Fabrication of polarization-independent single-mode waveguides in   lithium niobate crystal with femtosecond laser pulses
  We report on fabrication of depressed cladding optical waveguides buried in lithium niobate crystal with shaped femtosecond laser pulses. Depressed cladding waveguides of variable mode-field sizes are fabricated by forming the four sides of the cladding using a slit-beam shaping technique. We show that the waveguides fabricated by our technique allows single-mode propagation of the light polarized in both vertical and horizontal directions. 
Jia Qi, Peng Wang, Yang Liao, Wei Chu, Zhengming Liu, Zhaohui Wang,   Lingling Qiao, Ya Cheng
physics.optics