CN117629057A - Device and method for measuring anti-interference environment signals based on white light interferometry - Google Patents
Device and method for measuring anti-interference environment signals based on white light interferometry Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02015—Interferometers characterised by the beam path configuration
- G01B9/02032—Interferometers characterised by the beam path configuration generating a spatial carrier frequency, e.g. by creating lateral or angular offset between reference and object beam
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/14—Measuring arrangements characterised by the use of optical techniques for measuring distance or clearance between spaced objects or spaced apertures
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02055—Reduction or prevention of errors; Testing; Calibration
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02083—Interferometers characterised by particular signal processing and presentation
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02083—Interferometers characterised by particular signal processing and presentation
- G01B9/02084—Processing in the Fourier or frequency domain when not imaged in the frequency domain
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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
- G01J1/00—Photometry, e.g. photographic exposure meter
- G01J1/02—Details
- G01J1/0295—Constructional arrangements for removing other types of optical noise or for performing calibration
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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
- G01J1/00—Photometry, e.g. photographic exposure meter
- G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
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Abstract
The invention discloses a device and a method for measuring an anti-interference environment signal based on white light interferometry, wherein the method comprises the following steps: s1, adjusting reference light in a reference arm to cause beat frequency interference with signal light passing through an event point to be detected; s2, regulating the polarization state of the reference light to obtain a time domain interference signal under a certain polarization direction included angle; s3, carrying out Fourier transform on the time domain interference signal to obtain a frequency domain signal, and carrying out low-frequency filtering; then carrying out inverse Fourier transform and normalizing to obtain an interference peak; s4, repeating the measurement for a plurality of times, and adjusting the angle of the polarization state of the reference light to cover a complete period; s5, convolving the multiple interference peaks; s6, carrying out Lorentz curve fitting on the convolution result of the time domain interference peak to obtain a signal for finally eliminating the environmental disturbance. The invention can eliminate the phenomena of peak value splitting, sawtooth deformation and the like of the measurement signal of the white light interference system under the disordered disturbance environment, and can also eliminate other low-frequency noise caused by the environment disturbance.
Description
Technical Field
The invention relates to the field of optical measurement, in particular to a device and a method for measuring an anti-interference environment signal based on white light interferometry.
Background
White light interferometry is an effective means and solution for measuring optically weak signals. The intensity detection and distance positioning of extremely weak signals can be realized by utilizing the extremely short coherence length of white light.
However, almost all the existing white light interference detection devices can only be measured in a static environment, the devices cannot have large or rapid disturbance, and the environment where the to-be-detected points are located also has to be a stable static environment. Once the equipment itself shakes or the to-be-measured product is in a complex disturbance environment, the disturbance of the environment not only can introduce more low-frequency noise, but also can change the optical fiber shape of the test sample, thereby affecting the polarization state change of light in the optical fiber shape, the conditions can lead to thicker substrate noise of a measured curve, meanwhile, a single smooth interference peak can deform into a plurality of peaks, the measurement result is complex and difficult to identify, the distance precision is difficult to judge, and the signal intensity also jumps in a large range due to the rapid continuous change of the polarization state, and the measurement error is suddenly increased.
Disclosure of Invention
The invention mainly aims to provide a device and a method for measuring an anti-interference environment signal based on white light interferometry, which can greatly improve the signal-to-noise ratio of a final test result in a dynamic environment and truly and accurately restore the interference peak condition of a to-be-measured point.
The technical scheme adopted by the invention is as follows:
a method for measuring an immunity environment signal based on white light interferometry is provided, which comprises the following steps:
s1, adjusting reference light in a reference arm to enable the reference light to generate beat frequency interference with signal light passing through an event point to be detected, and generating a time domain interference signal; the reference light and the signal light are formed by splitting broad spectrum light emitted by a white light source;
s2, adjusting the angle of the polarization state of the reference light to obtain a time domain interference signal under a certain polarization direction included angle;
s3, carrying out Fourier transform on the time domain interference signal to obtain a frequency domain signal, and carrying out low-frequency filtering; performing inverse Fourier transform on the filtered frequency domain signals to obtain time domain interference spectrums, and normalizing the time domain interference spectrums to obtain interference peaks;
s4, repeating the measurement for a plurality of times, adjusting the angle of the polarization state of the reference light to cover a complete period, obtaining signals of N beat frequency interferometry, and correspondingly obtaining N interferometry peaks, wherein N is an integer;
s5, convolving the N times of interference peaks to obtain a convolution result of the time domain interference peaks;
s6, carrying out Lorentz curve fitting on the convolution result of the time domain interference peak to obtain a signal for finally eliminating the environmental disturbance.
