CN116295038B - Nanoscale two-dimensional displacement measuring device and method based on super-surface grating - Google Patents
Nanoscale two-dimensional displacement measuring device and method based on super-surface grating Download PDFInfo
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- CN116295038B CN116295038B CN202310597156.1A CN202310597156A CN116295038B CN 116295038 B CN116295038 B CN 116295038B CN 202310597156 A CN202310597156 A CN 202310597156A CN 116295038 B CN116295038 B CN 116295038B
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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
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
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Abstract
The invention discloses a nanoscale two-dimensional displacement measuring device and method based on a super-surface grating, wherein the device comprises a light source module, the super-surface grating, a reflecting module and a detecting module; the super-surface grating is used for dividing left-handed or right-handed circularly polarized light generated by the light source module into different diffraction orders; the incident light passes through the ultra-surface grating twice through the reflection module, and the two orthogonal polarization component intensities of the emergent light are respectively mapped to the two-dimensional transverse displacement of the ultra-surface relative to the optical axis; and measuring the power of two orthogonal polarizations of the emergent light through the detection module, and solving the phase of the measured power to obtain the in-plane displacement. The device and the method utilize the super surface to measure the two-dimensional transverse displacement, and have the advantages of simple structure, large measuring range and high sensitivity.
Description
Technical Field
The invention relates to the technical field of optical precision displacement measurement, in particular to a nano-scale two-dimensional displacement measurement device and method for a super-surface grating.
Background
Optical displacement measurement plays an important role as a rapid, non-contact method in the field of semiconductor manufacturing and the like. Along with the extension of the photoetching technology to process nodes of 10 nanometers and below in the advanced integrated circuit manufacturing, the photoetching technology meets the requirement of sub-nanometer level on the alignment precision, and simultaneously, the requirement on multi-degree-of-freedom displacement measurement is also provided.
Diffraction-based overlay error measurement (DBO) is one of the most commonly used methods, which has proven to be an effective overlay error measurement technique with sub-nanometer measurement accuracy and good repeatability, and is widely used in lithography in industry. However, to achieve two-dimensional in-plane displacement measurements, DBO markers typically need to contain multiple sets of gratings, taking up a large amount of wafer area, resulting in a low number of final devices. On the other hand, in the field of nanophotonics, various optical precision displacement measurement schemes with high integration level have appeared in recent years, for example, a scheme of combining optical antenna pair with structural light illumination can reach sub-nanometer resolution, but only one-dimensional displacement can be measured, and the method is not suitable for a scene of multi-dimensional displacement measurement. The directional scattering by utilizing the spherical optical antenna can be used for in-plane two-dimensional displacement measurement, but the measurement range is only hundred nanometers, and a complex imaging post-processing process is required, so that the problems of low signal reading speed, low signal-to-noise ratio and the like exist.
Therefore, there is a need to develop a two-dimensional displacement measurement scheme with high measurement accuracy, wide range, simple signal reading and integration.
Disclosure of Invention
In order to solve the technical problems, the invention provides a nano-scale two-dimensional displacement measuring device and method based on a super-surface grating, which divide left-handed or right-handed circularly polarized light generated by a light source module into different diffraction orders; the incident light passes through the ultra-surface grating twice through the reflection module, and the two orthogonal polarization component intensities of the emergent light are respectively mapped to the two-dimensional transverse displacement of the ultra-surface relative to the optical axis; and measuring the power of two orthogonal polarizations of the emergent light through the detection module, and solving the phase of the measured power to obtain the in-plane displacement.
The invention aims at realizing the following technical scheme:
a nanoscale two-dimensional displacement measuring device based on a super-surface grating comprises a light source module, the super-surface grating, a reflection module and a detection module;
the light source module comprises a laser, a half wave plate, a first polarization beam splitter prism, a first reflecting mirror, a first acousto-optic modulator, a second acoustic optical modulator, a second reflecting mirror, a second polarization beam splitter prism, a first quarter wave plate, a first non-polarization beam splitter prism and a monitoring power meter;
the reflection module comprises a lens, a space filter and a third reflector which are sequentially arranged;
the detection module comprises a second unpolarized beam splitter prism, a second quarter wave plate, a first analyzer, a first measurement power meter, a third quarter wave plate, a second analyzer and a second measurement power meter.
