Spectroscopic confocal measurement structure

Abstract

The present application relates to the technical field of spectrum analysis, and particularly relates to a spectrum confocal measurement structure, comprising a light source, a Y-type optical fiber coupler, a dispersion lens and a spectrometer; wherein the Y-type optical fiber coupler has a common end, a first bifurcated end and a second bifurcated end, the first bifurcated end is connected with the light source, the second bifurcated end is connected with the spectrometer, and the common end is connected with the dispersion lens; the spectrometer comprises a collimating lens, a longitudinal dispersion grating, a cylindrical lens, a beam splitter prism, a first multi-frequency grating, a second multi-frequency grating and a plane array detector, the collimating lens, the beam splitter prism and the second multi-frequency grating are sequentially arranged along a first direction, the first multi-frequency grating, the beam splitter prism and the longitudinal dispersion grating are sequentially arranged along a third direction, and the cylindrical lens and the plane array detector are sequentially arranged on an optical path on a side of the longitudinal dispersion grating away from the beam splitter prism. The present application is conducive to realizing high light flux, high resolution and wide waveband measurement.

Description

Technical Field

[0001] This invention belongs to the field of spectral analysis technology, and particularly relates to a spectral confocal measurement structure. Background Technology

[0002] Spectroscopic confocal measurement is a non-contact, high-precision three-dimensional measurement technology. It uses the axial dispersion of a dispersive objective lens to encode the wavelength of light waves with the focal position, and uses a spectrometer to decode the wavelength to obtain the focal position information. It can realize the three-dimensional contour measurement of transparent samples and multi-layer structures, providing a brand-new measurement method for surface morphology, workpiece thickness, roughness, and deviation of target objects.

[0003] However, existing confocal spectral measuring instruments suffer from low light throughput when using dispersive spectrometers. Although spatial heterodyne spectrometers can solve this problem, when a wide-band spectrum enters a spatial heterodyne spectrometer, the interferograms of different wavelengths will interfere with each other, reducing the instrument's signal-to-noise ratio and limiting the instrument's ability to detect multispectral and weak spectral characteristic signals. Summary of the Invention

[0004] In view of this, the present invention aims to provide a spectral confocal measurement structure that is advantageous for achieving high light flux, high resolution and wide spectral band measurement.

[0005] To achieve the above objectives, the technical solution created by this invention is implemented as follows:

[0006] This invention provides a spectral confocal measurement structure, comprising: a light source, a Y-type fiber coupler, a dispersive lens, and a spectrometer; wherein the Y-type fiber coupler has a common end, a first branch end, and a second branch end, the first branch end being connected to the light source, the second branch end being connected to the spectrometer, and the common end being connected to the dispersive lens; the spectrometer includes a collimating lens, a longitudinal dispersive grating, a cylindrical lens, a beam splitter prism, a first multi-frequency grating, a second multi-frequency grating, and an area array detector, the collimating lens, the beam splitter prism, and the second multi-frequency grating being arranged sequentially along a first direction, the first multi-frequency grating, the beam splitter prism, and the longitudinal dispersive grating being arranged sequentially along a third direction, and the cylindrical lens and the area array detector being arranged sequentially on the optical path away from the beam splitter prism of the longitudinal dispersive grating.

[0007] Furthermore, the polychromatic light emitted by the light source enters the Y-type fiber coupler through the first branch end. After passing through the Y-type fiber coupler, the polychromatic light enters the dispersive lens from the common end. The polychromatic light undergoes axial dispersion through the dispersive lens, causing light of different wavelengths to be focused at different axial positions behind the dispersive lens. The light of the focused wavelength on the surface under test is reflected by the object under test to form the probe light. The probe light enters the Y-type fiber coupler through the common end, and after passing through the Y-type fiber coupler, it enters the spectrometer from the second branch end.

