A displacement sensor based on grating reflection and four-step reflector

Abstract

The present invention belongs to the technical field of displacement sensors, and specifically relates to a displacement sensor based on grating reflection and a four-step reflector, comprising a light source, a semi-transparent and semi-reflective mirror, a one-dimensional grating, a step reflector, and a four-quadrant detector, wherein the semi-transparent and semi-reflective mirror is arranged in the light path direction of the light source, the one-dimensional grating is arranged in the light path direction of the semi-transparent and semi-reflective mirror, the step reflector is arranged in the light path direction of the one-dimensional grating, and the four-quadrant detector is arranged in the reflected light path of the semi-transparent and semi-reflective mirror. The present invention utilizes the self-imaging effect of the nano-grating to detect the change in the output light intensity of the semi-transparent and semi-reflective mirror to realize the output of the A and B phase optical signals of the optical signal, thereby reducing the difficulty of electrical subdivision and realizing high-sensitivity displacement measurement. In addition, the present invention does not require auxiliary optical elements such as polarizers and half-wave plates, which significantly simplifies the measurement structure, reduces the cost of the device, and is conducive to the realization of structural miniaturization and integrated application.

Description

Technical Field

[0001] The present invention belongs to the technical field of displacement sensors, and in particular relates to a displacement sensor based on grating reflection and a four-step reflector. Background Art

[0002] Weak displacement measurement technology is one of the key technologies that affects the processing accuracy of precision machinery, semiconductor devices, etc. With the increasing demand for industries such as MEMS high-precision processing in recent years, the research and development of high-resolution, small-volume displacement measurement devices has become an increasingly urgent task. Displacement sensor devices based on nanogratings have the advantages of being immune to electromagnetic interference, high precision and high resolution, and therefore have been widely used. At present, nanograting multi-dimensional displacement sensor devices are mainly based on the interference effect between different orders of diffraction beams. In order to achieve the overlap of light beams in different diffraction directions and then achieve interference, this method usually requires a variety of optical elements such as polarizers and glass slides, so there are the following problems: 1. The structure is complex and not easy to miniaturize and integrate; 2. The cost is high, which is not conducive to low-cost mass production. Summary of the Invention

[0003] To address the technical issues of the complex structure and difficulty in miniaturization of the above-mentioned existing grating-type multi-dimensional displacement sensors, the present invention provides a displacement sensor based on grating reflection and a four-step reflector. Based on the principle of nano-grating self-imaging, high-sensitivity displacement detection can be achieved by detecting the light intensity reflected by the grating structure. By adopting a one-dimensional grating and a step reflector structure, displacement detection in two dimensions can be achieved simultaneously.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0005] A displacement sensor based on grating reflection and a four-step reflector comprises a light source, a semi-transparent and semi-reflective mirror, a one-dimensional grating, a step reflector and a four-quadrant detector, wherein the semi-transparent and semi-reflective mirror is arranged in the light path direction of the light source, the one-dimensional grating is arranged in the light path direction of the semi-transparent and semi-reflective mirror, the step reflector is arranged in the light path direction of the one-dimensional grating, and the four-quadrant detector is arranged in the reflected light path of the semi-transparent and semi-reflective mirror.

[0006] The step reflector includes a first reflector area, a second reflector area, a third reflector area, a fourth reflector area and a base, and the first reflector area, the second reflector area, the third reflector area and the fourth reflector area are respectively fixedly connected to the base.

[0007] The four-quadrant detector is electrically connected to an electrical subdivision module, and the electrical subdivision multiple M of the electrical subdivision module is 8000.

[0008] The first reflector region and the second reflector region are arranged side by side on the base, and the third reflector region and the fourth reflector region are arranged side by side on the base.

[0009] The heights of the first reflector region, the second reflector region, the third reflector region, and the fourth reflector region decrease in sequence.

[0010] The light source is a laser, the wavelength λ of the laser is 635 nm, and the power of the laser is 1.2 mW.

[0011] The grating duty cycle of the one-dimensional grating is 0.5, the grating ruling depth h of the one-dimensional grating is 0.53 μm, the grating material of the one-dimensional grating is Si, and the grating thickness of the one-dimensional grating is 536 nm.

[0012] The step mirror is arranged on the self-imaging area of the one-dimensional grating.

