Fig. 5: Integrated spectral processing of a microcomb.

a Schematic for on-chip processing of a silicon nitride-based octave-spanning microcomb. PM: polarization maintaining. Here a PM fiber is used to link the two chips for convenience in testing, but finite element simulations suggest that direct facet-to-facet coupling with ~1 dB loss should be possible. b Experimental spectra measured at the three output ports. The microcomb shown in the inset of Fig. 4b is used as the input. c Measured (symbols) and simulated (solid lines) octave-wide transfer functions. The measured transfer function is extracted from the transmission of the comb teeth in (b). At the 1 μm port, extinction ratios of (16.2 ± 0.8) and (20.9 ± 2.2) dB are measured in the 1.55 and 2 μm bands, respectively. Similarly, at the 1.55 μm port, extinction ratios of (20.2 ± 0.7) and (25.6 ± 2.1) dB are measured in the 1 and 2 μm bands, and at the 2 μm port, extinction ratios of (26.1 ± 0.8) and (22.7 ± 0.9) dB are measured in the 1 and 1.55 μm bands. d Magnified comparison of the outputs at the three ports in the individual spectral bands. Separation of the three spectral bands into the three ports with 15–25 dB of contrast is observable, along with 14 dB of pump suppression after comb generation from the ring filter (light blue comb tooth). The uncertainties reported in (c) correspond to line-to-line fluctuations in the comb spectra and include variations in coupling, and are one standard deviation values