Optimization of the apodization strength for linearly chirped Bragg grating dispersion compensators in optical fiber communications links P. FERNÁNDEZ, J.C. AGUADO, J. BLAS, F. GONZÁLEZ , I. DE MIGUEL, J. DURÁN, R.M. LORENZO, E.J. ABRIL, M. LÓPEZ Dept. of Signal Theory, Communications and Telematic Engineering. University of Valladolid Campus Miguel Delibes, Cmno. del Cementerio s/n, 47011 SPAIN Abstract: - The optimization of apodized linearly chirped fiber Bragg gratings in the field of chromatic dispersion compensation is discussed in terms of group delay response and pulse recompression. To develop this study two prototype scenarios are considered to show the different behavior of the compensating devices in function of the link length. Simulation results for 20 ps gaussian pulses transmitted and recompressed with different grating designs over the both links are presented. The maximum deviation error and the regression slope parameters are introduced to compare the quality of the group delay response to establish an optimum design of the apodization strength. Key-Words: - Bragg gratings, dispersion compensation, pulse recompression, apodization , chirp, group delay ripple, compression ratio. 1 Introduction Degradation of transmitted signals due to chromatic dispersion is one of the major limiting factors in long haul optical communication links, since transmission rates are constantly increasing and the loss of optical fiber becomes lower. Several techniques have been proposed to achieve dispersion compensation and pulse recompression as prechirped pulse transmission or dispersion shifted fibers. However, the first one does not cancel the dispersion completely, and the second one requires modifying existing fiber links. In recent years, there has been increasing interest in dispersion compensating fiber Bragg gratings because they are entirely passive and their size, cost and fiber compatibility make them very attractive devices[1]. Given that the group delay response plays a decisive role in the dispersion compensation behavior [2], a detailed study of the design parameters that influence this delay function would be helpful to achieve optimum results. In this paper we present a study about the effect of the apodization strength in function of the total amount of dispersion to be compensated, this is, the fiber link length. Two general prototypes has been considered, and we have computed the simulated results for gaussian pulses transmitted and recompressed with the different ALCFBG’s designs. In Section II we develop the dispersion compensation design and in Section III we present and discuss the computed results for the different apodization strength profiles in the two scenarios. Finally, In Section IV the main conclusions are presented. 2 Dispersion compensation design For a determined optical link, with an specified length L f and dispersion parameter D f , we can design a Bragg grating that can achieve the opposite dispersion level in order to cancel this undesirable effect. Some of the parameters as the linear chirp will be determined by the time delay slope required, but others as apodization function and modulation depth open a wide variety of possibilities to improve the response of the device. The minimum length required to compensate the dispersion introduced by the fiber link is [3]: n L D c L f f 2 0 l ∆ = (1) Where c is vacuum speed, n is the refractive index of the fiber, and ∆λ is the bandwidth to compensate for chromatic dispersion. In fact, L 0 is the required length for a uniform grating. Nevertheless, we can apodize the Bragg grating, but in that case we should use a greater length to compensate the reduction of the coupling strength caused by the apodization profile at the grating ends [4]. In order to establish an optimum profile to acquire the best dispersion compensation, several parameters have been reported in previous works, as the performance versus the apodization factor or the grating length. [5]. However, the