Biomedical subjects

Daan Lenstra

Publications and source records attributed to Daan Lenstra.

7 recordsLinked to original sources

PubMed2004

Connection between phase singularities and the radiation pattern of a slit in a metal plate.

We report a new fundamental relation between the minima of the far-zone radiation pattern of a narrow slit in a metal plate and the location of phase singularities in the intermediate field. If a system parameter such as the wavelength is changed, a previously unappreciated singular optics phenomenon occurs: namely, the transition of a near-zone phase singularity into a singularity of the radiation pattern. Our results have significance for the design of novel nanoscale light sources and antennas.

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PubMed2004

Spontaneously excited pulses in an optically driven semiconductor laser.

In optically injected semiconductor lasers, intrinsic quantum noise alone, namely, the spontaneous emission and the shot noise, are capable of exciting intensity multipulses from a steady state operation. Noisy lasers exhibit self-pulsations in the locking region of the corresponding deterministic system. The interpulse time statistics are studied in parameter regions near k-homoclinic (Shilnikov) bifurcations where the corresponding deterministic model exhibits single-, double-, and triple-pulse excitability. These statistics differ significantly among each other, and they could be used to characterize regions of different multipulse excitability in a real laser device.

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PubMed2004

Filtered optical feedback induced frequency dynamics in semiconductor lasers.

We demonstrate experimentally and numerically that, by spectrally filtering the delayed optical feedback into a semiconductor laser, one can elicit novel dynamics in the frequency of the laser output light on a time scale that is set by the delay time of the feedback. In particular, we show that through a judicious choice of the filter bandwidth, and its frequency relative to that of the laser, one can produce controlled oscillations in the frequency of light from the laser.

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PubMed2003

Nonlinear dynamics of a semiconductor laser with filtered optical feedback and the influence of noise.

We investigate the influence of quantum noise on the highly complex nonlinear dynamics that arise in a single-mode semiconductor laser subject to filtered optical feedback. Our numerical study, which utilizes rate equations that are augmented by Langevin noise terms to account for the spontaneous-recombination noise, shows that for relatively broad filters the noise may lead to qualitatively different dynamics than predicted by a deterministic analysis. In particular, we find that certain attractors that are predicted in the absence of noise may no longer be available when the effects of noise are correctly incorporated. For narrow bandwidth filters we demonstrate optical-injection-like behavior and identify locking of the semiconductor laser to the relaxation oscillation side peaks. In general, the results indicate that shot noise in the laser can influence the dynamics quite substantially.

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PubMed2003

Light transmission through a subwavelength slit: waveguiding and optical vortices.

The anomalous (i.e., more than 100%) light transmission through a subwavelength slit in a thin metal plate is accompanied by a combination of waveguiding and phase singularities of the field of power flow near the slit. The crucial role of these phase singularities (such as optical vortices and saddle points) in exciting the waveguide modes is systematically studied. We predict transmission efficiencies as high as 300% for certain configurations.

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PubMed2002

Global quantitative predictions of complex laser dynamics.

We demonstrate unprecedented agreement between a theoretical two-dimensional bifurcation diagram and the corresponding experimental stability map of an optically injected semiconductor laser over a large range of relevant injection parameter values. The bifurcation diagram encompasses both local and global bifurcations mapping out regions of regular, chaotic, and multistable behavior in considerable detail. This demonstrates the power of dynamical systems modeling for the quantitative prediction of nonlinear dynamics and chaos of semiconductor lasers.

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PubMed2002

Multipulse excitability in a semiconductor laser with optical injection.

An optically injected semiconductor laser can produce excitable multipulses. Homoclinic bifurcation curves confine experimentally accessible regions in parameter space where the laser emits a certain number of pulses after being triggered from its steady state by a single perturbation. This phenomenon is organized by a generic codimension-two homoclinic bifurcation and should also be observable in other systems.

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