Reconfigurable silicon photonic filter stage for signal processing and monitoring

A reconfigurable silicon-photonic filter stage for the processing and monitoring of input signals is demonstrated and employed. The device consists of a balanced Mach-Zehnder interferometer with two ring resonators nested in each arm and built-in germanium photodetectors at its output ports. The transfer function of the device is adjustable through thermo-optic tuning of optical phase delays within each of the four resonators and between the two interferometer arms. Response examples include bandpass filters of variable bandwidth, as well as narrow bandpass and narrow band-stop shapes. The device is used in the wavelength division demultiplexing of a 16 Gbit/s on-off-keying data channel, with spacing of only 26 GHz between adjacent channels. A basic optical spectrum analyzer is realized by scanning the transmission wavelength of a narrowband filter response and reading the output from the on-chip detector. The device supports agile processing and monitoring input signals.