Dynamic regimes and damping of relaxation oscillations in III-V/Si external cavity lasers

We report how external cavity IIIV/Si hybrid lasers operate in regimes of ultradamped relaxation oscillations or in turbulent and selfpulsing regimes. The different regimes are reached by detuning the lasing wavelength respect to the mirror effective reflectivity peak and are the consequence of the dispersive narrow band reflectivity of the silicon photonics mirror, the linewidth enhancement factor and fourwave mixing in the gain medium

Dynamics and tolerance to external optical feedback of III-V/Si hybrid lasers with dispersive narrowband mirror

We report how external cavity III-V/Si hybrid lasers operate in regimes of ultra-damped relaxation oscillations or in unstable regimes as consequence to the dispersive mirror, non-zero linewidth enhancement factor and four-wave mixing in the gain medium. Tolerance to external optical feedback is also discussed

Comparative beach surveys using an unmanned aerial system, ground-based GPS, terrestrial laser scanning, and airborne laser scanning

Profiles and sediment size distribution on mixed sand and gravel beaches are highly variable, both spatially and temporally, and cost-effective high-resolution monitoring schemes are needed to capture this variability. The potential for the use of UAS for coastal monitoring remains relatively untested in comparison to established remote sensing techniques. This paper reports on a field experiment in Pevensey Bay, East Sussex, England, in which simultaneous measurements were carried out using UAV-based photogrammetry, RTK-GPS, and both terrestrial and airborne laser scanning. The central objective of this research was to compare the accuracy of the TLS, ALS, and UAV-based surface modelling to draw conclusions for operational beach monitoring. The analysis was carried out through point cloud inter-comparison, comparison of point cloud performance against RTK-GPS transect data, and evaluation of differences between elevation models that were generated based on the point clouds. The point cloud comparison focused on the vertical differences between respective data sets, and showed that the UAV-based point cloud had positive offsets of 9cm (RMS 10cm) and 6cm (RMS 8cm) compared to the TLS and ALS point clouds, respectively. Analysis was also carried out to evaluate the extent to which surface sediment characteristics affected measurement accuracy of the different methods. Data comparison on beach gravel, beach sand, cobble, foreshore dry sand, foreshore wet sand and soft mud showed the best agreement between UAV, TLS and ALS data on gravel beach sections. For nearly all surface types UAV and ALS data showed better agreement than UAV to TLS data

CW and comb regimes in III-V SiN hybrid lasers with frequency-selective narrow band mirror

We investigate the stability of III-V SiN hybrid lasers. By detuning the lasing frequency with respect to the narrowband mirror reflectivity peak, we observe regimes of ultra-damped relaxation oscillations, turbulence, and combs, caused by the interplay of four-wave mixing, Henry alpha-parameter and the narrowband reflectivity

Stability of a III-V/Si hybrid laser with a frequency-selective SiN mirror

We study the stability of a hybrid laser source consisting of a III-V reflective semiconductor optical amplifier (RSOA) edge-coupled to a silicon photonic mirror, based on two coupled high-Q microring resonators, providing a narrow band effective reflectivity. We simulate the laser dynamics through a model of time-delayed algebraic equations accounting for the frequency-selective mirror reflectivity, demonstrating single-mode emission, self-pulsing, and turbulent regimes. Further, we identify the regions of higher CW operation in terms of bias current and laser detuning with respect to the reflectivity peak. Finally, we test the CW laser stability with respect to optical feedback, mimicking the effect of spurious back-reflections from the passive parts of the circuit, and demonstrate ultra-stable CW operation for a sizeable range of detuning

Design of hybrid laser structures with QD-RSOA and silicon photonic mirrors

We compare the design of three different single mode laser structures consisting in a Reflective Semiconductor Optical Amplifier coupled to a silicon photonic external cavity mirror. The three designs differ for the mirror structure and are compared in terms of SOA power consumption and side mode suppression ratio (SMSR). Assuming then a Quantum Dot active material, we simulate the best laser design using a numerical model that includes the peculiar physical characteristics of the QD gain medium. The simulated QD laser CW characteristics are shown and discussed