Three ytterbium phthalocyanine compounds, ytterbium bis- phthalocyanine (Yb(Pc)₂), ytterbium bis- [(tetrakis- (tertiary-pentyloxy) phthalocyanine)] [Yb(Pc(t-OR₅)₄)₂], bis-ytterbium tris- [(tetrakis- (tertiary-pentyloxy) phthalocyanine)] [Yb₂(Pc(t-OR₅)₄)₃] have been synthesized and characterized by electronic spectrum, MS and element analysis. The Uv-vis spectrum indicated lower aggregation trend and red shift of Q bands with phthalocyanine ring increasing from dimer to trimer. The nonlinear optical properties of these compounds in THF solution were investigated by Z-scan method used 532 nm picosecond laser under open and close aperture condition. Both compounds showed reverse saturation absorption and nonlinear self-focus refraction effect. The nonlinear absorption and refraction capacity decreased with the order: Yb2(Pc(t-OR₅)₄)₃ >Yb(Pc(t-OR₅)₄)₂> Yb(Pc)₂.

We report on our investigations of the third order optical properties of two novel prophyrin dimers and their optical limiting behaviors. Our experiments were performed by using single beam z-scan technique and with Q-switched Nd: YAG nanosecond laser pulses at 532nm and CW laser at 532nm respectively for two different optical limiting mechanisms, strong excited state absorption (ESA) and thermal self-defocusing. In the experiments with pulsed laser, the open aperture results indicated that the two dimers showed strong excited state absorption which occurs when the excited state has an absorption cross-section higher than that of ground state. In the experiments with CW laser, optical limiting behaviors have also been observed. In this case, the third order optical nonlinearitiy is caused by thermal self-defocusing mechanism. Our results indicated that both novel prophyrin dimers showed potential use in optical limiters, optical switches and optical modulators.

We regard the bilayer consisting of a subwavelength layer of linear negative index material (NIM) and a Kerr-type nonlinear layer of conventional positive index material as a combined defect for a one-dimensional photonic crystal and investigate the effect of the thin film on the hysteretic behavior of the Goos-Hänchen shift and the incident intensity. We find that a subwavelength layer of linear negative index material (NIM) significantly modifies the characteristic of hysteretic behavior of lateral shift for the transmitted beam. Anomalous bistable shift occurs as the absolute value of magnetic permeability of the NIM layer increases. We also find that the sequence of the thin film of NIM and the nonlinear layer has a major impact on bistable shift. These results may be useful for NIMs characterization and for designing novel photonic-crystal-based devices.

Solitons have been found in many physical branches. Previous investigations on solitons mainly focused on various nonlinear dispersive media in nature. It is well known that in the nonlinear dispersive medium, soliton formation is due to the exact balance between the nonlinearity and the group velocity dispersion (GVD). When the signs of nonlinearity and GVD are the same, that is, the positive (focusing) nonlinearity vs. positive (normal) GVD, or the negative (defocusing) nonlinearity vs. negative (anomalous) GVD, the interaction between nonlinearity and GVD may lead to the generation of dark solitons. In this paper, we study the formation and propagation of dark electromagnetic solitons in the metamaterials, artificial structures that display properties beyond those available in naturally occurring materials. We use an extended Tanh-function expansion method to solve the nonlinear equation for ultrashort electromagnetic pulse propagation in metamaterial with a nonlinear polarization, and get dark solitary solutions under various conditions. It is found that, due to the role of the second-order nonlinear dispersion resulted from the dispersive magnetic permeability, dark solitons can be formed in the absence of linear dispersion, or even in the case of anomalous linear GVD for a focusing nonlinearity, challenging the traditional conditions for dark soliton formation.

Metamaterials (MMs) are artificial structures that display properties beyond those available in naturally occurring materials. The most notable MM is the negative-index material with simultaneously negative electric and magnetic responses. Recently, MMs exhibiting negative electric and magnetic properties in the infrared and optical frequencies have been realized, which will affect substantially the conventional optics and their applications in devices of compact cavities, adaptive lenses, tunable mirrors, isolators, converters, and so on. Moreover, MMs with nonlinear electric and/or magnetic response have also been demonstrated. This will further stimulate intense investigation in MM-based nonlinear optics due to the richness and the potential applications of the nonlinear property of MMs. In this paper, we report on our recent progress on investigation of some typical third-order nonlinear optical phenomena in MMs, such as modulation instability, soliton propagation, self-focusing, and so on. The controllability and the novel properties of the nonlinear phenomena in MMs are demonstrated.

We investigate the relationship between the hybrid form of center metal-atom and the third order nonlinear optical property in a class of 1,3-dithiole-2-thione-4,5-dithiolato-S, S' bis-chelate transition metal complexes for the first time by z-scan. We find that in bis-chelate complexes when the center metal-atom takes the sp³ hybrid form which construct a tetrahedron construction have better third order nonlinear refraction property than in the form of dsp² hybrid which construct a plane construction and for nonlinear absorption property the case is quite contrary. Cation group have shielding effect on both nonlinear refraction and nonlinear absorption property for this kind of materials.

The numerical simulations of self-organization have been considered in the self-pumped phase conjugate compact loop mirrors based on a photorefractive crystal PRC BaTiO₃ . We show that under optimal condition the nonlinear reflection coefficient of such mirror achieves the maximum value 0.80 - 0.90 at the maximum conjugate fidelity equal to 0.95 - 0.98. In this geometry the conjugate wave-front is generated due to scattering from a dynamic hologram produced in the self-intersection region of the forward and backward beams. As a result, the scenario of passing to unstable generation regimes in this case is the same as self-pumped loop phase-conjugate-mirror (PCM) but substantially differs from a single-crystal double PCM.

The light filament generated by focusing 50 fs laser pulses with a single pulse energy of 0.83 mJ using a 111 cm focal length lens in air is used to propel micro glass beads. It is found that the propulsion efficiencies at various longitudinal positions of the filament did not follow the filament's plasma distribution along the laser propagation direction. However, the variation of the propulsion distances agrees well with the evolution of the measured ablation rates at different locations along the filament. It hints that it is the ablative material removal that gives the main contribution to the propulsion of the micro beads. Further numerical simulations taking into account both the nonlinear propagation of the femtosecond laser pulse and the ablation dynamics confirm our interpretation.

We experimentally demonstrate that adiabatic compression of femtosecond pulse can be achieved by employing the management of quadratic cascading nonlinearity in quasi-phase-matching gratings. Cascading nonlinearity is not a simple analogy with third-order optical nonlinearity in term of the engineering properties of the magnitude and focusing (or defocusing) nonlinearity. Femtosecond pulse compression is investigated based on type-I (e: o + o) collinear QPM geometry of aperiodically poled MgO-doped LiNbO₃ (MgO: LN). Group-velocity-matching condition is chosen to generate quadratic femtosecond soliton consisting of fundamental (FF) and second harmonic (SH) pulses. Adiabatic-like compression process is observed in the length of 50 mm linearly chirped QPM. Cascading nonlinearity is local managed, instead of dispersion management used in fiber adiabatic soliton compression. Quadratic soliton including FF and SH pulses are obtained from the compression of 95 fs FF pulse in the initial experiments. Dependence on the phase mismatch and group velocity mismatch, cascading nonlinearity has a flexible property and presents a new challenge for exploring femtosecond pulse shaping and control. The demonstrated pulse compression and control based on cascading nonlinearity is useful for generation of shorter pulses with clean temporal profiles, efficient femtosecond second harmonic generation and group-velocity control.

