Broad area Vertical-Cavity Surface-Emitting Lasers (VCSELs) have peculiar polarization properties which are a field of study by itself.1-3 These properties have already been used for localized structure generation, in a simple configuration, where only one polarization component was used.4 Here, we present new experimental and theoretical results on the complex polarization behavior of localized structures generated in an optically-injected broad area VCSEL. A linear stability analysis of the spin-flip VCSEL model is performed for the case of broad area devices, in a restrained and experimentally relevant parameter set. Numerical simulations are performed, in one and two dimensions. They reveal existence of vector localized structures. These structures have a complex polarization state, which is not simply a linear polarization following the one of the optical injection. Experimental results confirm theoretical predictions. Applications of this work can lead to the encoding of small color images in the polarization state of an ensemble of localized structures at the surface of a broad area VCSEL.
We consider a broad area vertical-cavity surface-emitting laser (VCSEL) subject to optical injection. We experimentally investigate the spontaneous formation of a Cavity Soliton (CS) in a medium size (80μm diameter) VSCEL. CSs are generated and erased when sweeping optical injection power and proper frequency detuning between the master laser and the VCSEL is set.
Spin-polarized lasers are highly attractive spintronic devices providing characteristics superior to their conventional purely charge-based counterparts. Spin-polarized vertical-cavity surface emitting lasers (spin-VCSELs) promise to offer lower thresholds, enhanced emission intensity, spin amplification, full polarization control, chirp control and ultrafast dynamics. In particular, the ability to control and modulate the polarization state of the laser emission with extraordinarily high frequencies is very attractive for many applications like broadband optical communication and ultrafast optical switches. After briefly reviewing the state of research in this emerging field of spintronics, we present a novel concept for ultrafast spin-VCSELs which has the potential to overcome the conventional speed limitation for directly modulated lasers and to reach modulation frequencies significantly above 100 GHz. The concept is based on the coupled spin-photon dynamics in birefringent micro-cavity lasers. By injecting spin-polarized carriers in the VCSEL, oscillations of the coupled spin-photon system can by induced which lead to oscillations of the polarization state of the laser emission. These oscillations are decoupled from conventional relaxation oscillations of the carrier-photon system and can be much faster than those. Utilizing these polarization oscillations is thus a very promising approach to develop ultrafast spin-VCSELs for high speed optical data communication in the near future.
Spin-controlled vertical-cavity surface-emitting lasers (VCSELs) have been intensively studied in recent years because
of the low threshold feasibility and the nonlinearity above threshold, which make spin-VCSELs very promising for
spintronic devices. Here we investigate the circular polarization dynamics of VCSELs on a picosecond time scale after
pulsed optical spin injection at room temperature. A hybrid excitation technique combining continuous-wave (cw)
unpolarized electrical excitation slightly above threshold and pulsed polarized optical excitation is applied. The
experimental results demonstrate ultrafast circular polarization oscillations with a frequency of about 11 GHz. The
oscillations last inside the first undulation of the intensity relaxation oscillations. Via theoretical calculations based on a
rate equation model we analyze these oscillations as well as the underlying physical mechanisms.
Self-sustained pulsations in the output of an InAs quantum dot laser diode in the MHz range are reported for the
first time. The characteristics (shape, range and frequency) are presented for the free running laser and when
optical feedback in the Littrow configuration is applied. The frequency resolved optical spectra reveal different
envelope shifts between the two cases. This might be related to a change of phase-amplitude coupling across
the gain maximum in agreement with the expectation for a two level system. The time scale and bifurcation
scenario suggest that these are opto-thermal pulsation like those reported in quantum well amplifiers.
The dynamics of a broad-area vertical-cavity surface-emitting laser (VCSEL) with frequency-selective feedback
supporting bistable spatial solitons is analyzed experimentally and theoretically. The transient dynamics of a
switch-on of a soliton induced by an external optical pulse shows strong self-pulsing at the external-cavity round-trip
time with at least ten modes excited. The numerical analysis indicates an even broader bandwidth and a
transient sweep of the center frequency. It is argued that mode-locking of spatial solitons is an interesting and
viable way to achieve three-dimensional, spatio-temporal self-localization and that the transients observed are
preliminary indications of a transient cavity light bullet in the dynamics, though on a non negligible background.
Spin-polarized lasers offer new encouraging possibilities for future devices. We investigate the polarization dynamics of
electrically pumped vertical-cavity surface-emitting lasers after additional spin injection at room temperature. We find
that the circular polarization degree exhibits faster dynamics than the emitted light. Moreover the experimental results
demonstrate a strongly damped ultrafast circular polarization oscillation due to spin injection with an oscillation
frequency of approximately 11GHz depending on the birefringence in the VCSEL device. We compare our experimental
results with theoretical calculations based on rate-equations. This allows us to predict undamped long persisting ultrafast
polarization oscillations, which reveal the potential of spin-VCSELs for ultrafast modulation applications.
Optical pattern formation is studied far beyond threshold in a single-mirror feedback scheme using sodium vapor as the nonlinear medium. Patterns with twelve fundamental wave vectors arise form hexagons in a secondary bifurcation. Besides irregular patterns, quasi patterns and superlattices are obtained. Even after a tertiary bifurcation the patterns remain stationary. Fourier filtering experiments show that the harmonics of the fundamental wave vectors are essential for the stability of the secondary and tertiary patterns. A novel Fourier filtering technique is used for a measurement of the neutral stability curve and proves experimentally the existence of multiple instability regions existing due to the periodicity of the Talbot effect.
Polarization selection in small-area vertical-cavity
surface-emitting lasers (VCSELs) is studied experimentally in
dependence on injection current and substrate temperature in the
vicinity of the minimum threshold condition. Different types of
polarization switching (PS) are observed and analyzed: PS from the
high to the low frequency mode, PS from low to high frequency and
double switching (from high to low and back to high frequency).
Whereas PS from the high to the low frequency mode is due to a
change of sign of linear dichroism, the optical spectra show
dynamical transition states for the other case which hint to the
relevance of nonlinear effects. A comparison to the predictions of
the SFM-model based on phase-amplitude coupling is given. The
interplay of spatial and polarization effects can depend strongly
on the ambient temperature.
We report on the observation of dissipative localized structures in an optical pattern–forming system. After an experimental and theoretical analysis of the mechanism which stabilizes these structures we focus on the demonstration of possible applications of localized structures for information processing.
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