Spectral confocal displacement measurement system and measurement method based on wavelength modulation

Abstract

The present invention relates to the field of optical detection, and in particular to a spectral confocal displacement measurement system and a measurement method based on wavelength modulation. The measurement system includes a tunable laser, a dichroic mirror, a dispersive lens, a pinhole, a photodiode and a modulator; the tunable laser is used to output laser light; the modulator is used to calculate the wavelength modulation function of the tunable laser according to the nonlinear relationship between the wavelength of the dispersive lens and the axial focusing position, and the output wavelength of the tunable laser is nonlinearly modulated by the wavelength modulation function, so that the change rate of the output wavelength of the tunable laser is adapted to the axial resolution of the dispersive lens; the dichroic mirror is used to reflect and transmit the light beam; the dispersive lens is used to disperse the light beam and focus it to different positions of the sample; the photodiode is used to receive each beam of reflected light reflected by the sample and convert the optical signal into an electrical signal; the pinhole is used to suppress defocused light. The present invention can improve the measurement accuracy and the stability of the measurement results.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical detection, and in particular relates to a spectral confocal displacement measurement system and a measurement method based on wavelength modulation. Background Art

[0002] In the 1980s, scientists began to study confocal microscopy, which achieved high-resolution imaging of samples by introducing optical sectioning technology into optical microscopes. In the 1990s, with the development of spectral analysis technology, combining spectral information with confocal imaging can provide richer sample information, which promoted the development of spectral confocal displacement sensors.

[0003] Spectral confocal displacement sensors have the advantages of high precision, non-contact, fast measurement, no mechanical scanning, and strong adaptability. These advantages make spectral confocal displacement sensors widely used in many fields.

[0004] At present, the light source of the spectral confocal displacement sensor usually adopts a wide-band white light source and a spectrometer, which has the following disadvantages:

[0005] 1. Since the spectral width of white light source is wide, it is easy to cause spectral overlap, thus affecting the resolution and accuracy of measurement;

[0006] 2. Due to the high background noise of the white light source, the signal-to-noise ratio is low, resulting in a decrease in measurement accuracy;

[0007] 3. The spectral characteristics of the white light source will drift with time and environmental conditions, thus affecting the stability of the measurement results;

[0008] 4. Using a spectrometer on the detector end will increase the cost of the spectral confocal displacement sensor. Summary of the invention

[0009] In view of this, the present invention aims to provide a spectral confocal displacement measurement system and method based on wavelength modulation to solve the problem that traditional spectral confocal displacement sensors use a wide-band white light source, resulting in low measurement accuracy and unstable measurement results.

[0010] To achieve the above object, the technical solution created by the present invention is implemented as follows:

[0011] A spectral confocal displacement measurement system based on wavelength modulation includes a tunable laser, a dichroic mirror, a dispersion lens, a pinhole, a photodiode and a modulator; wherein:

[0012] Tunable laser is used to output laser light;

[0013] The modulator is used to calculate the wavelength modulation function of the tunable laser according to the nonlinear relationship between the wavelength and the axial focusing position of the dispersion lens, and nonlinearly modulate the output wavelength of the tunable laser through the wavelength modulation function, so that the change rate of the output wavelength of the tunable laser is adapted to the axial resolution of the dispersion lens;

[0014] The dichroic mirror is arranged in the light-emitting direction of the tunable laser and is used for reflecting and transmitting the light beam;

[0015] The dispersion lens is arranged in the reflection direction of the dichroic mirror and is used to disperse the light beam and focus it to different positions of the sample;

[0016] The photodiode is arranged in the reflection direction of the dichroic mirror, and is used to receive each beam of reflected light reflected by the sample and convert the optical signal into an electrical signal;

[0017] The pinhole is arranged in the incident direction of the photodiode and close to the photodiode to suppress out-of-focus light.

[0018] Furthermore, suppose that the nonlinear relationship between the wavelength of the dispersion lens and the axial focusing position is for:

[0019]

[0020] in, represents the axial focus position, Indicates wavelength;

[0021] The modulator uses the numerical interpolation method to inversely solve equation (1) and obtain the wavelength modulation function .

[0022] Furthermore, the modulator uses the numerical interpolation method to inversely solve equation (1) and obtain the wavelength modulation function The specific process is:

[0023] Nonlinear relationship between wavelength and axial focus position of a dispersive lens Discretize and construct a discretized wavelength-displacement table;

[0024] By linear interpolation or spline interpolation, at a given time t, the nonlinear relationship between the wavelength and the axial focus position of the dispersion lens is converted into Substitute the equation for wavelength variation over time and calculate the corresponding wavelength modulation function :

[0025] (2);

[0026] in, The nonlinear relationship between the wavelength and the axial focus position of the dispersion lens The inverse function of

[0027] The wavelength modulation function solved by iteratively updating the optimization algorithm , thereby obtaining a wavelength modulation function that meets the requirements of the spectral confocal displacement measurement system.

