The photonic spin Hall effect (SHE) has been intensively studied and widely applied, especially in spin photonics. However, the SHE is weak and is difficult to detect directly. In this paper, we propose a method to enhance SHE with the guided-wave surface-plasmon resonance (SPR). By covering a dielectric with high refractive index on the surface of silver film, the photonic SHE can be greatly enhanced, and a giant transverse shift of horizontal polarization state is observed due to the evanescent field enhancement near the interface at the top dielectric layer and air. The maximum transverse shift of the horizontal polarization state with 11.5 μm is obtained when the thickness of Si film is optimum. There is at least an order of magnitude enhancement in contrast with the transverse shift in the conventional SPR configuration. Our research is important for providing an effective way to improve the photonic SHE and may offer the opportunity to characterize the parameters of the dielectric layer with the help of weak measurements and development of sensors based on the photonic SHE.

Single layers of tin selenide (SnSe), which have a similar structure as graphene and phosphorene, also show excellent optoelectronic properties, and have received much attention as a two-dimensional (2D) material beyond other 2D material family members. Surface plasmon resonance (SPR) sensors based on three monolayer SnSe allotropes are investigated with the transfer matrix method. The simulated results have indicated that the proposed SnSe-containing biochemical sensors are suitable to detect different types of analytes. Compared with the conventional Ag-only film biochemical sensor whose sensitivity is 116°/RIU, the sensitivities of these SnSe-based biochemical sensors containing α-SnSe, δ-SnSe, ε-SnSe, were obviously increased to 178°/RIU, 156°/RIU and 154°/RIU, respectively. The diverse biosensor sensitivities achieved with these three SnSe allotropes suggest that these 2D materials can adjust SPR sensor properties.

Surface plasmon resonance (SPR) with two-dimensional (2D) materials has been proposed to enhance the sensitivity of biosensors. Here, we will apply SPR to greatly enhance and control the Goos-Hänchen (GH) shift. It is theoretically shown that the GH shifts can be significantly enhanced in the SPR structure coated with a graphene-MoS₂ heterostructure. By changing the layer number of graphene or MoS₂, the giant GH shifts can be obtained. Maximum GH shift (235.8λ) can be obtained when 2 layers of MoS₂ and 3 layers of graphene are combined. Moreover, the GH shift can be positive or negative depending on the layer number of MoS₂ and graphene. When the GH shift is used as the interrogation for the biosensor, it has a superior sensitivity. By comparing the sensitivity based on the SPR with only Au coating or Au-graphene coating, the sensitivity of the GH shift-interrogated biosensor can be enhanced by nearly 300 times, and hence paves the way for further applications in fundamental biological studies and environmental monitoring.

Black phosphorus (BP), a promising new two-dimensional (2D) material, has drawn a lot of attentions in academia and industry due to its extraordinary physical and chemical properties. In this paper, we theoretically demonstrate a monolayer BP that achieves coherent perfect absorption (CPA) at the THz/infrared band. It is found that quasi-CPA point does exist at the THz/infrared band. The CPA, which has a relative bandwidth of 141.3% and a coherent absorptivity of more than 90%, can be implemented at the quasi-CPA wavelength through a proper phase modulation. Moreover, the coherent absorptivity can be modulated with a high modulation depth by means of the phase difference between the two coherent counter-propagating beams. The angular selectivity of the monolayer BP is also investigated. The CPA wavelength is divided into two wavelength branches for TE and TM polarization at oblique incidence. In addition, the CPA wavelength can be tuned from THz to infrared band by adjusting the electron doping of the BP while maintaining the modulation depth of 10⁴. Hence, our results may be potentially used for coherent modulations in terahertz/infrared detections and signal processing with 2D materials.

Graphene terahertz (THz) surface plasmons provide hope for developing functional devices in the THz frequency. By coupling graphene surface plasmon polaritons (SPPs) and a planar waveguide (PWG) mode, Fano resonances are demonstrated to realize an ultrasensitive terahertz biosensor. By analyzing the dispersion relation of graphene SPPs and PWG, the tunable Fano resonances in the terahertz frequency are discussed. It is found that the asymmetric lineshape of Fano resonances can be manipulated by changing the Fermi level of graphene, and the influence of the thickness of coupling layer and air layer in sandwich structure on the Fano resonances is also discussed in detail. We then apply the proposed Fano resonance to realize the ultrasensitive terahertz biosensors, it is shown that the highest sensitivities of 3260 RIU−1 are realized. Our result is two orders of a conventional surface plasmon resonance sensor. Furthermore, we find that when sensing medium is in the vicinity of water in THz, the sensitivity increases with increasing refractive index of the sensing medium.