CN116222802B - Measuring method and measuring device for central wavelength of light source - Google Patents
Measuring method and measuring device for central wavelength of light source Download PDFInfo
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- CN116222802B CN116222802B CN202310501801.5A CN202310501801A CN116222802B CN 116222802 B CN116222802 B CN 116222802B CN 202310501801 A CN202310501801 A CN 202310501801A CN 116222802 B CN116222802 B CN 116222802B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J9/00—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength
- G01J9/02—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength by interferometric methods
- G01J9/0246—Measuring optical wavelength
Abstract
The disclosure describes a method and a device for measuring a center wavelength of a light source, the method comprising: using a light source to emit a measuring beam to a sample to be measured; the control driving module drives the interference objective lens to move in a preset step length and synchronously controls the sampling module to uniformly sample the sample to be tested; constructing a relation curve of the sampling frame number and the optical interference signal forming each frame of image, and performing digital quadrature demodulation on the optical interference signal of each frame of image to obtain the amplitude and the phase of the relation curve at each frame of image; constructing an envelope Gaussian curve of the relation curve, and obtaining the peak position of the envelope Gaussian curve; fitting the image frame sequence of the multi-frame images at the peak positions and the fitting slope of the phase of the relation curve at each frame of images, and calculating the central wavelength of the light source according to the fitting slope. Therefore, through the measuring method, the center wavelength of the light source can be directly measured and calibrated on the measuring device, and the measuring efficiency and convenience can be improved.
Description
Technical Field
The disclosure relates generally to the industry of intelligent manufacturing equipment, and in particular to a method and a device for measuring a central wavelength of a light source.
Background
Interferometers are optical instruments that measure optical path differences using the principles of interferometry to determine a physical quantity of interest. Any change in the optical path difference between two beams of coherent light causes very sensitive movement of the interference fringes, whereas the optical path change of a certain beam of coherent light is caused by a change in the geometrical path it passes through or the refractive index of the medium, so that a small change in the geometrical length or refractive index can be measured by the movement change of the interference fringes, thereby measuring other physical quantities related thereto. The measurement accuracy is determined by the accuracy of the measured optical path difference. The optical path difference changes by one wavelength every time the interference fringe moves by one fringe interval, so the interferometer measures the optical path difference by taking the wavelength of the light wave as a unit, and the measurement accuracy is relatively high. A white light interferometer is an optical instrument that measures a difference in optical path length using white light as a light source to measure a physical quantity.
The center wavelength of the white light source can be understood as the wavelength of the light component where the energy is maximum in the wavelength range, and accurate measurement and calibration of the center wavelength of the light source can improve the measurement accuracy of the white light interferometer. In the prior art, a separate light source wavelength measuring instrument such as a spectrometer is typically used to measure the center wavelength of the light source, and the measurement typically requires that the light source be removed from the light source interferometer for testing.
However, the disassembly of the instrument is generally cumbersome, time consuming and labor costly, and may damage the instrument.
Disclosure of Invention
The present disclosure has been made in view of the above-described conventional circumstances, and an object thereof is to provide a measurement method and a measurement device that can directly measure the center wavelength of a light source in a measurement device, thereby improving the efficiency and convenience of measurement and improving the measurement accuracy of the measurement device.
To this end, a first aspect of the present disclosure provides a method for measuring a center wavelength of a light source based on an optical interferometry technique, the method comprising: using a light source to emit a measuring beam to a sample to be measured; the method comprises the steps that a driving module is controlled to drive an interference objective lens to move in a preset step length, and a sampling module is synchronously controlled to uniformly sample a sample to be tested, wherein the sampling module collects reflected light beams, which are reflected by the sample to be tested, of the measuring light beams and are formed in the interference objective lens, so as to obtain optical interference signals for forming multi-frame images related to the sample to be tested; constructing a relation curve of the sampling frame number of the multi-frame images and the signal intensity of the optical interference signal, and carrying out digital quadrature demodulation on the signal intensity of each frame of image in the relation curve to obtain the amplitude and the phase of each frame of image in the relation curve; constructing an envelope Gaussian curve of the relation curve by using the obtained amplitude sequences of the multi-frame images, and obtaining the peak position of the envelope Gaussian curve; fitting an image frame sequence of the multi-frame images and a fitting slope of the phase of the relation curve at each frame of images at the peak position, and further solving the center wavelength of the light source according to the fitting slope.
In the first aspect of the disclosure, the center wavelength of the light source can be directly measured and calibrated on the measuring device, so that the efficiency and convenience of measurement can be improved; in addition, the driving module is controlled to drive the interference objective lens to move in a preset step length and synchronously control the sampling module to uniformly sample a sample to be measured, so that the synchronism of the scanning step length of the interference objective lens and the sampling of the sampling module can be improved, the accuracy of a constructed relation curve of the sampling frame number and the signal intensity can be improved, the calculated center wavelength of the light source can be more accurate, and the measuring precision of the measuring device can be improved.
In addition, in the measurement method according to the first aspect of the present disclosure, optionally, a relation between the signal intensity and the displacement of the interference objective lens is:
wherein, the liquid crystal display device comprises a liquid crystal display device,λfor the center wavelength of the light source,I(z)for the signal strength of the signal to be measured,I bg for the intensity of the background light,γin order for the modulation factor to be a factor,for the envelope gaussian curve,zfor the displacement of the interference objective lens,z 0 a scanning position with zero optical path difference of the center wavelength,σthe expression of (2) is:
wherein delta isλIs thatλIs used for the increment of (c),W c is the coherence length of the light source, andthe phase distribution of the optical interference signal along with the displacement of the interference objective lens is as follows:
Wherein, the liquid crystal display device comprises a liquid crystal display device,θ(z)is a phase distribution. Therefore, the relation between the signal intensity and the displacement of the interference objective lens can be conveniently obtained, and the position of the optical interference signal along with the interference objective lensAnd (3) phase distribution of the shift.
