Modulation and demodulation method and system of laser interference distance sensor

Abstract

The invention relates to the technical field of laser interference distance sensors, and discloses a modulation and demodulation method and system for a laser interference distance sensor, and the method comprises the steps: obtaining a carrier wave which carries out the phase modulation of an initial optical signal, and an interferometer photoelectric signal which is obtained through the distance detection of the initial optical signal; fourier transform is carried out on the interferometer photoelectric signal to obtain a Fourier transform result; respectively obtaining intensity values of a plurality of odd harmonics and a plurality of even harmonics of the Fourier transform result, a phase value of a pth odd harmonic and a phase value of a qth even harmonic, and calculating the number of the odd harmonics and the number of the even harmonics based on the intensity values and the phase values of the odd harmonics and the number of the even harmonics in combination with a theoretically calculated response function or calibration function. And resolving the phase transfer function, and calculating through the resolved phase transfer function to obtain the target distance information. According to the method, the demodulation process of each measurement point is independent, a filtering process is avoided, measurement errors caused by filtering are eliminated, meanwhile, large modulation depth is not needed, and the requirement for a modulator is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of laser interference distance sensors, and in particular to a modulation and demodulation method and system of a laser interference distance sensor. Background Art

[0002] In the field of laser interferometer distance sensors, how to modulate the detection signal and demodulate the target distance is the key to accurately measure the target distance.

[0003] The phase-generated carrier algorithm based on single-interference-arm sinusoidal phase modulation is a typical method for solving interferometer-type laser interferometer distance sensors. However, the filtering process required by this type of method will cause spectral distortion of the signal, which will produce large errors when applied to situations such as step distance changes. Moreover, it is mostly based on complex calculation processes such as low-pass filtering, differentiation, and integration, and has a large amount of calculation.

[0004] The method in the paper (DOI: 10.1515 / teme-2019-0012) can solve the above problems, but it requires the modulator to produce a large amplitude phase modulation, which increases the performance requirements of the modulator and reduces the effective modulation bandwidth of modulators such as piezoelectric ceramics, thereby reducing the distance measurement frequency; at the same time, because it can only use the linear region of the transfer function, it also has higher requirements for the sampling rate.

[0005] Therefore, a modulation and demodulation method is needed which is simple in calculation, can make full use of the transfer function, and does not require large-amplitude phase modulation. Summary of the invention

[0006] The present invention provides a modulation and demodulation method and system for a laser interferometer distance sensor, aiming to accurately measure the target distance or displacement with a smaller phase modulation amplitude in the case of high-frequency components in distance changes such as step measurement, and reduce the calculation complexity.

[0007] The present invention is achieved through the following technical solutions:

[0008] A modulation and demodulation method for a laser interferometer distance sensor, comprising:

[0009] Acquire an interferometer photoelectric signal including a carrier wave that phase modulates an initial optical signal and target distance information obtained by distance detection of the initial optical signal;

[0010] Performing Fourier transform on the interferometer photoelectric signal to obtain a Fourier transform result;

[0011] The intensity values ​​at several odd harmonics and several even harmonics of the Fourier transform result and the phase value of the pth odd harmonic and the phase value of the qth even harmonic are respectively obtained, and based on the intensity values ​​and phase values ​​at the odd harmonics and the even harmonics, combined with a theoretically calculated response function or a calibration function, the phase transfer function is solved, and then the target distance information is calculated through the solved phase transfer function.

[0012] As an optimization, the specific process of obtaining the interferometer photoelectric signal with carrier and target distance information is as follows:

[0013] Performing sinusoidal phase modulation on the initial optical signal emitted by the laser to obtain a carrier, and at the same time, performing distance detection on the initial optical signal to obtain returned target distance information;

[0014] The photoelectric detector collects the carrier and target distance information to obtain an interferometer photoelectric signal

[0015] Where DC is direct current, A is the signal strength, Φ(d) is the phase transfer function of phase change caused by distance change, and f m is the phase modulation frequency, C is the modulation depth, It is the initial phase of modulation.

[0016] As an optimization, the specific process of respectively obtaining the intensity values ​​and phase values ​​at several odd harmonics and several even harmonics of the Fourier transform result is:

[0017] A1. Calculate the intensity values ​​of several odd harmonics and several even harmonics of the Fourier transform result, wherein the intensity values ​​of the first x odd harmonics of the Fourier transform result are expressed as:

[0018]

[0019] The intensity values ​​of the first y even harmonics of the Fourier transform result are expressed as:

[0020]

[0021] Where x and y are both positive integers, φ=Φ(d), Respectively represent k 1 and k 2 order Bessel function;

[0022] A2. Calculate the sum of the intensities of the first x odd harmonics and the first y even harmonics, and get:

[0023]

[0024] Where l1 represents the parameter sign of the sum of the intensities of the first x odd harmonics, l2 represents the parameter sign of the sum of the intensities of the first y even harmonics, and F(f odd,x |φ) represents the function sign of the sum of the intensities of the first x odd harmonics, F(f even,y |φ) represents the function symbol of the sum of the intensities of the first y even harmonics, f odd,x represents the first x odd harmonics of the Fourier transform result, f even,y represents the first y even harmonics of the Fourier transform result;

[0025] A3. Obtain the initial phase value of the pth odd harmonic and the initial phase value of the qth even harmonic, wherein the initial phase value of the pth odd harmonic is expressed as:

[0026]

[0027] The initial phase value of the qth even harmonic is expressed as:

[0028]

[0029] Wherein, sgn{·} is a sign function, |pq|=2r, and r is an integer not less than 0.

