Surface topography measuring device and method, object surface height calculation method

Abstract

The application provides a surface topography measuring device and method, and an object surface height calculation method, and applies to the technical field of optical precision measurement, and comprises a fiber F-P interference measuring head and a three-dimensional displacement table; the fiber F-P interference measuring head is composed of a fiber head array and a microlens array, and an object to be measured is fixed on the three-dimensional displacement table; a light beam is transmitted to the fiber F-P interference measuring head, is emitted from an exit surface of the microlens array after passing through the fiber head array and the microlens array, and is collimated and irradiated to the surface of the object to be measured; and the three-dimensional displacement table drives the object to be measured to perform three-dimensional movement to measure the surface topography of the object to be measured. Through the scanning measurement scheme of the combination of the fiber head array and the microlens array and the three-dimensional displacement table, the problems of small measurement range and slow measurement speed of the fiber F-P interference measuring head are solved, the measurement range and the measurement speed of the fiber F-P interference surface topography detection product are improved, and the cost thereof is reduced.

Description

Technical Field

[0001] This application relates to the field of optical precision measurement technology, specifically to a surface morphology measurement device and method, and a method for calculating the height of an object surface. Background Technology

[0002] With the rapid development of precision equipment manufacturing, surface morphology measurement has important applications in production processes such as component size measurement, component surface defect measurement, and quality control. Optical non-contact measurement based on optical inspection has become a research and application hotspot in the field of surface morphology measurement due to its advantages such as high measurement accuracy, wide applicability to measurement objects, and ease of automation and modularization.

[0003] In optical non-contact measurement methods, compared with traditional lens-based interferometers, all-fiber interferometers offer advantages such as compact and flexible structure, high sensitivity, and strong environmental adaptability. Common fiber interferometers include fiber Mach-Zehnder interferometers, fiber Michelson interferometers, and fiber FP interferometers (Fabry-Pérot interferometers). However, fiber Mach-Zehnder and fiber Michelson interferometers, due to their beam-splitting structures, suffer from complex system structures and the need for reference arms in surface topography measurement applications, hindering system integration for surface topography detection. Fiber FP interferometers, on the other hand, are common-path interferometers. Their working principle involves altering the phase change of the FP cavity interference field by changing the cavity length. Due to their unique working principle and common-path structure, fiber FP interferometers used for displacement measurement offer advantages such as high sensitivity, strong stability, and simple structure.

[0004] However, fiber FP interferometers are currently typically used in scenarios such as one-dimensional displacement measurement and object micro-vibration measurement, but not in three-dimensional surface topography measurement. At the same time, traditional intensity demodulation fiber FP interferometers also have problems such as small measurement range and low stability.

[0005] Therefore, a new technical solution is needed to apply fiber optic FP interferometers to three-dimensional surface topography measurement. Summary of the Invention

[0006] In view of this, embodiments of this specification provide a surface topography measurement device and method, and a method for calculating the surface height of an object, to solve the technical problems of low accuracy, poor stability, small measurement range, and slow measurement speed of existing fiber optic FP interferometric probe ranging principle schemes.

[0007] The embodiments in this specification provide the following technical solutions:

[0008] This specification provides a surface topography measurement device, including: an optical fiber FP interferometer probe and a three-dimensional displacement stage;

[0009] The fiber optic FP interferometer probe consists of a fiber optic head array and a microlens array, with the object to be measured fixed on a three-dimensional displacement stage;

[0010] The light beam is transmitted to the fiber optic FP interferometer probe, and after passing through the fiber optic head array and microlens array, it is emitted from the exit surface of the microlens array and collimated onto the surface of the object under test.

[0011] A three-dimensional displacement stage moves the object under test in three dimensions to measure the surface morphology of the object.

[0012] Preferably, the microlens array is composed of multiple microlens units arranged side by side;

[0013] The exit surface of each microlens unit and the reflection area of ​​the corresponding object under test surface constitute an FP cavity.

[0014] Preferably, the incident surfaces of the fiber optic head array and the microlens units are opposite each other, and the fiber optic head array is composed of multiple fiber optic units, with each fiber optic unit corresponding to a microlens unit.

[0015] Preferably, each optical fiber unit includes an optical fiber, a protective tube, and a frustum;

[0016] The optical fiber is fused to the small cylindrical surface of the frustum, and the protective tube is fused to the large cylindrical surface of the frustum.

[0017] The arc surface of the frustum is opposite to the incident surface of the microlens unit.

[0018] Preferably, the three-dimensional displacement stage includes a first displacement stage, a second displacement stage, and a third displacement stage;

[0019] The first displacement stage is fixedly connected to the second displacement stage. The object to be measured is fixed on the first displacement stage, and the fiber optic head array and microlens array are fixed on the third displacement stage.

[0020] The first and second displacement stages control the object under test to perform two-dimensional motion in the first plane, while the third displacement stage controls the fiber head array and microlens array to perform one-dimensional motion in a direction perpendicular to the first plane.

