Abstract
Abstract Optical frequency comb (OFC) based on the whispering-gallery-mode microresonator has various potential applications in fundamental and applied areas. Once the solid microresonator is fabricated, its structure parameters are generally unchanged. Therefore, realizing the tunability of the microresonator OFC is an important precondition for many applications. In this work, we proposed and demonstrated the tunable Kerr and Raman-Kerr frequency combs using the ultrahigh-quality-factor (Q) functionalized silica microsphere resonators, which are coated with iron oxide nanoparticles on their end surfaces. The functionalized microsphere resonator possesses Q factors over 108 and large all-optical tunability due to the excellent photothermal performance of the iron oxide nanoparticles. We realized a Kerr frequency comb with an ultralow threshold of 0.42 mW and a comb line tuning range of 0.8 nm by feeding the control light into the hybrid microsphere resonator through its fiber stem. Furthermore, in order to broaden the comb span, we realized a Raman-Kerr frequency comb with a span of about 164 nm. Meanwhile, we also obtained a comb line tuning range of 2.67 nm for the Raman-Kerr frequency comb. This work could find potential applications in wavelength-division multiplexed coherent communications and optical frequency synthesis.
Highlights
Once the solid microresonator is fabricated, its structure erating the Optical frequency comb (OFC) in the whispering gallery modes (WGMs) microresonators is derived parameters are generally unchanged
By combining with degenerate and nondegenerate FWM processes, an OFC can be realized as the Kerr frequency comb requires phase matching in a wide wavelength range, which is dominated by the group velocity dispersion (GVD) in the resonator [5, 6, 16]
The total GVD in the silica microsphere resonator should be anomalous in the 1550 nm band, and this can be used to compensate the resonant frequency shift, which is induced by the self-phase and cross-phase modulation excited by the pump light [16]
Summary
Once the solid microresonator is fabricated, its structure erating the OFCs in the WGM microresonators is derived parameters are generally unchanged. After (Q) functionalized silica microsphere resonators, which that, efficient microresonator OFC generation is realized are coated with iron oxide nanoparticles on their end using on-chip platforms [1] and fiber-coupled WGM resosurfaces.
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