Miniature integrated precise grating vortex interference displacement sensor

Abstract

A miniature integrated precise grating vortex interference displacement sensor adopts an optical-mechanical-electrical integrated structural design and mainly comprises a laser diode chip, a packaging cover plate integrating a phase modulation micro-nano metasurface and a lens, a beam splitter and a photoelectric detector. After laser emitted by the laser diode chip passes through the phase modulation micro-nano metasurface, a Gaussian beam is converted into a vortex beam, the vortex beam is incident to the grating to be diffracted, and symmetrical-level diffracted light is incident to the beam splitter through the lens and converges at the beam splitter to form vortex light conjugate coherence. The coherent light field is converted into an image signal and an electric signal by a detector, and then the displacement to be measured is analyzed. A precise grating vortex interference displacement sensor structure is designed in an integrated manner, so that the interference optical path of a vortex diffraction beam is shortened, the influence of air disturbance is reduced, and the measurement precision is improved; the precise grating vortex interference displacement sensor is miniaturized in volume, is compatible with the current common semiconductor technology, and can form an optical MEMS displacement sensor.

Description

Technical Field

[0001] The present invention relates to the technical field of high-end equipment precision motion control, and in particular to a micro-integrated precision grating vortex interferometry displacement sensor. Background Art

[0002] Optical interferometry measurement technology, represented by laser interferometry and grating interferometry, is currently the most popular cross-scale precision positioning technology and one of the core supporting technologies for improving the precision of high-end equipment.

[0003] Laser interferometry technology, based on the laser wavelength, is currently recognized as the technology with the highest theoretical accuracy for large-scale displacement measurement. The vortex beam is used as the carrier for sensing phase changes in the interferometer, forming a vortex light interferometer. Compared with the traditional laser interferometer, the vortex light interferometer produces concentric petal-shaped or spiral vortex interference fringes through the coaxial coherent superposition of the vortex beam and its conjugate beam or plane wave beam. By selecting the appropriate topological charge and the pixel resolution of the array camera, the measurement resolution can reach the picometer level. However, whether it is the traditional laser interferometry measurement technology or the vortex light interferometry measurement technology, the laser wavelength is used as the measurement reference, and both cannot avoid the inherent problems of long interference arms and sensitivity to environmental disturbances. The measurement stability in the field environment or long-term service process is the key challenge it faces.

[0004] Compared with laser interferometry technology, grating interferometry technology uses the physical pitch of the grating as the measurement reference rather than the laser wavelength, and has the following advantages: the physical pitch is stable, the interference arm length is extremely short and unchanged, so it is insensitive to environmental disturbances and has good long-term measurement stability; no long reflector is required on the workpiece stage, so the workpiece stage has a lighter load and better dynamic performance.

[0005] From the perspective of the excitation light source, the applicant of this patent has changed the interference mode of the current grating interferometry technology, which generally uses Gaussian beams as carriers, and proposed a new grating interferometry measurement method using vortex light as the carrier, and has an invention patent (Ye Guoyong et al., A precision grating displacement measurement device and measurement method excited by vortex beams, patent number: ZL 202210494629.0, authorization date: June 16, 2023). However, the measurement device and measurement method invented by patent ZL 202210494629.0 still face the following key problems: (1) The optical path structure using separate optical elements has a large reading unit volume and is not suitable for application scenarios with limited installation space; (2) The optical path structure using separate optical elements has a long interference optical path and is affected by environmental disturbances; (3) There are many optical elements in the optical path, such as dove prisms and reflectors, and each optical element needs to be precisely adjusted, which makes it difficult to assemble the optical path of the reading unit. Summary of the invention

[0006] In order to overcome the shortcomings of the above-mentioned prior art, the present invention provides a micro-integrated precision grating vortex interferometry displacement sensor, which adopts the method of optical-mechanical-electrical integration structure design of laser diode chips, micro-nano supersurfaces, lenses, spectrometers, photodetectors, etc. to form a micro-integrated precision grating vortex interferometry MEMS displacement sensor.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A miniature integrated precision grating vortex interference displacement sensor comprises a diffraction grating and an optical MEMS structure reading unit.

