Control over spectral content via differential pumping of a monolithic passively mode-locked quantum dot laser

A monolithic two-section quantum dot semiconductor laser is differentially pumped to form non-uniform current injection in the gain region. We show that the nature of the spectral content in the output signal is affected by this differential pumping; despite the fact that the separately pumped gain regions are not electrically isolated in this device. Both negative (red-shift) and positive (blue-shift) spectral chirps were observed during mode-locked operation. It is also demonstrated that mode locked operation is achieved with a much larger set of injection current / absorber bias voltage pairs than was previously possible with single-pad current injection.