Multiple-beam colloidal quantum dot lasers in a waveguide-grating-waveguide microcavity

Abstract

In this work, multiple-beam colloidal quantum dot lasers are achieved in a double waveguide-grating (waveguide-grating-waveguide, W-G-W) microcavity. The grating is fabricated simply using interference lithography, and CdSe/CdS/ZnS colloidal quantum dots (CQDs) are spin-coated as the gain to form an active waveguide-grating structure. The photoresist film, which is not completely etched to the bottom, provides another waveguide-grating structure. In the W-G-W structure, low-threshold multiple-beam laser output is realized under optical pumping with emission peaks at 664.6 and 645.2 nm. The oblique laser is derived from a quasi-propagation mode. The thresholds of the two laser modes are 22.7 and 28.3 μJ/cm2, respectively, and both laser modes are TE0 modes. In addition, the emission wavelengths of the two modes of the designed distributed feedback laser can be flexibly tuned by changing the thickness of the CQDs' waveguide layer. The presence of quasi-propagation modes provides another method for designing compact laser sources, which could help in the design of wireless communication networks, hyperspectral 3D sensing, and color laser displays.