CN1126945C - Virtual synthesis wave long-chain absolute distance interferometry and its equipment for implementing one - Google Patents

Abstract

The invention belongs to the technical field of absolute distance measurement, and relates to a virtual synthetic wavelength chain absolute distance interferometric method and a realization device. Two double-beam interferometers used in a straight line are modulated by piezoelectric ceramics and tunable lasers are used to measure the wavelength value and the phase of the single-wavelength interference signal while the wavelength is tuned, and calculate the virtual synthetic wave interference fringes. decimal order. A series of virtual synthetic wavelength chains from large to small are obtained by tuning the laser, and the rough and fine measurement of the absolute distance is completed. The invention has the characteristics of high measurement accuracy of fractional fringes and can complete the process from rough measurement to precise measurement at one time, is suitable for internal and external dimension measurement, and can be used for making micro-sized measuring heads.

Description

Absolute distance interferometry method and implementation device of virtual synthetic wavelength chain

technical field

The invention belongs to the technical field of absolute distance measurement, and in particular relates to the improvement of a synthetic wavelength absolute distance interferometric method.

Background technique

The absolute distance measurement method without guide rail has a broad application prospect in precision measurement. Compared with the relative measurement method with guide rail, it has obvious advantages. Even wrong. One of the most commonly used absolute distance interferometry methods is the synthetic wavelength method, which uses the beat waves (ie synthetic waves) of two light waves to form interference signals in the interference system. For a given distance to be measured, when the beat wave wavelength ( That is, when the synthesized wavelength) is long enough, the integer order of the synthesized wave interference signal can be uniquely determined, so the distance to be measured can be accurately measured only by measuring the fractional order of the interference signal. In the synthetic wave absolute distance interferometry system, it is necessary to directly measure the fractional order of the synthetic wave interference signal. The light source used for this purpose must be able to emit two or more stable wavelengths at the same time, usually through one or more lasers Realized, such as CO ₂ laser, 3.39μm band dual-wavelength HeNe laser, 0.6328μm longitudinal Zeeman HeNe laser and 0.6328μm dual longitudinal mode HeNe laser. It can be seen that the synthetic wavelength absolute distance interferometry method has the following two limitations:

1. Due to the use of multi-wavelength lasers or multiple single-wavelength lasers as light sources, the wavelength interval is a fixed value, so only some fixed synthetic wavelengths can be obtained. If the number of lasers is increased in order to obtain a suitable synthetic wavelength, it will make the system become quite complicated.

2. Another disadvantage of the fixed synthetic wavelength is that if the synthetic wavelength cannot be obtained long enough, it is necessary to increase the rough measurement means of the distance to be measured to uniquely determine the integer order of the synthetic wave interference signal.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the traditional synthetic wave absolute distance interferometry technology, and design a method and measurement system for absolute distance interferometry using virtual synthetic wavelength chains. This method does not directly measure the fractional order of the synthetic wave interference fringe, and has the characteristics of high precision in the measurement of the fractional fringe and can complete the process from rough measurement to fine measurement at one time. It is suitable for internal and external dimension measurement and can be used to make micro-sized probes .

A kind of virtual synthetic wavelength chain absolute distance interferometry method that the present invention proposes is characterized in that, comprises the following steps:

(1) A pair of single-side AR-coated glass lenses are arranged in parallel, and their non-coated surfaces A and C are opposite; then a pair of flat reflective lenses are placed between the pair of glass lenses, and the end faces B and D of the two reflective lenses Parallel to the two glass lenses, and the reflective surfaces of the two reflective lenses are respectively opposite to the two glass lenses, d ₁ and d ₂ are the distances between A, B and C, D respectively, d=d ₁ +d ₂ is distance to be measured;

(2) Divide the light beam emitted by the wavelength-tunable monochromatic light source into two paths of incident light, which are respectively incident on the four surfaces of A, B and C, D. The reflected light from the A and B surfaces return along the original path to interfere, and the reflected light from the C and D surfaces return along the original path to interfere, which constitutes two double-beam interferometers on a straight line;

(3) Use piezoelectric ceramics to drive any pair of mirrors to move along the optical axis at a constant speed υ, so that the interference signals of the two interferometers produce a Doppler frequency shift of the same size but opposite direction, so that d to be measured is included In the phase term of an AC signal, the measurement of the order of interference fringes is transformed into a phase measurement of the AC signal;

