Dispositivi ottici per il controllo spettrale dei segnali

Frequency shifts of optical pulses can be achieved exploiting propagation in nonlinear crystals. Spectral blue-shifts and red-shifts, originating from a phase-mismatched second harmonic generation process under conditions of strong group-velocity mismatch, can be efficiently controlled by acting on pulse intensity and phase-mismatch. We show theoretically and experimentally that spectral blue-shifts and spectral red-shifts in a range of 100 nm are achieved by propagating 40 fs pulses with a 70 nm spectrum centered at 1450 nm in a 25-mm-long periodically poled stoichiometric lithium tantalate crystal. This crystal can be exploited for the realization of a single-pass device that tunes the carrier frequency output from a femtosecond fiber laser with continuity and over a broad range.