Hugo Thienpont - Academia.edu (original) (raw)

Papers by Hugo Thienpont

Journal of Lightwave Technology, 2016

By utilizing a fully-vectorial three-dimensional coldcavity optical simulation, we analyze the sp... more By utilizing a fully-vectorial three-dimensional coldcavity optical simulation, we analyze the spectral, polarization, and modal-losses behavior of a vertical-cavity surface-emitting laser with a nematic liquid-crystal (LC) overlay. We identify phenomena responsible for mode and polarization selectivities and show how they can be controlled by varying design geometry parameters, such as LC thickness and oxide aperture diameter, or by electrooptically tuning the LC director. We present possibility of achieving voltage-controlled polarization switching of a fundamental mode or transverse mode switching within the same polarization. Furthermore, we show that it is theoretically possible to obtain improved single-mode operation by means of increased higher order transverse mode discrimination. Finally, we point out a way to destabilize the diode by equalizing the modal losses of all the analyzed modes.

Vertical-Cavity Surface-Emitting Lasers XVII, 2013

ABSTRACT We study theoretically the spectral and polarization threshold characteristics of Vertic... more ABSTRACT We study theoretically the spectral and polarization threshold characteristics of Vertical-Cavity Surface-Emitting Lasers with nematic and cholesteric liquid crystal overlay: LC-VCSELs. In the first case, we demonstrate the possibility of selecting between two orthogonal directions of linear polarization (LP) of the fundamental mode (x or y LP) by choosing appropriate NLC length and to achieve strong polarization discrimination: threshold gain difference as large as several times the threshold gain. We also demonstrate an active control of light polarization by electro-optically tuning the LC director and show that either polarization switching between x and y LP modes or continuous change of the LP direction is possible. For cholesteric LC-VCSEL we show that it becomes a coupled system with different spectral, threshold and polarization characteristics than the ones of the stand-alone VCSEL. Due to the existence of a band gap for circularly polarized light in the liquid crystal, lasing occurs in almost circularly polarized modes at the LC side.

Scientific reports, Jan 5, 2016

We report the experimental observation of two-dimensional vector cavity solitons in a Vertical-Ca... more We report the experimental observation of two-dimensional vector cavity solitons in a Vertical-Cavity Surface-Emitting Laser (VCSEL) under linearly polarized optical injection when varying optical injection linear polarization direction. The polarization of the cavity soliton is not the one of the optical injection as it acquires a distinct ellipticity. These experimental results are qualitatively reproduced by the spin-flip VCSEL model. Our findings open the road to polarization multiplexing when using cavity solitons in broad-area lasers as pixels in information technology.

Optics Express, 2015

We optimize the wavelength tuning range of a Vertical-Cavity Surface-Emitting Laser with an intra... more We optimize the wavelength tuning range of a Vertical-Cavity Surface-Emitting Laser with an intracavity layer of nematic Liquid Crystal (LC-VCSEL) lasing around 1.3 μm. The tunability is obtained by applying voltage to the liquid crystal layer, which esentially is to vary the refractive index from the extraordinary to the ordinary. We achieve 71.6 nm continuous tuning (without mode hopping) with liquid crystal thickness of about 3.2 μm. We investigate the impact of ambient temperature on the LC-VCSEL tuning range and show that mode-hop tuning can be achieved in the temperature range from −10 • C to 50 • C where the LC is in nematic phase.

Optics express, Jan 31, 2011

We show experimentally that polarization mode hopping in quantum dot vertical cavity surface emit... more We show experimentally that polarization mode hopping in quantum dot vertical cavity surface emitting lasers (VCSELs) takes place between nonorthogonal elliptically polarized modes. In contrast to quantum well VCSELs the average dwell time decreases with injection current. This decrease is by 8 orders of magnitude: from seconds to nanoseconds and is achieved without any modifications of the VCSEL internal anisotropies. The observed scaling happens in a range of currents as wide as 8 times the threshold value.

