Optoelectronics

 

Ikeda-like dynamics of optoelectronic oscillators with delay

Optoelectronic oscillators are ideal implementations of Ikeda-like system, which are typically self-sustained oscillators with delayed nonlinear feedback. They typically consist in a semiconductor laser feeding a Mach-Zehnder modulator, whose output is delayed in a fiber delay line, detected with a photo-detector, amplified, filtered and finally fed back to the radio-frequency input of the modulator. Typically, this same architecture can be declined into two different technologies, depending on the bandwidth of the filter and the length of the fiber delay line inserted into path of the feedback loop. When the filter bandwidth is large and the fiber delay line is short, the system can display wideband hyperchaos; on the other hand, when the filter is narrowband and the delay line is long, the system outputs a single-mode signal. Other configurations are also possible, thereby enabling curious dynamical features such as narrowband hyperchaos. In the microwave domain, we typically work around 10 GHz (X-band), where we find most applications for this research. Activities in this area include the nonlinear and stochastic dynamics of wideband, narrowband, and even supercontinuum optoelectronic oscillators.

We have also recently started to explore the complex dynamics of OEOs with intermediate frequencies (IF). Even though the IF dynamics is scaled down and is much slower than in the X-band for example, the spectrum of the dynamics can still span over more than 8 orders of magnitude. Therefore, such IF optoelectronic systems are ideal experimental benchmarks to invstigate the nonlinear dynamics of OEOs, such as multinonlinear behavior or phase-locking.

Further reading:
Chembo et al. (2005)
Chembo et al. (2019)

 

Nonlinear semiconductor laser dynamics

Vertical-Cavity Surface Emitting Lasers (VCSELs) offer numerous advantages comparatively to their edge-emitter counterpart, To name just a few, VCSELs are intrinsically single-longitudinal mode lasers, and they have a significantly lower threshold current, as well as a lower power consumption. They are very cost effective because they can simultaneously be fabricated in a planar structure, and then tested “on wafer”; this planar structure also allows for easy integration in two-dimensional arrays. The circular cross-section of VCSELs produces low-divergence beams (thus limiting the need of corrective optics), and enables a highly efficient laser-fiber coupling. VCSELs are nowadays particularly spread in optical fiber data transmission (mostly in gigabit-ethernet networks), free-space optical communications, absorption spectroscopy, laser printers, sensors, pointers and trackers. A difficult challenge in most of VCSELs applications is the design high-power, single-mode, and single-polarization output beams. This is for example a critical issue in optical communication networks with ultra-dense wavelength-division multiplexing, where the spectral spacing between adjacent channels can be as low as 25 GHz. The control of the emission properties of VCSELs can be achieved using polarization- and frequency-selective feedback.

Edge-emitting semiconductor lasers display as well a very rich variety of complex behaviors. In particular, chaos may arise when the dynamical dimensionalty of the laser is increased. Several techniques are commonly used to induce chaos in semiconductor lasers, even though they can be gathered into two principal groups, namely parameter modulation and external feedback. Following the mainstream trend of research in chaos theory, great attention has been been paid to the collective dynamics of coupled semiconductor lasers in their chaotic regime. Along that line, the synchronization of such chaotic lasers became a focus of strong interest, and the determination of the necessary and/or sufficient conditions for their synchronization is still a difficult challenge, which has turned to be crucial when chaotic semiconductor lasers became eligible for chaos cryptography.

Further reading:
Chembo & Woafo (2003)
Chembo et al. (2009)