[0021] Preferably, it also includes: a laser, an optical fiber combiner, an optical fiber circulator, a displacement stage control host computer, a spectrometer, and a computer;

[0022] A laser is a broadband light source used to output laser light;

[0023] The laser beam is split into multiple beams by an optical fiber combiner. These beams are then transmitted to the optical fiber FP interferometer probe after passing through an optical fiber circulator. The beams are emitted from the exit surface of the microlens array and collimated onto the surface of the object under test. The beams are reflected back and forth between the surface of the object under test and the exit surface of the microlens array, forming a multi-beam interference field in multiple FP cavities. The reflected portion of the multi-beam interference field is transmitted to the spectrometer through the optical fiber circulator.

[0024] The three-dimensional displacement stage uses displacement sensors to detect displacement in real time and feeds the displacement data back to the host computer controlling the displacement stage. The host computer controls the three-dimensional displacement stage to perform three-dimensional motion based on the displacement data and preset motion trajectory, and feeds the motion data of the three-dimensional motion back to the computer.

[0025] The computer completes the surface morphology measurement of the object under test based on the motion data fed back from the host computer controlled by the displacement stage and the spectral data on the spectrometer.

[0026] This specification also provides a surface morphology measurement method, applicable to the above-described surface morphology measurement device, including:

[0027] The laser emitted by the laser is split into multiple beams by an optical fiber combiner. These multiple beams are then transmitted to the optical fiber FP interferometer probe after passing through an optical fiber circulator. They are emitted from the exit surface of the microlens array and collimated onto the surface of the object under test. The beams reflect back and forth between the surface of the object under test and the exit surface of the microlens array, forming a multi-beam interference field in multiple FP cavities. The reflected portion of the multi-beam interference field is transmitted to the spectrometer through the optical fiber circulator. The exit surface of each microlens unit in the microlens array and the corresponding reflection area on the surface of the object under test constitute an FP cavity.

[0028] The three-dimensional displacement stage uses displacement sensors to detect displacement in real time and feeds the displacement data back to the host computer controlling the displacement stage. The host computer controls the three-dimensional displacement stage to perform three-dimensional motion based on the displacement data and preset motion trajectory, and feeds the motion data of the three-dimensional motion back to the computer.

[0029] The computer completes the surface morphology measurement of the object under test based on the motion data fed back from the host computer controlled by the displacement stage and the spectral data on the spectrometer.

[0030] Preferably, the three-dimensional displacement platform includes a first displacement platform, a second displacement platform, and a third displacement platform, comprising:

[0031] The first and second displacement stages are adjusted so that the microlens array illuminates the initial sampling point of the object under test. The relative position of the fiber FP interferometer probe and the object under test is adjusted by the third displacement stage to obtain the first distance between the fiber FP interferometer probe and the object under test at the initial sampling point.

[0032] The third displacement stage remains unchanged, and the object under test makes continuous one-dimensional motion in the second direction under the drive of the first displacement stage. The first cavity length data of the FP cavity at each moment in the one-dimensional motion is calculated by the spectral data during the one-dimensional motion. Based on the first cavity length data and the first distance, the second distance of each sampling point on the surface of the object under test in the second direction relative to the initial sampling point is obtained.

[0033] The third displacement stage remains unchanged, and the object under test makes continuous one-dimensional motion in the first direction under the drive of the second displacement stage. The second cavity length data of the FP cavity at each moment in the one-dimensional motion is calculated by the spectral data in the one-dimensional motion. Based on the second cavity length data and the first distance, the third distance of each sampling point on the surface of the object under test in the first direction relative to the initial sampling point is obtained.

[0034] The surface morphology of the object under test is measured based on the first distance, the second distance, and the third distance.

[0035] Preferably, during the process of the object under test undergoing continuous one-dimensional motion in the second direction under the drive of the first displacement stage, and during the process of the object under test undergoing continuous one-dimensional motion in the first direction under the drive of the second displacement stage, the cavity length of the FP cavity formed by the surface of the object under test and the fiber FP interferometer probe changes.

[0036] This specification also provides an embodiment of a method for calculating the surface height of an object, applied to the above-mentioned surface topography measurement method, including:

[0037] Step 1: Obtain the interferogram based on the initial reflection spectrum of the FP cavity, and track and record the center wavelength of a resonance peak in the interferogram. The exit surface of each microlens unit in the microlens array and the corresponding reflection area on the surface of the object under test constitute the FP cavity.

[0038] Step 2: Calibrate the cavity length change and the wavelength change of the center wavelength of the resonant peak of the FP cavity to obtain the correspondence between the cavity length change and the wavelength change.

[0039] Step 3: Based on the wavelength change and corresponding relationship during the measurement of the object under test, obtain the cavity length change of the FP cavity;

[0040] Step 4: Obtain the surface height of the object to be measured based on the change in cavity length.

