Experimental studies on the structural dependence of stimulated Raman-like scattering in solid-core photonic crystal fibers

The tight confinement of both optical and acoustic fields in their µm-sized fiber cores of photonic crystal fibers (PCFs) can lead to enhanced Brillouin light scattering in the forward direction, which is well-known as the stimulated Raman-like scattering (SRLS). In general, the gain spectra of SRLS in PCFs are dominated by the PCF core sizes. Meanwhile, their exact dependences upon the surrounding hollow channels have not been systematically studied in experiments. In this work, we investigated a series of PCF samples with systematically varied core diameters and air-filling ratios and unveiled several key impacts of the PCF air channels upon their gain spectrum in terms of the gain strength, the frequency shift and multi-peak structure, together with physical interpretations of the underlying mechanism. Our work provides some practical guidance for PCF design in potential applications that employ SRLS in mode-locked lasers and opto-acoustic isolators.