Interferometer light path calibration method

Abstract

The invention relates to the technical field of interferometers, in particular to an interferometer light path calibration method and method.The interferometer light path calibration method comprises the steps that an interferometer is started, a measurement light beam and a reference light beam generated by the interferometer are combined through a polarization splitting prism and then are emitted towards an observation screen, and a measurement light spot and a reference light spot are formed on the observation screen; adjusting a reflector group of the interferometer to enable the measurement light spot to coincide with the reference light spot; the observation screen is removed, an optical fiber is connected, and the combined light beams are coupled into the optical fiber; the output end of the optical fiber is connected to detection equipment, a light current signal is obtained through detection of the detection equipment, and the ratio of an alternating-current voltage component to a direct-current voltage component is shown; and a lambda / 4 wave plate in the interferometer is adjusted until the ratio reaches a preset condition, and calibration is completed. The method is accurate and reliable, is simple and convenient to operate, has repeatability, can give consideration to space alignment and polarization matching, and facilitates the improvement of the stability and measurement precision of an interference system.

Description

Technical Field

[0001] The present application relates to the technical field of interferometers, and in particular to a method for calibrating an interferometer optical path. Background Art

[0002] As a high-precision optical measuring instrument, the interferometer is widely used for the precise measurement of physical quantities such as length, displacement, vibration, refractive index, and surface topography. Its operating principle is based on the interference effect of light, extracting measured information by measuring the phase difference between the measurement beam and a reference beam. To obtain a stable and high-contrast interferometer signal, it is crucial that the measurement and reference beams are well matched in terms of space, polarization, and phase.

[0003] In practical systems, due to factors such as optical component assembly errors, mechanical stress, and temperature drift, the measurement and reference beams often suffer from spatial misalignment and polarization mismatch. Spatial misalignment prevents the two beams from fully overlapping after combining, reducing the intensity coupling efficiency; while polarization mismatch significantly weakens the contrast of the interference signal, affecting the system's signal-to-noise ratio and measurement accuracy.

[0004] Traditional optical path calibration methods typically rely on visually observing interference fringes or using cameras to capture the light spot distribution, followed by manual adjustment of mirrors to achieve rough alignment. These methods are highly subjective, have limited accuracy, and are difficult to quantitatively evaluate. Furthermore, for interferometric systems that use polarization beam splitters (PBSs) for beam combining, optimizing the polarization state is often overlooked, resulting in suboptimal interferometric efficiency even with good spatial alignment. Summary of the Invention

[0005] The purpose of this application is to provide an interferometer optical path calibration method that is accurate and reliable, easy to operate and repeatable, can take into account both spatial alignment and polarization matching, and is conducive to improving the stability and measurement accuracy of the interferometer system.

[0006] This application is implemented as follows: The interferometer optical path calibration method provided in this application includes: The interferometer is started, and the measuring beam and the reference beam generated by the interferometer are combined through a polarization beam splitter prism and emitted toward the observation screen, thereby forming a measuring light spot and a reference light spot on the observation screen; Adjusting the reflective mirror assembly of the interferometer so that the measurement light spot and the reference light spot coincide with each other; The observation screen is removed and an optical fiber is connected, and the combined light beam is coupled into the optical fiber; The output end of the optical fiber is connected to a detection device, and a photocurrent signal is obtained by detection by the detection device, and the ratio of the AC voltage component to the DC voltage component is displayed; The λ / 4 wave plate in the interferometer is adjusted, and the ratio of the AC voltage component to the DC voltage component is observed until the ratio of the AC voltage component to the DC voltage component reaches a preset condition, thereby completing the calibration.

[0007] As an optional implementation manner, the method further includes adjusting the λ / 4 wave plate in the interferometer and observing the ratio of the AC voltage component to the DC voltage component until the ratio of the AC voltage component to the DC voltage component reaches a preset condition and the calibration is completed: Removing the measuring beam, detecting the output AC signal of the reference beam through a detection device, and obtaining a reference beam leakage signal component; removing the reference beam, detecting the output AC signal of the measuring beam through a detection device, and obtaining a measuring beam leakage signal component; The λ / 4 wave plate is adjusted until the ratio of the output AC signal of the reference beam to the reference beam leakage signal component and the ratio of the output AC signal of the measurement beam to the measurement beam leakage signal component meet preset conditions to achieve polarization crosstalk suppression.

