Grating displacement measuring device

Abstract

The application provides a grating displacement measurement device, comprising: a light beam emitting unit for generating a first light beam and a second light beam with different frequencies; a light beam shaping unit comprising a Wollaston prism and a non-polarized light splitting prism; a grating; and a signal receiving unit comprising a first detector and a second detector; the first light beam and the second light beam are incident on the non-polarized light splitting prism through the Wollaston prism, the first light beam and the second light beam are orthogonal in polarization and have a separation angle after passing through the Wollaston prism; a part of the first light beam and the second light beam are reflected back to the Wollaston prism after being turned by the non-polarized light splitting prism, and are combined to form a reference light which is transmitted to the first detector; another part of the first light beam and the second light beam are incident on the grating, and are diffracted by the grating to form a measurement light which is transmitted to the second detector, so as to calculate the displacement of the grating in the horizontal direction according to the detected reference light and measurement light. The technical scheme of the application can improve the measurement repeatability and ensure the accuracy of the grating displacement measurement.

Description

Technical Field

[0001] This invention relates to the field of integrated circuit manufacturing, and in particular to a grating displacement measuring device. Background Technology

[0002] Existing grating displacement measurement devices use a combination of semi-transparent and semi-reflective elements to separate the reference optical path. The structure is dispersed, and the separated reference optical path has only a single polarization state, resulting in strong stray signal interference and poor measurement repeatability.

[0003] Therefore, how to improve the existing grating displacement measurement device to enhance the repeatability of the measurement is an urgent problem to be solved. Summary of the Invention

[0004] The purpose of this invention is to provide a grating displacement measuring device that can improve measurement repeatability and ensure the accuracy of grating displacement measurement.

[0005] To achieve the above objectives, the present invention provides a grating displacement measuring device, comprising:

[0006] A beam emitting unit is used to generate a first beam and a second beam with different frequencies;

[0007] A grating ruler reading head includes a beam shaping unit, which includes a Wollaston prism and a non-polarizing beam splitter.

[0008] grating;

[0009] The signal receiving unit includes a first detector and a second detector;

[0010] In this process, the first beam and the second beam are incident on the unpolarized beam splitter through the Wollaston prism. After passing through the Wollaston prism, the first beam and the second beam are polarized orthogonally and have a separation angle. A portion of the first beam and the second beam incident on the unpolarized beam splitter are deflected by the unpolarized beam splitter and reflected back to the Wollaston prism. After being combined by the Wollaston prism, they form a reference beam that is transmitted to the first detector. Another portion of the first beam and the second beam incident on the unpolarized beam splitter continue to be incident on the grating. After being diffracted by the grating, they form a measurement beam that is transmitted to the second detector, so as to calculate the horizontal displacement of the grating based on the detected reference beam and the measurement beam.

[0011] Optionally, the beam shaping unit further includes a first linear polarizer and a second linear polarizer, wherein the first beam is incident on the Wollaston prism via the first linear polarizer, and the second beam is incident on the Wollaston prism via the second linear polarizer, so as to eliminate stray light in the first beam and the second beam.

[0012] Optionally, the beam shaping unit further includes a first collimating lens and a second collimating lens. The first beam is collimated by the first collimating lens and then incident on the first linear polarizer. The second beam is collimated by the second collimating lens and then incident on the second linear polarizer. The collimated first beam and the second beam are parallel.

[0013] Optionally, the beam shaping unit further includes a third linear polarizer and a first coupling lens, and the reference light is transmitted to the first detector after passing through the third linear polarizer and the first coupling lens in sequence.

[0014] Optionally, the grating ruler reading head further includes a diffraction backscattering unit, which includes a first corner bevel prism and a second corner bevel prism. In the other part, the first beam and the second beam continue to be incident on the grating. The -1st order diffracted light of the first beam, after being diffracted once by the grating, is incident on the first corner bevel prism and reflected back to the grating. The +1st order diffracted light of the second beam, after being diffracted once by the grating, is incident on the second corner bevel prism and reflected back to the grating. The -1st order diffracted light and the +1st order diffracted light are then diffracted a second time by the grating and transmitted to the second detector.

[0015] Optionally, the diffraction backscattering unit further includes a fourth linear polarizer and a fifth linear polarizer. The -1st order diffracted light of the first beam and the -1st order diffracted light of the second beam after one diffraction by the grating are incident on the fourth linear polarizer to filter out the -1st order diffracted light of the second beam and obtain the -1st order diffracted light of the first beam. The +1st order diffracted light of the first beam and the +1st order diffracted light of the second beam after one diffraction by the grating are incident on the fifth linear polarizer to filter out the +1st order diffracted light of the first beam and obtain the +1st order diffracted light of the second beam.

