Andreas Molitor

Unifying intensity noise and second-order coherence properties of amplified spontaneous emission sources

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.

Ultrabroadband ghost imaging exploiting optoelectronic amplified spontaneous emission and two-photon detection.

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.

Stokes vector characterization of the polarization behavior of vertical-cavity surface-emitting lasers

We demonstrate that a full polarization analysis in terms of the Stokes vector parameters is necessary to determine the polarization state of light emitted by vertical-cavity surface-emitting lasers (VCSELs). For three selected representative VCSEL devices, we measured the injection current dependence of the three Stokes parameters and compared these results with linearly selected polarization P-I curves, clearly demonstrating that a complete polarization analysis is required to unveil the full polarization behavior.

Investigations on the Intensity Noise of Surface Grating Relief VCSELs

We present polarization-resolved intensity noise investigations of oxide-confined vertical-cavity surface-emitting lasers (VCSELs) with an integrated small-area surface grating. We demonstrate that the reduction of the complex polarization and transverse mode behavior via the introduced high dichroism of the grating relief lead to an improved, quite simple noise behavior. The observed noise behavior is in good qualitative agreement with a two-mode noise model.

Investigations on spatio-spectrally resolved Stokes polarization parameters of oxide-confined vertical-cavity surface-emitting lasers

Recently, we have shown [Opt. Lett.37, 4799 (2012)] that the amount of unpolarized light, quantified by the degree of polarization (DOP), is strongly enhanced by increasing the oxide aperture of vertical-cavity surface-emitting lasers (VCSELs). Here, we reveal the physical mechanism of the DOP reduction when investigating spatio-spectrally resolved Stokes polarization parameters of transverse multi-mode VCSELs. These results uncover a complementary polarization behavior of each particular transverse mode contributing to the total emission, resulting in the observed unpolarized state of light.

Spatially resolved Stokes parameters of small-area vertical-cavity surface-emitting lasers: experiment and simulation

We present experimental investigations on spatially resolved Stokes parameters of vertical-cavity surface-emitting lasers (VCSELs) with a small aperture diameter of 3 μm and a monolithically integrated surface grating on top of the structure to technologically control the polarization. As expected, the grating fixes the state of polarization, but still shows both a spatially nonuniform linear polarization distribution of the fundamental transverse mode as well as an interesting eight-lobe pattern of circular polarization in terms of change of sign. These experimental findings are reproduced by numerical simulations using a fully vectorial three-dimensional model.

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.

Tailoring wave chaos in vertical-cavity surface-emitting lasers via polarization control.

We demonstrate that polarization control in combination with the geometrical shape affects wave chaos phenomena in vertical-cavity surface-emitting lasers (VCSELs). In a grating-polarization-stabilized VCSEL, we demonstrate wave chaos in one polarization mode and a transition from wave chaos to regular behavior in the other orthogonal polarization mode. We quantify the amount of chaoticity via the Brody nearest-neighbor distribution. Comparing with a reference VCSEL without a surface-grating, we explain these results and their injection current dependence by the surface-grating-induced mode selection and a change in the effective resonator shape.

Investigations on Spectro-Temporally Resolved Stokes Polarization Parameters of Transverse Multi-Mode Vertical-Cavity Surface-Emitting Lasers

We present comprehensive studies of the temporal polarization behavior of oxide-confined vertical-cavity surface-emitting lasers (VCSELs) in terms of Stokes polarization parameters (SPPs) on microsecond time scales. The observed complex temporal polarization dynamics of the total emission will be attributed, after its spectrally decomposition, to the polarization contributions of each individual transverse mode. We demonstrate that the main physical origin for the complex polarization dynamics is the dynamic evolution of the device temperature. Finally, we compare reconstructed with directly measured temporally resolved SPPs, which allow us to understand the dynamics of the degree of polarization of transverse multi-mode VCSELs.

Photon statistics of Quantum Dot Superluminescent Diodes at the transition from amplified spontaneous emission to stimulated emission

Quantum Dot Superluminescent Diodes (QD-SLDs) have shown their superior potential to generate “new” light with fascinating 1^st and 2^nd order coherence properties due to their emission out of quantum dot states at the border of Amplified Spontaneous Emission (ASE) and Stimulated Emission (SE) [1,2]. Recently it has been demonstrated, that the photon statistics from a QD-SLD can be significantly influenced by cooling the device below 200K. Thereby, a reduction of the 2^nd order coherence degree g⁽²⁾(0) - the central value of the normalized temporal intensity correlation function g⁽²⁾(τ)=〈 I(t+τ)I(t)〉/〈I(t)〉² - from a value of 2, reflecting thermal bunched photon statistics, to a value of 1.33, close to coherent Poissonian photon statistics was observed [3].