WO2024077503A1 - Système et procédé de démodulation de déplacement absolu d'interféromètre utilisant comme référence un spectre d'absorption d'un gaz - Google Patents

Système et procédé de démodulation de déplacement absolu d'interféromètre utilisant comme référence un spectre d'absorption d'un gaz Download PDF

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WO2024077503A1
WO2024077503A1 PCT/CN2022/124758 CN2022124758W WO2024077503A1 WO 2024077503 A1 WO2024077503 A1 WO 2024077503A1 CN 2022124758 W CN2022124758 W CN 2022124758W WO 2024077503 A1 WO2024077503 A1 WO 2024077503A1
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interferometer
interference
wavelength
absorption spectrum
detector
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PCT/CN2022/124758
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Chinese (zh)
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宁雅农
刘统玉
杨青山
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广东感芯激光科技有限公司
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
    • G01D5/35306—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement
    • G01D5/35309—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using multiple waves interferometer
    • G01D5/35312—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using multiple waves interferometer using a Fabry Perot
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D18/00—Testing or calibrating apparatus or arrangements provided for in groups G01D1/00 - G01D15/00
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
    • G01N21/45—Refractivity; Phase-affecting properties, e.g. optical path length using interferometric methods; using Schlieren methods

Definitions

  • the present invention relates to the technical field of photoelectric measuring instruments and interferometric sensors, and in particular to an interferometer absolute displacement demodulation system, method and application using a gas spectrum reference.
  • interference sensors based on the F-P interference principle generally sense by acting on the F-P cavity to cause the cavity length to change.
  • the two mirrors of the interferometer are the inner surface of the film at one end and the tip of the optical fiber at the other end, which constitute the core sensitive element of the F-P interferometer.
  • the incident light is reflected at the two end faces of the F-P cavity, the reflected light beam generates an interference signal at the signal detector.
  • This interference signal or interference fringes changes with the change of the F-P cavity length. By demodulating the change of the interference fringes, the sensing and measurement of the measured parameter can be realized.
  • the demodulation of interferometer fringes refers to extracting the change value of the interferometer optical cavity length from the interference fringe information of the interferometer.
  • demodulation methods for extracting the cavity length of conventional interferometers which are mainly divided into three categories: light intensity demodulation method, spectral demodulation method and low coherence interference demodulation method.
  • the system structure corresponding to the light intensity demodulation method is simple and the response speed is fast, but the requirements for the control of cavity length accuracy and light source stability are too high.
  • the spectral demodulation method uses a more complex spectrum acquisition system. Due to the generally high cost of spectrometers, the wide application of this method is limited.
  • the cavity length change of the sensor interferometer can be demodulated by using the cross-correlation relationship between different types of interferometers (reference interferometers) and Fabry-Perot cavities (sensing interferometers).
  • This low coherence interference technology can be divided into two types: time scanning type and space scanning type.
  • the reference interferometer generates a series of optical path differences on the time axis or space axis respectively.
  • the interference fringes can be demodulated by using the peak position of any fringe relative to the peak position of the zero-order fringe of the central wavelength interference fringe.
  • This demodulation method has a relatively complex structure and the cost of precision mechanical scanning is also high.
  • the wavelength scanning laser light source By using a wavelength scanning light source as the light source of the interferometer, utilizing the wavelength readability of the wavelength scanning laser light source, plus the wavelength value at the maximum or minimum value of the interference fringe intensity, it is also possible to demodulate the interference fringes and invert the change in the interference cavity length.
  • the wavelength scanning laser light source has high power consumption and high cost, especially for small sensors. Power consumption, cost, and volume limit this method.
  • the wavelength scanning laser light source needs to correct its wavelength reading as a precise measurement value in a large temperature change range. How to achieve small size, low power consumption, low cost, and high-precision interference demodulation is a technical problem in designing fiber optic interferometer sensors.
  • the sensor demodulation principle using F-P interferometer as an example is as follows:
  • the reflected output light intensity of the fiber Fabry-Perot sensor with a specific cavity length of L is in a cosine function relationship with the light frequency, and the distribution formula of the reflected light intensity I is:
  • the output light intensity of the interferometer contains the information of the FP cavity length.
  • the demodulation method of the interferometer is to use the change information of I to invert the change of L.
  • the change of phase is caused by the change of the interference cavity length L and the wavelength ⁇ , so the phase can be changed accordingly by changing the interference cavity length or changing the laser wavelength, that is:
  • the demodulation method using the interference fringe tracking method or the phase change tracking method has the advantages of simple signal processing and fast measurement speed, this method has the problem of limited dynamic range.
