Gas pressure measuring device and method based on TS-DFT technology

Abstract

The invention discloses a gas pressure measurement device and method based on a 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 pickup device, a time domain broadening amplification module and a gas pressure measuring module. The output light of the femtosecond laser seed source passes through the fiber bragg grating and the filter, spectrums needed for measurement of different target gases are selected, then a single pulse is selected through the pulse picker and transmitted into the time domain broadening amplification module, and a relatively flat pulse envelope can be obtained by adopting multi-stage amplification. The broadened pulse is divided into reference light and measuring light, the relative delay of the reference light is adjusted through an optical fiber delay line, the measuring light passes through a gas pool containing target gas and is coupled by a coupler to enter a time domain broadening amplification module, and a generated signal is received by a photoelectric detector and is transmitted to a data acquisition and processing module. The method has the advantages of fast sampling, high spectral resolution, large dynamic range and the like.

Description

Technical Field

[0001] The present invention relates to a gas pressure measuring device and method, and in particular to a gas pressure measuring device and method based on TS-DFT technology. Background Art

[0002] The measurement of engine gas pressure helps to diagnose the sealing of cylinders and piston rings. Traditional pressure measurement is mainly achieved through pressure sensors, but this method is a contact measurement with great limitations and short life. With the rapid development of absorption spectroscopy technology, it has been widely used in pressure measurement research. The more commonly used absorption spectroscopy pressure measurement method is mainly based on TDLAS (tunable diode laser absorption spectroscopy technology), but its wavelength scanning range is limited. When multiple absorption peaks need to be measured, multiple lasers need to be used, resulting in a complex system. At the same time, the traditional measurement method can only complete one measurement for dynamic changes occurring on a microsecond time scale, which cannot meet the pressure measurement requirements during the combustion process. Summary of the invention

[0003] In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a gas pressure measurement device and method based on TS-DFT technology. The femtosecond laser used has the advantages of wide spectral range and high repetition frequency. By combining the femtosecond laser with the time domain broadening method, high-speed and high-resolution measurement of the pressure generated by the gas mixture during the combustion process can be achieved.

[0004] The objective of the present invention is achieved through the following technical solutions:

[0005] The invention discloses a gas pressure measuring device based on TS-DFT technology, comprising a femtosecond laser seed source, a spectrum selection module, a pulse picker, a time domain broadening and amplification module and a gas pressure measuring 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 includes a fiber grating and a fiber filter.

[0008] The time domain stretching and amplification module comprises a first time domain stretching and amplification module and a second time domain stretching and amplification module, wherein the first time domain stretching and amplification module comprises a first high dispersion compensating 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 stretching and amplification module comprises a third high dispersion compensating 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 measurement module includes a second optical fiber coupler, a second high dispersion compensation optical fiber, an optical fiber delay line, a second optical fiber polarization controller, a first optical fiber collimator, a gas pool, a second optical fiber collimator, a third optical fiber coupler, a second time domain broadening and amplification module, a photoelectric detector, and a digital acquisition and processing module.

[0010] 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-way operation of the laser in the oscillation cavity; the polarizer and the first optical fiber polarization controller are combined to 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 then the spectrum for the target gas measurement is selected through the optical fiber filter; the spectrum selects a single pulse through the pulse picker, enters the first high-dispersion compensation optical fiber for time domain broadening, and the broadened pulse is coupled with the second pump source through the second wavelength division multiplexer into the second doped optical fiber for amplification; the amplified pulse passes through the The second optical fiber coupler is divided into two paths, the first path is used as reference light to enter the second high dispersion compensation optical fiber to be widened in the time domain, and then the relative delay is adjusted by the optical fiber delay line, and the polarization state of the reference light is adjusted by the second optical fiber polarization controller; the second path is used as measurement light to enter the gas pool through the first optical fiber collimator, and then coupled into the optical fiber through the second optical fiber collimator, and interferes with the reference light at the third optical fiber coupler; the interference signal is time-domain widened through the third high dispersion compensation optical fiber, and the widened pulse is coupled with the third pump source through the third wavelength division multiplexer to enter the third doped optical fiber for amplification, and the interference signal after time-domain widening and amplification is received by the photodetector and transmitted to the data acquisition and processing module.

[0011] Preferably, the doped optical fiber is an erbium-doped gain optical fiber, an 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.

[0012] Preferably, the entire optical path of the femtosecond laser oscillator is temperature-controlled to eliminate the influence of ambient temperature changes on the repetition frequency.

[0013] The present invention discloses a measurement method of a gas pressure measurement device based on TS-DFT technology: using the gas pressure measurement module in the gas pressure measurement device to obtain a time domain interference signal when there is no gas absorption and a time domain interference signal when there is gas absorption, using the time domain interference signal when there is no gas absorption as a reference signal, and using the time domain interference signal when there is gas absorption as a measurement signal. Fourier transform the interference signal and the measurement signal respectively to obtain a radio frequency spectrum, and normalize the radio frequency spectrum. Select appropriate absorption spectrum lines for linear fitting, and use background subtraction and frame averaging to find a matching theoretical spectrum to achieve gas pressure measurement.

