Semiconductor ring lasers as optical neurons

In a homogeneously-broadened ring laser strong coupling between the counter-propagating travelling waves leads to stable oscillation in one direction at a time. Such behaviour has never been reported for semiconductor ring lasers in spite of the fact that their gain saturation has a homogeneous character. To explain this different nature of the mode competition, we have calculated the strength of the nonlinear coupling between the counter-propagating travelling waves in a semiconductor ring laser. Crucial elements of the calculation are the carrier diffusion in the amplifying medium and the large mismatch losses at the amplifier facets; the latter lead to a spatially non-uniform amplitude of the eigenmodes of the ring cavity. Additionally, we show how reflection from one of the facets leads to a linear coupling of the counter-propagating waves with a mixed conservative-dissipative nature. The final result of the mode competition depends on the interplay of linear and nonlinear coupling. Experimental results are presented for both a double-sided and a single-sided AR-coated semiconductor amplifier in a ring cavity. For the first ring the observed behaviour agreed well with theory, for the second ring only partial agreement was found.

In this paper, we investigate the possibility of using optical injection to efficiently suppress the time-delay (TD) signatures of chaotic signals in a large experimentally accessible parameter range of semiconductor ring lasers (SRLs). We also study how this optical injection can improve the signal bandwidths. The injection signal is obtained from a master SRL with either optical self- or cross-feedback. For optical self-feedback configurations, it is found that the suppression of TD signatures is similar to what has been found in injected Fabry–Perot semiconductor lasers, i.e., narrow range of parameters with respect to the detuning and injection strengths. For cross-feedback configurations, however, the TD signatures can be suppressed in a wide range of parameters; meanwhile, the bandwidths are significantly improved for the same range of parameters. This is particularly useful for the security in chaos-based communications and also for generating random bits with improved properties.

Mode beating via third order nonlinearity in semiconductor ring lasers has been analyzed using a frequency-domain multimode rate equation model. Compared with Fabry-Perot lasers, semiconductor ring lasers are 1.33, 2, and 4 times more efficient in self-gain compression, cross-gain compression, and four-wave mixing processes, respectively, due to its travelling-wave nature. It is shown that, using dual (pump and signal) external optical injections into the ring laser cavity, multiple modes can be locked in phase via the strong four wave mixing phenomenon. This results in modulation of the light wave at the mode beating frequencies which could be used for RF optical carrier generation.

We investigate the directional mode-hopping in semiconductor ring lasers in the limit of small noise intensity. We show how only long time scales are involved in the hopping process. In such limit, the initial stochastic rate equations can be reduced to an auxiliary Hamiltonian system, and the dependence of the hopping on the laser parameters can be investigated. The predictions made from the reduced model agree well with the results obtained by simulating the full rate-equation system.

Third order nonlinearity in semiconductor ring lasers has been numerically analysed. Compared with Fabry-Perot lasers, semiconductor ring lasers are 4 times more efficient in four-wave mixing processes, due to its travelling-wave nature.

This paper demonstrates an optical node that simultaneously carries out multicast optical switching and all-optical label swapping. While the optical payload is being forwarded by a fast optical switch matrix, the optical label is processed by a semiconductor ring laser (SRL) bistable. Old address bits in the label are erased by optically blocking the switching of the ring laser and new address bits are inserted by modulating the output from SRL directly. This label swapping scheme is the first demonstration of bit-level data processing using the all-optical logic capabilities of a semiconductor ring laser.

用半导体环形激光器产生混沌信号

We have measured unidirectional laser operation in a semiconductor ring laser, controlled through the biasing of a coupled waveguide cavity. The devices fabricated consist of a circular ridge waveguide 2 /spl mu/m wide formed on InGaAs/InGaAsP and GaAs/AlGaAs material systems. The direction of the dominant mode switches as the laser current is increased, and can also be switched by altering the bias of the coupled guide. The subordinate mode is completely suppressed, spectral measurements indicating that any output is purely spontaneous emission.

Delay systems subject to delayed optical feedback have recently shown great potential in solving computationally hard tasks. By implementing a neuro-inspired computational scheme relying on the transient response to optical data injection, high processing speeds have been demonstrated. However, reservoir computing systems based on delay dynamics discussed in the literature are designed by coupling many different stand-alone components which lead to bulky, lack of long-term stability, non-monolithic systems. Here we numerically investigate the possibility of implementing reservoir computing schemes based on semiconductor ring lasers as they are scalable and can be easily implemented on chip. We numerically benchmark our system on a chaotic time-series prediction task.