  • one of the purposes of the present invention is to provide an interferometer absolute displacement demodulation system using a gas spectrum reference, by using a scanning laser as the light source of the interferometer sensor, using the absorption spectrum of a reference gas with an absorption peak within the wavelength scanning range of the scanning laser as the absolute spectrum reference position, and combining the fixed wavelength and half width of the absorption spectrum line, or a calibration method for time-to-phase conversion of two absorption spectrum lines, thereby completing the absolute value measurement of the interferometer cavity length;
  • the present invention can be applied to the interferometric demodulation of various interferometric sensors, and has the advantages of high resolution and high accuracy in measuring the absolute cavity length of the interferometer cavity;
  • the demodulation method of the interferometer absolute displacement demodulation system using gas absorption spectrum reference of the present invention can be used in various sensor devices based on the interference principle, and has broad application prospects; when this demodulation method is used in an interferometer sensor device, it can not only reduce the power consumption and volume of the sensor, but also can be used in a low-power, miniaturized, and lightweight interferometer sensor, thereby reducing the demodulator cost of the existing interferometer sensor and simplifying the structure of the entire detection device.
  • the second object of the present invention is to provide a demodulation method for an interferometer absolute displacement demodulation system using a gas spectrum reference, using the absorption spectrum of a reference gas having an absorption peak within the wavelength scanning range of the scanning laser as the absolute spectrum reference position, and combining the fixed wavelength and half-width of the absorption spectrum line, or a calibration method for converting two absorption spectrum lines from time to phase, thereby completing the absolute value measurement of the interferometer cavity length.
  • the measured cavity length of the present invention is called the absolute length because the measurement process is based on the fixed wavelength and half-width of the absorption spectrum line, which are physical quantities that will not change under normal temperature and pressure conditions; therefore, the absolute interferometric cavity length measurement characteristics of the present invention overcome the above-mentioned problems of the traditional interference fringe tracking method, and are crucial for all applications requiring long-term static measurement.
  • the third object of the present invention is to provide an interferometer absolute displacement demodulation device using a gas absorption spectrum reference, which uses an adjustable laser as a light source and a gas absorption spectrum as a reference, and calculates the absolute measurement value of the interference cavity length L of the interferometer and the measurement value of its change ⁇ L through a pre-calibrated time-phase relationship, thereby achieving high-efficiency, high-precision, low-power, and low-cost interference demodulation.
  • An interferometer absolute displacement demodulation system using gas absorption spectrum reference is used to measure the absolute cavity length of the interferometer interference cavity;
  • the demodulation system includes a scanning laser connected in the optical path, a fiber isolator, a fiber coupler, an interferometer, a detector, a signal amplifier, and a microprocessor;
  • the detector includes a signal detector and a reference detector;
  • the fiber coupler includes a 2 ⁇ 2 fiber coupler; and also includes a gas reference chamber, the reference chamber is connected to the reference detector, and the gas reference chamber is filled with a reference gas with an absorption peak within the wavelength scanning range of the scanning laser;
  • the scanning laser is driven by a sawtooth wave driver and generates a wavelength scanning beam;
  • the laser beam emitted by the scanning laser passes through the optical fiber isolator and is coupled to the first connection end of the 2 ⁇ 2 optical fiber coupler, and is output from the second connection end of the 2 ⁇ 2 optical fiber coupler to enter the interferometer.
  • the interference reflected light generated by the interferometer returns through the 2 ⁇ 2 optical fiber coupler and is absorbed by the signal detector at the third connection end to generate interference fringes; the interference reflected light is output from the fourth connection end of the 2 ⁇ 2 optical fiber coupler to the gas reference chamber, and the light beam transmitted by the reference gas is connected to the reference detector and generates absorption spectrum lines in the reference detector;
  • the interference fringe signal collected by the signal detector and the absorption spectrum line signal collected by the reference detector are amplified by the signal amplifier respectively, and are sent to the microprocessor for signal intensity normalization processing after analog-to-digital conversion; the microprocessor calculates the absolute measurement value of the interference cavity length L of the interferometer and the measurement value of its change ⁇ L through a pre-calibrated time-
  • the interferometer absolute displacement demodulation system also includes a scanning laser, a fiber isolator, a 1 ⁇ N fiber splitter, N-1 2 ⁇ 1 fiber couplers, N-1 signal detectors, N-1 interferometers, a reference gas chamber and a reference detector, wherein N ⁇ 2;
  • the laser beam emitted by the scanning laser passes through the optical fiber isolator and is coupled to the 1 ⁇ N optical fiber splitter.
  • the laser beam is divided into N paths, one path is output from the 1-path connection end of the 1 ⁇ N optical fiber splitter to the reference gas chamber, and the beam transmitted by the reference gas is connected to the corresponding reference detector, and an absorption spectrum line is generated in the reference detector;
  • the remaining beams are connected from the other N-1 output ends of the 1 ⁇ N optical fiber splitter to the first connection ends of the corresponding N-1 2 ⁇ 1 optical fiber couplers, and are output from the corresponding second connection ends of the 2 ⁇ 1 optical fiber couplers to enter the corresponding N-1 interferometers, and the interference reflection light generated by the interferometer returns through the third connection end of the 2 ⁇ 1 optical fiber coupler to enter the corresponding signal detector, and generates interference fringes;
  • the interference fringe signal is collected by the corresponding signal detector, and the absorption spectrum line signal is collected by the corresponding reference detector and amplified by the signal amplifier respectively
  • the demodulation system includes a scanning laser connected in the optical path, a fiber isolator, a 2 ⁇ 1 fiber coupler, an interferometer, a detector with a reference gas chamber inside, a signal amplifier, and a microprocessor;
  • the laser beam emitted by the scanning laser passes through the optical fiber isolator and is coupled to the first connection end of the 2 ⁇ 1 optical fiber coupler, and is output from the second connection end of the 2 ⁇ 1 optical fiber coupler to enter the interferometer.