Physics and Simulation of Optoelectronic Devices XXIII, 2015

Chaotic Lidar systems (CLIDAR) are used for high-resolution ranging. They are based on the correl... more Chaotic Lidar systems (CLIDAR) are used for high-resolution ranging. They are based on the correlation of a chaotic signal waveform with the signal that is reflected back from the target. We report a novel CLIDAR system based on the autocorrelation of the signal obtained by the superposition of the chaotic signal waveform and the signal that is reflected from the target. A simplified setup with just one detector is required in contrast to the two detectors used in standard CLIDAR systems. Our experimental results are obtained with a 1550-nm vertical-cavity surface-emitting laser (VCSEL) with chaotic dynamics due to optical feedback. Our CLIDAR system provides an autocorrelation function with several sharp minima. The position of the target is obtained from the location of those minima. A theoretical analysis of the CLIDAR system is also presented. A rate equation model for the polarization of a VCSEL subject to optical feedback is the basis for the simulation of the CLIDAR system. A comparison between our theoretical and experimental results is performed, resulting in a good agreement in the chaotic signal but in a different sign of the CLIDAR signal.

SPIE Proceedings, 2012

ABSTRACT

Physical Review E, 2009

We report theoretically on the interplay between polarization switching and bifurcations to nonli... more We report theoretically on the interplay between polarization switching and bifurcations to nonlinear dynamics in a vertical-cavity surface-emitting laser ͑VCSEL͒ subject to orthogonal optical injection. Qualitatively different bifurcation scenarios leading to polarization switching are found and mapped out in the plane of the injection parameters, i.e., the frequency detuning vs injection strength plane. A Hopf bifurcation mechanism on the two-polarization-mode solution determines the injection-locking boundaries and influences polarization switching induced by optical injection. We furthermore report on a torus bifurcation emerging from a two-linearly polarized ͑LP͒ mode time-periodic dynamics before polarization switching and injection locking appear. It corresponds to an interesting combination of relaxation oscillation dynamics in the x-LP mode together with wave mixing dynamics in the injected y-LP mode. In agreement with recent experiments, we unveil a period-doubling route to chaos that involves both VCSEL orthogonal LP modes. The corresponding region of chaotic dynamics coincides with abrupt changes in the polarization switching boundaries in the plane of the injection parameters.

Physical Review A, 2009

We show that a 40-m-diameter vertical-cavity surface-emitting laser ͑VCSEL͒ is capable of support... more We show that a 40-m-diameter vertical-cavity surface-emitting laser ͑VCSEL͒ is capable of supporting spatially localized structures with linear polarization, orthogonal to the principal polarization. The VCSEL is biased above the lasing threshold and emits a well-defined linear polarization ͑principal polarization͒. A holding beam with orthogonal polarization is injected into the cavity, and a localized structure is spontaneously switched on. The orthogonally polarized localized structure is shown to be bistable when the injection current is varied. Numerical results based on a rate equation model support the experimental findings.

Physical Review A, 2004

We report on an experimental and theoretical investigation of the residence time distribution ͑RT... more We report on an experimental and theoretical investigation of the residence time distribution ͑RTD͒ of the polarization mode-hopping regime in vertical-cavity surface-emitting lasers ͑VCSELs͒ subject to optical feedback. The RTD exhibits discontinuity and oscillations, as a result of the fast intensity oscillations at the delay time that accompany the slow mode hopping. We furthermore show numerically that an external noise source on the injection current allows observation of a coherence resonance phenomenon in VCSELs induced by time-delayed feedback.

Physical Review A, 2003

In this paper, we present a theoretical and experimental analysis of stochastic effects observed ... more In this paper, we present a theoretical and experimental analysis of stochastic effects observed in polarization switching vertical-cavity surface-emitting lasers. We make a thorough comparison between theoretical predictions and experiments, comparing measured quasipotentials and dwell times. The correspondence between our theoretical model based on stochastic intensity rate equations and the experiments is found to be very good.

Journal of the Optical Society of America B, 2009

We present a comprehensive study of the bifurcation routes in a generic model of a two-polarizati... more We present a comprehensive study of the bifurcation routes in a generic model of a two-polarization-mode semiconductor laser when subject to orthogonal optical injection, relevant to a single-transverse-mode verticalcavity surface-emitting laser. For positive detunings, polarization switching (PS) occurs as the intensity of the noninjected mode gradually decreases and eventually shuts down, in some cases accompanied along the way by the onset and the subsequent vanishing of relaxation oscillations. We identify a Hopf bifurcation on a twopolarization-mode solution, which supports the onset of relaxation oscillation time-periodic dynamics in both injected (x-linearly polarized) and noninjected (y-linearly polarized) modes. For sufficiently large negative detunings, PS is a sharp transition occurring either at the injection-locking point or at a subcritical Hopf bifurcation and is often part of a hysteresis cycle.

