Two-axis homodyne grating interference displacement measurement method and system based on Wollaston prism and four-quadrant detector

Abstract

The invention discloses a two-axis homodyne grating interference displacement measurement method and system based on a Wollaston prism and a four-quadrant detector, belongs to the field of grating interference displacement measurement, and is suitable for two-axis homodyne grating interference displacement measurement of horizontal and vertical displacement synchronous measurement. The method is used for solving the problem that a Wollaston prism (WP) is not matched with a four-quadrant detector (QPD) in a biaxial homodyne grating interference displacement measurement occasion in the prior art. The polarization direction of a certain device or a light beam of a light path is rotated, so that the direction of the optical axis connecting line of the double light beams is perpendicular to the normal direction of the interface of the Wollaston prism, and at the moment, the double light beams form four light spots which are distributed in a square shape through the Wollaston prism; the problem that the optical path of the double-axis parallel light is not matched with the optical path of the rotating Wollaston prism is solved, and effective utilization of four pixels of the four-quadrant detector is achieved.

Description

Technical Field

[0001] The invention belongs to the field of grating interferometry, in particular to the field of two-axis homodyne grating interferometry displacement measurement for synchronously measuring horizontal and vertical displacements. Background Art

[0002] Grating interferometry is a commonly used precision displacement measurement scheme. Compared with traditional dual-beam interferometry schemes such as the Michelson interferometry scheme, the biggest feature of grating interferometry is that it uses the grating pitch as a reference and can measure the displacement within the grating plane. The grating pitch reference is insensitive to the refractive index of air and is suitable for more demanding measurement environments. On this basis, grating interferometry is often used for two-axis displacement measurement by using the characteristics of the laser wavelength reference that can measure the displacement perpendicular to the grating plane. With the rapid development of advanced manufacturing, two-axis grating displacement measurement technology that simultaneously measures the grating plane and perpendicular to the grating plane has been applied in high-end manufacturing equipment such as lithography machines. In-depth research has also been conducted at home and abroad on two-axis grating displacement measurement methods.

[0003] In principle, grating interferometers can be divided into homodyne grating interferometers and heterodyne grating interferometers. Homodyne grating interferometer is the earliest, most basic and most widely used grating displacement measurement system, which is implemented using a single-frequency light source. The principle structure is simple, but it cannot distinguish the direction of movement, and a four-channel detection structure needs to be added, which will result in a large optical path volume and limit integration in high-end equipment systems. The heterodyne grating interferometer light source uses a dual-frequency laser. Although only two signals, reference and measurement, are needed to distinguish the direction of movement and no four-channel detection structure is required, the dual-frequency light source is more complex in structure and more expensive than a single-frequency light source. Therefore, in actual applications, homodyne grating interferometry is widely used, and the miniaturization and integration of the two-axis homodyne grating interference optical path is an important topic in this field.

[0004] At present, the domestic patent layout in the field of two-axis homodyne grating interferometry for synchronous measurement of horizontal and vertical displacement is not mature:

[0005] For example, Tsinghua University and Beijing Huazhuo Jingke Technology Co., Ltd., as applicants, have published two patent documents: CN103759654A and CN103759655A, which disclose two two-axis displacement measurement systems based on zero-difference grating interferometry, which can achieve optical four-segmentation. However, both use three dichroic prisms and three wave plates to form a four-channel detection structure, which has many optical path components, is large in size and difficult to assemble and adjust.

[0006] Related public research includes: Lu Zhengang and others from Harbin Institute of Technology proposed a two-axis displacement measurement method based on the principle of zero-difference laser grating interference in the research paper "Two-degree-of-freedom displacement measurement system based on doublediffraction gratings". This method uses zero-order diffraction light to form a laser interference optical path to measure the vertical displacement of the grating. The displacement of the grating plane is measured by forming a grating interference optical path using positive and negative first-order diffraction light. In this scheme, the laser interference optical path and the grating interference optical path share a grating, but the measurement optical paths are independent of each other, making the system complex and large in size; and the same four-channel detection structure with three diffraction prisms and wave plates is used. Wei Gao and his team from Tohoku University in Japan proposed a vertically incident differential measurement homodyne grating interferometry scheme in their research paper “Position and out-of-straightness measurementof a precision linear air-bearing stage by using a two-degree-of-freedomlinear encoder”. This scheme can realize two-axis measurement in the same grating interferometry optical path, but still uses three dichroic prisms and wave plates to form a four-channel detection structure. At the same time, the vertical displacement of the grating in this scheme will cause the influence of optical axis offset, and its vertical range is small.

