Optical angle sensor and angle measurement method thereof

Abstract

The application discloses an optical angle sensor and an angle measuring method thereof, and belongs to the technical field of micro-nano optical sensing and precision measurement. The optical angle sensor is a full dielectric reflection type guided mode resonance structure, and a substrate, a waveguide layer and a one-dimensional subwavelength diffraction grating layer are sequentially stacked from bottom to top. When a TE polarized linearly polarized light matched with a target working wavelength is vertically incident, a single degenerate state guided mode resonance reflection peak is generated at the target working wavelength. When oblique incidence occurs, the resonance degenerate state is removed, and the two guided mode resonance reflection peaks are split, and the double-peak central wavelength spacing monotonously increases with the increase of the incident angle. The application inverses the incident angle by measuring the double-peak spacing, avoids the system error caused by absolute wavelength measurement and the dependence on a high-resolution spectrometer, has an extremely simple structure, is easy to integrate, has strong anti-electromagnetic interference capability, and is suitable for angle measurement in the fields of precision manufacturing, aerospace, laser processing and the like.

Description

Technical Field

[0001] This invention relates to the field of optical sensing and precision angle measurement technology, and in particular to an optical angle sensor based on guided mode resonance effect and its angle measurement method. Background Technology

[0002] Angle measurement is a key technology in precision optics, instrumentation, aerospace, and other fields. Traditional angle sensors, such as photoelectric encoders and gyroscopes, while highly accurate, suffer from problems such as complex structure, large size, susceptibility to electromagnetic interference, or high cost. Optical angle sensors have attracted attention due to their advantages such as non-contact operation and high sensitivity, such as sensors based on interference and diffraction principles. However, their systems are usually complex and require extremely high stability of the optical path.

[0003] In recent years, metasurfaces, as artificial two-dimensional materials composed of subwavelength structural units, have provided new avenues for the miniaturization and integration of optical devices. Among them, metasurface filters based on the guided-mode resonance principle can achieve extremely narrow-band filtering characteristics. Their spectra are extremely sensitive to structural parameters and the external environment, and their application in sensing fields has been explored. In existing technologies, GMR sensors mostly utilize the wavelength drift of a single resonance peak with the analyte for measurement. However, wavelength drift measurement requires a precise spectrometer, resulting in a complex and costly system, and is also susceptible to factors such as light source fluctuations and temperature drift. Summary of the Invention

[0004] In view of the defects and shortcomings of the existing technology, the present invention aims to provide an optical angle sensor and its angle measurement method based on the guided mode resonance degeneracy unwinding effect, and solve the core problems of existing angle measurement schemes such as complex structure, poor anti-interference ability, large system error and difficulty in integration.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] On one hand, the present invention provides an optical angle sensor, which, from bottom to top, comprises a substrate, a waveguide layer and a subwavelength diffraction grating layer; The substrate, located at the bottom layer, serves to provide mechanical support and an optical base for the device; The waveguide layer, located between the subwavelength diffraction grating layer and the substrate, is used to support and constrain guided mode transmission. The subwavelength diffraction grating layer is composed of one-dimensional periodically arranged parallel all-dielectric grating strips. The grating period p of the subwavelength diffraction grating layer is smaller than the target operating wavelength, forming a subwavelength periodic structure. The grating period p is the distance between the corresponding edges of two adjacent grating strips. A complete grating period includes one grating strip width w and the spacing s between adjacent grating strips, satisfying p = w + s. The refractive index of the grating strips is higher than the refractive index of the air medium in the sensor's operating environment. When TE-polarized linearly polarized light, matching the target operating wavelength, is incident perpendicularly on the optical angle sensor, the propagation constants of the +1st and -1st order diffracted waves of the TE polarization are symmetrical, and the excited guided mode resonance states are degenerate, generating a single degenerate guided mode resonance reflection peak at the target operating wavelength. When the TE-polarized linearly polarized light is incident on the optical angle sensor at a non-zero angle, two guided mode resonance reflection peaks formed by degenerate state splitting are generated near the target operating wavelength, and the center wavelength spacing between the two guided mode resonance reflection peaks monotonically increases with the increase of the incident angle.

