Optical Tamm States Research Articles

Chiral Optical Tamm States at the Interface between an All-Dielectric Polarization-Preserving Anisotropic Mirror and a Cholesteric Liquid Crystal

As a new localized state of light, the chiral optical Tamm state exists at the interface between a polarization-retaining anisotropic mirror and a substance with optical activity. Considering a hybrid structure comprising a metal-free polarization-preserving mirror and a cholesteric liquid crystal, we highlight the high Q factor arising from the all-dielectric framework. The intensity of localized light decreases exponentially with increasing distance from the interface. The penetration of the field into the cholesteric liquid crystal is essentially prohibited for wavelengths lying in the photonic bandgap and close to the cholesteric pitch length. The dielectric mirror has its own photonic bandgap. The energy transfer along the interface can be effectively switched off by setting the tangential wave vector to zero. The spectral behavior of the chiral optical Tamm state is observed both as reflection and transmission resonance. This Fano resonance is analogous to the Kopp–Genack effect. Our analytics are well in line with precise calculations, which may pave a new route for the future development of intelligent design for laser and sensing applications.

Tunable and Multichannel Terahertz Perfect Absorber Due to Tamm Plasmons with Topological Insulators

In this paper, Tamm plasmons with topological insulators in a composite structure consisting of Bi2Se3, spacer layer, and one-dimensional photonic crystal (1DPC) have been demonstrated theoretically. The perfect absorption has been realized in the terahertz regime because of the optical Tamm states (OTSs) excited at the interface between Bi2Se3 and 1DPC. The perfect absorption can be realized for both TE and TM waves, and it is noted that the perfect absorption can be obtained at any incident angle by simultaneously changing the wavelength of incident light for TE-polarizations. Moreover, the perfect absorption can be realized at different wavelengths with the change of the chemical potential and the thickness of Bi2Se3. The thickness and the dielectric constant of the spacer layer will also play a vital role in the performance of the perfect absorber. Especially, the multichannel perfect absorption phenomenon can be achieved by choosing the appropriate thickness of the spacer layer. This tunable and multichannel terahertz perfect absorber has great application potential in the solar energy, photodetection, and THz biosensor.

Narrow-band plasmon absorption enabled by manipulating geometric phase of plasmonic waveguides

We investigate the relationship between the absorption performance and the topological properties of metal-dielectric-metal (MDM) plasmonic waveguides, where 1D photonic crystals are inserted inside the waveguide core. We demonstrate that the reflection phase, within the bandgaps of the considered MDM waveguide, is related to both the geometric Zak phase in a bulk band and the formation of the optical Tamm state. The strong field confinement induced by the optical Tamm state results in narrow-band absorption of the propagating surface plasmons. We also show that both the reflection phase and the bandgap topological characteristics of the MDM waveguide can be manipulated by varying the geometric parameters of the inserted photonic crystals. By suitably designing the topological properties of the plasmonic waveguide, narrow-band plasmon absorption is achieved at specific bandgaps. An absorption band with a linewidth smaller than 7 nm and a high quality factor of 91.5 is obtained which can potentially be used for filtering, sensing, imaging, etc. Our work provides a novel way to design topological plasmonic devices for nanoscale integrated photonic circuits.

Tamm phonon-polaritons: Localized states from phonon-light interactions

We present experimental evidence of optical Tamm states at the interface of a one-dimensional photonic crystal made of porous Si and hexagonal SiC. This phenomenon occurs in the mid-infrared within the Reststrahlen band where SiC optically behaves as a metal due to phonons. We name the observed interface states Tamm phonon-polaritons by analogy to Tamm plasmon-polaritons at the interface of a photonic crystal and a metal. The high quality factor of the observed resonance makes polar dielectrics attractive materials to achieve Tamm states in the mid-infrared, which could benefit applications such as selective thermal emission and mid-infrared sensing.

The interaction between optical Tamm state and microcavity mode in a planar hybrid plasmonic-photonic structure

We have studied the mode hybridization between the optical Tamm state and a microcavity mode in a planar hybrid plasmonic-photonic crystal structure. The optical Tamm state appears as an allowed mode within the photonic stop gap of the photonic crystal structure. Unlike the conventional microcavity mode which localizes its energy inside the structure, the Tamm mode localizes its optical energy at the interface between the plasmonic layer and photonic crystal structure. The strong coupling between the Tamm and microcavity mode is achieved through evoking the Tamm mode dependence of the top layer thickness of the hybrid structure. The Tamm and microcavity mode exhibit an avoided crossing characteristics in the strong coupling regime with a Rabi splitting of 4.3 meV. The electric field intensity is calculated to confirm the indistinguishability of individual modes in the exact coupling regime. The electric field intensity is spatially localized both at the interface and deep within the photonic crystal structure. The structural parameters that would influence the strong coupling between the modes are also discussed.

