Compact four-beam interferometer, manufacturing method and measuring method

Abstract

The invention belongs to the technical field of object space attitude measurement, and particularly discloses a compact four-beam interferometer, a manufacturing method and a measuring method. The interferometer comprises a glass base, four photoelectric detectors located on the same detection plane, and two optical fiber collimators, a lateral displacement beam splitter prism, a depolarization beam splitter prism and a plane mirror which are sequentially arranged along a first direction, wherein the first direction is perpendicular to the detection plane; the two optical fiber collimators, the lateral displacement beam splitter prism and the two depolarization beam splitter prisms are fixed on the plane of the glass base; the two optical fiber collimators are used for emitting laser in a first direction to form two beams of laser; the lateral displacement beam splitter prism is used for dividing the two laser beams into four laser beams; the detection plane is perpendicular to the plane of the glass base, and the two depolarization beam splitting prisms are located on the detection plane. According to the invention, multiple degrees of freedom of an object can be stably and accurately measured in a laser interference mode.

Description

Technical Field

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

[0002] The spatial posture of an object is determined by 6 degrees of freedom, of which the position state is determined by 3 linear quantities and the posture is determined by 3 angular quantities. With the continuous development of modern science and technology, many fields such as aerospace, mechanical processing and assembly have put forward urgent requirements for simultaneously obtaining spatial posture parameters of multiple degrees of freedom. Laser interferometry is one of the most effective methods to achieve large-scale high-precision length measurement. At the same time, high-precision laser interferometer is an important tool for ultra-precision measurement in cutting-edge scientific research and advanced manufacturing. For example, there is a huge demand in the fields of gravitational wave detection, inertial sensing, CNC machine tools and lithography machine manufacturing.

[0003] For laser interferometry technology and applications, the main bottlenecks that affect the improvement of its measurement accuracy are the characteristics of key units such as the laser interferometry method principle, the interferometric light source, the interferometric optical element, and the interferometric signal processing card, as well as the stability of the actual measurement environment. How to stably and accurately measure multiple degrees of freedom of an object through laser interferometry is a technical problem that needs to be solved in this field. Summary of the invention

[0004] In view of the defects of the prior art, the purpose of the present application is to stably and accurately measure multiple degrees of freedom of an object by laser interferometry.

[0005] To achieve the above-mentioned purpose, 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 prism, a depolarizing beam splitter prism 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, and the first plane 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 a 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 another 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, the above-mentioned emission of laser light in the first direction to form two laser beams is explained. 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 a laser beam, and the other fiber collimator emits another laser beam to form two laser beams. Since they are emitted in the same direction (the first direction), the two laser beams remain parallel.

[0013] Here, the first plane and the second plane are exemplified, the glass base can be placed horizontally, the first plane and the second plane are parallel to the plane of the glass base, in vertical height, the first plane is the lower layer relative to the second plane, the second plane is the upper layer relative to the first plane, and the first plane and the second plane can constitute the upper and lower layers. Accordingly, two of the four laser beams are located at the lower layer, and the other two are located at the upper layer.

[0014] Here, the above-mentioned depolarizing beam splitter prism is used to transmit and reflect laser light. For any two of the above-mentioned four laser beams, the first laser and the second laser, which are located in the same plane, the two depolarizing beam splitters are used to transmit the first laser and the second laser to the plane reflector, and reflect the first laser and the second laser to the second photodetector and the first photodetector respectively, and reflect the first laser and the second laser reflected by the plane reflector to the first photodetector and the second photodetector respectively. The first photodetector and the second photodetector can both receive two laser beams, and the two laser beams (the first laser and the second laser) received by one photodetector interfere to form a group of interference beams. The first laser and the second laser 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 first laser and the second laser to the second photodetector and the first photodetector respectively is explained. 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 in 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 in 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 light beams can be obtained through four photodetectors, and then based on the four groups of interference light beams, phase change data corresponding to the four groups of interference light 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 light 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, which is close to being 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 can 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.

[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 fiber of the optical fiber collimator is a polarization-maintaining optical fiber.

