Parametric generation and phase locking of multiple sidebands in the regime of full-back-conversion

Parametric interaction allows both forward and backward energy transfers among the three interacting waves. The back-conversion effect is usually detrimental when unidirectional energy transfer is desired. In this theoretical work, we manifest that the back-conversion effect underpins the direct generation of the picosecond pulse train without the need for a laser resonator. The research scenario is an optical parametric amplification (OPA) that consists of a second-order nonlinear medium, a quasi-continuous pump laser and a sinusoidal amplitude-modulated seed signal. The back-conversion of OPA can transfer the modulation peaks (valleys) of the incident signal into output valleys (peaks), which inherently induces spectral sidebands. The generation of each sideband is naturally accompanied with a phase shift of +/-pi. In the regime of full-back-conversion, the amount and amplitude of the sidebands reach the maximum simultaneously, and their phase constitutes an arithmetic sequence, leading to the production of a picosecond pulse train. The generated picosecond pulse train can have an ultrahigh repetition rate of 40 GHz or higher, which may facilitate ultrafast applications with ultrahigh speed.

Automated summary

Parametric interaction enables energy transfers in both forward and backward directions among three waves. The back-conversion effect, though usually undesirable, is shown in this theoretical work to be the key to directly generating picosecond pulse trains without the need for a laser resonator. By using an optical parametric amplification setup with a second-order nonlinear medium, a quasi-continuous pump laser, and a sinusoidal amplitude-modulated seed signal, the modulation peaks (valleys) of the input signal can be transformed into output valleys (peaks) through the back-conversion process, resulting in the production of spectral sidebands and a picosecond pulse train. This picosecond pulse train can have an ultrahigh repetition rate of 40 GHz or higher, making it suitable for ultrafast applications.