[0007] The four-channel detection structure formed by three beam splitting prisms and wave plates is the main reason for the complex optical structure and large size of the two-axis zero-difference grating interferometry, which makes the miniaturization of the optical path difficult and the difficulty of installation and adjustment. In recent years, a new combination structure based on Wollaston prism and four-quadrant detector has been proposed in the field of interference, which can realize interference and beam splitting in one, with fewer devices and small size, which is conducive to the miniaturization of the optical path. For example, Guo Xuanbiao of Harbin Institute of Technology proposed a laser interferometry optical path based on Wollaston prism and four-quadrant detector in his master's thesis "Research on Key Technologies of Single-Frequency Laser Interferometry Vibration", which can realize single-axis displacement measurement. However, since the Wollaston prism needs to be rotated 45° for installation, this solution is currently only applicable to single-axis measurement and cannot realize multi-axis measurement. In addition, this solution only uses two pixels of a four-quadrant detection device, which causes waste.

[0008] Therefore, the present invention proposes a two-axis homodyne grating interferometric displacement measurement method and system based on a Wollaston prism and a four-quadrant detector, which solves the problem that the combined structure of the Wollaston prism and the four-quadrant detector is not compatible with two-axis displacement measurement. Summary of the invention

[0009] The invention is used to solve the problem of incompatibility between a Wollaston prism (WP) and a four-quadrant detector (QPD) in the prior art in two-axis homodyne grating interference displacement measurement.

[0010] To achieve the above object, the present invention provides the following technical solutions:

[0011] The present invention provides a two-axis homodyne grating interferometric displacement measurement method based on a Wollaston prism and a four-quadrant detector, the measurement method comprising the following steps:

[0012] Step S1: Splitting the light beam emitted by the light source into biaxial parallel light;

[0013] Step S2: The biaxial parallel light passes through the interferometer group and is divided into reference light and measuring light. The reference light is reflected back to the interferometer group; the measuring light passes through the refractive element, is incident on the measuring grating, is diffracted and returns to the interferometer group along the original path, and overlaps with the reference light; the two overlapping light beams are incident on the four-channel interference light receiving unit, and are first divided into two parts by the non-polarizing beam splitter prism and the wave plate QWP assembly, and the two parts then pass through the first WP and the second WP respectively, and by adjusting the posture of the optical element in the optical path or the polarization direction of the incident light, the two parts of light each generate a set of four light spots distributed in a square on the QPD;

[0014] Step S3: Photoelectric detection and signal processing are performed on the four light spot signals to realize the calculation of displacement information.

[0015] Furthermore, there is a preferred embodiment in which the above optical element posture adjustment method can be designed as follows:

[0016] The non-polarizing beam splitter prism NPBS1, the first WP, the second WP, ​​the first QPD, and the second QPD are all rotated 45° around the optical axis.

[0017] Furthermore, the present invention provides a two-axis homodyne grating interferometric displacement measurement system of a rotating beam splitter prism, which is used to realize two-axis homodyne grating interferometric displacement measurement through the optical element posture adjustment method described in the above preferred embodiment, and the displacement measurement system includes a single-frequency laser light source, a non-polarizing beam splitter prism NPBS1, an interferometer group, a measuring grating and a four-channel interference light receiving unit;

[0018] The interferometer group includes a polarization beam splitter prism PBS, a first QWP, a second QWP, a reflector, and a refractive element;

[0019] The four-channel interference light receiving unit includes a non-polarization beam splitter prism NPBS2, a third QWP, a first WP, a second WP, ​​a first QPD, and a second QPD;

[0020] A first QWP and a second QWP are respectively arranged on two sides of the polarization beam splitting prism PBS;

[0021] A third QWP is provided on one surface of the non-polarizing beam splitter prism NPBS2;

[0022] A single-frequency laser light source emits a single-frequency laser, which is divided into a biaxial parallel light after passing through a non-polarizing beam splitter prism NPBS1. The biaxial parallel light enters a polarizing beam splitter prism PBS and is divided into four beams of light, of which two beams of s-polarized light are reflected back to the polarizing beam splitter prism PBS through a reflector, and the s-polarized light becomes p-polarized light, which serves as a reference light; the other two beams of p-polarized light are incident on a measuring grating at a Littrow angle after passing through a refractive element and return to the polarizing beam splitter prism PBS along the original path, serving as measuring light, and coincide with the reference light; the two coincident light beams are first divided into two parts through a non-polarizing beam splitter prism NPBS2 and a third QWP assembly, and the two parts then pass through a first WP and a second WP respectively, each of which generates a set of four light spots distributed in a square on the first QPD and the second QPD.