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

[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 at the central hole of the glass mount, use the optical platform as a reference, adjust the laser emitted by the fiber collimator to be parallel to the optical platform, and 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, and then solidify the two glass mounts and the glass base;

[0030] Along the first direction, a plane reflector is placed in front of the glass mounting seat 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 the plane reflector can reflect the laser beams emitted by the fiber collimators back into the fiber collimators along the original paths when there is no obstruction between the fiber collimators and the plane reflector). The two fiber collimators are used to emit laser beams along the first direction;

[0031] Along a first direction, a lateral displacement beam splitter prism is placed in front of two glass mounting bases to form four mutually parallel beams, and then the lateral displacement beam splitter prism and the glass base are solidified, two of the four laser beams are located in a first plane, and the other two are located in a second plane, and the first plane and the second plane are parallel to the plane of the glass base;

[0032] Along the first direction, two depolarizing beam splitter prisms are respectively placed in front of the lateral displacement beam splitter prism, and the contrast of the interference light beams detected by the four photodetectors is maximized by adjusting the two depolarizing beam splitter prisms and the plane reflector. Then, the two depolarizing beam splitter prisms are solidified with the glass base, and the beam splitting planes of the two depolarizing beam splitter prisms are kept vertical. The right-angle opening formed by the beam splitting planes of the two depolarizing beam splitter prisms faces the optical fiber collimator. The four photodetectors and the depolarizing beam splitter prisms are located on 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 of 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 interference beam and the phase change data of the fourth interference beam

[0036] Determine a displacement change Δx(t) of the plane reflector based on the phase change data and the wavelength of the interference light beam, determine a pitch angle change Δα(t) of the plane reflector 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 determine a yaw angle change Δβ(t) of the plane reflector 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, 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 counterclockwise by 90 degrees with the plane of the glass base as the rotation plane, and the third direction is a direction determined by rotating the first direction clockwise by 90 degrees 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. Among the two sides mentioned, the side viewed from the glass base along the second direction can be referred to as the left side of the glass base, and the side viewed from the glass base along the third direction can be referred to as the right side of the glass base.

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

[0040]

[0041] Where λ is the wavelength of the interference beam and t is the time.

[0042] In a possible implementation, determining the pitch angle change Δα(t) of the plane reflector 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) by the following formula:

[0043]

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

[0045] In a possible implementation, determining the yaw angle change Δβ(t) of the plane reflector 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) by the following formula:

[0046]

[0047] Wherein, λ represents the wavelength of the interference light 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 prior art:

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

[0050] (2) Two fiber collimators, a lateral displacement beam splitter prism, and two depolarizing beam splitters are fixed on the plane of the glass base to form a compact whole that is close to being 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 a 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 result. The above-mentioned compact design, good common-mode suppression capability and the depolarization characteristics of the depolarizing beam splitter can 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 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 curve diagram 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 seat; 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 solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

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

[0060] In the embodiments of the present 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 the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

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

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

[0063] (1) Lateral displacement beam splitter

[0064] Lateral displacement beam splitter is an optical element, which is made of a right angle prism and an oblique prism. The bonding surface of this prism is coated with polarization beam splitter film, and its main function is to produce two parallel polarized light beams. The lateral displacement of these two beams is determined by the length of the oblique prism.

[0065] (2) Depolarizing beam splitter

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

[0067] (3) Polarization-Maintaining Fiber

[0068] Polarization-Maintaining Fiber (PM Fiber) is a type of fiber that can maintain the polarization state of the incident light beam without changing during transmission. The design of this fiber makes it have strong birefringence characteristics, so that it can maintain the polarization direction of light.

[0069] (4) UV glue

[0070] Ultraviolet glue, also known as UV glue or ultraviolet curing glue. UV glue is a one-component, low-viscosity, high-strength acrylic adhesive with the characteristics of long shelf life, no solvent, fast curing speed, good transparency, and good heat and chemical resistance. This adhesive is generally cured by ultraviolet light, with a fast curing speed and can be dry in a few 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 an adjacent dark fringe in the interference image to the sum of the two.

[0073] The calculation formula of contrast is: contrast = (maximum brightness - minimum brightness) / (maximum brightness + minimum brightness). The value range of contrast is between 0 and 1. When the contrast is 0, it means that the interference fringes disappear completely, that is, there is no interference phenomenon; when the contrast is 1, it means that the difference in brightness of the interference fringes is the largest, and the interference phenomenon is most obvious.

[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 a compact four-beam interferometer provided in an embodiment of the present application, Figure 2 is a side view of a compact four-beam interferometer provided in an embodiment of the present application, such as 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 on 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 later optical devices.

[0078] The glass mounting seat 2 has a size of 10×10×10 mm and is made of K9 glass. The center position of the glass mounting seat needs to be a through circular hole with a diameter of 3 mm, so as to facilitate the adjustment of the posture of the optical fiber collimator and to fix it as a whole with the glass mounting seat.

[0079] The optical fiber collimator 3 is cylindrical in shape, with a diameter of 3 mm, a length of 9 mm, a pigtail length of 1 m, a polarization-maintaining optical fiber, a design wavelength of 1064 nm, and an output beam type of a fundamental mode Gaussian beam. The use of polarization-maintaining optical fiber can avoid changes in the polarization direction of the laser caused by factors such as optical fiber bending or stress, ensure the contrast of the interference beam, and improve the detection effect of the photodetector.

