CN102865820B - Light path compensation based laser heterodyne interference measurement method and light path compensation based laser heterodyne interference measurement device - Google Patents

Abstract

The laser heterodyne interferometry method and device based on optical path compensation belong to the field of laser application technology; the present invention uses spatially separated reference light and measuring light, and performs optical path compensation design, and simultaneously the method produces two opposite Doppler frequency According to the moving direction and speed of the measured target, the two measuring signals are selectively used for interferometric measurement; the invention not only reduces the influence of temperature changes on the measurement, but also eliminates the frequency mixing in the interferometer. Overlap phenomenon improves the measurement accuracy of heterodyne interferometry; at the same time, it solves the problem that the frequency difference of laser light source limits the measurement speed.

Description

Laser heterodyne interferometry method and device based on optical path compensation

technical field

The invention belongs to the technical field of laser applications, and mainly relates to a laser heterodyne interferometry method and device based on optical path compensation. the

Background technique

Laser heterodyne interferometry is widely used in ultra-precision machining, lithography machines, and three-coordinate measuring machines because of its strong anti-interference ability, large measurement range, high signal-to-noise ratio, and easy realization of high precision. With the continuous development of ultra-precision engineering, higher and higher requirements are put forward for machining accuracy and production efficiency; at the same time, new challenges are raised for the measurement accuracy, resolution and speed of heterodyne interferometry. the

In laser heterodyne interferometry, the nonlinear error severely limits the further improvement of measurement accuracy and resolution. Scholars at home and abroad have done a lot of research on the nonlinear error of laser heterodyne interferometry. The nonlinear error originates from the optical aliasing in the interferometric light path, and the traditional interferometry system cannot avoid the optical aliasing in the interferometry, which limits the improvement of its measurement accuracy and resolution. the

T.L.Schmitz and J.F.Beckwith proposed a method of interferometer transformation (Ascousto-optic displacement-measuring interferometer: a new heterodyne interferometer with Anstromlevel periodic error. Journal of Modern Optics 49, pages 2105-2114). Compared with traditional measurement methods, this method uses an acousto-optic frequency shifter as a beam splitter to separate the measurement beam from the reference beam. The method can reduce the frequency aliasing of the reference light and the measurement light, and is beneficial to reduce the non-linear error of the measurement, thereby improving the measurement accuracy and resolution. However, the device has a complex and special structure, and cannot be widely used in ultra-precision machining and measurement. the

Ki-Nam Joo et al. developed a new laser interferometer structure (Simple heterodyne laser interferometer with subnanometer periodic errors. Optics Letters/Vol.34, No.3/Fe bruary 1, 2009). The structure separates the reference beam and the measurement beam in space, eliminates frequency aliasing in interferometry, and completely eliminates nonlinear errors, thereby improving measurement accuracy and measurement resolution. In addition, the device has a simple structure and low cost, and is more conducive to the application in the field of ultra-precision measurement compared with the previous measurement method. However, the measurement speed of this method is still restricted by the frequency difference of the light source, which limits its wide application in the field of high-speed measurement. the

The above interferometric methods and devices all have the problem that the measurement speed is restricted by the frequency difference of the light source. With the continuous improvement of ultra-precision machining requirements for measurement speed, the frequency difference of the interferometer light source is also increasing, which leads to the structure of the laser light source becoming more and more complex and the cost more and more expensive, which seriously limits the wide application of laser interferometry. application. Moreover, there is a conflict between measurement resolution and measurement speed. In order to improve the measurement speed and resolution of the interferometer at the same time, scholars at home and abroad have conducted a lot of research on signal processing systems and proposed corresponding solutions. However, the existing signal processing systems are generally complex in structure, expensive in cost and require a lot of special designs. chips; and limited by the level of existing semiconductor chips, it is difficult to improve the interferometric performance. the

To sum up, none of the existing laser heterodyne interferometry methods can meet the requirements of high precision and high measurement speed of the interferometer for ultra-precision machining measurement, which severely limits the development of ultra-precision machining measurement. the

Contents of the invention

Aiming at the defects of the above-mentioned existing laser heterodyne interferometer, the present invention proposes a laser heterodyne interferometry method and device based on optical path compensation, which improves the measurement accuracy of laser heterodyne interferometry and solves the limitation of the measurement speed by the frequency difference of the laser light source. question. the