[0008] As an optional embodiment, before removing the measuring beam, detecting the output AC signal of the reference beam using a detection device, and obtaining a reference beam leakage signal component; and removing the reference beam, detecting the output AC signal of the measuring beam using a detection device, and obtaining a measuring beam leakage signal component, the method includes: Block the movable reflector and the fixed reflector at the same time, and obtain the dark AC signal in the interferometer through the detection device, which is recorded as AC1; The removing of the measuring beam, detecting the output AC signal of the reference beam by a detection device, and obtaining the reference beam leakage signal component includes: Block the moving mirror in the interferometer and detect the output AC signal of the reference beam through the detection device, which is recorded as AC2; where the reference beam leakage signal component = AC2-AC1; The removing of the reference beam, detecting the output AC signal of the measuring beam by a detection device, and obtaining the leakage signal component of the measuring beam comprises: The fixed reflector in the interferometer is blocked, and the output AC signal of the measuring beam is detected by the detection device, which is recorded as AC3; among which, the leakage signal component of the measuring beam = AC3-AC1.

[0009] As an optional embodiment, adjusting the λ / 4 wave plate until the ratio of the output AC signal of the reference beam to the reference beam leakage signal component and the ratio of the output AC signal of the measurement beam to the measurement beam leakage signal component meet a preset condition to achieve polarization crosstalk suppression includes: The λ / 4 wave plate is rotated around the optical axis until the ratio of the minimum value of AC2 to the leakage signal component of the reference beam and the ratio of the minimum value of AC3 to the leakage signal component of the measurement beam reach preset conditions.

[0010] As an optional embodiment, when adjusting the λ / 4 wave plate fails to make the ratio of the output AC signal of the reference beam to the reference beam leakage signal component and the ratio of the output AC signal of the measurement beam to the measurement beam leakage signal component meet preset conditions, the method further includes: Replace the polarizing beamsplitter prism with one with a higher extinction ratio.

[0011] As an optional implementation manner, adjusting the reflective mirror assembly of the interferometer so that the measurement light spot and the reference light spot coincide with each other includes: Adjust the angle between the reflector group and the optical axis; The rotating prism group in the interferometer is rotated around the optical axis.

[0012] As an optional implementation, removing the measuring beam, detecting the output AC signal of the reference beam by a detection device, and obtaining the reference beam leakage signal component includes: The reference beam leakage signal component = AC2-AC1+AC4; wherein AC4 is the noise signal present in the detection device; The removing of the reference beam, detecting the output AC signal of the measuring beam by a detection device, and obtaining the leakage signal component of the measuring beam comprises: Measure the beam leakage signal component = AC3-AC1+AC4.

[0013] As an optional implementation manner, adjusting the reflective mirror assembly of the interferometer so that the measurement light spot and the reference light spot coincide with each other includes: Measure the center distance between the reference spot and the measurement spot, denoted as d; The reflecting mirror group of the interferometer is adjusted so that d≤D*N%; wherein the distance from the observation screen to the polarization beam splitter prism is recorded as D; and the value range of N is 5-6.

[0014] As an optional implementation manner, adjusting the λ / 4 wave plate in the interferometer and observing the ratio of the AC voltage component to the DC voltage component until the ratio of the AC voltage component to the DC voltage component reaches a preset condition, and completing the calibration includes: The ratio of the AC voltage component to the DC voltage component is greater than or equal to 0.7.

[0015] As an optional embodiment, adjusting the λ / 4 wave plate until the ratio of the output AC signal of the reference beam to the reference beam leakage signal component and the ratio of the output AC signal of the measurement beam to the measurement beam leakage signal component meet a preset condition to achieve polarization crosstalk suppression includes: The ratio of the output AC signal of the reference beam to the reference beam leakage signal component is greater than or equal to 7, and the ratio of the output AC signal of the measurement beam to the measurement beam leakage signal component is greater than or equal to 7.

