Silicon-on-Insulator (SOI) has emerged as promising material choice for various integrated optoelectronic devices. Two
issues make SOI attractive for complex optical systems: the cost reduction due to compatibility with CMOS technology
and high refractive index contrast between core and cladding, which is an important property for good confinement of
light and efficient guiding and coupling in sub-micron waveguides. However, for those devices that are intended to be
part of broadband optical networks, for example multiplexers and de-multiplexers, it is desirable to demonstrate a high
selectivity and a tunable response. Thus, it is necessary to provide wavelength selective elements with the ability to filter
input data streams producing a large Free Spectral Range (FSR), a small Full Width at Half Maximum (FWHM), and a
high quality factor (Q), all conditions set by communication standards. Owing to the generic and adaptable operation,
ring-resonator-types of filters in SOI are often considered as candidates to meet these demands. Herein two different
designs are investigated from both experimental and modelling standpoints in order to tailor the filter transfer function.
These are mutually coupled (Vernier) resonators and cascaded resonators based on small SOI photonic wires. Fabricated
filters designed to provide a large FSR and a polarisation independent (PI) response are analysed and improvements
proposed. Issues associated with temperature control of the transfer function have also been addressed.