Fig. 1. Principles of OIL-based low-noise amplification of DKS microcomb lines. (a) Conventional multi-wavelength source consists of a large number of discrete lasers showing severe random frequency drift; (b) DKS microcomb generated by an external cavity laser diode (ECDL) amplified by using an EDFA, but at the sacrifice of OSNR degradation; (c) OIL-laser-based DKS microcomb amplification scheme provides simultaneous low noise and high gain. (d) A conceptual image of an integrated chip-scale optical data transmitter using DKS comb lines as WDM data carriers, which are power boosted using the OIL laser scheme.

Fig. 2. Characterization of a DKS microcomb generated in a WGM microcavity. (a) Experimental setup for DKS microcomb generation, linewidth measurement, laser injection locking, and coherent data transmission. (b) Microscopy image of WGM micro-rod resonator used in experiment. (c) Optical spectrum of a single-DKS comb state generated in a WGM micro-resonator. (d) Measured linewidths of 20 DKS comb lines adjacent to the pump laser. (e) Self-heterodyne interferometer beat note spectrum measured for the exemplified comb lines #5 and #10.

Fig. 3. Characterization of OIL-based DKS comb line amplification. (a), (b) Measured optical spectra of initial DKS comb lines and slave lasers after OIL. (c) Comparison of the optical spectra between OIL slave lasers and DKS comb lines amplified by two-stage EDFAs. (d), (e) Measured linewidth beat note RF spectra of free-running and OIL slave lasers by using the delayed self-heterodyne interferometer method. (f) Comparison of the beat note between two adjacent DKS micro-comb lines before and after OIL.

Fig. 4. Comparison between the OIL-based low-noise amplification scheme and conventional EDFA scheme. The constellation diagrams of the received data plotted with blue represent the OIL scheme, and red is for the EDFA scheme. The BER for each channel is listed under each constellation diagram.