In this work we demonstrated the feasibility of a 10 Gbit/s optical soliton source based on direct modulation of a semiconductor laser. We also show that it is possible to reduce substantially the frequency chirp, induced by the direct modulation process, with a narrow optical filter. A peak power greater than 100 mW is achieved with an optical signal-to-noise ratio (OSNR) better than 39 dB. We measured the output timing jitter of the source and we show that its main contribution is due to the laser noise. We successfully test our source in a 45-km 5-channel WDM system. The stability and easy assembly of this type of source make them attractive for upgrading single or multichannel chromatic dispersion limited optical communication systems.

In this paper, we report theoretical and experimental results concerning the upconversion phenomena around 550 nm in Er³⁺-doped Ti:LiNbO₃ waveguides. This phenomena corresponds transitions between the levels ⁴S_3/2 implied by ⁴I_15/2. The waveguide is pumped near 980 nm with a laser diode. Two pump photons are used to bring the Er ions to the short lifetime level ⁴F_7/2. After a non-radiative transition to the level ⁴S_3/2, Er ions emit photons at 550 nm while falling down to the ⁴I_15/2 level. By using the theoretical model elaborated by McCumber we evaluate the homogeneous emission cross sections and we obtain the following maximum values of the cross sections (sigma) ^H_e(551.9 nm) equals 57.7 x 10^-26 m² for TE and (sigma) ^H_e(558.1 nm) equals 52.5 x 10^-26 m² for TM polarizations. By measuring the fluorescence radiation around (lambda) equals 550 nm, we determine the rising and falling times and we obtain C equals 0.198 x 10^-23 m³/s as the value of the modulus of the homogeneous upconversion factor the value. The results presented here can be used in the design of integrated optoelectronic circuits and in the modeling of the laser action and optical amplification in Er³⁺-doped Ti:LiNbO₃ waveguides when a 980 nm pumping is considered.

We report the experimental observation of (1+1)D self- confinement of laser beams in BSO crystals, photorefractive materials with strong optical activity (45 degree(s)/mm). Numerical simulations of light propagation in such conditions were used to check the experimental results. The possibility of obtaining self-contained beams with these materials is given by the application of really intense static electric fields which induce anomalous behaviour of the optical activity.

We demonstrate the generation of solitons in the photorefractive materials with strong optical activity and absorption. The general wave equations are processed by rotation and affine transformations in order to decouple the effects of photorefractivity and optical activity. Analytical solutions of these equations are found in the case of slowly varying envelope and low-intensity approximations. The solutions show the occurrence of breathing solitons in sillenite crystals with strong optical activity and absorption in a particular orientation with respect to the external electric field. The absorption is decreasing the soliton intensity with the propagation distance (which set a limit in the soliton channel length) and is increasing the breathing period.

We discuss single-photon counting technologies, in particular at the optical wavelength of 1550 nm and their application in quantum communication. In particular we discuss the case of quantum cryptography illustrating with experiments performed in our lab, supplemented by recent experiments by other groups. We furthermore discuss briefly more general protocols for quantum communication and address some experimental changes.

In this work, we elaborate on the compromise between the efficiency of the multiprocessor computer architecture for handling large classes of computing tasks and the good performance of optics for implementing shift invariant operations, in particular convolution. We derive a class of processors, optoelectronic cellular automata that can efficiently implement intensive, low level vision tasks in a time compatible with application constraints up to standard video rates. As one illustration, a parallel simulated annealing task performing motion detection on an image sequence is demonstrated.

Numerical studies of the propagation of ultrashort optical pulses in quadratic nonlinear media are presented. Two- parameter families of chirped stationary spatiotemporal solitons in dispersive quadratically nonlinear media are constructed in the presence of temporal walkoff. It is found that the walking spatiotemporal solitons are dynamically stable in most cases. We find also one-parameter families of spinning spatiotemporal bright solitons in dispersive media with quadratic nonlinearities and study their stability. The comparison with a simple variational approximation for the spinning spatiotemporal solitons demonstrates that, though the variational approximation is not very accurate, it correctly describes the qualitative features of the spinning spatiotemporal solitons. We show that the spinning spatiotemporal solitons are subject to a storing azimuthal instability. The instability breaks the spinning soliton into stable nonspinning light bullets.

The high-modulated phase gratings induced in photorefractive crystals are anharmonic. For small angles between incident beams (thin grating regime), an additional mixing can appear between the diffraction orders produced by harmonics of the anharmonic grating. This mixing yields significant changes in the self-diffraction spectra. Our theoretical and experimental results explain the effect of the grating anharmonicity on the self-diffraction on thin photorefractive gratings.

