Abstract
A theoretical study was performed on waveguiding characteristics of
a special Ti:LiNbO<sub>3</sub> structure that an array of strip waveguides is embedded in a planar
waveguide. First, a special Ti:LiNbO<sub>3</sub> structure was fabricated by diffusion of homogeneously coated Ti
film at first and then photolithographically patterned Ti-strips with different
widths of 4, 5, 6, 7, and 8 µm, and the transverse magnetic (TM) mode guided in the strip waveguides
of the special structure was characterized by near-field measurements. Second,
a 2-D refractive index profile is supposed for the special structure. Third,
based upon this supposed index profile model and the experimentally determined
mode field profile type, the mode sizes of the strip waveguides were calculated
using variational method and compared with the experimental results to verify
the validity of the index model supposed and the numerical method adopted.
Finally, the mode sizes and effective indexes of several lowest order TM modes
guided in the strip waveguides were calculated as a function of the initial
Ti-strip width for different waveguide parameters that include the surface
index increment and depth (width) of both the planar and strip waveguides.
The numerical results show that the field profile in the width direction is
influenced by many factors such as the initial Ti-strip width, waveguide width
and depth, and the surface index increment of the strip waveguide. Instead,
the mode field in the depth direction is only influenced by three factors
that include the depth of strip waveguide and the surface index increments
of both planar and strip waveguides. The single-mode condition depends on
all of these parameters.
© 2012 IEEE
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