Highly Efficient Rectangular Pulse Emission in a Mode-Locked Fiber Laser

Dissipative soliton resonance (DSR) has been experimentally investigated in a nonlinear polarization rotation (NPR) mode-locked Yb-doped fiber laser with a long cavity. The adjustable nonlinear transmission function of the NPR and the relatively large nonlinearity of the long cavity play key roles in the formation of high energy rectangular pulses in the DSR region. The intracavity optical-to-optical efficiency can be as high as 46%, and the maximum pulse energy can reach 54.6 nJ with the relatively low pump power of 299 mW. This is so far the highest efficiency in a DSR laser operated at 1-μm wavelength yet achieved to our knowledge. Furthermore, while maintaining the pulse amplitude almost constant and without the appearance of wave-breaking phenomena, the pulse duration could be tuned from 54 to 91 ns by increasing only the pump power.