CN113009500B - Sweep frequency interference ranging system - Google Patents
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- CN113009500B CN113009500B CN202110224954.0A CN202110224954A CN113009500B CN 113009500 B CN113009500 B CN 113009500B CN 202110224954 A CN202110224954 A CN 202110224954A CN 113009500 B CN113009500 B CN 113009500B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
- G01S17/06—Systems determining position data of a target
- G01S17/08—Systems determining position data of a target for measuring distance only
- G01S17/32—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
- G01S17/36—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated with phase comparison between the received signal and the contemporaneously transmitted signal
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/481—Constructional features, e.g. arrangements of optical elements
- G01S7/4817—Constructional features, e.g. arrangements of optical elements relating to scanning
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Abstract
The embodiment of the disclosure provides a laser projection unit and a sweep frequency interference ranging system. A laser projection unit comprising: a tunable laser capable of outputting laser light of which wavelength continuously varies within a scanning band; a first light-splitting element configured to split the laser light output by the tunable laser into a first light beam and a second light beam, wherein the first light beam is used as a projection light beam output by the laser projection unit; the gas absorption pool is arranged on the transmission path of the second light beam, and gas with a series of narrow-band absorption peaks in the scanning wave band is arranged in the gas absorption pool; and a first photodetector configured to receive the second light beam passing through the gas absorption cell and convert an optical signal of the second light beam into an electrical signal.
Description
Technical Field
The disclosure relates to the technical field of optical measurement, in particular to a laser projection unit and a sweep frequency interference ranging system.
Background
The laser interferometry is an ultra-high precision method of distance measurement based on the principle of interference of light, i.e., two rows of light rays having the same frequency and a fixed phase difference will produce interference phenomena. The more common laser interferometry ranging system is a specific application of a laser interferometry, and the measuring principle is as follows: the single-wavelength laser emitted by the laser is divided into a reflected beam and a transmitted beam by the light splitting element, wherein one beam is reflected by the fixed reflector, the other beam is reflected by the reflector of the object to be detected, and the reflected beam are converged into a coherent beam at the light splitting element, so that interference fringes are generated on the observation surface. The distance from the fixed reflecting mirror to the light splitting element is defined as a fixed arm, the distance from the fixed reflecting mirror to the light splitting element is defined as a moving arm, and the stripe brightness is related to the distance difference between the fixed arm and the moving arm: when the distance difference between the fixed arm and the movable arm is an integral multiple of the wavelength, bright stripes are generated on the observation surface; when the distance difference between the fixed arm and the movable arm is an odd multiple of half wavelength, dark fringes are produced on the observation surface. The movement distance of the movable arm can be calculated by counting the brightness change. The measuring method has high precision, but can only measure the relative moving distance, but can not measure the absolute position, namely can only realize the relative distance measurement.
The laser sweep interference ranging system can realize absolute ranging, and has the advantages of large measuring range, no ranging blind area, no dependence on cooperative targets and the like. In the laser sweep interference ranging system, a semiconductor laser is often used, because the semiconductor laser has the advantages of fast scanning frequency, simple and flexible modulation mode, small size, low cost and the like. However, the semiconductor laser has a significant disadvantage in that its output wavelength continuously varies with current and temperature, and the control accuracy of the current and temperature is generally not more than 1%, so that the output wavelength of the semiconductor laser cannot be precisely determined, thereby introducing a measurement error into the ranging process.
Disclosure of Invention
An object of an embodiment of the present disclosure is to provide a laser projection unit and a swept interference ranging system, which can accurately determine an output wavelength of a laser. The specific technical scheme is as follows:
an embodiment of a first aspect of the present disclosure proposes a laser projection unit comprising: a tunable laser capable of outputting laser light of which wavelength continuously varies within a scanning band; a first light-splitting element configured to split the laser light output by the tunable laser into a first light beam and a second light beam, wherein the first light beam is used as a projection light beam output by the laser projection unit; the gas absorption pool is arranged on the transmission path of the second light beam, and gas with a series of narrow-band absorption peaks in the scanning wave band is arranged in the gas absorption pool; and a first photodetector configured to receive the second light beam passing through the gas absorption cell and convert an optical signal of the second light beam into an electrical signal.