[0030] As an optimization, based on the intensity values ​​and phase values ​​at the odd harmonics and the even harmonics, combined with the theoretically calculated response function or calibration function, the phase transfer function is solved, and then the specific process of calculating the target distance information through the solved phase transfer function is as follows:

[0031] A4. Calculate the normalized harmonic intensity ratio:

[0032] σ(φ)=σ(φ(d))=(l1-l2) / (l1+l2)=[F(f odd,x |φ)-F(f even,y |φ)] / [F(f odd,x |φ)+F(f even,y |φ)];

[0033] A5. The process of obtaining the phase value intervals of odd harmonics and even harmonics of different target distance information through the calibration function is as follows:

[0034] Apply different target distance information to the target, repeat steps A1-A4, and obtain the initial phase value of the pth odd harmonic corresponding to different target distance information and the initial phase value of the qth even harmonic And the normalized harmonic intensity ratio σ(Φ(d)), then the initial phase value of the pth odd harmonic and the initial phase value of the qth even harmonic at different target distances d are binarized respectively, and the new phase value of the pth odd harmonic and the new phase value of the qth even harmonic are obtained, so as to analyze the law of the new phase values ​​of the odd harmonics and the even harmonics with different target distance information d, and obtain the intervals to which the new phase values ​​of the odd harmonics and the even harmonics with different target distance information d belong. The new phase value of the pth odd harmonic and the new phase value of the qth even harmonic are respectively and

[0035] Alternatively, the process of obtaining the intervals to which the phase values ​​of the odd harmonics and the even harmonics of different target distance information belong through the theoretically calculated response function is:

[0036] Repeat steps A1-A4, set the corresponding target distance information d through theory or simulation, and obtain the new phase of the pth odd harmonic corresponding to different target distance information and the new phase of the qth even harmonic and the normalized harmonic intensity ratio σ(Φ(d)), thereby analyzing the rules of the new phase values ​​of the odd harmonics and the even harmonics of different target distance information d, and obtaining the intervals to which the new phase values ​​of the odd harmonics and the even harmonics of different target distance information d belong;

[0037] A6. Calculating the phase transfer function based on the intervals to which the new phase values ​​of the odd harmonics and the even harmonics of different target distance information d belong;

[0038] A7. Calculate the target distance information by using the resolved phase transfer function on the interferometer photoelectric signal that needs to be used for distance detection later.

[0039] As an optimization, in A5, the specific process of binarizing the initial phase value of the pth odd harmonic and the initial phase value of the qth even harmonic is as follows:

[0040] A5.1. Set the initial phase value of the pth odd harmonic to According to the phase winding law, the first phase value is obtained by converting it into the range [0,2π);

[0041] A5.2. Perform interval classification statistics on the distribution of the first phase values ​​of different target distance information. If there are three enriched intervals [0, a), [a, b), and [b, 2π), add 2π to the first phase value belonging to the interval [0, a), and then perform interval classification statistics again to obtain two enriched intervals [a, b) and [b, a+2π), and then jump to A5.3. If there are two enriched intervals [0, a) and [a, 2π), jump directly to A5.3.

[0042] A5.3. Calculate the mean of the first phase values ​​in the two enrichment intervals respectively, and replace the values ​​in the corresponding intervals with the mean of the two first phase values. The value is completed Binarization, after binarization Recorded as

[0043] A5.4. Set the initial phase value of the qth even harmonic to According to the phase winding law, the second phase value is converted into the interval [0,2π);

[0044] A5.5. Perform interval classification statistics on the distribution of the second phase values ​​of different target distance information. If the statistics show three enriched intervals [0, a), [a, b), and [b, 2π), add 2π to the second phase value belonging to the interval [0, a), and then perform interval classification statistics again to obtain two enriched intervals [a, b) and [b, a+2π), and then jump to A5.6. If the statistics show two enriched intervals [0, a) and [a, 2π), jump directly to A5.6.

[0045] A5.6. Calculate the mean of the second phase values ​​in the two enrichment intervals respectively, and use the mean of the two second phase values ​​to replace the values ​​in the corresponding intervals. The value is completed Binarization, after binarization Recorded as

[0046] As an optimization, in A5.2 and A5.5, if the modulation function of the phase modulator is a standard sine function, the range of variation of different target distance information d must satisfy the requirement that the corresponding change of Φ(d) exceeds Then, the symmetry of the phase transfer function is used to obtain The phase transfer function of the region outside the region;

[0047] If the modulation function of the phase modulator is not a standard sinusoidal function, the variation range of different target distance information d must satisfy the requirement that the corresponding variation of Φ(d) exceeds 2π.

[0048] As an optimization, the phase transfer function Φ(d) based on the initial phase value of the pth odd harmonic and the initial phase value of the qth even harmonic and the normalized harmonic intensity ratio is expressed as:

[0049]

[0050] The phase transfer function Φ(d) based on the new phase value of the pth odd harmonic and the new phase value of the qth even harmonic and the normalized harmonic intensity ratio is expressed as:

[0051]

[0052] Where n is the refractive index of the optical transmission medium, λ is the wavelength of the light source, Represents the transfer function relationship obtained by experimental calibration, theoretical calculation or simulation.

