OPTICAL EQUALIZERS

Abstract

Fiber optics is one of the highest bandwidth communication channel types in the current communication industry. The needs for increasing speeds and capacities in modern data communication systems have lead to increasing hopes for the introduction of optical communication in a wide range of communication networks. In communications, a critical manifestation of distortion is inter-symbol interference (ISI), whereby symbols transmitted before and after a given symbol corrupt the detection of that symbol. All physical channels (at high data rates) tend to exhibit ISI. With the potential of an optical link‟s overwhelming advantages, it will be gainful to delve into techniques that can mitigate the effects of ISI and thus improving transmission speed and saves bandwidth. The equalizer attempts to extract the transmitted symbol sequence by counteracting the effects of ISI, thereby improving the probability of correct symbol detection. Its purpose is to reverse the effects that the channel has on the transmitted signal, with the aim of reproducing the original signal at the receiver end. The Decision Feedback Equalizer (DFE) and Blind Equalizer, which are non-linear structure‟s, is known to show superior performance when employed in channels that exhibit amplitude distortion. As such, it would be an ideal choice for a typical optical channel, which often suffers from amplitude distortion. The aim of my thesis project is to analyze a typical optical channel, study dispersion effect and perform channel equalization using an adaptive DFE algorithm and Blind equalization. Evaluation can be made on the employment of the DFE algorithm and with enhancements, like Fractionally-Spaced equalization and Activity Detection Guidance, to improve its stability. Brief introduction of Blind Equalization is also given, which is the latest technique in equalization. The FSE technique, when combined with the DFE, would offer improved effectiveness to amplitude distortion.