Instantaneous Dynamics of a Fiber Optical Parametric Oscillator Within Its Initiating Process

Abstract

A fiber optical parametric oscillator (FOPO) is an effective way of generating new wavelength lasers in non-conventional wavelength bands, but the complex nature behind it is challenging for both theoretical and experimental studies. Luckily, dispersive Fourier transformation, which has been emerging in recent years, provides us with a good method of demystifying this complexity. In this letter, we capture and report, for the first time, the instantaneous dynamics of the initiating process in a fiber optical parametric oscillator. We directly observe that the initiating process experiences three stages. The FOPO fully establishes the parametric oscillation during nearly 2000 round-trips, i.e., nearly 93 $\mu \text{s}$ . In the meantime, the spectrum of the amplifier spontaneous emission noise gradually narrows down and evolves into the characteristic spectrum of the parametric oscillation. In order to start parametric oscillation, the pump power needs to exceed a certain threshold, after reaching which the power of the residual pump decreases while the signal and idle light grow. As we expect, due to the four-wave mixing effect, the signal and idle light are completely synchronous. Moreover, the stability of the oscillation is very sensitive to a slight fluctuation of the pumping pulses.