  • the interference reflected light generated by the interferometer returns through the third connection end of the 2 ⁇ 1 optical fiber coupler and enters the detector with the reference gas chamber inside to generate interference fringes and absorption spectrum lines.
  • the interference fringe signals and absorption spectrum line signals are collected by the detector and amplified by the signal amplifier, and sent to the microprocessor after analog-to-digital conversion for signal intensity normalization processing.
  • the microprocessor calculates the absolute measurement value of the interference cavity length L of the interferometer and the measurement value of its change ⁇ L through a pre-calibrated time-phase relationship.
  • the interferometer absolute displacement demodulation system further includes a scanning laser, a fiber isolator, a 1 ⁇ N fiber splitter, N 2 ⁇ 1 fiber couplers, N signal detectors, N interferometers, and N detectors with the reference gas chamber inside, wherein N ⁇ 2;
  • the laser beam emitted by the scanning laser passes through the optical fiber isolator and is coupled to the 1 ⁇ N optical fiber splitter. After being divided into N beams by the 1 ⁇ N optical fiber splitter, the laser beam is output from the N-way connection ends of the 1 ⁇ N optical fiber splitter and connected to the first connection ends of N 2 ⁇ 1 optical fiber couplers respectively, and is output from the corresponding second connection ends of the 2 ⁇ 1 optical fiber couplers to enter the corresponding N interferometers.
  • the interference reflected light generated by the interferometer returns through the third connection end of the 2 ⁇ 1 optical fiber coupler and enters the corresponding N detectors with reference gas chambers inside to generate interference fringes and absorption spectra.
  • the detector collects the interference fringe signal and the absorption spectrum line signal and amplifies them respectively through the signal amplifier, and sends them to the microprocessor after analog-to-digital conversion for signal intensity normalization processing.
  • the microprocessor calculates the absolute measurement value of the interference cavity length L of the interferometer and the measurement value of its change ⁇ L through the pre-calibrated time-phase relationship.
  • the output end of the microprocessor is connected to a D/A analog-to-digital converter, and the D/A analog-to-digital converter is used to control the scanning laser current driving circuit to achieve tuning of the scanning laser.
  • Solution 1 Separating the signal detector and the reference gas chamber
  • a demodulation method of the interferometer absolute displacement demodulation system using gas absorption spectrum reference as described above comprises the following steps:
  • S1 The scanning laser light source, under the control of the sawtooth wave driving circuit, outputs a laser beam with a wavelength that changes with time within a scanning cycle;
  • the laser beam in S1 is coupled to the fiber coupler after passing through the fiber isolator and outputted to the interferometer and the gas reference chamber respectively.
  • the interference reflected light generated by the interferometer returns through the fiber coupler and enters the corresponding signal detector.
  • the interference reflected light generates interference fringes in the signal detector.
  • the light beam transmitted from the gas reference chamber is absorbed by the corresponding reference detector and generates absorption spectrum lines in the reference detector synchronously.
  • the signal detector and the reference detector collect the interference fringe signal and the absorption line signal generated in S2 and amplify them through the signal amplifier respectively, and send them to the microprocessor for signal strength normalization after analog-to-digital conversion;
  • S4 The microprocessor receives the interference fringe signal and the absorption spectrum line signal in S3, and calculates the interference cavity length of the interferometer and its change value through the pre-calibrated time-phase relationship.
  • Solution 2 A reference gas chamber is provided inside the detector
  • a demodulation method of the interferometer absolute displacement demodulation system using gas absorption spectrum reference as described above comprises the following steps:
  • S1 The scanning laser light source, under the control of the sawtooth wave driving circuit, outputs a laser beam with a wavelength that changes with time within a scanning cycle;
  • the laser beam in S1 is coupled to the fiber coupler after passing through the fiber isolator and is output and incident on the interferometer respectively.
  • the interference reflected light generated by the interferometer returns through the fiber coupler and enters the detector with the gas reference chamber inside.
  • the interference reflected light generates interference fringes in the detector and synchronously generates absorption spectrum lines.
  • S3 the interference fringe signal and the absorption line signal generated in S2 are collected by the detector, amplified by the signal amplifier, and sent to the microprocessor for signal strength normalization after analog-to-digital conversion;
  • S4 The microprocessor receives the interference fringe signal and the absorption spectrum line signal in S3, and calculates the interference cavity length of the interferometer and its change value through the pre-calibrated time-phase relationship.
