Among the most widely investigated devices for Integrated Optics are modulators

switches and spectrum analyzers using Ti-diffused LiNbO

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waveguides. For practical application of such devices the coupling problem of single-mode fibers to single-mode diffused waveguides seems to be one of the most basic and most important problems

To achieve the optimum efficiency in coupling single-mode fibers to single-mode planar waveguides

two conditions must be satisfied:(1) the field distribution of their modes must be matched; and (2) the lateral position between fiber and waveguide must be aligned precisely.An available device with end. fire coupling of single-mode fibers to Ti:LiNbO

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single-mode planar waveguides was designed and fabricated

according to the analysis of coupled mode theory in this paper. To reduce the waist of near-Gaussian beam emitted by fiber

a microlens was formed by arc discharge on the end of single-mode fiber.In this way

the mode distributions of single-mode fiber and single-mode planar waveguide were metched better. In order to achieve precise alignment

two-dimensional silicon V-grooves were used as the positioning alignment frame. The coupling efficiency up to 64% has been measured practically.