Tianlin Yang

Differentiation of dried sea cucumber products from different geographical areas by surface desorption atmospheric pressure chemical ionization mass spectrometry.

Without any sample pretreatment, mass spectral fingerprints of 486 dried sea cucumber slices were rapidly recorded in the mass range of m/z 50-800 by using surface desorption atmospheric pressure chemical ionization mass spectrometry (DAPCI-MS). A set of 162 individual sea cucumbers (Apostichopus japonicus Selenka) grown up in 3 different geographical regions (Weihai: 59 individuals, 177 slices; Yantai: 53 individuals, 159 slices; Dalian: 50 individuals, 150 slices;) in north China sea were successfully differentiated according to their habitats both by Principal Components Analysis (PCA) and Soft Independent Modeling of Class Analogy (SIMCA) of the mass spectral raw data, demonstrating that DAPCI-MS is a practically convenient tool for high-throughput differentiation of sea cucumber products. It has been found that the difference between the body wall tissue and the epidermal tissue is heavily dependent on the habitats. The experimental data also show that the roughness of the sample surface contributes to the variance of the signal levels in a certain extent, but such variance does not fail the differentiation of the dried sea cucumber samples.

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.

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.

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-Perot 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.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-Perot 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.

Optical resonant tunneling in photonic heterostructures containing a tunable dielectric layer

We demonstrate theoretically and experimentally that complete light transmission can be realized using a photonic heterostructure containing a tunable dielectric layer inserted between two different truncated photonic crystals (PCs). A perfect tunneling state is produced within enlarged photonic band gap (PBG) of the heterostructure by varying the thickness of inserted dielectric layer and the transmittance of the tunneling state depends on the dielectric layer thickness. Additionally, the tunneling state frequency varies with inserted layer thickness but is always located within the small overlapped PBG of two PCs. Therefore, both a perfect tunneling state and an ultrawide PBG can be realized in these heterostructures. The experimental results showed good agreement with theoretical values.