A compact four-beam interferometer, manufacturing method and measurement method

Abstract

The present application belongs to the technical field of object spatial attitude measurement, and specifically discloses a compact four-beam interferometer, a manufacturing method, and a measurement method. The interferometer includes: a glass base, four photodetectors located on the same detection plane, and two fiber collimators, a lateral displacement beam splitter, a depolarizing beam splitter, and a plane reflector arranged in sequence along a first direction, wherein the first direction is perpendicular to the detection plane; the two fiber collimators, the lateral displacement beam splitter, and the two depolarizing beam splitters are fixed to the plane of the glass base; the two fiber collimators are used to emit laser light along the first direction to form two laser beams; the lateral displacement beam splitter is used to split the two laser beams into four laser beams; the detection plane is perpendicular to the plane of the glass base, and the two depolarizing beam splitters are located on the detection plane. Through the present application, multiple degrees of freedom of an object can be stably and accurately measured using laser interferometry.

Description

Technical Field

[0001] The present application belongs to the technical field of object spatial attitude measurement, and more specifically, relates to a compact four-beam interferometer, a manufacturing method, and a measurement method. Background Art

[0002] An object's spatial attitude is determined by six degrees of freedom: its position is determined by three linear quantities, and its attitude is determined by three angular quantities. With the continuous advancement of modern science and technology, many fields, such as aerospace, machining, and assembly, have placed urgent demands on the simultaneous acquisition of spatial attitude parameters across multiple degrees of freedom. Laser interferometry is one of the most effective methods for achieving high-precision length measurement over a large area. High-precision laser interferometers are also a crucial tool for ultra-precision measurement in cutting-edge scientific research and advanced manufacturing. They are in great demand in fields such as gravitational wave detection, inertial sensing, CNC machine tools, and lithography equipment manufacturing.

[0003] The main bottlenecks hindering the improvement of laser interferometry technology and its applications are the principles of laser interferometry, the characteristics of key components such as the interferometric light source, interferometric optical elements, and interferometric signal processing cards, as well as the stability of the actual measurement environment. Stable and accurate measurement of multiple degrees of freedom of an object through laser interferometry is a pressing technical challenge in this field. Summary of the Invention

[0004] In response to the shortcomings of the prior art, the purpose of this application is to stably and accurately measure multiple degrees of freedom of an object through laser interferometry.

[0005] To achieve the above objectives, in a first aspect, the present application provides a compact four-beam interferometer, comprising: a glass base, four photodetectors located in the same detection plane, and two fiber collimators, a lateral displacement beam splitter, a depolarizing beam splitter, and a plane reflector arranged in sequence along a first direction, wherein the first direction is perpendicular to the detection plane;

[0006] Two fiber collimators, a lateral displacement beam splitter prism and two depolarizing beam splitters are fixed on the plane of the glass base;

[0007] Two optical fiber collimators are used to emit laser light in a first direction to form two laser beams (the two laser beams enter the laterally displaced beam splitter prism), and the two laser beams are located in a first plane, which is parallel to the plane of the glass base;

[0008] The lateral displacement beam splitter is used to split the two laser beams into four laser beams, two of the four laser beams are located in a first plane, and the other two (of the four laser beams) are located in a second plane, and the second plane is parallel to the plane of the glass base (the first plane and the second plane are different planes);

[0009] The detection plane is perpendicular to the plane of the glass base and the two depolarizing beam splitting prisms are located on the detection plane, two of the four photodetectors are located on one side of the glass base, and the other two (of the four photodetectors) are located on the other side of the glass base;

[0010] For two photodetectors on the same side, one is located in the first plane and the other is located in the second plane;

[0011] The laser output port of one fiber collimator points to a depolarizing beam splitter prism (the straight line where the laser output from one fiber collimator is located passes through one depolarizing beam splitter prism, and the straight line where the laser output from the other fiber collimator is located passes through another depolarizing beam splitter prism). The depolarizing beam splitter prism is used to transmit and reflect the laser, and the right-angle opening formed by the splitting planes of the two depolarizing beam splitters faces the fiber collimator.

