Electro-Optic Long Period Grating Based on Ti:LiNbO3 Optical Waveguide

We demonstrate electro-optic long period grating in Ti:LiNbO₃ strip waveguide embedded in a planar waveguide. The device was fabricated starting from a Z-cut congruent plate with a technological process in sequence of planar waveguide, strip waveguide, SiO₂ buffer layer, and periodical electrode. The rejection band of the device with a grating pitch 675 μm is observed at the 1.1-1.3-μm wavelength regime with a maximum contrast of 27 dB under the 360 V driving voltage. It is found that the band red-shifts linearly with the voltage increase. The shift is ~160 nm as the voltage is increased from 100 to 500 V and lasts 1 min. Accompanying the shift, the contrast reduces. The shift is attributed to different photorefraction effects in planar and strip waveguides. Higher than 360 V, the contrast decreases due to photorefraction effect and over-coupling phenomenon.