An optical tilt sensor and tilt detection method

Abstract

This invention discloses an optical tilt sensor and tilt detection method, belonging to the field of optical sensors. The optical tilt sensor includes a workpiece to be measured, a laser, a polarizing mirror, a resonant modulation module, a condenser, and a photoelectric converter. The laser generates monochromatic incident light; the polarizing mirror filters out s-polarized monochromatic light from the monochromatic incident light while allowing p-polarized monochromatic light to pass through; the resonant modulation module receives the reflected light formed by the p-polarized monochromatic light illuminating the workpiece and modulates the intensity of the reflected light to generate an analog signal of reflected light intensity; the photoelectric converter converts the analog signal of reflected light intensity into a digital signal. This invention solves the technical problems of poor resistance to environmental interference signals, nonlinear signal response, and large component size of current high-precision optical sensors, achieving high-precision, interference-resistant detection of the tilt angle of the workpiece to be measured in a smaller device size.

Description

Technical Field

[0001] This invention belongs to the field of optical sensors, specifically relating to an optical tilt sensor and a tilt detection method. Background Technology

[0002] An optical tilt sensor is a sensor used to measure the angle or position of an object. It utilizes optical principles and sensing technology to achieve non-contact angle measurement. An optical tilt sensor typically consists of a light source, optical elements, a detector, and a signal processing unit. In operation, an optical tilt sensor usually uses a light beam emission and reception method for measurement. The light source generates a beam of light, which is focused or dispersed by optical elements and then illuminates the object being measured. The object's reflection, scattering, or absorption of light causes changes in the characteristics of the light; these changes are received by the detector and converted into electrical signals. By analyzing and processing these electrical signals, the angle or position information of the object can be determined. It is commonly used to measure parameters such as angles, positions, and tilt angles of mechanical parts, and provides accurate data and feedback for automation control, navigation systems, and attitude stabilization.

[0003] In recent years, with the increasing demand for high-precision fabrication at the micro- and nano-scale and for precise control and monitoring of microsystems, the industry's requirements for the measurement accuracy of angular changes have also become increasingly stringent. For example, in the fabrication of micro- and nano-electronic devices, in order to achieve precise fabrication of micro- and nano-sized electronic structures, the rotation increment of the mechanical system typically needs to be controlled within 1 × 10⁻⁶. -4 Within a certain degree, this places strict requirements on the accuracy of the optical tilt sensor; for example, in the operation of a high-precision lithography machine, the drive system needs to control the rotational feed of the mask stage, substrate stage and alignment system to achieve nanometer-level precision control.

[0004] At present, there are still important technical problems in the application of optical tilt sensors, which greatly limit the improvement of measurement accuracy and applicable scenarios: (1) Poor resistance to environmental interference signals: Optical tilt sensors are sensitive to changes and interference in the environment, such as changes in light intensity, dust or pollutants, which may cause interference and errors in the measurement results; (2) Nonlinear signal response: Optical tilt sensors may have nonlinear errors in a large angle range, that is, the relationship between the output signal and the input angle is not completely linear, and compensation and calibration are required; (3) Large size of optical sensor components: Optical sensors usually require a relatively large size, usually in the centimeter range, and in extreme cases, in the meter range, to provide a path or reflection space for incident light, which limits the miniaturization and micronization of optical tilt detection systems. Summary of the Invention

[0005] To address the technical problems of poor resistance to environmental interference signals, nonlinear signal response, and large size of optical sensor components in current high-precision optical sensors, this invention provides an optical tilt sensor. The tilt angle testing method using the optical tilt sensor can achieve high-precision, interference-resistant detection of the tilt angle of the workpiece under test in a smaller device size.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: an optical tilt sensor, comprising a test platform for placing a workpiece to be tested, wherein a laser and a polarizing mirror are sequentially arranged along a coaxial axis on one side above the workpiece, and a resonant modulation module, a condenser, and a photoelectric converter are sequentially arranged along a coaxial axis on the other symmetrical side; the laser is used to generate monochromatic incident light; the polarizing mirror is used to filter out s-polarized monochromatic light in the monochromatic incident light and allow p-polarized monochromatic light to pass through; the resonant modulation module is used to receive the reflected light formed by the p-polarized monochromatic light illuminating the surface of the workpiece and modulate the intensity of the reflected light to generate a simulated signal of reflected light intensity; the photoelectric converter is used to convert the simulated signal of reflected light intensity into a digital signal.

