The major requirement for ultra high speed optical communications is ultra wide band, low cost and low voltage modulators. These modulators can be categorized mainly in two groups of electro-optic and electro-absorption modulators. Different types of electro-optic modulators have been developed, including LiNbO
3 electro-optic modulators [
1–
3], semiconductor GaAs electro-optic modulators [
4–
6] and polymer electro-optic modulators [
7]. Among these types of electro-optic modulators, polymer-based electro-optic modulators have more enhanced electro-optic coefficient than those of LiNbO
3 and GaAs semiconductor ones. However, most of the polymer electro-optic materials suffer from low thermal stabilities, and high initial electro-optic coefficients of polymer materials reduce with the time [
7]. This thermal instability does not exist in LiNbO
3 electro-optic modulators. Also, large electro-optic coefficient of this electro-optic modulator is lower than that polymers one, but it is still much larger than that of semiconductors one. As a result, significant progress has been made for this type of modulators, and they are commercially available now. Nevertheless, these devices based on LiNbO
3 cannot be incorporated with semiconductor integrated devices. Therefore, they are only appropriate for external modulation applications [
4]. However, compound semiconductors are suitable for such integration and have high refractive index and small dispersion of dielectric constant over a wide frequency band, up to optical frequencies. Due to these important advantages of LiNbO
3 electro-optic modulators, many efforts are made to design their structures with good capabilities, despite their very small electro-optic coefficients.