[0008] Furthermore, the probe light from the incident spectrometer is collimated by a collimating lens and then enters a beam splitter prism. The beam splitter prism splits the light into a first beam and a second beam. The first beam is diffracted by a first multi-frequency grating to form a first return beam, and the second beam is diffracted by a second multi-frequency grating to form a second return beam. Both the first and second return beams are incident on the beam splitter prism and interfere to form the beam to be measured. The beam to be measured is directed towards a longitudinal dispersion grating, which splits the beam to be measured longitudinally according to wavelength before it is incident on a cylindrical lens. The beam to be measured is longitudinally compressed by the cylindrical lens and then directed towards the array detector to form an interference signal.

[0009] Furthermore, the scribe lines of the longitudinal dispersion grating extend parallel to the first direction, the normal of the longitudinal dispersion grating forms an angle with the third direction, and the scribe line arrangement direction of the longitudinal dispersion grating forms an angle with the second direction.

[0010] Furthermore, the first multi-frequency grating includes four first sub-gratings arranged sequentially and connected along the second direction. Each first sub-grating has the same scribe line density, the same scribe line extension direction, and the scribe line extension direction of each first sub-grating is parallel to the second direction. Each first sub-grating has a different Littoral angle, and the angle between the normal of each first sub-grating and the third direction is the Littoral angle of the corresponding first sub-grating. The second multi-frequency grating includes four second sub-gratings arranged sequentially and connected along the second direction. Each second sub-grating has the same scribe line density, the same scribe line extension direction, and the scribe line extension direction of each second sub-grating is parallel to the second direction. Each second sub-grating has a different Littoral angle, and the angle between the normal of each second sub-grating and the first direction is the Littoral angle of the corresponding second sub-grating.

[0011] Furthermore, the scribe line density of the first sub-grating is the same as that of the second sub-grating, and the structure of the first multi-frequency grating is the same as that of the second multi-frequency grating.

[0012] Compared with existing technologies, the present invention achieves the following beneficial effects: The spectral confocal measurement structure provided by the present invention combines the advantages of a cross-dispersion spatial heterodyne spectrometer, avoiding the low light flux problem of using a dispersion spectrometer in spectral confocal measurement instruments, and can achieve high light flux, high resolution, and wide band measurement. Specifically, the spectral confocal measurement structure provided by the present invention can receive independent interferograms of different wavelengths from different pixel rows of a single detector (area array detector), which has the advantages of high signal-to-noise ratio, wide measurement band, high light flux, and high resolution; using a spatial heterodyne spectrometer instead of the dispersion spectrometer commonly used in existing spectral confocal measurement instruments eliminates the need for an entrance slit, thus improving the instrument's light flux; the combination of a longitudinal dispersion grating and a multi-frequency grating simultaneously achieves longitudinal and transverse dispersion spatial heterodyne interferometry measurements, which is beneficial to improving the instrument's signal-to-noise ratio; the multi-frequency grating is a Dolittle angle multi-frequency grating. The multi-frequency grating is designed with different Littorch angles for each sub-grating. Therefore, the grating line density of each sub-grating can be the same, which greatly simplifies the manufacturing difficulty of the multi-frequency grating and makes it easy to mass-produce sub-gratings by grating replication, thereby obtaining the first multi-frequency grating and the second multi-frequency grating. In this invention, the combination of cylindrical lens and longitudinal dispersion grating can make the light beams corresponding to different spectral ranges diffracted by the corresponding sub-gratings on the multi-frequency grating, thereby reducing the light flux loss caused by direct illumination. In addition, the separated interference fringes can also avoid the influence of oversaturated strong light on the interference fringes generated by light of other wavelengths. Attached Figure Description

[0013] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0014] Figure 1 A schematic diagram of the spectral confocal measurement structure described in the embodiment of the present invention;

[0015] Figure 2 A partial structural schematic diagram of the spectrometer described in the embodiments of the present invention;

