Regular Articles A study of green wavelength-division multiplexed optical communication systems using cascaded fiber bragg grating Marwa M. Tharwat a , Islam Ashry b , Ali Elrashidi b , Amr M. Mahros b,c,⇑ a Department of Electrical Engineering, Faculty of Engineering, King Abdulaziz University, Jeddah 21432, Saudi Arabia b Department of Engineering Mathematics and Physics, Faculty of Engineering, Alexandria University, Alexandria 21544, Egypt c Department of Physics, Faculty of Science, King Abdulaziz University, Jeddah 21432, Saudi Arabia article info Article history: Received 25 December 2013 Revised 27 April 2014 Available online 1 July 2014 Keywords: Fiber Bragg gratings Gain flattening Optical amplifiers abstract This paper studies the performance analysis of wavelength-division multiplexed optical communication systems (WDM). First, flat-gain erbium doped fiber amplifiers (EDFAs) are seriously needed to obtain proper and equal amplification of all channels. Such amplifiers can be designed by intrinsically modifying the host material or extrinsically using proper filters. In this research, we benefit from both the intrinsic and extrinsic methods to achieve sharp flat EDFA output gain using cascaded fiber Bragg gratings (FBGs). Second, the performance of our technique has been evaluated through calculating the bit error rate (BER) and signal-to-noise ratio (SNR) of a WDM system embedded with the reported EDFA flattening system. The parametric simulations of the FWHM of FBGs, SNR, optical power and the transmission distance have shown a noticeable improved performance. Sending data via an optical WDM system will be proven from comprehensive simulations to achieve high quality signal transmission spectrums, increased transmis- sion distances and low power consumption. By extension, the reported design using cascaded FBGs can also be generalized to equalize the gain of any arbitrary profile. Ó 2014 Elsevier Inc. All rights reserved. 1. Introduction Erbium doped fiber amplifier (EDFA) has been considered as one of the key devices in long-haul wavelength-division multi- plexed (WDM) optical communication systems [1–3]. These types of amplifiers have several advantages such as, high gain, low noise, and large bandwidth [2]. Unfortunately, the typical EDFA provides nonequalized gain for the transmitted channels in WDM systems [3]. This drawback results in low signal-to-noise ratio (SNR) and signal distortion. As a result, there is a strong motivation to equal- ize the gain of EDFAs to improve the transmission bandwidth and performance of WDM systems. The performance enhancement of EDFAs will meet the ever increasing demand for effective delivery of baseband signals using minimum energy consumption. This will help to construct the green communications systems which are environment-friendly and cost-effective. Several successful techniques have been developed in the liter- ature to equalize the gain of EDFAs which can be classified as intrinsic or extrinsic methods [4–6]. In intrinsic methods, the spectral properties of the erbium ions can be modified by using different host materials such as, fluoride-based and alumino- silicate glasses [7–9]. This method, however, can improve the flat- ness of EDFAs gain over a small bandwidth. On the other hand, extrinsic methods are characterized by the ability to improve the flatness of EDFAs gain over wider bandwidths. This can be achieved by using in-fiber filters such as, chirped fiber Bragg grating (FBG) [10], blazed FBG [11], and acoustooptic tunable filters [12]. The main limitation of using chirped FBG filter is the complexity of its fabrication, especially, when the equalization bandwidth is large. Blazed FBG depends on converting the guided modes to non- guided and, therefore, it is sensitive to environmental conditions. Also, acoustooptic filters consume high RF power. Another successful extrinsic technique used for flattening EDFA gain is designed by coupling different WDM channels out of the optical fiber to be equalized using variable optical attenuator (VOA) [13,14]. This technique can offer good flattening in the C and L bands with low ripples, however, its usage is limited by the high insertion loss and noise figure. In this paper, we report EDFA gain flattening using a new and simple configuration in which cascaded short period apodized FBGs connected in series with a modified host material EDFA. Each FBG is responsible for flattening only one channel in the WDM networks. The main advantages of the reported configuration over those found in the literature are numerous: The fabrication http://dx.doi.org/10.1016/j.yofte.2014.05.010 1068-5200/Ó 2014 Elsevier Inc. All rights reserved. ⇑ Corresponding author at: Department of Physics, King Abdulaziz University, Jeddah 21432, Saudi Arabia. E-mail address: amr.mahros@mena.vt.edu (A.M. Mahros). Optical Fiber Technology 20 (2014) 467–472 Contents lists available at ScienceDirect Optical Fiber Technology www.elsevier.com/locate/yofte