Efficient 1.5 μm Raman generation in methane-filled negative curvature hollow-core fiber

Efficient 1.5 μm fiber gas Raman source has been demonstrated for the first time in methane-filled negative curvature hollow-core fiber (NC-HCF) with ice-cream-cone shaped cladding. With 4.5 bar methane gas filled, an 8.8 m long NC-HCF was pumped with a 1064 nm microchip laser, generating Stokes spectral line at 1543.7 nm. A maximum Raman conversion efficiency of about 57% has been achieved with 24 mW coupled pump power, and the corresponding quantum conversion efficiency was 82.7%, a record level of such experiment.