Monolithic vertical-cavity surface-emitting laser with thermally tunable birefringence

Pusch, Tobias; Tona, Eros La; Lindemann, Markus; Gerhardt, Nils C.; Hofmann, Martin R.; Michalzik, Rainer

doi:10.1063/1.4980025

Cited by 24 publications

(12 citation statements)

References 13 publications

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“…Thus, f R ≈ γ p /π suggests that strongly enhanced birefringence may overcome the frequency limitations of conventional lasers. Among methods to enhance birefringence, for example, using anisotropic strain [18], heating effects [22,23] or photonic crystals [24], we focus on mechanical bending. For this purpose we use a standard 850 nm VCSEL [25], which is pumped with both a direct current above J th injecting spin-unpolarized carriers and a circularly polarized picosecond laser pulse exciting additional spinpolarized carriers (as an extension to purely optical spin pumping approaches, e.g.…”

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confidence: 99%

“…PM supports the data transfer up to 240 Gbit/s, showing a remarkable improvement in digital operation over conventional VCSELs, consistent with the increase off 3dB over f 3dB . Improvements by further increasing ∆f mechanically [23,29], via photonic crystal [24] or strained quantum well-based VCSELs [18], potentially allowf 3dB > 1 THz. Unlike common approaches in spintronics and spin-lasers [3,30] which seek to increase the spin relaxation time (1/γ s ), we find that short spin relaxation times are desirable for PM.…”

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confidence: 99%

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Ultrafast spin-lasers

Lindemann

Pusch

et al. 2019

Nature

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172

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The appeal of lasers can be attributed to both their ubiquitous applications and their role as model systems for elucidating nonequilibrium and cooperative phenomena [1]. Introducing novel concepts in lasers thus has a potential for both applied and fundamental implications [2]. Here we experimentally demonstrate that the coupling between carrier spin and light polarization in common semiconductor lasers can enable room-temperature modulation frequencies above 200 GHz, exceeding by nearly an order of magnitude the best conventional semiconductor lasers. Surprisingly, this ultrafast operation relies on a short carrier spin relaxation time and a large anisotropy of the refractive index, both commonly viewed as detrimental in spintronics [3] and conventional lasers [4]. Our results overcome the key speed limitations of conventional directly modulated lasers and offer a prospect for the next generation of low-energy ultrafast optical communication.The global internet traffic will continue its dramatic increase in the near future [5]. Short-range and energy-efficient optical communication networks provide most of the communication bandwidth to secure the digital revolution. Key devices for high-speed optical interconnects, in particular in server farms, are current-driven intensity-modulated vertical-cavity surface-emitting lasers (VCSELs) [4]. Analogous to a driven damped harmonic oscillator, modulated lasers have a resonance frequency f R for the relaxation oscillations of the light intensity [6]. For higher frequencies the response decays and reaches half of its low-frequency value at f 3dB ≈ 1 + √ 2f R , which quantifies the usable frequency range [4]. In conventional VCSELs the modulation bandwidth is limited by the dynamics of the coupled carrier-photon system and parasitic as well as thermal effects. The current record is f 3dB = 34 GHz [7]. Common approaches to enhance the bandwidth rely on the expression f R = v g aS/τ p /(2π), where v g is the group velocity, a the differential gain, S the photon density, and τ p the * markus.lindemann@rub.de † nils.gerhardt@rub.de arXiv:1807.02820v1 [cond-mat.mes-hall]

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confidence: 99%

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confidence: 99%

Ultrafast spin-lasers

Lindemann

Pusch

et al. 2019

Nature

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172

134

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“…The present work also motivates further studies on strained VCSELs capable of generating chaotic polarization fluctuations without any external mechanical forcing, e.g. using integrated thermal tuning 35 . This possibility opens the way towards advanced chaotic laser systems and applications, such as two-dimensional arrays of chaotic devices comprising hundreds of individual sources which could be highly desirable e.g.…”