[0023] Furthermore, the above-mentioned single-frequency laser is split into biaxial parallel light after passing through the non-polarization beam splitter prism NPBS1, and the angle between the optical axis line and the x-axis is 45°.

[0024] Furthermore, in another preferred embodiment, the above-mentioned method for adjusting the polarization direction of incident light can be designed as follows:

[0025] Rotate the polarization direction of incident light by 45°.

[0026] Furthermore, the present invention provides a two-axis homodyne grating interferometric displacement measurement system for rotating polarization direction, the displacement measurement system is used to realize two-axis homodyne grating interferometric displacement measurement through the incident light polarization direction adjustment method described in the above preferred embodiment, the displacement measurement system comprises a single-frequency laser light source, a non-polarizing beam splitter prism NPBS1, an interferometer group, a measuring grating and a four-channel interference light receiving unit;

[0027] The interferometer group includes a polarization beam splitter prism PBS, a first QWP, a second QWP, a reflector, and a refractive element;

[0028] The four-channel interference light receiving unit includes a non-polarization beam splitter prism NPBS2, a third QWP, a first WP, a second WP, ​​a first QPD, and a second QPD;

[0029] A first QWP and a second QWP are respectively arranged on two sides of the polarization beam splitting prism PBS;

[0030] A third QWP is provided on one surface of the non-polarizing beam splitter prism NPBS2;

[0031] A single-frequency laser light source emits a single-frequency laser, which is divided into a biaxial parallel light after passing through a non-polarizing beam splitter prism NPBS1. The biaxial parallel light enters a polarizing beam splitter prism PBS and is divided into four beams of light, of which two beams of s-polarized light are reflected back to the polarizing beam splitter prism PBS through a reflector, and the s-polarized light becomes p-polarized light, which serves as a reference light; the other two beams of p-polarized light are incident on a measuring grating at a Littrow angle after passing through a refractive element and return to the polarizing beam splitter prism PBS along the original path, serving as measuring light, and coincide with the reference light; the two coincident light beams are first divided into two parts through a non-polarizing beam splitter prism NPBS2 and a third QWP assembly, and the two parts then pass through a first WP and a second WP respectively, each of which generates a set of four light spots distributed in a square on the first QPD and the second QPD.

[0032] Furthermore, the angle between the s-polarized light and the p-polarized light and the optical axis of the Wollaston prism is 45°.

[0033] Furthermore, there is a preferred embodiment, the above optical element posture adjustment method can also be designed as follows:

[0034] The polarization beam splitter prism PBS, the non-polarization beam splitter prism NPBS2, the first WP, the second WP, ​​the first QPD, and the second QPD are all rotated 45° around the optical axis.

[0035] Furthermore, the present invention provides a two-axis homodyne grating interference displacement measurement system of a rotating interference prism, the system is used to realize two-axis homodyne grating interference displacement measurement through the optical element posture adjustment method described in the above preferred embodiment, and the displacement measurement system includes a single-frequency laser light source, a non-polarizing beam splitter prism NPBS1, an interferometer group, a measuring grating and a four-channel interference light receiving unit;

[0036] The interferometer group includes a polarization beam splitter prism PBS, a first QWP, a second QWP, a reflector, and a refractive element;

[0037] The four-channel interference light receiving unit includes a non-polarization beam splitter prism NPBS2, a third QWP, a first WP, a second WP, ​​a first QPD, and a second QPD;

[0038] A first QWP and a second QWP are respectively arranged on two sides of the polarization beam splitting prism PBS;

[0039] A third QWP is provided on one surface of the non-polarizing beam splitter prism NPBS2;

[0040] A single-frequency laser light source emits a single-frequency laser, which is divided into a biaxial parallel light after passing through a non-polarizing beam splitter prism NPBS1. The biaxial parallel light enters a polarizing beam splitter prism PBS and is divided into four beams of light, of which two beams of s-polarized light are reflected back to the polarizing beam splitter prism PBS through a reflector, and the s-polarized light becomes p-polarized light, which serves as a reference light; the other two beams of p-polarized light are incident on a measuring grating at a Littrow angle after passing through a refractive element and return to the polarizing beam splitter prism PBS along the original path, serving as measuring light, and coincide with the reference light; the two coincident light beams are first divided into two parts through a non-polarizing beam splitter prism NPBS2 and a third QWP assembly, and the two parts then pass through a first WP and a second WP respectively, each of which generates a set of four light spots distributed in a square on the first QPD and the second QPD.

