Unlike third-harmonic generation in a monochromatic field, which gives rise to a signal at the frequency
being the frequency of the pump field, a broadband ultrashort pump pulse can generate isolated spectral peaks that are substantially shifted from the frequency
. In the multimode guided-wave regime, this non-
third-harmonic generation maps adjacent guided modes of the third harmonic onto a manifold of spectral peaks around
. The spectral shifts and the widths of these peaks are controlled by the phase and group-velocity mismatch between the pump field and third-harmonic modes, as well as the length of nonlinear-optical interaction, allowing the spectral contents of the third-harmonic signal to be engineered by tailoring the dispersion of the pump and third-harmonic modes involved in the nonlinear-optical process. Photonic-crystal fibers possess a unique combination of properties required to achieve large frequency shifts in non-
third-harmonic generation, allowing efficient tunable frequency upconversion based on this phenomenon.
© 2005 Optical Society of America