Section: Discussion and Perspectivesmentioning

confidence: 60%

Strain induced polarization chaos in a solitary VCSEL

Raddo

Panajotov

Borges

et al. 2017

Sci Rep

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Physical curiosity at the beginning, optical chaos is now attracting increasing interest in various technological areas such as detection and ranging or secure communications, to name but a few. However, the complexity of optical chaos generators still significantly hinders their development. In this context, the generation of chaotic polarization fluctuations in a single laser diode has proven to be a significant step forward, despite being observed solely for quantum-dot vertical-cavity surface-emitting lasers (VCSELs). Here, we demonstrate experimentally that a similar polarization dynamics can be consistently obtained in quantum-well VCSELs. Indeed, by introducing anisotropic strain in the laser cavity, we successfully triggered the desired chaotic dynamics. The simplicity of the proposed approach, based on low-cost and easily available components including off-the-shelf VCSELs, paves the way to the wide spread use of solitary VCSELs for chaos-based applications. Polarization chaos from a solitary VCSELBesides its interest as a test-bed for a better understanding of the behaviour of complex nonlinear dynamical systems, optical chaos has been smartly exploited in chaotic laser radar 1 , secure communication or key distribution 2-6 , and high-speed random bit generators [7][8][9][10] . For all these applications, a laser subject to optical injection and/or time-delayed feedback is typically used as a source of chaos 11,12 . But this solution is also relatively complex to setup, run and maintain. In addition, it also makes the whole system quite expensive, hence creating a major hurdle that limits both the attractivity and further developments of these schemes. The discovery of polarization chaos [13][14][15][16] , i.e. chaotic polarization fluctuations that can be generated directly from a solitary laser diode, was expected to significantly change the current scenario. Indeed, having a single tiny laser generating chaotic fluctuations without any external perturbation would be the simplest and most efficient way of generating optical chaos. Nevertheless, polarization chaos has only been observed so far in one specific type of semiconductor laser: the quantum dot vertical-cavity surface-emitting lasers (VCSELs), grown and described by Hopfer et al. 17 . Even though the observation of polarization chaos has proven to be a very promising result, the commercial non-availability of such devices makes this optical source disconnected from real-world applications.In this article, we overcome this hurdle and demonstrate polarization chaos dynamics in a commercially available quantum-well (QW) VCSEL on which we mechanically applied in-plane anisotropic strain. By changing the orientation and the amount of applied strain, we tune the internal parameters of the gain medium 18-22 to successfully generate the desired chaotic output. Despite the emergence of a second-order mode and the difference in its polarization, our observations are in excellent agreement with previous experimental results reported for QD VCSELs 15. Mo...

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“…Birefringence controls of spin-VCSELs on silicon will be particularly challenging since heterogeneous integration of III-V materials on silicon is usually conducted by wafer bonding techniques [ 47 ] which tend to induce non-uniform stress distribution. Electrical birefringence tuning with sub-gigahertz accuracy [ 63 , 64 ] is one such promising approach. Since spin-VCSELs have a possibility of improving optical signal quality [ 65 ] and high-speed modulations [ 28 ], they are expected to be used also for optical data signal generators in the coherent optical communication systems.…”

Section: Discussion and Prospectsmentioning

confidence: 99%

Spin Laser Local Oscillators for Homodyne Detection in Coherent Optical Communications

Yokota

Yasaka

2021

Micromachines

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We numerically investigate spin-controlled vertical-cavity surface-emitting lasers (spin-VCSELs) for local oscillators, which are based on an injection locking technique used in coherent optical communications. Under the spin polarization modulation of an injection-locked spin-VCSEL, frequency-shifted and phase-correlated optical sidebands are generated with an orthogonal polarization against the injection light, and one of the sidebands is resonantly enhanced due to the linear birefringence in the spin-VCSEL. We determine that the peak strength and peak frequency in the spin polarization modulation sensitivity of the injection-locked spin-VCSEL depend on detuning frequency and injection ratio conditions. As a proof of concept, 25-Gbaud and 16-ary quadrature amplitude modulation optical data signals and a pilot tone are generated, and the pilot tone is used for the injection locking of a spin-VCSEL. An orthogonally-polarized modulation sideband generated from the injection-locked spin-VCSEL is used as a frequency-shifted local oscillator (LO). We verify that the frequency-shifted LO can be used for the homodyne detection of optical data signals with no degradation. Our findings suggest a novel application of spin-VCSELs for coherent optical communications.

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Monolithic vertical-cavity surface-emitting laser with thermally tunable birefringence

Cited by 24 publications

References 13 publications

Ultrafast spin-lasers

Ultrafast spin-lasers

Strain induced polarization chaos in a solitary VCSEL

Spin Laser Local Oscillators for Homodyne Detection in Coherent Optical Communications

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