(4) Determine the virtual synthesis wavelength of the first stage as λ _s1 > 2d, and the inter-stage transition condition as λ _s(i+1) > 4Δd _i , so as to determine the virtual synthesis wavelengths of the remaining stages, calculate the corresponding wavelength interval, and obtain a A series of virtual synthetic wavelength chains from large to small;

其中

从而得到待测距离d的精确值：2d＝(N_s+ε_s)λ_s，其中N_s为与虚拟合成波对应的整数级次。(5) During the wavelength tuning process, simultaneously measure the wavelength values λ ₁ , λ ₂ ... λ _N and the fractional orders δ ₁ , δ ₂ ... δ _N of the interference fringes corresponding to the single wavelength, and determine a virtual synthetic wavelength λ _s by calculation ${\mathrm{\λ}}_{\mathrm{the\; s}}=\frac{{\mathrm{\λ}}_1{\mathrm{\λ}}_2}{|{\mathrm{\λ}}_1-{\mathrm{\λ}}_2|},$ and the fractional order and integer order δ _s of its interference fringes

in

Thus, the exact value of the distance d to be measured is obtained: 2d=(N _s +ε _s )λ _s , where N _s is an integer order corresponding to the virtual synthetic wave.

The distance between any pair of lenses arranged in parallel can be an accurate known value, and then the distance between the other pair of lenses can be obtained by measuring the gap between the two pairs of lenses.

The present invention proposes a measurement device using the above-mentioned virtual synthetic wavelength chain absolute distance interferometry method, which is characterized in that it includes a tunable laser, which is arranged on the optical path of the laser to divide the light beam into two light beams Components, a pair of anti-reflection-coated glass lenses on one side arranged in parallel in the optical path and a pair of flat reflective lenses placed between the pair of glass lenses, the non-coated surfaces A and C of the glass lenses are opposite, and the two reflective lenses The end surfaces B and D are parallel to the two glass lenses, and the reflective surfaces of the two reflective lenses are respectively opposite to the two glass lenses. D respectively constitute a two-beam interferometer on a straight line, which is used to modulate the piezoelectric ceramics of any pair of lenses, two detectors and subsequent amplification and rectification circuits for respectively receiving the interference signals of the two interferometers, A phase meter for measuring the phase difference of the interference signal of the two interferometers, a wavelength meter and a data processing unit for measuring the light emitted by the laser. The light emitted by the laser is divided into two paths by the first beam splitter, and the reflected light is incident into the wavelength meter; the transmitted light is divided into two beams by the second beam splitter: one beam of light is reflected and then incident on the beam formed by A and B. Double-beam interferometer, the reflected light from the A and B surfaces interferes and returns along the original path, and then passes through the second beam splitter, and the transmitted light signal is received by the detector; the other beam is reflected by the necessary and the third ordinary After the beam splitter, it enters the double-beam interferometer composed of C and D. The reflected light on the C and D surfaces interferes and returns along the original path, and the part transmitted by the third beam splitter is received by another detector. The two detectors The interference signal received by the detector is sent to the phase meter for phase comparison after being amplified and shaped, and the obtained data is processed by the data processing unit to obtain the distance d to be measured.

The wavelength tuning range of the tunable laser is several nanometers to more than ten nanometers.

The device of the present invention can be used to measure the internal and external dimensions of the workpiece. When measuring the external dimensions, the non-coated surface of the above-mentioned pair of single-sided antireflection-coated glass lenses is closely attached to two of a standard gauge block. End face; when measuring the inner dimension, replace the above pair of flat reflective mirrors arranged between the glass mirrors with standard ceramic gauge blocks.

The invention uses two double-beam interferometers on a straight line, modulated by piezoelectric ceramics, so that the measurement of fractional fringes is converted into high-precision phase measurement; the light source adopts a tunable laser. It realizes the measurement of the wavelength value and the phase of the single-wavelength interference signal while the wavelength is tuned, and calculates the fractional order of the virtual synthetic wave interference fringe. A series of virtual synthetic wavelength chains from large to small are obtained by tuning the laser, and the rough and fine measurement of the absolute distance is completed.

The principle of the present invention is shown in Figure 1. M ₁₁ and M ₁₂ are glass sheets coated with an anti-reflection coating on one side, and their non-coated surfaces A and C are parallel to mirrors M ₁₃ and M ₁₄ respectively; and mirrors M ₁₃ , M ₁₄ is solidified together and moves at a uniform speed with a speed υ. d ₁ , d ₂ are the distances between M ₁₁ , M ₁₃ and M ₁₄ , M ₁₂ respectively, and d=d ₁ +d ₂ is the distance to be measured.