[0016] The beneficial effects of this application include: The interferometer optical path calibration method provided by the present application realizes the intuitive alignment of the spatial light spot by combining with an observation screen, and uses a photodetector to provide quantitative feedback on the ratio of the AC and DC components of the interference signal, thereby realizing the transformation from subjective experience adjustment to objective and precise control. The embodiment of the present application not only ensures the spatial overlap of the measurement beam and the reference beam by adjusting the reflector group to improve the coupling efficiency, but also further optimizes the polarization matching state of the two beams by adjusting the λ / 4 wave plate to maximize the interference contrast, thereby significantly improving the signal-to-noise ratio and system stability of the interference signal. The entire calibration process is simple to operate and highly repeatable, effectively overcoming the problem of insufficient calibration accuracy caused by human judgment errors and polarization mismatch in traditional methods, thereby improving the measurement accuracy, environmental adaptability and long-term working reliability of the interferometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0018] Figure 1 This is a flow chart of the interferometer optical path calibration method according to an embodiment of the present application; Figure 2 Schematic diagram of the existing single-axis interferometer structure. DETAILED DESCRIPTION

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Generally, the components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in the present application without creative work are within the scope of protection of the present application.

[0021] It should be noted that similar reference numerals and letters represent similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings. In addition, the terms "first," "second," "third," etc. are used only to distinguish the descriptions and are not to be understood as indicating or implying relative importance.

[0022] It should also be noted that, in the description of this application, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0023] In practical systems, due to factors such as optical component assembly errors, mechanical stress, and temperature drift, the measurement and reference beams often suffer from spatial misalignment and polarization mismatch. Spatial misalignment prevents the two beams from fully overlapping after combining, reducing the intensity coupling efficiency; while polarization mismatch significantly weakens the contrast of the interference signal, affecting the system's signal-to-noise ratio and measurement accuracy.

[0024] Traditional optical path calibration methods typically rely on visually observing interference fringes or using cameras to capture the light spot distribution, followed by manual adjustment of mirrors to achieve rough alignment. These methods are highly subjective, have limited accuracy, and are difficult to quantitatively evaluate. Furthermore, for interferometric systems that use polarization beam splitters (PBSs) for beam combining, optimizing the polarization state is often overlooked, resulting in suboptimal interferometric efficiency even with good spatial alignment.

[0025] In order to solve the above technical problems, an embodiment of the present application provides an interferometer optical path calibration method.

[0026] Reference Figure 1 As shown, the interferometer optical path calibration method provided in the embodiment of the present application includes: Initialize and position the interferometer, start the interferometer, and combine the measurement beam and reference beam generated by the interferometer through a polarization beam splitter prism and emit toward the observation screen, forming a measurement spot and a reference spot on the observation screen; Adjust the reflector group of the interferometer so that the measurement spot and the reference spot coincide; Remove the observation screen and connect the optical fiber, and couple the combined light beam into the optical fiber; The output end of the optical fiber is connected to a detection device, which detects the photocurrent signal and displays the ratio of the AC voltage component to the DC voltage component. Adjust the λ / 4 wave plate in the interferometer and observe the ratio of the AC voltage component to the DC voltage component until the ratio reaches the preset condition, and the calibration is completed.

[0027] It should be noted that the interferometer optical path calibration method provided in the embodiment of the present application uses a step-by-step, quantifiable closed-loop feedback mechanism to collaboratively optimize the spatial alignment and polarization matching state of the interferometer optical path to maximize the quality of the interference signal.

[0028] First, in the embodiment of the present application, an observation screen is provided at the receiving end, and the light spot formed by the measuring beam and the reference beam is visually observed by the human eye or an imaging device. The spatial overlap of the two light spots is achieved by adjusting the reflector group, thereby ensuring good mode matching of the two beams after beam combining, thereby improving the subsequent fiber coupling efficiency. Subsequently, the observation screen is removed and the optical fiber and detection equipment are connected to convert the combined light into a photocurrent signal, from which the AC voltage component and the DC voltage component are extracted, and the ratio of the AC voltage component to the DC voltage component (AC / DC) is calculated. This ratio directly reflects the contrast of the interference signal.

[0029] It should be noted that the detection equipment includes a photodetector and an oscilloscope. In DC coupling mode, the voltage difference between the zero level and the average level of the signal on the oscilloscope is the DC voltage component (DC). The voltage difference between the highest and lowest points of the signal read on the oscilloscope is the peak-to-peak AC voltage, and half of this value is the AC voltage component (AC).

[0030] This embodiment of the present application changes the polarization state of the beam by rotating at least one λ / 4 wave plate until the AC / DC ratio reaches a preset maximum value, indicating that the polarization states of the measurement and reference beams are optimally matched, resulting in optimal interferometry efficiency. This embodiment of the present application upgrades traditional subjective observation to objective, quantitative electrical signal feedback, balancing spatial alignment with polarization optimization, significantly improving calibration accuracy and the overall performance of the interferometer system.

