Thermally induced multi-wavelength filtering in electro-optic long period Ti:LiNbO 3 waveguide grating

We have studied thermal effect on filtering feature of electro-optic long period grating (LPG) in Ti-diffused LiNbO3 waveguide, and observed the phenomenon of thermally induced multi-wavelength filtering. At room temperature (20.8 °C), a rejection band due to LPG effect is observed at 1450 nm wavelength regime for a driving voltage of 115 V. As the temperature is increased, the band weakens gradually, and is no longer discernible at 27 °C. Meanwhile, three new dips with similar contrasts and wavelength intervals are resolved at shorter wavelengths 1190, 1265 and 1339 nm. Their contrasts increase with a rise in temperature and have a value of 20 dB at available temperature of 44.5 °C. The positions of these dips change little with the temperature, but red-shift with the increase of driving voltage. These dips are associated with thermally induced multi-mode interference.