In addition, in the measurement method according to the first aspect of the present disclosure, optionally, the initial light source wavelength is preset to beλ init Driving the interference objective lens to scan the sample to be detected, wherein the relation between the scanning step length of the interference objective lens and the initial light source wavelength is as follows:
wherein delta iszFor the scanning step size,Nfor the period phase shift frame number, 2NRepresenting the number of times the sampling module takes a picture in a signal period; the relation between the displacement of the interference objective lens and the scanning step length is as follows:
wherein, the liquid crystal display device comprises a liquid crystal display device,iand the image frame sequence of the interference objective lens at the sampling position is obtained. Therefore, by presetting an initial light source wavelength, the interference objective lens can be conveniently driven to scan the sample to be detected at a specified scanning step length.
In addition, in the measurement method according to the first aspect of the present disclosure, optionally, at each of the image frame sequences, digital quadrature demodulation is performed on the signal intensity within one signal period, to obtain:
wherein, the liquid crystal display device comprises a liquid crystal display device,ifor the frame sequence of the image in question, R(i)For the first modulated signal it is possible to provide,Q(i)for the second modulated signal to be a second modulated signal,I n represented in the image frame sequence asnThe gray values represented by the images at that time, thereby deriving the amplitude and the phase of the relationship at each of the image frame sequences:
wherein, the liquid crystal display device comprises a liquid crystal display device,a i in order to be amplitude-value,θ i is the phase. Therefore, the amplitude and the phase at each image frame sequence in the relation curve can be conveniently calculated.
In addition, in the measurement method related to the first aspect of the present disclosure, optionally, the amplitude sequence is subjected to gaussian fitting by using a least square method to obtain an envelope gaussian curve, where the amplitude sequence isa 1 ,a 2, …… , a M )，a M Representing the amplitude when the image frame sequence is M. Thus, the envelope gaussian can be obtained conveniently.
In addition, in the measurement method according to the first aspect of the present disclosure, optionally, the expression of the envelope gaussian curve is:
wherein A, B, C is a gaussian parameter, and natural logarithms are taken for both sides of the expression of the envelope gaussian, to obtain:
fitting the envelope gaussian curve using a least squares method to obtain:
wherein, the liquid crystal display device comprises a liquid crystal display device,m1 to 1m2 represents the range of the image frame sequence that participates in the envelope gaussian curve fitting. Therefore, the envelope Gaussian curve can be conveniently obtained by fitting the amplitude sequence by using a least square method.
In addition, in the present disclosureIn the measurement method according to the first aspect, optionally,m1 to 1mThe method for determining the range 2 comprises the following steps: determining the amplitude sequencea 1 ,a 2, …… , a M ) Is the maximum amplitude position of (a); taking the maximum amplitude position as the center, and acquiring the range of the image frame sequence near the maximum amplitude position asm1 to 1m2. Therefore, the range of the image frame participating in the envelope Gaussian curve fitting can be conveniently confirmed, noise entering the fitting range can be reduced, and fitting errors are increased.
In addition, in the measurement method according to the first aspect of the present disclosure, optionally, the gaussian curve parameters A, B, C are respectively biased and written as equationsEX=FAccording to the envelope Gaussian curve obtained by fitting, the expression of the peak position of the envelope Gaussian curve is:
wherein, the liquid crystal display device comprises a liquid crystal display device,Pand 0 is the peak position. Thus, the peak position of the envelope gaussian can be obtained conveniently.
In addition, in the measurement method according to the first aspect of the present disclosure, optionally, a range around the peak position is takenGPerforming linear phase fitting of the points by an expression of a phase distribution of the optical interference signal with displacement of the interference objective lens:
The slope of the phase of the optical interference signal relative to the displacement of the interference objective is obtained as:
and then obtaining the central wavelength of the light source:
wherein ""represents the multiplication and,kis the slope of the slope,θ 0 representing the initial phase distribution. Thus, the center wavelength of the light source can be obtained conveniently.
A second aspect of the present disclosure provides a measurement device for measuring a center wavelength of a light source based on an optical interferometry technique, the measurement device including: the device comprises a generation module, a time sequence synchronous generator, a driving module, an interference objective lens, a sampling module and a data processing module; the generating module is used for sending out measuring light beams to a sample to be measured through the interference objective lens; the time sequence synchronous generator is used for controlling the driving module to drive the interference objective lens to move in a preset step length and synchronously controlling the sampling module to uniformly sample the sample to be tested, wherein the sampling module collects the reflected light beam formed in the interference objective lens and reflected by the measuring light beam through the sample to be tested to obtain an optical interference signal for forming a multi-frame image related to the sample to be tested; the data processing module is used for: constructing a relation curve of the sampling frame number of the multi-frame images and the signal intensity of the optical interference signals, and carrying out digital quadrature demodulation on the signal intensity of each frame of image in the relation curve to obtain the amplitude and the phase of each frame of image in the relation curve; constructing an envelope Gaussian curve of the relation curve by using the obtained amplitude sequences of the multi-frame images, and obtaining the peak position of the envelope Gaussian curve; and obtaining the image frame sequence of the multi-frame images and the fitting slope of the phase of the relation curve at each frame of image near the peak position, and further obtaining the central wavelength of the light source according to the fitting slope.
In a second aspect of the disclosure, the center wavelength of the light source can be directly measured and calibrated on the measuring device, so that the efficiency and convenience of measurement can be improved; in addition, the driving module is controlled to drive the interference objective lens to move in a preset step length and synchronously control the sampling module to uniformly sample a sample to be measured, so that the synchronism of the scanning step length of the interference objective lens and the sampling of the sampling module can be improved, the accuracy of a constructed relation curve of the sampling frame number and the signal intensity can be improved, the calculated center wavelength of the light source can be more accurate, and the measuring precision of the measuring device can be improved.
According to the present disclosure, a measuring method and a measuring device for directly measuring the center wavelength of a light source on the measuring device can be provided, so that the efficiency and convenience of measurement can be improved, and the measurement accuracy of the measuring device can be improved.
