Multi-channel LIBS (laser-induced breakdown spectroscopy) optical fiber optical path signal processing method

Abstract

The invention discloses a multichannel LIBS (Laser-induced Breakdown Spectroscopy) optical fiber optical path signal processing method, which belongs to the field of optical signal transmission and comprises the following steps of: modulating pulse amplitude; performing up-sampling; the optical signal intensity modulator converts the electric signal into an optical signal for transmission; signal attenuation caused by dispersion in the transmission process of the optical fiber is compensated through an optical equalizer; the variable optical attenuator realizes real-time control on optical signals by attenuating transmission optical power; the receiving end converts the optical signal transmitted in the optical fiber into a pulse signal; performing synchronization; performing down-sampling; the feed-forward equalizer compensates the distortion and attenuation of the pulse signal in the transmission process by introducing phase and amplitude adjustment, thereby improving the receiving sensitivity and reliability of the pulse signal. And pulse amplitude demodulation: converting the received pulse signal into an original digital data stream signal. According to the invention, signal attenuation caused by dispersion in the transmission process of the optical fiber can be compensated, and the signal collection efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the field of optical signal transmission, and in particular to a multi-channel LIBS optical fiber optical path signal processing method. Background Art

[0002] Fiber optic transmission is a technology that uses optical fiber as a transmission medium to achieve information transmission through modulation, transmission and demodulation of optical signals. The core principle of fiber optic transmission is total reflection. When light is emitted from a high refractive index medium (such as the fiber core) to a low refractive index medium (such as the fiber cladding), if the incident angle is greater than a certain critical angle, the light will not pass through the cladding into the air or a medium with a lower refractive index, but will be totally reflected at the interface between the core and the cladding, thereby continuously reflecting and moving forward along the fiber axis to achieve guided transmission of light.

[0003] The basic steps of fiber optic transmission are as follows: (1) Light source emission: The starting point of fiber optic transmission is the light source, which usually uses a light source such as a laser or a light emitting diode (LED) to generate a stable light signal. These light sources can generate monochromatic or polychromatic light signals, depending on the application requirements. (2) Optical signal modulation: The optical signal needs to carry the information to be transmitted, so the optical signal needs to be modulated. This is usually achieved by converting the electrical signal into an optical signal through an optical modulator, or directly by modulating the laser. The modulation process can be direct intensity modulation (that is, the intensity change of the signal corresponds to the brightness change of the light) or phase modulation, so that the optical signal carries information. (3) Fiber optic transmission: The modulated optical signal is transmitted through the optical fiber. Optical fiber is a thin and long fiber made of high-purity glass or plastic with extremely high light transmittance and low loss characteristics. The interior of the optical fiber is composed of a core, a cladding and a sheath. The refractive index of the core is higher than that of the cladding. The principle of total reflection is used to allow the optical signal to be transmitted inside the optical fiber without escaping. (4) Optical signal demodulation: When the optical signal reaches the destination, it needs to be demodulated into the original electrical signal. This usually uses a photodetector (such as a PIN photodiode or APD avalanche photodiode) to convert the optical signal into an electrical signal, which is then demodulated and processed to recover the original information. (5) Signal processing: The demodulated electrical signal can be used in various applications, such as telephone communication, Internet transmission, data transmission, etc.

[0004] The prior art has the following problems: the signal attenuation caused by dispersion during the transmission of the optical fiber makes the signal collection efficiency low. Therefore, those skilled in the art provide a multi-channel LIBS optical fiber optical path signal processing method to solve the problems raised in the above background technology. Summary of the invention

[0005] The purpose of the present invention is to provide a multi-channel LIBS optical fiber optical path signal processing method, which can compensate for the signal attenuation caused by dispersion during the transmission of the optical fiber and improve the signal collection efficiency to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A multi-channel LIBS optical fiber optical path signal processing method comprises the following steps:

[0008] Pulse amplitude modulation, which converts the binary values ​​of a digital data stream into pulse signals with different amplitudes for transmission;

[0009] Upsampling is to increase the sampling rate of the signal and increase the number of samples;

[0010] Optical signal intensity modulation, that is, the light intensity changes with the change of electrical signal, thereby converting the electrical signal into an optical signal for transmission;

[0011] An optical equalizer is used to compensate for the signal attenuation caused by dispersion during optical fiber transmission, thereby improving signal collection efficiency.