[0028] Furthermore, the spectral confocal displacement measurement system based on wavelength modulation also includes a processor, which is used to receive the electrical signal output by the photodiode; the processor includes a filtering module, a fitting module and an extraction module; wherein,

[0029] The filtering module is used to filter the electrical signal using a filtering algorithm to obtain a smooth signal with noise removed;

[0030] The fitting module is used to fit the smooth signal into a Gaussian function. The specific form is as follows:

[0031]

[0032] Where A is the peak energy intensity of the smoothed signal, is the energy peak time of the smoothed signal, is the energy peak width of the smoothed signal;

[0033] The extraction module is used to extract the peak time from the Gaussian function And it is used as the energy peak position of the smoothed signal.

[0034] Furthermore, the wavelength tuning range of the tunable laser is 400-700 nm.

[0035] A wavelength modulation-based spectral confocal displacement measurement method implemented by the wavelength modulation-based spectral confocal displacement measurement system comprises the following steps:

[0036] S1: The laser light emitted by the tunable laser is incident on the dichroic mirror, reflected by the dichroic mirror and then incident on the dispersion lens, dispersed by the dispersion lens and focused on different positions of the sample, the sample reflects the dispersed light beam, and each reflected light beam is received by the photodiode after passing through the dispersion lens, the dichroic mirror and the pinhole in sequence; wherein, the modulator calculates the wavelength modulation function of the tunable laser according to the nonlinear relationship between the wavelength and the axial focusing position of the dispersion lens, and the modulator nonlinearly modulates the output wavelength of the tunable laser through the wavelength modulation function, so that the change rate of the output wavelength of the tunable laser is adapted to the axial resolution of the dispersion lens;

[0037] S2: The photodiode converts each beam of reflected light received into an electrical signal, and determines the energy peak position of each beam of reflected light according to the signal strength of each electrical signal;

[0038] S3: Combine the energy peak position of each reflected light beam with the wavelength modulation function to determine the axial position information of the sample.

[0039] Furthermore, the process of calculating the wavelength modulation function of the tunable laser by the modulator according to the nonlinear relationship between the wavelength and the axial focusing position of the dispersion lens is:

[0040] Assume that the nonlinear relationship between the wavelength and the axial focusing position of the dispersion lens is for:

[0041]

[0042] in, represents the axial focus position of the sample, Indicates wavelength;

[0043] The modulator uses the numerical interpolation method to inversely solve equation (1) and obtain the wavelength modulation function .

[0044] Furthermore, the modulator uses the numerical interpolation method to inversely solve equation (1) and obtain the wavelength modulation function The specific process is:

[0045] Nonlinear relationship between wavelength and axial focus position of a dispersive lens Discretize and construct a discretized wavelength-displacement table;

[0046] By linear interpolation or spline interpolation, at a given time t, the nonlinear relationship between the wavelength and the axial focus position of the dispersion lens is converted into Substitute the equation for wavelength variation over time and calculate the corresponding wavelength modulation function :

[0047] (2);

[0048] in, The nonlinear relationship between the wavelength and the axial focus position of the dispersion lens The inverse function of

[0049] Using optimization algorithms such as the least squares method, the wavelength modulation function is solved by iterative update , thereby obtaining a wavelength modulation function that meets the requirements of the spectral confocal displacement measurement system.

[0050] Furthermore, the process of determining the energy peak position of each reflected light beam according to the signal strength of each electrical signal is as follows:

[0051] The electric signal is filtered by using a filtering algorithm to obtain a smooth signal with noise removed;

[0052] Fit the smooth signal to a Gaussian function, the specific form is as follows:

[0053]

[0054] Where A is the peak energy intensity of the smoothed signal, is the energy peak time of the smoothed signal, is the energy peak width of the smoothed signal;

[0055] Extracting peak times from Gaussian functions And it is used as the energy peak position of the smoothed signal.

[0056] Furthermore, the process of combining the energy peak position of each reflected light beam with the wavelength modulation function to determine the axial position information of the sample is as follows:

[0057] Use the maximum value method to find the time t corresponding to the maximum energy peak position from the energy peak positions of each beam of reflected light;

[0058] Substitute the time t corresponding to the maximum energy peak position into the wavelength modulation function , find the wavelength λ corresponding to time t;

[0059] Then bring the wavelength λ into , obtain the axial focus position of the sample .

[0060] Compared with the prior art, the invention can achieve the following beneficial effects:

[0061] 1. Tunable lasers have a narrow spectral width, which does not cause spectral overlap and can provide higher spectral resolution and clearly distinguish optical signals of different wavelengths.

