Optics and Photonics Journal, 2013, 3, 318-323 http://dx.doi.org/10.4236/opj.2013.35049 Published Online September 2013 (http://www.scirp.org/journal/opj) 1.05 Tb/s Optical-OFDM Using ROF over 3600 km Fahad Almasoudi, Khaled Alatawi, Mohammad A. Matin Department of Electrical and Computer Engineering, University of Denver, Denver, USA Email: fahadma@hotmail.com Received June 19, 2013; revised July 20, 2013; accepted August 16, 2013 Copyright © 2013 Fahad Almasoudi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ABSTRACT In this paper, an effort is made to analyze the integration of direct detection optical orthogonal frequency division mul- tiplexing (DDO-OFDM) with wavelength division multiplexing (WDM) to reach high data rates of 1.050 Tb/s over 3600 km single mode fiber (SMF). The 1.050 Tb/s signal is generated by multiplexing 30 OFDM signals with 35 Gb/s for each OFDM. The performance of the system is studied by measuring the optical signal to noise ratio (OSNR) of each WDM channel; signal to noise ratio (SNR); and bit error rate (BER); while analyzing the constellation diagram of all users. Also, the relationship between the OSNR and BER is studied and it is noticed that as the OSNR increased, the BER decreased. As can be seen form the results, as the transmission distance increased the BER increases and to keep the BER less than 10 −3 we need to increase the OSNR. Keywords: BER; O-OFDM; DCF; ICI; ISI 1. Introduction The improvements in high-speed optical components and electronics support new optical communication systems with high data rates. Optical components can be shared between different WDM channels. WDM can increase bandwidth over optical fiber by sending several signals concurrently at different wavelengths [1]. Therefore, it can increase the system capacity while reducing the cost of the system. The possible bit rate for each WDM chan- nel has been increased to more than 40 Gb/s and this im- plementation gets a high possibility for dispersion [2]. Optical OFDM (O-OFDM) is one of the advanced and efficient modulation techniques that have been used in the modern optical communication systems. O-OFDM is used as the modulation technique in advanced optical communication systems because it offers robustness to narrowband interference and frequency selective fading [3]. It is being offered as the premier long-haul transmis- sion design in direct detection and coherent detection. The integration of DDO-OFDM with WDM will provide a small increase in the nonlinearity of the optical system even with high number of channels. In addition, the main goal of DDO-OFDM is to have a simple transmitter and receiver which will provide a low cost system when com- pared to other methods such as Coherent Optical OFDM (CO-OFDM) [3,4]. O-OFDM is a part of multicarrier modulation (MCM) where the data information is transmitted over many sub- carriers of lower rate. [4]. O-OFDM modulation technique provides a number of great advantages when it is used in the optical communi- cation system. It can reduce the amount of dispersion produced by multipath delay spread. Moreover, all O- OFDM symbols used a guard interval, which gives the advantage of eliminating Inter-Symbol Interference (ISI) produced by a dispersive channel [5]. Furthermore, the O-OFDM symbol is regularly extended to avoid Inter- Carrier Interference (ICI) [6]. In addition, using O- OFDM in long-haul systems can compensate the linear distortions in the optical fiber, such as group velocity dispersion (GVD). O-OFDM uses different subcarriers to send low rates in parallel data streams. The M-array Quadrature Ampli- tude Modulation (QAM) or Phase Shift Keying (PSK) is used to modulate the subcarriers before being transported on a high frequency microwave carrier. Because the duration of symbol is extremely longer than the root-mean-square (RMS) delay of the optical wireless channel, the multicarrier modulation has strong robustness to ISI. Consequently, O-OFDM multilevel quadrature amplitude modulation (MQAM) encourages the delivering of very high data rates [6-8]. In the optical communication system, the information is transmitted on the optical signal intensity and hence it can be only posi- tive (unipolar). In this paper, direct detection is used in- stead of coherent detection which means that there is no Copyright © 2013 SciRes. OPJ