[0041] Compared with the prior art, the beneficial effects that can be achieved by at least one of the above-mentioned technical solutions adopted in the embodiments of this specification include at least the following: the use of a spectral demodulation probe ranging scheme solves the problems of low accuracy and poor stability of the existing fiber FP interferometric probe ranging principle scheme, thereby improving the ranging accuracy and environmental stability of the fiber FP interferometric surface morphology detection product; the use of a scanning measurement scheme combining fiber head array and microlens array with a three-dimensional displacement stage solves the problems of small measurement range and slow measurement speed of the fiber FP interferometric probe, thereby improving the measurement range and measurement speed of the fiber FP interferometric surface morphology detection product and reducing its cost. Attached Figure Description

[0042] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 This is a schematic diagram of the structure of a surface morphology measuring device provided in an embodiment of this application;

[0044] Figure 2 This is a schematic diagram of the structure of a fiber optic FP interferometer probe provided in an embodiment of this application;

[0045] Figure 3 This is a schematic diagram of the structure of an optical fiber head unit provided in an embodiment of this application. Detailed Implementation

[0046] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0047] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0048] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this application, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number and aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0049] It should also be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this application. The drawings only show the components related to this application and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0050] Additionally, specific details are provided in the following description to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that practice can be carried out without these specific details.

[0051] In optical non-contact measurement methods, compared with traditional interferometers using lens combinations, all-fiber interferometers offer advantages such as compact and flexible structure, high sensitivity, and strong environmental adaptability. Common fiber interferometers include fiber Mach-Zehnder interferometers, fiber Michelson interferometers, and fiber FP interferometers. Among these, fiber Mach-Zehnder and fiber Michelson interferometers suffer from complex system structures and require reference arms in surface topography measurement applications due to their beam splitting path structures.

[0052] Patent document CN107796423A discloses a fiber optic interferometer using microlenses. This patent adds microlens coupling to the output end of the fiber optic interferometer. Utilizing the large numerical aperture and beam-converging effect of the microlenses, it improves the light-gathering capability of the detection system and the spatial resolution of sample detection. However, the use of a beam-splitting interferometer results in a complex probe structure, which is not conducive to the integration of a surface topography detection system. Patent document CN112097680A discloses a surface topography testing device and method based on a multi-cavity FP interferometer. This patent utilizes a fiber optic circulator to construct a multi-cavity fiber FP interferometer, which can simultaneously test the topography of the surface under test, eliminating the need for a scanning process and avoiding the time required for scanning and the mechanical vibration interference caused by scanning. In terms of probe principle, this patent uses intensity demodulation, which has poor stability compared to spectral demodulation. In terms of measurement scheme, multiple sets of fiber FP interferometers are used to completely cover a certain area of ​​the surface under test. This method has disadvantages such as a narrow measurement range, high requirements for optical system design, and a complex overall system. The displacement measurement principle of the FP interferometer is to calculate the displacement change based on the change of intensity signal, which is greatly affected by environmental interference; it does not use a scanning method in surface inspection systems, has requirements on the size of the measured part, and has a narrow range of applications.

[0053] The fiber optic FP interferometer is a common-path interferometer that works by changing the phase of the FP cavity interference field by altering the cavity length. Due to its unique working principle and common-path structure, fiber optic FP interferometers used for displacement measurement offer advantages such as high sensitivity, strong stability, and simple structure.

[0054] However, fiber FP interferometers are currently commonly used in scenarios such as one-dimensional displacement measurement and object micro-vibration measurement, and there are few reports of their application in three-dimensional surface topography measurement. At the same time, traditional intensity demodulation fiber FP interferometers also have problems such as small measurement range and low stability.

[0055] Based on this, the embodiments of this specification propose a processing solution: such as Figure 1 As shown, a fiber optic head array and a microlens array are combined with a three-dimensional displacement stage to measure the surface morphology of the object under test. At the same time, multiple irradiation points on the surface of the object under test are measured to improve the measurement speed.

[0056] The technical solutions provided by the various embodiments of this application are described below with reference to the accompanying drawings.

[0057] like Figures 1 to 3 As shown in the figure, this specification provides a surface topography measurement device, including: an optical fiber FP interferometer probe 104 and a three-dimensional displacement stage.

[0058] The fiber optic FP interferometer probe 104 consists of a fiber optic head array 201 and a microlens array 202, with the object to be measured 105 fixed on a three-dimensional displacement stage.

[0059] In the embodiments of this specification, the three-dimensional displacement stage includes a first displacement stage 106, a second displacement stage 107, and a third displacement stage 203; the first displacement stage 106 is fixedly connected to the second displacement stage 107, the object to be measured is fixed on the first displacement stage 106, and the fiber optic head array 201 and the microlens array 202 are fixed on the third displacement stage 203; the first displacement stage 106 and the second displacement stage 107 control the object to be measured to perform two-dimensional motion in a first plane, and the third displacement stage 203 controls the fiber optic head array and the microlens array to perform one-dimensional motion in a direction perpendicular to the first plane.

