Ranging method and device based on FMCW and dual-wavelength interference

Abstract

The invention relates to the technical field of laser ranging, in particular to a ranging method and device based on FMCW and dual-wavelength interference. The method comprises the steps of obtaining a first distance value obtained when the distance of a to-be-measured target is measured based on an FMCW distance measurement method, and determining a distance truth value range in combination with the distance measurement precision of the FMCW distance measurement method; obtaining a second distance value containing interference fringe series obtained when the distance of the to-be-measured target is measured based on the dual-wavelength interference ranging method; determining the value of the interference fringe series according to the distance truth value range and the second distance value; and substituting the value into the second distance value to obtain an absolute distance value of the to-be-measured target. According to the invention, the range of the distance value to be measured is reduced to the range of interference distance measurement by adopting FMCW distance measurement, then high-precision distance measurement in a small range is realized by utilizing interference distance measurement, and the measurement speeds of the FMCW distance measurement and the interference distance measurement are relatively high, so that the high measurement speed is realized. Therefore, the distance measurement method can realize high-speed, wide-range and high-precision distance measurement.

Description

Technical Field

[0001] The present invention relates to the technical field of laser ranging, and in particular to a ranging method and device based on FMCW and dual-wavelength interference. Background Art

[0002] At present, laser ranging is one of the most advanced technologies in the field of ranging. It has the advantages of non-contact, fast measurement speed, high measurement accuracy and large range. It is widely used in remote sensing, surveying and mapping, automated warehouses, robots, industrial automation and machining and other fields. However, the ranging accuracy, range and speed of laser distance sensors are mutually restricted. It is difficult for the same laser ranging sensor to have the three important functions of high precision, large range and fast measurement.

[0003] The existing laser ranging technology solutions mainly include time-of-flight ranging, frequency-modulated continuous wave ranging and laser interferometer ranging. The basic principles and main defects of these solutions are as follows:

[0004] 1. Time-of-flight ranging mainly relies on the time it takes for a laser pulse to return from a target object to calculate the distance. On the one hand, since the speed of light is very fast, it is difficult to detect the time it takes for the light to return, especially at close range; on the other hand, since general objects are diffusely reflected, the light that can be received by the detector is very weak, which also brings great difficulty to detection, especially at a long distance. Therefore, in order to achieve higher measurement accuracy, multiple measurements are usually required, and higher-precision measurement results can only be obtained based on the statistical values ​​of a large number of measurement results. This makes it difficult for the time-of-flight ranging method to take into account both measurement accuracy and measurement speed. At the same time, since the intensity of the received diffusely reflected light is inversely proportional to the square of the distance, it is difficult for time-of-flight ranging to achieve a large range.

[0005] 2. Frequency Modulated Continuous Wave (FMCW) ranging uses a beam of local oscillator light to mix with the signal light reflected by the object, amplifies the signal light and then detects it. Therefore, it can detect weak signals, and the detection range is relatively large, and it naturally has the characteristics of a large range. However, due to the limitations of frequency modulation nonlinearity, laser phase noise and hardware computing power, its ranging accuracy is usually difficult to break through the order of optical wavelength. In order to further improve the accuracy, it is also necessary to use the method of using multiple measurements to obtain statistical values. Since the amount of calculation required for frequency modulated continuous wave ranging itself is relatively large, multiple measurements will consume a lot of time, resulting in a slow measurement speed;

[0006] 3. Laser interferometer distance measurement uses the interference of two beams of light to measure distance. Since the interference of light is very sensitive to distance changes, the distance measurement accuracy of laser interferometer is very high, and it naturally has the characteristics of high precision. At the same time, since only the light intensity after interference needs to be measured to obtain the distance, the measurement speed is also very fast. However, the range of laser interferometer is usually very small, mainly because light is an electromagnetic wave, and its interference changes periodically with distance, and the change period is the wavelength of light. Since the wavelength of light is very short, it is easy to fold the distance, that is, different distances but the same signal, and the absolute distance cannot be obtained. Summary of the invention

[0007] In view of this, the present invention provides a distance measurement method and device based on FMCW and dual-wavelength interference to solve one of the problems existing in the above-mentioned prior art.

[0008] In a first aspect, the present invention provides a ranging method based on FMCW and dual-wavelength interference, the method comprising: obtaining a first distance value obtained when measuring the distance of a target to be measured based on the FMCW ranging method, and determining a distance true value range in combination with the ranging accuracy of the FMCW ranging method; obtaining a second distance value including an interference fringe order obtained when measuring the distance of the target to be measured based on the dual-wavelength interference ranging method; determining a value of the interference fringe order according to the distance true value range and the second distance value; and substituting the value into the second distance value to obtain an absolute distance value of the target to be measured.

[0009] In the present invention, FMCW distance measurement is first used to narrow the range of the distance value to be measured to the range of interference distance measurement, and then interference distance measurement is used to achieve high-precision distance measurement within a small range. The measurement speeds of both are relatively fast, thereby achieving a high measurement speed. Therefore, the distance measurement method can achieve high-speed, large-range, and high-precision distance measurement.

[0010] In an optional implementation, the second distance value is expressed by the following formula:

[0011]

[0012] Where M represents the unknown interference fringe order, λ 1 and λ 2 They represent the wavelengths of the two lights used in dual-wavelength interference, L lo Indicates the reference path length.