[0007] Furthermore, the substrate described in this invention has high optical transmittance within the target operating wavelength range.

[0008] Furthermore, the waveguide layer of the present invention has a refractive index higher than the average equivalent refractive index of the subwavelength diffraction grating layer, and is also higher than the refractive index of the substrate, forming an all-dielectric planar waveguide confinement structure.

[0009] Furthermore, the target operating wavelength is 1064nm, which is commonly used in near-infrared communication, but it can also be adapted to the visible light band or other near-infrared bands according to application requirements.

[0010] On the other hand, an angle measurement method based on the above-mentioned optical angle sensor is provided, including the following steps: S1, Calibration Dataset Establishment: Under standard atmospheric pressure air environment, using TE polarized linear light that matches the target working wavelength as the incident light source, the reflection spectrum of the optical angle sensor under different standard incident angles in the range of 0°~1° is collected, the center wavelength spacing of the two guided mode resonance reflection peaks corresponding to different standard incident angles is extracted, and a calibration dataset of different standard incident angles and the center wavelength spacing of the corresponding two guided mode resonance reflection peaks is established. S2, Zero-position calibration: TE-polarized linearly polarized light is incident perpendicularly onto the grating surface of the optical angle sensor, and the reflection spectrum is collected. If only a single degenerate guided-mode resonance reflection peak exists in the reflection spectrum, the current incident angle is calibrated to zero. =0°; If there are two guided-mode resonance reflection peaks in the reflection spectrum, fine-tune the incident angle of the incident light path until the reflection spectrum shows a single degenerate guided-mode resonance reflection peak, and complete the zero-position calibration; S3, Measurement of the angle to be measured: The incident light to be measured is adjusted to the TE polarization state and incident on the grating surface of the optical angle sensor that has completed zero-position calibration, and the reflection spectrum of the reflected beam of the sensor is collected; S4. The angle is inverted based on the number of guided-mode resonance reflection peaks in the reflection spectrum: if only a single degenerate guided-mode resonance reflection peak exists in the reflection spectrum, then the incident angle of the incident light to be measured is determined. =0°; If two guided-mode resonance reflection peaks exist in the reflection spectrum, extract the center wavelengths of the two guided-mode resonance reflection peaks from the reflection spectrum and calculate the center wavelength spacing between the two guided-mode resonance reflection peaks. The incident angle of the incident light to be measured is obtained by inversion based on the calibration dataset established in step S1.

[0011] The above technical solution has the following beneficial effects: This invention provides an optical angle sensor, which is an all-dielectric reflective guided-mode resonant structure. From bottom to top, a substrate, a waveguide layer, and a one-dimensional subwavelength diffraction grating layer are stacked sequentially. This invention features a simple structure, high sensitivity, and eliminates the need to monitor absolute wavelength changes. When TE-polarized linearly polarized light matching the target operating wavelength is incident perpendicularly on the optical angle sensor, a single degenerate guided-mode resonant reflection peak is generated at the target operating wavelength. When TE-polarized linearly polarized light matching the target operating wavelength is incident on the optical angle sensor at a non-zero angle, the resonant degeneracy is released, splitting into two guided-mode resonant reflection peaks, and the wavelength spacing between the center wavelengths of the two peaks monotonically increases with the incident angle. This invention utilizes the splitting effect of the guided mode resonance peak. Under oblique incidence conditions, the reflection spectrum exhibits a double-peak splitting phenomenon, and the wavelength spacing between the two reflection resonance peaks has a definite and sensitive functional relationship with the incident angle. By directly measuring the splitting spacing of the two peaks, the incident angle can be accurately measured. This avoids the errors caused by the wavelength drift of the light source in the single-peak drift method, avoids the systematic errors caused by measuring the absolute wavelength, and avoids the dependence on high-resolution spectrometers. The structure is extremely simple, easy to integrate, and has strong anti-electromagnetic interference capabilities, making it suitable for angle measurement in fields such as precision manufacturing, aerospace, and laser processing. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a schematic diagram of the structure of an optical angle sensor in one embodiment; Figure 2 A diagram showing the parameter settings for the optical angle sensor; Figure 3 Here is a simulated reflection spectrum of an optical angle sensor according to an embodiment, wherein: Figure 3 (a) is the angle of incidence. Reflectance spectrum at 0°; Figure 3 (b) is the angle of incidence. Reflectance spectrum at 0.1°; Figure 3 (c) is the angle of incidence. Reflectance spectrum at 0.2°; Figure 3 (d) is the angle of incidence. The reflectance spectrum curve at 0.3°. Detailed Implementation

