Moisture-induced drift in thermo-optic phase shifters composed of deuterated and fluorinated methacrylate polymer waveguides.

Using deuterated and fluorinated methacrylate polymer waveguides, we fabricated thermo-optic phase shifters that require a small electric power of 10 mW to cause a pi phase shift. The phase shifters had a phase drift that was greater at higher humidity and that was saturated in approximately 10 min. This phenomenon is ascribed to the moisture desorption-sorption of the waveguide polymers caused by heating-cooling on the basis of experimental results on the relationships among waveguide temperature increase, relative humidity, and moisture sorption of the waveguide polymers. This conclusion is supported by the calculation of temperature and moisture distribution in the waveguide when the thin-film heater is heated.