CN107228623A - absolute distance measurement method and system without guide rail - Google Patents

Abstract

The invention discloses a guide rail-free absolute distance measurement method and system, and relates to the field of laser distance measurement. Wherein the laser outputs first and second optical pulse sequences with different central wavelengths and repetition frequencies, and the first optical processing device performs spectrum expansion on the first optical pulse sequence so that the spectra of the first and second optical pulse sequences overlap; to be The distance measuring device makes the first light pulse sequence pass through the reflection of the target mirror and the reference mirror respectively to generate the target pulse sequence and the reference pulse sequence; the optical interference device makes the second light pulse sequence interfere with the target pulse sequence and the reference pulse sequence respectively, to generate a target interference signal and a reference interference signal; the information processing device obtains the distance difference between the target arm and the reference arm by using the difference between the phase spectrum lines of the target interference signal and the reference interference signal. The invention greatly simplifies the complexity of the distance measuring system, so that the absolute distance measuring method without guide rails can be truly applied to actual measurement occasions.

Description

Absolute distance measurement method and system without guide rail

technical field

The invention relates to the field of laser ranging, in particular to an absolute distance measuring method and system without a guide rail.

Background technique

Length measurement is the most basic measurement, and the length unit "meter (m)" is listed as one of the seven basic units in the International System of Units (SI). The precise measurement of large length or large size has a wide range of applications in the fields of high-end equipment manufacturing, space engineering and metrology technology, and has important scientific significance in the basic research of cutting-edge science and advanced technology.

Laser interferometry is the method with the highest precision in length measurement, but traditional laser interferometers usually use incremental displacement measurement methods, which need to be equipped with precision straight guide rails for the movement of the measuring mirror and whose length is at least greater than the measured distance, and The fringe count cannot be interrupted during the measurement, which greatly limits its application. In the occasions where the guide rail cannot be laid, the long-distance straightness of the guide rail is not enough, or the measurement process cannot be carried out continuously, the above method cannot be used at all. Therefore, carrying out large-length, high-precision absolute distance measurement technology research and instrument development is of great scientific significance for improving my country's original innovation capabilities in major precision engineering, space science experimental research, and precision metrology technology.

In the field of absolute large length measurement, the three elements of measurement range, measurement accuracy and measurement speed are the focus of most attention. Traditional large-length absolute distance measurement can be divided into two categories: time-of-flight method and interferometry method.

The time-of-flight method determines the measurement distance by measuring the time interval between pulse emission and return. Although the measurement range is large, due to the extremely fast speed of light, it is difficult for the accuracy of electronic devices to directly measure the time interval to exceed the picosecond level. Due to the limitation of time accuracy, the distance measurement accuracy can only reach the order of millimeters.

The traditional interferometry method is based on the optical path of the Michelson interferometer structure. The measurement distance is obtained by measuring the optical phase information between the reference arm and the measurement arm. The measurement resolution can reach nanometers, but the pure phase resolution cannot determine integers greater than 2π The period is therefore limited in range. Even if the multiple of the entire period of the light wave of the measured distance is obtained by counting interference fringes, it is only suitable for incremental displacement measurement and cannot achieve absolute distance measurement.

