Broadband and High Efficient 1530 nm Emission from Oxyfluoride Glass Ceramics Codoped with Er3＋ and Yb3＋ Ions

The emission at 1530nm and its applications in optical communications are discussed. The efficient width of the emission band △eff, which is up to 91 nm, is larger as compared with silica-based glass, bismuth glass and ZrF4-BaF2-LaFa-AIF3-NaF （ZBLAN） glass doped by Er^3＋ ions. Under the excitation of 785 nm laser, the emission integral intensity of 153Onto increases about five times in the glass ceramics higher than that in the glass. This is explained by the quantum cutting process by two-photon emission with phonon assistance. The results indicate that the glass ceramics are a promising candidate for developing broadband optical amplifiers in wavelength-division multiplexed systems.

Optically Controlled Coherent Backscattering from a Water Suspension of Positive Uniaxial Microcrystals

Coherent backscattering of light from a water suspension of zirconium silicate microcrystals is experimentallystudied.Optically controlled weak localization of photons is realized,which is due to the reorientation behaviors of positive uniaxial microcrystals induced by a linearly polarized pump beam.Because zirconium silicate particles are positive uniaxial microcrystals,their reorientation behaviors are contrary to negative ones.Our work widely extends the materials used in the light-controllable weak localization of photons.

Non-Paraxial Split-Step Semi-Vectorial Finite-Difference Method for Three-Dimensional Wide-Angle Beam Propagation

A wide-angle, split-step finite-difference method with the classical local one-dimensional scheme is presented to analyze the 3-D semi-vectorial wave equation. The method requires only matrix multiplication for beam propagation. To validate the effectiveness, numerical results for the eigen-mode propagation in tilted step-index channel waveguides are studied, and results show that the method has high accuracy and numerical efficiency.

Time-Resolved Femtosecond Degenerate Four-Wave Mixing in LiNbO3：Fe,Mg Crystal

Forward degenerate four-wave mixing （DFWM） processes are investigated with a femtosecond pulsed laser in lithium niobate crystal doubly-doped with magnesium and iron （LiNbO3：Fe, Mg）. The pulse energy dependence reveals a pure third-order nonlinear response, and the third-order nonlinear susceptibility x^（3） in the material is evaluated to be 4.96 × 10^-13 esu. The time-resolved DFWM process shows a response time of x^（3） shorter than 100fs, which is due to the nonresonant electronic nonlinearities. Our results indicate that LiNbO3 crystals have potentials for ultrafast real-time optical processing systems, which require a large and fast x^（3） optical nonlinearity.

Characterization of Photon Statistical Properties with Normalized Mandel Parameter

Normalized Mandel Parameter （Q） is introduced as a new measurement oi photon statistics. Dependences of Mandel parameter Q and corresponding normalized Mandel parameter （Q） on photon-counting time interval are experimentally investigated for pseudo-thermal light. We demonstrate that （Q） is more appropriate than Q, to measure the statistical deviation from Poisson distribution, because （Q） presents clearly both the intrinsic statistical properties and measuring effects. The advantages of （Q） in charactering nonclassical emissions are also discussed.

Quantitative analysis of the self-absorption and reemission effects on the emission spectrum of photoluminescence in right-angle excitation–detection configuration

A theoretical approach based on differential radiative transport is proposed to quantitatively analyze the self- absorption and reemission effects on the emission spectrum for right angle excitation-detection photoluminescence mea- surements, and the wavelength dependence of the reemission effect is taken into account. Simulations and experiments are performed using rhodamine 6G solutions in ethanol as model samples. It is shown that the self-absorption effect is the dominant effect on the detected spectrum by inducing pseudo red-shift and reducing total intensity; whereas the reemission effect partly compensates for signal decrease and also results in an apparent signal gain at the wavelengths without ab- sorption. Both effects decrease with the decrease in the sample concentration and the propagation distance of the emission light inside the sample. We therefore suggest that diluted solutions are required for accurate photoluminescence spectrum measurements and photoluminescence-based measurements.

