Date

2016

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Physics

First Adviser

Toulouse, Jean

Other advisers/committee members

Biaggio, Ivan; Dierolf, Volkmar; Kumar, Sushil; Rotkin, Slava; Ryf, Roland; Toulouse, Jean

Abstract

In the present work, we investigate possible solutions to the capacity limits ofoptical communication systems. Just as wavelength division multiplexing (WDM) has been used in the past twenty years, spatial division multiplexing (SDM) is now being explored to further increase the transmission capacity of fibers. In SDM, the spatial dimension of the fiber is the degree of freedom that is being exploited. SDM makes use of several spatial modes propagating in a single core multi-mode fiber or in a multi-core fiber in which the cores are coupled with each others. However for SDM to become a reality in transmission systems, the problem of amplification mustbe addressed. If the power is increased in these fibers, nonlinear effects will emerge within and between different modes of the multi-mode or multi-core fibers which can degrade the transmission performance. On the other hand, nonlinear effects such as stimulated Raman Scattering can be utilized to build optical amplifiers for multi-mode and multi-core fibers.In this thesis, we study theoretically and experimentally the inter-modal nonlinear effects of four-wave mixing (FWM) and Raman scattering in a graded-index few-mode fiber which supports 6 spatial and polarization modes. The efficiency of the four-wave mixing processes between the fundamental and higher order modes is experimentally measured for the non-degenerate four-wave mixing configuration with two pumps and one signal. The effect of the relative polarizations of the threewaves involved in the four-wave mixing process is also studied to understand the fluctuations in the idler powers generated through the nonlinear intermodal process. Finally, experiments are performed in a 70 km graded-index few-mode fiber with 3 spatial modes to understand the effect of different pumping schemes in a distributed Raman amplifier. We demonstrate experimentally that equalized gain in all three spatial modes is achieved by coupling the pump source into the higher order modes instead of the fundamental mode of a few-mode fiber. Distributed Raman amplification is then used in recirculating the signal through the fiber span and data transmission is successfully achieved over 1050 km.

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