Xulin Lin

Enhanced wavelength sensitivity of the self-collimation superprism effect in photonic crystals via slow light.

We demonstrate that the wavelength sensitivity of a self-collimation superprism in photonic crystals (PhCs) can be greatly improved via slow light. With the help of a saddle point Van Hove singularity, we present an approach to obtain such a wavelength-sensitive self-collimation superprism. Our superprism not only has extremely high wavelength sensitivity, but also can suppress beam divergence, irregular beam generation, and wavelength channel dropout, overcoming the limitations of traditional PhC-based superprisms. Based on our superprism, a high-performance compact demultiplexer is also proposed.

Millimeter-Scale and Large-Angle Self-Collimation in a Photonic Crystal Composed of Silicon Nanorods

We report the observation of a large-angle self-collimation phenomenon occurring in photonic crystals (PCs) composed of nanorods. Electromagnetic waves incident onto such PCs from directions covering a wide range of incident angles become highly localized along a single array of rods, which results in the narrow-beam propagation without divergence. A propagation length of 0.4 mm is experimentally observed over the wavelength ranging from 1540 nm to 1570 nm even in the large incident angle case, which is a very considerable length scale for on-chip optical interconnection.

Remote control of light behavior by transformation optical devices

Based on the transformation optics, a general method of light-behavior remote control is proposed. From this method, the important coefficients of a cavity, i.e. the quality factor Q and the resonant frequency ?0 could be tuned in a wide range by a transformation optical device in distance, so that the light behavior can be remotely controlled. To confirm this original idea, three schemes, such as, the remote modification of output energy current from an absorptive cavity, the remote control of lasing behaviors, and the remote tuning of the resonant frequency or photonic band-gap, are presented and confirmed by our numerical simulations based on finite-difference time-domain and finite-element methods. With some special advantages, e.g., without physical change or damage of original devices, large tuning range, and easily to hide the controller, this method could be widely used in optical/photonic or electromagnetic designs in the future.

Wide-range and tunable diffraction management using 2D rectangular lattice photonic crystals

We propose that 2D rectangular lattice photonic crystals composed of dielectric rods can be utilized for wide-range and tunable diffraction management. The control of diffraction for a normally incident beam is achieved by either properly choosing the operating frequency or changing the refractive index of the dielectric rods. The convergent, collimated, and divergent beam behaviors corresponding to a wide range of diffraction are clearly illustrated using FDTD simulations. The tunability of diffraction around the frequency of super-collimation is also analyzed and demonstrated.

Wideband tunable, high-power, graphene mode-locked ultrafast lasers

Ultrafast passively mode-locked lasers with spectral tuning capability and high output power have widespread applications in biomedical research, spectroscopy and telecommunications. Currently, the dominant technology is based on semiconductor saturable absorber mirrors (SESAMs). However, these typically have a narrow tuning range, and require complex fabrication and packaging. A simple, cost effective alternative is to use Single Wall Carbon Nanotubes (SWNTs) and Graphene. Wide-band operation is possible using SWNTs with a wide diameter distribution. However, SWNTs not in resonance are not used and may contribute to unwanted insertion losses. The linear dispersion of the Dirac electrons in graphene offers an ideal solution for wideband ultrafast pulse generation. Here, we report graphene saturable absorbers (GSA) for wideband tunable and high power ultrafast pulse generation. Tunable ultrafast pulses are generated with an Erbium-doped fiber laser mode-locked by GSA.

The Dynamical Study of the Metamaterial Systems

We investigate the dynamical characteristics of metamaterial systems, such as the temporal coherence gain of superlens, the causality limitation on the ideal cloaking systems, the relaxation process and essential elements in the dispersive cloaking systems, and extending the working frequency range of cloaking systems. The point of our study is the physical dispersive properties of meta-materials, which are well known to be intrinsically strongly dispersive. With physical dispersion, new physical pictures could be obtained for the waves propagating inside metamaterial, such as the “group retarded time” for waves inside superlens and cloak, the causality limitation on real metamaterial systems, and the essential elements for design optimization. So we believe the dynamical study of meta-materials will be an important direction for further research. All theoretical derivations and conclusions are demonstrated by powerful finite-difference time-domain simulations.