Before the femtosecond optical comb appeared, the light source used in the traditional interferometry method was a single-frequency continuous laser, but the appearance of the femtosecond optical comb changed all this, because it has an extremely narrow pulse width in the time domain (femtosecond On the order of magnitude, one femtosecond is equal to 10 ^-15 seconds) ultrashort pulse, and in the frequency domain, it corresponds to a wide spectrum composed of multiple discrete spectral lines, which is equivalent to simultaneously outputting multiple single-frequency lasers. Therefore, the femtosecond optical comb can use the above two methods to measure distance at the same time, so as to take into account the requirements of absolute distance measurement for range and accuracy. Representative methods such as femtosecond pulse optical balance cross-correlation method, synthetic wavelength method, spectral resolution interferometry . The absolute distance measurement method based on two optical combs with slightly different repetition frequencies as the light source is a major innovation to the traditional single optical comb distance measurement method. This method utilizes the slight difference in the repetition frequency between two optical combs, and uses the pulses of one optical comb (local optical comb) to asynchronously scan the pulses of the other optical comb (signal optical comb) in the time domain, The asynchronous sampling signal is obtained and the distance to be measured is calculated from it. The first advantage of this method is that it "slows down" the time-domain measurement process and reduces the requirements for the detector bandwidth, thereby realizing the time-domain detection of pulses, and at the same time expanding the measurement range without dead ends. At the same time, since the two-pulse coincidence process is automatic, real-time and repeated in the measurement process, there is no need to move auxiliary mechanical equipment such as guide rails. This is a new absolute distance measurement method, which is different from the traditional incremental displacement measurement method, and Because the measurement speed depends on the difference between the two pulse repetition frequencies, the measurement speed is very fast, which is beneficial to improve the real-time performance of the system and facilitate real-time feedback. Therefore, the dual-comb method not only combines the characteristics of large-scale and high-precision measurement of the ordinary single-comb method, but also has a very fast measurement speed. It truly combines the three elements of length measurement—range, accuracy and speed. The two are perfectly combined together, and different from the traditional incremental displacement measurement method, this is an absolute distance measurement method that does not need to move mechanical devices such as guide rails to avoid errors introduced thereby. However, this method has very strict requirements on the coherence of the two optical combs. The usual method is to lock the two optical combs to the ultra-stable cavity to narrow the linewidth of the comb teeth of the optical comb. For example, Coddington et al. This method realizes the measurement of the length of a section of optical fiber about 1.14km long, and the measurement accuracy reaches 5nm. However, since the system needs to achieve high precision, optical comb locking and ultra-stable laser technology are required at the same time, the technical threshold is high, the operation is complicated, and it is extremely difficult to realize.

Contents of the invention

Embodiments of the present invention provide a method and system for measuring absolute distance without a guide rail,

In order to solve the problems of low time resolution, incremental displacement measurement and difficulty in obtaining absolute distance information in the traditional ranging method, and to overcome the shortcomings of the traditional dual-comb ranging method with complex system and cumbersome operation, this paper The invention proposes a dual-wavelength pulse absolute ranging system that can output two sets of pulse sequences with slight differences in repetition frequency as a ranging light source. .

According to one aspect of the present invention, there is provided a guide rail-less absolute distance measuring system, comprising:

A laser for outputting a sequence of optical pulses, wherein the sequence of optical pulses includes a first sequence of optical pulses and a second sequence of optical pulses with different center wavelengths and repetition frequencies;

The first optical processing device is used to separate the first optical pulse sequence and the second optical pulse sequence from the optical pulse sequence output by the laser, and perform spectrum expansion on the first optical pulse sequence so as to make the first optical pulse sequence and the second optical pulse sequence Spectral overlap of light pulse trains;

The distance-measuring device is used to make the first optical pulse sequence after spectrum expansion pass through the reflection of the target mirror and the reference mirror in the distance-measuring device respectively, so as to generate the target pulse sequence and the reference pulse sequence;

An optical interference device, used to make the second optical pulse sequence interfere with the target pulse sequence and the reference pulse sequence respectively, so as to generate the target interference signal and the reference interference signal;

The information processing device is used to collect the target interference signal and the reference interference signal, and use the difference between the phase lines of the target interference signal and the reference interference signal to obtain the distance difference between the target arm corresponding to the target mirror and the reference arm corresponding to the reference mirror .

In one embodiment, the above system also includes:

The second optical processing device is used to divide the second optical pulse sequence into a first local pulse sequence and a second local pulse sequence, so that the optical interference device uses the first local pulse sequence to interfere with the target pulse sequence and the reference pulse sequence respectively.

