Laser interference measurement method based on phase modulation

Abstract

The invention discloses a laser interference measurement method based on phase modulation, and the method comprises the steps: enabling laser generated by a laser to sequentially pass through a beam expander and a polarizer to obtain linearly polarized light, and dividing the linearly polarized light into reference light and measurement light through a beam splitter prism; after the reference light passes through the first reflector and the phase modulator (controlled and modulated by the phase modulation driving circuit), the reference light and measuring light passing through the second reflector, the object to be measured, the objective lens and the pinhole converge at the beam splitter prism to form interference light, the photoelectric detector converts the interference light into an electric signal, and the electric signal is transmitted to the computer for analysis and processing through the signal processing circuit and the data acquisition card. And displacement, speed or deformation information of the to-be-measured object is obtained. A semiconductor laser (the wavelength is 630-680 nm, and the power is 10-50 mW), an electro-optic phase modulator (the modulation bandwidth is larger than 100 kHz, and the half-wave voltage is smaller than 5 V), a pinhole (the diameter is 50-150 microns), a high-sampling-frequency and high-resolution data acquisition card and the like are adopted.

Description

Technical Field

[0001] The present invention provides a laser interferometry method, and in particular relates to a laser interferometry method based on phase modulation. Background Art

[0002] Laser interferometry is a high-precision, non-contact measurement method with widespread applications in physical measurement, industrial inspection, micro-nano manufacturing, and other fields. Traditional laser interferometry methods typically use amplitude modulation or frequency modulation to achieve phase measurement. While these methods offer high accuracy, they still have limitations when used in complex measurement environments and in high-precision applications.

[0003] In existing laser interferometry measurement methods, the measurement accuracy of the laser interferometer is easily affected by environmental factors (such as temperature, vibration, etc.), resulting in poor measurement stability; when measuring some objects with high-speed movement or slight deformation, due to the weakness of the signal and the interference of noise, it is difficult to accurately extract the phase information, which affects the measurement accuracy and resolution; traditional laser interferometry measurement devices are relatively complex in structure, high in cost, and have high technical requirements for operators, which limits their promotion in some practical applications. Summary of the Invention

[0004] The present invention aims to solve the problems of existing laser interferometry methods in terms of measurement accuracy, stability and anti-interference ability, and provides a laser interferometry method based on phase modulation, which can achieve high-precision, high-stability and high anti-interference ability of displacement, velocity or deformation measurement.

[0005] In order to solve the above technical problems, the present invention provides the following technical solution: a laser interferometry method based on phase modulation, comprising the following steps:

[0006] Using a laser to generate laser light, and passing the laser light through a beam expander and a polarizer in sequence to obtain linearly polarized light;

[0007] The linearly polarized light is split into two beams by a beam splitter prism, one of which is used as reference light and the other as measurement light;

[0008] The reference light passes through the first reflector and the phase modulator in sequence, the phase modulator is connected to the phase modulation driving circuit, and the phase modulation driving circuit is used to control the phase modulator to perform phase modulation on the reference light to change the phase of the reference light;

[0009] The measuring light passes through the second reflector, the object to be measured, the objective lens, the pinhole and the photodetector in sequence, and the displacement, speed or deformation of the object to be measured will cause the phase of the measuring light to change;

[0010] The phase-modulated reference light and the measuring light are combined at a beam splitter prism to form interference light, and the interference light is converted into an electrical signal by a photodetector;

[0011] The electrical signal is transmitted to a signal processing circuit, the signal processing circuit is connected to a data acquisition card, the data acquisition card is connected to a computer, and the computer is used to analyze and process the collected electrical signal to determine the displacement, velocity or deformation information of the object to be measured and output the measurement result.

[0012] Preferably, the phase modulation driving circuit adopts a voltage-controlled oscillator and a power amplifier. The voltage-controlled oscillator generates a modulation signal, which is amplified by the power amplifier and then drives the phase modulator to perform phase modulation on the reference light.

[0013] Preferably: the signal processing circuit includes a filter, an amplifier and an analog-to-digital converter, the filter is used to filter the electrical signal to remove noise interference; the amplifier is used to amplify the filtered electrical signal; the analog-to-digital converter is used to convert the amplified analog electrical signal into a digital signal to facilitate acquisition by a data acquisition card.

[0014] Preferably, the computer processes the collected digital signal using a phase demodulation algorithm to extract phase information of the object to be measured, and further calculates the displacement, velocity or deformation of the object to be measured.

[0015] Preferably, the laser is a semiconductor laser with an output wavelength ranging from 630 nm to 680 nm and a power ranging from 10 mW to 50 mW.

