Abstract
In order to determine the Verdet constant of an air-core photonic bandgap
fiber (PBF), the birefringence of the fiber needs to be accurately known. We
used two methods to measure the linear and circular birefringence of a
commercial PBF around 1.5 $\mu{\hbox {m}}$. The linear birefringence beat length is found to vary
significantly with wavelength, ranging from 6.8 $\pm$ 0.2 cm at 1526.8 nm to 9.5 $\pm$ 0.4 cm at 1596.8 nm. The circular birefringence is observed to be
weaker by a factor of at least ten. The Verdet constant of this fiber,
measured using a Faraday-effect measurement, is 6.1 $\pm$ 0.3 mrad/T/m. This value is in broad agreement with the
prediction of a numerical model, and it confirms that the Verdet constant of
this fiber is dominated by the residual spatial overlap of the mode with
silica. It is also found to be 90 times weaker than the Verdet constant of a
solid-core fiber (SMF-28) measured by the same process (0.55 $\pm$ 0.01 rad/T/m, in agreement with published values). This
significantly reduced susceptibility to magnetic fields points to yet
another benefit of air-core fibers in the fiber optic gyroscope.
© 2009 IEEE
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