In step S6, the highest amplitude of the N interference peaks is specifically taken as the peak point of the fitting curve, the average value of the median points of the N interference peaks is taken as the midpoint of the fitting curve, and the average value of the half-height width of the N interference peaks is taken as the half-height width of the fitting curve.
In the above technical solution, adjusting the reference light in the reference arm in step S1 includes: the optical path of the reference light is continuously adjusted by controlling the optical fiber delay line in the reference arm, and beat frequency interference occurs when the optical path of the reference light is equal to the optical path of the signal light passing through the event point to be measured in the measuring arm.
By adopting the technical scheme, the optical fiber delay line continuously changes the optical path of light passing through the optical fiber delay line by moving the position of the internal reflector, so as to continuously change the arm length of the reference arm.
In the above technical solution, in step S1, adjusting the reference light in the reference arm includes shifting the frequency, and specifically shifting the reference light upward or downward by a fixed frequency.
The invention also provides a system for measuring anti-interference environment signals based on white light interferometry, which comprises:
the reference arm adjusting module is used for adjusting reference light in the reference arm to enable the reference light to generate beat frequency interference with signal light passing through an event point to be detected, and generating a time domain interference signal; the reference light and the signal light are formed by splitting broad spectrum light emitted by a white light source;
the polarization state adjusting module is used for adjusting the angle of the polarization state of the reference light to obtain a time domain interference signal under a certain polarization direction included angle;
the frequency domain transformation module is used for carrying out Fourier transformation on the time domain interference signals to obtain frequency domain signals and carrying out low-frequency filtering; performing inverse Fourier transform on the filtered frequency domain signals to obtain time domain interference spectrums, and normalizing the time domain interference spectrums to obtain interference peaks;
the convolution module is used for repeatedly measuring for many times, adjusting the angle of the polarization state of the reference light to cover a complete period, and convoluting N interference peaks in the obtained N beat frequency interference signals to obtain a convolution result of the time domain interference peaks, wherein N is an integer;
and the curve fitting module is used for carrying out Lorentz curve fitting on the convolution result of the time domain interference peak to obtain a signal for finally eliminating the environmental disturbance.
The invention also provides a device for measuring the anti-interference environment signal based on white light interferometry, which comprises:
a white light source;
the first optical fiber coupler is used for dividing the wide-spectrum light emitted by the white light source into two beams, wherein one beam of signal light enters the measuring arm, and the other beam of reference light enters the reference arm;
the measuring arm is provided with an event point to be measured, and the signal light is reflected back to enter the second optical fiber coupler after passing through the event point to be measured;
the reference arm is used for adjusting the reference light to enter the second optical fiber coupler after passing through the reference arm so as to generate beat frequency interference with the signal light; the reference arm is also used for adjusting the polarization state of the reference light in each beat frequency interference process;
the second optical fiber coupler is used for coupling the incident signal light of the measuring arm and the reference light of the reference arm;
the control and signal acquisition module is used for acquiring beat frequency interference signals;
a signal processor, configured to perform signal processing by using the method for measuring an anti-disturbance environmental signal based on white light interferometry according to claim 1, so as to obtain a final signal for eliminating environmental disturbance.
According to the technical scheme, the reference arm comprises the optical fiber delay line, the optical path of the reference light is continuously adjusted in a mode of controlling the optical fiber delay line, and beat frequency interference occurs when the optical path of the reference light is equal to the optical path of the signal light passing through the event point to be measured in the measuring arm.
With the above technical solution, the reference arm includes an electric polarization controller for randomly varying the polarization state of the reference light.
With the above technical solution, the reference arm further includes a frequency shifter for shifting the reference light upward or downward by a fixed frequency.
The invention also provides a computer storage medium, in which a computer program executable by a processor is stored, and the computer program executes the method based on the white light interferometry anti-disturbance environment signal according to the technical scheme.
