Xiaobin Ren

Controlling light transport by using a graded photonic crystal

Light transport in a graded photonic crystal is studied using the finite-difference time-domain technique. The photonic crystal consists of a square lattice of elliptical dielectric rods. Within a frequency window, light can propagate inside the photonic crystal with the beam width nearly unchanged. The propagation direction can be easily manipulated by the structure gradient, which is achieved by gradually varying the orientation of the elliptical rods. The degree of control over the flow of light can be modulated by changing the ellipticity. This provides a promising approach to design of optical devices for spatial-beam routing.

Tunable compact nanosensor based on Fano resonance in a plasmonic waveguide system

An ultracompact plasmonic refractive index sensor based on Fano resonance is proposed. The sensor comprises a metal-insulator-metal waveguide with a stub and a side-coupled split-ring resonator. The effect of structural parameters on Fano resonance and the refractive index sensitivity of the system are analyzed in detail by investigating the transmission spectrum. Simulation results show that Fano resonance has different dependences on the parameters of the sensor structure. The reason is further discussed based on the field pattern. The peak wavelength and lineshape can be easily tuned by changing the key parameters. Furthermore, dual Fano resonance effects with different frequency intervals are obtained, which are mainly induced by the symmetry breaking of the structure. The proposed sensor yields sensitivity higher than 1.4×103  nm/RIU and a figure of merit of 1.2×105. The sensitivity and figure of merit can be further improved by optimizing the geometry parameters.

Investigation on Yb3+∕Er3+∕Tm3+ tri-doped phosphate glass ceramic for white-light-emitting diode.

Yb3+∕Er3+∕Tm3+ tri-doped phosphate glass ceramics were prepared by a high-temperature melting method and thermal treatment technology. Upconversion (UC) emissions of the Yb3+∕Er3+∕Tm3+ tri-doped phosphate glass ceramic samples were studied under 975 nm excitation. The glass ceramic samples can simultaneously generate blue, green, and red emissions. The multicolor emission obtained was tuned to white light by adjusting the Er3+ ion concentration. The emission color of the sample doped with 8 mol.% Er3+ ion is white to the naked eye, and CIE coordinates (x=0.316, y=0.354) of the sample are close to the standard equal energy white-light illumination (x=0.333, y=0.333). The material will be useful in developing the white-light-emitting diode.

Self-Reference Refractive Index Sensor Based on Independently Controlled Double Resonances in Side-Coupled U-Shaped Resonators

A plasmonic, refractive, index nanosensor is investigated theoretically and numerically in two U-shaped cavities side-coupled to a metal–dielectric–metal (MDM) waveguide. A transparency window between two transmission dips is observed. The physical origin of the transmission phenomenon is revealed by mapping the magnetic field distribution. Independent double resonances are realized through the proposed design. Double resonances showed diverse responses to the variations of the structural dimensions. In particular, they presented different dependences on a refraction index of the medium in an individual resonator. One resonance exhibited a remarkable shift with the increase of the refraction index; however, the other resonance remained unchanged. On the basis of this unique characteristic of differing sensitivities, self-reference sensing is discussed. The nanosensor yielded a high sensitivity of 917 nm/RIU and a figure of merit of 180 RIU−1. This work is helpful in terms of the design of on-chip optical sensors with high sensitivity and improved detection accuracy in complicated environments.