[0060] Specifically, after the light beam is transmitted to the fiber optic FP interferometer probe 104, it passes through the fiber optic head array 201 and the microlens array 202, and is emitted from the exit surface of the microlens array 202 and collimated onto the surface of the object under test 105. Furthermore, the object under test 105 is driven to perform three-dimensional motion by a three-dimensional displacement stage in order to measure the surface morphology of the object under test 105.

[0061] Optionally, when the three-dimensional displacement stage moves the object under test 105 in three dimensions, the height between the exit surface of the microlens and the surface of the object under test changes, which causes the cavity length of the FP cavity formed by the exit surface of the microlens and the surface of the object under test to change. The surface height of the object under test 105 can be obtained from the change in the cavity length of the FP cavity, thus completing the surface morphology measurement of the object under test 105.

[0062] In this illustrative embodiment, the surface morphology of the object under test is measured by combining the fiber head array 201 and the microlens array 202 with a three-dimensional displacement stage. This improves the measurement range and speed of the fiber optic FP interferometer surface morphology detection product, reduces costs, improves the detection speed and range of the microscopic surface morphology detection product, and expands the scope of applications.

[0063] Furthermore, such as Figure 2 As shown, the microlens array 202 is composed of multiple microlens units arranged side by side; the exit surface of each microlens unit and the reflection area of ​​the corresponding surface of the object to be measured 105 form an FP cavity; the fiber head array 201 is opposite to the incident surface of the microlens unit, and the fiber head array 201 is composed of multiple fiber units, with each fiber unit corresponding to a microlens unit.

[0064] Furthermore, such as Figure 3As shown, each fiber unit includes an optical fiber 301, a protective tube 302, and a frustum 303; the optical fiber 301 is fused to the small cylindrical surface of the frustum 303, and the protective tube 302 is fused to the large cylindrical surface of the frustum 303; the arc surface of the frustum 303 is opposite to the incident surface of the microlens unit.

[0065] In the embodiments of this specification, the light beam is collimated and emitted onto the surface of the object to be measured 105 through the exit surface of the microlens array.

[0066] The surface topography measuring device in the embodiments of this specification further includes: a laser 101, an optical fiber combiner 102, an optical fiber circulator 103, a displacement stage control host computer 108, a spectrometer 109, and a computer 110.

[0067] The laser 101 is a broadband light source used to output laser light. The laser beam is split into multiple beams by the fiber combiner 102. These beams then pass through the fiber circulator 103 and are transmitted to the fiber FP interferometer probe 104. The beams are emitted from the exit surface of the microlens array 202 and collimated onto the surface of the object under test 105. The beams reflect back and forth between the surface of the object under test 105 and the exit surface of the microlens array 202, forming a multi-beam interference field within the multiple FP cavities. The reflection of this multi-beam interference field... Part of the data is transmitted to the spectrometer 109 via the fiber optic circulator 103; the three-dimensional displacement stage performs real-time displacement detection through the displacement sensor and feeds the displacement data back to the displacement stage control host computer 108 in real time. The displacement stage control host computer 108 controls the three-dimensional displacement stage to perform three-dimensional motion based on the displacement data and the preset motion trajectory, and feeds the motion data of the three-dimensional motion back to the computer 110; the computer 110 completes the surface morphology measurement of the object to be measured 105 based on the motion data fed back by the displacement stage control host computer 108 and the spectral data on the spectrometer 109.

[0068] In one alternative implementation, such as Figures 1 to 3As shown in the embodiments of this specification, a surface topography measurement device includes: a laser 101, an optical fiber combiner 102, an optical fiber circulator 103, an optical fiber FP interferometer probe 104, a test object 105, a one-dimensional displacement stage 106, a one-dimensional displacement stage 107, a displacement stage control host computer 108, a spectrometer 109, and a computer 110. The laser 101 is a broadband light source, and its output wavelength is determined by a combination of the surface reflectivity of the test object 105 and the spectral response range of the spectrometer 109. The test object 105 is fixed on the one-dimensional displacement stage 106, and the one-dimensional displacement stages 106 and 107 are fixed, with no relative movement between them. The one-dimensional displacement stage 203 is a component of the optical fiber FP interferometer probe 104, and its function is to fix the optical fiber head array 201 and the microlens array 202. One-dimensional displacement stages 106, 107, and 203 all utilize internally integrated high-precision displacement sensors, such as optical grating rulers, to detect their displacement in real time and feed the displacement data back to the displacement stage control host computer 108. The host computer 108, using the displacement data from the one-dimensional displacement stages 106, 107, and 203, and combining it with pre-set motion trajectories in each direction, controls the one-dimensional movement of the fiber optic FP interferometer probe 104 in the z-direction via one-dimensional displacement stage 203, and controls the two-dimensional movement of the object under test 105 in the x and y planes via one-dimensional displacement stages 106 and 107. One-dimensional displacement stages 106 and 107 respectively drive the object under test 105 to perform scanning movements in the y and x directions. The computer 110 calculates the relative height of each point on the surface of the object under test based on the displacement information data fed back by the host computer 108 and the spectral data from the spectrometer 109.

