Weisheng Hu

Photonic crystal channel drop filter with a wavelength-selective reflection micro-cavity

In the paper, a novel three-port channel drop filter in two dimensional photonic crystals (2D PCs) with a wavelength-selective reflection micro-cavity is proposed. In the structure, two micro-cavities are used. One is used for a resonant tunneling-based channel drop filter. The other is used to realize wavelength-selective reflection feedback in the bus wave-guide, which consists of a point defect micro-cavity side-coupled to a line defect waveguide based on photonic crystals. Using coupled mode theory in time, the conditions to achieve 100% drop efficiency are derived thoroughly. The simulation results by using the finite-difference time-domain (FDTD) method imply that the design is feasible.

Joint scheduling for optical grid applications

Optical networking technologies are expected to play an important role in creating an efficient infrastructure for supporting advanced grid applications. Since both the scheduling methods in grid computing and optical networks are limited to be directly used to achieve optical grid scheduling, we propose a new, to the best of our knowledge, joint scheduling model by extending the classic list scheduling algorithm to achieve communication contention aware task scheduling for the optical grid applications. An effective adaptive routing scheme is also proposed to improve the performance of the extended list scheduling. The impacts of different routing schemes on the extended list scheduling are comparatively investigated by simulations.

Mode-locked thulium fiber laser with MoS2

Liquid-phase exfoliated 2D material multilayer MoS2 is transferred onto a gold mirror and its saturable absorption at the 2 µm wavelength region is experimentally observed. This transferred MoS2 saturable absorber has a modulation depth of 13.6% and a saturation intensity of 23.1 MW cm−2. This saturable absorber is integrated into a linear Tm3+ fiber laser cavity, and stable fundamental-frequency mode-locking operation is realized at 2 µm with pulse energy of 15.5 nJ, pulse width of ~843 ps, and a repetition rate of 9.67 MHz. The laser spectral width is ~17.3 nm with a center wavelength of 1905 nm. This first presence of mode-locking with multilayer MoS2 sheets in the 2 µm wavelength region verifies that multilayer MoS2 is a good candidate for broadband mode-locking comparable to graphene, as well as a good mode-locker for achieving high pulse energy.

OPTICAL PROPERTIES OF PULSED LASER DEPOSITED ZnO THIN FILMS

Abstract With the help of the pulsed laser deposition technique, completely (001) textured ZnO thin films were achieved on (001) α-SiO2 single crystalline substrates at moderate substrate temperatures of 225–500°C. The films exhibited oscillated optical transmittance, from which the refractive indices vs the wavelength were calculated and fitted in Cauchys equation. The index dispersion showed the same tendency as that of the bulk ZnO crystal. By the prism-film coupling method a wave of 0.633 μm was well guided in the films. The m-lines for both TE and TM multimodes were sharp and clear. Light propagation lines were observed within the films and the propagation loss was determined to 2.8 dB/cm. Waveguide equations suiting the anisotropic waveguide structures were derived to determine the ordinary and extraordinary refractive indices. Values of no = 1.96 and ne = 1.98 were much closer to that of the bulk crystal. The as-deposited films were of high quality in crystallinity and optical properties.

On the spectrum-efficiency of bandwidth-variable optical OFDM transport networks

We investigated the high spectrum efficiency property of the bandwidth-variable optical OFDM (BV-OOFDM) transport networks. In contrast to mixed-line-rate (MLR) networks, BV-OOFDM enables flexible allocation and efficient utilization of the spectral resource.

Photonic microwave phase shifter/modulator based on a nonlinear optical loop mirror incorporating a Mach-Zehnder interferometer

We realize a novel photonic microwave phase shifter/modulator based on a nonlinear optical loop mirror incorporating a Mach-Zehnder interferometer. A near-linear phase shifter exceeding 180 degrees and a phase modulation with 2.5 Gbit/s baseband signal are obtained for a 10 GHz microwave signal by this proposed device.

Symmetric 40-Gb/s TWDM-PON With 39-dB Power Budget

Time- and wavelength-division multiplexed passive optical network (TWDM-PON) has been selected by full service access networks as a primary solution for next generation PON stage 2 in April 2012. In this letter, we propose and demonstrate a symmetric 40-Gb/s TWDM-PON with 39-dB power budget. A reflective semiconductor optical amplifier is used in optical network unit as a pre-amplifier to enhance the sensitivity of downstream signals. For the upstream direction, a thermally-tuned directly modulated laser with 10-Gb/s modulation rate is used as upstream colorless source, and a chirp management filter is employed in optical line terminal to mitigate chromatic dispersion therefore enabling fiber transmission. Symmetric 40-Gb/s TWDM-PON is experimentally demonstrated with a power budget of 39 dB, which could support 25-km fiber transmission and 1:1000 splitting ratio.

Delay of Broadband Signals Using Slow Light in Stimulated Brillouin Scattering With Phase-Modulated Pump

Slow light due to stimulated Brillouin scattering in fibers is a promising technique to realize all-optical data storage and synchronization. For delaying high-speed data, we demonstrate an approach to solve the problem of narrowband Brillouin gain by phase-modulating the Brillouin pump. The bit rate of the phase-modulating signal determines the Brillouin gain bandwidth. A 1.25-Gb/s nonreturn-to-zero pseudorandom binary sequence data is delayed by 520 ps with a phase-modulated pump operating at 2.5-Gb/s bit rate. We have also observed the pattern-dependent delay and distortion of the data caused by the filtering characteristics of Brillouin amplification, and we have suppressed the distortion by detuning the carrier of the signal away from the Brillouin gain peak

Task Scheduling and Lightpath Establishment in Optical Grids

Data-intensive Grid applications require huge data transferring between multiple geographically separated computing nodes where computing tasks are executed. For a future WDM network to efficiently support this type of emerging applications, traditional approaches to establishing lightpaths between given source destination pairs are not sufficient because a computing task may be executed on any one of several computing nodes having the necessary resources. Therefore, lightpath establishment has to be considered jointly with task scheduling to achieve best performance. In this paper, we study the optimization problems of jointly scheduling both computing resources and network resources. We first present the formulation of two optimization problems with the objectives being the minimization of the completion time of a job and minimization of the resource usage/cost to satisfy a job with a deadline respectively. When the objective is to minimize the completion time, we devise an optimal algorithm for a special type of applications. Furthermore, we propose efficient heuristics to deal with general applications with either optimization objective and demonstrate their good performances via simulation.

Optimized design of two-pump fiber optical parametric amplifier with two-section nonlinear fibers using genetic algorithm.

A new two-pump fiber optical parametric amplifier (FOPA) is presented, which is composed of two-section high nonlinear fibers (HNLFs). Genetic algorithm (GA), a multivariate stochastic optimization algorithm is applied to optimize parameters of two fiber segments, such as the length and dispersion coefficient of fiber. A broadband FOPA with twosection HNLFs is obtained using optimum design parameters, which theoretically provides a uniform gain of 20.3 dB with 0.2-dB uniformity over a 346-nm bandwidth.