[0013] In an optional embodiment, obtaining a second distance value including the interference fringe order when measuring the distance of a target to be measured based on a dual-wavelength interference ranging method includes: changing the reference path length, and using the dual-wavelength interference ranging method to measure multiple first interference light intensity signals corresponding to different reference path lengths; using theoretical calculations to obtain multiple second interference light intensity signals when the optical path difference between the reference path and the measurement path changes during dual-wavelength interference; matching the multiple first interference light intensity signals with the multiple second interference light intensity signals, and determining the second distance value including the interference fringe order based on the matching result.

[0014] In the present invention, the result of dual-wavelength interferometry is determined by sliding matching the measured data and the theoretical data, thereby reducing the interference of local noise on the measurement result and further improving the accuracy of the interferometric measurement.

[0015] In an optional embodiment, multiple first interference light intensity signals and multiple second interference light intensity signals are matched, and a second distance value containing unknown interference fringe orders is determined based on the matching results, including: sliding matching a curve formed by the multiple first interference light intensity signals on a curve formed by the multiple second interference light intensity signals to determine the position with the highest overlap; and determining the second distance value containing the interference fringe order based on the position with the highest overlap and the step size when changing the reference path length.

[0016] In an optional implementation, the overlap degree is calculated using the following formula:

[0017]

[0018] Where D i Represents the first interference light intensity signal, I i represents the second interference light intensity signal, n represents the number of first interference light intensity signals, and m represents the number of second interference light intensity signals.

[0019] In the present invention, the overlap calculation is performed using this formula, thereby being able to more accurately analyze the overlap and thereby determine the position with the highest overlap.

[0020] In an optional implementation, the second distance value is expressed by the following formula:

[0021]

[0022] Where M represents the interference fringe order, λ 1 and λ 2 They represent the wavelengths of the two lights used in dual-wavelength interference, L o represents the reference path length before the change, d represents the step size when changing the reference path length, k max Denotes δ 1 , δ2 , δ 3 , ..., δ m-n The optical path difference corresponding to the maximum value.

[0023] In the present invention, by adopting the formula to calculate the measured distance, a more accurate measurement result can be obtained.

[0024] In an optional implementation, before determining the value of the unknown interference fringe order according to the distance true value range and the second distance value, the method further includes: acquiring a first ranging error of the FMCW ranging method and a second ranging error of the dual-wavelength interference ranging method; and correcting the first distance value using the first ranging error, and correcting the second distance value using the second ranging error.

[0025] In the present invention, the measurement results of the FMCW ranging method and the dual-wavelength interference ranging method are corrected, thereby further improving the accuracy of the measurement results.

[0026] In a second aspect, the present invention provides a distance measuring device based on FMCW and dual-wavelength interference, the device comprising: a first distance acquisition module, used to obtain a first distance value obtained when measuring the distance of a target to be measured based on the FMCW ranging method, and determine the distance true value range in combination with the ranging accuracy of the FMCW ranging method; a second distance acquisition module, used to obtain a second distance value including an interference fringe order obtained when measuring the distance of the target to be measured based on the dual-wavelength interference ranging method; a value determination module, used to determine the value of the interference fringe order according to the distance true value range and the second distance value; an absolute distance calculation module, used to substitute the value into the second distance value to obtain the absolute distance value of the target to be measured.

[0027] In an optional embodiment, the device also includes: a first laser, a second laser, a combiner, a first optical splitter, a transceiver, a first mixer, a first detector and a signal processing module, wherein the output end of the first laser and the output end of the second laser are both connected to the input end of the combiner, the output end of the combiner is connected to the input end of the first optical splitter, the first output end of the first optical splitter is connected to one end of the transceiver, the second output end of the first optical splitter is connected to the first input end of the first mixer, the other end of the transceiver is connected to the second input end of the first mixer, the output end of the first mixer is connected to the input end of the first detector, and the output end of the first detector is connected to the signal processing module; when the FMCW ranging method is used for ranging, the first laser or the second laser is turned on to output a frequency modulation signal; when the dual-wavelength interference ranging method is used for ranging, the first laser and the second laser are turned on to output two optical signals with different wavelengths.

[0028] In the present invention, by using the same set of devices to perform FMCW ranging and dual-wavelength interference ranging, there is no need to switch hardware, only the software control needs to be switched, the measurement speed is fast, and it can be ensured that the results measured by the two measurement methods are the measurement of the same distance, thereby compensating for each other's measurement shortcomings.

[0029] In an optional embodiment, the device also includes: an adjustable delay line, a second spectrometer, a second mixer and a second detector; one end of the adjustable delay line is connected to the second output end of the first spectrometer, the other end of the adjustable delay line is connected to the input end of the second spectrometer, the two output ends of the second spectrometer are respectively connected to the first input end of the first mixer and the first input end of the second mixer, the third output end of the first spectrometer is connected to the second input end of the second mixer, the output end of the second mixer is connected to one end of the second detector, and the other end of the second detector is connected to the signal processing module.

[0030] In the present invention, by setting structures such as an adjustable delay line, a second optical splitter, a second mixer and a second detector, the determination of the measurement error is achieved, so that the same set of devices can be used to achieve measurement and correction. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 is a flow chart of a distance measurement method based on FMCW and dual-wavelength interference according to an embodiment of the present invention;

[0033] Figure 2 is a flow chart of dual-wavelength interferometry ranging of a ranging method based on FMCW and dual-wavelength interferometry according to an embodiment of the present invention;

[0034] Figure 3 is a schematic diagram of a curve showing a change in a theoretical interference light intensity signal along with a relative optical path difference between a reference arm and a measurement arm according to an embodiment of the present invention;

[0035] Figure 4 is a schematic diagram of a curve showing a change in an interference light intensity signal as the optical path length of a reference arm changes when there is no noise according to an embodiment of the present invention;