Further, the super-surface grating diffracts the incident parallel light into a plurality of diffraction orders, wherein three diffraction orders respectively realize three polarized projection processes; the super-surface grating comprises an elliptic cylindrical particle array which is processed on a light-transmitting substrate with nanometer precision and is manufactured according to structural parameters of optimal design in the length axis size and the long axis direction; the super-surface grating is always positioned on the focal plane of the lens in the two-dimensional transverse movement process.
Further, the super-surface structure parameters of the super-surface grating are obtained by an optimization algorithm, and the optimization algorithm comprises a multi-parameter gradient descent method.
Further, the material of the elliptic cylindrical particles of the super-surface grating is metal or a medium with high refractive index, comprising gold, silver, silicon, gaAs or TiO 2 。
The invention also provides a nano-scale two-dimensional displacement measurement method based on the super-surface grating, which comprises the following steps:
the linear polarization parallel light beams emitted by the lasers in the light source module rotate in the linear polarization direction after passing through the half wave plate, and then pass through the first polarization splitting prism to obtain two paths of parallel light with equal power and mutually perpendicular polarization; the transmitted light is p polarized, reflected by the first reflecting mirror, and then emitted by first-order diffraction after passing through the first acousto-optic modulator; the reflected light is s polarized, and the first-order diffraction light passing through the second acoustic optical modulator is reflected by the second reflecting mirror; the first acousto-optic modulator and the second acousto-optic modulator are controlled by a radio frequency signal source and are used for switching the switching states of the two light paths rapidly and alternately; the transmitted light and the reflected light are spatially combined by a second polarization splitting prism; the light after beam combination generates left-handed circularly polarized light and right-handed circularly polarized light through a first quarter wave plate respectively, and irradiates on a first unpolarized beam splitting prism; the reflected light of the first unpolarized beam splitter prism is illuminated to a monitoring power meter to obtain monitoring powerI.e. +.>、/>R represents right-hand circular polarized light incidence, L represents left-hand circular polarized light incidence; transmitting light to the super-surface grating through the first unpolarized beam-splitting prism; the super surface grating maps the left-hand or right-hand polarized light to three diffraction orders, three diffractionsThe order polarization states are +.>、/>、/>Namely, linear polarization with the included angle of 0 degree, 45 degrees and 90 degrees between the vibration direction and the x-axis is separated and enters the reflecting module in the propagation process;
the light field modulated by the space filter plate and the third reflector is reflected back to the super-surface grating with the same polarization state and incidence angle;
the three reflected polarized light lights are irradiated on the super-surface grating, and are diffracted by the super-surface grating to deflect back to the optical axis to interfere, so that signal light to be detected with uniform distribution of intensity and polarization space is emitted; the emergent signal light is reflected to the detection module through a first unpolarized beam splitting prism;
the second unpolarized beam splitting prism in the detection module divides the signal light into two paths; the light transmitted by the second unpolarized beam splitter prism passes through the second quarter wave plate and the first analyzer and is received by the first measuring power meter to measure the transmission powerI.e. +.>And->H represents a horizontal polarization component of the signal light; the reflected light from the second unpolarized beam splitter prism is received by a second measurement power meter after passing through a third quarter wave plate and a second analyzer, and the reflected power is measured>I.e. +.>And->V represents the signal light vertical polarization component; the second quarter wave plate and the third quarter wave plate act to compensate the depolarization effect in the light path; the main shaft direction of the first analyzer is along the x direction; the main shaft direction of the second analyzer is along the y direction;
the transmission powerAnd reflected power->Background noise when the pre-recorded no super surface is subtracted +.>Eliminating the influence of ambient light and light reflected by the surface of the optical element; monitoring power of a simultaneous recording monitoring power meter>The ratio is made, the influence of power jitter of the laser is eliminated, signals when left-handed circularly polarized light and right-handed circularly polarized light are incident are separated, and normalized power is obtained after normalization processing>、/>、/>And->The transmission power when the right-handed circular polarized light is incident, the transmission power when the left-handed circular polarized light is incident, the reflection power when the right-handed circular polarized light is incident and the reflection power when the left-handed circular polarized light is incident are respectively; will->And->、/>And->Drawing Lissajous figures for the two groups of power respectively and fitting to obtain phase differences; carrying out phase difference solution to obtain a phase shift-phase plane and fitting to obtain a phase slope +.>And->；
After the ultra-surface grating is moved, repeating the steps, obtaining transmission power and reflection power through measurement of a first measurement power meter and a second measurement power meter, and obtaining new normalized transmission power and reflection power through treatment、、/>And->And reversely solving the phase, calculating the phase difference between the phase difference and the initial position, and obtaining the two-dimensional displacement of the super-surface grating relative to the initial point according to the ratio of the phase difference to the phase slope.
