M.G. da Silva

Soliton switching in three-core nonlinear directional fiber couplers

We present an analytical investigation of the propagation and the switching of fundamental solitons in a three-core nonlinear fiber coupler with a variational method using the Lagrangian density formulation. The analytical solutions were obtained directly from the coupled nonlinear Schrodinger equations. The transmission characteristics of first order solitons obtained by the analytical procedure agree well with the results from numerical analysis. Three different geometries for the nonlinear three-core directional coupler were studied. Taking into account the length of the coupler and the critical power a comparative study between these geometries was done.

Analysis of soliton switching in dispersion-decreasing fiber couplers

We present an analytical and numerical investigation of the propagation and the switching of fundamental solitons in a two-core nonlinear fiber coupler constructed with dispersion decreasing fiber (DDF) with a variational method using the Lagrangian density formulation. The analytical solutions were directly obtained from the coupled nonlinear Schrodinger equations. Our simulations considering six different profiles, linear, hyperbolic, exponential, logarithm, constant and Gaussian. The transmission characteristics, the critical energy and the compression factor of first order solitons obtained by the analytical procedure agree well with the results from numerical analysis. Twin core nonlinear directional couplers that include loss are also examined. The inclusion of loss results in the increase of the critical power of the coupler and broadening of the switched pulses, while the switching characteristics deteriorate. To compensate for this worse behavior, associated to the loss, we have investigated the effect of the DDF profile on the performance of the coupler. We show that appropriate shaping of the DDF profile is quite effective to recover, almost completely, the original switching behavior associated to the lossless situation. It is concluded that the hyperbolic dispersion profile is nearly optimum to the recovery of the lossless switching behavior.

All-optical soliton switching in three-core nonlinear fiber couplers

We present an analytical investigation of the propagation and the switching of solitons in a three-core nonlinear fiber coupler with a variational method using the Lagrangian density formulation. The analytical solutions were directly obtained from the coupled nonlinear Schrodinger equations. The transmission characteristics of first order solitons obtained by the analytical procedure agrees well with the results from numerical analysis. In addition, the analysis show the existence of soliton eigenstates, in the three core nonlinear fiber coupler, where no coupling between the fibers was observed.

Multistable all-optical switching behavior of the asymmetric nonlinear directional coupler

Asymmetric dual core nonlinear directional couplers that include an increasing self phase modulation profile are examined. The asymmetry is associated with the self phase modulation profile of one of the channels (direct channel). Looking at the transmission characteristics of the device, through the direct channel, one observes that, when pumping in the direct channel, there is a decrease in the critical power which is lower compared with the symmetric coupler, and the critical power is a single-value function of the nonlinearity. For the pump power in the cross channel the transmission function of the coupler presents regions of multistability, where the coupler presents more than one critical power for certain values of the self phase modulation profile index. It was also observed that all the profiles under study, with increasing self phase modulation profile, present this behavior. For the studied profiles, one region of multistability was observed where three possible critical powers were observed. However, for the exponential profile, a second region was observed for a higher value of the self phase modulation profile parameter. It is concluded that to operate the asymmetric coupler in a single-value region for the critical power, the exponential self phase modulation profile presents the best behavior for the profiles under study.

Logic gates based in asymmetric couplers : Numerical analysis

Abstract In this work, we present a numerical investigation of the transmission and switching of fundamental solitons in asymmetric nonlinear directional couplers, constructed with dispersion decreasing fibers (DDF). In this configuration, the coupler consists of two separated parallel fibers, one with a DDF profile and the other with a constant profile. We obtained the characteristics of transmission, extinction ratio, and compression factor of the device. The truth tables for the logic gates AND, OR, and XOR were obtained. We concluded that the device presenting a constant profile provided the best performance of the studied logic gates. Logic gates AND, OR, and XOR operating with extinction coefficient around 16.6 dB were obtained.

Monitoring of hydrocarbon vapor diffusion in air using a thermal wave interferometer

A discussion on the use of thermal wave interference (TWI) for the monitoring of the transients of hydrocarbon in air is presented. The thermal wave signal was modeled using the logarithm-mixing model for the thermal diffusivity of a two-phase gas system in which the hydrocarbon vapor concentration in the air-filled TWI cell is a varying function of time. The time varying hydrocarbon vapor concentration was described assuming the simple Fick’s model for mass diffusion of the hydrocarbon vapor in the stagnant air column of the TWI cell. The transient TWI signal amplitude data fitting yielded two parameters, namely, the saturation concentration and the characteristic diffusion time. From the corresponding values of the diffusion time the hydrocarbon mass diffusivities were straightforwardly obtained. The obtained values for the hydrocarbon mass diffusivities were found to be in good agreement with the ones reported in the literature.