Using spectrally resolved femtosecond two- and three-pulse nonlinear spectroscopy we study the dynamics and coherence properties of excited carriers in ZnO/ZnMgO quantum wells (QW) and silicon quantum dot (QD) structures embedded in silicon nitride (SiN). The contribution of biexcitons in ZnO/ZnMgO quantum wells at room temperature is identified. For Si quantum dots embedded in SiN a very short dephasing time of < 180 fs at room temperature is observed.

The first hyperpolarizability (β) spectrum of an azobenzene derivative around its two-photon resonance region is detected carefully by hyper-Rayleigh scattering. The present work uses a fluorescence spectrometer (Edinburgh instruments, F900) as the detector instead of interference filter and photoelectric multiplier tube (PMT). For each wavelength, HRS emission spectrum accompanied with two-photon fluorescence (TPF) is carefully detected by changing the detection wavelength around half of the incident wavelength. Full width to half maximum (FWHM) of the spectrum is about 0.4nm, which is similar to that of the laser. When the incident wavelength moves into the two-photon resonance region, TPF signal increases quickly and should be eliminated. In order to receive accurate β spectrum, the data detected by the oscillograph should be made some emendations, such as TPF, incident energy, absorption and pulse width. Compared with the β spectrum detected in previous works, the spectrum received in this work presents a clearer profile. The β spectrum exhibits a similar profile as its UV-visible spectrum just with blue-shift of wavelength. It could be explained that the electronic vibration structure in two-photon progress is different from that in one-photon progress, while the broadening mechanism may be similar, considering the resonant two-state model (RTSM).

Optical bistability and switching are of great interest in the rapidly and developing field of photonics. Devices that display this behavior could potentially play a major role in the development of optical communication systems and computing. In this article we present experimental results concerning the optical bistability in ferroelectric of photorefractive BaTiO₃ crystal. Two laser beams were used to interact with the photorefractive crystal which resulted in the bistability of the intensity of transmitted wave. This was achieved without the application of any optical resonator. High contrast optical bistability is found experimentally in the pump-ratio dependence of the output intensity.

Multi-photon excitation in ZnO material by femtosecond (fs) laser pulses around 800 nm was clearly observed. Under the intense field generated by fs pulses, two-photon absorption process was found very efficient in the excitation of the band edge emission from ZnO material under detuning condition. Nonlinear optical effects, such as Stark effect and Rabi effect, that may emerge under intense field are suggested to be responsible for this efficient excitation via two-photon absorption process. We consider that this NLO route to generate photoluminescence in ZnO material is meaningful in the research of blue-violet semiconductor laser field.

The nonlinear optical properties of an organo-metallic compound, tetrabutylammonium bis(2-thioxo-1,3-dithiole-4,5-dithiolato)aurum, abbreviated as BuAu, are investigated by Z-scan technique with 28 ps pulse width at 532 nm. Strong reverse saturable absorption has been found, the effective excited-state absorption cross section is obtained as σ_eff = 1.818×10^-17 cm². The material also shows self-defocus and the nonlinear optical refractive index is measured as n₂ = -1.341×10^-12 esu with the concentration of 2×10^-3 mol/L. All the results suggest that this material has potential application as optical devices.

We report comprehensive temperature and photoexcitation intensity dependent studies of the photoinduced magnetization precession in Ga_1-xMn_xAs (x = 0.035) by time-resolved Kerr rotation measurements. We observe coherent oscillations of local Mn spins triggered by an ultrafast photo-induced reorientation of the easy axis due to changes in the magnetic anisotropy. The amplitude saturation of these oscillations above certain pump intensity is indicative of stabilization of the magnetic easy axis orientation on temperatures above ~Tc/2. We find that the observed magnetization precession damping (Gilbert damping) is strongly dependent on pump laser intensity, but largely independent of ambient temperature.

Stable second-order nonlinearity (SON) was created in Pyrex borosilicate glass by the temperature/electric field thermal poling method. The distribution and amplitude of the induced nonlinearity were characterized with second harmonic microscopy. It was found that the SON was located in a narrow layer around 1.9 μm under the anode surface. An effective d₃₃ as high as 0.24 pm/V was obtained; a value comparable to that obtained in fused silica samples. The migration of different mobile alkali ions during the poling process was characterized with energy dispersive x-ray spectrometry in conjunction with scanning electron microscopy (SEM). It was found that Na was depleted from a region about 3.3 μm beneath the anode surface, while K was first depleted from the immediate region under the anode, and then accumulated in the Na-depleted region with its peak at ~1.8 μm beneath the anode. SEM observation of the cross-section of the poled glass region, after it had been etched in diluted hydrofluoric acid for several minutes, revealed an etched trench, ~1.8 μm under the anode edge and ~0.3 μm in width; while in post-annealed samples, no such etched trench could be observed. A frozen-in space-charge field due to charge migration is believed to be responsible for the creation of the SON and the altered etching rate in the poled region.

The polarized light properties of stimulated Raman scattering (SRS) in elliptical core optical fiber is systematically studied. In experiments, eight- order Stokes lines and two- order anti-Stokes spectra are observed and some parameters are analyzed such as the polarization, Raman frequency shift of each-order Stokes spectra under different polarization state of pump light, and the experiential formula are also provided. The results are in good agreement with the experimental figures. Experiments indicate that each-order Stokes spectra polarization state of stimulated Raman scattering in the birefringence optical fiber is related not only with Raman medium but also with pump light polarization state. The influence of pump light polarization state on low-order Stokes frequency-shift is lower but higher on the high-order Raman Stokes frequency shift fluctuation.

The Raman scattering of I₂ liquid-core optical fiber under the condition of resonance absorption in liquid-core optical fiber is studied in this paper. Iodine is dissolved in transparent benzene to make solution of I₂ in benzene, and the absorption coefficients of the solution are measured at certain wavelengths. The absorption curve can be divided into non-resonance absorption region, pre-resonance absorption region, strict resonance absorption region, and post-resonance absorption region respectively. Resonance absorption Raman scattering experiments are conducted by a 532 nm frequency-doubled Nd:YVO₄ laser, and the wavelength is in the strict resonance absorption region of solution of I₂ in benzene. Compared with I₂, the absorption of benzene can be neglected. Non-resonance Raman scattering of the solution is performed using a 632.8 nm He-Ne laser, and no spectrum lines of I₂ are found. The study demonstrates that there is one spectrum line of I₂ in the Raman scattering spectrum in the I₂ liquid-core optical fiber, but this line is not found in the spectrum of the non-resonance and resonance absorption Raman scattering of I₂ solution in benzene using absorption cell. The experiments proved that I₂ Raman scattering, is greatly enhanced by using both resonance absorption and liquid-core optical fiber.

