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.