Passive picosecond and femtosecond mode-locking laser action of Yb<Superscript>3+</Superscript>:LuYSiO<Subscript>5</Subscript>

Efficient passive mode locking of a diode-pumped Yb³⁺:LuYSiO₅ (Yb:LYSO) laser is first demonstrated in experiment using a semiconductor saturable absorber mirror (SESAM), to the best of our knowledge. A stable pulse train with a repetition rate of 101 MHz is generated. The average output power of 2.13 W and the pulse duration of 3.9 ps. With a pair of SF10 uncoated prisms for dispersion compensation, we obtained pulses as short as 780 fs with center wavelength around 1042 nm, the average output power of 1.03 W and the peak power of 13.1 kW.     

A novel digital image covert communication scheme based on generalized FCM in DCT domain

A novel covert communication method of digital image is presented, based on generalized fuzzy c-means clustering (GFCM), human visual system (HVS) and discrete cosine transform (DCT). Therefore, the original image blocks are classified into two classes according to specified characteristic parameters. So one block is suited for embedding security information, but the other block is not. Hence the appropriate blocks can be selected in an image to embed the security information by selectively modifying the middle-frequency part of the original image in conjunction with HVS and DCT. Furthermore the maximal information strength is fixed based to the frequency masking. Also to improve performances of the proposed algorithm, the security information is modulated into the chaotic modulation array. The simulation results show that we can remarkably extract the hiding security information and can achieve good robustness with common signal distortion or geometric distortion and the quality of the embedded image is guaranteed.     

A mathematical model of medial consonant identification by cochlear implant users

The multidimensional phoneme identification model is applied to consonant confusion matrices obtained from 28 postlingually deafened cochlear implant users. This model predicts consonant matrices based on these subjects' ability to discriminate a set of postulated spectral, temporal, and amplitude speech cues as presented to them by their device. The model produced confusion matrices that matched many aspects of individual subjects' consonant matrices, including information transfer for the voicing, manner, and place features, despite individual differences in age at implantation, implant experience, device and stimulation strategy used, as well as overall consonant identification level. The model was able to match the general pattern of errors between consonants, but not the full complexity of all consonant errors made by each individual. The present study represents an important first step in developing a model that can be used to test specific hypotheses about the mechanisms cochlear implant users employ to understand speech.     

Photophysical property of rhodamine-cored poly(amidoamine) dendrimers: Simultaneous effect of spirolactam ring-opening and PET process on sensing trivalent chromium ion

Two novel poly(amidoamine) (PAMAM) dendrimers, comprising rhodamine B unit in the core and 1-phenyl-3-methyl-5-pyrazolone unit at the periphery, have been synthesized and characterized. Both dendrimers displayed high selectivity and sensitivity towards Cr³⁺ ion. As considering the potential of being applied as fluorescent sensors for Cr³⁺ ion, we studied the complexes formed between the dendrimers and Cr³⁺ ion. Different PAMAM dendrimers had different recognition mechanism towards Cr³⁺ ion. For dendrimer G2, the recognition of Cr³⁺ was mainly due to the ring-opening of spirolactam. However, it significantly depended on the simultaneous effect of ring-opening of spirolactam and photoinduced electron transfer (PET) in the case of dendrimer G3.     

A cost-effective WDM-PON architecture simultaneously supporting wired, wireless and optical VPN services

It is believed that next-generation passive optical networks (PONs) are required to provide flexible and various services to users in a cost-effective way. To address this issue, for the first time, this paper proposes and demonstrates a novel wavelength-division-multiplexed PON (WDM-PON) architecture to simultaneously support three types of services: 1) wireless access traffic, 2) optical virtual passive network (VPN) communications, and 3) conventional wired services. In the optical line terminal (OLT), we use two cascaded Mach-Zehnder modulators (MZMs) on each wavelength channel to generate an optical carrier, and produce the wireless and the downstream traffic using the orthogonal modulation technique. In each optical network unit (ONU), the obtained optical carrier is modulated by a single MZM to provide the VPN and upstream communications. Consequently, the light sources in the ONUs are saved and the system cost is reduced. The feasibility of our proposal is experimentally and numerically verified.     

Speckle imaging of spin fluctuations in a strongly interacting Fermi gas

Spin fluctuations and density fluctuations are studied for a two-component gas of strongly interacting fermions along the Bose-Einstein condensate-BCS crossover. This is done by in?situ imaging of dispersive speckle patterns. Compressibility and magnetic susceptibility are determined from the measured fluctuations. This new sensitive method easily resolves a tenfold suppression of spin fluctuations below shot noise due to pairing, and can be applied to novel magnetic phases in optical lattices.     

Space-time resolved approach for interacting quantum field theories

An alternative approach to the usual perturbative S-matrix evaluation of quantum field theories is presented which is nonperturbative and provides full space-time resolution. We study the dynamical development of the force between two fermion wave packets for the Yukawa system. The spatial distribution of the virtual bosons that act as mediators of the force can be analyzed along with the fermionic densities. Using a potential function for the fermion-fermion interaction is a good approximation to the field theoretical calculations when the Fock space is restricted to only one boson, but in the full quantum field theory the fermion-fermion force is enhanced by higher-order multiboson processes. Furthermore, the normally attractive fermion-fermion Yukawa force can, in principle, be manipulated to even be repulsive if the momentum modes available to the virtual bosons are restricted.     

Effective mass anisotropy of hot electrons in nonparabolic conduction bands of n-doped InGaAs films using ultrafast terahertz pump-probe techniques

The anisotropic effective mass of energetic electrons in an isotropic, nonparabolic conduction band is revealed using ultrafast THz-pump-THz-probe techniques in a n-doped InGaAs semiconductor thin film. A microscopic theory is applied to identify the origin of the observed anisotropy and to show that the self-consistent light-matter coupling contributes significantly to the THz response.     

Higher-order space-charge field effects on the self-deflection of two-photon bright photovoltaic spatial solitons

We investigate numerically the effects of higher-order space-charge field on the self-deflection of bright photovoltaic spatial solitons in two-photon photovoltaic photorefractive crystals under steady-state conditions. The expression for an induced space-charge electric field, including higher-order space-charge field terms is obtained. The dynamical evolution equation is built in which the effects that arise from these higher-order terms are considered. Numerical results indicate that bright photovoltaic solitons can bend towards both the same direction as the crystal's c-axis and the opposite direction, respectively. Specifically, self-deflection cannot occur for bright photovoltaic solitons if the strength of the photovoltaic field and the intensity of the input beam are appropriately selected. Relevant examples are provided.     

Reflection chromaticity of cholesteric liquid crystals with sandwiched periodical isotropic defect layers

We study one-dimensional photonic crystals made of cholesteric liquid crystals with sandwiched isotropic defect layers. Based on the Berreman Fast 4 × 4 matrix method, the dispersion relation of one-dimensional photonic crystals is calculated and the corresponding reflection chromaticity is obtained. It is found that the color shift could be controlled by adjusting the thickness and refractive index of the isotropic defect layers. Compared with conventional structures, the reflection chromaticity of this structure is insensitive to the incident angle, if the thickness ratio of the cholesteric liquid crystals to that of the isotropic defect layers and the refractive index of periodical isotropic defect layers are properly set. Furthermore, the common forbidden bands for both left and right circular polarizations can be obtained, and we also take the wavelength-dependent refractive indices into consideration and obtain the reflected light chromaticity with the incident angle increasing. The proposed device can be used as a reflective color filter in the display industry.