[0009] Furthermore, the MEMS structure reading unit includes a packaging substrate and a composite micro-nano structure packaging cover plate, the interior of the packaging substrate is processed into a working cavity by MEMS process, the composite micro-nano structure packaging cover plate is a transparent cover plate, on which a first lens and a second lens are opened, and the lower surface of the composite micro-nano structure packaging cover plate is integrated with a phase-modulating micro-nano metasurface, the phase-modulating micro-nano metasurface is located between the first lens and the second lens, and a laser diode chip is fixedly installed under the phase-modulating micro-nano metasurface; a spectrometer is fixedly installed on the lower surface of the working cavity, and a first photodetector and a second photodetector are respectively fixedly installed on the V-shaped sides of the working cavity, and the first photodetector 8 and the second photodetector are located on both sides of the spectrometer.

[0010] Furthermore, the wavelength of the laser diode chip is 450-950nm, and the power is 5-20mw.

[0011] Furthermore, the beam splitter is a non-polarized semi-transparent and semi-reflective beam splitter with an applicable wavelength range of 450-950nm.

[0012] Furthermore, the first photodetector is a photodetection array, and the second photodetector is a single silicon photocell.

[0013] Furthermore, the diffraction grating is a reflective phase grating, which can be a linear grating or a circular grating; for a linear grating, the grating groove is a non-blazed grating with a symmetrical structure, the groove is rectangular or sinusoidal, the grating pitch is 0.4-10μm, the groove depth is 220-290nm, and the groove ridge width is 0.8-1.2μm, so as to maximize the +1 and -1 diffraction efficiency. For a circular grating, the grating lines are located on the disk surface, the grating groove is a non-blazed grating with a symmetrical structure, the groove is rectangular or sinusoidal, the diameter is 50-300mm, the grating pitch is 0.4-10um, the groove depth is 220-290nm, and the groove ridge width is 0.8-1.2mm, so as to maximize the +1 and -1 level transmission efficiency.

[0014] Furthermore, the phase-modulated micro-nano metasurface is a geometric phase metasurface, and the topological charge number of the generated vortex light beam is 1-4.

[0015] A measurement method using the micro-integrated precision grating vortex interferometry displacement sensor comprises the following steps:

[0016] S1. The laser output from the laser passes through the micro-nano metasurface to generate a vortex beam. The vortex beam is incident on the grating and diffracted to generate vortex diffraction light of different orders.

[0017] S2. The vortex diffraction light of symmetrical order enters the beam splitter after being refracted by the lens structure, and the two beams form a conjugate relationship and are coherent;

[0018] S3. The conjugate vortex coherent light field is received by the photodetector;

[0019] S4. When the diffraction grating moves parallel to or rotates relative to the optical MEMS structure reading unit, the symmetrical order diffracted light undergoes frequency shift and thus generates a phase difference Δφ. The phase change Δφ caused by the measured displacement x is linearly related to the rotation angle of the coherent pattern of the equal conjugate vortex diffraction light, and the rotation direction corresponds to the measured displacement direction;

[0020] S5. The photodetector receives the coherent light field of the conjugate vortex diffraction light, wherein the first photodetector is a photodetection array, which converts the coherent light field into an image signal for fine counting of the non-integer period of the conjugate vortex interference fringes, and analyzes the displacement x1=F -1 (Δφ); the second photodetector is a single silicon photocell, which converts the coherent light field into an electrical signal, which is used to count the whole cycle of the conjugate vortex interference fringes, and obtains the whole cycle displacement x2=nP / 2, where n is the number of whole cycle counts and P is the pitch of the diffraction grating; the final displacement to be measured is x=x1+x2.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) Compared with the working mode of vortex optical interferometry measurement technology which uses laser wavelength as the measurement reference, the present invention proposes a miniature integrated precision grating vortex interferometry displacement sensor which uses grating pitch as the measurement reference, is insensitive to environmental disturbances, and has better service accuracy stability.

[0023] (2) Compared with the separate structure in the vortex beam excited precision grating displacement measurement device and measurement method invented by the applicant's authorized patent ZL 202210494629.0, the present invention proposes a miniature integrated precision grating vortex interference displacement sensor, which adopts an optomechanical integrated MEMS structure design, realizes the miniaturization of the sensor structure, reduces the interference optical path, and is suitable for high-precision displacement measurement in scenarios with limited installation space; it eliminates optical components such as dove prisms and reflectors, reduces the difficulty of position alignment when assembling multiple optical components, improves the sensor assembly efficiency, and is easier to mass produce. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a front view of a micro-integrated precision grating vortex interferometry displacement sensor in an embodiment;

[0025] Figure 2 is a micro-nano structure parameter optimization curve of the diffraction grating in the embodiment;

[0026] Figure 3 Schematic diagram of the packaging cover structure integrating the phase modulation micro-nano metasurface and the lens in the embodiment;

[0027] Figure 4 It is a vortex beam generated by the phase-modulated micro-nano metasurface in the embodiment;

[0028] Figure 5 is a mapping relationship diagram between vortex interference fringes and grating displacement in the embodiment;

[0029] Figure 6 It is the displacement analysis based on vortex interference fringes in the embodiment;

[0030] Figure 7 The micro-integrated precision grating vortex interferometry displacement sensor is used for angular displacement measurement. DETAILED DESCRIPTION

[0031] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0032] Example 1

[0033] refer to Figure 1-7 , a miniature integrated precision grating vortex interferometry displacement sensor, including a diffraction grating I and an optical MEMS structure reading unit II.