[0053] As an optimization, the intervals of the new phase values ​​of the odd harmonics obtained by combining the calibration function include interval 1 and interval 2, where:

[0054] Interval 1 is expressed as:

[0055] Interval 2 is expressed as:

[0056] The intervals to which the new phase values ​​of even harmonics belong include interval three and interval four, where:

[0057] Interval three is expressed as:

[0058] Interval 4 is expressed as:

[0059] Among them, k 3 represents an integer, are two possible values ​​obtained by binarizing the initial phase value of the odd harmonics. are two possible values ​​obtained by binarizing the initial phase value of the even harmonics;

[0060] The intervals of the new phase values ​​of the odd harmonics obtained by combining the theoretical response function include interval 1 and interval 2, where:

[0061] Interval 1 is expressed as:

[0062] Interval 2 is expressed as:

[0063] The intervals to which the new phase values ​​of even harmonics belong include interval three and interval four, where:

[0064] Interval three is expressed as:

[0065] Interval 4 is expressed as:

[0066] Among them, k 3 represents an integer, are two values ​​of the new phase of the odd harmonics obtained through the theoretical response function, These are two values ​​of the new phase of the even harmonics obtained through the theoretical response function.

[0067] As an optimization, in step A6, the phase transfer function after solution is expressed as:

[0068]

[0069] They respectively represent the transfer function relationships obtained by experimental calibration, theoretical calculation or simulation.

[0070] The present invention also discloses a modulation and demodulation system of a laser interferometer distance sensor, which is used to implement the modulation and demodulation method of the laser interferometer distance sensor mentioned above, and is characterized by comprising:

[0071] A signal generation and acquisition device, used for generating an initial optical signal and acquiring an interferometer photoelectric signal including a carrier wave phase-modulated on the initial optical signal and target distance information obtained by distance detection of the initial optical signal, comprising a laser and a photodetector, wherein the output end of the laser is connected to a first optical fiber coupler via an optical fiber, the input end of the photodetector is connected to a second optical fiber coupler, a phase modulator is connected between the first optical fiber coupler and the second optical fiber coupler, and an optical fiber circulator is also connected between the first optical fiber coupler and the second optical fiber coupler, the other end of the optical fiber circulator is connected to a collimator for transmitting an optical signal to a target reflector, and the distance between the collimator and the target reflector is the target distance signal;

[0072] A signal demodulation device is used to perform Fourier transform on the interferometer photoelectric signal to obtain a Fourier transform result, and then respectively obtain the intensity values ​​at several odd harmonics and several even harmonics of the Fourier transform result and the phase value of the pth odd harmonic and the phase value of the qth even harmonic, and based on the intensity values ​​and phase values ​​at the odd harmonics and the even harmonics, combined with a theoretically calculated response function or a calibration function, solve the phase transfer function, and then calculate the target distance information through the solved phase transfer function.

[0073] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0074] Compared with the phase generation carrier method, the demodulation process of each measurement point in the present invention is independent, there is no filtering process, and the measurement error caused by filtering is eliminated.

[0075] Compared with the phase generation carrier method, the present invention is simpler in calculation and only needs to calculate the Fourier transform result of a specific frequency point and combine it with interpolation fitting.

[0076] The value of the modulation depth C in the present invention is generally sufficient within the range of π, which is much smaller than the modulation depth requirement of the method in the paper (DOI: 10.1515 / teme-2019-0012), and the modulation is simple.

[0077] Compared with the paper (DOI: 10.1515 / teme-2019-0012), the present invention can make full use of the phase transfer function. Therefore, at the same measurement frequency, the same number of effective sampling points can be achieved with a lower sampling rate, thereby reducing the sampling rate requirement for the acquisition card. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0079] Figure 1 It is a flow chart of a modulation and demodulation method of a laser interferometer distance sensor according to the present invention;

[0080] Figure 2 This is a device connection diagram of a modulation and demodulation system of a laser interferometer distance sensor described in the present invention.

[0081] Marks and corresponding parts names in the attached drawings:

[0082] 1-laser; 2-optical fiber; 3-collimating mirror; 4-reference mirror; 5-piezoelectric ceramic ring; 6-target reflector; 7-optical fiber circulator; 8-photodetector; 9a-first optical fiber coupler; 9b-second optical fiber coupler; 10-phase modulator. DETAILED DESCRIPTION

[0083] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0084] This embodiment 1 provides a modulation and demodulation method of a laser interferometer distance sensor, such as Figure 1 As shown, including:

[0085] S1, obtaining an interferometer photoelectric signal including a carrier wave phase-modulated on an initial optical signal and target distance information obtained by distance detection of the initial optical signal;

[0086] The specific process is:

[0087] Performing sinusoidal phase modulation on the initial optical signal emitted by the laser to obtain a carrier, and at the same time, performing distance detection on the initial optical signal to obtain returned target distance information;

[0088] The light emitted by the laser is divided into two paths: a reference arm and a signal arm. After the reference arm is sinusoidally phase modulated, it interferes with the signal light that returns after passing through the irradiated target.

[0089] The photoelectric detector collects the carrier and target distance information to obtain an interferometer photoelectric signal

[0090] Where DC is direct current, A is the signal intensity, i.e. the intensity of the initial optical signal, Φ(d) is the phase transfer function of the phase change caused by the distance change, and f m is the phase modulation frequency, C is the modulation depth, It is the initial phase of modulation.

[0091] The interferometer photoelectric signal with the distance information between the carrier and the target is obtained through photoelectric detection.

