Gain measurement of broadband quantum dot SOA by two-section technique

In this experiment, the active layer is grown on a GaAs substrate and has two types of InAs QD layers. One is for 1.24 μm emitting wavelength. The other is for 1.28 μm emitting wavelength. The QD layers is grown within InGaAs/GaAs QWs for better carrier confinement. The device used in the experiment has two section double channel ridge waveguide fabricated on the wafer by wet etch. To prevent reflection of light from the facet back into the waveguide, the waveguide direction is tilted from facet normal by 7 degrees. The length of each section is 200 μm and 800 μm, respectively. The EL spectrums from both side of this device are measured under the same current density. The spectrum has two peaks at 1.25 μm and 1.17 μm. They correspond to the first quantized state and the second quantized state of the QDs. In addition, extra signals can be observed between 1100 nm and 1000 nm with 240 mA and 320 mA injection current. This is considered to be the contribution of QW states.