[0041] Furthermore, the angle between the optical axis connecting the two light beams separated by the non-polarization beam splitting prism NPBS2 and the third QWP assembly and the optical axis of the Wollaston prism is 45°.

[0042] The beneficial effects of the present invention are:

[0043] Most of the two-axis homodyne interferometric displacement measurement optical paths use three beam splitters and wave plates to form a four-channel detection structure, but the structure is complex, the volume is large, and the difficulty of installation and adjustment is large, which is not conducive to the miniaturization of the optical path. The combined module of Wollaston prism (WP) and quadrant detector (QPD) has been only used for single-degree-of-freedom interferometric displacement measurement. If it is used for two-axis homodyne interferometric displacement measurement, there will be a problem that the combined structure of Wollaston prism and quadrant detector is not compatible with the two-axis displacement measurement. The present invention combines two-axis homodyne grating interferometric displacement measurement with the combined module of Wollaston prism and quadrant detector. For the first time, by adjusting the posture of the optical element in the optical path or rotating the polarization direction of the light beam, it not only solves the optical path mismatch problem between the dual-axis parallel light and the rotating Wollaston prism, but also realizes the effective utilization of all pixels of the quadrant detector (QPD).

[0044] Furthermore, the present invention organically combines a combination module of a Wollaston prism (WP) and a quadrant detector (QPD) to achieve miniaturization of the optical path.

[0045] The present invention is suitable for realizing horizontal and vertical two-axis displacement measurement of a line grating by utilizing the single-frequency grating interference principle and through a four-channel detection structure based on a Wollaston prism (WP) and a four-quadrant detector (QPD). BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0047] Figure 1 It is an optical path structure diagram of the two-axis homodyne grating interferometric displacement measurement system of the rotating beam splitter prism of the present invention;

[0048] Figure 2 yes Figure 1 A three-dimensional diagram of the optical path structure of the two-axis homodyne grating interferometric displacement measurement system of the rotating beam splitter prism;

[0049] Figure 3 This is a schematic diagram of the angle between the s-polarized light and the p-polarized light and the x-axis being 45°;

[0050] Figure 4 It is an optical path structure diagram of the two-axis homodyne grating interferometric displacement measurement system for rotating polarization direction according to the present invention;

[0051] Figure 5 yes Figure 4 A three-dimensional diagram of the optical path structure of the two-axis homodyne grating interferometric displacement measurement system for rotating polarization direction. DETAILED DESCRIPTION

[0052] The specific embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

[0053] Embodiment 1: This embodiment aims at the problem that the Wollaston prism (WP) and the four-quadrant detector (QPD) are not compatible in the prior art in the two-axis homodyne grating interferometry displacement measurement occasion. Therefore, a two-axis homodyne grating interferometry displacement measurement method based on a Wollaston prism and a four-quadrant detector is proposed, and the method comprises the following steps:

[0054] Step S1: Splitting the light beam emitted by the light source into biaxial parallel light;

[0055] Step S2: The biaxial parallel light passes through the interferometer group and is divided into reference light and measuring light. The reference light is reflected back to the interferometer group; the measuring light passes through the refractive element, is incident on the measuring grating, is diffracted and returns to the interferometer group along the original path, and overlaps with the reference light; the two overlapping light beams are incident on the four-channel interference light receiving unit, and are first divided into two parts by the non-polarizing beam splitter prism and the wave plate QWP assembly, and the two parts then pass through the first WP and the second WP respectively, and by adjusting the posture of the optical element in the optical path or the polarization direction of the incident light, the two parts of light each generate a set of four light spots distributed in a square on the QPD;

[0056] Step S3: Photoelectric detection and signal processing are performed on the four light spot signals to realize the calculation of displacement information.

[0057] The two-axis homodyne grating interference displacement measurement method proposed in this embodiment uses a combination structure of a Wollaston prism (WP) and a four-quadrant detector (QPD) as a four-channel interference light receiving unit of a two-axis homodyne grating interferometer; and by adjusting the posture of certain optical elements in the optical path or the polarization direction of the incident light, the optical axis connection direction of the two light beams entering the four-channel interference light receiving unit is perpendicular to the direction of the Wollaston prism interface normal, so that the two light beams pass through the Wollaston prism and each form a group of four light spots distributed in a square on the four-quadrant detector, thereby solving the problem of optical path mismatch between the two-axis parallel light and the rotating Wollaston prism, that is, the problem that the combination structure of the Wollaston prism and the four-quadrant detector is not compatible with the two-axis displacement measurement.