[0036] Figure 5 is a schematic diagram of a curve showing a change in an interference light intensity signal as the optical path length of a reference arm changes when noise exists according to an embodiment of the present invention;

[0037] Figure 6 is a schematic diagram of sliding matching between a variation curve without noise and a theoretical curve according to an embodiment of the present invention;

[0038] Figure 7 is a schematic diagram of sliding matching between a variation curve with noise and a theoretical curve according to an embodiment of the present invention;

[0039] Figure 8 is a structural block diagram of a distance measuring device based on FMCW and dual-wavelength interference according to an embodiment of the present invention;

[0040] Fig. 9 is a structural schematic diagram of a distance measuring device based on FMCW and dual-wavelength interference according to an embodiment of the present invention;

[0041] Fig.10 is a structural schematic diagram of another distance measuring device based on FMCW and dual-wavelength interference according to an embodiment of the present invention;

[0042] Fig.11 is a schematic diagram of the structure of a core optical chip according to an embodiment of the present invention;

[0043] Fig.12 is a schematic diagram of the packaging structure of a distance measuring device based on FMCW and dual-wavelength interference according to an embodiment of the present invention;

[0044] Fig.13 It is a schematic diagram of the hardware structure of a computer device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0046] According to an embodiment of the present invention, an embodiment of a ranging method based on FMCW and dual-wavelength interference is provided. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0047] In this embodiment, a distance measurement method based on FMCW and dual-wavelength interference is provided, which can be used in electronic devices such as computers, mobile phones, tablet computers, etc. Figure 1is a flow chart of a distance measurement method based on FMCW and dual-wavelength interference according to an embodiment of the present invention, such as Figure 1 As shown, the process includes the following steps:

[0048] Step S101, obtaining a first distance value obtained when measuring the distance of a target to be measured based on an FMCW ranging method, and determining a true value range of the distance in combination with the ranging accuracy of the FMCW ranging method.

[0049] Specifically, the distance measurement principle of FMCW is as follows: a triangular wave (or other types, such as sawtooth wave, sine wave, etc.) linear frequency modulation signal is loaded to the laser, so that the frequency of the laser changes over time according to the triangular wave law. The period of the triangular wave is T, and the frequency change amplitude of the triangular wave is B. The laser output by the laser is divided into two beams, one beam is used as the local oscillator light and directly enters the mixer, and the other beam is used as the measurement light, which is emitted to the target to be measured. After being reflected by the target, it is received and transmitted to the mixer to mix with the local oscillator light. The mixed signal is usually received by a balanced photodetector and converted into an electrical signal. After the electrical signal is amplified by the amplifier circuit, it is sampled by the analog-to-digital converter to obtain a digital signal, and then the spectrum of the digital signal is calculated by Fourier transform or other calculation methods. The frequency value f of the signal peak is found through the spectrum, and then the first distance value L1 is calculated by the following formula:

[0050] L1=f / B*T*c / 4

[0051] In the formula, c represents the speed of light.

[0052] It should be noted that, in this embodiment, the FMCW device in the related art can be directly used to measure the distance of the target to be measured, and the target to be measured can be any object, that is, the distance measurement method of this embodiment can be applied in any scene to achieve distance measurement of any object. Therefore, in practical applications, this embodiment does not specifically limit the target to be measured. At the same time, when the FMCW device is used for distance measurement, the distance measurement accuracy of the device can also be obtained based on the device's manual or technical manual, and the distance measurement accuracy can also be calculated by the calculation formula of the distance measurement accuracy in the related art. This embodiment does not specifically limit the method for obtaining the distance measurement accuracy.

[0053] After the first distance value of the target to be measured is measured by the FMCW ranging method, the true range of the distance is determined based on the corresponding ranging accuracy. For example, if the first distance value measured is L1 and the ranging accuracy is δ, the true range of the distance is between L1-δ and L1+δ.

[0054] Step S102, obtaining a second distance value including the interference fringe order obtained when measuring the distance of the target to be measured based on the dual-wavelength interference ranging method.

[0055] Step S103, determining a value of the interference fringe order according to the true distance range and the second distance value.

[0056] Step S104: Substitute the value into the second distance value to obtain the absolute distance value of the target to be measured.

[0057] Among them, laser interferometry ranging methods include single-wavelength interferometry ranging, dual-wavelength interferometry ranging, and multi-wavelength interferometry ranging. The principle of laser interferometry ranging is that the laser frequency remains unchanged, and the output light is divided into two paths, one is the reference light and the other is the detection light. The detection light is emitted to the target to be measured, and is received after being reflected by the target, and mixed with the reference light, and then received by the detector and converted into an electrical signal. After the electrical signal is amplified by the amplifier circuit, it is sampled by the analog-to-digital converter to obtain a digital signal. Changing the optical path of the reference path will change the size of the final digital signal. When the digital signal reaches the maximum value, the optical path length of the reference path is l. According to the interference principle, the difference between the optical path length of the reference path and the distance length of the target to be measured is equal to an integer multiple of the wavelength of light.

[0058] Specifically, for single-wavelength interference, the electric field intensity of the reference path (the optical path formed by the reference beam) is The electric field strength of the measurement path (the light path formed by the target reflected light beam) is The detector detects light intensity of

[0059] The reference path amplitude A lo , the wavelength λ is known, and the reference path length L is changed lo The light intensity I shows periodic changes. According to the characteristics of the cosine function, when the light intensity I is the maximum, there is:

[0060]

[0061] Where N is an integer. The distance to be measured can be calculated: L rx =Nλ+L lo .