In one embodiment, the optical power of the first local pulse sequence is less than the optical power of the second local pulse sequence.

In one embodiment, the above system further includes a photodetector for detecting the repetition frequency of the second local pulse sequence to be used as a signal acquisition clock signal of the information processing device.

In one embodiment, the information processing device is used to collect the target interference signal and the reference interference signal in the time domain, respectively perform time-frequency domain transformation on the collected target interference signal and the reference interference signal, so as to obtain the first A phase spectrum line and a second phase spectrum line corresponding to the reference interference signal, by using the difference between the first phase spectrum line and the second phase spectrum line, the distance difference between the target arm and the reference arm is obtained.

In one embodiment, the difference between the first phase spectrum line and the second phase spectrum line is proportional to the distance difference between the target arm and the reference arm.

According to another aspect of the present invention, there is provided a method for measuring absolute distance without a guide rail, comprising:

The laser outputs an optical pulse sequence, wherein the optical pulse sequence includes a first optical pulse sequence and a second optical pulse sequence having different central wavelengths and repetition frequencies;

The first optical processing device separates the first optical pulse sequence and the second optical pulse sequence from the optical pulse sequence output by the laser, and performs spectrum expansion on the first optical pulse sequence, so that the first optical pulse sequence and the second optical pulse sequence spectral overlap;

The distance-measuring device makes the first light pulse sequence after spectrum expansion pass through the reflection of the target mirror and the reference mirror in the distance-measuring device respectively, so as to generate the target pulse sequence and the reference pulse sequence;

The optical interference device makes the second optical pulse sequence interfere with the target pulse sequence and the reference pulse sequence respectively, so as to generate the target interference signal and the reference interference signal;

The information processing device collects the target interference signal and the reference interference signal, and uses the difference between the phase spectrum lines of the target interference signal and the reference interference signal to obtain the distance difference between the target arm corresponding to the target mirror and the reference arm corresponding to the reference mirror.

In one embodiment, the second optical processing device divides the second optical pulse sequence into a first local pulse sequence and a second local pulse sequence, so that the optical interference device uses the first local pulse sequence to compare with the target pulse sequence and the reference pulse sequence respectively Intervene.

In one embodiment, the optical power of the first local pulse sequence is less than the optical power of the second local pulse sequence.

In one embodiment, the photodetector detects the repetition frequency of the second local pulse sequence to serve as a signal acquisition clock signal of the information processing device.

In one embodiment, the information processing device collects the target interference signal and the reference interference signal in the time domain;

respectively performing time-frequency domain transformation on the collected target interference signal and the reference interference signal to respectively obtain the first phase spectrum line corresponding to the target interference signal and the second phase spectrum line corresponding to the reference interference signal;

By using the difference between the first phase spectrum line and the second phase spectrum line, the distance difference between the target arm and the reference arm is obtained.

In one embodiment, the difference between the first phase spectrum line and the second phase spectrum line is proportional to the distance difference between the target arm and the reference arm.

Other features of the present invention and advantages thereof will become apparent from the following detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained according to these drawings without any creative effort.

Fig. 1 is a schematic diagram of an embodiment of the absolute distance measuring system without a guide rail of the present invention.

FIG. 2 is a schematic diagram of another embodiment of the absolute distance measuring system without guide rails of the present invention.

Fig. 3 is a schematic diagram of an embodiment of the configuration of the absolute distance measuring system without guide rails of the present invention.

Fig. 4 is a schematic diagram of an embodiment of the method for measuring absolute distance without a guide rail according to the present invention.

detailed description

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. The following description of at least one exemplary embodiment is merely illustrative in nature and in no way taken as limiting the invention, its application or uses. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

The relative arrangements of components and steps, numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present invention unless specifically stated otherwise.

At the same time, it should be understood that, for the convenience of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship.

Techniques, methods and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, such techniques, methods and devices should be considered part of the Authorized Specification.