Drawings
Embodiments of the present disclosure will now be explained in further detail by way of example only with reference to the accompanying drawings.
Fig. 1 is a functional block diagram showing a measurement device of a light source center wavelength according to an embodiment of the present disclosure.
Fig. 2 is a functional block diagram showing a data processing module according to an embodiment of the present disclosure.
Fig. 3 is a schematic diagram showing the configuration of a measurement device of the center wavelength of a light source according to an embodiment of the present disclosure.
Fig. 4 is a schematic diagram showing an internal structure of an interference objective lens according to an embodiment of the present disclosure.
Fig. 5 is a flowchart illustrating a method of measuring a center wavelength of a light source according to an embodiment of the present disclosure.
Fig. 6A is a graph illustrating white light interference patterns in a sphere test according to an embodiment of the present disclosure.
Fig. 6B is a schematic diagram illustrating a white light interference signal according to an embodiment of the present disclosure.
Fig. 6C is a composition diagram illustrating a white light interference signal according to an embodiment of the present disclosure.
Fig. 7 is a schematic diagram illustrating linear phase fitting in accordance with embodiments of the present disclosure.
Detailed Description
Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the following description, the same members are denoted by the same reference numerals, and duplicate descriptions are omitted. In addition, the drawings are schematic, and the ratio of the sizes of the components to each other, the shapes of the components, and the like may be different from actual ones.
It should be noted that the terms "comprises" and "comprising," and any variations thereof, in this disclosure, such as a process, method, system, article, or apparatus that comprises or has a list of steps or elements is not necessarily limited to those steps or elements expressly listed or inherent to such process, method, article, or apparatus, but may include or have other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
The present disclosure provides a measurement method and a measurement device for directly measuring and calibrating a center wavelength of a light source on a measurement device for measuring a three-dimensional morphology of a sample to be measured based on an interferometry technique. The measuring device may be an optical interferometer or an optical interferometry microscope.
In some examples, the optical interferometer may be a white light interferometer and the optical interferometry microscope may be a white light interferometry microscope. In this disclosure, need not disassemble the instrument and take out the light source and use professional instrument again to test the light source, can directly test on measuring device to can realize measuring and calibrating light source center wavelength (i.e. the center wavelength of light source) anytime and anywhere, can promote measuring efficiency and convenience. When the service time is prolonged and the light source is attenuated, the light source can be directly measured and calibrated on site, and the measuring accuracy of the measuring device to the sample to be measured can be improved.
Fig. 1 is a functional block diagram showing a measurement device 1 of a light source center wavelength according to an embodiment of the present disclosure. Fig. 2 is a functional block diagram showing a data processing module 60 according to an embodiment of the present disclosure. Fig. 3 is a schematic diagram showing the configuration of the measurement device 1 of the light source center wavelength according to the embodiment of the present disclosure.
Referring to fig. 1 to 3, the measuring device 1 for the center wavelength of the light source according to the present embodiment may be a device for measuring the three-dimensional morphology of the sample 70 to be measured based on the optical interferometry technique, and the measuring device 1 may measure the center wavelength of the light source 110.
In some examples, the light source 110 may be a white light source and the measurement device 1 may be a white light interferometer or a white light interferometry microscope. The center wavelength of the white light source may be the wavelength at which the energy distribution is greatest, or the wavelength at which the peak position of the white light interference signal is greatest.
Referring to fig. 1, in the present embodiment, the measuring apparatus 1 may include a generating module 10, a timing synchronization generator 20, a driving module 30, an interference objective lens 40, a sampling module 50, and a data processing module 60.
In some examples, the generation module 10 may be configured to emit the measuring beam L1 to the sample 70 under test via the interference objective 40.
In some examples, the timing synchronization generator 20 may be configured to control the driving module 30 to drive the interference objective lens 40 to move in a preset step, and synchronously control the sampling module 50 to uniformly sample the sample 70 to be measured, so that the sampling module 50 obtains multi-frame images about the sample 70 to be measured.
In some examples, the sampling module 50 may be configured to collect the reflected light beam L1' formed in the interference objective lens 40 that is reflected by the measuring light beam L1 through the sample 70 to be measured to obtain an optical interference signal for forming each of the multiple frames of images.
Referring to fig. 2, in some examples, the data processing module 60 may include a quadrature demodulation unit 610, an envelope gaussian curve fitting unit 620, and a linear phase fitting unit 630.
In some examples, the quadrature demodulation unit 610 may be configured to construct a relationship curve of the number of samples of the multiple frame images and the signal strength of the optical interference signal, and digitally quadrature demodulate the signal strength of each frame of the image in the relationship curve to obtain the amplitude and phase at each frame of the image in the relationship curve.
In some examples, the number of sampling frames may be a plurality of frames of images of the sample 70 to be measured acquired by the interference objective 40 during a scan.
In some examples, the envelope gaussian curve fitting unit 620 may construct an envelope gaussian curve of the relation curve using the obtained amplitude sequences of the multi-frame images, and obtain peak positions of the envelope gaussian curve.
In some examples, the linear phase fitting unit 630 may fit the image frame order of the multi-frame images near the peak position and the fitted slope of the phase of the relationship curve at each frame image, and then find the center wavelength of the light source 110 from the fitted slope.
In some examples, the image frame sequence may be a frame sequence represented by each of the multiple frames of images of the sample 70 to be measured acquired by the interference objective 40 during the scan.
