Wavelength-spacing controllable, dual-wavelength synchronously mode locked Er:fiber laser oscillator based on...

A wavelength-spacing controllable, dual-wavelength synchronously mode locked Er:fiber laser oscillator based on dual-branch nonlinear polarization rotation (NPR) technique was presented. The center wavelengths were at 1542 nm and 1561 nm, which had pulse durations of 1.38 ps and 1.70 ps, respectively. Experimentally, the synchronous mode locking was achieved by precisely adjusting the cavity length of one branch. A tolerance in the cavity length mismatch of 0.46 mm for synchronous mode locking was demonstrated. The frequency difference of the two pulse trains was measured to be less than 1 mHz. Additionally, this synchronously mode locked dual-wavelength laser had a wavelength tunable range of about 5.6 nm, and a controllable wavelength spacing from 10.5 nm to 28.2 nm, corresponding to a tunable frequency difference from 1.32 THz to 3.26 THz. To the best of our knowledge, this is the first demonstration of synchronously mode locked dual-wavelength output directly from a Er:fiber laser oscillator, using dual-branch NPR technique.