Z -cut X -propagating, LiNbO 3 :Ti planar waveguides have been characterized over a wide range of diffusion conditions. Measurements of Ti concentration and refractive indexes have revealed Gaussian profiles. Their dependence with diffusion conditions have been studied. The relation, established at several wavelengths ( \lambda = 0.6328 \mu m, 1.1523 μm, 1.523 μm), between extraordinary and ordinary refractive index change \Deltan_{e,0}(z) and titanium concentration C(z) is found to be nonlinear and of the form: \Deltan_{e,0}(z) = A_{e,0}(C_{0},\lambda) (C(z))^{\alpha_{e,0}} While \alpha_{e,0} is a constant, the proportionality coefficient A_{e,0} depends not only on the wavelength λ, but also on the diffusion conditions, characterized by C 0 , the Ti surface concentration of the diffused guide. Such a nonlinearity of Ti diffusion in LiNbO 3 has been revealed thanks to a complete and wide range investigation on both indiffused Ti and index profiles.

Wavelength dispersion of Ti induced refractive index change in LiNbO 3 as a function of diffusion parameters

Refractive index profile of optical waveguides is reconstructed from the measured transmitted near-field intensity. A Butterworth low-pass digital filter is employed in the frequency domain to remove impulsive and high frequency fluctuations which have severe effects on the procedure to calculate the index profile from the measured power intensity. The proposed method has been applied to measure the index profile of monomode optical fiber, Ti:LiNbO/sub 3/ and buried MgTi:LiNbO/sub 3/ channel waveguides.

An improved procedure to calculate the refractive index profile from the measured near-field intensity

The application of quantitative phase microscopy to refractive-index profiling of optical fibers is demonstrated. Phase images of axially symmetric optical fibers immersed in index-matching fluid are obtained, and the inverse Abel transform is used to obtain the radial refractive-index profile. This technique is straightforward, nondestructive, repeatable, and accurate. Excellent agreement, to within approximately 0.0005, between this method and the index profile obtained with a commercial profiler is obtained.

Refractive-index profiling of optical fibers with axial symmetry by use of quantitative phase microscopy

The refractive-index profiles of a single-mode fiber and a three-dimensional waveguide are measured by the propagation-mode near-field method. This paper describes the method applied to anisotropic waveguides. The near-field pattern is observed by vidicons, and the index profile is calculated from the measured data. The light transfer characteristic of an infrared vidicon is measured and the intensity data from the infrared vidicon is corrected for the power-law response.

Index profiling of three-dimensional optical waveguides by the propagation-mode near-field method

Secondary‐ion‐mass spectrometry (SIMS) and near‐field (NF) methods have been applied to study Ti:LiNbO3 optical waveguides. Ti concentration as a function of diffusion process parameters has been studied by the SIMS method. The main determining factors that were found to affect the depth‐diffusion behavior of titanium in LiNbO3 slab waveguides are the initial thickness of the dopant film and the diffusion temperature. Anisotropy in the diffusion rate for Xand has been applied to the refractive index profile reconstruction for single‐mode optical channel waveguides. A sharp change in the index at the air–guide interface has been observed, as expected. The dependence of refractive index change on Ti concentration has been found to be nonlinear, such as quadratic, approximately.

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Secondary‐ion‐mass spectrometry and near‐field studies of Ti:LiNbO3 optical waveguides

The refractive-index profile is readily calculated from the observed fundamental mode pattern using the scalar-wave equation. Index distributions of diffused Ti: LiNbO 3 waveguides were measured and are consistent with model calculations.

E. Bergmann

Papers

Index distribution of optical waveguides from their mode profile