Dispersion management dual-pass self-phase modulation-enabled spectral selection

Abstract

Self-phase modulation-enabled spectral selection (SESS) technology can generate wavelength-tunable femtosecond pulses, and it is expected to replace traditional complex optical parametric oscillators, and thus has attracted much attention. However, the positive dispersion in the fiber leads the modulation depth of the spectral lobes to decrease, while optical wave breaking hinders the spectral broadening. In order to solve the two problems, we propose a dual-pass SESS technology based on dispersion management which optimizes the shape of the front edge and rear edge of the pulse prior to the second pass by introducing negative dispersion, and compresses the pulse width for increasing the peak power of the pulse. The resulting spectrum features broader spectrum with a deeper modulation depth. By numerical simulation, we find that adjusting the value of the second-order dispersion compensated after the single pass, a broader spectral lobe can be obtained than both the single-pass case and the double-pass case without dispersion compensation. To verify our numerical simulation, we conduct experiments by using a 2-cm-long LMA-8 fiber for spectral broadening and several chirped mirrors to provide negative dispersion, which controls the nonlinear evolution of the pulse in the second pass of the LMA-8 fiber. We study the spectral output corresponding to different amounts of dispersion compensation and find that an optimal dispersion value is required to produce a clear and broader spectral lobe. We also investigate the effect of input pulse energy on spectral broadening under the same dispersion compensation conditions. With 15-nJ input pulse energy and –420 fs<sup>2</sup> dispersion compensation, the resulting SESS source delivers 6 nJ, 113-fs pulses with the peak wavelength at 920 nm.