According to the laser projection unit of the embodiment of the disclosure, when the laser projection unit works, the tunable laser outputs laser with continuously variable wavelength in a scanning wave band, the laser is divided into a first light beam and a second light beam by the first light splitting element, and the second light beam passes through the gas absorption tank and scans gas in the gas absorption tank in real time. Since the gas absorbs only light energy of a specific wavelength, it exhibits a series of narrow-band absorption peaks corresponding to the specific wavelength on the absorption spectrum. Thus, in the process of modulating the wavelength of the output laser light by the tunable laser, each time the wavelength of the laser light reaches a specific wavelength corresponding to the gas narrowband absorption peak, the electrical signal output by the first photodetector generates a dip peak, so that the first photodetector can accurately detect the moment when the laser wavelength reaches a plurality of specific wavelengths. That is, it can be considered that the wavelength of the projection light beam outputted from the laser projection unit is equal to the above-described specific wavelengths corresponding to the above-described several times, whereby an accurate determination of the laser wavelength is achieved. When the laser projection unit is applied to the laser scanning interference ranging system, the sampling time of the laser scanning interference ranging system can be set to be the time when the electric signal output by the first photoelectric detector has a dip peak, so that the laser wavelength corresponding to the data of the sampling point can be accurately determined, and the measuring error in the ranging process is effectively reduced.
In some embodiments of the present disclosure, the gas within the gas absorption cell comprises one or more of methane, ammonia, nitrogen, and carbon monoxide.
In some embodiments of the disclosure, the first light splitting element is a beam splitter, or an optical fiber is disposed between the tunable laser and the first light splitting element is a fiber optic beam splitter.
In some embodiments of the present disclosure, the laser projection unit further comprises a mirror configured to reflect the second light beam from the first light splitting element and transmitted in a first direction into a second direction such that the second light beam is transmitted in the second direction and passes through the gas absorption cell.
In some embodiments of the present disclosure, an optical fiber is disposed between the gas absorption cell and the first light splitting element.
In some embodiments of the present disclosure, the tunable laser is a semiconductor swept laser.
Embodiments of a second aspect of the present disclosure provide a swept frequency interferometric ranging system comprising: the laser projection unit according to any one of the above embodiments; the second light splitting element is configured to split the first light beam into a third light beam and a fourth light beam which is emitted to the object to be detected; a fixed mirror configured to reflect the third light beam to form a first reflected light beam directed toward the second light splitting element; the object to be measured reflecting mirror is configured to be arranged on an object to be measured and reflect the fourth light beam to form a second reflected light beam which is emitted to the second light splitting element and converged with the first reflected light beam at the second light splitting element; a second photodetector configured to receive a coherent light beam formed by the combination of a second reflected light beam and the first reflected light beam and to convert an optical signal of the coherent light beam into an electrical signal; and the sampling device is configured to sample the electric signal of the second photoelectric detector at the moment when the electric signal of the first photoelectric detector has a dip peak, and the data of the sampling points are used for determining the distance of an object to be detected.
