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Ti-concentration inhomogeneities in Ti:LiNbO3 waveguides
1Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
Optics Letters
|September 11, 2009
Summary
Distributed fluctuations in waveguide effective index explain nonideal optical characteristics in Ti-diffused LiNbO3 directional-coupler switches. These index variations, not from photolithography, are consistent with observed optical cross talk.
Area of Science:
- Photonics and Waveguide Optics
- Materials Science for Optoelectronics
Background:
- Ti-diffused Lithium Niobate (LiNbO3) is a key material for integrated optical devices.
- Directional-coupler switches exhibit nonideal optical characteristics, including optical cross talk.
- The origin of these nonideal characteristics has been attributed to various factors.
Purpose of the Study:
- To investigate the role of distributed fluctuations in the effective refractive index of waveguides.
- To determine if these index fluctuations explain the nonideal optical characteristics of Ti-diffused LiNbO3 directional-coupler switches.
- To identify the source of these spatial-index fluctuations.
Main Methods:
- Analysis of spatial fluctuations in the effective refractive index of channel waveguides.
- Comparison of index variations in undiffused Ti films and diffused Ti channel waveguides.
- Correlation of index inhomogeneity magnitude with optical cross talk levels.
Main Results:
- Distributed fluctuations in the effective index fully account for nonideal optical characteristics, including optical cross talk.
- Spatial-index fluctuations are not caused by the photolithographic processes used to define waveguides.
- Undiffused Ti films exhibit concentration variations approximately seven times larger than diffused Ti channel waveguides.
Conclusions:
- Spatial-index fluctuations in Ti-diffused LiNbO3 waveguides are the primary cause of nonideal optical performance.
- The observed index inhomogeneities originate from the diffusion process, not fabrication lithography.
- The magnitude of these inhomogeneities is sufficient to explain the optical cross talk in current devices.
