Abstract
Nonlinear Kerr micro-resonators have enabled fundamental breakthroughs in the understanding of dissipative solitons, as well as in their application to optical frequency comb generation. However, the conversion efficiency of the pump power into a soliton frequency comb typically remains below a few percent. We fabricate and characterize a hybrid Mach-Zehnder ring resonator geometry, consisting of a micro-ring resonator embedded in an additional cavity with twice the optical path length of the ring. The resulting interferometric back coupling enables to achieve an unprecedented control of the pump depletion: pump-to-frequency comb conversion efficiencies of up to 55% of the input pump power is experimentally demonstrated with a soliton crystal comb. We assess the robustness of the proposed on-chip geometry by generating a large variety of dissipative Kerr soliton combs, which require a lower amount of pump power to be accessed, when compared with an isolated micro-ring resonator with identical parameters. Micro-resonators with feedback enable accessing new regimes of coherent soliton comb generation, and are well suited for comb applications in astronomy, spectroscopy and telecommunications.
Highlights
Nonlinear Kerr micro-resonators have enabled fundamental breakthroughs in the understanding of dissipative solitons, as well as in their application to optical frequency comb generation
The dissipative Kerr solitons (DKSs) field generated in the ring that comes out at node 1 mixes with the pump field that is not coupled into the ring, creating the input field to the feedback section
We demonstrate that on-chip resonators with optical feedback support the generation of a rich variety of DKSs, while requiring a lower amount of pump power to be accessed when compared with a single micro-ring resonator architecture
Summary
Nonlinear Kerr micro-resonators have enabled fundamental breakthroughs in the understanding of dissipative solitons, as well as in their application to optical frequency comb generation. A key limitation of present DKS-based micro-resonator OFC sources, though, is the extremely low conversion efficiency of the pump power into the power of the comb lines[40]. This is notoriously the case when generating bright solitons in the anomalous dispersion region of the ring waveguide[25]. The interference of the fields from the ring and the feedback section enables unprecedented control of the pump depletion This permits us to numerically show that more than 80% of the input pump power can be transferred into the comb lines at the device output. Our approach brings Kerr micro-combs from being inherently lowefficiency devices into comb generators possessing efficiencies that even surpass those of laser sources
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