Owing to the wide tuning range, high-temperature stability, flexible design, and fast recovery dynamics, quantum dots (QDs) have been widely used in many research fields, such as lasers, photodetectors, solar cells, and displays. Among these, III–V InAs/GaAs QDs are especially suited for infrared optoelectronic applications due to their strong working stability and enhanced light output efficiency. The doping technique has been admitted as a very effective method to enhance the modal gain and temperature insensitivity for InAs/GaAs QDs-based devices. Additionally, doping could modulate critical optical responses, like light absorption and carrier recovery dynamics, making these QDs ideal for ultrafast applications. In this work, p-type (Be) doping and n-type (Si) doping were introduced into multilayer QDs to mitigate the adverse effects of grown-in interface states, which were verified by temperature-dependent photoluminescence (PL) characterization. The results show a significant increase in PL intensity for n-doped samples, which was attributed to the effective suppression of interface states. This enhancement correlates with doping levels, with PL intensity increasing from 1.71 to 2.72 times as Si concentration rises from 1 × 1018/cm3 to 3 × 1018/cm3. In contrast, p-doped samples show a slight decrease in PL intensity and a 20 nm blueshift in PL emission peak, indicating different interdiffusion behaviors between In and Ga atoms compared to that in n-doped ones. By integrating with distributed Bragg mirrors, QD semiconductor saturable absorption mirrors were developed, where n-doped QDs presented superior performance in mode-locked ultrafast lasers with the shortest pulse width and highest output power.

Ultrafast fiber lasers have shown exceptional performance across various domains, including material processing, medical applications, and optoelectronic communication. The semiconductor saturable absorber mirror (SESAM) is a key enabler of ultrafast laser operation. However, the narrow wavelength range and limited modulation depth of conventional SESAMs pose challenges to further advancing ultrafast fiber laser technology. To address these limitations, we explored the integration of guided mode resonance (GMR) effects to enhance light–matter interaction within the absorption layer. By incorporating subwavelength dielectric film gratings onto the cap layer of SESAMs, we excited GMR and formed a microcavity structure in conjunction with the distributed Bragg mirror (DBR). This design significantly improved the absorption efficiency of InAs quantum dots. The experimental results demonstrate that the modulation depth of the SESAM increased from 6.7% to 17.3%, while the pulse width was reduced by 2.41 times. These improvements facilitated the realization of a high-quality, stable ultrafast fiber laser. This study not only broadens the application potential of ultrafast lasers in diverse fields but also offers a practical pathway for advancing SESAM technology toward industrial-scale deployment.

Plasmons in graphene (Gr) show many fascinating characteristics, such as dynamic tunability, strong field confinement of light-matter interaction, and highly responsive, which has been widely exploited for a number of applications, including photodetectors, optical modulators, and sensors. In this paper, graphene plasmons (GPs) were motivated by implanting Au nanoparticles (Au NPs) into Ta2O5 thin layers adjacent to the Gr film, and the strong localized surface plasmon resonance (LSPR) effect has been proposed and demonstrated by placing the GPs structure on a III–V semiconductor quantum well saturable absorber (SA). It has been substantiated that the heightened interaction between light and Gr via LSPR predominantly occurs through the mechanisms of resonant energy transfer and local electromagnetic field enhancement, rather than direct electron transfer. Significant improvement on the nonlinear characteristics of the GPs modulated III–V semiconductor SA has been observed with a 17.1% large modulation depth and obviously improved working stability. A 1550 nm passive mode-locked laser has been successfully constructed with a pulse width down to 523 fs by integrating the SA into the laser cavity. This work lays the foundation for the development of high-performance mode-locked lasers and also demonstrates the substantial enhancement of nonlinear optical properties of various materials not limited to III–V semiconductors provided by this GPs' modulated structure; hence, these findings offer extensive prospects for applications in various photonics and optoelectronic devices.