Critical coupling vortex with grating-induced high Q-factor optical Tamm states

Observation of coupling interaction between surface plasmons and Tamm plasmons

The optical effect analogous to electromagnetically induced transparency (EIT) in atomic systems has attracted broad attention in the field of photonics due to its promising applications in optical storage and integrated devices. Herein, we firstly report the experimental observation of the EIT-like effect generated from the coupling between surface plasmons (SPs) and Tamm plasmons (TPs) in a hybrid multilayer system at the near-infrared band. This multilayer system is composed of a nanofabricated silver grating on a silver/Bragg mirror with a SiO2 spacer. The experimental results show that a narrow reflection peak can appear in the wide reflection spectral dip due to the coupling between the SPs in the silver grating and TPs in the silver/Bragg mirror, which agree well with the finite-difference time-domain (FDTD) simulations. It is also found that the dip position of the EIT-like spectrum presents a redshift with the increase of the silver grating width. These results will provide a new way, to the best of our knowledge, for the generation of the EIT-like effect and light spectral manipulation in multilayer structures.

Suppressing the radiation loss by hybrid Tamm-surface plasmon BIC modes

Tamm plasmon polaritons (TPPs), localized near the boundary of a dielectric Bragg reflector (DBR) and a thin metal film, have attracted much attention for the lower ohm loss and flexible excitation. However, the radiation loss resulting from the direct coupling to the surroundings hinders their applications. Here, we propose and experimentally demonstrate a new type of hybrid plasmonic quasi-bound state in the continuum (BIC) in a Tamm-surface plasmon polariton system to suppress the radiation loss. Leveraging the scattering of the periodic metal array, the TPP interacts with the surface plasmon polariton (SPP) mode and form a Friedrich-Wintgen type quasi-BIC state that originated from the interference of two surface waves with different natures. Through angle resolved reflectance spectrum measurement, the hybrid plasmonic quasi-BIC was observed in the experiment. Our work proposes a new method to design a high Q mode in plasmonic systems, and thus holds promise for applications in the field of light matter interactions.

Ultra-compact on-chip spectrometer based on thermally tuned topological miniaturized bound states in the continuum cavity

On-chip spectrometers are key components in many spectral sensing applications owing to their unique advantages in size and in situ detection. In this work, we propose and demonstrate a class of thermally tunable spectrometers by utilizing topological miniaturized bound states in the continuum (mini-BIC) cavities in a photonic crystal (PhC) slab combined with a metal micro-ring heater. We achieve a resolution of 0.19 nm in a spectral range of ∼6 nm, while the device's footprint is only 42×42μm2. The mini-BIC spectrometer works in nearly vertical incidence and is compatible with array operation. Our work sheds light on the new possibilities of high-performance on-chip spectrometers for applications ranging from bio-sensing to medicine.

Double-Resolved Beam Steering by Metagrating-Based Tamm Plasmon Polariton

We consider Tamm plasmon polariton in a subwavelength grating patterned on top of a Bragg reflector. We demonstrate dynamic control of the phase and amplitude of a plane wave reflected from such metagrating due to resonant coupling with the Tamm plasmon polariton. The tunability of the phase and amplitude of the reflected wave arises from modulation of the refractive index of a transparent conductive oxide layer by applying the bias voltage. The electrical switching of diffracted beams of the ±1st order is shown. The possibility of doubling the angular resolution of beam steering by using asymmetric reflected phase distribution with integer and half-integer periods of the metagrating is demonstrated.

A Bifunctional Silicon Dielectric Metasurface Based on Quasi-Bound States in the Continuum

Quasi-bound states in the continuum provide an effective and observable way to improve metasurface performance, usually with an ultra-high-quality factor. Dielectric metasurfaces dependent on Mie resonances have the characteristic of significantly low loss, and the polarization can be affected by the parameter tuning of the structure. Based on the theory of quasi-bound states in the continuum, we propose and simulate a bifunctional resonant metasurface, whose periodic unit structure consists of four antiparallel and symmetrical amorphous silicon columns embedded in a poly(methyl methacrylate) layer. The metasurface can exhibit an extreme Huygens’ regime in the case of an incident plane wave with linear polarization, while exhibiting chirality in the case of incident circular polarized light. Our structure provides ideas for promoting the multifunctional development of flat optical devices, as well as presenting potential in polarization-dependent fields.