[0016] Figure 3 A schematic diagram of the structure of the Y-type fiber coupler described in the embodiment of the present invention;

[0017] Figure 4 This is a schematic diagram of the structure of the first multi-frequency grating described in an embodiment of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0020] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0021] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0022] The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0023] refer to Figures 1 to 4This invention provides a spectral confocal measurement structure, comprising: a light source 2, a Y-type fiber coupler 3, a dispersive lens 4, and a spectrometer 10; wherein, the Y-type fiber coupler 3 has a common end 3c, a first branch end 3a, and a second branch end 3b, the first branch end 3a being connected to the light source 2, the second branch end 3b being connected to the spectrometer 10, and the common end 3c being connected to the dispersive lens 4; the spectrometer 10 includes a collimating lens 1, a longitudinal dispersive grating 7, a cylindrical lens 8, a beam splitter prism 6, a first multi-frequency grating 501, a second multi-frequency grating 502, and an area array detector 9, the collimating lens 1, the beam splitter prism 6, and the second multi-frequency grating 502 being arranged sequentially along a first direction X, the first multi-frequency grating 501, the beam splitter prism 6, and the longitudinal dispersive grating 7 being arranged sequentially along a third direction Z, and the cylindrical lens 8 and the area array detector 9 being arranged sequentially on the optical path of the longitudinal dispersive grating 7 away from the beam splitter prism 6.

[0024] The collimating lens 1, longitudinal dispersion grating 7, cylindrical lens 8, beam splitter prism 6, first multi-frequency grating 501, second multi-frequency grating 502, and area array detector 9 are arranged in a specific layout with the beam splitter prism 6 as the center. The first multi-frequency grating 501 and the second multi-frequency grating 502 are respectively arranged on adjacent sides of the beam splitter prism 6. The longitudinal dispersion grating 7, cylindrical lens 8, and area array detector 9 are arranged sequentially on one side of the beam splitter prism 6, which is opposite to the first multi-frequency grating 501. The collimating lens 1 is arranged on the other side of the beam splitter prism 6, which is opposite to the second multi-frequency grating 502. In some examples, the collimating lens 1 is located in front of the beam splitter prism 6, the first multi-frequency grating 501 is located above the beam splitter prism 6, the second multi-frequency grating 502 is located behind the beam splitter prism 6, the longitudinal dispersion grating 7 is located below the beam splitter prism 6, the cylindrical lens 8 is located below the longitudinal dispersion grating 7, and the area array detector 9 is located below the cylindrical lens 8.

[0025] Furthermore, the polychromatic light emitted by the light source 2 enters the Y-type fiber coupler 3 through the first branch end 3a. After passing through the Y-type fiber coupler 3, the polychromatic light enters the dispersive lens 4 from the common end 3c. The polychromatic light undergoes axial dispersion through the dispersive lens 4, causing light of different wavelengths to be focused at different axial positions behind the dispersive lens 4. The light of the focused wavelength of the surface under test is reflected by the object under test to form the probe light. The surface under test here is the surface under test of the object under test. The probe light enters the Y-type fiber coupler 3 through the common end 3c. After passing through the Y-type fiber coupler 3, it enters the spectrometer 10 from the second branch end 3b.

[0026] Furthermore, the probe light from the incident spectrometer 10 is collimated by the collimating lens 1 and then enters the beam-splitting prism 6. The beam-splitting prism 6 splits the light into a first beam and a second beam. The first beam is diffracted by the first multi-frequency grating 501 to form a first return beam, and the second beam is diffracted by the second multi-frequency grating 502 to form a second return beam. Both the first and second return beams are incident on the beam-splitting prism 6 and interfere to form the beam to be measured. This beam is then directed towards the longitudinal dispersion grating 7, which longitudinally separates the beam according to wavelength before directing it to the cylindrical lens 8. The beam is then longitudinally compressed by the cylindrical lens 8 and directed towards the area array detector 9, forming an interference signal. In some examples, the longitudinal dispersion grating 7 longitudinally separates the beam according to wavelength before directing it to the cylindrical lens 8, which then longitudinally compresses the beam before directing it towards the area array detector 9, forming an interference signal.

