CN102865821B - Optical-circuit balance type high speed, high resolution laser heterodyne interference measurement method and device - Google Patents

Abstract

The optical path balanced high-speed and high-resolution laser heterodyne interferometry method and device belong to the field of laser application technology; the invention adopts spatially separated reference light and measuring light, and carries out the balanced design of the measuring optical path. At the same time, the method produces two The interferometric signal of opposite Doppler frequency shift, and according to the motion direction and speed of the target to be measured, selectively use two measurement signals for interferometric measurement; the invention not only reduces the influence of temperature changes on the measurement, but also eliminates the interference The frequency aliasing phenomenon in the instrument improves the measurement accuracy of heterodyne interferometry; at the same time, it solves the problem that the frequency difference of the laser light source limits the measurement speed.

Description

Optical path balanced high-speed and high-resolution laser heterodyne interferometry method and device

technical field

The invention belongs to the technical field of laser applications, and mainly relates to an optical path balanced high-speed and high-resolution laser heterodyne interferometry method and device.

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.

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.

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.

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/February 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 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.

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.

Contents of the invention

Aiming at the shortcomings of the above-mentioned existing laser heterodyne interferometer, the present invention proposes an optical path balance type high-speed and high-resolution laser heterodyne interferometry method and device, which improves the measurement accuracy of laser heterodyne interferometry and solves the problem of laser light source frequency difference measurement. The problem with speed limits.

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

An optical path balanced high-speed and high-resolution laser heterodyne interferometry method, the steps of the method are as follows:

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

(2) A small 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 remaining two parallel beams are 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) The reference beam contains two parallel beams with frequencies f ₁ and f ₂ respectively. The reference beam is first transmitted by the first polarizing beam splitter, and then returned to the first polarizing beam splitter after being acted on by a quarter-wave plate and a plane mirror , at this time the polarization direction of the reference beam is rotated by 90°, reflected by the first polarization beam splitter, and then reflected by the reference prism back to the first polarization beam splitter, and reflected by the first polarization beam splitter, after a quarter After the action of the wave plate and the plane mirror, it returns to the first polarization beam splitter again. At this time, the polarization direction of the reference beam is rotated by 90°, and then it is transmitted back to the beam splitter through the first polarization beam splitter;

(5) The measurement beam contains two parallel beams with frequencies f ₁ and f ₂ respectively. The measurement beam enters the second polarization beam splitter and is transmitted, and then returns to the second 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 is rotated by 90°, and it is reflected into the measurement prism, and then reflected by the measurement prism and the second polarization beam splitter, and the reflected light returns again after being acted on by a quarter-wave plate and a plane mirror The second polarization beam splitter, at this time, the polarization direction of the measurement beam is rotated by 90°, and it is transmitted back to the beam splitter by the second polarization 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 measured target end plane mirror, use the switch circuit to select between the phase meter A and the phase meter B;

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

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

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 negative movement speed of the plane mirror at the measured target end is higher than the set value When the value is V ₂ , select the phase meter A; among them, let the direction of the plane mirror at the measured target end away from the second polarization beam splitter be the positive direction.

An optical path balanced high-speed and high-resolution laser heterodyne interferometry device, the device includes a frequency-stabilized laser, a beam splitter, a polarizing beam splitter B, a measuring prism, a quarter-wave plate B, a plane mirror B, a photodetector A, Photodetector B, the device also includes a polarization beam splitter A, a quarter wave plate A, a plane mirror A, a reference prism, a phase meter A, a phase meter B, a switch circuit, and a measurement circuit; The output end of the polarizing beam splitter A, a quarter wave plate A and a plane mirror A are placed in the reflection direction of the beam splitter in turn, and the reference prism is located in the reflection direction of the polarizing beam splitter A; the polarizing beam splitter B, a quarter The wave plate B and the plane mirror B are placed in the transmission direction of the beam splitter in turn, and the measuring prism is located in the reflection direction of the polarizing beam splitter B; the beam splitter outputs two interferometric beams, one of which is connected to the photodetector A, and the other is connected to the photodetector B; the output terminal of the photodetector A is connected to the input terminal of the phase meter A, and the output terminal of the photodetector B is connected to the input terminal of the phase meter B; the reference signal output terminal of the frequency-stabilized laser is respectively connected to the input terminals of the phase meter A and the phase meter B , the output terminals of phase meter A and phase meter B are simultaneously connected to the input terminal of the switch circuit; the output terminal of the switch circuit is connected to the input terminal of the measurement circuit;

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

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

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

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

The present invention has following characteristics and good effect:

(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.

(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.

(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.

(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.

