Spectral broadening in an array of subwavelength silicon waveguides pumped with fs pulses is studied. Adjusting input pulse position, different spectral patterns are observed and explained using the resonant emission from temporal supermode solitons.

In this Letter, we report group index measurements of the supermodes of an array of two strongly coupled silicon-on-insulator waveguides. We observe coupling-induced dispersion that is greater than the material and waveguide dispersion of the individual waveguides. We demonstrate that the system transforms from supporting the two supermodes associated with two coupled waveguides to the single mode of a slot waveguide within the investigated spectral range. During the cutoff of the antisymmetric supermode, an anti-crossing between the symmetric TM and antisymmetric TE supermodes has been observed.

A scalable and accurate technique for measuring the group index and dispersion of optical fibers is used to provide the first accurate measurements of dispersion slope in hollow-core photonic band-gap fibers. We present data showing group index, group-velocity dispersion and dispersion slope in hollow-core fibers guiding at both 800 nm and 1064 nm wavelength.

Silicon on insulator photonic wire waveguides offer tight sub-wavelength confinement of light, high nonlinearities and large and controllable geometrical Oroup Velocity Dispersion (OVD) [1]. Arranging wires in arrays brings about new opportunities for dispersion control. Strongly dispersive coupling between modes of adjacent wires causes substantial and controllable variation of the zero OVD wavelength between different supermodes [2]. This modifies the phase matching conditions for resonant (Cherenkov) radiation [3], which is one of the distinctive features of solitons in waveguides with sign-changing OVD [4].In this work we study theoretically and experimentally spectral broadening and excitation of solitonic supermodes in an array of three coupled silicon wires. Each wire is 220 nm thick, 380 nm wide and 3 mm long.The array is located on the silica glass substrate and surrounded by air. The wall-to-wall separation between the wires is 600 nm . For the chosen dimensions, the zero OVD wavelength of the quasi-TE mode of single wire is located at 1.62 �m. For pulses with the duration of � 100 fs, the dispersion and coupling lengths are matched around the pump wavelength of 1.5�m and are of the order of 1 mm.We model the array by using the set of coupled nonlinear equations for the amplitudes of supermodes Ej (1) where Dj is the dispersion operator ofj-th supermode (j=1,2,3) and rjprS are numerical coefficients. Extending the conventional analysis of Cherenkov radiation to the case of solitonic supermodes, we have found that, depending on the input conditions, up to five resonances can be observed [3]. Different patterns of resonances serve as unique "fingerprints" to different solitonic supermodes -thus allowing detection of solitonic supermodes by analyzing output spectra. Cherenkov radiation by solitonic supermodes make a significant contribution to the observed substantial and asymmetric spectral broadening from single-wire and narrow-band pump, see Fig. 1. We have used 120 fs pulses at 1.54 �m, the pump spot diameter illuminating the array is estimated at 1.45 �m. The output spectra are sensitive to the position of pump across the array face. As we shift the input pulse from the edge to the central wire, we observe a noticeable gap in the output spectrum between 1.7�m and 1.8�m, cf. selected areas in Figs. I(a) and (b). The radiation in this gap is associated with the anti symmetric supermode, which is not excited when the input pulse is focused on the central wire. The predicted changes in the output spectrum with variation of the input conditions have been confirmed in our experiments, see Figs. l(c) and (d). Our results pave the way for future research into frequency conversion and switching applications using spatio-temporal solitonic effects in periodic nanostructures.> a.. CIlFig. 1 Numerical (a,b) and experimentally measured (c,d) output spectra from the edge wire as functions of the input average power. Initial excitation is localized in the edge (a,c) or central (b,d) wire. References[I) R. M. Osgood ...

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