Data acquisition and analysis system for laser interference measurement and method thereof

Abstract

The invention relates to a data acquisition and analysis system and method for laser interference measurement, and aims to solve the problem of limited measurement precision caused by asynchronous signal acquisition, imperfect environmental interference compensation and algorithm errors of the existing system. The system comprises a photoelectric conversion unit, a signal conditioning unit, a high-speed synchronous acquisition unit, a real-time processing unit and an error compensation module. The photoelectric conversion unit adopts a four-quadrant PIN photodiode array to receive interference light signals and convert the interference light signals into analog electric signals; the signal conditioning unit performs gain adjustment and bandwidth limitation on the signal; the high-speed synchronous acquisition unit realizes femtosecond-level synchronous acquisition of signals; the real-time processing unit performs phase solution and eliminates harmonic errors based on an improved arc tangent algorithm; and the error compensation module fuses temperature sensor data and accelerometer data to realize thermal drift and vibration compensation.

Description

Technical Field

[0001] The present invention provides a data acquisition and analysis system and method thereof, belonging to the technical field of laser interferometry, and particularly relates to a data acquisition and analysis system and method for laser interferometry. Background Art

[0002] Laser interferometry devices are important instruments used in technical fields such as high-precision displacement measurement and topography analysis, based on the principle of optical interference. Their core function is to convert the weak optical signal output by the laser interferometer into a processable electrical signal and calculate the displacement information with nanometer-level precision through digital signal processing algorithms. Traditional laser interferometry systems are usually composed of photodetectors, signal conditioning circuits, analog-to-digital converters (ADCs), and digital processing units. They achieve displacement measurement through steps such as photoelectric conversion, signal amplification, filtering, sampling, and phase resolution. For example, the common quarter-wave plate coupled dual-detector structure can extract interference signals with a 90° phase difference, and combine the inverse tangent algorithm to resolve the phase change and thus obtain the displacement. However, when pursuing higher measurement accuracy, such systems are limited by signal acquisition synchronization, environmental interference compensation capabilities, and algorithm accuracy, making it difficult to meet the sub-nanometer measurement accuracy requirements in scenarios such as high-end manufacturing and ultra-precision machining.

[0003] The basic structure of existing laser interferometry devices generally consists of a photoelectric conversion module, a signal processing module, a data acquisition module, and a computational processing module. The photoelectric conversion module often uses a conventional photodetector array to receive the interferometric light signal. However, these detectors suffer from high dark current and poor phase consistency, easily introducing DC offset errors. The signal processing module typically features a fixed-gain amplifier and a simple filter. While these can adjust the signal amplitude and perform preliminary filtering, they cannot dynamically optimize the gain based on signal strength. Furthermore, the anti-aliasing filter has a fixed cutoff frequency, making it difficult to adapt to varying measurement bandwidth requirements. The data acquisition module often uses a conventional ADC architecture, which has large sampling clock deviations (typically in the nanosecond range), leading to asynchronous multi-channel signal acquisition and significant impact on phase measurement accuracy due to timing jitter noise. The computational processing module uses the traditional inverse tangent algorithm to calculate the phase, but this algorithm is prone to phase jump errors and lacks real-time compensation for environmental disturbances such as temperature drift and mechanical vibration. System errors can only be corrected through offline calibration, making it unsuitable for dynamic measurement scenarios. When measuring this basic structure with sub-nanometer precision, the measurement error usually exceeds 10nm, which makes it difficult to meet the stringent requirements for displacement measurement accuracy (<1nm) of high-end equipment such as extreme ultraviolet lithography machines and quantum sensors. Summary of the Invention

[0004] In order to solve the above problems, the present application provides a data acquisition and analysis system and method for laser interferometry, which solves the problems in the prior art of limited measurement accuracy caused by asynchronous signal acquisition, imperfect environmental interference compensation and algorithm errors.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions: a data acquisition and analysis system for laser interferometry, comprising: a photoelectric conversion unit, a signal conditioning unit, a high-speed synchronous acquisition unit, a real-time processing unit and an error compensation module;

[0006] The photoelectric conversion unit comprises a high-precision photodetector array for receiving the multi-path interference light signals output by the laser interferometer and converting them into analog electrical signals;

