An equal-path interferometer based on metal wire grid polarization modulation

Abstract

An equal-path interferometer based on metal wire grating polarization modulation belongs to the field of optical measurement technology. It aims to solve the problem of thermal drift error in zero-difference laser interferometry. The invention includes a single-frequency light source, a first prism, a second prism, a third prism, a first quarter-wave plate, a second quarter-wave plate, a third quarter-wave plate, a fourth quarter-wave plate, a first reflecting mirror, a second reflecting mirror, a reference reflecting mirror, a measurement target mirror, a cornerstone prism, and an interference signal calculation module. The metal wire grating beam-splitting surfaces of the first and second prisms are bonded to the front and rear sides of the third prism using adhesive bonding. The first prism is located at the output end of the single-frequency light source. The light beam is perpendicularly incident on the metal wire grating beam-splitting surface of the first prism, and after passing through the metal wire grating beam-splitting surface, it is split into a reflected reference beam and a transmitted measurement beam. This invention is sensitive to the deflection angle of the beam reflected by the target mirror and can be used to measure angular deflection.

Description

Technical Field

[0001] This invention belongs to the field of optical measurement technology, specifically relating to an equal optical path interferometer based on metal wire grating polarization modulation. Background Technology

[0002] Precise displacement measurement is directly related to the stability and reliability of precision machining processes. However, the contradiction between high precision and large detection range of measuring instruments has always been a challenge in precision displacement measurement. Laser interferometers are widely used in precision measurement due to their advantages of both high precision and large detection range. However, due to the high sensitivity of laser interferometers, they are easily affected by environmental vibration and thermal disturbances in actual measurement conditions. For example, in nanoscale positioning of electron beam lithography in a vacuum chamber, there are vibration disturbances from vacuum pumps and cooling systems, as well as thermal disturbances from internal motor heat sources.

[0003] Currently, the common solution is to use differential measurements to reduce environmental disturbances such as vibration and refractive index. However, in processing conditions, unavoidable thermal disturbances often occur. The thermal drift coefficient of commercial laser interferometers is typically between tens of nm and one hundred nm, and the measurement error caused by thermal drift cannot be ignored. For example, Agilent (now Keysight) analyzed and provided thermal drift test results for multiple interferometer groups (Agilent Laser and Optics User's Manual). The average thermal drift coefficient of differential laser interferometer groups such as the 10715A reached 150 nm / ℃, and even after compensation, it was still 50 nm / ℃. In addition, the temperature drift coefficient of the Renishaw RLD10-DI differential probe, which is commonly used in the industrial field, also reaches 50 nm / ℃, and its thermal drift error is between several nm and tens of nm.

[0004] To address the thermal drift problem of laser interferometers mentioned above, scholars often employ central differential interference structures to construct equal optical paths and suppress thermal drift errors. For example, in 1995, Shigeru Hosoe designed a compact symmetrical structure with two optical paths by calculating the optical paths of the measurement and reference beams, and used materials with negative refractive index temperature coefficients for thermal drift compensation (Hosoe S. Highly precise and stable displacement-measuring laser interferometer with differential optical paths[J]. Precision engineering, 1995, 17(4): 258-265.), thus designing a low-temperature drift central differential interference structure. However, this structure has the problem of high requirements for the initial installation position, which is not conducive to debugging. However, since common polarization beam splitting uses Brewster's law for beam splitting, the polarization modulation scheme is limited, and there is currently no better scheme to achieve differential measurement. Harbin Institute of Technology proposed using Koster prisms to adjust the optical path of polarized light to construct a central differential interference structure with balanced optical path. However, due to the small adjustment margin of the optical path of the Koster prisms, it also has the problem of being unfavorable to debugging. When laser interferometers are used for feedback in the manufacturing process, differential structures are required to avoid environmental interference such as vibration. However, the central differential optical path, due to its strict requirement for central symmetry, places high demands on the equipment under test, making it difficult to integrate into high-end equipment. On the other hand, general differential structures have advantages in high-end equipment integration due to their simpler optical path arrangement, but they generally suffer from large thermal drift errors caused by significant differences between the measurement and reference optical path structures. Summary of the Invention

[0005] The problem to be solved by this invention is to suppress the thermal drift error in zero-difference laser interferometry, and to propose an equal optical path interferometer based on metal wire grid polarization modulation.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] An equal optical path interferometer based on metal wire grid polarization modulation includes a single-frequency light source, a first prism, a second prism, a third prism, a first quarter-wave plate, a second quarter-wave plate, a third quarter-wave plate, a fourth quarter-wave plate, a first reflecting mirror, a second reflecting mirror, a reference reflecting mirror, a measurement target mirror, a corner cube prism, and an interference signal calculation module.