[0012] Here, we illustrate the above-mentioned process of emitting laser light along a first direction to form two laser beams. The first direction can be represented by a vector. The starting point of the vector can be a point in space, and the end point represents the direction. The laser light emitted by the fiber collimator propagates according to the direction of the vector, and the optical path of the laser light emitted by the fiber collimator remains parallel to the vector. One fiber collimator emits one laser beam, and the other fiber collimator emits another laser beam to form two laser beams. Because they are emitted in the same direction (the first direction), the two laser beams remain parallel.

[0013] Here, the first and second planes are used as an example. The glass base can be placed horizontally, with the first and second planes both parallel to the plane of the glass base. Vertically, the first plane is located below the second plane, while the second plane is located above the first plane. The first and second planes can form upper and lower layers. Accordingly, two of the four laser beams are located in the lower layer, while the remaining two are located in the upper layer.

[0014] The above-mentioned depolarizing beam splitter prism is used to transmit and reflect laser light. For any two of the four laser beams, the first laser beam and the second laser beam, located in the same plane, the two depolarizing beam splitters are used to transmit the first laser beam and the second laser beam to the plane mirror, and reflect the first laser beam and the second laser beam to the second photodetector and the first photodetector, respectively. The first photodetector and the second photodetector, reflected by the plane mirror, are also reflected to the first photodetector and the second photodetector, respectively. The first photodetector and the second photodetector can each receive two laser beams. The two laser beams (the first laser beam and the second laser beam) received by one photodetector interfere to form a set of interference beams. The first laser beam and the second laser beam are two laser beams located in the first plane or the second plane among the four laser beams, and the first photodetector and the second photodetector are two photodetectors located in the first plane or the second plane among the four photodetectors.

[0015] One of the two depolarizing beam splitter prisms may be named a first depolarizing beam splitter prism, and the other may be named a second depolarizing beam splitter prism.

[0016] Here, the above-mentioned process of transmitting the first laser and the second laser to the plane reflector is described. Specifically, the process may be: the first depolarizing beam splitter prism transmits the first laser to the plane reflector, and the second depolarizing beam splitter prism transmits the second laser to the plane reflector.

[0017] Here, the reflection of the above-mentioned first laser and second laser to the second photodetector and the first photodetector respectively is described. The specific process can be: the first depolarizing beam splitter prism reflects the first laser to the second depolarizing beam splitter prism, and then transmits it to the second photodetector located on the detection plane through the second depolarizing beam splitter prism; the second depolarizing beam splitter prism reflects the second laser to the first depolarizing beam splitter prism, and then transmits it to the first photodetector located on the detection plane through the first depolarizing beam splitter prism.

[0018] Here, the above-mentioned process of reflecting the first laser and the second laser reflected by the plane mirror to the first photodetector and the second photodetector respectively is explained. The process can be specifically as follows: the first depolarizing beam splitter prism reflects the first laser reflected by the plane mirror to the first photodetector located on the detection plane; the second depolarizing beam splitter prism reflects the second laser reflected by the plane mirror to the second photodetector located on the detection plane.

[0019] It can be understood that four groups of interference beams can be obtained through four photodetectors, and then based on the four groups of interference beams, phase change data corresponding to the four groups of interference beams can be obtained through phase demodulation, and multiple degrees of freedom can be determined based on the phase change data corresponding to the four groups of interference beams.

[0020] At the same time, two fiber collimators, a lateral displacement beam splitter prism, and two depolarizing beam splitter prisms are fixed on the plane of the glass base to form a compact whole that is nearly integrated (i.e., quasi-monolithic). Compared with the method of measuring through discrete optical components, the embodiment of the present application can ensure the stability of measurement by adopting this compact design.

[0021] In addition, compared with the single-beam interferometer, the four-beam interferometer provided in the embodiment of the present application has good common-mode suppression capability for environmental noise. The depolarization characteristics of the depolarizing beam splitter can avoid affecting the polarization of the laser and prevent the change of the splitting ratio from affecting the measurement results. The above-mentioned compact design, good common-mode suppression capability and the depolarization characteristics of the depolarizing beam splitter are combined to ensure the accuracy of the measurement. Experimental data show that the four-beam interferometer has displacement measurement capabilities at the picometer and nanoradian levels.

