الفهرس 
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Abstract
As information exchange demands are exploding in today’s communications, developing optical communications systems with increasing transmission capacities became a strong necessity. Optical communications systems rely heavily on the integration of different optical devices such as, detectors, modulators, and multiplexers. The performance of such devices are, unfortunately, usually dependent on the polarization state. Silicon photonics has emerged as a promising platform for building large scale photonic integrated circuits for optical communication systems due to the availability of low cost complementary metal-oxide semiconductor processing technology. Silicon-on-insulator platform is the main platform for silicon photonics due to its high index contrast which enables compact photonic devices. However, the high index contrast leads to a considerable optical birefringence and highly polarization dependent devices. To overcome this issue, polarization manipulating devices are of great demand. Silicon photonics cannot realize certain functions due to its centro-symmetric crystal structure and hence it has no electro-optic effect. On the other hand, liquid crystals are very interesting materials whose large electro-optic effect is essential for many applications. Therefore, the integration of silicon photonics with liquid crystals will produce chips with optimal electro-optic functionality. On the other hand, hybrid plasmonic waveguides are another interesting alternatives for designing highly efficient photonic devices. Hybrid plasmonic waveguides have the advantages of moderate loss, polarization diversity property, and compatibility with silicon platforms technology. This thesis focus on the design and development of tunable photonic devices to tackle the problem of the polarization dependence in optical communications systems. The modal analysis of a novel design of an ultra-compact polarization rotator based on silicon on insulator platform infiltrated with liquid crystal is reported and studied. This dissertation also presents novel designs for ultracompact transverse electric and transverse magnetic-pass polarizers based on hybrid plasmonic waveguide.