[0007] Furthermore, the wavelength of the monochromatic incident light is 1550 nm, and the power is 0.1–1.0 W / cm². 2 .

[0008] Furthermore, the measurement angle window size of the optical tilt sensor is 1×10⁻⁶. -4 Spend.

[0009] Furthermore, the resonance modulation module is a hemispherical arc structure, and the resonance modulation module includes a first layer, a second layer and a third layer that are sequentially bonded from the inside out. The first layer is used to refract the reflected light to generate a polarization angle; the second layer is used to generate a surface plasmonic resonance wave under the polarization angle generated by the refraction of the reflected light; and the third layer is used to generate a Fano resonance effect that participates in the modulation of the surface plasmonic resonance wave.

[0010] Furthermore, the material of the first layer is optical quartz or optical glass with a refractive index of less than 1.7; the inner diameter of the first layer is 200 μm and the thickness is 5 μm.

[0011] Furthermore, the material of the second layer is any one of gold, silver, molybdenum sulfide, tantalum sulfide, niobium selenide, molybdenum selenide, titanium carbide, and vanadium carbide thin film; the inner diameter of the second layer is 205 μm and the thickness is 5 μm.

[0012] Furthermore, the material of the third layer is a transparent oxide film with a refractive index higher than 1.8; the transparent oxide film is any one of glass, indium oxide, zinc oxide, and cadmium oxide films; the inner diameter of the third layer is 210 μm, the thickness is 10 μm, and the outer diameter is 220 μm.

[0013] Furthermore, it also includes a computer module, which is used to calculate the tilt angle test value of the workpiece under test based on the value of the digital signal and the power of the monochromatic incident light.

[0014] A tilt angle detection method includes the following steps: placing the workpiece to be tested on a test table, activating the optical tilt angle sensor described above, and outputting the tilt angle test value of the workpiece to be tested.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] (1) Strong resistance to environmental interference signals: This invention calculates the value of the digital signal generated by the photoelectric converter and the power of the monochromatic incident light of the laser, and uses the ratio of the two as the basis for calculating the tilt angle of the workpiece under test. Therefore, it can effectively avoid the direct changes in light signal caused by changes in the light intensity of the test environment, dust or pollutants, etc., and reduce interference and errors in the measurement process.

[0017] (2) Linear signal response: Benefiting from the surface plasmonic wave resonance absorption gain and the modulation of the light field intensity by the Fano resonance effect, the measurement angle window size is selected as 1×10. -4 The optical signal within the measurement angular window has a very high degree of linearity, which makes it possible to improve detection accuracy.

[0018] (3) Small size of optical sensor components: All components of the optical tilt sensor can be miniaturized. In particular, the size of the resonant modulation module can be effectively limited to within 1 mm. The overall size of the optical tilt sensor can be further reduced by rationally arranging the optical paths of the two components distributed on the coaxial line with the workpiece to be measured. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the optical tilt sensor device structure of Example 1;

[0020] Figure 2 This is a schematic diagram of the resonant modulation module in Example 1;

[0021] Figure 3 This is a schematic diagram of the tilt angle detection linear response performance of Example 1;

[0022] Among them, 1 is the laser, 2 is the polarizer, 3 is the workpiece to be tested, 4 is the test platform, 5 is the resonant modulation module, 51 is the first layer, 52 is the second layer, 53 is the third layer, 6 is the condenser, 7 is the photoelectric converter, and 8 is the computer module. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Example 1

[0025] The optical tilt sensor in this embodiment is shown in the schematic diagram below. Figure 1 As shown, the device includes a test platform 4 for placing the workpiece 3 to be tested. The workpiece 3 to be tested and the test platform 4 are arranged in parallel and vertically. The workpiece 3 to be tested is the object for which the sensor detects the tilt angle. The test platform 4 is used to place the workpiece to be tested and provides space for measuring the tilt angle of the workpiece 3 to be tested.

[0026] A laser 1 and a polarizer 2 are arranged in sequence along the coaxial axis on one side of the workpiece 3 to be tested, and a resonant modulation module 5, a condenser 6 and a photoelectric converter 7 are arranged in sequence along the coaxial axis on the other side symmetrically.