Further, each diffraction order realizes a designed polarized projection process, and the included angle between the diffraction direction and the optical axis isWherein->Is the laser wavelength and Λ is the structural period in the x-direction and y-direction.
Further, the space filter only allows the three diffraction orders to pass, and the space filter is made of an opaque material.
According to the technical scheme provided by the invention, the nanoscale two-dimensional displacement measuring device and method based on the super-surface grating are used for regulating and controlling the polarization distribution of incident light based on the super-surface grating twice, so that the intensity and polarization space of the emergent signal light are uniformly distributed, and the emergent signal is subjected to polarization projection to obtain the measured power. The method has the characteristics of high sensitivity, high measurement speed, wide range and the like, and can realize non-contact rapid measurement of nanoscale two-dimensional displacement.
Compared with the prior art, the invention has the beneficial effects that:
(1) The super-surface structure is adopted as a sensing device, has the characteristic of high integration, and can be applied to scenes with high-precision displacement measurement requirements and limited space.
(2) The optical path is simple in structure, an imaging system is not needed, polarization regulation and control are carried out by the ultra-surface grating, two-dimensional displacement information is mapped onto two orthogonal polarization component intensities of the signal light, the two-dimensional displacement can be obtained by measuring the intensity through a Malus law, and the optical path is concise and quick to measure.
(3) By switching the polarization state of the incident light, multipath phase shift signals can be obtained, no dead zone of measurement in a large measurement range can be realized, and high-precision displacement measurement can be realized, and experiments prove that the measurement precision of the system is better than 1 nm, and the measurement range is more than 100 mu m.
Drawings
FIG. 1 is a schematic structural diagram of a nanoscale two-dimensional displacement measurement device based on a super-surface grating according to an embodiment of the present invention;
FIG. 2 is a view of a super-surface scanning electron microscope used in an embodiment of the present invention;
FIG. 3 is a graph showing the time-power curve of a monitor laser for a right-handed circularly polarized light incident monitor power meter according to an embodiment of the present invention;
FIG. 4 is a graph showing the time-power curve of a monitor laser for a left-hand circularly polarized light incident monitor power meter according to an embodiment of the present invention;
FIG. 5 is a graph of displacement versus power measured by a first measured power meter and a second measured power meter in accordance with an embodiment of the present invention;
fig. 6 is a displacement-phase diagram of an embodiment of the invention recovered from measured power.
In the figure: 1. a laser; 2. a half-wave plate; 3. a first polarization splitting prism; 4. a first mirror; 5. a first acousto-optic modulator; 6. a second acoustic optical modulator; 7. a second mirror; 8. a second polarization splitting prism; 9. a first quarter wave plate; 10. a first unpolarized beam-splitting prism; 11. monitoring a power meter; 12. a super surface grating; 13. a lens; 14. a spatial filter; 15. a third mirror; 16. a second unpolarized beam-splitting prism; 17. a second quarter wave plate; 18. a first analyzer; 19. a first measurement power meter; 20. a third quarter wave plate; 21. a second analyzer; 22. a second measurement power meter.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the following detailed description of the embodiments of the present invention is given with reference to the accompanying drawings and the specific embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not to be construed as limiting the invention.