[0058] Implementation Method 2: See Figure 1 and Figure 2 This embodiment is described. This embodiment provides a two-axis homodyne grating interferometry displacement measurement system with a rotating beam splitter prism. The two-axis homodyne grating interferometry displacement measurement method based on a Wollaston prism and a four-quadrant detector described in the first embodiment is implemented according to the displacement measurement system.

[0059] The displacement measurement system is as follows Figure 1 and Figure 2 As shown, it includes a single-frequency laser light source, a non-polarization beam splitter prism NPBS1, an interferometer group, a measuring grating and a four-channel interference light receiving unit;

[0060] The interferometer group includes a polarization beam splitter prism PBS, a first QWP, a second QWP, a reflector, and a refractive element;

[0061] The four-channel interference light receiving unit includes a non-polarization beam splitter prism NPBS2, a third QWP, a first WP, a second WP, ​​a first QPD, and a second QPD;

[0062] A first QWP and a second QWP are respectively arranged on two sides of the polarization beam splitting prism PBS;

[0063] A third QWP is disposed on one surface of the non-polarization beam splitting prism NPBS2.

[0064] In order to realize two-axis homodyne grating interferometric displacement measurement, the present embodiment uses a combination structure of a Wollaston prism (WP) and a four-quadrant detector (QPD) as a four-channel interference light receiving unit of a two-axis homodyne grating interferometer. To achieve this purpose, the Wollaston prism (WP) needs to be rotated 45° so that both light beams have components on the optical axis of the Wollaston prism (WP) and interfere with each other to realize two-axis homodyne interferometric displacement measurement. At the same time, the corresponding four-quadrant detector (QPD) also needs to be rotated 45°. At this time, due to the Wollaston prism (WP), the two light beams have components on the optical axis of the Wollaston prism (WP) and interfere with each other to realize two-axis homodyne interferometric displacement measurement. ) rotation will bring about an optical path mismatch problem. In this embodiment, the non-polarization beam splitter prism NPBS1 is rotated 45° around the optical axis, and the Wollaston prism (WP) and the four-quadrant detector (QPD) are rotated in the same manner, so that the optical axis connection direction of the double light beams entering the four-channel interference light receiving unit is perpendicular to the normal direction of the Wollaston prism interface, so that the double light beams pass through the Wollaston prism and form a group of four square-distributed light spots on the four-quadrant detector, thereby solving the optical path mismatch problem between the dual-axis parallel light and the rotating Wollaston prism.

[0065] The specific optical path structure is:

[0066] The single-frequency laser light source emits a single-frequency laser, which is divided into a double-axis parallel light after passing through the non-polarization beam splitter prism NPBS1. Since the non-polarization beam splitter prism NPBS1 is rotated 45° around the optical axis, the angle between the optical axis line of the double-axis parallel light and the x-axis is 45°. That is, the direction of the optical axis line of the double-axis parallel light is perpendicular to the direction of the interface law of the Wollaston prism; the double-axis parallel light enters the polarization beam splitter prism PBS and is divided into four beams of light, of which two beams of s-polarized light are reflected back to the polarization beam splitter prism PBS through a reflector, and the s-polarized light becomes p-polarized light as a reference light; the other two beams of p-polarized light pass through the refractive element and enter the measuring grating at the Littrow angle and return to the polarization beam splitter prism PBS along the original path, as the measuring light, and overlap with the reference light; the two overlapped beams are divided into two parts through the non-polarization beam splitter prism NPBS2 and the third QWP assembly, and the two parts are respectively interfered by the first WP and the second WP, ​​and each of them generates a set of four square-distributed light spots on the first QPD and the second QPD.

[0067] Implementation method three, see Figure 3 and Figure 4 This embodiment is described. This embodiment provides a two-axis homodyne grating interferometry displacement measurement system for rotating polarization direction. The two-axis homodyne grating interferometry displacement measurement method based on Wollaston prism and four-quadrant detector described in the first embodiment is implemented according to the displacement measurement system.

