A real-time measurement device and method of microstructure dispersion curve

Abstract

The application discloses a kind of real-time measurement device and method of microstructure dispersion curve, and determination device includes broadband light source, exit optical fiber, collimating lens, polaroid, front column lens, prism, rear column lens, slit, imaging lens, reflection grating, CMOS image sensor.Broadband light source is emitted from optical fiber, collimated by collimating lens, polaroid selects polarization, focuses after front column lens, converges to prism surface at multiple angles;To-be-measured microstructure sample is placed on the surface above prism;Different wavelength light is reflected after surface wave is excited at different angles, and collimated by rear column lens, focuses after slit, and dispersed by imaging lens and reflection grating, and the light signal reflected from reflection grating is again passed through imaging lens, and collected by CMOS image sensor.According to the geometric relationship of optical path and known light source wavelength, the wavelength and excitation angle corresponding to the calibration pixel position are calculated, i.e.the dispersion curve of microstructure.The application device is stable and easy to measure, and sample replacement is convenient.

Description

Technical Field

[0001] This invention relates to the fields of nanophotonics and microstructure characterization, and particularly to a real-time measurement device and method for microstructure dispersion curves. Background Technology

[0002] In biosensing applications, various methods have been developed to achieve highly sensitive sensing. Researchers have integrated knowledge from multiple disciplines, including biology, chemistry, physics, medicine, and electronics, to implement numerous biosensing applications using various techniques, such as electrochemistry, impedance measurement, and image sensing. Surface wave sensing has become an increasingly important method and is one of the most widely used approaches for achieving highly sensitive biosensing. Particularly in the monitoring of living biological samples, surface wave sensing, with its high sensitivity, the ability to functionalize structural surfaces to capture target molecules, and its real-time label-free measurement capabilities, is widely used in cell subcomponent detection, medical diagnostics, and environmental monitoring. Furthermore, in the field of microstructure characterization, since surface wave coupling excitation depends not only on the refractive index of the structural material but also on the thickness of each layer, surface wave sensing also holds significant application potential in the development of thin film deposition methods, the design of suitable biomaterials, and multilayer structures. The aforementioned research based on microstructure and surface waves can all be obtained through the observation and analysis of the dispersion curves of the microstructure.

[0003] The dispersion curve of a microstructure generally characterizes the relationship between the frequency of light and the transmission constant of light during the interaction between light and matter. It can also be reflected by the relationship between different wavelengths and coupling angles. Therefore, the dispersion curve is of great significance in the study of various light-matter interactions. At present, relatively mature methods include dispersion curves and sensing measurements based on surface plasmon resonance, measuring the relationship between the intensity of reflected light and the incident angle or wavelength, and extracting the refractive index of the sample by scanning and tracking the resonance angle or wavelength of the one-dimensional dispersion curve. There is also a method that can simultaneously obtain the complete dispersion curve of wavelength and angle channels, namely the wavelength-angle spectrum surface plasmon resonance image method. The advantage of the complete dispersion curve compared with the one-dimensional dispersion curve is that image processing tools can be used to extract information about the change of the sample's refractive index. However, the existing technology has certain limitations. Therefore, the main problems of the above methods are: (1) Precise angle control is required. Generally, high-precision scanning devices are used to complete the angle scanning of different wavelengths, and the full angle measurement is completed by mechanical scanning, resulting in large scanning errors. In addition, the instruments are expensive and time-consuming, and the cost of angle control is high. (2) Limited spectral acquisition range: Due to limitations in optical path design and multimode fiber, existing technologies have a limited single measurement range when acquiring dispersion curves, making it difficult to implement large-scale, multispectral measurements. Additional acquisition and stitching require additional adjustment time. (3) Limited measurement function: Generally, dispersion curve measurement devices can only be used to complete dispersion curve measurements, resulting in low instrument reuse rate. (4) Low sample expandability: Existing dispersion curve measurement instruments are only for measuring the dispersion curve of a certain structure and cannot further load other samples onto the surface of the structure to complete biological in vivo sensing and detection. Summary of the Invention

