Microdomain Patterns Written by AFM-Tip Voltages in He-Implanted Optical Waveguides Formed on Z-Cut LiNbO3 Crystals

Implantation of He
⁺
-ions is an attractive method of creating optical waveguides in LiNbO
₃
. The advantages of this method are that, firstly, the main optical characteristics of He - implanted waveguides (denoted below as He-LiNbO
₃
) are identical to those of the bulk LiNbO
₃
, and, secondly, a He-implanted layer provides an abrupt boundary of the waveguide. We describe the AFM-tip domain writing in planar He-LiNbO
₃
formed on the polar surface of LiNbO
₃
plates. The data obtained are compared to the characteristics of AFM-tip domain writing in LNOI (LiNbO
₃
-on-insulator). This comparison is justified by the fact that LNOI represents a waveguide derived from He-LiNbO
₃
. The writing characteristics in LNOI and He-LiNbO
₃
are qualitatively similar, namely the dependences of the domain diameter on AFM-tip voltages U
_tip
and exposure times t
_p
are described by the linear and power laws, respectively. However, in He-LiNbO
₃
these dependences are less steep. A striking difference is manifested in the ferroelectric hysteresis loops. In (21) He-LiNbO
₃
their characteristics and spatial distribution depend on t
_p
, whereas in LNOI the loops are spatially uniform and frequency independent. These distinctions in the domain formation in two related media can be accounted for by the fact that on contrast to LNOI, domain (25) walls in He-LiNbO
₃
are pinned on the structurally damaged layer inherent in this waveguide.