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Publications of the VCSEL group
Articles on polarization properties of small-area VCSELs
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M. Giudici, S. Balle, T. Ackemann, S. Barland, J. R. Tredicce.
Polarization dynamics of vertical-cavity surface-emitting lasers
with optical feedback: experiment and model.
J. Opt. Soc. Am. B, 16,
2114-2113, 1999.
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T. Ackemann, M. Sondermann.
cw and transient characteristics of polarization switching in vertical-cavity
surface-emitting lasers.
cw and transient features of polarization switching in VCSELs are investigated experimentally
close to the threshold minimum in dependence of temperature and current in order to clarify
the interplay of linear anisotropies and nonlinear dispersion.
International Quantum Electronics
Conference - IQEC 2000, Nice, France, September 10 - 15, 2000.
IEEE Conference Digest, p.41, paper QTuD8
(download pdf)
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T.Ackemann, M.Sondermann.
Characteristics of polarization switching from the low to the high frequency
mode in vertical-cavity surface-emitting lasers.
Polarization selection in small-area vertical-cavity surface-emitting lasers (VCSELs)
is studied experimentally in dependence of injection current and substrate temperature
in the vincity of the minimum threshold condition. Polarization switching from the low
to the high frequency fundamental spatial mode is demonstrated. The effective birefringence
displays a minimum in the transition region. The observation of dynamical transition states
hints to the relevence of nonlinear effects. A comparison to the predictions of the SFM-model
based on phase-amplitude coupling is given.
Appl.Phys.Lett. 78, 3574, 2001.
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T.Ackemann, M.Sondermann.
Characteristics of polarization switching in vertical-cavity surface-emitting lasers.
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 due to
a change in sign of linear dichroism, the optical spectra show dynamical transition states for the other
case which hint to the relevence 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.
Proc.SPIE. 4286, 44, 2001.
(download pdf)
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M. Sondermann, H. Bohnet, T. Ackemann.
Low Frequency Fluctuations and Polarization Dynamics in Vertical-cavity
Surface-emitting Lasers with Isotropic Feedback.
Phys. Rev. A 67, 021802(R)-1-4, 2003.
(download pdf-file)
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M. Sondermann, H. Bohnet, M. Weinkath, T. Ackemann.
Dynamics and polarization effects in small-area vertical-cavity
surface-emitting lasers in free-running mode and with time-delayed
feedback.
Proc. SPIE 4942, 92, 2003.
(download pdf-file)
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A.V. Naumenko, N.A. Loiko, M. Sondermann, T. Ackemann
Description and analysis of low-frequency fluctuations in vertical-cavity surface-emitting lasers
with isotropic optical feedback by a distant reflector.
We analyze theoretically and experimentally the polarization dynamics of vertical-cavity surface-emitting
lasers exposed to isotropic optical feedback. The theoretical investigations are based on a model that takes into
account different inversion populations for charge carriers with opposite spin. In the deterministic case, we
observe toruslike synchronized low-frequency fluctuations of one or both polarization modes in the vicinity of
the solitary laser threshold, depending on the parameters and initial conditions. Both in experiment and in
simulations including spontaneous emission noise, asymmetric low-frequency fluctuations are observed above
and below the solitary laser threshold as well as a transition to coherence collapse further above threshold. The
amount of excitation of polarization degrees of freedom and thus the occurrence of simultaneous lowfrequency
fluctuations of both polarization modes is shown to depend on the magnitude of the dichroism. Apart
from the correlation properties on the external-cavity time scale, we find a good qualitative agreement between
experiments and simulations.
Phys. Rev. A 68, 033805, 2003.
(download pdf-file)
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M. Sondermann, M. Weinkath, T. Ackemann, J. Mulet, and S. Balle
Two-frequency emission and polarization dynamics at lasing threshold in vertical-cavity surface-emitting lasers.
Phys. Rev. A 68, 033822, 2003.
(download pdf-file)
- T. Ackemann, M. Sondermann, A. Naumenko, and N.A. Loiko
Polarization dynamics and low-frequency
fluctuations in vertical-cavity surface-emitting
lasers subjected to optical feedback.