[0027] The longitudinal dispersion grating 7 is used to achieve longitudinal dispersion, separating beams of different wavelengths at different angles in the longitudinal direction. The cylindrical lens 8 is used to compress the beam size only in the longitudinal direction and has no effect on the beam in the first direction X. The collimating lens 1 is used to collect the probe light containing spectral characteristics that enters the spectrometer 10 from the second bifurcation end 3b and collimate it into the subsequent optical path.

[0028] It should be noted that the first direction X, the second direction Y, and the third direction Z are all perpendicular to each other.

[0029] Furthermore, the scribe lines of the longitudinal dispersive grating 7 extend parallel to the first direction X, the normal of the longitudinal dispersive grating 7 forms an angle with the third direction Z, and the scribe line arrangement direction of the longitudinal dispersive grating 7 forms an angle with the second direction Y.

[0030] Furthermore, the first multi-frequency grating 501 includes four first sub-gratings 510 arranged sequentially and connected along the second direction Y. Each first sub-grating 510 has the same scribe line density, the same scribe line extension direction, and the scribe line extension direction of each first sub-grating 510 is parallel to the second direction Y. Each first sub-grating 510 has a different Littoral angle, and the angle between the normal of each first sub-grating 510 and the third direction Z is the Littoral angle of the corresponding first sub-grating 510. The second multi-frequency grating 502 includes four second sub-gratings arranged sequentially and connected along the second direction Y. Each second sub-grating has the same scribe line density, the same scribe line extension direction, and the scribe line extension direction of each second sub-grating is parallel to the second direction Y. Each second sub-grating has a different Littoral angle, and the angle between the normal of each second sub-grating and the first direction X is the Littoral angle of the corresponding second sub-grating.

[0031] In the first multi-frequency grating 501, each first sub-grating 510 rotates about its corresponding central axis AA1 extending along the scribe line direction, and the central axes of all first sub-gratings 510 coinciding with each other. In the second multi-frequency grating 502, each second sub-grating rotates about its corresponding central axis extending along the scribe line direction, and the central axes of all second sub-gratings coinciding with each other. The purpose of this design is to ensure that the zero optical path difference position of each sub-grating is as similar as possible.

[0032] Furthermore, the scribe line density of the first sub-grating 510 is the same as that of the second sub-grating, and the structure of the first multi-frequency grating 501 is the same as that of the second multi-frequency grating 502.

[0033] In some embodiments, the first multi-frequency grating 501 is rotated by a certain angle, for example, 0.1°, around the center normal of the grating surface of the first multi-frequency grating 501. This is used to generate two-dimensional interference fringes and avoid spectral confusion caused by the symmetrical wavenumbers on both sides of the Littor wavenumber in one-dimensional interference fringes.

[0034] It is understood that the first multi-frequency grating 501 and the second multi-frequency grating 502 provided by the present invention are multi-frequency gratings with Dolittle angles. The first multi-frequency grating 501 is spliced ​​together from four first sub-gratings 510 with the same grating density, and the second multi-frequency grating 502 is spliced ​​together from four second sub-gratings with the same grating density. Each sub-grating is arranged along the extension direction of the grating grating at a specific rotation angle. The grating grating gratings of each sub-grating have the same grating grating density, which greatly simplifies the manufacturing difficulty of the first multi-frequency grating 501 and the second multi-frequency grating 502. It is easy to mass-produce sub-gratings by grating replication and then obtain the corresponding multi-frequency grating by splicing.