  • the method of calibrating the pre-calibrated time-phase relationship and calculating the demodulation interference cavity length value and its change value based on the time-phase calibration is as follows:
  • the scanning laser light source under the control of the sawtooth wave driving circuit, outputs a laser beam whose wavelength changes with time within the actual scanning wavelength range;
  • the detector of the interferometer When there is only one absorption peak in a scanning cycle of the scanning laser, the detector of the interferometer generates interference fringes and absorption spectrum synchronously, and obtains the intensity curve of the corresponding interference fringes and absorption spectrum changing with time; the half width of the absorption spectrum is used to calibrate the time axis, so as to obtain the proportional relationship of converting the time axis value into the wavelength value;
  • the time axis can be calibrated to obtain a proportional relationship of converting the time axis value into the wavelength value; since the measurement error when calibrating with two absorption peaks is relatively small, the calibration accuracy is higher;
  • the minimum wavelength scanning range of the scanning laser can cover one or two absorption lines simultaneously in one scanning cycle; in 2), after obtaining the intensity curves of the corresponding interference fringes and absorption lines changing with time, the half-width of the absorption line relative to the time axis is measured; or, the difference in the relative positions of the central wavelengths of the two absorption lines on the time axis is measured, and the half-width of the absorption line or the difference in the central wavelengths of the two absorption lines is used to obtain the time axis.
  • the numerical value is converted into a proportional relationship of wavelength value to complete the system calibration; in the measurement of 3), the time difference between the Q point with the largest slope of the light intensity change of an interference fringe and the wavelength center of the absorption spectrum is measured and converted into the wavelength difference between the Q point and the wavelength center of the absorption spectrum.
  • the central wavelength of the known absorption spectrum is added or subtracted from this wavelength difference to obtain the absolute wavelength value ⁇ corresponding to the Q point of the interference fringe; in 4), it is described how to obtain the absolute value of the interference cavity length L by measuring the time difference between the two Q points with the largest slope of the light intensity change of an interference fringe; in 5), if the interference fringe is shifted due to the change of the interference cavity length, the change value of the interference cavity length can be obtained as long as the phase difference of the Q point relative to the center point of the absorption spectrum.
  • an interferometer absolute displacement demodulation device using gas absorption spectrum reference including the above-mentioned interferometer absolute displacement demodulation system and method using gas absorption spectrum reference, which uses an adjustable laser as a light source and a gas absorption spectrum as a reference, and calculates the absolute measurement value of the interference cavity length L of the interferometer and the measurement value of its change ⁇ L through a pre-calibrated time-phase relationship, thereby achieving high-efficiency, high-precision, low-power and low-cost interference demodulation.
  • the present invention has at least the following beneficial effects:
  • the present invention uses a scanning laser as the light source of the interferometer sensor. Under the condition that the wavelength scanning range of the scanning laser contains the absorption peak of the reference gas, the absorption spectrum of the reference gas is used as the absolute spectrum reference position, and the scanning time value is converted into a phase or wavelength value calibration method by combining the fixed wavelength and half-width of the absorption spectrum line, or the scanning time difference between two absorption spectrum lines, and the absolute value measurement of the interferometer cavity length is completed in conjunction with the wavelength difference of the half-period of the interference fringe.
  • the change in the interference cavity length is obtained by measuring the change in the Q point of the interference fringe relative to the absorption peak wavelength, so as to achieve the demodulation purpose of the interferometer.
  • the present invention is applied to the interference sensor and has the advantages of high resolution and high accuracy in measuring the absolute cavity length of the interference cavity.
  • the measured cavity length of the present invention is called absolute length because the measurement process is based on the fixed wavelength and half-width of the absorption spectrum, which are physical quantities that will not change under normal temperature and pressure conditions; therefore, the absolute interference cavity length measurement characteristics of the present invention overcome the above-mentioned problems of the traditional interference fringe tracking method, which is crucial for all applications requiring long-term static measurement;
  • the demodulation method of the interferometer absolute displacement demodulation system using gas absorption spectrum reference of the present invention can be used in various sensor devices based on the interference principle, and has a very broad application prospect; when this demodulation method is used in an interferometer sensor device, it can not only reduce the power consumption and volume of the sensor, but also can be used in a low-power, miniaturized, and lightweight interferometer sensor, thereby reducing the demodulator cost of the existing interferometer sensor and simplifying the structure of the entire detection device;
  • the interferometer absolute displacement demodulation system using gas absorption spectrum reference of the present invention can be a single detection channel, or multiple detection channels can reuse a laser light source; the present invention can further simplify the interferometer demodulation device by using a detector with a reference gas chamber, which is convenient for increasing the number of detection channels and has strong practicality;
  • the demodulation method of the present invention can measure the length of the F-P interferometer cavity very quickly, which can reach the microsecond level, therefore, by continuously measuring the length of the F-P interferometer cavity, this demodulation method can also be used to measure the amplitude change and vibration frequency of a mirror of the interferometer caused by mechanical vibration;
  • the demodulation system of the present invention has strong versatility and can be applied to various sensing devices based on the interference principle to achieve high-efficiency, high-precision, low-power and low-cost interference demodulation.