[0080] like Figure 1 and 2 As shown, two optical fiber collimators emit lasers 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 , which is 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 two beams of 10 mm, a reflectance 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 splitting ratio of 50:50.

[0082] like Figure 2 As shown, the lateral displacement beam splitter prism splits 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. The depolarizing characteristics of the depolarizing beam splitter prism 5 can prevent 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 light 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 heterodyne detection requirements.

[0087] Example 2

[0088] The embodiment of the present application also 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 central hole of the glass mounting base, use the optical platform (a horizontally placed platform) as a reference, adjust the laser emitted by the fiber collimator to be parallel to the optical platform, and then use ultraviolet glue to cure the two to form a whole.

[0090] Step S102: Fix the glass base on the optical platform and keep it parallel to the optical platform, then place the whole formed by curing the two glass mounts and the fiber collimator on the glass base, and the frequency difference between the lasers emitted by the two fiber collimators can be 10kHz. Adjust the two glass mounts so that the two laser beams are parallel to each other and parallel to the optical platform, thereby forming two heterodyne beams, and finally cure the two glass mounts and the glass base.

[0091] Step S103: Place the plane reflector directly in front of the glass mount (the plane reflector 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 reflected by the plane reflector returns along the original path.

[0092] Step S104: Place the lateral displacement beam splitter prism in front of the two glass mounts, so that four parallel light beams can be formed. The four light beams are divided into two layers, the upper and lower layers have two laser beams each, and the design spacing between the upper and lower light beams is 10mm, that is, the four light beams can form the four vertices of a 10×10mm square in space. Finally, solidify the lateral displacement beam splitter prism and the glass base.

[0093] Step S105: Place two beam splitters in front of the lateral displacement beam splitter prism. All four beams are transmitted and reflected. The transmitted light is reflected back through the plane reflector and combined with the reflected light of another beam of light in the same layer. The two beams interfere with each other. Four groups of interference beams will be formed according to the above rules. The contrast of the interference beams is maximized by adjusting the position and posture of the two beam splitters and the plane reflector to ensure the detection effect of the photoelectric detector. Then, the two beam splitters are solidified with the glass base.

[0094] The interfering beam can be monitored by four photodetectors and converted into electrical signals. 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, wherein 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. The two sides mentioned here can be referred to as the left side of the glass base 1 when viewed from the glass base along the second direction 9, and the right side of the glass base 1 when viewed from the glass base along the third direction 10. 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 monolithic glass base of suitable size by UV glue, which can enhance the robustness and integrity of the instrument compared to the measurement method using discrete optical components.

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

[0098] Example 3

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

[0100] Step S201, based on the interference light beams detected by the four photodetectors, phase change data of the first interference light 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, based on the phase change data and the wavelength of the interference light beam, determine the displacement change Δx(t) of the plane reflector, 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, determine the pitch angle change Δα(t) of the plane reflector, and 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, determine the yaw angle change Δβ(t) of the plane reflector.

[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, 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 counterclockwise by 90 degrees with the plane of the glass base as the rotation plane, and the third direction is a direction determined by rotating the first direction clockwise by 90 degrees with the plane of the glass base as the rotation plane.

[0103] Specifically, when using the interferometer, the plane reflector is fixed on the object to be measured. The movement of the object to be measured relative to the glass base will drive the plane reflector to move relative to the glass base. The phases of the four sets of interference signals contain the displacement information of the four points on the plane reflector. 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 10×10 mm square. Therefore, the displacement change Δx(t) of the plane reflector 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 change Δα(t) and yaw 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 spacing 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 the present application has the ability to measure three degrees of freedom: single-axis displacement, pitch angle (pitch) and yaw angle (yaw).

[0110] 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. And the quasi-monolithic compact structure has the advantages of high stability and high precision, and can be widely used in the fields of gravitational wave detection, inertial sensing, vibrometer, seismometer, etc.

[0111] Figure 3 is a displacement measurement sensitivity curve diagram of the compact four-beam interferometer provided in the embodiment of the present application, Figure 4is a curve diagram of the angle measurement sensitivity of the compact four-beam interferometer provided in the embodiment of the present application, such as 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 capability of measuring displacements at the picometer and nanoradian levels.

[0112] It should be understood that expressions such as "including" and "may include" that may be used in the present 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 the present application, terms such as "including" and / or "having" 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 of 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 a limitation on the embodiments of the present application.

