Mid-infrared supercontinuum generation in As2S3-silica “nano-spike” step-index waveguide

01.01.2014, 00:00

Newsletter 7

The bandwidth of a supercontinuum is limited by the window of transparency of the nonlinear medium – usually an optical fiber made from fused silica. To extend the spectrum beyond 2 µm into the mid-IR, the waveguide core must be made from materials that are transparent in this wavelength range. A capillary fibre with a 1 µm bore, one of its ends being tapered down to zero diameter, was pressure-filled with As2S3 glass. The resulting “nano-spike” (Section A in the figure) allows high launch efficiencies into the 2-mm-long uniform waveguide (section B). Ultrashort (65 fs) pulses at wavelength 2 µm, delivered from a Tm-doped fiber laser, are launched into the sub-wavelength As2S3 strand. Soliton fission and dispersive wave generation along the uniform section result in an octave-spanning supercontinuum out to nearly 4 µm at launched energies of only 18 pJ. This nano-spike device provides a unique means of solving the long-standing problem of efficiently coupling light into single-mode high-contrast step-index waveguides of sub-wavelength diameter.
The spectra generated will have immediate uses in metrology and infrared spectroscopy.

Contact: shangran.xie(at)mpl.mpg(dot)de
Group: Russell Division (collaboration with IMRA Inc. and University of Rennes)
Reference: N. Granzow et al., Opt. Exp. 21, 10969-10977 (2013).