  • FIG1 is a connection diagram of an interferometer absolute displacement demodulation system using a gas absorption spectrum reference according to Example 1 of the present invention
  • FIG2 is a schematic diagram of an interferometer absolute displacement demodulation system using a gas absorption spectrum reference according to embodiments 1-3 of the present invention, in which the system can simultaneously generate interference fringes and reference gas absorption peaks within one wavelength scanning cycle;
  • Example 3 is a schematic diagram of calculating the phase difference ⁇ between the two Q points of an interference fringe where the slope of the light intensity change is the largest in the interferometer absolute displacement demodulation system calibration principle using the gas absorption spectrum reference in Example 1-3 of the present invention;
  • FIG4 is a schematic diagram of the calibration relationship of using two absorption peaks to convert time into phase in the calibration principle of the interferometer absolute displacement demodulation system using gas absorption spectrum reference in Embodiment 1-3 of the present invention
  • FIG5 is a schematic diagram of the connection of an interferometer absolute displacement demodulation system using a gas absorption spectrum reference according to Embodiment 2 of the present invention.
  • FIG6 is a schematic diagram of the connection of 15 detection channels of an interferometer absolute displacement demodulation system using gas absorption spectrum reference according to Embodiment 3 of the present invention.
  • FIG. 7 is a schematic diagram of the connection of 16 detection channels of an interferometer absolute displacement demodulation system using gas absorption spectrum reference in Example 3 of the present invention.
  • an interferometer absolute displacement demodulation system using gas absorption spectrum reference the demodulation system is used to measure the absolute cavity length of the interferometer interference cavity;
  • the demodulation system includes a scanning laser 1 connected to form a path, a fiber isolator 2, a fiber coupler 3, an interferometer 4, a detector 5, a signal amplifier (not shown in the figure), and a microprocessor (not shown in the figure);
  • the detector 5 is a conventional C-band photoelectric detector; specifically, the detector 5 includes a signal detector 51 and a reference detector 52; the fiber coupler 3 includes a 2 ⁇ 2 fiber coupler 31; the demodulation system also includes a gas reference chamber 6, which is connected to the reference detector 52; the gas reference chamber 6 is filled with a reference gas having an absorption peak within the wavelength scanning range of the scanning laser 1; the output end of the microprocessor is connected to a D/A analog-to-digital converter, which is used to control the scanning laser current drive circuit to achieve wavelength tuning of the scanning laser 1; the scanning laser 1 is driven by a sawtooth wave driver (not shown in the drawings) and generates a wavelength scanning beam;
  • the laser beam emitted by the scanning laser 1 passes through the optical fiber isolator 2 and is coupled to the first connection end 311 of the 2 ⁇ 2 optical fiber coupler.
  • One path of the laser beam is output from the second connection end 312 of the 2 ⁇ 2 optical fiber coupler 31 and incident on the interferometer 4.
  • the interference reflected light generated by the interferometer 4 returns through the 2 ⁇ 2 optical fiber coupler 31 and enters the corresponding signal detector 51 through the third connection end 313.
  • Another path of the interference reflected light is output from the fourth connection end 314 of the 2 ⁇ 2 optical fiber coupler 31 to the gas reference chamber 6 and enters the corresponding reference detector 52.
  • the interference reflected light generates interference fringes in the signal detector 51, and the light beam transmitted through the reference gas is absorbed by the corresponding reference detector 52 and generates absorption spectrum lines synchronously.
  • the signal detector 51 and the reference detector 52 collect interference fringe signals and absorption line signals and amplify them respectively through the signal amplifier, and send them to the microprocessor for signal strength normalization processing after analog-to-digital conversion.
  • the microprocessor calculates the absolute measurement value of the interference cavity length L of the interferometer and the measurement value of its change ⁇ L through a pre-calibrated time-phase relationship.
  • the microprocessor drives the scanning laser 1 to send a wavelength scanning signal; the output end of the microprocessor is connected to a D/A analog-to-digital converter (not shown in the drawings), and the D/A analog-to-digital converter (not shown in the drawings) is used to control the scanning laser current drive circuit to achieve tuning of the scanning laser; and the interference fringe signals and absorption spectrum line signals collected by the signal detector and the reference detector are amplified by a linear transimpedance amplifier, digitized by an A/D analog-to-digital converter, and then output to the microprocessor for signal intensity normalization processing.
  • the interferometer 4 is an F-P interferometer
  • the scanning laser 1 is a VCSEL laser.
  • the output wavelength of the VCSEL laser can be changed accordingly to form a scanning wavelength range; at the same time, a gas with a characteristic absorption peak is selected within the scanning wavelength range of the VCSEL laser, such as methane gas, and injected into the reference gas chamber.
  • the laser light wave is synchronously received by the signal detector 51 and the reference detector 52; the F-P interferometer generates interference fringes in the signal detector 51, and the reference gas chamber synchronously generates absorption spectra in the reference detector 52, as shown in FIG2 .