[0007] The signal conditioning unit is connected to the photoelectric conversion unit via an SMA coaxial interface and includes a low-noise amplifier and an anti-aliasing filter for performing gain adjustment and bandwidth limitation on the analog electrical signal;

[0008] The high-speed synchronous acquisition unit is connected to the signal conditioning unit via a differential analog input channel and includes an ADC module controlled by an FPGA for synchronously acquiring multiple signals at a sampling rate of ≥1GSPS;

[0009] Preferably, the real-time processing unit is connected to the high-speed synchronous acquisition unit via an LVDS data bus, comprising:

[0010] Phase calculation module: calculates the interference fringe phase in real time based on the improved arc tangent algorithm;

[0011] Displacement calculation module: converts phase difference into displacement;

[0012] Preferably, the error compensation module is integrated into the real-time processing unit and includes:

[0013] Temperature sensor: real-time monitoring of detector temperature;

[0014] Vibration compensation algorithm module: integrates external accelerometer data;

[0015] Nonlinear correction module: Compensation based on pre-calibrated interferometer error curve.

[0016] Preferably, the photodetector array adopts a four-quadrant PIN photodiode layout, the phase difference of the output signal of each quadrant is 90°, and the detector dark current is ≤1nA.

[0017] Preferably, the programmable gain amplifier of the signal conditioning unit has a gain range of 0-60 dB and a step accuracy of 0.1 dB; and the cutoff frequency of the anti-aliasing filter can be configured to be 10 MHz-100 MHz.

[0018] Preferably, the ADC module adopts a time-interleaved architecture, includes a 4-channel 16-bit ADC chip, and the clock deviation between each channel is ≤50fs.

[0019] Preferably, the phase solving module executes the following formula:

[0020]

[0021] Where I1-I4 are the sampling values ​​of the four-way interference signal, ΔT is the temperature drift compensation term, and k is the temperature coefficient.

[0022] A method for collecting and analyzing data for laser interferometry, comprising the following steps:

[0023] Step S01: Synchronously capture four interference light signals with a 90° phase difference through a photodetector array;

[0024] Step S02: Adaptively amplifying the weak signal using a programmable gain amplifier, with the gain value dynamically adjusted according to the signal amplitude; Step S03: Limiting the signal bandwidth to 80% of the Nyquist frequency using an anti-aliasing filter;

[0025] Step S04: triggering the FPGA to generate a synchronous sampling clock, controlling the multi-channel ADC to acquire signals with a clock deviation of ≤100ps; Step S05: executing in the real-time processing unit:

[0026] Calculating instantaneous phase based on improved arc tangent algorithm Eliminate harmonic errors;

[0027] Fusion of temperature sensor data to calculate thermal drift compensation ΔL t ;

[0028] Calculate the vibration compensation amount ΔL by combining accelerometer data v ;

[0029] Step S06: Output the final displacement Where λ is the laser wavelength and n is the refractive index of the medium.

[0030] Preferably, the improved inverse tangent algorithm in step S05 adopts iterative phase unwrapping, and when the phase jump exceeds π, a 2π compensation cycle is automatically added.

[0031] Preferably: the gain adjustment in step S02 follows: gain value G = 20·log 10 (V_ref / V_in), where V_ref is 80% of the ADC range and V_in is the input signal amplitude.

[0032] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:

[0033] The claims of the present invention solve the technical problem of limited measurement accuracy in existing laser interferometry measurement systems due to asynchronous signal acquisition, imperfect environmental interference compensation and algorithm errors. Specifically, the DC component error is eliminated through a four-quadrant photodetector array and a 90° phase difference design, and a femtosecond-level synchronous acquisition circuit is used to reduce timing jitter noise. Real-time monitoring of hardware-level environmental interference is achieved through the integration of temperature sensors and accelerometers. The improved inverse tangent algorithm and iterative phase unwrapping technology are combined to overcome the jump error in traditional phase solution. At the same time, a programmable gain amplifier and an anti-aliasing filter are used to dynamically optimize the signal quality. Finally, a temperature-vibration joint compensation algorithm is implemented through a multi-channel synchronous processing architecture accelerated by FPGA hardware, and the displacement calculation is corrected to The composite model enables the system to achieve sub-nanometer measurement accuracy at a 1GSPS sampling rate, reducing the measurement error by more than 60% compared with traditional interferometers.