[0068] like Figure 3 and Figure 4 As shown, the optical elements required for the displacement measurement system described in this embodiment are the same as those of the displacement measurement system described in the above embodiment 2, and also include a single-frequency laser light source, a non-polarization beam splitter prism NPBS1, an interferometer group, a measurement grating and a four-channel interference light receiving unit;

[0069] The interferometer group includes a polarization beam splitter prism PBS, a first QWP, a second QWP, a reflector, and a refractive element;

[0070] The four-channel interference light receiving unit includes a non-polarization beam splitter prism NPBS2, a third QWP, a first WP, a second WP, ​​a first QPD, and a second QPD;

[0071] A first QWP and a second QWP are respectively arranged on two sides of the polarization beam splitting prism PBS;

[0072] A third QWP is disposed on one surface of the non-polarization beam splitting prism NPBS2.

[0073] The difference from the above-mentioned second embodiment is that, in this embodiment, the Wollaston prism (WP) and the four-quadrant detector (QPD) are not rotated by 45°, but the polarization direction of the incident light is rotated by 45°, so that the angle between the s-polarized light and the p-polarized light and the optical axis of the Wollaston prism is also 45°, as shown in FIG. Figure 4 As shown, there is no need to rotate the Wollaston prism 45°. The s-polarized light and p-polarized light also have components in the directions of the o-light and the e-light, and interference can also occur. Therefore, the optical path mismatch problem between the biaxial parallel light and the rotating Wollaston prism does not exist. In practical applications, the optical axis directions of the polarization beam splitter (PBS) and wave plates (QPW1, QPW2, QWP3) in the optical path need to change with the change of the polarization direction of the light beam.

[0074] Embodiment 4: This embodiment provides a two-axis homodyne grating interferometric displacement measurement system of a rotating interference prism, and the displacement measurement system is used to implement the two-axis homodyne grating interferometric displacement measurement method based on a Wollaston prism and a four-quadrant detector described in the above embodiment 1;

[0075] The optical elements required for the displacement measurement system described in this embodiment are the same as those of the displacement measurement system described in the above embodiment 2, and also include a single-frequency laser light source, a non-polarization beam splitter prism NPBS1, an interferometer group, a measurement grating, and a four-channel interference light receiving unit;

[0076] The interferometer group includes a polarization beam splitter prism PBS, a first QWP, a second QWP, a reflector, and a refractive element;

[0077] The four-channel interference light receiving unit includes a non-polarization beam splitter prism NPBS2, a third QWP, a first WP, a second WP, ​​a first QPD, and a second QPD;

[0078] A first QWP and a second QWP are respectively arranged on two sides of the polarization beam splitting prism PBS;

[0079] A third QWP is disposed on one surface of the non-polarization beam splitting prism NPBS2.

[0080] The difference from the above-mentioned second embodiment is that, in this embodiment, the Wollaston prism (WP) and the four-quadrant detector (QPD) are also rotated 45°, but the non-polarization beam splitter prism NPBS1 is not rotated. Instead, the polarization beam splitter prism PBS, the non-polarization beam splitter prism NPBS2, the Wollaston prism (WP) and the four-quadrant detector (QPD) are rotated 45° around the optical axis, which can also make the optical axis connection direction of the double light beams entering the four-channel interference light receiving unit perpendicular to the normal direction of the Wollaston prism interface, so that the double light beams pass through the Wollaston prism to form a group of four square-distributed light spots on the four-quadrant detector, thereby solving the optical path mismatch problem between the dual-axis parallel light and the rotating Wollaston prism.

[0081] The specific optical path structure is:

[0082] A single-frequency laser light source emits a single-frequency laser, which is divided into a biaxial parallel light after passing through a non-polarizing beam splitter prism NPBS1. The biaxial parallel light enters a polarizing beam splitter prism PBS and is divided into four beams of light, of which two beams of s-polarized light are reflected back to the polarizing beam splitter prism PBS through a reflector, and the s-polarized light becomes p-polarized light, which serves as a reference light; the other two beams of p-polarized light are incident on a measuring grating at a Littrow angle after passing through a refractive element and return to the polarizing beam splitter prism PBS along the original path, serving as measuring light and overlapping with the reference light; the two overlapping beams are divided into two parts through a non-polarizing beam splitter prism NPBS2 and a third QWP assembly, and are respectively incident on a first WP and a second WP, Since the Wollaston prism (WP) and the four-quadrant detector (QPD) are both rotated 45° around the optical axis, the two light beams incident on the Wollaston prism (WP) can interfere with each other; at the same time, since the polarization beam splitter prism PBS and the non-polarization beam splitter prism NPBS2 are also rotated 45° around the optical axis, the direction of the optical axis connection line of the two light beams incident on the Wollaston prism (WP) is perpendicular to the normal direction of the Wollaston prism interface, so that the double light beams pass through the first WP and the second WP, ​​respectively, and a group of four light spots distributed in a square are generated on the first QPD and the second QPD, thereby solving the optical path mismatch problem between the dual-axis parallel light and the rotating Wollaston prism.