[0034] The MEMS structure reading unit II includes a packaging substrate 6 and a composite micro-nano structure packaging cover plate 2. A working cavity is machined inside the packaging substrate 6 through a MEMS process. The composite micro-nano structure packaging cover plate 2 is a transparent cover plate on which a first lens 4 and a second lens 5 are provided. A phase-modulating micro-nano metasurface 3 is integrated on the lower surface of the composite micro-nano structure packaging cover plate 2. The phase-modulating micro-nano metasurface 3 is located between the first lens 4 and the second lens 5. A laser diode chip 1 is fixedly installed below the phase-modulating micro-nano metasurface 3. A spectrometer 7 is fixedly installed on the lower surface of the working cavity. A first photodetector 8 and a second photodetector 9 are fixedly installed on the V-shaped sides of the working cavity, respectively. The first photodetector 8 and the second photodetector 9 are located on both sides of the spectrometer 7.

[0035] Preferably, the wavelength of the laser diode chip 1 is 450-950 nm, and the power is 5-20 mw.

[0036] Preferably, the beam splitter 7 is a non-polarized semi-transmissive and semi-reflective beam splitter with an applicable wavelength range of 450-950nm.

[0037] Preferably, the first photodetector 8 is a photodetection array, and the second photodetector 9 is a single silicon photocell.

[0038] The diffraction grating I is a reflective phase grating, which can be a linear grating or a circular grating; for the linear grating, the grating groove type is a non-blazed grating with a symmetrical structure, the groove type is rectangular or sinusoidal trapezoidal, the grating pitch is 0.4-10μm, the groove depth is 220-290nm, and the groove ridge width is 0.8-1.2μm, so as to maximize the +1 and -1 order diffraction efficiencies.

[0039] For circular gratings, the grating lines are located on the disk surface, the grating line groove type is a symmetrical non-blazed grating, the line groove type is rectangular or sinusoidal trapezoidal, the diameter is 50-300mm, the grating pitch is 0.4-10um, the groove depth is 220-290nm, and the groove ridge width is 0.8-1.2mm, so as to maximize the +1 and -1 level transmission efficiency.

[0040] Preferably, the phase-modulated micro-nano metasurface 3 is a geometric phase metasurface, and the topological charge number of the generated vortex light beam is 1-4.

[0041] Example 2

[0042] A measurement method using the micro-integrated precision grating vortex interferometry displacement sensor comprises the following steps:

[0043] S1. The laser output from the laser passes through the micro-nano metasurface to generate a vortex beam. The vortex beam is incident on the grating and diffracted to generate vortex diffraction light of different orders.

[0044] S2. The vortex diffraction light of symmetrical order enters the beam splitter after being refracted by the lens structure, and the two beams form a conjugate relationship and are coherent;

[0045] S3. The conjugate vortex coherent light field is received by the photodetector;

[0046] S4. When the diffraction grating moves parallel to or rotates relative to the optical MEMS structure reading unit, the symmetrical order diffracted light undergoes frequency shift and thus generates a phase difference Δφ. The phase change Δφ caused by the measured displacement x is linearly related to the rotation angle of the coherent pattern of the equal conjugate vortex diffraction light, and the rotation direction corresponds to the measured displacement direction;

[0047] S5. The photodetector receives the coherent light field of the conjugate vortex diffraction light, wherein the first photodetector 8 is a photodetection array, which converts the coherent light field into an image signal for fine counting of the non-integer period of the conjugate vortex interference fringes, and analyzes the displacement x1=F -1 (Δφ); the second photodetector 9 is a single silicon photocell, which converts the coherent light field into an electrical signal, which is used to count the whole cycle of the conjugate vortex interference fringes, and obtains the whole cycle displacement x2=nP / 2, where n is the number of whole cycle counts and P is the pitch of the diffraction grating; the final displacement to be measured is x=x1+x2.

[0048] The above is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered as the protection scope of the present invention. All components not specified in this embodiment can be implemented by existing technologies.