[0062] 2. Tunable lasers can provide higher light intensity, significantly improving the signal-to-noise ratio, thereby improving the stability and reliability of measurements.

[0063] 3. Tunable lasers have higher stability and consistency, which can reduce the impact of spectral drift on measurement.

[0064] 4. The nonlinear relationship between the wavelength of the dispersive lens and the focusing axial position is used to realize nonlinear modulation of the output wavelength of the tunable laser, so that the wavelength change of the tunable laser can be more closely matched with the relationship of the specific optical path position, thereby reducing the measurement error caused by the wavelength change.

[0065] 5. Through nonlinear modulation of the tunable laser output wavelength, more intensive wavelength sampling can be performed in the key measurement area (corresponding to a specific wavelength range), ensuring that the detailed information of the key measurement area is not neglected, further improving the measurement accuracy and optimizing the spectral resolution.

[0066] 6. The light source uses a tunable laser, which can reduce the linearity requirements of the dispersive objective lens used in the spectral confocal displacement sensor, thereby reducing the design difficulty of the dispersive objective lens, so that a non-spherical lens with a dispersive function can be used as a dispersive lens to achieve higher measurement accuracy.

[0067] 7. Using a photodiode as the detection end can reduce the cost of the spectral confocal displacement sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings:

[0069] Figure 1 It is a structural schematic diagram of a spectral confocal displacement measurement system based on wavelength modulation according to an embodiment of the invention.

[0070] Description of reference numerals:

[0071] 1. Tunable laser; 2. Dichroic mirror; 3. Dispersion lens; 4. Pinhole; 5. Photodiode; 6. Sample. DETAILED DESCRIPTION

[0072] In order to make the purpose, technical solution and advantages of the invention more clear, the invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described here are only used to explain the invention and do not constitute a limitation of the invention.

[0073] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0074] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0075] In the description of the invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

[0076] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0077] like Figure 1 As shown, the spectral confocal displacement measurement system based on wavelength modulation provided by the embodiment of the present invention includes a tunable laser 1, a dichroic mirror 2, a dispersive lens 3, a pinhole 4, a photodiode 5, a modulator (not shown in the figure) and a processor (not shown in the figure).

[0078] The description of each device is as follows:

[0079] The tunable laser 1 is used to output lasers of different wavelengths. The tunable laser 1 uses a model with a wavelength tuning range of 400-700nm to replace the white light source. Compared with the white light source, the advantages of the tunable laser 1 are reflected in the following aspects:

[0080] ① The tunable laser 1 has a narrow spectral width, which will not cause spectral overlap, and can provide higher spectral resolution and clearly distinguish optical signals of different wavelengths;

[0081] ② Tunable lasers can also provide higher light intensity, significantly improving the signal-to-noise ratio, thereby improving the stability and reliability of the measurement.

[0082] ③ Tunable lasers have higher stability and consistency, and can reduce the impact of spectral drift on measurements.

[0083] The modulator is used to calculate the wavelength modulation function of the tunable laser 1 according to the nonlinear relationship between the wavelength and the axial focusing position of the dispersion lens 3, and to nonlinearly modulate the output wavelength of the tunable laser 1 through the wavelength modulation function so that the change rate of the output wavelength of the tunable laser 1 is adapted to the axial resolution of the dispersion lens 3.

[0084] Assume that the nonlinear relationship between the wavelength and the axial focusing position of the dispersion lens 3 is for:

[0085]

[0086] in, represents the axial focus position, Indicates wavelength;

[0087] The modulator uses the numerical interpolation method to inversely solve the above equation and obtain the wavelength modulation function .

[0088] The modulator uses the numerical interpolation method to inversely solve the above equation and obtain the wavelength modulation function The specific process is:

[0089] Nonlinear relationship between wavelength and axial focus position of a dispersive lens Discretize and construct a discretized wavelength-displacement table;

[0090] By linear interpolation or spline interpolation, at a given time t, the nonlinear relationship between the wavelength and the axial focus position of the dispersion lens is converted into Substituting into the equation for wavelength variation over time, calculate the corresponding wavelength modulation function λ(t):

[0091] ;

[0092] in, The nonlinear relationship between the wavelength and the axial focusing position of the dispersion lens 3 is shown in FIG. The inverse function of

[0093] Using optimization algorithms such as the least squares method, the wavelength modulation function is solved by iterative update , thereby obtaining a wavelength modulation function that meets the requirements of the spectral confocal displacement measurement system.

[0094] The dichroic mirror 2 is arranged in the light emitting direction of the tunable laser 1 to realize the reflection and transmission of the light beam.