The invention aims to provide a nano-scale two-dimensional displacement measuring device based on a super-surface grating. The invention relates to a nano-scale two-dimensional displacement measuring device based on a super-surface grating, which comprises the following preferred specific embodiments:
as shown in fig. 1, includes a light source module, a super surface grating 12, a reflection module, and a detection module; the light source module provides laser with stable power and uniform polarization distribution, the super-surface grating 12 adds two-dimensional transverse displacement information to the twice modulated laser polarization, the reflection module reflects the super-surface transmitted light to be subjected to super-surface modulation again, the detection module obtains four paths of phase shift signal power through multipath measurement, and the measured two-dimensional displacement is calculated from the measurement result.
The light source module comprises a laser 1, a half-wave plate 2, a first polarization beam splitter prism 3, a first reflecting mirror 4, a first acousto-optic modulator 5, a second acoustic modulator 6, a second reflecting mirror 7, a second polarization beam splitter prism 8, a first quarter-wave plate 9, a first non-polarization beam splitter prism 10 and a monitoring power meter 11; the reflection module comprises a lens 13, a space filter 14 and a third reflecting mirror 15 which are sequentially arranged; the detection module comprises a second unpolarized beam splitter prism 16, a second quarter wave plate 17, a first analyzer 18, a first measurement power meter 19, a third quarter wave plate 20, a second analyzer 21 and a second measurement power meter 22.
The super surface grating 12 diffracts incident parallel light onto three diffraction orders of (0, +1), (0, -1), and (+1, 0), which correspond to the respective diffraction orders、/>And->Polarized projection of the polarization state. The super-surface grating is optimized by using a multi-parameter gradient descent algorithm to obtain structural parameters.
The ultra-surface grating 12 uses electron beam exposure, inductively coupled plasma etching and other processing technologies to process a nano-scale thickness film on a transparent substrate by using a silicon material, and processes an elliptic cylindrical particle array which is of nano-precision and is manufactured by the long-short axis size and the long axis direction according to the structural parameters of optimal design on the film, and fig. 2 shows an electron microscope diagram of the ultra-surface structure; the super surface grating 12 is always located in the focal plane of the lens during lateral movement.
The linear polarization parallel light beams emitted by the laser 1 rotate in the polarization direction after passing through the half wave plate 2, and then pass through the first polarization splitting prism 3 to obtain two paths of parallel light with equal power and mutually perpendicular polarization; the transmitted light is p polarized and exits through first-order diffraction of the first reflector 4 and the first acousto-optic modulator 5; the reflected light is s polarized, and is reflected by the first-order diffraction of the second acoustic optical modulator 6 and the second reflecting mirror 7; first soundThe optical modulator 5 and the second optical modulator 6 are controlled by a radio frequency signal source and are used for switching the switching states of the two optical paths rapidly and alternately; the transmitted light and the reflected light are spatially combined by the second polarization splitting prism 8; the light after beam combination generates left-handed circularly polarized light and right-handed circularly polarized light through a first quarter wave plate 9 respectively, and irradiates on a first unpolarized beam splitting prism 3; the light reflected by the first unpolarized beam splitter prism 10 is illuminated on the monitoring power meter 11 to obtain the monitoring power(i.e.)>、R represents right-hand circular polarized light incidence, L represents left-hand circular polarized light incidence, and the same applies below), as shown in fig. 3 and 4, respectively; the light is transmitted through the first non-polarizing beam splitter prism 10 to illuminate the super surface grating 12.
The super surface grating 12 diffracts the left-hand or right-hand polarized light into three diffraction orders (0, +1), (0, -1) and (+1, 0), the diffraction direction of which forms an angle with the optical axis，/>Is the laser wavelength and Λ is the structural period in the x-direction and y-direction. Which are respectively corresponding to->、/>And->Polarized projection of the polarization state is separated into the reflection module in the propagation process.