  • the scanning laser 1 may also be other types of scanning lasers, as long as the corresponding gas can be selected as an absorption spectrum reference within its scanning band and the beneficial effects of the present invention can be achieved, which will not be elaborated here.
  • the interferometer demodulation system of this embodiment can also be applied to other interferometers with the same working principle as the F-P interferometer, such as Sagnac interferometer, Michelson interferometer, etc.
  • the optical fiber isolator, optical fiber coupler, interferometer, detector, linear transimpedance amplifier (not shown in the drawings), A/D analog-to-digital converter, D/A analog-to-digital converter, microprocessor (not shown in the drawings), and sawtooth wave driver are all suitable for the interferometric cavity length demodulation system of the present invention, and their installation method, control method, working principle, and setting parameters can all refer to the prior art, and can be implemented as long as the beneficial effects of the present invention can be achieved.
  • This embodiment 1 also provides a demodulation method of an interferometer absolute displacement demodulation system using a gas absorption spectrum reference, comprising the following steps:
  • S1 The scanning laser light source, under the control of the sawtooth wave driving circuit, outputs a laser beam with a wavelength that changes with time within a scanning cycle;
  • the laser beam in S1 is coupled to the fiber coupler after passing through the fiber isolator and output to the interferometer and the gas reference chamber respectively.
  • the interference reflected light generated by the interferometer returns through the fiber coupler and enters the signal detector; the interference reflected light generates interference fringes in the signal detector; the light beam transmitted through the gas reference chamber is connected to the reference detector and generates absorption spectrum lines synchronously in the reference detector;
  • S3 The detector collects the interference fringe signal and the absorption line signal generated in S2 and amplifies them respectively through the signal amplifier, and sends them to the microprocessor for signal strength normalization after analog-to-digital conversion;
  • S4 The microprocessor receives the interference fringe signal and the absorption spectrum line signal in S3, and calculates the interference cavity length of the interferometer and its change value through the pre-calibrated time-phase relationship.
  • the demodulation method of this embodiment adopts a scanning laser as the light source of the interferometer sensor, uses the absorption spectrum of a reference gas with an absorption peak within the wavelength scanning range of the scanning laser as the absolute spectrum reference position, and combines the fixed wavelength and half-width of the absorption spectrum line, or a calibration method for converting the time value to the phase value of two absorption spectrum lines, and uses the interference fringes themselves to complete the absolute value measurement of the interference cavity length; the present invention is applied to the interference sensor, and has the advantages of high resolution and high accuracy in measuring the absolute cavity length of the interference cavity.
  • the method for calibrating the pre-calibrated time-phase relationship and the method for demodulating the interferometric cavity length value and its change value are as follows:
  • the scanning laser light source under the control of the sawtooth wave driving circuit, outputs a laser beam whose wavelength changes with time within the actual scanning wavelength range;
  • the detector of the interferometer synchronously generates interference fringes and absorption spectra, and obtains the intensity curves of the corresponding interference fringes and absorption spectra changing with time; the half width of the absorption spectrum is used to calibrate the time axis, so as to obtain the proportional relationship of converting the time axis value into the wavelength value;
  • the proportional relationship of converting the time axis value into the wavelength value can also be obtained;
  • the minimum wavelength scanning range of the scanning laser can cover one or two absorption lines simultaneously in one scanning cycle; in 2), after obtaining the corresponding interference fringes and the intensity curves of the absorption lines changing with time, the half-width of the absorption lines is measured relative to the time axis, or the difference in the relative positions of the central wavelengths of the two absorption lines on the time axis is measured, and the proportional relationship between the time axis value and the wavelength value is obtained by using the known half-width of the absorption lines or the known difference in the central wavelengths of the two absorption lines, thereby completing the system calibration; in the measurement of 3), an interference fringe is measured.
  • the time difference between the Q point where the slope of the light intensity change is the largest and the wavelength center of the absorption spectrum is converted into the wavelength difference between the Q point and the wavelength center of the absorption spectrum.
  • the absolute wavelength value ⁇ corresponding to the Q point of the interference fringe is obtained by adding or subtracting this wavelength difference from the known central wavelength of the absorption spectrum; in the above 4), it is described how to obtain the absolute value of the interference cavity length L by measuring the time difference between the two Q points where the slope of the light intensity change of an interference fringe is the largest; in the above 5), if the interference fringe is shifted due to the change of the interference cavity length, the change value of the interference cavity length can be obtained as long as the phase difference between the Q point and the center point of the absorption spectrum is obtained.
  • the wavelength value corresponding to each point of the interference fringes and the central wavelength value of the absorption spectrum are relatively fixed at the corresponding position on the time axis and will not change.
  • the half-width of the absorption spectrum is also fixed on the time axis. In this way, the absolute wavelength value can be obtained using the absorption spectrum, and the time axis can be calibrated using the half-width of the absorption spectrum, so that the time axis value can be converted into a wavelength value.
