Controllable Kerr and Raman-Kerr frequency combs in functionalized microsphere resonators

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.

All-Fiber Hyperparametric Generation Based on a Monolithic Fiber Fabry–Pérot Microresonator

“…The 30-dB bandwidth is less than 100 nm, which is much narrower than the experimental Raman-assisted hyperparametric generation. Raman-induced spectral broadening for Kerr combs in microresonators has been demonstrated in several recent works [16,21,24]; this results from the complex interplay between Kerr, Raman, and all-order dispersion. broadening for Kerr combs in microresonators has been demonstrated in several recent works [16,21,24]; this results from the complex interplay between Kerr, Raman, and all-order dispersion.…”

Nonlinear Optics in Microspherical Resonators

“…This occurrence is due to the cavity boundary conditions that introduce an additional degree of freedom: the frequency detuning of the pump from the eigenmode of the nonlinear resonator [23,47]. Zhang et al [10] proposed hybrid silica microspheres for generation of tunable Kerr and Raman-Kerr combs. The authors have coated the polar cap of the microsphere with iron oxide nanoparticles.…”

“…However, the size of a solid silica microsphere or microbottles is very difficult to change once it is fabricated. A successful way to tune solid WGMR is by coating them with functional materials, such as nanoparticles [10,11]. Hybrid microspheres were also used for Kerr switching [12,13].…”

“…The pink ring is the excited whispering gallery mode and the black polar cap represents the coated area with iron oxide nanoparticles. Reproduced with modifications from Ref [10]…”

Kerr-Raman Optical Frequency Combs in Silica Microsphere Pumped Near Zero Dispersion Wavelength

“…Many regimes of OFC generation achieved in on-chip WGMRs were also investigated in silica MSs and even observed for the first time, which enabled a significant progress in understanding nonlinear physics or discovering new effects. For example, Raman lasing was first demonstrated in a silica MS [14] and after that investigated on the basis of this and other platforms [15][16][17][18][19][20][21][22]. Kerr and Kerr-Raman OFCs generation was also investigated experimentally in a silica MS [16].…”