[0016] Optionally, the diffraction backscattering unit further includes a first wedge plate and a second wedge plate. The -1st order diffracted light of the first beam reflected by the first corner prism is incident on the grating after passing through the first wedge plate, and the +1st order diffracted light of the second beam reflected by the second corner prism is incident on the grating after passing through the second wedge plate, so that the -1st order diffracted light of the first beam and the +1st order diffracted light of the second beam propagate in the same direction after being diffracted twice by the grating.

[0017] Optionally, the diffraction back-emission unit further includes a sixth linear polarizer and a second coupling lens, and the measurement light is transmitted to the second detector after passing through the sixth linear polarizer and the second coupling lens in sequence.

[0018] Optionally, the beam emitting unit and the grating ruler reading head are connected via polarization-maintaining optical fiber.

[0019] Optionally, the signal receiving unit is connected to the grating ruler reading head via a multimode optical fiber.

[0020] Optionally, the ratio of the transmittance to the reflectance of the unpolarized beam splitter for the first beam is less than 1, and the ratio of the transmittance to the reflectance of the unpolarized beam splitter for the second beam is greater than 1.

[0021] Compared with the prior art, the grating displacement measurement device of the present invention includes: a beam emitting unit for generating a first beam and a second beam with different frequencies; a grating ruler reading head including a beam shaping unit, the beam shaping unit including a Wollaston prism and a non-polarizing beam splitter; a grating; and a signal receiving unit including a first detector and a second detector; wherein, the first beam and the second beam are incident on the non-polarizing beam splitter through the Wollaston prism, and the first beam after passing through the Wollaston prism is orthogonally polarized to the second beam and has a separation angle; a portion of the first beam and the second beam incident on the non-polarizing beam splitter are deflected by the non-polarizing beam splitter and reflected back to the Wollaston prism, and after being combined by the Wollaston prism, they are formed into a reference beam and transmitted to the first detector; another portion of the first beam and the second beam incident on the non-polarizing beam splitter continues to be incident on the grating, and after being diffracted by the grating, they are formed into a measurement beam and transmitted to the second detector, so as to calculate the horizontal displacement of the grating based on the detected reference beam and the measurement beam. In the grating displacement measurement device of the present invention, the reference light after separation based on the non-polarizing beam splitter prism and beam combining based on the Wollaston prism contains two polarization states, which can reduce the interference of stray signals, thereby improving the measurement repeatability and ensuring the accuracy of grating displacement measurement; and, by using the Wollaston prism and the non-polarizing beam splitter prism, the separation and beam combining of the optical path can be realized, simplifying the structure and making it compatible with small space installation requirements. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a grating displacement measuring device according to an embodiment of the present invention;

[0023] Figure 2 This is a schematic diagram of the polarization and separation of the first and second beams after passing through the Wollaston prism according to an embodiment of the present invention.

[0024] Figure 3 This is a schematic diagram of the polarization and separation of the first and second beams after passing through a linear polarizer and a Wollaston prism, according to an embodiment of the present invention.

[0025] Figure 4 This is a schematic diagram of adaptive beam combining of the reference optical path according to an embodiment of the present invention;

[0026] Figure 5 This is a top view schematic diagram of the measurement optical path according to an embodiment of the present invention.

[0027] Among them, the appendix Figures 1-5 The annotations in the attached figures are explained as follows:

[0028] 100 - Grating ruler reader; 101 - First collimating lens; 102 - Second collimating lens; 103 - First coupling lens; 104 - Second coupling lens; 105 - First linear polarizer; 106 - Second linear polarizer; 107 - Third linear polarizer; 108 - Sixth linear polarizer; 109 - Wollaston prism; 110 - Unpolarized beam splitter; 111 - Fourth linear polarizer; 112 - Fifth linear polarizer; 113 - First corner bevel prism; 114 - Second corner bevel prism; 115 - First wedge; 116 - Second wedge; 117 - Protective window; 200 - Beam emitting unit; 201 - First polarization-maintaining fiber; 202 - Second polarization-maintaining fiber; 301 - First multimode fiber; 302 - Second multimode fiber; 303 - First detector; 304 - Second detector; 400 - Grating. Detailed Implementation

[0029] To make the objectives, advantages, and features of the present invention clearer, the grating displacement measuring device proposed in this invention will be described in further detail below. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clearly illustrate the objectives of the embodiments of the present invention.

