Download MASTER THESIS

The aim of this chapter is to introduce the field of study of this thesis: the amplitude and phase
characterization of optical devices by RF scan. Before we enter the specific matter of this study, we review
and clarify the fundamental concepts required to develop and understand the subject matter of this
research.
The chapter is divided in two paragraphs.
In paragraph 2.1, we recall some basic concepts of the dispersion theory. In particular, we introduce the
concept of dispersion, with its two manifestations: the Intermodal or Modal dispersion and the Intramodal
or Chromatic dispersion. Once we specify the expression of the electric field which travels along the fibre,
we concentrate on the expression of the phase constant of the fundamental propagating mode β. This
parameter, by using a Taylor approximation, can be viewed as the sum of three parts (the underlying
assumption here is that the higher parts are neglected). Consequently, we explain the physical concepts
behind these new three parameters, i.e. phase velocity vf, group velocity vg and group delay dispersion
(GDD). As a conclusion to the paragraph, some features of the Chromatic Dispersion are discussed.
In paragraph 2.2, we focus on Mach-Zehnder Devices. In paragraph 2.2.1 we describe the Mach-Zehnder
Modulator with its behaviour and its different possible configurations (push-pull or asymmetric). In
paragraph 2.2.2 we briefly discuss the transfer function of MZ Interferometer (MZI) and then, delve deeper
into the transfer function of MZ Modulator and MZ Optical Filter. In this section, we also define two
important concepts related to the transfer function: the Sensitivity of the electrodes (Vc) and the half-wave
voltage (Vπ) and we finally show that the transfer functions of the MZ modulator, interferometer and
optical filter do not largely differ from each other.
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