[0012] The variable optical attenuator achieves real-time control of the optical signal by attenuating the transmission optical power;

[0013] The receiving end converts the optical signal transmitted in the optical fiber into a pulse signal and performs amplification and filtering.

[0014] Synchronization, that is, ensuring that the sending and receiving ends are consistent in time or frequency through a synchronization mechanism;

[0015] Downsampling is to reduce the sampling rate of the pulse signal and reduce the number of samples;

[0016] The feedforward equalizer compensates for the distortion and attenuation of the pulse signal during transmission by introducing phase and amplitude adjustments, thereby improving the receiving sensitivity and reliability of the pulse signal.

[0017] Pulse amplitude demodulation is to convert the received pulse signal into the original digital data stream signal.

[0018] As a further solution of the present invention: in the optical signal intensity modulation process, the optical intensity modulation signal is specifically:

[0019]

[0020] Where ω is the angular frequency of the modulation signal, ω c is the optical carrier frequency, and A is the direct current (DC) bias.

[0021] As a further solution of the present invention: the specific process of the optical equalizer compensating the attenuation of the optical fiber signal is:

[0022] The equalizer received signal is passed through a first dispersion compensation delay line to generate a first split signal, and a phase shifter is passed through to generate a second split signal;

[0023] Inputting the first split signal and the second split signal into a Jones matrix coupler for coupling to generate a third split signal, and at the same time, passing the coupled signals through a second dispersion compensation delay line to generate a fourth split signal;

[0024] Inputting the third split signal and the fourth split signal into a polarization beam combiner for polarization light coupling;

[0025] The polarized light coupled signal is input into a photodetector, and the optical signal is converted into a photocurrent signal by the photodetector;

[0026] The photocurrent signal is transmitted to the DSP chip for digital signal processing.

[0027] As a further solution of the present invention: the equalizer receives the signal specifically as follows:

[0028]

[0029] θ=ω 2 αL / 2, α=-Dλ 2 / 2πc

[0030] Where D is the fiber dispersion coefficient, L is the fiber length, and λ is the center wavelength, which refers to the center position of the wavelength distribution within a spectrum.

[0031] As a further solution of the present invention: the first segmentation signal is specifically:

[0032]

[0033] Among them, τ 1 represents the delay time of the first dispersion delay compensation line. The dispersion delay compensation line is used to introduce a specific time delay in the optical signal transmission process to compensate for the power attenuation and signal distortion caused by dispersion. By adjusting τ 1 The value can optimize the system performance, reduce signal distortion and improve transmission quality.

[0034] As a further solution of the present invention: the second segmentation signal is specifically:

[0035]

[0036] in, Indicates the phase shift amount of the phase shifter. The phase shifter is used to introduce a specific phase change during the optical signal transmission process to compensate for the power attenuation and other signal distortion caused by dispersion. The value can optimize the system performance, reduce signal distortion and improve transmission quality.

[0037] As a further solution of the present invention: the third segmentation signal and the fourth segmentation signal are specifically:

[0038]

[0039] Among them, τ 2 Represents the delay time of the second dispersion delay compensation line. The coupler introduces a relative phase shift of 90 degrees (π / 2), which helps to adjust the phase relationship of the signal to cooperate with the dispersion compensation delay line and the phase shifter to achieve more effective dispersion compensation.