[0027] Laser 1 is used to generate monochromatic incident light; the wavelength of the monochromatic incident light generated by laser 1 is 1550 nm, and the power of the incident light is 0.5 W / cm². 2 ;

[0028] Polarizing mirror 2 is used to filter the s-polarized monochromatic light in the monochromatic incident light and allow the p-polarized monochromatic light to pass through. Polarizing mirror 2 is a Glan Taylor prism.

[0029] like Figure 2 As shown, the resonance modulation module 5 is used to receive the reflected light formed by the p-polarized monochromatic light illuminating the workpiece 3 under test and to modulate the intensity of the reflected light to generate a simulated signal of the reflected light intensity; the resonance modulation module 5 has a hemispherical arc structure and includes a first layer 51, a second layer 52 and a third layer 53 that are sequentially bonded from the inside to the outside. The first layer 51 is used to refract the reflected light to generate a bias angle and reduce light reflection and scattering on the surface of the resonant absorption module. The inner diameter of the first layer is R0 = 200 μm and the thickness is 5 μm. The material of the first layer is N-BK7 glass with a refractive index of 1.619. The second layer 52 is used to generate a surface plasmonic resonance wave under the bias angle generated by the refraction of the reflected light, so as to achieve accurate resolution of the angle of refraction of the reflected light irradiating the resonant modulation module 5. The inner diameter of the second layer is R1 = 205 μm and the thickness is 5 μm. The material of the second layer is molybdenum selenide film. The third layer 53 is used to generate the Fano resonance effect that participates in the modulation of the surface plasmonic resonance wave, and enhance the detection linearity of the reflected light within the measurement angle window. The inner diameter of the third layer is R2 = 210 μm, the thickness is 10 μm, and the outer diameter is R3 = 220 μm. The material of the third layer is indium oxide film.

[0030] Concentrator 6 is used to converge the simulated signal of reflected light intensity generated by resonant absorption module 5, so that the simulated signal of reflected light intensity is on the same central axis as resonant modulation module 5, concentrator 6, and photoelectric converter 7.

[0031] The photoelectric converter 7 is used to convert the analog signal of reflected light intensity into a digital signal.

[0032] Computer module 8 is used to calculate the tilt angle of the workpiece 3 under test based on the value of the digital signal and the power of the monochromatic incident light.

[0033] The tilt angle detection method in this embodiment includes the following steps:

[0034] (1) Place the workpiece 3 to be tested on the test stage 4, and then adjust the surface of the workpiece 3 to a horizontal state; turn on the laser 1 and set the power of the monochromatic incident light to 0.5W / cm. 2 The measurement angle window size is 1×10 -4 Spend;

[0035] (2) Adjust the angle between the monochromatic incident light of the laser 1 and the surface of the workpiece 1 to be tested, so that under this optical path condition, the angle between the reflected light formed on the surface of the workpiece and the second layer 52 after refraction by the first layer 51 is equal to the deflection angle. In this embodiment, the deflection angle is 61.3851 degrees.

[0036] (3) Change the tilt angle of the surface of the workpiece 3 to be tested by using the test bench 4;

[0037] (4) Activate photoelectric converter 7 to convert the analog signal of reflected light intensity into a digital signal. The value of the digital signal is equal to P. out (W / cm 2 ).

[0038] (5) The computer module 8 will calculate the tilt angle test value θ of the workpiece 3 under test based on the value of the digital signal and the power of the monochromatic incident light, as follows:

[0039] According to the value P of the digital signal from photoelectric converter 7 out The intensity n1 of the reflected light is calculated using the following formula:

[0040] P out =n1hc / λ

[0041] Where c is the speed of light in air (3 × 10⁻⁶). 8 m / s, h is Planck's constant 6.62607015 × 10^ -34 J·s, wavelength of monochromatic incident light λ=1550nm;

[0042] Similarly, the intensity n0 of the incident light can be obtained from the following formula. It should be noted that P here... in It is equal to half the power of monochromatic incident light.

[0043] P in =n0hc / λ

[0044] The intensity attenuation rate η of monochromatic incident light satisfies the following formula:

[0045] η=(n0-n1) / n0

[0046] Based on the above algorithm, the light intensity attenuation rate η of the monochromatic incident light at that tilt angle can be obtained. From this, the tilt angle test value θ of the workpiece under test can be calculated. The relationship between the two is as follows:

[0047] η = -1771.8θ + 0.18591

[0048] The tilt angle test value θ of the workpiece under test is calculated.