[0030] An embodiment of the present invention provides a grating displacement measurement device, comprising: a beam emitting unit for generating a first beam and a second beam with different frequencies; a grating ruler reading head including a beam shaping unit, the beam shaping unit including a Wollaston prism and a non-polarizing beam splitter; a grating; and a signal receiving unit including a first detector and a second detector; wherein, the first beam and the second beam are incident on the non-polarizing beam splitter through the Wollaston prism, and the first beam after passing through the Wollaston prism is orthogonally polarized to the second beam and has a separation angle; a portion of the first beam and the second beam incident on the non-polarizing beam splitter are deflected by the non-polarizing beam splitter and reflected back to the Wollaston prism, and after being combined by the Wollaston prism, they form a reference beam and are transmitted to the first detector; another portion of the first beam and the second beam incident on the non-polarizing beam splitter continues to be incident on the grating, and after being diffracted by the grating, they form a measurement beam and are transmitted to the second detector, so as to calculate the horizontal displacement of the grating based on the detected reference beam and the measurement beam.

[0031] See below. Figures 1-5 This embodiment provides a more detailed description of the grating displacement measuring device. Among other things, Figures 1-5 The markings L0, L1, and L2 in the diagram all represent the polarization direction of light. Marking L0 also includes the polarization directions represented by markings L1 and L2. The polarization direction of marking L1 is parallel to the incident plane (i.e., p-polarized light), and the polarization direction of marking L2 is perpendicular to the incident plane (i.e., s-polarized light). Marking L0 includes both polarization directions parallel to and perpendicular to the incident plane.

[0032] The beam emitting unit 200 can be a dual-frequency heterodyne laser, used to generate a first beam F1 and a second beam F2 with different frequencies. Both the first beam F1 and the second beam F2 are linearly polarized light.

[0033] The dual-frequency heterodyne laser can be an ultraviolet, visible, or infrared laser, and the wavelengths of the first beam F1 and the second beam F2 are, for example, 632.99 nm, and the frequency difference between the first beam F1 and the second beam F2 is 20 MHz.

[0034] The beam emitting unit 200 and the grating ruler reading head 100 are connected via polarization-maintaining optical fiber. Figure 1 As can be seen, the first beam F1 can be transmitted to the grating ruler read head 100 via the first polarization-maintaining fiber 201, and the second beam F2 can be transmitted to the grating ruler read head 100 via the second polarization-maintaining fiber 202. The axes of the first polarization-maintaining fiber 201 and the second polarization-maintaining fiber 202 correspond to the polarization directions of the first beam F1 and the second beam F2, respectively, to ensure that the polarization states of the first beam F1 and the second beam F2 do not change significantly during their transmission in the first polarization-maintaining fiber 201 and the second polarization-maintaining fiber 202, respectively. Furthermore, by adjusting the rotation of the first polarization-maintaining fiber 201 and the second polarization-maintaining fiber 202, the orthogonality of the polarizations of the first beam F1 and the second beam F2 is initially ensured.

[0035] Preferably, the first polarization-maintaining fiber 201 and the second polarization-maintaining fiber 202 are single-mode fibers.

[0036] The grating ruler reading head 100 includes a beam shaping unit, which includes a Wollaston prism 109 and a non-polarizing beam splitter 110.

[0037] The grating 400 can be a one-dimensional diffraction grating.

[0038] The signal receiving unit includes a first detector 303 and a second detector 304.

[0039] The first beam F1 and the second beam F2 are incident on the unpolarized beam splitter 110 through the Wollaston prism 109. After passing through the Wollaston prism 109, the first beam F1 and the second beam F2 are polarized orthogonally and have a separation angle.

[0040] Preferably, the beam shaping unit further includes a first linear polarizer 105 and a second linear polarizer 106. The first beam F1 is incident on the Wollaston prism 109 via the first linear polarizer 105, and the second beam F2 is incident on the Wollaston prism 109 via the second linear polarizer 106. This eliminates most of the stray light in the first beam F1 and the second beam F2 through the first linear polarizer 105 and the second linear polarizer 106, respectively. It also eliminates the change in beam polarization state after the linearly polarized light of the first beam F1 and the second beam F2 is transmitted through the first polarization-maintaining fiber 201 and the second polarization-maintaining fiber 202.

[0041] like Figure 2 As shown, when the beam shaping unit does not include the first linear polarizer 105 and the second linear polarizer 106, the light emitted from the first beam F1 and the second beam F2 after passing through the Wollaston prism 109 contains stray light (i.e., Figure 2 (dashed arrow in the image) and non-stray light (i.e.) Figure 2 (Solid arrow in the text). For example... Figure 3 As shown, when the beam shaping unit includes the first linear polarizer 105 and the second linear polarizer 106, most of the stray light in the first beam F1 and the second beam F2 emitted from the first linear polarizer 105 and the second linear polarizer 106 respectively is eliminated, and only a small amount of stray light is emitted after passing through the Wollaston prism 109 to reduce crosstalk of stray light; and before being incident on the first linear polarizer 105 and the second linear polarizer 106, the polarization directions of the first beam F1 and the second beam F2, as indicated by label L0, both include polarization directions parallel to the incident plane and perpendicular to the incident plane. After passing through the first linear polarizer 105 and the second linear polarizer 106, the emitted first beam F1 only contains light with a polarization direction parallel to the incident plane (as indicated by label L1), and the emitted second beam F2 only contains light with a polarization direction perpendicular to the incident plane (as indicated by label L2). It should be noted that, in order to facilitate the explanation of the effects of the first linear polarizer 105 and the second linear polarizer 106 in removing stray light, Figure 3 The small amount of stray light emitted through the Wollaston prism 109 is not shown in the drawing, but only in... Figure 1 and Figure 5 The propagation path of the small amount of stray light emitted through the Wollaston prism 109 is shown in dashed lines.

