thank you all for your reply..i tried the suggestions posted by you people…i could see the phase change in the electrical signal but not in the optical signal…when i tried to modulate a NRZ data with optical sine wave all i could see is the electrical data phase has been changed and is being modulated(amplitude) on to the optical carrier but the phase of optical signal remains the same..actually am using version 7 and trying to design a optical QAM modulator in version 7. i would feel glad if i receive help from you people to design it.thank you