A gas pressure measuring device and method based on TS-DFT technology

Abstract

The application discloses a gas pressure measuring device and method based on TS-DFT technology, and belongs to the field of gas pressure measurement. The gas pressure measuring device comprises a femtosecond laser seed source, a spectrum selection module, a pulse picker, a time-domain broadening amplification module and a gas pressure measuring module. The output light of the femtosecond laser seed source passes through a fiber grating and a filter, selects the spectrum required for measuring different target gases, and then selects a single pulse through the pulse picker, and transmits the single pulse into the time-domain broadening amplification module, so that a relatively flat pulse envelope can be obtained through multi-stage amplification. The broadened pulse is divided into reference light and measuring light, the reference light is adjusted by a fiber delay line to adjust the relative delay, the measuring light passes through a gas cell containing a target gas, is coupled into the time-domain broadening amplification module through a coupler, the generated signal is received by a photoelectric detector, and is transmitted to a data acquisition and processing module. The application has the advantages of fast sampling, high spectral resolution, large dynamic range and the like.

Description

TECHNICAL FIELD

[0001] The application relates to a gas pressure measuring device and method, in particular to a gas pressure measuring device and method based on a TS-DFT technology. BACKGROUND

[0002] The measurement of engine gas pressure helps to diagnose the sealing performance of a cylinder and a piston ring. Traditional pressure measurement is mainly realized through a pressure sensor, but the method belongs to contact type measurement, has great limitations and a short service life. With the rapid development of absorption spectrum technology, the absorption spectrum technology is widely applied to the research of pressure measurement. A commonly used absorption spectrum technology pressure measurement method is mainly based on TDLAS (tunable diode laser absorption spectrum technology), but the wavelength scanning range is limited, and when multiple absorption peaks need to be measured, multiple lasers need to be used, resulting in a complex system. Meanwhile, the traditional measurement method can only complete one measurement for dynamic changes occurring in a microsecond time scale, and cannot meet the pressure measurement in the combustion process. SUMMARY

[0003] In order to solve the problems existing in the prior art, the purpose of the application is to provide a gas pressure measuring device and method based on a TS-DFT technology. The femtosecond laser has advantages of a wide spectral range and a high repetition frequency, and through the combination of the femtosecond laser and the time domain expansion method, high-speed and high-resolution measurement of the pressure generated by a gas mixture in a combustion process can be realized.

[0004] The purpose of the application is realized through the following technical solutions:

[0005] The application discloses a gas pressure measuring device based on a TS-DFT technology, which comprises a femtosecond laser seed source, a spectrum selection module, a pulse picker, a time domain expansion and amplification module and a gas pressure measurement module.

[0006] The femtosecond laser seed source comprises a first pump source, a first wavelength division multiplexer, a first doped optical fiber, a first optical fiber isolator, a polarizer, a first optical fiber polarization controller and a first optical fiber coupler.

[0007] The spectrum selection module comprises an optical fiber grating and an optical fiber filter.

[0008] The time domain expansion and amplification module comprises a first time domain expansion and amplification module and a second time domain expansion and amplification module. The first time domain expansion and amplification module comprises a first high dispersion compensation optical fiber, a second optical fiber isolator, a second pump source, a second wavelength division multiplexer and a second doped optical fiber. The second time domain expansion and amplification module comprises a third high dispersion compensation optical fiber, a third optical fiber isolator, a third pump source, a third wavelength division multiplexer and a third doped optical fiber.

[0009] The gas pressure measuring module comprises a second fiber coupler, a second high dispersion compensation fiber, a fiber delay line, a second fiber polarization controller, a first fiber collimator, a gas cell, a second fiber collimator, a third fiber coupler, a second time domain expansion amplification module, a photoelectric detector, and a digital acquisition and processing module.

[0010] The first pump source is coupled into the first doped fiber through a first wavelength division multiplexer; the first fiber isolator ensures the single operation of the laser in the oscillation cavity; the polarizer and the first fiber polarization controller form an equivalent saturated absorber; the first fiber coupler retains most of the energy in the oscillation cavity for oscillation, and the remaining energy is output outside the cavity, and the diffraction spectrum is obtained through the fiber grating, and then the spectrum for measuring the target gas is selected through the fiber filter; the spectrum is selected into a single pulse through the pulse picker, and then the pulse is input into the first high dispersion compensation fiber for time domain expansion; the expanded pulse is amplified through the second doped fiber coupled by the second wavelength division multiplexer; the amplified pulse is divided into two paths through the second fiber coupler, the first path is used as reference light to input into the second high dispersion compensation fiber to obtain time domain expansion, and then the relative delay is adjusted through the fiber delay line, and the polarization state of the reference light is adjusted through the second fiber polarization controller; the second path is used as measurement light to input into the gas cell through the first fiber collimator, and then the light is coupled into the fiber through the second fiber collimator, and interference is generated with the reference light at the third fiber coupler; the interference signal is time domain expanded through the third high dispersion compensation fiber, and then the expanded pulse is amplified through the third doped fiber coupled by the third wavelength division multiplexer; the interference signal after time domain expansion and amplification is received by the photoelectric detector, and then the signal is transmitted into the data acquisition and processing module.