The purpose of the present invention is achieved through the following technical solutions:

A laser heterodyne interferometry method based on optical path compensation, the method steps are as follows:

(1) The frequency-stabilized laser outputs two parallel beams with frequencies f ₁ and f ₂ respectively;

(2) A part of the two parallel beams is directly detected and converted into a reference signal for laser heterodyne interferometry, and its frequency difference is f _b = f ₁ -f ₂ , expressed as I _r ∝ cos(2πf _b t);

(3) The other part of the two parallel beams is divided into two parts by the beam splitter, the reflected part is used as the reference beam, and the transmitted part is used as the measuring beam;

(4) Among the reference beams, two reference beams with frequencies f ₁ and f ₂ are reflected by the reflective prism and the reference prism, and return to the beam splitter;

(5) In the measurement beam, two beams with frequencies f ₁ and f ₂ are transmitted by the polarization beam splitter, and then return to the polarization beam splitter after being acted on by a quarter-wave plate and a plane mirror. At this time, the polarization direction of the measurement beam Rotated by 90°, it is reflected by the polarizing beam splitter, and then reflected by the measuring prism back to the polarizing beam splitter, after being reflected by the polarizing beam splitter, it returns to the polarizing beam splitter again through the action of a quarter-wave plate and a plane mirror, at this time the measurement The polarization direction of the beam is rotated by 90°, and is transmitted back to the beam splitter by the polarizing beam splitter;

(6) By adjusting the reference prism and measuring prism, the measurement beam with frequency f ₁ interferes with the reference beam with frequency f ₂ to generate a measurement signal, expressed as I _m1 ∝cos[2π(f _b +Δf)t] ; The measurement beam whose frequency is f ₂ interferes with the reference beam whose frequency is f ₁ to generate another measurement signal, expressed as I _m2 ∝cos[2π(f _b -Δf)t], the two measurement signals have the same magnitude and sign Opposite Doppler shifts with frequencies _fb + Δf and _fb - Δf, respectively;

(7) After the two measurement signals are detected by the photodetector, they are respectively sent to two identical phase meters A and B, wherein, the phase meter A is used to process the measurement signal with a frequency of f _b + Δf, and the phase meter B is used for processing the measurement signal at frequency _fb - Δf;

(8) According to the moving direction and moving speed of the plane reflector at the measured target end, use a switch circuit to select between phase meter A and phase meter B;

(9) Calculate the displacement of the measured target according to the selected phase meter A or phase meter B. the

The two parallel light beams output by the frequency-stabilized laser are horizontal linearly polarized light or vertical linearly polarized light. the

When the phase meter is selected using a switch circuit, when the forward movement speed of the plane mirror at the measured target end is higher than the set value V ₁ , the phase meter B is selected; when the plane mirror at the measured target end moves negatively When the speed is higher than the set value V ₂ , select the phase meter A; among them, the direction in which the plane mirror at the measured target end is away from the second polarizing beam splitter is the positive direction.

A laser heterodyne interferometry device based on optical path compensation, the device includes a frequency-stabilized laser, a beam splitter, a polarization beam splitter, a measuring prism, a quarter-wave plate, a plane mirror, a photodetector A, and a photodetector B , the device also includes a reflective prism, a reference prism, a phase meter A, a phase meter B, a switch circuit, and a measurement circuit, wherein the beam splitter is located at the output end of the frequency-stabilized laser; the reflective prism is located in the reflection direction of the beam splitter, and the reference prism is located at the reflective prism the reflection direction of the polarization beamsplitter; the polarization beamsplitter is located in the transmission direction of the beamsplitter; the measuring prism is located in the reflection direction of the polarization beamsplitter; the quarter-wave plate and the plane mirror are placed in sequence in the transmission direction of the polarization beamsplitter; the output of the beamsplitter is two-way interference Measuring light beam, one of which is connected to photodetector A, and the other is connected to photodetector B; the output terminal of photodetector A is connected to the input terminal of phase meter A, and the output terminal of photodetector B is connected to the input terminal of phase meter B; the frequency-stabilized laser The output terminals of the reference signal are respectively connected to the input terminals of the phase meter A and the phase meter B, and the output terminals of the phase meter A and the phase meter B are simultaneously connected to the input terminals of the switch circuit; the output terminals of the switch circuit are connected to the measurement circuit. the