[0092] S2, performing Fourier transform on the interferometer photoelectric signal I(t) to obtain a Fourier transform result F(f);

[0093] S3. Obtain the intensity values ​​of several odd harmonics and several even harmonics of the Fourier transform result, as well as the phase value of the pth odd harmonic and the phase value of the qth even harmonic, respectively, and solve the phase transfer function based on the intensity values ​​and phase values ​​at the odd harmonics and the even harmonics in combination with a theoretically calculated response function or calibration function, and then obtain the target distance information through the solved phase transfer function calculation.

[0094] That is, according to F(f) at f=k 1 f m and f = k 2 f m The intensity value and phase value at the location are combined with the theoretically calculated response function or calibration function to calculate the phase Φ(d), and then the target distance information d is calculated.

[0095] f=(2k-1)f m and f = 2kf m (k=k 3 ={k 1 ,k 2 The intensity value and phase value at the position of the target are combined with the theoretically calculated response function or calibration function to calculate the phase Φ(d), and then the target distance information d is calculated.

[0096] It should be noted that, since the method of the present invention needs to collect phase values ​​corresponding to different target distance information to find the law of the phase transfer function, it is necessary to change the target distance information and then collect the phase value and intensity ratio accordingly.

[0097] With target distance information d = d1 For example, the phase term φ is expressed as φ 1 , the interferometer photoelectric signal obtained by photoelectric detection is

[0098] In some embodiments, the specific process of respectively obtaining the intensity values ​​and phase values ​​at several odd harmonics and several even harmonics of the Fourier transform result is:

[0099] First, calculate I(t|φ 1 )’s Fourier transform result has the first x odd harmonic frequencies and the first y even harmonic frequencies.

[0100] A1. Calculate the intensity values ​​of several odd harmonics and several even harmonics of the Fourier transform result, wherein the intensity values ​​of the first x odd harmonics of the Fourier transform result are expressed as:

[0101]

[0102] The intensity values ​​of the first y even harmonics of the Fourier transform result are expressed as:

[0103]

[0104] Where x and y are both positive integers. Respectively represent k 1 and k 2 Bessel function of order; here, x and y can be the same or different.

[0105] A2. Calculate the sum of the intensities of the first x odd harmonics and the first y even harmonics, and get:

[0106]

[0107] Where l1 represents the parameter sign of the sum of the intensities of the first x odd harmonics, l2 represents the parameter sign of the sum of the intensities of the first y even harmonics, and F(f odd,x |φ 1 ) represents the function symbol of the sum of the intensities of the first x odd harmonics, F(f even,y |φ 1 ) represents the function symbol of the sum of the intensities of the first y even harmonics, f odd，x represents the first x odd harmonics of the Fourier transform result, f even,y represents the first y even harmonics of the Fourier transform result, and the values ​​of x and y remain consistent throughout the calibration process and demodulation process;

[0108] A3. Obtain the initial phase value of the pth odd harmonic and the initial phase value of the qth even harmonic, and take The pth odd harmonics and The phase of the qth even harmonic of

[0109] Among them, the initial phase value of the pth odd harmonic is expressed as:

[0110]

[0111] The initial phase value of the qth even harmonic is expressed as:

[0112]

[0113] Where sgn{·} is the sign function, and the selection of p and q must follow the rule: |pq|=2r, r is an integer not less than 0, and p and q keep the same value throughout the calibration and demodulation process. Here, p does not have to be in the range of 1 to 2x-1, and q does not have to be in the range of 2 to 2y.

[0114] In some embodiments, based on the intensity values ​​and phase values ​​at the odd harmonics and the even harmonics, combined with a theoretically calculated response function or calibration function, the phase transfer function is solved, and then the specific process of calculating the target distance information through the solved phase transfer function is as follows:

[0115] A4. Calculate the normalized harmonic intensity ratio:

[0116] σ(φ 1 )=σ(Φ(d 1 ))=(l1-l2) / (l1+l2)=[F(f odd,x |φ 1 )-F(f even,y |φ 1 )] / [F(f odd,x |φ 1 )+[F(f even,y |φ 1 )]; (6)

[0117] A5. The process of obtaining the phase value intervals of odd harmonics and even harmonics of different target distance information through the calibration function is as follows:

[0118] Apply different target distance information to the target, repeat steps A1-A4, and obtain the initial phase value of the pth odd harmonic corresponding to different target distance information and the initial phase value of the qth even harmonic And the normalized harmonic intensity ratio σ(Φ(d)), then the initial phase value of the pth odd harmonic and the initial phase value of the qth even harmonic at different target distances d are binarized respectively, and the new phase value of the pth odd harmonic and the new phase value of the qth even harmonic are obtained, so as to analyze the law of the new phase values ​​of the odd harmonics and the even harmonics with different target distance information d, and obtain the intervals to which the initial phase values ​​of the odd harmonics and the even harmonics with different target distance information d belong. The new phase value of the pth odd harmonic and the new phase value of the qth even harmonic are respectively and

[0119] In this embodiment, the phase transfer function Φ(d) based on the initial phase value of the pth odd harmonic and the initial phase value of the qth even harmonic of the target distance information d is expressed as:

[0120]

[0121] Where n is the refractive index of the optical transmission medium and λ is the wavelength of the light source.