[0083] In summary, in order to use the combined module of a Wollaston prism (WP) and a four-quadrant detector (QPD) as a two-axis homodyne interferometric displacement measurement, the present invention adjusts the posture of certain elements in the optical path or rotates the polarization direction of the light beam so that the direction of the Wollaston prism interface normal direction that is the direction of the double-light beam optical axis connection line is perpendicular. At this time, the double light beams pass through the Wollaston prism to generate a group of four light spots distributed in a square on the four-quadrant detector, thereby solving the optical path mismatch problem between the two-axis parallel light and the rotating Wollaston prism.

[0084] In the above description, specific details such as specific system structures, technologies, etc. are proposed for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known optical paths, devices, circuits, and methods are omitted to prevent unnecessary details from hindering the description of the present application.

[0085] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features.

[0086] The above description is only the implementation mode of the present invention and is not limited to the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of the claims of the present invention.

Claims

1. A two-axis homodyne grating interferometric displacement measurement method based on a Wollaston prism and a four-quadrant detector, characterized in that: The method is: S1: Split the light beam emitted by the light source into biaxial parallel light; S2: The biaxial parallel light passes through the interferometer group and is divided into reference light and measurement light. The reference light is reflected back to the interferometer group; the measurement light passes through the refractive element, is incident on the measurement grating, is diffracted and returns to the interferometer group along the original path, and overlaps with the reference light; the two overlapping light beams are incident on the four-channel interference light receiving unit, firstly passed through the non-polarization beam splitter prism and wave plate QWP assembly to be divided into two parts, and then the two parts pass through the first WP and the second WP respectively. By adjusting the posture of the optical element in the optical path or the polarization direction of the incident light, the two parts of light each generate a set of four square-distributed light spots on the QPD; S3: Photoelectric detection and signal processing are performed on the four light spot signals to realize the calculation of displacement information.

2. The two-axis homodyne grating interferometry displacement measurement method based on Wollaston prism and four-quadrant detector according to claim 1, characterized in that: The method for adjusting the optical element posture is: The non-polarizing beam splitter prism NPBS1, the first WP, the second WP, ​​the first QPD, and the second QPD are all rotated 45° around the optical axis.

3. A two-axis homodyne grating interferometric displacement measurement system with a rotating beam splitter prism, characterized in that: The displacement measurement system is used to realize two-axis homodyne grating interferometric displacement measurement through the optical element posture adjustment method according to claim 2, and the displacement measurement system includes a single-frequency laser light source, a non-polarizing beam splitter prism NPBS1, an interferometer group, a measuring grating and a four-channel interference light receiving unit; The interferometer group includes a polarization beam splitter prism PBS, a first QWP, a second QWP, a reflector, and a refractive element; The four-channel interference light receiving unit includes a non-polarization beam splitter prism NPBS2, a third QWP, a first WP, a second WP, ​​a first QPD, and a second QPD; A first QWP and a second QWP are respectively arranged on two sides of the polarization beam splitting prism PBS; A third QWP is provided on one surface of the non-polarizing beam splitter prism NPBS2; A single-frequency laser light source emits a single-frequency laser, which is divided into a biaxial parallel light after passing through a non-polarizing beam splitter prism NPBS1. The biaxial parallel light enters a polarizing beam splitter prism PBS and is divided into four beams of light, of which two beams of s-polarized light are reflected back to the polarizing beam splitter prism PBS through a reflector, and the s-polarized light becomes p-polarized light, which serves as a reference light; the other two beams of p-polarized light are incident on a measuring grating at a Littrow angle after passing through a refractive element and return to the polarizing beam splitter prism PBS along the original path, serving as measuring light, and coincide with the reference light; the two coincident light beams are first divided into two parts through a non-polarizing beam splitter prism NPBS2 and a third QWP assembly, and the two parts then pass through a first WP and a second WP respectively, each of which generates a set of four light spots distributed in a square on the first QPD and the second QPD.

4. The two-axis homodyne grating interferometry displacement measurement system of the rotating beam splitter prism according to claim 3, characterized in that: The single-frequency laser is split into two-axis parallel light after passing through the non-polarizing beam splitter prism NPBS1, and the angle between the optical axis line and the x-axis is 45°.