[0034] Other advantages, objects and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art based on an examination of the following or may be learned from the practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a connection architecture diagram of a laser interferometry data acquisition and analysis system and method thereof according to the present invention;

[0036] Figure 2 This is an operation logic diagram of a laser interferometry data acquisition and analysis system and method thereof according to the present invention;

[0037] Figure 3 This is a flow chart of a laser interferometry data acquisition and analysis system and method thereof according to the present invention;

[0038] Figure 4 This is a timing diagram of a data acquisition and analysis system and method for laser interferometry of the present invention;

[0039] Figure 5 This is an overall flow chart of a data acquisition and analysis system and method for laser interferometry measurement according to the present invention. DETAILED DESCRIPTION

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0041] It should be noted that the terms “vertical”, “horizontal”, “up”, “down”, “left”, “right” and similar expressions used in this document are for illustrative purposes only and do not represent the only implementation method.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains; the terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention; the term "and / or" used herein includes any and all combinations of one or more of the associated listed items.

[0043] like Figure 1 、 2 Figure 3 shows a data acquisition and analysis system for laser interferometry measurement, comprising a photoelectric conversion unit, a signal conditioning unit, a high-speed synchronous acquisition unit, a real-time processing unit, and an error compensation module. The photoelectric conversion unit, consisting of a high-precision photodetector array, receives the multi-channel interference optical signals output by the laser interferometer and converts them into analog electrical signals. The signal conditioning unit, connected to the photoelectric conversion unit via an SMA coaxial interface, contains a low-noise amplifier and an anti-aliasing filter for gain adjustment and bandwidth limiting of the analog electrical signals. The high-speed synchronous acquisition unit, connected to the signal conditioning unit via differential analog input channels, includes an FPGA-controlled ADC module, enabling simultaneous acquisition of multiple signals at a sampling rate of ≥1 GSPS. The real-time processing unit, connected to the high-speed synchronous acquisition unit via an LVDS data bus, features a phase calculation module that calculates the interference fringe phase in real time using an improved inverse tangent algorithm, and a displacement calculation module that converts phase differences into displacements. The error compensation module, integrated within the real-time processing unit, includes a temperature sensor for real-time detector temperature monitoring, a vibration compensation algorithm that integrates external accelerometer data, and a nonlinear correction module that compensates for interferometer error based on a precalibrated interferometer error curve. Furthermore, the photodetector array adopts a four-quadrant PIN photodiode layout, the phase difference of the output signal of each quadrant is 90 degrees, and the detector dark current is ≤1nA; the programmable gain amplifier of the signal conditioning unit has a gain range of 0-60dB, a step accuracy of 0.1dB, and the anti-aliasing filter cutoff frequency can be configured to 10MHz-100MHz; the ADC module adopts a time-interleaved architecture, including a 4-channel 16-bit ADC chip, and the clock deviation between each channel is ≤50fs; the phase solver module executes the formula Where I1-I4 are the sampling values ​​of the four-way interference signal, ΔT is the temperature drift compensation term, and k is the temperature coefficient.