[0022] Therefore, the compact four-beam interferometer provided in the embodiment of the present application can stably and accurately measure multiple degrees of freedom of an object through laser interference.

[0023] In a possible implementation, the pigtail of the optical fiber collimator is a polarization-maintaining optical fiber.

[0024] In a possible implementation, the optical fiber collimator is fixed to the glass base via a glass mounting base, and the optical fiber collimator is placed at a central through-hole position of the glass mounting base.

[0025] In a possible implementation, the components on the glass base are cured using ultraviolet glue.

[0026] Specifically, the components on the glass base may include a glass mount, a fiber collimator, a lateral displacement beam splitter, and a depolarizing beam splitter.

[0027] In a second aspect, the present application provides a method for manufacturing a compact four-beam interferometer, comprising:

[0028] Place the fiber collimator in the center hole of the glass mount. Using the optical platform as a reference, adjust the laser emitted by the fiber collimator to be parallel to the optical platform. Then, solidify the fiber collimator on the glass mount.

[0029] Fix the glass base on the optical platform and keep it parallel to the optical platform. Then place two glass mounts on the glass base. Adjust the two glass mounts so that the two laser beams emitted by the two fiber collimators are parallel to each other and parallel to the optical platform. Then solidify the two glass mounts and the glass base.

[0030] Along the first direction, a plane reflector is placed directly in front of the glass mount and fixed on the optical platform so that the two laser beams emitted by the two fiber collimators are reflected back into the fiber collimators along the original paths (ensuring that there is no obstruction between the fiber collimators and the plane reflector and that the plane reflector can reflect the laser beams emitted by the fiber collimators back into the fiber collimators along the original paths). The two fiber collimators are used to emit laser light along the first direction;

[0031] A laterally displaced beam splitter is placed in front of two glass mounts along a first direction to form four parallel beams. The laterally displaced beam splitter and the glass mount are then solidified, with two of the four laser beams located in a first plane and the other two located in a second plane. The first and second planes are parallel to the plane of the glass mount.

[0032] Two depolarizing beam splitter prisms are placed directly in front of the laterally displaced beam splitter prism along a first direction. The two depolarizing beam splitter prisms and the plane reflector are adjusted to maximize the contrast of the interference light beams detected by the four photodetectors. The two depolarizing beam splitter prisms are then fixed to the glass base. The beam splitting planes of the two depolarizing beam splitter prisms remain perpendicular. The right-angle opening formed by the beam splitting planes of the two depolarizing beam splitter prisms faces the fiber collimator. The four photodetectors and the depolarizing beam splitter prisms are located in the same detection plane. The first direction is perpendicular to the detection plane, and the detection plane is perpendicular to the plane of the glass base.

[0033] In a possible implementation, the components on the glass base are cured using ultraviolet glue.

[0034] In a third aspect, the present application provides a measurement method for a compact four-beam interferometer, which is applied to the four-beam interferometer described in the first aspect or any possible implementation of the first aspect, including:

[0035] Based on the interference beams detected by four photodetectors, the phase change data of the first interference beam is obtained by phase demodulation Phase change data of the second interference beam Phase change data of the third interfering beam and the phase change data of the fourth interference beam

[0036] determining a displacement change Δx(t) of the plane reflecting mirror based on the phase change data and the wavelength of the interference light beam, determining a pitch angle change Δα(t) of the plane reflecting mirror based on the phase change data, the wavelength of the interference light beam, and the parallel spacing between the first plane and the second plane, and determining a yaw angle change Δβ(t) of the plane reflecting mirror based on the phase change data, the wavelength of the interference light beam, and the parallel spacing between the first plane and the second plane;

[0037] The first interference beam is an interference beam located in the first plane and traveling along the second direction, the second interference beam is an interference beam located in the first plane and traveling along the third direction, the third interference beam is an interference beam located in the second plane and traveling along the third direction, and the fourth interference beam is an interference beam located in the second plane and traveling along the second direction. The second direction is a direction determined by rotating the first direction 90 degrees counterclockwise with the plane of the glass base as the rotation plane, and the third direction is a direction determined by rotating the first direction 90 degrees clockwise with the plane of the glass base as the rotation plane.

