Optical bistability in metal-insulator-metal plasmonic Bragg waveguides with Kerr nonlinear defects

Graphene-tuned EIT-like effect in photonic multilayers for actively controlled light absorption of topological insulators

As newly emerging nanomaterials, topological insulators with unique conducting surface states that are protected by time-reversal symmetry present excellent prospects in electronics and photonics. The active control of light absorption in topological insulators are essential for the achievement of novel optoelectronic devices. Herein, we investigate the controllable light absorption of topological insulators in Tamm plasmon multilayer systems composed of a Bi_1.5Sb_0.5Te_1.8Se_1.2 (BSTS) film and a dielectric Bragg mirror with a graphene-involved defect layer. The results show that an ultranarrow electromagnetically induced transparency (EIT)-like window can be generated in the broad absorption spectrum. Based on the EIT-like effect, the Tamm plasmon enhanced light absorption of topological insulators can be dynamically tuned by adjusting the gate voltage on graphene in the defect layer. These results will pave a new avenue for the realization of topological insulator-based active optoelectronic functionalities, for instance light modulation and switching.

High-performance optical sensing based on electromagnetically induced transparency-like effect in Tamm plasmon multilayer structures

We present a novel kind of optical sensor based on the electromagnetically induced transparency (EIT)-like effect in a Tamm plasmon multilayer structure, which consists of a metal film on a dielectric Bragg grating with alternatively stacked TiO₂ and SiO₂ layers and a defect layer. The defect layer can induce a refractive-index-sensitive ultranarrow peak in the broad Tamm plasmon reflection dip. This nonintuitive phenomenon in analogy to the EIT effect in atomic systems originates from the coupling and destructive interference between the defect and Tamm plasmon modes in the multilayer structure. Taking advantage of this EIT-like effect, we achieve an ultrahigh sensing performance with a sensitivity of 416 nm/RIU and a figure of merit (FOM) of 682  RIU^-1. The numerical simulations agree well with the theoretical calculations. Additionally, the spectral line shape can be effectively tailored by changing the defect layer thickness, significantly promoting the dimensionless FOM from 0.76×10⁴ to more than 2.4×10⁴. Our findings will facilitate the achievement of ultrasensitive optical sensors in multilayer structures and open up perspectives for practical applications, especially in gas, biochemical, and optofluidic sensing.

Induced reflection in Tamm plasmon systems

We present an induced reflection response analogue to electromagnetically induced transparency (EIT) in a novel Tamm plasmon system, consisting of a thin metal film and a Bragg grating with a defect layer. The results show that an induced narrow peak can be generated in the original broad reflection dip, which is attributed to the coupling and interference between the Tamm plasmon and defect modes in the grating structure. It is found that the EIT-like induced reflection is strongly dependent on the thickness of defect layer, grating period number between the metal and defect layers, thickness of Bragg grating layer, refractive index of defect layer, and thickness of metal film. Additionally, the induced reflection can be dynamically tuned by adjusting the angle of incident light. The numerical simulations agree extremely well with theoretical calculations. The coupling strength between the Tamm plasmon and defect modes is determined by the above parameters. These results will provide a new avenue for light field control and devices in multilayer photonic systems.

Widely tunable SPP bandgap in a nonlinear metal-insulator-metal waveguide

In this article, we propose a novel kind of widely tunable surface plasmon polaritons (SPP) bandgap in a Kerr nonlinear metal-insulator-metal waveguide. By two identical gratings, the pump beam is coupled to two opposing SPP waves, which interfere with each other and results in SPP standing wave in the region between the two gratings. The refractive index of the Kerr nonlinear material is then periodically modulated by the SPP standing wave, and a SPP bandgap is formed. The position of the SPP bandgap can be tuned from 1.4 μm to 1.75 μm by adjusting the pump wavelength, and the relationship between the transmittance contrast of the bandgap and the pump power is also studied. Comparing with existing methods that directly modulate the refractive index (RI) or the width of the waveguide, in our work, the periodic modulation of the RI comes from the interference of the pump light, which can greatly simplify the fabrication. This work may find applications in the design of novel nonlinear devices for future all-optical integrated circuits.

Plasmon-induced transparency in metal-insulator-metal waveguide side-coupled with multiple cavities

We have demonstrated the analogue of electromagnetically induced transparency (EIT) in the metal-insulator-metal plasmonic waveguide, which consists of a bus waveguide side-coupled with a series of slot cavities. By finite-difference time-domain simulations, it is found that the resonance wavelength of the slot cavity can be controlled by adjusting the length of the cavity. Moreover, the EIT-like response is strongly dependent on the coupling separation between the corresponding adjacent cavities. Multiple-peak plasmon-induced transparency can be realized by cascading multiple cavities with different lengths and suitable cavity-cavity separations. This ultracompact plasmonic waveguide system may find important applications for multichannel plasmonic filter, nanoscale optical switching, and slow-light devices in highly integrated optical circuits and networks.

Plasmonic spectral splitting in multi-resonator-coupled waveguide systems

Spectral splitting is numerically investigated in a metal-insulator-metal plasmonic waveguide coupled with a series of disk cavities for the first time to our best knowledge. The finite-difference time-domain simulations find that, when an identical cavity is introduced into the single-cavity-coupled structure, a resonance peak emerges in reflection dip due to the plasmonic analogue of electromagnetically induced transparency. By cascading multiple cavities into the waveguide system, the resonance spectra are gradually split because of the phase-coupled effects. Particularly, the quality factors of splitting resonance spectra can be rapidly improved with increasing the number of coupled cavities. The proposed plasmonic systems may find potential applications in highly integrated optical circuits, especially for multichannel filtering, all-optical switching, and slow-light devices.

Slow light engineering in periodic-stub-assisted plasmonic waveguide

We investigate the slow light engineering in periodic-stub-assisted plasmonic waveguide based on transmission line theory. It is found that the dispersion relationship of the proposed waveguide can be easily modified by tuning the stub depth and the period. The theoretical results show that a large normalized delay bandwidth product of 0.65 can be achieved at 1550 nm, meanwhile maintaining the group index of 35. In addition, the proposed waveguide shows "S-shaped" dispersion curve, which implies that the group velocity dispersion parameter at the inflection point equals zero and a dispersion-free slow light waveguide can be realized. Due to the excellent buffering capacity, the proposed compact configuration can find important applications on optical buffers in highly integrated optical circuits.

Optical bistability based on an analog of electromagnetically induced transparency in plasmonic waveguide-coupled resonators

We have investigated numerically an optical bistability effect based on an analog of electromagnetically induced transparency (EIT) in a nanoscale plasmonic waveguide-coupled resonator system. The system consists of a metal-insulator-metal waveguide side-coupled with a slot cavity and a nanodisk cavity containing Kerr nonlinear material. By finite-difference time-domain simulations, the EIT-like spectral peak has a redshift with an increase of the dielectric constant of the nanodisk cavity. More importantly, we have achieved an optical bistability with threshold intensity about three times lower than that of recent literature [Appl. Opt.50, 5287 (2011)]. The results show that our plasmonic structure can find more excellent application in highly integrated optical circuits, especially all-optical switching.