Michael J. Wishon

A multi-GHz chaotic optoelectronic oscillator based on laser terminal voltage

A multi-GHz chaotic optoelectronic oscillator based on an external cavity semiconductor laser (ECL) is demonstrated. Unlike the standard optoelectronic oscillators for microwave applications, we do not employ the dynamic light output incident on a photodiode to generate the microwave signal, but instead generate the microwave signal directly by measuring the terminal voltage V(t) of the laser diode of the ECL under constant-current operation, thus obviating the photodiode entirely.

Low-frequency fluctuations in an external-cavity laser leading to extreme events.

We experimentally investigate the dynamical regimes of a laser diode subject to external optical feedback in light of extreme-event (EE) analysis. We observe EEs in the low-frequency fluctuations (LFFs) regime. This number decreases to negligible values when the laser transitions towards fully developed coherence collapse as the injection current is increased. Moreover, we show that EEs observed in the LFF regime are linked to high-frequency pulsing events observed after a power dropout. Finally, we prove experimentally that the observation of EEs in the LFF regimes is robust to changes in operational parameters.

Delay induced high order locking effects in semiconductor lasers

Multiple time scales appear in many nonlinear dynamical systems. Semiconductor lasers, in particular, provide a fertile testing ground for multiple time scale dynamics. For solitary semiconductor lasers, the two fundamental time scales are the cavity repetition rate and the relaxation oscillation frequency which is a characteristic of the field-matter interaction in the cavity. Typically, these two time scales are of very different orders, and mutual resonances do not occur. Optical feedback endows the system with a third time scale: the external cavity repetition rate. This is typically much longer than the device cavity repetition rate and suggests the possibility of resonances with the relaxation oscillations. We show that for lasers with highly damped relaxation oscillations, such resonances can be obtained and lead to spontaneous mode-locking. Two different laser types--a quantum dot based device and a quantum well based device-are analysed experimentally yielding qualitatively identical dynamics. A rate equation model is also employed showing an excellent agreement with the experimental results.

Reading a CD-ROM without a photodiode

We use a laser diode from a commercial CD/DVD-ROM drive to detect changes in the surface of a diffraction grating without a photodiode. Specifically, we exploit the changing terminal voltage in the laser-diode due to changing feedback strength as the laser is rastered across the gratings surface.

Feedback-induced discretisation of the relaxation oscillation frequency in a semiconductor laser

We explore both experimentally and numerically the dynamics of semiconductor lasers subject to delayed optical feedback and show that the external cavity repetition rate can be resonant with the relaxation oscillations leading to a discretisation of the relaxation oscillation frequency which evolves in a series of discrete steps, remaining almost constant along each step. Numerically, the steps are found to result from different Hopf bifurcation branches.

Multistate intermittency on the route to chaos of a semiconductor laser subjected to optical feedback from a long external cavity

We observe experimentally two regimes of intermittency on the route to chaos of a semiconductor laser subjected to optical feedback from a long external cavity as the feedback level is increased. The first regime encountered corresponds to multistate intermittency involving two or three states composed of several combinations of periodic, quasiperiodic, and subharmonic dynamics. The second regime is observed for larger feedback levels and involves intermittency between period-doubled and chaotic regimes. This latter type of intermittency displays statistical properties similar to those of on-off intermittency.

Chaotic laser voltage: An electronic entropy source

The chaotic terminal voltage dynamics of a semiconductor laser subjected to external optical feedback are utilized to directly generate electronic random number streams with minimal post-processing at rates of 40–120 Gb/s, thus obviating the need for optical-to-electrical conversion and facilitating integration with high-speed computers and devices. Furthermore, a comparison of the terminal voltage to the optical intensity being utilized as entropy sources is performed. It is shown that the voltage dynamics have an inherently larger entropy, a reduction in delay signature, and a more suitable distribution for generating random bit streams.

Simultaneous Bifurcation Diagrams of Carrier Number and Optical Intensity of External Cavity Laser

We present a simultaneous measurement of the route to chaos of the optical intensity and carrier density as the feedback strength is increased in an external cavity semiconductor laser (ECL).