Interferometer optical path calibration method

Abstract

This application relates to the field of interferometer technology, specifically to an interferometer optical path calibration method. The method includes: starting the interferometer; combining the measurement beam and reference beam generated by the interferometer via a polarizing beam splitter and then projecting them towards an observation screen, forming a measurement spot and a reference spot on the screen; adjusting the interferometer's mirror assembly to make the measurement spot and reference spot coincide; removing the observation screen and connecting it to an optical fiber, with the combined beam coupled into the optical fiber; connecting the output end of the optical fiber to a detection device, which detects the photocurrent signal and displays the ratio of the AC voltage component to the DC voltage component; adjusting the λ / 4 waveplate in the interferometer until the ratio reaches a preset condition, thus completing the calibration. This application is accurate, reliable, easy to operate, and repeatable, and can balance spatial alignment and polarization matching, which is beneficial for improving the stability and measurement accuracy of the interferometric system.

Description

Technical Field

[0001] This application relates to the field of interferometer technology, and more specifically, to an interferometer optical path calibration method. Background Technology

[0002] Interferometers, as high-precision optical measuring instruments, are widely used in the precise measurement of physical quantities such as length, displacement, vibration, refractive index, and surface morphology. Their working principle is based on the interference effect of light, extracting the measured information by measuring the phase difference between the measuring beam and the reference beam. To obtain a stable and high-contrast interference signal, good spatial, polarization, and phase matching between the measuring beam and the reference beam is crucial.

[0003] In practical systems, due to factors such as assembly errors of optical components, mechanical stress, and temperature drift, the measurement beam and the reference beam often suffer from spatial misalignment and polarization mismatch. Spatial misalignment prevents the two beams from completely overlapping after beam combining, reducing the optical 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 alignment methods typically rely on visual observation of interference fringes or the use of a camera to capture the light spot distribution, achieving coarse alignment through manual adjustment of the mirrors. These methods are highly subjective, have limited accuracy, and are difficult to quantitatively evaluate. Furthermore, for interferometric systems using polarization beam splitters (PBS) for beam combining, the optimization of polarization states is often neglected, resulting in unsatisfactory interference 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, reliable, easy to operate and repeatable, and can take into account both spatial alignment and polarization matching, which is beneficial to improving the stability and measurement accuracy of the interferometer system.

[0006] This application is implemented as follows:

[0007] The interferometer optical path calibration method provided in this application includes:

[0008] The interferometer is activated, and the measurement beam and reference beam generated by the interferometer are combined by a polarizing beam splitter and emitted toward the observation screen, forming a measurement spot and a reference spot on the observation screen.

[0009] Adjust the mirror group of the interferometer so that the measuring spot and the reference spot coincide;

[0010] Remove the observation screen and connect it to the optical fiber; the combined beam is then coupled into the optical fiber.

[0011] 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.

[0012] Adjust the λ / 4 waveplate in the interferometer and observe 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 the preset condition to complete the calibration.

[0013] As an optional implementation, after adjusting the λ / 4 waveplate in the interferometer and observing the ratio of the AC voltage component to the DC voltage component until the ratio reaches a preset condition and calibration is completed, the method further includes:

[0014] Remove the measuring beam, detect the output AC signal of the reference beam using a detection device, and obtain the leakage signal component of the reference beam; remove the reference beam, detect the output AC signal of the measuring beam using a detection device, and obtain the leakage signal component of the measuring beam.

[0015] Adjust the λ / 4 waveplate until the ratio of the output AC signal of the reference beam to the leakage signal component of the reference beam and the ratio of the output AC signal of the measurement beam to the leakage signal component of the measurement beam meet the preset conditions to achieve polarization crosstalk suppression.

[0016] As an optional implementation, before removing the measurement beam, detecting the output AC signal of the reference beam using a detection device, and obtaining the reference beam leakage signal component; and before removing the reference beam, detecting the output AC signal of the measurement beam using a detection device, and obtaining the measurement beam leakage signal component, the method includes:

[0017] Simultaneously blocking both the moving and fixed reflectors, the dark AC signal in the interferometer is obtained through the detection device and denoted as AC1.