The sweep frequency interference ranging system of the embodiment of the disclosure is characterized in that when the sweep frequency interference ranging system works, a tunable laser outputs laser with continuously variable wavelength in a scanning wave band, the laser is divided into a first beam and a second beam by a first beam splitting element, the first beam is further divided into a third beam and a fourth beam which is emitted to an object to be measured by a second beam splitting element, a fixed reflector reflects the third beam so as to form a first reflected beam, the object to be measured reflector arranged on the object to be measured reflects the fourth beam so as to form a second reflected beam, the first reflected beam and the second reflected beam are converged into a coherent beam at the second beam splitting element, and a second photoelectric detector receives the coherent beam and converts an optical signal of the coherent beam into an electric signal. In another aspect, the second light beam passes through the gas absorption cell and scans the gas in the gas absorption cell in real time. Since the gas absorbs only light energy of a specific wavelength, it exhibits a series of narrow-band absorption peaks corresponding to the specific wavelength on the absorption spectrum. Thus, in the process of modulating the wavelength of the output laser light by the tunable laser, each time the wavelength of the laser light reaches a specific wavelength corresponding to the gas narrowband absorption peak, the electrical signal output by the first photodetector generates a dip peak, so that the first photodetector can accurately detect the moment when the laser wavelength reaches a plurality of specific wavelengths. That is, it can be considered that the wavelength of the projection light beam outputted from the laser projection unit is equal to the above-described specific wavelengths corresponding to the above-described several times, whereby an accurate determination of the laser wavelength is achieved. Based on the method, the scanning interference ranging system is further provided with a sampling device, and the sampling device is configured to sample the electric signal of the second photoelectric detector at the moment when the electric signal of the first photoelectric detector has a dip peak, so that the laser wavelength corresponding to the data of the sampling point can be accurately determined. Furthermore, the distance of the object to be measured calculated according to the data of the sampling point is higher in accuracy.
In some embodiments of the present disclosure, the sampling device includes: a falling edge trigger electrically connected to the first photodetector, the falling edge trigger configured to emit a trigger signal when a dip spike occurs in an electrical signal of the first photodetector; and a high-speed analog-to-digital converter electrically connected to the falling edge trigger and the second photodetector, the high-speed analog-to-digital converter configured to sample an electrical signal of the second photodetector at a time when the trigger signal is received.
In some embodiments of the disclosure, the swept frequency interference ranging system further includes a digital processor electrically connected to the high-speed analog-to-digital converter, and the digital processor is configured to process data of the sampling point to obtain a distance of the object to be measured.
In some embodiments of the disclosure, the second light splitting element is a beam splitter, or an optical fiber is disposed between the first light splitting element and the second light splitting element is a fiber optic beam splitter.
Drawings
In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the drawings that are required for the embodiments or the description of the prior art will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present disclosure, and other embodiments may be obtained according to these drawings without inventive effort to a person of ordinary skill in the art.
FIG. 1 is a schematic diagram of a swept interference ranging system according to an embodiment of the disclosure;
FIG. 2 is an absorption spectrum of 1% methane gas (balance gas of nitrogen) around 1650 nm;
fig. 3 is a schematic diagram of a partial structure of a swept-frequency interferometric ranging system according to an embodiment of the disclosure.
Detailed Description
The following description of the technical solutions in the embodiments of the present disclosure will be made clearly and completely with reference to the accompanying drawings in the embodiments of the present disclosure, and it is apparent that the described embodiments are only some embodiments of the present disclosure, not all embodiments. Based on the embodiments in this disclosure, one of ordinary skill in the art would be able to devise all other embodiments that are derived from this application, which fall within the scope of this disclosure.
As shown in fig. 1, an embodiment of a first aspect of the present disclosure proposes a laser projection unit 10. The laser projection unit 10 comprises a tunable laser 11, a first spectroscopic element 12, a gas absorption cell 13 and a first photodetector 14. The tunable laser 11 is capable of outputting laser light S1 having a wavelength continuously varying in a scanning band, and the first spectroscopic element 12 is configured to separate the laser light S1 output by the tunable laser 11 into a first light beam S2 and a second light beam S3, wherein the first light beam S2 is a projection light beam output by the laser projection unit 10. The gas absorption cell 13 is disposed on a transmission path of the second light beam S3, the gas absorption cell 13 is filled with a gas having a series of narrowband absorption peaks in a scanning band, and the first photodetector 14 is configured to receive the second light beam S3 passing through the gas absorption cell 13 and convert an optical signal of the second light beam S3 into an electrical signal.
