Femtosecond Laser Writing of Optical-Lattice-Like Cladding Structures for Three-Dimensional Waveguide Beam Splitters in LiNbO3Crystal

The waveguide beam splitters with diverse configurations in LiNbO 3 crystal have been produced by direct femtosecond laser writing of a family of optical-lattice-like cladding structures. By on demand design of the lattice tracks with “defect” lines, the efficient beam guiding and tailoring have been implemented in the structures. With a family of three-element integration of structures, three-dimensional (3-D) 1 × 3 beam splitting at the telecommunication wavelength of 1550 nm was realized. Different from the Type I modification of LiNbO 3 waveguides, the guiding cores of the optical-lattice-like cladding waveguide structures we fabricated locate in regions that are surrounded by the laser-induced-tracks. This paper opens the alternative way to construct complex integrated platforms in LiNbO 3 crystal by using femtosecond laser writing.The work was supported by National Natural Science Foundation of China under Grant 11274203, and Ministerio de Econom´ıa y Competitividad (Project FIS2013-44174-P), Spai

Femtosecond laser written optical waveguides in z-cut MgO:LiNbO3 crystal: Fabrication and optical damage investigation

We report on the fabrication of the dual-line waveguides and cladding waveguide in z-cut MgO:LiNbO3 crystal by femtosecond laser inscription. Due to the diverse modification of refractive index along TE/TM polarization induced by femtosecond laser pulses, the two geometries exhibit different guiding performances: the dual-line waveguides only support extraordinary index polarization, whilst the depressed cladding waveguide supports guidance along both extraordinary and ordinary index polarizations. The measured optical damage of these waveguides at the wavelength of 532 nm is higher than that of the previously reported ion-implanted waveguides in Zr-doped LiNbO3. The propagation loss of depressed cladding waveguide is measured as low as 0.94 dB/cm at 632.8 nm wavelength. It is found that the optical damage threshold (∼105 W/cm2) of the dual-line waveguide is one order of magnitude higher than that of the cladding waveguide (∼104 W/cm2).The work was supported by the National Natural Science Foundation of China (Nos.11274203, and 11511130017) and Spanish Ministerio de Educación y Ciencia (FIS2013-44174-P)

Optical ridge waveguides in Yb:YAG laser crystal produced by combination of swift carbon ion irradiation and femtosecond laser ablation

We report on the fabrication of optical ridge waveguides in ytterbium-doped yttrium aluminum garnet (Yb:YAG) single crystal by applying swift C5+ ion irradiation and the followed femtosecond laser ablation. The planar waveguide layer is first produced by C5+ ion irradiation and the laser ablation is used to microstructure the planar waveguide surface to construct ridge structures. The lowest propagation loss of the ridge waveguide has been determined to be ~2.1 dB/cm. From the confocal micro-fluorescence and micro-Raman spectra obtained from the waveguide regions, the intensities, positions and widths of the emission-line peaks had no obvious changes with respect to those from the bulks, which indicate that C5+ ion irradiation does not affect the bulk-related properties of the Yb:YAG crystal significantly in the waveguide regions. The results obtained in this work suggest potential applications of the Yb:YAG ridge waveguides as integrated laser sources.The work is supported by the National Natural Science Foundation of China (No. U1332121) and Ministerio de Economía y Competitividad of Spain (FIS2013-44174-P). S.Z. acknowledges the funding by the Helmholtz-Gemeinschaft Deutscher Forschungszentren (HGF-VH-NG-713). This work was partially carried out in CLPU facility (Lab. 2) in the framework of the access agreement concerning USAL staff

Automatic classification method for software vulnerability based on deep neural network

Software vulnerabilities are the root causes of various security risks. Once a vulnerability is exploited by malicious attacks, it will greatly compromise the safety of the system, and may even cause catastrophic losses. Hence automatic classification methods are desirable to effectively manage the vulnerability in software, improve the security performance of the system, and reduce the risk of the system being attacked and damaged. In this paper, a new automatic vulnerability classification model (TFI-DNN) has been proposed. The model is built upon term frequency-inverse document frequency (TF-IDF), information gain (IG), and deep neural network (DNN): The TF-IDF is used to calculate the frequency and weight of each word from vulnerability description; the IG is used for feature selection to obtain an optimal set of feature word, and; the DNN neural network model is used to construct an automatic vulnerability classifier to achieve effective vulnerability classification. The National Vulnerability Database of the United States has been used to validate the effectiveness of the proposed model. Compared to SVM, Naive Bayes, and KNN, the TFI-DNN model has achieved better performance in multi-dimensional evaluation indexes including accuracy, recall rate, precision, and F1-score

Deconfined quantum critical point lost in pressurized SrCu2(BO3)2

In the field of correlated electron materials, the relation between the resonating spin singlet and antiferromagnetic states has long been an attractive topic for understanding of the interesting macroscopic quantum phenomena, such as the ones emerging from magnetic frustrated materials, antiferromagnets and high-temperature superconductors. SrCu2(BO3)2 is a well-known quantum magnet, and it is theoretically expected to be the candidate of correlated electron material for clarifying the existence of a pressure-induced deconfined quantum critical point (DQCP), featured by a continuous quantum phase transition, between the plaquette-singlet (PS) valence bond solid phase and the antiferromagnetic (AF) phase. However, the real nature of the transition is yet to be identified experimentally due to the technical challenge. Here we show the experimental results for the first time, through the state-of-the-art high-pressure heat capacity measurement, that the PS-AF phase transition of the pressurized SrCu2(BO3)2 at zero field is clearly a first-order one. Our result clarifies the more than two-decade long debates about this key issue, and resonates nicely with the recent quantum entanglement understanding that the theoretically predicted DQCPs in representative lattice models are actually a first-order transition. Intriguingly, we also find that the transition temperatures of the PS and AF phase meet at the same pressure-temperature point, which signifies a bi-critical point as those observed in Fe-based superconductor and heavy-fermion compound, and constitutes the first experimental discovery of the pressure-induced bi-critical point in frustrated magnets. Our results provide fresh information for understanding the evolution among different spin states of correlated electron materials under pressure.Comment: 6 pages, 4 figure