In the present embodiment, the measuring apparatus 1 may include: a generation module 10, a timing synchronization generator 20, a driving module 30, an interference objective lens 40, a sampling module 50, and a data processing module 60; the generating module 10 is used for emitting a measuring beam L1 to a sample 70 to be measured through the interference objective lens 40; the timing synchronization generator 20 is used for controlling the driving module 30 to drive the interference objective lens 40 to move with a preset step length and synchronously controlling the sampling module 50 to uniformly sample the sample 70 to be tested, wherein the sampling module 50 collects the reflected light beam L1' formed in the interference objective lens 40 and reflected by the measuring light beam L1 through the sample 70 to be tested to obtain an optical interference signal for forming a multi-frame image related to the sample 70 to be tested; the data processing module 60 is configured to: constructing a relation curve of the sampling frame number of the multi-frame images and the signal intensity of the optical interference signals, and carrying out digital quadrature demodulation on the signal intensity of each frame of image in the relation curve to obtain the amplitude and the phase of each frame of image in the relation curve; constructing an envelope Gaussian curve of the relation curve by using the amplitude sequences of the obtained multi-frame images, and obtaining the peak position of the envelope Gaussian curve; and the fitting slope of the image frame sequence of the multi-frame images and the phase of the relation curve at each frame of images is obtained near the peak position, and then the center wavelength of the light source 110 is obtained according to the fitting slope.
In the present disclosure, the center wavelength of the light source 110 can be directly measured and calibrated on the measuring device 1, so that the efficiency and convenience of measurement can be improved; in addition, by controlling the driving module 30 to drive the interference objective 40 to move in a preset step size and synchronously controlling the sampling module 50 to uniformly sample the sample 70 to be measured, the synchronism of the scanning step size of the interference objective 40 and the sampling of the sampling module 50 can be improved, the accuracy of the constructed relation curve of the sampling frame number and the signal intensity can be further improved, and the calculated center wavelength of the light source 110 can be further accurate, so that the subsequent measurement accuracy of the measuring device 1 can be improved.
Referring to fig. 3, in some examples, the measurement device 1 may further comprise a spectroscopic module 80. The beam splitting module 80 may be used to receive the measuring beam L1 and reflect the measuring beam L1 to the interference objective 40. The interference objective 40 may be used to form the reflected light beam L1 'and send the reflected light beam L1' to the sampling module 50 via the beam splitting module 80.
In some examples, the spectroscopy module 80 may be a spectroscopy tile.
In some examples, the interference signal formed when the measuring beam L1 interferes in the interference objective lens 40 may be referred to as an optical interference signal. In some examples, the interference signal formed when the reflected light beam L1' interferes in the interference objective lens 40 may also be referred to as an optical interference signal.
In some examples, the generation module 10 may include a light source 110 (see fig. 3) for being detected. The light source 110 may be used to emit a detected measuring beam L1.
In some examples, when the light source 110 is a white light source, the white light spectral width may be 40 nanometers to 120 nanometers. Thus, the center wavelength of the white light source can be conveniently measured within the range of 40-120 nanometers of the white light spectrum width.
In some examples, the generation module 10 may further include a first lens unit 120 and a second lens unit 130. The first lens unit 120 and the second lens unit 130 may be disposed between the light source 110 and the spectroscopic module 80. The first lens unit 120 may be a converging lens having a function of converging light beams, and the second lens unit 130 may be a collimating lens for converting light beams into collimated light. In this case, the measuring beam L1 can be converged into a beam after passing through the first lens unit 120 and then transmitted to the second lens unit 130, and the second lens unit 130 can convert the converged measuring beam L1 into a collimated beam and transmit the collimated beam to the spectroscopic module 80. This can reduce the divergence of the measuring beam L1 and thus reduce the energy loss of the measuring beam L1.
In some examples, the drive module 30 may be PZT (piezoelectric ceramics, piezoceramic) or a micro-drive motor.
In some examples, sampling module 50 may include a sampling camera 510. In some examples, sampling camera 510 may be a CCD (charge coupled device ) camera or a CMOS (Complementary Metal Oxide Semiconductor, complementary metal oxide semiconductor) camera. Thereby, the reflected light beam L1' can be converted into an electric signal forming a multi-frame image.
In some examples, the sampling module 50 may further include a third lens unit 520 located between the spectroscopic module 80 and the sampling camera 510. In some examples, the third lens unit 520 may be a converging lens having a converging light beam function. In this case, the third lens unit 520 can focus the reflected light beam L1' on the sampling camera 510.
In some examples, the data processing module 60 may be a computer.
In some examples, the sample 70 to be measured may be an ultra-smooth coupon.
In some examples, the interference objective 40 may reciprocate in directions Z and Z' shown in fig. 3 under the drive of the drive module 30.
In some examples, the preset step size of the driving module 30 may be 30 nm to 50 nm.
Referring to fig. 3, the method of measuring the center wavelength of the light source according to the present embodiment may be a method of measuring the center wavelength of the light source 110 by using the measuring device 1 for measuring the three-dimensional morphology of the sample 70 to be measured by the optical interferometry technique. In the present disclosure, the measurement method of the center wavelength of the light source may also be simply referred to as a measurement method or a method.
In some examples, the light source 110 may be a white light source and the measurement device 1 may be a white light interferometer or a white light interferometry microscope.
The white light interferometer is an optical instrument that measures the difference in optical paths by using the principle of white light interferometry, thereby measuring the relevant physical quantity in the sample 70 to be measured. In the present disclosure, the center wavelength of the white light source can be directly measured and calibrated on the white light interferometer, and the white light source is taken out without disassembling the white light interferometer, and then the measurement and calibration of the center wavelength of the white light source are performed by using a professional white light source center wavelength calibration device (such as a spectrometer and the like). Therefore, when the service time of the white light interferometer is prolonged and the white light source is attenuated, the center wavelength of the white light source can be directly measured and calibrated on the white light interferometer, and further the subsequent measurement accuracy of the white light interferometer can be improved.
Fig. 4 is a schematic diagram showing an internal structure of an interference objective lens 40 according to an embodiment of the present disclosure.
Referring to fig. 4, in some examples, the interference objective 40 may include a beam splitting unit 410 and a reference unit 420. The light splitting unit 410 may be configured to receive the measuring beam L1 and split the measuring beam L1 into a first sub-measuring beam L11 and a second sub-measuring beam L12. In some examples, the light splitting unit 410 may be further configured to reflect the first sub-measurement beam L11 to the reference unit 420 and transmit the second sub-measurement beam L12 to the target point on the sample 70 to be measured.
