Liquid refractive index sensing system and method based on optical waveguide structure and weak measurement

Abstract

The application discloses a liquid refractive index sensing system and method based on an optical waveguide structure and weak measurement. The application comprises an SLD light source, a Gaussian filter, a polarizer I, a polarizer II, an optical waveguide, a quarter-wave plate I, a quarter-wave plate II and a spectrometer. The SLD light source emits laser with a center wavelength of 830 nm, and the laser is pre-selected by the front selection polarizer after passing through the Gaussian filter. The light is emitted after multiple total internal reflections on the surface of the waveguide of the liquid to be measured, the phase of the p and s polarizations of the emitted light is adjusted by the wave plate, the light is post-selected by the post-selection polarizer, the emitted light is received by the spectrometer and the center wavelength is analyzed, and finally the refractive index of the liquid to be measured is calculated according to the center wavelength displacement by the computer. The application also provides a liquid refractive index sensing method based on an optical waveguide structure and weak measurement. The application realizes straight-line common path and multiple reflections through the optical waveguide, and has higher stability and sensitivity than traditional measurement methods.

Description

Technical Field

[0001] This invention relates to the field of high-precision liquid refractive index detection, and more particularly to a liquid refractive index sensing system and method based on optical waveguide structure and weak measurement. Background Technology

[0002] Optical detection methods sensitive to the refractive index of liquids have always been a hot topic in the research of novel refractive index sensors. Liquid refractive index measurement is widely used in many fields such as food, petrochemicals, pharmaceuticals, and chemicals. Especially in the determination of sugar, alcohol, and food additive content, precise measurement of the refractive index of liquid products is often required for characterization. Therefore, high-precision liquid refractive index measurement methods and instrument manufacturing have attracted much attention.

[0003] Traditional optical sensors include colorimetric sensors, fluorescence sensors, chemiluminescence sensors, Raman scattering sensors, and surface plasmon resonance sensors. These sensors offer advantages such as immunity to electromagnetic interference, resistance to acid and alkali corrosion, no need for reference sensors, and miniaturization of the probe structure. However, they suffer from complex manufacturing processes and high costs. While fluorescence and chemiluminescence sensors are inexpensive to manufacture, the former can only detect substances that emit ultraviolet light, limiting its applicability, while the latter requires raw materials to measure electrochemiluminescence, making it unsuitable for applications with high raw material costs. Summary of the Invention

[0004] To overcome the above problems, the present invention provides a liquid refractive index sensing system and method based on optical waveguide structure and weak measurement.

[0005] The first aspect of the present invention provides a liquid refractive index sensing system based on an optical waveguide structure and weak measurement, comprising an SLD light source (1), a Gaussian filter (2), a polarizer I (3), an optical waveguide (5), a quarter-wave plate I (6), a quarter-wave plate II (7), a polarizer II (8), and a spectrometer (9) arranged sequentially along the optical path. The optical waveguide (5) is a planar dielectric optical waveguide, which consists of a substrate, a dielectric film, and a capping layer. The capping layer in the planar dielectric optical waveguide is replaced with the liquid to be tested (4), the refractive index of which is less than that of the dielectric film, so that the light wave is confined to propagate within the dielectric film.

[0006] The SLD light source (1) emits laser light, which passes through a Gaussian filter (2) and then undergoes pre-selection through polarizer I (3). After pre-selection, the laser light reaches the optical waveguide (5) and is reflected multiple times by the test liquid (4) and the surface of the dielectric film before being emitted. The emitted laser light undergoes phase adjustment of p and s polarization through quarter-wave plate I (6) and quarter-wave plate II (7). After phase adjustment, the laser light undergoes post-selection through polarizer II (8). The post-selected laser light is incident on the receiving end of the spectrometer (9), and the spectrometer (9) performs center wavelength analysis to obtain the center wavelength displacement. The spectrometer (9) is electrically connected to a computer, and the computer calculates the refractive index of the test liquid (4) based on the center wavelength displacement. The second aspect of the present invention provides a liquid refractive index detection method based on an optical waveguide structure and a weak measurement liquid refractive index sensing system, wherein the computer calculates the refractive index of the test liquid (4) based on the center wavelength displacement, including the following steps:

