Mechanism and characteristics of a fast-tuning Brillouin/erbium fiber laser.

A fast-tuning Brillouin/erbium fiber laser (BEFL) is investigated on its mechanism and characteristics in detail, in which a 4 m erbium-doped fiber (EDF) as both the Brillouin gain and linear gain media is coiled on a piezoelectric transducer (PZT) for laser frequency modulations. We demonstrate the fast-tuning mechanism theoretically and experimentally that only the lasing cavity mode is modulated, instead of the previous presumption that the Brillouin frequency shift of the EDF is modulated synchronously with the lasing mode. And the maximum tuning range (~60 MHz) is limited by the bandwidth of the Brillouin gain spectrum. The frequency tuning amplitude is direct proportional to the voltage on the PZT. The tuning rates reach up to 48 kHz. The BEFL keeps high-coherence property under fast frequency modulation. Its phase noise remains about -124 dB/Hz1/2 (normalized to 1 m optical path difference) at 1 kHz under 32 kHz modulations. This fast-tuning BEFL presents a wide range of applications in fiber sensors, optical fiber communications, and so forth.