Numerical implementation of a VCSEL-based stochastic logic gate via polarization bistability.

We study the interplay of polarization bistability, spontaneous emission noise and aperiodic current modulation in vertical cavity surface emitting lasers (VCSELs). We demonstrate the phenomenon of logic stochastic resonance (LSR), by which the laser gives robust and reliable logic response to two logic inputs encoded in an aperiodic signal directly modulating the laser bias current. The probability of a correct response is controlled by the noise strength, and is equal to 1 in a wide region of noise strengths. LSR is associated with optimal noise-activated polarization switchings (the so-called "inter-well" dynamics if one considers the VCSEL as a bistable system described by a double-well potential) and optimal sensitivity to spontaneous emission in each polarization (the "intra-well" dynamics in the double-well potential picture). The robust nature of LSR in VCSELs offers interesting perspectives for novel applications and provides yet another example of a driven nonlinear optical system where noise can be employed constructively.

Generation of optical pulses in VCSELs below the static threshold using asymmetric current modulation.

We present a novel method for the generation of sub-nanosecond optical pulses in directly modulated vertical-cavity surface-emitting lasers (VCSELs) that operate, on average, below the cw threshold. Using the spin-flip model we demonstrate that irregular optical pulses in two orthogonal linear polarizations can be generated via asymmetric triangular modulation of period of a few nanoseconds, with a slow rising ramp followed by a fast decreasing one. For an optimal modulation asymmetry the effective threshold reduction is about 20%, the pulse amplitude is maximum and the dispersion of the pulse amplitude is minimum.