Abstract
Dramatic advances in supercontinuum generation have been made recently using photonic crystal fibers, but it is quite challenging to obtain an octave-spanning supercontinuum on a chip, partially because of strong dispersion in high-index-contrast nonlinear integrated waveguides. We show by simulation that extremely flat and low dispersion can be achieved in silicon nitride slot waveguides over a wavelength band of 500 nm. Different from most of previously reported supercontinua that were generated either by higher-order soliton fission in anomalous dispersion regime or by self-phase modulation in normal dispersion regime, a two-octave supercontinuum from 630 to 2650 nm (360 THz in total) can be generated by enhancing self-steepening in pulse propagation in nearly zero dispersion regime, when an optical shock as short as 3 fs is formed.
Highlights
One basic building block in nonlinear optics is a supercontinuum generator, which has experienced a revolutionary development after its realization using photonic crystal fibers (PCFs) [1,2]
The success of PCF-based supercontinuum generation is partially attributed to advanced dispersion engineering allowed by design freedom of the 2D lattice in the fiber cladding [2,5]
Benefiting from this, one can generate a two-octave supercontinuum on a chip by enhancing pulse selfsteepening, which paves the way for ultrafast and ultra-wideband applications on an integrated nano-photonics platform
Summary
One basic building block in nonlinear optics is a supercontinuum generator, which has experienced a revolutionary development after its realization using photonic crystal fibers (PCFs) [1,2]. To the best of our knowledge, demonstrated on-chip supercontinua have a spectral range of ~400 nm [10,11,12,13,14], far less than one octave, which is partially because of insufficient capability to engineer the dispersion of nonlinear waveguides. The dispersion profile of a silicon waveguide was made 20 times flatter by introducing a nano-scale slot structure [15], but this is still not sufficient to support more than one octave spectral broadening of femtosecond optical pulses. We intentionally modify the slot waveguide to obtain normal dispersion at all wavelengths because the supercontinuum generated in all-normal dispersion regime typically would have good spectral coherence [2,16]. One can tailor dispersion value and slope for various nonlinear applications by changing waveguide structural parameters with similar trends presented in Ref. [15]
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