[0095] The dispersion lens 3 is arranged in the reflection direction of the dichroic mirror 2 to achieve dispersion of the light beam, so that the light beams of different wavelengths after dispersion are focused to different positions of the sample 6 and reflected by the sample 6 .

[0096] The photodiode 5 is arranged in the reflection direction of the dichroic mirror 2 to receive each beam of reflected light reflected by the sample 6 and convert the optical signal into an electrical signal.

[0097] The pinhole 4 is arranged in the incident direction of the photodiode 5 and close to the photodiode 5 to suppress the defocused light and reduce the interference of the scattered light.

[0098] The processor performs data transmission with the photodiode 5 to receive the electrical signal output by the photodiode 5. The processor includes a filtering module (not shown in the figure), a fitting module (not shown in the figure) and an extraction module (not shown in the figure);

[0099] The filtering module is used to filter the electrical signal using a filtering algorithm to obtain a smooth signal with noise removed;

[0100] The fitting module is used to fit the smooth signal into a Gaussian function. The specific form is as follows:

[0101]

[0102] Where A is the peak energy intensity of the smoothed signal, is the energy peak time of the smoothed signal, is the energy peak width of the smoothed signal;

[0103] The extraction module is used to extract the peak time from the Gaussian function And it is used as the energy peak position of the smoothed signal.

[0104] The measurement principle of the interferometric confocal measurement system based on lateral encoding is:

[0105] The laser emitted by the tunable laser 1 is incident on the dichroic mirror 2, and after being reflected by the dichroic mirror 2, it is incident on the dispersion lens 3. After being dispersed by the dispersion lens 3, it is focused to different positions of the sample 6. The sample 6 reflects the dispersed light beam, and each beam of reflected light is received by the photodiode 5 after passing through the dispersion lens 3, the dichroic mirror 2, and the pinhole 4 in turn.

[0106] When the tunable laser 1 outputs laser light, the modulator nonlinearly modulates the output wavelength of the tunable laser 1 using a wavelength modulation function, so that the rate of change of the output wavelength of the tunable laser 1 is adapted to the axial resolution of the dispersion lens 3 .

[0107] The photodiode 5 converts each received reflected light beam into an electrical signal and transmits it to the processor. The processor determines the energy peak position of each reflected light beam based on the signal strength of each electrical signal, and combines it with the wavelength modulation function to determine the axial position information of the sample 6.

[0108] The above content describes in detail the spectral confocal displacement measurement system based on wavelength modulation provided by an embodiment of the present invention. Corresponding to the measurement system, an embodiment of the present invention also provides a measurement method implemented by using the measurement system.

[0109] The spectral confocal displacement measurement method based on wavelength modulation provided by an embodiment of the present invention comprises the following steps:

[0110] S1: The laser light emitted by the tunable laser is incident on a dichroic mirror, reflected by the dichroic mirror and then incident on a dispersive lens, dispersed by the dispersive lens and focused on different positions of the sample, the sample reflects the dispersed light beam, and each reflected light beam is sequentially transmitted through the dispersive lens, the dichroic mirror and the pinhole and then received by the photodiode; wherein, the modulator calculates the wavelength modulation function of the tunable laser according to the nonlinear relationship between the wavelength of the dispersive lens and the axial focusing position, and the modulator nonlinearly modulates the output wavelength of the tunable laser through the wavelength modulation function, so that the rate of change of the output wavelength of the tunable laser is adapted to the axial resolution of the dispersive lens.

[0111] The laser output by the tunable laser is reflected by the dichroic mirror to the dispersive lens. The function of the dispersive lens is to spatially expand the incident light beam along the axial direction according to the wavelength. The design characteristics of the dispersive lens determine that the dispersive lens has different refractive indices for light of different wavelengths, which is specifically manifested as a nonlinear relationship between the wavelength and the axial focusing position. This nonlinear relationship can be expressed by the formula:

[0112] ;

[0113] Where λ represents the wavelength, a0, a1,…, a n represents the fitting parameters, and n represents the order of the polynomial. For each wavelength λ, there is a unique axial focusing position , this relationship is determined by the dispersion characteristics of the dispersion lens.

[0114] In order to match the wavelength modulation of the tunable laser with the nonlinear characteristics of the dispersive lens, it is necessary to design a nonlinear modulation method in which the wavelength changes with time. The nonlinear modulation method is used to adjust the change rate of the output wavelength of the tunable laser, so that the modulation in different wavelength ranges is more precise, thereby maintaining a high axial resolution in the entire measurement range.