In this paper, we design a new nonlinear fiber by filling a highly nonlinear liquid into hollow-core photonic crystal fibers. The liquid-core photonic crystal fiber with carbon disulfide exhibits an extremely high nonlinear parameter γ which can be more than 20 times larger than that of a conventional PCF, which is desired for FOPA. By using Full Vector Finite Element Method (FEM) with hybrid edge/nodal elements and anisotropic perfectly matched layers we simulate the transverse intensity distribution, the nonlinear parameter γ, and the GVD of the fiber mode. Simulation shows such a PCF' structure has near-zero flattened dispersion and dispersion slope at the pump wavelength, which meet another crucial requirement for FOPA.

A photorefractive adaptive optical heterodyne detection system is proposed. Its principle is introduced and typical numerical calculation is illustrated, which includes the reference beam output power and minimum detectable signal power versus system global power ratio, the effect of crystal coupling strength on reference beam output power and minimum detectable signal power, and the minimum detectable signal power versus nonlinear coupling strength. Several key factors which affect the system characteristics strongly are pointed out. In the proposed system, only one photorefractive crystal is used to attain optical heterodyne detection. The system features simple structure, low noise and high responsibility. It also answers two key questions of heterodyne detection: 1) phase distortion; 2) coherent length of light source.

Intrinsic optical bistability is of great interest and has potential applications in all-optical communication. In the present work, we have extended occurrences of bistable chromatic switching to a new rare-earth-doped system, namely single Tm-doped laser crystal pumped at 648 nm avalanche wavelength. Intrinsic bistability and chromatic switching of fluorescence emission are theoretically predicted, based on the rate equation theory. By using a four-order Runge-Kutta technique, chromatic switching spectra and bistable hysteresis loop are studied numerically in detail. The numerical results show that intrinsic chromatic switching of visible-infrared spectra is achievable experimentally corresponding to the transitions of Tm ¹D₂→³H₆ (357 nm), ¹G₄→³H₆ (469 nm), ³H₄→³H₆ (787 nm), ³F₄→³H₆ (1716 nm), as pump power increases far beyond avalanche threshold from low power level. Furthermore, we have found that the chromatic switching appears bistable in the emission spectra for pump intensity in the vicinity of avalanche threshold. The bistable hysteresis loops of luminescence are also demonstrated numerically for the dominant emission band. Intrinsic bistable chromatic switching in Tm-doped crystal is mediated by resonant excited-state absorption up-conversion.

A novel configuration of ring cavity-coupled Michelson interferometer is proposed to create sharp asymmetric multiple-resonance line shape, in which a ring cavity is side-coupled to one arm and a phase shifter is introduced into the other arm for static phase compensation. Such asymmetric line shape allows the tuning of the system between zero and complete transmission, with a phase offset much narrower than the full width of the cavity resonance itself. As tuning between resonance peak and notch of such asymmetric profile, optical transmission becomes much more sensitive to the round-trip phase shift of ring cavity than that in the case of symmetric Lorentzian line shape. By cooperating Kerr nonlinearity and cavity feedback, novel hysteresis loops and intrinsic bistability are achievable by adjusting incident power. The shapes of hysteresis curves associated with asymmetric resonance line shape are different from those arising from symmetric line shape. By adjusting the static phase compensation of phase shifter, tunable hysteresis loop and asymmetric multiple-resonance transmission can be easy performed. The simply constructed device is a good reference for sensitive optical switch, filter and sensor.

We investigate numerically the propagation behaviors of an ultrashort laser pulse in a dense Λ-type three-level atomic medium by using the full Maxwell-Bloch equations without the slowly varying envelope approximation and the rotating-wave approximation. We find that with propagation distance and time increasing, variations of the Rabbi frequency and the population in a dense medium are quite different from those in a dilute medium even though Lorentz local field correction (LFC) is not considered. In a dilute medium, the populations occupied initially at the ground state are completely transferred into the lower excited-state with the increase of the propagation distance; however, in the dense medium, about a half is still kept on the ground state and the others are transferred into the lower excited-state. The population oscillation occurs at the input surface of a dense three-level medium due to carrier-wave Rabi oscillation, and the oscillating time with LFC is much longer than that without LFC; the time derivative of the electric field has stronger effects on the time evolution of the pulse in the dense medium than that in a dilute medium, which is clearly shown from the time evolution of the Rabi frequency; especially the oscillating amplitude with LFC in the trailing edge of the pulse is larger than that without LFC at the input surface of the three-level medium.

In this paper, after taking into account two situations that the polarization of the injection light is parallel or orthogonal with the solitary vertical-cavity surface-emitting laser (VCSEL) output light, the nonlinear dynamic characteristics of an optical injection VCSEL are investigated numerically. The simulated results show that VCSEL can exhibit periodic oscillations, deterministic chaos and other complex instabilities under optical injection. For parallel or orthogonal optical injection, the same injection coefficients have different effects on the output of VCSEL. By properly adjusting the injection strength or detuning frequency, the dynamical state of the laser output can be controlled to a fixed state, and the polarization of the VCSEL output light can also be controlled.

In order to supply a theoretical guide for chaotic telecommunication, the influences of the chromatic dispersion and nonlinearity in fiber on the chaotic synchronization have been investigated based on the theoretical models used to describe the dynamics of semiconductor laser subjected to the external optical feedback and signal transmission in fiber channel. The numerical simulation results show that, the fiber nonlinear effect is responsible for the phase varying of chaotic signal and do not affect the amplitude of the chaotic signal; due to chromatic dispersion, the amplitude characteristics of chaotic signal are distorted significantly and the system synchronization quality will be impaired; after propagating 200km in dispersion shifted fiber, a desirable system chaotic synchronization with a synchronized coefficient 0.99 can be achieved by adopting a amplifier before the received laser to compensate the fiber loss.

A highly nonlinear dispersion flattened microstructured fiber is proposed. The new structure adopts two claddings with different pitches, air-holes diameters and air-holes arrayed fashions. The characteristics of such microstructured fiber such as nonlinearity and dispersion properties are investigated. The influence of the cladding structure parameters on the nonlinear coefficient and geometric dispersion is analyzed by full-vector finite element method with perfectly matched layer. Highly nonlinear coefficient and the dispersion properties of fibers are tailored by adjusting the cladding structure parameters. A novel microstructured fiber with highly nonlinear coefficient and dispersion flattened which is suited for supercontinuum generation is designed.

Interesting in generation and exploration of mid-infrared radiation has induced using optical parametric effect in nonlinear optical crystal with high nonlinearity, high transmission, phase-matching ability, and high sensitivity in room temperature, such as AgGaSe₂(AGSe), AgGaS₂(AGS) crystals. To achieve mid-infrared radiation, we use difference frequency generation (DFG) in AGS or AGSe crystals by pumping with the output of optical parametric oscillator. The mid-infrared radiation tunable characteristics of AGS and AGSe crystals under type-I phase-matching have been analyzed based on optical parameter DFG theory. Beam walk-off angle and acceptance angle limit conversion efficiency and restrict the DFG tuning wavelength range. We focus to research for effective nonlinear coefficient, walk-off angle and acceptance angle as functions of wavelength, the relationship between conversion efficiency and acceptance angle, and crystals length impact on the process of frequency conversion. We obtained 10 μm wavelength with a 10 mm crystal length, 1030nm pump, walk-off angles and acceptance angles of AGS and AGSe crystals are 1.19°and 0.68°, 0.107°and 0.171°respectively. Results are very useful for mid-infrared experimental studies on AgGaS₂ and AgGaSe₂ crystals.