[0069] The fiber optic FP interferometer probe 104 includes a fiber optic head array 201, a microlens array 202, and a one-dimensional displacement stage 203. The fiber optic head array 201 and the microlens array 202 constitute a laser collimation system, ensuring that the laser emitted from the microlens array 202 is a well-collimated test beam. The exit surface of the microlens array 202 is planar, and its function is to form an FP interferometer cavity (FP cavity) with the area of ​​the surface of the object under test 105 illuminated by the laser spot. The object under test 105 and the test object 105 are the same object, but in different modes. The fiber optic head array 201 and the microlens array 202 are fixed to the one-dimensional displacement stage 203. The one-dimensional displacement stage 203 drives the fiber optic head array 201 and microlens array 202 to perform one-dimensional motion in the z-direction under the control of the displacement stage control host computer 108. The motion range is the distance between two adjacent focused light spots on the surface of the object under test 105. This distance can be calculated based on the specific parameters of the actual fiber optic head array 201 and microlens array 202 and their distance from the object under test 105. In practical applications, there is no perfectly collimated output beam with a divergence angle of 0°. Therefore, the motion range A of the one-dimensional motion stage 204 can be obtained according to formula (1):

[0070] A=D-D1-2·l1·θ+2·l2·a·θ; (1)

[0071] Where a represents the angular magnification of a single microlens unit in the microlens array; D represents the center-to-center distance between adjacent microlens units; θ represents the numerical aperture of the fiber head unit; D1 represents the core diameter of the optical fiber; l1 represents the distance between the microlens array and the end face of the optical fiber; and l2 represents the distance between the microlens array and the surface of the object under test.

[0072] Furthermore, the fiber optic head array 201 is composed of fiber optic head units, each including an optical fiber 301, a protective tube 302, and a frustum 303. Both the protective tube 302 and the frustum 303 are made of common optical materials and are connected as a single unit via fusion splicing. The specific material type depends on the material of the optical fiber 301 and the fusion splicing process. The optical fiber 301 is fused to the small cylindrical surface of the frustum 303, and the protective tube 302 is fused to the large cylindrical surface of the frustum 303. The measuring surface of the frustum 303 is treated with frosting or blackening to reduce the influence of scattered light on the measurement results. The inner diameter of the protective tube 302 is slightly larger than the diameter of the small cylindrical surface of the fused silica frustum 303 to reduce the stress on the optical fiber at the fusion splice point and protect the fiber optic fusion splice.

[0073] This specification also provides a surface morphology measurement method, applicable to the above-described surface morphology measurement device, including:

[0074] The laser emitted by the laser is split into multiple beams by an optical fiber combiner. These beams are then transmitted to the optical fiber FP interferometer probe via an optical fiber circulator. The beams are emitted from the exit surface of the microlens array and collimated onto the surface of the object under test. The beams reflect back and forth between the object's surface and the exit surface of the microlens array, forming a multi-beam interference field within multiple FP cavities. The reflected portion of this interference field is transmitted to the spectrometer via the optical fiber circulator. The exit surface of each microlens unit in the microlens array and the corresponding reflection area on the surface of the object under test constitute an FP cavity. A three-dimensional displacement stage uses a displacement sensor to detect displacement in real time and feeds the displacement data back to the stage control computer. The control computer uses the displacement data and a preset motion trajectory to control the three-dimensional displacement stage to perform three-dimensional motion and feeds the motion data back to the computer. Based on the motion data fed back from the control computer and the spectral data from the spectrometer, the computer completes the surface morphology measurement of the object under test.

[0075] Specifically, the laser emitted by laser 101 is split into several beams by fiber optic combiner 102. The beams are transmitted to fiber optic FP interferometer probe 104 through fiber optic circulator group 103. The beams are emitted from the end face of microlens array 202 inside fiber optic FP interferometer probe 104 and collimated onto the test surface 105. The beams are reflected back and forth between the test surface 105 and the exit surface of microlens array 202, ultimately forming a multi-beam interference field. The exit surface of each microlens unit in microlens array 202 and its corresponding reflection area on the test surface constitute an FP cavity. The reflection end of the multi-beam interference field is transmitted to spectrometer 109 through fiber optic circulator group 103. The change in cavity length of each FP cavity is calculated based on the spectral changes to obtain the relative height of each point on the surface of the test object.