  • the measured value of the wavelength difference ⁇ corresponding to the phase value difference between the two Q points of the interference fringe, or the wavelength difference corresponding to the half-width of the interference fringe can be obtained, and then used Thereby, the absolute measurement value of the interferometer cavity length L is further obtained.
  • the phase change value of the interference fringes Q point can be calculated by measuring the time difference between the Q point where the light intensity change slope of the interference fringes is the largest (as shown in Figure 3) and the center point of the absorption spectrum, and then using the calibration relationship between time and phase.
  • the measured value of the change in the interference cavity length ⁇ L can be obtained, thereby achieving the effect of demodulating the change in the interference cavity length from the interference fringe information.
  • the minimum wavelength scanning range of the scanning laser can simultaneously cover two absorption lines within one scanning cycle; in 3), after obtaining the intensity curves of the corresponding interference fringes and absorption lines changing with time, the data from the signal detector and the reference detector are normalized, and the time difference between the two Q points with the largest light intensity change slope of an interference fringe relative to the central wavelength of the absorption line is measured to obtain the measured value of the wavelength difference ⁇ corresponding to the phase value difference between the two Q points of the interference fringe, or the wavelength difference corresponding to the half-width of the interference fringe.
  • the wavelength scanning range of the VCSEL laser is expanded to about 2.73 nm to ensure that two absorption spectra are covered simultaneously within one scanning cycle; as shown in FIG4 , by measuring the relative positions of the two absorption spectra on the time axis and utilizing the fixed central wavelength characteristics of the two spectra, the time axis is calibrated and the time axis value can be converted into a wavelength value. Since the measurement error when calibrating with two absorption peaks is relatively small, this calibration method has higher accuracy.
  • the present invention can measure the absolute cavity length of the interference cavity by using one of the two calibration methods mentioned above.
  • the cavity length is called absolute length because the measurement process is based on the fixed wavelength of the absorption spectrum and the half-width of the spectrum, which are physical quantities that will not change under normal temperature and pressure conditions.
  • the two calibration methods can also be used at the same time to improve the measurement accuracy by cross-validation.
  • the sensing technology based on monochromatic light interferometry (as opposed to white light interferometry) in the prior art can only measure the relative length change ⁇ L (relative to an arbitrary initial value) and cannot determine the actual cavity length of the interference cavity.
  • the absolute interference cavity length measurement feature of the present invention is crucial for all applications requiring long-term static measurements.
  • the difference between the present embodiment 2 and the embodiment 1 is that the reference gas chamber 6 is provided inside the detector 5; the fiber coupler includes a 2 ⁇ 1 fiber coupler 32; the laser beam emitted by the scanning laser 1 is coupled to the first connection end 321 of the 2X1 fiber coupler 32 after passing through the fiber isolator 2, and is output from the second connection end 322 of the 2 ⁇ 1 fiber coupler 32 to enter the interferometer 4, and the interference reflected light generated by the interferometer 4 returns through the third connection end 323 of the 2 ⁇ 1 fiber coupler 32 to enter the detector 5 with the reference gas chamber 6 inside, and the detector 5 collects the interference fringe signal and the absorption spectrum line signal and amplifies them respectively through the signal amplifier, and sends them to the microprocessor for signal strength normalization processing after analog-to-digital conversion.
  • the detector 5 since a detector 5 having an internal reference gas chamber 6 is adopted, the detector 5 simultaneously collects interference fringe signals and absorption spectrum line signals and sends them after signal amplification and conversion.
  • the detector technology with its own reference gas chamber is independently developed (Chinese invention patent CN201810036930.0 A photoelectric detector with its own reference gas chamber and its preparation method) to design the interferometer absolute displacement demodulation system using the gas absorption spectrum reference, and the reference gas chamber is integrated into the detector, which can further simplify the interferometer demodulation device and make it more practical; and in a low-power, miniaturized, and lightweight interferometer sensor, the demodulator cost of the existing interferometer sensor is reduced and the structure of the entire detection device is simplified.
  • the method for pre-calibrating the time-phase relationship and demodulating the interference cavity length value and its change value may refer to Example 1.
  • this embodiment 3 provides an interferometer absolute displacement demodulation system multi-probe sensor multiplexing system and multi-channel detection using gas absorption spectrum reference on the basis of the above embodiments 1-2 to meet different needs.