[0007] (1) Let the length of the optical waveguide be L, the thickness be h, and the incident angle be θ. The number of reflections of the laser at the interface between the liquid and the dielectric film after pre-selection can be expressed as:

[0008]

[0009] In the formula, [] indicates rounding down. The total phase difference generated by reflection is Δ=qΔ0, where Δ0 is the phase difference of a single reflection, which is related to the incident angle θ, the refractive index n of the liquid, and the refractive index n0 of the optical waveguide. The incident angle is related to the tilt angle ε of the optical waveguide. Using geometric relationships, we can obtain the following from the law of refraction:

[0010]

[0011] The phase difference can be obtained from the Fresnel formula:

[0012]

[0013] (2) According to the weak measurement theory, the shift of the laser spectrum center can be expressed as:

[0014]

[0015] In the formula, k is the interaction intensity, Δλ is the laser spectral width, λ0 is the center wavelength of the laser, and A w For the weak value observed, Δ is the total phase difference caused by reflection, δ is the phase difference constant caused by the waveplate, and γ is a constant related to the polarizer angle.

[0016] (3) Combining the formulas from steps 1 and 2, the relationship between the center wavelength shift and the optical waveguide is obtained as follows:

[0017]

[0018] (4) The center wavelength displacement is measured by a spectrometer, and the total phase difference generated by reflection is obtained by reverse calculation. Based on the optical waveguide size, the refractive index of the liquid to be tested is obtained using formulas (1)-(5).

[0019] The principle of this invention is as follows: This invention designs a linear common-path weak measurement system. A polarization phase difference is introduced by the reflection of light at the waveguide interface. Weak value amplification is used for phase difference detection, and the liquid refractive index can be deduced from the measured center wavelength shift. According to weak measurement theory, when the measurement system has nearly orthogonal forward and backward selection states, the movement of a Gaussian pointer is used to obtain observations exceeding the range of eigenvalues, thus achieving weak value amplification. The weak value is defined as:

[0020]

[0021] Among them, |ψ i > and |ψ f > represents the before and after selected states of the system, and A is the observable operator for the system evolution. For optical systems, before and after selected states can be constructed using two nearly orthogonal polarizers, enabling the amplification of the measured object, such as the phase difference in polarization directions. Based on this, a weak measurement system with a straight common path can be designed. The phase difference between the two orthogonal polarization components introduced by the reflection of light at the liquid-waveguide interface is related to the refractive index of the liquid. The change in phase difference can be measured by shifting the center wavelength of the emitted spectrum, thus achieving real-time detection of the liquid's refractive index.

[0022] The beneficial effects of this invention are:

[0023] 1. Due to the sensitive response of weak measurement to minute polarization changes and the superposition of multiple phase differences, the new liquid refractive index detection method realized by this invention has high sensitivity.

[0024] 2. Due to the straight-line common path setting, the additional phase difference introduced by the environment after the polarized beam is separated is avoided. The optical path of the polarized light in both directions is the same, and the phase difference is only introduced by reflection. The measurement error is small and the system is stable.

[0025] 3. The linear system design facilitates integration, making the entire refractive index detection system easier to integrate. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of the present invention.

[0027] Figure 2 This is a schematic diagram of the working optical path of the optical waveguide of the present invention.

[0028] Explanation of reference numerals in the attached diagram: 1. SLD light source; 2. Gaussian filter; 3. Polarizer I; 4. Test liquid; 5. Optical waveguide; 6. Quarter-wave plate I; 7. Quarter-wave plate II; 8. Polarizer II; 9. Spectrometer. Detailed Implementation

[0029] The technical solution of this invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0030] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are used only for the convenience of describing the invention and simplifying the description. They 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 limiting the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0031] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" 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 can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0032] Example 1

[0033] See attached document Figure 1 Based on the optical waveguide structure and weak measurement liquid refractive index sensing system, according to the weak measurement principle, in a weak measurement system with Gaussian spectrum as pointer state, a suitable front and rear polarization states are selected, and the output pointer state contains weak values ​​with amplification coefficient to achieve weak value amplification. The measured value is read through the output pointer state.

