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We investigate the third-order optical nonlinearities in four novel porphyrin dimers (dimers A to D) and a monomeric porphyrin H2CPTPP measured by using the single-beam z-scan technique with a pulsed Q-switched Nd:YAG nanosecond laser at 532nm. All the samples show strong excited state absorption (ESA) and high value of χ(3) in the ns domain at this wavelength. We perform a comparison between dimer A and its monomer H2CPTPP in their third-order optical nonlinearity, and discuss the relationships between the values of χ(3) and the different bridging groups for all the dimers.

An intrinsically stable quantum key distribution system (QKD) with six polarization states encoded by phase modulation is introduced. The encoder and decoder are in the same structures that consist of two polarizing Sagnac interferometers connected in tandem. The six polarization states are determined and distinguished by different sets of phase shifts induced by two respective electrically-driven integrated phase modulators. A mean visibility of interference fringes is kept stable at 97.58% for an hour's performance. Theoretical and experimental analyses show that the proposed QKD system features intrinsically stability immune from environment fluctuation.

Employing the technique of symmetry reduction of analytic method, we solve the Ginzburg–Landau equation with varying nonlinear, dispersion, gain coefficients, and gain dispersion which originates from the limiting effect of transition bandwidth in the realistic doped fibres. The parabolic asymptotic self-similar analytical solutions in gain medium of the normal GVD is found for the first time to our best knowledge. The evolution of pulse amplitude, strict linear phase chirp and effective temporal width are given with self-similarity results in longitudinal nonlinearity distribution and longitudinal gain fibre. These analytical solutions are in good agreement with the numerical simulations. Furthermore, we theoretically prove that pulse evolution has the characteristics of parabolic asymptotic self-similarity in doped ions dipole gain fibres.

Au nanorods dispersed in aqueous solution were prepared with the electrochemical method. The absorption spectrum shows two absorption peaks corresponding to the perpendicular and transverse surface plasma resonance absorption of the nanorods. The third-order optical nonlinear properties are investigated by Z-scans. The signs of the nonlinear absorption coefficient and refractive index are reversed as the intensity of incident laser increases, which is due to the shape change of the gold nanoparticles melted by the intense laser pulses.

The evolution of soliton trains in dispersion-shifted fibres (DSFs) in the presence of third-order dispersion (TOD) is investigated. The results show that the collision of neighbouring solitons in the trains can be suppressed by means of a proper TOD, but the maximum transmission distance (or bandwidth) is limited by the increasing soliton separation that results from the TOD. It is also shown that the separation can be suppressed by adjusting the initial phase or amplitude difference between the solitons. These results are helpful to re-establish the potential application of the soliton-based optical-communication systems in DSFs.

A new approach is proposed to enhance supercontinuum (SC) spectrum generation in A dispersion-decreasing optical fibre with a new dispersion profile. The chromatic dispersion D(?,z) is a concave function of wavelengths and has no zero-dispersion wavelengths over the whole or part of the fibre as D(?,z) is positive. A flatter and much broader spectrum can be produced based on the scheme. The general criteria parameters are obtained for characterizing SC shapes in the optical fibres.

We first present the general solution and the simplest special solution of the doubly stochastic matrix used in deterministic entanglement concentration. Then, we give a better scheme to realize deterministic entanglement concentration. Under this scheme, the concentration is realized, and more importantly, two partially entangled pairs concentrate to four-particle Greenberger–Horne–Zeilinger (GHZ) states with a certain probability.

A new region where modulation stability occurs in the fibers with minimum group-velocity was found due to the fourth-order dispersion effect. The spectral extent of the region is analyzed and found to be affected by initial input power and the dispersion parameter.

The compression results of picosecond and femtosecond soliton pulses in the dispersion-decreasing fibers are reported in this paper. We found that the high-order dispersion has a great influence on the soliton compression. The expressions of optimum compression factor and optimum fiber length are obtained numerically.

We present a tumour cell growth process model including a multiplicative coloured noise and an additive coloured noise correlated. How the noise cross-correlation intensity λ and correlation time τ can affect the steady state properties of tumour cell growth model are discussed by solving an approximative Fokker–Planck equation. It is found that the increase of noise correlation time τ can cause the tumour cell number increasing, but the increase of multiplicative noise intensity can cause the tumour cell number extinction. We also find that the increase of cross-correlation intensity λ in the case of 0

A new method is proposed to compress soliton pulses in the normal dispersive optical fibers through cross-phase-modulation of two pulses. The optimum fiber length for optimum compression is obtained for given values of the pulses and fiber parameters.

