J.L.S. Lima

Photonic time-division multiplexing (OTDM) using ultrashort picosecond pulses in a terahertz optical asymmetric demultiplexer (TOAD)

Abstract The performance of a terahertz optical asymmetric demultiplexer (TOAD) operating with an ordinary fiber and with a DDF and DIF (dispersion decreasing and increasing fiber) configurations, for three lengths of fiber ( ξ =π/2,2π and 5π) and using soliton and quasi-soliton laser profiles for the control pulse, was studied. The numerical simulations show that the increase of the fiber length leads to the decrease of the power for the first and second demultiplexed pulses and leads to a broadening of these pulses, with the exception of the TOAD operating with the DDF fiber. For the TOAD operating with a basic telecommunication fiber one see that the increase of the power of the control power lead to a strong compression of the demultiplexed pulse. Operating the TOAD using a DDF fiber one can say that the control power necessary to demultiplex the signal pulse is always lower compared with the TOAD with the normal telecommunication fiber. This is a strong suggestion that the use of the DDF fiber will allow the use of less control power. Our simulations considering the TOAD operating with a DDF and DIF with a linear profile conclude that it is possible to operate the TOAD with lower control power using a DDF fiber setup. For this device the demultiplexed pulses will present a compression on time duration and will be insensitive to the time profile of the control pulse. We also did simulations with the TOAD operating with DDF in four different profiles: hyperbolic, exponential, linear and Gaussian. For all the profiles the increase of the length of the fiber also decreases the pump power of the three first peaks for the soliton and quasi-soliton regimes. The first critical power is always lower for the quasi-soliton regime compared to the soliton regime for all profiles under consideration and all lengths of the TOAD under consideration. It was also observed that for all the profiles and lengths of fiber one has pulse compression for the switched pulse. For the ξ =2π fiber with the hyperbolic profile, both soliton and quasi-soliton profiles present the lowest critical power and the highest compression factors for all the considered profiles.

Acousto-optic tunable filter (AOTF) with increasing non-linearity and loss

Abstract In this paper, we did a study of the transmission characteristics of the acousto-optic tunable filter (AOTF) operating with ultra-short light pulses (2 ps). Initially one considers the performance of the device, with several lengths, operating in the non-linear regime without loss. It was observed that the effect of dispersion and non-linearity has strong influence on the pulse propagation when one increases the length of the AOTF. For shorter length of the device the switched pulse is presenting time broadening for soliton and non-soliton profiles. For higher length of the device, pulse break-up was observed for non-soliton profile and time displacement for the soliton profile. Considering the AOTF with 4 dB/mm of loss, one considers the device of length 0.25 mm constructed with several increasing non-linearity profiles. In this paper, we compare five simple coefficients of self phase modulation (SPM) profiles, namely linear, Gaussian, exponential, logarithm and constant. One can observe that there is always an optimum value for β (final value of the profile Q ( ξ ) of the non-linearity) that one can obtain a switched pulse with the same time duration of the input pulse. Comparing the soliton and non-soliton pulse propagation, one can say that the constant profile present the lowest value for β comparing with the other profiles. This value is around 1.53 and 1.79 for the non-soliton and soliton propagation, respectively. One can also say that one can operate the AOTF in a configuration that one can avoid the pulse break-up and have a switched pulse with the same time duration compared with the lossy AOTF. With the increase of the β parameter the pulse is showing break-up even for the constant profile. One concludes that is possible to operate the AOTF in a soliton and non-soliton input profiles. The study of the AOTF operating with ultra-short optical pulses provides possibilities for achieving, high efficiency in ultra-fast all-optical signal processing, especially for optical switches, filters and optical transistors. The 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 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.

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.

Time-division multiplexing (OTDM) using ultrashort picosecond pulses in a terahertz optical asymmetric demultiplexer (TOAD)

The performance of a terahertz optical asymmetric demultiplexer (TOAD) operating with an ordinary fiber and with a DDF and DIF (dispersion decreasing and increasing fiber) configurations, for three length of fiber (/spl xi/=/spl pi//2, 2/spl pi/ and 5/spl pi/) and using soliton and quasi-soliton laser profile for the control pulse, was studied. We also did simulations with the TOAD operating with DDF in four different profiles: hyperbolic, exponential, linear and Gaussian. Operating the TOAD using a DDF fiber one can say that the control power necessary to demultiplex the signal pulse is always lower compared with the TOAD with the normal telecommunication fiber. For all the profiles the increase of the length of the fiber also decrease the pump power of the three first peaks for the soliton and quasi-soliton regime.