[0016] Preferably, the phase modulator is an electro-optical phase modulator, the modulation bandwidth of which is greater than 100 kHz and the half-wave voltage is less than 5V.

[0017] Preferably, the pinhole has a diameter of 50 μm to 150 μm, and is used to limit the divergence angle of light entering the photodetector, thereby improving the resolution and accuracy of the measurement system.

[0018] Preferably, the sampling frequency of the data acquisition card is greater than 1 MHz and the resolution is greater than 16 bits, so as to ensure that the phase information in the electrical signal can be accurately acquired.

[0019] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:

[0020] The present invention introduces a phase modulator into the reference light path and uses a phase modulation drive circuit to precisely control the phase modulator, so that the phase of the reference light undergoes controllable modulation changes. After the measuring light passes through the object to be measured, its phase will also change due to factors such as the displacement, speed or deformation of the object. When the two beams of light converge at the beam splitter prism to form interference light, the intensity information of the interference light contains the phase information of the object to be measured. The photodetector converts the interference light into an electrical signal, and the signal processing circuit filters, amplifies and performs analog-to-digital conversion on the electrical signal. Finally, the computer uses a phase demodulation algorithm to analyze and process the processed digital signal to extract the phase information of the object to be measured, thereby achieving high-precision measurement of its displacement, speed or deformation. This method effectively improves the anti-interference ability and measurement accuracy of the measurement system through phase modulation and demodulation technology, while simplifying the device structure, reducing costs, and improving the stability and reliability of the measurement.

[0021] 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

[0022] Figure 1 This is a system architecture diagram of a laser interferometry method based on phase modulation according to the present invention;

[0023] Figure 2 This is a light path flow chart of a laser interferometry method based on phase modulation of the present invention;

[0024] Figure 3 This is a signal processing flow chart of a laser interferometry method based on phase modulation of the present invention;

[0025] Figure 4 This is a timing diagram of a laser interferometry method based on phase modulation according to the present invention. DETAILED DESCRIPTION

[0026] 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.

[0027] 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.

[0028] 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.

[0029] As shown in the figure, the present invention provides a laser interferometry measurement method based on phase modulation, which generates laser light through a laser, and sequentially passes through a beam expander and a polarizer to obtain linearly polarized light, and then uses a beam splitter prism to split the linearly polarized light into two beams, a reference light and a measurement light, wherein the reference light sequentially passes through a first reflector and a phase modulator, the phase modulator is connected to a phase modulation drive circuit, and the drive circuit controls the phase modulator to perform phase modulation on the reference light, while the measurement light sequentially passes through a second reflector, an object to be measured, an objective lens, a pinhole and a photodetector, and the displacement, speed or deformation of the object to be measured will cause the phase change of the measurement light, and finally the phase-modulated reference light and the measurement light converge at the beam splitter prism to form interference light, and the photodetector converts the interference light into an electrical signal and transmits it to a signal processing circuit, the signal processing circuit is connected to a data acquisition card, and the data acquisition card is connected to a computer, and the computer analyzes and processes the collected electrical signal to determine the displacement, speed or deformation information of the object to be measured and output the measurement result, wherein the phase modulation drive circuit adopts a voltage-controlled oscillator and a power amplifier, and the voltage-controlled oscillator generates a modulation signal and transmits it to a power amplifier through a power amplifier. After amplification, the power amplifier drives the phase modulator to phase modulate the reference light. The signal processing circuit includes a filter, an amplifier, and an analog-to-digital converter. The filter is used to filter the electrical signal to remove noise interference. The amplifier is used to amplify the filtered electrical signal. The analog-to-digital converter is used to convert the amplified analog electrical signal into a digital signal for acquisition by the data acquisition card. The computer uses a phase demodulation algorithm to process the acquired digital signal to extract the phase information of the object to be measured, and then calculate the displacement, velocity, or deformation of the object to be measured. The laser is a semiconductor laser with an output wavelength range of 630nm to 680nm and a power range of 10mW to 50mW. The phase modulator is an electro-optical phase modulator with a modulation bandwidth greater than 100kHz, a half-wave voltage less than 5V, and a pinhole diameter of 50μm to 150μm. It is used to limit the divergence angle of light entering the photodetector and improve the resolution and accuracy of the measurement system. The sampling frequency of the data acquisition card is greater than 1MHz and the resolution is greater than 16bit to ensure that the phase information in the electrical signal can be accurately acquired.