Er³⁺-doped LiNbO₃ is widely used for the fabrication of integrated optic components. In the small gain approximation and the unsaturated regime in this paper we report some original results in the evaluation of the spectral optical gain and spectral noise figure in the bent Er³⁺-doped LiNbO₃ waveguide of the Mach-Zehnder interferometer pumped near 1484 nm using erfc, Gaussian and constant profile of the Er³⁺ ions in LiNbO₃ crystal. We used a quasi-two-level model to simulate the optical amplification in Er³⁺-doped LiNbO₃ straight and bent waveguide amplifiers and we demonstrated that rather high gains (similar to 1.1 dB) and low noise figures (similar to 3.3 dB) at the end of the bent arm of the Mach-Zehnder interferometer are achievable for 100 mW input pump power. The obtained results can be used for the design of the integrated Mach-Zehnder interferometers and optic devices.

Phase conjugate mirrors based on stimulated Brillouin scattering (SBS) in multimode undoped quartz fibers can be operated with high reflectivity. The reflectivity and threshold of the SBS process and the damage threshold of the fiber entrance surface were measured for fibers with core diameter of 25, 50, 100, 200 micrometers . With calibration of the measurement system such fibers can operate with more than 80% reflectivity and the damage threshold lies above 0.9 GW/cm². The SBS threshold is between 0.3 and 26 kW for all fibers investigated.

Bi₁₂TiO₂₀ single crystals doped with Cd, Cu, P, Cr, Ag, Al were grown by the top-seeded solution growth method (TSSG). The electrical measurements were carried out on different BTO samples. The electrical conductivity followed the Arrhenius low, with an activation energy ranged from 0.38 to 0.63 eV. Mobility and transport properties of charge photo carriers were investigated by the time-of-flight technique. For non-doped BTO and doped with Cu, P, Al and Cd the obtained values for drift mobility of electrons varying between (mu) equals10^-2 and 1 [cm²/V.s]. In the case of BTO doped with Al the dominant charge carriers were holes with mobility (mu) equals5x10^-3 [cm²/V.s]. These key photorefractive parameters were used to calculate the lifetime of charge carriers using the period of the recorded holographic photorefractive space gratings.

A variety of self-organized patterns were observed in liquid crystal modulators, generated because of their large and controllable nonlinearity. In this work, we investigated some fatty acids and mixtures with cholesterol, which showed, under certain conditions, thermotropic mesomorphism and a large sensitivity to the optical field. Depending on the transverse profile of the laser beam, a self-phase modulation and external self-focusing - illustrating the nonlinear wave propagation - were observed. A ring pattern, due to the steady-state far-field diffraction intensity distribution of the Gaussian beam of a helium-neon laser, transmitted through the samples, was experimentally and computer studied. This is useful both for building new photonic devices and for explaining some processes from the biological membrane.

In recent papers we presented a wave model for closed conservative bounded systems, whose behavior is described by the Schrodinger equation. For such a system, the Schrodinger equation is equivalent to the wave equation. The analysis of the wave properties reveals an intrinsic coherence of the electron motions. We approximate the fundamental and metastable states of laser active medium by closed conservative bounded systems. We show that the coherence of the laser radiation could be explained by a transition between these coherent states.

Selective buried waveguides have different regions, lying at various depths under the glass surface. This structure is formed by field-assisted inter-diffusion in an electrically inhomogeneous glass, with an electrical conductivity varying both spatially and in time. We present a simple, preliminary model of such a complex, two-dimensional structure. We explain the assumptions used to obtain a tractable model and discuss them in detail. Our results are illustrated by mono- mode structures, buried under normal electric field intensities. They are in qualitative agreement with experimental measurements. We discuss the improvements of the model, necessary to take into account spatial and temporal variations of glass properties.

In this paper we report some experimental results concerning the fabrication of Bragg gratings with submicronic period in Er-Yb-doped glass waveguides using interferometric method and of a monolithically integrated DFB laser. Also, a method used for monitoring the development process in real time using data acquisition program on a Labview platform and some results related to the characterization of the waveguides with gratings in reflection mode and a monolithically integrated DFB laser pumped at 980 nm are presented and discussed. These results can be used for the improvement of the fabrication processes of the above mentioned devices and optical integrated circuits.

Based on some experimental results we report in this paper the modeling of the maximum refractive index difference profile of the optical waveguides obtained in glass by double ion exchange (Ag⁺) using Gaussian and erfc functions. The dependences of the maximum refractive index difference, the center of the Gaussian and erfc functions in depth and width, respectively and the corresponding variances on the technological parameters: the width of the mask (window), the first and the second in-diffusion time of the ions were evaluated. The simulation results can be used for the analysis and the design of the optical integrated devices.

In this paper we present an analysis of the phase-matching conditions for internal second-harmonic generation in InGaAs quantum-well laser diodes in order to enhance the conversion efficiency. We have characterized the role of phase- mismatching in the spectral distribution of the internal second-harmonic generation in the CW operation of these lasers. The emission of pairs of narrow blue-green peaks having perfectly symmetrical spectral positions with respect to the central peak of pure second-harmonic generation at approximately 480 nm is most probably enhanced by a mechanism of reciprocal cancellation of the respective phase-mismatch vectors. This study is important for the assessment of the relationship between the structural parameters of the laser and the conditions which contribute to the stimulation of second-order optical nonlinearities in the laser active region.