Multipole resonance in the interaction of a spherical Ag nanoparticle with an emitting dipole

The effect of multipole resonance in the interaction between a spherical metallic nanoparticle （MNP） and an emitting dipole is studied with the Mie theory. The results show that the absorption peak of the MNP with respect to the field of the emitting dipole is blue-shifted with the decrease of the spacing between MNP and emitting dipole due to the enhanced multipole resonance. At a short distance, the enhanced multipole terms of scattering are not obvious compared with the dipole term. For the decay rate of the emitting dipole, multipole resonance brings about the enhancement of it largely at short spacing. For the radiative decay rate, the behavior is quite different. The dipole term is dominant at a short spacing, and the multipole term is dominant at a larger spacing.

Preparation and Size Characterization of Silver Nanoparticles Produced by Femtosecond Laser Ablation in Water

Femtosecond laser ablation of silver plate placed in water is used to produce nanoparticle suspension. The method is easy to operate and the suspension is relatively stable. The optical properties and the size distribution of the suspension are studied with UV-vis absorption spectroscopy and dynamic light scattering, respectively. The shape of the nanoparticles is investigated by an atomic force microscope, which is near spherical. There are two kinds of nanoparticles, small particles with diameter about 35 nm, and large particles with diameter about 120 nm.

A Novel Three-Dimensional Wide-Angle Beam Propagation Method Based on Split-Step Fast Fourier Transform

A novel three-dimensional wide-angle beam propagation method based on the split-step fast Fourier transform is developed. The formulation is based on the three-dimensional Helmholtz wave equation. Each propagation step is performed by utilizing both the FFT and split-step scheme. The solution of Helmholtz wave equation does not make the slowly varying envelope and one-way propagation approximations. To validate the efficiency and accuracy, numerical results for a propagation beam in a tilted step-index optical waveguide are compared with other beam propagation algorithms.

Raman scattering in In/InOx core-shell structured nanoparticles

The properties of Raman phonons are very important due to the fact that they can availably reflect some important physical information. An abnormal Raman peak is observed at about 558 cm-1 in In film composed of In/InOx core-shell structured nanoparticles, and the phonon mode stays very stable when the temperature changes. Our results indicate that this Raman scattering is attributed to the existence of incomplete indium oxide in the oxide shell.

Molecular dynamic simulations of surface morphology and pulsed laser deposition growth of lithium niobate thin films on silicon substrate

The molecular dynamic simulation of lithium niobate thin films deposited on silicon substrate is carried out by using the dissipative particle dynamics method. The simulation results show that the Si （111） surface is more suitable for the growth of smooth LiNbO3 thin films compared to the Si（100） surface, and the optimal deposition temperature is around 873 K, which is consistent with the atomic force microscope results. In addition, the calculation molecular number is increased to take the electron spins and other molecular details into account.

Photopolymerization-Induced Two-Beam Coupling and Light-Induced Scattering in Polymethyl Methacrylate

Light amplification due to two-beam coupling is realized in doped polymethyl methacrylate （PMMA） glasses. A coupling gain as large as 14 cm^-1 is obtained. The dynamic behaviour of absorption and light-induced scattering due to the process of photopolymerization are also studied. The results show that the amplification and its dynamic process enable possible applications of PMMA in optical devices.

Photoassociation of Atomic BEC within Mean-Field Approximation： Exact Solutions

We propose an exactly solvable method to study the coherent two-colour photoassociation of an atomic Bose- Einstein condensate, by linearizing the bilinear atom-molecule coupling, which allows us to conveniently probe the quantum dynamics and statistics of the system. By preparing different initial states of the atomic condensate, we can observe very different quantum statistical properties of the system by exactly calculating the quadrature- squeezed and mode-correlated functions.

Design of tunneling injection quantum dot lasers

To implement high quality tunneling injection quantum dot lasers, effects of primary factors on performance of the tunneling injection quantum dot lasers were investigated. The considered factors were tunneling probability, tun- neling time and carriers thermal escape time from the quantum well. The calculation results show that with increas- ing of the ground-state energy level in quantum well, the tunneling probability increases and the tunneling time decreases, while the thermal escape time decreases because the ground-state energy level is shallower. Longitudinal optical phonon-assisted tunneling can be an effective method to solve the problem that both the tunneling time and the thermal escape time decrease simultaneously with the ground-state energy level increasing in quantum well.