[0014] According to the Lambert-Beer law, when the intensity is I i The light beam is incident on a gas of length L. After absorption, the light intensity I o With the incident light intensity I i The relationship is:

[0015]

[0016] Where P is the total gas pressure, S(T) is the line intensity of the absorption line, is the normalized linear function of the absorption line, α f To measure the absorptivity of a gas at wavelength f, X is the concentration of the absorbing gas.

[0017]

[0018] S(T) is a function of temperature, and its temperature-dependent characteristics depend on the transition state energy level E″, T r is the reference temperature, Q(T) is the partition function, h is Planck's constant, c is the speed of light, k is the Boltzmann constant, and v 0 is the wave number at the center of the absorption peak. f Integrating in the frequency domain can extract the spectral characteristics of the absorption line, and the absorbance A is:

[0019]

[0020] The pressure is:

[0021]

[0022] Beneficial effects:

[0023] 1. The present invention discloses a gas pressure measurement device and method based on TS-DFT technology. The femtosecond laser seed source adopts overall temperature control processing, which can avoid the drift of repetition frequency caused by changes in ambient temperature. Different from the traditional phase-locked circuit method, the present invention does not require a repetition frequency locking device, thereby simplifying the composition of the gas pressure measurement device.

[0024] 2. The present invention discloses a gas pressure measurement device and method based on TS-DFT technology, which combines femtosecond laser with time domain broadening method, and can achieve high-speed and high-resolution measurement of the pressure generated by gas mixture during combustion. The present invention can not only simplify the device and test process. At the same time, the reference pulse and the detection pulse in the present invention are generated by the same oscillator, which has the advantages of high coherence, strong anti-interference ability, and long detection time compared with the situation where they are generated by different oscillators.

[0025] 3. The present invention discloses a gas pressure measurement device and method based on TS-DFT technology. The spectrum selects a single pulse through the pulse picker, and passes through the time domain broadening and amplification module and the gas pressure measurement module to achieve coherent detection of a single detection pulse and a reference pulse. The detection result within a single cycle can include complete gas absorption characteristics, and the measurement speed is fast.

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

[0027] Figure 1 This is a schematic diagram of the structure of a gas pressure measurement device based on TS-DFT technology;

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

[0029] In order to better illustrate the purpose and advantages of the present invention, the invention is further described below with reference to the accompanying drawings and examples.

[0030] Embodiment 1:

[0031] like Figure 1As shown, the present embodiment discloses a gas pressure measurement device based on TS-DFT technology, including a femtosecond laser seed source, a spectrum selection module, a pulse picker, a time domain broadening and amplification module and a gas pressure measurement 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 above spectrum selection module includes a fiber grating and a fiber filter.

[0034] The above-mentioned time domain stretching and amplification module includes a first time domain stretching and amplification module and a second time domain stretching and amplification module, wherein the first time domain stretching and amplification module includes a first high dispersion compensating 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 stretching and amplification module includes a third high dispersion compensating optical fiber, a third optical fiber isolator, a third pump source, a third wavelength division multiplexer, and a third doped optical fiber.

[0035] The gas pressure measurement module includes 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 pool, a second fiber collimator, a third fiber coupler, a second time domain broadening and amplification module, a photoelectric detector, and a digital acquisition and processing module.

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

[0037] The entire optical path of the femtosecond laser oscillator is temperature-controlled to eliminate the influence of ambient temperature changes on the repetition frequency.

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

[0039] The central wavelength of the spectrum after the above-mentioned spectrum selection module is 1550nm.

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

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

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

[0043] The present embodiment discloses a measurement method of a gas pressure measurement device based on TS-DFT technology, which is as follows: a first pump source is coupled into a first doped optical fiber through a first wavelength division multiplexer; a first optical fiber isolator ensures that the laser in the oscillation cavity operates in a single direction; a polarizer and a first optical fiber polarization controller are combined to form an equivalent saturated absorber; the first optical fiber coupler retains most of the energy in the oscillation cavity in the oscillation cavity for oscillation, and the remaining energy is output outside the cavity, and a diffraction spectrum is obtained through a fiber grating, and then a spectrum for measuring the target gas is selected through an optical fiber filter; a single pulse is selected through a pulse picker, and enters a first high-dispersion compensation optical fiber for time domain broadening, and the broadened pulse is coupled with a second pump source through a second wavelength division multiplexer to enter a second doped optical fiber for amplification; the amplified pulse is divided into two paths through a second optical fiber coupler, and the first path is used as a reference light to enter the second high-dispersion compensation optical fiber in the time domain The optical fiber delay line is used to adjust the relative delay, and the polarization state of the reference light is adjusted by the second optical fiber polarization controller; the second path is used as the measurement light and is injected into the gas pool through the first optical fiber collimator. The gas pool is filled with a mixture of 29% acetylene and 71% oxygen, and an igniter is installed. Then, it is coupled into the optical fiber through the second optical fiber collimator, and interferes with the reference light at the third optical fiber coupler; the interference signal is time-domain widened through the third high-dispersion compensation optical fiber, and the widened pulse and the third pump source are coupled into the third doped optical fiber through the third wavelength division multiplexer for amplification. The interference signal after time-domain widening and amplification is received by the photodetector and transmitted to the data acquisition and processing module to obtain the time-domain interference signal when there is no gas absorption and the time-domain interference signal when there is gas absorption. The time-domain interference signal when there is no gas absorption is used as the reference signal, and the time-domain interference signal when there is gas absorption is used as the measurement signal. Fourier transform is performed on the interference signal and the measurement signal respectively to obtain the RF spectrum, and it is normalized. Select appropriate absorption spectrum lines for linear fitting, and use background subtraction, frame averaging and other algorithms to find the matching theoretical spectrum. According to the Lambert-Beer law, the gas pressure can be measured.

