The Role of Carrier Diffusion in RNGH Instabilities of Quantum Cascade Lasers

Quantum Cascade Laser (QCL) structures exhibit features of multimode Risken-Nummedal-Graham-Haken (RNGH) instabilities [2,3] at low excess above lasing threshold, at pth2 ~ 1.1 [1]. The onset of such RNGH instabilities and excitation of regular self-pulsations may provide practical means to produce picosecond pulses in the MIR spectral range. However, conditions that would trigger such QCL dynamics have not been elucidated so far and these conditions cannot be inferred from conventional laser diodes (LDs), in which RNGH instabilities have not been observed in experiment

Méthode simple pour exprimer les harmoniques cubiques en fonction des harmoniques sphériques: application au groupeTd{_{\rm d}}

Nous proposons une méthode simple pour obtenir les fonctions de base des représentations irréductibles. Une procédure automatisée est proposée pour exprimer les opérateurs de projection comme combinaisons d'harmoniques sphériques. L'application de cet automate permet l'obtention des harmoniques cubiques (fonctions associées à la symétrie cubique) à partir desquelles les fonctions propres des bandes de conduction et de valence dans GaAs sont exprimées

Optical bistability in InGaN-based multisection laser diodes

Optical bistability is observed in cw-operating InGaN-based laser diodes including a saturable absorber (SA) section. The dependence of the light-current hysteresis on the SA section length and reverse bias (V(SA)) has been studied. An analytical approach is developed to estimate the carrier lifetime t(a) in the SA section from the measurements of the hysteresis width, which leads to t(a)=1.9 ns at zero bias. t(a) is found to decrease rapidly for higher reverse biases and a minimum of t(a)=0.4 ns is interpolated for flatband conditions. We explain the dependence of the carrier lifetime on V(SA) via the modification of the quantum-confined Stark effect

Passive mode-locking in the cavity of monolithic GaN-based multi-section laser diodes

We demonstrate picosecond pulse generation in the blue-violet wavelength region by passive mode-locking in monolithic GaN-based ridge waveguide laser diodes with integrated absorbers. For cavity lengths between 1.5 and 0.45 mm we observe pulse repetition frequencies between 34 and 92 GHz, and pulse widths down to 3 ps at absorber biases around -10V and 0V. The quality of the pulses is related to a broad and homogeneous spectrum. At zero absorber bias passive mode-locking is only achieved in long cavities with absorbers smaller than 10% of the cavity length. A laser diode with a longer center absorber exhibits higher harmonics with supermode noise. We study samples from three epitaxial designs with different quantum well numbers and widths. The bias-dependent carrier lifetime in the absorber is determined by electroluminescence decay and decreases below 40 ps at large negative bias

Static and dynamic properties of multi-section InGaN-based laser diodes

We have studied multi-section InGaN multiple-quantum-well (MQW) laser diodes grown on c-plane freestanding GaN substrate consisting of an absorber section (AS) and an amplifier gain section. As a result of the interplay between external bias applied to the AS and the internal piezoelectric and spontaneous polarization fields inherent to c-plane InGaN MQWs, the devices exhibit non-linear non-monotonic variations of the threshold current due to the quantum-confined Stark effect that takes place in the AS MQWs. We report on how this effect tailors the lasing characteristics and lasing dynamics, leading from a steady-state cw lasing regime for an unbiased AS to self-pulsation and Q-switching regimes at high negative absorber bias