Optical Wavelength Converters Based on Cross Gain Modulation and Cross Phase Modulation in Soa

All optical wavelength conversion is demonstrated at 10 Gbit/s over a wavelength span of 10 nm without any bit loss by the use of Semiconductor Optical Amplifier (SOA) in a Mach-Zehnder configuration. These wavelength conversion architectures are implemented by using SOA cross-gain modulation (XGM) and cross-phase modulation (XPM) techniques. We have compared the results of both techniques on the basics of Bit Error Rate (BER) and Quality factor. KeywordsSemiconductor Optical Amplifier (SOA), cross-gain modulation (XGM), cross-phase modulation (XPM), Mach-Zehnder Interferometer, BER, extinction ratio(ER). I.INTRODUCTION All optical wavelength converters are expected to become key components in the future broadband net works. Their most important use will be for avoidance of wavelength blocking in optical cross connects in wavelength division multiplexed (WDM) networks [1-4]. Thereby the converters increase the flexibility and the capacity of the network for a fixed set of wavelengths [5-6]. With the help of wavelength conversion a data stream at a specific wavelength is transferred to another one in order to be routed on a different wavelength path and release the original wavelength resource to another data stream. A. Semiconductor optical amplifiers (SOA)An SOA is an optoelectronic device that under suitable operating conditions can amplify an input light signal. A schematic diagram of a basic SOA is shown in Fig. 1.1. The active region in the device imparts gain to an input signal. An external electric current provides the energy source that enables gain to take place. An embedded waveguide is used to confine the propagating signal wave to the active region. However, the optical confinement is weak so some of the signal will leak into the surrounding lossy cladding regions. The output signal is accompanied by noise. This additive noise is produced by the amplification process itself and so cannot be entirely avoided. The amplifier facets are reflective causing ripples in the gain spectrum. In an SOA electrons (more commonly referred to as carriers) are injected from an external current source into the active region. The gain of an SOA is influenced both by the input signal power and internal noise generated by the amplification process. As the signal power increases the carriers in the active region become depleted leading to a decrease in the amplifier gain. This gain saturation can cause significant signal distortion. It can also limit the gain achievable when SOAs are used as multichannel amplifiers. A typical SOA gain versus output signal power characteristic is saturation output power shown in Fig. 1.2. A useful parameter for quantifying gain saturation is the saturation output power which is defined as the amplifier output signal power at which the amplifier gain is half the small-signal gain. 1275 OPTICAL WAVELENGTH CONVERTERS BASED ON CROSS GAIN MODULATION AND CROSS PHASE MODULATION IN SOA ISSN 2277-1956/V1N3-1274-1280 Figure 1. SOA structure Figure 1.2 Gain Saturation Semiconductor optical amplifiers (SOAs) are used in the cross gain modulation (XGM) mode or the cross phase modulation (XPM) mode for wavelength conversion. II. CROSS GAIN MODULATION BASED WAVELENGTH CONVERSION