[0014] The technical solution of the present invention will now be clearly and completely described through specific embodiments. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0015] Reference Figure 1 and Figure 2 One embodiment provides an optical angle sensor, which is an all-dielectric reflective structure based on the guided mode resonance effect, comprising a substrate 1, a waveguide layer 2 and a subwavelength diffraction grating layer 3 from bottom to top.

[0016] The substrate 1 is located at the bottom layer of the device, providing stable mechanical support and optical substrate for the device; The waveguide layer 2 is located between the subwavelength diffraction grating layer 3 and the substrate 1, and is used to support and constrain the transmission of the TE polarization guided mode within the waveguide layer.

[0017] The subwavelength diffraction grating layer 3 is composed of one-dimensional periodically parallel all-dielectric grating strips 3-1. The grating period p of the subwavelength diffraction grating layer 3 is less than the target operating wavelength, and it is a subwavelength periodic structure. The grating period p is the distance between the corresponding edges of two adjacent grating strips 3-1. A complete grating period includes the width w of one grating strip 3-1 and the spacing s between adjacent grating strips 3-1, satisfying p=w+s. The refractive index of the grating strips 3-1 is higher than the refractive index of the air medium in the sensor's working environment.

[0018] When TE-polarized linearly polarized light matching the target operating wavelength is incident perpendicularly on the optical angle sensor, the propagation constants of the +1st and -1st order diffracted waves of the TE polarization are symmetrical, and the excited guided mode resonance state is degenerate, generating a single high-reflectivity degenerate guided mode resonance reflection peak at the target operating wavelength. When the TE-polarized linearly polarized light is incident on the optical angle sensor at a non-zero angle, the propagation constants of the ±1st order diffracted waves are asymmetrical, the guided mode resonance degeneracy is released, and the original single resonance peak is split into two independent guided mode resonance reflection peaks, and the center wavelength spacing between the two guided mode resonance reflection peaks increases monotonically with the increase of the incident angle.

[0019] In the above embodiments, the refractive index of the waveguide layer 2 is higher than the average equivalent refractive index of the subwavelength diffraction grating layer 3, and is also higher than the refractive index of the substrate 1, forming an all-dielectric planar waveguide confinement structure.

[0020] Furthermore, by optimizing parameters, including the grating period p, grating strip width w, grating strip height g, and waveguide layer thickness d, where parameter optimization satisfies the following conditions, the effects of achieving stable single-peak degeneracy in vertical incidence, double-peak splitting in oblique incidence degeneracy, and monotonically increasing spacing are achieved: Phase matching condition: The grating period p satisfies the guided mode resonance phase matching equation, so that the ±1st order diffracted waves can be effectively coupled to excite the guided modes in the waveguide layer; Conditions for achieving degeneracy: The waveguide layer thickness d and the grating strip height g are optimized in synergy so that when the incident light is incident perpendicularly, the resonance peaks of the guided modes excited by the ±1st order diffraction waves of TE polarization completely coincide, thus achieving resonance state degeneracy. When the incident light is incident at an angle, the degeneracy is removed. Monotonic variation optimization condition: The grating fill factor f=w / p is in the range of 0.25~0.35, so that the distance between the two guided mode resonant reflection peaks increases monotonically with the increase of the incident angle within the range of 0°~1° incident angle.