[0004] To address the aforementioned issues, this invention provides a real-time measurement device and method for microstructure dispersion curves. The measurement method is convenient and fast, requires no complex optical equipment, and can instantly acquire and measure the dispersion curves of microstructures. It can also be used for spectral measurements and can be extended to applications of existing optical microscopy systems.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A real-time measurement device for microstructure dispersion curves includes a broadband light source, an output optical fiber, a collimating lens, a polarizer, a front cylindrical lens, a prism, a rear cylindrical lens, a slit, an imaging lens, a reflective grating, and a CMOS image sensor.

[0007] The microstructure sample to be tested is attached to the upper surface of the prism. The collimating lens, polarizer, and front cylindrical lens are arranged sequentially along the incident light path. The broadband light source is emitted through the output optical fiber and is focused by the collimating lens, polarizer, and front cylindrical lens in sequence, converging at multiple angles to the prism surface. The broadband light incident at different angles excites surface waves on the microstructure sample to be tested above the prism. The reflected light is collimated by the rear cylindrical lens and emitted. After passing through the slit, the emitted light is focused by the imaging lens and dispersed by the reflection grating. The light signal reflected from the reflection grating passes through the imaging lens again and is collected by the CMOS image sensor.

[0008] Furthermore, the polarizer is positioned and oriented according to the material and structure of the microstructure sample to be tested, so as to ensure that surface waves can be excited on the surface of the microstructure sample.

[0009] Furthermore, the distance between the imaging lens and the slit satisfies the imaging relationship, and the image of the slit can be recorded in the CMOS image sensor.

[0010] Furthermore, the hypotenuse of the upper surface of the prism is parallel to the horizontal plane.

[0011] Furthermore, the microstructure sample to be tested is grown on a transparent silica glass slide, and its thickness does not exceed 5 micrometers.

[0012] Furthermore, the reflective grating and the CMOS image sensor are located on both sides of the imaging lens, and the light emitted from the slit passes through the imaging lens twice. When the emitted light is focused by the imaging lens after passing through the slit, the light beam passes to the left of the center of the imaging lens, and the light signal reflected from the reflective grating passes to the right of the center of the imaging lens again to the CMOS image sensor.

[0013] Furthermore, the microstructure sample to be tested is a metal dielectric multilayer film or a photonic crystal structure.

[0014] Furthermore, the microstructure sample to be tested is tightly bonded to the upper surface of the prism using refractive index matching oil.

[0015] The method for determining the real-time dispersion curve of the microstructure according to the above-mentioned device includes the following steps:

[0016] Step 1: The broadband light source is emitted through the output fiber, collimated by the collimating lens, polarized by the polarizer, and focused by the front cylindrical lens. It then converges at multiple angles to the prism surface. Thus, white light incident at different angles excites surface waves on the microstructure sample to be tested above the prism. The reflected light is collimated by the rear cylindrical lens and emitted through the slit. It is then focused by the imaging lens and dispersed by the reflection grating. The light signal reflected from the reflection grating passes through the imaging lens again and is collected and recorded by the CMOS image sensor.

[0017] Step 2: Read the information recorded in the CMOS image sensor to obtain the dispersion curve image of the microstructure sample to be tested, calculate the angle information corresponding to the pixels in the acquired image, collect pixel windows at different wavelengths by incident light sources of different wavelengths, fit and determine the wavelength information corresponding to the pixels in the acquired image, complete the one-to-one matching between each pixel and wavelength, and then calculate the one-to-one matching relationship between each pixel and angle by recording the angle at which broadband light is incident on the prism by the front cylindrical lens and the beam width of the broadband light.

[0018] Step 3: Convert the coordinates of each pixel in the acquired dispersion curve image into wavelength and angle to complete the measurement of the dispersion curve.

[0019] Furthermore, the wavelength range of the measured dispersion curve is above 150 nm.

[0020] This invention utilizes the coupling excitation characteristics of surface waves to construct an optical path to obtain the device, which is then used to perform real-time measurement of the dispersion curve of a microstructure.