[0008] The metal wire grid beam-splitting surface of the first prism, the metal wire grid beam-splitting surface of the second prism, and the front and rear sides of the third prism are bonded together by adhesive.

[0009] The first prism is located at the output end of the single-frequency light source. The beam is incident perpendicularly on the metal wire grid beam splitting surface of the first prism. After passing through the metal wire grid beam splitting surface of the first prism, it is split into a reflected reference beam and a transmitted measurement beam.

[0010] A first quarter-wave plate is attached to the direction of reflected light on the metal wire grid beam-splitting surface of the first prism. The fast axis of the first quarter-wave plate makes an angle of 45° with the y-axis. A reference mirror is placed at a position parallel to the first quarter-wave plate, so that the reference beam is incident perpendicularly on the reference mirror.

[0011] A second quarter-wave plate and a first reflecting mirror are attached to the third prism in the opposite direction to the reflected light from the metal wire grid beam-splitting surface of the first prism, wherein the fast axis of the second quarter-wave plate forms a 45° angle with the y-axis.

[0012] The metal wire grid beam-splitting surface of the second prism forms a 45° angle with the measurement beam and is parallel to the metal wire grid beam-splitting surface of the first prism. A corner pyramid prism is attached parallel to the upper surface of the second prism along the transmission direction of the measurement beam through the metal wire grid beam-splitting surface of the second prism. The beam reflected by the corner pyramid prism is perpendicular to the upper surface of the second prism.

[0013] A third quarter-wave plate is attached to the third prism along the reflection direction of the metal wire grid beam splitting surface of the second prism. The fast axis of the third quarter-wave plate forms a 45° angle with the y-axis. The measurement target mirror is placed at a position parallel to the third quarter-wave plate, so that the measurement beam is perpendicularly incident on the measurement target mirror.

[0014] A fourth quarter-wave plate and a second reflecting mirror are attached sequentially to the side of the second prism in the opposite direction to the reflected light from the metal wire grid beam splitting surface of the second prism. The fast axis of the fourth quarter-wave plate forms a 45° angle with the y-axis. An interference signal calculation module is placed in the direction of the output of the composite beam formed by the interference of the reference beam and the measurement beam.

[0015] Furthermore, the direction of the metal wire grid on the beam-splitting surface of the first prism and the direction of the metal wire grid on the beam-splitting surface of the second prism are perpendicular to each other.

[0016] Furthermore, the metal wire grid in the first prism and the second prism is aluminum.

[0017] Furthermore, the single-frequency light source emits linearly polarized or circularly polarized light with frequency ν, which is incident on the metal wire grid beam-splitting surface of the first prism. The reflected light is the reference beam, which is horizontally polarized, and the transmitted light is the measurement beam, which is vertically polarized.

[0018] Furthermore, the optical path process of the reference beam in the aforementioned equal optical path interferometer based on metal wire grating polarization modulation is as follows:

[0019] The reference beam passes through the first quarter-wave plate, then through the reference mirror, and then through the first quarter-wave plate again to form the first vertically polarized reference beam;

[0020] The first vertically polarized reference light is transmitted through the metal wire grid beam-splitting surface of the first prism, passes through the second quarter-wave plate, then passes through the first mirror, and then passes through the second quarter-wave plate again to form the second horizontally polarized reference light.

[0021] The second horizontally polarized reference light is reflected by the metal wire grid beam-splitting surface of the first prism, passes through the third prism, then is transmitted through the metal wire grid beam-splitting surface of the second prism, is reflected by the pyramidal prism, then is transmitted through the metal wire grid beam-splitting surface of the second prism, then passes through the third prism, is reflected by the metal wire grid beam-splitting surface of the first prism, passes through the second quarter-wave plate, is reflected by the first mirror, and then passes through the second quarter-wave plate again to form the second vertically polarized reference light.

[0022] The second vertically polarized reference light is transmitted through the metal wire grid beam-splitting surface of the first prism, passes through the first quarter-wave plate, is reflected by the reference mirror, and passes through the first quarter-wave plate again to form the third horizontally polarized reference light.

[0023] The third horizontally polarized reference light is reflected by the metal wire grid beam-splitting surface of the first prism, completing the optical path process of the reference beam in the equal optical path interferometer based on metal wire grid polarization modulation.

