Low threshold, single-mode laser based on individual CdS nanoribbons in dielectric DBR microcavity

Single-mode lasers with low threshold are attractive for their potential applications in many areas, such as optical communication, signal processing and displays. Here we report a nanoscale single-mode laser with CdS nanoribbons (NRs) sandwiched between two dielectric distributed Bragg reflectors (DBRs). Under optical pumping, the band edge emission of CdS ribbons can be effectively confined and give lasing in the DBR microcavity, with the lasing threshold as low as ~8 μJ/cm², which is one order lower than those of bare CdS ribbons for comparison. More importantly, the CdS-DBR laser can realize single-mode emission, for the length of the resonance cavity can support a mode spacing larger than the bandwidth of the optical gain. Light polarization measurements demonstrate the single-mode lasing has a polarization degree as high as 97.4%. Time-resolved photoluminescence (TRPL) measurements further reveal that the lasing action comes from the electron-hole plasma recombination process. Moreover, the wavelength of the lasing mode can be broadly tuned by changing the thickness of CdS NRs. This low-threshold single-mode laser may find applications in highly integrated photonics devices and systems.