Dispersion property is an important fact to generate white light. Different structures could change the dispersion properties of fibers. This paper demonstrates how the white light was generated when the ultrashort pulse propagated in a tapered fiber. We simulated how the supercontinuum was generated in a variety of tapered fibers which have different parameters. The supercontinuum range could be reached from 680nm to1750nm. It is shown that the width and the shape of the supercontinuum depend on both the fiber parameters such as the diameter or the length of tapered waist regime and pulse peak power. The paper also discussed the influence of the different dispersion and nonlinear effects in detailed, including GVD (Grouped Velocity Dispersion), SPM (Self Phase Modulation), TOD (Third Order Dispersion), SS (Self Steeping), and SRS (Stimulated Raman Scattering). Through the numerical simulation, it presents when the ultrashort pulse propagates in tapered fibers with anonymous dispersion, the Stimulated Raman Scattering effect plays an important role in the long wave range of the supercontinuum. The influence of the higher order dispersion, especially third order dispersion, on the anti-Stokes part in the supercontinuum process was also discussed. A smoother and broader supercontinuum could be obtained after choosing the suitable parameters of the tapered optical fibers, especially the diameter or the length of tapered waist regime.

The magnitude and dynamic response of the third-order optical nonlinearities of squarylium and croconium dyes in methanol solution were measured by femtosecond degenerate four-wave mixing (DFWM) technique at 800 nm. Ultrafast nonlinear optical responses have been observed, and the magnitude of the second-order hyperpolarizabilities was evaluated to be 5.80 × 10^-31 esu for the squarylium dye and 8.69 × 10^-31 esu for the croconium dye, respectively. The large optical nonlinearities of the dyes can be attributed to their rigid and intramolecular charge transfer structure, and the instantaneous NLO responses of dyes are shorter than the experimental time resolution (50 fs), which is mainly contributed from the electron delocalization. The fast nonlinear response and large third-order optical nonlinearities show that the studied squarylium and croconium dyes might a kind of promising materials for the applications in all-optical switching and modulator.

The relation of the spectral angular dispersion with the fundamental wavelength(FW) and the grating period of simultaneously quasi phase matching(QPM) and group velocity(GV) matching in tilted second harmonic generation is carried out in periodically poled RbTiOAsO₄(PPRTA).The phase matching bandwidth of PPRTA of noncollinear (2D) phase matching with spectral angular dispersion( 31.37nm, 218.41nm ) is 58 times and 15 times of those of collinear(1D) phase matching( 0.54nm,14.38nm )as the fundamental wavelength is 0.8μm and 1.55μm has been obtained, respectively.

The linewidth of KBe₂BO₃F₂ crystal optical parametric oscillator (KBBF-OPO) has investigated using theoretical analysis and simulation in type-I phase matching (PM). The Linwidth ranges of 81~250nm with the spontaneous parametric emission, 230~690nm with the divergence angle of pumping beam, and 19~96nm the linewidth of signal light are obtained, respectively. It is shown that the linewidth of signal is very narrow far away from the degeneracy point and the linewidth increased near the degeneracy point and given the results that KBBF-OPO has smaller linewidths than that of CLBO-OPO in type I. The divergence angle of pumping beam and the off-axis of pumping beam influenced the signal linewidth more seriously than other factors do. These results are important for compression the linewidth of OPO signal and useful for construction high power KBBF-OPO laser.

Self- and cross-phase modulation (SPM, XPM) in fiber is expected to play a major role in ultrafast all-optical analog-to-digital conversion(ADC), which can overcome the obstacles of inherently limited operating speed of electronic ADC. In this paper, we propose novel optical coding method for all-optical ADC using nonlinear optical switches based on the Sagnac interferometer. The multiperiod transfer function, which is the key to coding, is achieved through an exact design of the Sagnac interferometer. We conducted proof-of-principle experiments and successfully demonstrated 2.6-bit all optical ADC with Gray code output. The proposed optical coding, combined with existing optical sampling and quantizing techniques, will enable ultrafast photonic ADC without electronics.

A simple and low-cost all-optical equivalent-time sampling system is present. The optical sampling was realized by XGM in SOA and pulse-broadening in low-bandwidth PIN. A system model is funded based on noisy SOA dynamic function and a simplified equivalent electric circuit model about PIN. The sampling-recovery process had been simulated to validate the measuring capability of the sampler. Sampling error caused by ASE noise of SOA, thermal noise of PIN and time-domain jitter of control pulse is discussed too. Simulation results show that SOA XGM sampler can efficiently sample low repetition rate optical short pulse or short pulse with poor stability.

The transfer property of light in the fiber based on the total reflection on the interface between core and cladding of fiber. But at the interface of total reflection, incident light spot and reflect light spot are not the same, and there is a small lateral shift between them, this is Gause-hasen displacement. But in the traditional optical waveguide theory, the effect of Gause-hasen displacement on dispersion were totally neglected. Considering the effect of Gause-hasen displacement, the expression of the time delay is presented. The theoretical results show that time delay distortion is a cause of the optical pulse dispersion, and Gause-hasen displacement really cause the dispersion of optical pulse. In the past, scientists only consider the effect of model dispersion, waveguide dispersion, material dispersion and polarization mode dispersion. Now, we must consider the effect from Gause-hasen displacement while we study the dispersion. In other words, the traditional research on the optical waveguide theory ignore the effect of the Gause-hasen displacement, which must induce an error. So we must pay more attention to this important problem in the future when the light transmitting in a fiber is studied.

A stokes-vector theory is introduced to simulate the azimuth and ellipticity trajectories of the both probe and conjugate pulses in a four-wave mixing (FWM) scheme. Based on a new polarization-dependent pulsed FWM model which is derived from the three-level system, the theoretical analyses are carried out for the optical sampling of picosecond optical pulses in a lattice-matched unstrained semiconductor optical amplifier (SOA) by use of strong ultrashort pump pulses. We take the TE- and TM-gain dependent effects into account. The polarization characteristics of the pulses involved in optical sampling process are analyzed in detail.

A basic scheme of the polarization insensitive four-wave-mixing all-optical wavelength conversion with a copolarization dual-pump configuration in a highly nonlinear photonic crystal fiber (PCF) is demonstrated. With two fiber Bragg Gratings and a Faraday rotator mirror, both the pumps and the signal make a dual pass through a highly nonlinear PCF. The rotation of the signal polarization by the Faraday rotator mirror guarantees that both orthogonal polarization components of the signal will efficiently mix with the two pumps to produce a polarization-insensitive multi-wavelength conversion. The design and simulation of the bismuth oxide-based PCF indicate that the desired dispersion properties can be tailored by the geometrical parameters of PCF microstructure. The propagation loss at 1550nm is about 0.8dB/m. The nonlinear coefficient is expected to be 1100W^-1km^-1 by using bismuth oxide-based glass and reducing the effective core area. The mode-field diameter of PCF is estimated to be 1.98μm and the predicted effective core area is 3.3μm². The polarization insensitive four-wave-mixing wavelength converter with copolarization dual-pump configuration shows the small polarization sensitivity, the high conversion efficiency and the simultaneous multi-wavelength conversion.

