Seed-injected, actively Q-switched fiber ring laser using an AOM of zero-order transmission

Abstract

Using an acousto-optic modulator of zero-order transmission as the Q-switch, single-frequency laser pulses were obtained in a ring cavity fiber laser with the seed injection technique. The acousto-optic modulator avoided the frequency-shift resulting from the RF driver signal in the first-order transmission. As the seed laser, a distributed-feedback fiber laser based on the π phase-shift fiber Bragg grating was directly inserted into the ring cavity. It decreased the cavity loss and improved the injection efficiency, compared with the common injection by an optical fiber coupler. With the seed laser power over 150 μW, the single-frequency laser pulses with the wavelength of 1550.12 nm were achieved and verified by a scanning Fabry–Perot interferometer. Under the pump power of 450 mW, the pulse duration ranged from 90 ns to 350 ns with the repetition frequency from 10 kHz to 50 kHz. The measured linewidth demonstrated that the pulse laser was almost transform limited: 1.9 MHz for a train of pulses of 50 kHz repetition frequency, 350 ns pulse duration and 36.2 mW maximum average power.