[0021] Compared with the prior art, the advantages of the present invention include:

[0022] (1) Simple structure and fast speed: It solves the problems of slow speed and inaccurate accuracy of conventional scanning and detection equipment that requires both rotation and high-precision angle scanning;

[0023] (2) Real-time measurement and convenient calibration: Through the combined action of grating and prism, the dispersion curve can be acquired in real time by CMOS image sensor without scanning. After the instrument is calibrated, the sample can be replaced and used directly without repeated calibration.

[0024] (3) Multi-point measurement: For non-uniform samples, the position of the focused light on the surface of the structure can be changed by moving the sample or changing the position of the focal point, so as to complete the measurement of the dispersion curve at different positions.

[0025] (4) Wide measurement wavelength range: Different wavelengths of dispersed light are passed through the same imaging lens multiple times to image the dispersion curve image on the CMOS image sensor, reducing the loss of imaging quality. The single measurement wavelength range reaches more than 150nm.

[0026] (5) Low cost: All components used are common optical components, which are inexpensive and easy to maintain;

[0027] (6) Good expandability: The upper surface is horizontal, making it easy to place microstructures, and the surface of the microstructures can be further attached to the sample to be sensed or imaged. The optical path can also be further extended by building an objective lens on top, directly expanding for use in optical microscopy systems, while realizing dispersion curve measurement and conventional optical microscopy imaging;

[0028] (7) High instrument reuse rate: When there is no sample, this measuring device can also be used as a conventional spectrometer to complete the characterization of far-field spectra.

[0029] (8) Polarization selectivity: The polarizer used in this invention can freely adjust the polarization of the incident light according to the structural characteristics of the sample to be tested, and can complete the measurement of the dispersion curve of the microstructure under different polarized light.

[0030] (9) Flexible adjustment and good stability: The light emitted from the rear cylindrical lens is confined into a linear beam through the slit and then incident on the grating. For uniform samples, the incident position can be selected through the slit to avoid non-uniform areas of the grating. For non-uniform samples, different sample positions can be selected through the slit for measurement.

[0031] In addition to the features and advantages described above, the invention also possesses other principles, features, and advantages. The invention will now be described in further detail with reference to the accompanying drawings and embodiments. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the real-time measurement device for the microstructure dispersion curve of the present invention.

[0033] Figure 2 This is a schematic diagram for angle calibration.

[0034] Figure 3 The diagram shows the dispersion curves and wavelength calibration diagrams of broadband light after passing through filters with different bandwidths.

[0035] Figure 4 This is the dispersion curve of the calibrated gold film.

[0036] Figure 5 This is the dispersion curve of the calibrated photonic crystal.

[0037] Figure 6 This is a graph showing the results of a traditional scanning method for measuring dispersion curves.

[0038] Figure 7 This is a graph showing the results of traditional gold film dispersion curve measurements. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The implementation of this invention will be described in detail below with reference to specific embodiments.

[0040] like Figure 1As shown, a real-time measurement device for the dispersion curve of a microstructure includes a broadband light source 1, an outgoing optical fiber 2, a collimating lens 3, a polarizer 4, a front cylindrical lens 5, a prism 6, a rear cylindrical lens 8, a slit 9, an imaging lens 10, a reflection grating 11, and a CMOS image sensor 12. The microstructure sample 7 to be measured is a gold film, which is closely attached to the upper surface of the prism 6. The broadband light source 1 is emitted through the outgoing optical fiber 2, collimated by the collimating lens 3, polarized by the polarizer 4 (TM selection), and focused by the front cylindrical lens 5, converging at multiple angles onto the surface of the prism 6. White light incident at different angles excites surface waves on the gold film above the prism. The reflected light is collimated by the rear cylindrical lens 8 and emitted. After passing through the slit 9, the emitted light is focused by the imaging lens 10 and dispersed by the reflection grating 11. The light signal reflected from the reflection grating 11 passes through the imaging lens 10 again and is collected by the CMOS image sensor 12. Based on the geometric relationships in the optical path, the wavelength and excitation angle corresponding to the pixel position can be calculated, which is the dispersion curve of the microstructure sample under test.

