Optimizing Semiconductor Saturable Absorption Mirrors Using Subwavelength Dielectric Gratings for Fiber Lasers

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.