Han Ye

The sensing characteristics of plasmonic waveguide with a ring resonator

A surface plasmon polaritons (SPPs) refractive index sensor which consists of two metal-insulator-metal (MIM) waveguides coupled to each other by a ring resonator is proposed. The transmission properties are numerically simulated by finite element method. The sensing characteristics of such structure are systematically analyzed by investigating the transmission spectrum. The results indicate that there exist three resonance peaks in the transmission spectrum, and all of which have a linear relationship with the refractive index of the material under sensing. Through the optimization of structural parameters, we achieve a theoretical value of the refractive index sensitivity as high as 3460nmRIU(-1). Furthermore, this structure can also be used as a temperature sensor with temperature sensitivity of 1.36nm/°C. This work paves the way toward sensitive nanometer scale refractive index sensor and temperature sensor for design and application.

Critical Thickness and Radius for Axial Heterostructure Nanowires Using Finite-Element Method

Finite-element methods are used to simulate a heterostructured nanowire grown on a compliant mesa substrate. The critical thickness is calculated based on the overall energy balance approach. The strain field created by the first pair of misfit dislocations, which offsets the initial coherent strain field, is simulated. The local residual strain is used to calculate the total residual strain energy. The three-dimensional model shows that there exists a radius-dependent critical thickness below which no misfit dislocations could be generated. Moreover, this critical thickness becomes infinity for a radius less than some critical values. The simulated results are in good agreement with the experimental data. The critical radius from this work is smaller than that obtained from previous models that omit the interaction between the initial coherent strain field and the dislocation-induced strain field.

The electronic and magnetic properties of (Mn,N)-codoped ZnO from first principles

The electronic and magnetic properties of (Mn,N)-codoped ZnO are studied within the framework of the density functional theory, by using the Perdew–Burke–Ernzerhof form of generalized gradient approximation. Five geometrical configurations of Mn doped ZnO are investigated and antiferromagnetic (AFM) properties of Mn doped ZnO are demonstrated. Furthermore, by investigating 13 geometrical configurations, for (Mn,N)-codoped ZnO, the ground state is changed from no-metallic AFM to half-metallic ferromagnetic, which is due to the strong hybridization between N 2p and Mn 3d states. In addition, the most stable configurations are found to be –O–Mn–N–Mn–O–.

Plasmonic metamaterial for electromagnetically induced transparency analogue and ultra-high figure of merit sensor

In this work, using finite-difference time-domain method, we propose and numerically demonstrate a novel way to achieve electromagnetically induced transparency (EIT) phenomenon in the reflection spectrum by stacking two different types of coupling effect among different elements of the designed metamaterial. Compared with the conventional EIT-like analogues coming from only one type of coupling effect between bright and dark meta-atoms on the same plane, to our knowledge the novel approach is the first to realize the optically active and precise control of the wavelength position of EIT-like phenomenon using optical metamaterials. An on-to-off dynamic control of the EIT-like phenomenon also can be achieved by changing the refractive index of the dielectric substrate via adjusting an optical pump pulse. Furthermore, in near infrared region, the metamaterial structure can be operated as an ultra-high resolution refractive index sensor with an ultra-high figure of merit (FOM) reaching 3200, which remarkably improve the FOM value of plasmonic refractive index sensors. The novel approach realizing EIT-like spectral shape with easy adjustment to the working wavelengths will open up new avenues for future research and practical application of active plasmonic switch, ultra-high resolution sensors and active slow-light devices.

Numerical analysis of a near-infrared plasmonic refractive index sensor with high figure of merit based on a fillet cavity

A near-infrared plasmonic refractive index (RI) sensor with figure of merit (FOM) as high as 124.6 is proposed and investigated numerically. The RI sensing is realized by employing the linear relation between resonant wavelength and RI of the material under detecting. Based on the fillet cavity coupled with two metal-insulator-metal waveguides, transmission efficiency (T) and optical resolution (FWHM) of the RI sensor are both improved to a great extent with T = 95% and FWHM = 12nm, keeping acceptable wavelength sensitivity of 1496nm/RIU within the near-infrared region. In addition, a sensitivity as high as 3476nm/RIU is obtained by optimizing the shape and size of fillet cavity. In general, the high FOM, transmittance and sensitivity achieved by our design may get further applications in biomedical science and nanophotonic circuits.

