CN112730337A

CN112730337A - Tunable ultra-narrow-band Fano resonance plasma sensor for visible light region

Info

Publication number: CN112730337A
Application number: CN202011457821.XA
Authority: CN
Inventors: 覃祺玮; 杨宏艳; 陈昱澎; 刘孟银; 苑立波
Original assignee: Guilin University of Electronic Technology
Current assignee: Guilin University of Electronic Technology
Priority date: 2020-12-11
Filing date: 2020-12-11
Publication date: 2021-04-30

Abstract

The invention relates to a tunable ultra-narrow-band Fano resonance plasma sensor in a visible light region, belonging to the technical field of nano integrated optics. The method is characterized in that: the invention firstly grows a waveguide layer on a dielectric substrate, and then grows a periodically arranged lattice point array on the waveguide layer, wherein the array is composed of a metal-dielectric-waveguide-substrate (from top to bottom). The tunable Fano resonance sensor has excellent performance, narrow line width at a resonance peak and extremely high amplitude sensitivity. The characteristic can be applied to optical devices such as biosensing, narrow-band filtering, nano laser and the like, and has great application value in the fields of optical communication and the like.

Description

Tunable ultra-narrow-band Fano resonance plasma sensor for visible light region

(I) technical field

The invention relates to a tunable ultra-narrow-band Fano resonance plasma sensor in a visible region, which can be used in the directions of biosensing, narrow-line-width filters, nano lasers and the like, and belongs to the technical field of nano integrated optics.

(II) background of the invention

Localized Surface Plasmon Resonance (LSPR) carried by noble metal nanocrystals and nanostructures can concentrate light into nanoscale spatial regions, enabling many important applications such as surface-enhanced raman scattering and sensing. Compared with a sensor based on Propagating Surface Plasmon Resonance (PSPR), the LSPR sensor is simple, economical, efficient, and suitable for measuring local refractive index changes caused by target molecule adsorption. However, the figure of merit (FOM) value of an LSPR sensor is the refractive index sensitivity divided by the plasmon resonance linewidth, typically 1-2 orders of magnitude less than the PSPR-based figure of merit (FOM). Due to strong radiation damping, the LSPR of metal nanostructures typically exhibit broad resonance peaks, which results in smaller FOM values, thereby limiting the performance of LSPR sensors.

To increase the FOM of the LSPR sensor, its refractive index sensitivity may be increased and/or the full width at half maximum (FWHM) of the LSPR may be reduced. By lifting the metal nanostructures above the substrate with the dielectric pillars, the refractive index sensitivity of the resulting LSPR sensor may be improved, since most spatial regions with enhanced electric fields are exposed to the environment and may be accessed by molecular species. More efforts have been made to reduce the FWHM value of LSPR and thus increase the FOM value. An effective way to reduce the FWHM value is to couple the LSPR to different resonant modes with smaller FWHM, i.e.: fano resonance occurs due to coupling between the wide super-radiation mode and the narrow sub-radiation mode. Current work has clearly demonstrated that Fano resonance can be achieved by introducing symmetry breaks or other approaches to construct multi-resonance interference. In addition, another approach to reducing the FWHM of the plasma is to form one-or two-dimensional arrays of metal nanoparticles.

However, despite rapid advances in this area, the bandwidth is still wide due to ohmic losses and strong radiative losses of the metal resonators and limits the achievable quality factor (Q-factor). The use of Fano resonance in the sensing field to better detect peaks and valleys remains a significant challenge to develop high-figure-of-merit (FOM) nanostructures. In addition, Fano resonant sensor devices that achieve high quality factor and narrow line width in the visible light band have been reported. To solve the above problems, we propose here a novel structure of periodic array nanoparticles in combination with waveguides, new coupled plasmon resonance modes achieving both narrow FWHM and high refractive index sensitivity. The resonant modes result from coupling between the wide linewidth LSPR and the waveguide modes, the structure maintaining strong destructive interference between the guided modes propagating in the waveguide layer and the LSPR of the metal nanoparticles. Since ohmic losses in the dielectric layer are avoided, resonance with a high quality factor can be achieved.

Disclosure of the invention

The invention aims to provide a tunable ultra-narrow-band Fano resonance plasma sensor with a visible light region, which has a simple structure and is easy to integrate. The sensor has excellent performance, and the narrow line width at the resonance peak can be used as a high-precision sensing device. The characteristic can be applied to optical devices such as biochemical sensing, narrow-band filtering, nano laser and the like, and has great application value in the fields of optical communication and the like. An efficient method is proposed to achieve generation of Fano resonance, in which a metal block is suspended in air by jacking up, in order to reduce the substrate effect, and the metal localized surface plasmon resonance can strongly couple with the guided modes different from the transmission in the waveguide layer, thereby generating a narrow-band hybrid mode with large electric field enhancement.