The reference prism is a corner cube prism, and the measuring prism is a rectangular prism. the

The reference prism is a rectangular prism, and the measuring prism is a corner cube prism. the

The reference prism is composed of two corner cube prisms, and the measuring prism is a corner cube prism. the

The reference prism is a corner cube, and the measuring prism is composed of two corner cubes. the

In the compensation optical path, the optical path of the single reflection of the light beam in the reflective prism is twice the optical path of the single reflection in the beam splitter. the

The present invention has the following characteristics and good effects:

(1) In the present invention, the reference light and the measurement light are separated in space, and there is no overlap before reaching the detector, which eliminates the root cause of the non-linear error of the interferometer. the

(2) In traditional interferometers, polarization beamsplitters are used to separate beams, and the adjustment of the interference mirror group is difficult and costly; in the present invention, ordinary non-polarization beamsplitters are used instead of polarization beamsplitters, because the polarization state of the laser light source does not change. Sensitive, which greatly reduces the difficulty of adjusting the interferometer group, and at the same time, the use of non-polarizing beam splitters can reduce the cost of the interferometer. the

(3) In the present invention, the two measurement signals that interferometer produces have the Doppler frequency shift of identical size, sign opposite, two measurement signals are selected according to the motion direction of object, can guarantee that Doppler frequency shift makes frequency difference all the time Increase. Compared with the traditional interferometer, the interferometer in the present invention makes the measurement speed no longer limited by the frequency difference of the laser light source, and the traditional small frequency difference laser can also be applied to high-speed measurement. the

(4) In the present invention, since the frequency difference of the laser is small, the signal processing system can use the common clock signal to obtain high resolution, which simplifies the design of the signal measurement system and reduces the cost of the system. the

Description of drawings

Accompanying drawing is the schematic diagram of device structure of the present invention

In the figure, 1 frequency-stabilized laser, 2 beam splitter, 3 reflecting prism, 4 reference prism, 5 polarizing beam splitter, 6 measuring prism, 7 quarter wave plate, 8 measuring flat mirror, 9 photodetector A, 10 Photoelectric detector B, 11 phase meter A, 12 phase meter B, 13 switch circuit, 14 measurement circuit. the

Detailed ways

The examples of the present invention will be described in detail below in conjunction with the accompanying drawings. the

A high-speed ultra-precision laser heterodyne interferometry device based on optical path compensation, the device includes a frequency-stabilized laser 1, a beam splitter 2, a polarization beam splitter 5, a measuring prism 6, a quarter-wave plate 7, and a measuring plane mirror 8 , photodetector A9, photodetector B10, the device also includes reflective prism 3, reference prism 4, phase meter A11, phase meter B12, switch circuit 13, measurement circuit 14, wherein, beam splitter 2 is located at the output of frequency stabilized laser 1 end; reflective prism 3 is located in the reflection direction of beam splitter 2, reference prism 4 is located in the reflection direction of reflective prism 3; polarizing beam splitter 5 is located in the transmission direction of beam splitter 2; measuring prism 6 is located in the reflection direction of polarizing beam splitter 5; A quarter-wave plate 7 and a plane mirror 8 are sequentially placed in the transmission direction of the mirror 5; the beam splitter 2 outputs two interferometric light beams, one of which is connected to the photodetector A9, and the other is connected to the photodetector B10; the photodetector The output terminal of A9 is connected to the input terminal of phase meter A11, and the output terminal of photodetector B10 is connected to the input terminal of phase meter B12; 1. The output end of the phase meter B12 is connected to the input end of the switch circuit 13 at the same time; the output end of the switch circuit 13 is connected to the measurement circuit 14 . the

A high-speed ultra-precision laser heterodyne interferometry method based on optical path compensation, the method steps are as follows:

(1) The frequency-stabilized laser 1 outputs two parallel beams with frequencies f ₁ and f ₂ respectively;

(2) A part of the two parallel beams is directly detected and converted into a reference signal for laser heterodyne interferometry, and its frequency difference is f _b = f ₁ -f ₂ , expressed as I _r ∝ cos(2πf _b t);

(3) The other part of the two parallel beams is divided into two parts by the beam splitter 2, the reflected part is used as the reference beam, and the transmitted part is used as the measuring beam;