[0076] The three-dimensional displacement platform includes a first displacement platform, a second displacement platform, and a third displacement platform. The process involves: adjusting the first and second displacement platforms so that the microlens array illuminates the initial sampling point of the object under test; adjusting the relative position of the fiber FP interferometer probe and the object under test using the third displacement platform to obtain the first distance between the fiber FP interferometer probe and the object under test at the initial sampling point; keeping the third displacement platform unchanged; and having the object under test undergo continuous one-dimensional motion in the second direction under the influence of the first displacement platform. The first cavity length data of the FP cavity at each moment during the one-dimensional motion is calculated using the spectral data. Based on the first cavity length data and the first distance, the second distance of each sampling point on the surface of the object under test in the second direction relative to the initial sampling point is obtained. The second direction is... Figure 1The third displacement stage remains unchanged, and the object under test undergoes continuous one-dimensional motion in the first direction under the influence of the second displacement stage. The second cavity length of the FP cavity at each moment during the one-dimensional motion is calculated using the spectral data. Based on the second cavity length and the first distance, the third distance of each sampling point on the surface of the object under test in the first direction relative to the initial sampling point is obtained. The first direction is... Figure 1 The x-direction in the measurement; based on the first distance, the second distance, and the third distance, the surface morphology measurement of the object to be measured is completed.

[0077] In the process of the object under test making continuous one-dimensional motion in the second direction under the drive of the first displacement stage, and the object under test making continuous one-dimensional motion in the first direction under the drive of the second displacement stage, the cavity length of the FP cavity formed by the surface of the object under test and the fiber FP interferometer probe changes.

[0078] Specifically, any point on the object under test is selected as the initial sampling point. One-dimensional displacement stages 106 and 107 are adjusted so that the microlens array 202 illuminates the initial sampling point. The relative position of the fiber optic FP interferometer probe 104 and the object under test is adjusted using the one-dimensional displacement stage 203 to maximize the feedback signal intensity. The first distance H0 between the interferometer probe 104 and the object under test is obtained based on feedback from a high-precision displacement sensor (such as a grating ruler) integrated within the one-dimensional displacement stage 203. The one-dimensional displacement stage 203 remains in its original position, and the object under test 105 undergoes continuous one-dimensional motion in the y-direction under the influence of the one-dimensional displacement stage 106. During this motion, the relative distance between each point on the object's surface and the fiber optic FP interferometer probe 104 changes, i.e., the cavity length of the FP cavity formed by the object's surface, corresponding points, and the fiber optic FP interferometer probe 104 changes. The first cavity length data H of the FP cavity at each moment during the motion is calculated through spectral changes. t1 H t2 ...H tn Where t1, t2...tn represent different times, and H t1 H t2 ...H tn Let H represent the cavity length at different times. Then, the height difference between each sampling point on the surface of the object under test in the y-direction relative to the initial sampling point, i.e., the second distance, is: H. t1 -H0、H t2 -H0……H tn-H0; complete the scanning of the surface of the object under test in the y direction; similarly, the one-dimensional displacement stage 203 remains unchanged, and the object under test 105 moves continuously in the x direction under the drive of the one-dimensional displacement stage 107, obtaining the third distance of each sampling point on the surface of the object under test in the x direction relative to the initial sampling point, thus completing the scanning of the surface of the object under test in the x direction; after the computer 110 calculates the relative height difference of each sampling point on the surface of the object under test based on the first distance, the second distance and the third distance, it combines the distance H0 between the initial sampling point and the interference probe 104 to complete the restoration and measurement of the surface morphology of the object under test.

[0079] The embodiments in this specification employ a spectral demodulation probe ranging scheme to improve the ranging accuracy and environmental stability of fiber optic FP interferometric surface topography detection products, enhance the detection accuracy of microscopic surface topography detection products, and expand their application scenarios.

[0080] This specification also provides an embodiment of a method for calculating the surface height of an object, applied to the above-mentioned surface topography measurement method, including:

[0081] Step 1: Based on the initial reflection spectrum of the FP cavity, obtain the interference pattern and track and record the center wavelength of a resonance peak in the interference pattern. The exit surface of each microlens unit in the microlens array and the corresponding reflection area on the surface of the object under test constitute the FP cavity.

[0082] Step 2: Calibrate the cavity length change and the wavelength change of the center wavelength of the resonant peak of the FP cavity to obtain the correspondence between the cavity length change and the wavelength change.

[0083] Step 3: Based on the wavelength change and corresponding relationship during the measurement of the object under test, obtain the cavity length change of the FP cavity.

[0084] Step 4: Obtain the surface height of the object to be measured based on the change in cavity length.

[0085] Specifically, the initial reflection spectra of each FP interferometer cavity are first obtained. The intensity of the reflected light interference spectrum output from each FP cavity can be expressed by formula (2):

[0086]

[0087] Where j = 1, 2, 3, ..., n, I j Indicates the light intensity of the interference field; A j B represents the intensity of reflected light from the exit surface of a single microlens unit. j Φ represents the intensity of light reflected from the surface of the object being measured. j Indicates the phase of the FP cavity; n air L represents the refractive index of air. jλ represents the distance from the exit surface of a single microlens unit to the irradiated surface of the object under test; λ represents the center wavelength of the resonance peak. When the phase meets the interferometer conditions, a stable interferogram will be formed on the spectrometer, forming multiple resonance peaks. The center wavelength of a certain resonance peak is tracked and recorded.

