November 2015
Spotlight Summary by Michael Frosz
Octave-spanning coherent supercontinuum generation in a silicon nitride waveguide
The supercontinuum reported in this work is not only spectrally coherent and spans more than one octave: it is also generated in a compact chip. The chip consists of a silicon nitride waveguide (Si3N4) with spatial dimensions chosen to give a narrow region of anomalous dispersion around the wavelength of the pump laser (~1 µm). Si3N4 provides high nonlinearity (10 times that of undoped silica), and it is also compatible with existing chip fabrication technology so that large-scale production on chips can more easily be achieved in the future. The high nonlinearity in combination with the dispersion engineering means that the sub-100-fs pulses coupled into the waveguide undergo extreme spectral broadening after just a few mm propagation length. The short propagation length is not only important for compactness, but more to keep the generated spectra coherent between adjacent pulses, as there is less opportunity for noise to build up along the propagation of the pulses. This is crucial for many applications, most notably carrier-envelope offset frequency detection. The experiments were performed with relatively low peak power pulses (less than half a kilowatt) coupled into the waveguide, even though the power incident on the waveguide is about 10 times higher due to low coupling efficiency. The authors point out that the coupling loss is not fundamental and can therefore be improved in future work. This means that the laser power requirement can be lowered further, which could lead to even more compact complete systems.
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Article Information
Octave-spanning coherent supercontinuum generation in a silicon nitride waveguide
Adrea R. Johnson, Aline S. Mayer, Alexander Klenner, Kevin Luke, Erin S. Lamb, Michael R. E. Lamont, Chaitanya Joshi, Yoshitomo Okawachi, Frank W. Wise, Michal Lipson, Ursula Keller, and Alexander L. Gaeta
Opt. Lett. 40(21) 5117-5120 (2015) View: Abstract | HTML | PDF