(4) Among the reference beams, two reference beams with frequencies f ₁ and f ₂ are reflected by the reflective prism 3 and the reference prism 4, and return to the beam splitter;

(5) Among the measuring beams, two beams with frequencies f ₁ and f ₂ are transmitted by the polarizing beam splitter 5, and then return to the polarizing beam splitting mirror after being acted on by the quarter-wave plate 7 and the plane mirror 8. At this time, the measuring beam The polarization direction of the polarized beam is rotated by 90°, reflected by the polarized beam splitter 5, and then reflected by the measuring prism 6 back to the polarized beam splitter 5, after being reflected by the polarized beam splitter 5, it passes through the quarter wave plate 7 and the plane mirror 8 again The action returns to the polarizing beam splitter 5, at this time the polarization direction of the measuring beam is rotated by 90°, and is transmitted back to the beam splitting mirror 2 by the polarizing beam splitter 5;

(6) By adjusting the reference prism 4 and the measurement prism 6, the measurement beam with frequency f ₁ interferes with the reference beam with frequency f ₂ to generate a measurement signal, expressed as I _m1 ∝cos[2π(f _b +Δf) t]; the measurement beam with frequency f ₂ interferes with the reference beam with frequency f ₁ to generate another measurement signal, expressed as I _m2 ∝cos[2π(f _b -Δf)t], the two measurement signals have the same magnitude , Doppler frequency shifts with opposite signs, whose frequencies are f _b +Δf and f _b -Δf respectively;

(7) The two measurement signals are respectively detected by photodetector A9 and photodetector B10;

(8) The photodetector A9 outputs a measurement signal whose frequency is _fb +Δf, and sends the signal to the phase meter A11 for processing;

(9) The photodetector B10 outputs a measurement signal whose frequency is _fb -Δf, and sends the signal to the phase meter B12 for processing;

(10) The processing signals of the phase meter A11 and the phase meter B12 are sent to the switch circuit 13 at the same time, and the two phase meters are selected according to the moving direction and speed of the measured object; the measurement range of the phase meter A11 and the phase meter B12 exists Some overlap. The overlapping part is used as the "hysteresis zone" for phase meter switching. When the moving speed of the measured target is higher than the upper limit V _th of the "hysteresis zone", the phase meter A11 is switched to the phase meter B12, and the output of the phase meter B12 is into the phase accumulator. Similarly, when the moving speed of the measured target is lower than the lower limit -V _th of the "hysteresis zone", the phase meter B12 switches back to the phase meter A11. When the measured target speed is in the "hysteresis zone", the switching operation of the phase meter is not performed, thereby eliminating the influence of circuit noise and speed noise on the switching operation.

(11) Send the signal selected by the switch circuit 13 to the measurement circuit 14 for processing, so as to obtain the motion information of the measured object. the

(11) Send the signal selected by the switch circuit 13 to the measurement circuit 14 for processing, so as to obtain the motion information of the measured object. the

(11) Send the signal selected by the switch circuit 13 to the measurement circuit 14 for processing, so as to obtain the motion information of the measured object. the

(11) Send the signal selected by the switch circuit 13 to the measurement circuit 14 for processing, so as to obtain the motion information of the measured object. the

Claims (9)

