Bloch surface wave exciter, nanoparticle spectrometer and measurement method thereof

Abstract

The present invention relates to a Bloch surface wave exciter based on nanoparticles, which is used in a spectrometer, comprising a glass substrate and a Bragg reflection unit arranged on the glass substrate, wherein the Bragg reflection unit is formed by alternating stacking of high-refractive index medium layers and low-refractive index medium layers, wherein the top layer is a defect layer, and the surface of the top layer is provided with nanoparticles. The present invention also provides a corresponding spectrometer and a measurement method thereof. The Bloch surface wave exciter of the present invention enables the in-plane size of the spectrometer to reach the nanometer level, and can measure smaller light source signals. Moreover, the preparation method of the present invention is simple and low in cost. In addition, when the spectrometer of the present invention is used, the requirements for the incident spectrum are simple, and there is no requirement for the polarization of the incident spectrum. At the same time, the present invention only needs to take a back focal plane image once, which is not only simple to operate, but also saves time.

Description

Technical Field

[0001] The present invention relates to the technical field of spectroscopy, and more specifically to a Bloch surface wave exciter, a Bloch surface wave modulated nanoparticle spectrometer and a measurement method thereof. Background Art

[0002] Spectroscopy is one of the most widely used technologies in industrial processes and basic scientific research. Its application areas include water quality monitoring, soil science, mineral detection, hyperspectral imaging, and medical vaccine research. Spectrometers are devices used for spectral detection. During use, spectrometers are required to be ultra-compact, low-cost, and time-saving. Traditional grating spectrometers such as Figure 1 As shown in Figure 1, this spectrometer has limitations on photon efficiency, resolution and spectral range, and its internal optical components are large in size, which limits the reduction in size of the spectrometer. Therefore, it is necessary to develop a new spectrometer that can be reduced to nanometer size.

[0003] Surface plasmon polaritons (SPPs) are localized electromagnetic waves that exist on the surface of a structure. They have a good ability to confine electromagnetic fields, and have the advantages of subwavelength propagation, local field enhancement, and high sensitivity to the surrounding environment. In addition, due to the sensitive nature of surface plasmon resonance to the refractive index of the surrounding analytes, it is widely used in laboratories to measure the attraction and dynamic analysis between biomolecules. The field enhancement effect of SPR has been applied to enhance fluorescence or Raman spectroscopy, which is a method for developing highly sensitive real-time spectral measurements. However, due to the low wavelength resolution of SPPs, it is very difficult to solve the inverse problem, that is, to directly obtain the spectrum of the incident light beam, the near-field fluorescence, and the Raman signal from the nanostructure.

[0004] Bloch surface waves (BSWs) can be regarded as a substitute for SPPs. They exist at the interface between a multilayer dielectric film composed of periodic high and low refractive index dielectric materials and the surrounding air. They are a new type of surface wave based on all-dielectric micro-nanostructures. BSWs have the advantages of field localization of SPPs. Compared with SPPs, BSWs have the advantages of low loss, compatibility with TE and TM modes, can be prepared on a CMOS material platform, and flexible dispersion characteristics. Dispersion elements that can excite BSWs can be used in spectrometers. At present, the commonly used methods for exciting BSWs include grating scattering, asymmetric slit scattering, and silver nanowire scattering. The grating scattering method has high scattering efficiency, but the size is large and not conducive to integration. The asymmetric slit scattering method can be used as a unidirectional coupler, but its structural design is complex and the size is relatively large. The silver nanowire scattering method is low-cost, but it is easy to oxidize, resulting in a short life and poor stability, and it also has the problem of large size. At the same time, the above three components all have certain requirements for incident light when exciting BSW, and the preparation methods of these three devices are relatively complicated, cannot be mass-produced, and have high costs. Summary of the invention

[0005] In order to solve the above problems in the prior art, the present invention provides a Bloch surface wave exciter, a Bloch surface wave modulated nanoparticle spectrometer and a measurement method thereof, which can reduce the spectrometer to nanometer size.

[0006] A nanoparticle-based Bloch surface wave exciter, used in a spectrometer, comprises a glass substrate and a Bragg reflection unit arranged on the glass substrate, wherein the Bragg reflection unit is formed by alternatingly stacking high-refractive index medium layers and low-refractive index medium layers, wherein the top layer is a defect layer, and nanoparticles are arranged on the surface of the top layer.

[0007] Furthermore, the nanoparticles are arranged on the surface of the top layer by a physical crushing method.

[0008] Preferably, the nanoparticles are Si nanoparticles.

[0009] Preferably, the size of the nanoparticles is 94 nm.

[0010] Furthermore, the material of the top layer is the same as that of the low refractive index medium layer.

