Axial spectral scans of polarization dependent third harmonic generation in a multimode photonic crystal fiber

Abstract

We demonstrate a nondestructive axial scanning technique for the spectrally resolved analysis of femtosecond nonlinear–optical transformation in photonic crystal fibers. This technique is applied to map the generation of a polarization–switched third harmonic of femtosecond Cr:forsterite laser pulses in a multimode silica photonic crystal fiber. Obtained results confirmed the intermodal phase–matching to be responsible for the observed polarization dependent multipeak third–harmonic generation. The axial scans revealed, that it is necessary to distinguish between the low and high energy excitation regime of the fiber sample. The proposed technique allows to measure the spectra of nonlinear signals generated in a photonic crystal fiber as a function of the propagation distance without cutting the fiber.

Keywords

• photonic crystal fiber
• third harmonic generation
• axial scan