The dynamics of vertical-cavity surface-emitting
lasers with isotropic optical feedback from a distant reflector
is studied experimentally and numerically. Low-frequency
fluctuations with sudden drop-outs of power are found to be
qualitatively independent of the amount of excitation of the second
polarization component. The latter is shown to be controlled
to a great extent by the intrinsic dichroism of the solitary laser.
The experimental findings are in very good qualitative agreement
with simulations. The characteristic features of a doublet
in the radio-frequency spectra around the external-cavity roundtrip
frequency are discussed.
Appl. Phys. B 77, 739-746, 2003.
The copyright is owned by Springer-Verlag, the original publication is available at
http://www.springerlink.com
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M. Sondermann, T. Ackemann, S. Balle, J. Mulet, and K. Panajotov
Experimental and theoretical investigations on elliptically polarized dynamical transition states in the polarization switching of vertical-cavity surface-emitting lasers.
The existence region of elliptically polarized dynamical states in the polarization dynamics of vertical-cavity surfaceemitting
lasers is investigated experimentally and theoretically. These states can occur in the vicinity of a polarization
switching from the fundamental transverse mode with lower emission frequency to the mode with higher frequency. It is
demonstrated experimentally that these states may occur in a single as well as in a double switching scenario. The
existence of the dynamical states is shown to be independent from the ellipticity of the state of polarization at the lasing
threshold. Furthermore, the in.uence of the detuning between the band gap and the cavity resonance on the occurrence
of the dynamical states is investigated.
Opt. Commun. 235, 421-434, 2004.
- M. Sondermann, M. Weinkath, and T. Ackemann
Polarization Switching to the Gain Disfavored Mode
in Vertical-Cavity Surface-Emitting Lasers
We report on the experimental observation of
current-induced polarization switching in vertical-cavity surface-
emitting lasers which is accompanied by a decrease of the
total output power at the switching point. The relaxation oscillation
frequency also decreases. This switching is interpreted as
a switching event from the mode with higher (unsaturated) net
gain to the gain disfavored mode. The experimental observations
are in qualitative agreement with a nonlinear dynamical model
taking into account spin degrees of freedom of carriers in a
semiconductor quantum well. Within the framework of this
model, we propose an explanation for the origin of a minimum
in the effective dichroism observed at the switching point, which
might also be relevant for other experiments.
IEEE J. Quant. Electr. 40, 97-104, 2004.
The copyright is owned by IEEE.
(download pdf-file)
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M. Sondermann and T. Ackemann
Correlation properties and drift phenomena in the dynamics of vertical-cavity surface-emitting lasers with optical feedback
We investigate experimentally the polarization dynamics of
vertical-cavity surface-emitting lasers with isotropic optical feedback operating
in the long-cavity regime. By means of an analysis of the correlation
properties in the time domain and in the frequency domain a connection
between a drift phenomenon and frequency components that deviate from
the harmonics of the external cavity round-trip frequency is revealed.
The latter frequency components are shown to result from an interaction
of external cavity dynamics and relaxation oscillations. An analogy to
the carrier-envelope effect in mode-locked lasers is drawn. Similar drift
phenomena are observed also for other laser systems with delay.
Opt. Exp. 13, 2707-2715, 2005.
The original publication is available at
http://www.opticsexpress.org/abstract.cfm?URI=OPEX-13-7-2707
Articles on spatio-temporal structures in broad-area VCSELs
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T. Ackemann, S. Barland, J.R. Tredicce, M. Cara, S. Balle, R. Jäger, M. Grabherr,
M. Miller, and K.J. Ebeling.
Spatial structures in broad-area vertical-cavity regenerative amplifiers.
We investigate the spatial structure of broad-area vertical-cavity
regenerative amplifiers with injection of a homogeneous beam. The
emerging patterns have a dominantly six-fold rotational symmetry
verifying the recent prediction of hexagons. The length scale is
controllable via the detuning and follows the prediction for
tilted waves.
Opt. Lett. 25, 814-816, 2000.