[0038] For example, two of the four photodetectors are located on one side of the glass base, and the other two are located on the other side of the glass base. Here, the two sides mentioned here can be referred to as the left side of the glass base when viewed from the glass base along the second direction, and the right side of the glass base when viewed from the glass base along the third direction.

[0039] In one possible implementation, determining the displacement change Δx(t) of the plane mirror based on the phase change data and the wavelength of the interference light beam includes determining the displacement change Δx(t) using the following formula:

[0040]

[0041] Here, λ represents the wavelength of the interfering light beam and t represents the time.

[0042] In one possible implementation, determining the pitch angle change Δα(t) of the plane mirror based on the phase change data, the wavelength of the interference light beam, and the parallel spacing between the first plane and the second plane includes determining the pitch angle change Δα(t) using the following formula:

[0043]

[0044] Wherein, λ represents the wavelength of the interference beam, d represents the parallel distance between the first plane and the second plane, and t represents the time.

[0045] In one possible implementation, determining the yaw angle change Δβ(t) of the plane mirror based on the phase change data, the wavelength of the interference light beam, and the parallel spacing between the first plane and the second plane includes determining the yaw angle change Δβ(t) using the following formula:

[0046]

[0047] Wherein, λ represents the wavelength of the interference beam, d represents the parallel distance between the first plane and the second plane, and t represents the time.

[0048] In general, the above technical solutions conceived by this application have the following beneficial effects compared with the existing technologies:

[0049] (1) Four groups of interference beams can be obtained through four photodetectors, and then the phase change data corresponding to the four groups of interference beams can be obtained through phase demodulation based on the four groups of interference beams. Based on the phase change data corresponding to the four groups of interference beams, multiple degrees of freedom can be determined.

[0050] (2) Two fiber collimators, a lateral displacement beam splitter, and two depolarizing beam splitters are fixed on the plane of the glass base to form a compact whole that is nearly integrated (i.e., quasi-monolithic). Compared with the method of measuring through discrete optical components, the embodiment of the present application can ensure the stability of measurement by adopting this compact design.

[0051] (3) Compared with the single-beam interferometer, the four-beam interferometer provided in the embodiment of the present application has good common-mode suppression capability for environmental noise. The depolarization characteristics of the depolarizing beam splitter can avoid affecting the polarization of the laser and prevent the change of the splitting ratio from affecting the measurement results. The above-mentioned compact design, good common-mode suppression capability and the depolarization characteristics of the depolarizing beam splitter can be combined to ensure the accuracy of the measurement. Experimental data show that the four-beam interferometer has the ability to measure displacements at the picometer and nanoradian levels. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 1 is a top view of a compact four-beam interferometer provided in an embodiment of the present application;

[0053] Figure 2 is a side view of a compact four-beam interferometer provided in an embodiment of the present application;

[0054] Figure 3 is a displacement measurement sensitivity curve diagram of the compact four-beam interferometer provided in an embodiment of the present application;

[0055] Figure 4 This is a graph of the angle measurement sensitivity of the compact four-beam interferometer provided in an embodiment of the present application.

[0056] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0057] 1: Glass base; 2: Glass mounting base; 3: Fiber collimator; 4: Lateral displacement beam splitter; 5: Depolarization beam splitter; 6: Plane reflector; 7: Photodetector; 8: First direction; 9: Second direction; 10: Third direction; 11: Detection plane; 12: First plane; 13: Second plane; 14: Right-angle opening. DETAILED DESCRIPTION

[0058] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0059] The terms "first," "second," and the like in the specification and claims herein are used to distinguish between different objects, rather than to describe a specific order of objects. For example, a first direction and a second direction are used to distinguish between different directions, rather than to describe a specific order of directions.

[0060] In the embodiments of this application, words such as "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of this application should not be interpreted as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0061] In the description of the embodiments of the present application, unless otherwise specified, "multiple" means two or more, for example, multiple processing units means two or more processing units, etc.; multiple elements means two or more elements, etc.

[0062] First, the technical terms involved in the embodiments of this application are introduced.