In the reflection module, light of three diffraction orders is deflected and converged by a lens 13, and then the modulated light field is reflected back to the super-surface grating 12 by a space filter 14 and a third reflector 15 in the same polarization state and incidence angle; the space filter 14 only allows the designed three diffraction orders to pass through, so that the interference of direct current components and other diffraction orders is eliminated;
the three reflected polarized lights are irradiated on the super-surface grating 12, and are diffracted by the super-surface grating 12 to deflect back to the optical axis to interfere, so that signal light to be detected with uniformly distributed polarization space is emitted; the intensity and polarization of the emergent light follow the two-dimensional displacement of the super surface in the XY planeAnd (3) a change. The outgoing signal light is reflected to the detection module by the first unpolarized beam splitter prism 10.
The second unpolarized beam splitter prism 16 in the detection module splits the signal light into two paths; the transmitted light is received by a first measuring power meter 19 after passing through a second quarter wave plate 17 and a first analyzer 18, and the transmitted power is measured(i.e.)>Andh represents a signal light horizontal polarization component); the reflected light is received by a second measuring power meter 22 after passing through a third quarter wave plate 20 and a second analyzer 21, and the reflected power +.>(i.e.)>And->V represents the signal light vertical polarization component); wherein the second quarter wave plate 17 and the third quarter wave plate 20 function to compensate for depolarization effects in the optical path; the primary axis of the first analyzer 18 is oriented in the x-direction; the main axis direction of the second analyzer 21 is along the y-direction.
Signal powerAnd->Background noise when the pre-recorded no super surface is subtracted +.>Eliminating the influence of ambient light and light reflected by the surface of the optical element; and then the monitoring power of the simultaneous recording monitoring power meter 11 +.>(i.e.)>And->) The ratio is made, the influence of power jitter of the laser 1 is eliminated, signals when left-handed circularly polarized light and right-handed circularly polarized light are incident are separated, and normalized signal power is obtained after normalization processing>、/>、/>And->As shown in fig. 5; the signal power at this time can be expressed as:
，
，
wherein, the liquid crystal display device comprises a liquid crystal display device,、/>as a phase term of the phase of the signal,for the phase slope +.>,/>Is the two-dimensional displacement of the super-surface grating, Λ is the structural period of the super-surface grating in the x direction and the y direction. Raster scanning the super surface grating 12 with step length of 100 nm to obtain +.>And->、/>And->Drawing Lissajous figures on the two groups of intensities respectively and fitting to obtain phase differences; carrying out phase difference solution to obtain a phase shift-phase plane and fitting to obtain a phase slope +.>And->As shown in fig. 6;
repeating the above steps after moving the ultra-surface grating 12, obtaining the transmission power and the reflection power by measuring with the first measuring power meter 19 and the second measuring power meter 22, and obtaining the new normalized power after processing、/>、/>And->And the phase is reversely solved, the phase difference between the initial position and the calculated phase difference is obtained, and the two-dimensional displacement of the super-surface grating 12 relative to the starting point is obtained according to the ratio of the phase difference to the phase slope.
According to the nano-scale two-dimensional displacement measuring device and method based on the super-surface grating, the signal light with the intensity and the polarization state which are uniformly distributed in space is obtained through the two-time polarization regulation and control of the super-surface, so that the two orthogonal polarization component intensities of the signal light are respectively mapped with two-dimensional displacement information, and the power is measured through the Malus law, so that the non-contact rapid measurement of the nano-scale two-dimensional displacement is realized. The method has the characteristics of high sensitivity, rapid measurement, wide range and the like.
Parts of the invention not described in detail are well known in the art. The above examples are merely illustrative of preferred embodiments of the invention, which are not exhaustive of all details, nor are they intended to limit the invention to the particular embodiments disclosed. Various modifications and improvements of the technical scheme of the present invention will fall within the protection scope of the present invention as defined in the claims without departing from the design spirit of the present invention.