The invention has the beneficial effects that: the method has the advantages that multiple groups of data are obtained by utilizing the rapid multiple changes of the polarization state in the beat frequency interference process, interference results for adjusting a certain polarization angle are obtained each time, the influence of polarization on interference intensity is avoided through polarization adjustment, and meanwhile, the measurement accuracy is improved; in addition, the obtained signals are subjected to low-frequency filtering, frequency domain transformation, convolution, normalization and curve fitting replacement in a multi-measurement mode, so that the phenomena of peak value splitting, sawtooth deformation and the like of a measurement signal result curve of a white light interference system in a disturbance environment are completely eliminated, other low-frequency noise caused by environmental disturbance can be eliminated, and a final test result can also have a very beautiful peak value curve and an excellent signal-to-noise ratio in a dynamically-changed measurement environment.
Further, the position of the internal reflector is moved through the optical fiber delay line, the optical path of light passing through the internal reflector is continuously changed, and the arm length of the reference arm is further continuously changed, so that the range to be measured of the signal arm with the corresponding length is measured.
Further, because the disturbance or the environmental noise is generally low frequency, such as tens of kHz or hundreds of kHz, by shifting the frequency of the reference light, the signal beat frequency can be more easily separated from the low frequency disturbance, so as to facilitate signal acquisition.
Of course, it is not necessary for any one product to practice the invention to achieve all of the advantages set forth above at the same time.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the following description will briefly explain the drawings used in the embodiments or the description of the prior art, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1A is a flow chart of a method for measuring anti-disturbance ambient signals based on white light interferometry according to an embodiment of the present invention;
FIG. 1B is a schematic diagram of a system for white light interferometry-based noise immunity environment signal according to an embodiment of the present invention;
FIG. 1C is a schematic diagram of an apparatus for measuring anti-disturbance ambient signals based on white light interferometry according to an embodiment of the present invention;
FIG. 2 is a diagram showing the contrast of beat signals of a white light interferometry system in a steady state and a disturbance state;
FIG. 3 is a schematic diagram of a time domain signal obtained by Fourier transforming a time domain interference signal to obtain a frequency spectrum and filtering low-frequency noise and then inverse Fourier transforming the frequency spectrum;
FIG. 4 is a schematic diagram showing contrast of interference peaks of a white light interference system after beat frequency signal amplitude normalization in a stable state and a disturbance state;
FIG. 5 is a graph showing the effect of the transformed interference signals after convolution one by one;
FIG. 6 is a schematic diagram of the fitted curve replacing the original time domain interference peak;
in fig. 1C: the device comprises a white light source 1, a first optical fiber coupler 2, a frequency shifter 3, an optical fiber delay line 4, an electric polarization controller 5, a circulator 6, a point DUT to be tested 7, a second optical fiber coupler 8, a control and acquisition module 9, a signal processor 10, a signal arm 11 and a reference arm 12.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
It should be noted that the illustrations provided in the embodiments of the invention are merely schematic illustrations of the basic concepts of the invention, and thus only the components related to the invention are shown in the drawings, rather than being drawn according to the number, shape and size of the components in actual implementation, and the form, number and proportion of each component in actual implementation may be arbitrarily changed, and the layout of the components may be more complex.
In the present invention, it should also be noted that, as terms such as "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", and the like are used, the indicated orientation or positional relationship is based on the orientation or positional relationship shown in the drawings, only for convenience of description and simplification of the description, and does not indicate or imply that the indicated apparatus or element must have a specific orientation, be configured and operated in the specific orientation, and thus should not be construed as limiting the present application. Furthermore, the terms "first," "second," and the like, as used herein, are used for descriptive and distinguishing purposes only and are not to be construed as indicating or implying a relative importance.
The method is mainly used for effectively eliminating the situation that the signal intensity of the point to be detected randomly jumps due to low-frequency disturbance noise of interference signals and dynamic change of polarization states in disturbance environments, and the original signal peak shape is recovered with high signal-to-noise ratio, so that the signals are more stable and the positioning is more accurate.
Example 1
As shown in fig. 1A, the method for measuring an anti-disturbance ambient signal based on white light interferometry of this embodiment includes the following steps:
s1, adjusting the optical path of reference light in a reference arm to enable the reference light to generate beat frequency interference with signal light passing through an event point to be detected, and generating a time domain interference signal; the reference light and the signal light are formed by splitting broad spectrum light emitted by a white light source;
s2, regulating the polarization state of the reference light to obtain a time domain interference signal under a certain polarization direction included angle;
s3, carrying out Fourier transform on the time domain interference signal to obtain a frequency domain signal, and carrying out low-frequency filtering; performing inverse Fourier transform on the filtered frequency domain signals to obtain time domain interference spectrums, and normalizing the time domain interference spectrums to obtain interference peaks;
s4, repeating the measurement for a plurality of times, and adjusting the angle of the polarization state of the reference light to cover a complete period to obtain N beat frequency interference signals and N interference peaks correspondingly;
s5, convolving the N times of interference peaks to obtain a convolution result of the time domain interference peaks;
s6, carrying out Lorentz curve fitting on the convolution result of the time domain interference peak to obtain a signal which finally eliminates the environmental disturbance.