[0041] Furthermore, the polarizer 4 is rotated to a suitable direction according to the specific material and structure of the microstructure sample to be tested, so as to ensure that surface waves can be excited on the surface of the microstructure sample to be tested.

[0042] Furthermore, the distance between the imaging lens 10 and the slit 9 satisfies the imaging relationship, and the image of the slit 9 can be recorded in the CMOS image sensor 12.

[0043] Furthermore, the reflective grating 11 and the CMOS image sensor 12 are located on both sides of the imaging lens 10, and the light emitted from the slit 9 passes through the imaging lens 10 twice; and when the emitted light is focused by the imaging lens 10 after passing through the slit 9, the light beam passes to the left of the center of the imaging lens 10, and the light signal reflected from the reflective grating 11 passes to the right of the center of the imaging lens 10 again.

[0044] Furthermore, the microstructure sample 7 to be tested is made to adhere tightly to the upper surface of the prism by means of refractive index matching oil.

[0045] The real-time measurement method for the microstructure dispersion curve described above includes the following steps:

[0046] Step 1: The broadband light source 1 is emitted through the output fiber 2, collimated by the collimating lens 3, polarized by the polarizer 4, and focused by the front cylindrical lens 5, and then converged at multiple angles onto the surface of the prism 6; the white light incident at different angles excites surface waves on the gold film above the prism; the reflected light is collimated by the rear cylindrical lens 8 and emitted; the emitted light is focused by the imaging lens 10 after passing through the slit 9 and dispersed by the reflection grating 11; the light signal reflected from the reflection grating 11 passes through the imaging lens 10 again and is collected and recorded by the CMOS image sensor 12.

[0047] Step Two: Read the information recorded in the CMOS image sensor 12, namely the dispersion curve image of the microstructure. Calculate the angle information corresponding to the pixels in the acquired image based on geometric relationships, such as... Figure 2 As shown. The incident light converges to point a on the surface of prism 6 after passing through the front cylindrical lens 5. The distance a from point a to the exit surface of the prism is determined to be h. By adjusting the exit light to be parallel, the distance ai from point a to the surface of the rear cylindrical lens 8 is equal to the focal length f of the rear cylindrical lens 8. Points b, c, d, and e are located at the edges of the light spots on prism 6 and rear cylindrical lens 8, respectively. The lengths of line segments bg, gc, di, and ie are measured to obtain line segments m3, m4, m1, and m2. The length of gi is fh, the length of dj is m1-m3, and the length of ke is m2-m4. Using the Pythagorean theorem, the corresponding hypotenuses bd and ce are calculated to obtain sinθ4 and sinθ2. Given that the refractive index of the prism is 1.52, sinθ3 and sinθ1 can be obtained using the law of refraction. Based on the parallel relationship, θ3 = θ5 and θ1 = θ6. Therefore, the image angle range is (45°-θ6, 45°+θ5). Simultaneously, multiple sets of known wavelength filters are selected and the light source is filtered before the image is captured and recorded. After image binarization, the pixel window positions corresponding to different wavelengths are recorded, such as... Figure 3 Figure (a) shows the results. Next, the relationship between all pixels and wavelengths is fitted to complete the wavelength calibration, as shown in Figure (a). Figure 3 The solid line in figure (b) is shown in the middle;

[0048] Step 3: Convert the pixel coordinates of the acquired dispersion curve image into wavelength and angle to complete the measurement of the dispersion curve, such as... Figure 4 As shown;

[0049] Step 4: Replace the sample with a photonic crystal containing a defect layer, rotate polarizer 4 by 90°, and directly observe its dispersion curve, as shown below. Figure 5 As shown, the dispersion curves of the acquired samples are smooth, and the wavelength and angle distributions of multiple modes are clearly visible, demonstrating high resolution and high contrast.

