Biomedical subjects

Jan Danckaert

Publications and source records attributed to Jan Danckaert.

6 recordsLinked to original sources

PubMed2006

Propagation of spatially partially coherent emission from a vertical-cavity surface-emitting laser.

Recently we observed a strong reduction of spatial coherence of the emission of large-aperture vertical-cavity surface-emitting lasers when they are driven by microsecond electrical pulses [Opt. Express 13, 9337 (2005)]. We study the influence of this partial spatial coherence on the propagation characteristics. The spatial decoherence manifests itself in the formation of a Gaussian far-field intensity distribution. We measure the transverse pulse profile from near to far field and see that the shape-invariant far-field regime starts after 140 microm in the pulsed regime as opposed to several centimeters in continuous wave operation. This value matches quantitatively calculations made with a novel partially coherent propagation model without any free fitting parameters.

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PubMed2005

Ghost stochastic resonance in vertical-cavity surface-emitting lasers: experiment and theory.

We study the polarization response of a vertical-cavity surface-emitting laser, driven simultaneously by noise and two (or more) weak periodic signals. In the bistable regime, we observe experimentally the occurrence of stochastic resonance at a frequency that is absent in the input driving signal. The presence of this so-called ghost resonance is confirmed theoretically.

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PubMed2004

Modulation frequency response of a bistable system with noise.

We present a method to construct a modulation frequency response curve for bistable systems in the presence of noise. To this end, a small sinusoidal modulation is applied to the system such that it switches between its two stable states. The response curve we construct yields information on the nature of the physical mechanism underlying the switching process and is furthermore comparable to the standard response curves of linear systems. Our semianalytical approach, which only needs approximate Kramer rates, is in good agreement with numerical simulations. The concept is applicable to a wide range of systems.

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PubMed2004

Waveguiding effects in self-pulsing vertical-cavity surface-emitting lasers.

Self-pulsing in semiconductor lasers containing a saturable absorber is well documented. We propose an alternative mechanism leading to self-pulsing in vertical-cavity surface-emitting lasers. We specifically consider waveguiding effects and determine the conditions for self-pulsing. Our theoretical and numerical results agree with experimental observations reported by Willemsen et al. [Appl. Phys. Lett. 77, 3514 (2000)].

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PubMed2003

Stochastic resonance in vertical-cavity surface-emitting lasers based on a multiple time-scale analysis.

We provide analytical evidence of stochastic resonance in polarization switching vertical-cavity surface-emitting lasers (VCSELs). We describe the VCSEL by a two-mode stochastic rate equation model and apply a multiple time-scale analysis. We were able to reduce the dynamical description to a single stochastic differential equation, which is the starting point of the analytical study of stochastic resonance. We confront our results with numerical simulations on the original rate equations, validating the use of a multiple time-scale analysis on stochastic equations as an analytical tool.

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PubMed2003

Polarization message encoding through vectorial chaos synchronization in vertical-cavity surface-emitting lasers.

We show that self-pulsating vertical-cavity surface-emitting lasers can exhibit vectorial chaos, i.e., chaos in both intensity and polarization. The achievable synchronization degree of two such lasers is high when using a continuous control scheme and unidirectional coupling. We propose a novel encryption scheme, where the phase of the vectorial field is modulated. Therefore, the total intensity of these lasers remains synchronized while the intensities in the polarization modes (de)synchronize following the phase modulation at a ps time scale. This technique allows for transmission of secure data at high bit rates that are not limited by the relaxation oscillation frequency.

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