[0013] A displacement sensor based on grating reflection and a four-step reflector includes the following steps:

[0014] S1. The semi-transparent and semi-reflective mirror is initially placed in the direction of the light path of the light source, and the laser emitted by the light source passes through the semi-transparent and semi-reflective mirror to illuminate the one-dimensional grating;

[0015] S2, a self-imaging area is formed behind the one-dimensional grating, and a step mirror is placed in the area to cause reflection;

[0016] S3. Place the four-quadrant detector directly on the light path reflected by the semi-transparent and semi-reflective mirror to detect the intensity of the reflected light;

[0017] S4. When the step reflector is displaced in the horizontal direction or the out-of-plane direction, the light intensity detected by the four-quadrant detector changes, and four sinusoidal signals with a 90° phase difference are output;

[0018] S5. Input the four-way signal into the electrical subdivision module for subdivision processing, and obtain the displacement of the step reflector in the horizontal or off-plane direction by counting the cycles of the output square wave signal.

[0019] The light source illuminates the one-dimensional grating vertically. At this time, the complex amplitude distribution on the plane behind the one-dimensional grating is:

[0020]

[0021] Among them, A n and A m is the Fourier coefficient, i is the intrinsic coefficient, n and m represent the harmonic series, x0 represents a certain position in the x direction, f xrepresents the spatial frequency in the x direction, z represents the distance from the plane, and k represents the plane wave number. In Fresnel diffraction, the transfer function of the system is

[0022]

[0023] Observe the spectrum of the light field distribution on the surface,

[0024]

[0025] After being reflected back to the grating by the reflector, the complex amplitude of the light field on the exit surface of the semi-transparent and semi-reflective mirror can be expressed as

[0026]

[0027]

[0028] Where Δx represents the relative displacement of the two gratings, n = m;

[0029] When the position of the one-dimensional grating is fixed, the position of the image is also fixed. When the step mirror is displaced in the horizontal direction of the plane, the phase of the transmitted light will change accordingly, resulting in a change in light intensity. The four-quadrant detector receives the change in light intensity, which in turn causes the electrical interpolation module to output a square wave signal. Similarly, when the step mirror is displaced in the out-of-plane direction, due to the different optical path differences, the four-quadrant detector receives the change in light intensity, and the interpolation circuit outputs a square wave signal.

[0030] Calculate the displacement using the displacement measurement formula:

[0031]

[0032] Where L is the measured displacement, d is the grating period, M is the electrical subdivision multiple, and Q is the number of square wave signal periods output by the electrical subdivision module.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] This invention utilizes the self-imaging effect of nanogratings to detect changes in the intensity of light output from a semi-transparent, semi-reflective mirror, thereby outputting the A and B phases of the optical signal. This reduces the difficulty of electrical segmentation and enables highly sensitive displacement measurement. Furthermore, the invention utilizes a linear optical path and comprises only a few components, such as a light source, a semi-transparent, semi-reflective mirror, a grating, a reflector, and a detector. It eliminates the need for additional optical components such as polarizers and half-wave plates, significantly simplifying the measurement structure and reducing device costs, facilitating structural miniaturization and integrated applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. Obviously, the drawings described below are merely exemplary, and those skilled in the art can, without inventive effort, derive other implementation drawings based on the provided drawings.

[0036] The structures, proportions, sizes, etc. illustrated in this specification are intended solely to complement the contents disclosed herein and to facilitate understanding and reading by persons skilled in the art. They are not intended to limit the conditions under which the present invention may be implemented and therefore have no substantive technical significance. Any structural modifications, changes in proportions, or adjustments in sizes, without affecting the efficacy and objectives of the present invention, shall remain within the scope of the technical contents disclosed herein.

[0037] Figure 1 It is a structural schematic diagram of the present invention;

[0038] Figure 2 Schematic diagram of the structure of the step reflector of the present invention;

[0039] Figure 3 It is the one-dimensional grating self-imaging distribution diagram of the present invention;

[0040] Figure 4 This is a diagram showing the relationship between the AB signal acquisition and light intensity of the present invention;

[0041] Figure 5 This is the principle diagram of the electrical subdivision module of the present invention.

[0042] Among them: 1 is the light source, 2 is the semi-transparent and semi-reflective mirror, 3 is the one-dimensional grating, 4 is the step reflector, 401 is the first reflector area, 402 is the second reflector area, 403 is the third reflector area, 404 is the fourth reflector area, 405 is the base, 5 is the four-quadrant detector, and 6 is the electrical subdivision module. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of this application, not all the embodiments. These descriptions are only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0044] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0045] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of such features. Throughout this application, unless otherwise specified, "plurality" means two or more.