[0031] The interferometer optical path calibration method provided in the embodiment of the present application realizes the intuitive alignment of the spatial light spot by combining with an observation screen, and uses a photodetector to provide quantitative feedback on the ratio of the AC and DC components of the interference signal, thereby realizing the transition from subjective experience adjustment to objective and precise control. The embodiment of the present application not only ensures the spatial overlap of the measurement beam and the reference beam by adjusting the reflector group to improve the coupling efficiency, but also further optimizes the polarization matching state of the two beams by adjusting the λ / 4 wave plate to maximize the interference contrast, thereby significantly improving the signal-to-noise ratio of the interference signal and the system stability. The entire calibration process is simple to operate and highly repeatable, effectively overcoming the problem of insufficient calibration accuracy caused by human judgment errors and polarization mismatch in traditional methods, thereby improving the measurement accuracy, environmental adaptability and long-term working reliability of the interferometer.

[0032] The interferometer can be calibrated using the above optical path calibration method. The following describes the structure of a common single-axis interferometer. Figure 2 As shown, 45° linearly polarized light is emitted from laser 1, passes through rotating prism assembly 2, and then passes through λ / 4 wave plate 3 and λ / 2 wave plate 4 before passing through polarization beam splitter prism 5. At this point, parallel polarized light is transmitted through polarization beam splitter prism 5, while perpendicular polarized light is reflected at the interface of polarization beam splitter prism 5.

[0033] After passing through the 45° λ / 4 wave plate 6, the parallel polarized light is reflected by the movable reflector 7 and passes through the 45° λ / 4 wave plate 6 again. At this time, the polarization state of the parallel polarized light is converted to vertical polarized light. The vertically polarized light is reflected at the interface of the polarization beam splitter prism 5, passes through the three reflection surfaces of the corner cone 10, and then emerges in parallel and reflects at the interface of the polarization beam splitter prism 5. The reflected light passes through the 45° λ / 4 wave plate 6, is reflected by the movable reflector 7, and passes through the 45° λ / 4 wave plate 6 again. At this time, the polarization state of the vertically polarized light is converted to parallel polarized light, which is transmitted through the polarization beam splitter prism 5 and emerges at the laser receiving end 11.

[0034] After passing through the 45° λ / 4 wave plate 8, the vertically polarized light is reflected by the fixed reflector 9 and passes through the 45° λ / 4 wave plate 8 again. At this time, the polarization state of the vertically polarized light is converted to parallel polarized light. The parallel polarized light is transmitted at the interface of the polarization beam splitter prism 5, passes through the three reflection surfaces of the corner cone 10, and then is emitted in parallel and transmitted at the interface of the polarization beam splitter prism 5. The transmitted light passes through the 45° λ / 4 wave plate 8, is reflected by the fixed reflector 9, and passes through the 45° λ / 4 wave plate 8 again. At this time, the polarization state of the parallel polarized light is converted to vertical polarized light, which is reflected by the polarization beam splitter prism 5 and emitted to the laser receiving end 11.

[0035] As an optional implementation, adjusting the λ / 4 wave plate in the interferometer and observing the ratio of the AC voltage component to the DC voltage component until the ratio of the AC voltage component to the DC voltage component reaches a preset condition, and after completing the calibration, the method further includes: Removing the measuring beam, detecting the output AC signal of the reference beam through a detection device, and obtaining a reference beam leakage signal component; removing the reference beam, detecting the output AC signal of the measuring beam through a detection device, and obtaining a measuring beam leakage signal component; Adjust the λ / 4 wave plate until the ratio of the output AC signal of the reference beam to the reference beam leakage signal component and the ratio of the output AC signal of the measurement beam to the measurement beam leakage signal component meet the preset conditions to achieve polarization crosstalk suppression.

[0036] It should be noted that after completing the primary calibration based on the AC / DC ratio, the embodiment of the present application further introduces a secondary calibration step for polarization crosstalk suppression, which achieves refined optimization of the system's polarization isolation performance by separating and detecting the undesired leakage signals of the measurement optical path and the reference optical path.