[0018] The removal of the measurement beam, by detecting the output AC signal of the reference beam through a detection device, and obtaining the leakage signal component of the reference beam, includes:

[0019] The moving mirror in the obstruction interferometer detects the output AC signal of the reference beam through the detection device, denoted as AC2; where the leakage signal component of the reference beam = AC2 - AC1;

[0020] The removal of the reference beam, the detection of the output AC signal of the measurement beam by the detection device, and the acquisition of the leakage signal component of the measurement beam include:

[0021] The fixed mirror in the obstruction interferometer detects the output AC signal of the measurement beam through the detection device, denoted as AC3; where the leakage signal component of the measurement beam = AC3 - AC1.

[0022] As an optional implementation, adjusting the λ / 4 waveplate until the ratio of the output AC signal of the reference beam to the leakage signal component of the reference beam and the ratio of the output AC signal of the measurement beam to the leakage signal component of the measurement beam meet preset conditions to achieve polarization crosstalk suppression includes:

[0023] Rotate the λ / 4 waveplate 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 the preset conditions.

[0024] As an optional implementation, when adjusting the λ / 4 waveplate fails to make the ratio of the output AC signal of the reference beam to the leakage signal component of the reference beam and the ratio of the output AC signal of the measurement beam to the leakage signal component of the measurement beam meet preset conditions, the method further includes:

[0025] Replace with a polarizing beam splitter with a higher extinction ratio.

[0026] As an optional implementation, adjusting the mirror group of the interferometer to make the measurement spot and the reference spot coincide includes:

[0027] Adjust the angle between the mirror assembly and the optical axis;

[0028] The rotating prism assembly in the interferometer is rotated around the optical axis.

[0029] As an optional implementation, the removal of the measurement beam, detection of the output AC signal of the reference beam by a detection device, and acquisition of the reference beam leakage signal component include:

[0030] The reference beam leakage signal component = AC2 - AC1 + AC4; where AC4 is the noise signal present in the detection device;

[0031] The removal of the reference beam, the detection of the output AC signal of the measurement beam by the detection device, and the acquisition of the leakage signal component of the measurement beam include:

[0032] The measured beam leakage signal component = AC3 - AC1 + AC4.

[0033] As an optional implementation, adjusting the mirror group of the interferometer to make the measurement spot and the reference spot coincide includes:

[0034] The center distance between the reference spot and the measurement spot is denoted as d;

[0035] Adjust the mirror group of the interferometer so that d ≤ D*N%; where D is the distance from the observation screen to the polarizing beam splitter; and N is in the range of 5-6.

[0036] As an optional implementation, adjusting the λ / 4 waveplate in the interferometer and observing the ratio of the AC voltage component to the DC voltage component until the ratio reaches a preset condition to complete the calibration includes:

[0037] The ratio of the AC voltage component to the DC voltage component is greater than or equal to 0.7.

[0038] As an optional implementation, adjusting the λ / 4 waveplate until the ratio of the output AC signal of the reference beam to the leakage signal component of the reference beam and the ratio of the output AC signal of the measurement beam to the leakage signal component of the measurement beam meet preset conditions to achieve polarization crosstalk suppression includes:

[0039] The ratio of the output AC signal of the reference beam to the leakage signal component of the reference beam is greater than or equal to 7, and the ratio of the output AC signal of the measurement beam to the leakage signal component of the measurement beam is greater than or equal to 7.

[0040] The beneficial effects of this application include:

[0041] The interferometer optical path calibration method provided in this application achieves intuitive alignment of the spatial light spot by combining it with an observation screen, and uses a photodetector to provide quantitative feedback on the ratio of AC to DC components of the interference signal, realizing a shift from subjective experience-based adjustment to objective and precise control. The embodiments of this application not only ensure spatial overlap between the measurement beam and the reference beam by adjusting the reflector group, improving coupling efficiency, but also further optimize the polarization matching state of the two beams by adjusting the λ / 4 waveplate, maximizing interference contrast and 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 insufficient calibration accuracy caused by human judgment errors and polarization mismatch in traditional methods, thereby improving the measurement accuracy, environmental adaptability, and long-term operational reliability of the interferometer. Attached Figure Description

[0042] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 This is a flowchart of the interferometer optical path calibration method according to an embodiment of this application;

[0044] Figure 2 This is a schematic diagram of an existing single-axis interferometer. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0046] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0047] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0048] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0049] In practical systems, due to factors such as assembly errors of optical components, mechanical stress, and temperature drift, the measurement beam and the reference beam often suffer from spatial misalignment and polarization mismatch. Spatial misalignment prevents the two beams from completely overlapping after beam combining, reducing the optical coupling efficiency; while polarization mismatch significantly weakens the contrast of the interference signal, affecting the system's signal-to-noise ratio and measurement accuracy.

