Integrated optical devices based on broadband epsilon-near-zero meta-atoms

We verify the feasibility of the proposed theoretical strategy for designing the broadband near-zero permittivity (ENZ) metamaterial at optical frequency range with numerical simulations. In addition, the designed broadband ENZ stack are used as meta-atoms to build functional nanophotonic devices with extraordinary properties, including an ultranarrow electromagnetic energy tunneling channel and an ENZ concave focusing lens.Comment: 3 pages, 3 figure

Steering between Bloch oscillation and dipole oscillation in parabolic optical waveguide arrays

We study the optical oscillations of supermodes in planar optical waveguide arrays with parabolically graded propagation constant in individual waveguide interacting through nearest neighbor couplings. In these arrays, we have identified a transition between a symmetric dipole oscillation (DO) and a symmetry-breaking Bloch oscillation (BO) under appropriate conditions. There exist obvious correspondences between gradon localization and various optical oscillations. By virtue of an analogue between the oscillation of optical system and that of a plane pendulum, we propose a shift of the graded profile to cause a transition from BO to DO. We confirm the optical transition by means of Hamiltonian optics, as well as by the field evolution of the supermodes. The results offer great potential applications in optical switching, which can be applied to design suitable optical devices.Comment: Submitted to JOSA B for publication

Integrated optical devices based on broadband epsilon-near-zero meta-atoms

We verify the feasibility of the proposed theoretical strategy for designing the broadband near-zero permittivity (ENZ) metamaterial at optical frequency range with numerical simulations. In addition, the designed broadband ENZ stack are used as meta-atoms to build functional nanophotonic devices with extraordinary properties, including an ultranarrow electromagnetic energy tunneling channel and an ENZ concave focusing lens. c 2012 Optical Society of America OCIS codes: 160.2710, 160.3918, 160.4236, 310.4165 Recently, materials with near-zero permittivity (ENZ) have been widely investigated in theory and engineering due to their anomalous electromagnetic properties. Owing to the exotic features, ENZ materials possess a great deal of exciting applications, such as directive antenna and waveguide which is related to the thickness of each layer (d i ) and the metallic inclusion filling ratio (f i ) in each layer. The s-parameter is defined as s = ε 2 /(ε 2 − ε 1 ). On the other hand, according to the Bergman spectral representation, the effective permittivity of the stack can be mathematically characterized as with a pair of spectral factors: the singularity (s i ) and the spectral density (F i ) corresponding to the operating frequency range and the desired effective permittivity. For the same ENZ stack, Eqs. The effective permittivity of the ENZ stack is retrieved from its reflectance S 11 and transmittance S 21 , according to the algorithm in Ref

Harmonic oscillations and their switching in elliptical optical waveguide arrays

We have studied harmonic oscillations in an elliptical optical waveguide array in which the coupling between neighboring waveguides is varied in accord with a Kac matrix so that the propagation constant eigenvalues can take equally spaced values. As a result, long-living Bloch oscillation (BO) and dipole oscillation (DO) are obtained when a linear gradient in the propagation constant is applied. Moreover, we achieve a switching from DO to BO or vice versa by ramping up the gradient profile. The various optical oscillations as well as their switching are investigated by field evolution analysis and confirmed by Hamiltonian optics. The equally spaced eigenvalues in the propagation constant allow viable applications in transmitting images, switching and routing of optical signals.Comment: 14 pages, 5 figure

Tunable photonic Bloch oscillations in electrically modulated photonic crystals

We exploit theoretically the occurrence and tunability of photonic Bloch oscillations (PBOs) in one-dimensional photonic crystals (PCs) containing nonlinear composites. Because of the enhanced third-order nonlinearity (Kerr type nonlinearity) of composites, photons undergo oscillations inside tilted photonic bands, which are achieved by the application of graded external pump electric fields on such PCs, varying along the direction perpendicular to the surface of layers. The tunability of PBOs (including amplitude and period) is readily achieved by changing the field gradient. With an appropriate graded pump AC or DC electric field, terahertz PBOs can appear and cover a terahertz band in electromagnetic spectrum

Tunable Hybridization at Mid Zone and Anomalous Bloch-Zener Oscillations in Optical Waveguide Ladders

We have studied the optical oscillation and tunneling of light waves in optical waveguide ladders formed by two coupled planar optical waveguide arrays. For the band structure, a mid-zone gap is formed due to band hybridization and its wavenumber position can be tuned throughout the whole Brillouin zone, which is different from the Bragg gap. By imposing a gradient in the propagation constant in each array, Bloch-Zener oscillation (BZO) is realized with Zener tunneling between the bands occurring at mid zone, which is contrary to the common BZO with tunneling at the center or edge of the Brillouin zone. The occurrence of BZO is demonstrated by using the field-evolution analysis. The tunable hybridization at mid zone enhances the tunability of BZO in the optical waveguide ladders. This work is of general and fundamental importance in understanding the coherent phenomena in lattice structures.Comment: Submitted to Optics Letter

Photonic Bloch-dipole-Zener Oscillations in Binary Parabolic Optical Waveguide Arrays

We have studied the propagation and Zener tunneling of light in the binary parabolic optical waveguide array (BPOWA), which consists of two evanescently coupled dissimilar optical waveguides. Due to Bragg reflections, BPOWA attains two minibands separated by a minigap at the zone boundary. Various coherent superpositions of optical oscillations and Zener tunneling occur for different parameters on the phase diagram. In particular, Bloch-Zener oscillation and a different type of Bloch-dipole-Zener oscillation are obtained by the field-evolution analysis. The results may have potential applications in optical splitting and waveguiding devices and shed light on the coherent phenomena in optical lattices.Comment: Submitted to JOSA

PLASER: Pronunciation Learning via Automatic Speech Recognition

PLASER is a multimedia tool with instant feedback designed to teach English pronunciation for high-school students of Hong Kong whose mother tongue is Cantonese Chinese. The objective is to teach correct pronunciation and not to assess a student's overall pronunciation quality. Major challenges related to speech recognition technology include: allowance for non-native accent, reliable and corrective feedbacks, and visualization of errors

Service learning and school community partnership

Background Service learning offered university students the opportunity to apply knowledge and skills in social care context while strengthening community health. This paper aimed at highlighting the essential features of the program in achieving sustainable outcomes. Project design and methods Students from different faculty, worked as a team to address the health issues of a less resourceful school. The students were required to plan and develop the related resources and products for matching the learning needs. Through the implementation, students shifted from following an instructive guide to acting on a more self-directed learning process at different stages of service. The health promotion programs could include nutritious breakfast, adequate exercises, healthy beverages and interpersonal communication. Efficacy of the service learning was assessed by the pre and post service survey on the attainment of generic skills of interpersonal effectiveness, problem solving, social responsibility and teamwork. Impact of the service was evaluated by the pre and post program testing. Individual learning experience was collected by the reflective journal writing. Significance and implication School community plays a major role in providing a healthy learning environment for children and adolescents. With the input of subject knowledge and field practice, faculty students attained improvement in generic skills. The school participants increased health knowledge and the importance of healthier lifestyle was reinforced. Both parties owned the program materials for the continuity of practice. The partnership creates initiatives of applying health-promoting school concepts. This project work also built up the ground work for a feasible framework of school health service and practice