[0035] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0036] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A spectral confocal measurement structure, characterized in that, include: Light source, Y-type fiber coupler, dispersive lens, and spectrometer; The Y-type fiber coupler has a common end, a first branch end, and a second branch end. The first branch end is connected to the light source, the second branch end is connected to the spectrometer, and the common end is connected to the dispersive lens. The spectrometer includes a collimating lens, a longitudinal dispersion grating, a cylindrical lens, a beam splitter, a first multi-frequency grating, a second multi-frequency grating, and an area array detector. The collimating lens, the beam splitter, and the second multi-frequency grating are arranged sequentially along a first direction, and the first multi-frequency grating, the beam splitter, and the longitudinal dispersion grating are arranged sequentially along a third direction. The cylindrical lens and the area array detector are arranged sequentially on the optical path of the longitudinal dispersion grating away from the beam splitter.

2. The spectral confocal measurement structure according to claim 1, characterized in that, The polychromatic light emitted by the light source enters the Y-type fiber coupler through the first branch end. After passing through the Y-type fiber coupler, the polychromatic light enters the dispersive lens from the common end. The polychromatic light undergoes axial dispersion through the dispersive lens, causing light of different wavelengths to be focused at different axial positions behind the dispersive lens. The light of the focused wavelength on the surface under test is reflected by the object under test to form a probe light. The probe light enters the Y-type fiber coupler through the common end and enters the spectrometer from the second branch end after passing through the Y-type fiber coupler.

3. The spectral confocal measurement structure according to claim 1, characterized in that, The probe light incident on the spectrometer is collimated by the collimating lens and then enters the beam splitter prism. The beam splitter splits the light into a first beam and a second beam. The first beam is diffracted by the first multi-frequency grating to form a first return beam, and the second beam is diffracted by the second multi-frequency grating to form a second return beam. Both the first and second return beams are incident on the beam splitter prism and interfere to form a beam to be tested. The beam to be tested is directed toward the longitudinal dispersion grating. The longitudinal dispersion grating splits the beam to be tested longitudinally according to wavelength and then directs it toward the cylindrical lens. The beam to be tested is longitudinally compressed by the cylindrical lens and then directed toward the area array detector to form an interference signal.

4. The spectral confocal measurement structure according to claim 1, characterized in that, The longitudinal dispersion grating has scribe lines extending in a direction parallel to the first direction, and the normal to the longitudinal dispersion grating has an angle with the third direction. The scribe line arrangement direction of the longitudinal dispersion grating also has an angle with the second direction.

5. The spectral confocal measurement structure according to claim 1, characterized in that, The first multi-frequency grating includes four first sub-gratings arranged sequentially and connected along the second direction. Each first sub-grating has the same scribe line density, the same scribe line extension direction, and the scribe line extension direction of each first sub-grating is parallel to the second direction. Each first sub-grating has a different Littoral angle, and the angle between the normal of each first sub-grating and the third direction is the Littoral angle of the corresponding first sub-grating. The second multi-frequency grating includes four second sub-gratings arranged sequentially and connected along the second direction. Each second sub-grating has the same scribe line density, the same scribe line direction, and the scribe line extension direction of each second sub-grating is parallel to the second direction. Each second sub-grating has a different Littoral angle, and the angle between the normal of each second sub-grating and the first direction is the Littoral angle of the corresponding second sub-grating.

6. The spectral confocal measurement structure according to claim 5, characterized in that, The scribe line density of the first sub-grating is the same as that of the second sub-grating, and the structure of the first multi-frequency grating is the same as that of the second multi-frequency grating.

7. The spectral confocal measurement structure according to claim 5, characterized in that, In the first multi-frequency grating, each first sub-grating rotates around the central axis extending along the scribe line direction of the corresponding first sub-grating, and the central axes extending along the scribe line direction of all the first sub-gratings coincide with each other; in the second multi-frequency grating, each second sub-grating rotates around the central axis extending along the scribe line direction of the corresponding second sub-grating, and the central axes extending along the scribe line direction of all the second sub-gratings coincide with each other.

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