1. A laser heterodyne interferometry method based on optical path compensation, characterized in that the method steps are as follows: (1) The frequency-stabilized laser outputs two parallel beams with frequencies f ₁ and f ₂ respectively; (2) A part of the two parallel beams is directly detected and converted into a reference signal for laser heterodyne interferometry, and its frequency difference is f _b = f ₁ -f ₂ , expressed as I _r ∝ cos(2πf _b t); (3) The other part of the two parallel beams is divided into two parts by the beam splitter, the reflected part is used as the reference beam, and the transmitted part is used as the measuring beam; (4) Among the reference beams, two reference beams with frequencies f ₁ and f ₂ are reflected by the reflective prism and the reference prism, and return to the beam splitter; (5) In the measurement beam, two beams with frequencies f ₁ and f ₂ are transmitted by the polarization beam splitter, and then return to the polarization beam splitter after being acted on by a quarter-wave plate and a plane mirror. At this time, the polarization direction of the measurement beam Rotated by 90°, it is reflected by the polarizing beam splitter, and then reflected by the measuring prism back to the polarizing beam splitter, after being reflected by the polarizing beam splitter, it returns to the polarizing beam splitter again through the action of a quarter-wave plate and a plane mirror, at this time the measurement The polarization direction of the beam is rotated by 90°, and is transmitted back to the beam splitter by the polarizing beam splitter; (6) By adjusting the reference prism and measuring prism, the measurement beam with frequency f ₁ interferes with the reference beam with frequency f ₂ to generate a measurement signal, expressed as I _m1 ∝cos[2π(f _b +Δf)t] ; The measurement beam whose frequency is f ₂ interferes with the reference beam whose frequency is f ₁ to generate another measurement signal, expressed as I _m2 ∝cos[2π(f _b -Δf)t], the two measurement signals have the same magnitude and sign Opposite Doppler shifts with frequencies _fb + Δf and _fb - Δf, respectively; (7) After the two measurement signals are detected by the photodetector, they are respectively sent to two identical phase meters A and B, wherein, the phase meter A is used to process the measurement signal with a frequency of f _b + Δf, and the phase meter B is used for processing the measurement signal at frequency _fb - Δf; (8) According to the moving direction and moving speed of the plane reflector at the measured target end, use a switch circuit to select between phase meter A and phase meter B; (9) Calculate the displacement of the measured target according to the selected phase meter A or phase meter B. 2. The laser heterodyne interferometry method based on optical path compensation according to claim 1, characterized in that the two parallel light beams output by the frequency-stabilized laser are horizontal linearly polarized light or vertical linearly polarized light. 3. The laser heterodyne interferometry method based on optical path compensation according to claim 1, wherein when a switch circuit is used to select, when the forward moving speed of the measured target is higher than the set value V ₁ , the phase meter is selected B; When the negative movement speed of the measured target is higher than the set value V ₂ , select the phase meter A; where the direction of the plane reflector at the measured target end away from the polarizing beam splitter is the positive direction. 4. A laser heterodyne interferometry device based on optical path compensation, the device includes a frequency-stabilized laser (1), a beam splitter (2), a polarizing beam splitter (5), a measuring prism (6), and a quarter-wave plate (7), plane reflector (8), photodetector A (9), photodetector B (10), it is characterized in that this device also comprises reflection prism (3), reference prism (4), phase meter A ( 11), phase meter B (12), switch circuit (13), measurement circuit (14), wherein, the beam splitter (2) is located at the output end of the frequency-stabilized laser (1); the reflective prism (3) is located at the beam splitter (2) The reflection direction of reference prism (4) is positioned at the reflection direction of reflection prism (3); Polarizing beam splitter (5) is positioned at the transmission direction of beam splitter (2); Measuring prism (6) is positioned at the reflection direction of polarizing beam splitter (5) Place a quarter-wave plate (7) and a flat reflector (8) successively on the transmission direction of the polarization beam splitter (5); the beam splitter (2) outputs two-way interferometric light beams, wherein one road is connected to the photodetector A ( 9), the other is connected to the photodetector B (10); the output terminal of the photodetector A (9) is connected to the input terminal of the phase meter A (11), and the output terminal of the photodetector B (10) is connected to the phase meter B (12) The input end, the reference signal output end of the frequency-stabilized laser (1) are respectively connected with the input ends of the phase meter A (11) and the phase meter B (12), and the output ends of the phase meter A (11) and the phase meter B (12) are simultaneously Connect the input end of the switch circuit (13); the output end of the switch circuit (13) is connected with the measurement circuit (14). 5. The laser heterodyne interferometry device based on optical path compensation according to claim 4, characterized in that the reference prism (4) is a corner cube prism, and the measuring prism (6) is a rectangular prism. 6. The laser heterodyne interferometry device based on optical path compensation according to claim 4, characterized in that the reference prism (4) is a rectangular prism, and the measuring prism (6) is a corner cube. 7. The laser heterodyne interferometry device based on optical path compensation according to claim 4, characterized in that the reference prism (4) is made up of two corner cubes, and the measuring prism (6) is a corner cube. 8. The laser heterodyne interferometry device based on optical path compensation according to claim 4, characterized in that the reference prism (4) is a corner cube, and the measuring prism (6) is composed of two corner cubes. 9. The laser heterodyne interferometry device based on optical path compensation according to claim 4, characterized in that the optical path of the single reflection of the light beam in the reflective prism (3) is the length of the optical path of the single reflection in the beam splitter (2). double.