الفهرس 
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Abstract
There are several kinds of modulators, depending on their structure, such as electro optic, acousto-optic, magneto-optic and electro-absorption modulators. Each employs a different physical mechanism and has different applications. The electro-optic modulator is the most important type in optical communication systems. Different configurations have been adopted, such as the Mach Zehnder interferometer (MZI) modulator, and the directional coupler modulator . High speed integrated electro-optic modulators and switches are the basic building blocks of modern wideband optical communications systems and represent the future trend in ultra-fast signal processing technology. As a result, a great deal of research effort has been devoted to developing low-loss, efficient and broadband modulators in which the radio frequency signal is used to modulate the optical carrier frequency. Most of the work done in the area of designing electrooptic modulators has been strongly focused on using LiNbO3. Interest in research in this field has arisen as lithium niobate devices have a number of advantages over others, including large electro-optic coefficients, low drive voltage, low bias drift, zero or adjustable frequency chirp, and the facility for broadband modulation with moderate optical and insertion losses and good linearity. LiNbO3, Aluminum gallium arsenide (AlGaAs), and polymer electrooptic modulators (EOMs) have been developed for extensive use in high speed and high transmission performance optical fiber transmission systems. this is because they can offer the advantages of modulation exceeding multi Gbit/sec combined with a low driving voltage, and they can eliminate the dynamic laser wavelength chirping which limits the span-rate system product due to their fiber dispersion characteristics. modulators fabricated on semiconductor substrates such as (AlGaAs) material is particularly attractive in that these exists the possibility of monolithic integration of these devices with other optoelectronic components. we have deeply investigated the recent progress of LiNbO3 based electro-optic devices using NRZ coding to handle the modulation bandwidth, switching voltage, cut-off frequency, transmission date rate, and transmission bit rate length product. The polymer electrooptic modulator have been CHAPTER I GENERAL INTRODUCTION AND BACKGROUND 7 developed devices with pulse code modulation scheme for high speed performance operation in modern optical communication networks. and ultra high speed semiconductor electrooptic modulator devices for multigigahertz operation systems.