We have fabricated bandpass filters based on -shifted long-period gratings for application in actively mode-locked erbium fiber lasers. Introducing the -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 , at a 3-GHz repetition rate. These all-fiber filters have the advantages of low insertion loss and a wide bandwidth (10–20 nm), and they do not require that a circulator be inserted into the laser cavity.
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