[0024] Furthermore, based on the fact that the angle between the beam-splitting surfaces of the first prism and the metal wire grid is 45°, the distance from the incident light to the beam-splitting surface of the first prism and the distance from the beam-splitting surface of the first prism and the second quarter-wave plate are also denoted as L. M1 Since the angle between the beam-splitting surfaces of the second prism metal wire grid is 45°, the distance from the beam-splitting surface of the second prism metal wire grid to the interface of the corner cube prism, and the distance from the beam-splitting surface of the second prism metal wire grid to the interface of the fourth quarter-wave plate are denoted as L. M2 The expression for the optical path length experienced by the reference beam in the aforementioned equal-path interferometer based on metal wire grating polarization modulation is as follows:

[0025]

[0026] Among them, L M1 L is the distance from the incident light to the reflection from the first prism metal wire grid beam-splitting surface to the interface of the first quarter-wave plate. C1 L is the distance from the incident point to the first quarter-wave plate and from the point of exit from the first quarter-wave plate. C2L is the distance from the incident point to the second quarter-wave plate and from the point of exit from the second quarter-wave plate. M1M2 L is the distance from the beam-splitting surface of the first prism metal wire grid to the beam-splitting surface of the second prism metal wire grid. M2 L is the distance from the incident point to the beam-splitting surface of the second prism metal wire grid to the interface of the third quarter-wave plate. Q It is the distance from the incident light on the cornerstone prism to the reflection light from the cornerstone prism.

[0027] Furthermore, the optical path process of the measurement beam in the aforementioned equal optical path interferometer based on metal wire grating polarization modulation is as follows:

[0028] The measurement beam passes through the third prism, is reflected by the metal wire grid beam splitter of the second prism, passes through the third quarter-wave plate, is reflected by the measurement target mirror, and passes through the third quarter-wave plate again to form the first horizontally polarized measurement beam.

[0029] The first horizontally polarized measurement light is transmitted through the metal wire grid beam-splitting surface of the second prism, passes through the fourth quarter-wave plate, is reflected by the second mirror, and passes through the fourth quarter-wave plate again to form the second vertically polarized measurement light.

[0030] The second vertically polarized measurement light is reflected by the metal wire grid beam-splitting surface of the second prism, reflected by the cornerstone prism, reflected by the metal wire grid beam-splitting surface of the second prism, reflected by the fourth quarter-wave plate, reflected by the second mirror, and then reflected by the fourth quarter-wave plate again to become the second horizontally polarized measurement light.

[0031] The second horizontally polarized measurement light is transmitted through the metal wire grid beam-splitting surface of the second prism, passes through the third quarter-wave plate, is reflected by the measurement target mirror, and passes through the third quarter-wave plate again to form the third vertically polarized measurement light.

[0032] The third vertically polarized measurement light is reflected by the metal wire grid beam-splitting surface of the second prism, passes through the third prism, and is transmitted through the metal wire grid beam-splitting surface of the first prism, thus completing the optical path process of the measurement beam in the equal optical path interferometer based on metal wire grid polarization modulation.

[0033] Furthermore, the expression for the optical path length experienced by the measurement beam in the aforementioned equal-path interferometer based on metal wire grating polarization modulation is as follows:

[0034]

[0035] Among them, L C3 L is the distance from the incident point to the exit point of the third quarter-wave plate. C4 The distance from the incident point to the exit point of the fourth quarter-wave plate;

[0036] Based on the aforementioned equal optical path interferometer based on metal wire grating polarization modulation, which is symmetrically designed and has the same coefficient of thermal expansion, L is obtained. M1 =L M2 Based on selecting quarter-wave plates of the same size and material to ensure L C1 =L C2 =L C3 =L C4 ; to ensure that the reference beam and the measurement beam have the same optical path length within the equal-path interferometer based on metal wire grating polarization modulation, thus obtaining L M =L C .

[0037] Furthermore, the third vertically polarized measurement light interferes with the third horizontally polarized reference light to form a composite beam, and the relationship between the phase of the composite beam signal and the optical path is as follows:

[0038]

[0039] in, The phase of the interference signal is λ, where λ is the laser wavelength and L is the wavelength. M To measure the optical path length of the beam, Δx is the displacement of the measuring mirror, and L C The optical path length traversed by the reference beam;

[0040] The synthesized beam then enters the interference signal solving module to invert and obtain displacement information.

[0041] The beneficial effects of this invention are:

[0042] The present invention discloses an equal-path interferometer based on metal wire grating polarization modulation. The measurement beam and reference beam are differentially divided within the metal wire grating mirror group, ensuring that their optical path lengths within the metal wire grating mirror group and optical elements are completely equal. Furthermore, the measurement target mirror and the reference mirror are both located on the same side of the mirror group. This effectively counteracts the effects of temperature fluctuations and changes in the refractive index of the medium on the two beams, theoretically suppressing thermal drift errors and significantly improving thermal stability compared to traditional zero-difference interferometers. The first and second prism metal wire grating beam-splitting surfaces are obtained by fabricating metal wire gratings, resulting in higher parallelism between the polarization beam-splitting planes.