[0115] The nonlinear modulation method is adopted to make the output wavelength of the tunable laser change within a certain time period. This nonlinear modulation method can be achieved by setting the wavelength modulation function through the modulator. For example, a polynomial or other function form can be selected to simulate the response of the spectral confocal sensor to a specific wavelength, that is, the scattered points of the nonlinear modulation are fitted into a continuous function by polynomial fitting or other fitting methods to obtain more points. For the linear modulation method, the output wavelength of the tunable laser will change uniformly over time. For the nonlinear modulation method of the output wavelength of the tunable laser, it is hoped that the rate of change of the output wavelength of the tunable laser in different ranges is adapted to the axial resolution of the dispersion lens. Specifically, in the wavelength range with higher axial resolution, it is hoped that the rate of change of the modulated wavelength is slower to ensure the axial resolution, while in the wavelength range with lower axial resolution, the rate of change of the wavelength can be faster.

[0116] In the spectral confocal displacement sensor, the relationship between wavelength and axial focus position is usually realized by optical elements such as dispersive lenses. The nonlinear relationship between wavelength and axial focus position can be expressed as:

[0117] ;

[0118] in, is the wavelength, is the axial focusing position corresponding to the wavelength, is a function of wavelength and axial focus position.

[0119] For wavelength ranges with higher axial resolution, the wavelength change needs to be slower for the following reasons:

[0120] (1) The axial focus position in the high axial resolution band has a greater response to wavelength changes, which means that any slight change in wavelength will cause a large change in the axial focus position. In this wavelength range, the measurement system is very sensitive to changes in the axial focus position, so the wavelength modulation rate must not be too fast. If the modulation rate is too fast, the measurement system may not be able to accurately capture changes in the axial focus position.

[0121] (2) In order to ensure the accuracy of the measurement system within these wavelength ranges, it is usually necessary to slow down the wavelength modulation rate. A slower wavelength modulation rate can make the measurement system more stable and accurate within this wavelength range and avoid measurement errors caused by too fast wavelength changes.

[0122] (3) Slow wavelength changes can give the measurement system enough time to respond and measure, ensuring more accurate axial position information. Especially in the range of high axial resolution, a small change in wavelength will cause a large change in the axial focusing position, which requires higher precision and a more stable measurement process.

[0123] For wavelength ranges with lower axial resolution, the wavelength change needs to be faster for the following reasons:

[0124] (1) The axial focus position in the low axial resolution band has a small response to wavelength changes, which means that a small change in wavelength will only cause a small change in the axial focus position. In order to obtain sufficient information in these ranges, it is usually necessary to enhance the change in the axial focus position by accelerating wavelength modulation.

[0125] (2) In the wavelength range with low axial resolution, the measurement system has a weak response to wavelength, so it is necessary to quickly modulate the wavelength to increase the response through multiple measurements. Rapid wavelength changes can obtain more measurement points in a shorter time, thereby improving the measurement efficiency and signal-to-noise ratio of the measurement system.

[0126] (3) Although the change in axial focus position caused by each wavelength change is small, by rapidly modulating the wavelength change, sufficient information can be accumulated frequently to make up for the shortcomings caused by low sensitivity. This method is suitable for situations where the displacement change is not significant but still requires relatively accurate measurement.

[0127] From the above analysis, it can be concluded that when designing a spectral confocal displacement measurement system, there is a direct trade-off between the wavelength modulation rate and the displacement sensitivity:

[0128] In the wavelength range with higher axial resolution, the wavelength modulation rate needs to be slower to avoid excessive axial focus position response caused by too fast wavelength changes. This ensures that the measurement system can accurately capture the subtle relationship between wavelength and axial focus position and maintain high-precision measurement.

[0129] In the wavelength range with low axial resolution, the wavelength modulation rate needs to be faster, and multiple rapid changes in wavelength are used to compensate for the shortcomings of the smaller axial focusing position response to obtain sufficient information, thereby improving measurement efficiency.

[0130] This design idea actually reflects the concept of signal amplification and suppression: in the band with high axial resolution, emphasis is placed on precisely controlling the speed of wavelength change; in the band with low axial resolution, signal strength is increased by speeding up the modulation speed, thereby compensating for the axial resolution limitation of the measurement system.

[0131] In summary, the relationship between wavelength modulation rate and axial resolution is determined by the response characteristics of the measurement system. In the wavelength range with high axial resolution, a slower wavelength change can ensure the accuracy and stability of the measurement system; while in the wavelength range with low axial resolution, a faster wavelength change can improve the signal strength and measurement efficiency. This design aims to achieve the best balance between measurement accuracy and efficiency by reasonably adjusting the wavelength modulation rate.

[0132] Controlling the rate at which the wavelength changes (i.e., the rate of wavelength modulation) can be achieved by adjusting the parameters of the modulator.

[0133] For slowing down the wavelength variation: The wavelength variation can be slowed down by reducing the frequency of the modulation signal, or by controlling the drive voltage of the modulator. For example, a linear or nonlinear control signal can be used to change the modulation rate of the wavelength.