The d is measured by using tunable lasers to form a virtual synthetic wavelength chain, and the incident light is perpendicular to the four surfaces of A, B and C, D respectively. The reflected light from the A and B surfaces return along the original path to interfere, and the reflected light from the C and D surfaces return along the original path to interfere, which constitutes two double-beam interferometers on a straight line.

Let the wavelength of the incident light be λ ₁ , when the mirrors M ₁₃ and M ₁₄ are fixed, the intensity distribution of the interference fringes of the two interferometers is $I_i=P_i+R_i\cos \left(2\mathrm{\π}\frac{2d_i}{{\mathrm{\λ}}_1}\right)(i=\mathrm{1,2})----\left(1\right)$ Where P _i is the DC component, and R _i is the amplitude of the interference signal.

When the mirrors M ₁₃ and M ₁₄ move at a constant speed υ (according to the direction shown in Figure 1), the optical path differences of the two interferometers become d ₁ +υt and d ₂ -υt respectively, so that $\mathrm{\Δ\; f}=\frac{2\mathrm{\υ}}{{\mathrm{\λ}}_1}$ (that is, the Doppler frequency shift generated when the mirror moves with υ), at this time, the intensity distribution of the interference fringes of the two interferometers is $I_1=P_1+R_1\cos \left(2\mathrm{\π}\frac{2(d_1+\mathrm{\υt})}{{\mathrm{\λ}}_1}\right)=P_1+R_{1}2\cos (2\mathrm{\π\Δft}+2\mathrm{\π}\frac{{2d}_1}{{\mathrm{\λ}}_1})$ $I_2=P_2+R_2\cos \left(2\mathrm{\π}\frac{2(d_2-\mathrm{\υt})}{{\mathrm{\λ}}_1}\right)=P_2+R_2\cos (2\mathrm{\π\Δft}-2\mathrm{\π}\frac{{2d}_2}{{\mathrm{\λ}}_1})---\left(2\right)$ It can be seen from this that the frequency of the two sets of interference signals is the same, but the phase difference is always Comparing formulas (1) and (2), it can be seen that d to be measured is a constant flow in formula (1), but it is reflected as a phase item of an AC signal in formula (2), so through this modulation method and this The design of two double-beam interferometer structures converts the measurement of the interference fringe order into the phase measurement of the AC signal. Suppose the distance d to be measured is expressed as follows

2d=(M ₁ +δ ₁ )λ ₁ (3) where M ₁ is an integer order, and δ ₁ is a decimal order. Due to the periodicity of the phase measurement, by comparing the phases of the two sets of interference signals, only the fractional order δ ₁ can be determined, but the integer order M ₁ cannot be uniquely determined, and a second wavelength is required for measurement.

When the incident light wavelength is _λ2 , the distance d to be measured can be expressed as formula (4)

2d=(M ₂ +δ ₂ )λ ₂ (4) where M ₂ and δ ₂ are integer order and decimal order respectively, and δ2 can also be obtained by phase measurement. Virtual synthetic wavelength consisting of λ ₁ and λ ₂ ${\mathrm{\λ}}_{\mathrm{the\; s}}=\frac{{\mathrm{\λ}}_1{\mathrm{\λ}}_2}{|{\mathrm{\λ}}_1-{\mathrm{\λ}}_2|},$ From equations (3) and (4), the distance d to be measured represented by the virtual synthetic wavelength can be obtained

其中 2d=(N _s +ε _s )λ _s (5) where N _s is the integer order corresponding to the virtual synthetic wave, and the single value is guaranteed by the selection and rough measurement of the virtual synthetic wave; ε _s is the decimal order, determined by The measured values of δ ₁ and δ ₂ are calculated by the following formula

in

Formula (5) is the calculation basis of the present invention. For a fixed distance d to be measured, if there is no additional rough measurement method, the first-level virtual synthesis wavelength λ _s1 should satisfy

λ _s1 >2d (7) At this time, the value of the integer level N _s1 corresponding to the first-level virtual synthesis wavelength can be uniquely determined, that is, N _s1 =0.