[0062] Specifically, if the first distance value L1=11030um is obtained by measuring the target using the FMCW ranging method, and the ranging accuracy δ is 20um, the true distance value range is between 11010 and 11050um. Based on the single-wavelength ranging principle, if a 1.55um laser is used to measure the same target again using the single-wavelength interference method, according to the above single-wavelength interference ranging principle, the result obtained may be N*1.55+165um. It can be found that any value between 6983 and 7009 of N meets the FMCW measurement result, and the value of N cannot be determined.

[0063] When dual-wavelength interferometry is used for ranging, the two lights will not interfere due to their different wavelengths, and the light intensity detected on the detector is the sum of the light intensities of the two wavelengths, that is:

[0064]

[0065] Change L lo The light intensity I shows periodic changes. According to the characteristics of the cosine function, when the light intensity I is the maximum, there is:

[0066]

[0067] and

[0068]

[0069] Where M and N are integers. The second distance value can be calculated:

[0070] If the dual-wavelength interferometric ranging method is used to measure the same target, the distances obtained based on the two measurements are equal, that is, It can be seen that the interference fringe order Therefore, combined with M being an integer, we can get the exact value of M and substitute it into the second distance value In order to obtain the absolute distance value.

[0071] Specifically, based on the dual-wavelength ranging principle, if the target is measured again using the dual-wavelength interference method using lasers with two wavelengths of 1.55um and 1.5um, the result may be M*[1.55*1.5 / (1.55-1.5)]+184um, that is, M*46.5+184um. At this time, only when M=233, it conforms to the FMCW measurement result. Therefore, the value of M is determined to be 233, and the final distance value can be obtained as 11018.5um. In addition, the true value of the distance measured by other methods is 11019um. It can be seen that the error between the distance measurement value and the true value is reduced to 0.5um compared with the error (11um) using only the FMCW method.

[0072] The distance measurement method based on FMCW and dual-wavelength interference provided by the embodiment of the present invention first uses FMCW distance measurement to narrow the range of the distance value to be measured to the range of interference distance measurement, and then uses interference distance measurement to achieve high-precision distance measurement within a small range. The measurement speeds of both are relatively fast, thereby achieving a high measurement speed. Therefore, the distance measurement method can achieve high-speed, large-range, and high-precision distance measurement.

[0073] In this embodiment, a distance measurement method based on FMCW and dual-wavelength interference is provided, and the method comprises the following steps:

[0074] Step S201, obtain a first distance value obtained when measuring the distance of the target to be measured based on the FMCW ranging method, and determine the true value range of the distance in combination with the ranging accuracy of the FMCW ranging method. Figure 1 Step S101 of the illustrated embodiment will not be described in detail here.

[0075] Step S202, obtaining a second distance value including the interference fringe order obtained when measuring the distance of the target to be measured based on the dual-wavelength interference ranging method. In the interference ranging, the distance value is determined by the signal strength, and the detection of the signal strength is easily interfered by noise. The noise on the strength will cause the error of the ranging result. In view of this, when the dual-wavelength interference ranging is based on the law of the dual-wavelength interference intensity change, the interference signal intensity change curve is used to determine the distance, thereby reducing the noise interference and improving the accuracy of the ranging result.

[0076] Specifically, Figure 2 As shown, the above step S202 includes:

[0077] Step S2021, change the reference path length, and use a dual-wavelength interference ranging method to measure multiple first interference light intensity signals corresponding to different reference path lengths; specifically, a dual-wavelength interference system with an adjustable reference arm can be used to achieve the change of the reference path length during measurement. For example, an adjustable delay line can be set in the reference path to achieve the change of the reference path length. When changing the reference path length, it can be increased linearly in a step size d. For example, if the initial reference path length is l0, the reference path length after each change is l0+d, l0+2d, l0+3d, etc. In this embodiment, the reference path length is increased to At the same time, in the process of changing the reference path length, the interference light intensity signal is collected and normalized to obtain n first interference light intensity signals, which are represented as D 1 , D 2 , D 3 , ..., D n .

[0078] Step S2022, using a theoretical calculation of multiple second interference light intensity signals when the optical path difference between the reference path and the measuring path changes during dual wavelength interference. When using interference distance measurement, the principle is to measure the distance based on the change in the optical path difference between the reference light and the measuring light. Therefore, in this step, the change in the interference light intensity signal when the optical path difference changes is analyzed theoretically. Specifically, the optical path difference between the reference arm and the measuring arm is increased from 0 to 1000 by a step length d by theoretical calculation. The variation curve of the interference light intensity signal in the process is obtained by normalization processing to obtain m data (m is greater than n, so as to facilitate subsequent matching), and the m data are m second interference light intensity signals, and are respectively represented as I 1 , I 2, I 3 , ..., I n .

[0079] Step S2023, matching the plurality of first interference light intensity signals with the plurality of second interference light intensity signals, and determining a second distance value including the interference fringe order based on the matching result.

[0080] In an optional implementation, the above step S2023 includes:

[0081] Step a1, slidingly matching the curve formed by the plurality of first interference light intensity signals on the curve formed by the plurality of second interference light intensity signals, and determining the position with the highest overlap. Specifically, since the number of the second interference light intensity signals is greater than the number of the first interference light intensity signals, the curve formed by the first interference light intensity signals can be slidingly matched on the curve formed by the first interference light intensity signals, and determining the position with the highest overlap between the two. The sliding matching process can be calculated using the following formula:

[0082]

[0083] Where D i Represents the first interference light intensity signal, I i represents the second interference light intensity signal, n represents the number of the first interference light intensity signal, and m represents the number of the second interference light intensity signal. Based on this formula, mn data can be calculated and recorded as: 1 , δ 2 , δ 3 , ..., δ m-n-1 Then determine the largest data from these mn data, and use the corresponding optical path difference as the position with the highest overlap, and record it as k max .

