ICTON-MW'08 Fr1A.1 978-1-4244-3485-5/08/$25.00 ©2008 IEEE 1 Characterization of the Semiconductor Optical Amplifier for Amplification and Photonic Switching Employing the Segmentation Model Abd El Aziz 1 , W. P. Ng 1 , Member, IEEE, Z. Ghassemlooy 1 , Senior Member, IEEE Moustafa H. Aly 2 Member OSA, R. Ngah 3 and M. F. Chiang 1 Northumbria Communications Research Laboratory 1 Northumbria University, Newcastle upon Tyne, UK Tel: (+44)1912273841, e-mail: {ahmed.shalaby, w.p.ng, fary.ghassemlooy@unn.ac.uk } 2 Arab Academy for Science and Technology and Maritime Transport, Alexandria, Egypt 3 Universiti Teknologi, Malaysia ABSTRACT This paper characterizes the gain and the carrier density responses of a semiconductor optical amplifier (SOA). In order to achieve the switching functions in SOA-based optical switches, such as Symmetric Mach-Zehnder (SMZ), the effect of the input signal on the total gain response of the SOA is investigated. The theoretical operation principle is demonstrated using a segmentation model that employs the complete rate equation with third order gain coefficients. Results obtained show the input boundaries and requirements in which the SOA can be efficiently used as an amplifier and as a switch. Keywords: carrier density, gain response, semiconductor optical amplifier (SOA), stimulated emission. 1. INTRODUCTION To overcome the speed bottleneck imposed by the optoelectronic conversions, ultrafast photonic networks rely on photonic signal processing. Semiconductor optical amplifier (SOA) is considered as the key component in the next generation of optical networks [1]. Not only can the SOA be used as a general gain unit but it also has many functional applications including all optical switching, wavelength conversion, and optical logic signal processing [2]. Ultrafast all-optical switches based on SOA, such as Mach-Zehnder Interferometers (MZIs) [3] are the most promising candidates for the realization of all-optical switching and processing applications compared to other all-optical switches, such as ultrafast-nonlinear interferometers (UNIs) and Terahertz Optical Asymmetric Demultiplexers (TOADs) due to their compact size, high stability, low switching energy, high integration potential and their fast and strong nonlinearity characteristics [4-6]. Moreover, the use of SOAs as in-line amplifiers is very suitable for bi-directional transmission in local and metropolitan systems and networks because of the lower cost of SOAs and no need for optical isolators as often used in different types of amplifiers such as erbium doped fiber amplifiers (EDFAs) [7]. The key characteristics of a SOA are the time evolution of the gain, carrier density and stimulation emission of an SOA following pump pulse propagation. In gain dynamics studies including pump and continuous wave (CW) probe propagation, a few models have been proposed [8, 9]. Several works have addressed the gain responses but without investigating a direct relationship to the wavelength of the signal and the applied bias current. Here, we propose a direct temporal analysis of the effect of the input signal wavelength, the applied bias current and the input power of the signal, based on a segmentation model that we have developed, which takes into account forward pump and probe propagation. In this paper, we investigate the optimum parameters of the SOA required in order to perform amplification and switching functions. The key optimizations are achieved by controlling the bias current to the corresponding input signal power within the wavelengths. The effect of the optimization of the carrier density and the gain responses in order to control amplification and switching are investigated. The SOA amplification process and model used is explained in the following section while section 3 presents the boundary conditions and requirements for the SOA to perform amplification and switching. The final section concludes the findings of the investigation. 2. SOA AMPLIFICATION PROCESS AND THE SEGMENTATION MODEL The process begins when a direct current (DC) is applied to the active region of the SOA, thus giving electrons in the valence band enough energy to overcome the energy gap and hence, populating the conduction and valence bands (energy levels) with electrons and holes, respectively [10]. The process which provides amplification is the stimulated emission. This process occurs when an incoming optical beam is launched into the active region of the SOA via the input facet of the amplifier; an incident photon collides with an excited electron from the conduction band releasing a stimulated photon with the same phase, frequency and direction. More identical photons are released by the collision of the incident beam of photons with more excited electrons