Tamm-plasmon polaritons in one-dimensional photonic quasi-crystals

Photonic crystal nanostructure as a photodetector for NaCl solution monitoring: theoretical approach

In this research, we have a theoretical simple and highly sensitive sodium chloride (NaCl) sensor based on the excitation of Tamm plasmon resonance through a one-dimensional photonic crystal structure. The configuration of the proposed design was, [prism/gold (Au)/water cavity/silicon (Si)/calcium fluoride (CaF₂)¹⁰/glass substrate]. The estimations are mainly investigated based on both the optical properties of the constituent materials and the transfer matrix method as well. The suggested sensor is designed for monitoring the salinity of water by detecting the concentration of NaCl solution through near-infrared (IR) wavelengths. The reflectance numerical analysis showed the Tamm plasmon resonance. As the water cavity is filled with NaCl of concentrations ranging from 0 g l^-1 to 60 g l^-1, Tamm resonance is shifted towards longer wavelengths. Furthermore, the suggested sensor provides a relatively high performance compared to its photonic crystal counterparts and photonic crystal fiber designs. Meanwhile, the sensitivity and detection limit of the suggested sensor could reach the values of 24 700 nm per RIU (0.576 nm (g l)^-1) and 0.217 g l^-1, respectively. Therefore, the suggested design could be of interest as a promising platform for sensing and monitoring NaCl concentrations and water salinity as well.

Critically coupled Fabry-Perot cavity with high signal contrast for refractive index sensing

Perfect absorption at a resonance wavelength and extremely low absorption at the wavelength range of off-resonance in a one-port optical cavity is required for refractive index (RI) sensing with high signal contrast. Here, we propose and analyze an absorption-enhanced Fabry-Perot (MAFP) cavity based on a critical coupling condition in a near-infrared wavelength range. For a one-port cavity, a thick bottom Au is used as a mirror and an absorber. To achieve the critical coupling condition, a top dielectric metasurface is employed and tailored to balance the radiation coupling and the absorption coupling rates, and the one-port cavity is theoretically analyzed using temporal coupled-mode theory. We investigate two types of MAFP structures for gas and liquid. The gas MAFP cavity shows a sensitivity of ~ 1388 nm/RIU and a full-width at half-maximum of less than 0.7 nm. This MAFP cavity resolves the RI change of 5 × 10^-4 with a reflectance signal margin of 50% and achieves a signal contrast of ~ 100%. The liquid MAFP cavity shows a sensitivity of ~ 996 nm/RIU when RI of liquid changes from 1.30 to 1.38. With tailoring the period of the metasurface maintaining its thickness, a signal contrast of ~ 100% is achieved for each specific RI range.

Gyroidal graphene/porous silicon array for exciting optical Tamm state as optical sensor

In this study, the optical Tamm state is excited for the first time using gyroidal graphene/porous silicon one-dimensional photonic crystal terminated by a gyroidal graphene layer. The gyroidal graphene and porous silicon are used to enhance the figure of merit and sensitivity of the based Tamm resonance photonic crystal sensor. By tuning different parameters like the angle of incidence, the thickness of the sample layer, and the thickness of the gyroidal graphene layer, we have reached the optimized sensor. The observation of resonant dips in the reflectance spectra is strong evidence that Tamm plasmon-polaritons exist with higher sensitivity (188.8 THz/RIU) and figure of merit (355,384 RIU-1) than previously reported structures. The proposed sensor recorded sensitivity and FoM higher 38% and 747% respectively than a similar structure composed of graphene sheets and porous silicon.

Infrared rainbow trapping via optical Tamm modes in an one-dimensional dielectric chirped photonic crystals

The phenomenon of trapping a broad spectrum of light is known as "rainbow trapping" and is achieved by using all-dielectric, hybrid metallo-dielectric, or all-metallic configurations. The latter architectures allow strong confinement but exhibit very high ohmic losses. This results in practical lifetimes of trapped modes to less than 1 ps. Therefore, novel strategies are required to be devised for trapping and, subsequently, releasing broadband electromagnetic field with lifetime >1ps. We present a rainbow trapping configuration using the excitation of multiple optical Tamm (OT) modes in an one-dimensional chirped photonic crystal (CPC) designed for adiabatically coupling counterpropagating modes. In the geometry, the backscattered phase undergoes multiple discontinuities (=π), which enables excitation of many OT modes in the presence of a thin plasmon-active metal, which is placed adjacent to the terminating layer of CPC. All the OT modes are spatially separated in the CPC, and the strong modal confinement manifests into group velocities as low as 0.17c. The time-domain simulations depict mode-localization in the dielectric sections of CPC, which manifest into lifetimes ∼3ps.

