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In this paper we did a study of logic gates obtained in the operation of a three-core non linear directional coupler (TNLDC) and an asymmetric two-core coupler (DNLDC) operating in the CW regime (the laser signals have the same wavelength). The symmetric three-core coupler (TNLDC), with their cores identical, in a planar arrangement, was studied using a control pulse applied to the first core. The second structure is an asymmetric twocore coupler (DNLDC). Looking at the transmission characteristics of the device, through the direct and cross channel, we did a study of the extinction ratio (Xratio) of these devices. For both devices we did a numerical investigation with the objective to implement logic gates. The DNLDC supplied AND, OR and XOR gates while the TNLDC supplied AND, NAND, OR, XOR and NOT gates. In comparing the performance of both switches operating as logic gates (DNLDC and TNLDC) we define, for the first time, a figure-of-merit of the logic gates (FOMELG). In this criteria the FOMELG is defined as a function of the extinction ratio of the gate outputs. Comparing the same gates of the three and two-core NLDC we observe that the logical gates of the three-core TNLDC present a better performance than the one of the two-core DNLDC considering the figure of merit FOMELG, besides the fact that is simpler to fabricate a symmetrical coupler (with identical cores) comparing with an asymmetric coupler. We believe that the use of this figure of merit will be useful in the study of the performance of logic gates to be used in communication systems.

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A new optical encryption method using an acousto-optic tunable filter (AOTF) operating simultaneously with pulse position modulation (PPM) and pulse amplitude modulation (PAM) is proposed in this paper. This device operates with ultrashort soliton light pulses (2ps), which are modulated in agreement with the technique of pulse modulation just mentioned. In this way any pulse carries naturally two bits of information but when the encryption proposed here, is applied, each encrypted pulse, carries four bits of information. We have analyzed the sixteen output possible situations, modulating the input pulses polarized in TE and TM modes allowing a variation in the PPM (ε PPM ) and PAM (ε PAM ) parameters for each modulation. We have defined all the possibility pairs of PPM-PAM parameters where the encrypting procedure is possible.

In this paper, we did a study of the effect of the presence of BIT (Bi4Ti3O12) in the dielectric and optical properties of the CaCu3Ti4O12 (CCTO) thick films. The films were prepared by the solid sate procedure. Mechanical alloying followed by the solid state procedure has been used successfully to produce powders of CaCu3Ti4O12 (CCTO) and BIT (Bi4Ti3O12) to be used in the composites. We also look at the effect of the grain size of the BIT and CCTO in the final properties of the composite film. The samples were studied using X‐Ray diffraction, scanning electron microscopy (SEM), Raman and infrared spectroscopy. We also did a study of the dielectric function (K) and dielectric loss (D) of the films. The role played by the grain size of CCTO and BIT in the dielectric constant and structural properties of the films are discussed. These measurements confirm the potential use of such materials for small high dielectric planar devices. These films are also attractive for capacitor applications and certainly for microelectronics, microwave devices (mobile phones for example), where the miniaturization of the devices is crucial. POLYM. COMPOS., 28:771–777, 2007. © 2007 Society of Plastics Engineers

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