[0030] In this implementation, each component works closely together to form a high-precision laser interferometry system. The functions and beneficial effects of each component are as follows:

[0031] Component connection and positional relationship: The laser light generated by the laser passes through the beam expander and polarizer in sequence, becomes linearly polarized light, and is emitted to the beam splitter prism. The beam splitter prism splits the linearly polarized light into two beams: reference light and measurement light. The reference light passes through the first reflector and the phase modulator in sequence. The phase modulator is connected to the phase modulation drive circuit, which controls the phase modulator to phase modulate the reference light. The measurement light passes through the second reflector, the object to be measured, the objective lens, the pinhole, and finally reaches the photodetector. The phase-modulated reference light and measurement light converge at the beam splitter prism to form interference light. The interference light is converted into an electrical signal by the photodetector and transmitted to the signal processing circuit, data acquisition card, and computer in sequence.

[0032] Component functions and beneficial effects:

[0033] Laser, beam expander and polarizer: The laser generates stable laser light, the beam expander enlarges the beam diameter, and the polarizer converts it into linearly polarized light, providing a suitable beam for subsequent interferometry measurement and ensuring the coherence of the measurement light and reference light, which is the basic guarantee for measurement accuracy.

[0034] Beam splitter prism: Splits linearly polarized light into measurement light and reference light, providing two coherent beams for measuring the displacement, velocity or deformation of an object. Its beam splitting efficiency and quality directly affect the interference effect and measurement accuracy.

[0035] Reference optical path components (first reflector, phase modulator, and phase modulation drive circuit): The first reflector changes the direction of the reference light path. The phase modulation drive circuit uses a voltage-controlled oscillator and a power amplifier to generate a modulation signal, driving the phase modulator to perform phase modulation on the reference light, making the phase of the reference light controllably variable. This provides a known phase reference for subsequent phase demodulation and is key to eliminating laser phase noise and improving measurement accuracy and resolution.

[0036] Measurement optical path components (second reflector, object to be measured, objective lens, pinhole and photodetector): The second reflector guides the measuring light to the object to be measured. The displacement, speed or deformation of the object to be measured causes the phase of the measuring light to change. The objective lens focuses the light beam. The pinhole limits the divergence angle of the light entering the photodetector, improving the resolution and accuracy of the measurement system. The photodetector converts the interference light into an electrical signal and is a key component in converting optical signals into electrical signals.

[0037] Signal processing circuitry, data acquisition cards, and computers: The signal processing circuitry, consisting of filters, amplifiers, and analog-to-digital converters, sequentially filters, amplifies, and converts electrical signals to digital form, removing noise interference, enhancing signal strength, and converting analog signals to digital form for easy acquisition by the data acquisition card. The data acquisition card's high sampling frequency and high resolution ensure accurate phase information acquisition. The computer, using a phase demodulation algorithm, processes the digital signal, extracts phase information from the object being measured, and calculates displacement, velocity, or deformation, achieving high-precision measurement. This core component is the analysis and processing core of the entire measurement system.

[0038] Summary of Innovation and Beneficial Effects: This invention innovatively applies phase modulation technology to laser interferometry. A phase modulation drive circuit precisely controls the phase modulator to phase-modulate the reference light. Combined with the phase variation of the measurement light, this allows the interfering light to carry rich phase information. After signal processing and computer analysis, high-precision measurement is achieved. The synergistic effect of various components addresses the shortcomings of existing laser interferometry methods in terms of accuracy, stability, and anti-interference capabilities. This method offers advantages such as high measurement accuracy, excellent stability, and strong anti-interference capabilities. It is widely applicable to physical quantity measurement, industrial inspection, and micro-nano manufacturing, providing a new solution for high-precision measurement.

[0039] As shown in the figure, the present invention is a laser interferometry measurement method based on phase modulation, which uses phase modulation technology to precisely modulate the reference light, and combines the phase difference of the measuring light caused by the change of the object to be measured to form interference light carrying the information of the object to be measured at the beam splitter prism. After being converted into an electrical signal by a photodetector, it is processed by a signal processing circuit composed of a filter, an amplifier and an analog-to-digital converter to obtain a digital signal suitable for computer processing. The computer uses a phase demodulation algorithm to extract the phase information of the object to be measured from the digital signal, thereby achieving high-precision measurement of its displacement, speed or deformation. At the same time, the wavelength range of 630nm to 680nm and the power A semiconductor laser with a power range of 10mW to 50mW is used as the light source. Together with an electro-optical phase modulator with a modulation bandwidth greater than 100kHz and a half-wave voltage less than 5V, a pinhole with a diameter of 50μm to 150μm, and a data acquisition card with a sampling frequency greater than 1MHz and a resolution greater than 16bit, they form a laser interferometry measurement system with high precision, high stability and high anti-interference capability. This effectively solves the shortcomings of existing laser interferometry measurement methods in terms of accuracy, stability and anti-interference capability, and can be widely used in many fields such as physical quantity measurement, industrial inspection, and micro-nano manufacturing, providing a new technical means to achieve high-precision and high-reliability measurement.

