Modeling and compensation of modal dispersion in graded-index multimode fiber

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Multimode fiber (MMF) has been used traditionally in local-area and campus-area networks. The large core size facilitates laser-to-fiber and fiber-to-fiber coupling, reducing component costs and the cost of setting up and maintaining a network. The propagation of multiple modes leads to modal dispersion, which traditionally has limited the bit rate-distance product to less than about 2 Gbit/s-km. Models for modal dispersion must take account of mode coupling by fiber imperfections and bents. Traditionally, mode coupling has been studied using a power-coupling model, which can accurately predict the population in different modes when using incoherent sources, such as light-emitting diodes. But the power coupling model is inherently unable to describe some effects in high-speed links using coherent laser sources, such as polarization dependence of impulse response. In the first part of this dissertation, we describe a field-coupling model for propagation in MMF, which is analogous to the model used to study polarizationmode dispersion in single-mode fiber. Our model allows computation of the fiber impulse response, given a launched electric-field profile and polarization. In order to model both spatial- and polarization-mode coupling, we divide the fiber into numerous short sections, each having random curvature and random angular orientation. This model can be described using only a few parameters. With the help of this model we investigate first-order and higher-order modal dispersion effects. We describe principal modes (PMs), which are free of modal dispersion. We describe how the PM group delays depend on the strength of mode coupling in the low-coupling regime (e.g., glass fibers) and the high-coupling regime (e.g., plastic fibers). We also explain the observed polarization dependence of the impulse response. Considering terms of higher order (in frequency), our model accounts for an observed filling-in between peaks in the impulse response and predicts a nonlinear relationship between input and output intensity waveforms. In the second part of this dissertation, we describe the use of an adaptive spatial light modulator (SLM) to launch light into PMs, preventing modal dispersion. Previously this technique has enabled transmission at bit rate-distance products over 200 Gbit/skm. We have extended the adaptive optics technique to include control of signal polarization. We have studied several alternative adaptive optical systems and have derived the optimal solution for each system. We show that the best performance is obtained by controlling each polarization independently using two SLMs.


Type of resource text
Form electronic; electronic resource; remote
Extent 1 online resource.
Publication date 2010
Issuance monographic
Language English


Associated with Bagher Shemirani, Mahdieh
Associated with Stanford University, Department of Electrical Engineering
Primary advisor Kahn, Joseph
Thesis advisor Kahn, Joseph
Thesis advisor Fan, Shanhui, 1972-
Thesis advisor Miller, D. A. B
Advisor Fan, Shanhui, 1972-
Advisor Miller, D. A. B


Genre Theses

Bibliographic information

Statement of responsibility Mahdieh Bagher Shemirani.
Note Submitted to the Department of Electrical Engineering.
Thesis Ph.D. Stanford University 2010
Location electronic resource

Access conditions

© 2010 by Mahdieh Bagher Shemirani
This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).

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