[0050] Traditional optical path alignment methods typically rely on visual observation of interference fringes or the use of a camera to capture the light spot distribution, achieving coarse alignment through manual adjustment of the mirrors. These methods are highly subjective, have limited accuracy, and are difficult to quantitatively evaluate. Furthermore, for interferometric systems using polarization beam splitters (PBS) for beam combining, the optimization of polarization states is often neglected, resulting in unsatisfactory interference efficiency even with good spatial alignment.

[0051] To address the aforementioned technical problems, this application provides an interferometer optical path calibration method.

[0052] Reference Figure 1 As shown in the embodiments of this application, the interferometer optical path calibration method includes:

[0053] The interferometer is initialized and positioned, and then started. The measurement beam and reference beam generated by the interferometer are combined by a polarizing beam splitter and then emitted toward the observation screen, forming a measurement spot and a reference spot on the observation screen.

[0054] Adjust the mirror group of the interferometer to make the measuring spot coincide with the reference spot;

[0055] Remove the observation screen and connect it to the optical fiber; the combined beam is then coupled into the optical fiber.

[0056] 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.

[0057] Adjust the λ / 4 waveplate in the interferometer and observe the ratio of the AC voltage component to the DC voltage component until the ratio reaches the preset condition to complete the calibration.

[0058] It should be noted that the interferometer optical path calibration method provided in this application embodiment optimizes the spatial alignment and polarization matching state of the interferometer optical path through a step-by-step, quantifiable closed-loop feedback mechanism to maximize the quality of the interference signal.

[0059] First, in this embodiment, an observation screen is set at the receiving end, and the light spot formed by the measurement beam and the reference beam is observed intuitively by the human eye or imaging equipment. The two light spots are spatially overlapped by adjusting the reflector group to ensure that the two beams are well matched in mode after beam combining, thereby improving the subsequent fiber coupling efficiency. Then, the observation screen is removed and the fiber and detection equipment are connected to convert the combined light into a photocurrent signal. The AC voltage component and DC voltage component are extracted from the signal, 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.

[0060] 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. On the oscilloscope, the voltage difference between the highest and lowest points of the signal is the AC voltage peak-to-peak value, and half of this value is the AC voltage component.

[0061] This application embodiment alters the beam polarization state by rotating at least one λ / 4 waveplate until the AC / DC ratio reaches a preset maximum value, indicating that the polarization states of the measurement light and the reference light have achieved optimal matching, resulting in optimal interference efficiency. This application embodiment upgrades traditional subjective observation to objective, quantitative electrical signal feedback, taking into account both spatial alignment and polarization optimization, significantly improving calibration accuracy and the overall performance of the interferometric system.

[0062] The interferometer optical path calibration method provided in this application achieves intuitive alignment of the spatial light spot by combining it with an observation screen, and uses a photodetector to provide quantitative feedback on the ratio of AC to DC components of the interference signal, realizing a shift from subjective experience-based adjustment to objective and precise control. This application not only ensures spatial overlap between the measurement beam and the reference beam by adjusting the reflector group, improving coupling efficiency, but also further optimizes the polarization matching state of the two beams by adjusting the λ / 4 waveplate, maximizing interference contrast and 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 insufficient calibration accuracy caused by human judgment errors and polarization mismatch in traditional methods, thereby improving the measurement accuracy, environmental adaptability, and long-term operational reliability of the interferometer.

[0063] The interferometer can be calibrated using the optical path calibration method described above. The structure of a common single-axis interferometer is explained below, with reference to... Figure 2 As shown, 45° linearly polarized light is emitted from laser 1, passes through rotating prism group 2, then through λ / 4 waveplate 3 and λ / 2 waveplate 4, and finally through polarizing beam splitter 5. At this time, parallel polarized light is transmitted through polarizing beam splitter 5, while perpendicularly polarized light is reflected at the interface of polarizing beam splitter 5.

[0064] Parallel polarized light passes through the 45° λ / 4 waveplate 6 and is reflected at the movable reflector 7. It then passes through the 45° λ / 4 waveplate 6 again, at which point 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 polarizing beam splitter 5, passes through the three reflecting surfaces of the pyramid 10, exits in parallel, and is reflected again at the interface of the polarizing beam splitter 5. The reflected light passes through the 45° λ / 4 waveplate 6, is reflected again by the movable reflector 7, and passes through the 45° λ / 4 waveplate 6 again. At this point, the polarization state of the vertically polarized light is converted to parallel polarized light, which is then transmitted through the polarizing beam splitter 5 and exits to the laser receiver 11.

