International Journal of Electrical, Electronic and Communication Sciences ISSN: 2517-9438 Vol:3, No:4, 2009 702 Abstract—In this paper, a post processing scheme is suggested for improvement of Bit Error-Rate (BER) in optical fiber transmission receivers. The developed scheme has been tested on optical fiber systems operating with a non-return-to-zero (NRZ) format at transmission rates of up to 10Gbps. The transmission system considered is based on well known transmitters and receivers blocks operating at wavelengths in the region of 1550 nm using a standard single mode fiber. Performance of improved detected signals has been evaluated via the analysis of quality factor and computed bit error rates. Numerical simulations have shown a noticeable improvement of the system BER after implementation of the suggested post processing operation on the detected electrical signals. Keywords—BER improvement, Optical fiber, transmission performance, NRZ. I. INTRODUCTION PTICAL transmission networks based on wavelength division multiplexing (WDM) architecture is dominating the all-optical data transportation with bit rates exceeding several terabit-per-second rates to serve the ever increasing demand of Internet Protocol (IP) networks [1, 2]. Thus, full optical operation of these networks will be most important features in the near future. Some of the main TCP/IP networking functions such as routing, add-drop multiplexing and demultiplexing and wavelength conversion, need to be functional to encapsulate the IP packet requirements into the optical layer [3]. The linear as well as the nonlinear characteristics of the optical fiber at higher bit rates, seriously limit the data transmission performance and it is therefore becoming necessary to develop approaches to improve regeneration of transmitted data. Experimental investigations have shown a considerable progress in this direction [4, 5, 6]. These were based on compensation techniques, filtering, developing optimized line coding, and further processing of received signal. However, lot of research work needs to be carried out to improve the increasing effective data transmission through these systems [7]. Hadj Bourdoucen is with the Department of Electrical and Computer Engineering, Sultan Qaboos University, POBox 33, Al-Khodh, Muscat, 123, Oman. (email : hadj@squ.edu.om). Amer Alhabsi is with the Department of Electrical and Computer Engineering, Sultan Qaboos University, POBox 33, Al-Khodh, Muscat, 123, Oman. (e-mail: alhabsi@squ.edu.om). Simulation of such systems plays an important role in determining expected behaviors of components and devices prior to their experimental implementation and testing. This is a cheaper method for evaluating their performance since experimental set-ups involved are still relatively expensive [8]. In this paper, the effect of post processing received data from an optical fiber system using a signal detection scheme is investigated for NRZ modulation code. The objective is to improve the quality of detected data by reducing embedded noise induced by linear and nonlinear effects of the transmission channel. It is worth noting that the photodetection process itself adds more complexity as it deals with signals where many interactions happen between data and noise. The train of distorted bits of data received by the photodetector and after being pre-filtered is further processed using the proposed scheme to improve the overall BER of the system. The optical channel considered in this work relays on a standard single mode fiber operating at 1550 nm with no chromatic compensation to evaluate the intrinsic effect of the suggested post processing scheme. II. MODELING AND SIMULATION Fig. 1 shows the main blocks of the layout diagram of the optical transmission system adopted for simulation. As it appears from the diagram, the optical transmitter is composed of a number of multiplexed WDM wavelengths i varying within the ITU-standard range and centered at 1550nm. This packet of wavelengths is modulated by an NRZ driving circuit that is fed with a (2 7 -1) pseudorandom bit sequence (PRBS) signal. Signal Post -Processing PRBS Data Input Signal Visualization Laser Sources & Drivers SMF NRZ Driving Circuit Detection & Filtering Fig. 1 Block Diagram of the system used in simulation The laser sources used for generating these wavelengths have a full width at half maximum (FWHM) of 10MHz at data bit rates of 10Gbps. Standard Single Mode Fiber (SMF) was used for all the links considered. Their main parameters are as Improvement of Bit-Error-Rate in Optical Fiber Receivers Hadj Bourdoucen and Amer Alhabsi O