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Narrow band wavelength selective devices were simulated.
Spectral properties of codirectional, contradirecional,
transmission resonant grating-assisted waveguide coupler
filters were studied. The simulations we performed were based
on waveguides made of Si3N4 and p-glass with SiO2 as clading
layers. Planar waveguide couplers and ridge waveguide couplers
were studied. Our goal is to design optical filters compatible
with silicon IC technology. Coupled-mode theory was used to
derive spectral response of the grating-assisted directional
couplers. A 24angstrom bandwidth could be achieved with a
forward coupling grating filter at 1.3 um center wavelength.
For backward coupling grating filters the bandwidth was about
half as narrow. Even narrower bandwidths could be achieved with
transmission rsonant grating filters with the bandwidth
determined by the coupling coefficient. We showed that
interference between waveguide modes have to be considered in
codirectionally coupled waveguide filters. Near ideal power
transfer efficiency could be achieved only if the two
waveguides are far from synchronous. We showed that side lobes
in the reflection spectrum of contradirectionally coupled
grating filters were significant for ridge waveguide couplers.
These direct-Bragg-reflection induced side lobes could be
suppressed by using a phase shifted grating. Transmission
resonant grating filters were showed to have a narrow
transmission peak inside the stopband, and so could be used in
dense WDM systems.
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