We have fabricated bandpass filters based on π-shifted long-period gratings for application in actively mode-locked erbium fiber lasers. Introducing the π-phase shift in the middle of the grating opens a bandpass within the core–cladding mode resonance peaks. With a 22-nm bandwidth filter inserted in an actively mode-locked erbium fiber sigma laser, solitonlike pulses are generated, with a power-dependent duration of ≈3–5 ps , at a 3-GHz repetition rate. These all-fiber filters have the advantages of low insertion loss (<0.5 dB) and a wide bandwidth (10–20 nm), and they do not require that a circulator be inserted into the laser cavity.
© 2001 Optical Society of America
O. Deparis, R. Kiyan, O. Pottiez, M. Blondel, I. G. Korolev, S. A. Vasiliev, and E. M. Dianov, "Bandpass filters based on π-shifted long-period fiber gratings for actively mode-locked erbium fiber lasers," Opt. Lett. 26, 1239-1241 (2001)