In this thesis, ridge Mach-Zehnder modulator is successfully fabricated by using proton exchange wet etching in gamma ray irradiated z-cut lithium niobate. To characterize the effect of gamma ray irradiation, the depth and the aspect ratio of the ridge structure are measured by surface profiler and electron microscope. Experimental results show that the depth and the aspect ratio of the gamma ray irradiated ridge structure are increased by about 30% and 87%, respectively. Owing to deeper vertical side walls, the optical field confinement is enhanced and the drive voltage is decreased from 7.9V to 6V.