In step S2, in one beat frequency interference, the polarization state of the reference light may be randomly changed, each time the polarization state is adjusted, the measurement result is scanned once for the measurement point, the K results are measured when the polarization state is adjusted for K times, and the maximum value of all interference peaks is taken as the measurement result of the final peak. The polarization state is adjusted by the following steps: all polarization directions can be adjusted once in each beat frequency interference, namely 360-degree traversal and rapid scanning are realized; or can be fixed in a certain direction, and can be adjusted to a different fixed direction before waiting for the next measurement, and can be traversed for 360 degrees after multiple measurements. When the polarization state is regulated once, namely the two corresponding arms interfere once with the current polarization included angle, the probability of smaller included angle of the two polarization is larger after multiple measurement, at the moment, the included angle of the polarization states of the two corresponding paths is the smallest when the maximum value of all interference peaks is selected, and the included angle is 0, namely the same direction, at the moment, the real reflection intensity of the event point to be measured is most approximate, and the more the measurement times are, the larger the probability of the same direction is, the more accurate and the more stable the measurement signal is.
Further, since white light is a broad spectrum light, its coherence length is extremely short (generally in the order of um to several tens of um, it can be approximately considered that coherence occurs when the lengths of the reference arm and the measurement arm are completely equal, therefore, in step S1, the optical path length of the reference light is continuously adjusted by controlling the optical fiber delay line in the reference arm, and beat interference occurs when the optical path length of the reference light is equal to the optical path length of the signal light passing through the event point to be measured in the measurement arm.
Further, when Lorentz curve fitting is performed in step S6, specifically, the highest amplitude of the N interference peaks is taken as the peak point of the fitted curve, the average value of the median points of the N interference peaks is taken as the midpoint of the fitted curve, and the average value of the half-height width of the N interference peaks is taken as the half-height width of the fitted curve. Because the position of the event point to be detected is unchanged, and each delay line scanning and data acquisition are synchronous, theoretically, the width and the center point position of each interference peak are completely the same, and the half-height width and the center position of the peak are averaged, so that the system error can be reduced, and the precision is improved.
In one embodiment of the invention, the fiber optic delay line can change the optical path of light passing therethrough by controlling scanning, thereby changing the overall reference arm length (optical path). For example, the fiber delay line can continuously change the optical path of light passing through the fiber delay line by moving the position of the internal reflector, thereby continuously changing the arm length of the reference arm.
FIG. 2 is a diagram showing the contrast of beat signals of a white light interferometry system in a steady state and a disturbance state; because disturbance or environmental noise is generally low frequency, such as tens of kHz or hundreds of kHz, and light frequency is generally in the range of THz magnitude, beat frequency detection is a mainstream signal detection means, the beat frequency mentioned in the foregoing is a beat frequency term part of a signal, no matter whether the light signal is a single frequency or a broad spectrum in a certain range, the beat frequency after beat frequency interference is not affected, and the final frequency is subtracted to become a moving fixed frequency, so that the beat frequency of the signal can be more easily separated from the low frequency disturbance, and signal acquisition is facilitated. The fixed frequency of reference light movement Δf is the beat frequency, so that the magnitude of Δf determines the detection and demodulation of the signal. If the fixed frequency deltaf is shifted to tens of MHz or hundreds of MHz, the signal detection filtering is convenient, and the environmental disturbance is isolated.
Therefore, the method and the device completely eliminate the phenomena of peak value splitting, sawtooth deformation and the like of a measurement signal result curve of the white light interferometry system under a disturbance environment by adjusting modes such as polarization state, frequency domain transformation, convolution, curve fitting replacement and the like, and can also eliminate other low-frequency noise caused by environmental disturbance. The final test result can have a very beautiful peak curve and an excellent signal to noise ratio in a dynamically changing measuring environment. Under the condition of ensuring that the positioning precision is unchanged and the peak value height is more accurate and stable, the limitation that the original white light interference system can only obtain a stable test result by measuring in a static environment is perfectly solved, and the application scene of the white light interference technology is greatly widened.
