Comb‐Like Frequency Conversions in Few Layer GaSe‐Integrated Microfiber Resonators

ABSTRACT

While advancements in optical fiber‐based second harmonic generation (SHG) have leveraged novel waveguide designs and two‐dimensional nonlinear material integration, conventional fiber schemes remain constrained by limited multi‐frequency control and restricted efficiency growth. We demonstrate an all‐fiber resonant SHG strategy achieving periodic enhancement and polarization modulation by integrating a few‐layer GaSe crystal with a microfiber knot resonator (MKR). Benefitting from MKR‐enabled resonant interaction with GaSe, which possesses ultrahigh second‐order nonlinear susceptibility, the maximum excitation of comb‐like SHG at resonant wavelengths achieves a 32‐fold enhancement compared to GaSe‐microfiber integration under continuous‐wave laser pumping. Meanwhile, the twisted MKR structure facilitates dynamic polarization‐dependent control of the split SHG wavelengths through pump polarization modulation. Experimental results further reveal distinct intensity patterns of SHG intensity in both under‐coupling and over‐coupling regimes. Our findings offer insights into accessing broad, efficient, polarization‐controllable SHG combs for multifunctional nonlinear photonic devices with on‐demand spectral tailoring capabilities.