Since the value of λ _s1 is relatively large, its measurement error is also relatively large, so the virtual synthetic wavelengths λ _s2 , λ _s3 , λ _s4 ... with gradually decreasing wavelengths should be selected for measurement step by step to improve the measurement accuracy. The principles of synthetic wavelength selection are as follows:

Assuming that the measured value of d is d _0i with the upper-level virtual synthetic wavelength λ _si , the error is Δd _i , namely

d=d _0i ±Δd _i (8) is the integer order N _{s(i +1) of the interference fringe that uniquely determines λ s(i} +1), then the λ _s(i+1) caused by the measurement error ±Δd _i The order uncertainty of interference fringes should be limited to 1 order, that is, $\frac{2\mathrm{\&Delta;}{d}_i}{{\mathrm{\&lambda;}}_{\mathrm{the\; s}(i+1)}}<0.5---\left(9\right)$ Therefore, the virtual synthetic wavelength λ _s(i+1) should satisfy formula (10)

λ _s(i+1) ＞4Δd _i (10) The order of the interference fringes of the virtual synthetic wavelength λ _s(i+1) is within the range of the following formula $\frac{{2d}_i}{{\mathrm{\&lambda;}}_{\mathrm{the\; s}(i+1)}}-0.5<N_{\mathrm{the\; s}(i+1)}+{\mathrm{\&epsiv;}}_{\mathrm{the\; s}(i+1)}<\frac{{2d}_i}{{\mathrm{\&lambda;}}_{\mathrm{the\; s}(i+1)}}+0.5---\left(11\right)$ ε _s(i+1) can be calculated by the fractional order of the single-wavelength interference signal measured by the phase meter according to formula (6), and then determine the integer order N _s(i+1) according to the following formula In the formula, the symbol int(N) represents the integer part of N.

Determine the first-level virtual synthetic wavelength and inter-stage transition conditions by formula (7) Determine the virtual synthetic wavelengths of the remaining levels by formula (10), calculate the corresponding wavelength interval, and then change the output of the tunable laser with reference to the theoretical wavelength interval during the measurement process Wavelength, the output wavelength of the laser is measured by the wavelength meter, and the phase difference of the interference signals of the two interferometers is measured by the phase meter to obtain the decimal order, and finally the gap length is calculated according to formulas (5) and (12) to determine the integer order. In this way, a series of virtual synthetic wavelength chains from large to small can be obtained by selecting an appropriate wavelength interval without additional rough measurement means, and the entire process from rough measurement to fine measurement of the gap d can be completed.

Features of the present invention:

1. A tunable laser is used as the light source. As long as the appropriate wavelength interval is selected, a series of virtual synthetic wavelengths from large to small can be formed to achieve step-by-step transition. The whole process from measurement to precision measurement.

2. The decimal order of the interference signal of the virtual synthetic wave is not directly measured, but determined by calculating the decimal order of the measured single-wavelength interference signal.

3. Compared with conventional modulation methods (such as acousto-optic modulation), this modulation method is simple and easy to use. The piezoelectric ceramics are used to drive the two mirrors to move at a constant speed υ, so that the interference signals of the two interferometers have the same size and The Doppler frequency shift in the opposite direction, so that d to be measured is included in the phase term of an AC signal, so that the decimal order measurement is transformed into the phase measurement of the AC signal.

4. This differentially designed interferometer is suitable for measuring internal and external dimensions, and also has great application prospects in the manufacture of micro-sized measuring heads.

Description of drawings

Fig. 1 is a schematic diagram of the principle of the present invention.

FIG. 2 is a schematic diagram of the overall composition of the measuring device in Embodiment 1 of the present invention.

FIG. 3 is a schematic diagram of a partial composition of a measuring device according to Embodiment 2 of the present invention.

Detailed ways

Embodiments of the present invention are described in detail as follows in conjunction with accompanying drawings:

Embodiment 1: Measuring the outer dimensions of the workpiece based on the size of the gauge block

The device of this embodiment is shown in Figure 2. In the figure, the light source L is a tunable external cavity semiconductor laser, and its emission wavelength range is _632nm to _638nm . The uncoated side is in close contact with the end face of gauge block _J1 . The end faces M ₂₃ and M ₂₄ of the workpiece J ₂ to be tested are parallel to M ₂₁ and M ₂₂ respectively. The piezoelectric ceramic drives the gauge block _J1 to move at a constant speed υ. The light emitted by the laser L is divided into two beams by the beam splitter _BS1 , and the reflected light enters the wavelength meter W. The transmitted light is divided into two beams by the beam splitter BS _2. One beam of light is incident on the non-coated surface of M ₂₁ and the end surface M ₂₃ of the workpiece J ₂ to be measured. _The non-coated surface of M ₂₁ The reflected light of the surface and _the end surface M ₂₃ interferes and returns along _the original path, and the part transmitted by the beam splitter BS ₂ is received by the detector D ₁ ; the other beam of light is incident on the M In the interferometer composed of the non-coated surface of ₂₂ and the end surface M ₂₄ of the workpiece J ₂ to be measured, the reflected light of the non-coated surface of M ₂₂ interferes with the end surface M ₂₄ and returns along the original path, and the part transmitted by the beam splitter BS ₃ Received by detector _D2 . The interference signals received by the two detectors are amplified and shaped, and then sent to a phase meter (not shown in the figure) for phase comparison.

