Luis Pesquera

Photonic information processing beyond Turing: an optoelectronic implementation of reservoir computing

Many information processing challenges are difficult to solve with traditional Turing or von Neumann approaches. Implementing unconventional computational methods is therefore essential and optics provides promising opportunities. Here we experimentally demonstrate optical information processing using a nonlinear optoelectronic oscillator subject to delayed feedback. We implement a neuro-inspired concept, called Reservoir Computing, proven to possess universal computational capabilities. We particularly exploit the transient response of a complex dynamical system to an input data stream. We employ spoken digit recognition and time series prediction tasks as benchmarks, achieving competitive processing figures of merit.

Nonlinear dynamics induced by parallel and orthogonal optical injection in 1550 nm Vertical-Cavity Surface-Emitting Lasers (VCSELs)

We report a first experimental study of the nonlinear dynamics appearing in a 1550 nm single-mode VCSEL subject to parallel and to orthogonal optical injection. For the first time to our knowledge we report experimentally measured stability maps identifying the boundaries between regions of different nonlinear dynamics for both cases of polarized injection. A rich variety of nonlinear behaviours, including periodic (limit cycle, period doubling) and chaotic dynamics have been experimentally observed.

Polarization behavior of birefringent multitransverse mode vertical-cavity surface-emitting lasers

An analysis has been undertaken of the effect of birefringence on the selection of polarization states of a weakly index guided vertical-cavity surface-emitting laser (VCSEL) supporting both a fundamental and a first-order transverse mode. It is shown that for small index steps polarization switching due to spatial-hole burning effects can occur. For larger index steps it is found that higher order modes can emerge which are orthogonally polarized to the dominant polarization of the fundamental mode.

Optoelectronic reservoir computing: tackling noise-induced performance degradation

We present improved strategies to perform photonic information processing using an optoelectronic oscillator with delayed feedback. In particular, we study, via numerical simulations and experiments, the influence of a finite signal-to-noise ratio on the computing performance. We illustrate that the performance degradation induced by noise can be compensated for via multi-level pre-processing masks.

Polarization selection in birefringent vertical-cavity surface emitting lasers

Summary form only given. Polarisation characteristics of vertical cavity surface-emitting lasers (VCSELs) exhibit significant differences to those of edge-emitting semiconductor lasers. In general the polarization of the fundamental transverse mode can change when the injected current is altered. It has also been noted that the strain induced during the fabrication causes birefringence in VCSELs. In this work we present numerical calculations that demonstrate that small refraction index anisotropies can select the polarization of VCSEL.

Polarization Bistability in 1550 nm Wavelength Single-Mode Vertical-Cavity Surface-Emitting Lasers Subject to Orthogonal Optical Injection

In this paper, we report on an experimental investigation of the bistable behavior of a 1550 nm single transverse and polarization mode vertical-cavity surface-emitting laser (VCSEL) when subjected to orthogonal optical injection. As the master laser wavelength is scanned near the resonance wavelength of the depressed linearly polarized fundamental mode, and for a fixed injected power, the VCSEL exhibits two successive polarization switchings (PSs). Both PSs exhibit bistable regions in such a way that a pure-frequency-induced polarization bistability is found. The width of both bistable regions has been measured as a function of the injected power and for different values of the VCSEL current. While the injection power is lesser than a certain value, the hysteresis width fluctuates around a constant level. Further increase of the injection power leads to a smaller constant value of the hysteresis width. The value of that transition value is independent of the VCSEL current. Power-induced polarization bistability - by fixing the master laser wavelength - is found near the transition value. Clockwise and anticlockwise power-hysteresis cycles are observed for short and long master laser wavelengths, respectively.

Terahertz bandwidth prediction for amplitude modulation response of unipolar intersubband semiconductor lasers

An analysis is performed of the direct-current (dc) amplitude modulation response of unipolar intersubband semiconductor lasers. It is shown that unipolar lasers have the potential for achieving terahertz dc modulation bandwidths.

Polarization Switching in Long-Wavelength VCSELs Subject to Orthogonal Optical Injection

Polarization switching (PS) appearing in long-wavelength vertical-cavity surface-emitting lasers (VCSELs) subject to orthogonal optical injection is investigated theoretically and experimentally. We have studied the injected optical power required for PS as a function of the frequency detuning between the injected light and the orthogonal linear polarization of the VCSEL. For a wide range of bias currents applied to the device, the injected power required for the occurrence of PS exhibited a minimum and a plateau with respect to the frequency detuning. The minimum (plateau) was found at negative (positive) frequency detuning. The bistable behavior of the polarization is described. Our experimental results confirm the theoretical predictions of Sciamanna and Panajotov. The levels of the minimum and the plateau were observed to increase as higher bias currents were applied to the VCSEL. A first theoretical and experimental observation of the disappearance and further appearance of PS when increasing the injected power in long-wavelength VCSELs is described. This situation is obtained for small levels of negative frequency detuning and for large enough values of applied bias current. A good overall qualitative agreement is found between our theoretical and experimental results.

Power and wavelength polarization bistability with very wide hysteresis cycles in a 1550nm-VCSEL subject to orthogonal optical injection

We have measured optical power and wavelength polarization bistability in a 1550 nm-Vertical Cavity Surface-Emitting Laser (VCSEL) subject to orthogonally-polarized optical injection into the orthogonal polarization of the fundamental transverse mode. Optical bistability with very wide hysteresis cycles, up to four times wider than previously reported results has been measured for both the optical power and wavelength domain. We also report the experimental observation of three different shapes of polarization bistability, anticlockwise, clockwise and X-Shape bistability, all of them with wide hysteresis cycles. This rich variety of behaviour at the important wavelength of 1550 nm offers promise for the use of VCSELs for all-optical signal processing and optical switching/routing applications.

Polarization selection and sensitivity of external cavity vertical-cavity surface-emitting laser diodes

A theoretical analysis has been undertaken of the polarization properties of birefringent vertical-cavity surface-emitting lasers (VCSELs) subject to weak optical feedback in an external cavity configuration. Attention is focussed on the competition between two orthogonal polarizations of the fundamental (LP/sub 01/) transverse mode of the device. It is shown that control of the emission polarization can be exercised even for very small external reflectivities (10/sup -4/%) by appropriate choice of optical feedback delays. The polarization selectivity is shown to be dependent upon the strength of optical feedback. Polarization is also shown to be highly sensitive to small changes in optical feedback delay. Thermally induced wavelength shift is shown to affect polarization behaviour.