Jiangtao Cheng

Ultrahigh Birefringent Photonic Crystal Fiber With Ultralow Confinement Loss Using Four Airholes in the Core

A simple photonic crystal fiber (PCF) design with a rectangular array of four airholes in the core region and a traditional circular-airhole cladding is proposed in this work. The modal birefringence is induced by the asymmetry of the rectangular distribution of four airholes and/or the elliptical shape of the holes. The traditional symmetric cladding structure results in good confinement loss performance by limiting the light in the core region. Therefore, the proposed design enables simultaneous realization of high birefringence and low confinement loss. Simulations based on the full-vector finite element method (FEM) with anisotropic (PML) show that ultrahigh single-mode birefringence (~ 10-2) and ultralow confinement losses ( < 0.002 dB/km) can be achieved at 1.55 mum wavelength. Dependence study of the birefringence and losses on several key parameters is also provided. Compared to previously studied PCF with asymmetric core or cladding structures, by having just four relatively large airholes in the core, this design could be much easier to be implemented with even better performance.

Highly efficient second harmonic generation in hyperbolic metamaterial slot waveguides with large phase matching tolerance

Highly efficient second harmonic generation (SHG) bridging the mid-infrared (IR) and near-IR wavelengths in a coupled hyperbolic metamaterial waveguide with a nonlinear-polymer-filled nanoscale slot is theoretically investigated. By engineering the geometrical parameters, the collinear phase matching condition is satisfied between the even hybrid modes at the fundamental frequency (3,100 nm) and the second harmonic (1,550 nm). Two modes manifest the great field overlap and the significant field enhancement in the nonlinear integration area (i.e. the slot), which leads to extreme large nonlinear coupling coefficient. For a low pumping power of 100 mW, the device length is as short as 2.19 µm and the normalized conversion efficiency comes up to more than 6.37 × 10(5) W(-1)cm(-2) which outperforms that of the plasmonic-based structures. Moreover, the efficient SHG can be achieved with great phase matching tolerance, i.e., a small theoretical fabrication-error sensitivity to filling ratio and a broad pump bandwidth in a compact device length of 2.19 µm using 100 mW pump. The proposed scheme links the mature near-IR devices to the mid-IR regime and have a great potential for integrated chip-scale all-optical signal processes.

The un-symmetric hybridization of graphene surface plasmons incorporating graphene sheets and nano-ribbons

Un-symmetric hybridization of graphene surface plasmons (GSPs) in waveguides incorporating graphene nano-ribbons and an underlying graphene sheet is theoretically studied. By tuning the chemical potential of the sheet, the characteristics of the hybrid modes can be shifted from sheet-like toward ribbon-like. The performance of hybrid modes reaches the maximum when phase match is satisfied. Superior to symmetric ribbon pairs, the favorable hybrid modes can be tuned at their best states, while the other modes are suppressed. The hybrid waveguide GSPs mode supported by this structure could extend the propagation distance by 46% over that of the modes for ribbon pairs.

Dispersion-modified, highly nonlinear holey fibre with a high index, slot-structure core

The group velocity dispersion (GVD) characteristics of a holey fibre design with a high index, slot structure in the core region are modified by introducing a simple cladding structure with a few large air holes. Our simulation results show that ultra-small mode effective areas and a high nonlinearity of the TE mode can be achieved, which is confined in the narrow slot by two silicon slabs in a glass fibre. This slot structure can be optimized to simultaneously achieve a very small Aeff and a single-TE-mode propagation. On the other hand, the proposed cladding can significantly reduce and flatten the large negative GVD of the slot structure, which could improve the nonlinear efficiency and interaction length for nonlinear applications. Our results indicate that an ultra-small Aeff of 0.16xa0µm2 and a flattened and reduced GVD with less than 10xa0psxa0nm − 1xa0km − 1 dispersion ripple within a 40xa0nm range at the 1.55xa0mm wavelength are achievable.

On-chip Plasmonic Nano-slits Array to Alleviate the Mass Transport Limitation in Microfluidic Biosensors

We propose on-chip plasmonic nano-slits array structures that can change the mass transport in a surface microfliudic biosensing system by providing additional optical gradient forces to targeted analytes. Both optical and fluidic effects are investigated.