[0063] (1) Lateral displacement beam splitter

[0064] A lateral displacement beamsplitter is an optical component composed of a right-angle prism and an rhombus prism bonded together. The bonded surfaces of these prisms are coated with a polarizing beamsplitter coating. Their primary function is to generate two parallel polarized beams. The lateral displacement of these two beams is determined by the length of the rhombus prism.

[0065] (2) Depolarizing beam splitter

[0066] A depolarizing beam splitter (NPBS) is an optical component that is formed by coating multiple interference films on the oblique surfaces of a right-angle prism and then gluing them together into a cubic structure. It can effectively process the different polarization components of the incident light, making them exhibit similar characteristics during the splitting process.

[0067] (3) Polarization-maintaining fiber

[0068] Polarization-Maintaining Fiber (PM fiber) is a type of fiber that maintains the polarization of an incident light beam during transmission. This fiber is designed to have strong birefringence, which allows it to maintain the polarization direction of light.

[0069] (4) UV glue

[0070] Ultraviolet (UV) glue, also known as UV glue or UV-curing glue, is a one-component, low-viscosity, high-strength acrylic adhesive. It boasts a long shelf life, contains no solvents, cures quickly, exhibits excellent transparency, and exhibits excellent heat and chemical resistance. This adhesive typically cures via UV light and cures quickly, drying to the touch within seconds.

[0071] (5) Contrast of interference beam

[0072] The contrast of an interference beam, also known as visibility or contrast, is a parameter used to quantitatively describe the clarity of interference fringes. It is defined as the ratio of the difference between the maximum intensity of a bright fringe and the minimum intensity of the adjacent dark fringe in the interference pattern to the sum of the two.

[0073] The formula for calculating contrast is: Contrast = (maximum brightness - minimum brightness) / (maximum brightness + minimum brightness). The contrast value ranges from 0 to 1. When the contrast is 0, the interference fringes disappear completely, indicating no interference. When the contrast is 1, the difference in brightness between the interference fringes is the greatest, indicating the most obvious interference.

[0074] The embodiments of the present application are described below in conjunction with the drawings in the embodiments of the present application.

[0075] Example 1

[0076] Figure 1 is a top view of the compact four-beam interferometer provided in an embodiment of the present application, Figure 2 is a side view of the compact four-beam interferometer provided in an embodiment of the present application, as shown in FIG. Figure 1 and 2 As shown, the interferometer includes: a glass base 1, two glass mounting seats 2, two fiber collimators 3, a lateral displacement beam splitter prism 4, two depolarizing beam splitter prisms 5, a plane reflector 6 and four photodetectors 7 located in the same detection plane 11.

[0077] The glass base 1 has dimensions of 20×30×10 mm in length, width and height, and is made of K9 glass with a polished and flat surface, which is convenient for the placement of optical devices in the later stage.

[0078] The glass mount 2 has a size of 10×10×10 mm and is made of K9 glass. The center of the glass mount 2 must be a through circular hole with a diameter of 3 mm to facilitate adjustment of the fiber collimator's posture and to fix it to the glass mount as a whole.

[0079] The fiber collimator 3 is cylindrical, 3mm in diameter, 9mm in length, and has a pigtail length of 1m. It uses polarization-maintaining fiber with a design wavelength of 1064nm and emits a fundamental-mode Gaussian beam. Using polarization-maintaining fiber prevents changes in laser polarization caused by fiber bending or stress, ensuring the contrast of the interfering beam and improving the detection performance of the photodetector.

[0080] like Figure 1 and 2 As shown, two optical fiber collimators emit laser light along a first direction 8 to form two laser beams (the two laser beams enter the laterally displaced beam splitter prism) and the two laser beams are located in a first plane 12 parallel to the plane of the glass base 1 .

[0081] The lateral displacement beam splitter prism 4 has a height of 20 mm, a designed parallel spacing of 10 mm between the two beams, a reflectivity ratio of 50:50, and a designed wavelength of 1064 nm. The lateral displacement beam splitter prism 4 can split the incident light into two parallel beams at a 50:50 splitting ratio.

[0082] like Figure 2 As shown, the lateral displacement beam splitter prism splits the two laser beams into four laser beams, two of which are located on a first plane 12, and the other two (of the four laser beams) are located on a second plane 13, which is parallel to the plane of the glass base 1 (the first plane and the second plane are different planes).