[0088] Then: calibrate the cavity length variation of the FP cavity and the wavelength variation of the center wavelength of the tracked resonant peak. Figure 1 In the structure, the object under test 105 is replaced by a planar optical element such as a mirror or a parallel plate. The surface roughness and surface reflectivity of the planar optical element are similar to those of the object under test 105. The test light emitted from the fiber optic FP interferometer probe 104 illuminates the planar optical element. The fiber optic FP interferometer probe 104 is moved along the z-direction using the third displacement stage 203. When the cavity length of the FP cavity changes, the center wavelength of the tracked resonance peak will change. The wavelength drift and displacement satisfy formula (3).

[0089]

[0090] in, λ represents the phase of the FP cavity; n represents the air refractive index; L represents the initial length of the FP cavity; ΔL represents the change in the length of the FP cavity due to the movement of the third displacement stage 203; λ represents the initial center wavelength of the resonance peak; Δλ represents the drift of the center wavelength of the resonance peak due to the change in the length of the FP cavity.

[0091] Specifically, the high-precision displacement sensor integrated inside the third displacement stage 203, such as a grating ruler, provides real-time feedback on the cavity length of the FP cavity formed by the fiber optic FP interferometer probe 104 and the standard planar optical element during the movement of the third displacement stage 203 along the z-direction. This is the distance between the fiber optic FP interferometer probe 104 and the standard planar optical element. Combined with the center wavelength drift of the tracked resonance peak fed back by the spectrometer 109, a one-to-one correspondence is established between the center wavelength drift of the tracked resonance peak and the change in the FP cavity length. This can be represented by a mapping table or a mapping formula.

[0092] Then: During the measurement, track the change in the center wavelength of a certain peak in the reflection interference spectrum, and according to the correspondence determined by the above calibration, such as a mapping table or mapping formula, compare or calculate the change in the cavity length of the corresponding FP cavity.

[0093] Finally, the surface height of the object under test is obtained based on the change in cavity length.

[0094] The embodiments in this specification track the change in wavelength of a certain peak of the reflection spectrum of the interference field to complete one-dimensional displacement measurement. Compared with the intensity demodulation fiber FP interferometer in the prior art, it has higher sensitivity and stronger anti-interference ability.

[0095] In the embodiments of this specification, the FP interferometric probe is composed of a fiber optic head array and a microlens array coupled together, which can simultaneously measure multiple illumination points on the surface of the object to be measured, thereby improving the measurement speed.

[0096] The embodiments in this specification employ non-contact measurement to ensure that the surface of the object being measured is not damaged.

[0097] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on describing the differences from other embodiments. In particular, the product embodiments described later are relatively simple since they correspond to the methods; relevant parts can be referred to the descriptions in the system embodiments.

[0098] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A surface morphology measuring device, characterized in that, include: Fiber FP interferometer probe and three-dimensional displacement stage, fiber optic circulator, spectrometer; The fiber FP interferometer probe consists of a fiber head array and a microlens array, and the object to be measured is fixed on the three-dimensional displacement stage. The microlens array is composed of multiple microlens units arranged side by side; the exit surface of each microlens unit and the reflection area of ​​the corresponding surface of the object to be tested form an FP cavity; The light beam is transmitted to the fiber optic FP interferometer probe, passes through the fiber optic head array and the microlens array, and is emitted from the exit surface of the microlens array. It is then collimated and illuminates the surface of the object under test. The beam is reflected back and forth between the surface of the object under test and the exit surface of the microlens array, forming a multi-beam interference field in multiple FP cavities. The reflected portion of the multi-beam interference field is transmitted to the spectrometer through the fiber optic circulator. The change in the cavity length of each FP cavity is calculated based on the spectral changes to obtain the relative height of each point on the surface of the object under test. When the three-dimensional displacement stage moves the object under test in three dimensions, the height of the microlens unit relative to the surface of the object under test changes, causing a change in the cavity length of the FP cavity formed by the exit surface of the microlens unit and the surface of the object under test. The surface height of the object under test is then obtained based on the change in the cavity length of the FP cavity, so as to measure the surface morphology of the object under test.

2. The surface morphology measuring device according to claim 1, characterized in that, The fiber optic head array is opposite to the incident surface of the microlens unit. The fiber optic head array is composed of multiple fiber optic units, and each of the multiple fiber optic units corresponds to one of the multiple microlens units.

3. The surface morphology measuring device according to claim 2, characterized in that, Each optical fiber unit includes an optical fiber, a protective tube, and a frustum; The optical fiber is fused to the small cylindrical surface of the frustum, and the protective tube is fused to the large cylindrical surface of the frustum. The arc surface of the frustum is opposite to the incident surface of the microlens unit.

