Guoping Zhang

Wideband slow light with low dispersion in lattice-shifted asymmetric photonic crystal waveguides

Abstract. We propose a different type of asymmetric photonic crystal waveguide to achieve slow light with improved normalized delay-bandwidth product and low group velocity dispersion. The lateral symmetry of the proposed waveguide is broken by periodically shifting the two rows of air holes adjacent to the line defect. Under two simple different procedures of shifting air holes, the group indices of 41, 50, 68, and 114 with bandwidths over 14.9, 11, 7.8, and 4.7 nm, and the group indices of 43, 54, 73, and 124 with bandwidths over 13.9, 10.4, 7.1, and 4.3 nm around 1550 nm are obtained, respectively. Low-dispersion slow light propagation is confirmed by studying the relative temporal pulse-width spreading with the two-dimensional finite-difference time-domain method.

Simulation investigation of a 160 Gbit∕s all-optical data distributor based on cross-phase modulation in highly nonlinear fiber

Abstract. Ultrafast-photonic logic circuits are crucial elements to perform ultrafast-optical signal processing functions in the next-generation ultrahigh-speed networks. A 160  Gbit/s all-optical data distributor based on cross-phase modulation in a single highly nonlinear fiber is investigated and demonstrated. The numerical calculation is conducted, and the result shows that the data distributor can be realized in 160  Gbit/s for the data signals of return-to-zero format with logical correctness and high quality. To evaluate the performance of the scheme, the Q-factor of the output signal on signal wavelength, the peak power of signals, the initial delay, and the filter position are calculated and discussed, respectively. The proposed data distributor is suitable for ultrafast applications for the emerging all-optical networks.

Photonic Data Selector Based on Cross-Phase Modulation in a Highly Nonlinear Fiber

We propose and demonstrate a simple design of 2-to-1 photonic data selector based on cross-phase modulation in highly nonlinear fiber. Correct output logic signals are obtained at 10Gbit/s using the nonreturn-to-zero input signals, without using any additional input light beam. The scheme would be a promising candidate for future ultrafast all-optical signal processing applications.

An Improved Dynamic Bandwidth Allocation Algorithm for GPON

Optical transmission is getting more popular in the access network due to the increasing demand for bandwidth. Gigabit-capable passive optical network (GPON) is the basic technology to support the structure of the next-generation fiber to the home (FTTH) system. ThLV paper analyzeG GPON protocols and network configuration, the information about dynamic bandwidth allocation (DBA) in GPON protocols, a new DBA algorithm based on the all the transmission containers (T- CONT) was proposed, elaborated the specific algorithm for improved scheme, and builds the GPON model for this algorithm and test its performance. The simulation results show this algorithm can satisfy the full service Quality of Service (QoS) requirements of GPON.

Optical Characterization of Bi-pyramid Gold and Silver Nanoshells by Finite Difference Time Domain Method

Optical characterization of both gold and silver bi-pyramid nano-shells are investigated using the finite difference time domain (FDTD) method. This method is a convenient way for describing both quantitatively and qualitatively the optical response of nano-oshells/nanoparticles of arbitrary geometry and shape that surrounding the active medium. The surface plasmon peaks of gold and silver bi-pyramid nano-shell can be tuned from visible to the near infrared region by controlling the size (aspect ratio), surface sharpness and polarization of light. Surface plasmons provide a powerful means of confining light to nano-shells, which in turn can enhance local electromagnetic fields and significantly amplify the signal finally used for surface enhanced Raman scattering (SERS).

Effect of Microstructure on Transmission Properties of Polycrystalline Transparent Ceramics

The transmission properties of polycrystalline transparent ceramics are influenced by the chemical composition and the microstructure of the material. The fundamental optical mechanism of transparent ceramics and the influencing factors on transmission properties were discussed in this paper. The Mie theory for light scattering is applied to calculate scattering coefficients of residual pores and optical birefringence. The in-line transmission curves of the transparent alumina were calculated as a function of pore size, porosity and grain size. The results show that scattering by the residual pores is the dominant influencing factors on transmission properties. The scattering by the residual pores increases with an increase in porosity and the maximum of the scattering was observed when the pore size close to the optical wavelength. Optical birefringence in the transparent ceramics with non-cubic crystal structure has an important effect on the in-line transmission. The in-line transmission increases with a decrease in grain size. Keywords: transparent ceramics; microstructure; light scattering; birefringence

Analysis of the optical characteristic of particles by the discrete dipole approximation method

The method for measuring particles size and concentration based on the light extinction is widely used in the particles measurement technology. In the light extinction method, the extinction efficiency factor is an important parameter. Using the Mie theory, the extinction efficiency factor of spherical particles and equivalent-volume spheres instead of nonspherical particles can be calculated. For analyzing the characteristics of the non-spherical particles, the discrete dipole approximation (DDA) method is presented in this paper. The extinction efficiency factors of spherical, ellipsoid and cylinder particles were calculated by using the DDA method under different size parameters, and compared with the results of the equivalent-volume spheres based on Mie theory. The calculation results show that the extinction efficiency factors of spherical particles obtained by two methods differ slightly under the whole size parameters. The extinction efficiency factor of non-spherical particles and equivalent-volume spheres have discrepancy in evidence. The discrepancy between them changes with the different parameters of shape and size. Furthermore, it should be noted that when the size parameter is less than a critical size parameter, the extinction efficiency factor of non-spherical particles obtained by two methods differ slightly, and when the size parameter is greater than a critical size parameter, the extinction efficiency factor of non-spherical particles obtained by two methods differ greatly along with the increase of the size parameter, the non-spherical effect on the extinction efficiency factor can not be ignored. By contrast with the Mie theory, the DDA method has greater potential in application.