Chang Sheng-Jiang

Magnetically Tunable Terahertz Switch and Band-Pass Filter

A novel design of a tunable terahertz switch and band-pass filter using liquid-crystal-filled photonic crystal waveguide is demonstrated. The effects of magnetic field on the photonic bandgaps and transmitting properties of a THz wave are investigated by using the plane wave expansion method and finite difference time domain method. The efficient photonic bandgap tuning is predicted such that the two-dimensional liquid-crystal-filled photonic crystal waveguide can serve as a switch and continuously tunable band-pass filter with controlling of the magnetic field.

Terahertz Wave Confinement in Pillar Photonic Crystal with a Tapered Waveguide and a Point Defect

We demonstrate a photonic crystal cavity with a tapered waveguide and a point defect to highly confine terahertz waves. The terahertz wave is first guided into the tapered waveguide, gradually compressed to its end, and finally confined in the point defect cavity. Numerical simulations with the finite-difference time-domain method indicate that the narrow band terahertz wave is highly confined in the point defect cavity with a quality factor of 5323. The demonstrated device may be used as an antenna for enhancing light-matter interactions in the point defect cavity at terahertz frequencies and may improve the sensitivity of terahertz near-field microscopy.

Examination of Validity of Paraxial Approximation in Second Harmonic Generation Microscopy under Low Numerical Aperture

By using a vectorial approach, the validity of paraxial approximation in second harmonic generation (SHG) microscopy under low numerical aperture (NA) is examined when the sample is a collagen fibril Due to the larger value of dzzx and tensorial nature of SHG, the component Ez of the focused field may have strong effect on the radiation pattern of SHG. Numerical results indicate that when the value of NA exceeds 0.3, the effect of Ez can not be neglected, which results in the invalidation of paraxial approximation in SHG microscopy despite the fact that SHG microscopy is still under low NA focusing.

Surface and bulk second-harmonic responses from a glass slide using tightly focused radially polarized light

The radially polarized beam is tightly focused by a high numerical aperture microscope objective with adjustable cover glass correction. The intensities of a second-harmonic (SH) signal as a function of the focal position inside a glass slide for different settings of cover glass correction are measured. As compared to linear polarization illumination, the surface responses at the two surfaces of the glass slide are more easily observed in the case of radial polarization. For the first time, to the best of our knowledge, we present the experimental demonstration that surface and bulk SH responses from solid centrosymmetric materials can be separately addressed by adjusting the cover glass correction thickness and the position of the focal exciting field.

Applying Hopfield neural network to QoS routing in communication network

The main goal of routing solutions is to satisfy the requirements of the Quality of Service (QoS) for every admitted connection as well as to achieve a global efficiency in resource utilization. In this paper proposes a solution based on Hopfield neural network (HNN) to deal with one of representative routing problems in uni-cast routing, i. e. the multi-constrained (MC) routing problem. Computer simulation shows that we can obtain the optimal path very rapidly with our new Lyapunov energy functions.

Adaptive Learning and Pruning Using Periodic Packet for Fast Invariance Extraction and Recognition

A new learning scheme using a periodic packet as the neuronal activation function is proposed for invariance extraction and recognition of handwritten digits. Simulation results show that the proposed network can extract the invariant feature effectively and improve both the convergence and the recognition rate.