The device will be fabricated in SOI platform with single-mode (λ ~ 1550 nm) rib waveguide integrated with a p-i-n structure for phase modulation in one of the output arms. The rib device (directional coupler) structure will be fabricated by reactive ion etching system with a suitable mask defined photolithographically. The p-type and n-type sections on the both sides of rib structure will be fabricated by diffusion dopings. The end-facets of the sample will be suitably polished for optical characterizations. We can estimate the phase change (because of plasma dispersion) by the intensity modulated (because of free carrier absorption) output measurement. The device has to be designed suitably so that the powers of the phase modulated light and un-modulated light are nearly equal.