Abstract
There has been a resurgence of interests in stimulated Brillouin
scattering (SBS) in optical fibers recently. This is largely due to the need
to overcome SBS for power scaling of single frequency fiber lasers. Complex
acoustic waveguide designs have been proposed for SBS suppression in optical
fibers. There is, therefore, a strong need for finding acoustic modes in
complex acoustic waveguides. Furthermore, leaky acoustic modes are often
ignored in recent works on SBS in optical fiber. Many leaky acoustic modes
involved in SBS in optical fibers often have comparable losses to guided
acoustic modes. The losses of both guided acoustic modes and many leaky
acoustic modes are dominated by the extremely high material loss of acoustic
waves in the GHz region in optical fibers. Therefore, it is very important
to consider these leaky acoustic modes in SBS in optical fibers, especially
for acoustic antiguide designs used for SBS suppressions, where those leaky
acoustic modes are often responsible for the peak SBS gain and consequently
SBS threshold. Even for optical fibers with guided acoustic waveguide, fine
features in SBS gain spectra can be better understood by studying the
additional contributions from leaky acoustic modes. In this work, we report,
for the first time, a complex vector acoustic mode solver capable of finding
both guided and leaky acoustic modes in arbitrary circular acoustic
waveguides. The validity of the mode solver is verified by comparing
simulated SBS gain spectra in two optical fibers, one with acoustic guide
and one with acoustic antiguide, to measured ones. This acoustic mode solver
can be used to provide highly accurate SBS gain spectrum in optical fibers.
It will be a critical tool in optical fiber designs for SBS suppressions and
enhancements. It will also be very important tool for understanding fine
spectral details of SBS in optical fibers.
© 2010 IEEE
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