Bandpass filters based on π-shifted long-period fiber gratings for actively mode-locked erbium fiber lasers

Abstract

We have fabricated bandpass filters based on $\pi$-shifted long-period gratings for application in actively mode-locked erbium fiber lasers. Introducing the $\pi$-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 $\approx 3–5 \mathrm{ps}$, at a 3-GHz repetition rate. These all-fiber filters have the advantages of low insertion loss $\left(<0.5 \mathrm{dB}\right)$ 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

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