Example 2
This embodiment is based on embodiment 1 and is mainly a system embodiment for implementing the method of embodiment 1.
As shown in fig. 1B, the system for measuring an immunity environment signal based on white light interferometry of this embodiment mainly includes:
the reference arm adjusting module is used for adjusting reference light in the reference arm to enable the reference light to generate beat frequency interference with signal light passing through an event point to be detected, and generating a time domain interference signal; the reference light and the signal light are formed by splitting broad spectrum light emitted by a white light source;
the polarization state adjusting module is used for adjusting the polarization state of the reference light to obtain a time domain interference signal under a certain polarization direction included angle;
the frequency domain transformation module is used for carrying out Fourier transformation on the time domain interference signals to obtain frequency domain signals and carrying out low-frequency filtering; performing inverse Fourier transform on the filtered frequency domain signals to obtain time domain interference spectrums, and normalizing the time domain interference spectrums to obtain interference peaks;
the convolution module is used for repeatedly measuring for a plurality of times, enabling the angle for adjusting the polarization state of the reference light to cover a complete period, and convoluting N interference peaks in the obtained N beat frequency interference signals to obtain a convolution result of the time domain interference peaks;
and the curve fitting module is used for carrying out Lorentz curve fitting on the convolution result of the time domain interference peak to obtain a signal which finally eliminates the environmental disturbance.
By implementing the method embodiment, the system may have the functions of the method embodiment. The system can completely avoid the phenomena of peak value splitting, sawtooth deformation and the like of a measurement signal result curve of the white light interferometry system under a disordered disturbance environment, and can also eliminate other low-frequency noise caused by the environment disturbance, so that a final test result can also have a very beautiful peak value curve and an excellent signal-to-noise ratio in a dynamically-changed measurement environment. Neither the positioning accuracy nor the peak height will change with the deformation of the original signal.
Example 3
This example is based on example 1 and is mainly an apparatus for carrying out the method of example 1.
As shown in fig. 1C, the apparatus for measuring an anti-disturbance ambient signal based on white light interferometry according to this embodiment includes:
a white light source 1 for emitting white light, which is broad spectrum light;
the first optical fiber coupler 2 divides the wide spectrum light emitted by the white light source into two beams, wherein one beam of signal light enters the measuring arm, and the other beam of reference light enters the reference arm;
the measuring arm 11 is provided with an event point to be measured, and the signal light is reflected back to enter the second optical fiber coupler after passing through the event point to be measured;
a reference arm 12, configured to adjust reference light (mainly adjust optical path and frequency), so that the reference light enters the second optical fiber coupler to perform beat interference with the signal light after passing through the reference arm; the reference arm is also used for randomly changing the polarization state of the reference light in each beat frequency interference process to obtain a time domain interference signal under an included angle of random polarization direction;
a second optical fiber coupler 8, in which the incident signal light of the measuring arm and the reference light of the reference arm are coupled to each other, and beat interference occurs;
the control and signal acquisition module 9 is used for controlling acquisition of beat interference signals;
the signal processor 10 is configured to perform signal processing by using the method based on white light interferometry anti-disturbance environment signal according to the above technical scheme, so as to obtain a final anti-disturbance environment signal. The signal processor 10 may be a computer.
As shown in fig. 1C, specifically, a measuring arm 11 and a reference arm 12 of the device for measuring signals in a disturbance environment based on white light interferometry are connected in parallel between the first optical fiber coupler 1 and the second optical fiber coupler 8, the measuring arm 11 comprises an optical fiber circulator 6, and the reference arm 12 comprises a frequency shifter 3, an optical fiber delay line 4 and an electric polarization controller 5 which are connected in sequence. The frequency shifter 3 may shift the frequency of the light up or down by a certain fixed frequency by some modulation means. The optical fiber delay line 4 can change the optical path length of light passing therethrough by controlling scanning, thereby changing the entire reference arm length (optical path length). The electro-polarization controller 5 randomly changes the polarization state of the light to either direction by changing the shape of the fiber. The control and signal acquisition module can also control the operation and work of the optical fiber delay line 4, the frequency shifter 3 and the electric polarization controller 5, and acquire signal data after beat frequency interference.