[0044] The specific description above further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A gas pressure measurement device based on TS-DFT technology, characterized in that: It includes a femtosecond laser seed source, a spectrum selection module, a pulse picker, a time domain broadening and 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 includes a fiber grating and a fiber filter; The time domain stretching and amplification module comprises a first time domain stretching and amplification module and a second time domain stretching and amplification module, wherein the first time domain stretching and amplification module comprises a first high dispersion compensating 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 stretching and amplification module comprises a third high dispersion compensating optical fiber, a third optical fiber isolator, a third pump source, a third wavelength division multiplexer, and a third doped optical fiber; The gas pressure measurement module includes a second optical fiber coupler, a second high dispersion compensation optical fiber, an optical fiber delay line, a second optical fiber polarization controller, a first optical fiber collimator, a gas pool, a second optical fiber collimator, a third optical fiber coupler, a second time domain broadening and amplification module, a photoelectric detector, 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-way operation of the laser in the oscillation cavity; the polarizer and the first optical fiber polarization controller are combined to 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 optical fiber grating, and then the spectrum for measuring the target gas is selected through the optical fiber filter; the spectrum selects a single pulse through the pulse picker, enters the first high-dispersion compensation optical fiber for time domain broadening, and the broadened pulse is coupled with the second pump source through the second wavelength division multiplexer to enter the second doped optical fiber for amplification; the amplified pulse is divided into two paths through the second optical fiber coupler, the first path is used as the reference light to enter the second high-dispersion compensation optical fiber to be broadened in the time domain, and then the relative delay is adjusted through the optical fiber delay line, and the polarization state of the reference light is adjusted through the second optical fiber polarization controller; The second path is used as the measuring light and is injected into the gas pool through the first optical fiber collimator, and then coupled into the optical fiber through the second optical fiber collimator, and interferes with the reference light at the third optical fiber coupler; The interference signal is time-domain stretched through the third high-dispersion compensation optical fiber, and the stretched pulse is coupled with the third pump source via a third wavelength division multiplexer into a third doped optical fiber for amplification. The interference signal after time-domain stretching and amplification is received by the photodetector and transmitted to the data acquisition and processing module.

2. A gas pressure measurement device based on TS-DFT technology as claimed in claim 1, characterized in that: The doped optical fiber is an erbium-doped gain optical fiber, an 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. A gas pressure measurement device based on TS-DFT technology as claimed in claim 1, characterized in that: The entire optical path of the femtosecond laser oscillator is temperature-controlled to eliminate the influence of ambient temperature changes on the repetition frequency.

4. A method for measuring gas pressure based on TS-DFT technology, implemented based on a gas pressure measuring device based on TS-DFT technology as claimed in claim 1, 2 or 3, characterized in that: The gas pressure measurement module in the gas pressure measurement device is used to obtain a time domain interference signal when there is no gas absorption and a time domain interference signal when there is gas absorption, and the time domain interference signal when there is gas absorption is used as a reference signal, and the time domain interference signal when there is gas absorption is used as a measurement signal; the interference signal and the measurement signal are respectively subjected to Fourier transformation to obtain a radio frequency spectrum, and the radio frequency spectrum is normalized; the absorption spectrum is selected for linear fitting, and the background subtraction method and the frame averaging method are used to find a matching theoretical spectrum, and the gas pressure is measured according to the Lambert-Beer law; According to the Lambert-Beer law, when the intensity is I i The light beam is incident on a gas of length L, and the light intensity after absorption is I o With the incident light intensity I i The relationship is: Where P is the total gas pressure, S(T) is the line intensity of the absorption line, is the normalized linear function of the absorption line, α f To measure the absorptivity of the gas at wavelength f, X is the concentration of the absorbing gas; S(T) is a function of temperature, and its temperature-dependent characteristics depend on the transition state energy level E″, T r is the reference temperature, Q(T) is the partition function, h is Planck's 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. f Integrate in the frequency domain to extract the spectral characteristics of the absorption line, and the absorbance A is: The pressure is:

Images