[0034] A liquid refractive index sensing system based on optical waveguide structure and weak measurement includes an SLD light source 1, a Gaussian filter 2, a polarizer I 3, an optical waveguide 5, a quarter-wave plate I 6, a quarter-wave plate II 7, a polarizer II 8, and a spectrometer 9 arranged sequentially along the optical path. The optical waveguide 5 is a planar dielectric optical waveguide, which consists of a substrate, a dielectric film, and a capping layer. The capping layer in the planar dielectric optical waveguide is replaced with the liquid to be tested 4. The refractive index of the liquid to be tested 4 is less than that of the dielectric film, so that the light wave is confined to propagate within the dielectric film.

[0035] The SLD light source 1 emits broadband light with a center wavelength of 830nm and a bandwidth ≥20nm. After passing through Gaussian filter 2, the laser undergoes pre-selection via polarizer I 3. After pre-selection, the laser reaches optical waveguide 5 and is reflected multiple times by the test liquid 4 and the surface of the dielectric film before exiting. The exited laser undergoes phase adjustment of p and s polarization via quarter-wave plate I 6 and quarter-wave plate II 7. The phase-adjusted laser undergoes post-selection via polarizer II 8. The post-selected laser is then incident on the receiving end of spectrometer 9, where spectrometer 9 performs center wavelength analysis to obtain the center wavelength shift. Spectrometer 9 is electrically connected to a computer, which calculates the refractive index of the test liquid 4 based on the center wavelength shift.

[0036] In this embodiment, the planar dielectric waveguide typically consists of a substrate, a dielectric film, and a capping layer, using the principle of total internal reflection to confine light waves within the dielectric film. This invention uses the test liquid instead of the capping layer to measure the refractive index of the test liquid; therefore, the refractive index of the test liquid must satisfy the condition n < n0.

[0037] When the lateral dimension of an optical waveguide is much larger than the wavelength of light, the diffraction phenomenon caused by the wave nature of light can generally be neglected, and the propagation of light within it can be handled using the laws of geometric optics.

[0038] Example 2

[0039] The liquid refractive index detection method based on optical waveguide structure and weak measurement liquid refractive index sensing system, that is, the computer calculates the refractive index of the liquid to be tested 4 based on the center wavelength displacement, includes the following steps:

[0040] (1) Due to the multiple reflections of light at the surface of the test liquid-waveguide, each reflection introduces a phase difference. Assuming the length of the optical waveguide is L, the thickness is h, and the incident angle is θ, the number of reflections of the pre-selected laser at the interface of the test liquid-dielectric film can be expressed as:

[0041]

[0042] In the formula, [] indicates rounding down. The total phase difference generated by reflection is Δ=qΔ0, where Δ0 is the phase difference of a single reflection, which is related to the incident angle θ, the refractive index n of the liquid, and the refractive index n0 of the optical waveguide. The incident angle is related to the tilt angle ε of the optical waveguide. Using geometric relationships, we can obtain the following from the law of refraction:

[0043]

[0044] The phase difference can be obtained from the Fresnel formula:

[0045]

[0046] (2) According to the weak measurement theory, the shift of the laser spectrum center can be expressed as:

[0047]

[0048] In the formula, k is the interaction intensity, Δλ is the laser spectral width, λ0 is the center wavelength of the laser, and A w For the weak value observed, Δ is the total phase difference caused by reflection, δ is the phase difference constant caused by the waveplate, and γ is a constant related to the polarizer angle.

[0049] (3) Combining the formulas from steps 1 and 2, the relationship between the center wavelength shift and the optical waveguide is obtained as follows:

[0050]

[0051] (4) The center wavelength displacement is measured by a spectrometer, and the total phase difference generated by reflection is obtained by reverse calculation. Based on the optical waveguide size, the refractive index of the liquid to be tested is obtained using formulas (1)-(5).

