"We report secure data transmission performed using chaotic lasers with different external cavity geometries and applying the chaotic masking method based on subcarrier and phase modulations of the chaotic optical carrier. Two semiconductor lasers with similar multimode emission spectra and self-optical feedback provided, respectively, by ring and linear external cavities, were optically coupled and chaotically synchronized into a master – slave scheme. The transmitted message frequency modulates the radio frequency signal which modulates in phase the master chaotic carrier. Based on the robustness of the used encryption method and the synchronization characteristics of the two lasers, the decryption is conducted by the simple radio frequency spectrum monitoring of the slave emission."

Polyvinyl alcohol is unique among polymers. Apart from its preparation, it is not built up in polymerization reactions from monomers, unlike most vinyl-polymers, and it is biodegradable in the presence of suitably acclimated microorganisms. It is an environmentally friendly material for a wide range of applications, from medical ones, based on its biocompatibility, to integrated optics. This paper reviews, in addition to the preparation and optimization of films of polyvinyl alcohol doped with different metal species, the role of dopants and doping technologies in the involved electronic mechanism. The optical properties were studied by UV-VIS-IR, Mössbauer spectroscopy, and other measurement techniques, with applications such as real-time holography, microlasers, optical sensors or nanophotonics in mind.

Starting from the concept of interference lithography, developed several years ago, which is currently used in fabrication of 2D and 3D simple shapes periodical structures in so called holographic lithography, or laser lithography, we analyze in this paper the possibility of practical application of the concept for the realization of non-periodic patterns into a commercial photoresist.

The injection current of an external-cavity semiconductor laser working in a regime of low-frequency fluctuations (LFFs) is modulated at several MHz. The rate of power dropouts in the laser emission is correlated with the amplitude and frequency of the modulating signal. The occurrence of dropouts becomes more regular when the laser is driven at 7 MHz, which is close to the dominant frequency of dropouts in the solitary laser. Driving the laser at 10MHz also induces dropouts with a periodicity of 0.1 mu s, resulting in LFFs with two dominant frequencies.

An experimental analysis of phenomena observed in the laser emission of a semiconductor laser operating with an external cavity system in the low-frequency fluctuations regime has been carried out. The chaotic behaviour of the semiconductor laser emission with external feedback is influenced by laser parameters. The optical feedback coefficient, the injection current and diode temperature greatly influence the chaotic system evolution. In this paper we present data about the control of the chaotic dynamics of semiconductor lasers for different sets of experimental parameters.

The paper deals with optical and electronic properties of the aluminophosphate glasses containing Fe–Mn and Fe–Cr ion pairs in different concentration. The influence of the mixed alkali ions over the electronic properties has been investigated. The optical behavior (optical transmission) of the glass samples has been studied by UV-VIS spectroscopy and the refractive index dependency on wavelength has been discussed. The transmission spectra show features specific for the doping transition ions (TM), revealing different oxidation states of iron (Fe 2+ /Fe 3+ ), manganese (Mn 2+ /Mn 3+ ) and chromium (Cr 3+ /Cr 6+ ) in the vitreous network. Mössbauer spectroscopy offers information regarding the TM oxidation states, redox processes and the iron coordination symmetry in the vitreous network. In the case of Fe–Mn doped glasses, the percentage of Fe 2+ is about 40% and a doubled iron content leads to an increasing of Fe 2+ percentage up to 53%. The replacing of lithium ions by natrium ions (mixed alkali effect) provides an increasing of the Fe 2+ percentage up to 56%. The occurrence of the tetrahedral or octahedral symmetry of Fe 2+ ions bonded by O 2− ions depends on the transition ion nature and Li + /Na + ratio. Infrared absorption spectra of the pair transition ions-doped aluminophosphate glasses reveal optical phonons specific for the phosphate glass matrix.

The chaotic behavior of on external-cavity semiconductor laser (ECSL) working in a regime of low-frequency fluctuations (LFFs) can be controlled by external electro-optical phase or intensity current modulation. It is shown by numerical simulation that, for specific values of the modulating frequency and amplitude, the phase difference between the laser power drop-out and the modulator remains constant in time leading to phase-synchronized states, steady LFFs, so called m:n phase synchronization. The degree of stabilization is determined by calculating Shannon's entropy and by the analyzing the stability of the phase locking. The synchronization regions are mapped and zones of low and high amplitude chaos are identified. The light emission can be stabilized from a regime of large amplitude chaotic oscillations corresponding to LFFs to one of low-amplitude chaotic or even periodic oscillations. The dynamics of the laser can be controlled when the period of the modulating signal is comparable with the laser itinerancy time between consecutive external-cavity modes.

The electron transfer processes induced by the ultraviolet exposure of the Fe and Sb doped polyvinyl alcohol (PVA) thin films were studied in comparison with those appeared in the correspondent mono (Fe or Sb) doped ones. Samples with different thickness and subjected to different exposures were analysed by optical absorption as well as by Fe-57 and Sb-121 Mossbauer spectroscopy. The influence of each element from the pair on the electronic mechanism activated by the ultraviolet exposure was investigated. Accordingly, the (Fe+Sb) doped PVA presents improved electronic characteristics, in respect to the specific behaviour of single metal doped polymer recording media for real time holography.

