  We demonstrate an integrated continuously tunable third-order ring filter
with a measured extinction ratio of 80dB, a 100x improvement over previously
demonstrated integrated 3rd or 6th order filters. Using integrated thermal
tuning elements, the filter can be tuned over 100% of its 48 GHz free spectral
range with 1.3 dB insertion loss. The filters are fabricated on a wafer-scale
foundry compatible Si3N4 low-loss platform enabling integration with a wide
variety of previously demonstrated passive and active elements. The high
extinction ratio, low loss, flat passband and steep roll-off is desirable for a
broad range of applications including pump-stokes separation for Brillouin
scattering, idler separation in four-wave mixing and separation of entangled
states for quantum communications that utilize nonlinear optics.
