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A numerical model has been implemented and used for the simulation of the optical frequency combs generated by gain-switching single mode laser diodes, either free-running or subjected to optical injection. The dynamical model consists of three rate-equations including stochastic noise terms. An exhaustive comparison between the simulated and the experimental temporal profiles and optical spectra, generated in a wide range of switching and optical injection conditions has been performed. The range of the explored conditions leads to a variety of scenarios including actual combs and broad incoherent spectra, and frequencies in the range of, and well below, the relaxation oscillation frequencies. The detailed maps generated provide guidelines for selecting suitable operation conditions for specific comb characteristics. The excellent quantitative agreement found in the entire range of the explored operation conditions supports the validity of the model for the analysis of the comb generation mechanisms. The model has been used for ascertaining the role of the frequency chirp in the evolution of the comb spectra and discussing the physics underlying the effects of the optical injection.

We have experimentally and theoretically analyzed the modal properties of semiconductor ring lasers and the wavelength jumps that occur in connection with directional switching above the threshold.

Abstract:We theoretically discuss the impact of the cavity configuration on the possible longitudinal mode multistability in homogeneously broadened lasers. Our analysis is based on the most general form of a Travelling-Wave Model for which we present a method that allows us to evaluate the monochromatic solutions as well as their eigenvalue spectrum. We find, in agreement with recent experimental reports, that multistability is more easily reached in Ring than in Fabry-Pérot cavities which we attribute to the different amount of Spatial-Hole Burning in each configuration.

The multimode dynamics of a two-level ring laser is explored numerically using a bidirectional traveling wave model retaining the spatial effects due to the presence of counter-propagating electric fields in the population inversion. Dynamical regimes where the emission in each direction occurs at different wavelengths are studied. Mode-locked unidirectional emission for large gain bandwidth and relatively small detuning is reported.

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We report on the experimental generation of broad and flat optical frequency combs (OFC) in a 1550 nm laser diode using gain switching with pulsed electrical excitation together with optical injection. The combination of both techniques allows the generation of high-quality OFCs at a repetition frequency of 500 MHz, showing a low-noise optical spectrum with unprecedent features in terms of width (108 tones within 10 dB) and flatness (56 tones within 3 dB) in comparison with those previously reported for this modulation frequency. The influence of the injection conditions on the OFC quality is studied. Using these two techniques, it has been possible to reduce the separation between tones, generating high spectral performance OFCs with a repetition rate of 100 MHz.

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