Generation of high fidelity 62-fs, 7-nJ pulses at 1035 nm from a net normal-dispersion Yb-fiber laser with anomalous dispersion higher-order-mode fiber.

Fiber oscillators operating in the normal dispersion regime allow generating high energy output pulses. The best stability of such oscillators is observed when the intracavity dispersion is close to zero. Intracavity dispersion compensation in such oscillators can be achieved using a higher-order mode fiber, which substantially reduces the higher order dispersion compared to all-normal dispersion oscillators or oscillators using intracavity gratings for dispersion compensation. Using this approach, we are able to obtain relatively high energy pulses, with high fidelity. Our modeling based on an analytic approach for oscillators operating in the normal dispersion regime predicts that at intermediate pulse energies an almost flat chirp can be obtained at the oscillator output enabling good pulse compression with a grating compressor close to Fourier limited duration. Here, we present a mode-locked ytterbium-doped fiber oscillator with a higher-order mode fiber operating in the net normal-dispersion regime, delivering 7.2 nJ pulses that can be dechirped down to 62 fs using a simple grating compressor.