[0083] The depolarizing beam splitter prism 5 has dimensions of 10×10×20 mm in length, width, and height, a reflectivity of 50:50, a design wavelength of 1064 nm, and is insensitive to polarization. By utilizing the depolarizing characteristics of the depolarizing beam splitter prism 5 , it is possible to avoid changes in the splitting ratio caused by changes in the polarization of the light beam.

[0084] like Figure 1 As shown, the right-angle opening 14 formed by the splitting planes of the two depolarization beam splitting prisms 5 faces the fiber collimator 3 .

[0085] The plane reflector 6 is a cylinder with a diameter of 25.4 mm (one end of the cylinder serves as a reflecting plane), a thickness of 6 mm, a design wavelength of 1064 nm, a reflectivity of 99.9%, and an incident angle of 0°.

[0086] The photoelectric detector 7 has an effective detection area of ​​a circular area with a diameter of 3.6 mm. The photoelectric material used is Si. The detection band is 350-1100 nm and the detection bandwidth is 12 MHz, which can meet the requirements of heterodyne detection.

[0087] Example 2

[0088] An embodiment of the present application further provides a method for manufacturing a compact four-beam interferometer, which includes the following steps S101 to S105.

[0089] Step S101: Place the fiber collimator at the center hole of the glass mount, use the optical platform (a horizontal platform) as a reference, adjust the laser emitted by the fiber collimator to be parallel to the optical platform, and then use UV glue to cure the two to form a whole.

[0090] Step S102: Secure the glass base to the optical platform, keeping it parallel to the platform. Then, place the two glass mounts and the fiber collimator, which are solidified, onto the glass base. The frequency difference between the lasers emitted by the two fiber collimators can be 10 kHz. Adjust the two glass mounts so that the two laser beams are parallel to each other and to the optical platform, thus forming two heterodyne beams. Finally, solidify the two glass mounts and the glass base.

[0091] Step S103: Place the plane mirror directly in front of the glass mount (the plane mirror is fixed on the object to be measured during the use of the interferometer) and fix it on the optical platform. At this time, the two laser beams emitted by the fiber collimator need to be reflected back into the fiber collimator along the original path. A fiber circulator can be used to monitor the optical power of the return light to determine whether the laser beams reflected by the plane mirror return along the original path.

[0092] Step S104: Place a lateral displacement beam splitter directly in front of the two glass mounts. This will form four parallel light beams. The four beams are divided into two layers, each containing two laser beams. The upper and lower layers are designed to have a spacing of 10 mm. That is, the four beams can form the four vertices of a 10 × 10 mm square in space. Finally, solidify the lateral displacement beam splitter and the glass mount.

[0093] Step S105: Two beam splitters are placed directly in front of the laterally displaced beam splitter. All four beams undergo a process of transmission and reflection. The transmitted light is reflected back by the plane reflector and combined with the reflected light from another beam on the same layer, causing the two beams to interfere. This pattern results in four sets of interfering beams. The positions and orientations of the two beam splitters and the plane reflector are adjusted to maximize the contrast of the interfering beams, ensuring detection efficiency for the photodetector. The two beam splitters are then bonded to the glass base.

[0094] The interfering beam can be monitored by four photodetectors and converted into an electrical signal. The phase meter is used to demodulate the phase information of the photoelectric signal. The two groups of interference beams in the lower layer are defined as the first interference beam and the second interference beam, and the two groups of interference beams in the upper layer are defined as the third interference beam and the fourth interference beam. The first interference beam and the fourth interference beam are located on the left side of the glass base 1, and the second interference beam and the third interference beam are located on the right side of the glass base 1.

[0095] It should be noted that if Figure 1 As shown, two of the four photodetectors are located on one side of the glass base, and the other two are located on the other side of the glass base. Regarding the two sides, the side viewed from the glass base along a second direction 9 may be referred to as the left side of the glass base 1, and the side viewed from the glass base along a third direction 10 may be referred to as the right side of the glass base 1. The second direction 9 is a direction determined by rotating the first direction 8 90 degrees counterclockwise with the plane of the glass base 1 as the rotation plane, and the third direction 10 is a direction determined by rotating the first direction 8 90 degrees clockwise with the plane of the glass base 1 as the rotation plane.