In some examples, the first sub-measurement beam L11 may be reflected to the reference unit 420 via the spectroscopic unit 410 and reflected by the reference unit 420 to form a first sub-measurement reflected beam L11'. In some examples, the second sub-measurement beam L12 may be transmitted to the target point via the spectroscopic unit 410 and reflected by the target point to form a second sub-measurement reflected beam L12'.
In some examples, the first sub-measurement reflected beam L11' and the second sub-measurement reflected beam L12' may form a reflected beam L1'. Specifically, the light splitting unit 410 may be further configured to combine the first sub-measurement reflected light beam L11' and the second sub-measurement reflected light beam L12' to form a reflected light beam L1'. In other words, the reflected light beam L1' may include a first sub-measurement reflected light beam L11' and a second sub-measurement reflected light beam L12'.
In some examples, the first sub-measurement reflected beam L11 'and the second sub-measurement reflected beam L12' may form interference, and the measuring device 1 may obtain the height information of the target point based on the optical interference signal formed by the first sub-measurement reflected beam L11 'and the second sub-measurement reflected beam L12'.
Fig. 5 is a flowchart illustrating a method of measuring a center wavelength of a light source according to an embodiment of the present disclosure.
Referring to fig. 5, in particular, the measurement method may include the steps of:
in step S100, the light source 110 is used to emit the measuring beam L1 to the sample 70.
In step S200, the control driving module 30 drives the interference objective lens 40 to move and synchronously controls the sampling module 50 to uniformly sample the sample 70 to be tested. Thereby, the sampling module 50 can be made to obtain a multi-frame image with respect to the sample 70 to be measured.
In some examples, the driving module 30 may be controlled to drive the interference objective lens 40 to move in a preset step size while synchronously controlling the sampling module 50 to uniformly sample the sample 70 to be measured.
In some examples, the sampling module 50 may be configured to collect the reflected light beam L1' formed in the interference objective lens 40 that is reflected by the measuring light beam L1 through the sample 70 to be measured to obtain an optical interference signal for forming each of the multiple frames of images.
In some examples, the timing synchronization generator 20 may be configured to control the driving module 30 to drive the interference objective lens 40 to move in a preset step, and synchronously control the sampling module 50 to uniformly sample the sample 70 to be measured, so that the sampling module 50 obtains multi-frame images about the sample 70 to be measured.
In step S300, a relationship curve between the number of sampling frames of the multi-frame image and the signal intensity of the optical interference signal may be constructed, and digital quadrature demodulation may be performed on the signal intensity of each frame of image in the relationship curve to obtain the amplitude and the phase at each frame of image in the relationship curve.
In step S400, an envelope gaussian curve of the relation curve may be constructed using the obtained amplitude sequences of the multi-frame images, and the peak position of the envelope gaussian curve may be obtained.
In step S500, a fitting slope of the image frame sequence of the multi-frame images and the phase of the relationship curve at each frame image may be obtained near the peak position, and the center wavelength of the light source 110 may be obtained from the fitting slope.
In some examples, the data processing module 60 may be configured to sequentially perform step S300, step S400, and step S500.
In the present disclosure, the center wavelength of the light source 110 can be directly measured and calibrated on the measuring device 1, so that the efficiency and convenience of measurement can be improved; in addition, the driving module 30 is controlled to drive the interference objective 40 to move in a preset step length, and the sampling module 50 is synchronously controlled to uniformly sample the sample 70 to be measured, so that the synchronism of the scanning step length of the interference objective 40 and the sampling of the sampling module 50 can be improved, the accuracy of the constructed relation curve of the sampling frame number and the signal intensity can be further improved, the calculated center wavelength of the light source 110 can be further accurate, and the subsequent measurement accuracy of the measuring device 1 can be further improved.
In some examples, the data processing module 60 may include a quadrature demodulation unit 610, an envelope gaussian curve fitting unit 620, and a linear phase fitting unit 630. In some examples, quadrature demodulation unit 610 may be used to perform step S300, envelope gaussian curve fitting unit 620 may be used to perform step S400, and linear phase fitting unit 630 may be used to perform step S500.
In some examples, the sampling module 50 may uniformly sample the sample 70 to be measured by controlling the driving module 30 to drive the interference objective lens 40 to uniformly move in a preset step. That is, the time interval of each frame of image sampled by the sampling module 50 may be the same.
In some examples, one data message for the sample 70 to be measured may be obtained for each frame of image. In other examples, multiple data information for the sample 70 to be measured may be obtained per frame of image. In some examples, data information for N frames (where N may be the number of periodic phase shift frames) may be acquired to reconstruct the three-dimensional surface topography of the sample 70 to be measured.
In the present disclosure, since the sampling module 50 samples the sample 70 to be measured while driving the interference objective lens 40 to move by a preset step length in a synchronous triggering manner, the sampling module 50 can sample as uniformly as possible during the scanning of the interference objective lens 40.
In the present disclosure, the calibration algorithm of the data processing module 60 may be divided into three data processing links that are connected in tandem. The three data processing links may include digital quadrature demodulation of step S300, envelope gaussian curve fitting of step S400, and linear phase fitting of step S500 in that order.
In step S300, the amplitude and phase of discrete sequence points on the envelope gaussian curve can be obtained by digital quadrature demodulation.
In step S400, the peak position (i.e., the center wavelength position) may be obtained by fitting an envelope gaussian curve, and thus the subsequent linear phase fitting region may be determined.
In step S500, the slope of the phase distribution line near the peak position can be obtained by linear phase fitting, and the center wavelength can be obtained from the slope of the phase distribution line.
In the method, linear phase fitting is adopted, and the center wavelength is obtained by utilizing a mode of processing multiple data sets and linear characteristics, so that the precision can be improved, and errors caused by the following factors can be reduced: non-uniformity of scanning step length of a driving motor, gray noise of a photosensitive chip in a CCD camera, and non-synchronism of hardware transmission for synchronous triggering.
