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

In this paper we did a study of the transmission characteristics of the AOTF operating with ultrashort light pulses (2ps), for soliton and non-soliton propagation regimes. In a preliminary study one has considered the performance of the device, with several lengths, operating in the nonlinear regime without loss and in the presence of loss. In this paper one considers the device of length 0.25mm with 4dB/mm of loss and constructed with several increasing non-linearity profiles. We compare five simple coefficients of self phase modulation (SPM) profiles, namely: linear, Gaussian, exponential, logarithm and constant. From our study, we suggest the best profile region of the non-linearity parameter to recover the original performance in the nonlinear transmission of the AOTF and to overcome the effect of the intrinsic loss in the device. Introduction The acoustic-optic tunable filter [1](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. Cross-connects are important in multi-wavelength networks because they can enable reconfigurable network architectures that can adapt to changing traffic patterns and enhance network survivability [2]. A multi-wavelength cross-connect capable of switching a moderate number of wavelengths could enable multihop networks providing access to millions of network nodes with a reasonable number of hops. The AOTF is attractive for this application because it provides simultaneous, transparent and nearly independent switching of many closely spaced and arbitrarily chosen wavelength channels, a large and flexibly addressed wavelength range, rapid tuning (order of a few μs) across the accessible wavelengths, low optical loss (3-4 dB/stage), and the potential for integration of several functions on the same substrate [2]. Recent improvements in the AOTF design included pass-band engineering to reduce side-lobs [3], flatten the wavelength response [4], which reduce the cross talk and increase the channel-width-to-channel-spacing ratio. In this paper, we did a study of the transmission characteristics of the AOTF operating with ultra-short light pulses (2ps of time duration, 1ps=10s). In a preliminary study one has examined the performance of the device, with several lengths, operating in the nonlinear regime without loss and in the presence of loss. Lossless device is an idealized situation. In practice, large or small, material loss is unavoidable, especially when nonlinearities are based on absorptive process in semiconductors. The absorption, uniformly distributed over the device, will set a limit to the operation of the device [5,6]. Considering the loss, in this paper, one investigates the effect of several increasing self phase modulation (SPM) profiles on the performance of the AOTF. Five closely SPM profiles named linear, Gaussian, exponential, logarithm and constant has been considered. From our preliminary study of the SPM profile, we observed that for the nonlinear AOTF with loss, the increasing nonlinear profile could lead to pulse compression or pulse break up depending on the length of the AOTF, propagation regime and the magnitude of the loss.