[0084] Step a2, determining a second distance value including the interference fringe order based on the position with the highest overlap and the step length when changing the reference path length. Specifically, the second distance value is expressed by the following formula:

[0085]

[0086] Where M represents the interference fringe order, λ 1 and λ 2 They represent the wavelengths of the two lights used in dual-wavelength interference, L o represents the reference path length before the change, d represents the step size when changing the reference path length, k max Denotes δ 1 , δ 2 , δ 3 , ..., δ m-nThe optical path difference corresponding to the maximum value.

[0087] In a specific implementation, the dual-wavelength interferometric ranging method is described by taking the two wavelengths of 1.55um and 1.5um as examples:

[0088] Theoretically calculate multiple second interference light intensity signals when the optical path difference between the reference path and the measurement path changes during dual-wavelength interference, and normalize the multiple second interference light intensity signals to form a curve of normalized intensity versus relative optical path difference dl between the reference path and the measurement path, i.e., a theoretical curve, such as Figure 3 shown.

[0089] By changing the reference path length, a dual-wavelength interferometric ranging method is used to measure multiple first interference light intensity signals corresponding to different reference path lengths, and after normalizing the multiple first interference light intensity signals, a curve of normalized intensity versus reference path (reference arm) optical path change l is formed. Figure 4 As shown in the figure, the change curve is the curve when there is no noise. From the figure, we can find the position with the maximum intensity to calculate the distance. The position with the maximum distance is 26.5um. However, when there is noise, the change curve is as follows Figure 5 As shown, based on this, when determining the position where the intensity signal is the largest, the wrong position 14.3um will be found.

[0090] Slide the noise-free curve on the theoretical curve to match the result. Figure 6 As shown. It can be found that at the position of 20um, the variation curve without noise has the highest coincidence with the theoretical signal curve. At this time, it can be known that the maximum value of the variation curve without noise is at 46.5um-20um=26.5um (46.5um is the period of the interference light intensity signal). Figure 7 As shown, for the variation curve with noise, it can also be slid and matched on the theoretical curve, and similar results can also be obtained. Based on the above analysis, when this method is used for dual-wavelength interferometric ranging, the basic optical path length l0 of the reference arm (i.e., the initial reference path length) is a fixed value after the interferometric optical path is designed, and the interferometric ranging result can be calculated as:

[0091] L=M*46.5um+l0-20um

[0092] It can be seen that when the dual-wavelength interferometric ranging method is used for ranging, a more accurate result can be obtained regardless of whether there is noise. Therefore, the method reduces the interference of noise on the measurement result and improves the accuracy of interferometric measurement.

[0093] Step S203, obtaining a first ranging error of the FMCW ranging method and a second ranging error of the dual-wavelength interference ranging method; using the first ranging error to correct the first distance value, and using the second ranging error to correct the second distance value.

[0094] Specifically, when obtaining the first ranging error of the FMCW ranging method, a branch for correction can be added to the original FMCW ranging system's light splitting (the branch includes an adjustable delay line, which is used to simulate the real distance to correct the measured distance). This branch also has local oscillator light and detection light mixed and then detected, and finally there are two detector electrical signals, and the distance values ​​are also obtained using the FMCW ranging method. The distance value calculated by the detector of the correction branch is theoretically equal to the optical path L of the delay line. D , but in fact the result L calculated for each measurement is C Since there is a certain gap between various interferences and the true value, the first ranging error in this embodiment is expressed as L C *L D When the first distance value is corrected by using the first distance measurement error, the measured target distance is corrected synchronously according to the error percentage between the actual measured value and the theoretical true value. Thus, the corrected first distance value is calculated using the following formula:

[0095] L1′=L1 / L C *L D

[0096] Where L1′ is the corrected distance value and L1 is the uncorrected measured value.

[0097] Similarly, when obtaining the second ranging error of the dual-wavelength interferometry ranging method, a correction branch can be added to the branch of the original dual-wavelength interferometry ranging system (the branch includes an adjustable delay line for simulating the real distance to correct the measured distance). The theoretical distance corresponding to the maximum signal detected by the detector in the correction branch is:

[0098] l1′=K*λ1*λ2 / (λ1-λ2)+l0

[0099] Where K is an integer and l0 is the optical path length of the correction branch. Since l0 is fixed after the chip is designed, and the length variation range of the adjustable delay line is determined, the size of K can be calculated. At the same time, if the actual value measured is l1, the second distance measurement error is expressed as the difference between the actual distance and the theoretical distance. Therefore, the corrected second distance value can be expressed by the following formula:

[0100] L2′=L2+l1′-l1

[0101] Wherein, L2′ is the corrected second distance value, and L2 is the uncorrected second distance value.

[0102] Step S204, determining the value of the interference fringe level according to the true distance range and the second distance value; see Figure 1 Step S103 of the illustrated embodiment will not be described in detail here.

[0103] Step S205: Substitute the value into the second distance value to obtain the absolute distance value of the target to be measured. Figure 1 Step S104 of the illustrated embodiment will not be described in detail here.

[0104] In this embodiment, a distance measuring device based on FMCW and dual-wavelength interference is also provided, which is used to implement the above-mentioned embodiments and preferred implementation modes, and the descriptions that have been made will not be repeated. As used below, the term "module" can implement a combination of software and / or hardware of a predetermined function. Although the devices described in the following embodiments are preferably implemented in software, the implementation of hardware, or a combination of software and hardware, is also possible and conceivable.

