Widely tunable single-frequency erbium-doped fiber lasers

In this letter, we report on experimental results on a 70-nm-wide quasi-continuously tunable single-frequency erbium-doped fiber (EDF) laser, in which the laser produced a single-longitudinal mode oscillation between 1510-1580 nm, an output power of 0.5 mW, and a tuning step of about 25 MHz. The cavity incorporates three tunable bandpass filters (TBFs): a bulk-grating-based TBF, a fiber-ring-cavity filter, and an autotracking saturable absorption-induced grating filter generated by an unpumped EDF. This laser had a frequency drift of 100 MHz and a signal-to-source spontaneous emission ratio higher than 60 dB.