[0021] In another embodiment, an angle measurement method based on the above-described optical angle sensor is also provided, comprising the following steps: S1, Calibration Dataset Establishment: Under standard atmospheric pressure air environment (standard atmospheric pressure, 25℃ room temperature air environment), using TE polarized linearly polarized light that matches the target working wavelength as the incident light source, the reflection spectra of the optical angle sensor at different standard incident angles within the range of 0°~1° and with a step size ≤0.05° are collected. The center wavelength spacing between the two guided mode resonance reflection peaks corresponding to different standard incident angles is extracted, and a calibration dataset of different standard incident angles and the center wavelength spacing between the corresponding two guided mode resonance reflection peaks is established. S2, Zero-position calibration: TE-polarized linearly polarized light is incident perpendicularly onto the grating surface of the optical angle sensor, and the reflection spectrum is collected. If only a single degenerate guided-mode resonance reflection peak exists in the reflection spectrum, the current incident angle is calibrated to zero. =0°; If there are two guided-mode resonance reflection peaks in the reflection spectrum, fine-tune the incident angle of the incident light path until the reflection spectrum shows a single degenerate guided-mode resonance reflection peak, and complete the zero-position calibration; S3, Measurement of the angle to be measured: The incident light to be measured is adjusted to the TE polarization state by a polarizer and incident on the grating surface of the optical angle sensor that has completed zero-position calibration. The reflection spectrum of the reflected beam from the sensor is collected by a spectrometer. S4. The angle is inverted based on the number of guided-mode resonance reflection peaks in the reflection spectrum: if only a single degenerate guided-mode resonance reflection peak exists in the reflection spectrum, then the incident angle of the incident light to be measured is determined. =0°; If two guided-mode resonance reflection peaks exist in the reflection spectrum, extract the center wavelengths of the two guided-mode resonance reflection peaks from the reflection spectrum and calculate the center wavelength spacing between the two guided-mode resonance reflection peaks. The incident angle of the incident light to be measured is obtained by inversion based on the calibration dataset established in step S1.

[0022] In one embodiment, based on COMSOL simulation and optimization calculations, when the target operating wavelength is 1064nm, the parameters of the optical angle sensor are set as follows: In one embodiment, the substrate 1 is made of quartz glass material with a refractive index of [missing information] at a target operating wavelength of 1064 nm. It exhibits high optical transmittance. The waveguide layer 2 is made of the same high refractive index dielectric material as the grating strip, with a refractive index of [missing information] at a wavelength of 1064 nm. The waveguide layer thickness d = 150 nm. The refractive index of waveguide layer 2 is higher than that of substrate 1 and the average equivalent refractive index of subwavelength diffraction grating layer 3, forming an all-dielectric planar waveguide confinement structure to support and confine the propagation of TE polarization guided modes within the waveguide layer. The material of grating strip 3-1 is the same as that of waveguide layer 2, and at a wavelength of 1064 nm, the refractive index of grating strip 3-1 is... The refractive index is 1.837, higher than the air medium refractive index (n0=1) of the sensor's operating environment; the grating strip width w=200nm, the grating strip height g=55nm, and the grating period p=710.4nm. The grating period p is less than the target operating wavelength of 1064nm, indicating a subwavelength periodic structure. The grating period p is the distance between the left edges of two adjacent grating strips 3-1. A complete grating period includes one grating strip width w=200nm and the spacing width s=510.4nm between adjacent grating strips, satisfying p=w+s. The length of grating strip 3-1 extends perpendicular to the grating period, with a length of 200μm, ensuring the incident beam completely covers the grating area. In the above embodiment, the target operating wavelength is 1064nm. Through rigorous coupled-wave analysis and optimization calculations using COMSOL Multiphysics finite element simulation software, the feasibility and sensitivity of the optical angle sensor in this embodiment are determined by… Figure 3 The simulation data shown fully verifies that Figure 3 This is a simulated reflection spectrum of the optical angle sensor from the above embodiment. (Refer to...) Figure 3 It can be seen that the optical angle sensor in the above embodiment can stably achieve the following effects: When TE-polarized linearly polarized light is incident perpendicularly (incident angle) When the wavelength is 0°, the reflection spectrum exhibits a single sharp degenerate guided-mode resonance reflection peak at the target wavelength of 1064 nm, with a peak reflectance close to 100%. Its full width at half maximum (FWHM) is extremely narrow, less than 0.05 nm. Figure 3 As shown in (a); When TE polarized linearly polarized light is at an incident angle When incident at a tiny angle of 0.1°, the original single resonance peak splits into two distinct guided-mode resonance reflection peaks, with a measurable gap between the center wavelengths of the two peaks. ,like Figure 3 As shown in (b); When the incident angle increases to =0.2°、 When θ = 0.3°, it can be observed that as θ increases, the distance between the two peaks increases sequentially. and ,and That is, the center wavelength spacing between the two guided-mode resonant reflection peaks increases monotonically with the increase of the incident angle, such as Figure 3 (c) Figure 3 As shown in (d).