Under the conditions of radius of the incident laser beam is much larger than the thermal diffusivity of the materials, the model has been established with the heat transfer theory and the finite element method. Analyze has been made out on the thermal interaction of long pulse laser and semiconductor Si and Ge. The influence of the radius of incident laser beam on the size of melting area on sample has been considered. The relation between the rate of the max melting radius on fused sample and the radius of incident laser beam Φ'/Φ and the laser fluence has been given out and discussed, which is of importance to the research on the interaction mechanism of the laser beam and semiconductor material.

Three novel dmit^2- complexes: [(CH₃)₄N][Co(dmit)₂], [(C₃H₇)₄N][Co(dmit)₂] and [(C₄H₉)₄N][Co(dmit)₂], (abbreviated as MeCo, PrCo and BuCo, respectively and dmit^2-=4,5-dithiolate-1,3-dithiole-2-thione), were synthesized and the third-order optical nonlinearities of their acetone solution of the same concentration were characterized by Z-scan technique at the wavelength of 1064 nm with laser duration of 40 ps. Their Z-scan curves all revealed a negative nonlinear refraction and a positive absorption at 1064nm.The molecular second hyperpolarizability γ of MeCo, PrCo and BuCo are 5.11×10^-31, 4.99×10^-31, 5.60×10^-31 (esu), respectively. The linear absorption coefficients α and the nonlinear absorption coefficient β of them are 0.3, 0.25, 0.32 (cm^-1) and 1.53×10^-12, 1.38×10^-12, 1.85×10^-12 (cm/W), respectively. The experiment results suggested that complexes with stronger linear absorption have larger nonlinear absorption and two-photon absorption. This difference is due to near resonant effect of sample with stronger absorption. So the linear absorption of complexes at 1064nm is a significant factor to influence the nonlinear absorption. These samples' large nonlinear absorption suggests that these materials have potential application in optical limiting.

The characteristics of periodically poled RbTiOAsO₄ (PPRTA) optical parametric oscillation (OPO) in collinear, quasi-collinear and noncollinear quasi phase matching (QPM) have been studied. The combination of temperature tuning and multi-period of PPRTA could provide a quasi-continuous wavelength tuning range of 1.4932 ~ 1.5937μm for signal wavelength and 3.2018 ~ 3.6992μm for idler wavelength as the period was 39, 39.5 and 40 μm, respectively, and the temperature between 20 and 120 degrees. The broadband wavelength range of 0.7352 ~ 0.9012μm for the pump wavelength 0.532μm has been obtained when the noncollinear angle was 4.90 degree and the period was 7.4μm.

In this paper, we proposed a novel variable operation of a DC-OFS based on double SFG+DFG nonlinearity process with double-pass configuration for the first time. In this scheme, the available nonlinear crystal length is used twice: forward for SFG and backward for DFG in each conversion and this device is called double-pass SFG+DFG wavelength converter as the SF wave propagates twice in the waveguide. We used the novel multiple-quasi-phase-matched LiNbO₃ (M-QPM-LN) waveguides having the continuously-phase-modulated domain structure, which can be operated by multiple pump wavelengths with minimum loss of efficiency. The frequency spacing of control signal-a is twice as large as the control signal-b. Conversion bandwidth is the frequency difference of control signal-b and control signal-a. We discussed Double-SFG+DFG-OFS with double-pass configuration theoretically and gave the formula of the input power of input signal, the two controlling light and pump light, which proposed a simple and feasible way to optimize the performance of the device. In this scheme, the advantages of the cascaded SFG+DFG scheme and the DC-OFS scheme are combined to a great extent. We believe this double-pass cascaded SFG+DFG DC-OFS must be better than single-pass cascaded SFG+DFG DC-OFS for constructing future flexible photonic networks.

Based on spatiotemporal nonlinear Schrödinger equation, we numerically study the modulation instability how to affect the self-focusing of broadband pulsed-beam with large chirp. We found that the chirp of the pulse can postpone the speed of the modulation growth from the simulation results. However, it is not work all along with increasing chirp value, but tend to a certain value. The curves of the contrast of chirped pulsed-beam will become superposition as chirp value is enough large when it propagates in nonlinear medium. Then, the influence of pulse bandwidth on modulation will become small, when the chirp has enough value in anomalous dispersion medium. At last, we also found that, in anomalous dispersion medium, temporal modulation growth and small-scale self-focusing can occur before the whole self-focusing, furthermore, the temporal instability will lead spatial focusing and splitting to bring forward.

In this paper, we consider spatial soliton propagation in Kerr nonlinear media with harmonic modulation of the refractive index, and investigate the effect of the lattice modulation for small-scale self-focusing of beam in optical lattice. Based on the modulation instability theory, the effect of lattice modulation on small-scale self-focusing of beam in optical lattice is studied both analytically and numerically. It is investigated how the perturbation changes with lattice modulation. Comparing the gain spectrum in lattice modulation with that without lattice modulation, we find that without the lattice modulation the perturbation gain increases with the input power when the input power is large enough to initiate the modulation instability. The gain of the noise is controlled when the lattice modulation is induced.

The numerical study of annealed proton exchanged (APE) waveguide in Z-cut periodically poled LiNbO₃ is presented using finite element method (FEM), compared with beam propagation method (BPM). Also given the analysis of the effects of different annealed time and annealed temperature on modes distribution.

In this paper, we proposed a novel numerical algorithm for nth-order cascaded Raman fiber lasers (CRFLs) with the combination of genetic algorithm (GA) and shooting method. Although shooting method possesses fast speed in solving nonlinear two-point boundary-value ordinary differential equations, calculating process may diverge if it is directly applied in the coupled equations of CRFLs when arbitrarily guessed initial values are out of the domain of convergence. To overcome the problem, genetic algorithm which has rather strong searching ability in global space is firstly employed to search for the initial value in convergent domain for each Stokes power; and then, the task of finding the more accurate initial values is finished by shooting method instead of GA whose searching ability is weak in local region. As an example, a sixth-order Ge-doped CRFL has been simulated by the novel algorithm. Calculated results show that the new method can effectively and quickly solve the coupled equations of the CRFL without the problem of divergence.

In a V-shaped three-level double-resonance configuration, there is strong quantum beats superimposed in a nutation signal in the probe laser response. In this paper, the beats in the dressed state nutation is studied theoretically within dressed state picture and the result is presented. An important conclusion is that the strong quantum beats in such a configuration occurred mainly as a result of the intrinsic coherence of the dressed states. Our result extends the coherent transient study in bared atomic transition to dressed state transitions.

