  Up-to-date network telemetry is the key enabler for resource optimization by
a variety of means including capacity scaling, fault recovery, network
reconfiguration. Reliable optical performance monitoring in general and
specifically the monitoring of the spectral profile of WDM signals in fixed-
and flex-grid architecture across the entire C-band remains challenging. This
article describes a spectrometer circuit architecture along with an original
data processing algorithm that combined can measure the spectrum quantitatively
across the entire C-band aiming at 1 GHz resolution bandwidth. The circuit is
composed of a scanning ring resonator followed by a parallel arrangement of
AWGs with interlaced channel spectra. The comb of ring resonances provides the
high resolution and the algorithm creates a virtual tuneable AWG that isolates
individual resonances of the comb within the flat pass-band of its synthesized
channels. The parallel arrangement of AWGs may be replaced by a time
multiplexed multi-input port AWG. The feasibility of a ring resonator
functioning over whole C-band is experimentally validated. Full tuning of the
comb of resonances over a free spectral range is achieved with a
high-resolution bandwidth of 1.30 GHz. Due to its maturity and low loss, CMOS
compatible silicon nitride is chosen for integration. Additionally, the whole
system demonstration is presented using industry standard simulation tool. The
architecture is robust to fabrication process variations owing to its data
processing approach.
