Abstract

Cobweb microstructured optical fibers are often strongly multimode in the visible and near infrared regions. This may lead to a number of intermodally phase-matched nonlinear processes. Here we describe a process of nonlinear generation of very high-order UV modes by pumping such fibers with 100 fs Ti:sapphire pulses. Wavelengths as short as 260 nm are generated through a mechanism distinct from supercontinuum generation.

© 2003 Optical Society of America

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References

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J. Opt. Soc. Am. B

Opt. Commun.

L. Tartara, I. Cristiani, V. Degiorgio, F. Carbone, D. Faccio, M. Romagnoli, W. Belardi �??Phasematched nonlinear interactions in a holey fiber induced by infrared super-continuum generation,�?? Opt. Commun. 215, 191 (2003).
[CrossRef]

J. Thogersen, J. Mark, �??Third harmonic generation in standard and erbium-doped fibers,�?? Opt. Commun. 110, 435 (1994).
[CrossRef]

Opt. Express

Opt. Lett.

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Figures (9)

Fig. 1.
Fig. 1.

Supercontinuum generated in two different spatial modes of the 2.5 µm core cobweb fiber: a) fundamental mode, and b) two-lobe higher-order mode. A blue flare on the right overlapping the red portion of the spectrum is due to the second-order diffraction off the grating.

Fig. 2.
Fig. 2.

Transverse fiber guidance scans for a) freshly cleaved fiber, and b) same fiber, but damaged by the input radiation clearly showing the altered morphology of the core tip. Inset: SEM image of a typical cobweb fiber used.

Fig. 3.
Fig. 3.

Far field image of one of the HOUVMs generated in 2.5 µm core MOF.

Fig. 4.
Fig. 4.

Examples of different far field mode profiles of ultraviolet radiation detected at the output of different core diameter microstructured fibers. Green colored images are obtained with white cards painted with the fluorescent marker.

Fig. 5.
Fig. 5.

Numerical modeling results for the 1.6 µm fiber. a) left, model of the MOF where the star-shaped silica guiding region (dark gray) is surrounded by the air region (light gray); a) right, far field calculation geometry; b), c), d) three modes of certain similarity to the observed ones with near-field intensity distributions shown on the left and far-field profiles—on the right. Modal effective indices are indicated as well.

Fig. 6.
Fig. 6.

Near field intensity distribution of 305 nm HOUVM generated in 2.5 µm core MOF. This image corresponds to the far-field distribution for 2.5 µm fiber shown in Fig. 4, lower panel.

Fig. 7.
Fig. 7.

Dependence of the UV spectra on the input average power for the case of a) 1.6 µm and b) 2.5µm core diameter MOFs. Intensity-color scaling is logarithmic.

Fig. 8.
Fig. 8.

Pump wavelength dependence of the UV spectra (left) and corresponding visible-infrared spectra (right) for 1.6µm core fiber and 660 mW average pump power.

Fig. 9.
Fig. 9.

Calculated dispersion profiles of the first 10 modes of a 1.6 µm MOF. Solid curves: lowest order modes having only one zero-dispersion point in the visible. Dashed curves: higher-order modes which have another zero-dispersion point in the infrared.

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