[0065] Vertically polarized light passes through the 45° λ / 4 waveplate 8 and is reflected at the fixed reflector 9, then passes through the 45° λ / 4 waveplate 8 again. At this point, the polarization state of the vertically polarized light is converted into parallel polarized light. The parallel polarized light is transmitted at the interface of the polarizing beam splitter 5, passes through the three reflecting surfaces of the pyramid 10, and exits in parallel, then is transmitted at the interface of the polarizing beam splitter 5 again. The transmitted light passes through the 45° λ / 4 waveplate 8, is reflected by the fixed reflector 9, and passes through the 45° λ / 4 waveplate 8 again. At this point, the polarization state of the parallel polarized light is converted into vertically polarized light, which is then reflected at the polarizing beam splitter 5 and exits to the laser receiver 11.

[0066] As an optional implementation, the method further includes adjusting the λ / 4 waveplate in the interferometer and observing the ratio of the AC voltage component to the DC voltage component until the ratio reaches a preset condition. After calibration, the method also includes:

[0067] Remove the measuring beam, detect the output AC signal of the reference beam using a detection device, and obtain the leakage signal component of the reference beam; remove the reference beam, detect the output AC signal of the measuring beam using a detection device, and obtain the leakage signal component of the measuring beam.

[0068] Adjust the λ / 4 waveplate until the ratio of the output AC signal of the reference beam to the leakage signal component of the reference beam and the ratio of the output AC signal of the measurement beam to the leakage signal component of the measurement beam meet the preset conditions to achieve polarization crosstalk suppression.

[0069] It should be noted that, after completing the first calibration based on the AC / DC ratio, this application embodiment further introduces a second calibration step for polarization crosstalk suppression, which achieves fine optimization of the system's polarization isolation performance by separating the unwanted leakage signals of the detection measurement optical path and the reference optical path.

[0070] The working principle is as follows: After ensuring optimal interference contrast through initial calibration, the measurement beam or reference beam is sequentially blocked, allowing only a single beam to operate. Ideally, there should be no interference signal (zero AC component). However, due to crosstalk caused by polarization mismatch, a non-zero AC signal (i.e., leakage signal component) will still be detected. The output AC signal and its leakage component of the reference beam and measurement beam operating independently are acquired by a detection device, and their ratio is calculated as a quantitative indicator of the crosstalk level. Subsequently, the λ / 4 waveplate is adjusted again to change the beam polarization state to minimize this ratio until the preset conditions are met. The above process essentially improves the extinction effect of the polarization beam splitter (PBS) through feedback control, effectively suppressing light leakage at cross paths, thereby reducing system noise, improving the signal-to-noise ratio and long-term stability, and achieving comprehensive calibration from "high interference efficiency" to "high polarization purity".

[0071] Further, before removing the measurement beam, detecting the output AC signal of the reference beam using a detection device, and obtaining the reference beam leakage signal component; before removing the reference beam, detecting the output AC signal of the measurement beam using a detection device, and obtaining the measurement beam leakage signal component, the method includes:

[0072] Simultaneously blocking both the moving and fixed reflectors, the dark AC signal in the interferometer is obtained through the detection device and denoted as AC1.

[0073] Remove the measuring beam, detect the output AC signal of the reference beam using a detection device, and obtain the reference beam leakage signal components, including:

[0074] The moving mirror in the obstruction interferometer detects the output AC signal of the reference beam through the detection device, denoted as AC2; where the leakage signal component of the reference beam = AC2 - AC1;

[0075] The reference beam is removed, and the output AC signal of the measurement beam is detected by a detection device. The leakage signal components of the measurement beam are obtained, including:

[0076] The fixed mirror in the obstruction interferometer detects the output AC signal of the measurement beam through the detection device, denoted as AC3; where the leakage signal component of the measurement beam = AC3 - AC1.

[0077] It should be noted that before implementing the above steps, a fixture for fixing the initial position of the Xi'an contact tightly moving mirror needs to be installed. In AC coupling mode, the corresponding AC signals are read on the oscilloscope when the moving mirror is blocked, the fixed mirror is blocked, and both the moving and fixed mirrors are blocked simultaneously.