[0023] based on Figure 3The simulation data shown indicates that the optical angle sensor achieves an angular sensitivity of approximately 24.7 nm / °. Combined with commercially available miniature spectrometers (with wavelength resolution better than 0.01 nm), the theoretical angular resolution of this optical angle sensor can reach the order of 0.0004°. In a practical system, achieving a measurement accuracy of 0.001° is feasible through signal averaging and algorithm optimization.

[0024] In summary, this invention provides an optical angle sensor and angle measurement method that is simple in structure, highly sensitive, and does not require monitoring of absolute wavelength changes. The core of this invention lies in utilizing the physical phenomenon that, upon oblique incidence, the degeneracy of the TE and TM modes, or symmetric and asymmetric modes, is decoupled from the reflection spectrum of a guided-mode resonant metasurface. This causes the single peak at perpendicular incidence to split into two peaks, and the wavelength spacing between the two peaks exhibits a definite and sensitive functional relationship with the incident angle. By directly measuring the splitting distance between the two peaks, the incident angle can be inferred, avoiding systematic errors caused by measuring absolute wavelength and dependence on high-resolution spectrometers.

[0025] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

[0026] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An optical angle sensor, characterized in that, From bottom to top, it includes a substrate, a waveguide layer, and a subwavelength diffraction grating layer; The substrate, located at the bottom layer, serves to provide mechanical support and an optical base for the device; The waveguide layer, located between the subwavelength diffraction grating layer and the substrate, is used to support and constrain guided mode transmission. The subwavelength diffraction grating layer is composed of one-dimensional periodically arranged parallel all-dielectric grating strips. The grating period p of the subwavelength diffraction grating layer is smaller than the target operating wavelength, forming a subwavelength periodic structure. The grating period p is the distance between the corresponding edges of two adjacent grating strips. A complete grating period includes one grating strip width w and the spacing s between adjacent grating strips, satisfying p = w + s. The refractive index of the grating strips is higher than the refractive index of the air medium in the sensor's operating environment. When TE-polarized linearly polarized light matching the target operating wavelength is incident perpendicularly on the optical angle sensor, a single degenerate guided mode resonance reflection peak is generated at the target operating wavelength; when the TE-polarized linearly polarized light is incident on the optical angle sensor at a non-zero angle, two guided mode resonance reflection peaks formed by degenerate splitting are generated near the target operating wavelength, and the center wavelength spacing of the two guided mode resonance reflection peaks increases monotonically with the increase of the incident angle.