The purpose of the invention is realized as follows:

specifically, the invention provides a tunable ultra-narrow-band Fano resonance plasma sensor in a visible light region. The method is characterized in that: the waveguide layer (2) growing on the substrate (1) and the cylindrical medium nano-pillars (3) and the metal nano-pillars (4) growing periodically on the waveguide layer. The dielectric nano-block (3) and the metal nano-block (4) in the sensor are stacked up and down for combination, and the metal nano-block (4) is positioned on the dielectric nano-block (3); the combined nano structures are periodically arrayed on the substrate along the X and Y directions; the light source is set to a plane polarized wave polarized parallel to the X axis and incident at an angle θ in the XZ plane.

In the scheme, the metal nano-column is made of noble metal gold (Au), the dielectric column is made of silicon dioxide with the refractive index of 1.45, and the waveguide layer is made of HfO with the refractive index of 2₂The substrate material is glass with a refractive index of 1.52. The radius of the metal nano-column is 120 nm; the radius of the silicon dioxide dielectric column is 100 nm. Thickness h of upper metal nano-pillar_mHeight of 100nm, height h of silicon dioxide dielectric column_dFixed at 300nm。

In the above scheme, the period P of the nano-arrays periodically arranged on the waveguide layer is 355nm to 460nm along the X direction and the Y direction.

In the scheme, the influence of the refractive index change on the position of a resonance peak and the line width is verified, and the refractive index change interval is set to be 1.330-1.450. Amplitude sensitivity detection was studied in the range of 1.3310-1.3345.

In the above scheme, the value range of the light source incidence angle theta is 6-20 degrees.

(IV) description of the drawings

FIG. 1 is a schematic diagram of a three-dimensional periodic array structure according to the present invention.

FIG. 2 is a two-dimensional side view of a single periodic structure of the present invention.

Fig. 3 is a comparison graph of the reflection spectrum of light waves incident at an angle of incidence of 10 ° and without a waveguiding layer according to the present invention.

FIG. 4 is a reflection spectrum obtained at an incident angle in the range of 6 to 20 degrees according to the present invention.

FIG. 5 is a reflection spectrum obtained by varying the periodic structure in the range of 355nm to 460nm according to the present invention.

FIG. 6 is a reflection spectrum obtained by changing the refractive index of the surrounding environment within the range of 1.330 to 1.450 according to the present invention.

FIG. 7 is a graph of the sensitivity of the refractive index at the resonance peak of the refractive index changes FR1, D1 and FR2 in the range of 1.330-1.450.

FIG. 8 is a reflection spectrum obtained by changing the refractive index of the surrounding environment within the range of 1.3310-1.3340.

FIG. 9 is a fitting curve of the sensitivity of the FR2 formant amplitude for the refractive index change in the range of 1.3310-1.3340.

(V) detailed description of the preferred embodiments

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings in conjunction with specific examples. It should be noted that directional terms such as "upper", "lower", "left", "right", "front", "rear", and the like in the examples are merely directions referring to the drawings. Accordingly, the directions used are for illustration only and are not intended to limit the scope of the present invention.

The invention is further illustrated below with reference to specific examples.

A tunable ultra-narrow band Fano resonance plasma sensor with a visible light region is shown in a three-dimensional perspective view in figure 1. The waveguide layer (4) growing on the substrate (5) and the cylindrical medium nano-pillars (3) and the metal nano-pillars (2) growing periodically on the waveguide layer. The sensor comprises a dielectric nano-block (3) and a metal nano-block (2), wherein the dielectric nano-block (3) and the metal nano-block (2) are stacked up and down to be combined, and the metal nano-block (2) is positioned on the dielectric nano-block (3); the combined nano structures are periodically arrayed on the substrate along the X and Y directions; the light source is set to be polarized parallel to the X-axis and incident at an angle θ in the XOZ plane.

For a clearer explanation the coupling of local surface plasmon resonance with waveguide mode excites Fano resonance. As shown in fig. 3, the reflection lines of the waveguide-less metal array are compared to the waveguide-layer metal array at an oblique incidence of 10 °. The valleys in the dotted lines in fig. 3 are asymmetric Fano-type formants (D1) formed by the suppression of radiation attenuation by the strong coupling between the dipole moments of the out-of-plane nanoparticles by the overlying metal under obliquely incident light, trapping light in the plane of the array. The resonant peak at the left side of the solid line is asymmetric Fano resonance generated by coupling of a TE guided mode of the waveguide and LSPR of the metal array, and the formation reason of the middle resonant valley is consistent with that of the dotted resonant valley. The left asymmetric Fano resonant line type is generated by coupling a transmission TM guided mode in the waveguide with a metal LSPR.

Further, to investigate the effect of the incident angle of light on the formants, we made far-field reflection lines between 6 ° and 20 °, as shown in fig. 4. The left Fano peak (FR1) is blue-shifted with increasing angle, and the middle out-of-plane dipole peak is red-shifted simultaneously with the right Fano peak (FR 2). It can be further seen that as the FWHM of the mid-plane out-of-plane dipole formants increases with increasing angle, the resonance intensities of FR1 and FR2 also change. As can be seen from FIG. 4, the Fano resonance peak of the reflection line has a better quality factor within the range of 10-14 degrees, which is calculated to be 690 at most and 236 at the FOM.