The effect of periodic phase modulation of light on a chaotic external-cavity semiconductor laser working in a regime of low-frequency fluctuations (LFFs) is studied numerically. It is observed that the phase modulation changes the time period between consecutive dropouts in the emitted laser intensity. A new variable ΦL is defined as the phase of the laser's LFFs, which increases in time with 2π after each power dropout event. The phase ΦPM of the periodic phase modulator is unfolded on the real axis and increases linearly at a rate given by the modulating frequency. It is shown that the phase difference between the laser and the modulator ΔΦ(t)=mΦL(t)−nΦPM(t), where m and n are integers, remains constant in time, leading to phase-synchronized states, for specific values of the modulating frequency and amplitude.

This paper presents experimental results concerning the influence of the additives on the physical properties of polymer films. Metal oxides/inorganic salts were used as additives in vinyl-polymers solutions. The physical properties of the metal doped polymer films can be significantly modified by the composition of the doping elements and the curing conditions of the polymer. Morphologic, electronic, magnetic and optic properties of the doped polymers were analysed by AFM, SEM, Mössbauer spectroscopy and optical measurements. The film composition and the deposition processes were optimized to allow a better control of the optical parameters (refractive index, transmission), to reduce the processing temperatures and to improve the chemical sensitivity of the films for sensor applications. These compounds can be easily spin coated onto a variety of directly patterned semiconductor substrates.

A series of four coordinated homologous of d(8) Ni(II), Pd(11), d(9) Cu(II) ions and 1-phenyl-3-methyl-4-azo-(2'-carboxyphenylene)-pyrazol-5-one (LH) as ligand were obtained for the metal to ligand ratio 112 with the general formulae [A W). These compounds were characterized by elemental analyses, FTIR, RPE spectra. The fundamental principles associated with exploiting metal to ligand charge transfer MLCT bands in the systems of poly (vinyl alcohol) (PVA) matrix embedded with these coordinative compounds, as thin films were studied by means of UV-VIS spectra. The effect of the polymeric matrix on the metal-to-ligand charge transfer was related to the MLCT transitions of the thin films of the free coordination compounds and was evaluated as a start point for a high hyperpolarizability coefficient, beta(0).

Melt spun ribbons of FexCu100−x were obtained by different procedures, in order to maximize the dispersion of the Fe atoms in the Cu matrix. Subsequent thermal and mechanical treatments were used for a controlled crystallization process of the soft magnetic phase. A detailed analysis of structural aspects and crystallization dynamics and their relation with the magnetic behavior of the Fe–Cu ribbons has been obtained via Mössbauer spectroscopy, X-ray diffraction (XRD) and magnetic measurements. In order to obtain composite permanent magnets with shape anisotropy, the optimal conditions and the suitable processing were established.

The a nalysis of phenomena that appear in the c haotic coupling process of two laser diodes operating with external cavity has been made using numerically simulation o f the Lang-Kobayashi type evolution rate. We present some characteristic cases of the coupling and the data coding transmission between the laser diodes, function of the number of laser active modes in master and slave. We analyze for these cases the efficiency of the decoding process.

Aluminophosphate glasses doped with Fe, Mn, and Cr have been obtained by a wet non-conventional method. Structural information was provided by IR absorption spectra in the range 2000-500 cm(-1). The optical behaviour (transmission and refractive index) of the samples has been studied by UV-VIS-NIR spectroscopy. The Fe valence state and the local coordination were also analysed via Fe-57 Mossbauer spectroscopy, whose data revealed the redox equilibrium in the Fe-doped glasses according to the redox potentials of the transition ions.

We present proof-of-principle results regarding the possibility of micro-engraving Potassium Dihydrogen Phosphate (KDP) crystals using laser ablation techniques. The results of the work show that this technique can be used for realizing integrated optics and micro-optics components that are based on such crystals, one of the envisaged directions being that of integrated electro-optical modulators.

The electronic mechanisms induced by the UV exposure of thin films of polyvinyl alcohol doped with pairs of mixed valence metal ions were studied in relation to their optical behaviour by Mossbauer spectroscopy and optical absorption. The results obtained definitely point to the role of each element from the pair in the electronic mechanism involved, with influence on the optical properties regarding applications in real-time holography and integrated optics.

The major target of conductive polymer technology development has been to combine the electrical and optical properties of conducting materials with the mechanical and processabilit y properties of commodity bulk polymers. Polyaniline was synthesized at – 15C using a polyethylenglycole / ice bath and doped with Fe ions. Polyaniline films (tenths of μm) were prepared by the gravity method. The dried films were exposed to UV (300nm <λ< 500nm, 10mW/cm), up to 25 min. The conduction mechanism vs. the exposure time was analyzed by resistively measurements and Mössbauer spectroscopy. Mössbauer measurements show that by applying the UV exposure, electrons from the polymer chains are trapped by the Fe ions, changing their valence from Fe to Fe. Corroborating this effect with the decreasing trend of the resistance in the UV exposed Fe doped polyaniline, it results directly that the polarons are the charge carries in the analyzed films and the final effect of the UV light is to increase their concentration. C. Valsangiacom et al. 648

The synchronization phenomena that appear in nonlinear dynamics of two coupled external cavity semiconductor lasers can be used in communications systems. Numerically solving the Lang-Kobayashi system of equations for such a system we analyze the possibility of transmitting encoded information by modulating either the transmitter output light or the transmitter injected current. The synchronizing of lasers chaotic orbits are analyzed using both the phase for electric fields and Hilbert phase for intensities of the diode lasers light.

The electronic mechanism responsible for the optical behavior of the mixed Fe and Sn doped polymers were studied in comparison with the correspondent single doped (Fe or Sn) ones. Optical absorption as well as Fe-57 and Sn-119 Mossbauer measurements were performed on different UV exposed films. The new data provided the role of each element from the pair on the involved electronic mechanism induced by irradiation.