[0040] As a further solution of the present invention: the photocurrent signal is specifically:

[0041]

[0042] As a further solution of the present invention: the process of the optical equalizer compensating for the attenuation of the optical fiber signal also includes signal processing of the photocurrent signal, specifically, for the photocurrent signal, an equalizer based on a convolutional neural network is used, and a 1D convolutional neural network is used on a field programmable gate array FPGA to achieve signal equalization.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] 1. The present application sets up an optical equalizer to compensate for the signal attenuation caused by dispersion during the transmission of the optical fiber and improve the signal collection efficiency.

[0045] 2. For photocurrent signals, this application is based on a convolutional neural network equalizer, and uses a 1D convolutional neural network on a field programmable gate array FPGA to achieve signal equalization, while meeting high throughput and achieving flexibility and low bit error rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a flow chart of a multi-channel LIBS optical fiber optical path signal processing method;

[0047] Figure 2 A flowchart of an optical equalizer compensating for fiber signal attenuation in a multi-channel LIBS fiber optical path signal processing method;

[0048] Figure 3 It is a flow chart of signal processing of photocurrent signal in a multi-channel LIBS optical fiber optical path signal processing method;

[0049] Figure 4 It is a structural diagram of a LIBS signal homogenization and collection device in a multi-channel LIBS optical fiber optical path signal processing method;

[0050] Figure 5 A structural diagram of a LIBS signal collection optical fiber in a multi-channel LIBS optical fiber optical path signal processing method;

[0051] Figure 6 Schematic diagram of the LIBS principle in a multi-channel LIBS fiber optic signal processing method.

[0052] Among them: 1. Optical path fixing and debugging module; 2. Laser focusing optical path module; 3. LIBS signal collection module; 4. LIBS signal collection optical fiber. DETAILED DESCRIPTION

[0053] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0054] As mentioned in the background technology of the present application, it has been found through research that the optical fiber in the existing optical fiber transmission method has certain defects due to signal attenuation caused by dispersion during the transmission process, resulting in low signal collection efficiency.

[0055] In order to solve the above-mentioned defects, the present application discloses a multi-channel LIBS optical fiber optical path signal processing method, which can compensate for the signal attenuation caused by dispersion during the transmission of the optical fiber and improve the signal collection efficiency.

[0056] The following will describe in detail how the solution of the present application solves the above technical problems in conjunction with the accompanying drawings.

[0057] See also Figure 1In an embodiment of the present invention, a multi-channel LIBS optical fiber optical path signal processing method includes the following steps: pulse amplitude modulation, that is, converting the binary value of a digital data stream into a pulse signal with different amplitudes for transmission; upsampling, that is, increasing the sampling rate of the signal and increasing the number of samples; optical signal intensity modulation, that is, the light intensity changes with the change of the electrical signal, thereby converting the electrical signal into an optical signal for transmission; using an optical equalizer to compensate for the signal attenuation caused by dispersion during the transmission of the optical fiber, thereby improving the signal collection efficiency; a variable optical attenuator realizes real-time control of the optical signal by attenuating the transmission optical power; the receiving end converts the optical signal transmitted in the optical fiber into a pulse signal, and amplifies and filters it; synchronization, that is, ensuring that the transmitting end and the receiving end are consistent in time or frequency through a synchronization mechanism; downsampling, that is, reducing the sampling rate of the pulse signal and reducing the number of samples; a feedforward equalizer compensates for the distortion and attenuation of the pulse signal during the transmission process by introducing phase and amplitude adjustment, thereby improving the receiving sensitivity and reliability of the pulse signal; pulse amplitude demodulation, that is, converting the received pulse signal into the original digital data stream signal. The present application compensates for the signal attenuation caused by dispersion during the transmission of the optical fiber by setting up an optical equalizer, thereby improving the signal collection efficiency.

[0058] In this embodiment, during the optical signal intensity modulation process, the optical intensity modulation signal is specifically:

[0059]

[0060] Where ω is the angular frequency of the modulation signal, ω c is the optical carrier frequency, and A is the direct current (DC) bias.