According to the laser projection unit 10 of the embodiment of the present disclosure, when in operation, the tunable laser 11 outputs laser light S1 with a wavelength continuously varying in a scanning band, the laser light S1 is split into a first light beam S2 and a second light beam S3 by the first light splitting element 12, and the second light beam S3 passes through the gas absorption cell 13 and scans the gas in the gas absorption cell 13 in real time. Since the gas absorbs only light energy of a specific wavelength, it exhibits a series of narrow-band absorption peaks corresponding to the specific wavelength on the absorption spectrum. Thus, in the wavelength modulation of the output laser light S1 by the tunable laser 11, each time the wavelength of the laser light S1 reaches a specific wavelength corresponding to the gas narrowband absorption peak, the electrical signal output from the first photodetector 14 is peaked, and thus, the timing at which the wavelength of the laser light S1 reaches several specific wavelengths can be accurately detected by the first photodetector 14. That is, it can be considered that the wavelength of the projection light beam output by the laser projection unit 10 is equal to the above-described several specific wavelengths, corresponding to the above-described several times, whereby an accurate determination of the wavelength of the laser light S1 is achieved. When the laser projection unit 10 is applied to the laser S1 sweep interference ranging system 1, the sampling time of the laser S1 sweep interference ranging system 1 can be set to be the time when the electrical signal output by the first photodetector 14 has a dip peak, so that the wavelength of the laser S1 corresponding to the data of the sampling point can be accurately determined, thereby effectively reducing the measurement error in the ranging process.
In some embodiments of the present disclosure, the gas within the gas absorption cell 13 includes one or more of methane, ammonia, nitrogen, and carbon monoxide. The following will be described by taking a combination of methane gas and nitrogen gas as an example:
FIG. 2 shows an absorption spectrum of 1% methane gas (nitrogen gas is used as balance gas) around 1650nm, which is a graph showing that the absorption spectrum contains a plurality of strong absorption peaks of 1644.73nm, 1647.44nm, 1650.16nm and the like, and an absorption peak appears at intervals of about 2.72nm, and the half-width is 0.08nm. The coverage range of the methane absorption spectrum line series is 1600-1650 nm. Since the absorption peak width is about 0.08nm, the calculation accuracy of the calculated laser S1 wavelength can reach 0.08nm.
In some embodiments of the present disclosure, the first beam splitter 12 is a beam splitter, which can split the laser light S1 into a first beam S2 and a second beam S3.
In other embodiments of the present disclosure, an optical fiber is disposed between the tunable laser 11 and the first light splitting element 12 is a fiber optic beam splitter. The arrangement of the optical fiber can construct a light transmission path for the laser S1 to transmit between the tunable laser 11 and the first spectroscopic element 12, and the light transmission path may be either linear or curved, so that the laser projection unit 10 is more flexible in structural arrangement. Based on the case of using an optical fiber as a light transmission path of the laser light S1, an optical fiber beam splitter may be used as the first spectroscopic element 12 to perform spectroscopic processing on the laser light S1.
In some embodiments of the present disclosure, the laser projection unit 10 further includes a mirror 15, the mirror 15 being configured to reflect the second light beam S3 coming from the first light splitting element 12 and transmitted in the first direction into the second direction, so that the second light beam S3 is transmitted in the second direction and passes through the gas absorption cell 13. In this embodiment, the transmission direction of the second light beam S3 can be changed by providing the reflecting mirror 15, and the changed direction (i.e., the second direction) can be selected according to the actual situation, which is advantageous for more flexibly arranging the positions of the gas absorption cell 13 and the first photodetector 14.
In other embodiments of the present disclosure, an optical fiber is provided between the gas absorption cell 13 and the first spectroscopic element 12, and since the optical fiber may be curved, by providing the optical fiber, an effect of changing the transmission direction of the second light beam S3 can also be obtained.
In some embodiments of the present disclosure, the tunable laser 11 is a semiconductor swept laser, which has advantages of fast scanning frequency, simple and flexible modulation, small size, low cost, and the like.