Critical lateral dimension for a nanoscale-patterned heterostructure using the finite element method

The finite element method (FEM) is used to simulate the combined strained InxGa1−xAs epitaxial layer and the interfacial dislocation on a nanoscale-patterned GaAs substrate. The critical thickness is calculated based on the overall energy balance approach. Three-dimensional models show that there exists a lateral dimension-dependent critical thickness below which no misfit dislocation is generated. Moreover, this critical thickness becomes infinite for a lateral dimension less than some critical value. The result indicates that an arbitrarily thick coherent epilayer is obtained when the substrate is patterned to a dimension smaller than the critical lateral dimension. The possibility of the dislocation-free growth derives from the three-dimensional stress relief mechanisms.

The optimal structure of two dimensional photonic crystals with the large absolute band gap.

This paper reports a new designed square lattice GaAs structure of two-dimensional photonic crystals with absolute band gap approach to 0.1623 (2πc/a), where a is the period of the square lattice. The optimal structure is obtained by combining the Geometry Projection Method and Finite Element Method. Both gradient information and symmetric control points are introduced to reduce the calculation cost. For benefit to the fabrication in reality, the structure is simplified by the combination of triangle and rectangular geometry. Through parameter optimization, the absolute band gap of the new structure is improved to 0.1735 (2πc/a), which is much larger than those reported before. The new PC structure is convenient and stab for fabrication, and may be found applications in the future optical devices.

Ultra-compact broadband mode converter and optical diode based on linear rod-type photonic crystal waveguide

In this paper, we present extremely compact designs of both broadband mode converter and optical diode in linear rod-type photonic crystal (PhC) waveguide with functional region consisting of only 4 × 1 unit cells of perfect PhC. The dielectric distribution inside functional region are optimized by combining geometry projection method and method of moving asymptotes. Bidirectional mode converter realizes above 60% transmission efficiency within bandwidth 0.02c/a, where c and a represent light velocity and PhC lattice constant respectively. Optical diode achieves above 19 dB unidirectionality for even mode within bandwidth 0.01c/a. Moreover, the proposed designs have reasonable tolerance of rod boundary fluctuation. We expect the results will help developing recipes for future PhC devices in all-optical integrated circuits.

Tuning the Fano resonances in a single defect nanocavity coupled with a plasmonic waveguide for sensing applications

A novel surface plasmon polaritons (SPPs) refractive index sensor based on a single defect nanocavity coupled with a metal–insulator–metal (MIM) waveguide is proposed and numerically simulated by using the finite difference time domain (FDTD) method with perfectly matched layer absorbing boundary condition. It is found that the defect structure can realize two Fano resonances and these two Fano resonances originate from two different mechanisms. The results demonstrate the liner correlation between the resonance wavelengths of the device and the refractive index of the material under sensing. Through the optimization of structural parameters, we achieve a theoretical value of the refractive index sensitivity as high as 1800.4 nmRIU−1. It could be utilized to develop ultra-compact nanodevice for high-resolution biological sensing.

Realization of compact broadband optical diode in linear air-hole photonic crystal waveguide.

In this paper, we present a compact broadband design for reciprocal optical diode in linear two-dimensional air-hole photonic crystal waveguide. The forward even-to-odd mode conversion and backward blockade of even mode are achieved by introducing the functional region with 1.2a×2.8a area. The inside dielectric distribution is obtained by finite element method combining geometry projection method and the method of moving asymptotes. In our design, only one asymmetrically deformed air hole locates in the functional region. The parabola-like unidirectionality keeps higher than 15dB within the operational bandwidth 0.01c/a (about 40nm when 1550nm is the center wavelength), and the maximum value reaches approximate 24 dB near the center frequency. Meanwhile, the forward transmission efficiency keeps higher than 89.9%. Moreover, the optical diode effect of the proposed design is validated in three-dimensional model and the tolerance of the imperfection in fabricating is demonstrated as well. This compact broadband optical diode can contribute to the all-optical integrated circuits.