[0078] As an optional implementation, the λ / 4 waveplate is adjusted until the ratio of the output AC signal of the reference beam to the leakage signal component of the reference beam and the ratio of the output AC signal of the measurement beam to the leakage signal component of the measurement beam meet preset conditions to achieve polarization crosstalk suppression, including:

[0079] Rotate the λ / 4 waveplate 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 the preset conditions.

[0080] This application sequentially blocks the reference beam or the measurement beam, measuring 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. The leakage signal components of the reference beam and the measurement beam are then obtained by combining the dark signal under complete blocking conditions. Subsequently, the λ / 4 waveplate is rotated around the optical axis to adjust its fast axis direction, thereby changing the polarization state of the beam and optimizing its reflection / transmission behavior in the polarization beam splitter, suppressing light leakage along 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 preset conditions, it indicates that the system polarization isolation has reached its optimal level, effectively reducing noise and phase errors introduced by crosstalk, and improving the stability and measurement accuracy of the interferometer.

[0081] It should be noted that the two λ / 4 waveplates can be rotated around the optical axis by adjusting the gear hobbing ring.

[0082] This embodiment of the application introduces an adjustable toothed hobbing ring to achieve synchronous and precise rotation of two λ / 4 waveplates. It utilizes a mechanical transmission structure to precisely control the azimuth angle of the waveplates, thereby optimizing the polarization state matching of the beam in the interferometer. The toothed hobbing ring is linked to the λ / 4 waveplate support; rotating the hobbing ring drives the two λ / 4 waveplates to rotate synchronously around the optical axis, ensuring consistent polarization state changes in the measurement and reference optical paths and avoiding asymmetric errors introduced by unilateral adjustment. This structure allows for continuous and fine-tuning of the relative angle between the fast axis of the λ / 4 waveplate and the main axis of the polarization beam splitter, enabling the measurement and reference beams to achieve optimal polarization orthogonality or the desired interference state when 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 optical path polarization matching. This mechanical adjustment method is simple in structure, has good repeatability, and is suitable for the assembly and maintenance of high-precision optical systems.

[0083] As an optional implementation, when adjusting the λ / 4 waveplate fails to make the ratio of the output AC signal of the reference beam to the leakage signal component of the reference beam and the ratio of the output AC signal of the measurement beam to the leakage signal component of the measurement beam meet preset conditions, the method further includes:

[0084] Replace with a polarizing beam splitter with a higher extinction ratio.

[0085] It should be noted that when adjusting the λ / 4 waveplate still fails to 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 it with a polarization beam splitter prism with a higher extinction ratio.

[0086] Polarization crosstalk in the optical path is fundamentally limited by the extinction performance of the polarization beam splitter, that is, its ability to suppress undesired polarized light. When the existing polarization beam splitter has an insufficient extinction ratio due to manufacturing errors, coating defects, or aging, even if the λ / 4 waveplate is adjusted to the optimal angle, there will still be significant light leakage, resulting in the crosstalk ratio failing to meet the standard. By replacing it with a polarization beam splitter with a higher extinction ratio, polarization crosstalk can be fundamentally reduced, and the system's ability to resolve orthogonal polarization states can be improved. This provides sufficient optimization space for subsequent adjustment of the λ / 4 waveplate, ensuring that the ratio of the output signal to the leakage signal meets the high-precision preset conditions, and ensuring that the interferometer achieves ideal polarization matching and long-term operational stability.

[0087] As an optional implementation, adjusting the interferometer's mirror assembly to make the measurement spot and the reference spot coincide includes:

[0088] Adjust the angle between the mirror assembly and the optical axis;

[0089] The rotating prism assembly in the rotating interferometer rotates around the optical axis.

[0090] It should be noted that the embodiments of this application achieve coordinated adjustment of the spatial orientation of the measurement beam and the reference beam by adjusting the angle between the reflector group and the optical axis and rotating the rotating prism group around the optical axis. Adjusting the angle between the reflector group and the optical axis changes the beam propagation direction, thereby moving the spot position laterally on the observation screen and achieving coarse alignment of the spot. Meanwhile, when the rotating prism group rotates around the optical axis, it precisely changes the spatial orientation or deflection angle of the emitted beam, achieving fine displacement and attitude adjustment of the spot. The combination of these two methods allows for large-scale position correction through angle tilting and fine-tuning through prism rotation, ensuring complete overlap of the measurement spot and the reference spot in position, angle, and mode. This improves beam combining efficiency and fiber coupling rate, laying a precise spatial alignment foundation for subsequent polarization matching and interference signal optimization.

