Raman-Kerr frequency combs in Zr-doped silica hybrid microresonators

Coherent Raman comb generation in H2O2aqueous solutions by crossing-pump stimulated Raman scattering

The cascaded stimulated Raman scattering (SRS) of 30% H₂O₂ aqueous solutions was investigated using a pulsed Nd: YAG laser with a wavelength of 532 nm. The transfer of excess electrons between H₂O₂ and H₂O molecules enhanced the SRS. Together, the decomposition of H₂O₂ and the intense SRS Stokes led to the generation of the crossing-pump effect of H₂O₂ aqueous solutions and the appearance of a new peak at 4229 cm^-1 that is excited by Stokes as the pump source. Crossing-pump not only reduced the threshold but also generated the broadband-coherent Raman comb, defined as a coherent radiation wavelength ranging from 434 to 831 nm (i.e., a Raman shift ranging from -4225 to 6756 cm^-1). The anti-Stokes SRS was attributed to the four-wave mixing (FWM) process.

Single-mode characteristic of a supermode microcavity Raman laser

Microlasers in near-degenerate supermodes lay the cornerstone for studies of non-Hermitian physics, novel light sources, and advanced sensors. Recent experiments of the stimulated scattering in supermode microcavities reported beating phenomena, interpreted as dual-mode lasing, which, however, contradicts their single-mode nature due to the clamped pump field. Here, we investigate the supermode Raman laser in a whispering-gallery microcavity and demonstrate experimentally its single-mode lasing behavior with a side-mode suppression ratio (SMSR) up to 37 dB, despite the emergence of near-degenerate supermodes by the backscattering between counterpropagating waves. Moreover, the beating signal is recognized as the transient interference during the switching process between the two supermode lasers. Self-injection is exploited to manipulate the lasing supermodes, where the SMSR is further improved by 15 dB and the laser linewidth is below 100 Hz.

Photonic Dissipation Control for Kerr Soliton Generation in Strongly Raman-Active Media

Microcavity solitons enable miniaturized coherent frequency comb sources. However, the formation of microcavity solitons can be disrupted by stimulated Raman scattering, particularly in the emerging crystalline microcomb materials with high Raman gain. Here, we propose and implement dissipation control-tailoring the energy dissipation of selected cavity modes-to purposely raise or lower the threshold of Raman lasing in a strongly Raman-active lithium niobate microring resonator and realize on-demand soliton mode locking or Raman lasing. Numerical simulations are carried out to confirm our analyses and agree well with experiment results. Our work demonstrates an effective approach to address strong stimulated Raman scattering for microcavity soliton generation.

Whispering gallery mode emission from dye-doped polymer fiber cross-sections fabricated by near-field electrospinning

Whispering gallery mode (WGM) resonators demonstrate great potential for photonic and sensing applications. Yet, these devices are often disadvantaged by costly materials or complex fabrication approaches, in addition to lack of manufacturing scalability. Near-field electrospinning (NFES), a recently emerged facile fiber fabrication method, offers a solution. Here, WGM resonances are reported in Rhodamine 6G-doped poly(vinyl) alcohol (PVA) microfibers via NFES. Diameters are tuned over a range of more than 10 μm by varying substrate stage speed. Fibers display uniform distribution of dye, smooth surfaces, and circular cross-sections, all critical for supporting WGMs. High quality (Q) resonances are confirmed within fiber cross-sections through polarization experiments, free-spectral range analysis, and Mie-theory-derived mode assignment. In addition to WGMs, groups of associated spiral or conical modes are observed due to taper-induced weak optical confinement along the fiber axis. Crosslinked, dye-doped PVA fibers are utilized to sense the ethanol concentration in ethanol-water mixtures and actuation mechanisms are evaluated by comparison to theoretical spectra. The demonstration of high-Q resonances within NFES polymer microfibers is a critical step toward simple, cost effective, high-volume fabrication of WGM resonators for optoelectronics and biomedical devices.