Limits...
Investigation of monolithic passively mode-locked quantum dot lasers with extremely low repetition frequency.

Xu T, Cao J, Montrosset I - Nanoscale Res Lett (2015)

Bottom Line: A modified multisection delayed differential equation model is proposed to accomplish simulations of both two-section and three-section passively mode-locked lasers with long cavity.According to the numerical simulations, it is shown that fundamental and harmonic mode-locking regimes can be multistable over a wide current range.In addition, we demonstrate that fundamental pulses with higher peak power can be achieved when the laser is designed to work in a region with smaller differential gain.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Terahertz Solid-State Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai, 200050 China.

ABSTRACT
The dynamical regimes and performance optimization of quantum dot monolithic passively mode-locked lasers with extremely low repetition rate are investigated using the numerical method. A modified multisection delayed differential equation model is proposed to accomplish simulations of both two-section and three-section passively mode-locked lasers with long cavity. According to the numerical simulations, it is shown that fundamental and harmonic mode-locking regimes can be multistable over a wide current range. These dynamic regimes are studied, and the reasons for their existence are explained. In addition, we demonstrate that fundamental pulses with higher peak power can be achieved when the laser is designed to work in a region with smaller differential gain.

No MeSH data available.


Related in: MedlinePlus

QD material gain as a function of the injection current density for the considered device. The material gains for the GS (blue line) and the ES (red line) are shown. The inserted first two markers indicate the threshold gain positions of the lasers without passive section (circle marker) and with a 4-mm-long passive section (cross marker). The last square marker corresponds to a threshold gain position which will be discussed later.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4384970&req=5

Fig4: QD material gain as a function of the injection current density for the considered device. The material gains for the GS (blue line) and the ES (red line) are shown. The inserted first two markers indicate the threshold gain positions of the lasers without passive section (circle marker) and with a 4-mm-long passive section (cross marker). The last square marker corresponds to a threshold gain position which will be discussed later.

Mentions: The GS and ES material gains gi/Γxy (Γxy = Γx*Γy) as a function of the injection current of the previously described device are shown in Figure 4. Based on the above discussions, the onset of the harmonic ML at high current could be partially attributed to the increase of the unsaturated gain which makes the gain overcome the losses easier. Since low repetition rate is our main target, the round trip time cannot be reduced; therefore, the only way to sustain the fundamental ML over a larger current span is to operate the laser in a condition of reduced differential gain (see Figure 4). Thanks to the reduced density of states, the QD medium always achieves early gain saturation at smaller current density compared with its bulk and quantum well counterparts, which means that the differential gain of this medium decreases rapidly when increasing the injection current, as shown in Figure 4. To achieve these operation conditions, we should increase the required threshold current of the laser, so that it would work at a current range with smaller differential gain. Different approaches have been attempted to obtain these favorable operation conditions as will be shown in the following.Figure 4


Investigation of monolithic passively mode-locked quantum dot lasers with extremely low repetition frequency.

Xu T, Cao J, Montrosset I - Nanoscale Res Lett (2015)

QD material gain as a function of the injection current density for the considered device. The material gains for the GS (blue line) and the ES (red line) are shown. The inserted first two markers indicate the threshold gain positions of the lasers without passive section (circle marker) and with a 4-mm-long passive section (cross marker). The last square marker corresponds to a threshold gain position which will be discussed later.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4384970&req=5

Fig4: QD material gain as a function of the injection current density for the considered device. The material gains for the GS (blue line) and the ES (red line) are shown. The inserted first two markers indicate the threshold gain positions of the lasers without passive section (circle marker) and with a 4-mm-long passive section (cross marker). The last square marker corresponds to a threshold gain position which will be discussed later.
Mentions: The GS and ES material gains gi/Γxy (Γxy = Γx*Γy) as a function of the injection current of the previously described device are shown in Figure 4. Based on the above discussions, the onset of the harmonic ML at high current could be partially attributed to the increase of the unsaturated gain which makes the gain overcome the losses easier. Since low repetition rate is our main target, the round trip time cannot be reduced; therefore, the only way to sustain the fundamental ML over a larger current span is to operate the laser in a condition of reduced differential gain (see Figure 4). Thanks to the reduced density of states, the QD medium always achieves early gain saturation at smaller current density compared with its bulk and quantum well counterparts, which means that the differential gain of this medium decreases rapidly when increasing the injection current, as shown in Figure 4. To achieve these operation conditions, we should increase the required threshold current of the laser, so that it would work at a current range with smaller differential gain. Different approaches have been attempted to obtain these favorable operation conditions as will be shown in the following.Figure 4

Bottom Line: A modified multisection delayed differential equation model is proposed to accomplish simulations of both two-section and three-section passively mode-locked lasers with long cavity.According to the numerical simulations, it is shown that fundamental and harmonic mode-locking regimes can be multistable over a wide current range.In addition, we demonstrate that fundamental pulses with higher peak power can be achieved when the laser is designed to work in a region with smaller differential gain.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Terahertz Solid-State Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai, 200050 China.

ABSTRACT
The dynamical regimes and performance optimization of quantum dot monolithic passively mode-locked lasers with extremely low repetition rate are investigated using the numerical method. A modified multisection delayed differential equation model is proposed to accomplish simulations of both two-section and three-section passively mode-locked lasers with long cavity. According to the numerical simulations, it is shown that fundamental and harmonic mode-locking regimes can be multistable over a wide current range. These dynamic regimes are studied, and the reasons for their existence are explained. In addition, we demonstrate that fundamental pulses with higher peak power can be achieved when the laser is designed to work in a region with smaller differential gain.

No MeSH data available.


Related in: MedlinePlus