Cathodoluminescence hyperspectral analysis of whispering gallery modes in active semiconductor wedge resonators.

Whispering gallery mode resonators are key devices for integrated photonics. Despite their generalization in fundamental and applied science, information on spatial confinement of light in these structures is mostly retrieved from purely spectral analysis. In this work, we present a detailed spectral and spatial characterization of whispering gallery modes in active semiconductor microdisk resonators by use of hyperspectral cathodoluminescence. By comparing our experimental findings to finite element simulations, we demonstrate that the combination of spectral and spatial measurements enables unique identification of the modes and even reveals specific features of the microresonator geometry, such as a wedge profile.

Tuning the strain-induced resonance shift in silicon racetrack resonators by their orientation.

In this work, we analyze the role of strain on a set of silicon racetrack resonators presenting different orientations with respect to the applied strain. The strain induces a variation of the resonance wavelength, caused by the photoelastic variation of the material refractive index as well as by the mechanical deformation of the device. In particular, the mechanical deformation alters both the resonator perimeter and the waveguide cross-section. Finite element simulations taking into account all these effects are presented, providing good agreement with experimental results. By studying the role of the resonator orientation we identify interesting features, such as the tuning of the resonance shift from negative to positive values and the possibility of realizing strain insensitive devices.

Laser optical feedback imaging controlled by an electronic feedback loop.

In autodyne interferometry, the beating between the reference beam and the signal beam takes place inside the laser cavity and therefore the laser fulfills simultaneously the roles of emitter and detector of photons. In these conditions, the laser relaxation oscillations play a leading role, both in the laser quantum noise, which determines the signal-to-noise ratio (SNR), and also in the laser dynamics, which determines the response time of the interferometer. In the present study, we have experimentally analyzed the SNR and the response time of a laser optical feedback imaging (LOFI) interferometer based on a Nd(3+) microchip laser, with a relaxation frequency in the megahertz range. More precisely, we have compared the image quality obtained when the laser dynamics is free and when it is controlled by a stabilizing electronic feedback loop using a differentiator. From this study, we can conclude that when the laser time response is shorter (i.e., the LOFI gain is lower), the image quality can be better (i.e., the LOFI SNR can be higher) and that the use of an adapted electronic feedback loop allows high-speed LOFI with a shot-noise limited sensitivity. Despite the critical stability of the electronic feedback loop, the obtained experimental results are in good agreement with the theoretical predictions.