[0037] The working principle is as follows: After a single calibration to ensure optimal interference contrast, the measurement beam or reference beam is sequentially blocked, allowing only a single path of light to operate. Ideally, there should be no interference signal (the AC component is zero), but due to optical path crosstalk caused by polarization mismatch, a non-zero AC signal (i.e., a leakage signal component) will still be detected. The output AC signal and its leakage component of the reference and measurement beams when operating independently are obtained through detection equipment, and the ratio of the two is calculated as a quantitative indicator of the degree of crosstalk. The λ / 4 wave plate is then adjusted again to change the polarization state of the beam to minimize this ratio until the preset conditions are met. The above process essentially further enhances the extinction effect of the polarization beam splitter (PBS) through feedback control, effectively suppressing cross-path light leakage, thereby reducing system noise, improving the signal-to-noise ratio, and long-term stability, achieving a comprehensive calibration from "high interference efficiency" to "high polarization purity."

[0038] Furthermore, the measuring beam is removed, and the output AC signal of the reference beam is detected by a detection device to obtain a reference beam leakage signal component. Before removing the reference beam, detecting the output AC signal of the measuring beam by a detection device to obtain a measuring beam leakage signal component, the method includes: Block the movable reflector and the fixed reflector at the same time, and obtain the dark AC signal in the interferometer through the detection device, which is recorded as AC1; Remove the measurement beam, detect the output AC signal of the reference beam through the detection device, and obtain the reference beam leakage signal components including: Block the moving mirror in the interferometer and detect the output AC signal of the reference beam through the detection device, which is recorded as AC2; where the reference beam leakage signal component = AC2-AC1; Remove the reference beam, detect the output AC signal of the measurement beam through the detection device, and obtain the leakage signal components of the measurement beam including: The fixed reflector in the interferometer is blocked, and the output AC signal of the measuring beam is detected by the detection device, which is recorded as AC3; among which, the leakage signal component of the measuring beam = AC3-AC1.

[0039] It should be noted that before implementing the above steps, it is necessary to fix the initial position of the Xi'an contact tight motion too. In AC coupling mode, the corresponding AC signals are read on the oscilloscope when the movable reflector, the fixed reflector, and both the movable reflector and the fixed reflector are blocked.

[0040] As an optional embodiment, adjusting the λ / 4 wave plate until the ratio of the output AC signal of the reference beam to the reference beam leakage signal component and the ratio of the output AC signal of the measurement beam to the measurement beam leakage signal component meet preset conditions to achieve polarization crosstalk suppression includes: The λ / 4 wave plate is rotated around the optical axis until the ratio of the minimum value of AC2 to the leakage signal component of the reference beam and the ratio of the minimum value of AC3 to the leakage signal component of the measurement beam reach preset conditions.

[0041] The present application sequentially blocks the reference beam or the measurement beam, measures the minimum AC signal AC2 when only the measurement beam is working, and the minimum AC signal AC3 when only the reference beam is working, respectively, and obtains the leakage signal components of the reference beam and the measurement beam in combination with the dark signal in the completely shading state; then rotates the λ / 4 wave plate around the optical axis to adjust its fast axis direction to change the polarization state of the light beam, thereby optimizing its reflection / transmission behavior in the polarization beam splitter prism and suppressing light leakage in undesired paths; when the ratio of AC2 to the leakage signal component of the measurement beam, and the ratio of AC3 to the leakage signal component of the reference beam both reach the preset conditions, it indicates that the system polarization isolation has reached the optimal level, effectively reducing the noise and phase error introduced by crosstalk, and improving the stability and measurement accuracy of the interferometer.

[0042] It should be noted that the two λ / 4 wave plates can be rotated around the optical axis by adjusting the hobbing ring.

[0043] The embodiments of the present application utilize an adjustable hobbing ring to achieve precise synchronous rotation of two λ / 4 wave plates. This mechanism utilizes a mechanical transmission structure to precisely control the wave plate's azimuth angle, thereby optimizing the polarization matching of the interferometer's optical beams. The hobbing ring is linked to the λ / 4 wave plate holder. Rotating the hobbing ring drives the two λ / 4 wave plates to rotate synchronously about the optical axis, ensuring consistent polarization state changes in the measurement and reference optical paths and avoiding asymmetry errors introduced by unilateral adjustment. This structure allows for continuous and fine-tuned adjustment of the relative angle between the λ / 4 wave plate's fast axis and the polarization beamsplitter's principal axis, ensuring optimal polarization orthogonality or the desired interference state when the measurement and reference beams are combined. This maximizes the contrast of the interference signal (e.g., AC / DC ratio) or minimizes polarization crosstalk, achieving efficient and stable calibration of the interferometer's polarization matching. This mechanical adjustment method offers simple structure and excellent repeatability, making it suitable for the assembly and maintenance of high-precision optical systems.