In this embodiment, a wavelength meter with a measurement uncertainty of 2×10 ^-6 is used, and the measurement accuracy of the phase meter can reach 0.1°. The computer automatically collects data from the wavelength meter and the phase meter simultaneously for data processing. Under general constant temperature conditions, gauge blocks with different lengths were selected, and the outer dimensions of the workpiece were measured based on the size of the gauge blocks. The measurement results are shown in Table 1:

Table 1 Example 1 measurement results Gauge block length used (μm) Gap measurement value (μm) Work piece length (μm) Deviation from mean value (μm) 89999.78 2603.1 87396.7 2.2 2605.1 87394.7 0.2 2605.7 87394.1 -0.4 90999.78 3608.0 87391.8 -2.7 3606.2 87393.6 -0.9 91999.80 4602.4 87397.4 2.9 4605.7 87394.1 -0.4 4604.6 87395.2 0.7 4606.7 87393.1 -1.4

It can be calculated from the above table that the standard deviation of a single measurement is 1.7 μm, and the limit deviation of the average value is less than 2.5 μm (calculated according to normal distribution). Finally, the length of the workpiece is 87394.5±2.5μm.

The following takes a group of measurement data in Example 1 as an example to illustrate how to use the virtual synthetic wavelength chain to calculate, as shown in Table 2

Table 2 Calculation method using virtual synthetic wavelength chain I λ(nm) (°) δ λ _s (μm) ε _s N _s ′ N _s d(μm) 1 635.7217 90.5 0.2514 12323.90 0.4031 0 0 2484.0 2 635.6889 235.6 0.6545 2179.56 0.4261 2.2793 2 2643.9 3 635.8743 82.2 0.2284 879.91 0.8827 6.0094 5 2588.1 4 636.3342 124.5 0.3457 314.78 0.5717 16.4438 16 2608.3 5 637.6231 278.6 0.7740 105.52 0.3764 49.4356 49 2605.1 6 633.7934 54.2 0.1505 In the table, i is the serial number; λ and  are the measured values of the wavelength and the phase difference of the corresponding interference signal; the decimal order of the single-wavelength interference signal λ _s is the virtual synthetic wavelength; the virtual synthetic wave fractional order ε _s is calculated by formula (6); N _s ′ is the interference signal order (including integer series and decimal level) roughly measured value, that is ${N_{\mathrm{the\; s}}}^{\&prime;}=\frac{{2d}_{i-1}}{{\mathrm{\&lambda;}}_{\mathrm{the\; s}}}.$ For the first-stage synthesis wavelength λ _s1 >2d, N _s1 ′=0. The integer order N _s in Table 1 is calculated according to formula (12), and the distance d to be measured in the last column is calculated according to formula (5).

According to the above rules, the actual calculation is as follows (the above calculation results are listed in Table 1): (1). For the first-level virtual synthesis wavelength, N _s1 = 0, ε _s1 = 0.403, λ _s1 = 12323.9 μm, $d_1=\frac{(N_{\mathrm{the\; s}1}+{\mathrm{\&epsiv;}}_{\mathrm{the\; s}1}){\mathrm{\&lambda;}}_{\mathrm{the\; s}1}}{2}=2484.0\mathrm{\&mu;m};$ (2). For the second-stage virtual synthesis wavelength, λ _s2 = 2179.6 μm, ε _s2 = 0.426, N _s2 ′ = 2.279, ε _s2 <2.279+0.5-int(2.279+0.5), then N _s2 =2 $d_2=\frac{(N_{\mathrm{the\; s}2}+{\mathrm{\&epsiv;}}_{\mathrm{the\; s}2}){\mathrm{\&lambda;}}_{\mathrm{the\; s}2}}{2}=2643.9\mathrm{\&mu;m};$ (3). By analogy, until the last level of synthetic wavelength is calculated. The final result is d = 2605.1 μm.