Applying Tamm plasmon polaritons for determining the birefringence of a thin film

The anisotropy of a thin film can be created by a wide variety of methods and it has found many applications. Liquid crystal (LC) molecules are aligned in a specific orientation on a rubbed polyimide film for conventional LC displays (LCDs). The rubbing process on the polyimide film controls the azimuthal and polar angles of the LCs, and it can cause physicochemical anisotropy on the polyimide film and produce the birefringence Δn in the azimuthal direction. Knowing the rubbing-induced optical axis of polyimide films is crucial for achieving optimum electro-optical properties of LCDs. The rubbing-induced Δn and the resolution less than 2 deg for determining the optical axis of the rubbed polyimide are obtained by applying Tamm plasmon polaritons in this Letter.

Flexible control of light trapping and localization in a hybrid Tamm plasmonic system

A hybrid Tamm plasmonic system is proposed to investigate light manipulation at near-infrared frequency. The numerical results reveal that two remarkable absorption peaks are generated due to the different types of resonant modes excited in the structure, which can be well explained theoretically by guided-mode resonance (GMR) and Tamm plasmon polaritons. It is found that the electromagnetic energy can be easily trapped in different parts of the structure. More importantly, strong interaction between the two modes can be achieved by adjusting the structure period or incident angle, resulting in obvious mode hybridization and exhibiting unique energy-transfer characteristics. In addition, the active modulation of GMR-based absorption can be controlled in a continuous type by tuning the polarization angle or in a jump type by adjusting the chemical potential of graphene. This work should be useful for developing many high-performance optoelectronic devices, including sensors, modulators, detectors, etc.

Strong longitudinal coupling of Tamm plasmon polaritons in graphene/DBR/Ag hybrid structure

In this paper, strong longitudinal coupling of the Tamm plasmon polaritons (TPPs) is investigated in a graphene/DBR/Ag slab hybrid system. It is found that TPPs can be excited at both the top graphene and the bottom silver slab interface, which can strongly interact with each other in this coupled structure. Numerical simulation results demonstrate that the vertical Tamm plasmon coupling can be either tuned by adjusting the geometric parameters or actively controlled by the Fermi energy in graphene sheet as well as the incident angle of light, allowing for strong light-matter interaction with a tunable dual-band perfect absorption. Moreover, the coupling strength of the hybrid modes exhibits a large tuning range, from a large Rabi splitting to an extremely narrow induced transparency in this coupled regime. Coupled mode theory has been employed to explain the strong coupling phenomenon. The controllable TPP coupling with an ultrahigh dual-band absorption capability offered by this simple layered structure opens new avenues for developing a broad range of graphene-based active optoelectronic and polaritonic devices.

Multiple adjustable optical Tamm states in one-dimensional photonic quasicrystals with predesigned bandgaps

We proposed an approach to get multiple and adjustable optical Tamm states (OTSs) by constructing a structure consisting of a metal layer and one-dimensional photonic quasicrystals with preassigned bandgaps. In the structure, multiple OTSs excited simultaneously in each bandgap were observed. We explored the physics mechanism of the multiple OTSs by analyzing the electric field intensity distribution in the structure. Besides, the results also show that the thickness of the top layer gives one more degree of freedom in designing multiple OTSs. Finally, we demonstrated that one additional OTS can be obtained independently by adding another bandgap to the proposed structure.

An Optical Fiber Refractive Index Sensor Based on the Hybrid Mode of Tamm and Surface Plasmon Polaritons

A novel high performance optical fiber refractive index (RI) sensor based on the hybrid transverse magnetic (TM) mode of Tamm plasmon polariton (TPP) and surface plasmon polariton (SPP) is proposed. The structure of the sensor is a multi-mode optical fiber with a one dimensional photonic crystal (1 DPC)/metal multi-films outer coated on its fiber core. A simulation study of the proposed sensor is carried out with the geometrical optical model to investigate the performance of the designed sensor with respect to the center wavelength, bilayer period and the thickness of silver layer. Because the lights transmitted in the fiber sensor have much larger incident angles than those in the prism based sensors, the center wavelength of the 1 DPC should shift to longer wavelength. When the coupling between TM-TPP and SPP is stronger, the sensor exhibits better performance because the electromagnetic field of the TPP-SPP hybrid mode is enhanced more in the analyte. Compared to most conventional fiber surface plasmon resonance sensors, the figure of merit of the proposed sensor is much higher while the sensitivity is comparable. The idea of utilizing TPP-SPP hybrid mode for RI sensing in the solid-core optical fiber structure presented in this paper could contribute to the study of the fiber RI sensor based on TPP.