A three-dimensional wave model for the stimulated Brillouin scattering (SBS) is built and analytically treated, in case of slowly varying envelope approximation and stationary regime. More complete analytical expressions for pump and Stokes wave intensities and for SBS reflectivity are found. A good agreement between theoretical and experimental data for reflectivities is shown for Gaussian transverse profile of the pump beam.

Phenol is a major pollutant under strict effluent restriction. Its toxicity is well known, both in aquatic environment and human health. Among the purification technologies, adsorption is widely used in ecological procedures for chemical industry, for water and air purification. In order to check up the adsorbent properties of different adsorbent materials, it is necessary to determine some modeling parameters as the diffusion constants and concentration profiles in the vicinity of the adsorbent. The visualization and measuring method used in this work is double-exposure holographic interferometry using a Bi₁₂TiO₂₀ (BTO) photorefractive crystal (PRC) as reusable recording material and a low cost laser diode, as coherent light source. By holographic methods, we are studying phenol adsorption on granulated active coal and active coal powder. The visualization of the diffusion layer and measurements of its dynamics have been performed.

The experimental study of heat diffusion in glass by a compact schlieren system is presented. The schlieren system has been set up with a single transverse mode laser diode as light source. We have used a plane thermal source (a heated metal plate) to generate thermal fields in a plane glass plate sitting perpendicular to the thermal source. The schlieren images were recorded using a CCD camera and a video recorder connected to a PC. A specific software did a further digital image processing. The experimental results have been checked against a theoretical model of the heat diffusion in an infinite medium at a strong and short thermal excitation by a plane thermal source. A good agreement between experimental and theoretical results was found, up to some differences between the experimental conditions and the theoretical hypotheses, which validate this method as a quantitative one in such experiments.

We prepared a copolymer of the maleic anhydride with styrene, to which a colored structure designated for the functionalization was added. The new polymer was used to prepare reverse-mode PDLC films. Reverse-mode PDLC are designed for applications where it is important that the failure of the device is a transparent state, rather than a scattering one. We obtained reverse-mode PDLC using a nematic liquid crystal with negative anisotropy (Delta) (epsilon) <0, LCM 3141 (NIOPIK), and we measured the optical transmission of the film. The system was switched from OFF-transparent state to the ON-scattering one, by a sufficiently small voltage, but with a rather low contrast ratio.

A lot of research studies have been devoted to image protection, either by cryptographic methods (e.g. Opt. Eng. 35, Sept. 1996) or by watermarking techniques (e.g. Proc. SPIE Vol. 3971). In a previous study, the authors reconsidered and improved the cryptographic mixing transformations proposed by CE Shannon for natural language, obtaining a strong cipher for images, as well. The present paper goes deeply inside of the image protection problem: (1) by presenting some variants for the cryptographic mixing transformations which are good even when burst errors appear in the cryptogram; (2) by enabling the use of an m-gram substitution in the mixing functions; (3) by advancing a bridge between cryptographic methods and watermarking techniques. The illustrations are obtained out of processing: (a) computer-simulated random images obeying different probability laws and autocorrelation functions, (b) natural images, and (c) test images.

In optical field analysis, like restoration of optical phase from phase-modulated images, data acquisition is the primary step in practical reconstruction algorithm. The relation between the experimental sampling rate and the sampling rate request by a particular algorithm is very important. A prior knowledge of the field characteristics cannot be ever done. In this paper we present a self-consistence criterion, based on Wittaker-Shannon theorem, for fields reconstruction algorithms. The criterion correlate the energy of the output database using primary data acquisition with the energy of a database obtained by sub-sampling initial data and can increase the confidence in the result of a reconstruction algorithm applied to a specific input field. We apply the criterion to validate the phase restoration of a following- pass, inverse cosine transform algorithm.

The possibilities of the laser-thermal diagnostics of the hidden defects in the solid state materials and multilayer structures are reported. The approach is based on the spectral analysis of the thermal radiation flux induced by the high power pulsed laser-surface interaction. To prove the method, the next things have been studied: (1) the distribution of the temperature and thermal radiation fields in the metal and semiconductor structures that is heated by the pulsed laser radiation under various laser regimes and material parameters; (2) the kinetics of surface and interface charge carriers recombination in the multilayer structures; (3) the thermal emission of the inherent radiation of multilayer structures that determines their basic characteristics: sizes of the macrodefects, thickness of interlayers, depth of penetration, thermal and electric conductivity, rate of heating and cooling of the local areas under the laser beam spot. It was found that even small variation in conditions of the laser-surface interaction due to the metal and dielectric defects and heterogeneity in the material structure can produce large changes in the amplitude and spectra of the laser induced thermal radiation, so such a technique could serve as a powerful tool for noninvasive inspection and express control of the hidden topology in the material structure, and the velocity of the surface carriers recombination of semiconductors can be monitored and controlled well.