Strain induced polarization chaos in a solitary VCSEL

Abstract

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...

Ultrafast spin-lasers

“…Lasers based on two-dimensional materials [34] which support very large strain and thus high birefringence [18] may offer unprecedented bandwidths. A surprising path towards desired performance relying on a high birefringence and short spin relaxation times may also stimulate other advances and unexplored phenomena in spintronics such as utilizing polarization chaos in VCSELs for secure communication and highspeed random bit generators [35]. Our results show the enormous potential of spin-lasers, further motivating developing electrically pumped spin-lasers at room-temperature [36].…”

Spin-lasers: spintronics beyond magnetoresistance

“…As in the research on their conventional counterparts, one can envision that spin-lasers could provide a versatile platform to study fundamental phenomena, from phase transitions to chaos [12,98]. These possibilities are now even richer by the control of spin degrees of freedom [99]. Furthermore, the instabilities found in lasers directly resemble instabilities in electronic devices [13].…”

Chaos-Preserving Reduction of the Spin-Flip Model for VCSELs: Failure of the Adiabatic Elimination of the Spin-Population Difference

“…On the contrary, a rather low value of the spin-flip rate seems to be a crucial ingredient to obtain polarization chaos in solitary VCSELs [29]. Obviously, this observation suggest that, at least for these peculiar experimental cases [10], [11], the spin-population difference could actually play a significant role in the laser dynamics. Hence, we can naturally wonder where is the limit of validity for the approximation allowing the adiabatic elimination of the spinpopulation difference.…”

“…The normalized injection current µ is varied from 1 to 10; the higher limit corresponds, in this theoretical framework, to 10 times the laser threshold without anisotropies which is already largely above the current range commonly considered [11]. Although more complex dependencies appear to be needed for an accurate estimation of the laser threshold, see e.g.…”