[0096] The optical components are bonded to a single piece of glass base with UV glue, which enhances the robustness and integrity of the instrument compared to measurements made with separate optical components.

[0097] A compact four-beam interferometer can be manufactured using the above optical path design and construction method.

[0098] Example 3

[0099] An embodiment of the present application further provides a measurement method for a compact four-beam interferometer, which includes the following steps S201 and S202.

[0100] Step S201: Based on the interference beams detected by the four photodetectors, phase change data of the first interference beam is obtained by phase demodulation. Phase change data of the second interference beam Phase change data of the third interference beam and the phase change data of the fourth interference beam

[0101] Step S202: determining the displacement change Δx(t) of the plane mirror based on the phase change data and the wavelength of the interference light beam, determining the pitch angle change Δα(t) of the plane mirror based on the phase change data, the wavelength of the interference light beam and the parallel spacing between the first plane and the second plane, and determining the yaw angle change Δβ(t) of the plane mirror based on the phase change data, the wavelength of the interference light beam and the parallel spacing between the first plane and the second plane.

[0102] The first interference beam is an interference beam located in the first plane and traveling along the second direction, the second interference beam is an interference beam located in the first plane and traveling along the third direction, the third interference beam is an interference beam located in the second plane and traveling along the third direction, and the fourth interference beam is an interference beam located in the second plane and traveling along the second direction. The second direction is a direction determined by rotating the first direction 90 degrees counterclockwise with the plane of the glass base as the rotation plane, and the third direction is a direction determined by rotating the first direction 90 degrees clockwise with the plane of the glass base as the rotation plane.

[0103] Specifically, when using the interferometer, the plane mirror is fixed on the object to be measured. The movement of the object relative to the glass base will drive the plane mirror to move relative to the glass base. The phase of the four sets of interference signals contains the displacement information of the four points on the plane mirror. The phase changes are The corresponding displacement changes are x1(t), x2(t), x3(t), and x4(t), which are the four vertices of a 10×10mm square. Therefore, the displacement change Δx(t) of the plane mirror can be given by the phase change detected by the detector:

[0104]

[0105] Where λ = 1064 nm is the wavelength of the interference beam.

[0106] The pitch angle change Δα(t) and yaw angle change Δβ(t) of the plane mirror can also be given by the phase change detected by the detector:

[0107]

[0108] Where d = 10 mm is the parallel distance between the upper and lower beams. Since the offset angle is very small, the above inverse tangent approximation can be used when solving the problem.

[0109] It can be seen that the compact four-beam interferometer provided in this application has the ability to measure three degrees of freedom: single-axis displacement, pitch angle, and yaw angle.

[0110] Compared to single-beam interferometers, the four-beam interferometers provided in the present application have excellent common-mode noise rejection. Their compact, quasi-monolithic structure offers advantages such as high stability and precision, making them suitable for a wide range of applications, including gravitational wave detection, inertial sensing, vibrometers, and seismometers.

[0111] Figure 3 is a displacement measurement sensitivity curve diagram of the compact four-beam interferometer provided in an embodiment of the present application, Figure 4is a graph showing the angle measurement sensitivity of the compact four-beam interferometer provided in an embodiment of the present application. Figure 3 and 4 As shown, through the actual measurement of the compact four-beam interferometer provided in the embodiment of the present application, the displacement measurement sensitivity of the interferometer at 1 Hz can reach better than Pitch and yaw angle measurement sensitivity can reach better than It can be seen that the compact four-beam interferometer provided in the embodiment of the present application has the displacement measurement capability at the picometer level and nanoradian level.

[0112] It should be understood that expressions such as "include" and "may include" used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as "include" and / or "have" may be interpreted as indicating specific characteristics, numbers, operations, constituent elements, components, or combinations thereof, but may not be interpreted as excluding the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0113] The directional terms mentioned in the embodiments of the present application, such as "top", "bottom", "inside", "outside", "left", "right", etc., are only references to the directions in the drawings. Therefore, the directional terms used are for better and clearer explanation and understanding of the embodiments of the present application, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the embodiments of the present application.

