Introduction
This thesis originates from the great interest that optical technology research places on all- optical signal processing. Nowadays optical signals are processed electronically afterwards an opto-electrical conversion; after being processed, the outgoing signal is then reconverted into an optical signal. Such a system requires an opto-electro-optical regenerator, constituted by an optical receiver as first stage and a new source as final stage. These early considerations show how the availability of stable and compact all-optical processing devices could reduce actual complexity. Furthermore, the push for higher and higher transmission capacity has led to the project and realization of OTDM (Optical Time Division Multiplexing) systems at 160 Gb/s and more. Such signals can’t be processed electronically because of bandwidth limitation of electronic devices; thus all-optical processing, exploiting ultrafast nonlinear phenomena, becomes necessary.
Recently, the availability of new conception high nonlinear fibers is making possible the implementation of simple, compact and efficient subsystems for all-optical processing. In this thesis we will analyze some of these new fibers and we will characterize their behaviour by exploiting them for the implementation of interferometric schemes used in all-optical processing (Nonlinear Optical Loop Mirror, NOLM). Moreover, we will present some preliminary experimental results which confirm their efficiency and their suitability for the realization of all-optical transmission systems.
This thesis is structured as follows: Chapter 1 gives a brief overview on the scenario where all-optical processing would enter. In Chapter 2, two of the most widely exploited nonlinear effects are described: Self-Phase Modulation and Cross-Phase Modulation. In Chapter 3 we will see how these effects can be exploited through interferometric structures; in particular we will analyze the Nonlinear Optical Loop Mirror (NOLM) scheme. Chapter 4 describes the
1
simulation software we implemented using the LabVIEW package; it computes the NOLM input-output power characteristic. In Chapter 5 the fibers we used in our experimental measurements are described and in Chapter 6 the achieved results are shown, drawing attention on the use of the realized devices for all-optical regeneration.
2