4. The surface morphology measuring device according to claim 1, characterized in that, The three-dimensional displacement stage includes a first displacement stage, a second displacement stage, and a third displacement stage; The first displacement stage is fixedly connected to the second displacement stage, the object to be measured is fixed on the first displacement stage, and the fiber optic head array and the microlens array are fixed on the third displacement stage. The first and second displacement stages control the object under test to perform two-dimensional motion in a first plane, and the third displacement stage controls the fiber head array and the microlens array to perform one-dimensional motion in a direction perpendicular to the first plane.

5. The surface morphology measuring device according to any one of claims 1-4, characterized in that, Also includes: Laser, fiber optic combiner, displacement stage control host computer and computer; The laser is a broadband light source used to output laser light; The laser beam is split into multiple beams by the fiber combiner, and the multiple beams are transmitted to the fiber FP interferometer probe after passing through the fiber circulator. The multiple beams are emitted from the exit surface of the microlens array and collimated onto the surface of the object under test. The three-dimensional displacement stage uses displacement sensors to detect displacement in real time and feeds the displacement data back to the displacement stage control host computer in real time. The displacement stage control host computer controls the three-dimensional displacement stage to perform three-dimensional motion based on the displacement data and preset motion trajectory, and feeds the motion data of the three-dimensional motion back to the computer. The computer completes the surface morphology measurement of the object under test based on the motion data fed back by the host computer controlled by the displacement stage and the spectral data on the spectrometer.

6. A method for measuring surface morphology, characterized in that, The surface topography measuring device according to any one of claims 1-5 comprises: The laser emitted by the laser is split into multiple beams by an optical fiber combiner. These multiple beams are then transmitted to the optical fiber FP interferometer probe after passing through an optical fiber circulator. They are emitted from the exit surface of the microlens array and collimated onto the surface of the object under test. The beams are reflected back and forth between the surface of the object under test and the exit surface of the microlens array, forming a multi-beam interference field in multiple FP cavities. The reflected portion of the multi-beam interference field is transmitted to the spectrometer through the optical fiber circulator. The exit surface of each microlens unit in the microlens array and the corresponding reflection area on the surface of the object under test constitute the FP cavity. The three-dimensional displacement stage uses displacement sensors to detect displacement in real time and feeds the displacement data back to the displacement stage control host computer in real time. The displacement stage control host computer controls the three-dimensional displacement stage to perform three-dimensional motion based on the displacement data and the preset motion trajectory, and feeds the motion data of the three-dimensional motion back to the computer. The computer completes the surface morphology measurement of the object under test based on the motion data fed back by the host computer controlled by the displacement stage and the spectral data on the spectrometer.

7. The surface morphology measurement method according to claim 6, characterized in that, The three-dimensional displacement platform includes a first displacement platform, a second displacement platform, and a third displacement platform, including: The first and second displacement stages are adjusted so that the microlens array illuminates the initial sampling point of the object under test. The relative position of the fiber FP interferometer probe and the object under test is adjusted by the third displacement stage to obtain the first distance between the fiber FP interferometer probe and the object under test at the initial sampling point. The third displacement stage remains unchanged, and the object under test performs continuous one-dimensional motion in the second direction under the drive of the first displacement stage. The first cavity length data of the FP cavity at each moment in the one-dimensional motion is calculated by the spectral data during the one-dimensional motion. Based on the first cavity length data and the first distance, the second distance of each sampling point on the surface of the object under test in the second direction relative to the initial sampling point is obtained. The third displacement stage remains unchanged, and the object under test performs continuous one-dimensional motion in the first direction under the drive of the second displacement stage. The second cavity length data of the FP cavity at each moment in the one-dimensional motion is calculated by the spectral data in the one-dimensional motion. Based on the second cavity length data and the first distance, the third distance of each sampling point on the surface of the object under test in the first direction relative to the initial sampling point is obtained. The surface morphology measurement of the object under test is completed based on the first distance, the second distance, and the third distance.

8. The surface morphology measurement method according to claim 7, characterized in that, During the process of the object under test undergoing continuous one-dimensional motion in the second direction under the drive of the first displacement stage, and during the process of the object under test undergoing continuous one-dimensional motion in the first direction under the drive of the second displacement stage, the cavity length of the FP cavity formed by the surface of the object under test and the fiber FP interferometric probe changes.

9. A method for calculating the height of an object's surface, characterized in that, The surface topography measurement method applied to any one of claims 6-8 includes: Step 1: Obtain the interferogram based on the initial reflection spectrum of the FP cavity, and track and record the center wavelength of a resonance peak in the interferogram. The exit surface of each microlens unit in the microlens array and the corresponding reflection area on the surface of the object under test constitute the FP cavity. Step 2: Calibrate the cavity length change of the FP cavity and the wavelength change of the center wavelength of the resonant peak to obtain the correspondence between the cavity length change and the wavelength change; Step 3: Based on the wavelength change and the corresponding relationship during the measurement of the object under test, obtain the cavity length change of the FP cavity; Step 4: Obtain the surface height of the object under test based on the change in cavity length.

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