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 polarization beam splitter A, 4 quarter wave plate A, 5 plane mirror A, 6 reference prism, 7 polarization beam splitter B, 8 measuring prism, 9 quarter wave plate Wave plate B, 10 plane mirror B, 11 photodetector A, 12 photodetector B, 13 phase meter A, 14 phase meter B, 15 switch circuit, 16 measurement circuit.

Detailed ways

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

An optical path balanced high-speed and high-resolution laser heterodyne interferometry device, the device includes a frequency-stabilized laser 1, a beam splitter 2, a polarization beam splitter B7, a measuring prism 8, a quarter-wave plate B9, a plane mirror B10, a photoelectric detector Device A11, photodetector B12, it is characterized in that the device also includes polarization beam splitter A3, quarter wave plate A4, plane mirror A5, reference prism 6, phase meter A13, phase meter B14, switch circuit 15, measuring circuit 16 Wherein, beam splitter 2 is positioned at the output end of frequency-stabilized laser 1; Polarization beam splitter A3, quarter-wave plate A4 and plane mirror A5 are placed on the reflection direction of beam splitter 2 successively, and reference prism 6 is positioned at polarization beam splitter A3 In the reflection direction; polarizing beam splitter B7, quarter-wave plate B9 and plane mirror B10 are sequentially placed in the transmission direction of beam splitter 2, and measuring prism 8 is located in the reflection direction of polarizing beam splitter B7; beam splitter 2 outputs two-way interferometric measurements Light beam, one of which is connected to photodetector A11, and the other is connected to photodetector B12; the output terminal of photodetector A11 is connected to the input terminal of phase meter A13, and the output terminal of photodetector B12 is connected to the input terminal of phase meter B14; the frequency-stabilized laser 1 The reference signal output end is respectively connected with the input end of the phase meter A13 and the phase meter B14, and the output ends of the phase meter A13 and the phase meter B14 are connected to the input end of the switch circuit 15 at the same time; the output end of the switch circuit 15 is connected to the input end of the measurement circuit 16;

An optical path balanced high-speed and high-resolution laser heterodyne interferometry method, the steps of the method are as follows:

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

(2) A small 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 remaining two parallel beams are 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) The reference beam contains two parallel beams with frequencies f ₁ and f ₂ respectively. The reference beam is first transmitted by the polarizing beam splitter A3, and then returned to the polarizing beam splitter A3 after being acted on by the quarter-wave plate A4 and the plane mirror A5. When the polarization direction of the reference beam is rotated by 90°, it is reflected by the polarizing beam splitter A3, and then reflected by the reference prism 6 back to the polarizing beam splitter A3, and is reflected by the polarizing beam splitter A3, and is acted by the quarter wave plate A4 and the plane mirror A5 Then return to the polarizing beam splitter A3 again, at this time, the reference beam polarization direction is rotated by 90°, and then transmitted back to the beam splitter 2 through the polarizing beam splitter A3;

(5) The measurement beam contains two parallel beams with frequencies f ₁ and f ₂ respectively. The measurement beam enters the polarization beam splitter B7 and is transmitted, and then returns to the polarization beam splitter B7 after being acted on by the quarter-wave plate B9 and the plane mirror B10. At this time, the polarization direction of the measuring beam rotates by 90°, is reflected into the measuring prism 8, and then reflected by the measuring prism 8 and the polarizing beam splitter B7, and the reflected light returns again after being acted on by the quarter-wave plate B9 and the plane mirror B10 Polarizing beam splitter B7, at this time, the polarization direction of the measuring beam is rotated by 90°, and it is transmitted back to beam splitter 2 by polarizing beam splitter B7;

(6) By adjusting the reference prism 6 and the measurement prism 8, 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 the photodetector A11 and the photodetector B12;

(8) The photodetector A11 outputs a measurement signal whose frequency is f _b +Δf, and sends the signal to the phase meter A13 for processing;

(9) The photodetector B12 outputs _a measurement signal whose frequency is fb-Δf, and sends the signal to the phase meter B14 for processing;

(10) The processing signal of phase meter A13 and phase meter B14 is sent into switch circuit 15 simultaneously, according to the plane mirror B10 motion direction and the speed of motion of the measured target end, select between the two phase meters; the measurement of phase meter A13 and phase meter B14 There is some overlap in scope. The overlapping portion is used as the "hysteresis zone" for phase meter switching. When the forward moving speed of the plane mirror B10 is higher than the upper limit V1 _of the "hysteresis zone", the phase meter A13 is switched to the phase meter B14, and the phase meter B14 outputs is fed into the phase accumulator. Similarly, when the moving speed of the plane mirror B10 is lower _than the lower limit -V2 of the "hysteresis zone", the phase meter B14 switches back to the phase meter A13. When the speed of the measured target 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, wherein the direction in which the plane mirror B10 is away from the polarizing beam splitter B7 is the positive direction .