[0044] As an optional embodiment, when adjusting the λ / 4 wave plate fails to make the ratio of the output AC signal of the reference beam to the reference beam leakage signal component and the ratio of the output AC signal of the measurement beam to the measurement beam leakage signal component meet preset conditions, the method further includes: Replace the polarizing beamsplitter prism with one with a higher extinction ratio.

[0045] It should be noted that when adjusting the λ / 4 wave plate still cannot make the ratio of the output AC signal of the reference beam and the measurement beam to their corresponding leakage signal components meet the preset conditions, this application improves the polarization isolation capability of the system by replacing the polarization splitter prism with a higher extinction ratio.

[0046] Polarization crosstalk in the optical path is fundamentally limited by the extinction performance of the polarization beamsplitter prism, that is, its ability to suppress undesired polarization light. When the extinction ratio of an existing polarization beamsplitter prism is insufficient due to manufacturing errors, coating defects, or aging, significant light leakage will still occur even if the λ / 4 wave plate is adjusted to the optimal angle, resulting in a crosstalk ratio that fails to meet the required standards. By replacing the polarization beamsplitter prism with one with a higher extinction ratio, polarization crosstalk can be fundamentally reduced, improving the system's ability to resolve orthogonal polarization states. This provides sufficient optimization space for subsequent adjustment of the λ / 4 wave plate, ensuring that the ratio of the output signal to the leakage signal meets the high-precision preset conditions, ensuring that the interferometer achieves ideal polarization matching and long-term operational stability.

[0047] As an optional implementation, adjusting the reflective mirror assembly of the interferometer so that the measurement light spot and the reference light spot coincide with each other includes: Adjust the angle between the reflector group and the optical axis; The rotating prism group in the rotating interferometer rotates around the optical axis.

[0048] It should be noted that the embodiment of the present application realizes the coordinated adjustment of the spatial pointing of the measurement beam and the reference beam by adjusting the angle between the reflector group and the optical axis and rotating the rotary prism group around the optical axis. It should be noted that adjusting the angle between the reflector group and the optical axis can change the propagation direction of the light beam, thereby moving the position of the light spot laterally on the observation screen to achieve coarse alignment of the light spot; and when the rotary prism group rotates around the optical axis, it can accurately change the spatial orientation or deflection angle of the outgoing light beam to achieve fine displacement and posture adjustment of the light spot. The combination of the two can achieve large-scale position correction through angle tilt and fine-tuning through prism rotation, ensuring that the measurement spot and the reference spot are completely overlapped in position, angle and mode, improving the beam combining efficiency and fiber coupling rate, and laying a precise spatial alignment foundation for subsequent polarization matching and interference signal optimization.

[0049] As an optional embodiment, removing the measuring beam, detecting the output AC signal of the reference beam by a detection device, and obtaining the reference beam leakage signal component includes: Reference beam leakage signal component = AC2-AC1+AC4; where AC4 is the noise signal present in the detection device; Remove the reference beam, detect the output AC signal of the measurement beam through the detection device, and obtain the leakage signal components of the measurement beam including: Measure the beam leakage signal component = AC3-AC1+AC4.

[0050] It should be noted that under single-optical-path operation, ideally there should be no interfering AC signals. However, due to polarization crosstalk and system noise, the detection device will still output a non-zero AC component. AC1 is the dark background AC signal (primarily reflecting environmental and circuit noise) when both beams are blocked, AC2 is the AC signal when only the reference beam is operating (including reference light leakage and noise), AC3 is the AC signal when only the measurement beam is operating, and AC4 is the inherent noise signal of the detection device. Using the formulas "reference beam leakage signal component = AC2-AC1+AC4" and "measurement beam leakage signal component = AC3-AC1+AC4," not only is AC1 deducted, but the inherent noise signal AC4 of the detection system itself is also compensated, thereby more accurately separating the actual optical path leakage component caused by polarization mismatch. The method of the embodiment of the present application improves the accuracy of leakage signal identification, avoids misjudgment due to noise interference, provides a highly reliable feedback basis for subsequent fine adjustment of the λ / 4 wave plate based on the leakage ratio, and further enhances the stability and reliability of calibration.

