Widely wavelength-tunable mode locked Er-doped fiber oscillator from 1532 nm to 1594 nm with high signal-to-noise ratio

Abstract

A widely wavelength tunable mode locked Er-doped fiber laser oscillator based on nonlinear polarization rotation (NPR) effect was demonstrated. By intentionally introducing a position-and-width adjustable slit and a pair of reflective gratings into the cavity, which worked as a wavelength and bandwidth tunable spectral filter, continuous wavelength tunable mode locked operation from 1532 nm to 1594 nm was achieved, corresponding to a tuning range of 62 nm, which is a new record for mode locked continuously wavelength-tunable single mode Er-doped fiber oscillators based on nonlinear polarization rotation, to the best of our knowledge. During the wavelength tuning, the pulse durations for different wavelengths changed slightly and closed to the Fourier-transform limit. The signal-to-noise ratio (SNR) of the radio frequency (RF) spectrum of the output pulses is higher than 89 dB over the entire wavelength tuning range, superior to the typical SNR of 50–70 dB reported in most papers. In addition, the pulse duration could be tuned from 904 fs to 1339 fs by adjusting the width of the slit, for which the corresponding spectral bandwidth changed from 3.4 nm to 1.7 nm.