A waveband-tunable multiwavelength erbium-doped fiber laser based on a novel integrated structure of nonlinear polarization rotation and an unbalanced in-line Sagnac interferometer is proposed and demonstrated. An ultrabroadband lasing spectrum with 140 wavelength lasing peaks periodically distributed from 1563 to accompanied by a lasing linewidth of , a free spectral range (FSR) of , and a signal-to-noise ratio (SNR) of has been achieved. A laser with high-wavelength lasing and waveband tunability was also achieved by merely adjusting the polarization controllers. The wavebands can be tuned from 1567 to continuously. Thirty-one lasing wavelengths in a flattened spectrum has been achieved with a SNR of , a linewidth of , and a FSR of . Good stability of the laser operating at room temperature has been verified by using an optical spectrum analyzer to measure every 2 min for a half-hour.
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