We investigate the adiabatic enhanced compression of ultrashort pulses from a distributed feedback laser operated at 1550 nm in fibres with slowly decreasing dispersion (FSDD). High-quality pulse compressions from 4.4 ps down to 1.1 ps in a 100 m FSDD and from 4.4 ps down to 830 fs in a 500 m FSDD are obtained. The Raman self-frequency shift of femtosecond pulses in the compression is observed. Theoretical analyses are in good agreement with experimental results.

We report on the enhanced pulse compression due to the interaction of positive third-order dispersion and cross-phase-modulation effects in birefringent fibres. Polarization soliton compression along the slow axis can be enhanced in birefringent fibres with positive third-order dispersion, and the polarization soliton compression along the fast axis can be enhanced in fibres with negative third-order dispersion. Moreover, the third-order dispersion parameter can be optimized to obtain the optimal pulse compression.

The influence of the third-order dispersion (TOD) on the polarization mode dispersion (PMD) is investigated. It is found that the TOD effect destroys orthogonal polarization modes in optical birefringent fibres. A new method is proposed to compensate for the PMD by means of cascading the fibres with the positive and negative TOD. This has proven to be practicable in long transmissions.

Starting from our definition of apodization profile functions, we discover the optimal profiles and the characteristics of defined apodization functions in sidelobe suppression. It is shown by numerical analysis that the optimal grating length is 45?mm to compensate for dispersion induced by 100?km fibres and the smoothness of the ripples in time-delay characteristics is related to the defined parameters.

Optical storage caused by photo-induced anisotropy in poly[3'-methyl-4'-bis(N,N-oxyethylene)imino-4-nitro-azobenzene sebacoyl] film is studied by degenerate four-wave mixing. Molecule orientation gratings which are stable for three months are produced. The grating in the sample can be "erased" by using circular polarized light. So an azobenzene polymer thin film can be used many times to restore optical information.

A novel idea is proposed to suppress the soliton self-frequency shift of femtosecond soliton pulse in dispersion-decreasing fibers. The expression of the soliton self-frequency shift as a function of the pulse width and the fiber dispersion parameter is derived. The numerical simulation is also given, and is in agreement with analytical results.

Using deformed boson algebra, we study the property of two-mode coherent states in noncommutative phase space. When a two-mode field evolves in the noncommutative phase space, it can acquire an extra θ-dependent phase compared to the case of commutative space. This phase is detectable and may be used to test noncommutativity.

Vis/NIR spectroscopy, in combination with partial least square (PLS) analysis and a back-propagation neural network, is investigated to identify endothelium corneum gigeriae galli (ECGG). The spectral features of ECGGs and their counterfeits are reasonably differentiated in vis/NIR region, which provides enough qualitative information to establish the relationship between the spectra and samples for identification. After pretreatment of the spectral data, cross validation is implemented for extracting the best number of principal components. Then the calibration and validation set are performed well. The PLS and back propagation neural network (BPNN) model gives the BPNN to be 0.9941 and the root mean square residual (RMSR) to be 0.0775 for the calibration set, and the multiple correlation coefficient (MCC) to 0.9874 and the RMSE to 0.1134 for the validation set. Thus the PLS and BPNN model is reliable and practicable. Through testing, a recognition accuracy of 100% is achieved. The present study could offer a new approach for fast and nondestructive discrimination of ECGG and its counterfeit.

A flashlamp-pumped Cr:LiSAF laser system with a voltage controlled Q-switch structure in the cavity is designed. A dual-wavelength and dual-pulse tunable laser output is gained. The relation of laser output behavior with input energy is studied experimentally. The output is dual-pulsed with the energy of the 32 mJ/pulse producing the total output energy of 64 mJ and the pulse width is about 27 ns at 850 nm. Then, we use one LBO crystal as the frequency doubling crystal to obtain a dual wavelength (448.1 nm and 449.15 nm) and dual pulse laser. The output for one wavelength is about 10.3 mJ and the line width is less than 0.02 nm.

The behavior of an extended dislocation near an elliptical blunt crack is investigated. The equilibrium separation between Shockley partials and the critical value of stacking fault energy for the formation of extended dislocations by dissociation reaction as well as the extended dislocation emission criterion are developed. The results show that the equilibrium separation increases as the extended dislocation tends to the blunt crack. If the stacking fault energy is comparable to the critical energy for dissociation in a perfect medium, complete dislocations can dissociate to form extended dislocations near the blunt crack. The critical stress intensity factor (SIF) for extended dislocation emission increases with the stacking fault energy and the curvature radius of the blunt crack tip. Moreover, the critical SIF for extended dislocation emission is far lower than the critical SIF for edge dislocation emission.