International Journal of Emerging Technology and Advanced Engineering Website: (ISSN , Volume 2, Issue 6, June 2012)

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1 Website: (ISSN , Volume 2, Issue 6, June 12) Comparison of, and Modulation Formats for High Bit Rate WDM-PON System using AWG Malti 1, Meenakshi Sharma 2, Anu Sheetal 3 1 Sai Institute of Engg. & Tech., Amritsar, Punjab, India 2 Sri Sai College of Engg. & Tech., Pathankot, Punjab, India 3 GNDU, Regional Campus, Gurdaspur, Punjab, India Abstract--In this paper, we have simulated 8 channel WDM-PON system for downstream signals using carrier suppressed return-to-zero (), duobinary return-to-zero () and the modified duobinary return-to-zero () modulation formats. WDM-PON system has been analyzed by varying input power from to dbm for different modulation formats in order to find the optimum modulation format for a high bit rate optical transmission system. Further, the system is evaluated 2.5Gb/s & 5Gb/s bit rates upto 13km in terms of Q value and eye opening for, and data formats. It is found that is superior to and and system gives optimum performance at input power P in =15dBm. Keywords: WDM-PON,,,, OLT, ONU. I. INTRODUCTION Passive optical networks are receiving much interest because they represent the cheapest way to provide fiber to the home [1]. Wavelength Division Multiplexed Passive Optical Networks (WDM-PONs) are expected to play a key role in realizing the next generation scalable and flexible access networks. A WDM-PON receives a dedicated wavelength for each Optical network Unit (ONU) thus providing better privacy, scalability. A WDM-PON solution provides scalability because it can support multiple wavelengths over the same fiber infrastructure, is inherently transparent to the channel bit rate, and it does not suffer power-splitting losses [2,3]. The bandwidth demand in the access networks has been increasing rapidly over the past several years. Residential subscribers demand first-mile access solutions that have high bandwidth and offer media-rich services. Similarly, corporate users demand broadband infrastructure through which they can connect their local-area networks to the internet backbone. The predominant broadband access solutions deployed today are the digital subscriber line (DSL) and community antenna television (CATV) / (cable TV) based networks. However, both of these technologies have limitations because they are based on infrastructure that was originally built for carrying voice and analog TV signals, respectively; although variations of DSL such as very-highbit-rate DSL (VDSL), which can support up to 5Mbits/s of downstream bandwidth, are gradually emerging. The maximum distance over which VDSL can be supported is limited to 15ft. Passive Optical Networks (PONs) have evolved to provide much higher bandwidth in the access network. The PON is an access network based on Optical Fiber. It is designed to provide virtually unlimited bandwidth to the subscriber. A passive Optical network is a single, shared optical fiber that uses a passive optical splitter to divide the signal towards individual subscribers. PON is called passive because other than at the central office there are no active elements within the access network. PON networks are basically point to multipoint (P2MP) networks, which is best for distributive services. In P2MP networks, the entire transmission capacity is divided among all subscribers for individual internet access. The most important aspect of PON architecture is its simplicity. The Optical Line Terminal (OLT) is the main element of the network and it is usually placed in the Local Exchange. Optical Network Units (ONUs) serve as an interface to the network and are deployed on a customer s side. ONUs are connected to the OLT by means of optical fiber and no active elements are present in the link. A WDM-PON solution provides scalability because it can support multiple wavelengths over the same fiber infrastructure, is inherently transparent to the channel bit rate, and it does not suffer power-splitting losses. In the downstream direction of the WDM-PON, the wavelength channels are routed from the OLT to the ONUs by a passive Arrayed Waveguide Grating (AWG) router, which is deployed at a Remote Node (RN) where the passive splitter is used in a TDM-PON. 83