Claims (7)
1. The nano-scale two-dimensional displacement measuring device based on the super-surface grating is characterized by comprising a light source module, the super-surface grating (12), a reflection module and a detection module;
the light source module comprises a laser (1), a half-wave plate (2), a first polarization beam splitter prism (3), a first reflecting mirror (4), a first acousto-optic modulator (5), a second acoustic modulator (6), a second reflecting mirror (7), a second polarization beam splitter prism (8), a first quarter-wave plate (9), a first non-polarization beam splitter prism (10) and a monitoring power meter (11); the linear polarization parallel light beams emitted by the laser (1) in the light source module rotate in the linear polarization direction after passing through the half wave plate (2), and then pass through the first polarization splitting prism (3) to obtain two paths of parallel light with equal power and mutually perpendicular polarization; the transmitted light is p polarized, reflected by the first reflecting mirror (4), passes through the first acousto-optic modulator (5) and exits by first-order diffraction; the reflected light is s polarized, and the first-order diffraction light passing through the second acoustic modulator (6) is reflected by the second reflecting mirror (7); the transmitted light and the reflected light are spatially combined by a second polarization splitting prism (8); the light after beam combination generates left-handed circularly polarized light and right-handed circularly polarized light through a first quarter wave plate (9) and irradiates on a first unpolarized beam splitting prism (10); the light reflected by the first unpolarized beam splitter prism (10) is illuminated to a monitoring power meter (11);
the reflection module comprises a lens (13), a space filter (14) and a third reflection mirror (15) which are sequentially arranged;
the detection module comprises a second unpolarized beam splitter prism (16), a second quarter wave plate (17), a first analyzer (18), a first measurement power meter (19), a third quarter wave plate (20), a second analyzer (21) and a second measurement power meter (22); the second unpolarized beam splitter prism (16) splits the signal light into two paths; the transmitted light passing through the second unpolarized beam splitter prism (16) passes through the second quarter wave plate (17) and the first analyzer (18) and is received by the first measuring power meter (19); the reflected light passing through the second unpolarized beam splitter prism (16) is received by a second measurement power meter (22) after passing through a third quarter wave plate (20) and a second analyzer (21);
the light source module provides laser with stable power and uniform polarization distribution, the super-surface grating adds two-dimensional transverse displacement information to the twice modulated laser polarization, the reflection module reflects super-surface transmitted light to be modulated again through the super-surface, the detection module obtains four paths of phase shift signal power through multipath measurement, and the measured two-dimensional displacement is obtained through calculation of measurement results.
2. The nano-scale two-dimensional displacement measuring device based on the super-surface grating according to claim 1, wherein the super-surface grating (12) diffracts incident parallel light into a plurality of diffraction orders, and three diffraction orders respectively realize three polarized projection processes; the super-surface grating (12) comprises an elliptic cylindrical particle array which is processed on a light-transmitting substrate with nanometer precision; the super-surface grating (12) is always positioned on the focal plane of the lens (13) in the two-dimensional transverse movement process.
3. The nano-scale two-dimensional displacement measuring device based on the super-surface grating according to claim 2, wherein the super-surface structure parameters of the super-surface grating (12) are obtained by an optimization algorithm, and the optimization algorithm comprises a multi-parameter gradient descent method.