[0134] To speed up the wavelength change: the wavelength change can be accelerated by increasing the frequency of the modulation signal or increasing the modulation voltage, and the wavelength output of the laser can be quickly adjusted.

[0135] S2: The photodiode converts each received reflected light beam into an electrical signal, and determines the energy peak position of each reflected light beam according to the signal strength of each electrical signal.

[0136] At the detection end, the energy of each beam of reflected light (referred to as scattered light) reflected by the sample is received by a photodiode. The photodiode converts the received light signal into an electrical signal and determines the energy peak of each wavelength based on the intensity of the output signal. This process can be expressed by the following formula:

[0137] ;

[0138] in, Indicated in t The light energy received at any moment, I It represents the normalized light intensity signal collected by the photodiode, and P is a constant. The processor monitors the electrical signal output by the photodiode in real time, and can record the energy value corresponding to each scattered light beam received by the photodiode in real time.

[0139] The electrical signal corresponding to each scattered light beam output by the photodiode will change with time. By detecting the peak value of the electrical signal, the relationship between the wavelength and energy position of each scattered light beam can be accurately determined. The detection process can be divided into two steps: signal filtering and fitting analysis. In the peak detection process based on filtering and fitting, the noise of the light signal collected by the photodiode is suppressed, and the peak position is accurately extracted from the filtered signal.

[0140] Since the normalized light intensity signal I ( t ) is often affected by noise, so it is necessary to first normalize the light intensity signal I ( t ) is filtered. In a specific example of the present invention, a Kalman filter is used to filter I ( t ) for denoising. The Kalman filter is a recursive algorithm suitable for noisy signals. The Kalman filter predicts and corrects future signals based on the current signal estimate and the noise model.

[0141] The mathematical model of the Kalman filter is:

[0142]

[0143] in, is the signal prediction value at time t+1, K t is the Kalman gain, which is calculated based on the covariance matrix of the noise. The recursive formula of the Kalman filter allows the signal estimate to be updated at each time step, and finally the smoothed signal I is obtained. filtered (t). The smoothed signal after filtering I filtered (t) should have less noise and retain the key components of the signal, especially the signal shape near the peak is clearer.

[0144] However, the present invention is not limited to using the Kalman filter to normalize the light intensity signal. I ( t ) for denoising, other filters can also be used to normalize the light intensity signal I ( t ) for denoising.

[0145] In order to more accurately extract the smoothed signal I filtered The peak value of (t) is obtained by using Gaussian fitting to accurately locate the peak position. filtered After Gaussian fitting, (t) is fitted into a Gaussian function, which is as follows:

[0146]

[0147] Where A is the peak energy intensity (because of normalization, A=1), is the energy peak time of the smoothed signal, i.e., the target to be extracted; is the standard deviation of the Gaussian distribution and is used to characterize the energy peak width.

[0148] After Gaussian fitting is completed, the energy peak time t is extracted by optimization method. peak As the smoothed signal Ifiltered The energy peak position of each scattered light can be obtained by analyzing the energy peak position of each scattered light.

[0149] The optimization method may be a nonlinear least squares method, such as the Levenberg-Marquardt algorithm, which can effectively extract the peak time. The specific process is as follows:

[0150] ①Define the loss function

[0151] Assume there is a set of known spectral numbers y i and the corresponding time point t i , we want to fit a model to extract the peak position. Assuming the fitted model is f(t), the loss function can be defined as:

[0152]

[0153] Among them, θ is the parameter to be optimized, including peak position, width, and intensity.

[0154] ②Optimization algorithm

[0155] The Levenberg-Marquardt algorithm is used to optimize and update the parameters. The core idea of ​​the algorithm is to minimize the loss function R by continuously updating the parameter θ. The Levenberg-Marquardt algorithm combines the advantages of the Gauss-Newton method and the gradient descent method, and has good stability and convergence in the optimization process.

[0156] Iterative process: Calculate the gradient and Hessian matrix in each iteration and update the parameters until the loss function is minimized.

[0157] Termination condition: When the loss function changes less than the preset threshold or the maximum number of iterations is reached, the algorithm stops.

[0158] ③ Extract peak position

[0159] Through the optimization process, the time parameter tpeak of the peak is obtained, and the intensity, position and other parameters of the peak are determined through the fitting results.

[0160] S3: Combine the energy peak position of each reflected light beam with the wavelength modulation function to determine the axial position information of the sample.

[0161] The process of combining the energy peak position of each reflected light beam with the wavelength modulation function to determine the axial position information of the sample is:

[0162] Use the maximum value method to find the time t corresponding to the maximum energy peak position from the energy peak positions of each beam of reflected light;

[0163] Substitute the time t corresponding to the maximum energy peak position into the wavelength modulation function , find the wavelength λ corresponding to time t;

[0164] Then bring the wavelength λ into , obtain the axial focus position of the sample .