[0051] As an optional implementation, adjusting the reflective mirror assembly of the interferometer so that the measurement light spot and the reference light spot coincide with each other includes: Measure the center distance between the reference spot and the measurement spot, denoted as d; Adjust the reflector group of the interferometer so that d ≤ D*N%; where the distance from the observation screen to the polarization beam splitter prism is recorded as D; the value range of N is 5-6.

[0052] As an optional implementation, adjusting the λ / 4 wave plate in the interferometer and observing the ratio of the AC voltage component to the DC voltage component until the ratio of the AC voltage component to the DC voltage component reaches a preset condition, completing the calibration includes: The ratio of the AC voltage component to the DC voltage component is greater than or equal to 0.7.

[0053] It should be noted that the λ / 4 wave plate is adjusted to achieve a ratio of the AC voltage component to the DC voltage component of the interference signal of 0.7 or higher. This ratio reflects the contrast of the interference fringes; a higher ratio indicates a stronger interference effect. When AC / DC ≥ 0.7, the polarization states of the measurement and reference beams are nearly ideally matched, significantly improving the interference efficiency. By adjusting the λ / 4 wave plate to optimize the polarization state, the system achieves a high-contrast operating state, thereby improving signal quality and measurement accuracy.

[0054] As an optional embodiment, adjusting the λ / 4 wave plate until the ratio of the output AC signal of the reference beam to the reference beam leakage signal component and the ratio of the output AC signal of the measurement beam to the measurement beam leakage signal component meet preset conditions to achieve polarization crosstalk suppression includes: The ratio of the output AC signal of the reference beam to the reference beam leakage signal component is greater than or equal to 7, and the ratio of the output AC signal of the measurement beam to the measurement beam leakage signal component is greater than or equal to 7.

[0055] It should be noted that the present application sets the ratio of the output AC signal of the reference beam and the measurement beam to their corresponding leakage signal components to be greater than or equal to 7 as the judgment condition for polarization crosstalk suppression. This ratio reflects the relative intensity relationship between the main interference signal and the undesired leakage signal in the system. The larger the ratio, the higher the polarization isolation and the smaller the crosstalk. When the ratio of the two optical paths reaches or exceeds 7, it means that the polarization state of the two beams of light has been well matched with the transmission / reflection axis of the polarization beam splitter prism by adjusting the λ / 4 wave plate, effectively suppressing the crosstalk between the optical paths caused by polarization impurity. This quantitative threshold provides a clear, repeatable and objective criterion for the calibration process, which not only avoids the uncertainty of human judgment, but also ensures the stable operation of the interferometer under high contrast and low noise conditions, thereby significantly improving the measurement accuracy, signal-to-noise ratio and long-term working stability of the system.

[0056] The foregoing description is merely a preferred embodiment of the present application and is not intended to limit the present application. Persons skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A method for calibrating an interferometer optical path, characterized in that: include: The interferometer is started, and the measuring beam and the reference beam generated by the interferometer are combined through a polarization beam splitter prism and emitted toward the observation screen, thereby forming a measuring light spot and a reference light spot on the observation screen; Adjusting the reflective mirror assembly of the interferometer so that the measurement light spot and the reference light spot coincide with each other; The observation screen is removed and an optical fiber is connected, and the combined light beam is coupled into the optical fiber; The output end of the optical fiber is connected to a detection device, and a photocurrent signal is obtained by detection by the detection device, and the ratio of the AC voltage component to the DC voltage component is displayed; The λ / 4 wave plate in the interferometer is adjusted, and the ratio of the AC voltage component to the DC voltage component is observed until the ratio of the AC voltage component to the DC voltage component reaches a preset condition, thereby completing the calibration.

2. The interferometer optical path calibration method according to claim 1, characterized in that: The method further comprises adjusting the λ / 4 wave plate in the interferometer and observing the ratio of the AC voltage component to the DC voltage component until the ratio of the AC voltage component to the DC voltage component reaches a preset condition and the calibration is completed. Removing the measuring beam, detecting the output AC signal of the reference beam through a detection device, and obtaining a reference beam leakage signal component; removing the reference beam, detecting the output AC signal of the measuring beam through a detection device, and obtaining a measuring beam leakage signal component; The λ / 4 wave plate is adjusted until the ratio of the output AC signal of the reference beam to the reference beam leakage signal component and the ratio of the output AC signal of the measurement beam to the measurement beam leakage signal component meet preset conditions to achieve polarization crosstalk suppression.