4. A nano-scale two-dimensional displacement measuring device based on a super-surface grating according to claim 3, wherein the material of the elliptic cylindrical particles of the super-surface grating (12) is metal or a medium with high refractive index, comprising gold, silver, silicon, gaAs or TiO 2 。
5. A method of measuring a nano-scale two-dimensional displacement measuring device based on a super-surface grating according to any one of claims 1 to 4, comprising the steps of:
the linear polarization parallel light beams emitted by the laser (1) in the light source module rotate in the linear polarization direction after passing through the half wave plate (2), and then pass through the first polarization splitting prism (3) to obtain two paths of parallel light with equal power and mutually perpendicular polarization; the transmitted light is p polarized, reflected by the first reflecting mirror (4), passes through the first acousto-optic modulator (5) and exits by first-order diffraction; the reflected light is s polarized, and the first-order diffraction light passing through the second acoustic modulator (6) is reflected by the second reflecting mirror (7); the first acousto-optic modulator (5) and the second acousto-optic modulator (6) are controlled by a radio frequency signal source and are used for rapidly and alternately switching the switching states of the two light paths; the transmitted light and the reflected light are spatially combined by a second polarization splitting prism (8); the combined light is respectively generated into left-handed circularly polarized light and right-handed circularly polarized light through a first quarter wave plate (9) and irradiates to a first non-transparent lightA polarization beam splitter prism (10); the light reflected by the first unpolarized beam splitter prism (10) is illuminated to a monitoring power meter (11) to obtain monitoring powerI.e. +.>、/>R represents right-hand circular polarized light incidence, L represents left-hand circular polarized light incidence; transmitting light illumination through said first non-polarizing beam splitting prism (10) onto a super surface grating (12); the super surface grating (12) maps the left-hand or right-hand polarized light to three diffraction orders, and the polarization states of the three diffraction orders are respectively +.>、/>、/>Namely, linear polarization with the included angle of 0 degree, 45 degrees and 90 degrees between the vibration direction and the x-axis is separated and enters the reflecting module in the propagation process;
the modulated light field is deflected and converged by the lens (13) in the reflecting module, and is reflected back to the super-surface grating (12) by the space filter (14) and the third reflecting mirror (15) in the same polarization state and incidence angle;
three beams of reflected polarized light are irradiated on the super-surface grating (12), and are diffracted by the super-surface grating (12) to deflect back to an optical axis to interfere, so that signal light to be detected with uniform distribution of intensity and polarization space is emitted; the emergent signal light is reflected to the detection module through a first unpolarized beam splitting prism (10);
the second unpolarized beam splitter prism (16) in the detection module divides the signal light into two paths; transmitted light through a second non-polarizing beam-splitting prism (16)The transmitted power is measured after passing through a second quarter wave plate (17) and a first analyzer (18) and being received by a first measuring power meter (19)I.e. +.>And->H represents a horizontal polarization component of the signal light; reflected light passing through the second unpolarized beam splitter prism (16) is received by the second measurement power meter (22) after passing through the third quarter wave plate (20) and the second analyzer (21), and reflected power is measured>I.e. +.>And->V represents the signal light vertical polarization component; the second quarter wave plate (17) and the third quarter wave plate (20) act as offset compensation effects in the optical path; the main axis direction of the first analyzer (18) is along the x direction; the main shaft direction of the second analyzer (21) is along the y direction;
the transmitted power and the reflected powerSubtracting out pre-recorded background noise when no super surface existsEliminating the influence of ambient light and light reflected by the surface of the optical element; and the monitoring power of the monitoring power meter (11) recorded at the same time>The ratio is made, the influence of power jitter of the laser (1) is eliminated, signals when left-handed circularly polarized light and right-handed circularly polarized light are incident are separated, and normalization processing is carried out to obtain normalized +.>、/>、/>、/>The transmission power when the right-handed circular polarized light is incident, the transmission power when the left-handed circular polarized light is incident, the reflection power when the right-handed circular polarized light is incident and the reflection power when the left-handed circular polarized light is incident are respectively; will->And->、/>And->Drawing Lissajous figures for the two groups of power respectively and fitting to obtain phase differences; carrying out phase difference solution to obtain a phase shift-phase plane and fitting to obtain a phase slope +.>And->；
Repeating the above steps after moving the ultra-surface grating (12), and measuring by a first measuring power meter (19) and a second measuring power meter (22)To the transmission power and the reflection power, and obtaining new normalized transmission power and reflection power after processing、/>、/>And->And reversely solving the phase, calculating the phase difference between the phase difference and the initial position, and obtaining the two-dimensional displacement of the super-surface grating relative to the initial point according to the ratio of the phase difference to the phase slope.
6. The method of measuring according to claim 5, wherein each diffraction order implements a projection process of a designed polarization whose diffraction direction is at an angle to the optical axisWherein->Is the laser wavelength and Λ is the structural period in the x-direction and y-direction.
7. The measurement method according to claim 5, characterized in that the spatial filter (14) allows only the three diffraction orders to pass, the spatial filter (14) being made of an opaque material.
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