[0122] From formula (4) and (5), we can see that the phase of odd harmonics is There are only two discrete possible values ​​of , but in the actual calibration process, due to factors such as measurement error, the phase of the actually measured odd harmonics There may be multiple different values. In this case, the phase of the odd harmonics needs to be adjusted according to the calibration results. Binarize it and obtain the phase of the odd harmonic with only two possible values, and the difference between these two possible values ​​is π These two values ​​are recorded as and After binarization Recorded as Similarly, according to the calibration results, the phase of the even harmonics Binarize to obtain only two possible values, and the difference between these two possible values ​​is π Recorded as and After binarization Recorded as

[0123] Thus, the phase transfer function Φ (d 1 ) (The phase of odd harmonics and the transfer function obtained by binarizing even harmonics):

[0124]

[0125] In theory, formula (7) and formula (8) express the same meaning. The difference is that formula (7) is based on theoretical calculation or simulation to obtain the transfer function h. There are only two possible values ​​for the value of , and there will be no error. However, formula (8) is obtained for experiments (or simulation with noise added), and the phase value has errors, so it needs to be binarized to obtain a new phase value

[0126] Alternatively, A5 may also be: the process of obtaining the intervals to which the phase values ​​of the odd harmonics and the even harmonics of different target distance information belong through the theoretically calculated response function is:

[0127] Repeat steps A1-A4, set the corresponding target distance information d through theory or simulation, and obtain the new phase of the pth odd harmonic corresponding to different target distance information and the new phase of the qth even harmonic and the normalized harmonic intensity ratio σ(Φ(d)), thereby analyzing the rules of the new phase values ​​of the odd harmonics and the even harmonics of different target distance information d, and obtaining the intervals to which the new phase values ​​of the odd harmonics and the even harmonics of different target distance information d belong;

[0128] It should be noted that the new phase It refers to the phase after binarization. The calibration process requires the initial phase to be binarized, and the phase obtained by theoretical or noise-free simulation is directly the binarized phase, that is, the new phase.

[0129] It should also be noted that binarization is only used during experimental calibration, and can only be performed after all different target distances d have been calibrated. The reason is that the formula in step A3 shows that, whether it is an odd or even harmonic, its phase value has only two possible values. However, during the experiment, under the influence of noise, this theoretical value will have errors in the local position. For this reason, the calibrated phase results need to be binarized to eliminate the influence of noise. In some embodiments, in A5, the specific process of binarizing the initial phase value of the pth odd harmonic and the initial phase value of the qth even harmonic is:

[0130] A5.1. Set the initial phase value of the pth odd harmonic to According to the phase winding law, the first phase value is obtained by converting it into the range [0,2π);

[0131] A5.2. Perform interval classification statistics on the distribution of the first phase values ​​of different target distance information. If there are three enriched intervals [0, a), [a, b), and [b, 2π), add 2π to the first phase value belonging to the interval [0, a), and then perform interval classification statistics again to obtain two enriched intervals [a, b) and [b, a+2π), and then jump to A5.3. If there are two enriched intervals [0, a) and [a, 2π), jump directly to A5.3.

[0132] A5.3. Calculate the mean of the first phase values ​​in the two enrichment intervals respectively, and replace the values ​​in the corresponding intervals with the mean of the two first phase values. The value is completed Binarization, after binarization Recorded as

[0133] A5.4. Set the initial phase value of the qth even harmonic to According to the phase winding law, the second phase value is converted into the interval [0,2π);

[0134] A5.5. Perform interval classification statistics on the distribution of the second phase values ​​of different target distance information. If the statistics show three enriched intervals [0, a), [a, b), and [b, 2π), add 2π to the second phase value belonging to the interval [0, a), and then perform interval classification statistics again to obtain two enriched intervals [a, b) and [b, a+2π), and then jump to A5.6. If the statistics show two enriched intervals [0, a) and [a, 2π), jump directly to A5.6.

[0135] A5.6. Calculate the mean of the second phase values ​​in the two enrichment intervals respectively, and use the mean of the two second phase values ​​to replace the values ​​in the corresponding intervals. The value is completed Binarization, after binarization Recorded as

[0136] It should be noted that the enriched interval means that when performing probability distribution statistics on the phase, there will be two or three probability peaks. By classifying the data according to the degree of proximity around these two or three peaks, two or three enriched intervals can be obtained.

[0137] Theoretically, during the calibration process, the target distance information d is required to have a large enough range so that the change of Φ(d) exceeds 2π. This situation is suitable when the modulation function of the phase modulator is not a standard sinusoidal function. At this time, the range of different target distance information d must be able to make the corresponding change of Φ(d) exceed 2π. The above process can obtain the range of λ / 2 of the target distance information d, that is, the range of 2π of Φ. A one-to-one mapping relationship, and you can take and The intervals that are continuous and do not jump are written as piecewise functions:

[0138]

[0139] However, in fact, in A5.2 and A5.5, if the modulation function of the phase modulator is a standard sine function, the range of variation of different target distance information d must satisfy the requirement that the corresponding variation of Φ(d) exceeds Then, the symmetry of the phase transfer function is used to obtain The phase transfer function of the region outside the region.

[0140] Since the change of Φ(d) exceeds 2π, and One of them must have a jump in the value of π within the range of change. And the jump point is Φ=Φ 0 ,but

[0141]

[0142] According to the above formula, as long as the range of d is large enough so that the change of Φ(d) exceeds 2π, the distance d can be obtained by symmetry. In the range of changes, that is, in the range of 2π changes of Φ(d), Φ(d) and One-to-one mapping relationship.