[0042] The Wollaston prism 109 is a birefringent prism. When a beam of light with a certain elliptic polarization is incident on the Wollaston prism 109, the outgoing light consists of two beams with completely orthogonal polarization (the orthogonality and degree of polarization are determined by the uniformity of the crystal material of the Wollaston prism 109 itself), and there is a separation angle of 2φ. Based on this characteristic, we can fine-tune the incident polarization state of the first beam F1 and the second beam F2 by rotating the first linear polarizer 105 and the second linear polarizer 106. When the polarization directions of the first beam F1 and the second beam F2 are respectively aligned with the crystal axis direction of the Wollaston prism 109, the polarization directions of the beams emitted from the Wollaston prism 109 remain orthogonal and have a separation angle of 2φ. Figure 2 It can be seen that the polarization direction of the stray light in the first beam F1 emitted from the Wollaston prism 109, as indicated by label L2, is perpendicular to the incident plane, while the polarization direction of the non-stray light in the first beam F1 emitted from the Wollaston prism 109, as indicated by label L1, is parallel to the incident plane. Therefore, the stray light and non-stray light in the first beam F1 emitted from the Wollaston prism 109 are orthogonally polarized and have a separation angle of 2φ; and, from Figure 2 It can be seen that the polarization direction of the stray light in the second beam F2 emitted from the Wollaston prism 109, as indicated by label L1, is parallel to the incident plane, while the polarization direction of the non-stray light in the second beam F2 emitted from the Wollaston prism 109, as indicated by label L2, is perpendicular to the incident plane. Therefore, the stray light and non-stray light in the second beam F2 emitted from the Wollaston prism 109 are orthogonally polarized and have a separation angle of 2φ; and, from Figure 2 and Figure 3 It can be seen that the non-stray light in the first beam F1 emitted from the Wollaston prism 109 and the non-stray light in the second beam F2 emitted from the Wollaston prism 109 are polarized orthogonally and have a separation angle of 2φ.

[0043] Wherein, the separation angle 2φ≈2arcsin[(no-ne)*tanθ]; no and ne are the refractive indices of the birefringent crystal in two directions, and θ is the slope angle of the Wollaston prism 109.

[0044] Preferably, the beam shaping unit further includes a first collimating lens 101 and a second collimating lens 102. The first beam F1 is collimated by the first collimating lens 101 and then incident on the first linear polarizer 105. The second beam F2 is collimated by the second collimating lens 102 and then incident on the second linear polarizer 106. The collimated first beam F1 and the second beam F2 are parallel.

[0045] The first beam F1 is transmitted from the first polarization-maintaining fiber 201 to the first collimating lens 101, and the second beam F2 is transmitted from the second polarization-maintaining fiber 202 to the second collimating lens 102. The positions of the first collimating lens 101 and the second collimating lens 102, as well as the port positions of the first polarization-maintaining fiber 201 and the second polarization-maintaining fiber 202, can be adjusted to ensure that the first beam F1 and the second beam F2 are emitted in parallel after collimation.

[0046] Furthermore, the collimated spot diameter D depends on the numerical aperture NA of the polarization-maintaining fiber and the focal length f of the collimating lens, and the calculation formula is D = 2 * NA * f.

[0047] The first collimating lens 101 and the second collimating lens 102 may be composed of a single spherical or aspherical lens.

[0048] The first beam F1 and the second beam F2 are incident on the unpolarized beam splitter 110 through the Wollaston prism 109. A portion of the first beam F1 and the second beam F2 incident on the unpolarized beam splitter 110 are deflected by the unpolarized beam splitter 110 and reflected back to the Wollaston prism 109. After being combined by the Wollaston prism 109, they form a reference beam and are transmitted to the first detector 303. For ease of distinction, the optical path of the portion of the first beam F1 and the second beam F2 reflected back from the unpolarized beam splitter 110 is defined as the reference optical path.

[0049] Preferably, the beam shaping unit further includes a third linear polarizer 107 and a first coupling lens 103. The reference light, after being combined by the Wollaston prism 109, is transmitted to the first detector 303 after passing through the third linear polarizer 107 and the first coupling lens 103 in sequence.