[0011] Preferably, the doped fiber is an erbium-doped gain fiber, a ytterbium-doped gain fiber, or a thulium-doped gain fiber, wherein the first doped fiber, the second doped fiber, and the third doped fiber are gain fibers with the same doping type.

[0012] Preferably, the entire optical path of the femtosecond laser oscillator is subjected to temperature control treatment to eliminate the influence of environmental temperature change on the repetition frequency.

[0013] The measuring method of the gas pressure measuring device based on the TS-DFT technology disclosed in the application is as follows: the time-domain interference signal without gas absorption and the time-domain interference signal with gas absorption are obtained by using a gas pressure measuring module in the gas pressure measuring device, the time-domain interference signal without gas absorption is taken as a reference signal, and the time-domain interference signal with gas absorption is taken as a measuring signal. Fourier transform is performed on the interference signal and the measuring signal respectively to obtain a radio frequency spectrum, and the radio frequency spectrum is normalized. A suitable absorption spectral line is selected for linear fitting, and background subtraction and frame averaging are used to find a matching theoretical spectrum, so that the measurement of the gas pressure is realized.

[0014] According to the Lambert-Beer law, when a light beam with an intensity I i is incident on a gas with a length L, the relationship between the light intensity I o after absorption and the incident light intensity I i is as follows:

[0015]

[0016] In the formula, P is the total pressure of the gas, S(T) is the linear intensity of the absorption spectral line, is the linear function of the normalized absorption spectral line, and a f is the absorption rate of the measured gas at the wavelength f, and X is the concentration of the absorption gas.

[0017]

[0018] S(T) is a function of temperature, and the characteristics of the change with temperature depend on the transition state energy level E'', T r is a reference temperature, Q(T) is a partition function, h is the Planck constant, c is the speed of light, k is the Boltzmann constant, and v0 is the wave number at the center of the absorption peak. By integrating a f in the frequency domain, the spectral characteristics of the absorption spectral line can be extracted, and the absorbance A is as follows:

[0019]

[0020] The pressure is as follows:

[0021]

[0022] Advantages:

[0023] 1. The gas pressure measuring device and method based on the TS-DFT technology disclosed in the application, the femtosecond laser seed source is treated by overall temperature control, which can avoid the drift of the repetition frequency caused by the change of the environmental temperature, and is different from the traditional phase-locked circuit mode. The application does not need a frequency locking device, and simplifies the composition of the gas pressure measuring device.

[0024] 2. The gas pressure measuring device and method based on the TS-DFT technology can realize high-speed and high-resolution measurement of the pressure generated by a gas mixture in a combustion process by combining a femtosecond laser with a time-domain broadening method.

[0025] 3. The gas pressure measuring device and method based on the TS-DFT technology can realize coherent detection of a single detection pulse and a reference pulse by selecting a single pulse from a spectrum through the pulse picker, passing through the time-domain broadening amplification module and the gas pressure measuring module, and the detection result in a single cycle can contain complete gas absorption characteristics, and the measurement speed is fast.

[0026] 4. The gas pressure measuring device and method based on the TS-DFT technology can obtain a relatively flat pulse envelope by using multi-stage amplification, and can improve the sampling rate and the spectral resolution by using a multiple time-domain broadening method. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a structural schematic diagram of the gas pressure measuring device based on the TS-DFT technology.

[0028] 1- first pump source, 2- first wavelength division multiplexer, 3- first doped optical fiber, 4- first optical fiber isolator, 5- polarizer, 6- first optical fiber polarization controller, 7- first optical fiber coupler, 8- fiber grating, 9- fiber filter, 10- pulse picker, 11- first high dispersion compensation optical fiber, 12- second optical fiber isolator, 13- second wavelength division multiplexer, 14- second pump source, 15- second doped optical fiber, 16- second optical fiber coupler, 17- second high dispersion compensation optical fiber, 18- optical fiber delay line, 19- second optical fiber polarization controller, 20- third optical fiber coupler, 21- first optical fiber collimator, 22- gas cell, 23- second optical fiber collimator, 24- third high dispersion compensation optical fiber, 25- third optical fiber isolator, 26- second wavelength division multiplexer, 27- third pump source, 28- third doped optical fiber, 29- photodetector, 30- digital acquisition and processing module. DETAILED DESCRIPTION

[0029] In order to better illustrate the purpose and advantages of the present application, the content of the application will be further described below in combination with the drawings and examples.