As shown in fig. 1, an embodiment of the second aspect of the present disclosure proposes a swept interference ranging system 1 including a laser projection unit, a fixed mirror 20, an object to be measured mirror 30, a second spectroscopic element 40, a second photodetector 50, and a sampling device 60. The laser projection unit is the laser projection unit 10 in any of the above embodiments. The second beam splitter 40 is configured to split the first beam S2 into a third beam S4 and a fourth beam S5 directed to the object to be measured, and the fixed mirror 20 is configured to reflect the third beam S4 to form a first reflected beam S6 directed to the second beam splitter 40. The object-to-be-measured mirror 30 is configured to be disposed on the object to be measured and reflect the fourth light beam S5 to form a second reflected light beam S7 that is directed to the second light-splitting element 40 and merges with the first reflected light beam S6 at the second light-splitting element 40. The second photodetector 50 is configured to receive a coherent light beam formed by combining the second reflected light beam S7 and the first reflected light beam S6, and to convert an optical signal of the coherent light beam into an electrical signal. The sampling device 60 is configured to sample the electrical signal of the second photodetector 50 at the moment when the electrical signal of the first photodetector 14 exhibits a dip spike, and the data of the sampling point is used to determine the distance of the object to be measured.
In the sweep interference ranging system 1 of the embodiment of the present disclosure, when in operation, the tunable laser 11 outputs laser light S1 with a wavelength continuously varying in a scanning band, the laser light S1 is split into a first beam S2 and a second beam S3 by the first beam splitter 12, the first beam S2 is further split into a third beam S4 and a fourth beam S5 directed to an object to be measured by the second beam splitter 40, the fixed mirror 20 reflects the third beam S4 to form a first reflected beam S6, the object to be measured mirror 30 disposed on the object to be measured reflects the fourth beam S5 to form a second reflected beam S7, the first reflected beam S6 and the second reflected beam S7 are then combined into a coherent beam S8 at the second beam splitter 40, and the second photodetector 50 receives the coherent beam S8 and converts an optical signal of the coherent beam S8 into an electrical signal.
On the other hand, the second light beam S3 passes through the gas absorption cell 13 and scans the gas in the gas absorption cell 13 in real time. Since the gas absorbs only light energy of a specific wavelength, it exhibits a series of narrow-band absorption peaks corresponding to the specific wavelength on the absorption spectrum. Thus, in the wavelength modulation of the output laser light S1 by the tunable laser 11, each time the wavelength of the laser light S1 reaches a specific wavelength corresponding to the gas narrowband absorption peak, the electrical signal output from the first photodetector 14 is peaked, and thus, the timing at which the wavelength of the laser light S1 reaches several specific wavelengths can be accurately detected by the first photodetector 14. That is, it can be considered that the wavelength of the projection light beam output by the laser projection unit 10 is equal to the above-described several specific wavelengths, corresponding to the above-described several times, whereby an accurate determination of the wavelength of the laser light S1 is achieved. Based on this, the swept interference ranging system 1 is further provided with a sampling device 60, where the sampling device 60 is configured to sample the electrical signal of the second photodetector 50 at the moment when the electrical signal of the first photodetector 14 has a dip peak, so that the wavelength of the laser S1 corresponding to the data of the sampling point can be accurately determined. Furthermore, the distance of the object to be measured calculated according to the data of the sampling point is higher in accuracy.