Claims

1. A micro-integrated precision grating vortex interferometry displacement sensor, characterized in that: It includes a diffraction grating (I) and an optical MEMS structure reading unit (II).

2. A micro-integrated precision grating vortex interferometry displacement sensor as claimed in claim 1, characterized in that: The MEMS structure reading unit (II) comprises a packaging substrate (6) and a composite micro-nano structure packaging cover plate (2), wherein a working cavity is machined inside the packaging substrate (6) by a MEMS process, and the composite micro-nano structure packaging cover plate (2) is a transparent cover plate, on which a first lens (4) and a second lens (5) are provided, and a phase modulating micro-nano metasurface (3) is integrated on the lower surface of the composite micro-nano structure packaging cover plate (2), wherein the phase modulating micro-nano metasurface (3) is located between the first lens (4) and the second lens (5), and a laser diode chip (1) is fixedly installed below the phase modulating micro-nano metasurface (3); a beam splitter (7) is fixedly installed on the lower surface of the working cavity, and a first photodetector (8) and a second photodetector (9) are fixedly installed on the V-shaped side surfaces of the working cavity, respectively, and the first photodetector (8) and the second photodetector (9) are located on both sides of the beam splitter (7).

3. A micro-integrated precision grating vortex interferometry displacement sensor as claimed in claim 2, characterized in that: The wavelength of the laser diode chip (1) is 450-950nm, and the power is 5-20mw.

4. A micro-integrated precision grating vortex interferometry displacement sensor as claimed in claim 2, characterized in that: The beam splitter (7) is a non-polarized semi-transparent and semi-reflective beam splitter, and is applicable to a wavelength range of 450-950 nm.

5. A micro-integrated precision grating vortex interferometry displacement sensor as claimed in claim 2, characterized in that: The first photodetector (8) is a photodetection array, and the second photodetector (9) is a single silicon photocell.

6. The micro-integrated precision grating vortex interferometry displacement sensor according to claim 1, characterized in that: The diffraction grating (I) is a reflective phase grating, which can be a linear grating or a circular grating; for the linear grating, the grating groove type is a non-blazed grating with a symmetrical structure, the groove type is rectangular or sinusoidal trapezoidal, the grating pitch is 0.4-10μm, the groove depth is 220-290nm, and the groove ridge width is 0.8-1.2μm, so as to maximize the +1 and -1 order diffraction efficiency; for the circular grating, the grating lines are located on the disk surface, the grating groove type is a non-blazed grating with a symmetrical structure, the groove type is rectangular or sinusoidal trapezoidal, the diameter is 50-300mm, the grating pitch is 0.4-10um, the groove depth is 220-290nm, and the groove ridge width is 0.8-1.2mm, so as to maximize the +1 and -1 order transmission efficiency.

7. The micro-integrated precision grating vortex interferometry displacement sensor according to claim 1, characterized in that: The phase-modulated micro-nano metasurface (3) is a geometric phase metasurface, and the topological charge number of the generated vortex beam is 1-4.

8. A measurement method using the micro-integrated precision grating vortex interferometry displacement sensor as described in any one of claims 1 to 7, characterized in that: The steps include: S1. The laser output from the laser passes through the micro-nano metasurface to generate a vortex beam. The vortex beam is incident on the grating and diffracted to generate vortex diffraction light of different orders. S2. The vortex diffraction light of symmetrical order enters the beam splitter after being refracted by the lens structure, and the two beams form a conjugate relationship and are coherent; S3. The conjugate vortex coherent light field is received by the photodetector; S4. When the diffraction grating moves parallel to or rotates relative to the optical MEMS structure reading unit, the symmetrical order diffracted light undergoes frequency shift and thus generates a phase difference. Phase change caused by the measured displacement x It is linearly related to the rotation angle of the coherent pattern of the equal conjugate vortex diffraction light, and the rotation direction corresponds to the measured displacement direction; S5. The photodetector receives the coherent light field of the conjugate vortex diffraction light, wherein the first photodetector (8) is a photodetection array, which converts the coherent light field into an image signal for fine counting of the non-integer period of the conjugate vortex interference fringes and analyzing the displacement of the less than integer period. The second photodetector (9) is a single silicon photocell, which converts the coherent light field into an electrical signal for counting the whole cycle of the conjugate vortex interference fringes, and obtains the whole cycle displacement x2=nP / 2, where n is the number of whole cycle counts and P is the grating pitch of the diffraction grating; the final displacement result to be measured is x=x1+x2.

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