[0011] Preferably, the thickness of each layer of the high refractive index medium is 88 nm.

[0012] Preferably, the thickness of each layer of the low refractive index medium is 105 nm.

[0013] The present invention also provides a Bloch surface wave modulated nanoparticle spectrometer, which includes an incident objective lens, a dispersion element, a collection objective lens, a collection lens and an imaging camera in sequence along the direction of the spectral signal to be measured, and the dispersion element is the above-mentioned nanoparticle-based Bloch surface wave exciter.

[0014] The present invention also provides a measurement method for a Bloch surface wave modulated nanoparticle spectrometer, characterized in that it comprises: step S1, providing the above-mentioned Bloch surface wave modulated nanoparticle spectrometer; step S2, irradiating a known spectrum to a dispersion element of the Bloch surface wave modulated nanoparticle spectrometer, acquiring a back focal plane image of the dispersion element through an imaging camera, and extracting a Bloch surface wave part from the acquired back focal plane image; step S3, selecting a certain wavelength range, sampling the extracted Bloch surface wave part at a fixed interval within the wavelength range, and acquiring a wavelength-related spectrum library; step S4, irradiating a spectrum to be measured to the dispersion element, acquiring a back focal plane image of the dispersion element again through the imaging camera, extracting a Bloch surface wave part again from the re-acquired back focal plane image, and converting the re-extracted Bloch surface wave part into a column vector; step S5, solving the spectrum to be measured according to the spectrum library and the column vector.

[0015] Preferably, the wavelength range in step S3 is 550nm-680nm.

[0016] Preferably, the interval in step S3 is 1 nm.

[0017] The present invention provides a Bloch surface wave exciter based on nanoparticles. The size of the nanoparticles is only about 100nm, which is conducive to integration, so that the in-plane size of a spectrometer using the Bloch surface wave exciter as a dispersion element can reach the nanometer level, and a smaller light source signal can be measured. In addition, the present invention adopts a physical crushing method to prepare nanoparticles, and the preparation method is simple, low-cost, and batch preparation is possible. In addition, when the spectrometer of the present invention is used, the requirements for the incident spectrum are simple, and there is no requirement for the polarization of the incident spectrum. At the same time, the present invention only needs to take a back focal plane image once, which is not only simple to operate, but also saves time. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the structure of a traditional grating spectrometer.

[0019] Figure 2 It is a schematic structural diagram of a nanoparticle spectrometer modulated by Bloch surface waves according to the present invention.

[0020] Figure 3 yes Figure 2 Schematic diagram of the structure of the optical chip based on nanoparticle-induced BSW.

[0021] Figure 4 yes Figure 3 Cross-sectional view of .

[0022] FIG5(a) is a FDTD simulation of the surface light field distribution of the BSW excited by the dispersion element of the present invention, FIG5(b) is a far-field angular spectrum pattern calculated by FDTD, and FIG5(c) is the experimental result corresponding to FIG5(b)

[0023] Figure 6(a)-Figure 6(h) The present invention is a schematic diagram of the use process of the Bloch surface wave modulated nanoparticle spectrometer.

[0024] Figure 7(a)-Figure 7(f) It is a schematic diagram of the result of spectral reconstruction of Figure 6(h). DETAILED DESCRIPTION

[0025] The preferred embodiments of the present invention are given below in conjunction with the accompanying drawings and described in detail.

[0026] like Figure 2 As shown, the Bloch surface wave modulated nanoparticle spectrometer according to the present invention includes an incident objective lens 1, a dispersion element 2, a collection objective lens 3, a collection lens 4 and an imaging camera 5 in sequence along the direction of the spectrum signal to be measured. The spectrum is irradiated to the incident objective lens 1, and is converged and incident on the dispersion element 2, which excites the dispersion element 2 to generate BSW, and the leaked light field is collected by the collection objective lens 3, and is focused by the collection lens 4 and transmitted to the imaging camera 5.

[0027] The dispersion element 2 is a nanoparticle-based Bloch surface wave exciter (i.e., an optical chip for exciting BSW), such as Figure 3 and Figure 4 As shown, the dispersion element 2 includes a glass substrate 21, a Bragg reflection unit 22 and nanoparticles 26. The Bragg reflection unit 22 is arranged on the glass substrate 21, and the nanoparticles 26 are arranged on the top layer 25 of the Bragg reflection unit 22. The Bragg reflection unit 22 and the nanoparticles 26 work together to excite the BSW.