2. The optical angle sensor according to claim 1, characterized in that, The refractive index of the waveguide layer is higher than the average equivalent refractive index of the subwavelength diffraction grating layer, and also higher than the refractive index of the substrate, forming an all-dielectric planar waveguide confinement structure.

3. The optical angle sensor according to claim 1 or 2, characterized in that, By optimizing parameters, including grating period p, grating strip width w, grating strip height g, and waveguide layer thickness d, the following conditions are met to stably achieve the effects of a single peak in the vertically incident degenerate state, the elimination of double-peak splitting in the obliquely incident degenerate state, and a monotonically increasing spacing: Phase matching condition: The grating period p satisfies the guided mode resonance phase matching equation, so that the ±1st order diffracted waves can be effectively coupled to excite the guided modes in the waveguide layer; Conditions for achieving degeneracy: The waveguide layer thickness d and the grating strip height g are optimized in synergy so that when the incident light is incident perpendicularly, the resonance peaks of the guided modes excited by the ±1st order diffraction waves of TE polarization completely coincide, thus achieving resonance state degeneracy. When the incident light is incident at an angle, the degeneracy is removed. Monotonic variation optimization condition: The grating fill factor f=w / p is in the range of 0.25~0.35, so that the distance between the two guided mode resonant reflection peaks increases monotonically with the increase of the incident angle within the range of 0°~1° incident angle.

4. The optical angle sensor according to claim 1, characterized in that, The target operating wavelength is 1064nm, and the refractive index of the waveguide layer is... substrate refractive index The refractive index of the grating strips 1.

837.

5. The optical angle sensor according to claim 3, characterized in that, The grating strip width w = 200 nm, the grating strip height g = 55 nm, the grating period p = 710.4 nm, and the waveguide layer thickness d = 150 nm; the length of the grating strip extends in a direction perpendicular to the grating period, and the length dimension is greater than 100 μm.

6. An angle measurement method based on the optical angle sensor according to claim 1, 2, 4, or 5, characterized in that, Includes the following steps: S1, Calibration Dataset Establishment: Under standard atmospheric pressure air environment, using TE polarized linear light that matches the target working wavelength as the incident light source, the reflection spectrum of the optical angle sensor under different standard incident angles in the range of 0°~1° is collected, the center wavelength spacing of the two guided mode resonance reflection peaks corresponding to different standard incident angles is extracted, and a calibration dataset of different standard incident angles and the center wavelength spacing of the corresponding two guided mode resonance reflection peaks is established. S2, Zero-position calibration: TE-polarized linearly polarized light is incident perpendicularly onto the grating surface of the optical angle sensor, and the reflection spectrum is collected. If only a single degenerate guided-mode resonance reflection peak exists in the reflection spectrum, the current incident angle is calibrated to zero. =0°; If there are two guided-mode resonance reflection peaks in the reflection spectrum, fine-tune the incident angle of the incident light path until the reflection spectrum shows a single degenerate guided-mode resonance reflection peak, and complete the zero-position calibration; S3, Measurement of the angle to be measured: The incident light to be measured is adjusted to the TE polarization state and incident on the grating surface of the optical angle sensor that has completed zero-position calibration, and the reflection spectrum of the reflected beam of the sensor is collected; S4. The angle is inverted based on the number of guided-mode resonance reflection peaks in the reflection spectrum: if only a single degenerate guided-mode resonance reflection peak exists in the reflection spectrum, then the incident angle of the incident light to be measured is determined. =0°; If two guided-mode resonance reflection peaks exist in the reflection spectrum, extract the center wavelengths of the two guided-mode resonance reflection peaks from the reflection spectrum and calculate the center wavelength spacing between the two guided-mode resonance reflection peaks. The incident angle of the incident light to be measured is obtained by inversion based on the calibration dataset established in step S1.

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