[0143] In this embodiment, the intervals to which the new phase values ​​of the odd harmonics obtained in combination with the calibration function belong include interval 1 and interval 2, where:

[0144] Interval 1 is expressed as:

[0145] Interval 2 is expressed as:

[0146] The intervals to which the new phase values ​​of even harmonics belong include interval three and interval four, where:

[0147] Interval three is expressed as:

[0148] Interval 4 is expressed as:

[0149] Among them, k 3 represents an integer, are two possible values ​​obtained by binarizing the initial phase value of the odd harmonics. are two possible values ​​obtained by binarizing the initial phase value of the even harmonics;

[0150] The intervals of the new phase values ​​of the odd harmonics obtained by combining the theoretical response function include interval 1 and interval 2, where:

[0151] Interval 1 is expressed as:

[0152] Interval 2 is expressed as:

[0153] The intervals to which the new phase values ​​of even harmonics belong include interval three and interval four, where:

[0154] Interval three is expressed as:

[0155] Interval 4 is expressed as:

[0156] Among them, k 3 represents an integer, are two values ​​of the new phase of the odd harmonics obtained through the theoretical response function, These are two values ​​of the new phase of the even harmonics obtained through the theoretical response function.

[0157] A6. Calculating the phase transfer function based on the intervals to which the new phase values ​​of the odd harmonics and the even harmonics of different target distance information d belong;

[0158] In step A6, the solved phase transfer function is expressed as:

[0159]

[0160] They respectively represent the transfer function relationships obtained by experimental calibration, theoretical calculation or simulation.

[0161] A8. Calculate the target distance information by using the resolved phase transfer function on the interferometer photoelectric signal that needs to be used for distance detection later.

[0162] The target distance information d is obtained according to the phase transfer function after solution. 1 The calculation is as follows:

[0163]

[0164] They respectively represent the transfer function relationships obtained by experimental calibration, theoretical calculation or simulation.

[0165] Embodiment 2 also discloses a modulation and demodulation system of a laser interferometer distance sensor, such as Figure 2 As shown, a modulation and demodulation method for implementing a laser interferometer distance sensor described in Example 1 includes:

[0166] A signal generation and acquisition device, used for generating an initial optical signal and acquiring an interferometer photoelectric signal including a carrier wave phase-modulated on the initial optical signal and target distance information obtained by distance detection of the initial optical signal, comprising a laser and a photodetector, wherein the output end of the laser is connected to a first optical fiber coupler via an optical fiber, the input end of the photodetector is connected to a second optical fiber coupler, a phase modulator is connected between the first optical fiber coupler and the second optical fiber coupler, and an optical fiber circulator is also connected between the first optical fiber coupler and the second optical fiber coupler, the other end of the optical fiber circulator is connected to a collimator for transmitting an optical signal to a target reflector, and the distance between the collimator and the target reflector is the target distance signal;

[0167] A signal demodulation device is used to perform Fourier transform on the interferometer photoelectric signal to obtain a Fourier transform result, and then respectively obtain the intensity values ​​at several odd harmonics and several even harmonics of the Fourier transform result and the phase value of the pth odd harmonic and the phase value of the qth even harmonic, and based on the intensity values ​​and phase values ​​at the odd harmonics and the even harmonics, combined with a theoretically calculated response function or a calibration function, solve the phase transfer function, and then calculate the target distance information through the solved phase transfer function.

[0168] Next, the present invention is described through specific implementation examples.

[0169] The light emitted by the laser 1 enters the circulator 7 through the optical fiber 2 and is transmitted to the collimator 3. After being collimated by the collimator, it is transmitted to the reference mirror 4. The light beam is divided into two beams at the reference mirror 4. One beam is reflected back to the focusing mirror 3 and then enters the optical fiber after being focused, and reaches the photodetector 8 through the circulator 7; the other beam passes through the reference mirror 4, passes through the light hole of the piezoelectric ceramic 5, and returns to the collimator 3 after being reflected by the target reflector 6, and then enters the photodetector 8 through the circulator 7. The two beams of light interfere and are converted into photoelectric signals I(t) by the photodetector 8 and then collected. The reference mirror 4 is made to generate sinusoidal oscillations by controlling the piezoelectric ceramic 5 through voltage, thereby providing sinusoidal phase modulation for the reference light.

[0170] After I(t) is collected, the target distance is then calculated using the aforementioned method.

[0171] The values ​​of x, y, p, and q can be refined here: x=y=p=q=1.

[0172] Here we can refine the calculation of d: if used as a distance sensor, the absolute distance measurement range is λ / 2n, where n is the refractive index of the medium. If the optical path difference between the two arms is kλ / 2, the distance zero point is kλ / 2, then the target distance d = λΦ(d) / 4πn.

[0173] Take f(f|φ 1 )={F(f odd,x |φ 1 ),F(f even,y |φ 1 )}, and the phases of the pth odd harmonic and the qth even harmonic are obtained to obtain the intervals to which the phases of the odd harmonics and the even harmonics belong:

[0174]

[0175] When used as a displacement sensor, the displacement can be calculated as Unwrap{Φ(d(t))}·λ / 4πn_Φ(d(t 0 ))·λ / 4πn where n is the refractive index of the medium, Unweap{·} represents the phase unwrapping function, and t 0 is the initial time of measurement.

[0176] Here, the values ​​of x, y, p, and q can be refined: x=y=2, p=q=1.

[0177] Then, calculating the sum of the powers of odd and even harmonics, we get

[0178]

[0179] Finally, the normalized harmonic strong power value is calculated based on the sum of the power of odd harmonics and even harmonics, and the target distance information is calculated based on the corresponding interval combined with the decoupled phase transfer function.