5. The two-axis homodyne grating interferometry displacement measurement method based on Wollaston prism and four-quadrant detector according to claim 1, characterized in that: The method for adjusting the polarization direction of incident light is: Rotate the polarization direction of incident light by 45°.

6. A two-axis homodyne grating interferometric displacement measurement system with a rotating polarization direction, characterized in that: The displacement measurement system is used to realize two-axis homodyne grating interferometric displacement measurement through the incident light polarization direction adjustment method according to claim 5, and the displacement measurement system includes a single-frequency laser light source, a non-polarizing beam splitter prism NPBS1, an interferometer group, a measuring grating and a four-channel interference light receiving unit; The interferometer group includes a polarization beam splitter prism PBS, a first QWP, a second QWP, a reflector, and a refractive element; The four-channel interference light receiving unit includes a non-polarization beam splitter prism NPBS2, a third QWP, a first WP, a second WP, ​​a first QPD, and a second QPD; A first QWP and a second QWP are respectively arranged on two sides of the polarization beam splitting prism PBS; A third QWP is provided on one surface of the non-polarizing beam splitter prism NPBS2; A single-frequency laser light source emits a single-frequency laser, which is divided into a biaxial parallel light after passing through a non-polarizing beam splitter prism NPBS1. The biaxial parallel light enters a polarizing beam splitter prism PBS and is divided into four beams of light, of which two beams of s-polarized light are reflected back to the polarizing beam splitter prism PBS through a reflector, and the s-polarized light becomes p-polarized light, which serves as a reference light; the other two beams of p-polarized light are incident on a measuring grating at a Littrow angle after passing through a refractive element and return to the polarizing beam splitter prism PBS along the original path, serving as measuring light, and coincide with the reference light; the two coincident light beams are first divided into two parts through a non-polarizing beam splitter prism NPBS2 and a third QWP assembly, and the two parts then pass through a first WP and a second WP respectively, each of which generates a set of four light spots distributed in a square on the first QPD and the second QPD.

7. The two-axis homodyne grating interferometry displacement measurement system for rotating polarization direction according to claim 6, characterized in that: The angle between the s-polarized light and the p-polarized light and the optical axis of the Wollaston prism is 45°.

8. The two-axis homodyne grating interferometry displacement measurement method based on Wollaston prism and four-quadrant detector according to claim 1, characterized in that: The method for adjusting the optical element posture can also be: The polarization beam splitter prism PBS, the non-polarization beam splitter prism NPBS2, the first WP, the second WP, ​​the first QPD, and the second QPD are all rotated 45° around the optical axis.

9. A two-axis homodyne grating interferometric displacement measurement system with a rotating interferometric prism, characterized in that: The system is used to realize two-axis homodyne grating interferometric displacement measurement through the optical element posture adjustment method described in claim 8, and the displacement measurement system includes a single-frequency laser light source, a non-polarizing beam splitter prism NPBS1, an interferometer group, a measuring grating and a four-channel interference light receiving unit; The interferometer group includes a polarization beam splitter prism PBS, a first QWP, a second QWP, a reflector, and a refractive element; The four-channel interference light receiving unit includes a non-polarization beam splitter prism NPBS2, a third QWP, a first WP, a second WP, ​​a first QPD, and a second QPD; A first QWP and a second QWP are respectively arranged on two sides of the polarization beam splitting prism PBS; A third QWP is provided on one surface of the non-polarizing beam splitter prism NPBS2; A single-frequency laser light source emits a single-frequency laser, which is divided into a biaxial parallel light after passing through a non-polarizing beam splitter prism NPBS1. The biaxial parallel light enters a polarizing beam splitter prism PBS and is divided into four beams of light, of which two beams of s-polarized light are reflected back to the polarizing beam splitter prism PBS through a reflector, and the s-polarized light becomes p-polarized light, which serves as a reference light; the other two beams of p-polarized light are incident on a measuring grating at a Littrow angle after passing through a refractive element and return to the polarizing beam splitter prism PBS along the original path, serving as measuring light, and coincide with the reference light; the two coincident light beams are first divided into two parts through a non-polarizing beam splitter prism NPBS2 and a third QWP assembly, and the two parts then pass through a first WP and a second WP respectively, each of which generates a set of four light spots distributed in a square on the first QPD and the second QPD.

10. The two-axis homodyne grating interferometric displacement measurement system of the rotating interference prism according to claim 9, characterized in that: The angle between the optical axis connecting the two light beams separated by the non-polarizing beam splitter prism NPBS2 and the third QWP assembly and the optical axis of the Wollaston prism is 45°.

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