[0028] The Bragg reflection unit 22 is formed by alternately stacking high refractive index medium layers 23 and low refractive index medium layers 24, and the top layer 25 is a defect layer. The high refractive index medium layers 23 and the low refractive index medium layers 24 form a periodic structure. Since the defect layer is provided at the top of the periodic structure, a defect field is generated, and the defect field is BSW. The material and thickness of the high refractive index medium layer 23 and the low refractive index medium layer 24 can be set differently according to actual needs. In this embodiment, the material of the high refractive index medium layer 23 is Si 3 N 4 , with a thickness of 88nm; the material of the low refractive index medium layer 24 is SiO 2, with a thickness of 105nm. The material of the top layer 25 is the same as that of the low refractive index medium layer 24, and its thickness can be set differently according to actual needs. In this embodiment, the thickness of the top layer 25 is 240nm. In this way, the spectrometer of the present invention can measure the spectrum in the wavelength range between 550-680nm. In other embodiments, for spectra in different wavelength ranges, high refractive index medium layers 23, low refractive index medium layers 24 and top layer 25 of other thicknesses can be set. In addition, high refractive index medium layers 23, low refractive index medium layers 24 and top layer 25 of other thicknesses can also be set according to different environments.

[0029] The nanoparticles 26 are placed on the top layer 25 by physical crushing: the nanoparticles 26 are crushed into powder, the powder is dissolved in an alcohol solvent, and then the powder is spin-coated on the surface of the top layer 25 by a coating machine. This method is simple to operate and low in cost, and can be used to mass-produce nanoparticles suitable for the exciter. The nanoparticles 26 can be made of metal materials with high refractive index or other materials with strong scattering properties, such as Au nanoparticles, TiO 2 Nanoparticles, etc. In the present embodiment, the nanoparticles 26 are Si nanoparticles. The size of the nanoparticles 26 is about 100nm. In the present embodiment, the size of the nanoparticles 26 is 94nm, which can achieve more accurate measurement while reducing the size. In other embodiments, the nanoparticles 26 can also be set to different sizes according to actual conditions. In this way, the present invention can realize a nano-sized device for exciting BSW, so that the in-plane size of the spectrometer reaches the nanometer level, and a smaller light source signal can be measured. In addition, since the nanoparticles are isotropic structures, incident light of any polarization can excite BSW, so the dispersion element 2 of the present invention has simple requirements for the incident light and has no requirements for the polarization of the incident light. The resolution of the spectrometer of the present invention is 2nm and the range is 130nm.

[0030] The experimental results of the dispersion element 2 of the present invention are shown in Figures 5(a)-(c). In Figure 5(a), the direction of the white arrow is the polarization direction of the incident light, and x and y are the spatial field distributions. The excitation principle of BSW is: the Gaussian light field is vertically incident on the nanoparticles, and the nanoparticles scatter the incident light field. When the momentum matching is satisfied, BSW will be excited, and BSW will be transmitted along the radial direction of the nanoparticles. When the incident light is polarized along the vertical direction, the strongest area of ​​the scattering direction of the nanoparticles is perpendicular to the polarization direction of the incident light, and when it is parallel to the polarization direction, it is the weakest area for exciting BSW, that is, there will be some dark lines in the surface excitation field. In Figure 5(b), k x / k 0 , k y / k 0They are the wave vector distribution of BSW in the x direction and in the y direction. When BSW is transmitted on the surface, it will couple to the far field at a certain angle, which is reflected as an arc in the far field image. When the incident light is polarized light, BSW presents two plate arcs in the far field. The strongest light spot in the middle is the incident Gaussian light field, which is incident at an angle of about 0 degrees. In Figure 5(c), the white solid double arrow is the polarization direction of the incident Gaussian light field, the white bright arc is BSW, and the white part in the middle is the incident Gaussian light field. The incident wavelength is 620nm.

[0031] The present invention also provides a measurement method of a Bloch surface wave modulated nanoparticle spectrometer, comprising the following steps:

[0032] Step S1, providing the above-mentioned Bloch surface wave modulated nanoparticle spectrometer.

[0033] Step S2, irradiate the known spectrum to the dispersive element 2, obtain the back focal plane image of the dispersive element 2 through the imaging camera 5, as shown in Figure 6 (a), and extract the Bloch surface wave part from the obtained back focal plane image. It should be noted that, since the nanoparticles 26 in the dispersive element 2 are isotropic structures, the spectrometer of the present invention has simple requirements for the incident spectrum and has no requirements for the polarization of the incident spectrum.

[0034] Step S3, select a certain wavelength range, and perform sampling in the extracted Bloch surface wave part at a fixed interval within the wavelength range, and after sampling, a dispersion diagram as shown in FIG6(b) can be formed, and the data form corresponding to the dispersion diagram is shown in FIG6(c), so that a spectrum library E related to wavelength is obtained. In this embodiment, the wavelength range is 550nm-680nm, and the interval is 1nm.