[0050] See Figure 4 This illustrates that the first beam F1 and the second beam F2 pass through the Wollaston prism 109 in one pass. Figure 4 The Wollaston prism 109 on the left side of the middle section and the secondary passage through the Wollaston prism 109 ( Figure 4 The optical path of the Wollaston prism 109 on the right side of the middle, from Figure 4As can be seen, using the same birefringent prism (i.e., the Wollaston prism 109) for beam angle correction, due to the reversibility of the optical path, after the first beam F1 and the second beam F2 pass through the Wollaston prism 109 once, a portion of the first beam F1 and the second beam F2 are incident on the unpolarized beam splitter 110. After being deflected by the unpolarized beam splitter 110, they are reflected back and pass through the Wollaston prism 109 a second time at the same incident angle. This portion of the first beam F1 and the second beam F2 will exit from the Wollaston prism 109 at a parallel angle (i.e., after beam combining) and then be incident on the third linear polarizer 107. Before being incident on the third linear polarizer 107, the two beams F2 have the same propagation angle and their spot positions are guaranteed to coincide. Then, the polarization is adjusted by the third linear polarizer 107 so that the first beam F1 and the second beam F2 in the reference optical path exiting the third linear polarizer 107 are polarized in the same way. The first beam F1 and the second beam F2, which are parallel to each other, exiting the third linear polarizer 107 are focused at the same point by the first coupling lens 103 and transmitted to the first detector 303. An effective beat frequency signal is formed on the detection surface of the first detector 303 to obtain the frequency difference information between the first beam F1 and the second beam F2 in the reference optical path, which is used as a reference signal for subsequent displacement measurement.

[0051] And, as Figure 1 and Figure 4 As shown, after the first beam F1 and the second beam F2 pass through the Wollaston prism 109 twice, the reference light after being combined by the Wollaston prism 109 contains two polarization states, namely the polarization direction of the first beam F1 parallel to the incident plane and the polarization direction of the second beam F2 perpendicular to the incident plane.

[0052] The first beam F1 and the second beam F2 are incident on the unpolarized beam splitter 110 via the Wollaston prism 109. Another portion of the first beam F1 and the second beam F2 incident on the unpolarized beam splitter 110 continue to be incident on the grating 400, and after diffraction by the grating 400, are formed into measurement light and transmitted to the second detector 304 to calculate the horizontal displacement of the grating 400 based on the detected reference light and the measurement light. For ease of distinction, the optical path after the other portion of the first beam F1 and the second beam F2 exits the unpolarized beam splitter 110 is defined as the measurement optical path.

[0053] Since the first beam F1 and the second beam F2 emitted from the unpolarized beam splitter 110 are orthogonally polarized and have a separation angle of 2φ, the first beam F1 and the second beam F2 in the measurement optical path illuminate the grating 400 at a nearly perpendicular angle, producing diffracted light of different diffraction orders. According to the diffraction principle of a rectangular grating, the diffraction order m and the diffraction angle θs are related to the grating period d, the illumination wavelength λ, and the illumination angle i, and the calculation formula is d*(sin(i)±sin(θs))=m*λ. By designing a suitable grating period d (e.g., 833.33nm, 1000nm, etc.), the maximum diffraction order can be ±1 order. Therefore, the first beam F1 and the second beam F2 in the measurement optical path have 0th order and ±1st order diffraction light, respectively. The 0th order diffraction light does not participate in the measurement. The ±1st order diffraction light of the first beam F1 and the ±1st order diffraction light of the second beam F2 carry the displacement information of the grating 400. According to the grating Doppler effect, when the grating 400 undergoes horizontal displacement along the structure perpendicular to the long side of the rectangle, the diffraction light will carry the displacement information. The -1st order diffraction light produces a negative phase change with the displacement, and the +1st order diffraction light produces a positive phase change with the displacement.

[0054] like Figure 1 and Figure 5 As shown, the grating ruler reading head 100 further includes a diffraction backscattering unit, which includes a first corner bevel prism 113 and a second corner bevel prism 114. In the other part, the first beam F1 and the second beam F2 continue to be incident on the grating 400. After the first diffraction of the first beam F1 by the grating 400, the -1st order diffracted light is incident on the first corner bevel prism 113 and reflected back to the grating 400. After a second diffraction by the grating 400, it is transmitted to the second detector 304. Similarly, in the other part, the first beam F1 and the second beam F2 continue to be incident on the grating 400. After the first diffraction of the second beam F2 by the grating 400, the +1st order diffracted light is incident on the second corner bevel prism 114 and reflected back to the grating 400. After a second diffraction by the grating 400, it is transmitted to the second detector 304.