[0040] In this embodiment, the device also involves some devices or technologies under the existing technology during use. For example, the power supply system of the laser adopts a conventional DC regulated power supply to ensure that the laser can operate under a stable voltage and ensure the stability and consistency of the laser output; the installation and fixation of optical components such as beam expanders and polarizers adopt existing optical adjustment frames and optical breadboard technologies, and by precisely adjusting the position and angle of the optical components, accurate collimation and alignment of the optical path are achieved to ensure that the light beam can be accurately transmitted between various components according to design requirements; the filter in the signal processing circuit adopts existing active filtering or passive filtering technology, and the appropriate filter type and parameters are selected according to the actual signal frequency and noise characteristics to effectively remove noise interference and improve signal quality; the data transmission between the data acquisition card and the computer adopts universal USB or PCIe interface technology to ensure that the data can be quickly and stably transmitted to the computer for processing and analysis. In terms of materials, the laser can be made of InGaAs (indium gallium arsenide) semiconductor material, which has good luminous efficiency and stability; the lens of the beam expander can be made of optical quartz glass or BK7 optical glass material, which has high transmittance and good optical performance; the electro-optical crystal of the phase modulator can be made of LiNbO3 (lithium titanate) crystal, which has a large electro-optic coefficient and good modulation performance; the photodetector can be made of silicon (Si) photodiode, which has high sensitivity and fast response characteristics, and can effectively convert interference light into electrical signals.

[0041] 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 laser interferometry method based on phase modulation, characterized in that: The following steps are involved: A. generating laser light by using a laser, and passing the laser light through a beam expander and a polarizer in sequence to obtain linearly polarized light; B. The linearly polarized light is split into two beams by a beam splitter prism, one of which is used as a reference beam and the other as a measurement beam; C. The reference light passes through a first reflector and a phase modulator in sequence, wherein the phase modulator is connected to a phase modulation driving circuit, and the phase modulation driving circuit is used to control the phase modulator to perform phase modulation on the reference light to change the phase of the reference light; D. The measuring light passes through the second reflector, the object to be measured, the objective lens, the pinhole, and the photodetector in sequence. The displacement, velocity, or deformation of the object to be measured will cause a phase change in the measuring light. E. The phase-modulated reference light and the measurement light are combined at a beam splitter prism to form interference light, and the interference light is converted into an electrical signal by a photodetector; F. The electrical signal is transmitted to a signal processing circuit, which is connected to a data acquisition card, which is connected to a computer. The computer is used to analyze and process the collected electrical signal to determine the displacement, velocity or deformation information of the object to be measured and output the measurement results.

2. The laser interferometry method based on phase modulation according to claim 1, characterized in that: The phase modulation driving circuit adopts a voltage controlled oscillator and a power amplifier. The voltage controlled oscillator generates a modulation signal, which is amplified by the power amplifier and then drives the phase modulator to perform phase modulation on the reference light.

3. The laser interferometry method based on phase modulation according to claim 1, characterized in that: The signal processing circuit includes a filter, an amplifier and an analog-to-digital converter, wherein the filter is used to filter the electrical signal to remove noise interference; the amplifier is used to amplify the filtered electrical signal; The analog-to-digital converter is used to convert the amplified analog electrical signal into a digital signal so as to facilitate data acquisition by the data acquisition card.

4. The laser interferometry method based on phase modulation according to claim 1, characterized in that: The computer processes the collected digital signals using a phase demodulation algorithm to extract the phase information of the object to be measured, and further calculates the displacement, velocity or deformation of the object to be measured.

5. The laser interferometry method based on phase modulation according to claim 1, characterized in that: The laser is a semiconductor laser with an output wavelength ranging from 630 nm to 680 nm and a power ranging from 10 mW to 50 mW.

6. The laser interferometry method based on phase modulation according to claim 1, characterized in that: The phase modulator is an electro-optical phase modulator, the modulation bandwidth of which is greater than 100kHz and the half-wave voltage is less than 5V.

7. The laser interferometry method based on phase modulation according to claim 1, characterized in that: The pinhole has a diameter of 50 μm to 150 μm and is used to limit the divergence angle of light entering the photodetector, thereby improving the resolution and accuracy of the measurement system.

8. The laser interferometry method based on phase modulation according to claim 1, characterized in that: The sampling frequency of the data acquisition card is greater than 1 MHz and the resolution is greater than 16 bits, so as to ensure that the phase information in the electrical signal can be accurately acquired.

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