[0165] Example 1

[0166] The nonlinear relationship between the wavelength and the axial focusing position of the dispersive lens is expressed as:

[0167]

[0168] in, represents the wavelength, Indicates wavelength The corresponding axial focusing position (usually refers to the displacement in the direction of the optical axis).

[0169] The nonlinear relationship between the wavelength and the axial focus position of the dispersive lens is approximately linear or nonlinear. In a simple case, the nonlinear relationship between the wavelength and the axial focus position of the dispersive lens can be set as:

[0170]

[0171] Where: α is a constant representing the change in axial focus position per unit wavelength change, is the reference wavelength, usually chosen as the initial wavelength of the measurement system.

[0172] In practical applications, it is necessary to control the change of wavelength to achieve control of the axial focus position. The present invention changes the wavelength through nonlinear modulation to achieve higher precision displacement measurement. For this purpose, a wavelength modulation function is designed to achieve accurate control of the axial focus position through nonlinear modulation of the wavelength.

[0173] The wavelength modulation function is designed as follows:

[0174] The wavelength change is controlled by constructing a nonlinear wavelength modulation function. A common modulation method is to use a sine wave or exponential function to control the amplitude and rate of wavelength change.

[0175] A specific wavelength modulation function can be expressed as:

[0176]

[0177] Where λ(t) is the wavelength that changes with time; λ0 is the reference wavelength (initial wavelength); A is the modulation amplitude, which represents the intensity of the wavelength modulation; ω is the modulation frequency (i.e., the periodicity of the modulation); ϕ is the initial phase; and β is the exponential decay factor, which controls the decay rate of the wavelength modulation.

[0178] The characteristic of the wavelength modulation function is that the wavelength will oscillate around the reference wavelength λ0, but the amplitude will gradually decay over time. This nonlinear modulation method can adjust the wavelength change at different time periods, thereby optimizing the measurement accuracy of the displacement.

[0179] According to the nonlinear relationship between the wavelength and the axial focusing position of the dispersion lens , the axial focusing position can be adjusted by controlling the change of wavelength.

[0180] When the wavelength modulation function is When , the process of displacement z(t) changing with time can be expressed as:

[0181]

[0182] Among them, α is the sensitivity of the axial focus position change, A controls the amplitude of the wavelength change, ω controls the frequency of the wavelength change, and β controls the attenuation speed of the wavelength change.

[0183] The above relationship shows that the displacement z(t) shows a decaying oscillation pattern over time. By adjusting the parameters A, ω and β, the accuracy of the displacement change can be controlled in different wavelength ranges. By designing a nonlinear wavelength modulation function and combining the wavelength-displacement relationship of the dispersive lens, precise control of the displacement can be achieved. In practical applications, the modulation parameters such as amplitude, frequency and attenuation factor can be adjusted as needed to optimize the performance of the measurement system. Through numerical simulation and experimental verification, the modulation strategy can be further optimized to meet the accuracy requirements under different measurement conditions.

[0184] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the disclosure of the present invention can be performed in parallel, sequentially or in different orders, as long as the desired results of the technical solution disclosed in the present invention can be achieved, and this document does not limit this.

[0185] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A spectral confocal displacement measurement system based on wavelength modulation, characterized in that: It includes a tunable laser, a dichroic mirror, a dispersive lens, a pinhole, a photodiode and a modulator; wherein, Tunable laser is used to output laser light; The modulator is used to calculate the wavelength modulation function of the tunable laser according to the nonlinear relationship between the wavelength and the axial focusing position of the dispersion lens, and nonlinearly modulate the output wavelength of the tunable laser through the wavelength modulation function, so that the change rate of the output wavelength of the tunable laser is adapted to the axial resolution of the dispersion lens; Assume that the nonlinear relationship between the wavelength and the axial focusing position of the dispersion lens is for: in, represents the axial focus position, Indicates wavelength; The modulator uses the numerical interpolation method to inversely solve equation (1) and obtain the wavelength modulation function ; The modulator uses the numerical interpolation method to inversely solve equation (1) and obtain the wavelength modulation function The specific process is: Nonlinear relationship between wavelength and axial focus position of a dispersive lens Discretize and construct a discretized wavelength-displacement table; By linear interpolation or spline interpolation, at a given time t, the nonlinear relationship between the wavelength and the axial focus position of the dispersion lens is converted into Substitute the equation for wavelength variation over time and calculate the corresponding wavelength modulation function : （2）； in, The nonlinear relationship between the wavelength and the axial focus position of the dispersion lens The inverse function of The wavelength modulation function solved by iteratively updating the optimization algorithm , thereby obtaining a wavelength modulation function that meets the requirements of the spectral confocal displacement measurement system; The dichroic mirror is arranged in the light-emitting direction of the tunable laser and is used for reflecting and transmitting the light beam; The dispersion lens is arranged in the reflection direction of the dichroic mirror and is used to disperse the light beam and focus it to different positions of the sample; The photodiode is arranged in the reflection direction of the dichroic mirror, and is used to receive each beam of reflected light reflected by the sample and convert the optical signal into an electrical signal; The pinhole is arranged in the incident direction of the photodiode and close to the photodiode to suppress out-of-focus light.