[0061] In this embodiment, if Figure 2As shown, the specific process of the optical equalizer compensating the attenuation of the optical fiber signal is as follows: the equalizer received signal is passed through the first dispersion compensation delay line to generate the first split signal, and the second split signal is generated through the phase shifter; the first split signal and the second split signal are input into the Jones matrix coupler for coupling to generate the third split signal, and at the same time, the coupled signal is passed through the second dispersion compensation delay line to generate the fourth split signal; the third split signal and the fourth split signal are input into the polarization beam combiner for polarization light coupling; the signal after polarization light coupling is input into the photodetector, and the optical signal is converted into a photocurrent signal through the photodetector; the photocurrent signal is transmitted to the DSP (Digital Signal Processor) chip for digital signal processing. Among them, the phase shifter is a control device that can adjust the phase of the wave, and its definition is mainly based on its frequency response characteristics over the operating frequency bandwidth and the change characteristics of the wavefront plane. Specifically, the phase shifter has a flat group delay frequency response over the operating frequency bandwidth, and the wavefront plane does not change with the change of the inserted phase. This characteristic enables the phase shifter to maintain the phase stability of the signal in a variety of applications, thereby meeting specific signal processing requirements. Jones matrix coupler combines the characteristics of fiber coupler with the descriptive ability of Jones matrix. Specifically, it refers to the use of Jones matrix to describe the transmission and coupling process of optical signals in coupler in the design and analysis of fiber coupler, which includes the change of polarization state of optical signal, light intensity distribution and possible phase difference. The working principle of polarization beam combiner is based on the polarization characteristics of light and the polarization selection characteristics of optical film. Specifically, it realizes the separation and combination of light beams by coating optical film on the bonding surface so that the light beam with specific polarization state can be totally reflected or totally transmitted. In the beam combining process, two beams with perpendicular polarization directions are superimposed to form a beam with higher power laser output. Photodetector converts the received optical radiation signal into electrical signal (current or voltage) through specific materials or mechanisms, thereby realizing the detection, measurement and control of optical signal. This conversion process not only enables photodetector to detect optical signals instead of human eyes, but also becomes the extension of human eyes in the field of light detection due to its wide spectral response range.

[0062] In this embodiment, the equalizer receives the signal specifically as follows:

[0063]

[0064] θ=ω 2 αL / 2, α=-Dλ 2 / 2πc

[0065] Where D is the fiber dispersion coefficient, L is the fiber length, and λ is the center wavelength, which refers to the center position of the wavelength distribution within a spectrum.

[0066] In this embodiment, the first segmentation signal is specifically:

[0067]

[0068] Among them, τ 1 represents the delay time of the first dispersion delay compensation line. The dispersion delay compensation line is used to introduce a specific time delay in the optical signal transmission process to compensate for the power attenuation and signal distortion caused by dispersion. By adjusting τ 1 The value can optimize the system performance, reduce signal distortion and improve transmission quality.

[0069] In this embodiment, the second segmentation signal is specifically:

[0070]

[0071] in, Indicates the phase shift amount of the phase shifter. The phase shifter is used to introduce a specific phase change during the optical signal transmission process to compensate for the power attenuation and other signal distortion caused by dispersion. The value can optimize the system performance, reduce signal distortion and improve transmission quality.

[0072] In this embodiment, the third segmentation signal and the fourth segmentation signal are specifically:

[0073]

[0074] Among them, τ 2 Represents the delay time of the second dispersion delay compensation line. The coupler introduces a relative phase shift of 90 degrees (π / 2), which helps to adjust the phase relationship of the signal to cooperate with the dispersion compensation delay line and the phase shifter to achieve more effective dispersion compensation.