[0043] The present invention discloses an equal optical path interferometer based on metal wire grid polarization modulation, which is sensitive to the deflection angle of the beam reflected from the target mirror and can be used to measure angular deflection. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the structure of an equal optical path interferometer based on metal wire grid polarization modulation according to the present invention;

[0045] Figure 2This is a perspective view of an equal optical path interferometer based on metal wire grid polarization modulation as described in this invention.

[0046] Figure 3 This is a two-dimensional optical path diagram of the reference beam and the measurement beam inside the mirror group of an equal optical path interferometer based on metal wire grid polarization modulation, as described in this invention, wherein (a) is the diagram corresponding to the reference beam and (b) is the diagram corresponding to the measurement beam. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described specific embodiments are merely a part of the embodiments of the invention, and not all of them. The components of the specific embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations, and the invention may also have other embodiments.

[0048] Therefore, the following detailed description of specific embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected specific embodiments of the invention. All other specific embodiments obtained by those skilled in the art based on these specific embodiments without inventive effort are within the scope of protection of this invention.

[0049] To further understand the invention's content, features, and effects, the following specific embodiments are provided, along with accompanying drawings. Figure 1 - Appendix Figure 3 Detailed explanation is as follows:

[0050] Example 1:

[0051] An equal optical path interferometer based on metal wire grid polarization modulation includes a single-frequency light source 1, a first prism 2, a second prism 3, a third prism 4, a first quarter-wave plate 5, a second quarter-wave plate 6, a third quarter-wave plate 7, a fourth quarter-wave plate 8, a first reflecting mirror 9, a second reflecting mirror 10, a reference reflecting mirror 11, a measurement target mirror 12, a corner cube prism 13, and an interference signal calculation module 14.

[0052] The metal wire grid beam-splitting surface of the first prism 2, the metal wire grid beam-splitting surface of the second prism 3, and the front and rear sides of the third prism 4 are bonded together by adhesive.

[0053] The first prism 2 is located at the output end of the single-frequency light source 1. The beam is incident perpendicularly on the metal wire grid beam splitting surface of the first prism 2. After passing through the metal wire grid beam splitting surface of the first prism 2, it is divided into a reflected reference beam and a transmitted measurement beam.

[0054] A first quarter-wave plate 5 is attached to the direction of reflected light on the metal wire grid beam-splitting surface of the first prism 2. The fast axis of the first quarter-wave plate 5 makes an angle of 45° with the y-axis. A reference mirror 11 is placed at a position parallel to the first quarter-wave plate 5, so that the reference beam is perpendicularly incident on the reference mirror 11.

[0055] Along the opposite direction of the reflected light from the metal wire grid beam-splitting surface of the first prism 2, the second quarter-wave plate 6 and the first reflecting mirror 9 are attached sequentially to the third prism 4, wherein the fast axis direction of the second quarter-wave plate 6 forms a 45° angle with the y-axis.

[0056] The metal wire grid beam-splitting surface of the second prism 3 forms a 45° angle with the measurement beam and is parallel to the metal wire grid beam-splitting surface of the first prism 2. A corner pyramid prism 13 is attached parallel to the upper surface of the second prism 3 along the transmission direction of the measurement beam through the metal wire grid beam-splitting surface of the second prism 3. The corner pyramid prism 13 reflects the beam perpendicular to the upper surface of the second prism 3.

[0057] A third quarter-wave plate 7 is attached to the third prism 4 along the reflection direction of the metal wire grid beam splitting surface of the second prism 3. The fast axis of the third quarter-wave plate 7 forms a 45° angle with the y-axis. The measurement target mirror 12 is placed at a relative position parallel to the third quarter-wave plate 7, so that the measurement beam is perpendicularly incident on the measurement target mirror 12.

[0058] In the opposite direction to the reflected light from the metal wire grid beam splitting surface of the second prism 3, a fourth quarter-wave plate 8 and a second reflector 10 are attached sequentially to the side of the second prism 3, wherein the fast axis direction of the fourth quarter-wave plate 8 forms a 45° angle with the y-axis; and an interference signal calculation module 14 is placed in the direction of the output of the composite beam formed by the interference of the reference beam and the measurement beam.

[0059] Furthermore, the direction of the metal wire grid on the metal wire grid beam-splitting surface of the first prism 2 and the direction of the metal wire grid on the metal wire grid beam-splitting surface of the second prism 3 are perpendicular to each other.

