Guiqiang Du

Phase-sensitive Bloch surface wave sensor based on variable angle spectroscopic ellipsometry

In this paper, we propose a phase-sensitive Bloch surface wave sensor based on the variable angle spectroscopic ellipsometry and numerically simulate the phase behavior of the sensor. The simulation results show that the dependence of resonant phase is step-like when BSWs are excited. In contrast to the reflectance behavior, even though losses of the dielectric layers are very small, the resonance dip in the reflectivity will be shallow while the step-like change of the reflection phase of the BSW still be remarkable. This means that phase detection is an alternative to reflectivity intensity detection for the sensing applications of the BSWs in this case. Our experimental results indicate that phase detection for the BSW sensors has the potential to achieve the higher sensitivity and the lower limit of detection.

Phase properties of Bloch surface waves and their sensing applications

We study the phase properties of Bloch surface waves (BSWs) on truncated one-dimensional photonic crystals and find an abrupt change of the phase induced by BSWs. The phase of the BSW device shows a prominent response to the refractive index changes of the environment under resonance conditions. Furthermore, we demonstrate that the phase sensitivity of the BSW device is higher by nearly 1 order of magnitude than its amplitude sensitivity in terms of the figure of merit. This means that phase detection can be utilized to enhance the sensitivity of the BSW devices.

Optical Tamm states in hetero-structures with highly dispersive planar plasmonic metamaterials

Optical Tamm states (OTSs) in hetero-structures consisting of highly dispersive planar plasmonic metamaterials and truncated photonic crystal (PC) are investigated numerically. Compared to conventional OTSs in metal-PC structures, the reflectance of tunneling mode can be reduced from −10.2 dB to −32.0 dB, with an optimized Q-factor up to 17 times higher simultaneously. Further study on electromagnetic (EM) field distribution confirms that EM waves are highly localized at some special points. The confinement along the propagating direction provided by OTSs and the in-plane localization originated from the planar plasmonic metamaterials give rise to the three-dimensional enhancement of sub-wavelength EM localization corporately. As the advantages above are not at a cost of extra device volume, this structure is promising to be applied in highly sensitive dielectric sensing, nonlinear optical devices, and so on.

Enhancement of optical effects in zero-reflection metal slabs based on light-tunneling mechanism in metamaterials

Metals have many extraordinary optical properties. However, thick metals are nice mirrors, which prevent light penetrating deep into them. Since the skin depth is very thin, most optical properties of bulk metals are unavailable. In this paper, we review the way of reducing reflections in thick metal slabs by coating dielectric photonic crystals, based on the light-tunneling mechanism in metamaterials. Owing to the boost of local fields in the metals, many optical effects such as nonlinear effects, optical extinction (absorption) and optical rotation are greatly enhanced in these simple structures. The enhancement of optical effects in thick metals may be very useful in some optical devices including optical switches and diodes, absorbers, insulators and so on.

Electronic resonant tunneling on graphene superlattice heterostructures with a tunable graphene layer

We have theoretically investigated the electronic resonant tunneling effect in graphene superlattice heterostructures, where a tunable graphene layer is inserted between two different superlattices. It is found that a complete tunneling state appears inside the enlarged forbidden gap of the heterostructure by changing the thickness of the inserted graphene layer and the transmittance of the tunneling state depends on the thickness of the inserted layer. Furthermore, the frequency of the tunneling state changes with the thickness of the inserted graphene layer but it always located in the little overlapped forbidden gap of two graphene superlattices. Therefore, both a perfect tunneling state and an ultrawide forbidden gap are realized in such heterostrutures. Since maximum probability densities of the perfect tunneling state are highly localized near the interface between the inserted graphene layer and one graphene superlattice, it can be named as an interface-like state. Such structures are important to fabricate high-Q narrowband electron wave filters.

Experimental investigation of multiple near-perfect absorptions in sandwich structures containing thin metallic films

We experimentally investigated near-perfect optical absorption in sandwich structures comprising a thin metallic film whose thickness is larger than the skin depth, a top dielectric layer and a truncated photonic crystal. Single and multiple near-perfect absorptions were realized by tuning the thickness of the top layer. Based on the electromagnetic field intensity distributions at the absorption wavelengths, single near-perfect absorption originated from the tunneling effect of the optical Tamm state, while multiple near-complete absorptions mainly originated from Fabry-Perot resonances. Additionally, the structures showed good one-way absorption properties. The experimental results agreed well with theoretical values. These structures may be important for the fabrication of single or multichannel perfect absorbers.

Multiple and broadband near-perfect absorption in heterostructures containing transparent conducting oxides

We demonstrate theoretically that the multiple and wideband near-perfect absorption can be realized in heterostructures that are composed of two different truncated photonic crystals (PCs), where one contains conducting-indium tin oxide (ITO) films. Furthermore, near-complete absorption can be achieved over a wide angle of incidence for both TE and TM polarizations. The width of the absorption band is determined by the overlapped range between the pass band of the PC containing ITO films and the forbidden band of the other PC. Moreover, the absorption band can be broadened by increasing the incident angle for the TE polarization. These absorption properties are important for designing multiple or broadband near-perfect absorbers in the visible and near infrared regions.

Broad flattop transparent photonic band in truncated photonic crystals composed of the symmetric unit cell

We theoretically show that a one-dimensional finite all-dielectric periodic structure composed of symmetric unit cells can possess a broad flattop transparent photonic band. In contrast to the conventional viewpoint that the thickness of the truncated photonic crystals affects the transmission within the pass band, the transparent photonic band is insensitive to the change of the periodic number since the equivalent refractive indices of our structures can be nearly equal to that of the background in a wide frequency range. With easy fabrication, this broad flattop transparent photonic band will play an important role in the broadband filtering.

Perfect absorption of the graphene with truncated photonic crystals

We theoretically investigated the optical absorption properties of graphene monolayer on the top of the truncated dielectric photonic crystals deposited on a prism in the visible range. Perfect absorption are realized since the Bloch modes are excited on the surface of the graphene monolayer. Furthermore, it is found that total absorption can be achieved at special oblique incident angles for both transverse electric and transverse magnetic polarizations. These absorption properties are important for designing high-quality graphene-based optoelectronic devices.