Repetition rate control of an LD-pumped femtosecond erbium-doped fiber laser using a sub ring cavity

Abstract

With a view to generating femtosecond pulses from lasers, an additive pulse modelocking (APM) technique has recently been developed, in which a nonlinear Fabry-Perot cavity plays an important role in narrowing the output pulse by using interference.1 The pulse operation mechanism of the laser can be classified as fast saturable absorber modelocking. An alternative way to obtain nonlinear interference is to use an optical fiber loop instead of the nonlinear Fabry Perot fiber cavity. Doran and Wood presented an interesting idea for switching the pulse which is accompanied by simultaneous pulse shaping, the so called nonlinear optical loop mirror (NOLM).2 Fermann et al. presented a modified NOLM, which is called the nonlinear amplifying loop mirror (NALM).3 An EDFA is installed inside the loop mirror which is terminated by a 50 : 50 coupler. Thus, low threshold switching can be realized in the NALM.