Based on the control of the linear losses of the cavity, we demonstrate the possibility to achieve filterless laser emission above 1.6 μm, from a C-band double-clad Er:Yb doped fiber amplifier. The concept is validated in both continuous wave and mode-locked regimes, using a figure-of-eight geometry. A unidirectional ring cavity is also tested in the continuous regime. Spectral properties of laser emissions are characterized as a function of the intracavity linear losses.

We experimentally demonstrate a passively mode-locked Er:Yb doped double-clad fiber laser using a graphene nanocoated optical taper. Averaging 20 μm of clad diameter with a length of 6 mm, such a saturable absorber enables a strong light–graphene interaction owing to the evanescent field of the excited cladding mode. With the highest pump power of 5 W, the 326th harmonic mode locking of soliton bunches with an average output power of 520 mW was obtained in a fiber ring cavity that has a fundamental frequency of 1.67 MHz. This is the highest average output power yet reported in graphene-based passively mode-locked fiber lasers.

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High power diffraction-limited 1064 nm fiber lasers operating in the nanosecond regime can be used for long-range LIDAR and micromachining applications. Peak power is limited by non-linearities, there is therefore an interest to develop fibers exhibiting a very large mode field effective area. New fibers are being developed in the frame of the 4F consortium ("French laser Fibers for Factories of the Future") to fulfill this need. We report on results obtained with a new 39 µm core diameter polarization maintaining ytterbium doped fiber that has been manufactured using the powder sintering technology. It features a large cladding absorption close to 20 dB/m at 976 nm (small signal) and a mode field diameter close to 32 µm. We built a pulsed MOPA. The preamplifier generates 2.5 ns pulses at 1064 nm with 8.5 W average power at 1 MHz pulse repetition frequency. The power amplifier is based on the 39 µm core fiber with 215/230µm hexagonal cladding counterpumped at 976 nm. It features 72 % slope efficiency delivering 72.2 W average power at a pulse repetition rate of 1 MHz. An end-cap was spliced to the fiber output to increase the damage threshold. At 100 kHz a peak power of 351 kW was measured for an average power of 59.9 W. The efficiency is then 70 %. This good efficiency shows that the composition was well optimized. We also studied the influence of the bending radius on the slope efficiency. We do not observe any slope efficiency reduction down to 25 cm bending diameter. It decreased to 68 % for the 20 cm bending diameter. The laser shows a quasisinglemode output beam with a good quality factor M² of 1.2.