[0044] In this implementation, the organic combination of various components achieves breakthroughs in multiple technical challenges of existing laser interferometry systems. The four-quadrant photodetector array eliminates DC component errors in the interference signal at the source through a 90° phase difference design, improving signal purity. The femtosecond synchronous acquisition circuit, with its ultra-low clock deviation characteristics (≤50fs), effectively suppresses timing jitter noise during multi-channel signal acquisition, ensuring phase measurement accuracy. The temperature sensor integrated into the FPGA architecture and the external accelerometer form a hardware-level environmental perception network, capturing temperature fluctuations and mechanical vibration interference sources in real time. An improved inverse tangent algorithm, combined with iterative phase unwrapping technology, eliminates phase jump errors through a dynamic 2π compensation mechanism, improving phase measurement accuracy to the order of 0.01°. The programmable gain amplifier dynamically adjusts the gain (0-60dB) based on the signal amplitude, and, in conjunction with the anti-aliasing filter, precisely limits the signal bandwidth to 80% of the Nyquist frequency, achieving distortion-free amplification of weak signals. This multi-module synergy mechanism enables the system to reduce the displacement measurement standard deviation to 0.2nm at a sampling rate of 1GSPS, which is 65% lower than the measurement error of traditional interferometers under the same working conditions. Especially in scenarios such as high-precision machining and ultra-precision positioning, the temperature-vibration joint compensation algorithm uses the formula The implemented composite error correction model can eliminate the influence of environmental factors on measurement results in real time, providing reliable technical support for dynamic displacement measurement with nanometer-level precision, and significantly improving the applicability and measurement credibility of laser interferometry technology in the field of high-end manufacturing.

[0045] like Figure 3 、 4 5, a data acquisition and analysis method for laser interferometry measurement, the steps are as follows: first, four interference light signals with a phase difference of 90° are synchronously captured by a photodetector array; then, a programmable gain amplifier is used to adaptively amplify the weak signal, and the gain value is dynamically adjusted according to the signal amplitude; then, the signal bandwidth is limited to 80% of the Nyquist frequency by an anti-aliasing filter; then, the FPGA is triggered to generate a synchronous sampling clock, and the multi-channel ADC is controlled to acquire signals with a clock deviation of ≤100ps; in the real-time processing unit, the instantaneous phase is solved based on the improved inverse tangent algorithm. Eliminate harmonic errors and simultaneously integrate temperature sensor data to calculate thermal drift compensation ΔL t , calculate the vibration compensation amount ΔL by combining the accelerometer data v ;Finally, output the final displacement Where λ is the laser wavelength and n is the refractive index of the medium. The improved inverse tangent algorithm uses iterative phase unwrapping. When the phase jump exceeds π, a 2π compensation cycle is automatically added. The gain adjustment follows the gain value G = 20·log 10(V_ref / V_in), V_ref is 80% of the ADC range, and V_in is the input signal amplitude.

[0046] It should be noted that the signal conditioning unit uses the AD8421 ultra-low-noise amplifier (input noise 1.8nV / √Hz); the ADC module uses the AD9265BCPZ-2.5 (16-bit, 125MSPS / channel); and the clock synchronization circuit is based on the AD9528 clock distributor (jitter <50fs).

[0047] Additionally, in this embodiment, based on the above method, this embodiment involves the following related contents:

[0048] Traditional phase calculation method: In traditional laser interferometry, the inverse tangent algorithm is usually used to calculate the phase. The formula is: Where I1 and I2 are two orthogonal interference signals. However, this method is susceptible to harmonic errors and will cause discontinuities when the phase jumps, affecting the measurement accuracy.

[0049] Improved inverse tangent algorithm and iterative phase unwrapping: The improved inverse tangent algorithm used in this method can effectively eliminate harmonic errors. The formula is: Where I1-I4 are the sampling values ​​of the four-way interference signal, ΔT is the temperature drift compensation term, and k is the temperature coefficient. At the same time, when the phase jump exceeds π, the iterative phase expansion automatically increases the 2π compensation cycle to ensure the continuity and accuracy of the phase: If but (Addition and subtraction are determined according to the phase change trend)

[0050] Anti-aliasing filter cutoff frequency selection: According to the Nyquist sampling theorem, to prevent signal aliasing, the anti-aliasing filter cutoff frequency is usually set to half the sampling frequency (the Nyquist frequency). In this method, the signal bandwidth is limited to 80% of the Nyquist frequency, that is, f_{cutoff} = 0.8 × (f_{sampling} / 2). This can effectively reduce high-frequency interference while preserving the signal's main frequency components.

[0051] Calculation of thermal drift compensation: Temperature changes will affect the accuracy of laser interferometry. The thermal drift compensation ΔL t The calculation formula is: ΔL t =α×L0×ΔT, where α is the thermal expansion coefficient of the material, L0 is the initial length, and ΔT is the temperature change.

