Fiber Laser with a Pulse Repetition Rate of Up to 12 GHz and Harmonic Mode-Locking Stabilization Through Optoacoustic Interaction

The study experimentally investigates resonance effects that arise when the frequency of one of the guided acoustic wave Brillouin scattering modes in an optical fiber aligns with the harmonic of the fundamental frequency of the fiber cavity. For precise frequency tuning, mechanical tension was applied to a segment of the fiber cavity stripped of its cladding. The experiments have demonstrated that, following the adjustments, harmonic mode-locking occurs exclusively at pulse repetition rates (PRR), which are integral multiples of the resonant acoustic frequency. A significant reduction in supermode noise accompanies this laser operation, thus increasing the maximum PRR to ~12 GHz. The effects thus observed can be attributed to the formation of a high-Q optoacoustic grating within the fiber.