Sodium-doped InP/ZnSeS/ZnS quantum dots as a saturable absorber for passive Q-switched fiber lasers

In this work, sodium-doped InP/ZnSeS/ZnS (InP–Na) QDs was fabricated by thermal injection method for the first time. The nonlinear optical properties were first demonstrated by realizing a modulation depth of 7.85% and saturable intensity of 2.2 MW cm−2 by two-detector method. The Q-switching operations were carried out by integrating InP–Na QDs as saturable absorber (SA) in a fiber laser ring cavity system. Q-switched laser pulses with a pulse width of 139 ns were generated. The ability of effective pulse width compression can be attributed to the short exciton recovery time of SA, as confirmed by transient absorption and time-resolved photoluminescence. This is the first demonstration of Na-doped InP/ZnSeS/ZnS QDs and using it as SA for generating ultrafast laser pulses. Therefore, this study extends the research scope of InP-based QDs in optical communications, nonlinear photonics and ultrafast photonics. •Na–InP QDs was fabricated by thermal injection method for the first time.•The nonlinear optical performance of Na–InP QDs has been studied.•Passive Q-switched fiber laser based on Na–InP SA was demonstrated.•InP-based QDs have potential applications in nonlinear photonics.