Transition from Backscattering Speckles to Phase Conjugation in LiNbO3：Fe

We investigate the backscattering for converging beams in iron-doped lithium niobate crystals. Due to the nonlinear properties of the crystal, backscattering exhibits temporally fluctuating speckles that make a transition to the phase conjugate of the incident beam under certain circumstances. Our observation seems to point to a new kind of self-pumped phase conjugation in photorefractive media.

Beam control in tri-core photonic lattices

We report on theoretical investigations of beam control in one-dimensional tri-core photonic lattices （PLs）. Linear splitting is illustrated in tri-core PLs; the effect of defect strength on the splitting is discussed in depth for single-wavelength light. We reveal that splitting disappears when the defect strength trends to zero, while reoccurring under nonlinearity. Multi-color splitting and active control are also proposed in such photonic structures.

Laser-Driven Silver Nanowire Formation： Effect of Femtosecond Laser Pulse Polarization

We report our laser-driven method used to make large quantities of straight thin silver nanowires, and experimentally demonstrate that femtosecond laser pulse polarization has a prominent effect on formation of non-spherical shapes of nanoscale particles. Further, our experiment directly reveals that the underlying mechanism is ptasmon- plasmon interaction, which can be controlled by poIarization and plays a decisive role in this non-synthetic method for metal nanowire formation.

Nonlinear optical properties of graphene-based materials

Graphene,a two-dimensional carbon atom sheet,has attracted tremendous attention and research interest because of its exceptional physical properties.Graphene has high mobility and optical transparency,in addition to flexibility,robustness and environmental stability.The main focus so far has been on fundamental physics and electronic devices.However,because the linear dispersion of the Dirac electrons enables ultrawideband tunability,we believe its true potential lies in photonics and optoelectronics.In this review,we introduce recent advances in the nonlinear optical properties of graphene-based materials.The rise of graphene in nonlinear optics is shown by several recent results,ranging from saturable absorbers and the four-wave mixing effect to giant two-photon absorption,reverse saturable absorption and optical limiting.The relevant forms of the graphene-based materials include pure graphene,graphene oxide and graphene hybrids.

Q-switched and mode-locked Er-doped fiber laser using PtSe2 as a saturable absorber

We report a passively Q-switched and mode-locked erbium-doped fiber laser(EDFL) based on PtSe_2, a new two-dimensional material, as a saturable absorber(SA). Self-started Q-switching at 1560 nm in the EDFL was achieved at a threshold pump power of 65 mW, and at the maximum pump power of 450 m W, the maximum single Q-switched pulse energy is 143.2 n J. Due to the polarization-dependent characteristics of the PtSe_2-based SA, the laser can be switched from the Q-switched state to the mode-locked state by adjusting the polarization state. A mode-locked pulse train with a repetition rate of 23.3 MHz and a pulse width of 1.02 ps can be generated when the pump power increases to about 80 m W, and the stable mode-locked state is maintained until the pump power reaches its maximum 450 m W. The maximum single mode-locked pulse energy is0.53 nJ. This is the first time to our knowledge that successful generation of stable Q-switched and mode-locked pulses in an Er-doped fiber laser has been obtained by using PtSe_2 as a saturable absorber.

Solution-processable graphene mesh transparent electrodes for organic solar cells

Graphene mesh electrodes （GMEs） with good conductivity and transparency have been fabricated by the standard industrial photolithography and 02 plasma etching process using graphene solutions. Organic photovoltaic （OPV） cells using GMEs as the transparent electrodes with a blend of poly-（3-hexylthiophene） phenyl-C61-butyric acid methyl ester （P3HT/PC61BM） as the active layer have been fabricated and exhibit a power conversion efficiency （PCE） of 2.04%, the highest PCE for solution-processed graphene transparent electrode-based solar cells reported to date.