Initially, ghost imaging (GI) was demonstrated with entangled light from parametric down conversion. Later, classical light sources were introduced with the development of thermal light GI concepts. State-of-the-art classical GI light sources rely either on complex combinations of coherent light with spatially randomizing optical elements or on incoherent lamps with monochromating optics, however suffering strong losses of efficiency and directionality. Here, a broad-area superluminescent diode is proposed as a new light source for classical ghost imaging. The coherence behavior of this spectrally broadband emitting opto-electronic light source is investigated in detail. An interferometric two-photon detection technique is exploited in order to resolve the ultra-short correlation timescales. We thereby quantify the coherence time, the photon statistics as well as the number of spatial modes unveiling a complete incoherent light behavior. With a one-dimensional proof-of-principle GI experiment, we introduce these compact emitters to the field which could be beneficial for high-speed GI systems as well as for long range GI sensing in future applications.

We present joint investigations of relative intensity noise (RIN) and second-order coherence properties of amplified spontaneous emission (ASE) generated by a superluminescent diode. We introduce a generalized intensity noise description for ASE sources that contains the shot noise contribution but also accounts for first- and second-order coherence properties reflecting the process of light generation. We find excellent agreement between pump-current-dependent RIN values and this new description, with the perspective of particular interesting consequences for the realization of low-noise broadband emitters.

Ghost imaging (GI) is one of the recent fascinating and probably counterintuitive topics of quantum optics. Here, we present an alternative classical GI scheme using spectrally ultrabroadband amplified spontaneous emission from an optoelectronic quantum dot based superluminescent diode source. This light source exhibits highly incoherent properties regarding both first- and second-order correlations with a 70 nm-wide optical spectrum as well as thermal-like photon statistics. Exploiting a two-photon-absorption detection method, we demonstrate for the first time, to the best of our knowledge, a GI experiment handling the corresponding femtosecond correlation timescales. By introducing compact broadband light sources to GI, this work contributes toward practical application of GI.

We experimentally investigate the full polarization behavior of mid-infrared emitting quantum cascade lasers (QCLs) in terms of measuring the complete Stokes parameters, instead of only projecting them on a linear polarization basis. We demonstrate that besides the pre-dominant linear TM polarization of the emitted light as governed by the selection rules of the intersubband transition, small non-TM contributions, e.g., circularly polarized light, are present reflecting the birefringent behavior of the semiconductor quantum well waveguide. Surprisingly unique is the persistence of these polarization properties well below laser threshold. These investigations give further insight into understanding, manipulating, and exploiting the polarization properties of QCLs, both from a laser point of view and with respect toward applications.

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.