[0105] This embodiment provides a distance measurement device based on FMCW and dual-wavelength interference, such as Figure 8 As shown, including:

[0106] The first distance acquisition module 81 is used to acquire a first distance value obtained when measuring the distance of the target to be measured based on the FMCW ranging method, and determine the true value range of the distance in combination with the ranging accuracy of the FMCW ranging method.

[0107] The second distance acquisition module 82 is used to acquire a second distance value including the interference fringe order obtained when measuring the distance of the target to be measured based on the dual-wavelength interference ranging method.

[0108] The value determination module 83 is used to determine the value of the interference fringe order according to the distance true value range and the second distance value.

[0109] The absolute distance calculation module 84 is used to substitute the value into the second distance value to obtain the absolute distance value of the target to be measured.

[0110] The further functional description of each of the above modules is the same as that of the above corresponding embodiments and will not be repeated here.

[0111] In an optional embodiment, if Fig. 9As shown, a distance measuring device can be constructed using structures such as lasers, mixers, and detectors to achieve FMCW distance measurement and dual-wavelength interference distance measurement. Specifically, the distance measuring device includes a first laser, a second laser, a combiner, a first optical splitter, a transceiver, a first mixer, a first detector, and a signal processing module. The output end of the first laser and the output end of the second laser are both connected to the input end of the combiner, the output end of the combiner is connected to the input end of the first optical splitter, the first output end of the first optical splitter is connected to one end of the transceiver, the second output end of the first optical splitter is connected to the first input end of the first mixer, the other end of the transceiver is connected to the second input end of the first mixer, the output end of the first mixer is connected to the input end of the first detector, and the output end of the first detector is connected to the signal processing module. The transceiver includes a transmitter and a receiver. The transmitter and the receiver can adopt different structures or the same structure, that is, a coaxial design of transmission and reception.

[0112] When the FMCW ranging method is used to measure the distance based on the device, the first laser or the second laser is turned on to output a frequency modulated continuous wave signal (for example, a frequency modulated signal such as a triangle wave, a sawtooth wave or a sine wave can be applied to the turned-on laser to make it output a frequency modulated continuous wave signal); the signal is divided into two beams through a combiner (because there is only one beam of signal, the combiner only transmits the signal and no beam combining processing is required) and a first optical splitter, one of which is input to the first mixer, and the other is irradiated on the target to be measured through the transmitter in the transceiver. The reflected light of the target to be measured is received by the receiver in the transceiver and is also input to the first mixer. The first mixer mixes the two received beams and inputs them to the first detector. The first detector converts the received optical signal into an electrical signal, and inputs the electrical signal into the signal processing module for processing to obtain a first distance value.

[0113] When the dual-wavelength interference ranging method is used to measure the distance based on the device, the first laser and the second laser are both turned on, and no modulation signal is required. At this time, the optical signals output by the two lasers are first combined by the combiner, and then split by the first beam splitter. After that, the beam transmission method is the same as that of FMCW ranging, but because the ranging principles of the two are different, the processing methods of the signal processing module are different.

[0114] The present invention can complete FMCW and dual-wavelength interference ranging on a set of hardware, and the two cooperate with each other to quickly obtain high-precision ranging results within a relatively large range.

[0115] In an optional implementation, the measured distance can be corrected by adding other structures to the distance measuring device. Fig.10As shown, the device also includes: an adjustable delay line, a second optical splitter, a second mixer and a second detector; one end of the adjustable delay line is connected to the second output end of the first optical splitter, the other end of the adjustable delay line is connected to the input end of the second optical splitter, the two output ends of the second optical splitter are respectively connected to the first input end of the first mixer and the first input end of the second mixer, the third output end of the first optical splitter is connected to the second input end of the second mixer, the output end of the second mixer is connected to one end of the second detector, and the other end of the second detector is connected to the signal processing module. At this time, the device can work in the following manner:

[0116] First, use the FMCW ranging method to measure the distance. At this time, only one laser needs to be turned on, and the first laser or the second laser is selected. A frequency modulation signal (which can be any frequency modulation signal such as a triangle wave, a sawtooth wave, a sine wave, etc.) is applied to it to generate a frequency modulated continuous wave. The signal detected by the second detector is used to calculate the length of the adjustable delay line, and the signal detected by the first detector is used to calculate the distance of the target to be measured. By comparing the error between the delay line length measured by the second detector and the actual delay line length, the error amount of this measurement, i.e., the first ranging error, is obtained. The distance value of the target to be measured is corrected according to the error amount, which can improve the accuracy and precision of FMCW ranging.

[0117] Then use the dual-wavelength interference method to measure the distance. At this time, two lasers need to be turned on. The lasers do not need to apply modulation signals. The length of the adjustable delay line changes linearly and uniformly. The signals of the two detectors are collected synchronously. The distance between the first beam splitter and the second mixer is calculated by the signal detected by the second detector, and the distance of the target to be measured is calculated by the signal detected by the first detector. Compare the error between the distance between the first beam splitter and the second mixer measured by the second detector and the actual design distance to obtain the error of this measurement and the second ranging error. According to the error, the distance of the target to be measured is corrected, which can improve the precision and accuracy of dual-wavelength interference ranging.

[0118] In this embodiment, the same set of hardware is used for FMCW ranging and dual-wavelength interference ranging. There is no need to switch the hardware, only the software control needs to be switched. The measurement speed is fast, and it can be ensured that the results measured by the two measurement methods are the measurement of the same distance, thus making up for each other's measurement shortcomings.