Non-reciprocal Transmission of Electromagnetic Waves in Asymmetric Photonic Crystals

Abstract The non-reciprocal transmission properties of transverse electric (TE) mode waves are investigated for two asymmetric, complex photonic crystals composed of magnetic gyrotropic and normal media. Three pairs of non-reciprocal transmission peaks in three different bandgaps for forward and backward waves occur because of optical Tamm states (OTSs) at the interface between the photonic crystals. Numerical results indicate that the non-reciprocal transmission properties are influenced by the incident angles, gyrotropic permeability, and number of layers of the photonic crystals. The asymmetric structure with multiple non-reciprocal transmission peaks at a certain incident angle can provide promising opportunities for the design of multichannel isolators.

Highly Selective CMOS-Compatible Mid-Infrared Thermal Emitter/Detector Slab Design Using Optical Tamm-States.

In this work, we propose and evaluate a concept for a selective thermal emitter based on Tamm plasmons suitable for monolithic on-chip integration and fabrication by conventional complementary metal oxide semiconductor (CMOS)-compatible processes. The original design of Tamm plasmon structures features a purely one-dimensional array of layers including a Bragg mirror and a metal. The resonant field enhancement next to the metal interface corresponding to optical Tamm states leads to resonant emission at the target wavelength, which depends on the lateral dimensions of the bandgap structure. We demonstrate the application of this concept to a silicon slab structure instead of deploying extended one dimensional layers thus enabling coupling into slab waveguides. Here we focus on the mid-infrared region for absorption sensing applications, particularly on the CO2 absorption line at 4.26 µm as an example. The proposed genetic-algorithm optimization process utilizing the finite-element method and the transfer-matrix method reveals resonant absorption in case of incident modes guided by the slab and, by Kirchhoff’s law, corresponds to emittance up to 90% depending on different choices of the silicon slab height when the structure is used as a thermal emitter. Although we focus on the application as an emitter in the present work, the structure can also be operated as an absorber providing adjusted lateral dimensions and/or exchanged materials (e.g., a different choice for metal).

Spatial confinement of the optical Tamm states under patterned metal films

Optical Tamm states are defect electromagnetic modes which appear at the discontinuity of the optical crystal. Being trapped at the interface of a dielectric Bragg mirror and a metal they demonstrate a tight localization in the direction perpendicular to the interface. Here we study the trapping of the Tamm states in the interface plane by patterning of the metal layer. In particular, we propose a method of metal film deposition based on a electro-induced lithography which possesses a nanometer lateral resolution.

Manipulating optical Tamm state in the terahertz frequency range with graphene

The optical Tamm state (OTS), which exists generally at the interface between metal and a dielectric Bragg mirror, has been studied extensively in the visible and near infrared spectra. Nevertheless, OTS in the terahertz (THz) region normally receives far less attention. In this Letter, we demonstrate the physical mechanism of OTS at the interface between graphene and a dielectric Bragg mirror in the THz frequency band by applying the transfer matrix method and dispersion characteristics. Based on such mechanisms, we propose an efficient method that can precisely generate and control OTS at a desired angle and frequency. Moreover, we show that the OTS is dependent on the optical conductivity of graphene, making the graphene–dielectric-Bragg-mirror a good candidate for dynamic tunable OTS device in the THz frequency range.

对称结构光子晶体的表面光学Tamm态

对称结构光子晶体的表面光学Tamm态

Enhanced Reflected Group Delay with Optical Tamm State via Graphene-Dielectric Bragg Mirror Configuration

Group delay of the optical pulse reflected from the structure composed of graphene and one dimensional photonic crystal (1D PC) is studied. It is shown that the large negative group delay in this configuration can be realized due to the excitation of the optical Tamm state (OTS) at a graphene-dielectric interface. The reflected group delay can be enlarged negatively and can be switched from positive to negative or vice versa. We show that the conductivity of graphene has a significant influence on reflected group delay, making the graphene-PC structure be a good candidate for dynamic tunable optical delay device in the THz frequencies. Furthermore, the influences of the relaxation time of graphene, the incident angel, and the dispersion characteristics of top layer on group delay are clarified.

Graphene Tamm plasmon-induced giant Goos–H?nchen shift at terahertz frequencies

In this Letter, we have shown that a giant Goos–Hanchen shift of a light beam reflected at terahertz frequencies can be achieved by using a composite structure, where monolayer graphene is coated on one-dimensional photonic crystals separated by a dielectric slab. This giant Goos–Hanchen shift originates from the enhancement of the electrical field, owing to the excitation of optical Tamm states at the interface between the graphene and one-dimensional photonic crystal. It is shown that the Goos–Hanchen shift in this structure can be significantly enlarged negatively and can be switched from negative to positive due to the tunability of graphene’s conductivity. Moreover, the Goos–Hanchen shift of the proposed structure is sensitive to the relaxation time of graphene and the thickness of the top layer, making this structure a good candidate for a dynamic tunable optical shift device in the terahertz regime.

Colored semitransparent polymer solar cells with a power conversion efficiency of 9.36% achieved by controlling the optical Tamm state

Herein, 9.36% PCE of ST-PSCs was achieved by controlling the OTS formed at the interface between thin Ag and EAL/1DPCs.

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.