2. The spectral confocal displacement measurement system based on wavelength modulation according to claim 1, characterized in that: It also includes a processor for receiving the electrical signal output by the photodiode; the processor includes a filtering module, a fitting module and an extraction module; wherein, The filtering module is used to filter the electrical signal using a filtering algorithm to obtain a smooth signal with noise removed; The fitting module is used to fit the smooth signal into a Gaussian function. The specific form is as follows: Where A is the peak energy intensity of the smoothed signal, is the energy peak time of the smoothed signal, is the energy peak width of the smoothed signal; The extraction module is used to extract the peak time from the Gaussian function And it is used as the energy peak position of the smoothed signal.

3. The spectral confocal displacement measurement system based on wavelength modulation according to claim 1, characterized in that: The wavelength tuning range of the tunable laser is 400-700nm.

4. A spectral confocal displacement measurement method based on wavelength modulation, implemented using the spectral confocal displacement measurement system based on wavelength modulation according to any one of claims 1 to 3, characterized in that: The steps include: S1: The laser light emitted by the tunable laser is incident on the dichroic mirror, reflected by the dichroic mirror and then incident on the dispersion lens, dispersed by the dispersion lens and focused on different positions of the sample, the sample reflects the dispersed light beam, and each reflected light beam is received by the photodiode after passing through the dispersion lens, the dichroic mirror and the pinhole in sequence; wherein, the modulator calculates the wavelength modulation function of the tunable laser according to the nonlinear relationship between the wavelength and the axial focusing position of the dispersion lens, and the modulator nonlinearly modulates the output wavelength of the tunable laser through the wavelength modulation function, so that the change rate of the output wavelength of the tunable laser is adapted to the axial resolution of the dispersion lens; The process of calculating the wavelength modulation function of the tunable laser by the modulator according to the nonlinear relationship between the wavelength and the axial focusing position of the dispersion lens is: Assume that the nonlinear relationship between the wavelength and the axial focusing position of the dispersion lens is for: in, represents the axial focus position of the sample, Indicates wavelength; The modulator uses the numerical interpolation method to inversely solve equation (1) and obtain the wavelength modulation function ; The modulator uses the numerical interpolation method to inversely solve equation (1) and obtain the wavelength modulation function The specific process is: Nonlinear relationship between wavelength and axial focus position of a dispersive lens Discretize and construct a discretized wavelength-displacement table; By linear interpolation or spline interpolation, at a given time t, the nonlinear relationship between the wavelength and the axial focus position of the dispersion lens is converted into Substitute the equation for wavelength variation over time and calculate the corresponding wavelength modulation function : （2）； in, The nonlinear relationship between the wavelength and the axial focus position of the dispersion lens The inverse function of Using optimization algorithms such as the least squares method, the wavelength modulation function is solved by iterative update , thereby obtaining a wavelength modulation function that meets the requirements of the spectral confocal displacement measurement system; S2: The photodiode converts each beam of reflected light received into an electrical signal, and determines the energy peak position of each beam of reflected light according to the signal strength of each electrical signal; S3: Combine the energy peak position of each reflected light beam with the wavelength modulation function to determine the axial position information of the sample.

5. The spectral confocal displacement measurement method based on wavelength modulation according to claim 4, characterized in that: The process of determining the energy peak position of each beam of reflected light according to the signal strength of each electrical signal is as follows: The electric signal is filtered by using a filtering algorithm to obtain a smooth signal with noise removed; Fit the smooth signal to a Gaussian function, the specific form is as follows: Where A is the peak energy intensity of the smoothed signal, is the energy peak time of the smoothed signal, is the energy peak width of the smoothed signal; Extracting peak times from Gaussian functions And it is used as the energy peak position of the smoothed signal.

6. The spectral confocal displacement measurement method based on wavelength modulation according to claim 5, characterized in that: The process of combining the energy peak position of each reflected light beam with the wavelength modulation function to determine the axial position information of the sample is: Use the maximum value method to find the time t corresponding to the maximum energy peak position from the energy peak positions of each beam of reflected light; Substitute the time t corresponding to the maximum energy peak position into the wavelength modulation function , find the wavelength λ corresponding to time t; Then bring the wavelength λ into , obtain the axial focus position of the sample .

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