Abstract
Broadband optical frequency combs are extremely versatile tools for precision spectroscopy, ultrafast ranging, as channel generators for telecom networks, and for many other metrology applications. Here, we demonstrate that the optical spectrum of a soliton microcomb generated in a microresonator can be extended by bichromatic pumping: one laser with a wavelength in the anomalous dispersion regime of the microresonator generates a bright soliton microcomb while another laser in the normal dispersion regime both compensates the thermal effect of the microresonator and generates a repetition-rate-synchronized second frequency comb. Numerical simulations agree well with experimental results and reveal that a bright optical pulse from the second pump is passively formed in the normal dispersion regime and trapped by the primary soliton. In addition, we demonstrate that a dispersive wave can be generated and influenced by cross-phase-modulation-mediated repetition-rate synchronization of the two combs. The demonstrated technique provides an alternative way to generate broadband microcombs and enables the selective enhancement of optical power in specific parts of a comb spectrum.
Highlights
Broadband optical frequency combs are extremely versatile tools for precision spectroscopy, ultrafast ranging, as channel generators for telecom networks, and for many other metrology applications
One of the pump lasers, within the C-band (1530–1565 nm), is used to generate a primary bright soliton microcomb, where the overall group velocity dispersion of the microresonator is anomalous. Another pump laser in the O-band (1260–1360 nm) is used both to compensate the thermal effect of the microresonator during soliton generation[28] and to generate a second frequency comb via Kerr cross-phase modulation (XPM) with the primary soliton pulse, which leads to an extension of the comb spectra into the normal dispersion regime
A 1.5 μm wavelength external cavity diode laser (ECDL) with a short-term linewidth of
Summary
Broadband optical frequency combs are extremely versatile tools for precision spectroscopy, ultrafast ranging, as channel generators for telecom networks, and for many other metrology applications. We demonstrate that the optical spectrum of a soliton microcomb generated in a microresonator can be extended by bichromatic pumping: one laser with a wavelength in the anomalous dispersion regime of the microresonator generates a bright soliton microcomb while another laser in the normal dispersion regime both compensates the thermal effect of the microresonator and generates a repetition-rate-synchronized second frequency comb. We show that a dispersive wave (DW) can be generated in the auxiliary frequency comb at a wavelength, where phase matching occurs due to the forced synchronization of the repetition rate, in contrast to conventional models, in which the DW position is determined by higher-order dispersion These results can be used to selectively amplify the optical power in regions of microcombs that are of interest, e.g., for optical frequency metrology
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