Graphene Tamm plasmon-induced low-threshold optical bistability at terahertz frequencies

In this paper, the low-threshold optical bistability (OB) of a reflected light beam at terahertz frequencies is achieved by using a multilayer structure where monolayer graphene is coated on one-dimensional photonic crystal (1D PC) separated by a top layer. This low-threshold OB phenomenon originates from the enhancement of the electrical field owing to the excitation of optical Tamm states (OTSs) at the interface between the graphene and 1D PC. It is found that the hysterical behavior of the reflected light can be electrically controlled by properly varying the applied voltage on the graphene. Moreover, the bistable behavior of the proposed structure is proved sensitive to incidence angle and the dispersion characteristics of the top layer, thus making this configuration a prime candidate for future experimental investigation at the terahertz range.

Optical Tamm state aided room-temperature amplified spontaneous emission from carbon quantum dots embedded one-dimensional photonic crystals

Optical Tamm state (OTS) aided room-temperature amplified spontaneous emission (ASE) from carbon quantum dots (CQDs) embedded all-dielectric one-dimensional photonic crystals (1DPhCs) is presented. 1DPhCs, constituting twelve pairs of alternating quarter wave thick SiO2 and TiO2 thin films are fabricated by sol-gel synthesis route. The 1DPhCs are covered with ~50 nm thick silver thin film to obtain the Tamm structures. CQDs are prepared using organic precursors (onion pulp) and incorporated in the TiO2 matrix of the final four pairs of the 1DPhCs. OTSs are observed in the reflection spectra at a detection angle of ~15°, at ~648 nm and ~618 nm, for the samples with and without CQDs respectively. Comparisons of enhancement of photoluminescence from samples with and without CQDs are presented. ASE at ~648 nm corresponding to the OTS of the CQDs incorporated Tamm structure, and suppression of emission within the photonic stop-band is demonstrated.

Coupled Chiral Optical Tamm States in Cholesteric Liquid Crystals

The modes formed by two coupled chiral optical Tamm states localized at the interfaces between a photonic cholesteric liquid crystal conjugated with polarization-preserving anisotropic mirrors have been analytically and numerically investigated. These modes are only excited at the diffracting polarization of incident light. As the cholesteric layer thickness decreases, the spectral splitting of the localized state frequency is predicted. The splitting value depends on the crystal layer thickness. At the nondiffracting circular polarization, the localized modes are not excited, and the system becomes similar to the Fabry–Pérot cavity containing an anisotropic helical structure.

Tunable Terahertz Absorption with Optical Tamm State in the Graphene-Bragg Reflector Configuration

Tunable terahertz absorption in the interface between graphene and dielectric Bragg reflector (DBR) has been numerically demonstrated. The near perfect absorption mainly originates from the enhancement of the electric field owing to the excitation of the optical Tamm state (OTS) at the interface between graphene and dielectric Bragg mirror. It has been found that the absorption peak occurs at specific incident angles, which can be employed for realizing the frequency and angular absorbers. Further, we demonstrate that the position of the absorption peak can be tuned by changing the Fermi energy of graphene. Moreover, the behaviors of the near perfect absorption are strongly related to the dielectric constants and thicknesses of the surrounding dielectrics. The tunability of graphene-DBR structure absorption may help to find favorable applications for the realization of high-performance graphene optoelectronic devices.

Multichannel unidirectional perfect absorbers on sandwich structures with truncated symmetric photonic crystals

We experimentally studied unidirectional perfect absorbers with asymmetric sandwich structures composed of two thick metallic films with different thicknesses and a truncated symmetric photonic crystal (PC). Single-channel and multichannel near-perfect absorbers were obtained by adjusting period number of the PC. According to electromagnetic field intensity distributions at absorption wavelengths, the physical mechanism of near-perfect absorption derived from the coupling effect between optical Tamm state and Fabry-Pérot resonance. The unidirectional absorption phenomena were attributed to weak electric field distributions at absorption wavelengths for opposing directions of light incidence. The experimental values showed good agreement with theoretical results.

An efficient and directional optical Tamm state assisted plasmonic nanolaser with broad tuning range

In recent years, nanolasers based on plasmonic crystal nanocavity structures have attracted significant interest. However, the performance of such lasers is affected significantly by the coupling of the lasing emission to both reflection and transmission sides of the device and to multiple spatial modes in the far field due to higher-order diffraction from plasmonic crystals as well. In this work, we propose a nanolaser design that overcomes the performance degradation of plasmonic crystal based nanolasers and increases the emission intensity significantly. In the proposed nanolaser structure, a nanometer-thick gain medium has a one-dimensional photonic crystal on one side and a metal nanohole array on the other side. An incident pump pulse through the one-dimensional photonic crystal excites optical Tamm states at the metal-gain medium interface that are amplified by the stimulated emission of the gain medium. We find that the intensity of the extraordinary optical transmission through the metal nanohole array increases significantly due to the excitation of optical Tamm states with wavevector perpendicular to the nanohole array surface. We also find that the subwavelength periodicity in the nanohole array confines the lasing emission to the zero-th order mode only, and hence, makes the far-field pattern highly directional. Moreover, the laser emission wavelength can be tuned over a broad range by changing the thicknesses of the photonic crystal layers, gain medium, and in real-time, by changing the angle of incidence of the pump pulse.