Ultraviolet-Enhanced Flat Supercontinuum Light Generated in Cascaded Photonic Crystal Fiber

We demonstrate that by using a cascaded configuration of five solid-core photonic crystal fiber (PCF) samples with progressively decreasing core diameters, ultraviolet light with wavelengths as short as ∼300 nm can be generated in a supercontinuum (SC) set-up. With a nanosecond laser as the pump light, the modulation instability effect leads to the generation of multiple optical solitons in the first PCF sample which has a close-to-zero dispersion value at the pump wavelength (∼1064 nm). The following PCF samples with decreasing core diameters enhance the waveguide nonlinearity, and at the same time provide continuously-shorter phase-matching wavelengths for dispersive-wave emission, thereby pushing the short-wavelength edge of the SC spectrum into the deep ultraviolet spectral region. While the PCF splicing technique ensures the compactness of this SC set-up, the generated SC spectrum, spanning ∼350 nm to ∼2000 nm with a flat spectral profile, may be applied in fluorescence microscopy and biochemical imaging.