E.F. de Almeida

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.

Infrared and complex dielectric function studies of LiNbO3 in niobate glass-ceramics

Niobate glasses and ceramics [(x Nb2O5 (0.5 − x) P2O5) 0.5 Li2O] were prepared by the melt-quenching method and analysed by means of infrared spectroscopy, X-ray powder diffraction and complex impedance methods. LiNbO3 crystals were detected for high niobium content samples. The study of the complex dielectric function of the LiNbO3 ceramics revealed a very broad acoustic resonance mode around 3 MHz. This resonance was associated to the thickness mode of the LiNbO3 plate ceramic resonator. Electrical poling was performed at 300°C for 6 hours under an applied dc potential of 1 kV. Strong changes were observed on the complex dielectric function of the niobate ceramic after the poling. The study of the properties of these ferroelectric ceramics is important in view of possible applications in ultrasonic devices such as delay lines and transducers.

Structure of iron niobophosphate glasses investigated by DTA, infrared and Mössbauer spectroscopy

Activation energies for crystallization of 50 glasses, with x = 0, 5 and 10 mol%, were determined by differential thermal analysis (DTA). The structure was investigated by infrared and M?ssbauer spectroscopy. Samples with x = 5 mol% of show larger activation energy . Absorptions at P-O-P, P=O, and units are presents in these glasses. P=O absorptions disappear at compositions with x = 5 and 10 mol% of , which shows absorption around , attributed to units. According to M?ssbauer results high spin and at distorted octahedral sites are present in samples with x = 5 and 10 mol% of , thus working as a network modifier.

Acousto-Optic Tunable Filter (AOTF) Revisited: Ultrashort Optical Pulses Crosstalk Studies on the Lossy Filter

We examine again the crosstalk level (Xtalk) and extinction ratio (Xratio) of an acousto-optic tunable filter (AOTF) operating with ultrashort light pulses (2 ps), now considering the loss effect. The compression factor was studied for the switched pulse with lossy AOTF (α dB = 4 dB/mm) considering five nonlinearity profiles. One can observe that there is always an optimum value for δ (final value of the nonlinearity) that one can obtain a switched pulse with the same time duration of the input pulse (C = 1). The compression factor for the switched pulse along the filter length shows that for the constant profile, the compression factor is around 1 all over the device. The study of the crosstalk level (Xtalk) of this device, considering the optimum values of δ obtained from the compression studies, as a function of the pump power (P 0) was done. The acousto-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 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.

Dielectric Complex Function Studies of LiNbO3 in Niobate Glass-Ceramics

Niobate glasses and ceramics [(xNb 2 O 5 . (0.5-x) P 2 O 5 ) . 0.5 Li 2 O] were prepared by the melt-quenching method and analyzed by means of infrared spectroscopy, X-ray powder diffraction and complex impedance methods. LiNbO 3 crystals were detected for high niobium content samples. The study of the complex dielectric function of the LiNbO3 ceramics revealed a very broad acoustic resonance mode around 3 MHz. This resonance was associated to the thickness mode of the LiNbO 3 plate ceramic resonator. Electrical poling was performed at 300 °C for 6 h under an applied dc electric field of 7 kV/cm. Strong changes were observed on the complex dielectric function of the niobate ceramic after the poling. The study of the properties of these ferroelectric ceramics is important in view of possible applications in ultrasonic devices such as delay lines and transducers.