Numerical Analysis of the Crosstalk on an Integrated Acousto-Optic Tunable Filter (AOTF) for Network Applications

In this article, we did a study of the crosstalk level (Xtalk) and extinction ratio (Xratio) of an acousto-optic tunable filter (AOTF) operating with ultra-short light pulses (2 ps). It is clear that the transmission bandwidth decreases as the length of the device increases. The compression factor was studied for the switched pulse in an AOTF without loss considering five nonlinearity profiles. One can observe that there is always an optimum value for β (final value of the nonlinearity) that one can obtain a switched pulse with the same time duration of the input pulse. The study of the crosstalk level, of this device, considering the optimum values of β obtained from the compression studies, as a function of the pump power (P0) was done. For the soliton profile at 1 W of pump power one can notice that the Gaussian profile presents the lower Xtalk value (−13 dB), and the constant profile presents the worst value (−9.8 dB). However, if one is looking for a specific Xtalk value, one can conclude that with the constant profile one can obtain this value with a lower power. For the quasi-soliton profile of the same device, with low pump power (1 W), one can notice again that the Gaussian profile presents the lower Xtalk value (−13 dB) and the constant profile presents the worst value (−9.87 dB). This fact can be explained because, with pump power at 1 W, soliton and quasi-soliton profiles lead equivalent input pulses and under the same conditions produce equal results. The Xtalk level, considering all the profiles as a function of the β value, was studied. For all the profiles one has a strong increase of the Xtalk level with the increase of the final β value of the nonlinearity profile. Comparing all the profiles one can conclude that the Gaussian profile presents the lower Xtalk value in the range of β values in use. At the same time the value of the Xtalk for this profile does not change much with the change in the β value, presenting values in interval (−13 dB; −11.7 dB). The studies of the Xratio of the same device operating with the input pulses with the soliton and quasi-soliton profiles reveal that for all the nonlinearity profiles the Xratio increases with an increase in pump power. For the quasi-soliton profile one can notice that there is a minimum of the Xratio as a function of the pump power. The Xratio considering all the profiles as a function of the β value shows that for all the profiles one has a strong increase of the Xratio level with the increase of the final β value of the nonlinearity profile. Comparing all the profiles one can conclude that the Gaussian profile presents the lower Xratio value in the range of β values in use. One can conclude that the operation of the AOTF in a switching configuration is worse for high pump power as observed for Xtalk. The study of the crosstalk level and the extinction ratio on the AOTF operating with ultra-short optical solitons provides possibilities for achieving high efficiency in ultra fast all-optical signal processing, especially for optical switches, filters, and optical transistors. The acoustic-optic tunable filter (AOTF) has attracted great attention in recent years, in part because it appears to be a suitable basis for multi-wavelength optical cross-connects. It is probably the only known tunable filter that is capable of selecting several wavelengths simultaneously. This capability can be used to construct a multi-wavelength router.

Numerical analysis in triangular and planar three-core nonlinear optical fiber couplers (TNLDC) operating logical gates

In this paper, we investigate the switching process in triangular symmetric and planar symmetric three-core nonlinear fiber coupler (TNLDC) and we have numerically shown, via the coupled nonlinear Schrodinger equations (NLSEs), that logic gates AND, OR and NXOR can be constructed from a triangular TNLDC while the planar TNLDC produced logical gates AND, NAND, OR, and XOR. We consider two basic models. The first, one triangular symmetrical structure with three cores in an equilateral-triangle arrangement and using a control signal (CS) applied to the first core and the second model present a transverse symmetrical structure with three cores in a parallel equidistant arrangement (or planar symmetrical structure), however the position of the control signal (CS) is applied to the input of the first fiber (core 1). 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. In comparing the performance of both switches operating as logic gates we will use the figure-of-merit of the logic gates [FOMELG(dB)] defined as a function of the extinction ratio of the gate outputs.

Analysis of Ultrashort Pulse Switching in an Acousto-optic Tunable Filter (AOTF) with Loss

In this paper, we did a study of the transmission characteristics of the AOTF operating with ultrashort light pulses (2ps). Initially one consider the performance of the device, with several lengths, operating in the nonlinear regime without loss. It was observed that the effect of dispersion and nonlinearity has strong influence on the pulse propagation when one increase the length of the AOTF. For shorter length of the device the switched pulse is presenting time broadening. For higher length of the device, pulse breakup was observed. Considering the AOTF with 4 dB/mm of loss, one consider the device of length 0.25 mm constructed with an increasing nonlinearity profile. It was observed that the increase in β (increase of the final value of the profile Q(ξ) of the nonlinearity) lead the switched pulse from broadening to optical compression. One can say that one can operate the AOTF in a configuration that one can avoid the pulse break up and have a switched pulse with a shorter time duration compared with the lossy AOTF. The second AOTF present a higher length (0.76 mm) with higher loss (40 dB/mm) is leading the switched pulse to a strong broadening. In the presence of the nonlinear profile configuration we start having pulse break up. With the increase of the β parameter the pulse is showing break-up where the more intense pulse is shorter than the input pulse. One can say that is possible to operate the AOTF in a situation where the switched pulse present a less intense satellite pulse. The study of the AOTF operating with ultra short optical solitons provides possibilities for achieving, high efficiency in ultrafast all-optical signal processing, especially for optical switches, filters and optical transistors. The acoustic-optic tunable filter (AOTF) has attracted great attention in recent years, in part because it appears to be a suitable basis for multi-wavelength optical cross-connects. It is probably the only known tunable filter that is capable of selecting several wavelengths simultaneously. This capability can be used to construct a multi-wavelength router.

Four wave mixing in a dispersion decreasing fiber (DDF) for a WDM system

Numerical investigation of the propagation of ultrashort pulses in the region of 1.55 mum and the conversion efficiency for the FWM and modulation instability of ordinary and different dispersion decreasing fibers for WDM systems was studied.