Nonlinear dynamics of a laser-generated single cavitation bubble near an elastic boundary is investigated by a fiber-optic diagnostic technique based on optical beam deflection (OBD). The maximum bubble radii and the bubble life-time for each oscillation cycle are determined according to the characteristic signals. It is shown that with the increase of the number of oscillating cycles, the maximum radii and the life-time of the bubble are decreased sharply. Furthermore, the effect of material elasticity on nonlinear dynamics of cavitation bubble has also been investigated in some detail. The maximum bubble size and thus the bubble life time decreases with an increase in elastic modulus. In addition, increasing elastic modulus leads to a significant decrease of the collapse amplitude and the bubble energy. These results are valuable in the fields of cavitation erosion, collateral damage in laser surgery, and cavitation-mediated enhancement of pulsed laser ablation of tissue.

A complete set of reflection and transmission coefficients of microwave for a stratified unmagnetized laser-induced-plasma slab by using the scattering matrix method (SMM) is presented. The nonuniform unmagnetized laser-induced-plasma slab is modeled by a number of subslabs, and each subslab has a fixed electron density. Because the field in each subslab can be represented by the sum of the reflected and incident components, the partial reflection and transmission coefficients can be obtained by successively matching boundary conditions at all interfaces. In plasma, the surface reflecting the microwave is defined by the critical surface, where the plasma angular frequency equals to the microwave angular frequency. The partial reflection coefficients of microwave at the critical surface as the functions of the microwave frequency, and collision frequency for a Lorentz electron density profile are investigated.

The Electromagnetically Induced Transparency (EIT) is associated with a Λ three-level system and the spectral position of EIT window can be changed by varying the frequency of the coupling field, however, at large detuning the EIT will evolve into a dispersion-like feature and transparency property of EIT become less obvious. In this paper, it is shown that we can perform EIT frequency tuning by a radio-frequency (rf) field. In the cascade quasic-Λ four-level system, the absorption profile of probe field is calculated by solving the equations of motion of the density matrix. It is shown that the Autler-Townes doublet originates from the rf-field induced dynamic Stark effect and the spectral position of EIT window is determined by the frequency detuning of the coupling field. When the frequency detuning of the coupling field is half of the rf Rabi frequency, the EIT feature remain its absorptive profile. The frequency tuning rang of EIT is determined by the rf Rabi frequency, and can be explained using a dressed-state analysis. Therefore, frequency tuning range of EIT can be controlled by the rf Rabi frequency.

In the paper the amplification of ultrabroad bandwidth pulse in inhomogeneously broadening gain medium is theoretically investigated. Based on the analysis of the properties of the pulse with very strong chirp, we build a theoretical simulation model to analyzing the amplification of highly chirped pulse which includes the effects of homogeneous or inhomogeneous broadening. By our model, the difference between the inhomogeneously and homogeneously broadening amplification can be identified by numerical simulations. Then we simulate the compensation of Chirped pulse amplification (CPA), and it can optimize the laser design.

The ultra-short pulse optical parametric amplification based on continuous wave pump and pulse signal model is investigated by solving three nonlinear Schrödinger equations numerically. The effect of the order of soliton is presented by comparing the evolution process of signal pulse and the changing of root mean square width of signal. The phenomenon of signal pulse splitting and the broadening of the pulse will appear in the amplification process. Larger order of the soliton makes the pulse split at first, then begin to broaden. Smaller order of the soliton leads to the broadening of pulse firstly, then the pulse begin to split after propagating in a section of fiber.

Two independent self-mode-locked Ti:sapphire lasers were synchronized by a thin fused silica slab. The relative carrier-envelope phase slip was directly detected by beat frequency measurement. A simple optical feedback model was used to simulate the synchronization process.

Models of mode-locked fiber laser include rate equation, Nonlinear Schr&diaero;dinger (NLS) equation model and time domain model. On the basis of combining the rate equation and NLS equation, we have developed a novel mode-locked fiber laser model, which can not only describe the dispersion and nonlinear effect of fiber, but also take consideration of the reciprocity of pump photon and signal photon. With the proposed model, we have made an investigation on the propagation characteristics of mode-locked signal, pump and amplified spontaneous emission (ASE) along longitudinal fiber by numerical method. The numerical results show that optical single pulse results from noise while the density of level 1 is decreasing and the density of level 2 is increasing. And the mode-locked pulse becomes stable when both of two densities are stable. The simulations also show that the pump and ASE power attenuate exponentially along longitudinal doped fiber, and the attenuation rates of pump and ASE power increase as the doped density does.

By third-order nonlinear coupling and tightly focusing the beams in a single crystal of BBO, high intensity broad-bandwidth femtosecond pulses are used to generate 50μJ of light at 270nm (up to 1% THG efficiency). It is proved that the major contribution to the THG observed is the third-order process, not the cascaded second-order process. And the primary reasons why THG efficiency is about 1% is that 1ωlight is frequency-chirp beams and BBO crystal isn't tuned to optimized angle. At last, the methods to improve the third harmonic conversion efficiency have been put forward.

Silicon crystal is a kind of centrosymmetric materials, which has no second-order optical effects at dipole approximation. However, the inversion symmetry of silicon crystals will be broken by the built-in field or the DC electric field applied to it. We theoretically studied the response of the third-order susceptibility to the electric field and deduced the effective second-order susceptibility tensors when the electric fields applied to silicon are along the [111], [110] and [001] directions, respectively. The results show that the forms of the effective second-order susceptibilities of Si are consistent with those of C_3V, C_2V and C_4V symmetry groups of crystals which indicate that silicon crystals should belong to C_3V, C_2Vand C_4V symmetry groups instead of O_h symmetry group, respectively. So silicon crystals will exhibit some second-order nonlinear optical properties corresponding to related symmetric crystals under the corresponding incident electric fields. This research method of the electric field-induced second-order nonlinear optical processes can also be used to other centrosymmetric materials.

Multiphoton-absorption properties of π -conjugated symmetrical A - π - D - π - A chromophore, 3,6-Bis[2-{4-[5-(4-tert-butyl-phenyl)-[1,3,4]oxadiazol-2-yl]-phenyl}-vinyl]-N-ethylcarbazolyl, has been experimentally studied by using femtosecond laser pulse. At the wavelengths from 1205nm to 1570nm, the molecule shows large three-photon absorption (3PA) properties. The 3PA cross section reaches 4.5 * 10^-24cm⁶·GW^-2 at 1255nm. The output/input characteristic curve measured by nonlinear transmission method demonstrated a good optical power limiting performance based on 3PA mechanism. Luminous blue-green (about 477nm) up-conversion fluorescence excited by infrared laser pulse from 1205nm to 1570nm was easily observed in the quartz cuvette along the laser propagation direction. The material was also theoretically studied using Gaussian 03' software. The geometry, electronic structure, ground state charge distribution and excited state charge distribution were systematically calculated by HF/6-31G(d) and CIS/6-31G(d) method. Calculation results show that the obvious three-photon absorption and frequency up conversion fluorescence of this chromophore is attributed to its rigidity of chemical structure and effective charge transfer from the excited terminal units to the π -conjugated bridging units. The 1,3,4-oxadiazole is considered to be a good electron-acceptor and the key part in this charge transfer route. Particularly, for the first time we give the analytical solution to nonlinear transmission in a 3PA process when the incident beam has a Gaussian spatial profile.