[0049] The tilt angle of the surface of the workpiece 3 under test can be changed by using a photoelectric tracking turntable to adjust the tilt angle of the workpiece under test, or by introducing slight vibrations into the test platform to slightly change the tilt angle of the workpiece under test.

[0050] Example 2

[0051] Same as Example 1, except that the power of the monochromatic incident light is 0.1 W / cm. 2 .

[0052] Example 3

[0053] Same as Example 1, except that the power of the monochromatic incident light is 1 W / cm². 2 .

[0054] Comparative Example 1

[0055] Same as Example 1, except that the measurement angle window size is 5×10. -4 Spend.

[0056] Comparative Example 2

[0057] Same as Example 1, except that the measurement angle window size is 1×10. -3 Spend.

[0058] The technical conditions and performance test results of Examples 1-3 and Comparative Examples 1-2 are shown in Table 1. The schematic diagram of the tilt angle detection linear response performance of Example 1 is shown in Table 1. Figure 3 As shown.

[0059] Table 1. Technical conditions and performance test results of the embodiments and comparative examples.

[0060]

[0061] Generally, as the power of monochromatic incident light decreases, the intensity of the direct light decreases due to factors such as changes in ambient light intensity, dust, or contaminants. Therefore, changes in the direct light signal caused by variations in light intensity, dust, or contaminants are unavoidable, leading to interference and errors during the measurement process.

[0062] However, by comparing the data from Examples 1-3, it can be shown that the influence of different monochromatic incident light powers on the light intensity attenuation rate of the monochromatic incident light is very slight. When the power of the monochromatic incident light increases from 0.1 to 1, the light intensity attenuation rate of the monochromatic incident light only increases from 19.51% to 20.36%, indicating that the signal processing method of the present invention can effectively avoid the above-mentioned problems. The change in monochromatic incident light power (from 0.1 to 1 W / cm²) 2 The invention did not cause a significant change in effective accuracy, indicating that it has high anti-interference performance against changes in ambient light intensity during the test environment. Even under conditions of significant changes in ambient light intensity, the effective accuracy of the tilt angle test value can still be maintained at 1×10⁻⁶. -5 Within a certain range. This invention utilizes the power of monochromatic incident light and the digital signal generated by the photoelectric converter for calculation, effectively offsetting the influence of changes in ambient light intensity on the measurement results. This design ensures that changes in ambient light intensity do not interfere with the measurement results and guarantees high measurement accuracy.

[0063] By comparing the data from Example 1 and Comparative Examples 1 and 2, the following conclusions can be drawn: for the linear regression goodness of fit R... 2 Impact: Linear regression fit R in Example 1 2 The value is 0.9956, and the R-value of Comparative Example 1 is... 2 The value is 0.9626, and the R-value of Comparative Example 2 is... 2 The value was 0.9414. It was observed that the linear regression fit decreased with increasing measurement angle window size, indicating a worsening linear relationship between the measured tilt angle value and the actual tilt angle value of the workpiece. The effective accuracy was 1 / 10 of the measurement angle window size. Regarding the effect on effective accuracy: the effective accuracy of Example 1 was 1 × 10⁻⁶. -5 The effective precision of Comparative Example 1 is 5 × 10⁻⁶. -5 The effective precision of Comparative Example 2 is 1×10⁻⁶. -4 It can be observed that the effective accuracy decreases as the measurement angle window size increases. This is because as the measurement angle window size increases, the dispersion of every two adjacent tilt angle test values ​​increases, leading to a decrease in the effective measurement accuracy.

[0064] Therefore, with a fixed power of monochromatic incident light, increasing the measurement angle window size in this invention will adversely affect the linear regression fitting goodness and effective accuracy. The selection of the measurement angle window size should comprehensively consider the balance between measurement requirements and system accuracy. The measurement angle window size in Examples 1-3 is 1×10⁻⁶. -4 The degree is appropriate.

[0065] The linear response performance of tilt detection was tested in the examples and comparative examples. A graph of the light intensity attenuation rate of monochromatic incident light versus the rotational feed rate for the measurement angle window size was plotted. The linear regression fit degree R was calculated through linear fitting. 2 As a basis for judgment, the specific steps are as follows:

[0066] (1) Installation: Use the AOM360D photoelectric tracking turntable as the control device, place it between the workpiece to be tested and the test table, and the three are on the same central axis.