[0052] Calculation of vibration compensation: Mechanical vibration will also affect the measurement results. The vibration compensation ΔL v The calculation formula is: ΔL v=K×a where K is the vibration transfer function and a is the vibration acceleration measured by the accelerometer.

[0053] Although the present invention has been disclosed above in terms of preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A data acquisition and analysis system for laser interferometry, characterized in that: include: Photoelectric conversion unit, signal conditioning unit, high-speed synchronous acquisition unit, real-time processing unit and error compensation module; The photoelectric conversion unit comprises a high-precision photodetector array for receiving the multi-path interference light signals output by the laser interferometer and converting them into analog electrical signals; The signal conditioning unit is connected to the photoelectric conversion unit via an SMA coaxial interface and includes a low-noise amplifier and an anti-aliasing filter for performing gain adjustment and bandwidth limitation on the analog electrical signal; The high-speed synchronous acquisition unit is connected to the signal conditioning unit through a differential analog input channel, and includes an ADC module controlled by an FPGA, which is used to synchronously acquire multiple signals at a sampling rate of ≥1GSPS.

2. The laser interferometry data acquisition and analysis system according to claim 1, characterized in that: The real-time processing unit is connected to the high-speed synchronous acquisition unit via an LVDS data bus, and comprises: Phase calculation module: Real-time calculation of interference fringe phase based on improved inverse tangent algorithm; Displacement calculation module: converts phase difference into displacement.

3. The laser interferometry data acquisition and analysis system according to claim 1, characterized in that: The error compensation module is integrated into the real-time processing unit and includes: Temperature sensor: real-time monitoring of detector temperature; Vibration compensation algorithm module: integrates external accelerometer data; Nonlinear correction module: Compensation based on pre-calibrated interferometer error curve.

4. The laser interferometry data acquisition and analysis system according to claim 1, characterized in that: The photodetector array adopts a four-quadrant PIN photodiode layout, the phase difference of the output signal of each quadrant is 90 degrees, and the detector dark current is ≤1nA.

5. The laser interferometry data acquisition and analysis system according to claim 1, characterized in that: The programmable gain amplifier of the signal conditioning unit has a gain range of 0-60dB and a step accuracy of 0.1dB; the cutoff frequency of the anti-aliasing filter can be configured to be 10MHz-100MHz.

6. The laser interferometry data acquisition and analysis system according to claim 1, characterized in that: The ADC module adopts a time-interleaved architecture and includes a 4-channel 16-bit ADC chip, with a clock deviation of ≤50fs between channels.

7. The laser interferometry data acquisition and analysis system according to claim 1, characterized in that: The phase solver module performs the following formula: Where I1-I4 are the sampling values ​​of the four-way interference signal, ΔT is the temperature drift compensation term, and k is the temperature coefficient.

8. A method for data acquisition and analysis for laser interferometry, characterized in that: The following steps are involved: Step S01: Synchronously capture four interference light signals with a 90° phase difference through a photodetector array; Step S02: Adaptively amplifying the weak signal using a programmable gain amplifier, with the gain value dynamically adjusted according to the signal amplitude; Step S03: Limiting the signal bandwidth to 80% of the Nyquist frequency using an anti-aliasing filter; Step S04: triggering the FPGA to generate a synchronous sampling clock, controlling the multi-channel ADC to acquire signals with a clock deviation of ≤100ps; Step S05: executing in the real-time processing unit: Calculating instantaneous phase based on improved arc tangent algorithm Eliminate harmonic errors; Fusion of temperature sensor data to calculate thermal drift compensation ΔL t ; Calculate the vibration compensation amount ΔL by combining accelerometer data v ; Step S06: Output the final displacement Where λ is the laser wavelength and n is the refractive index of the medium.

9. The laser interferometry data acquisition and analysis method according to claim 6, characterized in that: The improved inverse tangent algorithm in step S05 adopts iterative phase unwrapping, and when the phase jump exceeds π, a 2π compensation cycle is automatically added.

10. The laser interferometry data acquisition and analysis method according to claim 6, characterized in that: The gain adjustment in step S02 follows: gain value G=20·log 10 (V_ref / V_in), where V_ref is 80% of the ADC range and V_in is the input signal amplitude.

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