Guangtao Cao

Formation and evolution mechanisms of plasmon-induced transparency in MDM waveguide with two stub resonators

We demonstrate the realization of plasmonic analog of electromagnetically induced transparency (EIT) in a system composing of two stub resonators side-coupled to metal-dielectric-metal (MDM) waveguide. Based on the coupled mode theory (CMT) and Fabry-Perot (FP) model, respectively, the formation and evolution mechanisms of plasmon-induced transparency by direct and indirect couplings are exactly analyzed. For the direct coupling between the two stub resonators, the FWHM and group index of transparent window to the inter-space are more sensitive than to the width of one cut, and the high group index of up to 60 can be achieved. For the indirect coupling, the formation of transparency window is determined by the resonance detuning, but the evolution of transparency is mainly attributed to the change of coupling distance. The consistence between the analytical solution and finite-difference time-domain (FDTD) simulations verifies the feasibility of the plasmon-induced transparency system. It is also interesting to notice that the scheme is easy to be fabricated and may pave the way to highly integrated optical circuits.

Combined theoretical analysis for plasmon-induced transparency in waveguide systems.

We propose a novel combination of a radiation field model and the transfer matrix method (TMM) to demonstrate plasmon-induced transparency (PIT) in bright-dark mode waveguide structures. This radiation field model is more effective and convenient for describing direct coupling in bright-dark mode resonators, and is promoted to describe transmission spectra and scattering parameters quantitatively in infinite element structures by combining it with the TMM. We verify the correctness of this novel combined method through numerical simulation of the metal-dielectric-metal (MDM) waveguide side-coupled with typical bright-dark mode, H-shaped resonators; the large group index can be achieved in these periodic H-shaped resonators. These results may provide a guideline for the control of light in highly integrated optical circuits.

Plasmon-induced transparency in a single multimode stub resonator

We investigate electromagnetically induced transparency (EIT)-like effect in a metal-dielectric-metal (MDM) waveguide coupled to a single multimode stub resonator. Adjusting the geometrical parameters of the stub resonator, we can realize single or double plasmon-induced transparency (PIT) windows in the plasmonic structure. Moreover, the consistency between analytical results and finite difference time domain (FDTD) simulations reveals that the PIT results from the destructive interference between resonance modes in the stub resonator. Compared with previous EIT-like scheme based on MDM waveguide, the plasmonic system takes the advantages of easy fabrication and compactness. The results may open up avenues for the control of light in highly integrated optical circuits.

Uniform theoretical description of plasmon-induced transparency in plasmonic stub waveguide

We investigate a classic analog of electromagnetically induced transparency (EIT) in a metal-dielectric-metal (MDM) bus waveguide coupled to two stub resonators. A uniform theoretical model, for both direct and indirect couplings between the two stubs, is established to study spectral features in the plasmonic stub waveguide, and the theoretical results agree well with the finite difference time domain simulations. Adjusting phase difference and coupling strength of the interaction, one can realize the EIT-like phenomena and achieve the required slow light effect. The theoretical results may provide a guideline for the control of light in highly integrated optical circuits.

Slow light based on plasmon-induced transparency in dual-ring resonator-coupled MDM waveguide system

We report a theoretical and numerical investigation of the plasmon-induced transparency (PIT) effect in a dual-ring resonator-coupled metal–dielectric–metal waveguide system. A transfer matrix method (TMM) is introduced to analyse the transmission and dispersion properties in the transparency window. A tunable PIT is realized in a constant separation design. The phase dispersion and slow-light effect are discussed in both the resonance and non-resonance conditions. Finally, a propagation constant based on the TMM is derived for the periodic system. It is found that the group index in the transparency window of the proposed structure can be easily tuned by the period p, which provides a new understanding, and a group index ∼51 is achieved. The quality factor of resonators can also be effective in adjusting the dispersion relation. These observations could be helpful to fundamental research and applications for integrated plasmonic devices.

Theoretical Analysis of Plasmon-Induced Transparency in Ring-resonators Coupled Channel Drop Filter Systems

The plasmon-induced transparency (PIT) in ring-resonators coupled channel drop filter (CDF) systems is investigated theoretically and numerically in this paper. A coupled mode theory-based transfer matrix method (CMT-TMM) is introduced owning to the symmetric and evanescent coupling, which is confirmed by the finite-difference time-domain (FDTD) simulation results. The drop waveguide provides the necessary optical feedback for the interference effect in realizing the PIT, and a new way for adjusting PIT effect in a fixed structure is also given. Finally, the phase and the group dispersion in the transparency window are discussed for investigating the slow light effect in our systems, and a group index of ~22 is obtained. The proposed plasmonic systems possess both the slow light and the dropping properties and may have potential and flexible applications in fundamental research of integrated plasmonic devices.

Systematic Theoretical Analysis of Selective-Mode Plasmonic Filter Based on Aperture-Side-Coupled Slot Cavity

By taking the aperture as a resonator, we propose an analytical model to describe the dynamic transmission in metal-dielectric-metal (MDM) waveguide aperture-side-coupled with slot cavity. The theoretical results and the finite-difference time-domain (FDTD) simulations agree well with each other, and both demonstrate the mode selectivity and filtering tunability of the plasmonic structure. By adjusting the phase shifts in slot cavity or resonance frequency determined by the aperture, one can realize the required transmission spectra and slow light effect. The theoretical analysis may open up avenues for the control of light in highly integrated optical circuits.

Theoretical analysis and applications on nano-block loaded rectangular ring

We propose compact and switchable optical filters based on nano-block loaded rectangular rings, and investigate the selection property numerically and theoretically. A simple and convenient phase model is established for the theoretical analysis. The dependent factors, such as the number, size, and positions of the loaded blocks, are discussed in detail. It is found that a longer wavelength can be obtained without increasing the device dimension, and the selected wave is more sensitive to the length of the loaded blocks. The loading positions play key roles in the realization of separating the second-order modes. Finally, applications of this proposed structure are discussed simply. We find that the loaded filter device provides a more compact size than the unloaded one for the same properties, and a tunable plasmon induced transparency based switch effect is also achieved. These findings suggest potential applications in compact filters, tunable slow light devices, and sensor fields.

Tunable filter and optical buffer based on dual plasmonic ring resonators

We demonstrate the realization of on chip plasmon-induced transparency using dual ring resonators coupling to metal–dielectric–metal bus waveguide. The theoretical results agree well with the finite-difference time-domain simulative ones. Moreover, by adjusting the radius, width, as well as the coupling distance can efficiently operate the wavelengths and bandwidths of our filter. In theory, we propose a feasible method to improve the trade-off between transmission and quality factor. Finally, the ultra-compact structure possesses slow light effect and manifests a low group velocity, which provides a guideline to control the light and has potential application in optical filter and optical buffer.

Investigating the direct coupling between plasmonic cavities in the case of the second-order resonant mode

In this paper, we present a metal-dielectric-metal (MDM) waveguide side-coupled with bright-dark-bright mode cavities and double bright-dark mode cavities. The former shows a prominent plasmonic analogue of electromagnetically induced transparency (EIT) spectra response, the latter shows double plasmonic analogue of EIT spectra response. The direct coupling strength between bright and dark mode resonators in the case of the second-order resonant mode is investigated in detail in our researches. The transmission spectrum and the slow light effects as a function of the cavity–cavity separation between resonators are further studied. Our researches investigate the coupling strength effects on the transmission and scattering properties in the case of the high-order resonance mode, which may provide a guideline for the control of light in highly integrated optical circuits.