[0067] (2) Optical path setting: Adjust the incident angle of the monochromatic incident light to keep the reflection angle of the reflected light equal to it, observe the value of the digital signal of the photoelectric converter, and make the value of the digital signal reach the maximum value. This is the optimal optical path.

[0068] (3) Calibration: Connect it to the corresponding control system or computer and calibrate the turntable horizontally. The calibration process usually involves comparison and adjustment using a reference sample with a known tilt angle.

[0069] (4) Turntable step size setting: Set the rotation speed of the turntable to 1 arcsec / min, and the minimum angle step size to 1×10. -5 This allows us to obtain the actual values ​​of each tilt angle of the workpiece under test.

[0070] (5) Test parameter settings: Start the optical tilt sensor to begin tilt angle measurement, and set the power of the monochromatic incident light to 0.5 W / cm. 2 The measurement angle window size is 1×10 -4 Degree; sampling frequency set to 50 times / s, measurement time 5 minutes;

[0071] (6) Data processing: Simultaneously record the actual tilt angle value of the workpiece under test and the tilt angle test value output by the computer module, and calculate the linear correlation between the two sets of data to obtain the linear regression fit degree R. 2 .

Claims

1. An optical tilt sensor comprising a test bench (4) in which a workpiece (3) to be measured is placed, characterized in that, A laser (1) and a polarizer (2) are arranged coaxially on one side of the workpiece (3) to be tested, and a resonant modulation module (5), a condenser (6), and a photoelectric converter (7) are arranged coaxially on the other side symmetrically. The laser (1) is used to generate monochromatic incident light. The polarizer (2) is used to filter the s-polarized monochromatic light in the monochromatic incident light and allow the p-polarized monochromatic light to pass through. The resonant modulation module (5) is used to receive the reflected light formed by the p-polarized monochromatic light illuminating the surface of the workpiece (3) to be tested and to modulate the intensity of the reflected light to generate a simulated signal of the reflected light intensity. The photoelectric converter (7) is used to convert the analog signal of reflected light intensity into a digital signal; the resonant modulation module (5) is a hemispherical arc structure, and the resonant modulation module (5) includes a first layer (51), a second layer (52) and a third layer (53) that are sequentially attached from the inside to the outside. The first layer (51) is used to refract the reflected light to generate a bias angle; the second layer (52) is used to generate a surface plasmonic resonance wave under the bias angle generated by the refraction of the reflected light; and the third layer (53) is used to generate a Fano resonance effect that participates in the modulation of the surface plasmonic resonance wave.

2. The optical tilt sensor according to claim 1, characterized in that, The monochromatic incident light has a wavelength of 1550 nm and a power of 0.1-1.0 W / cm 2 .

3. The optical tilt sensor according to claim 1, characterized in that, The optical tilt sensor has a measurement angle window size of 1 x 10 -4 degrees.

4. The optical tilt sensor according to claim 3, characterized in that, The material of the first layer (51) is optical quartz or optical glass with a refractive index of less than 1.7; the inner diameter of the first layer (51) is 200 μm and the thickness is 5 μm.

5. The optical tilt sensor according to claim 1, characterized in that, The material of the second layer (52) is any one of gold, silver, molybdenum sulfide, tantalum sulfide, niobium selenide, molybdenum selenide, titanium carbide, and vanadium carbide thin film; the inner diameter of the second layer (52) is 205 μm and the thickness is 5 μm.

6. The optical tilt sensor according to claim 1, characterized in that, The material of the third layer (53) is a transparent oxide film with a refractive index higher than 1.8; the transparent oxide film is any one of glass, indium oxide, zinc oxide, and cadmium oxide films; the inner diameter of the third layer (53) is 210 μm, the thickness is 10 μm, and the outer diameter is 220 μm.

7. The optical tilt sensor according to claim 1, characterized in that, It also includes a computer module (8), which is used to calculate the tilt angle test value of the workpiece (3) to be tested based on the value of the digital signal and the power of the monochromatic incident light.

8. A tilt angle detection method, characterized in that, Place the workpiece to be tested on the test bench, activate the optical tilt sensor according to any one of claims 1 to 7, and output the tilt angle test value of the workpiece to be tested.

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