[0180] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A modulation and demodulation method for a laser interferometer distance sensor, characterized in that: include: Acquire an interferometer photoelectric signal including a carrier wave that phase modulates an initial optical signal and target distance information obtained by distance detection of the initial optical signal; Performing Fourier transform on the interferometer photoelectric signal to obtain a Fourier transform result; The intensity values ​​at several odd harmonics and several even harmonics of the Fourier transform result and the phase value of the pth odd harmonic and the phase value of the qth even harmonic are respectively obtained, and based on the intensity values ​​and phase values ​​at the odd harmonics and the even harmonics, combined with a theoretically calculated response function or a calibration function, the phase transfer function is solved, and then the target distance information is calculated through the solved phase transfer function.

2. The modulation and demodulation method of a laser interferometer distance sensor according to claim 1, characterized in that: The specific process of obtaining the interferometer photoelectric signal with carrier and target distance information is as follows: Performing sinusoidal phase modulation on the initial optical signal emitted by the laser to obtain a carrier, and at the same time, performing distance detection on the initial optical signal to obtain returned target distance information; The photoelectric detector collects the carrier and target distance information to obtain an interferometer photoelectric signal Where DC is direct current, A is the signal strength, Φ(d) is the phase transfer function of phase change caused by distance change, and f m is the phase modulation frequency, C is the modulation depth, It is the initial phase of modulation.

3. The modulation and demodulation method of a laser interferometer distance sensor according to claim 2, characterized in that: The specific process of respectively obtaining the intensity values ​​and phase values ​​at several odd harmonics and several even harmonics of the Fourier transform result is as follows: A1. Calculate the intensity values ​​of several odd harmonics and several even harmonics of the Fourier transform result, wherein the intensity values ​​of the first x odd harmonics of the Fourier transform result are expressed as: The intensity values ​​of the first y even harmonics of the Fourier transform result are expressed as: Where x and y are both positive integers, φ=Φ(d), denote k1 and k2 order Bessel functions respectively; A2. Calculate the sum of the intensities of odd harmonics and even harmonics respectively, and get: Where l1 represents the parameter sign of the sum of the intensities of the first x odd harmonics, l2 represents the parameter sign of the sum of the intensities of the first y even harmonics, and F(f odd,x |φ) represents the function sign of the sum of the intensities of the first x odd harmonics, F(f even,y |φ) represents the function symbol of the sum of the intensities of the first y even harmonics, f odd,x represents the first x odd harmonics of the Fourier transform result, f even,y represents the first y even harmonics of the Fourier transform result; A3. Obtain the initial phase value of the pth odd harmonic and the initial phase value of the qth even harmonic, wherein the initial phase value of the pth odd harmonic is expressed as: The initial phase value of the qth even harmonic is expressed as: Wherein, sgn{·} is a sign function, |pq|=2r, and r is an integer not less than 0.

4. The modulation and demodulation method of a laser interferometer distance sensor according to claim 3, characterized in that: Based on the intensity values ​​and phase values ​​at the odd harmonics and the even harmonics, combined with the theoretically calculated response function or calibration function, the phase transfer function is solved, and then the specific process of calculating the target distance information through the solved phase transfer function is as follows: A4. Calculate the normalized harmonic intensity ratio: σ(φ)=σ(φ(d))=(l1-l2) / (l1+l2)= [F(f odd,x |φ)-F(f even,y |φ)] / [F(f odd,x |φ)+F(f even,y |φ)]; A5. The process of obtaining the phase value intervals of odd harmonics and even harmonics of different target distance information through the calibration function is as follows: Apply different target distance information to the target, repeat steps A1-A4, and obtain the initial phase value of the pth odd harmonic corresponding to different target distance information and the initial phase value of the qth even harmonic And the normalized harmonic intensity ratio σ(Φ(d)), thereby analyzing, and then binarizing the initial phase value of the p-th odd harmonic and the initial phase value of the q-th even harmonic at different target distances d, respectively, to obtain the new phase value of the p-th odd harmonic and the new phase value of the q-th even harmonic, thereby analyzing the rules of the new phase values ​​of the odd harmonics and the even harmonics with different target distance information d, and obtaining the intervals to which the new phase values ​​of the odd harmonics and the even harmonics with different target distance information d belong, and the new phase value of the p-th odd harmonic and the new phase value of the q-th even harmonic are respectively and Alternatively, the process of obtaining the intervals to which the phase values ​​of the odd harmonics and the even harmonics of different target distance information belong through the theoretically calculated response function is: Repeat steps A1-A4, set the corresponding target distance information d through theory or simulation, and obtain the new phase of the pth odd harmonic corresponding to different target distance information and the new phase of the qth even harmonic and the normalized harmonic intensity ratio σ(Φ(d)), thereby analyzing the rules of the new phase values ​​of the odd harmonics and the even harmonics of different target distance information d, and obtaining the intervals to which the new phase values ​​of the odd harmonics and the even harmonics of different target distance information d belong; A6. Calculating the phase transfer function based on the intervals to which the new phase values ​​of the odd harmonics and the even harmonics of different target distance information d belong; A7. Calculate the target distance information by using the resolved phase transfer function on the interferometer photoelectric signal that needs to be used for distance detection later.

5. The modulation and demodulation method of a laser interferometer distance sensor according to claim 4, characterized in that: In A5, the specific process of binarizing the initial phase value of the pth odd harmonic and the initial phase value of the qth even harmonic is as follows: A5.

