Abstract
We have proposed and fabricated two kinds of
planar-lightwave-circuits-type polarization beam splitters (PBSs) using
trenches filled with low-refractive-index material: a narrowband-type and a
wideband-type. Both PBSs consisted of two 3-dB couplers and two waveguide
arms with trenches of different lengths. A narrowband-type PBS used
silica-based waveguides on silica substrates. On the other hand, a
wideband-type PBS used silica-based waveguides on silicon. The local lateral
refractive index difference $(\Delta)$ was increased by introducing a pair of trenches. Due to the local
lateral enhanced optical confinement structure, the propagation constants of
waveguides constructed using trenches filled with a low-refractive-index
material depend strongly on the polarization. A narrowband-type PBS, which
had the same arm lengths can have a high polarization extinction ratio,
although the working bandwidth is restricted. However, a wideband-type PBS,
which had the different arm lengths can function over a broad wavelength
range, provided that the maximum polarization extinction ratio is
acceptable. We optimized the structures of both types of PBS by carrying out
simulations. In these simulations, the narrowband-type PBS exhibited a
maximum polarization extinction ratio of ${-}34.5$ dB for the through-path at 1555 nm, ${-}42.7$ dB for the cross-path at 1545 nm, whereas the wideband-type PBS
exhibited a ${-}10$ dB polarization extinction ratio bandwidth of 105 nm. Our
fabricated narrowband-type PBS exhibited a ${-}10$ dB polarization extinction ratio bandwidth of 45 nm for both the
through-path and the cross-path. At this bandwidth, the insertion loss was
less than 9.0 dB. The maximum polarization extinction ratio was ${-}28.9$ dB for the through-path at 1570 nm, and ${-}27.5$ dB for the cross-path at 1535 nm.The wideband-type PBS exhibited a ${-}10$ dB polarization extinction ratio bandwidth of more than 105 nm
for both paths. It exhibited an insertion loss of less than 4.4 dB and a
maximum polarization extinction ratio of ${-}22.8$ dB for the through-path at 1605 nm, ${-}20.0$ dB for the cross-path at 1535 nm at this bandwidth.
© 2009 IEEE
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