Abstract
Asymmetrical Mach–Zehnder Interferometer (MZI) structures on a
submicrometer silicon-on-insulator platform are designed and analyzed when
used as a polarization beam splitter (PBS). The analysis shows that it is
allowed to use 2$\,\times\,$2 power splitter/combiner couplers with a balanced ratio (50:50)
for only one polarization by selecting the output ports for TE and TM polarizations
appropriately. This makes the design much easier and more flexible. Examples
for the design of MZI-based PBSs using directional couplers as well as multimode
interference couplers are given. Finally, compensating the positive or negative
wavelength shifts due to fabrication errors is proposed by using a thermal-optical
effect on the two MZI arms separately. The numerical calculation shows that
a small temperature increase (e.g., 30 $^{\circ}$C) is enough to compensate the wavelength
shift due to an arm-waveguide width deviation of 50 nm. The parameters of
MZI arm waveguides are chosen appropriately in order to make the MZI wavelength
shifts (due to the fabrication errors) almost polarization independent, so
that the thermal compensation approach could push the central wavelengths
for both polarizations back to the designed value.
© 2011 IEEE
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