Characteristic research of the waveguide by nanosecond laser pulses on LiNbO_3

摘要

The damage threshold and morphology of optical material have been investigated by 800nm, 75MHz, 30fs laser pulses, in 40 magnification and 0.65 numerical aperture (NA) objective in the Z-LiNbO_3 crystals. The influence of several experimental parameters, for example energy per pulse, a ser scanning speed, or repeat time on writing quality and the characters of relative microstructures has been analyzed and studied in theory. The damage structural change, from small refractive index changes to micro explosion structure in LiNbO_3 induced by high intensity nanosecond laser is studied. Nonlinear interactions of nanosecond laser and transparent material are discussed. The subsurface morphology of the processed structures inside the LiNbO_3 was obtained by a Nikon optical microscope. Particularly, we find that the wider width of the buried channel with the increase of energy per pluse, repeat time and the reduce of scanning speed. It was caused by the avalanche ionization and multi-photon absorption of lithium on the processed area, and which is also lead to the refractive index change rang by the writing conditions. The result shows that the propagation of optical waveguide could achieve ideal effect when the energy per pluse is under 300mW, the scanning speed is from 0.05mm/s to 0.2mm/s, and the focus depth is from 350μm to 400μm.At last, in this approach, the insertion loss of 1×4 optical splitter is less than 1dB/cm.