[0114] In addition, in the embodiments of the present application, the mathematical concepts mentioned are symmetry, equality, parallelism, verticality, etc. These limitations are all for the current state of the art, rather than being absolutely strict definitions in a mathematical sense, and allow a small amount of deviation, approximation to symmetry, approximation to equality, approximation to parallelism, approximation to verticality, etc. are all possible. 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 is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A compact four-beam interferometer, characterized in that: include: A glass base, four photoelectric detectors located on the same detection plane, and two optical 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 points to a depolarizing beam splitter prism, the depolarizing beam splitter prism is used to transmit and reflect laser light, and the right-angle opening formed by the beam splitting planes of the two depolarizing beam splitter prisms faces the fiber collimator.

2. The compact four-beam interferometer according to claim 1, characterized in that: The pigtail fiber of the optical fiber collimator adopts polarization-maintaining optical fiber.

3. The compact four-beam interferometer according to claim 1, characterized in that: The optical fiber collimator is fixed on the glass base through a glass mounting seat, and the optical fiber collimator is placed at the central through-hole position of the glass mounting seat.

4. The compact four-beam interferometer according to any one of claims 1 to 3, characterized in that: The components on the glass base are cured by ultraviolet glue.

5. A method for manufacturing a compact four-beam interferometer, characterized in that: include: Placing the optical fiber collimator at the central perforation position of the glass mounting seat, taking the optical platform as a reference, adjusting the laser emitted by the optical fiber collimator to be parallel to the optical platform, and then curing the optical fiber collimator on the glass mounting seat; Fixing a glass base on the optical platform and keeping it parallel to the optical platform, then placing two glass mounts on the glass base, adjusting the two glass mounts so that the two laser beams emitted by the two optical fiber collimators are parallel to each other and parallel to the optical platform, and then solidifying the two glass mounts and the glass base; Along the first direction, a plane reflector is placed in front of the glass mount and fixed on the optical platform, so that the two laser beams emitted by the two optical fiber collimators are reflected back into the optical fiber collimators according to the original paths. The two optical fiber collimators are used to emit lasers along the first direction; Along the first direction, a lateral displacement beam splitter is placed in front of the two glass mounting seats to form four mutually parallel laser beams, and then the lateral displacement beam splitter and the glass base are solidified, two of the four laser beams are located in a first plane, and the other two are located in a second plane, and the first plane and the second plane are parallel to the plane of the glass base; Along the first direction, two depolarizing beam splitter prisms are respectively placed in front of the lateral displacement beam splitter prism, and the contrast of the interference light beams detected by the four photodetectors is maximized by adjusting the two depolarizing beam splitter prisms and the plane reflector. Then, the two depolarizing beam splitter prisms are solidified to the glass base, and the beam splitting planes of the two depolarizing beam splitter prisms are kept vertical. 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.

6. The method for manufacturing a compact four-beam interferometer according to claim 5, characterized in that: The components on the glass base are cured by ultraviolet glue.

7. A measurement method for a compact four-beam interferometer, characterized in that: The compact four-beam interferometer as claimed in any one of claims 1 to 4 comprises: 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 interference beam and the phase change data of the fourth interference beam Determine a displacement change Δx of the plane reflector based on the phase change data and the wavelength of the interference light beam, determine a pitch angle change Δα of the plane reflector 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 determine a yaw angle change Δβ of the plane reflector 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 light beam is an interference light beam located in the first plane and traveling along the second direction, the second interference light beam is an interference light beam located in the first plane and traveling along the third direction, the third interference light beam is an interference light beam located in the second plane and traveling along the third direction, the fourth interference light beam is an interference light beam located in the second plane and traveling along the second direction, the second direction is a direction determined by rotating the first direction counterclockwise by 90 degrees with the plane of the glass base as the rotation plane, and the third direction is a direction determined by rotating the first direction clockwise by 90 degrees with the plane of the glass base as the rotation plane.

8. The measuring method of the compact four-beam interferometer according to claim 7, characterized in that: Determining the displacement change Δx of the plane reflector based on the phase change data and the wavelength of the interference light beam includes determining the displacement change Δx by the following formula: Where λ is the wavelength of the interference beam and t is the time.

9. The measuring method of the compact four-beam interferometer according to claim 7, characterized in that: The step of determining the pitch angle variation Δα of the plane reflector based on the phase variation data, the wavelength of the interference light beam, and the parallel spacing between the first plane and the second plane comprises determining the pitch angle variation Δα by the following formula: Wherein, λ represents the wavelength of the interference light beam, d represents the parallel distance between the first plane and the second plane, and t represents the time.

10. The measuring method of the compact four-beam interferometer according to claim 7, characterized in that: Determining the yaw angle change Δβ of the plane reflector 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 by the following formula: Wherein, λ represents the wavelength of the interference light beam, d represents the parallel distance between the first plane and the second plane, and t represents the time.

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