[0091] As an optional implementation, removing the measurement beam, detecting the output AC signal of the reference beam using a detection device, and obtaining the reference beam leakage signal component includes:

[0092] Reference beam leakage signal component = AC2 - AC1 + AC4; where AC4 is the noise signal present in the detection equipment;

[0093] The reference beam is removed, and the output AC signal of the measurement beam is detected by a detection device. The leakage signal components of the measurement beam are obtained, including:

[0094] The measured beam leakage signal component = AC3 - AC1 + AC4.

[0095] It should be noted that, ideally, there should be no interference AC signal in single-beam operation. 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 when both beams are blocked (mainly reflecting environmental and circuit noise), AC2 is the AC signal when only the reference beam is working (including reference beam leakage and noise), AC3 is the AC signal when only the measurement beam is working, and AC4 is the inherent noise signal of the detection device. By using the formulas "reference beam leakage signal component = AC2 - AC1 + AC4" and "measurement beam leakage signal component = AC3 - AC1 + AC4", not only is AC1 subtracted, 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 this application improves the accuracy of leakage signal identification, avoids misjudgment caused by noise interference, provides a highly reliable feedback basis for subsequent fine adjustment of the λ / 4 waveplate based on the leakage ratio, and further enhances the stability and reliability of calibration.

[0096] As an optional implementation, adjusting the interferometer's mirror assembly to make the measurement spot and the reference spot coincide includes:

[0097] The center distance between the reference spot and the measurement spot is denoted as d;

[0098] Adjust the interferometer's mirror group so that d ≤ D*N%; where D is the distance from the observation screen to the polarizing beam splitter; and N ranges from 5 to 6.

[0099] As an optional implementation, the λ / 4 waveplate in the interferometer is adjusted, and the ratio of the AC voltage component to the DC voltage component is observed until the ratio reaches a preset condition, thus completing the calibration.

[0100] The ratio of the AC voltage component to the DC voltage component is greater than or equal to 0.7.

[0101] It should be noted that by adjusting the λ / 4 waveplate, the ratio of the AC voltage component to the DC voltage component of the interference signal is made greater than 0.7. This ratio reflects the contrast of the interference fringes; the higher the ratio, the stronger the interference effect. When AC / DC ≥ 0.7, it indicates that the polarization states of the measurement light and the reference light are nearly ideally matched, and the interference efficiency is significantly improved. By adjusting the λ / 4 waveplate to optimize the polarization state, the system achieves a high-contrast operating state, thereby improving signal quality and measurement accuracy.

[0102] As an optional implementation, the λ / 4 waveplate is adjusted until the ratio of the output AC signal of the reference beam to the leakage signal component of the reference beam and the ratio of the output AC signal of the measurement beam to the leakage signal component of the measurement beam meet preset conditions to achieve polarization crosstalk suppression, including:

[0103] The ratio of the output AC signal of the reference beam to the leakage signal component of the reference beam is greater than or equal to 7, and the ratio of the output AC signal of the measurement beam to the leakage signal component of the measurement beam is greater than or equal to 7.

[0104] It should be noted that this application sets the ratio of the output AC signal of both the reference beam and the measurement beam to their corresponding leakage signal components to be greater than or equal to 7 as a criterion 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 both optical paths reaches or exceeds 7, it indicates that the polarization state of the two beams has been well matched with the transmission / reflection axis of the polarization beam splitter by adjusting the λ / 4 waveplate, effectively suppressing the crosstalk between optical paths caused by impure polarization. This quantization threshold provides a clear and repeatable objective criterion for the calibration process, not only avoiding the uncertainty of human judgment, but also ensuring 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.

[0105] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for calibrating the optical path of an interferometer, characterized in that, include: The interferometer is activated, and the measurement beam and reference beam generated by the interferometer are combined by a polarizing beam splitter and emitted toward the observation screen, forming a measurement spot and a reference spot on the observation screen. Adjust the mirror group of the interferometer so that the measuring spot and the reference spot coincide; Remove the observation screen and connect it to the optical fiber; the combined beam is then coupled 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 waveplate in the interferometer and observe 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 the preset condition. Remove the measuring beam, detect the output AC signal of the reference beam using a detection device, and obtain the leakage signal component of the reference beam; Remove the reference beam, detect the output AC signal of the measurement beam using a detection device, and obtain the leakage signal component of the measurement beam; Adjust the λ / 4 waveplate until the ratio of the output AC signal of the reference beam to the leakage signal component of the reference beam and the ratio of the output AC signal of the measurement beam to the leakage signal component of the measurement beam meet the preset conditions, thereby achieving polarization crosstalk suppression and completing the calibration.