Nonlinear optical properties of perylene derivatives were studied by femtosecond Z-scan technique. 3,4,9,10-Perylenetetracarboxylic dianhydride (PTCDA), 3,4,9,10-perylenetetracarboxylic diimide (PTCDI), and perylene-66 (dibenzthiophenoperylene-N,N'-dicyclohexylimide), were studied. Tetrahydrofuran was used as a solvent for perylene- 66. The solubility of PTCDA and PTCDI is very poor. Their colloidal solution was prepared by the irradiation of the third harmonics of a pulsed YAG laser to opaque suspension of PTCDA and PTCDI. Transparent colloidal solution was obtained within 50 minutes of UV irradiation. Colloidal solution of quinacridone was also studied. Two-photon absorption cross sections of these dyes were measured by open aperture Z-scan method using a femtosecond laser. The dependence of two-photon cross section on laser wavelength was measured in the wavelength range of 780-820 nm.

First-order hyperpolarizabilities of H-shape azobenzenes in gas and in THF have been theoretically studied by Hartree-Fock method and basis set sto-3g with Onsager model, including 4,5-bis((E)-(4-nitrophenyl)diazenyl)anthracene-1,8-diol, 4,5-bis((E)-(4-(trifluoromethyl)phenyl)diazenyl)anthracene-1,8-diol, 4,5-bis((E)-(3-chloro-4-fluorophenyl)diazenyl) anthracene-1,8-diol and 4,5-bis((E)-(4-chlorophenyl)diazenyl)anthracene-1,8-diol. Compared with corresponding azobenzene monomers, H-shape azobenzenes had much larger first-order hyperpolarizabilities. There were four factors which could obviously influence their first-order hyperpolarizabilities. Firstly, H-shape azobenzenes possessed dihedral angles of approximate ten degrees caused by coulomb repulsions with weakening dipole's changes between ground states and excited states. Meanwhile, dihedral angle induced energy gap between HOMO and LUMO to increase. Secondly, dipole-dipole interaction was considered as perturbation which caused strong energy splitting of each molecular orbital with the lessening of energy gap. Thirdly, hyper-conjugated effect existed in H-shape azobenzene and it induced energy gap to decline. Fourthly, solvent effects could obviously enhance their first-order hyperpolarizabilities by comparing results in gas with results in THF. These factors competed and affected each other. The latter three factors lastly overcame coulomb repulsion, which explained that H-shape azobenzenes' first-order hyperpolarizabilities were much larger than corresponding monomers'.

On the basis of non-linear coupled-mode theory, the dispersion relation of a dimensional periodic structure is analyzed and slow Bragg soliton solutions are given. The approximation approach for non-linear coupled-mode theory is studied by assuming adiabatic evolution of the soliton passed through fiber Bragg grating which is apodized by using a hyperbolic tangent apodization function in the middle of the FBG. And in the presence of apodization, the velocity equation of Bragg soliton is found. In this paper, we have simulated the motion tracks and velocities of Bragg solitons, analyzed effects of different parameters on motion track and velocity of Bragg soliton, and obtained different time-displacement curves and time-velocity curves. It is shown that the final steady velocity of soliton can be found by choosing specifical parameters, thereby, slow Bragg solitons whose propagate velocity through the grating is far lower than the speed of light in glass can obtained. We have presented detailed simulative results that agree with theoretical analysis.

Nonlinear optical responses of cyanine dyes in solution were studied by resonant femtosecond degenerate four-wave mixing (DFWM) technique. The folded box-CARS type geometry with the three linearly polarized beams of fundamental output of a regenerative amplified Ti:sapphire laser was used for the DFWM experiment. The wavelength of the laser was adjusted to the absorption band of the samples. Temporal profiles of a DFWM signal of cyanine dyes were measured with a time resolution of 0.3 ps, and were found to consist of three components, the coherent instantaneous nonlinear response (electronic response) and the medium and slow responses. The decay constant of ca. 100 ps can be attributed to the relaxation time of rotation around the short axis of the dye molecule. We think the decay constant of several ps can be attributed to the relaxation time of rotation around the long axis of the dye molecule. The effective value of the electronic component of the molecular hyperpolarizability, γ_e, was determined to be as large as 1.2 × 10^-28 esu at 780 nm for NK-2014. The dependence of γ_e of NK-2014 on the laser wavelength was measured.

In this paper, we performed experimental and quantum-chemical studies on a series of symmetrically substituted phenylenevinylene chromophores with different lengths of conjugated chains and different electro negativity of substitution groups to provide an insight into the nature of the two-photon absorption (TPA) processes and to reveal structure-property relations. TPA spectra were obtained at the wavelengths ranging from 600 to 1000 nm with 6ns laser pulses of 10Hz repetition rate. The TPA spectra show that absorption band is mainly related to the transition of electrons btween the orbital localized at phenyl rings of the conjugated chains. Quantum-chemical calculations were performed with MOLCAO (Molecular Orbital as a Linear Combination of Atomic Orbitals) method to calculate the positions of the electronic levels and the shapes of the molecular orbitals. Considering all of the series of symmetrically substituted phenylenevinylene chromophores, the planar structure and the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) is influenced significantly by the length of conjugated chains and the electro negativity of substitution groups. Structure-property relations revealed that the TPA cross section tends to be enhanced by an increase in the electro negativity of the substitution groups and tends to be reduced by an interruption of the conjugated chain.

The optical nonlinear properties of water-soluble quantum dot have been investigated by using the Z-scan technique with the second-harmonic generation(532nm) of the mode-locked Nd:YAG laser. According to the absorption spectrum, it is concluded that the absorption at 532nm is the two photon absorption process. On the basis of the open-aperture Z-scan measurements, the TPA coefficients and corresponding TPA cross sections for the four different pulse irradiances are presented. The experimental results show the water-soluble CdSeS quantum dot possesses large two-photon absorption (TPA) at 532nm wavelength. In addition, we also calculate the nonlinear refractive index and third-order nonlinear susceptibility. It is found that the two photon absorption coefficients depend on the intensity of the laser and the nonlinear refractive index is independent of the laser irradiance. All the results indicate that it is possible for CdSeS quantum dot be a promising material for biological fluorescence label and imaging.

Research of the interaction process between high energy pulse laser using millisecond pulse width and a PIN junction photodiode is presented. A 3-D physical modeling of the interaction is accommodated for the thermal interaction analysis. Considering variety of the thermophysical parameters, numerical method is utilized to solve governing equations of heat transfer with heat generation term. For different magnitudes of pulse energy,axial and radial temperature distribution as function of time and position before melting have been calculated, and the relevant physical process has been discussed. In addition, influence of different magnitudes of pulse energy on the temperature rise in the material composing photodiode is investigated. Numerical results show that heat conduction has effect to the whole course between laser and material interaction. Moreover, the rate of temperature rise has a deep effect for different magnitudes of pulse energy during laser irradiation.