Fig. 6A is a graph illustrating white light interference patterns in a sphere test according to an embodiment of the present disclosure. Fig. 6B is a schematic diagram illustrating a white light interference signal according to an embodiment of the present disclosure. Fig. 6C is a composition diagram illustrating a white light interference signal according to an embodiment of the present disclosure.
Referring to fig. 6A-6C, in some examples, the light source 110 may be a white light source that for sphere testing may form a white light interference pattern that is bright in the center (high energy) and dark around (low energy) as in fig. 6A. A graph of the white light interference signal forming the white light interference pattern and a composition graph of the white light interference signal may be shown in fig. 6B and 6C, respectively.
Referring to fig. 6B and 6C, the white light interference signal may be generally represented as a cosine signal whose envelope is modulated by a gaussian function, the visibility of the white light interference pattern being non-constant and varying with different scanning positions on the sample 70 to be measured by the interference objective lens 40. When the optical path difference between the measuring beam and the reference beam is zero, the interference signal exhibits a maximum value, which is called a coherent peak. The coherence peaks represent the relative height information of corresponding data points on the surface of the sample 70 to be measured, and the relative heights of all data points combine to form the overall topography of the sample 70 to be measured.
As shown in fig. 6C, the white light interference signal may be a superimposed signal of all monochromatic light (e.g., seven-color light) interference signals. When the peak positions of the seven colored lights are overlapped, the signal intensity of the white light interference signal is maximum, and the peak positions are the central wavelength positions of the white light sources.
In some examples, the relationship between the signal strength of the optical interference signal and the displacement of the interference objective 40 is:
wherein, the liquid crystal display device comprises a liquid crystal display device,λas the center wavelength of the light,I(z)may be the signal strength of a white light interference signal,I bg for the intensity of the background light,γin order for the modulation factor to be a factor,is an envelope gaussian curve, also known as the amplitude signal of a white light interference signal,zin order to interfere with the displacement of the objective lens 40,z 0 for a scanning position with zero optical path difference at the center wavelength, exp represents an exponential function, cos represents a cosine function,σthe expression form of (a) is as follows:
wherein, the liquid crystal display device comprises a liquid crystal display device,can cover the area of coherence length, deltaλIs thatλIs used for the increment of (c),W c for the coherence length of the light source 110,and->The phase distribution of the white light interference signal with the displacement of the interference objective lens 40 is:
wherein, the liquid crystal display device comprises a liquid crystal display device,θ(z)is a phase distribution. Thus, the relation between the signal intensity of the white light interference signal and the displacement of the interference objective lens 40 and the phase distribution of the white light interference signal along with the displacement of the interference objective lens 40 can be conveniently obtained.
In some examples, the scan position where the center wavelength optical path difference is zero, i.e., represents the scan position of the interference objective lens 40 where the two beams of coherent light have zero optical path difference.
In some examples, the background light intensity may be the light intensity of the environment in which the measuring device 1 is located, for example, the light intensity generated by an indoor light fixture.
In some of the examples of the present invention,γmay be a parameter that measures the modulation depth. In some of the examples of the present invention,γmay be a parameter calculated from the maximum and minimum magnitudes on the relationship curve.
In some examples, the displacement of the interference objective 40 may be a vertical displacement.
In some of the examples of the present invention,I(z)the superimposed light intensity of all the monochromatic light of the measuring beam L1 in the vicinity of its center wavelength may be used.
In step S200, the initial light source wavelength may be preset to beλ init The interference objective 40 may be driven to scan the sample 70 to be measured, and the relation between the scanning step size of the interference objective 40 and the initial light source wavelength may be:
wherein delta iszFor the scanning step (alternatively referred to as the displacement of the interference objective 40 between adjacent image frame sequences),Nfor periodic phase shift frame number, expressed in halfNumber of times of photographing by sampling module 50 in each period, 2NRepresenting the number of shots taken by the sampling module 50 in a single signal period; the relation between the displacement of the interference objective 40 and the scanning step is:
Wherein, the liquid crystal display device comprises a liquid crystal display device,iimage frame sequence (or frame number) of scan positions (sampling positions) for the interference objective. Thus, by presetting an initial light source wavelength, the interference objective lens 40 can be conveniently driven to scan the sample 70 to be measured at a prescribed scanning step.
In some examples, the driving module 30 drives the interference objective lens 40 to move with a preset step, that is, it means that the driving module 30 drives with the preset step, and accordingly controls the interference objective lens 40 to scan the sample 70 to be measured with a corresponding scanning step.
In some examples, the initial light source wavelength may be a coarse light source wavelength that is randomly set.
In some examples, the number of periodic phase shift frames (steps) may be 4 to 32. The number of the periodic phase steps is not suitable to be set too small, otherwise, the data volume is insufficient, and the calculation progress is lost; and is not set too large, otherwise it would result in too much data being processed to affect the processing speed.
The data processing procedure of the data processing module 60 is described in detail below.
In step S300, the amplitude signal of the interference signal is generated due to the white lightFor a time-lapse signal, the white light interference signal may be considered to be less attenuated in a single signal period. / >
In some examples, at each image frame sequence, digital quadrature demodulation of the signal strength of the white light interference signal over one signal period yields:
wherein, the liquid crystal display device comprises a liquid crystal display device,ifor the frame sequence of the image,R(i)for the first modulated signal it is possible to provide,Q(i)for the second modulated signal to be a second modulated signal,I n represented in the image frame sequence asnThe gray value represented by the image at the time, thereby obtaining the image frame sequenceAmplitude and phase at:
wherein, the liquid crystal display device comprises a liquid crystal display device,a i in order to be amplitude-value,θ i is the phase.
In some of the examples of the present invention,R(i)it may be a horizontally modulated signal that,Q(i)may be a vertical modulated signal.
The amplitude and the phase of each frame of image frame sequence can be obtained through digital quadrature demodulation. Therefore, the amplitude and the phase of the image frame sequence in the relation curve can be conveniently calculated.
