In this paper; the surface plasmon resonance (SPR) sensor with a porous silica film was studied. The effect of the thickness and porosity of the porous silica film on the performance of the sensor was analyzed. The results indicated that the figure of merit (FOM) of an SPR sensor can be enhanced by using a porous silica film with a low-refractive-index. Particularly; the FOM of an SPR sensor with 40 nm thick 90% porosity porous silica film; whose refractive index is 1.04 was improved by 311% when compared with that of a traditional SPR sensor. Furthermore; it was found that the decrease in the refractive index or the increase in the thickness of the low-refractive-index porous silica film can enlarge the FOM enhancement. It is believed that the proposed SPR sensor with a low-refractive-index porous silica film will be helpful for high-performance SPR sensors development.

In this paper, we propose a surface plasmon resonance (SPR) sensor based on two-dimensional (2D) materials (graphene, MoS₂, WS₂ and WSe₂) hybrid structure, and theoretically investigate its sensitivity improvement in the visible region. The thickness of metal (Au, Ag or Cu) and the layer number of each 2D material are optimized using genetic algorithms to obtain the highest sensitivity for a specific wavelength of incident light. Then, the sensitivities of proposed SPR sensors with different metal films at various wavelengths are compared. An Ag-based SPR sensor exhibits a higher sensitivity than an Au- or Cu-based one at most wavelengths in the visible region. In addition, the sensitivity of the proposed SPR sensor varies obviously with the wavelength of incident light, and shows a maximum value of 159, 194 or 155°/RIU for Au, Ag or Cu, respectively. It is demonstrated that the sensitivity of the SPR sensor based on 2D materials’ hybrid structure can be further improved by optimizing the wavelength of incident light.

In this paper, we presented a design method of a surface plasmon resonance (SPR) biosensor with high performance using a genetic algorithm (GA). The constraint conditions of the sensitivity and the reflectivity at the resonance angle were used in the merit function (MF) of GA to achieve simultaneous optimization of the sensitivity and the resolution. By using the proposed method, we designed an Au-Ag-TiO₂-graphene based SPR biosensor at first and compared its performance with a traditional Au-graphene based SPR biosensor. The resolution of the designed biosensor was nearly three times that of the traditional one on the premise of the same sensitivity. In addition, a series of SPR biosensors with sensitivities ranging from 50 to 180°/RIU and improved resolutions was designed by using different target sensitivities in MF. A comparison of the designed biosensors with the traditional Au-graphene SPR biosensor was also done, and the biosensors with higher sensitivity and meanwhile higher resolution than the traditional one were demonstrated to be existed. Lastly, the influences of target reflectivity at the resonance angle and the prism on the design of the Au-Ag-TiO₂-graphene based SPR biosensor were investigated. It is believed that the proposed design method based on the genetic algorithm could be applied to optimize the performances of a SPR biosensor with an arbitrary multilayer structure.

By adding an absentee layer on the top of the metallic layer, the figure of merit (FOM) of a surface plasmon resonance (SPR) sensor with Kretschmann configuration was enhanced, without changing the resonance angle and the reflectance at the resonance angle. Comparing with a traditional SPR sensor, the FOM of the SPR sensor with an absentee layer composed of either 1367 nm thick KCl or 235 nm thick ${\mathrm{Si}}_3{\mathrm{N}}_4$ can be improved by 5.53% or 11.41%, respectively. The enhancement of the FOM should be attributed to the faster decrease of the full width at half-maximum than the sensitivity after an absentee layer was applied in the SPR sensor.

This paper proposes a smart window for radiative cooling with adjustable transparency by leveraging the phase transition property of VO₂. The proposed smart window exhibits daytime visible light transmission and near-infrared light reflection, all-day radiative cooling, and a nighttime privacy protection feature. It comprises a bottom layer of VO₂/Ag/VO₂ and top cubic two-dimensional SiO₂ gratings, with structural parameters optimized by the genetic algorithm to ensure excellent optical performance. In the daytime, 75.4% visible light transmittance and 87.8% near-infrared reflectance can be achieved by utilizing the dielectric state of VO₂. It also achieves low light transmission of 9.8% by using the metallic state of VO₂, which is suitable for nighttime privacy protection. Furthermore, it has an all-day outside emissivity of 98.2% for radiative cooling, together with a low inside emissivity of 1.9% for effectively inhibiting the radiation heat transfer. In addition, the proposed structure is insensitive to the angles of incidence and the polarization of light, making it advantageous for radiative cooling. During the daytime, it reduces the temperature by 17.7 K compared to a glass of equal thickness when the non-radiative heat coefficient is 12 W/m²/K. At night, it achieves a cooling power of 124.7 W/m², achieving a cooling effect of 8.9 K below ambient temperature. The proposed smart window is promising for various application scenarios for radiative cooling and privacy protection and could be used as windows for buildings and vehicles.