A Femtosecond Erbium‐Doped Fiber Laser with a Nonlinear Amplifying Loop Mirror Pumped by Laser Diodes and with Repetition Rate Control of Its Output Pulses

An erbium‐doped fiber laser with a nonlinear amplifying loop mirror pumped by 1.48‐μm laser diodes was fabricated. A 290‐femtosecond (fs) short pulse was obtained successfully from this laser. The oscillation wavelength was 1.56 μm and the output peak power was as high as 16 W when the pump power was 20 mW. The oscillation threshold was about 50 mW. However, once the laser started oscillation, it continued to oscillate even when the pump power was 10 mW. The repetition rate of the output pulses changed randomly from 5 MHz (fundamental repetition rate) to 2 GHz and could not be controlled. However, using a subring cavity with a length which is 1/n that of the main cavity (n is an integer), a constant pulse repetition rate of 125 MHz was obtained.