Low-frequency self-pulsing in single-section quantum-dot laser diodes and its relation to optothermal pulsations

Abstract

Self-sustained pulsations in the output of an InAs quantum dot laser diode in the MHz range are reported. The characteristics (shape, range, and frequency) are presented for the free-running laser and when optical feedback in the Littrow configuration is applied. Bistability in the light-current characteristics is observed for operating wavelengths smaller than the gain peak, but it is not present for wavelengths above the gain peak and for the free-running laser, except at elevated temperatures. The temporal evolution of the envelopes of the optical spectra is very different for operation below, around, and above the gain peak, which might be related to a change of phase-amplitude coupling across the gain maximum, in agreement with the expectation for a two-level system. The time scale and the bifurcation scenario, supported by an initial blueshift of the emission wavelength of each longitudinal mode in time-resolved optical spectra, suggests that these are optothermal pulsations similar to those reported in quantum well amplifiers [Phys. Rev. E 68, 036209 (2003)]. The mechanism of pulsation seems to be a destabilization of bistable states (due to saturable absorption in the beam wings) by a slow thermal change in the waveguiding properties

Self-sustained pulsations in a quantum-dot laser

“…The profile of the pulse consists of a jump up, a slower decay, followed by a drop out that are reminiscent of the experimental time traces observed in Ref. [4]. Our objective is not to simulate the experiments reported in Ref.…”

“…In order to explain the self-pulsations in quantum-dot (QD) lasers, the saturable absorption was assumed to be the result of inhomogeneous broadening of the gain and the existence of several confined QD states [3]. A recent experimental investigation of an InAs QD laser without a saturable absorber reported on large amplitude self-sustained pulsations in the MHz range [4]. The MHz range and the nonmonotonic change of the pulsation frequency with current exclude the passive Q-switching mechanism.…”

“…Our objective is not to simulate the experiments reported in Ref. [4] but to determine from this model what bifurcation mechanism could lead to large period oscillations.…”

“…The absence of dominant RO oscillations in the experiments [4] motivates us to adiabatically eliminate all material variables in the laser rate equations and to consider only an equation for the normalized complex amplitude of the electrical field E(t). A similar simplification has previously been exploited in Ref.…”

Обострение оптических импульсов в вертикально-излучающих лазерах с активной областью на основе субмонослойных квантовых точек InGaAs

“…Для реализации режима самопульсаций необходимо по-местить в лазерный резонатор насыщающийся поглотитель [4]. В на-стоящее время опубликовано значительное число экспериментальных и теоретических работ [5][6][7], в которых обсуждаются условия достижения режима самопульсаций как в полосковых торцевых полупроводниковых лазерах, так и в вертикально-излучающих лазерах (ВИЛ), где для ограничения тока инжекции используется ионная имплантация или се-лективное окисление, что обеспечивает формирование насыщающегося поглотителя в непрокачиваемой части активной области. Альтерна-тивным подходом к генерации оптических импульсов пикосекундной длительности является использование режима переключения усиления, который реализуется при накачке полупроводниковых лазеров наносе-кундными импульсами тока [8][9][10].…”