High repetition rate figure eight laser with extracavity feedback

Abstract
The operation of an erbium figure eight all-fibre laser with a fundamental repetition rate of 28.5 MHz is reported. The feedback of light rejected by the nonlinear amplifying loop mirror back into the laser is found to stabilise mode locking enhance startup, shorten the pulse lenght to 275fs, and provide a simple means of multiplying the repetition rate.