[0119] In a specific implementation, the ranging device based on FMCW and dual-wavelength interference is described by taking a silicon photonic integrated ranging system as an example:

[0120] Among them, the structure of the core optical chip is as follows Fig.11As shown, the two side couplers on the left serve as coupling devices for the input of two lasers with different wavelengths. The light input from the two lasers is combined into a waveguide through a directional coupler. The directional coupler here is specially designed to be used as a combiner, which allows light of different wavelengths to be output from the same port. Then, after passing through two directional couplers in series, the combined light is divided into three beams. The directional coupler here needs to optimize the two wavelengths and try to keep the splitting ratio of the two wavelengths consistent, that is, to ensure that the optical power ratio of the two medium wavelengths in the three beams after splitting is consistent. These three beams of light enter the multimode interference coupler (Multimode Interference coupler, MMI coupler), the delay line and a side coupler on the right, respectively. The side coupler here serves as a transmitter; the MMI splitting ratio is 3dB, serving as a mixer; the delay line is composed of a long waveguide surrounded by a heater, and the waveguide is covered with a heater. The optical path of the delay line is changed by heating, serving as an adjustable delay line. The light after the adjustable delay line is divided into two beams by a directional coupler. The directional coupler here needs to optimize the two wavelengths and try to keep the splitting ratio of the two wavelengths consistent, that is, to ensure that the optical power ratio of the two middle wavelengths in the two beams after the splitting is consistent. The two beams enter the two MMIs respectively. The other side coupler on the right side acts as a receiver, and the received light enters the MMI. The light after MMI mixing enters the balanced photodetector (BPD).

[0121] The core optical chip is packaged before use and then placed on the substrate. Fig.12 As shown, two DFB lasers (Distributed Feedback Laser), microlenses and isolators are also arranged on the substrate, and a shell is arranged around the substrate, and the substrate and the structure thereon are arranged in the shell. The two DFB lasers collimate the light beams through the microlenses, pass through the isolators (to prevent the reflected light from returning to the inside of the laser), and then are focused by the microlenses and aligned with the side couplers, and coupled to the core optical chip. There are corresponding metal wires on the substrate to supply power to the core optical chip, send control signals, and transmit BPD signals. The light emitted by the side coupler as a transmitter on the core optical chip is emitted into space through the optical window, and usually needs to pass through a lens to collimate the light beam. The light returning from the target object also needs to be converged to the side coupler as a receiver through a lens, and coupled back to the chip for mixing and detection. At the same time, there should also be corresponding driving circuits on the periphery, such as using FPGA to control and process signals of the entire system.

[0122] The embodiment of the present invention also provides a computer device having the above Figure 8 The ranging device based on FMCW and dual-wavelength interferometry is shown.

[0123] See also Fig.13 , Fig.13 is a schematic diagram of the structure of a computer device provided by an optional embodiment of the present invention, such as Fig.13 As shown, the computer device includes: one or more processors 10, a memory 20, and interfaces for connecting various components, including high-speed interfaces and low-speed interfaces. Various components are connected to each other using different buses for communication, and can be installed on a common mainboard or installed in other ways as needed. The processor can process the instructions executed in the computer device, including instructions stored in or on the memory to display the graphical information of the GUI on an external input / output device (such as, a display device coupled to the interface). In some optional embodiments, if necessary, multiple processors and / or multiple buses can be used together with multiple memories and multiple memories. Similarly, multiple computer devices can be connected, and each device provides some necessary operations (for example, as a server array, a group of blade servers, or a multi-processor system). Fig.13 A processor 10 is taken as an example.

[0124] The processor 10 may be a central processing unit, a network processor or a combination thereof. The processor 10 may further include a hardware chip. The hardware chip may be a dedicated integrated circuit, a programmable logic device or a combination thereof. The programmable logic device may be a complex programmable logic device, a field programmable gate array, a general purpose array logic or any combination thereof.

[0125] The memory 20 stores instructions executable by at least one processor 10, so that at least one processor 10 executes the method shown in the above embodiment.

[0126] The memory 20 may include a program storage area and a data storage area, wherein the program storage area may store an operating system, an application required for at least one function; the data storage area may store data created by the use of a computer device based on the presentation of a small program landing page, etc. In addition, the memory 20 may include a high-speed random access memory, and may also include a non-transient memory, such as at least one disk storage device, a flash memory device, or other non-transient solid-state storage device. In some optional embodiments, the memory 20 may optionally include a memory remotely arranged relative to the processor 10, and these remote memories may be connected to the computer device via a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0127] The memory 20 may include a volatile memory, such as a random access memory; the memory may also include a non-volatile memory, such as a flash memory, a hard disk or a solid state drive; the memory 20 may also include a combination of the above types of memory.

[0128] The computer device further comprises a communication interface 30 for the computer device to communicate with other devices or a communication network.

[0129] The embodiment of the present invention also provides a computer-readable storage medium. The method according to the embodiment of the present invention can be implemented in hardware, firmware, or can be implemented as a computer code that can be recorded in a storage medium, or can be implemented as a computer code that is originally stored in a remote storage medium or a non-temporary machine-readable storage medium and will be stored in a local storage medium through a network download, so that the method described herein can be stored in such software processing on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. Among them, the storage medium can be a magnetic disk, an optical disk, a read-only storage memory, a random access memory, a flash memory, a hard disk or a solid-state hard disk, etc.; further, the storage medium can also include a combination of the above types of memories. It can be understood that a computer, a processor, a microprocessor controller, or programmable hardware includes a storage component that can store or receive software or computer code. When the software or computer code is accessed and executed by a computer, a processor, or hardware, the method shown in the above embodiment is implemented.

