|
An optical TE--TM mode beam splitter is a fundamental device
and will be useful in integrated devices for fiber
communications and sensors. Many approaches have been taken to
implement the device. In our work an adiabatic Si--based Y--
branch TE--TM mode beam splitter has been investigated. The
materials used to simulate the device are silicon dioxide, p--
glass, silicon nitride which are all compatible with the mature
silicon technology. Besides, the input and output waveguides
are the p--glass core which are convinient to couple with the
fiber for their close refractive indices. An adiabatic device
in which power is not transferred from one mode to another as
the modes propagate across the device has the adavantage that
it needs no critical lengths to be adjusted or tuned. In our
device the TE field will choose the nitride core and the TM
field the p--glass core for their close refractive indices,
respectively. The design considerations are adiabatic
conditions and coherent interferences. For achievement of the
adiabatic passage through the device the branching angle must
be small, around several milliradians in our device. For the
branch is realized in the available photography, there must
have steps along the branching waveguide. To avoid the coherent
interference effect which increases the crosstalk at the
output, the step lengths must be small. The analytical tool is
the MPFE (Mode Propagation by the Fourier Expansion) method.
|