Further, the polarization type of the white light source may be a single mode, and the wavelength of the white light source may be in the O-band (wavelength range 1530nm to 1565 nm), the C-band (wavelength range 1530nm to 1565 nm), or the L-band (wavelength range 1530nm to 1565 nm) or the like.
The output end of the white light source 1 is connected with the input end of the first optical fiber coupler 2, one path of the output end of the first optical fiber coupler 2 is used as signal light, the other path of the output end of the first optical fiber coupler is used as reference light and connected with the input end of the optical fiber circulator 6, the other path of the output end of the optical fiber coupler is used as reference light and connected with the frequency shifter 3, and after the output end of the frequency shifter 3, the output end of the frequency shifter is sequentially connected with the optical fiber delay line 4 and the electric polarization controller 5, and finally the output end of the frequency shifter is connected with the second optical fiber coupler 8; the second port of the fiber circulator 6 in the signal arm (i.e. the measuring arm) is connected with the to-be-measured article (and the to-be-measured event point DUT, design Under Test), and the 3 rd port is connected with the second fiber coupler 8.
The white light source 1 emits wide-spectrum light, the wide-spectrum light is divided into two paths through the first optical fiber coupler 2, one path of the wide-spectrum light is used as signal light to enter the optical fiber circulator 6, the signal light is reflected by the event point DUT to be detected at the 2 nd port and then enters the second optical fiber coupler 8 from the 3 rd port, the other path of the wide-spectrum light is used as reference light to enable the reference light to shift frequency delta f through the frequency shifter 3, the reference light enters the optical fiber delay line 4, the optical path of the reference light is continuously adjusted, the reference light enters the electric polarization controller 5 finally, the polarization state of the reference light is randomly changed, and the reference light finally enters the second optical fiber coupler 8. And interfere with the beat frequency of the signal light reflected back from the DUT at this point. Since white light is broad spectrum light, its coherence length is extremely short (typically on the order of um to tens of um, which can be approximated as occurring when the two arms are exactly equal in length).
The optical fiber delay line 4, the frequency shifter 3 and the electric polarization controller 5 are controlled by a control and signal acquisition module 9 to operate and work.
The signal processor 10 controls the data acquisition time and the scanning time of the optical fiber delay line to be synchronous on software, and reads the acquired scanning interference data to the upper computer. When the interference structure is built, the total optical path of reflected light of the sample to be detected is controlled to fall in the total optical path range of the reference arm of the delay line scanning.
And (3) regulating the electric polarization controller, scanning a measurement result once for each time of rotating the polarization state of the to-be-measured point, regulating the polarization state for N times, measuring the result for N times, and taking the maximum value of all interference peaks as the measurement result of the final peak value.
The two arms are interfered with each other at the current polarized included angle once for each measurement, and the smaller the two polarized included angles are, the larger the probability is (at this time, the maximum value of all interference peaks is selected to be corresponding to the polarized included angle of the two paths of light, and the included angle is 0, namely the same direction, at this time, the real reflection intensity of the point to be measured is closest to the moment, the more the measurement times are, the larger the probability of the same direction is, and the more accurate and stable the intensity measurement is).
Because the position of the event point is unchanged and each delay line scanning and data acquisition are synchronous, theoretically, the width and the center point position of each interference peak are completely the same, and the half-height width and the center position of the peak are averaged to further reduce the system error and improve the precision.
The static interference signal accords with the uniform broadening type of the spectral line, adopts Lorentz curve fitting and accords with the actual interference spectral lineUnder the condition, taking the highest amplitude value of the interference peaks in all the groups of results as a peak value point A of a fitting curve, and taking the average value of the median points of all the groups of interference peaks as a midpoint x of a fitting signal 0 And width of half height of all peaksAveraging, and fitting the whole beat frequency interference peak by using a Lorentz curve; wherein->。
The base noise in the scanning result curve is filtered by FFT and then is transformed back by inverse FFT, the noise thickness is greatly reduced, and meanwhile, a plurality of groups of data are convolved, so that the environment and system noise are eliminated, and the signal to noise ratio is greatly improved.