In order to better illustrate the beneficial effects of the embodiments of the present disclosure, the following describes the principle of ranging by using the swept laser S1 in conjunction with the swept interference ranging system 1 described above:
let the wave number of the laser S1 be k, and the modulation range of the wave number of the tunable laser 11 be k 1 To k 2 The output of the second photodetector 50 is I, which is a fixed arm Z r And a moving arm Z s Wherein the arm Z is fixed r Refers to the path taken by the first reflected beam S6 to the junction of the first reflected beam S6 and the second reflected beam S7 by the fixed mirror 20, and moves the arm Z s Refers to the path taken by the second reflected beam S7 to the junction of the first reflected beam S6 and the second reflected beam S7 by the object-to-be-measured mirror 30. For simplicity, the dc constant is omitted, and according to the interference principle of light, the output value is:
I(k,Z r ,Z s )＝Acos(2k(Z r -Z s ))
in ranging using the sweep method, the electronics control the tunable laser 11 wavenumber to scan with a triangle wave of about 1 Khz. Because the scanning speed is very fast and is far higher than the movement speed of the object to be detected, the moving arm Z is considered to be in each scanning s Is a fixed value, so k in the function is an independent variable, let θ=z r -Z s ，Z r Is of known value, θ is to be measured, and can be obtained
I(k)＝Acos(2θk)
The modulation range of the wavenumber of the tunable laser 11 is k 1 To k 2 It is contemplated that the signal from the second photodetector 50 is sampled N times during each scan cycle to perform a digital Fourier transform of N points, which results in
t is the sampling point ordinal number, Δk=k 2 -k 1 Is the modulation range of the wave number. The method can obtain:
the signal is analyzed by a digital Fourier transform FFT to obtain a frequency term f=2θ Δk/N, so that θ=fN/(2Δk) is obtained, and the distance of the object to be measured is further calculated by θ.
Based on the principle of the sweep laser S1 ranging, the resolution of the frequency term f is 1/N. 2ΔθΔk/n=1/N at the minimum resolution, Δθ=1/(2Δk). The measurement resolution of the system is thus the inverse of the modulation range of the 1/2 laser S1. Assuming that the wavelength modulation range of a certain tunable laser 11 is 1400-1600 nm, the modulation range of the wave number is k=6250-7142 cm -1 (note: wavenumber and wavelength are reciprocal relationships), Δk=892 cm -1 The resolution is Δθ=5.6 μm. In terms of measurement range, 2θΔk/N < pi/2, θ < pi×N/Δk/4. When n=16384, θ < 14cm, i.e. the maximum measurement range is 14cm.
In some embodiments of the present disclosure, the gas within the gas absorption cell 13 includes one or more of methane, ammonia, nitrogen, and carbon monoxide. Still taking the combination of methane gas and nitrogen gas as an example, 1% methane gas (taking nitrogen gas as balance gas) contains a plurality of strong absorption peaks of 1644.73nm, 1647.44nm, 1650.16nm and the like, and one absorption peak appears every about 2.72nm, and the half-peak width is 0.08nm. The coverage range of the methane absorption spectrum line series is 1600-1650 nm. Since the absorption peak width is about 0.08nm, the calculation accuracy of the calculated laser S1 wavelength can reach 0.08nm. The uncertainty in the amount of the modulation range ak of the wave number of the laser light S1 is reduced to the order of 50 ppm. It can be deduced that when measuring a distance of 10mm, the deviation due to the Δk error is only 10nm, thus greatly improving the measurement accuracy.
In some embodiments of the present disclosure, as shown in fig. 3, the sampling device 60 includes a falling edge trigger 61 and a high-speed analog-to-digital converter 62, the falling edge trigger 61 is electrically connected to the first photodetector 14, the falling edge trigger 61 is configured to emit a trigger signal when a dip spike occurs in the electrical signal of the first photodetector 14, the high-speed analog-to-digital converter 62 is electrically connected to the falling edge trigger 61 and the second photodetector 50, and the high-speed analog-to-digital converter 62 is configured to sample the electrical signal of the second photodetector 50 when the trigger signal is received. In this embodiment, the first photodetector 14 is connected to the second photodetector 50 through the falling edge trigger 61 and the high-speed analog-to-digital converter 62, and the falling edge trigger 61 can trigger the high-speed analog-to-digital converter 62 to sample the electrical signal of the second photodetector 50 at the moment when the electrical signal of the first photodetector 14 has a falling peak, so that not only can the accurate determination of the laser S1 wavelength corresponding to the data of the sampling point be ensured, but also the automatic control of the sampling process is realized, thereby being beneficial to improving the sampling efficiency.
