The main objective of the work presented in this thesis was to study and investigate various novel optical fibre devices. They are so simple yet so full of potential. A simple length of dual core fibre in which one core is doped with Erbium and the other has no Erbium has been designed , fabricated and demonstrated to be capable of performing at least four different tasks successfully. Truly, this dual-core fibre has proved to be an idea medium for conveying and providing the necessary

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... ies to operate as a "C" and "L" band amplifiers, wavelength selector and optical switch within optical network systems. Its construction is simple, inexpensive and repeatable. The gain-flattening amplifiers for both the C-band and L-band using nonlinear dual-core Erbium doped fibres have been studied extensively. Both amplifiers were successfully designed, fabricated and demonstrated experimentally. They have respectively given very flat gain characteristics over a wide bandwidth experimentally. For the C-band EDFA, the gain variation was less than 0.7 dB with a high gain of 20 dB within the 30 nm wavelength range. For the L -band