In all examples shown and discussed herein, any specific values should be construed as exemplary only, and not as limitations. Therefore, other examples of the exemplary embodiment may have different values.

It should be noted that like numerals and letters denote like items in the following figures, therefore, once an item is defined in one figure, it does not require further discussion in subsequent figures.

Fig. 1 is a schematic diagram of an embodiment of the absolute distance measuring system without a guide rail of the present invention. As shown in Figure 1, the measurement system includes:

The laser 1 is used to output an optical pulse sequence, wherein the optical pulse sequence includes a first optical pulse sequence and a second optical pulse sequence with different center wavelengths and repetition frequencies, and the repetition frequency of the first optical pulse sequence and the second optical pulse sequence is There are minor differences.

The first optical processing device 2 is used to separate the first optical pulse sequence and the second optical pulse sequence from the optical pulse sequence output by the laser 1, and perform spectrum expansion on the first optical pulse sequence, so that the first optical pulse sequence and the second optical pulse sequence Spectral overlap of two light pulse trains.

The distance-measuring device 3 is configured to make the spectrum-expanded first optical pulse sequence be reflected by the target mirror and the reference mirror in the distance-measuring device respectively, so as to generate a target pulse sequence and a reference pulse sequence.

Optionally, the distance-measuring device 3 may be a Michelson interferometer. In the distance-measuring device 3, the first light pulse sequence is reflected by the target mirror and the reference mirror in the distance-measuring device respectively, so as to generate a target pulse sequence passing through the target arm and a reference pulse sequence passing through the reference arm.

Since Michelson interferometers are known to those skilled in the art, they will not be described here.

The optical interference device 4 is used to make the second optical pulse sequence interfere with the target pulse sequence and the reference pulse sequence respectively, so as to generate a target interference signal and a reference interference signal.

The information processing device 5 is used to collect the target interference signal and the reference interference signal, and use the difference between the phase lines of the target interference signal and the reference interference signal to obtain the distance difference between the target arm corresponding to the target mirror and the reference arm corresponding to the reference mirror .

Based on the guide rail-less absolute distance measurement system provided by the above-mentioned embodiments of the present invention, the dual-wavelength pulse absolute distance measurement system built by using two sets of pulse sequences that can output two sets of pulse sequences with slight differences in repetition frequency as the distance measurement light source overcomes the traditional distance measurement The shortcomings of the method are realized to achieve large-range, high-precision, fast and real-time measurement.

Optionally, the information processing device 5 collects the target interference signal and the reference interference signal in the time domain, and performs time-frequency domain transformation on the collected target interference signal and the reference interference signal respectively to obtain the first phase spectrum corresponding to the target interference signal line and the second phase spectrum line corresponding to the reference interference signal, by using the difference between the first phase spectrum line and the second phase spectrum line, the distance difference between the target arm and the reference arm is obtained.

Wherein, the difference between the first phase spectrum line and the second phase spectrum line is proportional to the distance difference between the target arm and the reference arm.

Fig. 2 is a schematic diagram of an embodiment of the absolute distance measuring system without guide rails of the present invention. Compared with the embodiment shown in Figure 1, in Figure 2, the measurement system further includes:

The second optical processing device 6 is used to divide the second optical pulse sequence into a first local pulse sequence and a second local pulse sequence, so that the optical interference device 4 uses the first local pulse sequence to interfere with the target pulse sequence and the reference pulse sequence respectively .

Optionally, the optical power of the first local pulse sequence is smaller than the optical power of the second local pulse sequence. For example, the optical power ratio of the first local pulse sequence to the second local pulse sequence is 3:7.

In addition, in the embodiment shown in FIG. 2 , a photodetector 7 is also included for detecting the repetition frequency of the second local pulse sequence, so as to serve as a signal acquisition clock signal of the information processing device 5 .

The present invention will be described below through a specific example.