In some embodiments of the present disclosure, the swept interference ranging system 1 further includes a digital processor 70, where the digital processor 70 is electrically connected to the high-speed analog-to-digital converter 62, and the digital processor 70 is configured to process the data of the sampling point to obtain the distance of the object to be measured.
In some embodiments of the present disclosure, the second beam splitting element 40 is a beam splitter that can split the first beam S2 into a third beam S4 and a fourth beam.
In other embodiments of the present disclosure, an optical fiber is disposed between the first and second light splitting elements 12, 40 and the second light splitting element 40 is a fiber optic beam splitter. The optical fibers may be arranged to form a light conducting path for the first light beam S2 to pass between the first light splitting element 12 and the second light splitting element 40, and the light conducting path may be either linear or curved, which is beneficial to making the structure arrangement of the swept interference ranging system 1 more flexible. Based on the case of using an optical fiber as the light transmission path of the first light beam S2, an optical fiber beam splitter may be used as the second light splitting element 40 to perform the light splitting process on the laser light S1.
An embodiment of a third aspect of the present disclosure proposes a ranging method, including:
generating a laser beam S1 with a continuously variable wavelength, and dividing the laser beam S1 into a first beam S2 and a second beam S3;
the first light beam S2 is further divided into a third light beam S4 and a fourth light beam S5, and the third light beam S4 is directed to the fixed mirror 20 provided at a predetermined distance, and the fourth light beam S5 is directed to the object mirror 30;
receiving the first reflected light beam S6 from the fixed mirror 20 and the second reflected light beam S7 from the object-to-be-measured mirror 30, and converging the first reflected light beam S6 and the second reflected light beam S7 into a coherent light beam S8;
converting the coherent light beam S8 into a first electrical signal;
passing the second light beam S3 through a gas having a series of narrowband absorption peaks and converting the second light beam S3 passing through the gas into a second electrical signal;
sampling the first electrical signal at the moment when the second electrical signal has a dip peak, and recording the wavelength of the second light beam S3 at the moment;
and processing the data of the sampling point and the recorded wavelength data of the second light beam S3 to obtain the distance of the object to be measured.
According to the ranging method of the embodiment of the present disclosure, the laser light S1 is divided into a first light beam S2 and a second light beam S3, wherein the first light beam S2 is used for being projected to the fixed mirror 20 and the object mirror 30 and forming a coherent light beam S8 after being reflected, and the second light beam S3 passes through a gas having a series of narrow-band absorption peaks. The coherent light beam S8 is converted into a first electrical signal, and the second light beam S3 passing through the gas is converted into a second electrical signal, and the first electrical signal is sampled at the moment when the second electrical signal exhibits a dip peak, while the wavelength of the second light beam S3 is recorded at the moment. Through the process, the corresponding laser S1 wavelength of the data of the sampling point can be accurately determined, so that the distance of the object to be detected calculated according to the data of the sampling point has more accurate precision.
In some embodiments of the present disclosure, the processing the sampled data and the recorded wavelength data of the second light beam S3 includes:
performing fast digital Fourier transform on the data of the sampling points to obtain a frequency domain diagram;
finding the maximum value of the frequency f according to the frequency domain diagram;
calculating theta according to the following formula, and obtaining the distance of the object to be detected according to the distance;
where θ represents the difference between the fixed arm and the movable arm, where the fixed arm refers to the distance traveled by the first reflected beam S6 transmitted by the fixed mirror 20 to the junction of the first reflected beam S6 and the second reflected beam S7, the movable arm refers to the distance traveled by the second reflected beam S7 transmitted by the object mirror 30 to the junction of the first reflected beam S6 and the second reflected beam S7, f is a frequency term obtained by performing the fast digital fourier transform on the data of the employed point, N represents the number of sampling points, and Δk represents the modulation range of the wave number of the laser S1.