The method for eliminating the disturbance-resistant signal measured by the white light interferometer by the device comprises the following steps:
s1, after light emitted by a white light source passes through a first optical fiber coupler, a light source signal is divided into two paths and respectively enters a measuring arm and a reference arm. When the optical paths of the two arms are equal, the two paths of light generate measurement signal beat frequency interference in the second optical fiber coupler, and the second optical fiber coupler outputs disturbance beat frequency signals with DUT reflection intensity information, namely time domain interference signals;
s2, carrying out Fourier transform on the obtained time domain interference signals to obtain frequency domain signals, filtering out all low-frequency items in the frequency spectrum, only retaining beat frequency items, carrying out inverse Fourier transform to obtain pure time domain interference spectrum, taking amplitude of the interference spectrum, and normalizing to obtain interference peaks; as shown in fig. 3, a schematic diagram of a time domain signal is obtained by performing fourier transform on a time domain interference signal to obtain a frequency spectrum and filtering low-frequency noise and performing inverse fourier transform;
s3, randomly changing the polarization state of the reference arm through the electric polarization controller, scanning the optical fiber delay line, and obtaining N groups of normalized interference peak results after the inverse Fourier transform according to the steps S1 and S2; FIG. 4 is a schematic diagram showing contrast of interference peaks of a white light interference system after beat frequency signal amplitude normalization in a steady state and a disturbance state;
s4, carrying out convolution on each group of results in sequence to obtain a final high signal-to-noise ratio time domain interference peak result; as shown in fig. 5, the curve effect diagram is a curve effect diagram of the interference signals after the transformation processing after one-by-one convolution;
s5, taking the highest amplitude value of the interference peaks in all the group results as a peak value point A of a fitting curve, and taking the average value of the median points of all the group interference peaks as a midpoint x of a fitting signal 0 And taking the average of the half-widths of all peaks as the half-width of the fitting signalThe whole beat frequency interference peak is fitted by using a Lorentz curve; wherein->；
S6, replacing the original convolved time domain interference peak by the fitted curve to obtain a final signal processing result, wherein the final signal processing result is shown in FIG. 6 and is a schematic diagram of replacing the original time domain interference peak by the fitted curve.
The working band, polarization, splitting ratio, electric or manual operation, etc. of the light source, the optical fiber delay line, the frequency shifter, the polarization controller and the optical fiber coupler in this embodiment are not limited to those mentioned in the embodiments, and those skilled in the art can flexibly select devices with different indexes and performances according to the device or method to achieve similar effects.
In conclusion, the device and the method effectively realize that the signal to noise ratio of the test result of the reflected signal of the point to be tested in the dynamic environment is improved by using the white light system, and the interference peak condition of the point to be tested can be truly and accurately restored, and the phenomena that the signal intensity is difficult to accurately measure and the position positioning accuracy of the event point is poor due to the fact that the interference peak is deformed and split caused by disturbance are eliminated.
Example 4
The present application also provides a computer readable storage medium, such as a flash memory, a hard disk, a multimedia card, a card memory (e.g., SD or DX memory, etc.), a Random Access Memory (RAM), a Static Random Access Memory (SRAM), a read-only memory (ROM), an electrically erasable programmable read-only memory (EEPROM), a programmable read-only memory (PROM), a magnetic memory, a magnetic disk, an optical disk, a server, an App application store, etc., having stored thereon a computer program that when executed by a processor performs a corresponding function. The computer readable storage medium of the present embodiment when executed by a processor implements the method of the method embodiment based on white light interferometry of an anti-disturbance ambient signal.
It should be noted that each step/component described in the present application may be split into more steps/components, or two or more steps/components or part of the operations of the steps/components may be combined into new steps/components, as needed for implementation, to achieve the object of the present invention.
The sequence numbers of the steps in the above embodiments do not mean the order of execution, and the execution order of the processes should be determined by the functions and the internal logic, and should not be construed as limiting the implementation process of the embodiments of the present application.
It will be understood that modifications and variations will be apparent to those skilled in the art from the foregoing description, and it is intended that all such modifications and variations be included within the scope of the following claims.
Claims (10)
1. A method for measuring an immunity environment signal based on white light interferometry, comprising the steps of:
s1, adjusting reference light in a reference arm to enable the reference light to generate beat frequency interference with signal light passing through an event point to be detected, and generating a time domain interference signal; the reference light and the signal light are formed by splitting broad spectrum light emitted by a white light source;
s2, adjusting the angle of the polarization state of the reference light to obtain a time domain interference signal under a certain polarization direction included angle;
s3, carrying out Fourier transform on the time domain interference signal to obtain a frequency domain signal, and carrying out low-frequency filtering; performing inverse Fourier transform on the filtered frequency domain signals to obtain time domain interference spectrums, and normalizing the time domain interference spectrums to obtain interference peaks;
s4, repeating the measurement for a plurality of times, adjusting the angle of the polarization state of the reference light to cover a complete period, obtaining signals of N beat frequency interferometry, and correspondingly obtaining N interferometry peaks, wherein N is an integer;
s5, convolving the N times of interference peaks to obtain a convolution result of the time domain interference peaks;
s6, carrying out Lorentz curve fitting on the convolution result of the time domain interference peak to obtain a signal for finally eliminating the environmental disturbance.