As shown in FIG. 3 , the laser 301 is a dual-wavelength mode-locked laser, which can generate two mode-locked optical pulse sequences with a slight repetition frequency difference. Looking at the two pulse sequences on the spectrometer, they belong to two adjacent spectral peaks, and their central wavelengths are 1533nm and 1542nm respectively (the actual wavelength value may vary with the mode-locking state), precisely because The difference of different light wavelengths to the refractive index in the cavity finally leads to the difference of the respective repetition frequencies of the two pulse sequences with different center wavelengths. The two pulse trains are separated by a CWDM wavelength division multiplexer 302 before taking measurements with this light source. Here, one of the pulse sequences (1542nm here) is selected as the first optical pulse sequence, and the other pulse sequence (1533nm) is selected as the second optical pulse sequence for asynchronous sampling. After the first optical pulse sequence is amplified and the spectrum is broadened by the erbium-doped fiber amplifier EDFA 303, its spectrum can cover the 1533nm wave band, and then pass through a narrow-band filter 304 with a 3dB width of about 0.8nm, and only the first optical pulse sequence is kept in the Spectrum near 1533nm.

Secondly, the amplified and filtered optical pulse sequence is converted into spatial light through a fiber collimator (FC) 305, and enters into a spatial optical path of a Michelson interferometer structure. In this way, through the optical path (reference arm) between the polarization beam splitting prism PBS 306 and the interferometer reference mirror 307, and the optical path (target arm) between the polarization beam splitting prism PBS 306 and the objective mirror 308, the reference mirror 307 and the objective mirror 308 are respectively Reflected back to the reference pulse and the target pulse. These two pulse sequences are bundled together at the tail end of the interferometer, coupled into an optical fiber through a collimator (FC), and enter one of the input ends of a 2×2 fiber coupler 309, and simultaneously pass through a fiber coupler 311 Part of the power (30%) of the second optical pulse sequence is connected to the other input terminal of the coupler 309 , and the output terminal of the coupler 309 is connected to a balanced detector (BPD) 310 . The remaining power (70%) of the second optical pulse sequence is detected by a photodetector (PD) 312, and its repetition frequency f _r1 can be obtained. After passing through a filter (LPF) 313 and an electrical amplifier (AMP) 314, it is obtained as The external clock signal of the high-speed AD acquisition card 315.

Subsequently, the interferogram analysis module 316 intercepts and separates the collected two-way interference signals in the time domain, calculates and performs Fourier transform on them respectively, and obtains their corresponding phase spectra. The phase values corresponding to the Fourier frequencies on the two phase spectra are subtracted to obtain a phase spectrogram reflecting the phase difference of the two signals, and the distance to be measured is calculated through the phase spectrogram.

The relevant theoretical analysis and algorithm are as follows:

As shown in Figure 3, the electric field expressions of the 1542nm pulse sequence (signal pulse) and the 1533nm pulse sequence (local pulse) separated by the CWDM wavelength division multiplexer 302 can be expressed as:

Among them, E _ref (t) and E _tar (t) respectively represent the pulse sequence returned by the 1542nm pulse sequence (signal pulse) through the Michelson interferometer reference arm and measurement arm, f _r and f ₀₁ are the repetition frequency and system Frequency shift, τ represents the delay between the measurement arm and the reference arm. And E _LO (t) represents 1533nm pulse sequence (local pulse), f _r + _Δfr and f ₀₂ are its repetition frequency and system frequency shift respectively. Therefore, when the signals involved in formulas (1) and (2) interfere with the electric field involved in formula (3), the interference signal of the reference arm and the interference signal of the measuring arm obtained on the photodetector can be expressed as:

I _ref = (E _ref +E _LO )(E _ref +E _LO ) ^* (4)

I _tar ＝(E _tar +E _LO )(E _tar +E _LO ) ^* (5)

Substituting formulas (1), (2) and (3) into formulas (4) and (5), due to the balanced detection method, the DC square sub-item expanded in formulas (4) and (5) will be eliminated, Only the relevant sub-items E _ref E _LO or E _tar E _LO remain. And the high-frequency components are filtered out by low-pass filtering, and only the frequency components from zero to _0.5fr are retained. Therefore, the electric field of the reference arm interference signal and the measurement arm interference signal obtained by sampling the data acquisition card (AD) can be expressed as:

Wherein, the value of i ranges from 0 to N/2, and N is usually called a conversion factor, and its value is equal to (f _r +Δf _r )/Δf _r .