[0060] Furthermore, the metal wire grid in the metal wire grid beam-splitting surface of the first prism 2 and the metal wire grid beam-splitting surface of the second prism 3 is aluminum.

[0061] Furthermore, the single-frequency light source 1 emits linearly polarized or circularly polarized light with frequency ν, which is incident on the metal wire grid beam-splitting surface of the first prism 2. The reflected light is the reference beam, which is horizontally polarized, and the transmitted light is the measurement beam, which is vertically polarized.

[0062] Furthermore, the optical path process of the reference beam in the aforementioned equal optical path interferometer based on metal wire grating polarization modulation is as follows:

[0063] The reference beam passes through the first quarter-wave plate 5, then through the reference mirror 11, and then through the first quarter-wave plate 5 again to form the first vertically polarized reference beam;

[0064] The first vertically polarized reference light is transmitted through the metal wire grid beam splitting surface of the first prism 2, passes through the second quarter-wave plate 6, then passes through the first reflecting mirror 9, and then passes through the second quarter-wave plate 6 again to form the second horizontally polarized reference light.

[0065] The second horizontally polarized reference light is reflected by the metal wire grid beam-splitting surface of the first prism 2, passes through the third prism 4, then is transmitted through the metal wire grid beam-splitting surface of the second prism 3, reflected by the cornerstone prism 13, then transmitted through the metal wire grid beam-splitting surface of the second prism 3, then passes through the third prism 4, is reflected by the metal wire grid beam-splitting surface of the first prism 2, passes through the second quarter-wave plate 6, is reflected by the first reflecting mirror 9, and then passes through the second quarter-wave plate 6 again to form the second vertically polarized reference light.

[0066] The second vertically polarized reference light is transmitted through the metal wire grid beam splitting surface of the first prism 2, passes through the first quarter-wave plate 5, is reflected by the reference mirror 11, and passes through the first quarter-wave plate 5 again to form the third horizontally polarized reference light.

[0067] The third horizontally polarized reference light is reflected by the metal wire grid beam splitter of the first prism 2, completing the optical path process of the reference beam in the equal optical path interferometer based on metal wire grid polarization modulation.

[0068] Furthermore, based on the fact that the angle between the beam-splitting surfaces of the first prism and the metal wire grid is 45°, the distance from the incident light to the beam-splitting surface of the first prism and the distance from the beam-splitting surface of the first prism and the second quarter-wave plate are also denoted as L. M1 Since the angle between the beam-splitting surfaces of the second prism metal wire grid is 45°, the distance from the beam-splitting surface of the second prism metal wire grid to the interface of the corner cube prism, and the distance from the beam-splitting surface of the second prism metal wire grid to the interface of the fourth quarter-wave plate are denoted as L. M2 The expression for the optical path length experienced by the reference beam in the aforementioned equal-path interferometer based on metal wire grating polarization modulation is as follows:

[0069]

[0070] Among them, L M1 L is the distance from the incident light to the reflection from the first prism metal wire grid beam-splitting surface to the interface of the first quarter-wave plate. C1 L is the distance from the incident point to the first quarter-wave plate and from the point of exit from the first quarter-wave plate. C2 L is the distance from the incident point to the second quarter-wave plate and from the point of exit from the second quarter-wave plate.M1M2 L is the distance from the beam-splitting surface of the first prism metal wire grid to the beam-splitting surface of the second prism metal wire grid. M2 L is the distance from the incident point to the beam-splitting surface of the second prism metal wire grid to the interface of the third quarter-wave plate. Q It is the distance from the incident light on the cornerstone prism to the reflection light from the cornerstone prism.

[0071] Furthermore, the optical path process of the measurement beam in the aforementioned equal optical path interferometer based on metal wire grating polarization modulation is as follows:

[0072] The measurement beam passes through the third prism 4, is reflected by the metal wire grid beam splitter of the second prism 3, passes through the third quarter-wave plate 7, is reflected by the measurement target mirror 12, and passes through the third quarter-wave plate 7 again to form the first horizontally polarized measurement beam.

[0073] The first horizontally polarized measurement light is transmitted through the metal wire grid beam splitter of the second prism 3, passes through the fourth quarter-wave plate 8, is reflected by the second mirror 10, and passes through the fourth quarter-wave plate 8 again to form the second vertically polarized measurement light.

[0074] The second vertically polarized measurement light is reflected by the metal wire grid beam-splitting surface of the second prism 3, reflected by the cornerstone prism 13, reflected by the metal wire grid beam-splitting surface of the second prism 3, reflected by the fourth quarter-wave plate 8, reflected by the second mirror 10, and then reflected again by the fourth quarter-wave plate 8 to form the second horizontally polarized measurement light.

