The Reduction of FWM effects using Duobinary Modulation in a Two-Channel D-WDM System Laxman Tawade*, Shantanu Jagdale*, Prof.Dr.Shankar Deosarkar * * Vidya Pratishthan’s College of Engineering, Baramati, India. tawadelaxman@rediffmail.com , shantanujagdale@gmail.com, sbdeosarkar@yahoo.com Abstract In this paper we show that the adoption of a duo binary Modulation scheme reduces the impact of FWM in a DWDM system. The levels of the FWM products are reduced by around 10 dB which will offer a significant performance benefit in digital systems. We have taken into consideration great demand for high data rate & have designed optical fiber system for 40 Gbps. Keywords-dispersion shifted fiber (DSF), Dense wavelength division multiplexing (DWDM), Four wave mixing (FWM), Bit error rate (BER). 1. Introduction In order to meet the huge capacity demands imposed on the core transmission network by the explosive growth in data communications the number of optical channels in dense-WDM optical networks is being increased. Since the gain bandwidth of EDFAs is limited, these requirements for a very large number of channels means that he channel spacing will have to be small. The current ITU grid specifies 100 GHz channel spacing, but systems are being considered with 50 GHz to 25GHz channel spacing. At these spacing, the non- linear effects of the optical fibre can induce serious system impairments and modulation schemes are now being developed which are robust to both the linear and non-linear behaviour of fibre. Duobinary modulation techniques are known to compress the optical spectrum, thereby facilitating the tighter packing of channels into the EDFA gain window. It has also been reported that the 2- level variant of duo binary signaling [1,2] almost eliminates the impact of SBS since the optical carrier component is suppressed [3]. Four-Wave-Mixing (FWM) is another non linear effect that can limit the performance of WDM systems [4,5]. In this paper, we experimentally demonstrate that a 2- level duo binary modulation format suppresses the FWM non-linear effects in two closely spaced WDM channels. This is particularly prevalent in optical networks employing dispersion shifted fibre (DSF) [6]. To our knowledge, this is the first experimental demonstration of same. The experimental setup is validated using simulation software Optisystem. 2. Experimental Set up Two experiments were conducted; one was to determine the level of FWM products in a conventional binary modulated system, and one to determine the level of the FWM products in a 2-level duo binary system. The average launch power was kept as constant as practicable for all of the experiments. The experimental set-up is shown in figure 1. A pattern generator drives the optical transmitter in both experiments. The pattern generator produces a PRBS at a bit rate of 40 Gbit/s. we have used CW LASER 1 which is operating at wavelength 1552nm & given power is 4 mw the optical transmitter generates a modulated optical signal (binary or duobinary depending on the experiment) which is combined with the second unmodulated optical carrier in the 2dB optical combiner. Second CW LASER 2 operating at wavelength 1551nm & given power is 3 mw. An EDFA follows the coupler to increase the launch power into the fibre to +10dBm. The signals are then transported