[0052] This invention constructs a linear co-path weak measurement optical path system. Quantum weak measurement is a high-precision signal detection technology that has emerged in recent years, attracting widespread attention and application due to its unique advantages in weak value amplification. Compared to traditional optical sensors, weak measurement sensors offer advantages such as high sensitivity, wide applicability, and no need for raw material consumption. Compared to dual-path single-transmission weak measurement systems, the linear co-path configuration avoids additional phase differences introduced by environmental influences after polarization beam separation, resulting in smaller measurement errors. Furthermore, the optical waveguide configuration amplifies the phase difference of the polarized light by multiple reflections at the liquid-waveguide interface, leading to higher measurement accuracy. Based on the small size and mature manufacturing process of the optical waveguide, the entire weak measurement optical path system can be integrated, facilitating the measurement of liquid refractive index in practical production and daily life.

[0053] The embodiments described in this specification are merely examples of implementations of the inventive concept. The scope of protection of this invention should not be considered as limited to the specific forms stated in the embodiments. The scope of protection of this invention also extends to equivalent technical means that can be conceived by those skilled in the art based on the inventive concept.

Claims

1. A method for detecting the refractive index of a liquid based on an optical waveguide structure and a weak measurement liquid refractive index sensing system, characterized in that: The liquid refractive index sensing system includes an SLD light source (1), a Gaussian filter (2), a polarizer I (3), an optical waveguide (5), a quarter-wave plate I (6), a quarter-wave plate II (7), a polarizer II (8), and a spectrometer (9) arranged sequentially along the optical path. The optical waveguide (5) is a planar dielectric optical waveguide, which consists of a substrate, a dielectric film, and a capping layer. The capping layer in the planar dielectric optical waveguide is replaced with the liquid to be tested (4). The refractive index of the liquid to be tested (4) is less than that of the dielectric film, so that the light wave is confined to propagate within the dielectric film. The SLD light source (1) emits laser light, which passes through a Gaussian filter (2) and then through polarizer I (3) for pre-selection. After pre-selection, the laser light reaches the optical waveguide (5) and is reflected multiple times by the test liquid (4) and the surface of the dielectric film before being emitted. The emitted laser light passes through quarter-wave plate I (6) and quarter-wave plate II (7) for phase adjustment of p and s polarization. After phase adjustment, the laser light passes through polarizer II (8) for post-selection. The post-selected laser light is incident on the receiving end of the spectrometer (9), and the spectrometer (9) performs center wavelength analysis to obtain the center wavelength shift. The spectrometer (9) is electrically connected to a computer, and the computer calculates the refractive index of the test liquid (4) based on the center wavelength shift. The liquid refractive index detection method, in which the computer calculates the refractive index of the liquid to be tested (4) based on the center wavelength displacement, includes the following steps: (1) Let the length of the optical waveguide be... Thickness is The angle of incidence is The number of reflections of the laser at the interface between the test liquid and the dielectric film after pre-selection can be expressed as: In the formula, This indicates that rounding down gives the total phase difference caused by reflection. ,in The phase difference of a single reflection is related to the angle of incidence. Liquid refractive index and optical waveguide refractive index The incident angle is related to the waveguide tilt angle. Regarding this, using geometric relationships and the law of refraction, we obtain: The phase difference can be obtained from the Fresnel formula: (2) According to the weak measurement theory, the shift of the laser spectrum center can be expressed as: In the formula, For the interaction strength, For laser spectral width, The center wavelength of the laser. For the observed weak value, The total phase difference caused by reflection. The phase difference constant generated by the waveplate It is a constant related to the polarizer angle; (3) Combining the formulas from steps 1 and 2, the relationship between the center wavelength shift and the optical waveguide is obtained as follows: (4) The center wavelength displacement is measured by a spectrometer, and the total phase difference generated by reflection is obtained by reverse calculation. Based on the optical waveguide size, the refractive index of the liquid to be tested is obtained using formulas (1)-(5).

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