Xunan Chen

Realizing near-perfect absorption at visible frequencies

Sub-wavelength hole array (SHA) combined with thick metal layer (TML) is shown to have simultaneous suppressed transmission and reflection, resulting near-perfect absorption. Unlike the simultaneous electric and magnetic resonances in electric ring resonator and cut wire [PRL, 100, 207402 (2008)], such behavior results from strong anti-symmetric surface plasmons coupling supported by SHA and TML. The polarization-free characteristic permits to construct an ideal absorber for some practical applications in turbid backgrounds.

Analysis of optical SHG in photonic crystal consisting of centro-symmetric dielectric

Optical second harmonic generation (OSHG) in a two-dimension photonic crystal consisting of centro-symmetric dielectric is investigated. The calculation model and analyzing method for OSHG are discussed. Based on Finite Difference-Time Domain algorithm, the electromagnetic field distribution in the structure and the intensity of second harmonic generation along the waveguide are analyzed. The results show that the acute spatial variation of electro-magnetic field results in the radiation of OSHG, and the intensity of OSHG is proportional to the square of the waveguide length. When the beam intensity of the pumping wave with a wavelength of 10.6 microm is 1.3MW/mm2, the power conversion efficiency is 0.268% for a silicon photonic crystal with a length of 40 microm.

Analysis of sensing performance of Gaussian-shaped metallic nanogratings

A new type of structure which is composed of a Gaussian profile-shaped metallic nanograting, was put forth from the nanofabrication point of view. Dependence of the structural parameters on the sensitivity was analyzed by means of a multiple multipole program (MMP) method. One of the important applications of the nanograting is in biosensing: immunoassay. Our numerical simulation results showed that the sensitivity to refractive index of 490 nm/RIU and the reflection spectra at site of full-width at halfmaximum (FWHM) ~9 nm can be obtained through the optimized structure. The figure of merit (FOM) of the sensor can exceed 55. The resonant wavelength increases linearly with increasing of the refractive index of bio-samples. These reflection properties make the nanograting more suitable to be used in the localized surface plasma resonance (LSPR)-based biosensors for immunoassay.

Design of Gaussian-Shaped and Double Sides Flanked Metallic Nano-Grating Surface Plasma Resonance Biosensors

In this paper, a new type of gaussian-shaped metallic nano-grating surface plasma resonance (NGSPR) biosensors and the design optimization process are presented in nano fabrication point of view. The influence of structural factors of nano- corrugations on the sensitivity of NGSPR sensors was investigated using the multiple multipole program (MMP) method. Biosensors with the line width of the gaussion profile about 50nm and the depth of the gaussion profile about 30nm show narrow and deep reflection peaks .The wavelength of the resonance reflection can be customized by adjusting the grating period. We predict that a high refractive idex sensitivity about 420nm/RIU can be obtained using our optimized structure. Sharp reflection resonance peaks with the full-width at half-maximum (FWHM) of 6nm will further increase the figure of merit (FOM) of the sensor. These reflection properties make it possible to be used as NGSPR biosensors.

Acetic Acid Vapor Detection via Field Ionization From Carbon Nanotube

A novel, high-efficiency detector for acetic acid vapor in ambient air is described. The design uses carbon nanotubes, grown on silicon substrate by CVD. Application of a positive bias to the carbon nanotubes generates electric fields sufficient to field-ionize passing gas-phase atoms especially for organic vapor. Under the pressure of one standard atmospheric pressure (atm), the detector was demonstrated to be capable of ionizing and detecting the acetic acid vapor and with a linear response over the entire range from 0 to 100 ppm AA.