[0050] In contrast, Figure 6 A schematic diagram of a traditional scanning method for measuring dispersion curves is shown (Review of Scientific Instruments 84, 033107 (2013)). It is clear that due to the discontinuity of the angular scan and the need for precision control, the dispersion curve is very uneven, resulting in low measurement accuracy. Figure 7The previous paper showed measurement results for a traditional gold film (Rev. Sci. Instrum. 85, 093107 (2014)). However, the measurement wavelength and angle ranges of this paper are much smaller than those shown in this paper, which is not conducive to a comprehensive characterization of the sample's dispersive properties. Furthermore, its dispersion curve has blurred edges and low contrast. In addition, its incident light requires beam shaping, and the light is focused on a single point on the gold film, making it a single-point measurement unsuitable for large-scale characterization of the sample.

[0051] The relevant principles of the technical solution of this invention are as follows:

[0052] When a broadband light source is incident on the surface of a microstructure at multiple angles, surface wave excitation can generally be achieved by utilizing the high refractive index of the prism and the low refractive index difference of the air on the surface of the microstructure. Within a certain wavelength range, for each wavelength of incident light, there is always an incident angle that can excite surface waves, resulting in almost no light reflection in the reflection direction corresponding to this excitation angle. That is, the reflectivity of the reflected light is almost everywhere in space, except in the reflection direction corresponding to the surface wave excitation angle, where it is close to 0. If a CMOS image sensor is used to collect the reflected light information at this time, it will appear that most pixels have large gray values, while the pixels in the reflection direction corresponding to the excitation angle have very small gray values. However, a broadband light source includes multiple wavelengths, and the superposition of multiple wavelengths of light will result in large gray values ​​for all pixels in space. Therefore, by using a grating to disperse the light of different wavelengths in a direction perpendicular to the angle, the surface wave coupling angles corresponding to different wavelengths can be observed in another direction. This two-dimensional wavelength-angle relationship is the dispersion curve.

[0053] Since the horizontal and vertical coordinates of images captured by CMOS image sensors are in pixels, the calibration is converted into an exit angle using the geometric relationships between optical elements. Specifically, the calibration method records two geometric parameters: the angle α at which broadband light is incident on the prism by the front cylindrical lens, and the beam width D of the broadband light, as well as the positions of the light spot on the rear cylindrical lens and the prism. The focal length of the front cylindrical lens is f, and the refractive index of the prism is n. Therefore, the range of incident angles can be obtained from the geometric relationships, corresponding to the upper and lower limits of the horizontal coordinate, thus establishing a one-to-one matching relationship between each pixel and the angle. Then, broadband light is sequentially incident onto the CMOS image sensor as quasi-monochromatic light using filters of different wavelengths. Based on the bright areas in the CMOS image sensor at this point, the vertical coordinate is converted into wavelength, finally completing the calibration.

[0054] This invention provides a real-time measurement device and method for the dispersion curve of microstructures. Using a lens, polarizer, and front cylindrical lens, a broadband light source is focused onto the surface of a prism as linearly polarized light. Then, utilizing the surface wave resonance characteristic, white light incident at different angles excites surface waves on the surface of the microstructure under test. A rear cylindrical lens collimates the reflected light, and after passing through a slit, the image is collected by a reflection grating, imaging lens, and CMOS image sensor. This image is the dispersion curve of the microstructure under test. The device is convenient and fast, requiring no complex optical equipment, and can instantly acquire and measure the dispersion curve of microstructures. It also supports spectral measurements and can be extended to applications of existing optical microscopy systems.

