Subharmonic Generation in a Bandwidth Clamped Actively Mode-Locked Fiber Laser

We propose and demonstrate a new photonic subharmonic generation mechanism through an injection locking process in an actively mode-locked fiber ring laser, whose gain bandwidth is narrower than the frequency of the injection signal. Through the recursion equation, the operation principle and subharmonic injection locking condition are theoretically analyzed. In the experiment demonstration, a 10-GHz subharmonic signal locked by a 20-GHz injection signal is obtained. The measured phase noise at 10 kHz frequency offset is
${-}{\rm 109}~{\rm dBc}/{\rm Hz}$
. The results agree with the theoretical predication well and show a great potential to operate at a very high frequency and large frequency dividing ratio.