Modal Gain Characteristics of A Two-section InGaAs/GaAs Double Quantum Well Passively Mode-locked Laser with Asymmetric Waveguide

Monolithic two-section InGaAs/GaAs double quantum well (DQW) passively mode-locked lasers (MLLs) with asymmetric waveguide, concluding the layers of P-doped AlGaAs waveguide and no-doped InGaAsP waveguide, emitting at ∼1.06µm, with a fundamental repetition rate at ∼19.56GHz have been demonstrated. Modal gain characteristics, such as a gain bandwidth and a gain peak wavelength of the MLL, as a function of the saturable absorber (SA) bias voltage ( V a ) as well as the injection current of gain section ( I g ), were investigated by the Hakki-Paoli method. With the increase of V a , the lasing wavelength and net modal gain peak of the MLL both exhibited red-shifts to longer wavelength significantly, while the modal gain bandwidth was compressed. Both the net modal gain bandwidth and gain peak of the MLL followed a polynomial distribution versus the reverse bias at the absorber section. In addition, for the first time, it was found that V a had an obvious effect on the differential gain of the MLL.