[0055] The diffraction backscattering unit further includes a fourth linear polarizer 111 and a fifth linear polarizer 112, wherein the fourth linear polarizer 111 and the fifth linear polarizer 112 have orthogonal polarization states. Due to the slight angular deviation and orthogonal polarization states between the -1st order diffracted light of the first beam F1 and the -1st order diffracted light of the second beam F2 after one diffraction by the grating 400, after the -1st order diffracted light of the first beam F1 and the -1st order diffracted light of the second beam F2 are incident on the fourth linear polarizer 111, the -1st order diffracted light of the second beam F1 is filtered out by the fourth linear polarizer 111, and the -1st order diffracted light of the first beam F1 passes through the fourth linear polarizer 111 and then enters the first corner cube prism 113; Theoretically, because the +1st order diffracted light of the first beam F1 and the +1st order diffracted light of the second beam F2 have a slight angular deviation and orthogonal polarization states after being diffracted once by the grating 400, when these two beams are incident on the fifth linear polarizer 112, the +1st order diffracted light of the first beam F1 is filtered out by the fifth linear polarizer 112, while the +1st order diffracted light of the second beam F2 passes through the fifth linear polarizer 112 and then enters the second corner cube prism 114. By setting the fourth linear polarizer 111 and the fifth linear polarizer 112, crosstalk caused by multiple diffractions can be avoided.

[0056] The diffraction backscattering unit further includes a first wedge plate 115 and a second wedge plate 116. The -1st order diffracted light of the first beam F1 reflected by the first corner prism 113 is incident on the grating 400 after passing through the first wedge plate 115. The +1st order diffracted light of the second beam F2 reflected by the second corner prism 114 is incident on the grating 400 after passing through the second wedge plate 116. Since there is a small angular offset between the first beam F1 and the second beam F2, the first wedge plate 115 and the second wedge plate 116 are respectively set at the exit ends of the first corner prism 113 and the second corner prism 114. The angle between the first beam F1 and the second beam F2 is calibrated by the first wedge plate 115 and the second wedge plate 116, so that the -1st order diffracted light of the first beam F1 and the +1st order diffracted light of the second beam F2 propagate in the same direction after being diffracted twice by the grating 400.

[0057] Therefore, after secondary diffraction, the first beam F1 and the second beam F2 in the measurement light respectively carry the displacement information of the grating 400. Since the -1st order diffraction of the first beam F1 produces a negative phase change with the displacement, and the +1st order diffraction of the second beam F2 produces a positive phase change with the displacement, the displacement information carried has opposite phase changes.

[0058] In addition, the diffraction backscattering unit also includes a sixth linear polarizer 108 and a second coupling lens 104. The measurement light is transmitted to the second detector 304 after passing through the sixth linear polarizer 108 and the second coupling lens 104 in sequence. After secondary diffraction, since the first beam F1 and the second beam F2 in the measurement light have orthogonal polarization states, the sixth linear polarizer 108 is used to polarize and combine the first beam F1 and the second beam F2 in the measurement light. This results in the measurement light containing two polarization states (i.e., the polarization direction of the first beam F1 parallel to the incident plane and the polarization direction of the second beam F2 perpendicular to the incident plane). The second coupling lens 104 then couples the measurement light before transmitting it to the second detector 304.

[0059] It should be noted that the first linear polarizer 105, the second linear polarizer 106, the fourth linear polarizer 111 and the fifth linear polarizer 112 are placed in a direction parallel to the optical axis, and the third linear polarizer 107 and the sixth linear polarizer 108 are placed in a direction with an angle of 45° to the optical axis.

[0060] Furthermore, the signal receiving unit and the grating ruler reading head 100 are connected via multimode optical fiber. Figure 1 As can be seen, the reference light emitted through the first coupling lens 103 is transmitted to the first detector 303 through the first multimode fiber 301, and the measurement light emitted through the second coupling lens 104 is transmitted to the second detector 304 through the second multimode fiber 302.

[0061] The displacement information carried by the measurement light detected by the second detector 304 is demodulated based on the signal of the reference light detected by the first detector 303 to obtain the horizontal displacement information of the grating 400. A differential measurement method can be used, since the displacement information carried by the first beam F1 and the second beam F2 in the measurement light detected by the second detector 304 have opposite phase changes. Therefore, the horizontal displacement information of the grating 400 can be obtained by subtracting the two.