[0055] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for measuring the real-time dispersion curve of a microstructure, the device comprising a broadband light source (1), an outgoing optical fiber (2), a collimating lens (3), a polarizer (4), a front cylindrical lens (5), a prism (6), a rear cylindrical lens (8), a slit (9), an imaging lens (10), a reflection grating (11), and a CMOS image sensor (12). The microstructure sample (7) to be tested is attached to the upper surface of the prism (6). The collimating lens (3), polarizer (4), and front cylindrical lens (5) are arranged in sequence along the incident light path. The broadband light source (1) is emitted through the outgoing optical fiber (2), and after being focused by the collimating lens (3), polarizer (4), and front cylindrical lens (5) in sequence, it converges to the surface of the prism (6) at multiple angles. The broadband light incident at different angles excites surface waves on the microstructure sample (7) to be tested above the prism (6). The reflected light is collimated by the rear cylindrical lens (8) and emitted. After passing through the slit (9), the emitted light is focused by the imaging lens (10) and dispersed by the reflection grating (11). The light signal reflected from the reflection grating (11) passes through the imaging lens (10) again and is collected by the CMOS image sensor (12). The reflective grating (11) and the CMOS image sensor (12) are located on both sides of the imaging lens (10). The light emitted from the slit (9) passes through the imaging lens (10) twice. When the emitted light is focused by the imaging lens (10) after passing through the slit (9), the light beam passes to the left of the center of the imaging lens (10). The light signal reflected from the reflective grating (11) passes to the right of the center of the imaging lens (10) again to the CMOS image sensor (12). Its features are, The determination method includes the following steps: Step 1: The broadband light source (1) is emitted through the output fiber (2), collimated by the collimating lens (3), polarized by the polarizer (4) to select the appropriate polarization, and focused by the front cylindrical lens (5). It then converges at multiple angles to the surface of the prism (6). Thus, white light incident at different angles excites surface waves on the microstructure sample (7) to be tested above the prism. The reflected light is collimated by the rear cylindrical lens (8) and emitted through the slit (9). It is then focused by the imaging lens (10) and dispersed by the reflection grating (11). The light signal reflected from the reflection grating (11) passes through the imaging lens (10) again and is collected and recorded by the CMOS image sensor (12). Step 2: Read the information recorded in the CMOS image sensor (12), that is, obtain the dispersion curve image of the microstructure sample to be tested, calculate the angle information corresponding to the pixels in the acquired image, collect the pixel windows under different wavelengths by incident light sources of different wavelengths, fit and determine the wavelength information corresponding to the pixels in the acquired image, complete the one-to-one matching between each pixel and wavelength, and then calculate the one-to-one matching relationship between each pixel and angle by recording the angle of broadband light incident on the prism by the front cylindrical lens (5) and the beam width of the broadband light. Step 3: Convert the coordinates of each pixel in the acquired dispersion curve image into wavelength and angle to complete the measurement of the dispersion curve.

2. The method for determining the real-time measurement device of the microstructure dispersion curve according to claim 1, characterized in that, The polarizer (4) is set in a specific position and orientation according to the material and structure of the microstructure sample (7) to be tested, so as to ensure that surface waves can be excited on the surface of the microstructure sample (7).

3. The method for determining the microstructure dispersion curve using the real-time measurement device according to claim 1, characterized in that, The distance between the imaging lens (10) and the slit (9) satisfies the imaging relationship, and the image of the slit (9) can be recorded in the CMOS image sensor (12).

4. The method for determining the real-time measurement device of the microstructure dispersion curve according to claim 1, characterized in that, The hypotenuse of the upper surface of the prism (6) is parallel to the horizontal plane.

5. The method for determining the real-time measurement device of the microstructure dispersion curve according to claim 1, characterized in that, The microstructure sample (7) to be tested is grown on a transparent silica glass slide with a thickness not exceeding 5 micrometers.

6. The method for determining the microstructure dispersion curve using the real-time measurement device according to claim 1, characterized in that, The microstructure sample (7) to be tested is a metal dielectric multilayer film or a photonic crystal structure.

7. The method for determining the real-time measurement device of the microstructure dispersion curve according to claim 6, characterized in that, The microstructure sample (7) to be tested is tightly attached to the upper surface of the prism (6) by means of refractive index matching oil.

8. The method for determining the real-time measurement device of the microstructure dispersion curve according to claim 1, characterized in that, The wavelength range of the measured dispersion curve is above 150 nm.

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