[0030] Example 1:

[0031] As Figure 1As shown, the gas pressure measuring device based on the TS-DFT technology disclosed in the embodiment comprises a femtosecond laser seed source, a spectrum selection module, a pulse picker, a time-domain expansion and amplification module, and a gas pressure measuring module.

[0032] The femtosecond laser seed source comprises a first pump source, a first wavelength division multiplexer, a first doped optical fiber, a first optical fiber isolator, a polarizer, a first optical fiber polarization controller, and a first optical fiber coupler.

[0033] The spectrum selection module comprises a fiber grating and a fiber filter.

[0034] The time-domain expansion and amplification module comprises a first time-domain expansion and amplification module and a second time-domain expansion and amplification module.

[0035] The gas pressure measuring module comprises a second optical fiber coupler, a second high-dispersion compensation optical fiber, a fiber delay line, a second optical fiber polarization controller, a first optical fiber collimator, a gas cell, a second optical fiber collimator, a third optical fiber coupler, a second time-domain expansion and amplification module, a photodetector, and a digital acquisition and processing module.

[0036] The doped optical fiber is an erbium-doped gain optical fiber.

[0037] The entire optical path of the femtosecond laser oscillator is subjected to temperature control treatment to eliminate the influence of environmental temperature changes on the repetition frequency.

[0038] The center wavelength of the femtosecond laser oscillator is 1550 nm, the spectral coverage range is 1500 nm-1650 nm, and the pulse width is 100 fs.

[0039] The center wavelength of the spectrum after the spectrum selection module is 1550 nm.

[0040] The pulse picker extracts single pulses at a rate of 2 MHz.

[0041] The second-order dispersion of the high-dispersion compensation optical fiber near 1550 nm is 252 ps 2 / km, and the third-order dispersion is -1.44 ps 3 / km

[0042] The bandwidth of the photodetector is 10 GHz.

[0043] The measuring method of the gas pressure measuring device based on the TS-DFT technology comprises the following steps: a first pump source is coupled into a first doped optical fiber through a first wavelength division multiplexer; a first optical fiber isolator ensures the single operation of laser in an oscillation cavity; a polarizer and a first optical fiber polarization controller are combined to form an equivalent saturated absorber; a first optical fiber coupler retains most of the energy in the oscillation cavity for oscillation, and the remaining energy is output outside the cavity, and then diffraction spectrum is obtained through a fiber grating, and then a spectrum for measuring a target gas is selected through a fiber filter; a single pulse is selected through a pulse picker, and then the single pulse is input into a first high dispersion compensation optical fiber for time domain expansion; the expanded pulse and a second pump source are coupled into a second doped optical fiber through a second wavelength division multiplexer for amplification; the amplified pulse is divided into two paths through a second optical fiber coupler, the first path is used as reference light to input into a second high dispersion compensation optical fiber for time domain expansion, and then the reference light is adjusted in relative delay through a fiber delay line and in polarization state through a second optical fiber polarization controller; the second path is used as measurement light to input into a gas cell through a first optical fiber collimator, the gas cell is filled with a mixture of 29% acetylene and 71% oxygen, and an igniter is installed; then the measurement light is coupled into an optical fiber through a second optical fiber collimator, and interference with the reference light occurs at a third optical fiber coupler; the interference signal is input into a third high dispersion compensation optical fiber for time domain expansion, and then the expanded pulse and a third pump source are coupled into a third doped optical fiber through a third wavelength division multiplexer for amplification; the interference signal after time domain expansion and amplification is received by a photoelectric detector, and then the interference signal is transmitted into a data acquisition and processing module to obtain a time domain interference signal without gas absorption and a time domain interference signal with gas absorption; the time domain interference signal without gas absorption is used as a reference signal, and the time domain interference signal with gas absorption is used as a measurement signal. Fourier transform is performed on the interference signal and the measurement signal respectively to obtain radio frequency spectrum, and then the radio frequency spectrum is normalized. A suitable absorption spectrum is selected for linear fitting, and algorithms such as background subtraction and frame averaging are used to find a matching theoretical spectrum, and then the measurement of gas pressure is realized according to the Lambert-Beer law.

[0044] The above detailed description further illustrates the purpose, technical solutions and advantages of the application, and it should be understood that the above description is only a specific embodiment of the application and is not used to limit the protection scope of the application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application should be included in the protection scope of the application.

