to control the polarization-maintaining mode of the detection light input to the dual parallel Mach-Zehnder modulator; the second polarization controller is disposed between the erbium-doped fiber amplifier and the first fiber coupler, and the second polarization controller is configured to control the polarization-maintaining mode of the detection light output from the dual parallel Mach-Zehnder modulator. The light source assembly includes a light source, a second wavelength division multiplexer, and an active phase-shifting fiber grating; the light source is configured to generate pump light of a first wavelength; the second wavelength division multiplexer is connected between the light source and the active phase-shifting fiber grating; the second wavelength division multiplexer is configured to transmit the pump light of the first wavelength to the active phase-shifting fiber grating and output laser light of a second wavelength; wherein the second wavelength is greater than the first wavelength; A third fiber optic coupler and an electro-optic modulator; the third fiber optic coupler is disposed between the second wavelength division multiplexer and the electro-optic modulator; the electro-optic modulator is connected to the input end of the first fiber optic coupler, and the electro-optic modulator is configured to modulate the detection light.

2. The distributed optical fiber detection optical source system based on pulsed close-comb frequency modulation according to claim 1, characterized in that, The increase in the frequency of the detection light is positively correlated with the number of times the detection light circulates within the frequency-shifting cavity, and the time it takes for the detection light to circulate once within the frequency-shifting cavity is less than or equal to the pulse width of the detection light.

3. The distributed optical fiber detection optical source system based on pulsed dense comb frequency modulation according to claim 1, characterized in that, The modulation device further includes: an isolator and a filter; The isolator is disposed between the first fiber coupler and the optical switch, and the isolator is configured to isolate the return light. The filter is positioned between the dual parallel Mach-Zehnder modulator and the first wavelength division multiplexer, and the filter is configured to filter noise.

4. The distributed optical fiber detection optical source system based on pulsed close-comb frequency modulation according to claim 1, characterized in that, It also includes: a first signal generator and a second signal generator; The first signal generator is connected to the electro-optic modulator, and the first signal generator is used to control the electro-optic modulator; The second signal generator is connected to the dual parallel Mach-Zehnder modulator, and the second signal generator is used to control the dual parallel Mach-Zehnder modulator.

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