Uniform and heavily Ge-doped silicon oxy-nitride film is obtained by optimized fabrication of silicon oxy-nitride film. Based on an optimal design of waveguide coupler, hydrogen loading and ultraviolet (UV) irradiation intensity, single-mode channel waveguides and waveguide couplers, made from germanium-doped silicon oxy-nitride, are fabricated by an UV irradiation from a KrF excimer laser on a planar waveguide. The maximum index increase is up to 1.03 times for heavy Ge-loading (about 20% atomic fraction) waveguide core after the UV irradiation, and the transmission loss of the UV-written channel waveguide is 0.28~0.32 dB/cm. Experimental results demonstrate that the index increase in the Ge-doped silicon oxy-nitride with UV irradiation intensity is not linear, and it can be controlled by changing the hydrogen loading pressure and time, UV intensity and Ge-loading level.