[0075] The second horizontally polarized measurement light is transmitted through the metal wire grid beam splitter of the second prism 3, passes through the third quarter-wave plate 7, is reflected by the measurement target mirror 12, and passes through the third quarter-wave plate 7 again to form the third vertically polarized measurement light.

[0076] The third vertically polarized measurement light is reflected by the metal wire grid beam-splitting surface of the second prism 3, passes through the third prism 4, and is transmitted through the metal wire grid beam-splitting surface of the first prism 2, thus completing the optical path process of the measurement beam in the equal optical path interferometer based on metal wire grid polarization modulation.

[0077] Furthermore, the expression for the optical path length experienced by the measurement beam in the aforementioned equal-path interferometer based on metal wire grating polarization modulation is as follows:

[0078]

[0079] Among them, L C3 L is the distance from the incident point to the exit point of the third quarter-wave plate. C4 The distance from the incident point to the exit point of the fourth quarter-wave plate;

[0080] Based on the aforementioned equal optical path interferometer based on metal wire grating polarization modulation, which is symmetrically designed and has the same coefficient of thermal expansion, L is obtained. M1 =L M2 Based on selecting quarter-wave plates of the same size and material to ensure L C1 =L C2 =L C3 =L C4 ; to ensure that the reference beam and the measurement beam have the same optical path length within the equal-path interferometer based on metal wire grating polarization modulation, thus obtaining L M =L C .

[0081] Furthermore, the third vertically polarized measurement light interferes with the third horizontally polarized reference light to form a composite beam, and the relationship between the phase of the composite beam signal and the optical path is as follows:

[0082]

[0083] in, The phase of the interference signal is λ, where λ is the laser wavelength and L is the wavelength. M To measure the optical path length of the beam, Δx is the displacement of the measuring mirror, and L C The optical path length traversed by the reference beam;

[0084] The synthesized beam then enters the interference signal solving module to invert and obtain displacement information.

[0085] Furthermore, the third prism 4 is parallelogram in shape; the metal wire grid beam-splitting surface of the first prism 2 and the metal wire grid beam-splitting surface of the second prism 3 are respectively bonded to the two sides of the third prism 4 by adhesive bonding; a first quarter-wave plate 5 is attached to the left side of the first prism 2, and a reference reflector 11 is disposed on the outer side of the first quarter-wave plate 5; a single-frequency light source 1 and an interference signal calculation module 14 are disposed on the front side of the first prism 2; a fourth quarter-wave plate 8 and a second reflector 10 are attached to the right side of the second prism 3 in sequence, and a pyramidal prism 13 is attached to the rear side of the second prism 3; a third quarter-wave plate 7 is attached to the left side of the third prism 4, and a measurement target mirror 12 is disposed on the outer side of the third quarter-wave plate 7, and the third quarter-wave plate 7 is parallel to the fourth quarter-wave plate 8; a second quarter-wave plate 6 and a first reflector 9 are attached to the right side of the third prism 4 in sequence, and the second quarter-wave plate 6 is parallel to the first quarter-wave plate 5.

[0086] Furthermore, the measurement beam and the reference beam are differentially divided within the metal wire grating mirror assembly to ensure that their optical path lengths within the metal wire grating mirror assembly and the optical element are exactly equal. When the temperature fluctuates, the change in optical path length between the reference beam and the measurement beam within the metal wire grating mirror assembly is consistent. This effectively offsets the effects of temperature fluctuations and changes in the refractive index of the medium on the two beams, and can suppress thermal drift errors.