(11) Send the signal selected by the switch circuit 15 to the measurement circuit 16 for processing, so as to obtain the motion information of the plane mirror B10 at the measured target end.

Claims (8)

1. a kind of optical path balance type high-speed high-resolution laser heterodyne interferometry method is 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 small 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 remaining two parallel beams are 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) The reference beam contains two parallel beams with frequencies f ₁ and f ₂ respectively. The reference beam is first transmitted by the first polarizing beam splitter, and then returned to the first polarizing beam splitter after being acted on by a quarter-wave plate and a plane mirror , at this time the polarization direction of the reference beam is rotated by 90°, reflected by the first polarization beam splitter, and then reflected by the reference prism back to the first polarization beam splitter, and reflected by the first polarization beam splitter, after a quarter After the action of the wave plate and the plane mirror, it returns to the first polarization beam splitter again. At this time, the polarization direction of the reference beam is rotated by 90°, and then it is transmitted through the first polarization beam splitter and returns to the beam splitter; (5) The measurement beam contains two parallel beams with frequencies f ₁ and f ₂ respectively. The measurement beam enters the second polarization beam splitter and is transmitted, and then returns to the second 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 is rotated by 90°, and it is reflected into the measurement prism, and then reflected by the measurement prism and the second polarization beam splitter, and the reflected light returns again after being acted on by a quarter-wave plate and a plane mirror The second polarization beam splitter, at this time, the polarization direction of the measurement beam is rotated by 90°, and it is transmitted back to the beam splitter by the second polarization 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 measured target end plane mirror, use the switch circuit to select between the phase meter A and the phase meter B; (9) Calculate the displacement of the measured target according to the selected phase meter A or phase meter B. 2. The optical path balanced high-speed and high-resolution laser heterodyne interferometry method according to claim 1, characterized in that the two parallel beams output by the frequency-stabilized laser are horizontal linearly polarized light or vertical linearly polarized light. 3. The optical path balance type high-speed and high-resolution laser heterodyne interferometry method according to claim 1 is characterized in that when using a switch circuit to select, when the forward moving speed of the measured target end plane mirror is higher than the set value V ₁ , select phase meter B; when the negative moving speed of the measured target end plane mirror is higher than the set value V ₂ , select phase meter A; wherein, the direction that the measured target end plane mirror is away from the second polarizing beam splitter is positive direction. 4. An optical path balanced high-speed and high-resolution laser heterodyne interferometry device, the device includes a frequency-stabilized laser (1), a beam splitter (2), a polarizing beam splitter B (7), a measuring prism (8), a quadrant One wave plate B (9), plane mirror B (10), photodetector A (11), photodetector B (12), it is characterized in that the device also includes polarizing beam splitter A (3), a quarter Wave plate A (4), plane mirror A (5), reference prism (6), phase meter A (13), phase meter B (14), switch circuit (15), measurement circuit (16); wherein, the beam splitter ( 2) Located at the output end of the frequency-stabilized laser (1); the polarization beam splitter A (3), the quarter-wave plate A (4) and the plane mirror A (5) are sequentially placed on the reflection direction of the beam splitter (2), The reference prism (6) is located on the reflection direction of the polarizing beam splitter A (3); the polarizing beam splitter B (7), the quarter wave plate B (9) and the plane mirror B (10) are placed on the beam splitter (2) in sequence In the transmission direction, the measuring prism (8) is located in the reflection direction of the polarizing beam splitter B (7); the beam splitter (2) outputs two interferometric beams, one of which is connected to the photodetector A (11), and the other is connected to the photodetector device B (12); the output terminal of the photodetector A (11) is connected to the input terminal of the phase meter A (13), and the output terminal of the photodetector B (12) is connected to the input terminal of the phase meter B (14); the frequency-stabilized laser (1 The reference signal output terminals of ) are respectively connected with the input terminals of phase meter A (13) and phase meter B (14), and the output terminals of phase meter A (13) and phase meter B (14) are simultaneously connected with the input of switch circuit (15) terminal; the output terminal of the switch circuit (15) is connected to the input terminal of the measuring circuit (16). 5. The high-speed and high-resolution laser heterodyne interferometry device according to claim 4, wherein when the reference prism (6) is a corner cube, the measuring prism (8) is a rectangular prism. 6. The high-speed and high-resolution laser heterodyne interferometry device according to claim 4, wherein when the reference prism (6) is a rectangular prism, the measurement prism (8) is a corner cube. 7. The high-speed and high-resolution laser heterodyne interferometry device according to claim 4, wherein when the reference prism (6) is composed of two corner cubes, the measuring prism (8) is a corner cube. 8. The high-speed and high-resolution laser heterodyne interferometry device according to claim 4, wherein when the reference prism (6) is a corner cube, the measuring prism (8) is composed of two corner cubes.