[0046] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0047] In this embodiment, if Figure 1 As shown, it is mainly composed of a light source 1, a semi-transparent and semi-reflective mirror 2, a one-dimensional grating 3, a step reflector 4, and a four-quadrant detector 5. The semi-transparent and semi-reflective mirror 2 is initially placed at the center of the light source 1, and the laser emitted by the light source 1 irradiates the one-dimensional grating 3. A self-imaging area is formed behind the one-dimensional grating 3, and the step reflector 4 is placed in this area to cause it to reflect. The four-quadrant detector 5 is directly placed behind the output port of the semi-transparent and semi-reflective mirror 2 to detect the intensity of the reflected light; when the step reflector 4 is displaced in the x direction or the out-of-plane direction, the light intensity detected by the detection surface of the four-quadrant detector 4 changes, and four sinusoidal signals with a phase difference of 90° are output. Afterwards, the four signals are input into the electrical subdivision module 6 for subdivision processing, and the displacement of the step reflector 4 in the x or out-of-plane direction can be obtained by counting the period of the output square wave signal.

[0048] Furthermore, the first reflector area 401, the second reflector area 402, the third reflector area 403, and the fourth reflector area 404 of the step reflector 4 are fixed on the base 405, and the first, second, third, and fourth quadrant detection surfaces of the four-quadrant detector 5 can respectively detect the first reflector area 401, the second reflector area 402, the third reflector area 403, and the fourth reflector area 404 of the step reflector 4.

[0049] The displacement measurement calculation formula can be given by the following formula:

[0050]

[0051] Where L is the measured displacement, d is the grating period, M is the electrical subdivision multiple, and Q is the number of periods of the square wave signal output by the subdivision circuit.

[0052] Specific implementation parameters are as follows:

[0053] Laser wavelength: λ = 635 nm;

[0054] Laser power: 1.2mW;

[0055] Grating period: d = 800 nm;

[0056] Grating duty cycle: 0.5;

[0057] Grating ruling depth: h = 0.53 μm;

[0058] Grating material: Si;

[0059] Electrical subdivision multiple: M=8000.

[0060] The specific analysis is as follows:

[0061] The grating thickness of the one-dimensional grating 3 is set to 536 nm to ensure that the generated self-imaging area has a better effect, so as to optimize the sinusoidality of its output signal.

[0062] When the laser 1 is vertically irradiated on the one-dimensional grating 3, the complex amplitude distribution on the plane behind the one-dimensional grating 3 is:

[0063]

[0064] Among them, A n . is the Fourier coefficient, i is the intrinsic coefficient, n and m represent the harmonic series, x0 represents a certain position in the x direction, f x represents the spatial frequency in the x direction, z represents the distance from the plane, and k represents the plane wave number. In Fresnel diffraction, the transfer function of the system is

[0065]

[0066] Observe the spectrum of the light field distribution on the surface,

[0067]

[0068] After being reflected back to the grating by the reflector, the complex amplitude of the light field on the exit surface of the semi-transparent and semi-reflective mirror can be expressed as

[0069]

[0070]

[0071] Where Δx represents the relative displacement of the two gratings, and n=m.

[0072] Because in The image of the grating can be observed at a distance of . As can be seen from the previous equation, when the position of the one-dimensional grating 3 is fixed, the position of the image is also fixed. When the step mirror 4 is displaced in the x-direction of the plane, the phase of the transmitted light will change accordingly, resulting in a change in light intensity. The four-quadrant detector 5 receives this change in light intensity, which in turn causes the electrical interpolation module 6 to output a square wave signal. Similarly, when the step mirror 4 is displaced in the off-plane direction, the four-quadrant detector 5 also receives the change in light intensity due to the different optical path differences, and the electrical interpolation module 6 then outputs a square wave signal.

[0073] For example, when the step reflector 4 is displaced, the output signals of the 1st and 3rd quadrant detection surfaces of the four-quadrant detector 5 are processed by the subdivision circuit, and the number of cycles of the output square wave signal is 20,000. According to formula (1), the displacement detected in the x-direction at this time is 800 nm / 8000 × 20,000 = 2 μm.

[0074] The above only describes in detail the preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in this field without departing from the purpose of the present invention, and various changes should be included in the scope of protection of the present invention.