[0087] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0088] Although this application has been described above with reference to specific embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of this application. In particular, as long as there is no structural conflict, the features in the specific embodiments disclosed in this application can be combined with each other in any way. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, this application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. An equal optical path interferometer based on metal wire grating polarization modulation, characterized in that, Includes a single-frequency light source (1), a first prism (2), a second prism (3), a third prism (4), a first quarter-wave plate (5), a second quarter-wave plate (6), a third quarter-wave plate (7), a fourth quarter-wave plate (8), a first reflecting mirror (9), a second reflecting mirror (10), a reference reflecting mirror (11), a measuring target mirror (12), a corner cube prism (13), and an interference signal calculation module (14); The metal wire grid beam-splitting surface of the first prism (2), the metal wire grid beam-splitting surface of the second prism (3), and the front and rear sides of the third prism (4) are bonded together by adhesive. The first prism (2) is located at the output end of the single-frequency light source (1). The beam is incident perpendicularly on the metal wire grid beam splitting surface of the first prism (2). After passing through the metal wire grid beam splitting surface of the first prism (2), it is divided into a reflected reference beam and a transmitted measurement beam. A first quarter-wave plate (5) is attached to the direction of reflected light on the metal wire grid beam splitting surface of the first prism (2). The fast axis of the first quarter-wave plate (5) makes an angle of 45° with the y-axis. A reference mirror (11) is placed at a position parallel to the first quarter-wave plate (5) so that the reference beam is perpendicularly incident on the reference mirror (11). Along the opposite direction of the reflected light from the metal wire grid beam-splitting surface of the first prism (2), the second quarter-wave plate (6) and the first reflecting mirror (9) are attached to the third prism (4) in sequence, wherein the fast axis direction of the second quarter-wave plate (6) forms a 45° angle with the y-axis. The metal wire grid beam-splitting surface of the second prism (3) forms a 45° angle with the measurement beam and the metal wire grid beam-splitting surface of the second prism (3) is parallel to the metal wire grid beam-splitting surface of the first prism (2). A corner pyramid prism (13) is attached parallel to the upper surface of the second prism (3) along the transmission direction of the measurement beam through the metal wire grid beam-splitting surface of the second prism (3). The beam reflected by the corner pyramid prism (13) is perpendicular to the upper surface of the second prism (3). A third quarter-wave plate (7) is attached to the third prism (4) along the reflection direction of the metal wire grid beam splitting surface of the second prism (3). The fast axis of the third quarter-wave plate (7) forms a 45° angle with the y-axis. The measurement target mirror (12) is placed at a position parallel to the third quarter-wave plate (7) so that the measurement beam is perpendicularly incident on the measurement target mirror (12). In the opposite direction of the reflected light from the metal wire grid beam splitting surface of the second prism (3), a fourth quarter-wave plate (8) and a second reflector (10) are attached to the side of the second prism (3) in sequence. The fast axis direction of the fourth quarter-wave plate (8) forms a 45° angle with the y-axis. An interference signal calculation module (14) is placed in the direction of the output of the composite beam formed by the interference of the reference beam and the measurement beam.

2. The equal optical path interferometer based on metal wire grating polarization modulation according to claim 1, characterized in that, The direction of the metal wire grid on the metal wire grid beam-splitting surface of the first prism (2) and the direction of the metal wire grid on the metal wire grid beam-splitting surface of the second prism (3) are perpendicular to each other.

3. The equal optical path interferometer based on metal wire grating polarization modulation according to claim 2, characterized in that, The metal wire grid in the first prism (2) and the second prism (3) is made of aluminum.

4. The equal optical path interferometer based on metal wire grating polarization modulation according to claim 3, characterized in that, The single-frequency light source (1) emits linearly polarized or circularly polarized light with frequency ν, which is incident on the metal wire grid beam splitting surface of the first prism (2). The reflected light is the reference beam, which is horizontally polarized, and the transmitted light is the measurement beam, which is vertically polarized.

5. The equal optical path interferometer based on metal wire grating polarization modulation according to claim 4, characterized in that, The optical path process of the reference beam in the aforementioned equal-path interferometer based on metal wire grating polarization modulation is as follows: The reference beam passes through the first quarter-wave plate (5), then through the reference mirror (11), and then through the first quarter-wave plate (5) again to form the first vertically polarized reference beam; The first vertically polarized reference light is transmitted through the metal wire grid beam splitting surface of the first prism (2), passes through the second quarter-wave plate (6), then passes through the first reflector (9), and passes through the second quarter-wave plate (6) again to form the second horizontally polarized reference light; The second horizontally polarized reference light is reflected by the metal wire grid beam-splitting surface of the first prism (2), passes through the third prism (4), then is transmitted through the metal wire grid beam-splitting surface of the second prism (3), is reflected by the pyramidal prism (13), then is transmitted through the metal wire grid beam-splitting surface of the second prism (3), then passes through the third prism (4), is reflected by the metal wire grid beam-splitting surface of the first prism (2), passes through the second quarter-wave plate (6), is reflected by the first reflecting mirror (9), and passes through the second quarter-wave plate (6) again to form the second vertically polarized reference light; The second vertically polarized reference light is transmitted through the metal wire grid beam splitting surface of the first prism (2), passes through the first quarter-wave plate (5), is reflected by the reference mirror (11), and passes through the first quarter-wave plate (5) again to form the third horizontally polarized reference light; The third horizontally polarized reference light is reflected by the metal wire grid beam splitting surface of the first prism (2), completing the optical path process of the reference beam in the equal optical path interferometer based on metal wire grid polarization modulation.

