Photonic Integrated Filter With Widely Tunable Bandwidth

We present a comprehensive design, fabrication, and characterization analysis of compact silicon-on-insulator bandpass filters with widely tunable bandwidth. The filter architecture is based on an unbalanced Mach–Zehnder interferometer loaded with a pair of ring resonators. A wide bandwidth tunability (from 10% to 90% FSR) can be achieved by controlling the resonant frequency of the rings while preserving a good filter off-band rejection. Design rules are provided that take into account fabrication tolerances as well as losses. Furthermore, the use of tunable couplers allows a more flexible shaping of the spectral response of the filter. The sensitivity with respect to nonlinear effects is carefully investigated. Operation over a wavelength spectrum of ${20} \ {\rm n}{\rm m}$ is demonstrated, making the device suitable for channel subset selection in WDM systems, reconfigurable filters for gridless networking and adaptive filtering of signals.