Journal of the Optical Society of America B, 1999

We have analyzed the effect of the photon energy and temperature dependence of both the gain and ... more We have analyzed the effect of the photon energy and temperature dependence of both the gain and the total losses inside the cavity to understand the polarization behavior of vertical-cavity surface-emitting lasers. The assumption that the losses are dominated by free-carrier absorption in the p-doped mirror is made. Developing a new theoretical approach, we are able to predict different polarization switching regimes in which switching occurs from the high-to the low-frequency mode, from the low-to the high-frequency mode, or both consecutively. All these predictions have been experimentally verified by our measurements on GaAs/AlGaAs proton-implanted vertical-cavity surface-emitting lasers.

Journal of the Optical Society of America B, 2010

We analyze theoretically nonlinear dynamics of an optically injected two-mode quantum dot laser l... more We analyze theoretically nonlinear dynamics of an optically injected two-mode quantum dot laser lasing simultaneously from the ground and excited states. We show that although the external optical signal is injected into the ground-state mode alone, it can lead to the generation of regular picosecond pulses and pulse packages in the intensity of the excited-state mode. Generation of regular streams of picosecond pulses is attributed to an intrinsic gain switching mechanism where the relaxation time is modulated by the oscillations in the occupation of the ground and excited energy states.

Laser Physics Letters, 2013

We demonstrate both theoretically and experimentally that a vertical-cavity surface-emitting lase... more We demonstrate both theoretically and experimentally that a vertical-cavity surface-emitting laser with an overlay of cholesteric liquid crystal (CLC-VCSEL) becomes a coupled system with different spectral, threshold and polarization characteristics from those of the stand-alone VCSEL. Due to the existence of a band gap for circularly polarized light in the liquid crystal, the output light becomes almost circularly polarized with the opposite handedness of the CLC. We also show that it is even possible to replace the VCSEL top distributed Bragg reflector by a CLC overlay.

IEEE Photonics Technology Letters, 1998

We demonstrate a new mechanism for polarization switching in slightly anisotropic vertical-cavity... more We demonstrate a new mechanism for polarization switching in slightly anisotropic vertical-cavity surface-emitting lasers (VCSEL's) based on index guiding due to the effect of thermal lensing. This polarization switching takes place when the laser operates on the short-wavelength side of the gain maximum. The two orthogonal linear polarizations correspond to slightly different wavelengths and switching occurs from shorter toward longer laser wavelength as the drive current increases. Polarization modulation has been observed up to 50 MHz with a polarization contrast ratio of 20:1.

IEEE Journal of Quantum Electronics, 2009

In this paper, we summarize our recent results on nonlinear polarization-and transverse-mode dyna... more In this paper, we summarize our recent results on nonlinear polarization-and transverse-mode dynamics of vertical-cavity surface-emitting lasers (VCSELs) induced by optical injection (OI) or current modulation. Due to the surface emission and cylindrical symmetry, VCSELs lack strong polarization anisotropy and may undergo polarization switching (PS). Furthermore, VCSELs may emit light in multiple transverse modes. This provides new features to the rich nonlinear dynamics induced in VCSELs by an external perturbation. We demonstrate for the case of orthogonal OI that new Hopf bifurcation on a two-polarization-mode solution delimits the injection locking (IL) region and that PS and IL of first-order transverse mode lead to a new resonance tongue for large positive detunings. Similarly, the underlying polarization-mode competition leads to chaotic-like behavior in case of gain switching and the presence of two transverse modes additionally reduces the possibility of regular dynamics.

Applied Physics Letters, 2007

The authors present the experimental results showing how the external mirror reflectivity affects... more The authors present the experimental results showing how the external mirror reflectivity affects the polarization properties of a vertical cavity surface emitting laser subject to optical feedback from an extremely short external cavity. The amplitude of modulation of the polarization switching current with the external cavity length is found to be proportional to the external mirror reflectivity, confirming its key role in achieving polarization control and stabilization of such lasers using optical feedback. Numerical simulations presented here show good agreement with experiments.

Applied Physics Letters, 2006

iap.tu-darmstadt.de

We investigate experimentally the influence of delayed optical feedback from a short external cav... more We investigate experimentally the influence of delayed optical feedback from a short external cavity on the emission dynamics of vertical-cavity surface-emitting semiconductor lasers (VCSELs). We unveil the presence of pulse packages (PP) in the total intensity of the emitted light. The investigations of the polarization resolved temporal dynamics show that for currents corresponding to a stable polarization emission of the solitary VCSELs the PP dynamics usually occur in the dominant polarization mode only, defining type I PP ...