From step S300, a sequence of magnitudes of the signal may be obtained: (a 1 ,a 2, …… , a M )，a M Representing the amplitude when the image frame sequence is M.
In some examples, the sequence of magnitudes may be gaussian fitted using a least squares method to obtain an envelope gaussian. Thus, the envelope gaussian can be obtained conveniently.
In some examples, the interference objective 40 may scan M frames of images and form the M frames of images into an image sequence under the drive of the drive module 30, i.e. In the coordinates +.>Can be taken out of the image sequence at the planar position of +. >Gray value (or value called signal intensity) at: />. The sampling frame number of the images in the image sequence is taken as the abscissa, the signal intensity or gray value of each frame of the images is taken as the ordinate, so that the +.>An optical interference curve at (as shown in fig. 6B).
In some examples, the expression of the envelope gaussian may be written as:
wherein A, B, C is a gaussian curve parameter.
Taking the natural logarithm of the two sides of the expression of the envelope Gaussian curve, the following is obtained:
fitting an envelope Gaussian curve by using a least square method to obtain:
wherein, the liquid crystal display device comprises a liquid crystal display device,m1 to 1m2 denotes the fitting range of the image frames involved in gaussian curve fitting. If noise data enters the fitting range, fitting errors are greatly increased, and even fitting distortion occurs. Therefore, the least square method is used for fitting the amplitude sequence, so that an envelope Gaussian curve can be conveniently obtained, and the fitting range is kept atm1 to 1m2, the fitting accuracy can be improved.
In some of the examples of the present invention,m1 to 1mThe method for determining the range of 2 can be as follows: determining amplitude sequencea 1 ,a 2, …… , a M ) Is the maximum amplitude position of (a); the range of acquiring the image frames around (e.g., on the left and right sides of) the maximum amplitude position is centered around the maximum amplitude position m1 to 1m2. Therefore, the range of the image frame participating in the envelope Gaussian curve fitting can be conveniently confirmed, noise entering the fitting range can be reduced, and fitting errors are increased.
In some examples, the Gaussian curve parameters may be separately biased and written as equationsEX=FAccording to the envelope Gaussian curve obtained by fitting, the expression of the peak position of the envelope Gaussian curve is as follows:
wherein, the liquid crystal display device comprises a liquid crystal display device,Pand 0 is the peak position. Thus, the peak position of the envelope gaussian can be obtained conveniently.
Specifically, the gaussian curve parameters (i.e. A, B, C) are respectively biased to obtain:
written as equationEX=FMatrix form of (a), namely:
due toEIs a symmetric matrix, and thus coefficient vectorsX=E -1 F。
According to the envelope Gaussian curve obtained by fitting, the expression of the peak position can be obtained as follows:
wherein, the liquid crystal display device comprises a liquid crystal display device,P 0 is the peak position. The step can obtain the peak position of the amplitude by fitting an envelope Gaussian curve. Thus, the peak position of the envelope gaussian can be obtained conveniently.
Fig. 7 is a schematic diagram illustrating linear phase fitting in accordance with embodiments of the present disclosure.
Referring to fig. 7, in step S500, a "displacement" may be fitted near the peak position -phase distribution->"phase curve.
In some examples, a range around the peak position may be takenJThe individual points are fitted with a linear phase.
In some of the examples of the present invention,Jcan be equal toN（NFor a periodic phase shift frame number). In this case, since the sensitivity of the signal near the peak position is the highest, the range near the peak position is usedNThe linear phase fitting of the individual points can improve the accuracy of the fitting, while the signals far from the peak position (on both sides of the peak position) are gradually attenuated, so that the fitting error is increased by adopting the signals.
Has been obtained in step S300iAmplitude and phase at:
by the expression of the phase distribution of the white light interference signal with the displacement of the interference objective lens 40:
the slope of the phase of the resulting white light interference signal relative to the displacement of the interference objective 40 is:
and then the center wavelength of the light source 110:
wherein ""represents the multiplication and,kis the slope of the slope,θ 0 representing the initial phase distribution. Thereby, the center wavelength of the light source 110 can be obtained conveniently.
In some examples, it can be understood that the phase of the white light interference signal increases linearly with respect to the displacement or frame number, with a slope of a fixed value。
In some of the examples of the present invention, JThe value of (2) may take a value of 4 to 32. In this case, ifNThe data with larger noise component on the boundary of the coherent area is obtained if the data quantity is too large; if the amount of data involved in the fitting is too small, the accuracy of the fitting is insufficient.
In the present disclosure, the center wavelength of the light source 110 can be directly measured and calibrated on the measuring device 1, so that the efficiency and convenience of measurement can be improved; in addition, the driving module 30 is controlled to drive the interference objective lens 40 to move in a preset step length, and the sampling module 50 is synchronously controlled to uniformly sample the sample 70 to be measured, so that the synchronism of the scanning step length of the interference objective lens 40 and the sampling of the sampling module 50 can be improved, the accuracy of the constructed relation curve of the sampling frame number and the signal intensity of the white light interference signal can be improved, the calculated center wavelength of the light source 110 can be more accurate, and the subsequent measurement accuracy of the measuring device 1 can be improved.
While the disclosure has been described in detail in connection with the drawings and embodiments, it should be understood that the foregoing description is not intended to limit the disclosure in any way. Modifications and variations of the present disclosure may be made as desired by those skilled in the art without departing from the true spirit and scope of the disclosure, and such modifications and variations fall within the scope of the disclosure.