Similarly, we studied the effect of the structure period on the formants, as shown in fig. 5, and as can be seen from the whole that as the period increases, the red shift phenomenon occurs in FR1, D1 and FR2, and the line types of FR1 and FR2 change, because as the period changes, the phase changes when the plasmon waveguide mode is coupled with the metal dipole moment, so that the line type changes. Meanwhile, when the period is relatively small, the D1 and FR2 resonance peaks are mutually coupled, so that the electromagnetic transparency-like phenomenon is realized, and the quality factor is extremely high.

Further, in order to verify the influence of the refractive index change on the position of the resonance peak and the line width, the refractive index change interval of the sensing device is set to be 1.330-1.450, as shown in fig. 6. To more clearly understand the refractive index sensing sensitivity of the sensing device, a sensitivity fit graph as shown in fig. 7 was made. It can be clearly seen that the refractive index sensitivity of FR1 was 34nm/RIU, the refractive index sensitivity of the out-of-plane dipole formants was 416nm/RIU, and the refractive index sensitivity of FR2 was 206 nm/RIU. In addition, research finds that the resonance intensity of FR2 is sensitive to small changes of refractive index near the ambient refractive index of 1.33, so that a reflection spectral line with the ambient refractive index of 1.3310-1.3340 is simulated and calculated, as shown in FIG. 8, in order to more intuitively show the amplitude sensitivity of the sensing device, an amplitude sensitivity fitting curve as shown in FIG. 9 is made, and as can be seen in the figure, the amplitude sensitivity of FR2 can reach 12200%/RIU.

In summary, it can be seen from fig. 6 and 7 that our design can be applied to the detection of wavelength shift sensitivity in the background refractive index range (1.27-1.45). This range includes the refractive indices of water, sodium chloride solutions, sucrose solutions, etc. common in experiments, and almost all nuclei, cytoplasm (1.350-1.405) and local parts of cytoplasm with high refractive indices among biological cells. In addition, it can be seen from FIGS. 8 and 9 that there is very high resolution and figure of merit (FOM) in the background index range of 1.3310-1.3340. It can be shown that the tunable ultra-narrow-band Fano resonance plasmon sensor in the visible light region has extremely narrow FWHM and higher Q value in the visible light band, and lower detection sensitivity limit.

It should be noted that the above-mentioned embodiments are illustrative, but not restrictive, and the present invention is not limited to the above-mentioned embodiments. Other embodiments within the teachings of this invention will become apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein.

Claims

1. The invention relates to a tunable ultra-narrow-band Fano resonance plasma sensor in a visible light region, belonging to the technical field of nano integrated optics. The method is characterized in that: the waveguide layer (4) growing on the substrate (5) and the cylindrical medium nano-pillars (3) and the metal nano-pillars (2) growing periodically on the waveguide layer. The sensor comprises a dielectric nano-block (3) and a metal nano-block (2), wherein the dielectric nano-block (3) and the metal nano-block (2) are stacked up and down to be combined, and the metal nano-block (2) is positioned on the dielectric nano-block (3); the combined nano structures are periodically arrayed on the substrate along the X and Y directions; the light source is set to a plane wave polarized parallel to the X-axis and incident at an angle θ in the XOZ plane.

2. The ultra-narrow band Fano resonance plasmon sensor tunable in the visible region of claim 1, wherein: the range of the incident angle theta of the plane wave light source is 6-20 degrees.

3. The ultra-narrow band Fano resonance plasmon sensor tunable in the visible region of claim 1, wherein: the metal nano-block is made of noble metal gold (Au), the dielectric block is made of silicon dioxide with the refractive index of 1.45, the waveguide layer is made of HfO2 with the refractive index of 2, and the substrate is made of glass with the refractive index of 1.52.

4. The ultra-narrow band Fano resonance plasmon sensor tunable in the visible region of claim 1, wherein: the radius R of the upper layer metal block is 120 nm; the radius r of the lower silicon dioxide dielectric column is 100 nm.

5. The ultra-narrow band Fano resonance plasmon sensor tunable in the visible region of claim 1, wherein: the influence of the refractive index change of the sensor on the position of a resonance peak and the line width is set to be 1.3-1.45 of the refractive index change interval.

6. The ultra-narrow band Fano resonance plasmon sensor tunable in the visible region of claim 1, wherein: the sensor sensing interval is positioned in a visible light wave band, and the resonant peak wavelength can be regulated and controlled by adjusting the period of the sensor and the angle of incident light.

7. The ultra-narrow band Fano resonance plasmon sensor tunable in the visible region of claim 1, wherein: in the range of 1.3310-1.3340 background refractive index, the change of the resonance intensity of the FR2 formant is sensitive to the change of the refractive index and can be used for high-sensitivity amplitude sensitivity sensing.