A novel all-optical multicast scheme based on cavity-enhanced four wave mixing in a monolithically integrated semiconductor ring laser (SRL) is proposed. By employing an injecting optical signal resonant with a cavity mode of the SRL, one-to-seven all-optical multicast by means of highly efficient simultaneous multi-wavelength conversion has been experimentally demonstrated up to multi-gigabit data rates. The scheme offers several advantages including low power penalty, reconfigurability, monolithic integration and low cost.

In this work, we study theoretically the dynamical behavior of two semiconductor ring lasers (SRLs). One is subject to negative optoelectronic feedback and the other laser is subject to incoherent optical feedback. Relying on asymptotic methods, we are able to reduce the original set of five equations used to describe the dynamical behavior of SRLs with negative optoelectronic feedback (SRL-NOEF) or incoherent optical feedback (SRL-IOF) to two equations and one map with time delay valid on time-scales longer than the relaxation oscillations (ROs). The equations of the reduced models turn out to be the same for both systems. As we vary the feedback strength, the devices under consideration in this work display both continuous wave operation and a period-doubling route to chaos. The two counter-propagating intensities of both systems exhibit in-phase chaotic behavior for small delay times comparable to the period of relaxation oscillations. For delay times significantly longer than the period of ROs, the two counter-propagating modes show in anti-phase chaotic oscillations. Moreover, for long delay times, we find that the counter-propagating intensities of both systems depict the same dynamical behaviors when their feedback strengths are increased.

The switching dynamics of a semiconductor ring laser is investigated in this study using a small signal rate-equation-based analysis. Numerical simulation results confirm that, after the initial triggering pulse, the transient behavior of the laser is dominated by mode competition superposition and photon-carrier coupling process.

We review three two-mode models for different semiconductor laser structures: Vertical-Cavity Surface-Emitting Lasers (VCSELs), Twin-Stripe Semiconductor-Lasers (TSSL), and Semiconductor Ring Lasers (SRL). The VCSELs model and TSSL model display rich dynamic behavior when a saturable absorber is embedded in the cavity. VCSELs with saturable absorber showed polarization chaos, which found applications in encoded communications; TSSLs with saturable absorber show coherent locked states as well as chaotic behavior; and SRLs show a complex two-mode dynamics giving rise to bidirectional operation, alternate oscillations and spontaneous symmetry breaking toward quasi-unidirectional bistable solutions, with potential applications to all-optical switching.

We report on cavity-enhanced four-wave mixing (FWM) in 1.55- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mu</i> m semiconductor ring lasers (SRLs). External optical injection into one of the cavity modes of the ring laser induces a FWM signal up to detuning frequencies of 1.5 THz. Mode-locked signals at 34.5 GHz with a linewidth as small as 5 kHz were measured. Initial results show similar characteristics with a distributed feedback laser monolithically integrated next to the SRL.

Wave instability-the process that gives rise to turbulence in hydrodynamics1-represents the mechanism by which a small disturbance in a wave grows in amplitude owing to nonlinear interactions. In photonics, wave instabilities result in modulated light waveforms that can become periodic in the presence of coherent locking mechanisms. These periodic optical waveforms are known as opticalfrequency combs2-4. In ring microresonator combs5,6, an injected monochromatic wave becomes destabilized by the interplay between the resonator dispersion and the Kerr nonlinearity of the constituent crystal. By contrast, in ring lasers instabilities are considered to occur only under extreme pumping conditions7,8. Here we show that, despite this notion, semiconductor ring lasers with ultrafast gain recovery9,10 can enter frequency comb regimes at low pumping levels owing to phase turbulence11-an instability known to occur in hydrodynamics, superconductors and Bose-Einstein condensates. This instability arises from the phase-amplitude coupling of the laser field provided by linewidth enhancement12, which produces the needed interplay of dispersive and nonlinear effects. We formulate the instability condition in the framework of the Ginzburg-Landau formalism11. The localized structures that we observe share several properties with dissipative Kerr solitons, providing a first step towards connecting semiconductor ring lasers and microresonator frequency combs13.