[0075] In this embodiment, the photocurrent signal is specifically:

[0076]

[0077] In this embodiment, the process of compensating the optical fiber signal attenuation by the optical equalizer also includes signal processing of the photocurrent signal, such as Figure 3As shown, specifically, for the photocurrent signal, a convolutional neural network-based equalizer is used, and a 1D convolutional neural network is used on a field programmable gate array (FPGA) to achieve signal equalization. More specifically, each second shunt module receives an input stream and divides it into two equal-length streams (i.e., the third shunt module). Multiple such modules are arranged in a hierarchical manner to feed data to each convolution module instance in a cyclic manner. Due to the interdependence between consecutive symbols, splitting the input stream will increase the bit error rate in the boundary area of ​​each sequence. Therefore, the overlap generation module adds overlap to each subsequence. In this way, the bit error rate remains roughly the same for the entire process. Afterwards, the first confluence module combines the divided sequences into an output stream. The overlap is then discarded by the confluence deduplication module. The second shunt module and the second confluence module are arranged in a hierarchical manner, rather than implementing only one module that operates on several streams. This improves the routability and timing of the design. Using only one module greatly increases the path length from the second shunt module and the second confluence module to each processing unit. Combined with high congestion areas, this will result in a huge net delay, limiting the achievable clock frequency. By introducing a plurality of second flow-dividing modules and second flow-merging modules, the critical path is shortened, thereby increasing the achievable clock frequency and thus improving the obtainable throughput.

[0078] In this embodiment, the present application uses a LIBS signal homogenization collection device to collect optical path signals, wherein, Figure 4 As shown, the LIBS signal homogenization and collection device includes an optical path fixing and debugging module 1, a laser focusing optical path module 2 is fixedly connected to the center of the top surface of the optical path fixing and debugging module 1, and four evenly distributed LIBS signal collection modules 3 are fixedly connected to the outside of the laser focusing optical path module 2, and each multi-channel LIBS signal collection module 3 is embedded with a LIBS signal collection optical fiber 4. Figure 5 This is a structural diagram of the LIBS signal collection optical fiber 4. The detection end is connected to the LIBS signal collection module 3, and the collection end is connected to the multi-channel optical fiber spectrometer. There are 4 detection ends on the left side of the optical fiber diagram, each with 4 fiber cores and arranged in a central symmetrical manner (such as Figure 5 There are 4 optical fibers on the right side of the optical fiber drawing, each with 4 cores arranged linearly (as shown in Figure 5As shown); the four optical fibers at the right collection end are connected to the multi-channel optical fiber spectrometer in turn; the four optical fibers at the left detection end are connected to the lens of the LIBS signal collection module 3 in turn; the signal collected by any lens of the four LIBS signal collection modules 3 is coupled to each optical fiber at the detection end, and the signal is evenly distributed to the collection end on the right by the 4 cores of each optical fiber, and the other three lenses and each optical fiber at the corresponding detection end are the same, so that each optical fiber at the detection end can collect signals from four lenses to achieve the purpose of signal homogenization collection, and the problem of uneven multi-channel signals (some channels have saturated signals and some channels have weak signals) caused by the traditional LIBS acquisition module (each lens uses a single optical fiber to connect to the spectrometer) when encountering samples with uneven material surfaces will not occur. The working principle of the LIBS signal homogenization collection device is specifically as follows: the laser enters the laser focusing optical path from the laser light inlet of the laser focusing optical path module 2, and then focuses on the target and bombards the sample surface. When the laser exceeds the breakdown threshold of the sample, a small amount of material will be ablated and excited to generate plasma. When the laser pulse ends, the plasma quickly diffuses and cools. During this period, the atoms and ions in the excited state migrate from the high energy state back to the low energy state, and radiate characteristic light radiation (LIBS signal) with a specific wavelength. The LIBS signal is then collected by the LIBS signal collection module 3, and the peak position (qualitative) and peak intensity (quantitative) in the plasma emission spectrum (LIBS signal spectrum) are analyzed by a high-resolution spectrometer to identify the type and corresponding content of the elements in the sample, thereby achieving the purpose of material detection. The LIBS principle is as follows: Figure 6 shown.