2. The method of claim 1, wherein in step S6, when the lorentz curve fitting is performed, specifically, taking the highest amplitude of the N interference peaks as peak points of the fitting curve, taking the average value of the median points of the N interference peaks as the middle point of the fitting curve, and taking the average value of the half-height widths of the N interference peaks as the half-height width of the fitting curve.
3. The method of claim 1, wherein adjusting the reference light in the reference arm in step S1 comprises: the optical path of the reference light is continuously adjusted by controlling the optical fiber delay line in the reference arm, and beat frequency interference occurs when the optical path of the reference light is equal to the optical path of the signal light passing through the event point to be measured in the measuring arm.
4. A method of measuring an anti-disturbance ambient signal based on white light interferometry according to claim 3, wherein the optical delay line continuously varies the optical path through which light passes, and thereby continuously varies the reference arm length, by moving the internal mirror position.
5. The method of claim 1, wherein adjusting the reference light in the reference arm in step S1 comprises shifting the frequency, in particular shifting the reference light up or down by a fixed frequency.
6. A system for white light interferometry-based immunity to environmental signals, comprising:
the reference arm adjusting module is used for adjusting reference light in the reference arm to enable the reference light to generate beat frequency interference with signal light passing through an event point to be detected, and generating a time domain interference signal; the reference light and the signal light are formed by splitting broad spectrum light emitted by a white light source;
the polarization state adjusting module is used for adjusting the angle of the polarization state of the reference light to obtain a time domain interference signal under a certain polarization direction included angle;
the frequency domain transformation module is used for carrying out Fourier transformation on the time domain interference signals to obtain frequency domain signals and carrying out low-frequency filtering; performing inverse Fourier transform on the filtered frequency domain signals to obtain time domain interference spectrums, and normalizing the time domain interference spectrums to obtain interference peaks;
the convolution module is used for repeatedly measuring for many times, adjusting the angle of the polarization state of the reference light to cover a complete period, and convoluting N interference peaks in the obtained N beat frequency interference signals to obtain a convolution result of the time domain interference peaks, wherein N is an integer;
and the curve fitting module is used for carrying out Lorentz curve fitting on the convolution result of the time domain interference peak to obtain a signal for finally eliminating the environmental disturbance.
7. An apparatus for white light interferometry-based immunity to environmental signals, comprising:
a white light source;
the first optical fiber coupler is used for dividing the wide-spectrum light emitted by the white light source into two beams, wherein one beam of signal light enters the measuring arm, and the other beam of reference light enters the reference arm;
the measuring arm is provided with an event point to be measured, and the signal light is reflected back to enter the second optical fiber coupler after passing through the event point to be measured;
the reference arm is used for adjusting the reference light to enter the second optical fiber coupler after passing through the reference arm so as to generate beat frequency interference with the signal light; the reference arm is also used for adjusting the polarization state of the reference light in each beat frequency interference process;
the second optical fiber coupler is used for coupling the incident signal light of the measuring arm and the reference light of the reference arm;
the control and signal acquisition module is used for acquiring beat frequency interference signals;
a signal processor, configured to perform signal processing by using the method for measuring an anti-disturbance environmental signal based on white light interferometry according to claim 1, so as to obtain a final signal for eliminating environmental disturbance.
8. The apparatus for measuring an anti-interference environment signal based on white light interferometry according to claim 7, wherein the reference arm comprises an optical fiber delay line, and wherein the optical path length of the reference light is continuously adjusted by controlling the optical fiber delay line, and wherein beat interference occurs when the optical path length of the reference light is equal to the optical path length of the signal light passing through the event point to be measured in the measuring arm.
9. The apparatus for white light interferometry-based immunity to environmental signals of claim 7 wherein the reference arm comprises an electro-dynamic polarization controller for randomly varying the polarization state of the reference light.
10. The apparatus for white light interferometry-based immunity to environmental signals of claim 7 wherein the reference arm further comprises a frequency shifter for shifting the reference light up or down by a fixed frequency.
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