  • the interferometer absolute displacement demodulation system further includes a 1 ⁇ 8 optical fiber splitter 7;
  • the optical fiber coupler 3 further includes a 1 ⁇ 2 optical fiber coupler 33;
  • the 1 ⁇ N fiber splitter is a 1 ⁇ 8 fiber splitter 7, as shown in FIG5 , and is composed of one 1 ⁇ 2 fiber coupler 33 and two 1 ⁇ 8 fiber splitters 7, as shown in FIG6 ;
  • the laser beam emitted by the scanning laser 1 is coupled to a first connection end 331 of a 1 ⁇ 2 fiber coupler 33 through the fiber isolator 2, and the second connection end 332 and the third connection end 333 of the 1 ⁇ 2 fiber coupler 33 are respectively connected to one of the 1 ⁇ 8 fiber splitters 7;
  • the 15 connection ends of the two 1 ⁇ 8 fiber splitters 7 are respectively connected to the first connection ends 321 of 15 2 ⁇ 1 fiber couplers 32;
  • the second connection end 322 of the 2 ⁇ 1 fiber coupler 32 is respectively connected to 15 F-P interferometers 4, and the third connection ends 323 of the 15 2 ⁇ 1 fiber couplers 32 are respectively connected to 15 signal detectors;
  • the 16th path of the 1 ⁇ 8 fiber splitter 7 is connected to a reference gas chamber 6 filled
  • the signals measured by all detectors are respectively amplified by a linear transimpedance amplifier, digitized by an analog-to-digital converter (A/D), and then output to the microprocessor for signal intensity normalization processing, and the absolute measurement value of the interference cavity length L of the interferometer and the measurement value of its change ⁇ L are calculated through the pre-calibrated time-phase relationship.
  • the output end of the microprocessor is connected to a digital-to-analog converter (D/A) for controlling the laser current driving circuit to achieve tuning of the VCSEL.
  • D/A digital-to-analog converter
  • the reference gas chamber can be provided inside the detector; using a detector with its own reference gas chamber, that is, the mediation system saves the need to separately divide one optical path to connect to a reference gas chamber filled with methane, but all 16 paths are connected to the corresponding detector, which adds one detection path compared to the implementation scheme of separately setting up a reference gas chamber to connect to the reference detector, so that the number of multiplexed multi-probe sensors of the entire system reaches 16.
  • the interferometer absolute displacement demodulation system using gas absorption spectrum reference is designed, and the reference gas chamber is integrated into the detector, which can further simplify the interferometer demodulation device and make it more practical; and in low-power, miniaturized, and lightweight interferometer sensors, the demodulator cost of existing interferometer sensors is reduced, and the entire detection device is simplified.
  • the number of multi-probe sensors multiplexed in this system can be further increased to meet the needs of different applications.
  • the method for pre-calibrating the time-phase relationship and demodulating the interference cavity length value and its change value may refer to Example 1.
  • the 1 ⁇ 8 optical fiber splitter may also be other optical fiber splitters that split no less than 2 paths, as long as they meet the technical solution of the present invention.
  • the present invention also provides a demodulation device of an interferometer absolute displacement demodulation system and method using a gas absorption spectrum reference, which uses an adjustable laser as a light source and a gas absorption spectrum as a reference, and calculates the absolute measurement value of the interference cavity length L of the interferometer and the measurement value of its change ⁇ L through a pre-calibrated time-phase relationship, thereby achieving high-efficiency, high-precision, low-power, and low-cost interference demodulation.
  • a gas absorption spectrum reference which uses an adjustable laser as a light source and a gas absorption spectrum as a reference, and calculates the absolute measurement value of the interference cavity length L of the interferometer and the measurement value of its change ⁇ L through a pre-calibrated time-phase relationship, thereby achieving high-efficiency, high-precision, low-power, and low-cost interference demodulation.

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Abstract

L'invention concerne un système et un procédé de démodulation de déplacement absolu d'interféromètre utilisant comme référence un spectre d'absorption de gaz. Le système de démodulation comprend un dispositif laser à balayage (1), un isolateur de fibre optique (2), un coupleur de fibre optique (3), un interféromètre (4), un détecteur de signal (51), un détecteur de référence (52), un amplificateur de signal, un microprocesseur et une chambre de gaz de référence (6), qui sont connectés dans un chemin optique, la chambre de gaz de référence (6) étant remplie d'un gaz de référence dont le pic d'absorption se situe dans la plage de balayage de longueur d'onde du dispositif laser à balayage (1). Dans le système et le procédé de démodulation au moyen du spectre d'absorption d'un gaz de référence dont le pic d'absorption se situe dans la plage de balayage en longueur d'onde du dispositif laser à balayage (1) comme emplacement de référence absolu du spectre, et en combinaison avec un procédé d'étalonnage pour transformer une longueur d'onde fixe d'une raie spectrale d'absorption et une demi-largeur de la raie spectrale, ou un espacement de longueur d'onde entre deux raies spectrales d'absorption, d'un axe de temps à un axe de longueur d'onde ou à un axe de phase, la mesure de la valeur absolue de la longueur de la cavité d'une cavité d'interférence est complétée au moyen de l'utilisation conjointe de points caractéristiques d'une frange d'interférence elle-même. Le système et le procédé de démodulation sont applicables à divers appareils de détection basés sur le principe de l'interférométrie, ce qui permet de réaliser une démodulation des interférences avec une grande efficacité, une grande précision, une faible consommation d'énergie et un faible coût.
PCT/CN2022/124758 2022-10-09 2022-10-12 Système et procédé de démodulation de déplacement absolu d'interféromètre utilisant comme référence un spectre d'absorption d'un gaz WO2024077503A1 (fr)

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