2 Website: (ISSN , Volume 2, Issue 6, June 12) The AWG is a passive optical device with the special property of periodicity, which is the cyclic nature by which multiple spectral orders are routed to the same output port from an input port. Bock et al. [4] described WDM/TDM-PON architecture by using Free Spectral Range (FSR) periodicity and AWG. In this a shared tunable laser, photo receiver, DBA and remote modulation were used for transmitter and receiver. Transmission test showed correct operation at 2.5Gb/s up to 3km. By mean of optical transmission test the authors demonstrated that this architecture was feasible and offered good performance with low optical losses as compared to other PON architectures. Calabretta et al. [5] presented an innovative architecture to realize a single feeder bidirectional WDM/TDM-PON on modified NRZ (DPSK) downstream signals at kb/s and narrowband AWG. AWG was used as channel distributor and simultaneously demodulator for all the DPSK channels. Semiconductor Optical Amplifier (SOA) was used for bidirectional amplification and compensated splitter losses. In this remodulated upstream signals were obtained at 1Gb/s. The experimental result showed error free transmission for both upstream and downstream signals. Feny et al. [6] discussed a scheme in which modified NRZ format was used to realize multicast WDM-PON by adjusting downstream extinction ratio and achieved good BER rate performance for upstream signals. Han et al. [7] proposed a WDM-PON model with multicast capability like high scalability multi-wavelength converter and single copy broadcast capability by employing multistage AWGs at remote node. The result of this architecture was evaluated in terms of cost, scalability, link capacity and bandwidth per user in both upstream and downstream signals. In this architecture, the existing passive star coupler was replaced by a special passive optical device. Bosco et al. [8] demonstrated the use of NRZ, RZ and modulation formats in an ultra dense wavelengthdivision multiplexing (UDWDM) scenario at Gb/s with 5GHz channel spacing. They showed that, due to the narrow transmission filtering, the RZ pulse becomes NRZlike, and the modulation is duobinary coded. Furthermore, they established that NRZ modulation does not benefit from the introduction of a transmission optical filter, while it takes advantage of the orthogonal polarization launch of adjacent channels, but its performance is still worse than the RZ and performance in a UDWDM scenario. Dahan and Eisenstein et al. [9] compared the performance of three different modulation formats non return-to-zero (NRZ), return-to-zero (RZ) and carriersuppressed RZ (CS-RZ) for -Gb/s channels spaced at 1GHz using backward-pumped distributed Raman amplification over transmission distance of 375 km. They proved that the CS-RZ format achieves good performances in forward-pumped Raman amplification and backward pumped configuration because of the high nonlinear regime. Rajniti et al. [1] compared the performance of two modulation formats non return-to-zero (NRZ), return-tozero (RZ) for 2.5Gb/s bidirectional WDM/TDM-PON using narrowband AWG. They investigated the impact of extinction ratio (ζ) of Mach-Zehnder (MZ) amplitude modulator on the performance of WDM-PON for varying optical fiber lengths. The system performance had been analyzed by varying the value of ζ from 2 to 22dB. They found that the system gave optimum performance at extinction ratio (ζ) value db. Further, the effect of variation in the input power (from to dbm) and transmission distance upto 6km was observed in terms of Q value and eye opening for NRZ and RZ data formats. They found that NRZ was superior to RZ and system gave optimum performance at input power P in =1dBm. In this paper, we have extended the work of reference [1], they compared the performance of two modulation formats non return-to-zero (NRZ), return-to-zero (RZ) for 2.5Gb/s bidirectional WDM/TDM-PON using narrowband AWG by varying input power (from to dbm) and transmission distance upto 6km. We have evaluated the system performance by using advanced modulation formats and transmission distance upto 13km has been observed in terms of Q value and eye opening factor. Here, in section 2, the system description and simulation parameters have been described. In section 3, the results of the simulated system have been reported for different modulation data formats, signal input power, bit rate and distance. Finally in section 4, conclusions are made. II. SYSTEM DESCRIPTION AND SIMULATION The schematic of optical communication system simulation setup is shown in Fig.1. An externally modulated CW DFB Laser Array having eight number of output ports, frequency of 155nm, channel spacing of 1GHz with variable input power (from to dbm) is used. The WDM multiplexer also operates at the frequency of 155nm with the bandwidth 1GHz and channel spacing of 1GHz. 84

3 International Journal of Emerging Technology and Advanced Engineering Website: (ISSN , Volume 2, Issue 6, June 12) DFB Laser Array WDM Multiplexer / or Modulator EDFA Power = 1dBm & Bit rate = 2.5Gb/s AWG 1*8 Fiber AWG 8*8 Circulators Power Splitter Circulators PIN Detector Optical Transmitter Low Pass Bessel Filter BER Analyser 15 Power = 15dBm & Bit rate = 2.5Gb/s Q measurement 3R- Regenerator 1 Fig.1: Schematic of Simulation Setup Three different types of modulation formats carrier suppressed return to zero (), duobinary return to zero () and modified return to zero () has been used. An Erbium Doped Fiber Amplifier with gain 17dB and noise figure 6dB is used in the transmitter to boost the optical signal to the desired power level. The EDFA is followed by power splitter and upstream circulator with return loss and isolation of 6dB Array waveguide grating AWG (8 8) with frequency of 193.4THz and bandwidth = 1GHz is used for upstream and AWG (1 8) with frequency of 155 nm and bandwidth of 1GHz is used for downstream. A bidirectional Single Mode Fiber SMF fiber with parameters attenuation of.24db/km, dispersion slope of.75 ps/km-nm 2 and dispersion at 155nm is 16.75ps/km-nm has been used and the length of fiber has been varied up to 13km. III. RESULTS AND DISCUSSION Three modulation formats have been compared by varying input power and transmission distance up to 13km for WDM-PON system in terms of Q value [db] and eye opening factor. The Fig. 2, 2 and 2 shows the graphical representation of Q value as a function of transmission distance at varied input power and bit rate of 2.5Gb/s for, and data formats for downstream data respectively Power = dbm & Bit rate = 2.5Gb/s Fig.2 Length Vs Q.factor for, and modulation formats at bit rate = 2.5Gb/s P in = 1dBm P in = 15dBm P in = dbm It is cleared from the graphs with increase in power and length of fiber, the system performance has also been increased. But after P in = 15dBm the system performance has been degraded due to more dominance of non linear effects like Cross Phase Modulation (XPM) and Four Wave Mixing (FWM). 85