Normally, m and n are not equal, so i is not equal to m or n. But if f _r , _Δfr , f ₀₁ and f ₀₂ are determined, there is a unique correspondence between i and m in formula (7). According to formulas (6) and (7), the phase difference expressions of the corresponding spectral lines of the measuring arm and the reference arm are obtained:

In the formula, L represents the distance difference between the measuring arm and the reference arm, that is, the distance to be measured. c is the speed of light in vacuum, and n _g is the correction value of the air refractive index. Formula (8) is the phase difference spectrum of the measurement arm interference signal and the reference arm interference signal finally obtained in the third step. According to the formula (8), it is easy to know that the phase difference spectrum is a linear curve: Among them, φ(0) is the intercept of the curve on the vertical axis. According to the formula (8), that is, when the ordinal number i is zero, the light frequency mf _r + f ₀₁ passes through the distance to be measured. The light phase change experienced, as mentioned above If f _r , _Δfr , f ₀₁ and f ₀₂ are determined, then the optical frequency _mfr + f ₀₁ is uniquely determined, and b is the slope of the curve. The specific method to solve the distance to be measured is as follows:

The first step is to use the time-of-flight method to solve the rough value of the distance to be measured. Calculate the rough value of the distance to be measured through the slope b, and solve the slope according to the formula (8)

Then the rough value of the measured distance is:

In the field of length measurement, we generally refer to the maximum range of the measurement system as the fuzzy range. From the formula (9), it can be known that the fuzzy range of the time-of-flight method is

Taking the repetition frequency f _r =58MHz as an example, the fuzzy range is about 2.6m, which is the maximum range that can be measured by this method.

The second step uses the interferometry method to solve the distance precision value. According to the principle of laser interferometry ranging, the precise value of the distance to be measured can be expressed as:

λ ₀ is the wavelength value corresponding to the optical frequency mf _r + f ₀₁ , and the large number k is determined by the roughly measured value L _tof in the previous step. The necessary condition is that the uncertainty of L _tof is at least better than λ ₀ /2. In formula (10) value is The part that is less than the multiple of the full period of 2π, that is, the remainder obtained by dividing φ(0) by 2π. From formula (10), it can be seen that the fuzzy range of the interferometry is λ ₀ 2, which reaches the resolution of light wavelength order.

The third step is to use the cursor principle to expand the maximum range. To sum up, even if the time-of-flight method is adopted, its maximum measurement range is only on the order of m, which cannot cope with longer-distance measurements. The measuring range can be extended by the vernier principle. The specific method is to measure the distance L ₁ through the original system first, then exchange the roles of the two pulse sequences (that is, the 1533nm pulse sequence is used as the signal pulse, and the 1542nm pulse sequence is used as the local pulse), and re-measure to obtain the distance _L2 . Then the two measurement results can be expressed as:

D=mR ₁ +L ₁ =mR ₂ +L ₂ (11)

Wherein D is the distance to be measured, and R_1 and R_2 are respectively the fuzzy ranges of the time-of-flight method in the two measurements, namely:

In order to ensure that m on the left and right sides of the equation (11) is the same, the condition needs to be met:

D<R ₁ R ₂ /(R ₁ +R ₂ )

R ₁ , R ₂ , L ₁ , and L ₂ are known, and m can be obtained by solving m according to formula (11). Taking f _r ≈58MHz and Δf _r ≈800Hz as an example, the maximum range can reach 187km!

