Evaluation of Fano resonance and phase analysis of plasma induced transparency in photonic nanostructure based on equivalent circuit analysis

Fano resonance and plasma induced transparency (PIT) have been widely observed in various plasmonic nanostructures. Fano resonance takes place in weak coupling regime where coupling constant between two electromagnetic modes is lower than damping constant of system. Hence, extracting coupling and damping coefficients from resonance spectrum is the key to distinguish between Fano resonance and other resonances. In this paper, we propose a simple and realizable coupled LC circuit to analyze Fano resonance and PIT. Weak and strong coupling regime are distinguished by comparing coupling constant with damping constant. Meanwhile, we gain deep insight into Fano resonance and PIT in circuit by analyzing circuit phase and understand their connection with resonance in photonic structure. Furthermore, we extend the equivalent circuit model to the field involved short-range plasmon polarization or multi-orders dark modes. Since there are no specific parameters associated with photonic nanostructure, the proposed equivalent circuit can be used in most plasmonic resonance system as an universal model.

Demonstration of Dipole-Induced Transparency Using Mirrored Split-Ring Resonator Metasurface For Microwave Applications

In this paper, dipole-induced transparency in the microwave regime is proposed and verified using experimental and simulation studies. A single layer mirrored Split-Ring Resonator (SRR) metasurface array working under the H⊥excitation scenario is used to achieveout-of-phase electric dipole moments on the metasurface for a normal incident plane wave. The emergence of the transparency window is accompanied by the destructive interference between out-of-phase oscillating electric dipole moments on the metasurfaceand is verified in computations by studying the radar Cross Section in full-wave electromagnetic simulations.We used the multipole scattering theory to validate the results computationally. The coupling effects are studied numerically, and the emergence of the transparency window is studied experimentally using transmission measurements inside an anechoic chamber using a vector network analyzer.

Effects of neighboring transitions on the mechanisms of electromagnetically induced absorption and transparency in an open degenerate multilevel system

In this study, optical Bloch equations with and without neighboring hyperfine states near the degenerate two-level system (DTLS) in the challenging case of $$^{85}$$ 85 Rb D2 transition, which involves the Doppler broadening effect, are solved. The calculated spectra agree well with the experimental results obtained based on the coupling-probe scheme with orthogonal linear polarizations of the coupling and probe fields. The mechanisms of electromagnetically induced absorption (electromagnetically induced transparency) for the open $$F_g=3 \rightarrow F_e=2$$ F g = 3 → F e = 2 and 3 transitions (open $$F_g=2 \rightarrow F_e=2$$ F g = 2 → F e = 2 and 3 transitions) are determined to be the effect of the strong closed $$F_g=3 \rightarrow F_e=4$$ F g = 3 → F e = 4 transition line (strong closed $$F_g=2 \rightarrow F_e=1$$ F g = 2 → F e = 1 transition line); this finding is based on a comparison between the calculated absorption profiles of the DTLS without neighboring states and those of all levels with neighboring states, depending on the coupling and probe power ratios. Furthermore, based on the aforementioned comparison, the crucial factors that enhance or reduce the coherence effects and lead to the transformation between electromagnetically induced absorption and electromagnetically induced transparency, are (1) the power ratios between the coupling and probe beams, (2) the openness of the excited state, and (3) effects of the neighboring states due to Doppler broadening in a real atomic system.

Quadruple plasmon-induced transparency and tunable multi-frequency switch in monolayer graphene terahertz metamaterial

A monolayer graphene metamaterial composed of a graphene block and four graphene strips, which has the metal-like properties in terahertz frequency range, is proposed to generate an outstanding quadruple plasmon-induced transparency (PIT). Additional analyses show that the forming physical mechanism of the PIT with four transparency windows can be explained by strong destructive interference between the bright mode and the dark mode, and the distributions of electric field intensity and electric field vectors under the irradiation of the incident light. Coupled mode theory (CMT) and finite-difference time-domain (FDTD) method are employed to study the spectral response characteristics of the proposed structure, and the theoretical and simulated results are in good agreement. It is found that a tunable multi-frequency switch and excellent optical storage can be achieved in the wide PIT window. The maximum modulation depth is up to 99.7%, which corresponds to the maximum extinction ratio of 25.04 dB and the minimum insertion loss of 0.19 dB. In addition, the time delay is as high as 0.919 ps, the corresponding group refractive index is up to 2755. Thus, the proposed structure provides a new method for the design of terahertz multi-frequency switches and slow light devices.