[0130] A part of the present invention may be applied as a computer program product, such as a computer program instruction, which, when executed by a computer, can call or provide the method and / or technical solution according to the present invention through the operation of the computer. Those skilled in the art should understand that the existence of the computer program instruction in a computer-readable medium includes, but is not limited to, a source file, an executable file, an installation package file, etc., and accordingly, the way in which the computer program instruction is executed by the computer includes, but is not limited to: the computer directly executes the instruction, or the computer compiles the instruction and then executes the corresponding compiled program, or the computer reads and executes the instruction, or the computer reads and installs the instruction and then executes the corresponding installed program. Here, the computer-readable medium may be any available computer-readable storage medium or communication medium accessible to the computer.

[0131] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A distance measurement method based on FMCW and dual-wavelength interferometry, characterized in that: The method comprises: Acquire a first distance value obtained when measuring the distance of the target to be measured based on the FMCW ranging method, and determine the true value range of the distance in combination with the ranging accuracy of the FMCW ranging method; Acquire a second distance value including the interference fringe order obtained when measuring the distance of the target to be measured based on the dual-wavelength interference ranging method; Determining a value of the interference fringe order according to the true distance range and the second distance value; Substituting the value into the second distance value obtains the absolute distance value of the target to be measured.

2. The method according to claim 1, characterized in that: The second distance value is expressed by the following formula: In the formula, M represents the unknown interference fringe order, λ1 and λ2 represent the wavelengths of the two lights used in dual-wavelength interference, and L lo Indicates the reference path length.

3. The method according to claim 1, characterized in that Obtaining a second distance value including the interference fringe order obtained when measuring the distance of the target to be measured based on the dual-wavelength interference ranging method, including: The reference path length is changed, and a dual-wavelength interference ranging method is used to measure a plurality of first interference light intensity signals corresponding to different reference path lengths; Theoretically calculate multiple second interference light intensity signals when the optical path difference between the reference path and the measurement path changes during dual-wavelength interference; The plurality of first interference light intensity signals are matched with the plurality of second interference light intensity signals, and a second distance value including the order of interference fringes is determined based on the matching result.

4. The method according to claim 3, characterized in that Matching the plurality of first interference light intensity signals with the plurality of second interference light intensity signals, and determining a second distance value including an unknown interference fringe order based on the matching result, comprising: Sliding matching is performed on a curve formed by a plurality of first interference light intensity signals on a curve formed by a plurality of second interference light intensity signals to determine a position with the highest overlap; A second distance value including the order of interference fringes is determined based on the position with the highest overlap and the step size when changing the reference path length.

5. The method according to claim 3, characterized in that: The overlap is calculated using the following formula: Where D i Represents the first interference light intensity signal, I i represents the second interference light intensity signal, n represents the number of first interference light intensity signals, and m represents the number of second interference light intensity signals.

6. The method according to claim 5, characterized in that The second distance value is expressed by the following formula: In the formula, M represents the interference fringe order, λ1 and λ2 represent the wavelengths of the two lights used in dual-wavelength interference, and L o represents the reference path length before the change, d represents the step size when changing the reference path length, k max Represents δ1, δ2, δ3,…, δ m-n The optical path difference corresponding to the maximum value.

7. The method according to claim 1, characterized in that Before determining the value of the unknown interference fringe order according to the distance true value range and the second distance value, the method further includes: Obtain a first ranging error of the FMCW ranging method and a second ranging error of the dual-wavelength interference ranging method; The first distance value is corrected using the first ranging error, and the second distance value is corrected using the second ranging error.

8. A distance measuring device based on FMCW and dual-wavelength interference, characterized in that: The device comprises: A first distance acquisition module is used to obtain a first distance value obtained when measuring the distance of the target to be measured based on the FMCW ranging method, and determine the true value range of the distance in combination with the ranging accuracy of the FMCW ranging method; A second distance acquisition module, used to acquire a second distance value including the interference fringe order obtained when measuring the distance of the target to be measured based on the dual-wavelength interference ranging method; A value determination module, used to determine the value of the interference fringe order according to the true value range of the distance and the second distance value; The absolute distance calculation module is used to substitute the value into the second distance value to obtain the absolute distance value of the target to be measured.

9. The device according to claim 8, characterized in that The device further includes: a first laser, a second laser, a combiner, a first optical splitter, a transceiver, a first mixer, a first detector and a signal processing module, wherein the output end of the first laser and the output end of the second laser are both connected to the input end of the combiner, the output end of the combiner is connected to the input end of the first optical splitter, the first output end of the first optical splitter is connected to one end of the transceiver, the second output end of the first optical splitter is connected to the first input end of the first mixer, the other end of the transceiver is connected to the second input end of the first mixer, the output end of the first mixer is connected to the input end of the first detector, and the output end of the first detector is connected to the signal processing module; When the FMCW ranging method is used for ranging, the first laser or the second laser is turned on to output a frequency modulation signal; When the dual-wavelength interference ranging method is used for ranging, the first laser and the second laser are turned on to output two optical signals with different wavelengths.

10. The device according to claim 9, characterized in that The device also includes: an adjustable delay line, a second spectrometer, a second mixer and a second detector; one end of the adjustable delay line is connected to the second output end of the first spectrometer, the other end of the adjustable delay line is connected to the input end of the second spectrometer, the two output ends of the second spectrometer are respectively connected to the first input end of the first mixer and the first input end of the second mixer, the third output end of the first spectrometer is connected to the second input end of the second mixer, the output end of the second mixer is connected to one end of the second detector, and the other end of the second detector is connected to the signal processing module.

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