CN206431044U - The refractive index sensing unit resonated based on metal dielectric waveguide coupled resonator Fano - Google Patents

Abstract

The utility model discloses a refractive index sensing unit based on the Fano resonance of a metal dielectric waveguide coupling resonant cavity, which comprises a metal silver substrate (1), and the metal silver substrate (1) is provided with an input device located on the same straight line. A waveguide cavity (2) and an output waveguide cavity (5), the metallic silver substrate (1) is provided with a rectangular resonant cavity (4) between the input waveguide cavity (2) and the output waveguide cavity (5), the The axis of the rectangular resonant cavity (4) is perpendicular to the axis of the transmission waveguide cavity; the metal silver substrate (1) is provided with a ring resonant cavity (3) on one side of the rectangular resonant cavity (4). The utility model "refractive index sensing unit based on the Fano resonance of metal dielectric waveguide coupling resonator cavity" can enhance the accuracy of measurement, and will not affect the substance to be measured because it is a micro measurement. In principle, the scheme is simple, easy to operate, and has good market application value.

Description

Refractive Index Sensing Unit Based on Metal Dielectric Waveguide Coupled Resonator Fano Resonance

technical field

The utility model belongs to the field of surface plasmon optics and the field of micro-nano systems, in particular to a refractive index sensing unit based on the Fano resonance of a metal dielectric waveguide coupled resonant cavity.

Background technique

The development of computer technology and Internet technology has made its operating speed and information processing capability increasingly powerful, and the limitations of traditional electronic circuit-based information transmission in terms of heat loss have become more and more obvious. Photonic devices are superior to electronic devices in terms of low heat loss and high-speed processing capabilities, and with the development of nanotechnology, photonic devices are getting closer to practical roads. The discovery of the surface plasmon resonance phenomenon breaks through the limitation of the traditional optical diffraction limit and brings new opportunities for the development of nanophotonic devices.

Surface Plasmon Polaritons (SPPs) are defined as charge density waves, which are the result of coupling between plasmons and photons, and the amplitude of their light field decays exponentially in the direction perpendicular to the interface. SPPs overcome the limitation of light diffraction limit, making it possible to fabricate nanophotonic devices. In recent years, with the widespread application of metallic subwavelength waveguide devices, SPPs have attracted extensive research and have become an emerging discipline, such as biosensors, SPPs lithography, and ultra-high-resolution imaging.

Metal-Insulator-Metal (MIM) based on SPPs has attracted extensive attention due to its ease of chip integration. Plasma structures are becoming more and more important as sensors in many fields, such as physics, chemistry, biology, energy and information fields, etc.

Contents of the invention

The purpose of this utility model is to propose a surface plasmon refractive index sensing unit, which is a MIM structure coupled by a ring resonant cavity and a rectangular resonant cavity. This high-sensitivity refractive index sensing unit is used for the refractive index measurement of different media , using the finite element method to study its sensing performance, by changing the refractive index of the transmission medium, the sensitivity of the designed sensing unit is 1000nm/RIU.

The utility model is realized by adopting the following technical solutions:

A refractive index sensing unit based on the Fano resonance of metal dielectric waveguide coupling resonator, comprising a metal silver substrate, the metal silver substrate is provided with an input waveguide cavity and an output waveguide cavity located on the same straight line, the metal silver A rectangular resonant cavity is arranged on the substrate between the input waveguide cavity and the output waveguide cavity, and the axis of the rectangular resonant cavity is perpendicular to the axis of the transmission waveguide cavity; one side of the metallic silver substrate is located on the rectangular resonant cavity. ring resonator.

When in use, for the solution to be tested: draw a small amount of the solution to be tested and drop it on the sensing unit to fill the resonance chamber. The tunable laser light source is coupled into the input port, the output port is connected to the photodetector, and the laser wavelength is adjusted at the same time. The transmission curve is analyzed by a spectrum analyzer, and the peak wavelength λ ₁ is recorded, compared with the corresponding wavelength at the peak in the vacuum (refractive index n ₀ =1) state λ ₀ . The refractive index n ₁ of the solution to be measured can be obtained:

n ₁ =n ₀ +(λ ₁ -λ ₀ )/S

where S is the sensitivity of the refractive index sensor.

For the gas to be measured, it is only necessary to place the sensing unit in the environment of the gas to be measured, the principle is the same as above, and will not be repeated here.

The utility model "refractive index sensing unit based on the Fano resonance of metal dielectric waveguide coupling resonator cavity" can enhance the accuracy of measurement, and will not affect the substance to be measured because it is a micro measurement. In principle, the scheme is simple, easy to operate, and has good market application value.

Description of drawings

Fig. 1 shows a schematic diagram of a two-dimensional structure of a plasmonic refractive index sensing unit.

FIG. 2 shows a schematic diagram of a three-dimensional structure of a plasmonic refractive index sensing unit.

Figure 3 shows the transmission curve when the refractive index of the medium is changed, and the wavelength interval between the peaks of adjacent transmission curves is 20nm.

Fig. 4 shows the fitting curve of the sensitivity of the refractive index sensing unit, the black squares represent the simulated values, and the straight lines represent the fitting results. It can be seen from the figure that the sensitivity of the refractive index sensing unit of this structure is 1000nm/RIU.