Embodiment 2: The internal dimension of the workpiece is measured based on the size of the ceramic gauge block. The workpiece to be measured is a glass tube for refractive index measurement, and the size to be measured is the distance between the windows at both ends of the glass tube. The local composition of this embodiment is shown in Figure 3, J ₂ is a standard ceramic gauge block, the windows at both ends of the glass tube J ₁ are M ₃₁ and M ₃₂ , and the windows at both ends of the glass tube M ₃₁ and M ₃₂ are respectively connected to The end faces M ₃₃ and M ₃₄ of the ceramic gauge block are parallel. The two windows are also coated with AR coating on one side, and the inner dimension D _x between the two windows is the dimension to be measured. The rest of its measuring device and measuring method are the same as in Example 1, and will not be repeated.

Claims (4)

1. A virtual synthetic wavelength chain absolute distance interferometry method, characterized in that, comprising the following steps: (1) A pair of single-side AR-coated glass lenses are arranged in parallel, and their non-coated surfaces A and C are opposite; then a pair of flat reflective lenses are placed between the pair of glass lenses, and the end faces B and D of the two reflective lenses Parallel to the two glass lenses, and the reflective surfaces of the two reflective lenses are respectively opposite to the two glass lenses, d ₁ and d ₂ are the distances between A, B and C, D respectively, d=d ₁ +d ₂ is distance to be measured; (2) Divide the light beam emitted by the wavelength-tunable monochromatic light source into two paths of incident light, which are respectively incident on the four surfaces of A, B, C, and D. The reflected light on the surface returns along the original path and interferes, that is, two double-beam interferometers on a straight line are formed; (3) Use piezoelectric ceramics to drive any pair of mirrors to move along the optical axis at a constant speed υ, so that the interference signals of the two interferometers produce a Doppler frequency shift of the same size but opposite direction, so that d to be measured is included In the phase term of an AC signal, the measurement of the order of interference fringes is transformed into a phase measurement of the AC signal; (4) Determine the virtual synthesis wavelength of the first stage as λ _s1 > 2d, and the inter-stage transition condition as λ _s(i+1) > 4Δd _i , so as to determine the virtual synthesis wavelengths of the remaining stages, calculate the corresponding wavelength interval, and obtain a A series of virtual synthetic wavelength chains from large to small; (5) During the wavelength tuning process, simultaneously measure the wavelength values λ ₁ , λ ₂ ... λ _N and the fractional orders δ ₁ , δ ₂ ... δ _N of the interference fringes corresponding to the single wavelength, and determine a virtual synthetic wavelength λ _s by calculation ${\mathrm{\&lambda;}}_{\mathrm{the\; s}}=\frac{{\mathrm{\&lambda;}}_1{\mathrm{\&lambda;}}_2}{|{\mathrm{\&lambda;}}_1-{\mathrm{\&lambda;}}_2|},$ and the fractional order and integer order δ _s of its interference fringes in

Thus, the exact value of the distance d to be measured is obtained: 2d=(N _s +ε _s )λ _s , where N _s is an integer order corresponding to the virtual synthetic wave. 2. The method for interferometry of absolute distances of virtual synthetic wavelength chains as claimed in claim 1, wherein the distance between any pair of lenses arranged in parallel is an accurate known value, and the distance between the two pairs of lenses is measured. The distance between the other pair of lenses is obtained. 3. A measuring device using the method of absolute distance interferometry of a virtual synthetic wavelength chain as claimed in claim 1, characterized in that it comprises a tunable laser, which is arranged on the optical path of the laser and divides the light beam into two beams of light A light splitting element, a pair of single-side AR-coated glass lenses and a pair of flat reflective lenses placed between the glass lenses in parallel, the non-coated surfaces A and C of the glass lenses are opposite, and the two reflective lenses The end surfaces B and D are parallel to the two glass lenses, and the reflective surfaces of the two reflective lenses are respectively opposite to the two glass lenses. D respectively constitute a two-beam interferometer on a straight line, which is used to modulate the piezoelectric ceramics of any pair of lenses, two detectors and subsequent amplification and rectification circuits for respectively receiving the interference signals of the two interferometers, A phase meter for measuring the phase difference of the interference signal of the two interferometers, a wavelength meter and a data processing unit for measuring the light emitted by the laser. 4. The device for measuring the absolute distance of a virtual synthetic wavelength chain as claimed in claim 3, wherein the wavelength tuning range of the tunable laser is several nanometers to more than ten nanometers.

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