PRODUCTION OF TI-DIFFUSED LINBO3 OPTICAL WAVEGUIDE DEVICE THEREFOR

PURPOSE: To prevent external diffusion and to obtain a waveguide having low optical loss by performing thermal diffusion in a substrate while maintaining the environment in the furnace tube as a mixture of heated oxygen and water vapor. CONSTITUTION: Water 7 in a mixing vessel 6 is heated by a heater 9 while heaters 10, 11 in pipes 5, 8 are kept on. Then a valve 15 of an oxygen cylinder 4 is opened to supply oxygen to the pipe 5. The oxygen is heated by a heater 10 and introduced into the water 7 in the mixing vessel 6. In this process, the saturated vapor pressure of water is stabilized and the mixture gas is made to flow from the vessel 6 to the pipe 8. Since the pipe 8 is heated by the heater 11 and the mixture gas of oxygen and water vapor flowing through the pipe 8 is maintained at about 60 deg.C, the mixture gas is introduced into the furnace tube 3 without condensing. Thereby, the atmosphere in the furnace tube 3 is prepared as a mixture of oxygen and water vapor preliminarily heated. Thus, production of external diffusion can be prevented when a substrate 2 is heated in this atmosphere to produce a Ti-diffused LiNbO3 optical waveguide.