[0079] The present invention compensates for the signal attenuation caused by dispersion during the transmission of optical fiber by setting up an optical equalizer, thereby improving the signal collection efficiency. For photocurrent signals, the present application is based on a convolutional neural network equalizer, and uses a 1D convolutional neural network on a field programmable gate array (FPGA) to achieve signal equalization, while meeting high throughput and achieving flexibility and low bit error rate.

[0080] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

[0081] What is described above is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A multi-channel LIBS optical fiber optical path signal processing method, characterized in that: The following steps are involved: Pulse amplitude modulation, which converts the binary values ​​of a digital data stream into pulse signals with different amplitudes for transmission; Upsampling is to increase the sampling rate of the signal and increase the number of samples; Optical signal intensity modulation, that is, the light intensity changes with the change of electrical signal, thereby converting the electrical signal into an optical signal for transmission; An optical equalizer is used to compensate for the signal attenuation caused by dispersion during optical fiber transmission, thereby improving signal collection efficiency. The variable optical attenuator achieves real-time control of the optical signal by attenuating the transmission optical power; The receiving end converts the optical signal transmitted in the optical fiber into a pulse signal and performs amplification and filtering. Synchronization, that is, ensuring that the sending and receiving ends are consistent in time or frequency through a synchronization mechanism; Downsampling is to reduce the sampling rate of the pulse signal and reduce the number of samples; The feedforward equalizer compensates for the distortion and attenuation of the pulse signal during transmission by introducing phase and amplitude adjustments, thereby improving the receiving sensitivity and reliability of the pulse signal. Pulse amplitude demodulation is to convert the received pulse signal into the original digital data stream signal.

2. A multi-channel LIBS optical fiber optical path signal processing method according to claim 1, characterized in that: In the optical signal intensity modulation process, the optical intensity modulation signal is specifically: Where ω is the angular frequency of the modulation signal, ω c is the optical carrier frequency and A is the DC bias.

3. A multi-channel LIBS optical fiber optical path signal processing method according to claim 2, characterized in that: The specific process of the optical equalizer compensating the optical fiber signal attenuation is as follows: The equalizer received signal is passed through a first dispersion compensation delay line to generate a first split signal, and a phase shifter is passed through to generate a second split signal; Inputting the first split signal and the second split signal into a Jones matrix coupler for coupling to generate a third split signal, and at the same time, passing the coupled signals through a second dispersion compensation delay line to generate a fourth split signal; Inputting the third split signal and the fourth split signal into a polarization beam combiner for polarization light coupling; The polarized light coupled signal is input into a photodetector, and the optical signal is converted into a photocurrent signal by the photodetector; The photocurrent signal is transmitted to the DSP chip for digital signal processing.

4. A multi-channel LIBS optical fiber optical path signal processing method according to claim 3, characterized in that: The equalizer receives the signal specifically as follows: Where D is the fiber dispersion coefficient, L is the fiber length, and λ is the center wavelength, which refers to the center position of the wavelength distribution within a spectrum.

5. A multi-channel LIBS optical fiber optical path signal processing method according to claim 4, characterized in that: The first segmentation signal is specifically: Wherein, τ1 represents the delay time of the first dispersion delay compensation line.

6. A multi-channel LIBS optical fiber optical path signal processing method according to claim 5, characterized in that: The second segmentation signal is specifically: in, Indicates the phase shift amount of the phase shifter.

7. A multi-channel LIBS optical fiber optical path signal processing method according to claim 6, characterized in that: The third segmentation signal and the fourth segmentation signal are specifically: Wherein, τ2 represents the delay time of the second dispersion delay compensation line.

8. A multi-channel LIBS optical fiber optical path signal processing method according to claim 7, characterized in that: The photocurrent signal is specifically:

9. A multi-channel LIBS optical fiber optical path signal processing method according to claim 8, characterized in that: The optical equalizer also includes signal processing of the photocurrent signal during the process of compensating for the optical fiber signal attenuation. Specifically, for the photocurrent signal, an equalizer based on a convolutional neural network is used, and a 1D convolutional neural network is used on a field programmable gate array to achieve signal equalization.

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