Nature Photonics Research Highlight: From UV to mid-IR

From UV to mid-IR

Appl. Phys. Lett. 95, 161103 (2009)

Supercontinua—ultrabroad bandwidth light pulses usually created by propagating intense optical pulses through a strongly nonlinear media — are attractive for many applications including spectroscopy, optical coherence tomography and the creation of tunable ultrafast femtosecond light sources. So far, however, supercontinuum generation has been limited between UV and nearinfrared wavelengths for silica photonic crystal fibres and 0.8–4.5 μm for fluoride fibres. Now, Guanshi Qin and colleagues from Toyota Technological Institute in Japan report that broader operation from the UV to wavelengths as long as 6–8 μm in the midinfrared can be achieved by using a short length of ZrF4–BaF2–LaF3–AlF3–NaF fluoride fibre and a high peak pump power. The team investigated a 2-cm-long step-index fluoride fibre with a core diameter of 9 μm, a numerical aperture of 0.2 and a zero-dispersion wavelength of 1.65 μm. Using a 1,450 nm femtosecond laser emitting a peak power of 50 MW as a pump, supercontinuum light with wavelengths ranging from the UV to 6.28 μm was observed. The spectral broadening is said to be a result of self-phase modulation, Raman scattering and four-wave mixing. According to the researchers, the use of a fibre with a larger numerical aperture, such as air-cladding microstructured fibre, could further extend the wavelength to 8 μm.