Claims

1. A gas pressure measuring device based on TS-DFT technique, characterized by: The application relates to a femtosecond laser seed source, a spectrum selection module, a pulse picker, a time-domain expansion amplification module and a gas pressure measurement module. The femtosecond laser seed source comprises a first pump source, a first wavelength division multiplexer, a first doped optical fiber, a first optical fiber isolator, a polarizer, a first optical fiber polarization controller and a first optical fiber coupler. The spectrum selection module comprises a fiber grating and a fiber filter. The time-domain expansion amplification module comprises a first time-domain expansion amplification module and a second time-domain expansion amplification module. The gas pressure measurement module comprises a second optical fiber coupler, a second high-dispersion compensation optical fiber, a fiber delay line, a second optical fiber polarization controller, a first optical fiber collimator, a gas cell, a second optical fiber collimator, a third optical fiber coupler, a second time-domain expansion amplification module, a photodetector and a digital acquisition and processing module. The first pump source is coupled into the first doped optical fiber through the first wavelength division multiplexer; the first optical fiber isolator ensures the single operation of the laser in the oscillation cavity; the polarizer and the first optical fiber polarization controller form an equivalent saturated absorber; the first optical fiber coupler retains most of the energy in the oscillation cavity for oscillation, and the remaining energy is output outside the cavity, and the diffraction spectrum is obtained through the fiber grating and the fiber filter selects the spectrum for the target gas measurement; the spectrum passes through the pulse picker to select a single pulse, enters the first high-dispersion compensation optical fiber for time-domain expansion, and the expanded pulse and the second pump source are coupled into the second doped optical fiber through the second wavelength division multiplexer for amplification; the amplified pulse is divided into two paths through the second optical fiber coupler, the first path is used as reference light to enter the second high-dispersion compensation optical fiber for time-domain expansion, and then passes through the fiber delay line to adjust the relative delay and passes through the second optical fiber polarization controller to adjust the polarization state of the reference light; The second path is used as measurement light to pass through the first optical fiber collimator to enter the gas cell, and then passes through the second optical fiber collimator to enter the optical fiber, and the interference signal is generated at the third optical fiber coupler; The interference signal passes through the third high-dispersion compensation optical fiber for time-domain expansion, and the expanded pulse and the third pump source are coupled into the third doped optical fiber through the third wavelength division multiplexer for amplification, the time-domain expanded and amplified interference signal is received by the photodetector and is transmitted into the digital acquisition and processing module.

2. The gas pressure measuring device based on TS-DFT technique as claimed in claim 1, wherein: The doped optical fiber is an erbium-doped gain optical fiber, a ytterbium-doped gain optical fiber or a thulium-doped gain optical fiber, wherein the first doped optical fiber, the second doped optical fiber and the third doped optical fiber are gain optical fibers with the same doping type.

3. The gas pressure measuring device based on TS-DFT technique as claimed in claim 1, wherein: The whole optical path of the femtosecond laser seed source is subjected to temperature control treatment to eliminate the influence of environmental temperature change on the repetition frequency.

4. A gas pressure measurement method based on TS-DFT technique, implemented by a gas pressure measurement device based on TS-DFT technique as claimed in claim 1, 2 or 3, characterized in that: The time-domain interference signal without gas absorption and the time-domain interference signal with gas absorption are obtained by using a gas pressure measuring module in the gas pressure measuring device, the time-domain interference signal without gas absorption is taken as a reference signal, and the time-domain interference signal with gas absorption is taken as a measurement signal; Fourier transform is performed on the interference signal and the measurement signal respectively to obtain a radio frequency spectrum, and the radio frequency spectrum is normalized; an absorption spectrum line is selected for linear fitting, and background subtraction and frame averaging are used to find a matching theoretical spectrum, and according to the Lambert-Beer law, the measurement of the gas pressure is realized; According to Lambert-Beer's law, when a light beam with intensity I i is incident to a gas with length L, the light intensity I o after absorption is related to the incident light intensity I i as follows: where P is the total pressure of the gas, S(T) is the line intensity of the absorption line, is a linear function of the normalized absorption line, and a f is the measured absorption of the gas at wavelength f, and X is the concentration of the absorbing gas. S(T) is a function of temperature, the characteristic of which varies with temperature depending on the transition state energy level E", T r Q(T) is the partition function, h is the Planck constant, c is the speed of light, k is the Boltzmann constant, v0 is the wave number at the center of the absorption peak; by α f The spectral characteristics of the absorption spectrum are extracted by integrating in the frequency domain, and the absorbance A is: The pressure is:

Images