Fabrication techniques of lithium niobate waveguides

Abstract

In the paper, the most commonly used fabrication techniques of optical waveguides in lithium niobate are reviewed. Diffusion processes such as out-diffusion of lithium oxide from the crystal surface, in-diffusion of metals, ion exchange and proton exchange, and ion implantation are analysed. The characteristics of LiNbO 3 optical waveguides prepared by the different technological procedures, are reported in relation with the fabrication conditions. High quality optical waveguides on lithium niobate can be produced by Ti in-diffusion in a dry O 2 atmosphere at temperatures above 1000°C for long diffusion times (>10h). However, despite the large amount of research done in this field, correlations between optical properties and structural characteristics have not yet been established.

Measurement of coupling characteristics of an Ni:LiNbO3 directional coupler with a combinational-type waveguide structure

“…When the beam propagates through the active 2 region with length L, it will be gradually coupled into W . 2 After propagating a distance equal to the coupling length L , c the light is totally transferred into W . If the active region 2 length L is longer than L , the light will then be coupled c back and forth between the two parallel waveguides.…”

Ti-free optical waveguiding regions produced by LiNbO_3 etching during the indiffusion of Ti

“…Optical waveguides in LiNbO 3 can be formed by locally increasing the refractive index through diffusion or implantation of ions [2], laser writing [3,4], or microstructuring [5,6]. In this Letter we present the observation, first to our knowledge, of optical waveguiding beneath etched trenches in LiNbO 3 .…”

Measurement of coupling coefficients of Ni:LiNbO3 directional couplers

“…2 , the guiding optical field is completely coupled into W . 2 In this letter, the multiple waveguide array method was employed to measure the coupling coefficient and coupling w x length L of an Ni:LiNbO directional coupler 6 . This c 3 method was demonstrated by an array of eight directional couplers with different active region lengths.…”