Tailored first- and second-order coherence properties of quantum dot superluminescent diodes via optical feedback

We demonstrate experimentally that the first- and second-order coherence properties of light emitted by a quantum dot superluminescent diode can be simultaneously tailored by well-controlled optical feedback. Depending on feedback intensity and feedback spectral range we achieve a spectral width Δλ between 120 and 0.26 nm, corresponding to a coherence length in first order in the range between 13 and 5820 μm, while the central second-order coherence degree g((2))(τ=0) is tuned gradually from a thermal value of g((2))(0)~1.8 down to the coherent laser limit of g((2))(0)=1.0. These results are complemented by comprehensive investigations of relative intensity noise, which are in excellent agreement with the observed intensity correlation behavior.