(download pdf)
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T. Ackemann, S. Barland, M. Cara, S. Balle, J.R. Tredicce, R. Jäger,
M. Grabherr, M. Miller, and K.J. Ebeling.
Spatial mode structure of bottom-emitting broad-area vertical-cavity lasers.
The spatial mode structure of circular broad-area bottom emitting
VCSELs is investigated close to threshold. The devices display
very high order flower-like Laguerre modes as well as structures
with a cartesian symmetry in spite of the original O(2) symmetry.
The latter resemble in some case tilted waves more than
Hermite-Gaussian modes. Spatial structures appear for both sides
of the detuning between gain peak and cavity resonance. The
results indicate the necessity to refine the theoretical models to
include realistic boundary conditions and inhomogeneities.
J. Opt. B: Quantum Semiclass. Opt, 2, 406-412, 2000
(Link
to the Journal's web site at IOP)
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T. Ackemann, S. Barland, M.Giudici, J.R. Tredicce, S. Balle, R. Jäger, M. Grabherr,
M. Miller, and K.J. Ebeling.
Patterns in broad-area microcavaties.
The emergence of spatial structures with an approximate hexagonal symmetry is observed in broad-area
amplifying microcavaties with injection of a homogeneous beam. The length scale is controllable via
the detuning. Optical bistability occurs close to the longitudinal resonance.
phys.stat.sol.(b), 221, 133-136, 2000.
(download ps)
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T. Ackemann, W. Grosse-Nobis, G.L.Lippi.
The Gouy phase shift, the average phase lag of Fourier components of Hermite-Gaussian modes
and their applications to resonance conditions in optical cavities
An interpretation of the Gouy phase shift is proposed which relates the finite Gouy phase
reduction of a Gaussian mode the the averaged phase retardation of the tilted waves in its Fourier
spectrum compared to an on-axis plane wave. This provides a unified approach to resonance conditions
in optical cavities with plane and curved mirrors. The possible relationship to pattern selection
in nonlinear cavities is discussed.
Opt.Commun. 189, 5, 2001.
(download ps)
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I.V. Babushkin, N.A. Loiko, and T. Ackemann.
Secondary bifurcations and transverse standing wave patterns in anisotropic microcavity lasers close to the first laser threshold.
It is well known that in a laser-in the limit of an infinite extent of the transverse aperture-traveling tilted
waves are excited at the laser threshold for positive detuning between the frequency of the gain maximum of
the active medium and the cavity frequency [Phys. Rev. A 45, 8129 (1992)]. However, a transverse standing
wave is unstable. In this paper, it is shown that in anisotropic lasers there can be a chain of secondary
bifurcations very close to threshold, which stabilizes the standing wave and then destabilizes it again through
a supercritical Hopf bifurcation. The parameter dependence of these bifurcations is discussed. The investigations
are motivated by interest in pattern formation in vertical-cavity surface-emitting lasers in which the
rotational symmetry is broken due to the dependence of the reflectance of the Bragg reflectors on the polarization
vector of the field. The applicability of the results to other class-B lasers is discussed.
Phys. Rev. A 67, 013813-1-8, 2003.
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I.V. Babushkin, N.A. Loiko, and T. Ackemann.
Eigenmodes and symmetry selection mechanisms in circular large-aperture vertical-cavity surface-emitting lasers.
The characteristics of the spatial eigenmodes of vertical-cavity surface-emitting lasers with a large circular
aperture are considered close to the lasing threshold. Experiments yield patterns based on rotational symmetry
("flowerlike" patterns) or on Cartesian symmetry (stripelike patterns) for very close operating conditions. The
former are compatible with the boundary conditions whereas the latter are expected in infinite devices. Theoretically,
the problem is considered in the framework of an eigenmode analysis of a linear partial differential
equation for the optical field valid at threshold. This formulation allows for a simple implementation of
asymmetries due to the reflection properties of Bragg mirrors as well as of transverse variations of gain and
refractive index due to the device structure or due to imperfections in the growth process. A sharp transition
between flowerlike modes and stripelike modes is shown to occur, if the device aperture is increased.
Phys. Rev. E 69, 066205-1-14, 2004.
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