Claims

1. A displacement sensor based on grating reflection and a four-step reflector, characterized by: The invention comprises a light source (1), a semi-transparent and semi-reflective mirror (2), a one-dimensional grating (3), a step reflector (4) and a four-quadrant detector (5), wherein the semi-transparent and semi-reflective mirror (2) is arranged in the light path direction of the light source (1), the one-dimensional grating (3) is arranged in the light path direction of the semi-transparent and semi-reflective mirror (2), the step reflector (4) is arranged in the light path direction of the one-dimensional grating (3), and the four-quadrant detector (5) is arranged in the reflected light path of the semi-transparent and semi-reflective mirror (2); The step reflector (4) comprises a first reflector region (401), a second reflector region (402), a third reflector region (403), a fourth reflector region (404) and a base (405); the first reflector region (401), the second reflector region (402), the third reflector region (403) and the fourth reflector region (404) are respectively fixedly connected to the base (405); The first reflector region (401) and the second reflector region (402) are arranged side by side on the base (405), and the third reflector region (403) and the fourth reflector region (404) are arranged side by side on the base (405); The heights of the first reflector region (401), the second reflector region (402), the third reflector region (403), and the fourth reflector region (404) decrease in sequence.

2. The displacement sensor based on grating reflection and four-step reflector according to claim 1, characterized in that: The four-quadrant detector (5) is electrically connected to an electrical subdivision module (6), and the electrical subdivision multiple M of the electrical subdivision module (6) is 8000.

3. The displacement sensor based on grating reflection and four-step reflector according to claim 1, characterized in that: The light source (1) adopts a laser, the wavelength λ of the laser is 635 nm, and the power of the laser is 1.2 mW.

4. The displacement sensor based on grating reflection and four-step reflector according to claim 1, characterized in that: The grating duty cycle of the one-dimensional grating (3) is 0.5, the grating ruling depth h of the one-dimensional grating (3) is 0.53 μm, the grating material of the one-dimensional grating (3) is Si, and the grating thickness of the one-dimensional grating (3) is 536 nm.

5. The displacement sensor based on grating reflection and four-step reflector according to claim 1, characterized in that: The step reflector (4) is arranged on the self-imaging area of the one-dimensional grating (3).

6. A displacement sensor based on grating reflection and a four-step reflector according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. The semi-transparent and semi-reflective mirror is initially placed in the direction of the light path of the light source, and the laser emitted by the light source passes through the semi-transparent and semi-reflective mirror to illuminate the one-dimensional grating; S2, a self-imaging area is formed behind the one-dimensional grating, and a step mirror is placed in the area to cause reflection; S3. Place the four-quadrant detector directly on the light path reflected by the semi-transparent and semi-reflective mirror to detect the intensity of the reflected light; S4. When the step reflector is displaced in the horizontal direction or the out-of-plane direction, the light intensity detected by the four-quadrant detector changes, and four sinusoidal signals with a 90° phase difference are output; S5. Input the four-way signal into the electrical subdivision module for subdivision processing, and obtain the displacement of the step reflector in the horizontal or off-plane direction by counting the cycles of the output square wave signal.

7. The displacement sensor based on grating reflection and four-step reflector according to claim 6, characterized in that: The light source illuminates the one-dimensional grating vertically. At this time, the complex amplitude distribution on the plane behind the one-dimensional grating is: Among them, A n and A m is the Fourier coefficient, i is the intrinsic coefficient, n and m represent the harmonic series, x0 represents a certain position in the x direction, f x represents the spatial frequency in the x direction, z represents the distance from the plane, and k represents the plane wave number. In Fresnel diffraction, the transfer function of the system is Observe the spectrum of the light field distribution on the surface, After being reflected back to the grating by the reflector, the complex amplitude of the light field on the exit surface of the semi-transparent and semi-reflective mirror can be expressed as Where Δx represents the relative displacement of the two gratings, n = m; When the position of the one-dimensional grating is fixed, the position of the image is also fixed. When the step mirror is displaced in the horizontal direction of the plane, the phase of the transmitted light will change accordingly, resulting in a change in light intensity. The four-quadrant detector receives the change in light intensity, which in turn causes the electrical interpolation module to output a square wave signal. Similarly, when the step mirror is displaced in the out-of-plane direction, due to the different optical path differences, the four-quadrant detector receives the change in light intensity, and the interpolation circuit outputs a square wave signal. Calculate the displacement using the displacement measurement formula: Where L is the measured displacement, d is the grating period, M is the electrical subdivision multiple, and Q is the number of square wave signal periods output by the electrical subdivision module.

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