Abstract
In this paper, we describe polarization-insensitive phase trimming of
silica-based waveguides with both 193- and 244-nm ultraviolet (UV) light and
the trimming of both phase error and polarization dependence. A wide beam
of 193-nm UV light from an ArF excimer laser is useful for phase trimming
multiple waveguides. We utilize stress-release grooves to control birefringence
generation while phase trimming, and we reduce the birefringence change during
refractive index change by 95%. At the same time, we found that this grooved
structure enhances the refractive index increase with UV light. We also utilize
244-nm UV light from a frequency doubled Ar ion laser with high space coherence,
which is suitable for trimming the phase error of a single waveguide. We control
UV-induced birefringence by controlling the size of the 244-nm laser beam
light, and we reduce the birefringence change during phase trimming by 98%.
In addition, we investigate the change in the refractive index and stress
distribution of our waveguide when UV light is irradiated, and discuss the
differences of polarization-insensitive phase trimming between 193- and 244-nm
UV light. Finally, we utilize these techniques to eliminate the polarization-dependent
phase error of an asymmetric Mach–Zehnder interferometer. We successfully
demonstrate the individual trimming of the center wavelength and its polarization
dependence.
© 2009 IEEE
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