In the figure: 1-metal silver substrate, 2-input waveguide cavity, 3-ring resonant cavity, 4-rectangular resonant cavity, 5-output waveguide cavity.

detailed description

Specific embodiments of the present utility model will be described in detail below in conjunction with the accompanying drawings.

A refractive index sensing unit based on the Fano resonance of the metal dielectric waveguide coupling resonator, as shown in Figure 2, includes a metal silver substrate 1, and the metal silver substrate 1 is provided with an input waveguide cavity 2 located on the same straight line and an output waveguide cavity 5, the metal silver substrate 1 is provided with a rectangular resonant cavity 4 between the input waveguide cavity 2 and the output waveguide cavity 5, the axis of the rectangular resonant cavity 4 is in line with the transmission waveguide cavity (input waveguide cavity 2 It is perpendicular to the axis of the output waveguide cavity 5 ); a ring resonant cavity 3 is provided on one side of the rectangular resonant cavity 4 on the metallic silver substrate 1 . The center of the ring resonator 3 is located on the axis of the rectangular resonator 4 .

As shown in Figure 1, the refractive index sensing unit is composed of a MIM waveguide coupled rectangular cavity and a ring cavity. The refractive index of the silver (Ag) layer is ε _m , the shaded part in the figure. White represents the dielectric layer, which can be composed of the solution or gas to be measured. In order to ensure that the fundamental mode (TM ₀ ) propagates in the waveguide, the width of the transmission waveguide cavity (input waveguide cavity and output waveguide cavity), ring resonator, and rectangular resonator is set to d=50nm, and the coupling distance g ₁ =g ₂ = g ₃ =10nm. In the ring resonant cavity, the inner diameter r ₁ =90nm, the outer diameter r ₃ =140nm, and the height h=100nm of the rectangular resonant cavity. The optical input port and the optical output port are placed at the left and right ends of the input waveguide cavity and the output waveguide cavity respectively.

In order to illustrate the transmission characteristics of the refractive index sensing unit, the following explanations are theoretically given:

The dielectric constant of silver can be derived using the Debye-Drude dispersion model, the formula is as follows:

Among them, ε _∞ =3.8344 and ε _s =-9530.5 are the infinite frequency permittivity and static permittivity, respectively. τ=7.35×10 ^-15 represents the relaxation time, σ=1.1486×10 ⁷ S/m represents the conductivity of silver.

In order to explain the Fano resonance phenomenon in the simulation results, Sj±(j=1 or 2) represents the SPPs wave, and κ ₁ , κ ₂ , and κ ₃ represent the coupling coefficients between the cavities, respectively. If light of a specific frequency is incident (frequency ω), A _S and _AR represent the light field amplitudes of the rectangular resonant cavity and the ring resonant cavity respectively, and their relationship with time is as follows:

Among them, i is the imaginary number unit, ω _s and ω _R are the resonant frequencies of the rectangular resonator and the ring resonator respectively. According to energy conservation, the amplitude relationship between the incident and outgoing light waves is as follows:

At the same time, the transfer function T is the following equation:

In order to illustrate the influence of the change of the medium refractive index on the waveguide transmission curve, as shown in Figure 3, the medium refractive index is set to 1.00, 1.02, 1.04, 1.06, 1.08, respectively, and the refractive index difference is 0.02. According to the simulation results, it is found that with the increase of the refractive index of the medium, the transmission line is red-shifted. This is because the effective refractive index of the medium increases while increasing the refractive index. As shown in Figure 4, when the refractive index increases by 0.02RIU, the wavelength corresponding to the Fano resonance peak moves to the long-wave direction by 20nm. After calculation, the sensitivity is 1000nm/RIU.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the utility model without limitation. Although detailed descriptions have been made with reference to the embodiments of the utility model, those of ordinary skill in the art should understand that the technical solutions of the utility model Modifications or equivalent replacements do not deviate from the spirit and scope of the technical solutions of the present utility model, and all of them should be covered by the protection scope of the claims of the present utility model.

Claims (2)

1. A refractive index sensing unit based on the Fano resonance of a metallic dielectric waveguide coupling resonator, characterized in that: it includes a metallic silver substrate (1), and the metallic silver substrate (1) is provided with An input waveguide cavity (2) and an output waveguide cavity (5), the metal silver substrate (1) is provided with a rectangular resonant cavity (4) between the input waveguide cavity (2) and the output waveguide cavity (5), so The axis of the rectangular resonant cavity (4) is perpendicular to the axis of the transmission waveguide cavity; the metallic silver substrate (1) is provided with a ring resonant cavity (3) on one side of the rectangular resonant cavity (4). 2. The refractive index sensing unit based on Fano resonance of metal dielectric waveguide coupling resonator according to claim 1, characterized in that: the width d=50nm and the height h=100nm of the rectangular resonator (4); The inner diameter r ₁ =90nm and the outer diameter r ₃ =140nm of the ring resonant cavity (3); the coupling between the transmission waveguide cavity and the rectangular resonant cavity (4) and between the rectangular resonant cavity (4) and the ring resonant cavity (3) The spacing g ₁ =g ₂ =g ₃ =10nm; the transmission waveguide cavity width d=50nm.