Mode-locking a Mamyshev oscillator using an auxiliary, starting arm

The procedure for starting a Mamyshev oscillator using an auxiliary, starting arm is shown at left. The oscillator itself is at the bottom-right of the screen, while the laptop at the upper-right depicts the spectrum.

After an opaque card is passed through the cavity, mode-locking is initially unable to resume on its own. The spectrum shows only an ASE peak superimposed with narrower peaks, corresponding to ASE filtered through the two bandpass filters. Flipping a mirror engages the starting cavity, allowing unstable Q-switching to occur in the auxiliary cavity. The Q-switched pulses then seed the main cavity, and when the starting arm is disengaged, the main cavity reaches a mode-locked state (as evidenced by the reappearance of a broad, energetic spectrum).

This process is shown from another angle at right.

Below: schematic of the main cavity (left), alongside a cut-out of the starting arm (right).

For more information, read the paper here.