[0114] In addition, in the embodiments of the present application, the mathematical concepts mentioned include symmetry, equality, parallelism, and perpendicularity. These limitations are all for the current state of the art, rather than being absolutely strict definitions in a mathematical sense. A small amount of deviation is allowed, and it is possible to be approximately symmetric, approximately equal, approximately parallel, or approximately perpendicular. For example, A and B are parallel, which means that A and B are parallel or approximately parallel, and the angle between A and B can be between 0 and 10 degrees. A and B are perpendicular, which means that A and B are perpendicular or approximately perpendicular, and the angle between A and B can be between 80 and 100 degrees.

[0115] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A measurement method for a compact four-beam interferometer, characterized in that: The invention is applied to a compact four-beam interferometer, which comprises: a glass base, four photodetectors located on the same detection plane, and two fiber collimators, a lateral displacement beam splitter, a depolarizing beam splitter, and a plane reflector arranged in sequence along a first direction, wherein the first direction is perpendicular to the detection plane; Two optical fiber collimators, the lateral displacement beam splitter prism and two depolarization beam splitter prisms are fixed on the plane of the glass base; Two optical fiber collimators are used to emit laser light along the first direction to form two laser beams, and the two laser beams are located in a first plane, and the first plane is parallel to the plane of the glass base; The lateral displacement beam splitter prism is used to split the two laser beams into four laser beams, two of the four laser beams are located in the first plane, and the other two are located in the second plane, and the second plane is parallel to the plane of the glass base; The detection plane is perpendicular to the plane of the glass base and two depolarizing beam splitters are located on the detection plane. Two of the four photodetectors are located on one side of the glass base, and the other two are located on the other side of the glass base. For the two photodetectors on the same side, one is located on the first plane and the other is located on the second plane. The laser output port of a fiber collimator is directed toward a depolarizing beam splitter prism, the depolarizing beam splitter prism is used to transmit and reflect the laser, and the right-angle opening formed by the beam splitting planes of the two depolarizing beam splitter prisms faces the fiber collimator; The method comprises: Based on the interference beams detected by four photodetectors, the phase change data of the first interference beam is obtained by phase demodulation , the phase change data of the second interference beam , the phase change data of the third interference beam and the phase change data of the fourth interference beam ; Determine the displacement change of the plane mirror based on the phase change data and the wavelength of the interference beam , and determining the pitch angle change of the plane mirror based on the phase change data, the wavelength of the interference light beam and the parallel spacing between the first plane and the second plane , and determining a yaw angle change of the plane mirror based on the phase change data, the wavelength of the interference light beam, and the parallel spacing between the first plane and the second plane ; The first interference beam is an interference beam located in the first plane and traveling along the second direction, the second interference beam is an interference beam located in the first plane and traveling along the third direction, the third interference beam is an interference beam located in the second plane and traveling along the third direction, and the fourth interference beam is an interference beam located in the second plane and traveling along the second direction. The second direction is a direction determined by rotating the first direction 90 degrees counterclockwise with the plane of the glass base as the rotation plane, and the third direction is a direction determined by rotating the first direction 90 degrees clockwise with the plane of the glass base as the rotation plane.

2. The measurement method of the compact four-beam interferometer according to claim 1, characterized in that: The displacement change of the plane mirror is determined based on the phase change data and the wavelength of the interference beam. , including determining the displacement change by the following formula : ； in, represents the wavelength of the interfering beam, Indicates time.

3. The measurement method of the compact four-beam interferometer according to claim 1, characterized in that: The pitch angle change amount of the plane mirror is determined based on the phase change data, the wavelength of the interference light beam and the parallel distance between the first plane and the second plane. , including determining the pitch angle change using the following formula : in, represents the wavelength of the interfering beam, represents the parallel distance between the first plane and the second plane, Indicates time.

4. The measurement method of the compact four-beam interferometer according to claim 1, characterized in that: The yaw angle change of the plane mirror is determined based on the phase change data, the wavelength of the interference light beam and the parallel distance between the first plane and the second plane. , including determining the yaw angle change using the following formula : in, represents the wavelength of the interfering beam, represents the parallel distance between the first plane and the second plane, Indicates time.

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