3. The interferometer optical path calibration method according to claim 2, characterized in that: The measuring beam is removed, and the output AC signal of the reference beam is detected by a detection device to obtain a leakage signal component of the reference beam; Before removing the reference beam and detecting the output AC signal of the measuring beam by a detection device and obtaining a leakage signal component of the measuring beam, the method includes: Block the movable reflector and the fixed reflector at the same time, and obtain the dark AC signal in the interferometer through the detection device, which is recorded as AC1; The removing of the measuring beam, detecting the output AC signal of the reference beam by a detection device, and obtaining the reference beam leakage signal component includes: Block the moving mirror in the interferometer and detect the output AC signal of the reference beam through the detection device, which is recorded as AC2; where the reference beam leakage signal component = AC2-AC1; The removing of the reference beam, detecting the output AC signal of the measuring beam by a detection device, and obtaining the leakage signal component of the measuring beam comprises: The fixed reflector in the interferometer is blocked, and the output AC signal of the measuring beam is detected by the detection device, which is recorded as AC3; among which, the leakage signal component of the measuring beam = AC3-AC1.

4. The interferometer optical path calibration method according to claim 3, characterized in that: The step of adjusting the λ / 4 wave plate until a ratio of an output AC signal of the reference beam to a leakage signal component of the reference beam and a ratio of an output AC signal of the measurement beam to a leakage signal component of the measurement beam meet a preset condition to achieve polarization crosstalk suppression includes: The λ / 4 wave plate is rotated around the optical axis until the ratio of the minimum value of AC2 to the leakage signal component of the reference beam and the ratio of the minimum value of AC3 to the leakage signal component of the measurement beam reach preset conditions.

5. The interferometer optical path calibration method according to claim 2, characterized in that: When adjusting the λ / 4 wave plate fails to make the ratio of the output AC signal of the reference beam to the reference beam leakage signal component and the ratio of the output AC signal of the measurement beam to the measurement beam leakage signal component meet a preset condition, the method further includes: Replace the polarizing beamsplitter prism with one with a higher extinction ratio.

6. The interferometer optical path calibration method according to any one of claims 1 to 5, characterized in that: The adjusting the reflector assembly of the interferometer so that the measurement light spot and the reference light spot coincide with each other comprises: Adjust the angle between the reflector group and the optical axis; The rotating prism group in the interferometer is rotated around the optical axis.

7. The interferometer optical path calibration method according to claim 3 or 4, characterized in that: The removing of the measuring beam, detecting the output AC signal of the reference beam by a detection device, and obtaining the reference beam leakage signal component includes: The reference beam leakage signal component = AC2-AC1+AC4; wherein AC4 is the noise signal present in the detection device; The removing of the reference beam, detecting the output AC signal of the measuring beam by a detection device, and obtaining the leakage signal component of the measuring beam comprises: Measure the beam leakage signal component = AC3-AC1+AC4.

8. The interferometer optical path calibration method according to any one of claims 1 to 5, characterized in that: The adjusting the reflector assembly of the interferometer so that the measurement light spot and the reference light spot coincide with each other comprises: Measure the center distance between the reference spot and the measurement spot, denoted as d; The reflecting mirror group of the interferometer is adjusted so that d≤D*N%; wherein the distance from the observation screen to the polarization beam splitter prism is recorded as D; and the value range of N is 5-6.

9. The interferometer optical path calibration method according to any one of claims 1 to 5, characterized in that: The step of adjusting the λ / 4 wave plate in the interferometer and observing the ratio of the AC voltage component to the DC voltage component until the ratio of the AC voltage component to the DC voltage component reaches a preset condition and completing the calibration includes: The ratio of the AC voltage component to the DC voltage component is greater than or equal to 0.

7.

10. The interferometer optical path calibration method according to any one of claims 2 to 5, characterized in that: The step of adjusting the λ / 4 wave plate until a ratio of an output AC signal of the reference beam to a leakage signal component of the reference beam and a ratio of an output AC signal of the measurement beam to a leakage signal component of the measurement beam meet a preset condition to achieve polarization crosstalk suppression includes: The ratio of the output AC signal of the reference beam to the reference beam leakage signal component is greater than or equal to 7, and the ratio of the output AC signal of the measurement beam to the measurement beam leakage signal component is greater than or equal to 7.

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