Dispersive self-Q-switching in self-pulsating DFB lasers

Abstract

Self-pulsations reproducibly achieved in newly developed lasers with two distributed feedback sections and with an additional phase tuning section are investigated. The existence of the dispersive self-Q-switching mechanism for generating the high-frequency self-pulsations is verified experimentally for the first time. This effect is clearly distinguished from other possible self-pulsation mechanisms by detecting the single-mode type of the self-pulsation and the operation of one section near the transparency current density using it as a reflector with dispersive feedback. The operating conditions for generating this self-pulsation type are analyzed. It is revealed that the required critical detuning of the Bragg wavelengths of the two DFB sections is achieved by a combination of electronic wavelength tuning and current-induced heating. The previous reproducibility problems of self-pulsations in two-section DFB lasers operated at, in principle, suited current conditions are discussed, and the essential role of an electrical phase-control section for achieving reproducible device properties is pointed out. Furthermore, it is demonstrated that phase tuning can be used for extending the self-pulsation regime and for optimizing the frequency stability of the self-pulsation. Improved performance of the devices applied as optical clocks thus can be expected

Self-Pulsation in Multisection Distributed Feedback Laser Diode with a Novel Dual Grating Structure

“…3). A single-mode self-pulsation is the main feature of dispersive self-Q-switching, and line broadening is natural because the main idea of dispersive self-Q-switching is the conversion from a wavelength modulation to an amplitude modulation [11], [14]. Figure 3 shows the change of the optical spectrum with the current increase of the reflector section.…”

“…If the peak wavelength reached the flat region of the reflection spectrum, the RF spectrum disappeared. It was reported [11], [16] that the self-pulsation turned on and off periodically when the current of the phase section increased. However, we did not find any periodicity.…”

“…When the injection currents of both sections are above threshold, mode beating between the modes of each section is possible. In a multisection DFB LD, the optical signal of each section is injected into the other section and this gives rise to a phase correlation between the two modes [10], [11]. The merit of mode beating is that the repetition rate is related to the mode spacing and can be varied.…”

“…7). As dispersive Q-switching and mode beating are impossible below threshold [10], [11], [13], there should be another mechanism that produces this pulsation. Reference [18] theoretically suggested self-mode locking in an external cavity LD.…”

Demonstration of self-pulsating InP-on-Si DFB laser diodes

“…There are two mechanisms responsible for the self-pulsations. The first one is referred to as dispersive self-Q-switching [3], and it was first reported in [4]. This mechanism can result in self-pulsations at very high frequencies e.g.…”