[0062] Preferably, the ratio of transmittance to reflectance of the unpolarized beam splitter 110 for the first beam F1 is less than 1 (e.g., 1 / 9), and the ratio of transmittance to reflectance of the unpolarized beam splitter 110 for the second beam F2 is greater than 1 (e.g., 9). Figure 1 As shown, after the first beam F1 is incident on the unpolarized beam splitter 110, a portion of the first beam F1 is transmitted through the unpolarized beam splitter 110 and reflected back to the Wollaston prism 109, while another portion of the first beam F1 is reflected by the unpolarized beam splitter 110 and exits to the grating 400; after the second beam F2 is incident on the unpolarized beam splitter 110, a portion of the second beam F2 is reflected by the unpolarized beam splitter 110 and reflected back to the Wollaston prism 109, while another portion of the second beam F2 is transmitted through the unpolarized beam splitter 110 and exits to the grating 400.

[0063] Since the light emitted onto the grating 400 experiences significant energy reduction after two diffractions, by selecting a non-polarizing beam splitter 110 with a transmittance-to-reflectance ratio less than 1, the energy of the light emitted from the first beam F1 after reflection by the non-polarizing beam splitter 110 and then emitted onto the grating 400 can be greater than the energy of the light emitted from the first beam F1 after transmission through the non-polarizing beam splitter 110 and then reflected back to the Wollaston prism 109. Furthermore, by selecting a non-polarizing beam splitter 110 with a transmittance-to-reflectance ratio greater than 1, it is possible to... The light energy of the second beam F2, after being transmitted through the unpolarized beam splitter 110 and exiting to the grating 400, is greater than the light energy of the second beam F2, after being reflected by the unpolarized beam splitter 110 and reflected back to the Wollaston prism 109. This results in the light energy exiting from the unpolarized beam splitter 110 and exiting to the grating 400 being greater than the light energy reflected back from the unpolarized beam splitter 110 and exiting to the Wollaston prism 109. Consequently, the signal intensity of the reference light detected by the first detector 303 is equal to or nearly equal to the signal intensity of the measurement light detected by the second detector 304.

[0064] In addition, such as Figure 1 and Figure 5As shown, although there are still a small amount of stray light in the first beam F1 and the second beam F2 emitted from the first linear polarizer 105 and the second linear polarizer 106 respectively, after passing through the Wollaston prism 109, the stray light (i.e., the light shown by the dashed line) in the first beam F1 emitted to the grating 400 is orthogonally polarized with a separation angle of 2φ, and the stray light (i.e., the light shown by the dashed line) in the second beam F2 emitted to the grating 400 is also orthogonally polarized with a separation angle of 2φ. Therefore, after two diffractions by the grating 400, the stray light in the first beam F1 and the stray light in the second beam F2 cannot be incident on the sixth linear polarizer 108, and only the non-stray light can be incident on the sixth linear polarizer 108, thereby preventing the stray light from being detected by the second detector 304 and eliminating the interference of stray light.

[0065] Furthermore, from Figure 1 and Figure 5 As can be seen, the structures of the fourth linear polarizer 111, the first corner bevel prism 113, and the first wedge plate 115 are symmetrical with those of the fifth linear polarizer 112, the second corner bevel prism 114, and the second wedge plate 116, making the temperature and pressure fluctuations the same and the phase of the disturbance the same. Therefore, when the horizontal displacement information of the grating 400 is obtained by subtracting using the differential method, the phase of the disturbance is eliminated by subtraction, thereby reducing the temperature and pressure fluctuations and some assembly and adjustment errors, and thus improving the system's anti-interference ability against temperature and pressure changes.

[0066] Furthermore, the grating ruler reading head 100 is located within a sealed cavity (not shown) to avoid contaminating the optical path and reduce temperature and pressure fluctuations. And, as... Figure 1 As shown, the side of the sealed cavity near the grating 400 is a transparent protective window 117, so that the light beam can pass through the protective window 117.

[0067] In summary, the grating displacement measuring device provided by the present invention includes: a beam emitting unit for generating a first beam and a second beam with different frequencies; a grating ruler reading head including a beam shaping unit, the beam shaping unit including a Wollaston prism and a non-polarizing beam splitter; a grating; and a signal receiving unit including a first detector and a second detector; wherein, the first beam and the second beam are incident on the non-polarizing beam splitter through the Wollaston prism, and the first beam after passing through the Wollaston prism is orthogonally polarized to the second beam and has a separation angle; a portion of the first beam and the second beam incident on the non-polarizing beam splitter are deflected by the non-polarizing beam splitter and reflected back to the Wollaston prism, and after being combined by the Wollaston prism, they are formed into a reference beam and transmitted to the first detector; another portion of the first beam and the second beam incident on the non-polarizing beam splitter continues to be incident on the grating, and after being diffracted by the grating, they are formed into a measurement beam and transmitted to the second detector, so as to calculate the horizontal displacement of the grating based on the detected reference beam and the measurement beam. In the grating displacement measurement device of the present invention, the reference light after separation based on the non-polarizing beam splitter prism and beam combining based on the Wollaston prism contains two polarization states, which can reduce the interference of stray signals, thereby improving the measurement repeatability and ensuring the accuracy of grating displacement measurement; and, by using the Wollaston prism and the non-polarizing beam splitter prism, the separation and beam combining of the optical path can be realized, simplifying the structure and making it compatible with small space installation requirements.

