arXiv subjects

C. Y. Chang

Publications and source records attributed to C. Y. Chang.

4 recordsLinked to original sources

arXiv2017

Visualizing the Phase-Space Dynamics of an External Cavity Semiconductor Laser

We map the phase-space trajectories of an external-cavity semiconductor laser using phase portraits. This is both a visualization tool as well as a thoroughly quantitative approach enabling unprecedented insight into the dynamical regimes, from continuous-wave through coherence collapse as feedback is increased. Namely, the phase portraits in the intensity versus laser-diode terminal-voltage (serving as a surrogate for inversion) plane are mapped out. We observe a route to chaos interrupted by two types of limit cycles, a subharmonic regime and period-doubled dynamics at the edge of chaos. The transition of the dynamics are analyzed utilizing bifurcation diagrams for both the optical intensity and the laser-diode terminal voltage. These observations provide visual insight into the dynamics in these systems.

nlin.CD↗

arXiv2017

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 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.

physics.app-ph↗

arXiv2017

Tunable X-band optoelectronic oscillators based on external-cavity semiconductor lasers

Laser diodes with optical feedback can exhibit periodic intensity oscillations at or near the relaxation-oscillation frequency. We demonstrate optoelectronic oscillators based on external-cavity semiconductor lasers in a periodic dynamical regime tunable over the entire X-band. Moreover, unlike standard optoelectronic oscillators, we need not employ the time-dependent optical intensity incident on a photodiode to generate the microwave signal, but rather have the option of generating the electrical microwave signal directly as a voltage $V(t)$ at the laser-diode injection terminals under constant current operation; no photodiode need be involved, thus circumventing optical-to-electrical conversion. We achieve a timing jitter of $\lesssim 10$ ps and a quality factor of $\gtrsim 2\times 10^5$ across the entire X-band, that ranges from 6.79 GHz to 11.48 GHz. Tuning is achieved by varying the injection current $J$.

physics.app-ph↗

arXiv2004

Finger-gate array quantum pumps:pumping characteristics and mechanisms

We study the pumping effects, in both the adiabatic and nonadiabatic regimes, of a pair of \QTR{it}{finite} finger-gate array (FGA) on a narrow channel. Connection between the pumping characteristics and associated mechanisms is established. The pumping potential is generated by ac biasing the FGA pair. For a single pair (N=1) of finger gates (FG's), the pumping mechanism is due to the coherent inelastic scattering of the traversing electron to its subband threshold. For a pair of FGA with pair number $N>2$, the dominant pumping mechanism becomes that of the time-dependent Bragg reflection. The contribution of the time-dependent Bragg reflection to the pumping is enabled by breaking the symmetry in the electron transmission when the pumping potential is of a predominant propagating type. This propagating wave condition can be achieved both by an appropriate choice of the FGA pair configuration and by the monitoring of a phase difference $ϕ$ between the ac biases in the FGA pair. The robustness of such a pumping mechanism is demonstrated by considering a FGA pair with only pair number N=4.

cond-mat.mes-hall↗