Claims (10)
1. The measuring method for measuring the center wavelength of the white light source based on the optical interferometry technology is characterized by comprising the following steps: using the white light source to emit measuring light beams to a sample to be measured; the method comprises the steps that a driving module is controlled to drive an interference objective lens to move in a preset step length, and a sampling module is synchronously controlled to uniformly sample a sample to be tested, wherein the sampling module collects reflected light beams, which are reflected by the sample to be tested, of the measuring light beams and are formed in the interference objective lens, so as to obtain optical interference signals for forming multi-frame images related to the sample to be tested; constructing a relation curve of the sampling frame number of the multi-frame images and the signal intensity of the optical interference signal, and carrying out digital quadrature demodulation on the signal intensity of each frame of image in the relation curve to obtain the amplitude and the phase of each frame of image in the relation curve; constructing an envelope Gaussian curve of the relation curve by using the obtained amplitude sequences of the multi-frame images, and obtaining the peak position of the envelope Gaussian curve; and obtaining a fitting slope of an image frame sequence of the multi-frame images and a phase of the relation curve at each frame of image near the peak position, and further obtaining a center wavelength of the white light source according to the fitting slope, wherein the center wavelength of the white light source is the wavelength at which the energy distribution is maximum.
2. The method of measuring according to claim 1, wherein,
the relation between the signal intensity and the displacement of the interference objective lens is as follows:
wherein, the liquid crystal display device comprises a liquid crystal display device,λfor the center wavelength of the white light source,I(z)for the signal strength of the signal to be measured,I bg for the intensity of the background light,γin order for the modulation factor to be a factor,for the envelope gaussian curve,zfor the displacement of the interference objective lens,z 0 a scanning position with zero optical path difference of the center wavelength,σthe expression of (2) is:
wherein delta isλIs thatλIs used for the increment of (c),W c is the coherence length of the white light source, andthe phase distribution of the optical interference signal along with the displacement of the interference objective lens is as follows:
wherein, the liquid crystal display device comprises a liquid crystal display device,θ(z)for the phase distribution.
3. The method of measuring according to claim 2, wherein,
presetting the initial white light source wavelength asλ init Driving the interference objective lens to scan the sample to be detected, wherein the relation between the scanning step length of the interference objective lens and the initial white light source wavelength is as follows:
wherein delta iszFor the scanning step size of the scanning device,Nfor the period phase shift frame number, 2NRepresenting the acquisition within a signal periodThe number of times the sample module shoots;
the relation between the displacement of the interference objective lens and the scanning step length is as follows:
wherein, the liquid crystal display device comprises a liquid crystal display device, iScanning the image frame sequence of positions for the interference objective.
4. The method of measuring according to claim 3, wherein,
and carrying out digital quadrature demodulation on the signal intensity in one signal period at each image frame sequence to obtain:
wherein, the liquid crystal display device comprises a liquid crystal display device,ifor the frame sequence of the image in question,R(i)for the first modulated signal it is possible to provide,Q(i)for the second modulated signal to be a second modulated signal,I n represented in the image frame sequence asnThe gray value represented by the image at that time, the magnitude and the phase of the relationship at each of the image frame sequences:
wherein, the liquid crystal display device comprises a liquid crystal display device,a i for the amplitude value of the signal to be described,θ i is the phase.
5. The measuring method according to claim 4, wherein,
performing Gaussian fitting on the amplitude sequence by using a least square method to obtain the envelope Gaussian curve, wherein the amplitude sequence is [ ], and the amplitude sequence is [ ]a 1 ,a 2, …… , a M )，a M Representing the amplitude when the image frame sequence is M.
6. The measurement method according to claim 5, wherein,
the expression of the envelope Gaussian curve is as follows:
wherein A, B, C is a Gaussian curve parameter,
taking natural logarithms from two sides of the expression of the envelope Gaussian curve to obtain:
fitting the envelope gaussian curve using a least squares method to obtain:
wherein, the liquid crystal display device comprises a liquid crystal display device, m1 to 1m2 represents the range of the image frame order that participates in the envelope gaussian curve fitting.
7. The measuring method of claim 6, wherein,
m1 to 1mThe method for determining the range 2 comprises the following steps:
determining a maximum amplitude position in the amplitude sequence;
taking the maximum amplitude position as the center, and acquiring the range of the image frame sequence near the maximum amplitude position asm1 to 1m2.
8. The measuring method of claim 6, wherein,
respectively solving partial derivatives of the Gaussian curve parameters and writing the partial derivatives as equationsEX=FAccording to the envelope Gaussian curve obtained by fitting, the expression of the peak position of the envelope Gaussian curve is:
wherein, the liquid crystal display device comprises a liquid crystal display device,Pand 0 is the peak position.
9. The measurement method according to claim 8, wherein,
taking the range around the peak positionJThe individual points are subjected to a linear phase fit,
by the expression of the phase distribution of the optical interference signal with the displacement of the interference objective lens:
the slope of the phase of the optical interference signal relative to the displacement of the interference objective is obtained as:
and further obtaining the center wavelength of the white light source:
wherein ""represents the multiplication and, kIs the slope of the slope,θ 0 representing the initial phase distribution.
10. The measuring device is used for measuring the center wavelength of a white light source based on an optical interferometry technology, and is characterized by comprising a generating module, a time sequence synchronous generator, a driving module, an interference objective lens, a sampling module and a data processing module; the generating module is used for sending out measuring light beams to a sample to be measured through the interference objective lens; the time sequence synchronous generator is used for controlling the driving module to drive the interference objective lens to move in a preset step length and synchronously controlling the sampling module to uniformly sample the sample to be tested, wherein the sampling module collects the reflected light beam formed in the interference objective lens and reflected by the measuring light beam through the sample to be tested to obtain an optical interference signal for forming a multi-frame image related to the sample to be tested; the data processing module is used for: constructing a relation curve of the sampling frame number of the multi-frame images and the signal intensity of the optical interference signal, and carrying out digital quadrature demodulation on the signal intensity of each frame of image in the relation curve to obtain the amplitude and the phase of each frame of image in the relation curve; constructing an envelope Gaussian curve of the relation curve by using the obtained amplitude sequences of the multi-frame images, and obtaining the peak position of the envelope Gaussian curve; and obtaining the image frame sequence of the multi-frame images and the fitting slope of the phase of the relation curve at each frame of image near the peak position, and further obtaining the central wavelength of the white light source according to the fitting slope, wherein the central wavelength of the white light source is the wavelength at which the energy distribution is maximum.
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