In some embodiments of the present disclosure, the modulation range Δk of the wavenumber is found by the following equation:
wherein t represents the ordinal number of the sampling point, k t The wave number, k, of the laser S1 corresponding to the data representing the t-th sampling point 1 The laser S1 wave number corresponding to the data representing the 1 st sampling point.
According to the principle of the sweep laser S1 ranging described above, it is known that,
thus, the calculation formula for Δk can be obtained as:
it is noted that relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
The various embodiments of the disclosure are described in a related manner, and identical and similar parts of the various embodiments are all mutually referred to, and each embodiment is mainly described in terms of differences from other embodiments.
The foregoing description is only of the preferred embodiments of the present disclosure, and is not intended to limit the scope of the present disclosure. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present disclosure are included in the protection scope of the present disclosure.
Claims (8)
1. A swept frequency interferometric ranging system, comprising:
the laser projection unit comprises a tunable laser, a first light splitting element, a gas absorption cell and a first photoelectric detector; the tunable laser can output laser with continuously variable wavelength in a scanning wave band; the first light splitting element is configured to split the laser light output by the tunable laser into a first light beam and a second light beam, wherein the first light beam is used as a projection light beam output by the laser projection unit; the gas absorption tank is arranged on the transmission path of the second light beam, and gas with a series of narrow-band absorption peaks in the scanning wave band is arranged in the gas absorption tank; the first photodetector is configured to receive the second light beam passing through the gas absorption cell and convert an optical signal of the second light beam into an electrical signal;
a second light-splitting element configured to split the first light beam into a third light beam and a fourth light beam directed to an object to be measured;
a fixed mirror configured to reflect the third light beam to form a first reflected light beam directed toward the second light splitting element;
the object to be measured reflecting mirror is configured to be arranged on an object to be measured and reflect the fourth light beam to form a second reflected light beam which is emitted to the second light splitting element and converged with the first reflected light beam at the second light splitting element;
a second photodetector configured to receive a coherent light beam formed by the combination of a second reflected light beam and the first reflected light beam and to convert an optical signal of the coherent light beam into an electrical signal; a kind of electronic device with high-pressure air-conditioning system
The sampling device is configured to sample the electric signal of the second photoelectric detector at the moment when the electric signal of the first photoelectric detector has a dip peak, and the data of the sampling point are used for determining the distance of an object to be detected; the sampling device comprises a falling edge trigger and a high-speed analog-to-digital converter; the falling edge trigger is electrically connected with the first photoelectric detector and is configured to emit a trigger signal when the electrical signal of the first photoelectric detector is subjected to a falling peak; the high-speed analog-to-digital converter is electrically connected with the falling edge trigger and the second photodetector, and is configured to sample an electrical signal of the second photodetector at a time when the trigger signal is received.
2. The swept interference ranging system of claim 1, wherein the gas within the gas absorption cell comprises one or more of methane, ammonia, nitrogen, and carbon monoxide.
3. A swept interference ranging system according to claim 1, wherein the first beam splitting element is a beam splitter, or wherein an optical fiber is disposed between the tunable laser and the first beam splitting element is a fiber optic beam splitter.
4. A swept interference distance measuring system according to claim 1, wherein the laser projection unit further comprises a mirror configured to reflect the second light beam from the first light splitting element and transmitted in a first direction into a second direction such that the second light beam is transmitted in the second direction and passes through the gas absorption cell.
5. A swept interference ranging system as claimed in claim 1, wherein an optical fiber is provided between the gas absorption cell and the first spectroscopic element.
6. A swept interference ranging system according to any one of claims 1 to 5, wherein the tunable laser is a semiconductor swept laser.
7. The swept interference ranging system of claim 1, further comprising a digital processor electrically coupled to the high speed analog to digital converter, the digital processor configured to process the data at the sampling point to obtain the distance of the object to be measured.
8. A swept interference ranging system according to claim 1, wherein the second light splitting element is a beam splitter, or an optical fiber is disposed between the first light splitting element and the second light splitting element is an optical fiber beam splitter.
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