2. The interferometer optical path calibration method according to claim 1, characterized in that, The removal of the measurement beam involves detecting the output AC signal of the reference beam using a detection device and obtaining the leakage signal component of the reference beam. Before removing the reference beam, detecting the output AC signal of the measurement beam using a detection device, and obtaining the leakage signal component of the measurement beam, the method includes: Simultaneously blocking both the moving and fixed reflectors, the dark AC signal in the interferometer is obtained through the detection device and denoted as AC1. The removal of the measurement beam, by detecting the output AC signal of the reference beam through a detection device, and obtaining the leakage signal component of the reference beam, includes: The moving mirror in the obstruction interferometer detects the output AC signal of the reference beam through the detection device, denoted as AC2; where the leakage signal component of the reference beam = AC2 - AC1; The removal of the reference beam, the detection of the output AC signal of the measurement beam by the detection device, and the acquisition of the leakage signal component of the measurement beam include: The fixed mirror in the obstruction interferometer detects the output AC signal of the measurement beam through the detection device, denoted as AC3; where the leakage signal component of the measurement beam = AC3 - AC1.

3. The interferometer optical path calibration method according to claim 2, characterized in that, Adjusting the λ / 4 waveplate until the ratio of the output AC signal of the reference beam to the leakage signal component of the reference beam and the ratio of the output AC signal of the measurement beam to the leakage signal component of the measurement beam meet preset conditions, thereby achieving polarization crosstalk suppression, includes: Rotate the λ / 4 waveplate 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 the preset conditions.

4. The interferometer optical path calibration method according to claim 1, characterized in that, When adjusting the λ / 4 waveplate fails to make the ratio of the output AC signal of the reference beam to the leakage signal component of the reference beam and the ratio of the output AC signal of the measurement beam to the leakage signal component of the measurement beam meet preset conditions, the method further includes: Replace with a polarizing beam splitter with one that has a higher extinction ratio.

5. The interferometer optical path calibration method according to any one of claims 1-4, characterized in that, Adjusting the mirror group of the interferometer to make the measurement spot and the reference spot coincide includes: Adjust the angle between the mirror assembly and the optical axis; The rotating prism assembly in the interferometer is rotated around the optical axis.

6. The interferometer optical path calibration method according to claim 2 or 3, characterized in that, The removal of the measurement beam, by detecting the output AC signal of the reference beam through a detection device, and obtaining the leakage signal component of the reference beam, includes: The reference beam leakage signal component = AC2 - AC1 + AC4; where AC4 is the noise signal present in the detection device; The removal of the reference beam, the detection of the output AC signal of the measurement beam by the detection device, and the acquisition of the leakage signal component of the measurement beam include: The measured beam leakage signal component = AC3 - AC1 + AC4.

7. The interferometer optical path calibration method according to any one of claims 1-4, characterized in that, Adjusting the mirror group of the interferometer to make the measurement spot and the reference spot coincide includes: The center distance between the reference spot and the measurement spot is denoted as d; Adjust the mirror group of the interferometer so that d ≤ D*N%; where D is the distance from the observation screen to the polarizing beam splitter; and N is in the range of 5-6.

8. The interferometer optical path calibration method according to any one of claims 1-4, characterized in that, The calibration process involves adjusting the λ / 4 waveplate in the interferometer and observing the ratio of the AC voltage component to the DC voltage component until the ratio reaches a preset condition. The ratio of the AC voltage component to the DC voltage component is greater than or equal to 0.

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9. The interferometer optical path calibration method according to any one of claims 1-4, characterized in that, Adjusting the λ / 4 waveplate until the ratio of the output AC signal of the reference beam to the leakage signal component of the reference beam and the ratio of the output AC signal of the measurement beam to the leakage signal component of the measurement beam meet preset conditions, thereby achieving polarization crosstalk suppression, includes: The ratio of the output AC signal of the reference beam to the leakage signal component of the reference beam is greater than or equal to 7, and the ratio of the output AC signal of the measurement beam to the leakage signal component of the measurement beam is greater than or equal to 7.

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