The hyperchaotic orbits in the nonlinear three-wave coupling can be controlled by applying a small control wave. For a given set of linear frequency mismatch and growth-damping parameters, periodic orbit can be achieved by adjusting the amplitude of the control wave. The range of the amplitude of the control wave is determined by calculating the Lyapunov exponent of the three-wave coupling system. Numerical simulations show that the period number differs on the account of the amplitude of the control wave. Increasing the amplitude of the control wave from 0, the hyperchaotic state of the three-wave coupling system results in conversion to periodic 4, subsequently it is converted into period 2, and then into period 1.

In order to improve the efficiency of optical polymers' function in photonic applications, the effect of local environment on small molecules of Disperse Red 1 and their dynamic behavior is studied. Poly Styrene Sulfonic Acid polymer used as host material to make highly doped polymeric thin films. By studying the samples' spectra in vitro and in situ, and investigating the photo-anisotropic effects on samples, it is shown that dye-polymer interaction can be the dominant factor in local environment around the dye molecules. Therefore, it can be used to increase significantly the response intensity and improve the performance of photonic devices.

An intelligent optimization technique based on particle swarm optimization is proposed to identify parameters of chaotic optical systems. The feasibility of this approach was demonstrated with the computer simulation through identifying the parameters of Bragg acoustic-optical bistable system. The performance of the particle swarm optimization technique was compared with the more common genetic algorithm in terms of parameter accuracy and computation time. Simulation results demonstrated that the particle swarm optimization has better performance than the genetic algorithm in solving the parameter identification problem of chaotic optical systems.

The phase conjugation properties of self-pumped phase conjugation (SPPC), mutually pumped phase conjugation (MPPC), SPPC and MPPC coexisting are researched in Cu:KNSBN crystal with Q-switched single longitudinal mode YAG pulse laser pumping. The dependence of the reflectivity of phase conjugation on the incidence position and angle are obtained experimentally. The results show the optimal incident parameter exists in photorefractive phase conjugation effect.

In this paper, all-optical wavelength conversion based on FWM in ROF system is theoretically analyzed. It can be used to generate the optical millimeter wave signals and to implement the all-optical frequency up/down conversion in ROF systems. Due to the ultrafast nonlinear response of the HNL-DSF, it is possible to realize terahertz waveform all-optical mixing or up-conversion. All-optical frequency up-conversions of an optical IF signal to the upper frequency band using FWM without serious crosstalk were demonstrated. Based on analysis of the all-optical wavelength conversion in high-nonlinear fiber, main factors related to the conversion efficiency are presented. Methods to increase the conversion efficiency have been discussed. With the longer high-nonlinear fiber, the higher nonlinear coefficient, the appropriate power of the pump, the appropriate polarization between the signal and the bump, and high efficiency to implement the wavelength conversion can be achieved. The theoretical analysis is verified by the simulation results.

Multiphoton ionization spectrum of NO in the wavelength region of 495.0~575.0 nm with a Nd:YAG laser pumped an Optical Parameter Generator and Amplifier as excitation source is presented. The spectral bands are assigned by measuring the variation of the ionization signal versus laser intensity together with calculation. The results show that NO molecules are ionized via C²Π(v'=2,3), D²Σ(v'=2,3) intermediate resonant states and by (3+1) process in 495.0~535.0 nm wavelength region. While the spectral bands come from the transition of NO molecule from the ground electronic state to C²Π(v'=0,1), D²Σ(v'=0,1) and N²Δ(v'=1,2) intermediate resonant ones in 535.0~575.0 nm wavelength region. In this region, NO molecule is ionized by (3+2) and (4+1) multiphoton process. The molecule constants about NO(C²Π, D²Σ and N²Δ) states are calculated from the center wavelength of the spectral bands. It is also found that owing to the special electron configuration of NO, this molecule doesn't follow the normal transition selection rule of the diatomic molecule during the multi-photon process.

Sol-gel-processed TiO₂/SiO₂ films doped with organic azo dye have been investigated. The film was spin-coated on the ITO coated glass substrate and rapidly condensed by evaporation of the solvent from the liquid film. The thickness of the hybrid films can be varied from 0.2 to 0.6 micron. When the prehydrolyzed tetraethoxysilane (TEOS) sol and titania precursor(titanium butoxide) are mixed together with various molar ratios, the refractive index of the film may vary from 1.49 to 1.81 at 1300nm. The film is aged at 80°C for 2 h and then corona poled at 120°C for 1 h so that the dye molecules are dispersed in numerous pores of the oxide matrix. The absorbance spectra of the film measured by a UV-visible spectrophotometer show that the process of aging and poling in the sample preparation causes the pores in the oxide matrix to shrink and nonlinear molecules are aligned in the direction of the poling field and are trapped in the pores. The electro-optic coefficient r₃₃ is 42 pm/V at a fundamental wavelength of 1300nm. The nonlinearity is stable at 80°C for 2500h at least. The excellent thermal stability of the hybrid organic/inorganic film is an advantage for optical applications.

We investigate the existence, stability and propagation dynamics of spatial solitons supported by an interface separating 1D different-order Bessel optical potentials. The profiles of surface solitons are determined by the order and the modulation depth of Bessel potential. Influences of the order and modulation depth of Bessel potential besides the interface on the stability of surface solitons are discussed. We show that the surface solitons supported by present model have a wide stability region in their existence domain even for higher-order Bessel potential or the difference of the order of Bessel function on the opposite side of the interface is relatively large (e.g. n_l = 2, n_r = 5). The experimental realization of the model we discussed is also proposed. Numerical simulation of the propagation of surface solitons verifies our stability analysis. This study may enrich the concept of optical surface soliton.

Adopting noise initiation mode of stimulated Brillion scattering (SBS), the influence of phonon lifetime and gain coefficient of medium on power limiting characteristic is numerically investigated. By using actual parameters of three media, CCl₄, Acetone, and CS₂, the waveforms of transmitted pulses are simulated. It shows that, different media have little effect on the front peak of waveform, while have an obvious effect on the height of power limiting platform. When using the medium which has short phonon lifetime and small gain coefficient, the height of power limiting platform is comparatively high. When using the medium which has long phonon lifetime and large gain coefficient, the height of power limiting platform is comparatively low. In experiment, focusing 1064nm, 8ns, 18mJ pulses into these three media respectively, the waveforms of transmitted pulses are obtained. And it is shown that, the experimental results are in good agreement with the conclusions of theoretical simulations.

We have demonstrated efficient three-photon excitation in a number of nonlinear organic materials developed at our center or in cooperation with other research groups. The three-photon absorption (3PA) properties of these materials are studied using a femtosecond Ti:sapphire oscillator-amplifier laser system associated with an optical-parametric amplifier. Considering the transverse intensity distribution of the incident beam during measurements, the 3PA induced nonlinear transmission of the incident beam with a Gaussian transverse spatial profile is derived. Some of the 3PA-active materials are highly fluorescent while some others are nonfluorescent. In one of these materials, vibrational resonance enhanced broadband multiphoton absorption was founded. These materials can be used in optical power limiting and stabilization, frequency-upconversion imaging and microscopy etc. Some recent experiments of three-photon pumped power limiting and stabilization are briefly presented.

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