Proton Exchanged LiNbO3 and LiTaO3 Optical Waveguides and Integrated Optic Devices
Yu. N. Korkishko1 ( korkishk-AT-chem-DOT-miee-DOT-ru.gif ), V. A. Fedorov1, S. M. Kostritskii1, A. N. Alkaev1, E. I. Maslennikov1, E. M. Paderin1, D. V. Apraksin1, and F. Laurell2
 1Moscow Institute of Electronic Technology (Technical University), 103498 Moscow, Zelenograd, Russia.
 2Department of Physics II, Royal Institute of Technology, S-10044 Stockholm, Sweden.

Lithium niobate, LiNbO3, and Lithium tantalate, LiTaO3, are very important ferroelectric crystals with various acoustical and optical applications. One of basic methods to make optical waveguides in these crystals is proton exchange (PE) [1]. We showed that PE structures exhibit very complex structural chemistry. Seven HxLi1-xNbO3 crystallographic phases have been identified in PE LiNbO3 [2,3] and six HxLi1-xTaO3 phases in PE LiTaO3 waveguides [2,4].

Reflection second-harmonic generation (SHG) from the polished waveguide end face is used to investigate the second-order nonlinear optical properties of different HxLi1-xNbO3 and HxLi1-xTaO3 phases. A detailed correlation is done between the nonlinear properties, the processing conditions, the refractive index changes and the optical losses of the waveguides. It is found that the nonlinearity, strongly reduced after the initial PE, is found to be restored and even increased after annealing [5]. However, this apparent increase of the nonlinearity is accompanied by a strong degradation of the quality of the SHG reflected beam in the region of initial waveguides. It has been also shown that the nonlinear properties of annealed proton exchanged LiNbO3 waveguides can be effectively recovered by the reverse proton exchange technique. The Soft Proton Exchange technique [6] has been shown to produce high-quality waveguides with essentially undegraded nonlinear optical properties.

Electrooptical and photorefractive properties of different crystalline phases HxLi1-xNbO3 generated in PE LiNbO3 optical waveguides have been determined.

The knowledge obtained from basic research enabled us to develop new technologies for making integrated-optic devices in LiNbO3 and LiTaO3 as well as to realize the advanced devices such as high-speed waveguide modulators integrated with amplifiers/ lasers for operation at the 1.5 m communication wavelength and high-precision interferometric fiber optical gyro. The physics and technology of these devices are discussed.

References
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  2. Yu.N.Korkishko, V.A.Fedorov, Ion exchange in single crystals for integrated optics and optoelectronics (Cambridge International Science Publishing, Cambridge, UK) 1999, 516 pages
  3. Yu.N.Korkishko, V.A.Fedorov, IEEE J. Sel.Topics Quantum Electron. 2, 187 (1996).
  4. D.B.Maring, R.F.Tavlykaev, R.V.Ramaswamy, Yu.N.Korkishko, V.A.Fedorov, J.M.Zavada, Appl.Phys.Lett., 73, 423, (1998).
  5. Yu. N. Korkishko, V.A. Fedorov,and F. Laurell, IEEE.J.Sel. Topics Quant. Electron., 6, 18 (2000).
  6. Yu.N.Korkishko, V.A.Fedorov, O.Y.Feoktistova. J. Lightwave Technology, 18, 562 (2000).