1. Set the initial phase value of the pth odd harmonic to According to the phase winding law, the first phase value is obtained by converting it into the range [0,2π); A5.

2. Perform interval classification statistics on the distribution of the first phase values ​​of different target distance information. If there are three enriched intervals [0, a), [a, b), and [b, 2π), add 2π to the first phase value belonging to the interval [0, a), and then perform interval classification statistics again to obtain two enriched intervals [a, b) and [b, a+2π), and then jump to A5.

3. If there are two enriched intervals [0, a) and [a, 2π), jump directly to A5.

3. A5.

3. Calculate the mean of the first phase values ​​in the two enrichment intervals respectively, and replace the values ​​in the corresponding intervals with the mean of the two first phase values. The value is completed Binarization, after binarization Recorded as A5.

4. Set the initial phase value of the qth even harmonic to According to the phase winding law, the second phase value is converted into the interval [0,2π); A5.

5. Perform interval classification statistics on the distribution of the second phase values ​​of different target distance information. If the statistics show three enriched intervals [0, a), [a, b), and [b, 2π), add 2π to the second phase value belonging to the interval [0, a), and then perform interval classification statistics again to obtain two enriched intervals [a, b) and [b, a+2π), and then jump to A5.

6. If the statistics show two enriched intervals [0, a) and [a, 2π), jump directly to A5.

6. A5.

6. Calculate the mean of the second phase values ​​in the two enrichment intervals respectively, and use the mean of the two second phase values ​​to replace the values ​​in the corresponding intervals. The value is completed Binarization, after binarization Recorded as 6. The modulation and demodulation method of a laser interferometer distance sensor according to claim 5, characterized in that: In A5.2 and A5.5, if the modulation function of the phase modulator is a standard sine function, the range of variation of different target distance information d must satisfy the requirement that the corresponding change of Φ(d) exceeds Then, the symmetry of the phase transfer function is used to obtain The phase transfer function of the region outside the region; If the modulation function of the phase modulator is not a standard sinusoidal function, the variation range of different target distance information d must satisfy the requirement that the corresponding variation of Φ(d) exceeds 2π.

7. The modulation and demodulation method of a laser interferometer distance sensor according to claim 5, characterized in that: The phase transfer function Φ(d) based on the initial phase value of the pth odd harmonic and the initial phase value of the qth even harmonic and the normalized harmonic intensity ratio is expressed as: The phase transfer function Φ(d) based on the new phase value of the pth odd harmonic and the new phase value of the qth even harmonic and the normalized harmonic intensity ratio is expressed as: Where n is the refractive index of the optical transmission medium, λ is the wavelength of the light source, Represents the transfer function relationship obtained by experimental calibration, theoretical calculation or simulation.

8. The modulation and demodulation method of a laser interferometer distance sensor according to claim 7, characterized in that: The intervals to which the new phase values ​​of the odd harmonics obtained by combining the calibration function belong include interval 1 and interval 2, where: Interval 1 is expressed as: Interval 2 is expressed as: The intervals to which the new phase values ​​of even harmonics belong include intervals three and four, where: Interval three is expressed as: Interval 4 is expressed as: Where k3 represents an integer, are two possible values ​​obtained by binarizing the initial phase value of the odd harmonics. are two possible values ​​obtained by binarizing the initial phase value of the even harmonics; The intervals of the new phase values ​​of the odd harmonics obtained by combining the theoretical response function include interval 1 and interval 2, where: Interval 1 is expressed as: Interval 2 is expressed as: The intervals to which the new phase values ​​of even harmonics belong include intervals three and four, where: Interval three is expressed as: Interval 4 is expressed as: Where k3 represents an integer, are two values ​​of the new phase of the odd harmonics obtained through the theoretical response function, are two values ​​of the new phase of the even harmonics obtained through the theoretical response function.

9. The modulation and demodulation method of a laser interferometer distance sensor according to claim 8, characterized in that: In step A6, the solved phase transfer function is expressed as: They respectively represent the transfer function relationships obtained by experimental calibration, theoretical calculation or simulation.

10. A modulation and demodulation system for a laser interferometer distance sensor, used to implement a modulation and demodulation method for a laser interferometer distance sensor according to any one of claims 1 to 9, characterized in that: include: A signal generation and acquisition device, used for generating an initial optical signal and acquiring an interferometer photoelectric signal including a carrier wave phase-modulated on the initial optical signal and target distance information obtained by distance detection of the initial optical signal, comprising a laser and a photodetector, wherein the output end of the laser is connected to a first optical fiber coupler via an optical fiber, the input end of the photodetector is connected to a second optical fiber coupler, a phase modulator is connected between the first optical fiber coupler and the second optical fiber coupler, and an optical fiber circulator is also connected between the first optical fiber coupler and the second optical fiber coupler, the other end of the optical fiber circulator is connected to a collimator for transmitting an optical signal to a target reflector, and the distance between the collimator and the target reflector is the target distance signal; A signal demodulation device is used to perform Fourier transform on the interferometer photoelectric signal to obtain a Fourier transform result, and then respectively obtain the intensity values ​​at several odd harmonics and several even harmonics of the Fourier transform result and the phase value of the pth odd harmonic and the phase value of the qth even harmonic, and based on the intensity values ​​and phase values ​​at the odd harmonics and the even harmonics, combined with a theoretically calculated response function or a calibration function, solve the phase transfer function, and then calculate the target distance information by solving the solved phase transfer function.

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