Fig. 4 is a schematic diagram of an embodiment of the method for measuring absolute distance without a guide rail according to the present invention. in:

In step 401, the laser outputs an optical pulse sequence, wherein the optical pulse sequence includes a first optical pulse sequence and a second optical pulse sequence with different center wavelengths and repetition frequencies.

Step 402, the first optical processing device separates the first optical pulse sequence and the second optical pulse sequence from the optical pulse sequence output by the laser, and performs spectrum expansion on the first optical pulse sequence, so that the first optical pulse sequence and the second optical pulse sequence Spectral overlap of light pulse trains.

Step 403 , the device to be measured makes the first light pulse sequence after spectral expansion be reflected by the target mirror and the reference mirror in the device to be measured respectively, so as to generate a target pulse sequence and a reference pulse sequence.

Step 404, the optical interference device makes the second optical pulse sequence interfere with the target pulse sequence and the reference pulse sequence respectively, so as to generate a target interference signal and a reference interference signal.

Optionally, the second optical processing device divides the second optical pulse sequence into a first local pulse sequence and a second local pulse sequence. The optical interference device uses the first local pulse sequence to interfere with the target pulse sequence and the reference pulse sequence respectively to generate the target interference signal and the reference interference signal

Wherein, the optical power of the first local pulse sequence is smaller than the optical power of the second local pulse sequence.

Step 405, the information processing device collects the target interference signal and the reference interference signal, and uses the difference between the phase spectrum lines of the target interference signal and the reference interference signal to obtain the distance difference between the target arm corresponding to the target mirror and the reference arm corresponding to the reference mirror .

Optionally, the photodetector detects the repetition frequency of the second local pulse sequence to serve as a signal acquisition clock signal of the information processing device.

Optionally, the information processing device collects the target interference signal and the reference interference signal in the time domain, and performs time-frequency domain transformation on the collected target interference signal and the reference interference signal respectively, so as to respectively obtain the first phase spectral lines corresponding to the target interference signal The second phase spectral line corresponding to the reference interference signal; by using the difference between the first phase spectral line and the second phase spectral line, the distance difference between the target arm and the reference arm is obtained.

Wherein, the difference between the first phase spectrum line and the second phase spectrum line is proportional to the distance difference between the target arm and the reference arm.

Based on the guide rail-less absolute distance measurement method provided by the above-mentioned embodiments of the present invention, the dual-wavelength pulse absolute distance measurement system built by using two sets of pulse sequences that can output two sets of pulse sequences with slight differences in repetition frequency as the distance measurement light source overcomes the traditional distance measurement The shortcomings of the method are realized to achieve large-range, high-precision, fast and real-time measurement.

By implementing the present invention, a dual-wavelength mode-locked pulse laser that can simultaneously output two pulse sequences with slight differences in repetition frequency is used instead of the traditional dual-comb scheme as an absolute ranging light source without guide rails, which greatly simplifies the complexity of the ranging system The degree makes it possible for the absolute ranging method without a guide rail to be applied to actual measurement occasions.

Those of ordinary skill in the art can understand that all or part of the steps for implementing the above embodiments can be completed by hardware, and can also be completed by instructing related hardware through a program. The program can be stored in a computer-readable storage medium. The above-mentioned The storage medium mentioned may be a read-only memory, a magnetic disk or an optical disk, and the like.

The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and changes will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to better explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention and design various embodiments with various modifications as are suited to the particular use.

Claims (12)

1. a kind of absolute distance measurement system without guide rail, it is characterised in that including：

Laser, for output optical pulse sequence, wherein light pulse sequence includes having different centre wavelength and repeats frequency The first light pulse sequence and the second light pulse sequence of rate；

First optical processing device, for isolating the first light pulse sequence and second from the light pulse sequence that laser is exported Light pulse sequence, carries out spectrum extension, to make the first light pulse sequence and the second light pulse sequence by the first light pulse sequence Spectra overlapping；

Measured device, for extending spectrum after the first light pulse sequence respectively by the target mirror in measured device and The reflection of reference mirror, to generate target pulse sequence and reference pulse sequence；

Optical interferometric devices, for making the second light pulse sequence be done respectively with target pulse sequence and reference pulse sequence Relate to, to generate target interference signal and refer to interference signal；

Information processor, for gathering target interference signal and referring to interference signal, and utilizes target interference signal and reference The difference of the phase spectral line of interference signal, obtains the distance between the corresponding target-arm of target mirror and the corresponding reference arm of reference mirror Difference.