[0035] Step S4, irradiate the measured spectrum α to the dispersion element 2, obtain the back focal plane image of the dispersion element 2 as shown in Figure 6(d) again through the imaging camera 5, extract the Bloch surface wave part as shown in Figure 6(e) from the re-acquired back focal plane image again, and convert the re-extracted Bloch surface wave part into the column vector I as shown in Figure 6(f).

[0036] Step S5, according to the spectrum library E obtained in step S3 and the column vector I obtained in step S4, the spectrum to be measured α is solved. Generally speaking, α can be solved by the formula E×α=I, but since both E and I have errors during measurement, the spectrum to be measured cannot be obtained by direct solution, and an intelligent iterative algorithm is required to solve α, and the solution result is shown in Figure 6(h).

[0037] Figure 7(a)-Figure 7(f)It is a schematic diagram of the result of spectrum reconstruction of Figure 6(h), which proves that the present invention can realize the measurement of unknown spectrum, and the unknown spectrum to be measured includes both single narrowband wavelength and broadband spectrum. Figure 7(a) is the single wavelength reconstruction result of five wavelengths of 550, 580, 600, 630 and 650nm, Figure 7(b) is the reconstruction result under the enlarged 600nm wavelength, Figure 7(c) is the reconstruction result of dual wavelengths of 630 and 635nm, Figure 7(d) is the reconstruction result of three wavelengths of 580, 585 and 590nm, Figure 7(e) is the reconstruction result of six wavelengths under 580-630nm, Figure 7(f) is the reconstruction result of seven wavelengths under 580-640nm, among which the intensity of 630nm wavelength is not equal to that of other wavelengths.

[0038] It can be seen from the above steps that when the spectrometer of the present invention is used, it is not necessary to use the position of the measured light spot to scan the grating to measure the spectrum to be measured. It only needs to take a back focal plane image once, extract the BSW part and solve the spectrum to be measured according to the spectrum library. Compared with the existing method of using the spectrometer, it is not only simple to operate, but also saves time.

[0039] The above is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. The above embodiment of the present invention can also be modified in various ways. That is, all simple, equivalent changes and modifications made according to the claims and the description of the present invention fall within the scope of protection of the claims of the present invention. The contents not described in detail in the present invention are all conventional technical contents.

Claims

1. A nanoparticle-based Bloch surface wave exciter for use in a spectrometer, characterized in that: The invention comprises a glass substrate and a Bragg reflection unit arranged on the glass substrate, wherein the Bragg reflection unit is formed by alternately stacking high-refractive index medium layers and low-refractive index medium layers, wherein the top layer is a defect layer, and nanoparticles are arranged on the surface of the top layer by a physical crushing method, and the nanoparticles are Si nanoparticles, and the material of the top layer is the same as that of the low-refractive index medium layer.

2. The nanoparticle-based Bloch surface wave exciter according to claim 1, characterized in that: The size of the nanoparticles was 94 nm.

3. The nanoparticle-based Bloch surface wave exciter according to claim 1, characterized in that: The thickness of each high refractive index medium layer is 88 nm.

4. The nanoparticle-based Bloch surface wave exciter according to claim 1, characterized in that: The thickness of each low refractive index medium layer is 105 nm.

5. A Bloch surface wave modulated nanoparticle spectrometer, which comprises an incident objective lens, a dispersion element, a collection objective lens, a collection lens and an imaging camera in sequence along the direction of the spectral signal to be measured, characterized in that: The dispersive element is a nanoparticle-based Bloch surface wave exciter according to any one of claims 1-4.

6. A measurement method of a Bloch surface wave modulated nanoparticle spectrometer, characterized in that: include: Step S1, providing the Bloch surface wave modulated nanoparticle spectrometer according to claim 5; Step S2, irradiating the known spectrum to the dispersion element of the Bloch surface wave modulated nanoparticle spectrometer, acquiring a back focal plane image of the dispersion element through an imaging camera, and extracting the Bloch surface wave part from the acquired back focal plane image; Step S3, selecting a certain wavelength range, sampling the extracted Bloch surface wave part at a fixed interval within the wavelength range, and obtaining a wavelength-dependent spectrum library; Step S4, irradiating the spectrum to be measured to the dispersive element, acquiring a back focal plane image of the dispersive element again through the imaging camera, extracting a Bloch surface wave portion again from the acquired back focal plane image, and converting the extracted Bloch surface wave portion into a column vector; Step S5, solving the spectrum to be measured according to the spectrum library and the column vector.

7. The measuring method of the Bloch surface wave modulated nanoparticle spectrometer according to claim 6, characterized in that: The wavelength range in step S3 is 550nm-680nm.

8. The measuring method of the Bloch surface wave modulated nanoparticle spectrometer according to claim 6, characterized in that: The interval in step S3 is 1 nm.

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