[0068] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the protection scope of the claims.

Claims

1. A grating displacement measurement apparatus, characterized by, include: A beam emitting unit is used to generate a first beam and a second beam with different frequencies; A grating ruler reading head includes a beam shaping unit, which includes a Wollaston prism and a non-polarizing beam splitter. grating; The signal receiving unit includes a first detector and a second detector; In this process, the first beam and the second beam are incident on the unpolarized beam splitter through the Wollaston prism. After passing through the Wollaston prism, the first beam and the second beam are polarized orthogonally and have a separation angle. A portion of the first beam and a portion of the second beam incident on the unpolarized beam splitter are deflected by the unpolarized beam splitter and reflected back to the Wollaston prism. After being combined by the Wollaston prism, they form a reference beam that is transmitted to the first detector. Another portion of the first beam and another portion of the second beam incident on the unpolarized beam splitter continue to be incident on the grating. After being diffracted by the grating, they form a measurement beam that is transmitted to the second detector, so as to calculate the horizontal displacement of the grating based on the detected reference beam and the measurement beam.

2. The grating displacement measurement device of claim 1, wherein, The beam shaping unit further includes a first linear polarizer and a second linear polarizer. The first beam is incident on the Wollaston prism through the first linear polarizer, and the second beam is incident on the Wollaston prism through the second linear polarizer, so as to eliminate stray light in the first beam and the second beam.

3. The grating displacement measuring device as described in claim 2, characterized in that, The beam shaping unit further includes a first collimating lens and a second collimating lens. The first beam is collimated by the first collimating lens and then incident on the first linear polarizer. The second beam is collimated by the second collimating lens and then incident on the second linear polarizer. The collimated first beam and the second beam are parallel.

4. The grating displacement measuring device as described in claim 1, characterized in that, The beam shaping unit further includes a third linear polarizer and a first coupling lens. The reference light is transmitted to the first detector after passing through the third linear polarizer and the first coupling lens in sequence.

5. The grating displacement measuring device as described in claim 1, characterized in that, The grating ruler reading head further includes a diffraction backlighting unit, which includes a first corner bevel prism and a second corner bevel prism. After the other part of the first beam and the other part of the second beam continue to be incident on the grating, the -1st order diffracted light of the first beam after the first diffraction by the grating is incident on the first corner bevel prism and reflected back to the grating. The +1st order diffracted light of the second beam after the first diffraction by the grating is incident on the second corner bevel prism and reflected back to the grating. The -1st order diffracted light and the +1st order diffracted light are then diffracted a second time by the grating and transmitted to the second detector.

6. The grating displacement measuring device as described in claim 5, characterized in that, The diffraction backscattering unit further includes a fourth linear polarizer and a fifth linear polarizer. The -1st order diffracted light of the first beam and the -1st order diffracted light of the second beam after one diffraction by the grating are incident on the fourth linear polarizer to filter out the -1st order diffracted light of the second beam and obtain the -1st order diffracted light of the first beam. The +1st order diffracted light of the first beam and the +1st order diffracted light of the second beam after one diffraction by the grating are incident on the fifth linear polarizer to filter out the +1st order diffracted light of the first beam and obtain the +1st order diffracted light of the second beam.

7. The grating displacement measuring device as described in claim 5, characterized in that, The diffraction backscattering unit further includes a first wedge plate and a second wedge plate. The -1st order diffracted light of the first beam reflected by the first corner prism is incident on the grating after passing through the first wedge plate, and the +1st order diffracted light of the second beam reflected by the second corner prism is incident on the grating after passing through the second wedge plate, so that the -1st order diffracted light of the first beam and the +1st order diffracted light of the second beam propagate in the same direction after being diffracted twice by the grating.

8. The grating displacement measuring device as described in claim 5, characterized in that, The diffraction back-emission unit also includes a sixth linear polarizer and a second coupling lens. The measurement light is transmitted to the second detector after passing through the sixth linear polarizer and the second coupling lens in sequence.

9. The grating displacement measuring device as described in claim 1, characterized in that, The beam emitting unit and the grating ruler reading head are connected by a polarization-maintaining optical fiber.

10. The grating displacement measuring device as described in claim 1, characterized in that, The signal receiving unit is connected to the grating ruler reading head via a multimode optical fiber.

11. The grating displacement measuring device as described in claim 1, characterized in that, The ratio of the transmittance to the reflectance of the unpolarized beam splitter for the first beam is less than 1, and the ratio of the transmittance to the reflectance of the unpolarized beam splitter for the second beam is greater than 1.

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