2. system according to claim 1, it is characterised in that also include：

Second optical processing device, for the second light pulse sequence to be divided into first earth pulse sequence and second earth pulse sequence Row, so that optical interferometric devices are done with target pulse sequence and reference pulse sequence respectively using first earth pulse sequence Relate to.

3. system according to claim 2, it is characterised in that

The luminous power of first earth pulse sequence is less than the luminous power of the second local pulse train.

4. system according to claim 2, it is characterised in that also include：

Photodetector, the repetition rate for detecting the second local pulse train, is adopted using the signal as information processor Collect clock signal.

5. the system according to any one of claim 1-4, it is characterised in that

Information processor is used to gather target interference signal in time domain and refers to interference signal, respectively to the target dry of collection Relate to signal and with reference to interference signal carry out time-frequency domain conversation, with respectively obtain the corresponding first phase spectral line of target interference signal and With reference to the corresponding second phase spectral line of interference signal, by using the difference of first phase spectral line and second phase spectral line, mesh is obtained Mark the distance between arm and reference arm difference.

6. system according to claim 5, it is characterised in that

The difference of first phase spectral line and second phase spectral line is directly proportional to the distance between target-arm and reference arm difference.

7. a kind of absolute distance measurement method without guide rail, it is characterised in that including：

Laser output optical pulse sequence, wherein light pulse sequence include the with different centre wavelength and repetition rate One light pulse sequence and the second light pulse sequence；

The first light pulse sequence and the second smooth arteries and veins are isolated in the light pulse sequence that first optical processing device is exported from laser Sequence is rushed, the first light pulse sequence spectrum extension is subjected to, to make the light of the first light pulse sequence and the second light pulse sequence Spectrum is overlapping；

Measured device makes the first light pulse sequence after spectrum extension respectively by the target mirror in measured device and reference The reflection of mirror, to generate target pulse sequence and reference pulse sequence；

Optical interferometric devices make the second light pulse sequence be interfered respectively with target pulse sequence and reference pulse sequence, with life Into target interference signal and refer to interference signal；

Information processor gathers target interference signal and refers to interference signal, and using target interference signal and with reference to interference letter Number phase spectral line difference, obtain the distance between the corresponding target-arm of target mirror and the corresponding reference arm of reference mirror difference.

8. method according to claim 7, it is characterised in that also include：

Second light pulse sequence is divided into first earth pulse sequence and the second local pulse train by the second optical processing device, with Just optical interferometric devices are interfered with target pulse sequence and reference pulse sequence respectively using first earth pulse sequence.

9. method according to claim 8, it is characterised in that

The luminous power of first earth pulse sequence is less than the luminous power of the second local pulse train.

10. method according to claim 8, it is characterised in that also include：

Photodetector detects the repetition rate of the second local pulse train, using the signal acquisition clock as information processor Signal.

11. the method according to any one of claim 7-10, it is characterised in that

Information processor gathers target interference signal in time domain and refers to interference signal；

Target interference signal and reference interference signal respectively to collection carries out time-frequency domain conversation, to respectively obtain target interference letter Number corresponding first phase spectral line with reference to the corresponding second phase spectral line of interference signal；

By using the difference of first phase spectral line and second phase spectral line, the distance between target-arm and reference arm difference are obtained.

12. method according to claim 11, it is characterised in that

The difference of first phase spectral line and second phase spectral line is directly proportional to the distance between target-arm and reference arm difference.