6. The equal optical path interferometer based on metal wire grating polarization modulation according to claim 5, characterized in that, Since the angle between the beam-splitting surfaces of the first prism and the metal wire grating is 45°, the distance from the incident light to the beam-splitting surface of the first prism and the distance from the beam-splitting surface of the first prism and the second quarter-wave plate are also denoted as L. M1 Since the angle between the beam-splitting surfaces of the second prism metal wire grid is 45°, the distance from the beam-splitting surface of the second prism metal wire grid to the interface of the corner cube prism, and the distance from the beam-splitting surface of the second prism metal wire grid to the interface of the fourth quarter-wave plate are denoted as L. M2 The expression for the optical path length experienced by the reference beam in the aforementioned equal-path interferometer based on metal wire grating polarization modulation is as follows: ； Among them, L M1 L is the distance from the incident light to the reflection from the first prism metal wire grid beam-splitting surface to the interface of the first quarter-wave plate. C1 L is the distance from the incident point to the first quarter-wave plate and from the point of exit from the first quarter-wave plate. C2 L is the distance from the incident point to the second quarter-wave plate and from the point of exit from the second quarter-wave plate. M1M2 L is the distance from the beam-splitting surface of the first prism metal wire grid to the beam-splitting surface of the second prism metal wire grid. M2 L is the distance from the incident point to the beam-splitting surface of the second prism metal wire grid to the interface of the third quarter-wave plate. Q It is the distance from the incident light on the cornerstone prism to the reflection light from the cornerstone prism.

7. The equal optical path interferometer based on metal wire grating polarization modulation according to claim 6, characterized in that, The optical path process of the measurement beam in the aforementioned equal-path interferometer based on metal wire grating polarization modulation is as follows: The measurement beam passes through the third prism (4), is reflected by the metal wire grid beam splitter of the second prism (3), passes through the third quarter-wave plate (7), is reflected by the measurement target mirror (12), and passes through the third quarter-wave plate (7) again to form the first horizontally polarized measurement beam; The first horizontally polarized measurement light is transmitted through the metal wire grid beam splitting surface of the second prism (3), passes through the fourth quarter-wave plate (8), is reflected by the second mirror (10), and passes through the fourth quarter-wave plate (8) again to form the second vertically polarized measurement light; The second vertically polarized measurement light is reflected by the metal wire grid beam splitting surface of the second prism (3), reflected by the corner prism (13), reflected by the metal wire grid beam splitting surface of the second prism (3), reflected by the fourth quarter-wave plate (8), reflected by the second mirror (10), and reflected again by the fourth quarter-wave plate (8) to form the second horizontally polarized measurement light. The second horizontally polarized measurement light is transmitted through the metal wire grid beam splitting surface of the second prism (3), passes through the third quarter-wave plate (7), is reflected by the measurement target mirror (12), and passes through the third quarter-wave plate (7) again to form the third vertically polarized measurement light; The third vertically polarized measurement light is reflected by the metal wire grid beam splitter of the second prism (3), passes through the third prism (4), and is transmitted through the metal wire grid beam splitter of the first prism (2), thus completing the optical path process of the measurement beam in the equal optical path interferometer based on metal wire grid polarization modulation.

8. The equal optical path interferometer based on metal wire grating polarization modulation according to claim 7, characterized in that, The expression for the optical path length experienced by the measuring beam in the aforementioned equal-path interferometer based on metal wire grating polarization modulation is as follows: ； Among them, L C3 L is the distance from the incident point to the exit point of the third quarter-wave plate. C4 The distance from the incident point to the exit point of the fourth quarter-wave plate; Based on the aforementioned equal optical path interferometer based on metal wire grating polarization modulation, which is symmetrically designed and has the same coefficient of thermal expansion, L is obtained. M1 =L M2 Based on selecting quarter-wave plates of the same size and material to ensure L C1 =L C2 =L C3 =L C4 ; to ensure that the reference beam and the measurement beam have the same optical path length within the equal-path interferometer based on metal wire grating polarization modulation, thus obtaining L M =L C .

9. An equal optical path interferometer based on metal wire grating polarization modulation according to claim 8, characterized in that, The third vertically polarized measurement light interferes with the third horizontally polarized reference light to form a composite beam. The relationship between the phase of the composite beam signal and the optical path is as follows: ； in, The phase of the interference signal is λ, where λ is the laser wavelength and L is the wavelength. M To measure the optical path length of the beam, Δx is the displacement of the measuring mirror, and L C The optical path length traversed by the reference beam; The synthesized beam then enters the interference signal solving module to invert and obtain displacement information.

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