4 International Journal of Emerging Technology and Advanced Engineering Website: (ISSN , Volume 2, Issue 6, June 12) It has been observed that the system give repeaterless transmission up to 128km. When bit rate = 2.5Gb/s, the gives better performance as compared to and modulation data formats Power = 1dBm & Bit rate = 5Gb/s It is clear from the graphs as the bit rate increases the system performance has been decreased. It has been observed that gives better performance as compared to and, when bit rate = 5Gb/s. It is also observed that at bit rate = 5Gb/s shows optimum performance at input power P in = 15dBm as compared to and. We have evaluated the system performance by varying bit rate at 2.5Gb/s and Gb/s and it is observed that the system gives optimal transmission when the data is transmitted at the bit rate of 2.5Gb/s. Fig.4.shows the eye diagrams for downstream data respectively for, and modulation formats at distance 6km. These results further endorse the results of earlier discussion. The results obtained are also consistent with the results reported in [8] Power = 15dBm & Bit rate = 5Gb/s Power = dbm & Bit rate = 5Gb/s Fig.3 Length Vs Q.factor for, and modulation formats at bit rate = 5Gb/s.P in = 1dBm P in = 15dBm P in = dbm The Fig. 3, & shows the graphical representation of Q value as a function of transmission distance at varied input power and bit rate of 5Gb/s for, and data formats for downstream data respectively. 86

5 Website: (ISSN , Volume 2, Issue 6, June 12) Fig.4. Received Eye diagrams at bit rate 5Gb/s for downstream over transmission distance 6 km when input power P in = dbm for modulation formats IV. CONCLUSIONS In this paper, we have simulated the WDM-PON system by varying input power P in from to dbm, bit rate at 2.5Gb/s, 5Gb/s and 1Gb/s and length of fiber up to 13km. It is observed that at bit rate 2.5Gb/s, the faithful transmission distance covered is 128km and at bit rate 5Gb/s, the faithful transmission distance covered is1km.further, it is concluded that at bit rate 2.5Gb/s and 5Gb/s the and shows the optimum performance. REFERENCES [1] Asier Villafranca Velasco, Member, OSA, Juan Carlos Aguado, and María Ángeles Losada Binué Juan José Martínez, Juan Ignacio Garcés Gregorio, Member, IEEE, Alicia López Lucia, Novel WDM-PON Architecture Based on a Spectrally Efficient IM-FSK Scheme Using DMLs and RSOAs, journal of lightwave technology, vol. 26, no. 3, february 1, 8. [2] Zhaowen Xu, Yang Jing Wen, Wen-De Zhong, Attygalle, M, Xiaofei Cheng, Yixin Wang, Tee Hiang Cheng,Chao Lu WDM- PON architecture with a single shared interferomatric filter for carrier reuse upstream, Journal of Lightwave Technology, Vol.25 (7). [3] Manish Choudhary, Bipin Kumar Analysis of next generation PON architecture for optical broadcast access networks IEEE Comm. Mag. (6). [4] Carlos Bock, Josep Prat, Stuart D. Walker Hybrid WDM/TDM- PON using AWG FSR and featuring centralized light generation and dynamic bandwidth allocation, Spanish ministerio technology project TIC2-53 (5). [5] N.Calabretta,M.Presi,R.Proietti,G.Contestabile and E.Ciaramella A bidirectional WDM/TDM-PON using DPSK downstream signals and a narrowband AWG, IEEE Photonics Technology Letters. Vol.19.No.16 (7). [6] Hanlin Feny, Fengqing Liu A novel scheme of multicast WDM- PON using modified NRZ signal format, Proceedings of the IEEE INFOCOM (9). [7] Kyeong-Eun Han, Kyoung-Min Yoo, Won Hyuk Yang, Young- Chon Kim Design of AWG based WDM-PON architecture with multicast capability, Proceedings of the IEEE INFOCOM (8). [8] G. Bosco, A. Carena, V. Curri, R. Gaudino, P. Poggiolini, On the use of NRZ, RZ, and Modulation at Gb/s with narrow DWDM channel spacing, J. Lightwave Technol. (9) (2) [9] D. Dahan, G. Eisenstein, Numerical comparison between distributed and discrete amplification in a point-to-point -Gb/s -WDMbased transmission system with three different modulation formats, J. Lightwave Technol. (2) 379. [1] Rajniti, Anu Sheetal Comparison of RZ and NRZ Data Formats for 2.5Gb/s Bidirectional WDM/TDM-PON using Narrowband AWG International Journal of VLSI and Signal Processing Applications, Vol. 1, Issue 2, May 11,(95-11),ISSN